Nanomaterials and their role in advancing biodiesel feedstock production: A comprehensive review

Sustainable socio-economic development largely depends on the sustainability of the energy supply from economic, environmental, and public health perspectives. Fossil fuel combustion only meets the first element of this equation and is hence rendered unsustainable. Biofuels are advantageous from a public health perspective, but their environmental and economic sustainability might be questioned considering the conflicts surrounding their feedstocks, including land use change and fuel vs. food conflict. Therefore, it is imperative to put more effort into addressing the downsides of biofuel production using advanced technologies, such as nanotechnology. In light of that, this review strives to scrutinize the latest developments in the application of nanotechnology in producing biodiesel, a promising alternative to fossil diesel with proven environmental and health benefits. The main focus is placed on nanotechnology applications in the feedstock production stage. First, the latest findings concerning the application of nanomaterials as nanofertilizers and nanopesticides to improve the performance of oil crops are presented and critically discussed. Then, the most promising results reported recently on applying nanotechnology to boost biomass and oil production by microalgae and facilitating microalgae harvesting are reviewed and mechanistically explained. Finally, the promises held by nanomaterials to enhance animal fat production in livestock, poultry, and aquaculture systems are elaborated. Despite the favorable features of using nanotechnology in biodiesel feedstock production, the presence of nanoparticles in living systems is also associated with important health and environmental challenges, which are critically covered and discussed in this work.


Introduction
Although most scenarios developed by the governments are currently designed based on the fact that demands for energy in various sectors are on the rise, there are many arguments concerning how the role of fossil fuels should be minimized given the undesirable environmental and health effects, with global warming and climate change placed at their epicenter (Zhou and Feng, 2017). Sustainable production of eco-friendly alternatives to fossil fuels is the main remedy to this challenge (Dueso et al., 2018). Besides offering improved environmental impacts, biofuels are also associated with other benefits, including rural job creation, foreign exchange savings, and greater energy security (Bluhm et al., 2012).
Biodiesel is considered the most promising and acceptable among biofuels due to its reproducibility, biodegradability, non-toxicity, and sulfur-free nature. Biodiesel highly resembles diesel in terms of physicochemical properties, eliminating the need for considerable engine modifications. Biodiesel combustion in diesel engines, either in pure or blended form with diesel, reduces some of the major exhaust emissions, particularly particulate matter and carbon monoxide (Nabi et al., 2009). The production cycle of this alternative fuel, including oil feedstock production, oil extraction, and biodiesel production, is also a well-understood process with available technologies at a commercial scale (Nigam and Singh, 2011).
Generally, biodiesel is produced from three main generations of feedstock, including first-generation feedstock, i.e., vegetable oil (Demirbaş, 2002), second-generation feedstock, i.e., animal fats and waste oils (Goodrum et al., 2003), and third-generation feedstocks, i.e., microbial and microalgal oil (Ray et al., 2022). Oily vegetables and crops (i.e., first-generation) are the main feedstock for commercial biodiesel production (Demirbas, 2002). More than 350 oily vegetables and crops are recognized under different soil and climate conditions as feedstocks for biodiesel production (Ghazali et al., 2015). Vegetable oils are attractive not only because of their renewability but also because they hold an energetic content close to diesel fuel (Demirbas, 2005). Nevertheless, these feedstocks face serious criticism as their production has led to global land use change (deforestation) and food vs. fuel conflict. Despite the emergence of higher-generation biodiesel feedstock and its criticism, the biodiesel production industry worldwide relies predominantly on oily vegetables and crops. Therefore, efforts are focused on boosting their productivity to diminish their negative environmental footprints.
Traditionally, fertilizers and pesticides are used to increase crop yield (Zhao et al., 2016a), but they are also largely attributed to serious human health and environmental burdens (Sharma and Singhvi, 2017). A major secondgeneration biodiesel feedstock is animal fat. This feedstock is generally regarded as a more sustainable option than the first-generation feedstock from both environmental and economic points of view, but some health concerns, for example, the transmission risk of bovine spongiform encephalopathy by beef tallow has limited substantial biodiesel production from this low-cost feedstock. Finally, microalgae, the main third-generation biodiesel feedstock, offers many advantages, such as high lipid contents, high growth rate, and photosynthesis rate (Duran et al., 2018). Microalgae can also grow in nonagricultural land with waste and saline waters (Zhu et al., 2017) without pesticides or herbicides (Chiaramonti et al., 2017). However, increasing microalgal biomass and oil yield and enhancing algal biomass harvesting are still among the main challenges compromising the overall feasibility of using this promising biodiesel feedstock.
Among the technologies offered to overcome the obstacles faced in enhancing the biodiesel feedstocks, "nanotechnology" or, more specifically,

Nanotechnology applications in feedstock production
Based on feedstocks, biodiesel is classified into five different generations/categories (Fig. 1). All these oil feedstocks face numerous production challenges. For instance, applying chemical fertilizers and pesticides in vegetable oil production causes significant health and environmental problems. Some of the mentioned challenges can be potentially resolved using nanotechnology.

Vegetable oils
Generally, oily vegetables and crops (edible and non-edible) are the main feedstocks for biodiesel production. Over 350 oily vegetables and crops are currently cultivated worldwide as biodiesel feedstocks (Ghazali et al., 2015). Edible vegetable oils are renewable resources with energy values close to diesel fuel (Demirbas, 2005). However, their application in the biodiesel industry has triggered serious competition with food commodities Table 1.
Comparison between the current review paper and previously published review papers on the application of nanotechnology in biodiesel feedstock production.

Type of feedstock Reference
Vegetable oils Algal oils Animal fats  production for land and water resources. Despite this unfavorable competition and the introduction of second-and third-generation feedstocks to address the challenge, edible oils, oily vegetables, and crops still retain the highest share in biodiesel production (Fig. 2).
Efforts have been made to increase the yield of oily vegetables and crops. Traditionally, chemical species (e.g., fertilizers, herbicides, and pesticides) have been used effectively to improve crop yield (Mirbakhsh, 2023). However, applying chemical species is not sustainable because of their environmental and health impacts (Vijayakumar et al., 2023). Alternatively, innovative nanotechnology-based approaches have been developed to maximize the feedstock yield (farm output yield) using minimal resources. Figure 3 depicts the potential applications of nanotechnology in agriculture.
Generally, the insertion of nanoscale materials into plants can provide the programmed, time-controlled release of agrochemicals (e.g., fertilizers, pesticides, and herbicides) as well as target-specific delivery of biomolecules (e.g., nucleotides, proteins, and activators) (Fraceto et al., 2016;Sohrabi et al., 2023). The application of nanotechnology in the production of oil crops fits into two major categories: nanofertilizers (Liu and Lal, 2014; and nanopesticides (Guan et al., 2010). This section presents a comprehensive examination of the advantages and disadvantages associated with using nanoparticles in agriculture. Understanding these factors is crucial for assessing the sustainability of nanoparticle applications in the production of biodiesel feedstock.

Nanofertilizers
Nanoparticles can significantly improve the agronomic and economic feasibility of vegetable oil feedstocks by acting as fertilizers or fertilizer enhancers (Liu and Lal, 2014;Mahapatra et al., 2022). In the former application, nanomaterials supply one or more nutrients a crop needs to promote its growth and yield (Dewdar et al., 2018). Compared to traditional fertilizers, some nanofertilizers are safe for beneficial soil microbiota and provide higher nutrient availability and lower nutrient run-off (Pandey, 2018;Kalwani et al., 2022). A summary of the effects of some macro/micronutrient nanofertilizers used to produce vegetable oil feedstocks is shown in Table 2.
The second group of nanofertilizers (i.e., nanomaterial-enhanced fertilizers) contains engineered nanomaterials that can increase plant nutrient consumption (i.e., absorption, uptake, transport, and penetration) efficiency ( Fig. 4) (Liu and Lal, 2015). These nanomaterials do not directly supply crops with nutrients while improving crop productivity, especially when co-applied with traditional fertilizers (Elsayed et al., 2022;Kumar et al., 2022a). The action mechanisms of the second nanofertilizer group include (i) binding to chemical fertilizers and facilitating their translocation into various plant organs, (ii) circulating (i.e., up, down, and radial movements) within the plant through symplastic or apoplastic pathways, (iii) modulating the absorption of soil chemical and microbial contents by plant, and (iv) penetrating plant cells through pore formation, endocytosis, plasmodesmata, and carrier proteins (Fig. 4).
Applying nanoparticles (e.g., cupric oxide, iron oxide, and zinc oxide) may not be eco-friendly (Azam et al., 2022). Nanoparticles may complicate the soil ecosystem process (e.g., the carbon or nitrogen cycle) by suppressing the growth of nematode Caenorhabditis elegans and earthworm Eisenia fetida, decreasing the diversity and population of the soil microbial community, and poisoning higher trophic groups in the soil food web (e.g., grazers) (Rashid et al., 2017). Nanomaterials may also render phytotoxic effects based on nature, size, dose, and exposure time. For example, cupric oxide increases the rate of organic matter decomposition in the soil while inhibiting pollen germination, seed germination, and root growth of various Arabidopsis thaliana ecotypes (probably because of the production of reactive oxygen species (ROS)) (Guerriero and Cai, 2018). A high concentration of nanoparticles, especially ≥20 nm, in the root zone can decrease crop production yield by interfering with the uptake of nutrients and water (Usman et al., 2020).
Besides soil nutrients and availability, crop yield is affected by soil pollution. Nanomaterials can extensively trap many soil and groundwater contaminants because of the large specific surface area (including microporous channels with network structures) and the high reactivity . Favorable engineered nanoparticles intended for in-situ remediation must show less toxicity, appropriate mobility within porous media, and sufficient lifetime and reactivity . Based on these criteria, nanoscale elemental or zero-valent metals (iron, nickel, and palladium) are considered promising adsorbents of transitional metals (arsenic and chromium) and persistent organic pollutants (Cecchin et al., 2017;Babu et al., 2022). Fe-based nanoparticles are more economically feasible (simple removal and recyclability) for water remediation due to their magnetic properties (Cundy et al., 2008). For soil remediation, ironbased nanoparticles (e.g., zero-valent iron (ZVI) nanoparticles) offer the unique advantage of being soil deliverable, while they are highly reactive to many plant-detrimental contaminants (heavy metals) (Zhao et al., 2016b). The typical modification methods of ZVI nanoparticles include their immobilization onto suitable supports, surface modification, and admixtures of compatible metals with ZVI nanoparticles (Fig. 5) (Xue et al., 2018). Figure 6 presents a schematic diagram summarizing the preparation and application of stabilized ZVI nanoparticles for in-situ contaminated soil and groundwater remediations.
Another iron-based nanoparticle is iron sulfide, which is chalcophilic in nature. This nanoparticle can remediate heavy metals (arsenic, cadmium, and chromium) due to its ability to donate electrons (releasing iron 2+  sulfur 2-). The immobilization of humic acid through electrostatic adsorption and organic complexation further enriches surface functional groups on iron(ii) sulfide nanoparticles, while carboxymethyl cellulose is used as a stabilizer to prevent the agglomeration of the nanoparticles. The novel composite (carboxymethyl cellulose-iron(ii) sulfide@ humic acid) can then efficiently remediate chromium(VI) from contaminated soil (Fig. 7) (Tan et al., 2020).
Despite significant agricultural productivity improvements, applying ironbased nanoparticles may be challenging because of the loss of reactivity with aging ( Fig. 8). During in-situ remediation of contaminated zones, the clustering tendency of ZVI nanoparticles reduces their mobility through soil pores by accelerating the deposition of soil particles (Cecchin et al., 2017).
ZVI nanoparticles can be cytotoxic against some microbial species through iron 2+ release, ROS generation, oxidative stress, and subsequent cell membrane disruption (Lefevre et al., 2016). Therefore, applying ZVI nanoparticles may knock out some important functional microorganisms for biogeochemical processes. At high concentrations, ZVI nanoparticles may decrease growth and aspiration in some plants by reducing the root adsorption efficiency of nutrients and water. This could be attributed to the accumulation of ZVI nanoparticles or iron 3+ (the oxidation product of ZVI nanoparticles) on roots and/or the internalization of ZVI nanoparticles into root epidermal cells (Jiang et al., 2018). In addition, ZVI nanoparticles may cause oxygen deficiency and iron 2+induced reductive effects in soils, negatively affecting plant growth (Jiang et al., 2018). More specifically, oxygen depletion affects both root growth/survival and the rhizosphere microbial community (Lefevre et al., 2016). Notably, the induction of oxidative stress by nanoparticles could be caused by the overexpression of ascorbate peroxidase, catalases, and superoxide dismutase when they enter plant tissues (Ding et al., 2017).
The application of nanotechnology for soil remediation can be combined with bioremediation to overcome the challenges mentioned (Cecchin et al., 2017). The developed technique, known as nanobioremediation, uses microbial or plant-derived nanoparticles (Yadav et al., 2017). The first step of nanobioremediation involves the application of biological nanoparticles at a concentration that is enough to bring the pollutants to an appropriate level for the biodegradation process (Usman et al., 2020). In the second step, microbial or phyto bioremediation ability is exploited to degrade various organic or inorganic pollutants (Hamedi et al., 2015). Through this strategy, the economic and/or environmental feasibilities of both mentioned remediation techniques are substantially improved.
An alternative to nanoscale elemental or zero-valent metals in agriculture is carbon-based nanomaterials (CNM) such as carbon nanotubes (CNTs), fullerenes, carbon nanodots, carbon nanofibers, graphene oxides, carbon nanohorns, and carbon nano-dots (Aacharya and Chhipa, 2020). Figure 9 shows some CNMs with a growth-promoting effect on plants. These compounds have been extensively applied as plant growth regulators, pest detection and control agents, pesticide sorbents, and nutrient carriers in agriculture ( Table 3). The engineering of nanoparticles could further        nanocarbons. Like water-soluble nanoparticles, the growth-stimulating effects of functionalized nanocarbons are due to their ability to enhance water conduction in plants by reaching the tracheal elements of xylem vessels (Singh et al., 2018). According to Table 3, the effects of CNMs on agriculture yield significantly depend on plant species, environmental stresses (e.g., drought or soil contaminants), and the type and amount of the incorporated CNMs. These factors play critical roles in CNM-induced phytotoxicity at anatomical, morphological, physiological, cellular, and genetic levels (Verma et al., 2019). More specifically, mixed effects of the CNMs' exposure on plants ranging from an increase in vegetative growth and yield of fruit/seed at lower concentrations of CNMs to the progressive decrease in these observations at higher concentrations of CNMs, have been documented ( Table 3). In general, at lower concentrations, CNMs are effective in enhancing (i.e., water uptake, water transport, seed germination, nitrogenase, photosystem, and antioxidant activities), activating (i.e., water channels proteins), and promoting (i.e., nutrition absorption), but all these beneficiary effects could change when CNM concentration is raised. Unlike in-vitro studies, the chronic phytotoxicity of CNMs has not been extensively examined by field studies (Mukherjee et al., 2016). It should be noted that soil physiological properties (e.g., soil components) modulate the toxicity of the incorporated CNM by affecting, for example, its reactivity and solubility (Mukherjee et al., 2016). This behavior further complicates the mechanistic understanding of cellular interactions between CNM and plants. Moreover, little is known about the effects of environmental factors on CNMs' stability, the release of their metals moiety, and the leach of adsorbed contaminants from CNMs (Mukherjee et al., 2016). Another concern about CNM fate is its unknown potential for bioaccumulation and/or biomagnification (Sangeetha et al., 2017). In light of these, future research should encompass the adverse impacts of nanomaterials on plants. Those impacts can be classified into different categories, nanomaterial phytotoxicity, reducing germination rate of seeds, decreasing fresh and dry biomass and length of roots and shoots, altering photosynthesis process, enhancing chromatin condensation, increasing deoxyribonucleic acid (DNA) damage, reducing the transpiration rate, enhancing lipid peroxidation, up-and down-regulation of various stressrelated genes, and inducing plant cell apoptosis (Tripathi et al., 2017).
By consuming plant materials contaminated by nanoparticles (e.g., cadmium, copper, iron, manganese, nickel, lead, and zinc) by animals and humans, the contamination could be further biomagnified throughout the food chain. The high reactivity and transportability of nanoparticles also raise safety concerns for workers in direct contact with the production and  application of these compounds (Iavicoli et al., 2017). More specifically, nanoparticles could be absorbed at different rates, depending on their types, into human (and animal) bodies through inhalation, ingestion, and skin contact. They could mainly interact with cells through adhesion, endocytosis, semiendocytosis, and penetration. The greater surface area of nanoparticles elicits a higher toxic dose response than similar concentrations of their bulk counterparts. For instance, exposure to leaked titanium dioxide nanoparticles in animals and humans induces tissue degradation and organ injury mainly through oxidative stress, apoptosis, and necrosis. Excessive inflammation because of the high amount of biomolecules oxidized by nanoparticles and ROS may further induce aging, cancer, and other diseases (Ranjan et al., 2019). The concentration of nanoparticles could play a significant role in their toxicity level. In a study, the toxicity of different concentrations of iron oxide nanoparticles on an animal model (i.e., zebrafish) was visualized by using a fluorescent dye (Congo red) conjugated with the nanoparticles. As shown in Figure 10, magnetic nanoparticles (i.e., Congo red@iron(II, III) oxide (Fe3O4) conjugates) exerted more toxicity on zebrafish larvae by increasing their concentration and resulting in the delay in hatching cycles at the concentration of 100 µg/m and mortality at concentrations exceeding 200 µg/mL (Jurewicz et al., 2020).
The level of nanoparticle toxicity may depend on the existence and type of surface coatings (i.e., ligands). Zheng et al. (2018) used the transcriptome sequencing technique and PCR to study the impact of magnetic nanoparticles (Fe3O4) coatings on adult zebrafish (Danio rerio). Compared to the naked nanoparticles, the fish exposure (7 d) to the starch-coated ones inflicted lower gill toxicity but more significant liver damage. This was due to higher bioaccumulation of positively charged naked Fe3O4 nanoparticles in gill cells with negatively charged surfaces. In contrast, starch-coated Fe3O4 nanoparticles had smaller sizes and showed a steric hindrance, preventing their attachment on collector surfaces in fish body. However, the very same property made the coated magnetic nanoparticles more transportable, leading to their higher accumulation in the liver. Figure 11 illustrates the differentially expressed gene profiles in the gill and liver tissues of fish exposed to magnetic nanoparticles.   Figure 12 shows the effect of uncoated, polyvinylpyrrolidone-coated, or citrated-coated silver nanoparticles on macrophages and HT29 epithelial cells. Uncoated and coated-Ag nanoparticles triggered oxidative stress and inflammatory responses, respectively (Nguyen et al., 2013). Accordingly, coated-silver nanoparticles resulted in cell enlargement and elongation, whereas uncoated ones induced cell shrinkage (Fig. 12). These findings implied that the absence of coating could be more toxic. However, the exact level of toxicity of any nanoparticles would significantly depend on their size and the nature of the coated ligand used and hence, should be investigated case by case. For instance, the application of toxic ligands (e.g., cetyltrimethylammonium bromide, poly(diallyldimethylammonium) chloride, bionic, and oleate) in nanoparticle functionalization may render more toxicity effects compared to naked nanoparticles (Bozich et al., 2014). On the contrary, citrate-coated nanoparticles induced lower cytotoxicity than polyvinylpyrrolidone-coated ones (Nguyen et al., 2013). This could be attributed to their difference in the extent they prevent silver nanoparticles from leaching.
In addition to bioavailability, coatings, through their surface charge, could also influence the cytotoxicity of nanoparticles. In fact, the surface charge of the coating is more significant in terms of cytotoxicity, whereas its composition is a significant factor from the ROS generation point of view. In this context, cadmium selenide/zinc sulfide core/shell nanoparticles with positively charged coatings (e.g., polyethylenimine or cysteamine) were absorbed more by cells (i.e., HaCaT keratinocytes) compared to their counterparts with negatively charged coatings (e.g., dihydrolipoic acid or glutathione) (Zheng et al., 2017).
The shape of nanoparticles is another determinant of their toxicity. For example, fiber-like nanoparticles show poor miscibility in application media and, hence, could release into the air. Following their release, these nanoparticles could be inhaled and cause blood contamination by directly entering the bloodstream from the lungs, ultimately reaching all other body organs. Another contributing factor to the health impacts of nanoparticles is their size. More specifically, the nano-sized dimension of these particles allows them to reach various susceptible body parts, for example, the brain, via crossing the blood-brain barrier, a physical barrier their bulk-size counterpart cannot cross (Dehhaghi et al., 2019). Once inside the brain, nanoparticles could induce various neurodegeneration diseases, including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, multiple sclerosis, and Parkinson's disease, potentially through rendering apoptosis, neuroinflammation, and neuronal cell loss (Dehhaghi et al., 2019). Therefore, it is crucial to carefully consider and engineer various aspects of nanoparticles before applying them in agriculture to ensure health and safety standards.

Nanopesticides
Conventional pesticides contain coarse particles and show less than 30% annihilation efficiencies against targeted pest species (Hayles et al., 2017; Rani et al., 2023) due to low biological activity, dispersibility, and stability (Zhang, 2018;Manzoor et al., 2023). These pesticides also have many side effects on the surrounding ecosystem and human health (Fig. 13).
The detrimental effects of conventional pesticides are generally persistent for a long time or could even be irreversible (Kah and Hofmann, 2014;Hennig et al., 2023). Therefore, novel plant protection methods against pests must be developed, among which nanopesticides are considered promising alternatives. Nanopesticides show higher mobility, solubility, dispersibility, durability, and leaf adhesion (Kah et al., 2013). Controlled release and favorable biocidal activities (even at low concentrations) are the other features of these compounds (Sun et al., 2019;Mubeen et al., 2023). Nanopesticides are categorized into (i) pesticides whose effective ingredients are nano-sized, usually in the form of a powder, nanodispersant, or microemulsion (Jiang et al., 2012), and (ii) those effective ingredients are in interaction with nanomaterials through encapsulation, entrapment, adsorption, and binding ( Fig. 14)  . The designation aims of the second group of nanopesticides are to improve the performance of a conventional pesticide, reduce its release into the environment, and minimize the exposure of nontargeted species (Jindal et al., 2017;Pan et al., 2023). Through this strategy, nanoparticles can protect pesticide agents against degradation, leaching, photolysis, and volatilization while improving the delivery and bioavailability of water-insoluble active ingredients (Sun et al., 2019; Paz-Trejo et al., 2023).
Despite the mentioned advantages of nanopesticides, concerns with respect to their biosafety and long-term ecological and health effects, especially on the labor exposed to these compounds, have emerged (Iavicoli et al., 2017). For example, nanopesticides can be evaporated before reaching the targeted-leaf surface when sprayed in tiny droplets . Notably, most emulsifiable concentrates and microemulsions used in nanopesticides are polar solvents (e.g., alcohols, benzenes, and ketones), some of which have high acute toxicity and easily find their way into animal and human bodies through contaminated farmlands and groundwater. Polar solvents are persistent and accumulate in the environment , which could widely cause acute poisoning and  Finally, the potential, extent, and environmental effects of the combined toxicity of nanopesticides and nanofertilizers are still poorly studied. Therefore, the fate of these compounds must be extensively studied before their commercial applications. Figure 15 illustrates the life-cycle assessment of nano-enabled products in agriculture (Iavicoli et al., 2017).

Microalgae oil
Microalgae with high lipid contents can be used as feedstock for thirdgeneration biodiesel production. These organisms could deliver a high photosynthesis rate and growth rate (Nan et (Imhoff et al., 2011). Regarding fuel properties (e.g., heating value, density, viscosity, and acid value), algal biodiesel is comparable to petrodiesel (Kings et al., 2017). Considering the advantages, algal oil could be regarded as a sustainable feedstock for biodiesel production if the two major elements jeopardizing its commercial feasibility (i.e., microalgal biomass cultivation and harvesting) are further improved.

Microalgae biomass cultivation
Direct use (as a micronutrient supplement) or indirect use (as a light scattering and absorption improver and antimicrobial agent) of nanoparticles can improve algae growth rate by improving growth-related physiological processes. Figure 16 summarizes the performance of nanoparticles as micronutrient supplements for enhancing microalgae growth and lipid accumulation. Low nanoparticle doses (i.e., <100 mg/L) typically produce higher performance efficiencies during microalgae cultivation. Regarding performance time, the lower nanoparticle doses could improve lipid productivity, lipid percentage, and biomass yield. Unlike these performance indicators, higher nanoparticle doses could enhance the growth rate factor (i.e., 200-300 mg/L). Moreover, the larger nanoparticle size within the investigated range could significantly affect the performance indicators: lipid percentage and biomass yield.
Concerning their direct use, nanomaterials can enhance cell size and lipid accumulation in microalgae by exerting oxidative stress and stimulating rapid nutrient uptake (Kang et al., 2014). This approach allows ZVI nanoparticles to be used as micronutrient supplements to improve photosynthesis rate, growth rate, and lipid production and accumulation while reducing the requirements for organic carbon sources (Sarma et al., 2014). These effects may be attributed to the provision of a suitable source of iron (i.e., ZVI nanoparticle oxidation to iron 2+ ) (Pádrová et al., 2015). In a study, the growth and physiology of three key coastal marine microalgae (Isochrysis galbana, Pavlova lutheri, and Tetraselmis suecica) were not negatively affected in the medium containing ZVI nanoparticles. Unlike the control, abundant, fully formed (perfectly spherical) large storage lipid bodies were identified within microalgal cells using cellular micromorphological analysis by transmission electron microscopy (Kadar et al., 2012). Both the diameter and number of oil droplets were increased in I. galbana in the presence of ZVI nanoparticles. Despite being healthy, all the mentioned microalgae developed a mesh of gel-like substances around their plasma membrane (Kadar et al., 2012). As ZVI nanoparticle is more bioavailable, significantly lower amounts were required to support algal growth than Fe-chelated ethylenediaminetetraacetic acid (the bulk analog). The higher bioavailability of ZVI nanoparticles could be attributed to their ability to be internalized by endocytosis and their facilitated penetration into the cytosol through higher interaction with the microalgae cell surface (Ševců et al., 2011). In another study, lipid accumulation was strongly enhanced in two eustigmatophycean algae (Trachydiscus minutus, Nannochloropsis limnetica) and four green algae (Raphidocelis subcapitata, Parachlorella kessleri, Dunaliella salina, Desmodesmus subspicatus) following the addition of 5.1 mg/L ZVI nanoparticle in Zehnder culture medium. ZVI nanoparticles could also increase the proportion of polyunsaturated fatty acids in the resultant algal lipid (Pádrová et al., 2015). This feature could be regarded as favorable in cold climates by enhancing the cold flow properties of the prospective biodiesel, while it could be considered unfavorable in hot climates by adversely influencing biodiesel's oxidative stability (Talebi et al., 2013).
Nanoparticles with bactericidal activities could be exploited as micronutrient elements while preventing the overgrowth of contaminating bacteria, a significant concern during commercial cultivation of mixotrophic microalgae. On this basis, magnesium aminoclay nanoparticles (concentration, 0.01-0.1 g/L) were successfully applied in Chlorella sp. KR-1 to suppress the growth of contaminating bacteria . Interestingly, lipid production was also improved by 25% compared to the control, reaching ~410 mg fatty acid methyl ester /L/d .
Regarding their indirect use, nanoparticles can enhance photosynthetic activity (i.e., by inducing the higher formation of carotenoid and chlorophyll pigment) (Eroglu et al., 2013) and overactivate key metabolic enzymes (e.g., nitrate reductase, glutamate-pyruvate transaminase, glutamate dehydrogenase, and glutamine synthase) . Limited light penetration in high-density cultures is a major constraint of commercial microalgae cultivation. Nanoparticles can provide effective ways to mitigate the adverse effect of uneven light distribution on microalgae growth, especially in photobioreactors that require a longer light path length (Wang et al., 2022;Xiao et al., 2022). Using this capability, light penetrability into microalgae suspension can be facilitated by doping nanoparticles within planar waveguide modules that uniformly dilute and redistribute the intense incident light (Sun et al., 2018). Some advantages of planar waveguide modules doped with nanoparticles include low cost, long lifespan, high luminance uniformity, and flexibility for cutting into any size with no need for secondary processing. Sun et al. (2016) exploited nanoscale organosilicon-particle-embedded planar waveguide modules to cultivate microalgae Nannochloropsis oculate in a lab-scale open raceway pond. Compared to the bare open raceway pond, remarkable enhancements in both biomass and lipid yields were achieved because of a significant increase in light distribution within the microalgal culture. Upon encountering the nanoscale organosilicone particles, organosiliconparticle-embedded planar waveguide modules scatter the incident light irradiated into the planar waveguide from its edge and transmit it forward within it (Fig. 17).
In another study, the light scattering effect of silica nanoparticles led to a uniform distribution of light within a reactor during the photosynthetic process while promoting the growth rate of microalgal cells (Giannelli and Torzillo, 2012). Nanoparticles can also enhance light absorption in microalgal culture and subsequently increase both pigment and biomass production (Aratboni et al., 2023). For example, blue light absorption in microalgal cultures can selectively be improved by applying plasmonic filters made of silver nanoparticles with polymer films (Estime et al., 2015). Besides light, nanoparticles can increase the absorption rate and efficiency of available carbon dioxide, further supporting photosynthesis in microalgae (Li et al., 2022;Yang et al., 2022a). In this context, both the growth rate and fatty acid methyl ester productivity of chemoautotrophic microalgae could be improved (Jeon et al., 2017).
Despite the mentioned favorable properties, the steadily increasing application of engineered metal-based nanoparticles in microalgae cultivation has caused growing concerns about their fate in aquatic environments. When entering aquatic compartments, nanoparticles will be exposed to a highly dynamic physical and chemical environment that can modify their physicochemical properties (Vale et al., 2016). Such physical, chemical, and biological modifications (transformations) are the main processes that will define the behavior of nanoparticles in water (Turan et al., 2019). More specifically, physical processes include homo/hetero aggregation, agglomeration, sedimentation, and deposition (Fig. 18a), whereas chemical counterparts encompass photochemical reactions, redox reactions (oxidation, sulfidation), and dissolution (Fig. 18b).
These reactions significantly depend on nanoparticle properties (concentration, size, coating material, shape, and oxidation level) and environmental conditions (pH, ionic strength, and dissolved organic matter) . Figure 19 illustrates the adsorption, dissolution, transformation, and stabilization / aggregation behaviors of magnetic   nanoparticles in the presence of dissolved organic matter. For example, through dissolution (process IV in Fig. 19), the common thin oxide coating on zerovalent magnetic nanoparticles (copper(II) oxide on copper zero-valent magnetic nanoparticles) is removed by natural organic matter through the dissolution process. This process allows sufficient oxidation of the exposed zero-valent magnetic nanoparticles with oxygen (copper(I) oxide formation) .
Organic matter can generally alter the toxicity of magnetic nanoparticles by modifying ROS generation, steric hindrance, electrostatic repulsion, bioavailability of the dissolved nanoparticles, and suspension stabilization (Fig. 20).
Generally, aggregation/agglomeration increases the size of nanoparticles and decreases their concentration in solution, accelerating deposition (Zhang et al., 2018). The rate and size of metal nanoparticle aggregation positively correlate with their concentrations in suspension. Many environmental factors can influence the aggregation process and the stability of metal nanoparticles in aquatic systems. For example, natural organic matter attaches to the particle surface and increases particle stability, whereas ionic strength not only affects the particle surface charge like the pH values do but also alters the electrical double layer.
It should be noted that the existence of natural nanoparticles, colloids and their aggregates, and metallic pollutants further complicate the physicochemical speciation in the exposure medium and determine different biological reactivity. The key chemo-and bio-dynamic processes driving the interactions in the mixtures of engineered nanoparticles (ENPs) and metallic pollutants with aquatic (micro)organisms are shown in Figure 21  .
Exposure to high doses of nanoparticles may reduce biomass and lipid production by suppressing microalgae growth through a direct or indirect mechanism (Fig. 16). The former is done by the adhesion of nanoparticles onto cell membranes, leading to their disruption (Fig. 22)   lipid peroxidation and over-activation of two antioxidative enzymes, i.e., superoxide dismutase and peroxidase. Once ROS is accumulated beyond the threshold, algal photosynthesis, mitochondrial membrane, and DNA will be compromised. Based on "omics" analysis, genes encoding RuBisCo of carbon fixation (rbcL), electron transport chain (atpA, psbD, petF, psaB, cox3, and nad5), light-harvesting proteins of the photosystem, and the reaction center protein of PSII (D1), are suppressed upon exposure to high concentrations of nanoparticles. Moreover, nanoparticles can downregulate the proteins involved in photosynthesis (cytochrome b6-f complex). These interventions eventually reduce the production of nicotinamide adenine dinucleotide phosphate and adenosine triphosphate, and hence, inhibit the assimilation of carbon dioxide and subsequently decrease the rate of sugar synthesis in the Calvin cycle (Chen et al., 2019).
The algal toxicity of nanoparticles could be affected by their oxidation level. This feature is generally influenced by the age of the nanoparticles and the conditions of their surrounding environment. For example, at similar particle sizes (20-30 nm), the algal toxicity of iron nanoparticles varies proportionally to their oxidation level; ZVI>Fe3O4>iron(III) oxide>α-iron(III) oxide>γ-iron(III) oxide (Lei et al., 2016). From the size perspective, the algal toxicity of nanoparticles generally decreases by increasing particle size (Raghupathi et Fig. 16 for the relationship between nanoparticle size and performance indices). This issue was experimentally shown by Zhang et al. (2016), who reported that zinc oxide nanoparticles were more toxic on Skeletonema costatum than their bulk counterparts. It was observed that the algicidal activity of the zinc oxide nanoparticles was linearly correlated with their intracellular accumulation.
Another mechanism through which some metallic nanoparticles (silver and copper(II) oxide) could cause toxicity is the dissolution of bioavailable metal ions. To investigate that, Angel et al. (2013) experimentally tested the impacts of different coatings on the dissolution rate of silver nanoparticles. It was found that polyvinylpyrrolidone-coated silver nanoparticles had a lower dissolution rate and, subsequently, a lower toxicity effect than their citrate-coated counterparts. Besides the coating materials, the rate of nanoparticle dissolution depends on water organic matter. For example, organic chlorine compounds induced silver nanoparticle dissolution. On the contrary, the dissolution rate of silver nanoparticles decreased with increasing the nanoparticle size, i.e., micron-sized silver nanoparticles had a slower dissolution rate than their nano-sized counterparts (Angel et al., 2013).
Since most nanoparticles used in microalgae cultivation may ultimately enter the natural aquatic environments, studying their effects on microorganisms is of crucial importance. In natural ecosystems, most microorganisms exist in multi-species aggregates (Nozhevnikova et al., 2015). These microbial aggregates comprise a substratum (abiotic and/or biotic) for the attachment of complex consortia of microbial cells (archaea, bacteria, microalgae, protozoa, and fungi) that are embedded in a mucilaginous matrix composed of extracellular polymeric substances (Tang et al., 2018). Figure 23 outlines the exposure routes of aggregated microorganisms to nanoparticles in an aquatic environment. To some extent, the microbial community could adapt itself to nanoparticle exposure. Unlike the planktonic state, higher resistance against nanoparticles is shown by microbial aggregates. This could be obtained through two main mechanisms, including (i) community adaptation and (ii) aggregated structure. Figure 24 illustrates the key protection mechanisms against nanoparticle exposure in microbial aggregates. A detailed study of these resistance mechanisms is crucial for engineering fewer toxic nanoparticles for beneficial microorganisms (Tang et al., 2018).

Microalgae biomass harvesting
Microalgae harvesting is one of the main challenges associated with their application as biodiesel feedstock (  The technique involves the interaction between magnetic nanoparticles and microalgae cells, followed by applying an external magnetic field to separate the nanoparticle-microalgae complex. The efficiency of this technique significantly depends on microalgae species, incubation/cultivation age, nanoparticle concentration, culture medium pH, temperature, and both microalgae cell and magnetic nanoparticle surface characteristics (Wang et al., 2015). At the peak value of the microalgae growth phase, the efficiency of magnetic separation is maximum because of higher collisions between magnetic nanoparticles and cells (Hu et al., 2013). Compared to fresh cultures, older cultures have lower surface functional groups. This improves the availability of a given concentration of magnetic nanoparticles to absorb more cells in old cultures and enhance harvest efficiency . However, there is an age threshold after which the efficiency declines. More specifically, following the biomass peak point, microalgae cells undergo autolysis, releasing organic matter, and reducing the availability of magnetic nanoparticles for microalgae cells (Wang et al., 2015). Compared to colonial microalgae, unicellular microalgae have larger specific surface areas because of their  The key chemo-and bio-dynamic processes driving the interactions in the mixtures of metal-containing ENPs and metallic pollutants with aquatic (micro)organisms. These particles are generally diffused in the medium at different rates and reach the (micro)organism surface (1). ENPs might also aggregate (2) or sorb metal pollutants (3). The metal fraction of the ENPs might also release through the dissolution process (4). Once at the organisms' surface, the adsorption of these particles on the cell wall/membrane occurs (5). Following adherence to the cell wall/membrane, the particles can penetrate the cells (6) through endocytosis in the case of "particle-ingestive" organisms, alteration in cell membrane permeability in the case of "particle-proof" organisms, or other possible mechanisms. It should be noted that the transportation of dissolved metallic pollutants could be carried out through active (e.g., via essential trace metal transporters) or facilitated (e.g., via channel-mediated diffusion) transportation. Following the transportation into the cells, ENPs, and metallic pollutants interact with intracellular structures and biomolecules, such as DNA, lipids, and proteins, affecting vital cellular processes (7). ENPs or metallic contaminants could also be transformed    smaller cell size and, hence, require a lower concentration of magnetic nanoparticles (Xu et al., 2011). The surface charge of most microalgae cells is negative at a wide range of pH values (Hu et al., 2013). For example, Chlorella spp. contains abundant hydroxyl and carboxyl groups on their surfaces (Toh et al., 2014b). Therefore, nanoparticles with positively charged surfaces must be used to create an electrostatic attraction and flocculate negatively charged microalgae.
Concerning metal oxides, the pH of the culture medium is another significant parameter influencing their harvest efficiency. This is because the pH of the medium can change the nanoparticles' surface charge by mediating the loss or gain of protons. More specifically, the charge of hydroxyl groups on the surface of metal oxides turns negative and positive at pH above and below the isoelectric point, respectively (Lee et al., 2014a). Hence, metal oxides such as Fe3O4 (isoelectric point of 6.8) perform best in an acidic pH range of 4-6 (Hu et al., 2013) while offering negligible magnetic separation efficiencies (∼10%) under neutral pH, i.e., 7 due to their negatively charged surfaces (Toh et al., 2014a). The presence of some ions in the culture medium may also affect magnetic separation efficiency. Ions such as magnesium 2+ and calcium 2+ improve the flocculation efficiency (Sukenik and Shelef, 1984), whereas some ions, such as phosphate ions (monopotassium phosphate salt), can decrease the efficiency by changing magnetic nanoparticle surface charge from positive to negative (Prochazkova et al., 2013). In addition, the recovery of microalgae biomass is reduced by reducing the temperature of the culture medium. This reduction could be attributed to lower magnetic nanoparticle distribution and mobility at lower temperatures (i.e., higher medium viscosity) (Nassar, 2010).
Nanoparticles used for the magnetic separation of microalgae could be categorized into naked and surface-functionalized magnetic nanoparticles. In fact, naked magnetic nanoparticles could be engineered into functionalized ones to achieve higher harvesting efficiencies. For this purpose, surface coatings and other modifications with materials such as positively charged polymers or cationic surfactants with positively charged functional groups are utilized (Zheng et al., 2016). For instance, a cationic surfactant, e.g., cetylpyridinium bromide, cetylpyridinium chloride, or cetrimonium bromide, can be used for the decoration of Fe3O4 nanoparticles   (Fig. 26).
Cationic polyelectrolyte (poly diallyldimethylammonium chloride) (Lim et al., 2012) and cationic polymer (polyethylenimine) (Hu et al., 2014a) were coated on Fe3O4 to improve the electrostatic interaction between the nanoparticle and microalgae biomass. The corresponding efficiencies of ∼99% and 97% were achieved for the magnetic separation of Chlorella sp. and Corymbia ellipsoidea in the presence of the Fe3O4 nanoparticles, respectively (Lim et al., 2012). Fe3O4 nanoparticles coated with cationic polyacrylamide have also been applied for magnetic separation of C. ellipsoidea and Botryococcus braunii (Fig. 27) (Wang et al., 2014a). At pH 7, the adsorption  (3-aminopropyl)triethoxysilane-coated nanoparticles size by ~10.8 times (from 108 nm to 1.17 µm) (Seo et al., 2014). Oleaginous Chlorella sp. HQ was magnetically separated by sponge-like nanocomposites (graphene-Fe3O4/polydiallyldimethylammonium chloride), synthesized using Fe3O4, graphene oxide, and cationic polymer diallyldimethylammonium chloride (Liu et al., 2016b). The harvesting performance of the nanocomposites was compared to those of naked Fe3O4 and graphene-functionalized Fe3O4. A higher harvesting efficiency was achieved by graphene-Fe3O4 over Fe3O4 (62.7% vs. 80.1%) owing to the beneficial contributions (high surface area, lightweight, stable dispersion) of graphene sheets. Incorporating the polymer (graphene-Fe3O4 /polydiallyldimethylammonium chloride) further improved the harvesting efficiency of graphene-Fe3O4 by 8.6% (Liu et al., 2016b). Moreover, the nanocomposites graphene-Fe3O4/polydiallyldimethylammonium chloride showed a wider pH activity range due to the presence of graphene oxide. These advantages could be attributed to the strong interactions (electrostatic attraction and hydrogen bonds) between the graphene sheets and the polymer diallyldimethylammonium chloride through their active sites. The presence of the polymer could improve microalgae flocculation through adsorption bridging and electrostatic interactions of its nitrogen + groups with the negatively charged microalgae cells.
Magnetic separation is popular because of its economic feasibility and ease of application . With the same energy input, greater amounts of biomass and total extracted lipid contents could be obtained when conventional harvesting techniques are replaced by magnetic separation using magnetic nanoparticles, especially using those with cell-disruption capabilities (Seo et al., 2016). The environmental feasibility of the separation process can also be improved by implementing this technique owing to the possibility of recycling both magnetic nanoparticles and the spent culture medium after harvest (Lee et al., 2013a). These advantages reduce energy consumption, water usage, and nanoparticles' negative effects on the environment. Compared to naked magnetic nanoparticles, their functionalized counterparts provide higher separation efficiencies while delivering more rapid processes, lower energy consumption, and wider pH activity ranges (Hu et al., 2014a).
Despite the advantages of magnetic separation, some technical and environmental constraints also exist. One of the main technical issues is the inefficient postharvest separation of magnetic nanoparticles from microalgae biomass under certain circumstances. This issue could significantly affect the environmental and economic feasibilities of the entire process by increasing energy consumption and reducing nanoparticle recycling and the purity of harvested microalgae biomass (Lee et al., 2015a). The technical issue of postharvest separation of magnetic nanoparticles could be, to some extent, overcome by increasing nanoparticle size at the expense of the amount required (Seo et al., 2014). The environmental risks of nanoparticles application (including magnetic ones) were explained earlier.
Magnetic nanoparticles can generate microbial toxicity via membrane depolarization and disruption of cell integrity. This is caused by the electrostatic interaction between the negatively charged bacterial membrane and the positively charged cationic polymer or free metal ions (Arias et al., 2018). Alternatively, magnetic nanoparticles can pass through cell membranes via passive diffusion, receptor-mediated endocytosis, clathrin-mediated endocytosis, and caveolin-mediated endocytosis (Patil et al., 2018). Upon entering the microbial cell, magnetic nanoparticles are enzymatically broken into iron 2+ ions (Patil et al., 2018), triggering lipid peroxidation, DNA damage, protein (gene expression), and organelle dysfunctions (actin polymerization, mitochondria) (Arias et al., 2018). Before entering the cells, hydrogen peroxide and other ROS could also be generated on the surface of magnetic nanoparticles through photocatalytic reaction under ultraviolet and visible lights . The transportation of these oxidative nanoparticles into microbial cells can intensify the mentioned cellular damage.

Animal fat
Meat production wastes increase with population growth and living standards because of higher demands for processed food. Animal fat is one of the most important fractions of such waste, mainly consumed by the soap and candle production industries, animal feed supplements, and lubricants. However, because of some health concerns, for example, the transmission risk of bovine spongiform encephalopathy by beef tallow, biodiesel production from this low-cost feedstock has grown substantially.

Livestock and poultry
Nanotechnology can improve feed efficiency and nutritional value (faster growth rate) while minimizing disease-related losses in livestock and poultry production (Chen and Yada, 2011). These advantages significantly increase the economic feasibility of animal husbandry, leading to higher fat production and availability for biodiesel production under the biorefinery concept. Nanoparticle-containing food supplements for animals (nanofeed®) enhance animal body defense against pathogens by boosting the immunity system or exerting antimicrobial effects (El Sabry et al., 2018). Additionally, nanoadditives could improve cell activities (as an antioxidant) (Hassan et al., 2017), anticancer mechanisms (Jain et al., 2018), phosphate utilization, and bone growth (Sekhon, 2014) in animals.
Despite the advantages of nanoparticles, some may damage the liver, lungs, and brain (as elaborated earlier). This issue necessitates the green synthesis and use of nanoparticles from plants (e.g., Aloe vera, Camellia sinensis, Azadirachta indica) for future applications. In general, nanomaterials, due to their very small size, are absorbed through the gastrointestinal tract, internalized into cells, and interact with cellular organelles and macromolecules (DNA, ribonucleic acid, protein). The mentioned interactions can cause cell mutation or deficient defense mechanisms by disturbing the biochemical pathways. The causes of genotoxicity induced by nanomaterials are either direct interaction of nanomaterials with genetic material (DNA, ribonucleic acid) or indirect damage by ROS (Dasgupta and Ranjan, 2018).

Aquaculture
With 40-65% oil content, fish and aquaculture wastes are suitable biodiesel feedstocks (Behçet, 2011). In aquaculture, nanotechnology can be used for water purification, quality enhancement, safety (waterborne pathogens removal), and aquatic feed production (Handy, 2012). For example, adding Se nanoparticles (a trace element essential for aquatic health) into the diets of crucian carp significantly increased the growth rate in terms of the final body weight (Zhou et al., 2009). The improvement is attributed to the function of Se as an essential antioxidant activating glutathione peroxidase enzyme. This enzyme plays a key role in cell viability and survival by preventing the Fenton reaction through scavenging hydrogen peroxide and preventing hydroxyl radical formation. The presence of other nanoparticles, such as iron nanoparticles, in sturgeon and young carp diets could also enhance fish growth rate. Notably, nanoparticles could deliver nutrients such as omega fatty acids, lycopene, and vitamins to cells (Jha et al., 2011).
Concerning water quality, the meritorious properties (small size, high reactivity, and large surface area) of iron-manganese binary nano-oxides reportedly allowed an efficient removal of arsenic(III) and arsenic(V) from groundwater before water application in aquaculture (Kong et al., 2013). Calcium-alginate-entrapped nanoscale iron is another functionalized nanoparticle with efficient arsenic removal capability from water resources (Bezbaruah et al., 2014). Lanthanum nanoparticles have been successfully used to absorb phosphates from water and prevent algal growth in fishponds (Ribi -Zelenovi et al., 2009). For pathogen suppression, fungal infections in rainbow trout were effectively prevented using Ag-coated water filters (Johari et al., 2016).

Concluding remarks and future directions
The role of nanotechnology and nanomaterials in boosting the productivity of different biodiesel feedstock generations was critically reviewed and discussed. Overall, the following main conclusions can be drawn from the published studies. new way. Fertilizers can be applied in nanoparticle form to deliver micro/macronutrients (e.g., zinc and calcium) or improve the functioning of fertilizers. Nanopesticides can be distributed efficiently on target species because of their small size. II. The cultivation and harvesting of microalgae can be improved by applying nanotechnology. Harvesting is one of the most important challenges associated with algal biodiesel. Magnetic nanomaterials offer easy scale-up along with fast and gentle processing and could thus be an effective strategy for microalgal harvesting. III. Nanotechnology could improve the performance and health status of livestock, poultry, and aquaculture systems. These production systems meet human nutritional needs and produce many waste oils/fats that could be used as biodiesel feedstock. Although nanotechnology could enhance crop yield, decrease fertilizer/pesticide loss, and protect the environment by replacing conventional fertilizers/pesticides, its potential negative effects on soil organisms are poorly understood. In addition, the leaching of nanoparticles into water bodies could have detrimental effects on human health and aquatic biota by releasing metal ions. Future studies should examine the leakage of nanoparticles into water bodies and the resulting health issues. IV. Despite the encouraging findings reported in the published studies about using magnetic nanomaterials in microalgae harvesting, their full retention, recovery, and reuse remain challenging. More specifically, magnetic nanoparticles are sensitive to corrosion in an aquatic environment because of their high reactivity, reducing their lifespan and making their full recovery impractical (Saikia et al., 2019). Accordingly, future research should focus on fully recovering magnetic nanomaterials in algal biodiesel systems, which is crucial from economic and environmental viewpoints. V. The performance and health status of livestock, poultry, and aquaculture systems could reportedly be improved with the aid of nanotechnology. Nevertheless, the potentially toxic effects of some nanoparticles on living organisms should be evaluated carefully.

Acknowledgments
The Citrate-reduced gold and biosynthesized silver  Smith, and Alfa Laval. He cumulatively participated in more than 33 million yuan of research and industrial projects, making him a unique researcher to expand top research work to industrial products. He aims to bridge the gap between universities and industries following the concept of Honeywell, Tesla Inc., and Lockheed Martin Corporation.
Hossein Shahbeik holds a PhD in Chemical Engineering (Biotechnology) from the Tarbiat Modares University, Iran. He is currently a Postdoctoral Researcher at Henan Agricultural University (China) and Universiti Malaysia Terengganu (Malaysia). Hossein`s research interests primarily include renewable energies, machine learning, thermochemical conversion processes, and sustainability assessment. He has publications in precious journals such as Renewable and Sustainable Energy Reviews and Chemical Engineering Journal. Dr. Shahbeik is the Guest Editor of "e-Prime" (Elsevier). Hossein has worked in the petrochemical industry for seven years as a senior engineer in the field of QC&QA.
Omid Mahian is a full Professor at Faculty of Mechanical Engineering and Mechanics, Ningbo University. He is also a visiting professor of the Department of Chemical Engineering, Imperial College London. Currently, he is a member of the Editorial Board of Energy (Elsevier), Renewable Energy (Elsevier), and Journal of Nanostructures in Chemistry (Springer), a senior associate editor of the Journal of Thermal Analysis and Calorimetry (Springer), and some other journals. His research direction mainly includes the application of nanotechnology in renewable energy (such as nanofluids application in solar collectors and solar desalination) and analysis of thermal systems. So far, he has published more than 100 SCI papers. He has papers in top journals, including Joule, Progress in Energy and Combustion Science, Physics Reports, and Nano Energy. He has received several international awards from conferences and innovation exhibitions for his contribution to the field of heat transfer and renewable energy.
Hassan Karimi-Maleh works as a professor in the School of Resource and Environment, University of Electronics Science and Technology of China (UESTC). He is a highly cited researcher selected by Clarivate Analytics 2018 (cross-filed), 2019 (Agriculture field) and 2020 (cross-filed), 2021 (Chemistry and Agriculture, two categories in one year), and 2022 (Chemistry and Agriculture, two categories in one year) and Top 1% Scientists in Chemistry and Agriculture simultaneously in ISI Essential Science Indicators from 2014 until now. He has published more than 400 SCI research papers with more than 23000 citations and an h-index of 92 (according to WOS report) and 27800 citations and h-index of 100 (according to Google Scholar). He works on the editorial board of more than 20 international journals, such as Alexandria Engineering Journal (coeditor in editor ELSEVIER IF 6.626). He also works as an adjunct Professor at University of Johannesburg, South Africa, and Lebanese American University, Lebanese. His main research interest includes the development of chemically modified sensors and biosensors using DNA and enzymes as biological recognition elements for food, biological, pharmaceutical, and environmental compounds analysis and investigating electrochemistry behavior of electroactive materials such as polymers, organic and inorganic compounds. Recently, he focused on synthesizing nanomaterials and their application in drug delivery and energy storage fields. He has a big network that works in 3 majors: Environmental, Energy, and Sensor.
Alawi Sulaiman is an associate professor in the Faculty of Plantation and Agrotechnology at Universiti Teknologi MARA. He has a Ph.D. degree in Bioprocess Engineering and has published over 90 articles that have received more than 2,000 citations. He has an h-index of 26 in the academic press. His current research interests include biomass utilization for higher-value bioproducts, biogas and biofertilizer production from organic wastes, wastewater treatment, and organic waste management. His Google Scholar profile can be found at the following link: https://scholar.google.com.my/citations?user=uIluALAAAAAJ&hl=en Changtong Mei is a professor in the College of Materials Science and Engineering at Nanjing Forestry University, China. He received his PhD degree from Nanjing Forestry University in 2004. He worked in Forintek Canada Corp., Vancouver, for 12 months as a visiting scientist from 2002 to 2003. His research group mostly focuses on biocomposites and fiber reinforced polymers.
Mohammadali Kiehbadroudinezhad (Member, IEEE) attained his Ph.D. in mechanical engineering specializing in biosystems-renewable energies from the University of Tehran, Iran, in 2021. His academic journey has been marked by dedication and excellence in sustainable energy. From 2019 to 2021, Kiehbadroudinezhad was a graduate researcher within the Department of Electrical and Computer Engineering at Dalhousie University in Halifax, Canada. This experience broadened his horizons and enriched his understanding of cutting-edge developments in the field. Currently, Kiehbadroudinezhad occupies the role of a Postdoctoral Fellow within the esteemed Division of Engineering at Saint Mary's University, located in Halifax, Canada. Mohammadali's contributions extend beyond academia, as evidenced by his prolific authorship of multiple research articles in high-impact Q1 journals, as well as his valuable contributions to book chapters focused on the domain of renewable energy. His patents in the field highlight his inventive prowess. Kiehbadroudinezhad expertise lies in the modeling and optimization of hybrid renewable energy systems, with a particular emphasis on the harmonious integration of wind, solar, and tidal energy sources. Furthermore, his investigations extend to energy storage, smart grid technologies, fuel cells, and environmental science, showcasing his holistic approach to solving complex energy challenges. He is a member of the editorial board of Energy Storage and Saving (ESS), where he plays a pivotal role in shaping the discourse around energy storage innovations. In addition to his multifaceted contributions, Kiehbadroudinezhad also holds a position as an Editor on the Editorial Board of Frontiers in Energy Research. College University Lahore, Pakistan. He has published over 200 papers on renewable energy, alternative fuels, waste-to-energy, catalytic pyrolysis, anaerobic digestion, and resource recovery. He has delivered over 50 invited talks and training sessions to various national and international forums. His work has been cited more than 12 thousand times in the peer-review press, with a total impact factor of over 1300 and an H-index of 61. He is a Senior Editor in Renewable & Sustainable Energy Reviews (Elsevier Impact Factor 15.9), Energy & Environment (Sage Impact Guillemin's research focus was the identification of blood biomarkers for MND and focus on mechanisms neuroinflammation and neurotoxicity. Prof Guillemin has been studying the involvement of tryptophan catabolism (via the kynurenine pathway-KP) in human several neurodegenerative diseases for more than 20 years. Prof Guillemin and his teams have conducted research that demonstrates the importance of the KP in multiple sclerosis, Alzheimer's disease, and motor neuron disease, which has diagnostic, prognostic, and therapeutic potential. This research has been extended to other diseases such as depression, suicide, autism, and cancers. His more than 380 publications have gained 25900 citations (h-index, 84)." Prof. Lam is active in research on the application of thermochemical processes such as pyrolysis and microwave heating in transforming waste and biomass into green energy and products applicable to industry for carbon capture (e.g., CO2 absorption), carbon emission reduction (e.g., gasification/ pyrolysis of hydrocarbon feedstock, CO2 utilization, and conversion), and environmental protection. He has secured 30 research grants, filed patents and commercialized inventions from his research team, and published over 440 articles in journals, such as Lancet, Nature, Science, Progress in Energy and Combustion Science, and Renewable and Sustainable Energy Reviews.

Dr. Abdul-Sattar
Wanxi Peng is a professor at the College of Forestry, Henan Agricultural University, China. He is the Laboratory Director at Henan Province Engineering Research Center for Forest Biomass Value-added Products. Professor Peng is an academician at the International Academy of Ecology & Life Protection Sciences, UN. He is also a fellow of the Engineered Science Society. He has published more than 300 papers with more than 6,000 citations (h-index: 42, May 2023, Scopus). Xiangmeng Chen, as a postdoctor, works at Henan Province International Collaboration Lab of Forest Resources Utilization and the School of Science of Henan Agricultural University. Engaged in the high-value utilization of biomass resources, the development and application of green fine chemicals, the preparation of new environmental protection materials, and other research fields.