Green hydrogen production through consolidated bioprocessing of lignocellulosic biomass using nanobiotechnology approach

Valorizing Bio-Waste and Residuals

The circular bioeconomy connects waste recycling with utilizing organic biomass waste for bioenergy, bio-based materials, and biochemical production. This integration promotes efficient resource utilization, reduced greenhouse gas emissions, and sustainable economic growth. Several technologies such as composting, anaerobic digestion, biochar production, gasification, pyrolysis, pelletization, and advanced thermal conversion technologies are utilized to manage agricultural waste efficiently. Waste-to-energy systems and food waste valorization techniques are employed to convert agro-waste into renewable energy sources such as bioethanol, biodiesel, and biogas through fermentation, transesterification, and anaerobic digestion. These biofuels offer renewable alternatives to fossil fuels, reducing greenhouse gas emissions and dependence on non-renewable resources. Rice husk, a globally abundant agricultural waste, can be utilized for energy production through technologies like direct combustion and fast pyrolysis. Biobutanol, synthesized from acetone-butanol-ethanol fermentation of agricultural residues like orange peel, presents a promising fuel option. Agricultural waste can also serve as feedstock for bio-based chemicals like organic acids, solvents, and polymers, reducing reliance on petroleum-based chemicals. Agro-waste materials like grass, garlic peel, and rice bran have shown potential for dye adsorption in wastewater treatment applications. Moreover, agricultural waste can be repurposed as animal feed, contributing to waste reduction and providing sustainable nutrition for livestock. Plant seeds and green biomass offer sustainable protein sources, while residues like straw and sawdust can be used for mushroom cultivation. Agro-waste biopolymers like starch and cellulose can be transformed into biodegradable plastics and biocomposites, offering eco-friendly alternatives. Additionally, agro-waste materials like straw, rice husks, and bamboo can be processed into construction materials, reducing environmental impact in building projects. Extracts from plant residues and fruit pomace can be utilized in pharmaceuticals, nutraceuticals, and cosmetics. Valorizing agro-waste for food, feed, fibers, and fuel offers opportunities to minimize waste and maximize resource efficiency, resulting in high-value products.

Photocatalytic nanomaterials and their implications towards biomass conversion for renewable chemical and fuel production

Photocatalytic processes have recently gained popularity as a sustainable and energy-efficient method for converting biomass. This article gives a comprehensive overview of recent improvements in the photocatalytic conversion of biomass into useful chemicals and fuels utilizing various photocatalytic materials. The work delves into the assessment of diverse biomass sources and their preparation techniques, in addition to the synthesis of plasmonic nanoparticles as photocatalysts from biomass, offering a thorough examination. This review article provides detailed techniques for fabricating and synthesizing plasmonic nanoparticles. Furthermore, the study discusses advancements in coupling photo-oxidation alongside the hydrogen evolution mechanism for water splitting. Furthermore, prospective research topics are suggested, such as conducting a systematic analysis of photocatalysis's redox potential, developing more effective catalysts, broadening the variety of reaction types, and establishing industrial-scale photocatalytic production. Plasmonic photocatalysts have been utilized to convert biomass into H2 for energy, and to explore hypothesized molecular routes for the photocatalytic oxidation of 5-hydroxymethylfurfural (HMF), which may then be converted into 2,5-furandicarboxylic acid (FDCA). This review also discusses the surface functionalization of nanophotocatalysts with -COOH, NH2, and OH groups to increase their reactivity. Reactive oxygen species (ROS) formed on the surface of nanophotocatalysts under UV or solar light play a crucial role in photocatalytic reactions. Our review has shown many challenges and difficulties related to CO2 hydrogenation reactions in the presence of sustainable H2, powered by renewable energy sources. This is very critical for achieving a transition to net-zero emissions. These technologies will drive forward the development of biomass conversion processes into CO2-based fuels. This paper explores recent advancements in the conversion of biomass-derived CO2 into valuable chemicals using plasmonic nanophotocatalysts. In addition to this, density functional theory (DFT) calculations also reveal how functional groups help stabilize these nanoparticles and enhance electron density through photo-adsorption. This study provides a remarkable and significant review that examines current trends, future directions, and ongoing debates in this field, focusing on reaction conditions, catalyst design, and proposed mechanisms for producing valuable chemicals. These chemicals include single-carbon compounds like formaldehyde, formic acid, and methanol, as well as C2 + compounds such as acetic acid, ethanol, methyl formate, and oxyethylene ethers. Additionally, it addresses the current state of liquid-phase CO2 hydrogenation in the presence of photocatalysts, highlighting existing challenges and potential research paths. The paper also provides an overview of the advances and challenges in the electro- and photocatalytic oxidation of HMF (hydroxymethylfurfural), detailing strategies for creating high-value chemicals through these oxidation processes. These methods, which may involve reactions like the hydrogen evolution reaction, organic substrate reduction, CO2 reduction reaction, or N2 reduction reaction, are summarized and analyzed. Furthermore, the catalytic efficiency and mechanisms of various catalyst types in these conversion systems are introduced and discussed. Electron paramagnetic resonance and scavenger studies reveal the major active species (˙OH and ˙O2 -) in the photocatalytic conversion of biomass to different value-added products.

Harnessing recalcitrant lignocellulosic biomass for enhanced biohydrogen production: Recent advances, challenges, and future perspective

Biohydrogen (Bio-H2) is widely recognized as a sustainable and environmentally friendly energy source, devoid of any detrimental impact on the environment. Lignocellulosic biomass (LB) is a readily accessible and plentiful source material that can be effectively employed as a cost-effective and sustainable substrate for Bio-H2 production. Despite the numerous challenges, the ongoing progress in LB pretreatment technology, microbial fermentation, and the integration of molecular biology techniques have the potential to enhance Bio-H2 productivity and yield. Consequently, this technology exhibits efficiency and the capacity to meet the future energy demands associated with the valorization of recalcitrant biomass. To date, several pretreatment approaches have been investigated in order to improve the digestibility of feedstock. Nevertheless, there has been a lack of comprehensive systematic studies examining the effectiveness of pretreatment methods in enhancing Bio-H2 production through dark fermentation. Additionally, there is a dearth of economic feasibility evaluations pertaining to this area of research. Thus, this review has conducted comparative studies on the technological and economic viability of current pretreatment methods. It has also examined the potential of these pretreatments in terms of carbon neutrality and circular economy principles. This review paves the way for a new opportunity to enhance Bio-H2 production with technological approaches.

Catalytic hydrolysis of agar using magnetic nanoparticles: optimization and characterization

BACKGROUND

Agar is used as a gelling agent that possesses a variety of biological properties; it consists of the polysaccharides agarose and porphyrin. In addition, the monomeric sugars generated after agar hydrolysis can be functionalized for use in biorefineries and biofuel production. The main objective of this study was to develop a sustainable agar hydrolysis process for bioethanol production using nanotechnology. Peroxidase-mimicking Fe3O4-MNPs were applied for agar degradation to generate agar hydrolysate-soluble fractions amenable to Saccharomyces cerevisiae and Escherichia coli during fermentation.

RESULTS

Fe3O4-MNP-treated (Fe3O4-MNPs, 1 g/L) agar exhibited 0.903 g/L of reducing sugar, which was 21-fold higher than that of the control (without Fe3O4-MNP-treated). Approximately 0.0181% and 0.0042% of ethanol from 1% of agar was achieved using Saccharomyces cerevisiae and Escherichia coli, respectively, after process optimization. Furthermore, different analytical techniques (FTIR, SEM, TEM, EDS, XRD, and TGA) were applied to validate the efficiency of Fe3O4-MNPs in agar degradation.

CONCLUSIONS

To the best of our knowledge, Fe3O4-MNP-treated agar degradation for bioethanol production through process optimization is a simpler, easier, and novel method for commercialization.

Coriolus versicolor laccase-based inorganic protein hybrid synthesis for application in biomass saccharification to enhance biological production of hydrogen and ethanol

In this study, a bio-friendly inorganic protein hybrid-based enzyme immobilization system using partially purified Coriolus versicolor laccase (CvLac) was successfully applied to biomass hydrolysis for the enhancement of sugar production aimed at generating biofuels. After four days of incubation, the maximum CvLac production was achieved at 140 U/mg of total protein in the presence of inducers such as copper and wheat bran after four days of incubation. Crude CvLac immobilized through inorganic protein hybrids such as nanoflowers (NFs) using zinc as Zn3(PO4)2/CvLac hybrid NFs (Zn/CvLac-NFs) showed a maximum encapsulation yield of 93.4% and a relative activity of 265% compared to free laccase. The synthesized Zn/CvLac-NFs exhibited significantly improved activity profiles and stability compared to free enzymes. Furthermore, Zn/CvLac-NFs retained a significantly high residual activity of 96.2% after ten reuse cycles. The saccharification of poplar biomass improved ∼2-fold in the presence of Zn/CvLac-NFs, with an 8-fold reduction in total phenolics compared to the control. The Zn/CvLac-NFs treated biomass hydrolysate showed high biological hydrogen (H2) production and ethanol conversion efficiency of up to 2.68 mol/mol of hexose and 79.0% compared to the control values of 1.27 mol of H2/mol of hexose and 58.4%, respectively. The CvLac hybrid NFs are the first time reported for biomass hydrolysis, and a significant enhancement in the production of hydrogen and ethanol was reported. The synthesis of such NFs based on crude forms of diverse enzymes can potentially be extended to a broad range of biotechnological applications.

Depolymerization of lignin: Recent progress towards value-added chemicals and biohydrogen production

The need for alternative sources of energy became increasingly urgent as demand for energy and the use of fossil fuels both soared. When processed into aromatic compounds, lignin can be utilized as an alternative to fossil fuels, however, lignin's complex structure and recalcitrance make depolymerization impractical. This article presented an overview of the most recent advances in lignin conversion, including process technology, catalyst advancement, and case study-based end products. In addition to the three established methods (thermochemical, biochemical, and catalytic depolymerization), a lignin-first strategy was presented. Depolymerizing different forms of lignin into smaller phenolic molecules has been suggested using homogeneous and heterogeneous catalysts for oxidation or reduction. Limitations and future prospects of lignin depolymerization have been discussed which suggests that solar-driven catalytic depolymerization through photocatalysts including quantum dots offers a unique pathway to obtain the highly catalytic conversion of lignin.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Impact of nanomaterials on sustainable pretreatment of lignocellulosic biomass for biofuels production: An advanced approach

Biomass to biofuels production technology appears to be one of the most sustainable strategies among various renewable energy resources. Herein, pretreatment is an unavoidable and key step to increase free cellulose availability and digestibility to produce green fuels. Various existing pretreatment technologies of lignocellulosics biomasses (LCBs) face distinct challenges e.g., energy consuming, cost intensive, may lead partial removal of lignin, complex inhibitors production as well as may cause environmental pollutions. These, limitations may be overcome with the application of nanomaterials, employed as nanocatalysts during the pretreatment process of LCBs. In this prospect, the present review focuses and summarizes results of numerous studies and exploring the utilizations of magnetic, carbon based nanostructure, and nanophotocatalysts mediated pretreatment processes along with their possible mechanisms to improve the biofuels production compared to conventional chemical based pretreatment approaches. Furthermore, different aspects of nanomaterials based pretreatment methods with their shortcomings and future prospects have been discussed.

Enzymatic Characterization of Unused Biomass Degradation Using the Clostridium cellulovorans Cellulosome

The cellulolytic system of Clostridium cellulovorans mainly consisting of a cellulosome that synergistically collaborates with non-complexed enzymes was investigated using cellulosic biomass. The cellulosomes were isolated from the culture supernatants with shredded paper, rice straw and sugarcane bagasse using crystalline cellulose. Enzyme solutions, including the cellulosome fractions, were analyzed by SDS-PAGE and Western blot using an anti-CbpA antibody. As a result, C. cellulovorans was able to completely degrade shredded paper for 9 days and to be continuously cultivated by the addition of new culture medium containing shredded paper, indicating, through TLC analysis, that its degradative products were glucose and cellobiose. Regarding the rice straw and sugarcane bagasse, while the degradative activity of rice straw was most active using the cellulosome in the culture supernatant of rice straw medium, that of sugarcane bagasse was most active using the cellulosome from the supernatant of cellobiose medium. Based on these results, no alcohols were found when C. acetobutylicum was cultivated in the absence of C. cellulovorans as it cannot degrade the cellulose. While 1.5 mM of ethanol was produced with C. cellulovorans cultivation, both n-butanol (1.67 mM) and ethanol (1.89 mM) were detected with the cocultivation of C. cellulovorans and C. acetobutylicum. Regarding the enzymatic activity evaluation against rice straw and sugarcane bagasse, the rice straw cellulosome fraction was the most active when compared against rice straw. Furthermore, since we attempted to choose reaction conditions more efficiently for the degradation of sugarcane bagasse, a wet jet milling device together with L-cysteine as a reducing agent was used. As a result, we found that the degradation activity was almost twice as high with 10 mM L-cysteine compared with without it. These results will provide new insights for biomass utilization.