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Green hydrogen, proposed as a sustainable alternative for conventional fuels, has gained utmost importance due to its reduced carbon footprint and potential application in maintaining balance between energy generation and demand. Utilization of hydrogen-based systems are challenged by cost effective storage methods. Bio-hydrogen storage technologies using cryogenic and adsorptive methods are discussed in this review paper, along with their operating conditions and storage capacities. An analysis of operational challenges and recent advancements in hydrogen storage techniques is presented. With a storage pressure of 70 MP, cryogenic hydrogen is almost twice as dense as compressed hydrogen. Technical challenges such as material cost and explosion risk can be addressed by hydrogen adsorption on activated carbon active sites. Maximum hydrogen storage capacity are reported by activated carbon obtained from Chitosan (6.77 wt%), Bamboo (6.6 wt%) and African palm shell (6.5 wt%) at 77 K and 4–20 Mpa. Further, nanotechnology approaches are presented in detail for increasing hydrogen storage capacity in pristine Si and Mg. The future perspectives in terms of technological, and economic aspects are discussed. • Detailed review on hydrogen storage methods is presented. • Role of cryogenics and adsorptive media are discussed. • The comparative performance of various methods is tabulated. • Existing research gap and future perspectives are analyzed. [ABSTRACT FROM AUTHOR]

The pressure on reducing greenhouse gas emissions has increased since the focus on climate change mitigation has grown. As the human development index is directly related to per capita energy consumption, sustainable energy production with reduced carbon footprint is the essential pathway for cleaner environment. Over numerous existing biological processes, hydrogen production via photo fermentation and photolysis of water is considered a more sustainable and economical method of hydrogen production. While both biological modes suffer from certain limitations, such as low yields and low production rates, practical implementation is still a long way off due to these limitations. The unique properties of nanomaterials (NMs) can help increase the efficiency of the biomass to biohydrogen process in significant ways. Applications of organic and inorganic nanoparticles in photocatalytic and photo fermentative hydrogen production is discussed in this paper. This review reports a wide range of applications of nanomaterials including the details of photo fermentative microorganisms and their mechanism of action. The maximum photo fermentative bio-H 2 production was reported in the presence of SiC–Fe 3 O 4 (3.02 mol H 2 /mol acetate), Ni (41 mol H 2 /mol sugar), graphite-C 3 N 4 (64.2 mol H 2 /mol sugar) whereas photocatalytic bio-H 2 yield was highest when Pd–Ni/CdS (54 mmol/g.h), Ni-MO/g-C 3 N 4 (1785 mmol/g.h) and CuO/TiO 2 (20.3 mmol/g.h) nanoparticles were employed. To design photocatalytic systems for practical and scalable use, the future research should be focused on deeper theoretical knowledge of mechanisms of light harvesting, ± charge separation and transport, surface biochemical reactions, semiconductor–liquid interactions, and reactor dynamics. [Display omitted] • Recent developments for improving water photolysis and photo-fermentation are reviewed. • Applications of organic and inorganic nanoparticles in hydrogen production are discussed. • The working principle and mechanism of hydrogen production are discussed. • The influence of key operating factors are presented. • Scope for future research was presented. [ABSTRACT FROM AUTHOR]

Environmental contamination caused by oxyanions like nitrate, selenate, chromate, and other related functional groups in water and wastewater is identified as a serious threat to human health. Among the different techniques attempted to remove or convert these compounds, reduction with the use of microorganisms has gained importance due to high selectivity and efficiency. Hydrogen-based membrane bioreactor (HMBR) is identified as a suitable method due to the non-toxic properties of hydrogen as an electron-donor, reduced secondary pollution, and easy generation of hydrogen through cost-effective novel methods. This research article is focused on the principle and mechanism of removal of anions, organic compounds, heavy toxic polyatomic metal ions, and antibiotics using hydrogen mediated microbial reduction process. Denitrification studies in HMBR at different operating conditions, namely membrane type, pH, nitrate concentration, and hydrogen partial pressure, are reviewed and the commonly reported efficiency ranges between 70 and 100%. The removal efficiencies attained by HMBR are as follows: perchlorate 30–100%, selenate 92–100%, phenol 87–99%, arsenate 60–68% and halogenoalkanes 45–99%. The mechanism of reduction in HMBR was explained with reference to nitrate, arsenate, chlorophenol, and chromate. [Display omitted] • Mechanism of Hydrogen based Membrane Reactor and applications for removal of pollutants are reviewed. • The working principle is discussed with schematic illustration. • The influence of key operating variables is discussed. • Scope for future research and research gap is presented. [ABSTRACT FROM AUTHOR]

Chlorpyrifos (CPF) is a highly toxic phosphate-rich organic pesticide (OP), identified as an emerging contaminant and used extensively in agricultural production. CPF persistence in the environment and its potential health hazards has become increasingly concerning worldwide in recent years due to exponential rise in food demand. Biodegradation of chlorpyrifos by microbial cultures is a promising approach to reclaiming contaminated soil and aquatic environments. The purpose of this review is to summarize the current understanding of microbiological aspects of xenobiotic chlorpyrifos biodegradation, including microbial diversity, metabolic pathways, and factors that modulate it. In both aerobic and anaerobic environments, CPF is biochemically broken down by a broad spectrum of bacteria and fungi. Hydrolysis, dehalogenation, and oxidation of chlorpyrifos are all enzymatic reactions that lead to its degradation. Biodegradation rate and efficiency are strongly influenced by parametric variables such as co-substrates abundance, pH, temperature, and initial chlorpyrifos concentration. The review provides evidence that microbial biodegradation is a viable method for remediating chlorpyrifos-contaminated sites in a sustainable and safe manner. [ABSTRACT FROM AUTHOR]

The contamination of aqueous environment by phenol poses a major threat due to its hyper toxic effects and removal of phenol is challenging due to its hydrophilic properties. This research study examines the surface encapsulation of iron oxide (IO) with bio-derived carbon-based date palm (DP) to make date palm-iron oxide (DP-IO) nanocomposite to potentially remediate phenol in aqueous environment. Phenol removal percentage is predominantly influenced by environmental factors, namely pH, nano sorbent loading, temperature, agitation speed, and initial phenol concentration. Under optimum conditions of 30 °C and pH 7.8, 80.30% of phenol was removed using a 0.75 g/L sorbent load with 100 mg/L initial phenol concentration. Langmuir isotherm fitted well (R2 > 0.997), supporting single-layer phenol attachment with maximum bio-sorption capacity of 72.46 mg/g. A pseudo-2nd-order (PSO) kinetic model is identified to be the most appropriate for the DP-IO sorption experiment (R2 >0.999). Scanning electron microscopic images, X-ray diffraction observations, FT-IR plots, and thermogravimetric analysis have been used to characterize. The removal mechanism involves unimolecular layer and chemisorption is identified as a rate determining step. The reuse potential proved that the synthesized nanocomposite as a sustainable solution for phenolic wastewater treatment. • Novel iron-oxide based nanocomposite was synthesized. • Optimal conditions for maximum phenol removal are identified. • Isotherm modeling was carried out. • Kinetic mechanism was studied. [ABSTRACT FROM AUTHOR]

The rapid consumption of metals and unorganized disposal have led to unprecedented increases in heavy metal ion concentrations in the ecosystem, which disrupts environmental homeostasis and results in agricultural biodiversity loss. Mitigation and remediation plans for heavy metal pollution are largely dependent on the discovery of cost-effective, biocompatible, specific, and robust detectors because conventional methods involve sophisticated electronics and sample preparation procedures. Carbon dots (CDs) have gained significant importance in sensing applications related to environmental sustainability. Fluorescence sensor applications have been enhanced by their distinctive spectral properties and the potential for developing efficient photonic devices. With the recent development of biomass-functionalized carbon dots, a wide spectrum of multivalent and bivalent transition metal ions responsible for water quality degradation can be detected with high efficiency and minimal toxicity. This review explores the various methods of manufacturing carbon dots and the biochemical mechanisms involved in metal detection using green carbon dots for sensing applications involving Cu (II), Fe (III), Hg (II), and Cr (VI) ions in aqueous systems. A detailed discussion of practical challenges and future recommendations is presented to identify feasible design routes. [Display omitted] • Applications of Biomass derived green carbon dots for sensing of metals are discussed. • Various methods of synthesis of green carbon dots are reviewed. • The mechanism of action of carbon dots is explained. • Future scope and challenges are discussed. [ABSTRACT FROM AUTHOR]

Selenium is targeted as a priority pollutant to be removed due to its high toxicity level and lethal effects. In this research, a novel nano sorbent was fabricated using ionic liquid on multiwalled carbon nanotubes (IL-MCNT) and employed for Selenium remediation from aqueous media. Besides solution pH, nanocomposite dosage, the initial selenium concentration, temperature and sorption time were also examined as operating variables. At optimal pH 2.0, 96% of the selenium was removed with maximum efficiency with 100 mg/L of IL-MCNT at 308 K, 45 min of contact time, and 110 g of IL-MCNT dosage. From kinetic studies, it appears that the Langmuir isotherm fits the observed data (R2 > 0.9813), supporting the hypothesis that monolayer attachment occurs. The Langmuir isotherm parameters are evaluated as qm = 125 mg/g and KL = 0.172 L/mg. As a result of testing several kinetic models, the pseudo-second-order model was the most suitable for experimental data (R2 > 0.9746). Scanning Electron Microscopy images, FTIR spectra, and thermogravimetric study were used to examine the synthesized nanomaterial. • Surface modification of CNT using IL is demonstrated. • SEM, FTIR and TGA analyses are carried out. • Optimal operating conditions are identified. • Kinetic and equilibrium studies are conducted. [ABSTRACT FROM AUTHOR]

• Modified CNT was synthesised. • Porous structure characterization were performed. • Effect of variables on phenol removal was studied. • Kinetic and isotherm modeling studies were conducted. Carbon nano tubes are functionalized to enhance their surface properties and target specificity. In this research, a novel ionic liquid functionalized carbon nanotube (IL-CNT) material was synthesized using 1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide and investigated for the phenol removal. The parametric experiments were performed to identify the optimal conditions for high removal performance. With an initial concentration of 50 mg/L and an IL-CNT dosage level 100 mg, 95.36% phenol removal was attained at optimal pH 6.0. The occurrence of monolayer attachment was verified through equilibrium studies. The Langmuir isotherm parameters are evaluated as q m =109.9 mg/g and K L = 0.196 L/mg. The kinetic experiments followed Pseudo Second Order model (R2 > 0.990). The synthesized nanomaterial was characterized using Scanning Electron Microscopic imaging, Fourier Transform Infra-Red spectra, X-Ray Diffraction analysis and Thermo Gravimetric Analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

Lead and Cadmium, identified as toxic heavy metals, cause significant imbalance in the eco-system due to their tendency to bioaccumulate. Remediation of heavy metals by conventional adsorptive materials suffer demerits related to low efficiency or removal. Among the variety of adsorbent materials used in the adsorption process, metal oxides- and graphene oxide magnetic nanocomposites have gained a considerable attention. The use of nanomaterials may help to reduce this contamination, but after use, they are difficult to remove from water. An added magnetic property to nanomaterials facilitates their retrieval after use. The magnetic properties of these hybrid magnetic nanocomposites, coupled with unique characteristics of organic and inorganic elements, have found extensive application in water treatment technology. Detailed discussion on functionalisation of magnetic nanocomposites and the enhanced performance are presented. Magnetic graphene oxide-covalently functionalized-tryptophan was reported to have the highest adsorption capacity of 766.1 mg/g for remediation of lead (II) ions and graphene oxide exhibited the highest adsorption capacity of 530 mg/g for Cd (II) ions. The adsorption mechanisms for heavy metal ions on the surface of novel adsorbents, particularly lead and cadmium, using magnetic nanocomposites have been explained with reference to the isotherm models studied. The future scope of research in this area of research is proposed. [ABSTRACT FROM AUTHOR]

• Detailed review on enhanced production of biohydrogen is presented. • Role of nanocatalysts, operating conditions and their mechanism of action are discussed. • Critical comparison of the nanocatalyst performance is tabulated. • Existing research gap and future perspectives are presented. Renewable energy research has gained momentum due to the fast consumption and lack of sustainability in conventional fuels. As biohydrogen emits no greenhouse gases and can be generated from a variety of waste biomass or feedstocks, it has been referred to as the most effective and cleanest form of energy among all biofuels. In spite of the success of photobiological and dark fermentation methods in generating biohydrogen, they are known to produce lower yields, creating serious obstacles for commercial production. The role of nanoscience and technology in improving the biohydrogen production is achieved through the use of nanomaterials with specific physiochemical and structural properties. In this review, metals, metal oxides, metal alloys, and inorganic nanomaterials are explored in order to improve biohydrogen production. Initial studies have focused on nano materials evaluation in biomass conversion and addressing the current status of nanomaterials in biohydrogen production. The best bio-H 2 yield is obtained in the presence of metal nanoparticles (NPs) such as Ag (2.4 mol H 2 / mol glucose), Cu (1.74 mol H 2 / mol glucose), Fe (3.10 mol H 2 / mol malate), alloys of Al/Cu/Fe (4.2 mol H 2 / sucrose) and Ni (2.54 mol H 2 /glucose). The review also addressed the mechanisms involved in changing feedstock into hydrogen through various microbial biorefineries. The life cycle analysis of various nanoparticles applications in biohydrogen production was discussed. [ABSTRACT FROM AUTHOR]

• Importance of nano additives and nanocatalysts for bioethanol production is discussed. • Performance of different nano catalysts are compared with respect to bioethanol yield. • Applications of nano biocatalysts for enhanced bioethanol yield are discussed. • Machine learning applications for bioethanol studies are reviewed. • Mechanism of nanoparticles for bioethanol production is elaborated. Renewable energy sources based on biomass are identified as sustainable solution to balance the carbon footprint and fuel requirements. The characteristics of bioethanol make it an ideal fuel additive due to its eco-friendliness and calorific value. Fermentation technology is used to convert carbohydrate-rich biomass into biofuel, but technical glitches and high costs have been identified as drawbacks. Nanomaterials have contributed significantly to bioethanol synthesis in terms of enhanced surface activity and selectivity. By using nanoparticles, various steps in the production of bio-alcohol can be made more efficient and cheaper. Based on the extensive review carried out, the best bioethanol yield reported were: dolomite at 121 °C (106%), methyl-functionalized cobalt ferrite– silica at 37 °C (126.9%) and calcium alginate at 37 °C (100%). Magnetic iron oxide covered cellulase yielded 60% in the temperature range of 24–96 °C and Silica-immobilized cellulase yielded 32 g/L at 25–60 °C. Methyl-functionalized cobalt ferrite–silica emerged as an efficient nano-bio catalyst as it gives highest ethanol yield at moderate temperature (37 °C) and pressure (1–2 atm). The mechanism of action of the nanoparticles is discussed in this research and the future directions of research are proposed. Machine learning applications for the prediction of bioethanol yield were discussed in detail. [ABSTRACT FROM AUTHOR]