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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]

• 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]

Dihydrogen, commonly named 'hydrogen', is a carbon–neutral and renewable fuel meeting environmental regulations in transportation and industrial production. Hydrogen is currently employed in fuel cells, hydrogen vehicles, and as an efficient energy carrier due to its high energy capacity of 121 kJ per g. Here we review hydrogen production by steam reforming of alcohols including methanol, ethanol, propanol, glycerol and butanol, with focus on catalysts, mechanisms, and analytical methods to characterize deposited carbon. In general, Ru- and Rh-based catalysts show efficient performance with almost 100% feedstock conversion and up to 89% of hydrogen yield, while Ni and Co catalysts exhibit lower ethanol conversion in the range of 40–100% depending on operating conditions. Nevertheless, Ni and Co catalysts have been mainly chosen as active metals for alcohols steam reforming due to their lower cost. [ABSTRACT FROM AUTHOR]

• Biological sequestration techniques for CO 2 reduction are described. • Bioenergy with carbon capture and storage concept is reviewed. • The economic feasibility and environmental outlook are reviewed. • A novel illustration of the artificial photosynthesis process is addressed. Drastic changes in climatic conditions accelerate the need for the implementation of emission reduction techniques to restrict global warming. Conventional technologies do face severe drawbacks in reducing carbon emissions. Carbon neutrality is considered as the most essential concept as it can alleviate the issues of greenhouse gas emissions while deriving energy and fuels from fossil origin. Several reduction technologies are proposed in the recent past, in which the integration of renewable energy resources such as solar and wind power are signified. The review aims to provide an understanding of the technology transition to attain carbon neutrality through production of carbon-free energies such as hydrogen and bioenergy. Despite the chemical and physical sequestration methods, the biological sequestration technique is given special attention for the mitigation of CO 2 emissions by utilizing photosynthetic microalgae. Of numerous microalgae, Chlorella vulgaris , a common eukaryotic microalga found in freshwater showed a maximum CO 2 fixation rate of about 3.35 g/L/d with 10 % CO 2 input. Apart from capturing and storing carbon in the geological site, the concept of utilizing and converting carbon into valuable byproducts is described elaborately. The possibilities for utilizing renewable energy sources for carbon-free energy production through unique prototypes are reviewed and elaborated. It mainly aids to utilize renewable resources more than conventional, which significantly minimizes the carbon footprint. The integration of bioenergy, carbon capture and storage concepts with renewable energy sources extends opportunities to minimize emissions and transition towards carbon neutrality and indeed can aid in achieving carbon negativity. The aforementioned concept was reported to produce about 12.5 million tons ton of hydrogen with 133 million tons of CO 2 recovery. An innovative prototype to resolve emission issues other than CO 2 was also addressed. Illustrations of the artificial photosynthesis process, convective vortex system and integrated multi energy system are disc proposed innovative carbon reduction technologies' economic feasibility and environmental outlook technologies are reviewed and presented. [ABSTRACT FROM AUTHOR]

Dihydrogen (H2), commonly named "hydrogen", is attracting research interest due to potential applications in fuel cells, vehicles, pharmaceuticals and gas processing. As a consequence, the recent discoveries of natural gas reservoirs have prompted the development of technologies for methane conversion to hydrogen. In particular, the catalytic decomposition of methane is a promising technology to generate COx-free hydrogen and multi-wall carbon materials. Carbon nanomaterial byproducts can be used in electronics, fuel cells, clothes, and for biological and environmental treatments. Recent research has investigated the performance of hydrogen production and the characteristic of carbon nanomaterials. Here, we review the decomposition of methane on Ni-based catalysts, with focus on the influence of reaction temperature, gas hourly space velocity, support, and promoter. Ni-based catalysts allow CH4 conversion higher than 70% with H2 yield of about 45% at more than 700 °C. We present catalyst regeneration by various techniques such as combustion. Reactors used for catalytic decomposition of methane include fluidized bed, fixed-bed and plasma reactors. [ABSTRACT FROM AUTHOR]

An efficient BiVO 4 nanocatalyst with Erbium (Er) and Yttrium (Y) doping was synthesized via a facile microwave irradiation route and the obtained materials were further characterized through various techniques such as p-XRD, FT-IR, FE-SEM, HR-TEM, UV–Vis DRS, PL, LSV, and EISanalysis. The obtained results revealed that the rare metals induce the stabilization of the monoclinic-tetragonal crystalline structure with a distinct morphology. The yttrium doped BiVO 4 (Y–BiVO 4) monoclinic-tetragonal exhibited anefficient photoelectrochemical water splitting and photocatalytic performanceare compared to bare BiVO 4. TheY-BiVO 4 indicated increased results of photocurrent of 0.43 mA/cm2and bare BiVO 4 0.24 mA/cm2. Also, the Y-doped BiVO 4 nanocatalyst showed the maximum photocatalytic activity for the degradation of MB, MO, and RhB. A maximum degradation of 93%, 85%, and 91% was achieved for MB, MO, and RhB respectively, within 180 min under the visible light illumination. The photocatalytic decomposition of acetaldehyde also was performed. The improved photoelectrochemical water splitting and photocatalytic activity are due to the narrowing the bandgap, leading to extending the photoabsorption capability and reducing the recombination rate of photoexcited electron-hole pairs through the formation inner energy state of the rare earth metals. The current study disclosed that the synthesis of nanomaterials with crystal modification could be a prospectivecontender forhydrogen energy production as well as to the photocatalytic degradation of organic pollutants.To the best of our knowledge, both photocatalytic and photoelectrochemical studies were never been reported before for this type of material. [Display omitted] • BiVO 4 nanocatalystdoped with Erbium (Er) and Yttrium (Y) was synthesized. • Nanocatalysts were characterized by p-XRD, FT-IR, FE-SEM, HR-TEM, UV–Vis DRS, PL, LSV, and EIS. • Raman analysis confirms the successful incorporation of rare metals into the BiVO 4 structure. • Y–BiVO 4 exhibited efficient photoelectrochemical water splitting and photocatalytic performance. • Maximum degradation of 93%, 85%, and 91% was achieved for MB, MO, and RhB respectively. [ABSTRACT FROM AUTHOR]