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• 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]

• 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]