Metal-organic frameworks (MOFs) for energy production and gaseous fuel and electrochemical energy storage applications.

The increasing energy demands in society and industrial sectors have inspired the search for alternative energy sources that are renewable and sustainable, also driving the development of clean energy storage and delivery systems. Various solid-state materials (e.g., oxides, sulphides, polymer and conductive nanomaterials, activated carbon and their composites) have been developed for energy production (water splitting-H2 production), gaseous fuel (H2 and CH4) storage and electrochemical energy storage (batteries and supercapacitors) applications. Nevertheless, the low surface area, pore volume and conductivity, and poor physical and chemical stability of the reported materials have resulted in higher requirements and challenges in the development of energy production and energy storage technologies. Thus, to overcome these issues, the development of metal-organic frameworks (MOFs) has attracted significant attention. MOFs are a class of porous materials with extremely high porosity and surface area, structural diversity, multifunctionality, and chemical and structural stability, and thus they can be used in a wide range of applications. In the present review, we precisely discuss the interesting properties of MOFs and the various methodologies for their synthesis, and also the future dependence on the valorization of solid waste for the recovery of metals and organic ligands for the synthesis of new classes of MOFs. Subsequently, the utilization of these interesting characteristics for energy production (water splitting), storage of gaseous fuels (H2 and CH4), and electrochemical storage (batteries and supercapacitors) applications are described. However, although MOFs are efficient materials with versatile uses, they still have many challenges, limiting their practical applications. Therefore, finally, we highlight the challenges associated with MOFs and show the way forward in overcoming them for the development of these highly porous materials with large-scale practical utility.

Potential of biofuel production from leather solid wastes: Indian scenario.

India is one among the major leather-producing countries in the world which shares close to one-fourth of the world's leather solid wastes and most of these wastes are not effectively utilized. These wastes are rich in protein and lipids that could be a potential feedstock for biofuel production, i.e., biogas, biodiesel, etc. Among the 150,000 tons of daily leather solid wastes in India, approximately 87,150 tons are shared by pre-tanning operations (i.e., raw trimmings, fleshing, and hair wastes) while the rest of the 62,850 tons are shared by tanning, post-tanning, and finishing operations (i.e., wet blue trimmings, chrome splits, shavings, buffing dust, crust trimming wastes). This review article shows that there is considerable bioenergy potential for the use of leather solid wastes as a green fuel. The biogas potential of leather solid wastes is estimated to be 40,532.9 m3/day whereas the biodiesel potential is estimated as 15,452.6 L/day. The bio-oil and bio-char potential of leather solid wastes is estimated to be 80,513.0 L/day and 45.8 tons/day, respectively. Several factors influence the biofuel process efficacy, which needs to be taken into consideration while setting up a biofuel recovery plant. The overall biofuel potential of leather solid wastes shows that this feedstock is an untapped resource for energy recovery to add commercial benefits to India's energy supply. Furthermore, in addition to the economic benefits for investors, the use of leather solid wastes for biofuel production will yield a positive environmental impact.

BiVO4 As a Sustainable and Emerging Photocatalyst: Synthesis Methodologies, Engineering Properties, and Its Volatile Organic Compounds Degradation Efficiency.

Bismuth vanadate (BiVO4) is one of the best bismuth-based semiconducting materials because of its narrow band gap energy, good visible light absorption, unique physical and chemical characteristics, and non-toxic nature. In addition, BiVO4 with different morphologies has been synthesized and exhibited excellent visible light photocatalytic efficiency in the degradation of various organic pollutants, including volatile organic compounds (VOCs). Nevertheless, the commercial scale utilization of BiVO4 is significantly limited because of the poor separation (faster recombination rate) and transport ability of photogenerated electron-hole pairs. So, engineering/modifications of BiVO4 materials are performed to enhance their structural, electronic, and morphological properties. Thus, this review article aims to provide a critical overview of advanced oxidation processes (AOPs), various semiconducting nanomaterials, BiVO4 synthesis methodologies, engineering of BiVO4 properties through making binary and ternary nanocomposites, and coupling with metals/non-metals and metal nanoparticles and the development of Z-scheme type nanocomposites, etc., and their visible light photocatalytic efficiency in VOCs degradation. In addition, future challenges and the way forward for improving the commercial-scale application of BiVO4-based semiconducting nanomaterials are also discussed. Thus, we hope that this review is a valuable resource for designing BiVO4-based nanocomposites with superior visible-light-driven photocatalytic efficiency in VOCs degradation.

A high-value biohythane production: Feedstocks, reactor configurations, pathways, challenges, technoeconomics and applications.

In recent years, the demand for high-quality biofuels from renewable sources has become an aspirational goal to offer a clean environment by alternating the depleting fossil fuels to meet future energy needs. In this aspect, biohythane production from wastes has received extensive research interest since it contains superior fuel characteristics than the promising conventional biofuel i.e. biogas. The main aim is to promote research and potentials of biohythane production by a systematic review of scientific literature on the biohythane production pathways, substrate/microbial consortium suitability, reactor design, and influential process/operational factors. Reactor configuration also decides the product yield in addition to other key factors like waste composition, temperature, pH, retention time and loading rates. Hence, a detailed emphasis on different reactor configurations with respect to the type of feedstock has also been given. The technical challenges are highlighted towards process optimization and system scale up. Meanwhile, solutions to improve product yield, technoeconomics, applications and key policy and governance factors to build a hydrogen based society have also been discussed.

Slaughterhouse and poultry wastes: management practices, feedstocks for renewable energy production, and recovery of value added products.

The slaughterhouse and poultry industry is possibly one of the fastest-growing sectors driven by the increasing demand in food availability. Subsequently, the wastes produced from the slaughterhouse and poultry industry are in huge quantities, which could be a promising resource for the recovery of value added products, and bioenergy production to minimize the dependence on fossil fuels. Furthermore, the wastes from slaughterhouses and poultry are a hub of pathogens that is capable of infecting humans and animals. This demands the emerging need for an effective and safe disposal method to reduce the spread of diseases following animal slaughtering. In light of that, the state of the production of slaughterhouse and poultry wastes was presented at first. Following this, the impact of solid waste exposure in terms of air, water, and soil pollution and the associated health challenges due to improper solid waste management practices were presented to highlight the importance of the topic. Secondly, the potency of these solid wastes and the various waste-to-energy technologies that have been employed for effective management and resource utilization of wastes generated from slaughterhouses and poultry were reviewed in detail. Finally, this review also highlights the opportunities and challenges associated with effective solid waste management, future requirements for the development of effective technologies for the recovery of value added products (like keratin, fibreboards), and biofuel production.

Recent developments on bismuth oxyhalides (BiOX; X = Cl, Br, I) based ternary nanocomposite photocatalysts for environmental applications.

Photocatalytic treatment of organic pollutants present in wastewater using semiconductor nanomaterials under light irradiation is one of the efficient advanced oxidation processes. Stable metal oxide (e.g. TiO2) based semiconductor photocatalytic systems have been mainly investigated for this purpose. Nevertheless, their large band gap (~3.2 eV) makes them inefficient in utilization of visible light portion of solar light leading to a lower degradation efficiency. Investigations have focused on the development of visible light responsive bismuth oxyhalides (BiOX; X = Cl, Br, I), one of the potential nanomaterials with unique layered structure, for efficient absorption of solar light for the degradation of pollutants. However, the rapid recombination rate of photogenerated charge carriers limits their practical applicability. To overcome such drawbacks, the development of BiOX based ternary nanocomposites received significant attention because of their unique structural and electronic properties, improved visible light response and increased separation and transfer rate of photogenerated charge carriers. This review aims to provide a comprehensive overview of the recent developments on bismuth oxyhalides-based ternary nanocomposites for enhanced environmental pollutants decomposition under visible light irradiation. The principles of photocatalysis, synthetic methodologies of bismuth oxyhalides and their characteristics such as heterojunctions formation, improved visible light response and separation rate of charge carriers and the mechanisms for enhanced visible light photocatalytic activity are discussed. In addition, the future prospects on the improvement in the photocatalytic activity of bismuth oxyhalides-based ternary nanocomposites are also discussed. This review could be beneficial for designing new ternary nanocomposites with superior visible light photocatalytic efficiency.

Fabrication and efficient visible light photocatalytic properties of novel zinc indium sulfide (ZnIn2S4) - graphitic carbon nitride (g-C3N4)/bismuth vanadate (BiVO4) nanorod-based ternary nanocomposites with enhanced charge separation via Z-scheme transfer.

Novel ZnIn2S4-g-C3N4/BiVO4 nanorod-based ternary nanocomposite photocatalysts with enhanced visible light absorption were synthesized and systematically characterized to confirm the formation of ZnIn2S4 marigold flowers, the layered structure of the g-C3N4, BiVO4 nanorods, and the formation of binary and ternary nanocomposites. The visible light absorption of BiVO4 was significantly improved after coupling with g-C3N4 and ZnIn2S4, which was confirmed by UV-visible diffuse reflectance spectroscopic analysis. Ternary ZnIn2S4-g-C3N4/BiVO4 nanocomposites exhibited excellent visible light photocatalytic decomposition efficiency (VL-PDE) when used for the degradation of congo red (CR) dye and metronidazole (MTZ) pharmaceutical, as well as excellent stability and reusability. The ternary 5%ZnIn2S4-50%-g-C3N4/BiVO4 nanocomposite showed higher VL-PDE for CR (81.5%) and MTZ (59%) degradation than the binary composites, g-C3N4 and BiVO4. Radical quenching experiments showed that h(+), OH, and O2(-) were the reactive radicals, validating that the Z-scheme charge carrier transfer mechanism was responsible for the enhanced VL-PDE of the ternary ZnIn2S4-g-C3N4/BiVO4 nanocomposites, which was further confirmed by photoluminescence analysis. Furthermore, kinetic studies showed that the degradation followed pseudo-first-order kinetics, and that the ternary photocatalysts could be reused up to three times with good stability. The enhanced visible light absorption, high surface area, high adsorption capacity, Z-scheme charge carrier transfer, and increased lifetime of photo-produced electron-hole pairs were responsible for the increased visible light photocatalytic decomposition efficiency.

Fabrication of hierarchically structured novel redox-mediator-free ZnIn2S4 marigold flower/Bi2WO6 flower-like direct Z-scheme nanocomposite photocatalysts with superior visible light photocatalytic efficiency.

Novel, hierarchically nanostructured, redox-mediator-free, direct Z-scheme nanocomposite photocatalysts were synthesized via a facile hydrothermal method followed by wet-impregnation. The photocatalysts had a ZnIn2S4 marigold flower/Bi2WO6 flower-like (ZIS/BW) composition, which led to superior visible-light photocatalytic efficiency with excellent stability and reusability. The hierarchical marigold flower and flower-like morphologies of ZIS and BW were confirmed by FE-SEM and TEM analyses and further revealed that formation of the hierarchical marigold flower-like ZIS structure followed the formation of nanoparticles, growth of the ZIS petals, and self-assembly of these species. Powder X-ray diffraction and UV-visible diffuse reflectance spectroscopy analyses as well as the enhancement in the surface area and pore volume of the composite provide evidence of strong coupling between hierarchical BW and the ZIS nanostructures. The efficiency of the hierarchical direct Z-scheme photocatalysts for photocatalytic decomposition of metronidazole (MTZ) under visible-light irradiation was evaluated. The hierarchically nanostructured ZIS/BW nanocomposites with 50% loading of ZIS exhibited superior visible-light photocatalytic decomposition efficiency (PDE) compared to the composites with other percentages of ZIS and pristine BW. A probable mechanism for the enhanced photocatalytic efficiency of the ZIS/BW composite in MTZ degradation under visible irradiation was proposed. Radical quenching studies demonstrated that h(+), ˙OH, and O2˙(-) are the primary reactive radicals involved, which confirms that the Z-scheme mechanism of transfer of charge carriers accounts for the higher photocatalytic activity. Kinetic analysis revealed that MTZ degradation follows pseudo-first-order kinetics and the reusability of the composite catalyst for up to four cycles confirms the excellent stability of the hierarchical structure. It is concluded that the hierarchical structure of the ZIS/BW photocatalyst, synergic effect, Z-scheme transfer of the charge carrier, high concentration of (˙OH) radical formation and the significant reduction in the charge carrier recombination account for the enhanced efficiency of the catalyst for photocatalytic decomposition of metronidazole by visible light under the present reaction conditions.

Preferential adsorption behavior of methylene blue dye onto surface hydroxyl group enriched TiO2 nanotube and its photocatalytic regeneration.

The present manuscript focus on the synthesis of surface hydroxyl group enriched titanium dioxide nanotube (TNT) by hydrothermal method for preferential adsorption of methylene blue (MB) dye. The mixture of methylene blue (MB) and rhodamine B (RhB) dye was used to study the preferential adsorption nature of TNT. The synthesized TNT were characterized by various techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, and ammonia-temperature programmed desorption (NH3-TPD) analysis. Result demonstrated that enhancement in the surface area of TNT and higher number of hydroxyl group on the surface of TNT. In the binary mixture, the adsorption of MB dye was 12.9 times higher as compared to RhB dye, which clearly indicated the preferential adsorption of MB dye on TNT surface. The preferential interaction of MB on TNT is due to the electrostatic interaction between the cationic MB and negatively charged TNT surface. The preferential adsorption of MB dye was studied by applying Langmuir, Freundlich and Sips isotherm; pseudo-first and second-order kinetic model. Furthermore, the regeneration of dye adsorbed TNT was carried out by eco-friendly photocatalytic process under the irradiation of ultraviolet light.