POROUS CARBON MATRIX WITH METAL COMPLEX HETEROSTRUCTURE TOWARDS INDUSTRIAL WASTE MANAGEMENT AND GREEN FUEL PRODUCTION

Abstract

Waste management is a major thrust projecting towards the goal of environmental remediation in the vision of 3R approach “Reduce-Reuse-Recycle”. Acknowledging the inherent value of things conventionally projected as waste, this study explores avenues for fostering innovation and developing solutions that not only benefit the environment but also contribute effectively to society. In light of this, the utilization of waste heat and excess seawater presents a viable pathway for producing green fuel via a renewable energy-mediated electrocatalytic approach. As need of the hour is to seek alternatives to fossil fuels in pursuit of achieving net-zero carbon emissions, thereby hydrogen generation emerges as a highly promising and environmentally friendly initiative. Similarly, wastewater contaminated with dye or antibiotics can be re-utilized via a cost-effective facile purification process adopting a photocatalytic technique. Owing to their (pollutant) high solubility in groundwater, the dye contaminants and antibiotic discharge are a major concern to water pollution, therefore degrading and/or purifying them remain crucial to enable their reuse within the manufacturing sectors, ultimately reducing the reliance on freshwater resources. By adopting these strategies, industries can reduce their environmental footprint and responsibly reuse the waste contributing to sustainable development. Integrating waste management with energy and water reuse practices aligns with the principles of circular economy and promotes a more sustainable and resilient approach to industrial processes. In this aspect, Carbon-based materials such as Graphene-CNTs (Gr-CNTs) play a crucial role by serving as the backbone of this waste management strategy. Having a 3D porous high surface area framework with inherently faster heat dissipation characteristics along with high electrical conductivity, Graphene-CNTs emerge as a remarkable template for both electrocatalytic and photocatalytic applications. Hence, this thesis primarily focuses on the designing of metal oxides/phosphides/selenides anchored Graphene-CNTs matrix towards photoassisted electrocatalytic energy generation and photocatalytic waste-water management. Considering this, the initial study focuses on constructing a heterostructure, wherein surface engineering of Ta2O5 via the creation of O2 vacancies and facile interface in Ta2O5-CNTs modulate the band gap of Ta2O5, thereby enhancing the efficient separation of photogenerated charge carriers. The as-synthesized material demonstrated effective photodegradation of textile dye water (Eriochrome Black T) with 95% degradation efficiency within 100 min of light exposure, with the goal of producing non-toxic purified water. The non-toxic end-products are evaluated via Toxicological analysis on the glial cell line (C6) which shows cellular viability of 72% as compared to 38% for bare EBT. The photocatalyst has shown reusability till 8 cycles revealing the potential applicability towards developing cartridge technology. Finally, the Filter-prototype demonstrates a drive towards the development of smart technology illustrating the faster rate of industrial dye-waste management via a renewable approach to deliver clean water to the environment. The limitations of the initial approaches such as material synthesis along with cost effectiveness is the major bottleneck towards its feasible commercialization in practical waste management. Therefore, the secondary alternative has highlighted where a simple and cost effective strategy has been adopted in developing Manganese Dioxide/Copper Oxide@Melamine Foam-Graphene-Carbon Nanotubes (MnO2/CuO@MF-Gr-CNT) heterostructure towards the purification dye as well as antibiotic-contaminated water. The smooth interface facilitated by CNTs as a mediator between MnO2 and CuO matrix allows faster redox kinetics resulting in the rapid degradation of pollutants under visible light illumination through Z-scheme. A trifunctional MnO2/CuO@MF-Gr-CNT is a highly proficient photocatalyst in degrading EBT, Loffler’s Methylene Blue (MB), and azithromycin with a degradation efficiency of 95.40%, 98.06%, and 96.44%, respectively under 100 min of illumination and produces environmentally benign biocompatible by-products. For practical applicability, a three-step cartridge aligned together to demonstrate a prototype filter technology where 80 mg catalyst beds in each column are utilized to purify 5 liters of Loffler’s Methylene Blue solution under continuous light irradiation in the batch process. This 3D high surface Gr-CNTs matrix not only inhibits catalyst agglomeration during the photo-illumination process but also provides a smooth pathway for effective separation of photo excitons as well as enhances adsorption followed by effective diffusion of dye/antibiotic molecules and thereby results in faster pollutant degradation. This matrix can be further employed for waste heat conversion to hydrogen production due to its intrinsic high thermal conductivity, which helps dissipate the heat generated at the interface during electrochemical analysis. In this approach, the in situ growth of selenium-anchored nickel phosphide on top of the 3D porous carbonaceous conductive (Melamine Foam Graphene-Carbon Nanotubes (MF-Gr-CNTs) matrix is adopted where the coupling of selenium tunes the electronic distribution as well as faster heat dissipation, facilitating the augmentation of numerous active sites. The developed electrocatalyst renders superior electrocatalytic performance with long-term durability for a minimum of 10 days at a high current density of 300 mA/cm2 with a small deviation of 2%, allowing the commercialization of the catalyst toward industrial-grade application. In smart utilization of waste heat to hydrogen fuel, the as-designed catalyst has shown remarkable performance with 19.2 mV of overpotential at 110oC and is simultaneously stable for 10 hours at 80oC due to its novel interfacial characteristic. The motivation for harvesting green fuel via photo-assisted water splitting, our major emphasis is projected towards the utilization of readily available water resources such as the deep blue (surplus amount of seawater) for large sustainable production of H2 as an essential fuel for upcoming energy demand. Fabrication of a 3D high-surface carbon-based heterostructure (Ni Foam-Graphene-CNTs) decorated with sharp-edged flakes of phosphorous inserted/intercalated tin selenide (SnSe-P) exhibits overpotential of 52 mV@10 mA/cm2, 93 mV@10 mA/cm2 and 198 mV@10 mA/cm2 in acidic, basic and neutral medium, respectively for Hydrogen generation. In addition, the as-designed catalyst outperforms with a significantly low overpotential of 122 mV@10 mA/cm2 with 72 hours of stability under alkaline seawater. The renewable strategy has been adopted using silicon solar cell (η = 10.66% ) to power up the electrolyzer demonstrates a stable photocurrent density of 6.40 mA/cm2 for at least 50 hours with the solar-to-hydrogen (STH) conversion efficiency of 7.70% accompanied with the estimated STH of 5.65% in alkaline seawater medium. The in-phase overlap between the px and py orbitals of Sn and P in NGC-SnSe-P (SnSe-3P/SWCNT) enables the s orbitals of H* and p orbitals of Sn to interact optimally closer to the Fermi level, which favors the adsorption H* intermediate of the HER process. This work may shed light on the development of versatile electrocatalysts for regulating the electrokinetics over wide operating conditions, typically for seawater electrolysis, adopting a renewable approach for the generation of plenteous amounts of green hydrogen towards a sustainable automobile sector. In summary, the thesis addresses waste management aspects related to transforming wastewater into non-toxic purified water and converting waste heat and surplus seawater into green fuel production with the help of nanostructured carbon-based heterojunctions with metal complexes.