SYNTHESIS, CHARACTERIZATION, AND ENGINEERING OF 2D-NANOMATERIALS FOR GAS SENSOR AND ENERGY HARVESTING HYDROELECTRIC CELL DEVICES

Abstract

The rapid advancement of technology has positioned nanomaterials at the forefront of multidisciplinary innovation, making them fundamental to modern scientific and engineering applications. Among various classes of nanomaterials, two-dimensional (2D) nanomaterials have attracted significant attention due to their unique structural, electronic, and surface properties. Their high surface-to-volume ratio, tunable band structure, and enhanced charge transport characteristics make them highly suitable for applications in sensing and sustainable energy systems. In this research work, 2D nanomaterials and their nanocomposites have been systematically explored for the fabrication of room-temperature chemiresistive gas sensors and energy-harvesting hydroelectric cell (HEC) devices. The increasing industrial utilization of volatile organic compounds (VOCs), particularly ethanol, in sectors such as pharmaceuticals, paints, food processing, and chemical manufacturing, has raised serious environmental and health concerns. Although ethanol is widely used, prolonged exposure to its vapors can result in adverse health effects, including respiratory irritation, nausea, headaches, central nervous system disorders, kidney dysfunction, and potential carcinogenic risks. Therefore, the real-time detection of ethanol vapor, especially under room-temperature conditions with low power consumption, remains a critical challenge in environmental monitoring and public safety. To address this issue, the present study focuses on the development of high performance ethanol gas sensors operating at room temperature using defect engineered 2D nanomaterials. Emphasis is placed on enhancing sensitivity, selectivity, rapid response-recovery behavior, and long-term stability through controlled material synthesis. In parallel, the increasing depletion of fossil fuels and the growing global energy demand necessitate the development of sustainable and environmentally benign energy technologies. To meet this demand, hydroelectric cell devices based on defect rich nanomaterials have been developed for room-temperature electricity generation by water splitting. The fabricated HEC systems demonstrate the capability to harvest vi Ph.D. Thesis (Hemant Kumar Arora) green energy sufficient to power LED devices, thereby validating their practical applicability. In pursuit of this objective, a room-temperature chemiresistive ethanol gas sensor based on solvothermally synthesized tin sulfide (SnS) nanoplates was developed and systematically studied. The sensor device was fabricated by depositing synthesized SnS powder onto indium tin oxide (ITO) substrates via electrophoretic deposition (EPD), ensuring uniform film formation and strong adhesion. The fabricated sensor exhibited a high response value (Rg/Ra) of 17.4 toward 400 ppm ethanol concentration at room temperature, along with rapid dynamic characteristics. Specifically, the device demonstrated a response time of 12.4 s and a recovery time of 20.2 s under ambient conditions. In addition, the sensor maintained stable operation over a continuous testing duration of 15 minutes and displayed excellent selectivity toward ethanol in comparison to other interfering gases. Remarkable repeatability was confirmed through three consecutive sensing cycles at 400 ppm ethanol concentration, with minimal variation in response magnitude. Based on the observed experimental results sensor gives room temperature operation, rapid kinetics, and stable sensing behavior highlight the strong potential of the SnS-based sensor for practical and industrial applications, representing a meaningful advancement in low-power gas sensing technology. Building upon the superior sensing performance demonstrated by the SnS-based nanomaterial, defect-engineered SnS was further investigated for application in hydroelectric cell (HEC) devices aimed at sustainable energy harvesting. The study explores an environmentally benign approach to electricity generation through room temperature water splitting using a solid-state nanomaterial platform. Mesoporous and highly crystalline two-dimensional (2D) SnS nanosheets were synthesized via a rapid, low-temperature solvothermal method to ensure controlled morphology and enhanced surface activity. The introduction of structural defects was strategically employed to promote water adsorption, facilitate ionic transport, and improve charge transfer efficiency. For device fabrication, the synthesized SnS material was pelletized, with a zinc electrode attached to one surface serving as the anode, while an inert silver electrode was applied to the opposite face to function as the cathode. The fabricated SnS-based HEC, with an effective area of 4 cm², exhibited a short-circuit current of 15 vii Ph.D. Thesis (Hemant Kumar Arora) mA and an open-circuit voltage of 0.74 V, corresponding to an off-load output power of 11.1 mW. Notably, the device maintained stable performance over an extended period of 30 days, demonstrating excellent operational reliability and durability under ambient conditions. The power generated through water-driven electrochemical processes confirms the feasibility of HEC technology as a low-cost and environmentally friendly energy source. Importantly, the operation of the HEC device does not involve the emission of toxic gases or greenhouse by-products, thereby aligning with global sustainability goals and carbon neutrality initiatives. Extending the application of SnS in hydroelectric cells, the study was further motivated to investigate a SnS–rGO nanocomposite with the aim of enhancing electrical output performance. The integration of reduced graphene oxide (rGO) was strategically undertaken to improve electrical conductivity, facilitate rapid charge transport, and strengthen interfacial charge separation within the hydroelectric cell (HEC) device. In this work, a SnS-rGO nanocomposite based HEC was successfully fabricated to promote environmentally sustainable electricity generation through room-temperature water splitting. The fabricated SnS-rGO HEC, with an active area of 4 cm², demonstrated a short-circuit current of 34 mA and an open-circuit voltage of 0.94 V, resulting in an off-load output power of 31.96 mW. This represents a significant improvement over the pristine SnS-based device. Remarkably, the device exhibited stable and consistent performance over a duration of 12 weeks, underscoring its long term reliability and operational durability under ambient conditions. These results highlight the effectiveness of nanocomposite engineering in enhancing power generation efficiency and establish the SnS-rGO nanocomposite as a promising candidate for green energy applications. In addition to electrical energy production, the evolution of hydrogen gas at the cathode during operation provides an added advantage, offering opportunities for clean hydrogen generation. These findings highlight the practical potential of defect-engineered SnS-rGO based hydroelectric cells as an alternative or complementary technology to conventional solar cells and fuel cells, particularly for eco-friendly energy applications. Future research directions may further expand both the sensing and energy-harvesting dimensions of this work by deepening the understanding of structure-defect-performance viii Ph.D. Thesis (Hemant Kumar Arora) relationships. On the sensing side, systematic control over vacancy concentration, surface functionalization, and carrier concentration could enable detection of ethanol and other volatile organic compounds at sub-ppm or even ppb levels. Advancements in device architecture are equally important. The development of flexible substrates, printed electrodes, and microfabricated sensor arrays would enable the integration of these materials into wearable health monitors, portable breath analyzers, and compact industrial safety systems. Sensor miniaturization combined with low-power operation opens the possibility of embedding these devices into smart textiles, handheld electronics, and distributed environmental sensing networks. Furthermore, the integration of wireless communication modules, cloud-based storage, and artificial intelligence–assisted signal processing can enable real-time data interpretation, anomaly detection, and predictive environmental modeling. Such intelligent systems would play a pivotal role in smart city infrastructure, industrial IoT networks, and automated safety management systems. From the energy perspective, further optimization of hydroelectric cell materials could focus on enhancing water adsorption kinetics, proton transport pathways, and long-term defect stability. Exploring alternative electrode materials, surface coatings, and scalable fabrication techniques may improve output efficiency and durability under diverse environmental conditions. The dual functionality of HEC devices simultaneous electricity generation and hydrogen evolution offers significant scope for sustainable hydrogen production technologies. Future studies could investigate hydrogen collection, storage, and integration with micro fuel cells, thereby creating hybrid energy systems suitable for power generation. A particularly promising avenue involves the development of fully self-powered sensing systems, where hydroelectric cells serve as the onboard energy source for gas sensors. Such integration would create autonomous monitoring platforms capable of operating independently of external power supplies. Overall, the convergence of defect engineered 2D nanomaterials, intelligent sensing technologies, and water-driven energy harvesting systems opens a broad horizon for next-generation sustainable devices that simultaneously address environmental monitoring, public safety, and clean energy production.