Abhaysinh Shivaji Khune

PhD

Lecturer/Instructor/Teacher

Atomic Force Microscopy (AFM) BET Surface Area Measurement Composite Material Confocal Raman Microscopy Fourier Transform Infrared (FTIR) Spectroscopy Gas Sensors Material Synthesis Raman Spectroscopy scanning electron microscopy Semiconductor Parameter Analyzer (SPA 4200A) Spin Coating Surface Functionalization UV/Vis spectrophotometry X-ray Diffraction

Peer-reviewed publication(s) 1st author peer-reviewed publication(s) Conference Poster(s)

My doctoral research titled “Detection of Air Pollutants Using Composite of Free-Based Porphyrin and Graphene” focuses on the design, fabrication, and evaluation of chemiresistive sensors based on composites of reduced graphene oxide (rGO) and free-based porphyrins for the detection of corrsoive gasses. Air pollution, driven by rapid industrialization and urbanization, introduces hazardous gases such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), ammonia (NH₃), carbon monoxide (CO), and so on into the atmosphere, posing serious threats to human health and the environment. Traditional sensors often face limitations such as poor selectivity, slow response, high operating temperatures, and limited reproducibility. In contrast, the rGO/porphyrin composites synthesized in this work aim to overcome these shortcomings by utilizing the excellent conductivity of rGO and the gas-binding specificity of porphyrins. The research begins with the synthesis of graphene oxide (GO) using the improved Hummers method, followed by thermal reduction using Tour’s method to obtain rGO. The structural, morphological, spectroscopic, and electrical properties of the synthesized materials were extensively characterized using techniques such as X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), and I–V measurements. Free-based porphyrins such as TAPP (5,10,15,20-Tetra(4-aminophenyl)porphyrin), TPTP (5,10,15,20-Tetra-p-tolylporphyrin), and MCPTPP (5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin) were synthesized and functionalized onto rGO to fabricate composite materials with enhanced sensing characteristics. The combination of the conductive nature of rGO and the selective gas-binding ability of porphyrins significantly improved the sensitivity and selectivity of the sensors. Sensor devices were fabricated by drop-casting these composites onto gold and indium tin oxide (ITO) electrode substrates. Their gas-sensing performance was tested at room temperature. Among the tested composites, the rGO/TAPP sensor exhibited high selectivity for SO₂ with a detection limit of 5 ppm, a response time of 57 seconds, and a recovery time of 61 seconds, along with excellent repeatability and stability. The rGO/TPTP sensor performed even better, with a lower detection limit of 1 ppm, a faster response time of 33 seconds, and a recovery time of 27 seconds, making it well-suited for practical SO₂ monitoring. For NO₂ detection, the rGO/MCPTPP sensor showed strong selectivity, repeatability, and a detection limit of 50 ppm, with a rapid response (31 seconds), recovery (81 seconds), and long-term stability beyond 60 days. These sensor systems demonstrated significant improvements in linearity, reproducibility, and durability compared to previously reported sensors. The rGO matrix provided excellent electrical conductivity and a high surface area for gas adsorption, while porphyrins contributed selectivity through π–π interactions and chemical affinity for target gas molecules. Compared to literature reports, the developed sensors showed superior performance under ambient conditions, addressing key challenges in chemiresistive sensing such as selective detection at low concentrations and long term operational reliability. A comparative study between rGO/MCPTPP and a ternary composite rGO/TPTP/MCPTPP revealed even better performance in terms of detection limits, response speed, and gas discrimination. The sensing mechanisms were explained using models of electron transfer and adsorption-desorption kinetics. Electrical analyses, including I–V characteristics and ChemFET measurements, supported theenhanced electrical behavior of the composites. This comprehensive study resulted in multiple peer-reviewed publications in journals such as Journal of Electronic Materials, Applied Physics A, Journal of Materials Science: Materials in Electronics, and Sensors and Actuators A: Physical highlighting the novelty and effectiveness of rGO/porphyrin composites for air pollutant sensing. The findings confirm the potential of functionalized graphene based materials in developing next-generation gas sensors that are portable, cost-effective, and capable of working efficiently at room temperature. The work concludes with suggestions for future research, including exploring new porphyrin derivatives, doping strategies for graphene, integration into wearable and IoT-based environmental monitoring devices, and testing in real-world mixed-gas environments. The successful synthesis, characterization, and application of these chemiresistive sensors pave the way for reliable, eco friendly, and practical solutions for air quality monitoring.