Ce-Doping-Induced Burstein-Moss Shift in Biogenically Synthesized ZnO for Multifunctional Gas Sensing, Photocatalytic, and Antimicrobial Applications

Abstract

Multifunctional materials capable of addressing air-quality monitoring, clean energy generation, and antimicrobial control are of significant interest for environmental and public health applications. In this work, pristine and cerium (Ce)-doped ZnO NPs were synthesized via an ecofriendly Ocimum tenuiflorum extract-assisted co-precipitation method, and the influence of Ce incorporation on structural, electronic, gas sensing, photocatalytic, and antimicrobial properties was systematically investigated. X-ray diffraction and electron microscopy analyses confirmed the formation of phase-pure wurtzite ZnO with Ce-induced lattice strain, reduced crystallite size, and enhanced defect density without secondary phase formation. UV-Vis diffuse reflectance spectroscopy revealed an apparent widening of the optical band gap upon Ce doping, attributed to a Burstein-Moss band-filling effect arising from increased carrier concentration and oxygen vacancy generation. Among all compositions, 2% Ce-doped ZnO (Ce2@Zn) exhibited superior NO 2 sensing performance, achieving a high response at an optimized operating temperature of 190 °C, along with excellent selectivity, reproducibility, and long-term stability. Ce doping also significantly enhanced photocatalytic hydrogen evolution, with Ce2@Zn producing hydrogen gas after 5 h under simulated solar irradiation, representing a six-fold improvement over pristine ZnO.Furthermore, Ce2@Zn demonstrated pronounced antibacterial activity against both Gramnegative and Gram-positive bacteria, driven by enhanced reactive oxygen species generation and optimized defect-mediated charge transfer. The results demonstrate that Ce-doping-induced electronic band modulation and biogenic synthesis synergistically ZnO as a multifunctional platform for gas sensing, photocatalytic hydrogen production, and antimicrobial applications.