Synthesis and Characterization of NiO/SnO₂ Nanocomposites Prepared via Sol-Gel Method for Enhanced Optical Properties and Ethanol Gas Sensing Applications

Nickel Oxide (NiO) and Tin Oxide (SnO₂) semiconductor nanomaterials have been a lot of attention recently due to their excellent optical, electrical and gas sensing characteristics. In this study, the NiO nanoparticles, SnO₂ nanoparticles and NiO/SnO₂ nanocomposites were successfully synthesized by a simple sol-gel process and then systematically characterized to investigate the structural, morphological, optical and gas sensing properties. The synthesized materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and UV-visible absorption spectroscopy. The XRD results were used for confirming the successful formation of the crystalline phases for individual oxides and nanocomposite structure. The average crystallites size of NiO, SnO₂ and NiO/SnO₂ nanocomposite was about 33.64nm, 13.80nm and 16.30nm respectively. The FE-SEM images showed nanoscale granular morphologies and higher grain aggregation in the nanocomposite sample. The existence of Ni, Sn and O was confirmed and their homogeneity was verified by EDS analysis.
Improved visible light absorption and red shift in absorption edge were observed with the incorporation of NiO into SnO₂, as indicated by optical characterization. The optical band gaps for NiO (3.7 eV) and SnO₂ (3.3 eV) were reduced to approximately 3.2–3.5 eV in NiO/SnO₂ nanocomposite, which results in better electronic interactions between both semiconductor phases. Moreover, as compared with the pristine NiO and SnO₂ gas sensors, the NiO/SnO₂ heterojunction sensor exhibited better gas sensing properties for ethanol gas sensing experiments. The nanocomposite displayed higher sensitivity, low operating temperature and excellent response and recovery properties with optimum sensing characteristics at around 225°C. This was believed to be due to the creation of p–n heterojunctions, an increase in oxygen adsorption sites, and charge transfer efficiency. The results obtained here show that NiO/SnO₂ nanomaterials prepared by sol-gel process have a potential as well as interesting application in advanced gas sensing and optoelectronic field.