Citrate-assisted hydrothermal synthesis of single crystalline ZnO nanoparticles for gas sensor application

ZnO nanoparticles (NPs) were synthesized from Zn(OH)2 using trisodiumcitrate-assisted hydrothermal process. The structure, surface morphology, optical property and surface area of ZnO NPs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy and BET-surface area analyzer, respectively. XRD results confirmed the complete conversion of wulfingite structure of Zn(OH)2 into the hexagonal wurtzite structure of ZnO after hydrothermal process. SEM and TEM images showed the formation of 100-150 nm ZnO NPs which were single crystalline in nature. PL spectroscopy showed only UV emission and no defect related visible emission in ZnO NPs. Experimental results showed that trisodiumcitrate suppressed the growth of ZnO along [0 0 0 1] direction which resulted into the formation of ZnO NPs. Gas response was examined for four gases namely CO, ethanol, acetaldehyde and NO2. Response increased with temperature for all gases except NO2. ZnO NPs showed response at room temperature for 5 ppm of NO2 gas. The results demonstrate that these ZnO NPs have some sort of selectivity for NO2 at low while for acetaldehyde at high working temperature.