TiO2 nanoparticles were synthesized via a simple hydrothermal method in a sodium hydroxide (NaOH) aqueous solution and washed with distilled water and different concentrations of hydrochloric acid which acted as the morphological/crystallographic controlling agent. Microscopy analysis showed that the size of the TiO2 nanoparticles could be easily tailored and tuned by varying the HCl concentration. The phase transformation from a mixture of anatase and rutile phases to pure anatase phase was observed at higher HCl concentration. The particle sizes were reduced while the Brunauer-Emmett-Teller surface area increased when increasing the HCl concentration, thus resulting in higher sensing response and selectivity to NO2 at room temperature. The X-ray photoelectron spectroscopy, photoluminescence and electron paramagnetic resonance studies also revealed that the 1.0 M sample contain high relative concentration of oxygen vacancy and Ti4+ and Ti3+ interstitial defect states which played a vital role modulating the sensing properties.
Tshabalala, Z. P., Motaung, D. E., Mhlongo, G. H., & Ntwaeaborwa, O. M. (2016). Facile synthesis of improved room temperature gas sensing properties of TiO2 nanostructures: Effect of acid treatment. Sensors and Actuators, B: Chemical, 224, 841–856. https://doi.org/10.1016/j.snb.2015.10.079