Heterostructural CuO-ZnO Nanocomposites: A Highly Selective Chemical and Electrochemical NO2 Sensor.

A simple one-step chemical method is employed for the successful synthesis of CuO(50%)-ZnO(50%) nanocomposites (NCs) and investigation of their gas sensing properties. The X-ray diffraction studies revealed that these CuO-ZnO NCs display a hexagonal wurtzite-type crystal structure. The average width of 50-100 nm and length of 200-600 nm of the NCs were confirmed by transmission electron microscopic images, and the 1:1 proportion of Cu and Zn composition was confirmed by energy-dispersive spectra, i.e., CuO(50%)-ZnO(50%) NC studies. The CuO(50%)-ZnO(50%) NCs exhibit superior gas sensing performance with outstanding selectivity toward NO2 gas at a working temperature of 200 °C. Moreover, these NCs were used for the indirect evaluation of NO2 via electrochemical detection of NO2 - (as NO2 converts into NO2 - once it reacts with moisture, resulting into acid rain, i.e., indirect evaluation of NO2). As compared with other known modified electrodes, CuO(50%)-ZnO(50%) NCs show an apparent oxidation of NO2 - with a larger peak current for a wider linear range of nitrite concentration from 20 to 100 mM. We thus demonstrate that the as-synthesized CuO(50%)-ZnO(50%) NCs act as a promising low-cost NO2 sensor and further confirm their potential toward tunable gas sensors (electrochemical and solid state) (Scheme 1).

Facile synthesis of highly porous CuO nanoplates (NPs) for ultrasensitive and highly selective nitrogen dioxide/nitrite sensing.

Copper oxide (CuO) nanoplates (NPs of ∼100 nm width) were successfully synthesized via a chemical method (emulsion method). Superior catalytic activities towards both chemical and electrochemical sensing of nitrite were achieved.

Ultrasensitive and bifunctional ZnO nanoplates for an oxidative electrochemical and chemical sensor of NO2: implications towards environmental monitoring of the nitrite reaction.

Herein, we focused on the one pot synthesis of ZnO nanoplates (NP edge thickness of ∼100 nm) using a chemical emulsion approach for chemical (direct) and electrochemical (indirect) determination of NO2. The structural and morphological elucidation of the as-synthesized ZnO NPs was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), thermogravimetric analysis (TGA) and BET-surface area measurements. The XRD studies of the as-synthesised NPs reveal that ZnO NPs have a Wurtzite type crystal structure with a crystallite size of ∼100 nm. Such ZnO NPs were found to be highly sensitive to NO2 gas at an operating temperature of 200 °C. Electrocatalytic abilities of these ZnO NPs towards NO2/NO2 - were verified through cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using aqueous 1 mM NO2 - (nitrite) in phosphate buffer (pH 7) solution. The results revealed enhanced activity at an onset potential of 0.60 V vs. RCE, achieved at a current density of 0.14 mA cm-2. These ZnO NPs show selective NO2 detection in the presence of other reactive species including CO, SO2, CH3OH and Cl2. These obtained results show that this chemical route is a low cost and promising method for ZnO NPs synthesis and recommend further exploration into its applicability towards tunable electrochemical as well as solid state gas sensing of other toxic gases.