Green and low-cost synthesis of zinc oxide nanoparticles and their application in transistor-based carbon monoxide sensing.

There has been steady progress in developing reliable and cost-effective strategies for the clean production of zinc oxide (ZnO) nanoparticles (NPs) owing to their unique structural and wide functional characteristics. While the green synthesis of such NPs from plant extracts has emerged as a sustainable and eco-friendly protocol, it is greatly restricted owing to the scarcity of potential natural precursors necessitating comprehensive investigations in this direction. Herein, we report a facile, low-cost green synthesis and characterization of ZnO NPs along with the demonstration of their usage as an active media in organic field-effect transistor (OFET) devices for sensing carbon monoxide (CO) gas. The ZnO NPs obtained from Nelumbo nucifera (lotus) leaf extract-mediated solution combustion synthesis at a much lower initiation temperature, the first of its kind, were characterized by various techniques such as UV-vis spectroscopy, XRD, EDX analysis, TEM and FESEM. The data derived from these experiments clearly evidence the formation of very pure and crystalline ZnO NPs possessing nearly spherical-shape with a size of 3-4 nm. The p-type organic field-effect transistor (OFET) device, fabricated using poly(3-hexylthiophene-2,5-diyl) (P3HT) and ZnO NPs, showed a field-effect mobility of 10-2 cm2 V-1 sec-1 with a slightly enhanced response of detecting CO gas at room temperature (RT). The phenomenon was further confirmed by the variation in electrical parameters of the OFET such as field-effect mobility (µ), on-current (I on), and off-current (I off). The selectivity and sensitivity of the fabricated device in CO gas detection was found to be more prominent than the other reducing gases (hydrogen sulphide, H2S and ammonia, NH3) and methanol vapours tested.

Voltammetric determination of trace metals Zn2+, Cd2+, Pb2+, Cu2+, Co+2 and Ni+2 in some medicinally important plants from Western Ghats, Karnataka State, India.

Trace metal levels in selected medicinal plant leaves from Western Ghats, Karnataka, India were studied A method for the determination of Zinc, Copper, Lead and Cadmium simultaneously in the pH of 4.5 in citrate buffer, and Cobalt and Nickel simultaneously in the pH 9.2 in ammonia buffer medium has been optimized. Electrochemical method, Differential Pulse Anodic Stripping Voltammetry (DPASV) has been used for quantification. The optimized procedure has been successfully applied for the determination of the above-mentioned metal ions in some medicinally important plant leaves from Western Ghats, Karnataka, India. The concentrations of trace metals in the medicinal plant samples were found to be in the ranges: 15.61-20.71 mg g(-1) for copper, 0.056-0.10 mg g(-1) for cadmium, 0.91-1.81 mg g(-1) for lead, 0.42-0.96 mg g(-1) for nickel, 1.21-1.97 mg g(-1) for cobalt and 23.29-32.52 mg g(-1) for zinc. The effect of pH, deposition time and potential has been studied and optimized. The study reveals that all the trace metals are well within the maximum permissible limits, therefore, medicinal plants of this region are very much suitable for medicinal use. The results are compared with the data obtained by atomic absorption spectroscopy.