Polymer-Assisted Coprecipitation Synthesized Zinc Oxide Nanoparticles and Their Uses for Green Chemical Synthesis via Photocatalytic Glucose Conversions

Biomass conversions to chemicals via various conventional technologies require high energy consumption, high temperature, high pressure, or high system cost. Alternatively, photocatalysis is one of the greener technologies because it utilizes the energy from lamps or natural sunlight with catalysts to synthesize chemicals under mild conditions and room temperature. In this work, zinc oxide (ZnO) particles were successfully synthesized using polyvinylpyrrolidone as an additive in coprecipitation to control the size and protect the aggregation. The crystal structure of hexagonal wurtzite was found in the obtained nanoparticles. The photocatalytic activities of the obtained samples were evaluated for the production of high-value chemicals (gluconic acid, xylitol, arabinose, and formic acid) via the photocatalytic conversion of glucose under UV-A irradiation. The photocatalytic results indicated the relationship of defects (i.e., oxygen vacancies and zinc vacancies) with glucose conversions. From the ZnO nanoparticles calcined at various temperatures from 400 to 700 °C, the one calcined at 700 °C showed the highest glucose conversion of 21.5% with a high yield of carboxylic acid products (gluconic acid and formic acid). The gluconic acid showed the highest yield of 15% for 180 min, while the formic acid, arabinose, and xylitol presented the highest yields of 7, 1, and 0.5% for 180 min, respectively. Pure ZnO nanoparticles can convert glucose into value-added products without adding an acid or base in the reaction.