Tailored routes for home-made Bi-doped ZnO nanoparticles. Photocatalytic performances towards o-toluidine, a toxic water pollutant

Herein we report the photodegradation of highly toxic o-toluidine in aqueous media (under UV irradiation), by using home-made bare and bismuth-doped ZnO nanoparticles. The latter powder was prepared by both a traditional impregnation method and by an innovative sol-gel synthesis, obtained using bismuth nitrate as precursor. Moreover, synthetic conditions (such as zinc salts and medium acidity) were varied in order to obtain different semiconductor nanopowders with diverse physico-chemical properties and, hence, photocatalytic performances. Both the disappearance and the mineralization of the pollutant molecule were followed by Linear Sweep Voltammetry and Total Organic Carbon techniques, respectively. Photocatalysis by-products were then identified by HPLC–MS (on eluates, after 3 h and 6 h) and ATR-FTIR (on used nanopowders) analyses. Thus, a new photodegradation pathway (with azo dimer derivatives in the first step) has been proposed. Bi-impregnated samples show high degree of mineralization, reducing the stability of the intermediates.