Platinum-modified bismuth molybdate flake balls as visible-light-responsive photocatalyst

Abstract

Solar photocatalysis is considered as one of the best methods for “green” purification of environment. Accordingly, efficient, stable, and low-price materials must be developed for possible commercial application. Herein, flower-like bismuth molybdate (Bi2MoO6) photocatalysts were successfully synthesized by CTAB-assisted hydrothermal process, and then surface modified with platinum by photodeposition. The obtained materials were characterized by various methods, including XRD, DRS, XPS, SEM, TEM, ESR, photoluminescence spectroscopy and photoelectrochemical tests. Photocatalytic activity was tested mainly for tetracycline (TC) antibiotic degradation under visible-light irradiation (λ > 420 nm), including scavenger tests and experiments for different operation conditions (TC concentration, photocatalyst dose, pH value, in the presence of inorganic salts, water taken from different reservoirs). It has been found that the best photocatalyst containing 0.5 wt% of platinum exhibits 94.2 % TC removal during 60-min visible-light irradiation, reaching the reaction rate constant of 0.0392 min−1 (exceeding the data reported up to now). It is proposed that exceptional photocatalytic performance is caused by the synergy between the uniform flower structure (efficient light harvesting and large specific surface area) and double function of platinum deposits, i.e., as a sink for electrons (hindering charge carriers’ recombination) and a plasmonic sensitizer (allowing energy transfer from excited platinum to oxygen). Superoxide radicals (•O2−) are the main oxidation species, as proven by the quenching experiments and EPR analysis. However, in the case of platinum-modified samples, singlet oxygen plays also an important role, and thus an energy transfer from plasmonic platinum to oxygen could be expected. Additionally, TC degradation pathways, elucidated by the detection of intermediates, and the toxicity data (TC and its degradation products), assessed by a quantitative structure–activity relationship (QSAR) method, have confirmed that photocatalytic degradation of TC is indeed an environmental-friendly method, highly recommended for the decomposition of persistent organic compounds.