Visible-light-driven photocatalytic degradation of naproxen by Bi-modified titanate nanobulks: Synthesis, degradation pathway and mechanism

Naproxen (NPX) as one of the typical pharmaceuticals and personal care products (PPCPs) has been constantly detected in aquatic environment recently which has potentially hazard to the human health and ecosystem. However, the practical applicability of photocatalysts in degradation of NPX is still restricted by challenges that most nanomaterials need to be stimulated by ultraviolet light and their limited photocatalytic activity under visible light. Therefore, we synthesized bismuth titanate nanobulks (Bi-TNB) through the two-step method of hydrothermal-calcining. The crystal structure, morphology, UV-vis diffuse reflectance spectra and surface adsorption performance of the as-prepared were investigated by XRD, SEM, UV-vis and BET. Several parameters which might influence the degradation efficiency were studied including initial NPX concentration, catalyst dosage, solution pH and concentration of anions, cations and humus. The results indicated that more than 99.9% of NPX (0.25 mg/L) was removed by Bi-TNB (0.5 g/L) at pH = 7. Reactive species scavenging experiments indicated that h(+) and O-2(center dot-) were the dominant active species involved the degradation of NPX. In photo degradation process, NPX was firstly decarboxylated and then further photocatalytic oxidized to form carboxylic acids of lower molecular weights and would be finally transformed into CO2 and H2O. PPCPs coexistence experiment showed that acetaminophen would hinder the removal of NPX by Bi-TNB. Both the reaction in different water matrices and degradation under the condition of sunlight indicated that Bi-TNB could be applied in degradation of NPX in environmental water systems. This study provides a new strategy for enhancing material photocatalytic performance to be used in practical applications.