Photocatalytic degradation of bisphenol A over Rh/TiO2 suspensions in different water matrices

Abstract

A series of noble metal-promoted Me/TiO2 (P25) photocatalysts (Me: Pt, Ru, Pd, Rh) of the same metal loading (0.5wt.%) were synthesized by the wet impregnation method and their photocatalytic activity was tested for the degradation of bisphenol A (BPA) under simulated solar irradiation. Results of H2 chemisorption, XRD, BET and UV–vis DRS experiments showed that dispersion of small metal crystallites on the TiO2 surface did not affect appreciably the phase composition (∼85% anatase), specific surface area (47–49m2/g) and optical band gap (3.2eV) of the semiconductor. Pt/TiO2 catalyst exhibited the higher efficiency under solar irradiation. In contrast to other Me/P25 catalysts investigated, the Rh/P25 catalyst exhibited increased activity for the title reaction in the presence of 20mg/L humic acid (HA), which was about 2.5 times higher than that obtained in ultrapure water (UPW). The apparent rate constant for the degradation of BPA in UPW+HA was found to increase proportionately with an increase of catalyst concentration in the range 50–400mg/L. The rate was not affected appreciably by the presence of inorganic ions contained in bottled water but decreased substantially in a secondary treated wastewater matrix. Results of liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) showed that degradation of BPA proceeds via two main pathways, which involve (i) hydroxylation, and (ii) cleavage of isopropylidene group with subsequent formation of para-substituted phenol derivatives.