Efficient degradation of 2,3,5-trimethylpyrazine by catalytic ozonation over MnOx supported on biochar derived from waste tea leaves

Abstract

In this study, a series of biochars derived from waste tea leaves and loaded with MnOx (Mn-nWT) was fabricated for use in heterogeneous catalytic ozonation (HCO). Excellent degradation of 2,3,5-trimethylpyrazine (TMP) was achieved. Characterization data indicated that Lewis acid sites, including multivalent Mn sites, oxygen vacancies and surface hydroxyl groups, were the main active sites responsible for the HCO activity of Mn-nWT. The Mn-nWT catalysts exhibited superior HCO activity compared with bulk biochar and MnOx under various experimental conditions. In particular, 0.05 g L−1 Mn-5WT gave 95.3% degradation of 5 μM TMP in 30 min at pH 7.0. Reactive oxygen species (mainly •OH) generated from catalytic decomposition of ozone by Mn-nWT contributed to the enhanced HCO performance. The second-order degradation rate constants of TMP with O3 and •OH are 2.3 ± 0.13 and (7.3 ± 1.31) × 109 M−1 s−1. The reusability and stability of Mn-5WT was demonstrated by outstanding TMP degradation efficiency (88.8%), negligible metal dissolution and minor differences in physical characterization after four cycles. Additionally, the impacts of water matrices (catalyst dose, ozone dose, pH, temperature, carbonate and natural organic matter) on the Mn-5WT HCO process were investigated thoroughly. This study found that loading of metal oxides onto biochar synergistically promoted the HCO process by enhancing the physical and chemical properties.