Wenping Dong,Chuanxi Yang,Lingli Zhang,Qiang Su,Xiaofeng Zou,Wenfeng Xu,Xingang Gao,Kang Xie,Weiliang Wang
This study investigates the degradation of nifedipine (NIF) by using a novel and highly efficient ultraviolet light combined with hydrogen peroxide (UV/H 2 O 2 ). The degradation rate and degradation kinetics of NIF first increased and then remained constant as the H 2 O 2 dose increased, and the quasi-percolation threshold was an H 2 O 2 dose of 0.378 mmol/L. An increase in the initial pH and divalent anions (SO 4 2- and CO 3 2- ) resulted in a linear decrease of NIF (the R 2 of the initial pH, SO 4 2- and CO 3 2- was 0.6884, 0.9939 and 0.8589, respectively). The effect of monovalent anions was complex; Cl - and NO 3 - had opposite effects: low Cl - or high NO 3 - promoted degradation, and high Cl - or low NO 3 - inhibited the degradation of NIF. The degradation rate and kinetics constant of NIF via UV/H 2 O 2 were 99.94% and 1.45569 min -1 , respectively, and the NIF concentration = 5 mg/L, pH = 7, the H 2 O 2 dose = 0.52 mmol/L, T = 20 ℃ and the reaction time = 5 min. The ·OH was the primary key reactive oxygen species (ROS) and ·O 2 - was the secondary key ROS. There were 11 intermediate products (P345, P329, P329-2, P315, P301, P274, P271, P241, P200, P181 and P158) and 2 degradation pathways (dehydrogenation of NIF → P345 → P274 and dehydration of NIF → P329 → P315).
Yulun Nie,Xiaofei Sun,Miao Wang,Xike Tian,Chao Yang,Chu Dai
UV-H 2 O 2 is the most widely used oxidizing system with established effectiveness and a high level of technical development for practical application. However, little attention was paid on the effect of suspended particles in natural water on organic contaminants removal via UV-H 2 O 2 technique. In this study, this effect of suspended particles to enhance the contaminant degradation was explored using silica/alumina-based oxides (MCM-41 and Al@MCM-41) as the representative. The results showed that MCM-41 had no effect on OFX degradation compared with UV-H 2 O 2 . While the degradation efficiency and reaction rate were greatly enhanced at a pH range of 3.0–9.0 especially at acidic pH values (3.0–5.0) in the presence of Al@MCM-41. The probe experiments proved that OFX adsorption followed by surface reaction process played an important role to enhance the performance of UV-H 2 O 2 . Based on the characterization results, the positive effect of suspended particles was not related to their surface area and pore size distribution, but dependent on the chemical composition and surface acid-base property. The suspended particles can provide an active surface composed of acid and base sites. The base site can create a local basic micro-environment by producing more • OH et al. While the dissociated acid sites in Al@MCM-41 with a negative charged surface favor OFX adsorption and then reaction with produced ROS . Our findings suggest that the enhanced performance of UVA-H 2 O 2 induced by suspended particles should be concerned.
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