Preparation of molecularly imprinted CNT/ZnO and photocatalytic degradation of bisphenol A

Abstract

With the rapid development of industry, environmental pollution has become a focused issue in worldwide. As one of the major environment pollutants, more than 100 tons of bisphenol A (BPA) are transferred to the environment every year with the extensive use of plastic products. When BPA is ingested through the food chain, it will gradually accumulate in the body, interfere with normal hormone secretion, and pose a serious effect on human health. Therefore, it is much important to effectively eliminate the BPA in the environment. Now, the methods for treating BPA are variable. The main methods have included biological method, adsorption method, electrochemical method, ozone oxidation method and photocatalytic oxidation technology. Among them, photocatalysis has been considered as one of the effective and promising technology for the elimination of contaminants from water, owing to the advantages of high efficiency, photochemical stability and cost-efficiency. However, the main active species during photocatalysis, such as hydroxyl radicals and superoxide radicals etc., do not target at any specific compound. Thus, to the best of our knowledge, photocatalysis shows no obvious selectivity in treatment of mixed pollutants system. However, for actual wastewaters, diverse components usually coexist together, where endocrine disruptors are usually present along with other non- or low-toxic organic substances with high concentrations, such as phenolic compound. Therefore, the pollutants with high concentration would occupy the major active sites, and be degraded antecedently, which increase the difficulty and cost of wastewater treatment. The emergence of molecular imprinting technology had provided an opportunity to solve the problem of the photocatalytic activity and selectivity of photocatalyst for degradation of target contaminants, because of specific affinity and size matching between target contaminants and imprinted cavities. The combination of photocatalytic oxidation technology and molecular imprinting technology can effectively improve the selectivity of the target during photocatalysis. In order to achieve the purpose of selective degradation of BPA, a molecularly imprinted photocatalytic material (MIP-CNT/ZnO) was prepared by surface imprinting, using BPA as template molecule, 2-vinyl pyridine (2-vp) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as crosslinking agent, CNT/ZnO as supporter, respectively. The structure of MIP-CNT/ZnO was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the imprinted polymer was successfully coated on the surface of CNT/ZnO and MIP-CNT/ZnO remained a wurtzite structure, which was the same to ZnO. Due to the recognition site on the surface of MIP-CNT/ZnO, the degradation rate of BPA by MIP-CNT/ZnO was significantly higher than diethylstilbestrol and phenol, and the degradation rates were 2.18 and 1.98 times of the latter two, respectively. The degradation rate of BPA with initial concentration of 10 mg/L could reach 83.44% after being irradiated by ultraviolet light for 210 min. The results demonstrated that molecularly imprinted photocatalyst exhibited excellent selectivity and catalytic ability. The present work could provide new perspectives for selective photocatalytic degradation, offer a new insight for the photocatalytic oxidation process and provide a possible way to remove low concentration and high toxicity organic pollutants in the water.