Fabrication of carbon nanotube functionalized MIL-101(Fe) for enhanced visible-light photocatalysis of ciprofloxacin in aqueous solution

Abstract

Abstract Improving the performance of metal–organic frameworks (MOFs) through modifications is an important issue to expand their potential applications. In the current study, multi-walled carbon nanotube functionalized MIL-101(Fe) (CNT@MIL-101(Fe)) was synthesized and used to construct a visible-light photocatalysis system for elimination of ciprofloxacin. CNT@MIL-101(Fe) has a lower band gap energy (2.19\u202feV) than MIL-101(Fe) (2.46\u202feV), rendering it the visible light absorption from 400\u202fnm to 565\u202fnm. In the CNT@MIL-101(Fe)-photocatalysis system, some optimized reaction conditions were: CNT doping ratio\u202f=\u202f5%, pH\u202f=\u202f3.0, [H2O2] vs. [CNT@MIL-101(Fe)] mass ratio\u202f=\u202f11.3. Under 2.0\u202fmW\u202fcm−2 visible light irradiation, degradation of ciprofloxacin followed an apparent pseudo-first-order kinetic reaction rate at 6.85\u202f×\u202f10−4\u202fs−1. Using CNT@MIL-101(Fe), faster activation and electron transfer were achieved due to the high conductibility of CNT, resulting in a higher removal efficiency of ciprofloxacin (3.02\u202fμM, ~90% at 45\u202fmin) than using MIL-101(Fe) (~65%). Furthermore, the iron ions leakage of CNT@MIL-101(Fe) was only half the one of MIL-101(Fe), suggesting a better stability in water. The reactive mechanism was confirmed to be OH oxidation, in which visible photocatalysis was the dominant reaction. Generally, CNT@MIL-101(Fe) has enhanced performance and stability, which can act as potential catalyst of organic contaminants.