Boosting PFOA photocatalytic removal from water using highly adsorptive and sunlight-responsive ZIF67/MIL-100(Fe) modified C3N4

Abstract

Per- and polyfluoroalkyl substances (PFAS) are widely used in many industrial and food processes. Their discharge into the environment shows a serious threat because of their toxicity, non-biodegradability and high mobility in water and soil. Photocatalytic reaction is confirmed an effective way for the degradation of PFOA. Photocatalytic materials with multifunctional properties can boost the generation of oxidizing materials, enhance the degradation efficiency of target pollutants. Herein, we report an easy-synthesis of ZIF67@C3N4 and MIL-100(Fe)@C3N4 by in-situ hydrothermal growth route for the photocatalytic degradation of perfluorooctanoic acid (PFOA). Unlike bare g-C3N4, ZIF67@C3N4 and MIL-100(Fe)@C3N4 composites exhibit higher specific surface areas which enhanced the adsorption properties. Moreover, the formed heterojunction systems boost the visible light responsive and the separation of photo-induced electrons, allowing excellent degradation of PFOA. Besides the same response to spectrum below 420 nm as C3N4, ZIF67@C3N4 holds a certain light absorption capacity between 500 and 600 nm, proving that ZIF67@C3N4-X has better light utilization capacity than ZIF67 and C3N4. With the increase of MIL-100(Fe) addition, the red-shift becomes significant. Through the preliminary photocatalytic tests using methylene blue as a representative organic pollutant, the results showed that ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% are the most effective. When ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% were applied comparatively towards the photocatalytic oxidation of PFOA, the results showed that the removal rates reached 79.2% and 60.5%, respectively, which is much higher than bare C3N4. The quenching tests indicated that photo-induced h+ played a major role in the photocatalytic degradation of PFOA by ZIF67@C3N4-24.4%, while O2- and h+ participated equality towards the PFOA degradation in MIL-100(Fe)@C3N4-70% system. Besides the photonic effects, it was suggested that the adsorption and electron shuttle effect also played significant role on the excellent removal of PFOA, wherein the adsorption e behavior of catalysts help the accumulation of PFOA nearby the photoactive C3N4 area. In addition, this process promoted further mineralization of generated intermediate products, making the system more sustainable.