Using floating photocatalyst mpg-C3N4/expanded perlite to treat natural organic matter under visible light

Abstract

In-situ application of powdered photocatalysts in water systems is particularly challenging owing to intrinsic hurdles, such as submersion in water without stirring, limited light penetration, limited material recovery, and metal-leaking from the metallic materials used. In this study, a floating mpg-C3N4/extended perlite (EP) photocatalyst was synthesized and applied for the first time in the treatment of natural organic matter (NOM) under visible light, overcoming the majority of limitations of conventional powdered photocatalysts. With the addition of 0.8 mM H2O2, the mpg-C3N4/EP photocatalytic system generated active species ·OH and ·O2−, and removed 41.8 ± 1.3% of the starting NOM at 2 g L−1 after 5 h of operation. Fluorescence measurements revealed a pronounced adsorption affinity of the photocatalyst and more effective destruction of NOM towards its constituents with higher degrees of aromaticity and functionalization. This was accompanied by the production of low-molecular-weight phenolic structures as a result of the incomplete mineralization of humic-like substances. Significant correlations between two fluorescent components (i.e., C1 and C2) and dissolved organic carbon were found, suggesting that the identified components could be utilized as reliable optical surrogates for monitoring the decomposition of the heterogeneous NOM by photocatalysis using floating mpg-C3N4/EP. Some of the advantages of the floating mpg-C3N4/EP complex over conventional powdered mpg-C3N4 for NOM treatment were: easy recovery, high performance without interference from common anions, and low dependency on stirring. Finally, the simple procedure to synthesize mpg-C3N4/EP facilitates its prospective industrial applications on a large scale.