Cyclodextrin functionalization enhancement in a CA-β-CD/g-C3N4/Ag2CO3 Z-type heterojunction towards efficient photodegradation of organic pollutants

Abstract

In this paper, modification of cyclodextrins by citric acid (CA-CD) was used as an oxygen source for doping g-C₃N₄ and then mixed with silver (Ag) compounds to prepare a composite photocatalyst, which solved the problems of the narrow range and poor light absorption of the g-C₃N₄ support. The compound photocatalysts of CA-β-CD/CN/Ag₂O, CA-β-CD/CN/Ag₃PO₄, and CA-β-CD/CN/Ag₂CO₃ were prepared by regulating the species and mass ratio of CD. Grafting of CD increases the hydroxyl and carboxyl functional groups of the g-C₃N₄ photocatalyst. Among the three modified cyclodextrins α-CD, β-CD, and γ-CD, we clarified that the CA-β-CD grafted with g-C₃N₄ had the best degradation effect at a ratio of 8 : 1. Among Ag₂O, Ag₃PO₄, and Ag₂CO₃, the degradation effect of 8 : 1 : 1 CA-β-CD/CN/Ag₂CO₃ on methyl orange (MO) could reach 98.2% at 30 min of simulated sunlight irradiation, 99.1% on activated black at 60 min of simulated sunlight irradiation, and 91.9% on norfloxacin at 90 min of simulated sunlight irradiation. CA-β-CD/CN/Ag₂CO₃ could be reused to degrade reactive black and the degradation rate remained above 92% after 4 cycles. Free radical scavenging and electron spin resonance (ESR) experiments have shown that CA-β-CD/CN/Ag₂CO₃ can rapidly produce more free radicals, and H⁺ and ˙O₂⁻ are the main active radicals in the degradation process. The Ag-based heterojunction formation can improve the separation efficiency of photo-generated charges and broaden the visible light absorption of the composite photocatalysts. This research provides a new train of thought for preparing an Ag-based composite photocatalyst modified by an organic macromolecule.