Well-constructed of hollow Z-heterojunction nanocatalysts MIL101(Fe)@CdIn2S4 using MIL-101 as a template for efficient photocatalytic degradation of tetracycline

Abstract

Hollow structures are employed extensively in the preparation of photocatalysts and the reduction of organic waste as a consequence of their advantageous characteristics, including reduced weight, shorter charge transport distances, higher specific surface areas, boosted photoabsorption capabilities and improved separation efficiency of charge carriers. Nevertheless, the intricate procedures associated with template selection and removal present considerable obstacles to their extensive implementation. Hereby, a simple two-step hydrothermal process was employed to synthesize octahedral hollow MIL-101(Fe)@CdIn₂S₄ (HMC) photocatalysts for efficient tetracycline (TC) degradation, with using MIL-101(Fe) as a template. The HMC photocatalyst maintains the intrinsic octahedral morphology of MIL-101(Fe). In comparison to the block morphology of CdIn₂S₄ (CIS), the unique hollow structure of HMC not only makes it easier for TC molecules to accumulate but also improves the absorption of visible light. Furthermore, the Z-type heterojunction formed between MIL-101(Fe) and CIS facilitates the secession of photogenerated charge carriers, thereby enhancing photocatalytic performance. Photocatalytic activity assessments demonstrate that 15 mg of HMC achieves a remarkable TC degradation rate of 97 % within 140 mins, and the degradation rate constants are 9.1 and 3.2 times greater, than those of MIL-101(Fe) and CIS. This represents a superior photocatalytic degradation efficiency when compared to previous studies, with the use of a smaller quantity of catalyst and a shorter reaction time. Moreover, this research investigates the synthesis conditions of HMC under various parameters and elucidates the dynamic CIS etching and in-situ growth on MIL-101(Fe). Morphological and microstructural analyses confirm the orderly and dense assembly of n-type CIS catalyst nanoparticles at the exterior of the MIL-101(Fe) crystal. A comprehensive investigation employing electron spin resonance (ESR), liquid chromatography-mass spectrometry (LC-MS), toxicity assays, and density functional theory (DFT) analyses was conducted to give a deeper understanding into the TC degradation process.