Construction of Z-scheme heterojunction ZIF-8-decorated ZnO/SiO2 for enhanced visible-light photocatalytic removal of organic pollutants and reduction of Cr (VI)

Abstract

The zeolitic imidazolate framework-8 (ZIF-8) demonstrates promising photocatalytic activity in wastewater treatment. Nevertheless, limited visible light utilization and arduous recyclability hinder its practical application. Herein, we fabricated ZIF-8 decorated zinc oxide/silica (ZnO/SiO2) hollow spheres by an in-situ strategy. This composite effectively photocatalytically degrades organic dyes and reduces Cr (VI) under the simulated sunlight. Results reveal that Z-scheme heterojunction construction between ZIF-8 and ZnO/SiO2 is formed and facilitates the effective separation and transport of electrons and holes, leading to nearly complete methylene blue (MB) degradation, 88.7 % of rhodamine B (RhB) removal, and 41.8 % Cr (VI) reduction within 30 min. Notably, the ZIF-8/ZnO/SiO2 composite exhibits enhanced visible-light utilization attributed to its reduced band gap (3.04 eV), thereby improving MB degradation compared to using solely ultraviolet light. Furthermore, the composite demonstrates remarkable reusability and stability, achieving over 99 % removal rate for MB after four photocatalysis cycles with minimal structural and morphological changes. This work demonstrates the remarkable photocatalytic activity ZIF-8/ZnO/SiO2 with its improved visible-light response, highlighting the potential of using modified ZIF-8 materials as promising and sustainable catalysts for wastewater treatment.