Hydrolyzed MOF based Mo@h-ZIF-8/ZnS composite for enhanced photodegradation of dye pollutants using a combined experimental and RSM approach

This work investigates the design and application of a Mo-doped hydrolyzed ZIF-8 (h-ZIF-8) composite on a ZnS substrate for the photodegradation of malachite green (MG) dye using an H₂O₂-assisted advanced oxidation process (AOP) under sunlight irradiation. The innovative h-ZIF-8 photocatalyst, synthesized via a simple aqueous reflux process, is more stable than standard methanol-synthesized ZIF-8, which generally disintegrates under extended water exposure. The partly hydrolyzed ZIF-8 structure, with hydroxyl groups substituting for the cleaved Zn-N bonds, allows for improved photocatalytic activity. Using Response Surface Methodology (RSM) and Central Composite Design (CCD), the best conditions for 99.14% MG degradation are as follows: 0.05 mM H₂O₂, 6.5 mg catalyst, 66.5 ppm MG, and 52.9 min of sunlight exposure. The experimental findings closely match RSM predictions, with 98.95% degradation achieved after 50 min. An all-solid-state Z-scheme electron transfer channel using Mo nanoparticles allows for efficient charge separation between the ZnS and h-ZIF-8 interfaces, which reduces electron-hole recombination and increases photocatalytic performance. High-resolution liquid chromatography-mass spectrometry (HR-LCMS) detects intermediate phases of MG breakdown and provides insight into the degradation route. The catalyst is resilient across several water matrices (tap, lake, and wetland water) and various coexisting inorganic (cations and anions) and organic substances, and successfully degrades many dye pollutants, including crystal violet, rhodamine B, brilliant green, Victoria blue, methylene blue, and Congo red, with over 80% efficiency. The catalyst remains 76% efficient after six cycles, demonstrating its reusability. This study demonstrates substantial progress in stabilizing ZIF-8 for solar energy conversion and water treatment applications, highlighting the potential of hydrolyzed ZIF-8 in sustainable environmental remediation.