Ag-Modified g-C₃N₅/CdS Z-Scheme Heterojunction for Enhanced Photodegradation of Norfloxacin and Electrocatalytic Hydrogen Evolution: Experimental and DFT Insights

The development of dual-functional materials for sustainable environmental remediation and electrochemical energy conversion remains an important research area. In this work, g-C₃N₅ (CN), 1% Ag-modified CN (ACN), cadmium sulfide (CdS), 20% CN/CdS (CCN), and 20% (1% ACN)/CdS (CACN) were synthesized via calcination and hydrothermal methods. Among them, CACN exhibited the highest photocatalytic performance, achieving 97% removal of norfloxacin (NOR) within 70 min under white LED irradiation, with a rate constant 3.45 times higher than that of pristine CdS. The composite also maintained stable performance over five consecutive cycles. Radical-scavenging and electron spin resonance (ESR) analyses indicated that superoxide radicals (O₂^•−) and hydroxyl radicals (OH^•) were the dominant reactive species involved in NOR degradation. High-performance liquid chromatography–mass spectrometry (HPLC–MS) analysis identified degradation intermediates and proposed possible transformation pathways. UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), Mott–Schottky analysis (MS), and density functional theory (DFT) calculations supported the formation of a Z-scheme charge–transfer mechanism. The Ag incorporations likely improved charge separation through localized surface plasmon resonance (LSPR) effects and the formation of Ohmic contacts. Furthermore, electrochemical evaluation showed that CACN supported on Ni foam exhibits enhanced hydrogen evolution reaction (HER) performance, delivering an overpotential (η) of 111 mV at 10 mA/cm² in 1 M KOH, with stable performance over 20 h. These findings demonstrate that CACN is a promising dual-functional material for antibiotic degradation and hydrogen production.