Mixed-Anion MnxCd1−xCr2S2Se2 Chalcospinels: Structural Characterization and Environmental Approach for Sensing and Remediation of 4−Nitrophenol

Monitoring and removing water pollutants such as 4−nitrophenol (4−NP) represents a major environmental challenge due to their toxicity and persistence. In this work, we synthesized a series of mixed chalcospinels MnxCd1−xCr2S2Se2 (x = 0.2, 0.4, 0.6, 0.8) by the ceramic route to investigate the influence of Mn/Cd substitution on their structural, electrochemical, and catalytic properties. The obtained phases were characterized by powder X−ray diffraction and Raman spectroscopy, confirming the preservation of the cubic spinel framework with composition-dependent lattice parameters and vibrational features. Dispersions of MnxCd1−xCr2S2Se2 with multiwalled carbon nanotubes (MWCNTs) were prepared and used to modify glassy carbon electrodes. Electrochemical measurements revealed sensitivity for 4-NP detection (for x = 0.2: LoD = 9.6 μM, LoQ = 29.0 μM; x = 0.8: LoD = 7.4 μM, LoQ = 22.4 μM), with the response varying systematically with Mn/Cd ratio. In parallel, heterogeneous catalytic assays were performed for the chemical reduction of 4−NP to 4−aminophenol (4−AP), a less toxic compound, using NaBH4 as the reducing agent. The catalytic activity exhibited a strong dependence on cation composition, with the Mn0.4Cd0.6Cr2S2Se2 phase achieving optimal performance, where only Mn0.4Cd0.6Cr2S2Se2 achieved 100% conversion of 4−NP. These findings demonstrate that MnxCd1−xCr2S2Se2 spinels are versatile materials with dual functionality as electrochemical sensors and heterogeneous catalysts, offering promising applications in environmental remediation and pollutant monitoring.