Tunable sulphur doping in CuFe2O4 for the efficient removal of arsenic through arsenomolybdate complex adsorption: kinetics, isothermal and mechanistic studies

Abstract

Arsenic is regarded as a highly toxic element that naturally exists in ground drinking water. Owing to its inherent carcinogenic nature, arsenic free water becomes necessary for a healthy life. To remove arsenic from the ground drinking water, the Bahawalnagar district of Pakistan was chosen for sample collection. For the complete removal of dissolved arsenic contents (As^III/As^V), ferrites have been found to be very effective in purifying natural water. In this study, sulphur-doped copper ferrites (CuFe₂S_xO_4−x) were synthesized for the first time using a hydrothermal strategy. XRD results revealed that CuFe₂S_xO_4−x has spinel cubic structures, whereas SEM results illustrate that spherical morphologies indicate higher adsorption of arsenic over CuFe₂S_xO_4−x. The purity and elemental compositions were confirmed by EDX results, whereas the stability was revealed by thermogravimetric analysis (TGA). For the quantitative study, dissolved arsenic contents were converted into an arsenomolybdate complex (AMC). The adsorption of AMC on CuFe₂S_xO_4−x was found to be a spontaneous process (ΔG = −13.41 kJ mol⁻¹). The adsorption kinetic performances of CuFe₂S_xO_4−x for AMC were well fitted by pseudo first order and had the correlation coefficient R² = 0.95458. The adsorption isotherm data for AMC removal were fitted with the Langmuir model (R² = 0.99981), whereas an electrostatic relationship between CuFe₂S_xO_4−x and AMC (R² = 0.66186) was revealed by the Temkin model. The maximum adsorption capacity observed on CuFe₂S_xO_4−x was 188.8 mg g⁻¹, which is higher than those from previous reports.