Removal of chromium from aqueous solution using a nanocomposite of nickel ferrite and polyaniline doped with 2-naphthalene sulfonic acid

Abstract

Chromium is a highly toxic, highly mobile heavy metal commonly found in industrial effluents. This study investigated the efficacy of a nickel ferrite/polyaniline/2-naphthalene sulfonic acid nanocomposite (PANI-NSA/NiFe2O4) in removing Cr(VI) from solution. NSA doping led to the formation of tubular-shaped rods, enhancing the material's surface area. Key adsorption parameters (pH, adsorbent dosage, agitation time, and initial pollutant concentration) were thoroughly examined and optimized. The adsorption process was notably pH-dependent, with maximal adsorption occurring at pH 2. The findings indicated a remarkable 99.9% removal of Cr(VI) from a 50 mg/L solution with a 25 mg adsorbent dose. Freundlich, Langmuir, and Two-Surface Langmuir isotherm models were tested, with the Two-Surface Langmuir model best describing the experimental results. Kinetics studies revealed rapid adsorption within the initial 30 min, followed by a slower rate, reaching maximum Cr(VI) removal within 24 h. Temperature studies revealed and enhanced adsorption capacity at higher temperatures, with a maximum adsorption capacity of 420.0 mg/g at 45 °C. Thermodynamic analysis indicated an endothermic and spontaneous adsorption process. The mechanism of Cr(VI) removal involved electrostatic attraction, reduction, and surface complexation. PANI-NSA/NiFe2O4 could be reused for up to five cycles, achieving 99% Cr(VI) removal from a 50 mg/L Cr(VI) solution in the first two cycles. Furthermore, tests on authentic chromium wastewater showed that a 40 mg dose in 50 mL liquid fully removed 50 mg/L Cr(VI). This study underscores the potential of PANI-NSA/NiFe2O4 for industrial applications in Cr(VI) removal, offering a promising solution for addressing the pressing issue of chromium pollution.