Evaluation of Fe–Mn–Zr Trimetal Oxide/Polyaniline Nanocomposite as Potential Adsorbent for Abatement of Toxic Dye from Aqueous Solution

Abstract

The discharge of industrial effluents containing harmful synthetic dyes has gone up significantly since the last few decades and poses a severe environmental threat. Among a wide variety of treatment techniques available for the remediation of dye-laden wastewater, the adsorption process has been reported to be an effective method. Nanoscale adsorbents derived from metal oxides and their composites have recently attracted attention due to their enhanced ability to adsorb contaminants. The removal of congo red (CR) dye from dye solution was studied using a new adsorbent Fe–Mn-Zr trimetal oxide nanocomposite synthesized with polyaniline (PANI). The structural characterization of the Fe–Mn-Zr/PANI was investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis and energy dispersive X-ray (EDX) analysis. It was observed that the adsorption process was substantially dependent on sonication time, the dose of adsorbent and the initial concentration of CR dye. Optimum solution pH was obtained as 5.0 from the effect of the pH study that has been performed for different initial concentrations of CR dye. The maximum percentage of adsorption efficiency for CR dye obtained was 89.25% at the initial concentration of 20 mg/L, with 0.2 g/L adsorbent dose and pH 5.0 within 15 min. In this work, kinetic analysis was performed utilizing pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic models, with the second-order kinetics model being shown to be the best fit. In comparison to pseudo-first-order kinetics, the experimental and calculated values of Qe for the pseudo-second-order kinetics were in good agreement. The isotherm study was performed by varying the initial CR concentration from 5 to 70 mg/L with 0.1–0.4 g/L adsorbent dose. The adsorption experiments are best fitted with the Langmuir isotherm, giving a CR dye adsorption capacity of 111.111 mg/g at pH 5.0. The correlation coefficient value (0.991) indicates an accurate fit for the Langmuir model. The primary adsorption mechanism is the electrostatic interaction between the sulfonated group (–SO3Na) of negatively charged CR dye molecules and the positively charged amine group (–NH2) of PANI surface. The response surface methodology (RSM) was studied to optimize the removal of the CR dye used with different experimental parameters like initial CR concentrations (5, 10, 15, 20 and 25 mg/L), with adsorbent dose (0.1–0.5 g/L), at reaction time (2 min, 4 min, 6 min, 8 min and 10 min) and solution pH: 5.0. Maximum CR dye removal of 97.78% was obtained at an optimum contact time of 15 min, with an initial CR dye concentration of 20 mg/L and adsorbent dose at 0.2 g/L.KeywordsMetal oxide nanoparticlesPolyanilineNanocompositeCongo redDye adsorptionResponse surface methodologyAdsorption mechanismKinetic studyIsotherm modellingCentral composite designOptimization