Polypyrrole-encapsulated metal oxide nanocomposite for adsorptive abatement of anionic dye from dye laden wastewater: Cost analysis and scale up design

Abstract

The present work demonstrates the fabrication of an organometallic material i.e. polypyrrole-encapsulated zinc oxide (PPy@ZnO) nanocomposite for adsorptive elimination of Eriochrome black-T (EBT) dye from water. The specific surface area and pore volume of the PPy@ZnO nanocomposite were observed to be 28.726 m2/g and 0.086 cc/g, respectively. At optimum experimental conditions of solution pH; 4.0, PPy@ZnO nanocomposite dose: 1.0 g/L, contact time: 30 min and initial EBT dye concentration: 50 mg/L, maximum EBT dye removal efficiency of ∼94±1.86% was obtained. The pseudo-second-order kinetic and Langmuir isotherm model provides the best fit for the adsorption experiments, with maximum EBT dye adsorption capacity of 277.78 mg/g. The prominent adsorption mechanisms include the hydrogen bonding, π–π interactions, and electrostatic attraction. The adsorption study is spontaneous (ΔG° < 0) and endothermic (ΔH° > 0, ΔS° > 0) in nature as indicated by the thermodynamics study. The reduction in EBT dye removal efficiency was insignificant (∼10±0.94%) in surface water as compared to other real water samples. Monovalent anions (i.e., NO3–and Cl–) have minimal impact on EBT removal efficiency with reduction in removal efficiencies in the range of 4.0±1.54% to ∼11.0±1.93%. Regeneration study suggests an overall ∼20±1.45% decrease in the EBT dye removal efficiency after 5th cycle of regeneration. Response surface methodology suggests the maximum adsorption efficacy of 95±1.68% at initial EBT dye concentration of 35 mg/L, PPy@ZnO dose of 0.85 g/L and contact time of 40 min. The estimated synthesis cost of PPy@ZnO nanocomposite was determined to be ∼117 USD/kg. Batch mode scale-up design suggests a minimum of 87.48 g of PPy@ZnO nanocomposite needs to be applied to treat 50 mg/L of EBT dye loaded wastewater (50 L volume) with 95% dye removal efficiency.