Adsorption optimization of uranium(VI) onto polydopamine and sodium titanate co-functionalized MWCNTs using response surface methodology and a modeling approach

Abstract The removal and recovery of uranyl ions from radioactive wastewater is of strategic significance and environmental value for radioactive pollution control and resource recovery. In this work, we designed and fabricated a ternary nanohybrids composites MWCNTs@PDA@TNSs and also optimized the experimental conditions (solution pH, initial concentration, adsorbent dose and contact time) via central composite design (CCD) in response surface methodology (RSM). The results showed that it could be achieved 99.45% of removal efficiency at optimum conditions of 0.31 g/L of adsorbent dose, 3.86 of pH, 37.86 min of contact time and 26.70 mg/L of initial concentration. The adsorption equilibrium could be achieved within 20 min and the adsorption process perfectly followed the pseudo-second-order model with a high correlation coefficient (R2 = 0.997 for MWCNTs and 0.992 for MWCNTs@PDA@TNSs), indicating the nature of chemical adsorption. The Langmuir isotherm model was more suitable to describe the experimental data with the predicted equilibrium capacity of 283.29 mg/g at 298 K, implying a monolayer adsorption. The tolerance experiment of common ions manifested that MWCNTs@PDA@TNSs had stronger adsorption capacity and affinity for U(VI) than MWCNTs, and was suitable for enriching uranium from multicomponent systems. The removal percentage of uranium reached 86.36% in simulating seawater when the dose was 1.8 g/L. Regeneration study confirmed that MWCNTs@PDA@TNSs possessed the high recyclability. After three regeneration cycles, the removal percentage could still reach 82.16%. In summary, our work will facilitate the development of functionalizing carbon-based materials for water remediation, and optimization of the adsorption conditions enable the realization of the practical needs for the cleanup of radioactive wastewater.