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Optimization of toxic metal adsorption on DEA-calix[4]arene appended silica resin using a central composite design

Samiha Gul, Fakhar N. Memon,
Published: 31 January 2022

Abstract: The present study is devoted to the application of Central Composite Design (CCD) to purify water contaminated with toxic metal ions (Pb2+, Cd2+ and Hg2+) using a p-tert-diethanolaminomethylcalix[4]arene (DEA-C4) based silica resin. The synthesized material was characterized using SEM, FTIR and EDX techniques. Three effective parameters (pH, adsorbent dosage and concentration of metal ion) were optimized by assessment with CCD. The data was analyzed using the quadratic model and the obtained results revealed the highest % adsorptions for Pb2+ (92.7), Cd2+ (93.7) and Hg2+ (88.2) at the optimum points for pH (5.4, 3.18 and 3.89), adsorbent dosage (23.8, 25.5 and 26.12 mg) and metal ion concentration (5.3, 7.62 and 7.18 ppm), respectively. Analysis of variance (ANOVA) results show a good fit for the regression model, showing R2 values of 0.99 for Pb2+, 0.99 for Cd2+ and 0.98 for Hg2+. Furthermore, the results from Freundlich adsorption isotherms suggest its favorability, as the values for n are >1 (i.e., 7.06, 8.85 and 13.2) and there are higher values for R2 = 0.97, 0.99 and 0.98 for Pb2+, Cd2+ and Hg2+, respectively. However, for the Langmuir isotherm, the value of the separation factor RL is >1 (1.01, 1.02 and 1.05 for Pb2+, Cd2+ and Hg2+, respectively), revealing its un-favorability. In kinetics, the pseudo-second-order kinetic model (Ho and McKay) shows R2 values of 0.998, 0.999 and 0.999 for Pb2+, Cd2+ and Hg2+, suggesting the chemical reaction seems significant in the rate controlling step. The thermodynamic results concluded that the reaction is spontaneous and exothermic in nature.
Keywords: optimized / model / contaminated / sup / metal ion

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