Heavy metal adsorption using PAMAM/CNT nanocomposite from aqueous solution in batch and continuous fixed bed systems

Novel fixed-bed adsorption investigations applying carbon nanotube (CNT) coated poly-amidoamine dendrimer (PAMAM) as an adsorbent have been studied for the adsorption of As(III) as arsenous acid, Co²⁺, and Zn²⁺ from aqueous solution. FTIR, SEM, ¹H NMR, TGA, TEM, Raman Spectra and zeta potential measurements have been employed for characterizing the synthetic nanocomposite and these techniques indicated that the dendrimer functionalized CNTs have been favorably synthesized. The effects of process parameters including flow rate, initial concentration and bed height on the duration of the breakthrough time, mass transfer zone, adsorption capacity and exhaustion time at breakthrough were investigated. Decreasing initial concentration and flow rate, and increasing bed height, increased the exhaustion and breakthrough times. In addition, the removal capacity at breakthrough was enhanced with decreasing flow rate, initial ion concentration and increasing bed height. The notably high maximum adsorption capacities at fixed bed breakthrough of the studied ions were 432 mg/g for As(III) as arsenous acid, 494 mg/g for Co²⁺, and 470 mg/g for Zn²⁺ at bed height of 12.0 cm, influent concentration of 100 mg/L and flow rate of 0.5 mL/min. Almost no previous fixed bed data for PAMAMS exist. Adsorption results were correlated using the Thomas, Yoon-Nelson, and Bohart-Adams models. Empirical breakthrough curves were found to be best fitted with the predicted curves produced by the Thomas and Yoon-Nelson equations. This study illustrates the efficiency of PAMAM/CNT nanocomposite for the adsorption of As(III), Co²⁺, and Zn²⁺ from aqueous solution.