Removal of Cr(III) from aqueous solution by silica-gel/PAMAM dendrimer hybrid materials
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Water pollution caused by Cr(III) is a serious environmental problem which bring adverse effect to environmental protection and public safety. Efficient removal of Cr(III) from aqueous solution is important for the remediation of Cr(III) pollution. Herein, a series of silica-gel/polyamidoamine (PAMAM) dendrimer hybrid materials (SG-G0~SG-G4.0) were used for the removal of Cr(III) from aqueous solution. The factors that affect the adsorption were extensively studied and the adsorption mechanism was demonstrated based on the experimental results and density functional theory (DFT) calculation. Result demonstrates the adsorption capacity of ester-terminated silica-gel/PAMAM dendrimers follow the order of SG-G2.5 > SG-G3.5 > SG-G1.5 > SG-G0.5, while that of amino-terminated ones decrease in the order of SG-G2.0 > SG-G4.0 > SG-G3.0 > SG-G1.0 > SG-G0. The highest adsorption is achieved at pH 4.0 for both ester- and amino-terminated materials. Adsorption kinetic indicates the adsorption equilibrium can be reached at about 240 and 180 min for amino- and ester-terminated hybrids, respectively. Adsorption kinetic can be well fitted by pseudo-second-order kinetic model with film diffusion process as the rate-limiting step. Adsorption isotherm follows Langmuir model with monolayer adsorption behavior. Fourier transform infrared spectra (FTIR) indicate the adsorption of Cr(III) by PAMAM dendrimer mainly involve the participation of N–H and C=O groups. DFT calculation demonstrates the uptake of Cr(III) by ester-terminated adsorbents mainly involves carbonyl oxygen and secondary amine nitrogen atoms to form tetra-coordinated chelate, while that of amino-terminated one tends to form hexa-coordinated chelates by carbonyl oxygen, primary and secondary amine nitrogen atoms.
KeywordsAdsorption Silica-gel PAMAM dendrimers Cr(III) Mechanism
The authors are grateful for the financial support by the National Natural Science Foundation of China (21307053 and 51673090), Natural Science Foundation of Shandong Province (ZR2018MB039), Science and Technology Research Program of Yantai (2017ZH060), The Key Program for Basic Research of Natural Science Foundation of Shandong Province (ZR2018ZC0946).
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