Preparation of mesoporous material from hydrotalcite/carbon composite precursor for chromium(VI) removal

The composite (LDH/C) of MgAl hydrotalcite and carbon was synthesized in the presence of glucose, which was used as the precursor of the corresponding MgAl mixed oxide (MgAlO C). The as-synthesized hydrotalcites and their corresponding mixed oxides were characterized by XRD, FTIR, SEM, BET/BJH and TG/DTA. The results showed that carbon in the LDH/C could act as a mesoporous template, and the MgAlO C had higher surface areas and more mesopores as well as higher Cr(VI) adsorption performance than the MgAl mixed oxide (MgAlO) prepared in the absence of glucose. The experimental data in the Cr(VI) adsorption by the MgAlO C was analyzed using various adsorption kinetic and thermodynamic models. The pesudo-second order and Elovich models fitted the experimental data. And the intraparticle diffusions model fitted the experimental data well at the second stage of adsorption (>30 min), indicating that the intraparticle diffusion in the Cr(VI) adsorption process was rate-limiting step. Combined with thermodynamic analysis, the activation energy (21.38 kJ·mol−1) suggested that the adsorption process was chemisorption nature. The results demonstrated that the intercalation of CrO42− into the interlyer spaces of the MgAlO C occurred by the reconstruction, and followed by the anion-exchange of interlayer –OH and CrO42− anions companying with diffusion in the entire adsorption process.