Adsorption Of Cr(?) By Polyaniline-magnetic Mesoporous Silica Composite

Due to industrial development, more and more pollutants have been released into the environment. Among them, heavy metal pollution problem is particularly serious. Generally, heavy metals is of high toxicity and nonbiodegradable, wastewater containing heavy metals which released into the environment, causing serious environmental and health risks.Circulatory movement of heavy metals in the medium, resulting in a permanent environmental pollution. This paper focuses on nanomaterials and its application for heavy metals removal. Based on the advantages of nanomaterials and adsorption, magnetic nanomaterials was organically modified and used for efficient management of heavy metals contaminants.In this study, magnetic mesoporous silica composite was in situ synthesized by mixing ferric iron precursor, F127 and TEOS, evenly, oxidizing Fe2+ to Fe3O4 by H2O2, and finally grafting with PANI to functionalize the composite. The characterization of PANI-magnetic mesoporous silica composite adsorbent was conducted by SEM, TEM and FTIR spectrometer. The spectra displayed that PANI was successfully grafted to magnetic mesoporous silica. And the process of modification did not change the hexagonal phase mesoporous structure. The zeta potentials of the PANI-magnetic mesoporous silica composite showed that the adsorbent had an isoelectric point at p H 9.9. Nitrogen adsorption-desorption isotherms and pore size distribution curves of the modified adsorbent indicated that its pore diameter was 3.75 nm.The influence of several operating parameters for adsorption of Cr(VI), such as contact time, p H, and initial concentration of Cr(VI), were investigated in batch mode to determine the optimum adsorption conditions. The optimal adsorption occurred at p H 5.0, while the maximum adsorption capacity and equilibration time for Cr(VI) were 193.85 mg/g, 430 min respectively. Its removal efficiency for heavy metals is much higher than natural clay. Besides, the synthetic adsorbent showed excellent regenerability, and kept 66% removal efficiency in the fifth absorption-desorption cycle.The fitting of the experimental data show ed that langmiur model well described the sorption isotherms with correlation coefficient of 0.99. Moreover, It was determined that adsorption for Cr(VI) obeyed pseudo-second-order kinetics and the intraparticle diffusion model. The adsorption was a spontaneous exothermic process, and consequently a lower temperature was favourable to the reaction. The negative entropy changes indicated that the order degree increased during the adsorption process.Finally, the effect of p H and XPS spectra of PANI-magnetic mesoporous silica composite adsorbent before and after Cr loading were studied, indicating that the proposed mechanism of Cr(VI) removal combined adsorption and reduction. Under acidic conditions(p H 2), the nitrogen atoms of imine and amine groups were protonated and formed bonds with negatively charged HCr O4- by electrostatic attraction. After being adsorbed onto PANI-magnetic mesoporous silica composite, Cr(VI) was reduced to Cr(III) by PANI, while the latter was partially oxidized from emeraldine form to pernigraniline.