Highly efficient removal of tannic acid from aqueous solution by chitosan-coated attapulgite

Chitosan-coated attapulgite (CCATP) was prepared for removing the organic pollutant tannic acid (TA) from aqueous solution. The structural and surface characteristics of the resulting materials were characterized by N2 sorption–desorption, X-ray diffraction technique, Fourier transform infrared spectroscopy, thermogravimetric analysis, and zeta potential measurements. Batch sorption tests indicated that CCATP exhibited higher sorption affinity towards aqueous TA with a higher sorption capacity than ATP. The sorption isotherm of TA onto CCATP fitted the Freundlich model well, implying that sorption process was heterogeneous. TA sorption onto CCATP could be well described by the pseudo-second-order kinetics. Sorption of TA onto CCATP was found to be strongly dependent on pH, ionic strength and temperature. The sorption of TA onto CCATP was a spontaneous and endothermic process. The sorption of TA cannot be merely attributed to electrostatic interaction, and the hydrogen bonding as well as van der Waals interactions are also formed between TA and CCATP. The TA loaded CCATP can be regenerated easily by acid treatment. All results indicate that CCATP has potential value in the removal of TA from water.

► The sorption rate of TA is remarkably enhanced after ATP modified by chitosan.
► The TA loaded CCATP can be regenerated easily by acid treatment.
► TA sorption is not only due to hydrogen bonding and electrostatic interactions.
► The van der Waals interaction also plays a crucial role in TA sorption.