Constructing a multi-layer adsorbent for controllably selective adsorption of various ionic dyes from aqueous solution by simply adjusting pH

This work prepared a novel adsorbent with multi-layer structure and verified its adsorption mechanism for various ionic dyes. By the methods of cross-linking and surface modification, a multi-layer composite (CTAB-Chitosan@Al2O3) was successfully synthesized, which showed an excellent adsorptive performance for various anionic dyes. The results indicated that the outer layer and the core adsorbed Congo Red (CO) and Reactive Blue (RB) well, and the middle layer played a leading role on adsorbing Methyl Orange (MO). The maximum adsorption capacity of CTAB-Chitosan@Al2O3 for MO, CO and RB was 327.87, 1250.00 and 1017.90 mg/g, respectively. The characteristics of the as-synthesized adsorbent were revealed by multi-method, including Fourier Transform Infra-Red spectra, X-ray powder diffraction, X-ray photoelectron spectra, Scanning Electron Microscope, Brunauer-Emmet-Teller surface area and Thermogravimetric analyzer, which verified that the comprehensive effects of electrostatic interaction and hydrogen bond was the main mechanism for CTAB-Chitosan@Al2O3 to adsorb ionic dyes. The pH value obviously influenced the surface charge of CTAB-Chitosan@Al2O3, and it was a convenient approach to regulate and control the adsorption process by only adjusting the pH value.