Experimental and DFT studies on highly selective separation of indium ions using silica gel/graphene oxide based ion-imprinted composites as a sorbent

Here, a novel adsorbent for selective separation and recovery of In(III) ions from the real wastewater was fabricated using ion imprinting technique with graphene oxide composite as the host materials. Several techniques, including Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetry (TGA) and Brunauer–Emmett–Teller (BET)were used to characterize the silica gel/graphene oxide based ion-imprinted composites (SG/GOIIC) and the obtained experimental results were combined with the Density Functional Theory (DFT) theoretical calculations to reveal the adsorption mechanism. The adsorption behaviors of SG/GOIIC towards In(III) ions was evaluated using both batch and fixed-bed experiments. The results shown that the adsorption ability of In(III) ions onto SG/GOIIC increased with the increase of pH range from 1.5 to 3.0, and that the adsorption equilibrium was reached within 50 min. The maximum uptake of SG/GOIIC calculated using Langmuir isotherm was estimated to 147.1 mg/g. Kinetics studies revealed that the pseudo-second-order was a better choice to describe the whole absorption process, while the isotherms of In(III) ions adsorption followed the Langmuir model. In addition, SG/GOIIC exhibited excellent affinity towards In(III) ions in water even in the presence of Sn(II), Cu(II), Zn(II), Al(III) and Fe(III) ions and the corresponding selectivity coefficients of SG/GOIIC for In/Sn, In/Cu, In/Zn, In/Al and In/Fe were 18.47, 22.99, 35.31, 16.67 and 8.52, respectively. The SG/GOIIC possessed good stability with adsorption rate maintained at 94.36% even after five cycles. More importantly, the SG/GOIIC composite was able to separate and to recover indium from real wastewater through fix-bed adsorption. This study proposed a new method to prepare adsorbent with excellent selectivity towards targeted ions and to figure out the difficulty of graphene oxide in separation from water.