Mechanism of selective gold adsorption on ion-imprinted chitosan resin modified by thiourea

Thiourea-modified chitosan-imprinted resin (IM-TUCS) and a corresponding nonimprinted resin (NIM-TUCS) were synthesized and characterized using adsorption experiments. The adsorption results showed that adsorption reached equilibrium within 4 h. The adsorption data were better fitted using the Langmuir model (R-2>0.99), and the gold adsorption capacities of IM-TUCS and NIM-TUCS were 933.2 and 373.7 mg.g(-1), respectively. The IM-TUCS adsorbent was more suitable for gold than other coexisting anions and cations. The possible mechanism underlying Au(III) adsorption on IM-TUCS was further investigated using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction analyses. The protonation of the amino group on the resin under low pH conditions promoted Au(III) adsorption; O, N and S in the C-OH, (CS)-S-= and C-NH2 groups contained in the IM-TUCS coordinated with Au(III) ions. The cross-linking of the imprinted resin provided holes that could hold Au(III), thus the imprinted resin supported more Au(III). The adsorption capacity of the IM-TUCS for Au(III) was significantly higher than that of the NIM-TUCS, which is attributed to the cross-linking of the imprinted resin. Moreover, the IM-TUCS showed specific recognition capabilities for Au(III). After elution with the eluent, IM-TUCS was reused for four cycles with a gold recovery rate of approximately 93%, revealing its high potential economic value.

Automated summary

Thiourea-modified chitosan-imprinted resin (IM-TUCS) exhibited higher gold adsorption capacity and specific recognition capabilities for Au(III) compared to nonimprinted resin (NIM-TUCS). Protonation of the amino group on the resin under low pH conditions promoted Au(III) adsorption, while the cross-linking structure provided holes that could hold Au(III). The IM-TUCS showed high potential economic value with a gold recovery rate of approximately 93% after reuse for four cycles.