Thanks to the high affinity, adsorbents with sulfur-containing groups are usually used to recover Au ions, but neglect of the availability and utilization of introduced groups often makes the effort wasted, limiting the practical application of adsorbents severely. Here, we designed and fabricated two ANF-based aerogels with free and anchored thiourea groups respectively, and the adsorption performance and key influence factors were investigated by combining experiments and MD simulations. The experimental results showed that two aerogels exhibited distinct performance of adsorbing Au ions. And MD simulations results disclosed the structure difference of thiourea groups on the surface of two aerogels. The one with better performance had freer sulfur-containing groups, and these groups were easy to change their conformation, resulting in easier interaction with Au ions. However, groups on the surface of the other one were anchored. This difference in structure and resultant performance indicated that the freedom of functional groups play a critical role in the process of adsorption. As a result, the calculated maximum adsorption capacity of aerogels with free thiourea groups is as high as 719.42 mg/g, and although the reusability of adsorbents decreases with the increase of recycle times, caused by the generation of Au (0) during adsorption process, its adsorption capacity is till as high as 461.9 mg/g. Alternatively, incineration is also a feasible approach, especially after several recycle times, because of the low cost of fabricated adsorbents. Therefore, aerogels prepared by structural design have advantages in the field of gold recovery, and the superior performance also demonstrates the significance of utilization of introduced functional groups in the designed adsorbents.
Lunlun Gong,Heng Yin,Chengming Nie,Xuran Sun,Xiuli Wang,Mei Wang
Although hybrid photocathodes built by immobilizing molecular catalysts to the surface of semiconductors through chemical linkages have been reported in recent years, systematic and comparative studies remain scarce about the impact of various anchoring groups on the performance, stability, and charge-transfer kinetics of molecular catalyst-decorated hybrid photocathodes for photoelectrochemical (PEC) H2 production. In this study, the molecular cobaloxime catalysts, CoPy-4-X (Py = pyridine, X = PO3H2, COOH, and CONH(OH)), bearing different anchoring groups were synthesized and covalently immobilized to the surface of the porous TiO2 layer coated on a p-Si plate or a fluorine-doped tin oxide glass. The influence of the anchoring groups on the performance of p-Si/TiO2/CoPy-4-X photocathodes was comparatively studied for PEC H2 evolution. Among the tested hybrid photocathodes, the one with a hydroxamate as an anchoring group displayed higher activity and lower charge-transfer resistance than that observed for the electrode with a carboxylate or a phosphonate as the anchoring group. Notably, the catalytic current of p-Si/TiO2/CoPy-4-CONH(OH) was attenuated only by 2.9% in the controlled potential photoelectrolysis tests in borate buffer solution at pH 9 at 0 V versus a reversible hydrogen electrode over 6 h. Moreover, the influence of anchoring groups on the interfacial electron transfer from the TiO2 layer to the immobilized cobaloxime catalyst and electron–hole recombination was studied by transient absorption spectroscopy. These results revealed that the hydroxamate as an anchoring group is superior to the carboxylate and phosphonate groups for speeding up the interfacial electron transfer and firmly immobilizing the molecular catalysts to the metal oxide semiconductors to build efficient and stable hybrid photoelectrodes.
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