Photo-Driven Ion Directional Transport across Artificial Ion Channels: Band Engineering of WS2 via Peptide Modification.

Biological photo-responsive ion channels play important roles in the important metabolic processes of living beings. To mimic the unique functions of biological prototypes, the transition metal dichalcogenides, owing to their excellent mechanical, electrical, and optical properties, are already used for artificial intelligent channel constructions. However, there remain challenges to building artificial bio-semiconductor nanochannels with finely tuned band gaps for accurately simulating or regulating ion transport. Here, two well-designed peptides are employed for the WS2 nanosheets functionalization with the sequences of PFPFPFPFC and DFDFDFDFC (PFC and DFC; P: proline, D: aspartate, and F: phenylalanine) through cysteine (Cys, C) linker, and an asymmetric peptide-WS2 membrane (AP-WS2M) could be obtained via self-assembly of peptide-WS2 nanosheets. The AP-WS2M could realize the photo-driven anti-gradient ion transport and vis-light enhanced osmotic energy conversion by well-designed working patterns. The photo-driven ion transport mechanism stems from a built-in photovoltaic motive force with the help of formed type II band alignment between the PFC-WS2 and DFC-WS2. As a result, the ions would be driven across the channels of the membrane for different applications. The proposed system provides an effective solution for building photo-driven biomimetic 2D bio-semiconductor ion channels, which could be extensively applied in the fields of drug delivery, desalination, and energy conversion.

First-principles study of CO2 hydrogenation on Cd-doped ZrO2: Insights into the heterolytic dissociation of H2.

Cd-doped ZrO2 catalyst has been found to have high selectivity and activity for CO2 hydrogenation to methanol. In this work, density functional theory calculations were carried out to investigate the microscopic mechanism of the reaction. The results show that Cd doping effectively promotes the generation of oxygen vacancies, which significantly activate the CO2 with stable adsorption configurations. Compared with CO2, gaseous H2 adsorption is more difficult, and it is mainly dissociated and adsorbed on the surface as [HCd-HO]* or [HZr-HO]* compact ion pairs, with [HCd-HO]* having the lower energy barrier. The reaction pathways of CO2 to methanol has been investigated, revealing the formate path as the dominated pathway via HCOO* to H2COO* and to H3CO*. The hydrogen anions, HCd* and HZr*, significantly reduce the energy barriers of the reaction.

Hydrogenation of CO2 to methanol over In-doped m-ZrO2: a DFT investigation into the oxygen vacancy size-dependent reaction mechanism.

Selective methanol synthesis via CO2 hydrogenation has been thoroughly investigated over defective In-doped m-ZrO2 using density functional theory (DFT). Three types of oxygen vacancies (Ovs) generated either at the top layer (O1_v and O4_v) or at the subsurface layer (O2_v) are chosen as surface models due to low Ov formation energy. Surface morphology reveals that O1_v has smaller oxygen vacancy size than O4_v. Compared with perfect In@m-ZrO2, indium on both O1_v and O4_v is partially reduced, whereas the Bader charge of In on O2_v remains almost the same. Our calculations show that CO2 is moderate in adsorption energy (∼-0.8 eV) for all investigated surface models, which facilitates the formate pathway for both O1_v and O4_v. O2_v is not directly involved in CO2 methanolization but could readily transform into O1_v once CO2/H2 feed gas is introduced. Based on the results, the synthesis of methanol from CO2 hydrogenation turns out to exhibit conspicuous vacancy size-dependency for both O1_v and O4_v. The reaction mechanism for small-sized O1_v is controlled by both the vacancy size effect and surface reducibility effect. Thus, H2COO* favors direct C-O bond cleavage (c-mechanism) before further hydrogenation to methanol, which is similar to the defective In2O3. The vacancy size effect is more competitive than the surface reducibility effect for large-sized O4_v. Therefore, H2COO* prefers protonation to H2COOH before C-O bond cleavage (p-mechanism) which is similar to the ZnO-ZrO2 solid solution. Furthermore, we also determined that stable-CH3O*, which is too stable to be hydrogenated, originates from the O1_v surface. In contrast, CH3O* with similar configuration is allowed to be further converted to methanol on O4_v. Overall, our findings offer a new perspective towards how reaction mechanisms are determined by the size of oxygen vacancies.