Stepwise Protonation of Three-Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis.

Three-dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D-bcu-COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D-bcu-COFs was initially modulated by functionalizing linear linkers with benzo-thiadiazole or benzo-selenadiazole groups. Furthermore, taking advantage of the well-exposed porphyrin and imine sites in 3D-bcu-COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo-selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Working retirees in Taiwan: examining determinants of different working status after retirement.

This study aims to investigate the factors influencing the work status of retirees after retirement, especially focusing on self-employment and unpaid work. Data was taken and analyzed from the "Taiwan Health and Retirement Study," a nationally representative sample of retired personnel aged 50-74 in 2015-2016. Four types of work status were classified after retirement: Fully retired, Paid work, Self-employment, and Unpaid work. Multinomial regression analysis was used to explore the factors related to participation in paid, self-employed, and unpaid work. Results show that pre-retirement occupation was significantly associated with paid work after retirement. For example, retirees in Taiwan who were employed by private enterprises or self-employed before retirement were more likely to engage in paid work after retirement than civil servants before retirement. Two other factors, namely pre-retirement job stress and work flexibility, prolong the careers of retired workers, especially in self-employment and unpaid work after retirement. Gender also significantly affects the choice of work after retirement. These findings can be used as a reference for future policies on the aging labor force.

Enhanced photocatalytic benzyl alcohol oxidation over Bi4Ti3O12 ultrathin nanosheets.

Ultrathin Bi4Ti3O12 nanosheets (NS) with the thickness about 3.9 nm were successfully synthesized by a hydrothermal method and were used as a photocatalyst for the oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). The photocatalytic performance of NS is about 8 times higher than that of bulk Bi4Ti3O12. In-situ FTIR of pyridine adsorption and NH3-TPD reveal that NS has more surface Lewis acid sites (Ti4+) for the adsorption and activation of BA. The photogenerated electrons (e-) and holes (h+) of NS can be fully used to produce the superoxide radicals and carbon-centered radicals, respectively. The monolayer nanosheet structure of NS not only greatly promotes the separation of photogenerated carriers, but also achieves the efficient activation of BA molecules via the CO⋯Ti coordination. This work successfully reveals the surface/interface interactions between the surface active sites of a photocatalyst and the reactive molecules via using ultrathin nanosheet as a molecular platform.

Unsaturated NiII Centers Mediated the Coordination Activation of Benzylamine for Enhancing Photocatalytic Activity over Ultrathin Ni MOF-74 Nanosheets.

Creating accessible unsaturated active sites in metal-organic frameworks (MOFs) holds great promise for developing highly efficient catalysts. Herein, ultrathin Ni MOF-74 nanosheets (NMNs) with high-density coordinatively unsaturated NiII centers are prepared as a photocatalyst. The results of in situ ATR-IR, Raman, UV-vis DRS, and XPS suggest that abundant NiII centers can act as the active sites for boosting benzylamine (BA) activation via forming -Ni-NH2- coordination intermediates. The generation of coordination intermediates assists the transfer of photo-generated holes to BA molecules for producing BA cation free radicals, better impelling the breaking of N-H bonds and the photooxidation of BA molecules. The photo-generated electrons further activate O2 molecules to O2•- radicals for triggering the reaction. The experiments reveal that the coordination activation of BA molecules may be a rate-determining step on NMNs rather than the adsorption and activation of O2 molecules. Moreover, NMNs possess a better ability for the separation of photo-generated carriers in comparison with bulk Ni MOF-74 (NMBs). As a result, NMNs achieve a kinetic rate constant of 0.538 h-1 for the photocatalytic oxidative coupling of BA under visible light, about 50 times higher than that of NMBs (0.0011 h-1). Finally, a probable synergetic catalytic mechanism with coordination activation and photocatalysis is discussed on a molecular level. This study not only highlights the importance of coordination activation for heterogeneous photocatalysis but also affords an inspiration for building ultrathin MOF nanosheets.