Study of Intermolecular Reconfiguration of Flexible COF-5 Film and Its Ultra-high Chemiresistive Humidity Sensitivity.

Recently, abundant active materials are developed to achieve the wearable detection of human body humidity. However, the limited response signal and sensitivity restrict further application due to their moderate affinity to water. Herein, we propose a flexible COF-5 film synthesized by a brief vapor-assisted method at room temperature. Intermediates are calculated by DFT simulation to investigate the interaction between COF-5 and water. The adsorption and desorption of water molecule result in a reversible deformation of COF layers while creating new conductive path by π-π stacking. The as-prepared COF-5 films are applied to the flexible humidity sensors, exhibiting a resistance change in 4 orders of magnitude with remarkable linear relation between log function of resistance and relative humidity (RH) in 11 %-98 % RH range. Applications including respiratory monitoring and non-contact switch are tested, providing a promising prospect for the detection of human body humidity.

Anions Regulation of 1D Perovskite Intrusion-Behavior for Efficient and Stable Perovskite Solar Cells.

Constructing a 1D/3D perovskite heterojunction has recently emerged as a prevalent approach for elevating the efficiency and stability of perovskite solar cells (PSCs), due to the excellent defect-passivation capacity and enhanced resistance to water and oxygen of 1D perovskite. However, the 1D perovskite commonly exhibits much poorer charge carrier transport ability when compared with its 3D counterpart. Tailoring the intrusion depth of a 1D perovskite into the 1D/3D heterojunction is thus of key importance for PSCs but remains a great challenge. We introduce herein a novel anion-regulation strategy that can effectively tune the intrusion behavior of 1D perovskite into 3D perovskite to form a 1D/3D heterojunction with gradual structure and gradient energy-level alignment. This gradual 1D/3D-perovskite interface leads to outstanding defect passivation performance, together with a desired balance between charge transport and moisture/oxygen blocking. Consequently, the PSCs with a 1D/3D perovskite heterojunction resulting from tetra-n-butylammonium acetate (TBAAc) treatment yield a remarkable enhancement in power conversion efficiency (PCE) from 18.4 to 20.1%. The unencapsulated device also demonstrates excellent stability and retains 90% of its initial PCE after 2400 h of storage in the air atmosphere with 30 ± 5% humidity at 25 ± 5 °C.

Photocatalytic CO2 reduction using La-Ni bimetallic sites within a covalent organic framework.

The precise construction of photocatalysts with diatomic sites that simultaneously foster light absorption and catalytic activity is a formidable challenge, as both processes follow distinct pathways. Herein, an electrostatically driven self-assembly approach is used, where phenanthroline is used to synthesize bifunctional LaNi sites within covalent organic framework. The La and Ni site acts as optically and catalytically active center for photocarriers generation and highly selective CO2-to-CO reduction, respectively. Theory calculations and in-situ characterization reveal the directional charge transfer between La-Ni double-atomic sites, leading to decreased reaction energy barriers of *COOH intermediate and enhanced CO2-to-CO conversion. As a result, without any additional photosensitizers, a 15.2 times enhancement of the CO2 reduction rate (605.8 µmol·g-1·h-1) over that of a benchmark covalent organic framework colloid (39.9 µmol·g-1·h-1) and improved CO selectivity (98.2%) are achieved. This work presents a potential strategy for integrating optically and catalytically active centers to enhance photocatalytic CO2 reduction.

Enhanced photocatalytic properties of TiO2 nanosheets@2D layered black phosphorus composite with high stability under hydro-oxygen environment.

Black phosphorus (BP) has gained great attention as a potential candidate in the photocatalytic field due to its tunable bandgap and high-mobility features, however, poor stability behavior and the high charge recombination of BP limit its practical application. In the present work, a liquid phase exfoliation method is employed to prepare layered BP. The as-prepared layered BP is decorated on TiO2 nanosheets to form a TiO2 nanosheets@BP composite, which stabilizes BP existence under a hydro-oxygen environment. Whereafter, the photocatalytic properties of the TiO2 nanosheets@BP composite towards the degradation of Rhodamine B (RhB) are proven to be greatly enhanced compared to those of pure layered BP and TiO2 nanosheets, and the photodegradation rate reached 98% after 120 minutes irradiation under UV-Vis light. It is worth mentioning that the photocatalytic cycling performance of the TiO2 nanosheets@BP composite remained at 92.5% under the irradiation of UV-Vis light after three cycles. The main reason for this lies in the fact that the formation of the TiO2 nanosheets@BP composite may favor light absorption and effectively reduce the recombination of electron-hole pairs.