Fabrication of Heterogeneous-Phase Solid-Solution Promoting Band Structure and Charge Separation for Enhancing Photocatalytic CO₂ Reduction: A Case of Zn<i>_X</i>Ca_1–<i>X</i>In₂S₄

Photocatalytic CO₂ reduction into solar fuels illustrates huge charm for simultaneously settling energy and environmental issues. The photoreduction ability of a semiconductor is closely correlated to its conduction band (CB) position. A homogeneous-phase solid-solution with the same crystal system always has a monotonously changed CB position, and the high CB level has to be sacrificed to achieve a benign photoabsorption. Herein, we report the fabrication of heterogeneous-phase solid-solution Zn<i>_X</i>Ca_1–<i>X</i>In₂S₄ between trigonal ZnIn₂S₄ and cubic CaIn₂S₄. The Zn<i>_X</i>Ca_1–<i>X</i>In₂S₄ solid solutions with orderly tuned photoresponsive range from 540 to 640 nm present a more negative CB level and highly enhanced charge-separation efficiency. Profiting from these merits, all of these Zn<i>_X</i>Ca_1–<i>X</i>In₂S₄ solid solutions exhibit remarkably strengthened photocatalytic CO₂ reduction performance under visible light (λ > 420 nm) irradiation. Zn_0.4Ca_0.6In₂S₄, bearing the most negative CB position and highest charge-separation efficiency, casts the optimal photocatalytic CH₄ and CO evolution rates, which reach 16.7 and 6.8 times higher than that of ZnIn₂S₄ and 7.2 and 3.9 times higher than that of CaIn₂S₄, respectively. To verify the crucial role of the heterogeneous-phase solid solution in promoting the band structure and photocatalytic performance, another heterogeneous-phase solid-solution Zn<i>_X</i>Cd_1–<i>X</i>In₂S₄ has been synthesized. It also displays an upshifted CB level and promoted charge separation. This work may provide a new perspective into the development of an efficient visible-light driven photocatalyst for CO₂ reduction and other photoreduction reactions

Facile <i>In Situ</i> Self-Sacrifice Approach to Ternary Hierarchical Architecture Ag/AgX (X = Cl, Br, I)/AgIO₃ Distinctively Promoting Visible-Light Photocatalysis with Composition-Dependent Mechanism

Three series of ternary hierarchical architecture photocatalysts Ag/AgX (X = Cl, Br, I)/AgIO₃ were fabricated for the first time by a facile <i>in situ</i> ion-exchange route. The novel ternary architectures are confirmed by XRD, XPS, SEM, TEM, EDX, and EDX mapping. In contrast to pristine AgIO₃, the Ag/AgX (X = Cl, Br, I)/AgIO₃ composites show extended absorption edges and highly boosted photoabsorption in the visible region, which are separately ascribed to the intrinsic absorption of AgX and the surface plasmon resonance (SPR) effect of Ag species. The photocatalysis activity of Ag/AgX (X = Cl, Br, I)/AgIO₃ composites is studied and compared <i>via</i> photodegradation of methyl orange (MO) under visible-light (λ > 420 nm) irradiation. It is interesting to find that the activity enhancement levels are different for Ag/AgX (X = Cl, Br, I)/AgIO₃ with four types of photocatalytic mechanism, which are closely related to the type of AgX or the component content in Ag/AgX (X = Cl, Br, I)/AgIO₃. The separation behaviors of charge carrier were also systematically investigated by the PL and EIS. The study may furnish new perspective into controllable fabrication of hierarchical architecture photocatalysts with multiform photocatalytic mechanism

In Situ Co-Crystallization for Fabrication of g‑C₃N₄/Bi₅O₇I Heterojunction for Enhanced Visible-Light Photocatalysis

We developed for the first time an in situ co-crystallization route for fabrication of a heterojunctional photocatalyst g-C₃N₄/Bi₅O₇I by adopting melamine and BiOI as coprecursors. This synthetic method enables intimate interfacial interaction with chemical bonding between g-C₃N₄ and Bi₅O₇I, which is beneficial for charge transfer at the interface. The photocatalysis properties of g-C₃N₄/Bi₅O₇I composites were studied by photodegradation of Rhodamine B (RhB) and phenol and generation of transient photocurrent with illumination of visible-light (λ > 420 nm), The results revealed that the g-C₃N₄/Bi₅O₇I composite shows enhanced photocatalytic reactivity compared to the pristine g-C₃N₄ and Bi₅O₇I samples. Investigations on the behaviors of charge carriers via electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra suggests that the g-C₃N₄/Bi₅O₇I heterojunctional structure constructed of the in situ co-thermolysis approach is responsible for the efficient separation and transfer of photogenerated electrons (e^–) and holes (h⁺), thus giving rise to the higher photocatalytic activity. The present work opens a new avenue for manipulation of high-performance semiconductor heterojunction for photocatalytic and photoelectrochemical application

Highly Efficient Bi₂O₂CO₃ Single-Crystal Lamellas with Dominantly Exposed {001} Facets

Herein we report the Bi₂O₂CO₃ single-crystal nanoplates with dominant {001} exposing facets fabricated via a controllable hydrothermal means. Exposed {001} reactive facets enable BOC-001 nanoplates efficient separation and migration of photoinduced electron–hole pairs, thereby resulting in highly enhanced photoreactivity pertaining to rhodamine B degradation, NO removal, and photocurrent generation. The present work provides a new reference for manipulation of facet-dependent photocatalytic activity of semiconductors

Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-Functional Applications of High-Performance CO₃^2–-Doped Bi₂O₂CO₃

We herein demonstrate self-doping of the CO₃^2– anionic group into a wide bandgap semiconductor Bi₂O₂CO₃ realized by a one-pot hydrothermal technique. The photoresponsive range of the self-doped Bi₂O₂CO₃ can be extended from UV to visible light and the band gap can be continuously tuned. Density functional theory (DFT) calculation results demonstrate that the foreign CO₃^2– ions are doped in the caves constructed by the four adjacent CO₃^2– ions and the CO₃^2– self-doping can effectively narrow the band gap of Bi₂O₂CO₃ by lowering the conduction band position and meanwhile generating impurity level. The photocatalytic performance is evaluated by monitoring NO removal from the gas phase, photodegradation of a colorless contaminant (bisphenol A, BPA) in an aqueous solution, and photocurrent generation. In comparison with the pristine Bi₂O₂CO₃ which is not sensitive to visible light, the self-doped Bi₂O₂CO₃ exhibits drastically enhanced visible-light photoreactivity, which is also superior to that of many other well-known photocatalysts such as P25, C₃N₄, and BiOBr. The highly enhanced photocatalytic performance is attributed to combination of both efficient visible light absorption and separation of photogenerated electron–hole pairs. The self-doped Bi₂O₂CO₃ also shows decent photochemical stability, which is of especial importance for its practical applications. This work demonstrates that self-doping with an anionic group enables the band gap engineering and the design of high-performance photocatalysts sensitive to visible light

Cu₂O Film via Hydrothermal Redox Approach: Morphology and Photocatalytic Performance

A hydrothermal approach is developed to fabricate Cu₂O film via <i>in situ</i> redox reaction between Cu²⁺ and Cu plate. The crystallization process under different conditions was demonstrated, and the crystal structure of Cu₂O was verified by XRD, Raman and XPS characterizations. Simply tuning the anionic groups of Cu²⁺ can generate different morphologies including rod-like arrays, cross-linked and truncated octahedrals. Mott–Schottky plots and PL spectra indicate that the rod-like arrays possess more copper vacancies than the other two morphologies. In photodegradation, the rod arrays exhibit much better performance, following by truncated and then cross-linked octahedrals. The photostability of the three morphologies was also determined. Although different surface reconstructions occur for the films owing to different charge transfer and consumption pathway, their photoactivities are all enhanced after the first run. Then rod arrays and cross-linked octahedrals show very stable activity, but truncated octahedrals show a gradually decreased activity. This work may be helpful for rationally modulating Cu₂O-based materials and understanding their deactive mechanism in photocatalysis

Amplifying Emission Enhancement and Proton Response in a Two-Component Gel

A glutamide gelator, <b>1</b>, was synthesized, and a weak emission enhancement was observed during its gelation. In addition, <b>1</b> could be an excellent scaffold for successfully embedding an energy acceptor, <b>2</b>, into its aggregate to obtain highly efficient energy transfer. An amplification of the emission enhancement was observed in the two-component gels compared to that of the neat gel of <b>1</b> during gel formation. For example, <b>1</b> induced only a 2.5-fold increase in emission intensity, whereas a 23-fold enhanced emission could be observed in the two-component gel with only 1.6 mol % <b>2</b>. Furthermore, two-component gels had an excited proton response. In systems with low acceptor concentrations, the hot solution red-shifted the fluorescence from blue to yellow upon the addition of a proton, which continuously blue-shifted with decreasing temperature to form the gel given that the binding of the gelator to the proton is weakened during coassembly. Moreover, the casting film formed by the two-component wet gel had an excellent response to volatile acids such as hydrochloric acid, trifluoroacetic acid, and so on and could be reversibly recovered by exposure to NH₃

Fabrication of Versatile Cyclodextrin-Functionalized Upconversion Luminescence Nanoplatform for Biomedical Imaging

Lanthanide-based upconversion nanoparticles (UCNPs) are a new type of luminescent tags that show great application potential in biomedical fields. However, a major challenge when applying UCNPs in biomedical research is the lack of a versatile strategy to make water-dispersible and biocompatible UCNPs with high simplicity in functionalization. To address this problem, in the present work, we employed 6-phosphate-6-deoxy-β-cyclodextrin (βPCD) as the novel ligand to fabricate a versatile upconversion luminescent nanoplatform. Using βPCD as the surface ligand not only enhances the stability and biocompatibility of the UCNPs under physiological conditions but also enables simple conjugation with various functional molecules, such as organic dyes and biomolecules, via the host–guest interaction between those molecules and the cyclodextrin cavity. The conjugated upconversion nanoprobe then displays excellent capability in labeling the cancer cells and tumor tissue slices for luminescent imaging. These results demonstrate that the versatile cyclodextrin-functionalized upconversion nanoplatform appears particularly flexible for further modifications, indicating great potential for applications in biosensing and bioimaging

Ultrafine NiO Nanosheets Stabilized by TiO₂ from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst

Faceted NiO nanoparticles preferentially exposing high surface energy planes demand attention due to their excellent electrocatalytic properties. However, the activity of faceted NiO nanoparticles generally remains suboptimal due to their large lateral size and thickness, which severely limits the availability of coordinatively unsaturated active reactive edge and corner sites. Here, ultrafine NiO nanosheets with a platelet size of ∼4.0 nm and thickness (∼1.1 nm) stabilized by TiO₂ were successfully prepared by calcination of a monolayer layered double hydroxide precursor. The ultrafine NiO nanosheets displayed outstanding performance in electrochemical water oxidation due to a high proportion of reactive NiO {110} facets, intrinsic Ni³⁺ and Ti³⁺ sites, and abundant interfaces, which act synergistically to promote H₂O adsorption and facilitate charge-transfer