Stable Ti 3+ Defects in Oriented Mesoporous Titania Frameworks for Efficient Photocatalysis

Microwave Synthesis of Pt Clusters on Black TiO2 with Abundant Oxygen Vacancies for Efficient Acidic Electrocatalytic Hydrogen Evolution

Oxygen vacancies-enriched black TiO₂ is one promising support for enhancing hydrogen evolution reaction (HER). Herein, oxygen vacancies enriched black TiO₂ supported sub-nanometer Pt clusters (Pt/TiO₂ -O_V ) with metal support interactions is designed through solvent-free microwave and following low-temperature electroless approach for the first time. High-temperature and strong reductants are not required and then can avoid the aggregation of decorated Pt species. Experimental and theoretical calculation verify that the created oxygen vacancies and Pt clusters exhibit synergistic effects for optimizing the reaction kinetics. Based on it, Pt/TiO₂ -O_V presents remarkable electrocatalytic performance with 18 mV to achieve 10 mA cm^-2 coupled with small Tafel slope of 12 mV dec^-1 . This work provides quick synthetic strategy for preparing black titanium dioxide based nanomaterials.

Charge Separation by Creating Band Bending in Metal-Organic Frameworks for Improved Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) have been intensively studied as a class of semiconductor-like materials in photocatalysis. However, band bending, which plays a crucial role in semiconductor photocatalysis, has not yet been demonstrated in MOF photocatalysts. Herein, a representative MOF, MIL-125-NH₂ , is integrated with the metal oxides (MoO₃ and V₂ O₅ ) that feature appropriate work functions and energy levels to afford the corresponding MOF composites. Surface photovoltage results demonstrate band bending in the MOF composites, which gives rise to the built-in electric field of MIL-125-NH₂ , boosting the charge separation. As a result, the MOF composites present 56 and 42 times higher activities, respectively, compared to the pristine MOF for photocatalytic H₂ production. Upon depositing Pt onto the MOF, ∼6 times higher activity is achieved. This work illustrates band bending of MOFs for the first time, supporting their semiconductor-like nature, which would greatly promote MOF photocatalysis.

3D/2D Heterojunction of CeO2/Ultrathin MXene Nanosheets for Photocatalytic Hydrogen Production

Two-dimensional (2D) nanomaterials benefit from the high specific surface area, unique surface properties, and quantum size effects, which have attracted widespread scientific attention. MXenes add many members to the 2D material family, mainly metal conductors, most of which are dielectrics, semiconductors, or semimetals. With excellent electron mobility, beneficial to electron-hole separation, and large functional groups that can be tightly coupled with other materials, MXenes have broad application prospects in photocatalysis. Meanwhile, the application of CeO₂-based materials in organic catalysis, photocatalytic water splitting, and photodegradation of organic pollutants has been extensively explored, and studies have found that CeO₂-based materials show good photocatalytic performance. In view of this, we synthesized regular octahedral CeO₂ with a homojunction in one step by a hydrothermal method and compounded it with ultrathin 2D material MXene, which exhibited fast carrier migration efficiency and a good interfacial effect, making the material show excellent photocatalytic activity. The results showed that the photocatalytic H₂ evolution performance of the MXene/CeO₂ heterojunction was significantly improved. In this study, a low-cost catalyst with high photocatalytic activity was prepared, presenting a new research idea for achieving a combined 3D/2D photocatalytic system.

Versatile Synthesis of Mesoporous Crystalline TiO2 Materials by Monomicelle Assembly

Mesoscale TiO₂ structures have realized many technological applications-ranging from catalysis and biomedicine to energy storage and conversion-because of their large mesoporosities offering desirable accessibility and mass transport. Tailoring mesoporous TiO₂ structures with novel mesoscopic and microscopic configurations is envisaged to offer ample opportunities for further applications. In this Review, we explain how to synthesize novel mesoporous TiO₂ materials and present recent examples. An emphasis is placed on a "monomicelle assembly" strategy as an emerging and powerful approach to direct the formation of mesostructured TiO₂ with precise control over its structural orientations and architectures. Furthermore, typical examples of mesoporous TiO₂ for applications in batteries and photocatalysis are highlighted. The Review ends with an outlook towards the synthesis of mesoporous TiO₂ with tailored architectures by self-assembly, which could pave the way for developing advanced energy conversion and storage devices.

Boosted Inner Surface Charge Transfer in Perovskite Nanodots@Mesoporous Titania Frameworks for Efficient and Selective Photocatalytic CO2 Reduction to Methane

Exploring high-efficiency and stable halide perovskite-based photocatalysts for the selective reduction of CO₂ to methane is a challenge because of the intrinsic photo- and chemical instability of halide perovskites. In this study, halide perovskites (Cs₃ Bi₂ Br₉ and Cs₂ AgBiBr₆ ) were grown in situ in mesoporous TiO₂ frameworks for an efficient CO₂ reduction. Benchmarked CH₄ production rates of 32.9 and 24.2 μmol g^-1  h^-1 with selectivities of 88.7 % and 84.2 %, were achieved, respectively, which are better than most reported halide perovskite photocatalysts. Focused ion-beam sliced-imaging techniques were used to directly image the hyperdispersed perovskite nanodots confined in mesopores with tunable sizes ranging from 3.8 to 9.9 nm. In situ X-ray photoelectronic spectroscopy and Kelvin probe force microscopy showed that the built-in electric field between the perovskite nanodots and mesoporous titania channels efficiently promoted photo-induced charge transfer. Density functional theory calculations indicate that the high methane selectivity was attributed to the Bi-adsorption-mediated hydrogenation of *CO to *HCO that dominates CO desorption.

General Microwave Route to Single-Crystal Porous Transition Metal Nitrides for Highly Sensitive and Stable Raman Scattering Substrates

The synthesis of metallic transition metal nitrides (TMNs) has traditionally been performed under harsh conditions, which makes it difficult to prepare TMNs with high surface area and porosity due to the grain sintering. Herein, we report a general and rapid (30 s) microwave synthesis method for preparing TMNs with high specific surface area (122.6-141.7 m² g^-1) and porosity (0.29-0.34 cm³ g^-1). Novel single-crystal porous WN, Mo₂N, and V₂N are first prepared by this method, which exhibits strong surface plasmon resonance, photothermal conversion, and surface-enhanced Raman scattering effects. Different from the conventional low-temperature microwave absorbing media such as water and polymers, as new concept absorbing media, hydrated metal oxides and metallic metal oxides are found to have a remarkable high-temperature microwave heating effect and play key roles in the formation of TMNs. The current research results provide a new-concept microwave method for preparing high lattice energy compounds with high specific surface.