Two-Dimensional C/TiO₂ Heterogeneous Hybrid for Noble-Metal-Free Hydrogen Evolution

Developing catalysts to improve excitonic charge-carrier transfer and separation properties is critical for solar energy conversion through photochemical catalysis. Layer staking of two-dimensional (2-D) materials has opened up opportunities to engineer heteromaterials for strong interlayer excitonic transition. However, scalable fabrication of heteromaterials with seamless and clean interfaces remains challenging. Here, we report an in situ growth strategy for synthesizing a 2-D C/TiO₂ heterogeneous hybrid. Layered structure of TiO₂ and chemically bonded Ti–C between graphitic carbon and TiO₂ generate synergetic effects, promoting interfacial charge transfer and separation, leading to more electrons participating in photoreduction for hydrogen evolution. The Ti–C bond as reactive sites, such as platinum behavior, makes it an interesting potential substitue for noble metals in hydrogen evolution. In the absence of noble metals, the C/TiO₂ hybrid exhibits a significant enhancement of hydrogen evolution from water splitting using solar light, ∼3.046 mmol h^–1 g^–1. The facile and scalable fabrication of 2-D heterogeneous hybrid with enhanced interfacial charge transfer and separation provides perspectives for the creation of 2-D heteromaterials in optoelectronics and solar-light-harvesting applications

Visible–Near-Infrared-Light-Driven Oxygen Evolution Reaction with Noble-Metal-Free WO₂–WO₃ Hybrid Nanorods

Understanding and manipulating the one half-reaction of photoinduced hole-oxidation to oxygen are of fundamental importance to design and develop an efficient water-splitting process. To date, extensive studies on oxygen evolution from water splitting have focused on visible-light harvesting. However, capturing low-energy photons for oxygen evolution, such as near-infrared (NIR) light, is challenging and not well-understood. This report presents new insights into photocatalytic water oxidation using visible and NIR light. WO₂–WO₃ hybrid nanorods were in situ fabricated using a wet-chemistry route. The presence of metallic WO₂ strengthens light absorption and promotes the charge-carrier separation of WO₃. The efficiency of the oxygen evolution reaction over noble-metal-free WO₂–WO₃ hybrids was found to be significantly promoted. More importantly, NIR light (≥700 nm) can be effectively trapped to cause the photocatalytic water oxidation reaction. The oxygen evolution rates are even up to around 220 (λ = 700 nm) and 200 (λ = 800 nm) mmol g^–1 h^–1. These results demonstrate that the WO₂–WO₃ material is highly active for water oxidation with low-energy photons and opens new opportunities for multichannel solar energy conversion

Fabrication and Properties of a Free-Standing Two-Dimensional Titania

The synthesis of free-standing two-dimensional titania (2-D TiO₂) with a reduced band gap presents complex challenges to synthetic chemists. Here, we report a free-standing 2-D TiO₂ sheet synthesized via a one-step solvothermal methodology, with a measured optical onset at ∼1.84 eV. Using first-principles calculations in combination with experiment, we propose that the as-formed 2-D TiO₂ sheets are layers of the lepidocrocite TiO₂ structure, but with large nonuniform strains consistent with its crumpled morphology. These strains cause a significant change in the quasiparticle band structure and optical absorption spectra, resulting in large absorption in the visible-light region. This narrow band gap 2-D TiO₂ can catalyze the formation of singlet oxygen and the degradation of dye pollutants with low-energy photons of solar light. Our work demonstrates that lattice strains intrinsic to 2-D materials, especially its crumpled, free-standing forms, can result in new and useful properties