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Solar water splitting into H 2 and O 2 upon a particulate photocatalyst relies on significant advances in material engineering where a number of important properties such as optical absorption, charge transportation, defect level, etc. can be manipulated. In this work, we have gained control over these properties for the wide band gap semiconductor Sr 2 TiO 4 and successfully actualized water splitting under visible light illumination. This has been realized by codoping La/N into the laminated perovskite structure of Sr 2 TiO 4 . Strong visible light absorption as far as 650 nm can be tailored by varying the La/N content in Sr 2−x La x TiO 4−y N y (0 ≤ x ≤ 0.5). Optimal photocatalytic H 2 and O 2 production has been achieved at x = 0.2, 0.3 and outweighs that of a number of typical perovskite oxynitrides. These activities are a function of several important parameters for photogenerated charges (e.g., concentration, mobility, and lifetime) which are all linked to La/N codoping levels. More strikingly, overall water splitting has been achieved at x = 0.2 with Rh/Cr 2 O 3 as a cocatalyst. Defects such as Ti 3+ species play a negative role in the photocatalytic activity, as they strongly promote charge recombination and shorten the electron lifetime. Theoretical calculations reveal the crucial role of N in uplifting the valence band maximum of Sr 2 TiO 4 by hybridization with O 2p orbitals. La, therefore, balances the charge discrepancies induced during N/O replacements which would otherwise be unfeasible for substantial doping. Our calculations also suggest that Sr 2 TiO 4 has a 2D charge transportation character which is extremely useful for charge separations.

Separation of photo-generated charges has played a crucial role in controlling the actual performance of a photocatalytic system. Here we have successfully fabricated g-C3N4/TiO2-B nanowire/tube heterostructures through facile urea degradation reactions. Owing to the effective separation of photo-generated charges associated with the type-II band alignment and intimate interfacial contacts between g-C3N4 and TiO2-B nanowires/tubes, such heterostructures demonstrate an improved photocatalytic activity over individual moieties. Synthetic conditions such as hydrothermal temperatures for the preparation of TiO2-B and the weight ratio of TiO2-B to urea were systematically investigated. A high crystallinity of TiO2-B as well as the proper growth of g-C3N4 on its surface are critical factors for a better performance. Our simple synthetic method and the prolonged lifetime of photo-generated charges signify the importance of type-II heterostructures in the photocatalytic applications.

Ultrathin nitrogen-doped perovskite nanosheets LaTaON have been fabricated by exfoliating Dion-Jacobson-type layered perovskite RbLaTaON. These nanosheets demonstrate superior photocatalytic activities for water splitting into hydrogen and oxygen and remain active with photon wavelengths as far as 600 nm. Their apparent quantum efficiency under visible-light illumination (λ ≥ 420 nm) approaches 1.29% and 3.27% for photocatalytic hydrogen and oxygen production, being almost 4-fold and 8-fold higher than bulk RbLaTaON. Their outstanding performance likely stems from their tiny thickness (single perovskite slab) that essentially removes bulk charge diffusion steps and extends the lifetime of photogenerated charges. Theoretical calculations reveal a peculiar 2D charge transportation phenomenon in RbLaTaON; thus, exfoliating RbLaTaON into LaTaON nanosheets has limited impact on charge transportation properties but significantly enhances the surface areas which contributes to more reaction sites.

As the core component of this emerging field, the broadband NIR light source needs to be small and exquisite to meet the application requirements. Compared with traditional broadband NIR light sources such as the bulky tungsten-halogen lamps, broadband NIR phosphor-converted light-emitting diodes (NIR pc-LEDs) is proposed as an ideal compact light source due to their advantages of environmental protection, energy-saving, long lifetime, and small size. [2] The strategy of NIR pc-LEDs is mainly realized by coating broadband NIR phosphor on a blue LED chip. Among them, one of the important research topics is the exploration of broadband NIR phosphors that can be excited by blue light.Cr 3+ ion with d 3 electron configuration is the commonly used activator for NIR emitting phosphors. When it's located in a weak octahedral crystal field in a host, broadband NIR emission can be obtained due to the 4 T 2 → 4 A 2 transition. [3] The Cr 3+ -doped garnet phosphors are a typical broadband NIR luminescent material, showing high quantum efficiency and robust thermal stability. For example, Ca

Layered semiconductor photocatalysts have been found to exhibit promising performance levels, probably linked to their interlayer framework that facilitates separation of charge carriers and the reduction/oxidation reactions. Layered titanates, however, generally demonstrate activities under UV irradiation, and therein lies the strong desire to extend their activity into the visible light region. Here, we investigated a series of layered perovskite by doping Sr2TiO4 with Cr and/or La in the hope to improve their visible light responses. Their crystal structures and other physicochemical properties were systematically explored. Our results show that La and Cr can be successfully accommodated in the layered structure and Cr is an efficient dopant for the extension of visible light absorbance. Much enhanced photocatalytic hydrogen evolution was observed after doping and was found to be composition-dependent. The highest hydrogen production rate approaches 97.7 μmol/h for Sr2Ti0.95Cr0.05O4-δ under full range irradiation (λ ≥ 250 nm) and 17 μmol/h for Sr2Ti0.9Cr0.1O4-δ under visible light irradiation (λ ≥ 400 nm), corresponding to an apparent quantum efficiency of 0.16% and 0.05%, respectively. Theoretical calculation reveals that the improved optical and photocatalytic properties are owing to a newly formed spin-polarized valence band from Cr 3d orbitals. The decreased unit cell parameters, reduced band gaps as well as anisotropic properties of layered architectures are likely the reasons for a better activity. Nevertheless, instability of these compounds in the presence of moisture and CO2 was also noticed, suggesting that protective atmospheres are needed for the storage of these photocatalysts.

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