Graphitic carbon nitride (g-C₃N₄) has become an attractive visible-light-responsive photocatalyst because of its semiconductor polymer compositions and easy-modulated band structure. However, the bulk g-C₃N₄ photocatalyst has the low separation efficiency of photogenerated carriers and unsatisfied surface catalytic performance, which leads to poor photocatalytic performance. As for this, MgTi₂O₅ with high chemical stability, wide band gap and negative conduction band was used as a suitable platform for coupling with g-C₃N₄ to enhance charge separation and promoted the photoactivity. Different from common approaches, here, we propose an innovative method to construct g-C₃N₄/MgTi₂O₅ nanocomposites featuring "0 + 1 > 1" magnification effect to improve g-C₃N₄ photocatalytic performance under visible light irradiation. Additionally, compositing metal oxides of MgTi₂O₅ with g-C₃N₄ has proven to be a proper strategy to accelerate surface catalytic reactions in g-C₃N₄, and the photoinduced carriers were modulated to maintain thermodynamic equilibrium, which convincingly promotes the photocatalytic activity. The photocatalytic performance of the nanocomposites was measured by hydrogen production and CO₂ reduction under visible light. The developed g-C₃N₄/MgTi₂O₅ nanocomposites with a 5 wt.% MgTi₂O₅ exhibits the highest H₂ and CO yield under visible light and excellent stability compare to the other MgTi₂O₅ contents in composites. According to surface photo-voltage spectra, electrochemical CO₂ reduction, photoluminescence, etc. The superior performance can be related to an enhanced electron lifetime, the promoted charge transfer and the increased electronic separation property of g-C₃N₄. Our work provides an approach to overcome the defect of pure g-C₃N₄, which accesses to composite with the second component matched well.

As a newly discovered member of the tungstate family, InWO₄ hollow nanospheres with a monoclinic wolframite structure were synthesized successfully. The crystal phase of InWO₄ was investigated via a combination of CASTEP geometric optimization and experimental simulation. InWO₄ has a space group of P2/c with two InWO₄ formula units per unit cell. The optimized cell dimensions are a = 5.16 Å, b = 5.97 Å, and c = 5.23 Å, with α = 90°, β = 92.11°, γ = 90°, giving a unit cell volume of 161.10 ų, which is consistent with the experimental measurements. More importantly, InWO₄ was a promising host material for different Ln³⁺ (Ln = Eu and Yb/Er) ions. For InWO₄: Yb³⁺/Er³⁺ excited at 980 nm, transitions from the ⁴G_11/2 (384 nm), ²H_9/2 (411 nm), and ⁴F_7/2 (487 nm) levels to the ground state (⁴I_15/2) of Er³⁺ were observed. In addition to the aforementioned properties, the InWO₄ hollow nanospheres can be used to improve the performance of dye-sensitized solar cells, which is chiefly attributed to theirlight scattering.

One-dimension carbon self-doping g-C₃N₄ nanotubes (CNT) with abundant communicating pores were synthesized via thermal polymerization of saturated or supersaturated urea inside the framework of a melamine sponge for the first time. A ~16% improvement in photoelectric conversion efficiency (η) is observed for the devices fabricated with a binary hybrid composite of the obtained CNT and TiO₂ compared to pure TiO₂ device. The result of EIS analysis reveals that the interfacial resistance of the TiO₂-dye|I₃^-/I^- electrolyte interface of TiO₂-CNT composite cell is much lower than that of pure TiO₂ cell. In addition, the TiO₂-CNT composite cell exhibits longer electron recombination time, shorter electron transport time, and higher charge collection efficiency than those of pure TiO₂ cell. Systematic investigations reveal that the CNT boosts the light harvesting ability of the photovoltaic devices by enhancing not only the visible light absorption but also the charge separation and transfer.

An effective photocatalytic hydrogen production catalyst comprising MgTiO₃/ MgTi₂O₅/TiO₂ heterogeneous belt-junctions was prepared using magnesium ions by a thermally driven doping method. The tri-phase heterogeneous junction was confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The as-prepared MgTiO₃/MgTi₂O₅/ TiO₂ heterojunctions exhibited a very high photocatalytic hydrogen production activity (356.1 mol∙g_0.1gcat∙h⁻¹) and an apparent quantum efficiency (50.69% at 365 nm) that is about twice of that of bare TiO₂ nanobelts (189.4 mol∙g_0.1gcat∙h⁻¹). Linear sweep voltage and transient photocurrent characterization as well as analysis of the electrochemical impedance spectra and Mott-Schottky plots revealed that the high photocatalytic performance is caused by the one-dimensional structure, which imparts excellent charge transportation characteristic, and the MgTiO₃/MgTi₂O₅/TiO₂ tri-phase heterojunction, which effectively drives the charge separation through the inherent electric field. This titanate-based tri-phase heterogeneous junction photocatalyst further enriches the catalyst system for photocatalytic hydrogen production.

Y(OH)₃: Eu³⁺ nanotubes were synthesized using a facile hydrothermal method, and then, Pt particles were grown on the surface of the nanotubes using a combination of vacuum extraction and annealing. The resulting Pt/Y₂O₃: Eu³⁺ composite nanotubes not only exhibited enhanced red luminescence under 255- or 468-nm excitation but could also be used to improve the efficiency of dye-sensitized solar cells, resulting in an efficiency of 8.33%, which represents a significant enhancement of 11.96% compared with a solar cell without the composite nanotubes. Electrochemical impedance spectroscopy results indicated that the interfacial resistance of the TiO₂-dye|I₃^-/I^- electrolyte interface of the TiO₂-Pt/Y₂O₃: Eu³⁺ composite cell was much smaller than that of a pure TiO₂ cell. In addition, the TiO₂-Pt/Y₂O₃: Eu³⁺ composite cell exhibited a shorter electron transport time and longer electron recombination time than the pure TiO₂ cell.

Synthesis of pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals has proven to be challenging. Here, pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals were prepared. Furthermore, a new magnesium titanate, Mg_1.2Ti_1.8O₅, was synthesized via a solution-based route for the first time. As hydrogen evolution photocatalysts, both pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals exhibit excellent hydrogen production efficiency. In comparison with pure MgTiO₃ nanocrystals, the asprepared Mg_1.2Ti_1.8O₅ nanocrystals exhibited four times as much photocatalytic hydrogen production activity, up to 40 μmol·h^–1. Photoelectrochemical analysis, including linear sweep voltammetry, transient photocurrent measurement, electrochemical impedance spectroscopy, and construction of Mott-Schottky plots, demonstrated that the enhanced photocatalytic activity was attributed to the large surface area, fast photoelectron transfer, higher carrier density, and efficient charge separation of the Mg_1.2Ti_1.8O₅ nanocrystals.