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.

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.

To develop efficient visible-light photocatalysis on α-Fe₂O₃, it is highly desirable to promote visible-light-excited high-energy-level electron transfer to a proper energy platform thermodynamically. Herein, based on the transient-state surface photovoltage responses and the atmosphere-controlled steady-state surface photovoltage spectra, it is demonstrated that the lifetime and separation of photogenerated charges of nanosized α-Fe₂O₃ are increased after coupling a proper amount of nanocrystalline SnO₂. This naturally leads to greatly improved photocatalytic activities for CO₂ reduction and acetaldehyde degradation. It is suggested that the enhanced charge separation results from the electron transfer from α-Fe₂O₃ to SnO₂, which acts as a proper energy platform. Based on the photocurrent action spectra, it is confirmed that the coupled SnO₂ exhibits longer visible-light threshold wavelength (~590 nm) compared with the coupled TiO₂ (~550 nm), indicating that the energy platform introduced by SnO₂ would accept more photogenerated electrons from α-Fe₂O₃. Moreover, electrochemical reduction experiments proved that the coupled SnO₂ possesses better catalytic ability for reducing CO₂ and O₂. These are well responsible for the much efficient photocatalysis on SnO₂-coupled α-Fe₂O₃.

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.