Fabrication of three-dimensional hierarchical porous 2D/0D/2D g-C3N4 modified MXene-derived TiO2@C: Synergy effect of photocatalysis and H2O2 oxidation in NO removal

One-step in-situ construction engineering of ZnO-Zn2SnO4 heterojunction for deeply photocatalytic oxidation of nitric oxide

The generation of hazardous intermediates during the process of photocatalytic nitric oxide (NO) oxidation presents a tough issue. Herein, a one-step microwave strategy was employed to introduce oxygen vacancies (OVs) into zinc oxide-zinc stannate (ZnO-Zn2SnO4) heterojunction, resulting in an improvement in the photocatalytic efficiency for NO removal. The construction ZnO-Zn2SnO4 heterojunction with the OVs (ZSO-3) owns a significant contribution towards highly efficient electron transfer efficiency (99.7%), which renders ZSO-3 to exert a deep oxidation of NO-to-nitrate (NO3-) rather than NO-to-nitrite (NO2-) or NO-to-nitrogen dioxide (NO2). Based on the solid supports of experimental and simulated calculations, it can be found that OVs play an irreplaceable role in activating small molecules such as NO and O2. Moreover, the enhanced adsorption capacity of small molecules, which guarantees the high yield of active radical due to the formation of S-scheme heterojunction. This work illuminates a novel viewpoint on one-step in-situ route to prepare Zn2SnO4-based heterojunction photocatalyst with deep oxidation ability of NO-to-NO3-.

S-scheme Cu3P/TiO2 heterojunction for outstanding photocatalytic water splitting

TiO2 photocatalysts are of great interest in the fields of environmental purification, new energy and so on, because of their non-toxicity, high stability, high redox ability and low cost. However, the photogenerated carriers are severely recombined, which limits the application of TiO2 photocatalysts. Herein, S-scheme Cu3P/TiO2 heterojunction composites were successfully synthesized by a simple and efficient microwave hydrothermal method, and the results show that the hydrogen production rate of Cu3P/TiO2 is 5.83 mmol∙g-1∙h-1 under simulated sunlight irradiation, which is 7.3 and 83.3 times higher than that of pure TiO2 and Cu3P, respectively. This excellent performance is derived from the internal electric field (IEF) and energy band bending generated by the S-scheme heterojunction formed between Cu3P and TiO2. The density functional theory (DFT) calculation indicates that the Cu3P possess smaller work function and more negative conduction band (CB) position than that of TiO2, which is very conducive to greatly improve the H+ reduction ability and hydrogen production performance. This work provides a new idea for the reveal of electron transfer paths and active sites in S-scheme heterojunctions and deepens the mechanism understanding.

Methanol steam reforming for hydrogen production over NiTiO3 nanocatalyst with hierarchical porous structure

Steam reforming for hydrogen production is one of the important research directions for clean energy. NiTiO3 catalysts with a hierarchical porous structure are prepared and applied to methanol steam reforming for hydrogen production. The results show that the optimum catalyst (10% Ni-Ti-Ox) not only has a hierarchical porous structure, but it also involves the coexistence of NiTiO3, anatase TiO2 and rutile TiO2. The formation of NiTiO3 is beneficial to the adsorption and activation of methanol molecules on the surface of the Ni-Ti-Ox catalyst, and the main intermediate species of the methanol molecular reaction are hydroxyl groups, methoxy species and formic acid species. Furthermore, the methanol steam reforming reaction is mainly dominated by methanol decomposition at low temperature (350-500 °C), while it is mainly dominated by methanol and water molecular reactions at high temperature (500-600 °C).

Architecture and Kinetic Studies of Photocatalytic H2O2 Generation and H2 Evolution through Regulation of Spatial Charge Transfer via Z-Scheme Path over a (001) Facet Engineered TiO2@MXene/B-g-C3N4 Ternary Hybrid

Spatial charge separation and migration are the critical shortcomings dominating the core energy conversion corridors of photocatalytic systems. Here, a biomimetic multi-interfacial architecture providing strong coupled interaction and rapid charge transmission for photostable and competent photocatalytic H2O2 production and H2 evolution is proposed. The triple-hybrid all-solid-state Z-scheme system was formed with the (001) facet exposed TiO2 nanosheets derived from MXene layers and B-g-C3N4 nanosheets (M/(001)TiO2@BCN) through an electrostatic self-assembly strategy with intimate electronic interaction due to Ti orbital modulation and proper stacking among the hybrids. The metallic and highly conductive MXene layers act as solid state electron mediators in the Z-scheme heterojunction that promote electron-hole separation and migration efficiency. Specifically, the MTBCN-12.5 composite provides optimum yield of H2O2 up to 1480.1 μmol h-1 g-1 and a H2 evolution rate of 408.4 μmol h-1 (with ACE 6.7%), which are 4 and 20 fold greater than the pristine BCN, respectively. The enhanced photocatalytic performance is systematically identified by the increased surface area, higher cathodic and anodic current densities of -1.01 and 2.27 mA cm-2, delayed charge recombination as supported by PL and EIS measurement, and excellent photostability. The Z-scheme charge transfer mechanism is validated by time-resolved photoluminescence (TRPL) analysis, cyclic voltametric analysis, and the radical trapping experiment as detected by PL analysis. This research marks a substantial advancement and establishes the foundation for future design ideas in accelerating charge transfer.

Heterostructured Nanoscale Photocatalysts via Colloidal Chemistry for Pollutant Degradation

With the further acceleration in the industrialization process, organic pollutants and gas pollution in the environment have posed severe threats to human health. It has been a global challenge regarding achieving an efficient solution to pollutant degradation. In such a context, photocatalysts have attracted researchers’ attention for their simplicity, efficiency, cleanliness and low cost. However, the single photocatalyst is facing a research bottleneck owing to its narrow light absorption spectrum and high photocarrier recombination rate. Given that heterojunctions can achieve efficient separation of photogenerated carriers in space, constructing heterostructured photocatalysts has become the most perspective method to improve the performance of photocatalysts. Furthermore, nanoparticles prepared through colloidal chemistry have the characteristics of high dispersion, stability and adsorption, further enhancing the degradation efficiency of heterostructured photocatalysts. This article reviews the primary methods for preparing heterostructured photocatalysts through colloidal chemistry, classifies the heterojunction types by transport routes of photogenerated carriers and summarizes the recent progress of heterostructured photocatalysts in pollutant degradation. To implement environmental remediation, it is crucial to explore economical and efficient photocatalysts for practical applications. It is hoped that this review will stimulate further exploration of colloidal heterostructured photocatalysts for pollutant degradation.