Atomic Level Interface Control of SnO2-TiO2 Nanohybrids for the Photocatalytic Activity Enhancement

Oxygen Vacancy Induced Atom-Level Interface in Z-Scheme SnO2/SnNb2O6 Heterojunctions for Robust Solar-Driven CO2 Conversion

The modulation of Z-scheme charge transfer is essential for efficient heterostructure toward photocatalytic CO₂ reduction. However, constructing a compact hetero-interface favoring the Z-scheme charge transfer remains a great challenge. In this work, an interfacial Nb-O-Sn bond and built-in electric field-modulated Z-scheme O_v-SnO₂/SnNb₂O₆ heterojunction was prepared for efficient photocatalytic CO₂ conversion. Systematic investigations reveal that an atomic-level interface is constructed in the O_v-SnO₂/SnNb₂O₆ heterojunction. Under simulated sunlight irradiation, the obtained O_v-SnO₂/SnNb₂O₆ photocatalyst exhibits a high CO evolution rate of 147.4 μmol h^-1 g^-1 from CO₂ reduction, which is around 3-fold and 3.3-fold of SnO₂/SnNb₂O₆ composite and pristine SnNb₂O₆, respectively, and favorable cyclability by retaining 95.8% rate retention after five consecutive tests. As determined by electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and density functional theory calculations, Nb-O-Sn bonds and built-in electric field induced by the addition of oxygen vacancies jointly accelerate the Z-scheme charge transfer for enhanced photocatalytic performance. This work provides a promising route for consciously modulating Z-scheme charge transfer by atomic-level interface engineering to boost photocatalytic performance.

Highly Active and Renewable Catalytic Electrodes for Two-Electron Oxygen Reduction Reaction

This study has shown that antimony-doped tin oxide (ATO) works as a robust "renewable catalyst" for the electrochemical synthesis of hydrogen peroxide (H₂O₂) from water and oxygen. Antimony doping into SnO₂ gives rise to remarkable electrocatalytic activity for two-electron oxygen reduction reaction (2e^--ORR) by water with a volcano-type relation between the activity and doping levels (x_Sb). Density functional theory simulations highlight the importance of an isolated Sb atom of ATO inducing the high activity and selectivity for 2e^--ORR due to the effects of O₂ adsorption enhancement, decrease in the activation energy, and lowering the adsorptivity of H₂O₂. Electrolysis by a normal three-electrode cell using ATO (x_Sb = 10.2 mol %) at -0.22 V (vs reversible hydrogen electrode) stably and continuously produces H₂O₂ with a turnover frequency of 6.6 s^-1. This remarkable activity can be maintained even after removing the surface layer of ATO by argon-ion sputtering.

Recent insights into SnO2-based engineered nanoparticles for sustainable H2 generation and remediation of pesticides

Due to the ongoing industrial revolution and global health pandemics, solar-driven water splitting and pesticide degradation are highly sought to cope with catastrophes such as depleting fossil reservoirs, global warming, and environmental degradation.

Photocatalytic Activity of Radial Rutile Titanium(IV) Oxide Microspheres for Aerobic Oxidation of Organics

Radial rutile TiO₂ nanorod homomesocrystals (TiO₂ -NR HOMCs) or the so-called "sea urchin-like TiO₂ microspheres" were synthesized by using a hydrothermal method. TiO₂ -NR HOMCs show photocatalytic activity for aerobic oxidative degradation of 2-naphthol under irradiation of UV- and visible light. Furthermore, extremely small iron oxide clusters were formed on the surface of TiO₂ -NR HOMCs (FeO_x /TiO₂ -NR HOMCs) by the chemisorption-calcination technique to reduce the band gap. The FeO_x -surface modification gives rise to drastic enhancement of the UV- and visible-light activity. Reversed double-beam photoacoustic spectroscopy measurements were performed for TiO₂ -NR HOMCs and FeO_x /TiO₂ -NR HOMCs to obtain the ERDT (energy-resolved distribution of electron traps)/CBB (conduction-band bottom) patterns. The ERDT/CBB pattern of TiO₂ -NR HOMCs consists of two components derived from rutile (C1) and amorphous TiO₂ (C2). In the pattern, the surface electron traps in C2 exist near the CBB to be removed by the FeO_x -surface modification. By taking this finding into consideration, the striking surface modification effect is ascribable to the electrocatalytic activity (or the action as an electron reservoir) of the FeO_x clusters for multiple ORR, the suppression of recombination, and the increase in the visible-light harvesting efficiency.

Switching of Electron Transport Direction from the Long Axis to Short Axis in a Radial SnO2(Head)-Rutile TiO2 Nanorod(Tail) Heteromesocrystal Photocatalyst

Heteroepitaxial growth of rutile TiO₂ nanorods from SnO₂ seeds yielded radial heteromesocrystals consisting of SnO₂(head) and rutile TiO₂ nanorod(tail) with the SnO₂(head) oriented toward the center (TiO₂-NR//SnO₂ HEMCs). Iron oxide clusters were formed on the surface by the chemisorption-calcination technique. The FeO_x-surface modification gives rise to drastic increases in the photocatalytic activity for aerobic oxidation of 2-naphthol under irradiation of UV and visible light. As a 2D-model for 3D-TiO₂-NR//SnO₂ HEMC, electrochemical measurements were performed for the rutile TiO₂-NR array formed on a fluorine-doped tin oxide (SnO₂:F) electrode. The results showed that the FeO_x clusters possess electrocatalytic activity for a multielectron oxygen reduction reaction, and the high photocurrent of the electrode is remarkably reduced by the FeO_x-surface modification. Consequently, the striking photocatalytic activity of FeO_x/TiO₂-NR//SnO₂ HEMCs was ascribable to the switching of the electron transport direction necessary for the charge separation from the long axis of the TiO₂ NR to the short axis.

Radial TiO2 Nanorod-Based Mesocrystals: Synthesis, Characterization, and Applications

Radial TiO2 nanorod-based mesocrystals (TiO2-NR MCs) or so-called “sea-urchin-like microspheres” possess not only attractive appearance but also excellent potential as photocatalyst and electrode materials. As a new type of TiO2-NR MCs, we have recently developed a radial heteromesocrystal photocatalyst consisting of SnO2(head) and rutile TiO2 nanorods(tail) (TiO2-NR//SnO2 HEMCs, symbol “//” denotes heteroepitaxial junction) with the SnO2 head oriented in the central direction in a series of the studies on the nanohybrid photocatalysts with atomically commensurate junctions. This review article reports the fundamentals of TiO2-NR MCs and the applications to photocatalysts and electrodes. Firstly, the synthesis and characterization of TiO2-NR//SnO2 HEMCs is described. Secondly, the photocatalytic activity of recent TiO2-NR MCs and the photocatalytic action mechanism are discussed. Thirdly, the applications of TiO2-NR MCs and the analogs to the electrodes of solar cells and lithium-ion batteries are considered. Finally, we summarize the conclusions with the possible future subjects.