Pt Single Atoms on TiO2 Can Catalyze Water Oxidation in Photoelectrochemical Experiments.

Photoelectrochemical water splitting on n-type semiconductors is highly dependent on catalysis of the rate-determining reaction of O2 evolution. Conventionally, in electrochemistry and photoelectrochemistry O2 evolution is catalyzed by metal oxide catalysts like IrO2 and RuO2, whereas noble metals such as Pt are considered unsuitable for this purpose. However, our study finds that Pt, in its single-atom form, exhibits exceptional cocatalytic properties for photoelectrochemical water oxidation on a TiO2 photoanode, in contrast to Pt in a nanoparticle form. The decoration of Pt single atoms onto TiO2 yields a remarkable current density of 5.89 mA cm-2 at 1.23 VRHE, surpassing bare TiO2 (or Pt nanoparticle decorated TiO2) by 2.52 times. Notably, this enhancement remains consistent over a wide pH range. By accompanying theoretical work, we assign this significant enhancement to an improved charge transfer and separation efficiency along with accelerated kinetics in the oxygen evolution reaction facilitated by the presence of Pt single atoms on the TiO2 surface.

Hierarchically Porous Few-Layer Carbon Nitride and Its High H+ Selectivity for Efficient Photocatalytic Seawater Splitting.

Photocatalysts for seawater splitting are severely restricted because of the presence of multiple types of ions in seawater that cause corrosion and deactivation. As a result, new materials that promote adsorption of H+ and hinder competing adsorption of metal cations should enhance utilization of photogenerated electrons on the catalyst surface for efficient H2 production. One strategy to design advanced photocatalysts involves introduction of hierarchical porous structures that enable fast mass transfer and creation of defect sites that promote selective hydrogen ion adsorption. Herein, we used a facile calcination method to fabricate the macro-mesoporous C3N4 derivative, VN-HCN, that contains multiple nitrogen vacancies. We demonstrated that VN-HCN has enhanced corrosion resistance and elevated photocatalytic H2 production performance in seawater. Experimental results and theoretical calculations reveal that enhanced mass and carrier transfer and selective adsorption of hydrogen ions are key features of VN-HCN that lead to its high seawater splitting activity.

Spontaneous Dewetting of Au-Thin Layers on Oxide- and Fluorine-Terminated Single Crystalline Anatase and Efficient Use in Photocatalytic H2 Production.

In the present work, the spontaneous dewetting of thin Au layers on single crystalline anatase nanosheets into narrow-disperse Au nanoparticles is investigated. Patterns of the Au particles can be formed on the main facets of anatase that provide a high co-catalytic activity for photocatalytic generation of H2 . Dewetting is distinctly influenced by the respective facets (001) and (101), the deposit thickness, and secondary thermal dewetting, but most strongly by the surface termination of the nanosheets. Fluoride termination not only leads to an enhanced Au-phobic behavior but strongly affects the co-catalytic activity for photocatalytic generation of H2 . While fluoride termination with or without Au decoration is detrimental for hole transfer, the interplay of the Au co-catalyst and surface fluoride yields highly beneficial effect for electron transfer. This results in a three-times higher photocatalytic H2 production for the F-terminated surface. The findings suggest that dewetting of Au on surface fluorinated TiO2 is an effective way to modulate surface dewetting and achieve a strongly enhanced photocatalytic activity.

Interfacial Carbon Makes Nano-Particulate RuO2 an Efficient, Stable, pH-Universal Catalyst for Splitting of Seawater.

An electrocatalyst composed of RuO2 surrounded by interfacial carbon, is synthesized through controllable oxidization-calcination. This electrocatalyst provides efficient charge transfer, numerous active sites, and promising activity for pH-universal electrocatalytic overall seawater splitting. An electrolyzer with this catalyst gives current densities of 10 mA cm-2 at a record low cell voltage of 1.52 V, and shows excellent durability at current densities of 10 mA cm-2 for up to 100 h. Based on the results, a mechanism for the catalytic activity of the composite is proposed. Finally, a solar-driven system is assembled and used for overall seawater splitting, showing 95% Faraday efficiency.

Titanium Vacancies in TiO2 Nanofibers Enable Highly Efficient Photodriven Seawater Splitting.

Photodriven seawater splitting is considered to be one of the most promising techniques for sustainable hydrogen production. However, the high salinity of seawater would deactivate catalysts and consume the photogenerated carriers. Metal vacancies in metal oxide semiconductors are critical to directed electron transfer and high salinity resistance; they are thus desirable but remain a challenge. We demonstrate a facile controllable calcination approach to synthesize TiO2 nanofibers with rich Ti vacancies with excellent photo/electro performances and long-time stability in photodriven seawater splitting, including photocatalysis and photo-electrocatalysis. Experimental measurements and theoretical calculations reveal the formation of titanium vacancies, as well as unidirectional electron trap and superior H+ adsorption ability for efficient charge transfer and resistance to corrosion by seawater. Therefore, atomic-/nanoscale characteristics and mechanism have been proposed to clarify the generation of titanium vacancies and the corresponding interfacial electron transfer.

Titanium Vacancies in TiO2 Nanofibers Enable Highly Efficient Photodriven Seawater Splitting.

Invited for the cover of this issue are Xiao-Yu Yang and co-workers at Wuhan University of Technology, Heinrich-Heine-Universität Düsseldorf, University of the Witwatersrand, and Ben-Gurion University of the Negev. The image depicts Ti vacancies in TiO2 as powerful drivers of photo- and photo-electrocatalytic seawater splitting for hydrogen production. Read the full text of the article at 10.1002/chem.202101817.

Spatial Heterojunction in Nanostructured TiO2 and Its Cascade Effect for Efficient Photocatalysis.

A highly efficient photoenergy conversion is strongly dependent on the cumulative cascade efficiency of the photogenerated carriers. Spatial heterojunctions are critical to directed charge transfer and, thus, attractive but still a challenge. Here, a spatially ternary titanium-defected TiO2@carbon quantum dots@reduced graphene oxide (denoted as VTi@CQDs@rGO) in one system is shown to demonstrate a cascade effect of charges and significant performances regarding the photocurrent, the apparent quantum yield, and photocatalysis such as H2 production from water splitting and CO2 reduction. A key aspect in the construction is the technologically irrational junction of Ti-vacancies and nanocarbons for the spatially inside-out heterojunction. The new "spatial heterojunctions" concept, characteristics, mechanism, and extension are proposed at an atomic-/nanoscale to clarify the generation of rational heterojunctions as well as the cascade electron transfer.

Confinement Effects in Zeolite-Confined Noble Metals.

Confinement of noble nanometals in a zeolite matrix is a promising way to special types of catalysts that show significant advantages in size control, site adjustment, and nano-architecture design. The beauty of zeolite-confined noble metals lies in their unique confinement effects on a molecular scale, and thus enables spatially confined catalysis akin to enzyme catalysis. In this Minireview, the confined synthesis strategies of zeolite-confined noble metals will be briefly discussed, showing the processes, advantages, features, and mechanisms. The confined catalysis carried on zeolite-confined noble metals will be summarized, and great emphasis will be paid to the confinement effects involving size, encapsulation, recognition, and synergy. Great progress of atomic sites in the size effect, supercage stabilization in the encapsulation effect, site adsorption in the recognition effect, and cascade reaction in the synergy effect are highlighted. This Minireview is concluded with challenges and opportunities in terms of the synthesis of zeolite-confined noble metals and their applications to design multifunctional catalysts with high catalytic activity, selectivity, and stability.

Hierarchically Dual-Mesoporous TiO2 Microspheres for Enhanced Photocatalytic Properties and Lithium Storage.

Hierarchically dual-mesoporous TiO2 microspheres have been synthesized by a solvothermal process in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4 ]) and diethylenetriamine (DETA) as co-templates. Secondary mesostructured defects in the hierarchical TiO2 microspheres produce oxygen vacancies, which not only significantly enhance photocatalytic activity in the degradation of methylene blue (1.7 times that with P25) and acetone (2.9 times that with P25), but are also beneficial for lithium storage. Moreover, we propose a mechanism to rationalize the role of this dual mesoporosity of the TiO2 microspheres in enhancing molecular diffusion, ion transportation, and electronic transitions.

Visualization of charge carriers in photocatalysts.

Surface photovoltage techniques combined with time-resolved spectroscopy methods provide an effective way to visualize the charge transfer dynamics in photocatalytic reactions.

Dual Pd-Acid Sites Confined in a Hierarchical Core-Shell Structure for Hydrogenation of Nitrobenzene.

A core-shell structured Pd@TS-1@meso-SiO2 catalyst with confined Pd nanometals has been fabricated by one-pot synthesis, impregnation method and sol-gel method. With the promotion of acid sites and protection of mesoporous silica shell, Pd@TS-1@meso-SiO2 shows higher activity than commercial comparison and higher stability than sample without mesoporous silica shell in the hydrogenation of nitrobenzene. The schematic illustration of the synergy effect is also proposed.

Confined Heterojunction in Hollow-Structured TiO2 and Its Directed Effect in Photodriven Seawater Splitting.

The high salinity of seawater often strongly affects the activity and stability of photocatalysts utilized for photodriven seawater splitting. The current investigation is focused on the photocatalyst H-TiO2/Cu2O, comprised of hydroxyl-enriched hollow mesoporous TiO2 microspheres containing incorporated Cu2O nanoparticles. The design of H-TiO2/Cu2O is based on the hypothesis that the respective hollow and mesoporous structure and hydrophilic surfaces of TiO2 microspheres would stabilize Cu2O nanoparticles in seawater and provide efficient and selective proton adsorption. H-TiO2/Cu2O shows hydrogen production performances of 45.7 mmol/(g·h) in simulated seawater and 17.9 mmol/(g·h) in natural seawater, respectively. An apparent quantum yield (AQY) in hydrogen production of 18.8% in water (and 14.9% in natural seawater) was obtained at 365 nm. Moreover, H-TiO2/Cu2O displays high stability and can maintain more than 90% hydrogen evolution activity in natural seawater for 30 h. A direct mass- and energy- transfer mechanism is proposed to clarify the superior performance of H-TiO2/Cu2O in seawater splitting.

Hierarchical zeolites containing embedded Cd0.2Zn0.8S as a photocatalyst for hydrogen production from seawater.

Uncovering an efficient and stable photocatalytic system for seawater splitting is a highly desirable but challenging goal. Herein, Cd0.2Zn0.8S@Silicalite-1 (CZS@S-1) composites, in which CZS is embedded in the hierarchical zeolite S-1, were prepared and show remarkably high activity, stability and salt resistance in seawater.

Design and synthesis of TiO2/C nanosheets with a directional cascade carrier transfer.

Directed transfer of carriers, akin to excited charges in photosynthesis, in semiconductors by structural design is challenging. Here, TiO2 nanosheets with interlayered sp2 carbon and titanium vacancies are obtained by low-temperature controlled oxidation calcination. The directed transfer of carriers from the excited position to Ti-vacancies to interlayered carbon is investigated and proven to greatly increase the charge transport efficiency. The TiO2/C obtained demonstrates excellent photocatalytic and photoelectrochemical activity and significant lithium/sodium ion storage performance. Further theoretical calculations reveal that the directional excited position/Ti-vacancies/interlayered carbon facilitate the spatial inside-out cascade electron transfer, resulting in high charge transfer kinetics.

A spatial homojunction of titanium vacancies decorated with oxygen vacancies in TiO2 and its directed charge transfer.

The n-p homojunction design in semiconductors could enable directed charge transfer, which is promising but rarely reported. Herein, TiO2 with a spatial n-p homojunction has been designed by decorating TiO2 nanosheets with Ti vacancies around nanostructured TiO2 with O vacancies. 2D 1H TQ-SQ MAS NMR, EPR and XPS show the junction of titanium vacancies and oxygen vacancies at the interface. This spatial homojunction contributes to a significant enhancement in photoelectrochemical and photocatalytic performance, especially photocatalytic seawater splitting. Density functional theory calculations of the charge density reveal the directional n-p charge transfer path at the interface, which is proposed at the atomic-/nanoscale to clarify the generation of rational junctions. The spatial n-p homojunction provides a facile strategy for the design of high-performance semiconductors.

Spatial acid-base-Pd triple-sites of a hierarchical core-shell structure for three-step tandem reaction.

Spatial catalytic acid-base-Pd triple-sites of a hierarchical core-shell structure have been successfully constructed for a three-step reaction, and exhibited excellent catalytic activity and stability. A catalytic mechanism has been systematically studied via single one- and two-step reactions, and possible molecular reactions have been proposed.

Hydrogen Evolution Enhancement over a Cobalt-Based Schottky Interface.

A proof-of-concept strategy for significant enhancement of hydrogen evolution reaction (HER) performance of transition metals via construction of a metal/semiconductor Schottky junction is presented. The decoration of low-cost commercial TiO2 nanoparticles on the surface of microscale Co dendrites causes a significant charge transfer across the Co/TiO2 Schottky interface and enhances the local electron density at the Co surface, confirmed by X-ray photoelectron spectroscopy results and density functional theory calculations. The Co/TiO2 Schottky catalyst displays superior HER activity with a turnover frequency of 0.052 s-1 and an exchange current density of 79 µA cm-2, which are about 4.3 and 4.0 times greater than that of pristine Co, respectively. Moreover, the Co/TiO2 Schottky catalyst displays excellent electrochemical durability for long-term operation in both alkaline solution and high saline solution. Theoretical calculations suggest that the Schottky junction plays an important role to optimize hydrogen adsorption free energy (ΔGH*) by tuning the electronic structure, which enhances the performance for HER of the Co/TiO2 Schottky catalyst. This study of modulating the electronic structure of the catalysts via the Schottky junction could provide valuable insights for designing and synthesizing low-cost, high-performance electrocatalysts.

Hierarchical MoS2 @TiO2 Heterojunctions for Enhanced Photocatalytic Performance and Electrocatalytic Hydrogen Evolution.

Hierarchical MoS2 @TiO2 heterojunctions were synthesized through a one-step hydrothermal method by using protonic titanate nanosheets as the precursor. The TiO2 nanosheets prevent the aggregation of MoS2 and promote the carrier transfer efficiency, and thus enhance the photocatalytic and electrocatalytic activity of the nanostructured MoS2 . The obtained MoS2 @TiO2 has significantly enhanced photocatalytic activity in the degradation of rhodamine B (over 5.2 times compared with pure MoS2 ) and acetone (over 2.8 times compared with pure MoS2 ). MoS2 @TiO2 is also beneficial for electrocatalytic hydrogen evolution (26 times compared with pure MoS2 , based on the cathodic current density). This work offers a promising way to prevent the self-aggregation of MoS2 and provides a new insight for the design of heterojunctions for materials with lattice mismatches.

Homojunction of Oxygen and Titanium Vacancies and its Interfacial n-p Effect.

The homojunction of oxygen/metal vacancies and its interfacial n-p effect on the physiochemical properties are rarely reported. Interfacial n-p homojunctions of TiO2 are fabricated by directly decorating interfacial p-type titanium-defected TiO2 around n-type oxygen-defected TiO2 nanocrystals in amorphous-anatase homogeneous nanostructures. Experimental measurements and theoretical calculations on the cell lattice parameters show that the homojunction of oxygen and titanium vacancies changes the charge density of TiO2 ; a strong EPR signal caused by oxygen vacancies and an unreported strong titanium vacancies signal of 2D 1 H TQ-SQ MAS NMR are present. Amorphous-anatase TiO2 shows significant performance regarding the photogeneration current, photocatalysis, and energy storage, owing to interfacial n-type to p-type conductivity with high charge mobility and less structural confinement of amorphous clusters. A new "homojunction of oxygen and titanium vacancies" concept, characteristics, and mechanism are proposed at an atomic-/nanoscale to clarify the generation of oxygen vacancies and titanium vacancies as well as the interface electron transfer.

[Comparison of transabdominal-hiatal approach and standard thoracoabdominal approach in radical gastrectomy for advanced proximal gastric cancer].

OBJECTIVE: To investigate the safety and efficacy of the transabdominal-hiatal approach of radical gastrectomy for the advanced proximal gastric cancer. METHODS: The clinical data of 40 advanced proximal gastric cancer patients with involvement of distal esophagus admitted in Tongcheng People's Hospital from June 2003 to September 2006 were analyzed retrospectively. Patients included 27 men and 13 women with a mean age of 56.1 years (range: 37 to 76 years). The data were compared with those of 40 proximal gastric cancer patients undergoing standard thoracoabdominal approach (control group) during the same period. RESULTS: As compared with the control group, the transabdominal-hiatal approach showed less blood loss [(181.3 ± 63.7) ml vs.(248.8 ± 79.7) ml], shorter operating time [(4.1 ± 0.6) h vs. (5.3 ± 0.7) h], shorter ICU stay [(6.5 ± 5.7) d vs. (19.4 ± 18.0) d] and shorter postoperative hospital stay [(14.0 ± 2.3) d vs.(18.7 ± 3.0) d] (all P<0.05). The complication rates of transabdominal-hiatal approach group and thoracoabdominal approach group were 7.5% (3/40) and 10.0% (4/40), and the 5-year survival rates were 51.3% and 60.0%, respectively (both P>0.05). CONCLUSION: The transabdominal-hiatal approach of radical gastrectomy for proximal gastric cancer is safe and effective, which may substitute the standard thoracoabdominal technique.