Analysis of the Promoted Activity and Molecular Mechanism of Hydrogen Production over Fine Au–Pt Alloyed TiO2 Photocatalysts

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

High-performance photocatalytic decomposition of PFOA by BiOX/TiO2 heterojunctions: Self-induced inner electric fields and band alignment

BiOX (X = Cl, Br and I) and BiOX/TiO₂ photocatalysts were prepared by a facile hydrothermal approach. The BiOX/TiO₂ heterojunctions demonstrated significantly enhanced efficiency for photocatalytic decomposition of perfluorooctanoic acid (PFOA) compared with sole BiOX or TiO₂. PFOA (10 mg L¹) was completely degraded by BiOCl(Br)/TiO₂ in 8 h. Moreover, BiOCl/TiO₂ attained deep decomposition of PFOA with a high defluorination ratio of 82%. The p-n heterojunctions between BiOX and TiO₂ were confirmed by a series of characterizations. The photo-induced holes would migrate from the valance band (VB) of TiO₂ to BiOX, driven by the built-in electric field (BIEF) near the interfaces of p-n heterojunctions, the inner electric fields (IEF) in BiOX and the higher VB position of BiOX. The X-ray diffraction (XRD) and TEM characterizations indicated that TiO₂ combined with BiOX along the [110] facet, which facilitated photo-induced electron transfer in the [001] direction, thus benefiting PFOA decomposition.

Insight into the Roles of Metal Loading on CO2 Photocatalytic Reduction Behaviors of TiO2

The photocatalytic reduction of carbon dioxide (CO₂) into value-added chemicals is considered to be a green and sustainable technology, and has recently gained considerable research interest. In this work, titanium dioxide (TiO₂) supported Pt, Pd, Ni, and Cu catalysts were synthesized by photodeposition. The formation of various metal species on an anatase TiO₂ surface, after ultraviolet (UV) light irradiation, was investigated insightfully by the X-ray absorption near edge structure (XANES) technique. CO₂ reduction under UV-light irradiation at an ambient pressure was demonstrated. To gain an insight into the charge recombination rate during reduction, the catalysts were carefully investigated by the intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence spectroscopy (PL). The catalytic behaviors of the catalysts were investigated by density functional theory using the self-consistent Hubbard U-correction (DFT+U) approach. In addition, Mott–Schottky measurement was employed to study the effect of energy band alignment of metal-semiconductor on CO₂ photoreduction. Heterojunction formed at Pt-, Pd-, Ni-, and Cu-TiO₂ interface has crucial roles on the charge recombination and the catalytic behaviors. Furthermore, it was found that Pt-TiO₂ provides the highest methanol yield of 17.85 µmol/g_cat/h, and CO as a minor product. According to the IMPS data, Pt-TiO₂ has the best charge transfer ability, with the mean electron transit time of 4.513 µs. We believe that this extensive study on the junction between TiO₂ could provide a profound understanding of catalytic behaviors, which will pave the way for rational designs of novel catalysts with improved photocatalytic performance for CO₂ reduction.

Ethanol Solvothermal Treatment on Graphitic Carbon Nitride Materials for Enhancing Photocatalytic Hydrogen Evolution Performance

Recently, Pt-loaded graphic carbon nitride (g-C₃N₄) materials have attracted great attention as a photocatalyst for hydrogen evolution from water. The simple surface modification of g-C₃N₄ by hydrothermal methods improves photocatalytic performance. In this study, ethanol is used as a solvothermal solvent to modify the surface properties of g-C₃N₄ for the first time. The g-C₃N₄ is thermally treated in ethanol at different temperatures (T = 140 °C, 160 °C, 180 °C, and 220 °C), and the Pt co-catalyst is subsequently deposited on the g-C₃N₄ via a photodeposition method. Elemental analysis and XPS O 1s data confirm that the ethanol solvothermal treatment increased the contents of the oxygen-containing functional groups on the g-C₃N₄ and were proportional to the treatment temperatures. However, the XPS Pt 4f data show that the Pt²⁺/Pt⁰ value for the Pt/g-C₃N₄ treated at ethanol solvothermal temperature of 160 °C (Pt/CN-160) is the highest at 7.03, implying the highest hydrogen production rate of Pt/CN-160 is at 492.3 μmol g⁻¹ h⁻¹ because the PtO phase is favorable for the water adsorption and hydrogen desorption in the hydrogen evolution process. In addition, the electrochemical impedance spectroscopy data and the photoluminescence spectra emission peak intensify reflect that the Pt/CN-160 had a more efficient charge separation process that also enhanced the photocatalytic activity.

Thermocatalytic Hydrogen Production Through Decomposition of Methane-A Review

Consumption of fossil fuels, especially in transport and energy-dependent sectors, has led to large greenhouse gas production. Hydrogen is an exciting energy source that can serve our energy purposes and decrease toxic waste production. Decomposition of methane yields hydrogen devoid of COx components, thereby aiding as an eco-friendly approach towards large-scale hydrogen production. This review article is focused on hydrogen production through thermocatalytic methane decomposition (TMD) for hydrogen production. The thermodynamics of this approach has been highlighted. Various methods of hydrogen production from fossil fuels and renewable resources were discussed. Methods including steam methane reforming, partial oxidation of methane, auto thermal reforming, direct biomass gasification, thermal water splitting, methane pyrolysis, aqueous reforming, and coal gasification have been reported in this article. A detailed overview of the different types of catalysts available, the reasons behind their deactivation, and their possible regeneration methods were discussed. Finally, we presented the challenges and future perspectives for hydrogen production via TMD. This review concluded that among all catalysts, nickel, ruthenium and platinum-based catalysts show the highest activity and catalytic efficiency and gave carbon-free hydrogen products during the TMD process. However, their rapid deactivation at high temperatures still needs the attention of the scientific community.

Cooperative Motion in Water-Methanol Clusters Controls the Reaction Rates of Heterogeneous Photocatalytic Reactions

Detailed information about the influences of the cooperative motion of water and methanol molecules on practical solid-liquid heterogeneous photocatalysis reactions is critical for our understanding of photocatalytic reactions. The present work addresses this issue by applying operando nuclear magnetic resonance (NMR) spectroscopy, in conjunction with density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, to investigate the dynamic behaviors of heterogeneous photocatalytic systems with different molar ratios of water to methanol on rutile-TiO₂ photocatalyst. The results demonstrate that methanol and water molecules are involved in the cooperative motions, and the cooperation often takes the form of methanol-water clusters that govern the number of methanol molecules reaching to the active sites of the photocatalyst per unit time, as confirmed by the diffusion coefficients of the methanol molecule calculated in the binary methanol-water solutions. Nuclear Overhauser effect spectroscopy experiments reveal that the clusters are formed by the hydrogen bonding between the -OH groups of CH₃OH and H₂O. The formation of such methanol-water clusters is likely from an energetic standpoint in low-concentration methanol, which eventually determines the yields of methanol reforming products.

One-pot, ligand-free, room-temperature synthesis of Au/Pd/ZnO nanoclusters with ultra-low noble metal loading and synergistically improved photocatalytic performances

Au/Pd/ZnO nanoclusters with ultra-low noble metal loadings were prepared by a one-step and ligand-free method at room temperature. HRTEM, ICP-MS, XPS, and elemental mapping analysis confirmed that the obtained Au/Pd/ZnO nanoclusters were composed of ZnO nanoclusters decorated with well-dispersed AuPd nanoparticles. Au/Pd/ZnO nanoclusters exhibited higher photocatalytic activity compared with those of pristine ZnO, Au/ZnO and Pd/ZnO. Moreover, the high catalytic activity of Au/Pd/ZnO nanoclusters could be maintained even after 5 cycles of photocatalytic reaction. A mechanism for the enhanced photocatalytic performance was also suggested, which was in light of the synergistic effects of the SPR effect from Au and the improved photogenerated charge carrier separation from Pd.

Improved charge separation and carbon dioxide photoreduction performance of surface oxygen vacancy-enriched zinc ferrite@titanium dioxide hollow nanospheres with spatially separated cocatalysts

Here, we describe the fabrication of surface oxygen vacancy-enriched ZnFe₂O₄@TiO₂ double-shell hollow heterostructure nanospheres (ZnFe₂O₄@H-TiO_2-x) coupled with spatially separated CoO_x and Au-Cu bimetallic cocatalysts. The ZnFe₂O₄@TiO₂ heterojunction and spatially separated dual cocatalysts can significantly promote the separation of photoinduced charge carriers. Combined with the unique hollow double-shell heterostructure characteristics and improved surface state properties, the hybrid nanospheres can efficiently adsorb and activate CO₂ molecules. These advantages cause the optimized catalyst to exhibit remarkably higher gas-phase photocatalytic CO₂ reduction activity than the control CoO_x/ZnFe₂O₄/Au-Cu and ZnFe₂O₄@H-TiO_2-x double-shell hollow nanospheres loaded with a single cocatalyst. Meanwhile, the Au-Cu bimetal effect boosts the CO₂ conversion rate and CH₄ selectivity. The optimized hybrid catalyst with a Au/Cu ratio of 1:1 provides a CH₄ yield of 21.39 μmol g^-1 h^-1 with 93.8% selectivity. This work provides a rational photocatalyst design to improve CO₂ conversion and CH₄ selectivity.

Shining light on transition metal sulfides: New choices as highly efficient antibacterial agents

Globally, millions of people die of microbial infection-related diseases every year. The more terrible situation is that due to the overuse of antibiotics, especially in developing countries, people are struggling to fight with the bacteria variation. The emergence of super-bacteria will be an intractable environmental and health hazard in the future unless novel bactericidal weapons are mounted. Consequently, it is critical to develop viable antibacterial approaches to sustain the prosperous development of human society. Recent researches indicate that transition metal sulfides (TMSs) represent prominent bactericidal application potential owing to the meritorious antibacterial performance, acceptable biocompatibility, high solar energy utilization efficiency, and excellent photo-to-thermal conversion characteristics, and thus, a comprehensive review on the recent advances in this area would be beneficial for the future development. In this review article, we start with the antibacterial mechanisms of TMSs to provide a preliminary understanding. Thereafter, the state-of-the-art research progresses on the strategies for TMSs materials engineering so as to promote their antibacterial properties are systematically surveyed and summarized, followed by a summary of the practical application scenarios of TMSs-based antibacterial platforms. Finally, based on the thorough survey and analysis, we emphasize the challenges and future development trends in this area.

The Mimic Enzyme Properties of Au@PtNRs and the Detection for Ascorbic Acid Based on Their Catalytic Properties

Being superior to natural enzymes, nanoenzymes are drawing a great deal of attention in the field of biosensing. Herein, we developed an ultrasensitive, stable and selective colorimetric assay having dual functionalities of Au-tipped Pt nanorods (NRs). The optical and catalytic properties of Au-tipped Pt NRs were monitored using a spectrophotometer and the chromogenic substrate 3, 3′, 5, 5′-tetramethylbenzidine (TMB) in the presence of H2O2, respectively. We found that Au-tipped Pt NRs exhibited excellent peroxidase-like activity, which decomposed hydrogen peroxide (H2O2) into oxygen (O2). The produced O2 oxidized the chromogenic substrate into a blue color product. The oxidation rate of the chromogenic substrate could be monitored using a spectrophotometer at 652 nm. Notably, the peroxidase-like activity of Au-tipped Pt NRs decreased in the presence of ascorbic acid (AA). The produced O2 preferentially reacted with AA, generating ascorbyl radicals (AA·) instead of oxidizing TMB, and thereby decreased the oxidation rate of TMB. Based on this inhibitory property, a selective colorimetric assay was developed using Au-tipped Pt NRs for the detection of AA. This work offers a novel detection method for AA.

Methanol photo-reforming with water on pure titania for hydrogen production

The behaviour of titania for the photo-reforming of methanol with water at ambient temperature has been examined. It is shown that the reactivity is very poor, compared with metal-loaded catalysts at low methanol levels in solution, but the rate becomes much higher at high methanol levels, such that the difference from metal-loaded samples is much less. The optimum yield is with approximately a 1 : 1 methanol/water solution. The reaction also proceeds well in the gas phase. During all such catalysis, the titania becomes blue, due to light absorption increasing across the range 400-800 nm. However, this does not result in visible range activity for the photo-reforming and is due to the reduction of the material in the presence of light and the formation of anion vacancies and Ti³⁺ centres. These anion vacancies are only very slowly re-oxidized in air on P25 titania, taking days to recover the original whiteness of the oxide. The performance of anatase, rutile and the mixed phase is compared. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Dual plasmonic nanostructures for switching polarity of hot electron-induced photocurrent

We report on the experimental investigation of polarity-switchable hot electron-induced photocurrents in dual-plasmonic nanostructures, consisting of two layers of gold nanoparticles (AuNPs) separated by a TiO₂ film. Hot electrons generated through the non-radiative decay of the localized surface plasmon resonances supported by the top and bottom layers of AuNPs can be simultaneously injected into the TiO₂ film in opposite directions and counteract each other. As a result, the polarity and magnitude of the net photocurrents can be tailored by controlling the population of hot electrons either generated from or collected by the two layers of AuNPs. We believe the wavelength-dependent photocurrent polarity switching could be useful for biosensors with a direct electrical readout and photoconversion applications.

A Dewetted-Dealloyed Nanoporous Pt Co-Catalyst Formed on TiO2 Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H2 Production

Pt nanoparticles are typically decorated as co-catalyst on semiconductors to enhance the photocatalytic performance. Due to the low abundance and high cost of Pt, reaching a high activity with minimized co-catalyst loadings is a key challenge in the field. We explore a dewetting-dealloying strategy to fabricate on TiO2 nanotubes nanoporous Pt nanoparticles, aiming at improving the co-catalyst mass activity for H2 generation. For this, we sputter first Pt-Ni bi-layers of controllable thickness (nm range) on highly ordered TiO2 nanotube arrays, and then induce dewetting-alloying of the Pt-Ni bi-layers by a suitable annealing step in a reducing atmosphere: the thermal treatment causes the Pt and Ni films to agglomerate and at the same time mix with each other, forming on the TiO2 nanotube surface metal islands of a mixed PtNi composition. In a subsequent step we perform chemical dealloying of Ni that is selectively etched out from the bimetallic dewetted islands, leaving behind nanoporous Pt decorations. Under optimized conditions, the nanoporous Pt-decorated TiO2 structures show a>6 times higher photocatalytic H2 generation activity compared to structures modified with a comparable loading of dewetted, non-porous Pt. We ascribe this beneficial effect to the nanoporous nature of the dealloyed Pt co-catalyst, which provides an increased surface-to-volume ratio and thus a more efficient electron transfer and a higher density of active sites at the co-catalyst surface for H2 evolution.

Dual Cocatalysts in TiO2 Photocatalysis

Semiconductor photocatalysis is recognized as a promising strategy to simultaneously address energy needs and environmental pollution. Titanium dioxide (TiO₂ ) has been investigated for such applications due to its low cost, nontoxicity, and high chemical stability. However, pristine TiO₂ still suffers from low utilization of visible light and high photogenerated-charge-carrier recombination rate. Recently, TiO₂ photocatalysts modified by dual cocatalysts with different functions have attracted much attention due to the extended light absorption, enhanced reactant adsorption, and promoted charge-carrier-separation efficiency granted by various cocatalysts. Recent progress on the component and structural design of dual cocatalysts in TiO₂ photocatalysts is summarized. Depending on their components, dual cocatalysts decorated on TiO₂ photocatalysts can be divided into the following categories: bimetallic cocatalysts, metal-metal oxide/sulfide cocatalysts, metal-graphene cocatalysts, and metal oxide/sulfide-graphene cocatalysts. Depending on their architecture, they can be categorized into randomly deposited binary cocatalysts, facet-dependent selective-deposition binary cocatalysts, and core-shell structural binary cocatalysts. Concluding perspectives on the challenges and opportunities for the further exploration of dual cocatalyst-modified TiO₂ photocatalysts are presented.

TiO2 Nanowire-Supported Sulfide Hybrid Photocatalysts for Durable Solar Hydrogen Production

As the feet of clay, photocorrosion induced by hole accumulation has placed serious limitations on the widespread deployment of sulfide nanostructures for photoelectrochemical (PEC) water splitting. Developing sufficiently stable electrodes to construct durable PEC systems is therefore the key to the realization of solar hydrogen production. Here, an innovative charge-transfer manipulation concept based on the aligned hole transport across the interface has been realized to enhance the photostability of In₂S₃ electrodes toward PEC solar hydrogen production. The concept was realized by conducting compact deposition of In₂S₃ nanocrystals on the TiO₂ nanowire array. Under PEC operation, the supporting TiO₂ nanowires functioned as an anisotropic charge-transfer backbone to arouse aligned charge transport across the TiO₂-In₂S₃ interface. Because of the aligned hole transport, the TiO₂ nanowire-supported In₂S₃ hybrid nanostructures (TiO₂-In₂S₃) exhibited improved hole-transfer dynamics at the TiO₂-In₂S₃ interface and enhanced hole injection kinetics at the electrode surface, substantially increasing the long-term photostability toward solar hydrogen production. The PEC durability tests showed that TiO₂-In₂S₃ electrodes can achieve nearly 90.9% retention of initial photocurrent upon continuous irradiation for 6 h, whereas the pure In₂S₃ merely retained 20.8% of initial photocurrent. This double-gain charge-transfer manipulation concept is expected to convey a viable approach to the intelligent design of highly efficient and sufficiently stable sulfide photocatalysts for sustainable solar fuel generation.

Recent Progress in Constructing Plasmonic Metal/Semiconductor Hetero-Nanostructures for Improved Photocatalysis

Hetero-nanomaterials constructed by plasmonic metals and functional semiconductors show enormous potential in photocatalytic applications, such as in hydrogen production, CO2 reduction, and treatment of pollutants. Their photocatalytic performances can be better regulated through adjusting structure, composition, and components’ arrangement. Therefore, the reasonable design and synthesis of metal/semiconductor hetero-nanostructures is of vital significance. In this mini-review, we laconically summarize the recent progress in efficiently establishing metal/semiconductor nanomaterials for improved photocatalysis. The defined photocatalysts mainly include traditional binary hybrids, ternary multi-metals/semiconductor, and metal/multi-semiconductors heterojunctions. The underlying physical mechanism for the enhanced photocatalysis of the established photocatalysts is highlighted. In the end, a brief summary and possible future perspectives for further development in this field are demonstrated.

Forming a Highly Active, Homogeneously Alloyed AuPt Co-catalyst Decoration on TiO2 Nanotubes Directly During Anodic Growth

Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO₂ nanotubes (NTs) can in situ be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during their anodic growth. For this, a metallic Ti substrate containing low amounts of dissolved Au (0.1 atom %) and Pt (0.1 atom %) is used for anodizing. The matrix metal (Ti) is converted to oxide, whereas at the oxide/metal interface direct noble metal particle formation and alloying of Au and Pt takes place; continuously these particles are then picked up by the growing nanotube wall. In our experiments, the AuPt alloy NPs have an average size of 4.2 nm, and at the end of the anodic process, these are regularly dispersed over the TiO₂ nanotubes. These alloyed AuPt particles act as excellent co-catalyst in photocatalytic H₂ generation, with a H₂ production rate of 12.04 μL h^-1 under solar light. This represents a strongly enhanced activity as compared to TiO₂ NTs decorated with monometallic particles of Au (7 μL h^-1) or Pt (9.96 μL h^-1).

Improving the Photo-Oxidative Performance of Bi2MoO6 by Harnessing the Synergy between Spatial Charge Separation and Rational Co-Catalyst Deposition

It has been reported that photogenerated electrons and holes can be directed toward specific crystal facets of a semiconductor particle, which is believed to arise from the differences in their surface electronic structures, suggesting that different facets can act as either photoreduction or photo-oxidation sites. This study examines the propensity for this effect to occur in faceted, plate-like bismuth molybdate (Bi₂MoO₆), which is a useful photocatalyst for water oxidation. Photoexcited electrons and holes are shown to be spatially separated toward the {100} and {001}/{010} facets of Bi₂MoO₆, respectively, by facet-dependent photodeposition of noble metals (Pt, Au, and Ag) and metal oxides (PbO₂, MnO _x, and CoO _x). Theoretical calculations revealed that differences in energy levels between the conduction bands and valence bands of the {100} and {001}/{010} facets can contribute to electrons and holes being drawn to different surfaces of the plate-like Bi₂MoO₆. Utilizing this knowledge, the photo-oxidative capability of Bi₂MoO₆ was improved by adding an efficient water oxidation co-catalyst, CoO _x, to the system, whereby the extent of enhancement was shown to be governed by the co-catalyst location. A greater oxygen evolution occurred when CoO _x was selectively deposited on the hole-rich {001}/{010} facets of Bi₂MoO₆ compared to when CoO _x was randomly located across all of the facets. The elevated performance exhibited for the selectively loaded CoO _x/Bi₂MoO₆ was ascribed to the greater opportunity for hole trapping by the co-catalyst being accentuated over other potentially detrimental effects, such as the co-catalyst acting as a recombination medium and/or covering reactive sites. The results indicate that harnessing the synergy between the spatial charge separation and the co-catalyst location on the appropriate facets of plate-like Bi₂MoO₆ can promote its photocatalytic activity.

Bimetallic Ag-Cu Supported on Graphitic Carbon Nitride Nanotubes for Improved Visible-Light Photocatalytic Hydrogen Production

This work, for the first time, reports visible-light active bare graphitic carbon nitride nanotubes (C₃N₄ NTs) for photocatalytic hydrogen generation, even in the absence of any cocatalyst. Upon uniform dispersion of the cocatalysts, Ag-Cu nanoparticles, on the well-ordered bare C₃N₄ NTs, they exhibit twice the H₂ evolution rate of the bare C₃N₄ NTs. The improved activity is attributed to their unique tubular nanostructure, strong metal-support interaction, and efficient photoinduced electron-hole separation compared to their bare and monometallic counterparts, evidenced by complementary characterization techniques. This work reveals that the H₂ production rates correlate well with the oxidation potentials of the sacrificial reagents used. Triethylamine (TEA) outperforms other sacrificial reagents, including triethanolamine (TEOA) and methanol. Mechanistic studies on the role of various sacrificial reagents in photocatalytic H₂ generation demonstrate that irreversible photodegradation of TEA into diethylamine and acetaldehyde via monoelectronic oxidation contributes to the improved H₂ yield. Similarly, TEOA is oxidized to diethanolamine and glycolaldehyde, whereas methanol is unable to quickly capture the photoinduced holes and remains intact due to the low oxidation potential.

Enhanced CO catalytic oxidation over an Au–Pt alloy supported on TiO2 nanotubes: investigation of the hydroxyl and Au/Pt ratio influences

The schematic illustrates the catalytic mechanism and reaction pathways of Au–Pt/TiO2 SNT catalysts with enhanced catalytic activity for CO oxidation.

Recyclable (Fe3O4-NaYF4:Yb,Tm)@TiO2 nanocomposites with near-infrared enhanced photocatalytic activity

Herein, the design and synthesis of a multifunctional (Fe₃O₄-NaYF₄:Yb,Tm)@TiO₂ photocatalyst through a facile sol–gel process combined with electrostatic self-assembly has been reported.

Sensitization of Pt/TiO2 Using Plasmonic Au Nanoparticles for Hydrogen Evolution under Visible-Light Irradiation

Au nanoparticles with different sizes (10, 20, 30, and 50 nm) were synthesized using a seed-assisted approach and anchored onto Pt/TiO₂ employing 3-mercaptopropionic acid as the organic linker. The sizes of the Au nanoparticles were controlled within a narrow range so that the size-dependent surface plasmonic resonance effect on sensitizing Pt/TiO₂ can be thoroughly studied. We found that 20 nm Au nanoparticles (Au₂₀) gave the best performance in sensitizing Pt/TiO₂ to generate H₂ under visible-light illumination. Photoelectrochemical measurements indicated that Au₂₀-Pt/TiO₂ exhibited the most efficient "hot" electrons separation among the studied catalysts, correlating well with the photocatalytic activity. The superior performance of Au-supported Pt/TiO₂ (Au₂₀-Pt/TiO₂) compared with Au anchored to TiO₂ (Au₂₀/TiO₂) revealed the important role of Pt as a cocatalyst for proton reduction. To elucidate how the visible-light excited hot electrons in Au nanoparticles involved in the proton-reduction reaction process, Au₂₀/TiO₂ was irradiated by visible light (λ > 420 nm) with the presence of Pt precursor (H₂PtCl₆) in a methanol aqueous solution under deaerated condition. Energy-dispersive X-ray spectroscopy mapping analysis on the recovered sample showed that Pt ions could be reduced on the surfaces of both Au nanoparticles and TiO₂ support. This observation indicated that the generated hot electrons on Au nanoparticles were injected into the TiO₂ conduction band, which were then subsequently transferred to Pt nanoparticles where proton reduction proceeded. Besides, the excited hot electrons could also participate in the proton reduction on Au nanoparticles surface.

Facile Aqueous-Phase Synthesis of the PtAu/Bi2O3 Hybrid Catalyst for Efficient Electro-Oxidation of Ethanol

In this work, we present a facile aqueous-phase synthesis of a hybrid catalyst consisting of PtAu alloy supported on Bi₂O₃ microspheres. Multistep reduction of HAuCl₄ and K₂PtCl₄ salts on Bi₂O₃ and subsequent annealing lead to the formation of this hybrid catalyst. To the best of our knowledge, this is the first report of using Bi₂O₃ as a catalyst support in fuel cell applications. The material was characterized by powder X-ray diffraction and various microscopic techniques. This composite showed remarkable activity as well as stability toward the electro-oxidation of ethanol in comparison to commercially available Pt/C. The order of the reactivity was found to be commercial Pt/C (50.4 mA/m²mg_Pt^-1) < Pt/Bi₂O₃(10) (108 mA/m²mg_Pt^-1) < PtAu/Bi₂O₃(10) (459 mA/m²mg_Pt^-1). The enhancement in the activity can be explained through cooperative effects, namely, ligand effects of gold and Bi₂O₃ support, which helps in removing carbon monoxide molecules to avoid the poisoning of the Pt active sites.

Titanocene dichloride (Cp2TiCl2) as a precursor for template-free fabrication of hollow TiO2 nanostructures with enhanced photocatalytic hydrogen production

A one-pot and template-free strategy for synthesizing hollow TiO₂ nanostructures (HTSs) is developed by using titanocene dichloride as a titanium source, acetone as a solvent, and ammonia as a basic source. Transmission electron microscopy (TEM) observations demonstrate that the morphology transformation undergoes solid, yolk-shell and then hollow structures, typical of an Ostwald ripening process. Comparative experiments suggest that the mismatched hydrolysis rate of chloride anion and organic cyclopentadiene in unique titanocene dichloride (Cp₂TiCl₂) molecules should be responsible for the formation of HTSs. The TiO₂ nanostructures exhibit controllable morphologies and tunable sizes by mainly adjusting the amounts of the titanium precursor or ammonia. The HTSs show much improved photocatalytic performance as compared with samples of other morphologies in water splitting application, due to the remarkably increased surface area and active sites, and enhanced mass transfer. Our findings reported herein may offer new perspectives in materials chemistry, and energy- and environment-related applications.

Loading of Co3O4 onto Pt-modified nitrogen-doped TiO2 nanocomposites promotes photocatalytic hydrogen production

Loading of Co₃O₄ onto a very low content (0.02 wt%) Pt-modified N–TiO₂ nanocomposite significantly promotes the efficiency of photocatalytic hydrogen production.

La2Sn2O7 enhanced photocatalytic CO2 reduction with H2O by deposition of Au co-catalyst

La₂Sn₂O₇ (LSO) micro/nanospheres, synthesized by a hydrothermal method, exhibited photocatalytic performance for CO₂ reduction.

A small bandgap semiconductor, p-type MnV2O6, active for photocatalytic hydrogen and oxygen production

Visible-light active MnV₂O₆ with suitable band positions for both water oxidation and reduction.

Low Pt-Loaded Mesoporous Sodium Germanate as a High-Performance Electrocatalyst for the Oxygen Reduction Reaction

Although Pt/C catalysts show relatively high activities for the oxygen reduction reaction (ORR) and great potential for use in polymer electrolyte membrane fuel cells, the large amount of Pt required and the poor stability of Pt/C-based catalysts remain big challenges. Herein, mesoporous Na4 Ge9 O20 micro-crystals have been successfully synthesized to serve as a new kind of electrocatalyst support owing to its special structural characteristics and high structural stability. After loading a low amount of Pt (5 wt %) nanoparticles of 2-5 nm in diameter, the obtained mesoporous Pt/Na4 Ge9 O20 composite shows not only high electrocatalytic activity for ORR in both acidic and alkaline electrolyte media, which are comparable to those of conventional 20 wt % Pt/C, but also remarkably enhanced Pt mass-specified ORR current density and durability. Synergetic catalytic effects between loaded Pt and the support for the ORR activity has been proposed.

The synergistic effect of a well-defined Au@Pt core-shell nanostructure toward photocatalytic hydrogen generation: interface engineering to improve the Schottky barrier and hydrogen-evolved kinetics

A well-defined co-catalyst system TiO2 nanotube-Au (core)-Pt (shell) was demonstrated to be the combination of the localized surface plasmon effect of gold and excellent proton reduction nature of platinum. Furthermore, surface engineering by the descending Fermi energies of gold and platinum was beneficial to electron transfer.

Tuning Phase Composition of TiO2 by Sn(4+) Doping for Efficient Photocatalytic Hydrogen Generation

The anatase-rutile mixed-phase photocatalysts have attracted extensive research interest because of the superior activity compared to their single phase counterparts. In this study, doping of Sn(4+) ions into the lattice of TiO2 facilitates the phase transformation from anatase to rutile at a lower temperature while maintaining the same crystal sizes compared to the conventional annealling approach. The mass ratios between anatase and rutile phases can be easily manipulated by varying the Sn-dopant content. Characterization results reveal that the Sn(4+) ions entered into the lattice of TiO2 by substituting some of the Ti(4+) ions and distributed evenly in the matrix of TiO2. The substitution induced the distortion of the lattice structure, which realized the phase transformation from anatase to rutile at a lower temperature and the close-contact phase junctions were consequently formed between anatase and rutile, accounting for the efficient charge separations. The mixed-phase catalysts prepared by doping Sn(4+) ions into the TiO2 exhibit superior activity for photocatalytic hydrogen generation in the presence of Au nanoparticles, relatively to their counterparts prepared by the conventional annealling at higher temperatures. The band allignment between anatase and rutile phases is established based on the valence band X-ray photoelectron spectra and diffuse reflectance spectra to understand the spatial charge separation process at the heterojunction between the two phases. The study provides a new route for the synthesis of mixed-phase TiO2 catalysts for photocatalytic applications and advances the understanding on the enhanced photocatalytic properties of anatase-rutile mixtures.

M-Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces

M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2 generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO2 substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M-Au/TiO2 was determined through photocatalytic H2 production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H2 yield was observed for Pt0.5-Au1/TiO2 and was around 1.3 ± 0.07 mmol h(-1) g(-1), with an apparent quantum yield (AQY) of 6.4%. Pt0.5-Au1/TiO2 also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt0.5-Au1/TiO2 catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt0.5-Au1/TiO2 composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt0.5-Au1/TiO2. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron-hole pair separation at Pt-Au interfaces and electron storage in metal particles. The Pt in Pt0.5-Au1/TiO2 is electronically and catalytically different from the Pt in Pt/TiO2 and it is predicted that the former suppresses the oxygen reduction reaction.