Pt-Enhanced Mesoporous Ti3+/TiO2 with Rapid Bulk to Surface Electron Transfer for Photocatalytic Hydrogen Evolution

In situ electrochemical regeneration of active 1,4-NADH for enzymatic lactic acid formation via concerted functions on Pt-modified TiO2/Ti

Nicotinamide adenine dinucleotide (NAD+) and its reduced form (NADH) are key cofactors serving as essential hydrogen acceptors and donors to facilitate energy and material conversions under mild conditions. We demonstrate direct electrochemical conversion to achieve highly efficient regeneration of enzymatically active 1,4-NADH using a Pt-modified TiO2 catalyst grown directly on a Ti mesh electrode (Pt-TOT). Spectral analyses revealed that defects formed by the inclusion of Pt species in the lattice of TiO2 play a critical role in the regeneration process. In particular, Pt-TOT containing approximately 3 atom% of Pt exhibited unprecedented efficiency in the electrochemical reduction of NAD+ at the lowest overpotential to date. This exceptional performance led to the production of active 1,4-NADH with a significantly high yield of 86 ± 3% at -0.6 V vs. Ag/AgCl (-0.06 V vs. RHE) and an even higher yield of 99.5 ± 0.4% at a slightly elevated negative potential of -0.8 V vs. Ag/AgCl (-0.2 V vs. RHE). Furthermore, the electrochemically generated NADH was directly applied in the enzymatic conversion of pyruvic acid to lactic acid using lactate dehydrogenase.

Ultrasound-Driven Defect Engineering in TiO2-x Nanotubes─Toward Highly Efficient Platinum Single Atom-Enhanced Photocatalytic Water Splitting

Single-atom catalysts (SACs) have demonstrated superior catalytic activity and selectivity compared to nanoparticle catalysts due to their high reactivity and atom efficiency. However, stabilizing SACs within hosting substrates and their controllable loading preventing single atom clustering remain the key challenges in this field. Moreover, the direct comparison of (co-) catalytic effect of single atoms vs nanoparticles is still highly challenging. Here, we present a novel ultrasound-driven strategy for stabilizing Pt single-atomic sites over highly ordered TiO2 nanotubes. This controllable low-temperature defect engineering enables entrapment of platinum single atoms and controlling their content through the reaction time of consequent chemical impregnation. The novel methodology enables achieving nearly 50 times higher normalized hydrogen evolution compared to pristine titania nanotubes. Moreover, the developed procedure allows the decoration of titania also with ultrasmall nanoparticles through a longer impregnation time of the substrate in a very dilute hexachloroplatinic acid solution. The comparison shows a 10 times higher normalized hydrogen production of platinum single atoms compared to nanoparticles. The mechanistic study shows that the novel approach creates homogeneously distributed defects, such as oxygen vacancies and Ti3+ species, which effectively trap and stabilize Pt2+ and Pt4+ single atoms. The optimized platinum single-atom photocatalyst shows excellent performance of photocatalytic water splitting and hydrogen evolution under one sun solar-simulated light, with TOF values being one order of magnitude higher compared to those of traditional thermal reduction-based methods. The single-atom engineering based on the creation of ultrasound-triggered chemical traps provides a pathway for controllable assembling stable and highly active single-atomic site catalysts on metal oxide support layers.

Efficient Photo-Assisted Thermal Selective Oxidation of Toluene Using N-Doped TiO2

Selective oxidation of toluene is a key reaction to produce high value-added products but remains a big challenge. In this study, we introduce a nitrogen-doped TiO₂ (N-TiO₂) catalyst to create more Ti³⁺ and oxygen vacancy (O_V), which act as active sites for selective oxidation of toluene via activating O₂ to superoxide radical (•O₂^-). Interestingly, the resulting N-TiO₂-2 exhibited an outstanding photo-assisted thermal performance with a product yield of 209.6 mmol·g_cat^-1 and a toluene conversion of 10960.0 μmol·g_cat^-1·h^-1, which are 1.6 and 1.8 times greater than those obtained under thermal catalysis. We showed that the enhanced performance under photo-assisted thermal catalysis was attributed to more active species generation by making full use of photogenerated carriers. Our work suggests a viewpoint to apply a noble-metal-free TiO₂ system in the selective oxidation of toluene under solvent-free conditions.

Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface

To understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO_2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti⁴⁺ to the lower oxidation state Ti^{(4- x)+}, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO_2-x-OV, thereby boosting O₂ adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O₂ (O_ads) and lattice O (O_lat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO_2-x-OV and TiO₂, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO₂ and H₂O in TiO_2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO₂ in TiO₂, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification.

Porous Silica Biofiber: A Reusable, Sustainable Fertilizer Reservoir

Nitrogen fertilizers, namely urea, are prone to leaching that causes inefficiency in crop production and environmental pollution; hence porous particles were explored for slow release. Nevertheless, discrete particles add cost; therefore, jute cellulose has been tested as twine to tether silica together for reusability. On the other hand, silica serves as an exoskeleton to give pore memory property to cellulose, which otherwise is susceptible to loss of porosity during irrigation. The composite shows ∼70% more absorption capacity in the fifth cycle than the fiber without silica coating. The urea release kinetics shows only <1/3 and 3/4 of urea release from the jute-silica composite compared to naked porous silica and cellulose, respectively. The slow and sustained release of fertilizer from the composite results in a continuous increase in the chlorophyll content in rice crops.

Enhanced Photocatalytic Antibacterial Properties of TiO2 Nanospheres with Rutile/Anatase Heterophase Junctions and the Archival Paper Protection Application

TiO2 has been generally studied for photocatalytic sterilization, but its antibacterial activities are limited. Herein, TiO2 nanospheres with rutile/anatase heterophase junctions are prepared by a wet chemical/annealing method. The large BET surface area and pore size are beneficial for the absorption of bacteria. The rutile/anatase heterojunctions narrow the bandgap, which enhances light absorption. The rutile/anatase heterojunctions also efficiently promote the photogenerated carriers' separation, finally producing a high yield of radical oxygen species, such as •O2- and •OH, to sterilize bacteria. As a consequence, the obtained TiO2 nanospheres with rutile/anatase heterojunctions present an improved antibacterial performance against E. coli (98%) within 3 h of simulated solar light irradiation, exceeding that of TiO2 nanospheres without annealing (amorphous) and TiO2 nanospheres annealing at 350 and 550 °C (pure anatase). Furthermore, we design a photocatalytic antibacterial spray to protect the file paper. Our study reveals that the TiO2 nanospheres with rutile/anatase heterojunctions are a potential candidate for maintaining the durability of paper in the process of archival protection.

Black titania an emerging photocatalyst: review highlighting the synthesis techniques and photocatalytic activity for hydrogen generation

The TiO₂ semiconductor photocatalyst is in the limelight of sustainable energy research in recent years because of its beneficial properties. However, its wide band-gap and rapid exciton recombination rate makes it a lame horse, and reduces its photocatalytic efficiency. Recently, researchers have developed facile methods for lowering the band-gap, so that it captures a wide range of solar spectrum, but the efficiency is still way behind the target value. After the discovery of black titania (B-TiO₂), the associated drawbacks of white TiO₂ and its modified forms were addressed to a large extent because it not only absorbs photons in a broad spectral range (UV to IR region), but also modifies the structural and morphological features, along with the electronic properties of the material, significantly boosting the catalytic performance. Hence, B-TiO₂ effectively converts solar energy into renewable chemical energy i.e. green fuel H₂ that can ultimately satisfy the energy crisis and environmental pollution. However, the synthesis techniques involved are quite tedious and challenging. Hence, this review summarizes various preparation methods of B-TiO₂ and the involved characterization techniques. It also discusses the different modification strategies adopted to improve the H₂ evolution activity, and hopes that this review acts as a guiding tool for researchers working in this field.

Polycarbonate/Titania Hybrid Films with Localized Photo-Induced Magnetic-Phase Transition

Materials that exhibit the photo-induced magnetic-phase transition of titania are receiving significant attention because they can be easily switched between diamagnetism and paramagnetism by UV irradiation. However, it is difficult to store photo-induced titanium (Ti³⁺) in air because of its easy oxidation upon oxygen exposure. In this study, titania/polycarbonate hybrid films were prepared using linear 1,6-hexanediol (PHMCD), cyclic 1,4-cyclohexanedimethanol (PCHCD), or their copolymerized carbonate oligomers using the sol-gel method. The oxygen permeability of the hybrid film decreased as the ratio of the ring structure increased by a factor of approximately 32 from PHMCD with only the chain structure to PCHCD with only the ring structure. These hybrid films can generate Ti³⁺ under a UV irradiation of 250 W for 2 h, and the difference in oxygen permeability significantly affected the lifetime of the Ti³⁺ by a factor of up to 120. In addition, the tensile tests and IR measurements demonstrated that UV irradiation had little effect on the mechanical intensity and matrix chemical structure. Moreover, the magnetic susceptibility of Ti³⁺ present in PCHCD was confirmed to be 6.2 (10^-3 emu/g(titania)) under an external magnetic field of 5 T induced using a superconducting quantum interference device.

Photocatalytic CO2 Reduction and Electrocatalytic H2 Evolution over Pt(0,II,IV)-Loaded Oxidized Ti Sheets

Energy recycling and production using abundant atmospheric CO₂ and H₂O have increasingly attracted attention for solving energy and environmental problems. Herein, Pt-loaded Ti sheets were prepared by sputter-deposition and Pt⁴⁺-reduction methods, and their catalytic activities on both photocatalytic CO₂ reduction and electrochemical hydrogen evolution were fully demonstrated. The surface chemical states were completely examined by X-ray photoelectron spectroscopy before and after CO₂ reduction. Gas chromatography confirmed that CO, CH₄, and CH₃OH were commonly produced as CO₂ reduction products with total yields up to 87.3, 26.9, and 88.0 μmol/mol, respectively for 700 °C-annealed Ti under UVC irradiation for 13 h. Pt-loading commonly negated the CO₂ reduction yields, but CH₄ selectivity was increased. Electrochemical hydrogen evolution reaction (HER) activity showed the highest activity for sputter-deposited Pt on 400 °C-annealed Ti with a HER current density of 10.5 mA/cm² at −0.5 V (vs. Ag/AgCl). The activities of CO₂ reduction and HER were found to be significantly dependent on both the nature of Ti support and the oxidation states (0,II,IV) of overlayer Pt. The present result could provide valuable information for designing efficient Pt/Ti-based CO₂ recycle photocatalysts and electrochemical hydrogen production catalysts.

A Ti-MOF Decorated With a Pt Nanoparticle Cocatalyst for Efficient Photocatalytic H2 Evolution: A Theoretical Study

Pt nanoparticles (NPs) are often used as cocatalysts to enhance the photocatalytic hydrogen production catalyzed by the metal organic framework (MOF) materials. The catalytic efficiency of many Pt/MOF systems can be greatly improved when Pt NPs are used as cocatalysts. In this work, the Pt/20%-MIL-125-(SCH₃)₂ was chosen as the template material to understand the functional role of a Pt metal cocatalyst in the catalytic process. Experimentally, the catalytic activity of Pt/20%-MIL-125-(SCH₃)₂ is more than 100 times that of the system without the help of Pt NPs. Firstly, we proposed a searching algorithm, which is based on the combined Monte Carlo (MC) method and principal component analysis (PCA) algorithm, to find that the most probable adsorption site of the Pt₁₃ nanocluster loaded on the (001) surface of 20%-MIL-125-(SCH₃)₂. Next, by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we revealed that the accumulation of some positive charges on the Pt₁₃ cluster and proton adsorbed on the Pt₁₃ cluster, which can promote the separation of photogenerated electrons and holes, thus improving the photocatalytic efficiency. This work not only provides a method to obtain the adsorption configuration of metal clusters on various MOFs but also provides a new insight into increasing photocatalytic efficiency for H₂ production in Pt/MOF systems.

Revisiting Pt/TiO2 photocatalysts for thermally assisted photocatalytic reduction of CO2

Artificial photosynthesis by a semiconductor-oxide-based photocatalysis is presently challenging due to low CO2 conversion rates and poor product selectivity. To promote CO2 reduction, Pt/TiO2 has been deemed as a classic photocatalyst. In this study, we restudy Pt/TiO2 for the thermally assisted photocatalytic reduction of CO2 and reveal a different story between photocatalysis and photothermal catalysis. For example, when using disordered Pt/TiO2-x, the CO2 conversion via photocatalysis at 298 K is not impressive. However, when the system temperature is increased to 393 K, the CO2 conversion rate is significantly enhanced by a factor of 155 as compared to that obtainable from pristine TiO2; further, surprisingly high selectivity of CH4 (87.5%) could be achieved. Thermally coupled photocatalysis yields the enhanced evolution of H2 side products over Pt (4.06 nm)/TiO2 and promoted H2 splitting over Pt (2.33 nm)/TiO2, which is seldom observed in conventional Pt/TiO2 photocatalysis. The synergy of improved charge separation at the Pt/TiO2-x interface induced by surface disordering and accelerated H2 consumption near smaller Pt nanoparticles by thermal assistance are believed to be critically important for the simultaneous enhancement of CO2 conversion rates and CH4 product selectivity. This study inspires revisiting not only Pt/TiO2 but also reactivating other semiconductor-oxide-based photocatalysts for use in thermally assisted photocatalysis.

Highly efficient hydrogen evolution reaction, plasmon-enhanced by AuNP-l-TiO2NP photocatalysts

A set of AuNPs-l-TiO₂NPs nanoaggregates which showed efficient covering of the semiconductor's surface by AuNPs, as well as suitable AuNP sizes for LSPR-sensibilization were used as highly efficient photocatalysts for photoinduced HER.

Anomalous Photoinduced Hole Transport in Type I Core/Mesoporous-Shell Nanocrystals for Efficient Photocatalytic H2 Evolution

Controlling the carrier dynamics in a semiconductor nanoparticulate photocatalyst is the key to developing catalytic activity. Generally, type I band alignment is unsuitable for photocatalysts because the photoinduced carriers accumulate in the narrow bandgap semiconductor. To avoid the termination of reactions and/or photocorrosion of materials caused by carrier accumulation, it is common to employ type II band alignment for photoenergy conversion systems instead of type I. However, CdS/ZnS core/mesoporous-shell heterostructures show superior photocatalytic activity despite having type I band alignment that is generally unfavorable for photocatalytic reactions. Transient absorption spectroscopy and time-resolved microwave conductivity revealed efficient photoinduced hole transfer from the CdS phase to the ZnS phase. The defect-mediated hole transfer from the CdS to the ZnS phase resulted in long-lived charge separation (>2.4 ms) leading to high photocatalytic performance. This study provides insight into defect-mediated carrier transfer in nanoparticulate photocatalysts, which could be used as a guideline for the design of highly active and stable nanoparticulate photocatalysts.

Hydrogenated TiO2 Nanorod Arrays Decorated with Carbon Quantum Dots toward Efficient Photoelectrochemical Water Splitting

Limited light harvesting and charge collection are recognized as grand challenges for the exploration of highly efficient TiO₂ photoanodes. To overcome these intrinsic shortcomings, we reported the designed photoanode based on TiO₂ nanoarrays with both hydrogenation treatment and surface decoration of carbon quantum dots (CQDs) toward efficient photoelectrochemical water splitting. The results revealed that hydrogenation treatment could cause the formation of oxygen vacancies to suppress the recombination of photoinduced carriers. Meanwhile, the decorated CQDs could not only play as the electron reservoirs to trap photoinduced electrons but also remarkably enhance the solar light harvesting due to their upconversion effect. The as-fabricated photoanodes exhibited a large photocurrent density of ∼3.0 mA/cm² at 1.23 V versus reversible hydrogen electrode under simulated sunlight, which was the highest one among hydrogenated TiO₂ photoanodes ever reported and was ∼6 times that of pristine analogues.

Mixed Titanium Oxide Strategy for Enhanced Photocatalytic Hydrogen Evolution

Titanium dioxide is a promising photocatalyst material for water splitting, but is limited by its low utilization of solar energy and rapid recombination of electron-hole pairs. Herein, a mixed titanium oxide strategy, utilizing TiO₂/Ti₂O₃ heterostructures consisting of in situ grown TiO₂ nanotubes with mixed anatase and rutile phases on bulk Ti₂O₃ materials, is demonstrated for efficient and recyclable hydrogen evolution from photocatalytic water splitting. Taking advantage of the formed heterostructures and the created porous structures, the photogenerated electrons from the conduction band of anatase TiO₂ can be first delivered to rutile TiO₂ and then transferred to Ti₂O₃. Meanwhile, the presence of Ti₂O₃ in TiO₂/Ti₂O₃ heterostructures can substantially promote the charge mobility and suppress the recombination of photogenerated electron-hole pairs. Hence, with a tuned band gap structure that enables rapid electron-hole separation, increased charge carrier density, and enhanced light absorption, the TiO₂/Ti₂O₃ heterostructures provide an enhanced photocatalytic hydrogen evolution rate as high as 1440 μmol g^-1 h^-1 under full-sunlight irradiation and without any other cocatalyst. This mixed titanium oxide strategy may open up new avenues for designing and constructing highly efficient TiO₂-based photocatalytic materials for various applications.

Copper Phosphide-Enhanced Lower Charge Trapping Occurrence in Graphitic-C3N4 for Efficient Noble-Metal-Free Photocatalytic H2 Evolution

Graphitic carbon nitride (g-C₃N₄) fundamental photophysical processes exhibit a high frequency of charge trapping due to physicochemical defects. In this study, a copper phosphide (Cu₃P) and g-C₃N₄ hybrid was synthesized via a facile phosphorization method. Cu₃P, as an electron acceptor, efficiently captures the photogenerated electrons and drastically improved the charge separation rate to cause a significantly enhanced photocatalytic performance. Moreover, the robust and intimate chemical interactions between Cu₃P and g-C₃N₄ offers a rectified charge-transfer channel that can lead to a higher H₂ evolution rate (HRE, 277.2 μmol h^-1 g^-1) for this hybrid that is up to 370 times greater than that achieved from using bare g-C₃N₄ (HRE, 0.75 μmol h^-1 g^-1) with a quantum efficiency of 3.74% under visible light irradiation (λ = 420 nm). To better determine the photophysical characteristics of the Cu₃P-induced charge antitrapping behavior, ultrafast time-resolved spectroscopy measurements were used to investigate the charge carriers' dynamics from femtosecond to nanosecond time domains. The experimental results clearly revealed that Cu₃P can effectively enhance charge transfer and suppress photoelectron-hole recombination.

Effect of Single-Atom Cocatalysts on the Activity of Faceted TiO2 Photocatalysts

The synergetic contribution of crystal facets and atomic cocatalysts toward the photoactivity of TiO₂ was fundamentally investigated. Atomic-level dispersed Pt and Au were deposited onto 001-faceted and 101-faceted TiO₂, separately. When used as photocatalysts for photocatalytic H₂ production, Pt/TiO₂-001 showed 1156 and 3 times higher H₂ evolution rate than that of cocatalyst-free TiO₂-001 and Pt-cocatalyzed TiO₂-101. The significantly improved photocatalytic performance was attributed to the efficient separation of high-energy electrons and the sufficient exposure of reactive sites. This study demonstrates a promising way to design single-atom-assisted photocatalysts for high-efficiency water splitting.

Improved photo-dechlorination at polar photocatalysts K3B6O10X (X = Cl, Br) by halogen atoms-modulated polarization

The material with larger distortion ability has better photocatalytic activity during the dechlorination of CPs.

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H₂-production reaction are highly required for improving its photocatalytic H₂-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H₂-evolution reaction of Cd_xZn_1-xS solid-solution photocatalysts in a sulfur-rich S^2-/SO₃^2- solution. Here, the suspensible Cd_xZn_1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn²⁺/Cd²⁺ mixing ions in a sulfur-rich Na₂S-Na₂SO₃ solution, and the resultant Cd_xZn_1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S^2-/SO₃^2- on the surface of these Cd_xZn_1-xS nanocrystals. It is found that the bandgap structure of Cd_xZn_1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd²⁺/Zn²⁺ molar ratio. The photocatalytic experimental results suggested that the suspensible Cd_xZn_1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H₂-production performance, and the suspensible Cd_0.6Zn_0.4S nanocrystals exhibit the highest photocatalytic H₂-generation performance of 717.19 μmol h^-1, a value higher than that of the sole CdS (320.99 μmol h^-1) and ZnS (5.89 μmol h^-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S^2- active site-mediated mechanism accounted for the high H₂-production activity of the suspensible Cd_xZn_1-xS nanocrystals, namely the numerous adsorbed S^2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible Cd_xZn_1-xS nanocrystals, but also serve as effective H⁺-capturing active sites to accelerate the interfacial H₂-production reaction. Meanwhile, an optimum bandgap structure of suspensible Cd_xZn_1-xS nanocrystals is also extremely required for promoting the photocatalytic H₂-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NOx removal under visible light: Improved charge separation and High selectivity

Development of biocompatible photocatalysts with improved charge separation and high selectivity is essential for effective removal of air pollutants. Iron-containing catalysts have attracted extensive attention due to their low-toxicity and high natural abundance. Here, carbon quantum dots (CQDs) modified FeOOH nanocomposites fabricated using a facile hydrothermal route showed enhanced NO removal efficiency (22%) compared to pure FeOOH. Moreover, generation of toxic NO₂ intermediates was significantly inhibited using the nanocomposites, demonstrating high selectivity for final nitrate formation. Photo-electrochemical results showed that both charge separation and transfer efficiency were significantly improved by CQDs addition, and the lifetime of photo-generated carriers was increased eventually. Density functional theory calculations further elucidated that the suppressed recombination of photo-induced electron-hole pairs was due to enhanced electron migration from the FeOOH to CQDs. A NO degradation mechanism was proposed based on detection of the reactive oxygen species using electron paramagnetic spectroscopy. In addition, the nanocomposite showed good biocompatibility and low cytotoxity, ensuring minimal environmental impact for potential application in large-scale.

Durian-Shaped CdS@ZnSe Core@Mesoporous-Shell Nanoparticles for Enhanced and Sustainable Photocatalytic Hydrogen Evolution

In artificial photosynthesis, the establishment of design guidelines for nanostructures to maximize the photocatalytic performance remains a great challenge. In contrast with the intense research into band-offset tuning for photocatalysts, the relationship between nanostructures and photoinduced carrier dynamics has still been insufficiently explored. We synthesized durian-shaped CdS@ZnSe core@mesporous-shell nanoparticles ( d-CdS/ZnSe NPs) and investigated the carrier dynamics in photocatalytic hydrogen evolution. The cocatalyst-free d-CdS/ZnSe NPs exhibited high photocatalytic activity for H₂ evolution (14.8% apparent quantum yield at 420 nm) and excellent stability (maintaining 80% activity after 72 h) under visible-light irradiation (>422 nm). The transient absorption measurement and flash photolysis time-resolved microwave conductivity unveiled that the ultra-long-lived charge separation (>6.2 ms) and swift hole transfer to the surfaces of ZnSe shell (11 ns) contribute the high catalytic activity and stability. The present work provides a novel insight into designing nanoparticulate photocatalysts with optimized performance.

New Insight into Procedure of Interface Electron Transfer through Cascade System with Enhanced Photocatalytic Activity

Recombination of photogenerated electron-hole pairs is extremely limited in the practical application of photocatalysis toward solving the energy crisis and environmental pollution. A rational design of the cascade system (i.e., rGO/Bi₂ WO₆ /Au, and ternary composites) with highly efficient charge carrier separation is successfully constructed. As expected, the integrated system (rGO/Bi₂ WO₆ /Au) shows enhanced photocatalytic activity compared to bare Bi₂ WO₆ and other binary composites, and it is proved in multiple electron transfer (MET) behavior, namely a cooperative electron transfer (ET) cascade effect. Simultaneously, UV-vis/scanning electrochemical microscopy is used to directly identify MET kinetic information through an in situ probe scanning technique, where the "fast" and "slow" heterogeneous ET rate constants (K_eff ) of corresponding photocatalysts on the different interfaces are found, which further reveals that the MET behavior is the prime source for enhanced photocatalytic activity. This work not only offers a new insight to study catalytic performance during photocatalysis and electrocatalysis systems, but also opens up a new avenue to design highly efficient catalysts in photocatalytic CO₂ conversion to useful chemicals and photovoltaic devices.

Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO2

This study describes the UV solution photodeposition of several earth-abundant 3d transition metals (Co, Ni, and Cu) onto the surface of nanoparticulate TiO2. Irradiated methanolic metal dichloride solutions with suspended Degussa P25-TiO2 (1-2 wt % metal to TiO2) yield visibly colored titanias, whereas the bulk TiO2 structure is unchanged; X-ray photoelectron spectroscopy confirms that metals are present on the titania surface in either reduced metal (Cu/Cu+) or metal cation states (Co2+ and Ni2+), and UV-vis diffuse reflectance spectroscopy shows new visible absorbance features. The analyzed bulk metal contents (∼0.04-0.6 at. %, highest for copper) are lower than the nominal metal solution content. Mixed-metal solution photodeposition reactions roughly parallel observations for single metals, with copper deposition being most favored. These 3d metal surface-modified titanias show significant (∼5-15×) improvement in UV photocatalytic H2 evolution versus unmodified TiO2. H2 evolution rates as high as 85 μmol/h (8500 μmol h-1 g-1) were detected for Cu-coated TiO2 using continuous monitoring of reactor headspace gases by portable mass spectrometry. Control experiments verify the necessity of the methanol sacrificial oxidant in both metal deposition and H2 evolution. In situ metal surface deposition is quickly followed by enhanced H2 evolution relative to TiO2, but at lower levels than isolated metal surface-modified titanias. The photodeposited 3d metal species on the TiO2 surface likely act to reduce electron-hole recombination by facilitating the transfer of photoinduced TiO2 conduction band electrons to protons in solution that are reduced to H2. This study demonstrates a facile method to modify photoactive TiO2 nanoparticles with inexpensive 3d transition metals to improve photocatalytic hydrogen evolution, and it shows the utility of quantitative real-time gas evolution monitoring by portable mass spectrometry.

Insights into the efficient charge separation and transfer efficiency of La,Cr-codoped SrTiO3 modified with CoP as a noble-metal-free co-catalyst for superior visible-light driven photocatalytic hydrogen generation

Doped SrTiO₃ modified with CoP as a co-catalyst for photocatalytic H₂ evolution was designed and fabricated in this work.

Adjusting the ratio of bulk single-electron-trapped oxygen vacancies/surface oxygen vacancies in TiO2 for efficient photocatalytic hydrogen evolution

Co-existence of bulk single-electron-trapped and surface oxygen vacancies favor the improvement of photocatalytic hydrogen evolution.