Photocatalysis with Reduced TiO2: From Black TiO2 to Cocatalyst-Free Hydrogen Production

Black titanium oxide: synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability

Since its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives.

Facile Synthesis of Organic-Inorganic Hybrid Heterojunctions of Glycolated Conjugated Polymer-TiO2-X for Efficient Photocatalytic Hydrogen Evolution

The utilization of the organic-inorganic hybrid photocatalysts for water splitting has gained significant attention due to their ability to combine the advantages of both materials and generate synergistic effects. However, they are still far from practical application due to the limited understanding of the interactions between these two components and the complexity of their preparation process. Herein, a facial approach by combining a glycolated conjugated polymer with a TiO2-X mesoporous sphere to prepare high-efficiency hybrid photocatalysts is presented. The functionalization of conjugated polymers with hydrophilic oligo (ethylene glycol) side chains can not only facilitate the dispersion of conjugated polymers in water but also promote the interaction with TiO2-X forming stable heterojunction nanoparticles. An apparent quantum yield of 53.3% at 365 nm and a hydrogen evolution rate of 35.7 mmol h-1 g-1 is achieved by the photocatalyst in the presence of Pt co-catalyst. Advanced photophysical studies based on femtosecond transient absorption spectroscopy and in situ, XPS analyses reveal the charge transfer mechanism at type II heterojunction interfaces. This work shows the promising prospect of glycolated polymers in the construction of hybrid heterojunctions for photocatalytic hydrogen production and offers a deep understanding of high photocatalytic performance by such heterojunction photocatalysts.

Enhanced photocatalytic performance of colored Ti2O3-Ti3O5-TiO2 heterostructure for the degradation of antibiotic ofloxacin and bactericidal effect

Removing emergent contaminants, such as pharmaceuticals, and inhibiting bacteria by photocatalysis represents an interesting alternative for water remediation. We report the effective preparation of colored powders containing Ti2O3, Ti3O5, and TiO2, by a simple thermal oxidation reaction of a Ti2O3 precursor from 400 °C to 800 °C. The material obtained at 500 °C (P500 sample) exhibited the highest photocatalytic performance under simulated solar light, reaching 54% degradation of antibiotic ofloxacin and a bacteria inactivation of 51% and 62% for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. The superoxide anion radical was the main specie contributing to the photodegradation of ofloxacin, while the hydroxyl radical showed negligible effect. A synergy between the physicochemical properties of the phases in the P500 sample contributes to the electrons transfer, visible light absorption capability and generation of reactive oxygen species, resulting in its remarkable photoactivity. The comparison in terms of surface-specific activity revealed that the P500 sample is more efficient than commercially available TiO2 P25. This fact opens the option of using commercially available Ti2O3 and TiO2 P25 to obtain composites for promoting photoinduced reactions using natural solar light.

Hierarchical Branched TiO2 Photo/Photoelectrocatalyst with Directed Charge Transfer for Efficient Hydrogen Production from Seawater

The directed electron transport channel design in semiconductors, which could promote charge utilization, is attractive but rarely reported. Hierarchical branched titanium dioxide (HB-TiO2), possessing a charge cascade transfer channel, was constructed by assembling titanium-defected TiO2 nanobranches on oxygen-defected TiO2 nanobelts. The interfacial Ti/O vacancies have been detected by X-ray photoelectron and electron paramagnetic resonance spectroscopies, and the vacancies act as the "bridge" of photogenerated carrier transport. This structure maintained high photoactivity in H2 production in different mass fractions of NaCl solutions. The photocurrent density of the HB-TiO2 photoanode in natural seawater is 3.9, 2.1, and 2.6 times that of oxygen-defected TiO2 nanobelts, titanium-defected TiO2 nanobranches, and their mixture, respectively. Besides, the charge transport mechanism from the inner lattice to the TiO2 surface is proposed.

Synergistic augmentation and fundamental mechanistic exploration of β-Ga2O3-rGO photocatalyst for efficient CO2 reduction

We explore the novel photodecomposition capabilities of β-Ga2O3 when augmented with reduced graphene oxide (rGO). Employing real-time spectroscopy, this study unveils the sophisticated mechanisms of photodecomposition, identifying an optimal 1 wt% β-Ga2O3-rGO ratio that substantially elevates the degradation efficiency of Methylene Blue (MB). Our findings illuminate a direct relationship between the photocatalyst's composition and its performance, with the quantity of rGO synthesis notably influencing the catalyst's morphology and consequently, its photodegradation potency. The 1 wt% β-Ga2O3-rGO composition stands out in its class, showing a notable 4.7-fold increase in CO production over pristine β-Ga2O3 and achieving CO selectivity above 98%. This remarkable performance is a testament to the significant improvements rendered by our novel rGO integration technique. Such promising results highlight the potential of our custom-designed β-Ga2O3-rGO photocatalyst for critical environmental applications, representing a substantial leap forward in photocatalytic technology.

Self-Modification of Defective TiO2 under Controlled H2/Ar Gas Environment and Dynamics of Photoinduced Surface Oxygen Vacancies

In recent years, defective TiO2 has caught considerable research attention because of its potential to overcome the limits of low visible light absorption and fast charge recombination present in pristine TiO2 photocatalysts. Among the different synthesis conditions for defective TiO2, ambient pressure hydrogenation with the addition of Ar as inert gas for safety purposes has been established as an easy method to realize the process. Whether the Ar gas might still influence the resulting photocatalytic properties and defective surface layer remains an open question. Here, we reveal that the gas flow ratio between H2 and Ar has a crucial impact on the defective structure as well as the photocatalyic activity of TiO2. In particular, transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS) revealed a larger width of the defective surface layer when using a H2/Ar (50 %-50 %) gas mixture over pure H2. A possible reason could be the increase in dynamic viscosity of the gas mixture when Ar is added. Additionally, photoinduced enhanced Raman spectroscopy (PIERS) is implemented as a complementary approach to investigate the dynamics of the defective structures under ambient conditions which cannot be effortlessly realized by vacuum techniques like TEM.

Modulation of π-Electron Density in Ultrathin 2D Layers of Graphite Carbon Nitride for Efficient Photocatalytic Hydrogen Production

The rational design and synthesis of novel semiconductor nano-/quantum materials have been ambitiously pursued in the field of photocatalysis as the technology is promising and critical for attaining future energy and environmental sustainability. Herein, the integrity of aromatic carbon into graphitic carbon nitride (CN) at the same molecular plane with a few 2D layers is achieved by using modulated precursors of CN, forming carbon regulated ultrathin CN (CUCN) with improved charge transfer kinetics and photocatalytic hydrogen production. The grafted graphite rings adjacent to carbon nitride frameworks induce a significant rearrangement and relocalization of the overall framework, and form conjugated sp2 hybridized interfaces and internal electric fields that drive the separation and directional transfer of photogenerated electrons from CN sheets towards intralayer graphite regions, where the photocatalytic hydrogen evolution reaction occurs extensively, yielding largely increased HER rate of 2231.8 µmol g-1 h-1 by 8.2 times relative to CN, as well as a remarkable apparent quantum yield of 2.93% under monochromatic light at 420 nm. The high physicochemical stability and low synthesis cost of CUCN make it a potential benchmark photocatalyst that can be readily modified via element doping, heterojunction introduction, defect engineering, and so on, to further enhance its HER performance.

Highly efficient mobility, separation and charge transfer in black SnO2-TiO2 structures with co-catalysts: the key step for the photocatalytic hydrogen evolution

Oxygen vacancies and co-catalysts enhance photocatalytic hydrogen production by improving the charge carrier separation. Herein, the black SnO2-TiO2 structure (BST) was synthesized for the first time by two consecutive methods. First, the sol-gel nucleation method allowed TiO2 to form on the SnO2 nanoparticles, creating a strong interaction and direct contact between them. Subsequently, this structure was reduced by NaBH4 during thermal treatment, generating (Ti3+/Sn2+) states to form the BST. Then, 2 wt% of Co, Cu or Pd was impregnated onto BST. The results showed that the activity raised with the presence of Ti3+/Sn2+ states, reaching a hydrogen generation rate of 147.50 μmol g-1 h-1 with BST in comparison with the rate of 99.50 μmol g-1 h-1 for white SnO2-TiO2. On the other hand, the interaction of the co-catalysts with the BST structure helped to increase the photocatalytic hydrogen production rates: 154.10 μmol g-1 h-1, 384.18 μmol g-1 h-1 and 480.20 μmol g-1 h-1 for cobalt-BST, copper-BST and palladium-BST, respectively. The results can be associated with the creation of Ti3+/Sn2+ at the BST interface that changes the lifetime of the charge carrier, improving the separation of photogenerated electrons and holes and the co-catalysts in the structures move the flat band position and increasing the photocurrent response to having electrons with greater reducing power.

Designing a highly near infrared-reflective black nanoparticles for autonomous driving based on the refractive index and principle

HYPOTHESIS

The development of highly NIR reflective black single-shell hollow nanoparticles (BSS-HNPs) can overcome the Light Detection and Ranging (LiDAR) sensor limitations of dark-tone materials. The crystalline phase of TiO2 and the refractive index can be controlled by calcination temperature. The formation of hollow structure and the refractive index is expected to simultaneously increase the light reflection and LiDAR detectability.

EXPERIMENTS

The BSS-HNPs are synthesized using the sol-gel method, calcination, NaBH4 reduction, and etching to form a hollow structure with true blackness. The computational bandgap calculation is conducted to determine the bandgap energy (Eg) of the white and black TiO2 with different crystalline structures. The blackness of the as-synthesized materials is determined by the Commission on Illumination (CIE) L*a*b* color system.

FINDINGS

The hydrophilic nature of BSS-HNPs enables the formulation of hydrophilic paints, allowing the mono-layer coating. With the synergistic effects of hollow structure and the refractive index, BSS-HNPs manifested superb NIR reflectance at LiDAR detection wavelengths. The high detectability, blackness, and hollow structure of BSS-HNPs can expand the variety of LiDAR-detectable dark-tone materials.

Preparation and Application of Co-Doped Zinc Oxide: A Review

Due to a wide band gap and large exciton binding energy, zinc oxide (ZnO) is currently receiving much attention in various areas, and can be prepared in various forms including nanorods, nanowires, nanoflowers, and so on. The reliability of ZnO produced by a single dopant is unstable, which in turn promotes the development of co-doping techniques. Co-doping is a very promising technique to effectively modulate the optical, electrical, magnetic, and photocatalytic properties of ZnO, as well as the ability to form various structures. In this paper, the important advances in co-doped ZnO nanomaterials are summarized, as well as the preparation of co-doped ZnO nanomaterials by using different methods, including hydrothermal, solvothermal, sol-gel, and acoustic chemistry. In addition, the wide range of applications of co-doped ZnO nanomaterials in photocatalysis, solar cells, gas sensors, and biomedicine are discussed. Finally, the challenges and future prospects in the field of co-doped ZnO nanomaterials are also elucidated.

Effect of Nitrogen Doping on the Photocatalytic Properties and Antibiofilm Efficacy of Reduced TiO2 Nanoparticles

Nanomaterial-mediated antibacterial photodynamic therapy (aPDT) emerges as a promising treatment against antibiotic-resistant bacterial biofilms. Specifically, titanium dioxide nanoparticles (TiO2 NPs) are being investigated as photosensitizers in aPDT to address biofilm related diseases. To enhance their photocatalytic performance in the visible spectral range for biomedical applications, various strategies have been adopted, including reduction of TiO2 NPs. However, despite improvements in visible-light photoactivity, reduced TiO2 NPs have yet to reach their expected performance primarily due to the instability of oxygen vacancies and their tendency to reoxidize easily. To address this, we present a two-step approach to fabricate highly visible-light active and stable TiO2 NP photocatalysts, involving nitrogen doping followed by a magnesium-assisted reductive annealing process. X-ray photoelectron spectroscopy analysis of the synthesized reduced nitrogen-doped TiO2 NPs (H:Mg-N-TiO2 NPs) reveals that the presence of nitrogen stabilizes oxygen vacancies and reduced Ti species, leading to increased production of reactive oxygen species under visible-light excitation. The improved aPDT efficiency translates to a 3-fold enhancement in the antibiofilm activity of nitrogen-doped compared to undoped reduced TiO2 NPs against both Gram-positive (Streptococcus mutans) and Gram-negative (Porphyromonas gingivalis, Fusobacterium nucleatum) oral pathogens. These results underscore the potential of H:Mg-N-TiO2 NPs in aPDT for combating bacterial biofilms effectively.

Electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites for persistent uranium recovery at a low potential

Electrochemical uranium extraction (EUE) from seawater is a very promising strategy, but its practical application is hindered by the high potential for electrochemical system, as well as the low selectivity, efficiency, and poor stability of electrode. Herein, we developed creatively a low potential strategy for persistent uranium recovery by electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites coupled with indirect reduction of uranium, finally achieving high selectivity, efficient and persistent uranium recovery. As-designed titanium dioxide rich in oxygen vacancies (TiO2-VO) electrode displayed an EUE efficiency of ∼99.9 % within 180 min at a low potential of 0.09 V in simulated seawater with uranium of 5∼20 ppm. Moreover, the TiO2-VO electrode also showed high selectivity (89.9 %) to uranium, long-term cycling stability and antifouling activity in natural seawater. The excellent EUE property was attributed to the fact that electrochemistry-assisted in-situ regeneration of oxygen vacancies and Ti(III) active sites enhanced EUE cycling process and achieved persistent uranium recovery. The continuous regeneration of oxygen vacancies not only reduced the adsorption energy of U(VI)O22+ but also serve as a storage and transportation channel for electrons, accelerating electron transfer from Ti(III) to U(VI) at solid-liquid interface and promoting EUE kinetic rate.

Upcycle polyethylene terephthalate waste by photoreforming: Bifunction of Pt cocatalyst

Upcycle polyethylene terephthalate (PET) waste by photoreforming (PR) is a sustainable and green approach to tackle environmental problems but with challenges to obtain valuable oxidation products and high purity hydrogen simultaneously. Noble metal cocatalysts are essential to enhance the overall PR reaction efficacy. In this work, TiO2 nanotubes (TiO2 NTs) decorated with single Pt atoms (Pt1/TiO2) or Pt nanoparticles (PtNPs/TiO2) are used in the photoreforming reaction (in one batch), and the oxidation products from ethylene glycol (EG, hydrolysed product of PET) in liquid phase and hydrogen are detected. With Pt1/TiO2, EG is oxidized to glyoxal, glyoxylate or lactate, and hydrogen evolution rate (r H2) reaches 51.8 μmol⋅h-1⋅gcat-1, that is 30 times higher than that of TiO2. For PtNPs/TiO2 (size of Pt NPs: 1.97 nm), hydrogen evolution reaches 219.1 μmol⋅h-1⋅gcat-1, but with the oxidation product of acetate only. DFT calculation demonstrates that for Pt NPs, the reaction path for hydrogen evolution is preferred thermodynamically, due to the formation of Schottky junction. On the oxidation of EG, theoretical and spectroscopic analysis suggest that bidentate adsorption of EG at the interface is facile on Pt1/TiO2, compared to that on PtNPs/TiO2 (two Pt sites), but oxidation products, adsorb less strongly, compared to PtNPs/TiO2, that eventually regulates the distribution of oxidation products. The results thus demonstrate the bifunctions of Pt in the PR reaction, i.e., electron transfer mediator for hydrogen evolution and reactive sites for molecules adsorption. The oxidation reaction is dominated by the adsorption-desorption behavior of molecules but the reduction reaction is controlled by the electron transfer. In addition, acidification of pretreated PET alkaline solution achieves separation of pure terephthalic acid (PTA), which further improves the reaction efficiency possibly by offering high density of active sites and acidic environment. Our work thus demonstrates that to upcycle PET plastics, an optimized process can be reached by atomic design of photocatalysts and proper treatment on the plastic wastes.

Vacancy-Driven High-Performance Metabolic Assay for Diagnosis and Therapeutic Evaluation of Depression

Depression is one of the most common mental illnesses and is a well-known risk factor for suicide, characterized by low overall efficacy (<50%) and high relapse rate (40%). A rapid and objective approach for screening and prognosis of depression is highly desirable but still awaits further development. Herein, a high-performance metabolite-based assay to aid the diagnosis and therapeutic evaluation of depression by developing a vacancy-engineered cobalt oxide (Vo-Co3O4) assisted laser desorption/ionization mass spectrometer platform is presented. The easy-prepared nanoparticles with optimal vacancy achieve a considerable signal enhancement, characterized by favorable charge transfer and increased photothermal conversion. The optimized Vo-Co3O4 allows for a direct and robust record of plasma metabolic fingerprints (PMFs). Through machine learning of PMFs, high-performance depression diagnosis is achieved, with the areas under the curve (AUC) of 0.941-0.980 and an accuracy of over 92%. Furthermore, a simplified diagnostic panel for depression is established, with a desirable AUC value of 0.933. Finally, proline levels are quantified in a follow-up cohort of depressive patients, highlighting the potential of metabolite quantification in the therapeutic evaluation of depression. This work promotes the progression of advanced matrixes and brings insights into the management of depression.

A triazine-based covalent organic framework decorated with cadmium sulfide for efficient photocatalytic hydrogen evolution from water

Construction of inorganic/organic heterostructures has been proven to be a very promising strategy to design highly efficient photocatalysts for solar driven hydrogen evolution from water. Herein, we report the preparation of a direct Z-scheme heterojunction photocatalyst by in situ growth of cadmium sulfide on a triazine-based covalent organic framework (COF). The triazine based-COF was synthesized by condensation reaction of precursors 1,3,5-tris-(4-formyl-phenyl) triazine (TFPT) and 2,5-bis-(3-hydroxypropoxy) terephthalohydrazide (DHTH), termed as TFPT-DHTH-COF. Widely distributed nitrogen atoms throughout TFPT-DHTH-COF skeletons serve as anchoring sites for strong interfacial interactions with CdS. The CdS/TFPT-DHTH-COF composite showed a hydrogen evolution rate of 15.75 mmol h-1 g-1, which is about 75 times higher than that of TFPT-DHTH-COF (0.21 mmol h-1 g-1) and 3.4 times higher than that of CdS (4.57 mmol h-1 g-1). With the properly staggered band alignment and strong interfacial interaction between TFPT-DHTH-COF and CdS, a Z-scheme charge transfer pathway is achieved. The mechanism has been systematically analyzed by steady state and time-resolved photoluminescence measurements as well as in situ irradiated X-ray photoelectron spectroscopy.

Highly efficient, selective, and stable photocatalytic methane coupling to ethane enabled by lattice oxygen looping

Light-driven oxidative coupling of methane (OCM) for multi-carbon (C2+) product evolution is a promising approach toward the sustainable production of value-added chemicals, yet remains challenging due to its low intrinsic activity. Here, we demonstrate the integration of bismuth oxide (BiOx) and gold (Au) on titanium dioxide (TiO2) substrate to achieve a high conversion rate, product selectivity, and catalytic durability toward photocatalytic OCM through rational catalytic site engineering. Mechanistic investigations reveal that the lattice oxygen in BiOx is effectively activated as the localized oxidant to promote methane dissociation, while Au governs the methyl transfer to avoid undesirable overoxidation and promote carbon─carbon coupling. The optimal Au/BiOx-TiO2 hybrid delivers a conversion rate of 20.8 millimoles per gram per hour with C2+ product selectivity high to 97% in the flow reactor. More specifically, the veritable participation of lattice oxygen during OCM is chemically looped by introduced dioxygen via the Mars-van Krevelen mechanism, endowing superior catalyst stability.

Charge carrier recombination processes, intragap defect states, and photoluminescence mechanisms in stoichiometric and reduced TiO2 brookite nanorods: an interpretation scheme through in situ photoluminescence excitation spectroscopy in controlled environment

The study of titanium dioxide (TiO2) in the brookite phase is gaining popularity as evidence has shown the efficient photocatalytic performance of this less investigated polymorph. It has been recently reported that defective anisotropic brookite TiO2 nanorods display remarkable substrate-specific reactivity towards alcohol photoreforming, with rates of hydrogen production significantly (18-fold) higher than those exhibited by anatase TiO2 nanoparticles. To elucidate the basic photo-physical mechanisms and peculiarities leading to such an improvement in the photoactive efficiency, we investigated the recombination processes of photoexcited charge carriers in both stoichiometric and reduced brookite nanorods via photoluminescence excitation spectroscopy in controlled environment. Through an investigation procedure employing both supragap and subgap excitation during successive exposure to oxidizing and reducing gaseous agents, we firstly obtained an interpretation scheme describing the main photoluminescence and charge recombination pathways in stoichiometric and reduced brookite, which includes information about the spatial and energetic position of the intragap states involved in photoluminescence mechanisms, and secondly identified a specific photoluminescence enhancement process occurring in only reduced brookite nanorods, which indicates the injection of a conduction band electron during ethanol photo-oxidation. The latter finding may shed light on the empirical evidence about the exceptional reactivity of reduced brookite nanorods toward the photo-oxidation of alcohols and the concomitant efficiency of photocatalytic hydrogen generation.

Triazine and Fused Thiophene-Based Donor-Acceptor Type Semiconducting Conjugated Polymer for Enhanced Visible-Light-Induced H2 Production

Conjugated polymers have attracted significant attention in the field of photocatalysis due to their exceptional properties, including versatile optimization, cost-effectiveness, and structure stability. Herein, two conjugated porous polymers, PhIN-CPP and ThIN-CPP, based on triazines, were meticulously designed and successfully synthesized using benzene and thiophene as building blocks. Based on UV diffuse reflection spectra, the photonic band gaps of PhIN-CPP and ThIN-CPP were calculated as 2.05 eV and 1.79 eV. The PhIN-CPP exhibited a high hydrogen evolution rate (HER) of 5359.92 μmol·g-1·h-1, which is 10 times higher than that of Thin-CPP (538.49 μmol·g-1·h-1). The remarkable disparity in the photocatalytic performance can be primarily ascribed to alterations in the band structure of the polymers, which includes its more stable benzene units, fluffier structure, larger specific surface area, most pronounced absorption occurring in the visible region and highly extended conjugation with a high density of electrons. The ΔEST values for PhIN-CPP and ThIN-CPP were calculated as 0.79 eV and 0.80 eV, respectively, based on DFT and TD-DFT calculations, which revealed that the incorporation of triazine units in the as-prepared CMPs could enhance the charge transfer via S1 ↔ T1 and was beneficial to the photocatalytic decomposition of H2O. This study presents a novel concept for developing a hybrid system for preparation of H2 by photocatalysis with effectiveness, sustainability, and economy.

Co-Ti Bimetallic Complex-Induced Phase Modulation of Co@Black TiO2 for Catalytic Hydrogenation of Cinnamaldehyde

Transition-metal-doped black titania, primarily in the anatase phase, shows promise for redox reactions, water splitting, hydrogen generation, and organic pollutant removal, but exploring other titania phases for broader catalytic applications is underexplored. This study introduces a synthetic approach using a Co-Ti bimetallic complex bridged by a 1,10-phenanthroline-5,6-dione ligand as a precursor for the synthesis of cobalt-doped black titania [Co@L2N@b-TiO2]. The synthesis involves precise control of pyrolysis conditions, yielding a distinct structure dominated by the rutile phase over anatase, with active cobalt encapsulated within a nitrogen-doped graphitic layer, primarily as Co0 rather than CoII and CoIII. The synthesized material is employed for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) under industrially viable conditions. The efficiency and selectivity of Co@L2N@b-TiO2 was compared with other catalysts, including cobalt-doped rutile TiO2 (Co@r-TiO2), anatase TiO2 (Co@a-TiO2), and black titania (Co@b-TiO2) as well as materials pyrolyzed under different atmospheres and temperatures, materials with phenanthroline ligands, and materials lacking any ligands. The superior performance of Co@L2N@b-TiO2 is attributed to its high surface area, stable Co0 within the nitrogen-doped graphitic layer, and composition of rutile and anatase phases of TiO2 and Ti2O3 (referred to as RAT), along with the synergistic interaction between RAT and Co0. These factors significantly influence the efficiency and selectivity of COL over hydrocinnamaldehyde (HCAL) and hydrocinnamyl alcohol (HCOL), indicating potential for broader applications beyond catalysis, particularly in designing of black titania-based materials.

A Novel Ratiometric Photoelectrochemical Biosensor Based on Front and Back Illumination for Sensitive and Accurate Glutathione Sensing

The ratiometric detection method has a strong attraction for photoelectrochemical bioanalysis due to its high reliability and real-time calibration. However, its implementation typically depends on the spatial resolution of equipment and the pairing of wavelength/potential with photoactive materials. In this paper, a novel ratiometric photoelectrochemical biosensor based on front and back illumination was prepared for the detection of glutathione (GSH). Unlike traditional ratio methods, this ratiometric biosensor does not require voltage and wavelength modulation, thereby avoiding potential crosstalk caused by voltage and wavelength modulation. Additionally, the formation of a heterojunction between mTiO2 and Ag2S is conducive to enhancing light absorption and promoting charge separation, thereby boosting the photocurrent signal. Apart from forming a heterojunction with TiO2, Ag2S also shows a specific affinity towards GSH, thus enhancing the selectivity of the mTiO2/Ag2S ratiometric photoelectrochemical biosensor. The results demonstrate that the ratiometric photoelectrochemical biosensor exhibits a good detection range and a low detection limit for GSH, while also possessing significant interference elimination capability. The GSH detection range is 0.01-10 mmol L-1 with a detection limit of 6.39 × 10-3 mmol·L-1. The relative standard deviation of 20 repeated detections is 0.664%. Impressively, the proposed novel ratiometric PEC biosensor demonstrates enviable universality, providing new insights for the design and construction of PEC ratiometric sensing platforms.

Reed-root-based solar-driven evaporator with a faster capillary water transfer rate for effective steam generation

Solar-driven steam evaporation technology, known for its low energy consumption and environmental friendliness, has emerged as a promising approach for seawater desalination, wastewater purification, etc. However, creating a low-cost solar evaporation system that simultaneously achieves rapid water transport, efficient light absorption, and salt tolerance remains challenging. Here, a dual-layer evaporator based on reed roots has been developed after a simple H2O2 delignification treatment and flame treatment, which exhibited enhanced water transport performance and photothermal properties. As excepted, delignification treatment enhanced the capillary water transport ability of reed roots, which is conducive to promoting the dilution of salt in the evaporator and preventing salt deposition. The evaporator demonstrates an impressive steam generation efficiency of 83.5 % and a remarkable water evaporation rate of 1.407 kg m-2 h-1 under 1 sun, thanks to its well-designed structure and optimized performance. Moreover, the evaporator exhibited excellent practical performance for outdoor applications and demonstrates a remarkable capacity for sewage purification, effectively treating heavy metal ion wastewater as well as dye wastewater. As a result, the objective of our research is to explore opportunities for the implementation of deployable, cost-effective, low-carbon-footprint solar water purification systems, particularly for some impoverished regions, to ensure the provision of high-quality water.

A Facile Strategy for the Preparation of N-Doped TiO2 with Oxygen Vacancy via the Annealing Treatment with Urea

Although titanium dioxide (TiO2) has a wide range of potential applications, the photocatalytic performance of TiO2 is limited by both its limited photoresponse range and fast recombination of the photogenerated charge carriers. In this work, the preparation of nitrogen (N)-doped TiO2 accompanied by the introduction of oxygen vacancy (Vo) has been achieved via a facile annealing treatment with urea as the N source. During the annealing treatment, the presence of urea not only realizes the N-doping of TiO2 but also creates Vo in N-doped TiO2 (N-TiO2), which is also suitable for commercial TiO2 (P25). Unexpectedly, the annealing treatment-induced decrease in the specific surface area of N-TiO2 is inhibited by the N-doping and, thus, more active sites are maintained. Therefore, both the N-doping and formation of Vo as well as the increased active sites contribute to the excellent photocatalytic performance of N-TiO2 under visible light irradiation. Our work offers a facile strategy for the preparation of N-TiO2 with Vo via the annealing treatment with urea.

High-Entropy Lithium Niobate Nanocubes for Photocatalytic Water Splitting under Visible Light

The vast compositional space available in high-entropy oxide semiconductors offers unique opportunities for electronic band structure engineering in an unprecedented large room. In this work, with wide band gap semiconductor lithium niobate (LiNbO3) as a model system, we show that the substitutional addition of high-entropy metal cation mixtures within the Nb sublattice can lead to the formation of a single-phase solid solution featuring a substantially narrowed band gap and intense broadband visible light absorption. The resulting high-entropy LiNbO3 [denoted as Li(HE)O3] crystallizes as well-faceted nanocubes; atomic-resolution imaging and elemental mapping via transmission electron microscopy unveil a distinct local chemical complexity and lattice distortion, characteristics of high-entropy stabilized solid solution phases. Because of the presence of high-entropy stabilized Co2+ dopants that serve as active catalytic sites, Li(HE)O3 nanocubes can accomplish the visible light-driven photocatalytic water splitting in an aqueous solution containing methanol as a sacrificial electron donor without the need of any additional co-catalysts.

Enhanced Photocatalytic H2 Generation by Light-Induced Carbon Modification of TiO2 Nanotubes

Titanium dioxide (TiO2) is the material of choice for photocatalytic and electrochemical applications owing to its outstanding physicochemical properties. However, its wide bandgap and relatively low conductivity limit its practical application. Modifying TiO2 with carbon species is a promising route to overcome these intrinsic complexities. In this work, we propose a facile method to modify TiO2 nanotubes (NTs) based on the remnant organic electrolyte retained inside the nanotubes after the anodization process, that is, without removing it by immersion in ethanol. Carbon-modified TiO2 NTs (C-TiO2 NTs) showed enhanced H2 evolution in photocatalysis under UV illumination in aqueous solutions. When the C-TiO2 NTs were subjected to UV light illumination, the carbon underwent modification, resulting in higher measured photocurrents in the tube layers. After UV illumination, the IPCE of the C-TiO2 NTs was 4.4-fold higher than that of the carbon-free TiO2 NTs.

Real-Time Multiscale Imaging of Heterogeneous Multistage Reactions: Insights into Nanoscale TiO2 Synthesis

Hydrothermal methods are widely used to synthesize functional inorganic materials. The interplay between the reactive species, solution chemistry, and the nanoscale product makes it challenging to control the reaction pathway to achieve a uniform product. Here, we resolve the heterogeneity that arises during hydrothermal synthesis across different length scales. We combine spatially resolved in situ X-ray pair distribution function (PDF) and small-angle X-ray scattering analysis, which are sensitive to structure on the atomic and nanoscale, with a novel time-lapse optical imaging strategy that reveals heterogeneity and phase separations across the entire reaction. For TiO2 synthesis via hydrothermal hydrolysis of TiCl4, we identify multiple cycles of TiO2 formation and separation that contribute to nonuniformity in the polymorphic product. The PDF data show that the characteristics of TiO2 formed during each formation-separation cycle differ, contributing to the ongoing challenge of precisely identifying reaction controls. The imaging strategy pioneered here provides an efficient in situ means to systematically compare how the reaction evolves under different chemical conditions, thereby advancing our understanding of functional inorganic material synthesis.

Long-Term Stability of Light-Induced Ti3+ Defects in TiO2 Nanotubes for Amplified Photoelectrochemical Water Splitting

This study shows that the simple approach of keeping anodic TiO2 nanotubes at 70 °C in ethanol for 1 h results in improved photoelectrochemical water splitting activity due to initiation of crystallization in the material amplified by the light-induced formation of a Ti3+ -Vo states under UV 365 nm illumination. For the first time, the light-induced Ti3+ -Vo states are generated when oxygen is present in the reaction solution and are stable when in contact with air (oxygen) for a long time (two months). We confirmed here that the amorphous or nearly amorphous structure of titania supports the survival of Ti3+ species in contact with oxygen. It is also shown that the ethanol treatment substantially improves the morphology of the titania nanotube arrays, specifically, less surface cracking and surface purification from C- and F-based contamination from the electrolyte used for anodizing.

The Underlying Catalytic Role of Oxygen Vacancies in Fatty Acid Methyl Esters Ketonization over TiOx Catalysts

Recently, interest in converting bio-derived fatty acid methyl esters (FAMEs) into added-value products has significantly increased. The selectivity of ketonization reaction in the conversion of the FAMEs has significantly hampered the efficiency of this process. Herein, this work reports the preparation of catalysts with different levels of oxygen vacancies while the crystal phase remained unchanged. The catalyst with the highest level of oxygen vacancy exhibited the maximum selectivity. The density functional theory (DFT) simulation showed an increase in interatomic distances leading to the formation of frustrated Lewis pairs (FLPs) upon the creation of oxygen vacancies. The surface measurements, type and density of acid sites of the catalysts, showed that the Lewis acid sites enhanced the selectivity for ketone production; while Bronsted acid sites increased the formation of by-products. Moreover, the ketone formation rate was directly proportional to acid density. The findings of this research provide a different approach for catalyst design, based on defects engineering and their effect on the surface activity, which could be used for enhancing the catalytic performance of novel metal oxides.

Oxygen evolution reaction (OER) active sites in BiVO4 studied using density functional theory and XPS experiments

Bismuth vanadate (BiVO4/BVO) has been widely studied as a photocatalytic water splitting semiconductor material in recent years because of its many advantages, such as its ease of synthesis and suitable band gap (2.4 eV). However, BVO still has some disadvantages, one of which is the low photocatalytic water oxidation activity. It is intriguing and unexpected to note that in the current literature, Bi atoms are taken as the oxygen evolution reaction (OER) active sites, while V metal atoms are not investigated in the OER, and the underlying reason for this remains unknown. In this work, using density functional theory (DFT) calculations and ab initio molecular dynamics simulations, we found that in BVO, the VO4 tetrahedron structure is very stable and there is strong surface reconstruction that leads to the V atoms on the surface having the same coordinates as in the bulk. For some high index surfaces, there are some theoretically predicted unsaturated V sites, but it is very easy to form a VO4 tetrahedron structure again by taking oxygen atoms from water. The other intermediates of OER are difficult to adsorb or desorb on this VO4 structure, which makes the V sites in BVO unsuitable as OER active sites. This VO4 structure remained stable during the molecular dynamics simulation at 300 and 673 K. The XPS characterization of various BVO morphologies validates our primary findings from DFT and molecular dynamics simulations. It reveals the presence of unsaturated Bi sites on the BVO surface, while unsaturated V sites are not observed. This study provides novel insights into the enhancement of OER activity of BVO and offers a fundamental understanding of OER activity in other photocatalysts containing V atoms.

Cationic Defect-Modulated Li-Ion Migration in High-Voltage Li-Metal Batteries

Li metal exhibits high potential as an anode material for next-generation high-energy density batteries. However, the nonuniform transport of Li+ ions causes Li-dendrite growth at the metal electrode, leading to severe capacity decay and a short cycling life. In this study, negatively charged lithiophilic sites (such as cationic metal vacancies) were used as hosts to regulate the atomic-scale Li+-ion deposition in Li-metal batteries (LMBs). As a proof of concept, three-dimensional (3D) carbon nanofibers (CNFs) decorated with negatively charged TiNbO4 grains (labeled CNF/nc-TNO) were confirmed to be promising Li hosts. Cationic vacancies caused by the carbothermal reduction of Nb5+ and Ti4+ ions generated a negatively charged fiber surface and strong electrostatic interactions that guided the Li+-ion flux to the shadowed areas underneath the fiber and throughout the fibrous mat. Consequently, circumferential Li-metal plating was observed in the CNF/nc-TNO host, even at a high current density of 10 mA cm-2. Moreover, CNF/nc-TNO asymmetric cells delivered a significantly more robust and stable Coulombic efficiency (CE) (99.2% over 380 cycles) than cells comprising electrically neutral CNFs without cationic defects (which exhibits rapid failure after 20 cycles) or Cu foil (which exhibits rapid CE decay, with a CE of 87.1% after 100 cycles). Additionally, CNF/nc-TNO exhibited high stability and low-voltage hysteresis during repeated Li plating/stripping (for over 4000 h at 2 mA cm-2) with an areal capacity of 2 mAh cm-2. It was further paired with high-voltage LiNi0.8Co0.1Mn0.1 (NCM811) cathodes, and the full cells showed long-term cycling (220 cycles) with a CE of 99.2% and a steady rate capability.

A fatty acid photodecarboxylase-mimicking photonanozyme with defect-induced enzymatic substrate-binding pockets

Hydrocarbon synthesis hints at the significance of in-depth investigations and detailed explanations of mimicking fatty acid photodecarboxylase (FAP). Considering the importance of photodecarboxylases in hydrocarbon synthesis, we present the potential of defective semiconductor nanomaterials as a novel type of photonanozymes (PNZs) that mimic enzyme-like performance, serving as alternatives to FAP. Ferrum-doped titanium dioxide (Fe-TiO2) was synthesized to introduce appropriate amounts of surface defects including reduced Ti3+ sites and oxygen vacancies, which reduce the band gap of TiO2 and enhance the visible-light absorption, thereby facilitating efficient charge trapping. Notably, the surface defects of Fe-TiO2 PNZs singularly act as enzymatic substrate-binding pockets that enable efficient carboxylic acid adsorption during the dark process, conversely facilitating the formation of more defects and boosting the FAP-like activity for photocatalytic decarboxylation reactions. This work provides a creative strategy for designing substrate-dependent higher-concentration defects as enzyme-like binding sites on promising PNZs that mimic natural photoenzymes.

Metastable Ni(I)-TiO2-x Photocatalysts: Self-Amplifying H2 Evolution from Plain Water without Noble Metal Co-Catalyst and Sacrificial Agent

Decoration of semiconductor photocatalysts with cocatalysts is generally done by a step-by-step assembly process. Here, we describe the self-assembling and self-activating nature of a photocatalytic system that forms under illumination of reduced anatase TiO2 nanoparticles in an aqueous Ni2+ solution. UV illumination creates in situ a Ni+/TiO2/Ti3+ photocatalyst that self-activates and, over time, produces H2 at a higher rate. In situ X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy show that key to self-assembly and self-activation is the light-induced formation of defects in the semiconductor, which enables the formation of monovalent nickel (Ni+) surface states. Metallic nickel states, i.e., Ni0, do not form under the dark (resting state) or under illumination (active state). Once the catalyst is assembled, the Ni+ surface states act as electron relay for electron transfer to form H2 from water, in the absence of sacrificial species or noble metal cocatalysts.

Nanomaterials-based precision sonodynamic therapy enhancing immune checkpoint blockade: A promising strategy targeting solid tumor

Burgeoning is an evolution from conventional photodynamic therapy (PDT). Thus, sonodynamic therapy (SDT) regulated by nanoparticles (NPs) possesses multiple advantages, including stronger penetration ability, better biological safety, and not reactive oxygen species (ROS)-dependent tumor-killing effect. However, the limitation to tumor inhibition instead of shrinkage and the incapability of eliminating metastatic tumors hinder the clinical potential for SDT. Fortunately, immune checkpoint blockade (ICB) can revive immunological function and induce a long-term immune memory against tumor rechallenges. Hence, synergizing NPs-based SDT with ICB can provide a promising therapeutic outcome for solid tumors. Herein, we briefly reviewed the progress in NPs-based SDT and ICB therapy. We highlighted the synergistic anti-tumor mechanisms and summarized the representative preclinical trials on SDT-assisted immunotherapy. Compared to other reviews, we provided comprehensive and unique perspectives on the innovative sonosensitizers in each trial. Moreover, we also discussed the current challenges and future corresponding solutions.

Green Synthesis of TiO2 Using Impatiens rothii Hook.f. Leaf Extract for Efficient Removal of Methylene Blue Dye

In this work, TiO2 nanoparticles (NPs) were effectively synthesized by a green method using the Impatiens rothii Hook.f. leaf (IL) extract as a capping and reducing agent. The as-synthesized TiO2 NPs were characterized by different characterization methods such as the Brunauer-Emmett-Teller (BET) analysis, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy (DRS), and X-ray diffraction (XRD) and Raman spectroscopy. The specific surface area from BET analysis was found to be 65 m2/g. The average crystallite size from XRD analysis and average particle size from SEM analysis were found to be ∼11 and ∼25 nm, respectively. The Raman spectroscopy and XRD results showed that the biosynthesized (IL-TiO2) nanoparticles were purely anatase phase. XPS analysis illustrated the formation of Titania with an oxidation state of +4. The DRS study showcased that a blue-shifted intense absorption peak of IL-TiO2 (3.39 eV) compared to the bulk material reported in the literature (3.2 eV). HRTEM micrograph showed the presence of grain boundary with d spacings of 0.352, 0.245, and 0.190, which correspond to the lattice planes of (101), (004), and (200), respectively. From the EDX analysis, the weight percents of titanium and oxygen were found to be 54.33 and 45.67%, respectively. The photoinduced degradation of methylene blue (MB) dye was investigated in the presence of biosynthesized IL-TiO2 NPs photocatalyst. The effect of parameters like catalyst dosage (30 mg/L), initial concentration of MB (15 ppm), pH (10.5), and contact time (100 min) on the removal efficiency was optimized. The maximum photodegradation efficiency under the optimized conditions was found to be 98%.

Black titania by sonochemistry: A critical evaluation of existing methods

In the field of photocatalysis, the fabrication of black titania is a booming topic, as it offers a system with improved solar light harvesting properties and increased overall efficiency. The darkening of white TiO2 powders can be ascribed to surface hydroxylation, oxygen vacancies, Ti3+ centres, or a combination thereof. A handful of studies suggests these defects can be conveniently introduced by acoustic cavitation, generated during sonochemical treatment of pristine TiO2 powders. In reproducing these studies, P25 TiO2 samples were ultrasonicated for various hours with a power density of 8000 W/L, resulting in powders that indeed became gradually darker with increasing sonication time. However, HAADF-STEM revealed that extensive erosion of the sonotrode tip took place and contaminated the samples, which appeared to be the primary reason for the observed colour change. This was confirmed by UV-Vis DRS and DRIFTS, that showed no significant alteration of the catalyst surface after sonication. EPR measurements showed that only an insignificant fraction of Ti3+ centres were produced, far less than in a TiO2 sample that was chemically reduced with NaBH4. No evidence of the presence oxygen vacancies could be found. The enhanced photocatalytic activities of ultrasonicated materials reported in literature can therefore not be ascribed to the synthesis of actual black (defected) TiO2, but rather to specific changes in morphology as a result of acoustic cavitation. Also, this study underlines the importance of considering probe erosion in sonochemical catalyst synthesis, which is an unavoidable side effect that can have an important impact on the catalyst appearance, properties and performance.

Popcorn-stick-like NH2-UiO-66/TiO2 nanotube nanocomposites toward optimized photocatalytic carbon oxidation with nitrogen dioxide

Developing photocatalytic technologies for pollutants removal with high harmless product selectivity is a significant challenge. Construction and optimization of nanocomposites junction with appropriate band alignments is an effective method for achieving this objective. Herein, a unique popcorn-stick-like NH2-UiO-66/TiO2 nanotube nanocomposites with staggered band alignment is fabricated. The small metal organic frameworks (MOFs) particles with diameters around 20 nm are uniformly dispersed on the surface of TiO2 nanoplates, creating a popcorn-stick-like structure. The resulting as-synthesized nanocomposites photocatalysts show distinguished photocatalytic activity for simultaneous removal of carbon particles and nitrogen dioxide with 100% NO2 conversion and 99% N2 selectivity, about 3.9 times higher than that of pristine TiO2. The significant enhancement is attributed to the rapid charge separation and transfer in TiO2 and NH2-UiO-66 interface and the visible light absorption. The enhanced charge transfer follows double charge transfer mechanism, which is confirmed by surface photovoltage spectroscopy, photoluminescence, transient photocurrent measurements, and electrochemical impedance spectroscopy. This study demonstrates the potential for the simultaneously removal of two pollutants using the composite of TiO2 and MOF materials with high surface area and visible light absorption ability, thereby providing the possible applications of NH2-UiO-66/TiO2 composites in environmental remediation including air purification and wastewater treatment.

Green Synthesis of ZnO and Black TiO2 Materials and Their Application in Photodegradation of Organic Pollutants

ZnO and black TiO2 have been selected as the most efficient materials for organic pollution abatement due to their increased efficiency when compared to other materials. However, the concept of green chemistry makes it desirable to design green synthesis approaches for their production. In this study, black TiO2 was synthesized using an environmentally safe synthetic technique with glycerol as a reductant. ZnO was prepared by using ionic-liquid-based microwave-assisted extracts of Polygonum minus. To investigate the materials' potential to photodegrade organic pollutants, methylene blue (MB) and phenol were chosen as model organic pollutants. Both materials were found to exhibit spherical morphologies and a mesoporous structure and were efficient absorbers of visible light. ZnO exhibited electron-hole pair recombination lower than that of black TiO2. Black TiO2 was discovered to be an anatase phase, whereas ZnO was found to have a hexagonal wurtzite structure. In contrast to black TiO2, which had a surface area of 239.99 m2/g and a particle size of 28 nm, ZnO had a surface area of 353.11 m2/g and a particle size of 32 nm. With a degradation time of 60 min, ZnO was able to eliminate 97.50% of the 40 mg/L MB. Black TiO2, on the other hand, could reduce 90.0% of the same amount of MB in 60 min. When tested for phenol degradation, ZnO and black TiO2 activities were reduced by nearly 15 and 25%, respectively. A detailed examination of both ZnO and black TiO2 materials revealed that ZnO has more potential and versatility for the degradation of organic pollutants under visible light irradiation.

Promoting Solar-driven Hydrogen Peroxide Production over Thiazole-based Conjugated Polymers via Generating and Converting Singlet Oxygen

Solar-driven synthesis of hydrogen peroxide (H2 O2 ) from water and air provides a low-cost and eco-friendly alternative route to the traditional anthraquinone method. Herein, four thiazole-based conjugated polymers (Tz-CPs: TTz, BTz, TBTz and BBTz) are synthesized via aldimine condensation. BBTz exhibits the highest H2 O2 production rate of 7274 μmol g-1  h-1 in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in situ diffuse reflectance infrared Fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (1 O2 ). The generation of 1 O2 occurs through the oxidation of superoxide radical (⋅O2 - ) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz, which promotes charge separation and reduces the barrier for H2 O2 production. This work provides new insight into the mechanism of photocatalytic O2 reduction and the molecular design of superior single-polymer photocatalysts.

Integrated Photochromic-Photothermal Processes for Catalytic Plastic Upcycling

Incorporating high-energy ultraviolet (UV) photons into photothermal catalytic processes may enable photothermal-photochemical synergistic catalysis, which represents a transformative technology for waste plastic recycling. The major challenge is avoiding side reactions and by-products caused by these energetic photons. Here, we break through the limitation of the existing photothermal conversion mechanism and propose a photochromic-photothermal catalytic system based on polyol-ligated TiO2 nanocrystals. Upon UV or sunlight irradiation, the chemically bonded polyols can rapidly capture holes generated by TiO2 , enabling photogenerated electrons to reduce Ti4+ to Ti3+ and produce oxygen vacancies. The resulting abundant defect energy levels boost sunlight-to-heat conversion efficiency, and simultaneously the oxygen vacancies facilitate polyester glycolysis by activating the nucleophilic addition-elimination process. As a result, compared to commercial TiO2 (P25), we achieve 6-fold and 12.2-fold performance enhancements under thermal and photothermal conditions, respectively, while maintaining high selectivity to high-valued monomers. This paradigm-shift strategy directs energetic UV photons for activating catalysts and avoids their interaction with reactants, opening the possibility of substantially elevating the efficiency of more solar-driven catalysis.

Interfacial States in Au/Reduced TiO2 Plasmonic Photocatalysts Quench Hot-Carrier Photoactivity

Understanding the interface of plasmonic nanostructures is essential for improving the performance of photocatalysts. Surface defects in semiconductors modify the dynamics of charge carriers, which are not well understood yet. Here, we take advantage of scanning photoelectrochemical microscopy (SPECM) as a fast and effective tool for detecting the impact of surface defects on the photoactivity of plasmonic hybrid nanostructures. We evidenced a significant photoactivity activation of TiO2 ultrathin films under visible light upon mild reduction treatment. Through Au nanoparticle (NP) arrays deposited on different reduced TiO2 films, the plasmonic photoactivity mapping revealed the effect of interfacial defects on hot charge carriers, which quenched the plasmonic activity by (i) increasing the recombination rate between hot charge carriers and (ii) leaking electrons (injected and generated in TiO2) into the Au NPs. Our results show that the catalyst's photoactivity depends on the concentration of surface defects and the population distribution of Au NPs. The present study unlocks the fast and simple detection of the surface engineering effect on the photocatalytic activity of plasmonic semiconductor systems.

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.

Synergistic Effect of Y Doping and Reduction of TiO2 on the Improvement of Photocatalytic Performance

Pure TiO2 and 3% Y-doped TiO2 (3% Y-TiO2) were prepared by a one-step hydrothermal method. Reduced TiO2 (TiO2-H2) and 3% Y-TiO2 (3% Y-TiO2-H2) were obtained through the thermal conversion treatment of Ar-H2 atmosphere at 500 °C for 3 h. By systematically comparing the crystalline phase, structure, morphological features, and photocatalytic properties of 3% Y-TiO2-H2 with pure TiO2, 3% Y-TiO2, and TiO2-H2, the synergistic effect of Y doping and reduction of TiO2 was obtained. All samples show the single anatase phase, and no diffraction peak shift is observed. Compared with single-doped TiO2 and single-reduced TiO2, 3% Y-TiO2-H2 exhibits the best photocatalytic performance for the degradation of RhB, which can be totally degraded in 20 min. The improvement of photocatalytic performance was attributed to the synergistic effect of Y doping and reduction treatment. Y doping broadened the range of light absorption and reduced the charge recombination rates, and the reduction treatment caused TiO2 to be enveloped by disordered shells. The remarkable feature of reduced TiO2 by H2 is its disordered shell filled with a limited amount of oxygen vacancies (OVs) or Ti3+, which significantly reduces the Eg of TiO2 and remarkably increases the absorption of visible light. The synergistic effect of Y doping, Ti3+ species, and OVs play an important role in the improvement of photocatalytic performances. The discovery of this work provides a new perspective for the improvement of other photocatalysts by combining doping and reduction to modify traditional photocatalytic materials and further improve their performance.

Reactive Deposition Versus Strong Electrostatic Adsorption (SEA): A Key to Highly Active Single Atom Co-Catalysts in Photocatalytic H2 Generation

In recent years, the use of single atoms (SAs) has become of a rapidly increasing significance in photocatalytic H2 generation; here SA noble metals (mainly Pt SAs) can act as highly effective co-catalysts. The classic strategy to decorate oxide semiconductor surfaces with maximally dispersed SAs relies on "strong electrostatic adsorption" (SEA) of suitable noble metal complexes. In the case of TiO2 - the classic benchmark photocatalyst - SEA calls for adsorption of cationic Pt complexes such as [(NH3 )4 Pt]2+ which then are thermally reacted to surface-bound SAs. While SEA is widely used in literature, in the present work it is shown by a direct comparison that reactive attachment based on the reductive anchoring of SAs, e.g., from hexachloroplatinic(IV) acid (H2 PtCl6 ) leads directly to SAs in a configuration with a significantly higher specific activity than SAs deposited with SEA - and this at a significantly lower Pt loading and without any thermal post-deposition treatments. Overall, the work demonstrates that the reactive deposition strategy is superior to the classic SEA concept as it provides a direct electronically well-connected SA-anchoring and thus leads to highly active single-atom sites in photocatalysis.

Fermi-level shift, electron separation, and plasmon resonance change in Ag nanoparticle-decorated TiO2 under UV light illumination

Noble metal nanoparticles are widely used as co-catalysts for storing and separating electrons in semiconductor photocatalysis. Thus, evaluating this ability is important and meaningful to understand the photocatalytic mechanism. Employing Ag nanoparticles, the present study combined in situ photoconductance and theoretical analysis to evaluate the Fermi-level (E_F) shift in a UV-illuminated Ag/TiO₂ system under gaseous conditions. Based on this, the role of the Ag nanoparticles in storing and separating electrons was discussed. It was found that the E_F of Ag/TiO₂ is located deeper in the gap and a variation in temperature has less effect on the E_F of Ag/TiO₂ compared to the undecorated TiO₂. The analysis showed that ∼46 electrons can be stored in 10 nm Ag nanoparticles under our experimental conditions, which does not change with temperature. The electron traps in TiO₂ can affect the electron distribution in the TiO₂ and Ag nanoparticles. It was observed that the localized surface plasmon resonance (LSPR) of the Ag nanoparticles exhibited a blue-shift under UV light illumination, which is generally ascribed to the electron storage in the Ag nanoparticles. However, we showed that the blue-shift is not related to the electron storage in the Ag nanoparticles, and thus it cannot be used as an indicator for evaluating their electron-storage ability. The in situ XPS analysis also does not support that the LSPR blue shift is associated with the reduction in the Ag₂O layer and TiO₂.

Facile and Simple Post Treatment Ball Milling Strategy for the Production of Low-Cost TiO2 Composites with Enhanced Photocatalytic Performance and Applicability to Construction Materials

A facile and cost-effective approach assisted by ball milling (BM) of commercial titanium dioxide (TiO₂), has been utilized to develop cheaper and efficient construction materials. At least three of the commercial and cheaper TiO₂ samples (BA01-01, BA01-01+ and R996, designated as A1, A4 and R1, respectively) were selected and subjected to BM treatment to enhance their photocatalytic efficiencies, if possible. It was noted, that the samples A1, A4 and R1 were typical composites of TiO₂ and calcium carbonate (CaCO₃) and contained varying proportions of anatase, and rutile phases of TiO₂ and CaCO₃. Two of the highly efficient commercial TiO₂ samples, Degussa P25 (simply designated as P25) and ST01 (Ishihara Ind.) were selected for making benchmark comparisons of photocatalytic efficiencies. The BM treated TiO₂ samples (designated as TiO₂-BM with respect to A1, A4 and R1) were evaluated for photocatalytic efficiencies both in both aqueous (methylene blue (MB)) and gaseous (NO_x) photodegradation reactions. Based on detailed comparative investigations, it was observed that A1-BM photocatalyst exhibited superior photocatalytic performances over A4-BM and R1-BM, towards both MB and NO_x photodegradation reactions. The difference of NO_x photodegradation efficiency between the mortar mixed with A1-BM and that mixed with ST01, and P-25 at 15% were 16.6%, and 32.4%, respectively. Even though the mortar mixed with A1-BM at 15% composition exhibited a slightly lower NO_x photodegradation efficiency as compared to mortar mixed with the expensive ST01 and P-25 photocatalysts, the present work promises an economic application in the eco-friendly construction materials for air purification considering the far lower cost of A1. The reasons for the superior performance of A1-BM were deduced through characterization of optical properties, surface characteristics, phase composition, morphology, microstructure and particle size distribution between pristine and BM treated A1 using characterization techniques such as diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, field emission scanning electron microscopy and particle size analysis.

Skin B/N-doped anatase TiO2 {001} nanoflakes for visible-light photocatalytic water oxidation

The limited visible-light-responsive photoactivities of most doped wide-bandgap photocatalysts with widened absorption range have long been the obstacles for the efficient conversion of solar energy to chemical energy by photocatalysis. The weak transport ability of visible-light-induced low-energy charge carriers, and numerous recombination centers arising from the energy-band modifiers along the transport path are two major factors responsible for such a mismatch. A potential solution is to shorten the transport path of photo-induced charges in well-modulated light absorbers with low-dimensional structure and the spatially concentrated dopants underneath their surfaces. As a proof of concept, skin B/N-doped red anatase TiO₂ {001} nanoflakes with the absorption edge up to 675 nm were synthesized in this study. Experimental results revealed that boron dopants in the TiO₂ nanoflakes from the hydrolysis of nanosized TiB₂ played a crucial role in controlling nitrogen doping in the surface layer of the nanoflakes. As visible light excitation occurs at the surface layer, the photons can be sufficiently absorbed by the formed energy levels at the surface layers, and the photogenerated charge carriers can effectively migrate to the surface, thus leading to efficient visible-light-responsive photocatalytic oxygen evolution activity from water oxidation.

Tailored Cl- Ligation on Supported Pt Catalysts for Selective Primary C-H Bond Oxidation

It is challenging to achieve high selectivity over Pt-metal-oxide catalysts widely used in many selective oxidation reactions because Pt is prone to over-oxidize substrates. Herein, our sound strategy for enhancing the selectivity is to saturate the under-coordinated single Pt atoms with Cl^- ligands. In this system, the weak electronic metal-support interactions between Pt atoms and reduced TiO₂ cause electron extraction from Pt to Cl^- ligands, resulting in strong Pt-Cl bonds. Therefore, the two-coordinate single Pt atoms adopt a four-coordinate configuration and thus inactivated, thereby inhibiting the over-oxidation of toluene over Pt sites. The selectivity for the primary C-H bond oxidation products of toluene was increased from 50.1 to 100%. Meanwhile, the abundant active Ti³⁺ sites were stabilized in reduced TiO₂ by Pt atoms, leading to a rising yield of the primary C-H oxidation products of 249.8 mmol g_cat^-1. The reported strategy holds great promise for selective oxidation with enhanced selectivity.

Modification of Anodic Titanium Oxide Bandgap Energy by Incorporation of Tungsten, Molybdenum, and Manganese In Situ during Anodization

In this research, we attempted to modify the bandgap of anodic titanium oxide by in situ incorporation of selected elements into the anodic titanium oxide during the titanium anodization process. The main aim of this research was to obtain photoactivity of anodic titanium oxide over a broader sunlight wavelength. The incorporation of the selected elements into the anodic titanium oxide was proved. It was shown that the bandgap values of anodic titanium oxides made at 60 V are in the visible region of sunlight. The smallest bandgap value was obtained for anodic titanium oxide modified by manganese, at 2.55 eV, which corresponds to a wavelength of 486.89 nm and blue color. Moreover, it was found that the pH of the electrolyte significantly affects the thickness of the anodic titanium oxide layer. The production of barrier oxides during the anodizing process with properties similar to coatings made by nitriding processes is reported for the first time.

Aluminium doped ZnO nanostructures for efficient photodegradation of indigo carmine and azo carmine G in solar irradiation

Aluminium doped zinc oxide (AZO) nanomaterials (AlxZn1-xO) with x fraction varying as 0.02 and 0.04 were synthesized using the auto-combustion method using glycine as a fuel. The synthesized catalysts were characterized with X-ray diffraction (XRD), UV–Visible Spectroscopy (UV–Vis), Raman spectroscopy, Photoluminescence (PL) spectroscopy, and High Resolution Transmission Electron Microscopy (HR-TEM). XRD results showed that synthesized materials possessed good crystallinity, while UV–VIS was employed to find the band gaps of synthesized materials. Raman was used to determine the vibrational modes in the synthesized nanoparticles, while TEM analysis was performed to study the morphology of the samples. Industrial effluents such as indigo carmine and azo carmine G were used to test the photodegradation ability of synthesised catalysts. Parameters such as the effect of catalyst loading, dye concentration and pH were studied. The reduction in crystallite size, band gap and increased lattice strain for the 4% AZO was the primary reason for the degradation in visible irradiation, degrading 97 and 99% equimolar concentrations of indigo carmine and azo carmine G in 140 min. The Al doped ZnO was found to be effective in faster degradation of dyes as compared to pure ZnO in presence of natural sunlight.