Core-Shell Nanostructured “Black” Rutile Titania as Excellent Catalyst for Hydrogen Production Enhanced by Sulfur Doping

Visible light driven (VLD) reduced TiO2-x nanocatalysts designed by inorganic and organic reducing agent-mediated solvothermal methods for electrocatalytic and photocatalytic applications

This work presents a comparative study on the structural, optical and electrochemical characteristics of visible light driven (VLD) reduced titanium dioxide (TiO2-x ) nanocatalysts synthesized via inorganic and organic synthetic routes. X-ray diffraction (XRD) patterns, Raman spectra and X-ray absorption fine structure (XAFS) analyses reflected anatase phase titania. Whereas, the quantitative EXAFS fit and XANES analysis revealed structural distortion due to the presence of oxygen and titanium vacancies with low valent Ti states in anatase lattices of certain nanocatalysts, which subsequently leads to better electrochemical and photocatalytic activities. Moreover, owing to the large surface area and mesoporous structures, the Mg-TiO2-x nanocatalysts exhibited enhanced water adsorption and ultimately increased overall water splitting with an OER overpotential equal to 420 mV vs. RHE at a current density of 10 mA cm-2 (Tafel slope = 62 mV dec-1), extended visible light absorbance, decreased photoluminescence (PL) intensity and increased carrier lifetime in comparison with commercial titania.

Study on the preparation of CdS/TiO2 corn straw biochar composite materials for photocatalytic reduction of CO2 and collaborative H2 production

A thermal synthesis method was employed in this work to prepare CdS/TiO2 corn straw biochar photocatalytic composite materials suitable for synergistic hydrogen production with the photocatalytic reduction of CO2. The structure and synergistic reaction of these composite materials were characterized by its photogenerated electron transfer process. Compared with pure TiO2, the energy band gap of the optimal CdS/TiO2 corn straw biochar composite material was reduced to 2.89 eV. The heterostructure coupling between TiO2 and CdS in the biochar accelerated the transfer of photogenerated electrons and reduced the recombination rate of photogenerated electrons and holes. Under visible light irradiation, the photocatalytic H2 yield of this CdS/TiO2 corn straw-derived biochar composite material was 1200 µmol·h-1·g-1, the CO yield was 150 µmol·h-1·g-1, and the CH4 yield was 55 µmol·h-1·g-1. The key to this synergistic reaction is the formation of heterojunctions between CdS and TiO2 as well as the rapid oxidation of holes in the composite material caused by the doping of biochar.

Constructing copper Phthalocyanine/Molybdenum disulfide (CuPc/MoS2) S-scheme heterojunction with S-rich vacancies for enhanced Visible-Light photocatalytic CO2 reduction

Constructing a heterojunction by combining two semiconductors with similar band structures is a successful approach to obtaining photocatalysts with high efficiency. Herein, a CuPc/DR-MoS2 heterojunction involving copper phthalocyanine (CuPc) and molybdenum disulfide with S-rich vacancies (13.66%) is successfully prepared by the facile hydrothermal method. Experimental results and theoretical calculations firmly demonstrated that photoelectrons exhibit an S-scheme charge transfer mechanism in the CuPc/DR-MoS2 heterojunction. The S-scheme heterojunction system has proven significant advantages in promoting the charge separation and transfer of photogenerated carriers, enhancing visible-light responsiveness, and achieving robust photoredox capability. As a result, the optimized 3CuPc/DR-MoS2 S-scheme heterojunction exhibits photocatalytic yields of CO and CH4 at 200 and 111.6 μmol g-1h-1, respectively. These values are four times and 4.5 times greater than the photocatalytic yields of pure DR-MoS2. This study offers novel perspectives on the advancement of innovative and highly effective heterojunction photocatalysts.

Comparative study of reactive oxygen species and tetracycline degradation pathways in catalytic peroxodisulfate activation by asymmetric mesoporous TiO2 and the corresponding controlled-release materials

The removal of trace amounts of antibiotics from water environments while simultaneously avoiding potential environmental hazards during the treatment is still a challenge. In this work, green, harmless, and novel asymmetric mesoporous TiO2 (A-mTiO2) was combined with peroxodisulfate (PDS) as active components in a controlled-release material (CRM) system for the degradation of tetracycline (TC) in the dark. The formation of reactive oxygen species (ROS) and the degradation pathways of TC during catalytic PDS activation by A-mTiO2 powder catalysts and the CRMs were thoroughly studied. Due to its asymmetric mesoporous structure, there were abundant Ti3+/Ti4+ couples and oxygen vacancies in A-mTiO2, resulting in excellent activity in the activation of PDS for TC degradation, with a mineralization rate of 78.6%. In CRMs, ROS could first form during PDS activation by A-mTiO2 and subsequently dissolve from the CRMs to degrade TC in groundwater. Due to the excellent performance and good stability of A-mTiO2, the resulting constructed CRMs could effectively degrade TC in simulated groundwater over a long period (more than 20 days). From electron paramagnetic resonance analysis and TC degradation experiments, it was interesting to find that the ROS formed during PDS activation by A-mTiO2 powder catalysts and CRMs were different, but the degradation pathways for TC were indeed similar in the two systems. In PDS activation by A-mTiO2, besides the free hydroxyl radical (·OH), singlet oxygen (1O2) worked as a major ROS participating in TC degradation. For CRMs, the immobilization of A-mTiO2 inside CRMs made it difficult to capture superoxide radicals (·O2-), and continuously generate 1O2. In addition, the formation of sulfate radicals (·SO4-), and ·OH during the release process of CRMs was consistent with PDS activation by the A-mTiO2 powder catalyst. The eco-friendly CRMs had a promising potential for practical application in the remediation of organic pollutants from groundwater.

Gradient oxygen doping triggered a microscale built-in electric field in CdIn2S4 for photoelectrochemical water splitting

Construction of a built-in electric field has been identified as an attractive improvement strategy for photoelectrochemical (PEC) water splitting by facilitating the carrier extraction from the inside to the surface. However, the promotion effect of the electric field is still restrained by the confined built-in area. Herein, we construct a microscale built-in electric field via gradient oxygen doping. The octahedral configuration of the synthesized CdIn2S4 (CIS) provides a structural basis, which enables the subsequent oxygen doping to reach a depth of ∼100 nm. Accordingly, the oxygen-doped CIS (OCIS) photoanode exhibits a microscale built-in electric field with band bending. Excellent PEC catalytic activity with a photocurrent density of 3.69 mA cm-2 at 1.23 V vs. RHE is achieved by OCIS, which is 3.1 times higher than that of CIS. Combining the results of thorough characterization and theoretical calculations, accelerating migration and separation of charge carriers have been determined as the reasons for the improvement. Meanwhile, the recombination risk at the doping centers has also been reduced to the minimum via optimal experiments. This work provides a new-generation idea for constructing a built-in electric field from the view point of bulky configuration towards PEC water splitting.

Visible Light-Driven Micromotors in Fuel-Free Environment with Promoted Ion Tolerance

Light-driven electrophoretic micromotors have gained significant attention recently for applications in drug delivery, targeted therapy, biosensing, and environmental remediation. Micromotors that possess good biocompatibility and the ability to adapt to complex external environments are particularly attractive. In this study, we have fabricated visible light-driven micromotors that could swim in an environment with relatively high salinity. To achieve this, we first tuned the energy bandgap of rutile TiO₂ that was hydrothermally synthesized, enabling it to generate photogenerated electron-hole pairs under visible light rather than solely under UV. Next, platinum nanoparticles and polyaniline were decorated onto the surface of TiO₂ microspheres to facilitate the micromotors swimming in ion-rich environments. Our micromotors exhibited electrophoretic swimming in NaCl solutions with concentrations as high as 0.1 M, achieving a velocity of 0.47 μm/s without the need for additional chemical fuels. The micromotors' propulsion was generated solely by splitting water under visible light illumination, therefore offering several advantages over traditional micromotors, such as biocompatibility and the ability to operate in environments with high ionic strength. These results demonstrated high biocompatibility of photophoretic micromotors and high potential for practical applications in various fields.

Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2

Photoelectrochemical reaction is emerging as a powerful approach for biomass conversion. However, it has been rarely explored for glucose conversion into value-added chemicals. Here we develop a photoelectrochemical approach for selective oxidation of glucose to high value-added glucaric acid by using single-atom Pt anchored on defective TiO₂ nanorod arrays as photoanode. The defective structure induced by the oxygen vacancies can modulate the charge carrier dynamics and band structure, simultaneously. With optimized oxygen vacancies, the defective TiO₂ photoanode shows greatly improved charge separation and significantly enhanced selectivity and yield of C₆ products. By decorating single-atom Pt on the defective TiO₂ photoanode, selective oxidation of glucose to glucaric acid can be achieved. In this work, defective TiO₂ with single-atom Pt achieves a photocurrent density of 1.91 mA cm^-2 for glucose oxidation at 0.6 V versus reversible hydrogen electrode, leading to an 84.3 % yield of glucaric acid under simulated sunlight irradiation.

NIR-photocatalytic regulation of arthritic synovial microenvironment

Synovial microenvironment (SME) plays a vital role in the formation of synovial pannus and the induction of cartilage destruction in arthritis. In this work, a concept of the photocatalytic regulation of SME is proposed for arthritis treatment, and monodispersive hydrogen-doped titanium dioxide nanorods with a rutile single-crystal structure are developed by a full-solution method to achieve near infrared-photocatalytic generation of hydrogen molecules and simultaneous depletion of overexpressed lactic acid (LA) for realizing SME regulation in a collagen-induced mouse model of rheumatoid arthritis. Mechanistically, locally generated hydrogen molecules scavenge overexpressed reactive oxygen species to mediate the anti-inflammatory polarization of macrophages, while the simultaneous photocatalytic depletion of overexpressed LA inhibits the inflammatory/invasive phenotypes of synoviocytes and macrophages and ameliorates the abnormal proliferation of synoviocytes, thereby remarkably preventing the synovial pannus formation and cartilage destruction. The proposed catalysis-mediated SME regulation strategy will open a window to realize facile and efficient arthritis treatment.

Nested order-disorder framework containing a crystalline matrix with self-filled amorphous-like innards

Solids can be generally categorized by their structures into crystalline and amorphous states with different interactions among atoms dictating their properties. Crystalline-amorphous hybrid structures, combining the advantages of both ordered and disordered components, present a promising opportunity to design materials with emergent collective properties. Hybridization of crystalline and amorphous structures at the sublattice level with long-range periodicity has been rarely observed. Here, we report a nested order-disorder framework (NOF) constructed by a crystalline matrix with self-filled amorphous-like innards that is obtained by using pressure to regulate the bonding hierarchy of Cu₁₂Sb₄S₁₃. Combined in situ experimental and computational methods demonstrate the formation of disordered Cu sublattice which is embedded in the retained crystalline Cu framework. Such a NOF structure gives a low thermal conductivity (~0.24 W·m⁻¹·K⁻¹) and a metallic electrical conductivity (8 × 10⁻⁶ Ω·m), realizing the collaborative improvement of two competing physical properties. These findings demonstrate a category of solid-state materials to link the crystalline and amorphous forms in the sublattice-scale, which will exhibit extraordinary properties.

The synthesis and characterization of new crystalline-amorphous hybrid materials is challenging. Here, the authors report the preparation of a nested order-disorder framework by applying high pressure to a nested copper chalcogenide Cu₁₂Sb₄S₁₃.

Photocatalytic Carbon Dioxide Conversion by Structurally and Materially Modified Titanium Dioxide Nanostructures

TiO₂ has aroused considerable attentions as a promising photocatalytic material for decades due to its superior material properties in several fields such as energy and environment. However, the main dilemmas are its wide bandgap (3–3.2 eV), that restricts the light absorption in limited light wavelength region, and the comparatively high charge carrier recombination rate of TiO₂, is a hurdle for efficient photocatalytic CO₂ conversion. To tackle these problems, lots of researches have been implemented relating to structural and material modification to improve their material, optical, and electrical properties for more efficient photocatalytic CO₂ conversion. Recent studies illustrate that crystal facet engineering could broaden the performance of the photocatalysts. As same as for nanostructures which have advantages such as improved light absorption, high surface area, directional charge transport, and efficient charge separation. Moreover, strategies such as doping, junction formation, and hydrogenation have resulted in a promoted photocatalytic performance. Such strategies can markedly change the electronic structure that lies behind the enhancement of the solar spectrum harnessing. In this review, we summarize the works that have been carried out for the enhancement of photocatalytic CO₂ conversion by material and structural modification of TiO₂ and TiO₂-based photocatalytic system. Moreover, we discuss several strategies for synthesis and design of TiO₂ photocatalysts for efficient CO₂ conversion by nanostructure, structure design of photocatalysts, and material modification.

Designing a Redox Heterojunction for Photocatalytic "Overall Nitrogen Fixation" under Mild Conditions

Ammonia and nitrates are the most fundamental and significant raw ingredients in human society. Till now, industrial synthetic ammonia by Haber-Bosch process and industrial synthetic nitrates by the Ostwald process have encountered increasingly serious challenges, i.e., high energy consumption, high cost, and environment-harmful gas emissions. Therefore, developing alternative approaches to achieve nitrogen fixation to overcome the inherent deficiencies of the well-established Haber-Bosch and Ostwald processes has fascinated scientists for many years, especially the simultaneous formation of ammonia and nitrate directly from N₂ molecules, which has been rarely studied. Herein, a heterojunction-based photocatalytic system is designed to successfully achieve "overall nitrogen fixation," a sustainable and simultaneous conversion of N₂ molecules into ammonia and nitrate products under mild conditions. In this heterojunction, interfacial charge redistribution (ICR) promotes selective accumulations of photogenerated electrons and holes in the CdS and WO₃ components. As a result, N₂ molecules can be activated and reduced to ammonia products with yields of 35.8 µmol h^-1 g^-1 by a multi-electron process, and synchronously oxidized into nitrate products with yields of 14.2 µmol h^-1 g^-1 by a hole-induced oxidation coupling process. This work provides a novel insight and promising approach to realize artificial nitrogen fixation under mild condition.

Ternary Transition Metal Sulfide as High Real Energy Cathode for Lithium-Sulfur Pouch Cell Under Lean Electrolyte Conditions

Fabrication of a highly porous sulfur host and using excess electrolyte is a common strategy to enhance sulfur utilization. However, flooded electrolyte limits the practical energy density of Li-S pouch cells. In this study, a novel Fe_0.34 Co_0.33 Ni_0.33 S₂ (FCN) is proposed as host for sulfur to realize Ah-level Li-S full cells demonstrating excellent electrochemical performances under 2 µL mg^-1 lean electrolyte conditions. Moreover, Kelvin probe force microscopy shows that the FCN surface contains positive charge with a potential of ≈70 mV, improving the binding of polysulfides through Lewis acid base interaction. In particular, the FCN@S possesses inherent electrochemical activity of simultaneous anionic and cationic redox for lithium storage in the voltage window of 1.8-2.1 V, which additionally contributes to the specific capacity. Due to the low carbon content (≈10 wt%), the sulfur loading is as high as ≈6 mg cm^-2 , approaching an outstanding energy density of 394.9 and 267.2 Wh kg^-1 at the current density of 1.5 and 4 mA cm^-2 , respectively. Moreover, after 60 cycles at 1.5 mA cm^-2 , the pouch cell still retains an energy of 300.2 Wh kg^-1 . This study represents a milestone in the practical applications of high-energy Li-S batteries.

Crystal Facet Engineering and Hydrogen Spillover-Assisted Synthesis of Defective Pt/TiO2-x Nanorods with Enhanced Visible Light-Driven Photocatalytic Activity

Hydrogen spillover can assist the introduction of defects such as Ti³⁺ and concomitant oxygen vacancies (V_O) in a TiO₂ crystal, thereby inducing a new level below the conduction band to improve the conductivity of photogenerated electrons and the visible light absorption property of TiO₂. Meanwhile, crystal facet engineering offers a promising approach to achieve improved activity by influencing the recombination step of the photogenerated electrons and holes. In this study, with the aim of achieving enhanced visible light-driven photocatalytic activity, rutile TiO₂ nanorods with different aspect ratios were synthesized by crystal facet engineering, and Pt-deposited TiO_2-x nanorods (Pt/TNR) were then obtained via reduction treatment assisted by hydrogen spillover. The reduction treatment at 200 °C induced the formation of surface Ti³⁺ exclusively, whereas surface Ti³⁺ and V_O were formed by performing the reduction at 600 °C. The Pt/TNR with a higher aspect ratio reduced at 200 °C exhibited the highest activity in photocatalytic H₂ production under visible light irradiation owing to the synergistic effect of the introduction of Ti³⁺ defects and the spatial charge carrier separation induced by crystal facet engineering.

Localized surface plasmon resonance effect enhanced Cu/TiO2 core–shell catalyst for boosting CO2 hydrogenation reaction

Inexpensive and nontoxic Cu/TiO2 catalysts based on the LSPR effect for boosting the CO2 hydrogenation reaction.

Enhancing the photocatalytic activity of defective titania for carbon dioxide photoreduction via surface functionalization

The hydrophilic surface of defective titanium dioxide lowers its adsorption capacity towards CO2 molecules.

Plasma-assisted rhodium incorporation in nickel–iron sulfide nanosheets: enhanced catalytic activity and the Janus mechanism for overall water splitting

Rh was incorporated in Fe-doped Ni3S2 nanosheets with the assistance of hydrogen plasma to significantly enhance the HER/OER catalytic activity. The operando evolution behavior and Janus catalytic mechanism of this catalyst were further revealed.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Enhanced photocatalytic degradation of organic contaminants over a CuO/g-C3N4 p-n heterojunction under visible light irradiation

As a kind of metal-free organic semiconductor photocatalyst, g-C₃N₄ has been widely explored for use in photocatalysis. However, the low quantum yield, small absorption range, and poor conductivity limit its large-scale application. Introducing another kind of semiconductor, particularly an oxide semiconductor, can result in some unexpected properties, such as an improved change transfer, enhanced light absorption, and better conductivity. In this work, CuO/g-C₃N₄ is successfully prepared through an impregnation and post-calcination method. A series of measurements support the formation of an organic-inorganic hybrid p–n heterojunction at the CuO (p-type) and g-C₃N₄ (n-type) interface. Furthermore, the photoactivity of the composite is evaluated via photocatalytic NO removal and the visible degradation of rhodamine B (RhB). Results show that the photocatalytic properties of CuO/g-C₃N₄ are almost twice as high as those of g-C₃N₄. In comparative tests, the photocatalytic degradation performance of Mix-CuO/g-C₃N₄ (the mixture of CuO and g-C₃N₄ nanosheets prepared by mechanically mixing) is even lower than that of pure g-C₃N₄. The degradation of RhB is only 19.7% under visible light after 30 min of irradiation. The improvement in the photoactivity of CuO/g-C₃N₄ results from the built-in electric field close to the formed p–n heterojunction, which switches the electron transfer mechanism from a double-charge transfer mechanism to a Z-scheme mechanism. In addition, the formed p–n heterojunction favors charge transfer, and thus the photocatalytic performance is significantly improved.

The p–n heterojunction could enhance the photocatalytic RhB degradation performance of Cu/g-C₃N₄.

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.

Metal chalcogenide-based core/shell photocatalysts for solar hydrogen production: Recent advances, properties and technology challenges

Metal chalcogenides play a vital role in the conversion of solar energy into hydrogen fuel. Hydrogen fuel technology can possibly tackle the future energy crises by replacing carbon fuels such as petroleum, diesel and kerosene, owning to zero emission carbon-free gas and eco-friendliness. Metal chalcogenides are classified into narrow band gap (CdS, Cu₂S, Bi₂S_3, MoS_2, CdSe and MoSe₂) materials and wide band gap materials (ZnS, ZnSe and ZnTe). Composites of these materials are fabricated with different architectures in which core-shell is one of the unique composites that drastically improve the photo-excitons separation, where chalcogenides in the core can be well protected for sustainable uses. Thus,the core-shell structures promote the design and fabrication of composites with the required characteristics. Interestingly, the metal chalcogenides as a core-shell photocatalyst can be classified into type-I, reverse type-I, type-II and S-type nanocomposites, which can effectively influence and significantly enhance the rate of hydrogen production. In this direction, this review is undertaken to provide a comprehensive overview of the advanced preparation processes, properties of metal chalcogenides, and in particular, photocatalytic performance of the metal chalcogenides as a core-shell photocatalysts for solar hydrogen production.

Atomic-level engineering of two-dimensional electrocatalysts for CO2 reduction

Carbon dioxide (CO₂) from the excessive consumption of fossil fuels has exhibited a huge threat to the planet's ecosystem. Electrocatalytic CO₂ reduction into value-added chemicals has been regarded as a promising strategy in CO₂ utilization and needs the development of advanced electrocatalysts for lowering the activation energy and enhancing selectivity in CO₂ reduction. Two-dimensional (2D) materials, benefiting from their unique geometrical structures, have been extensively studied in the electrocatalytic CO₂ reduction reaction (CO₂RR). In this review, we systematically overview atomic-level engineering strategies in 2D electrocatalysts for the CO₂RR, including thickness control, elemental doping, vacancy engineering, heterostructure construction, and single-atom loading. Meanwhile, we analyze the relationship between structures and activity in electrocatalysis, and present the future challenges and opportunities in the electrocatalytic CO₂RR, and we hope that this review will offer helpful guidance for developing electrocatalysts for the CO₂RR.

Toward efficient photocatalysts for light-driven CO2 reduction: TiO2 nanostructures decorated with perovskite quantum dots

Nanostructured TiO2 is often used for photocatalytic CO2 conversion due to its favorable electronic properties and stability, being coupled with large surface area and unique electrical properties. However, pure TiO2, without any expensive cocatalysts, can not provide highly efficient CO2 conversion because its bandgap and resulted limited numbers of photogenerated electrons and holes limit efficient energy conversion. Here, we demonstrate TiO2 nanotube (TNT) photocatalysts equipped with two different perovskite quantum dots (PQDs) made of CH3NH3PbBr3 and CH3NH3PbI3. The fundamental properties of the PQDs and TNT/PQD photocatalysts are investigated and their potential for more efficient CO2 conversion are discussed, to our best knowledge, for the first time. TNT/CH3NH3PbI3 QD photocatalysts absorb a wider range of light energy and show superior charge transport characteristics due to less sensitivity against surface states at TNT/CH3NH3PbI3 QD interface than the TNT/CH3NH3PbBr3 photocatalysts.

Preparation of hydrogen, fluorine and chlorine doped and co-doped titanium dioxide photocatalysts: a theoretical and experimental approach

Titanium dioxide (TiO₂) has a strong photocatalytic activity in the ultra-violet part of the spectrum combined with excellent chemical stability and abundance. However, its photocatalytic efficiency is prohibited by limited absorption within the visible range derived from its wide band gap value and the presence of charge trapping states located at the band edges, which act as electron–hole recombination centers. Herein, we modify the band gap and improve the optical properties of TiO₂ via co-doping with hydrogen and halogen. The present density functional theory (DFT) calculations indicate that hydrogen is incorporated in interstitial sites while fluorine and chlorine can be inserted both as interstitial and oxygen substitutional defects. To investigate the synergy of dopants in TiO₂ experimental characterization techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD), X-ray and ultra-violet photoelectron spectroscopy (XPS/UPS), UV–Vis absorption and scanning electron microscopy (SEM) measurements, have been conducted. The observations suggest that the oxide’s band gap is reduced upon halogen doping, particularly for chlorine, making this material promising for energy harvesting devices. The studies on hydrogen production ability of these materials support the enhanced hydrogen production rates for chlorine doped (Cl:TiO₂) and hydrogenated (H:TiO₂) oxides compared to the pristine TiO₂ reference.

Influence of lattice oxygen on the catalytic activity of blue titania supported Pt catalyst for CO oxidation

The role of oxygen defect sites in the reaction mechanism for CO oxidation using blue TiO₂ with a higher concentration of oxygen vacancies deposited by Pt nanoparticles is investigated.

Visible-light photocatalytic activity enhancement of red phosphorus dispersed on the exfoliated kaolin for pollutant degradation and hydrogen evolution

The semiconductor photocatalyst is crucial for dealing with the current environmental and energy crises. However, the large-scale applications of the reported semiconductor materials are hampered by the recombination of electrons and holes, low kinetic properties, and slow reaction rates. Herein, a three-dimensional structured kaolin/hydrothermally treated red phosphorus (K/HRP) composite photocatalyst was synthesized. The composition ratio was optimized, and the K₇/HRP composites (contained 7%) exhibited the highest photocatalytic activity. The rhodamine B photodegradation rate constant and the hydrogen production rate were 0.25 min^-1 and 252 μmol h^-1 g^-1, which were higher than those of HRP by 12.4 and 7.2 times, respectively. The enhancement of the HRP photocatalytic activity was attributed to the presence of K, which inhibited the overgrowth and the agglomeration of HRP and shortened the carrier migration distance. The electrostatic interaction between the K and the HRP effectively promoted the separation of photogenerated charge carriers. In addition, the three-dimensional structure of the K and the HRP construct enhanced the light absorption and provided a pollution-free and large-area transport interface for carriers. This work has paramount guiding importance in the preparation of high-efficiency, cheap, and recyclable nanocomposite photocatalyst materials.

Defect-engineered transition metal hydroxide nanosheets realizing tumor-microenvironment-responsive multimodal-imaging-guided NIR-II photothermal therapy

Exploiting two-dimensional nanomaterials as photo-based theranostic agents is promising for the highly efficient ablation of deep-tissue-buried tumors. However, they are limited by their poor absorption in the second near-infrared-light (NIR-II) bio-window (1000-1300 nm) and intrinsic nonbiodegradability. Herein, defect-rich sulfur-doped Ni(OH)2 (S-Ni(OH)2) nanosheets decorated with bovine serum albumin (BSA) as a novel theranostic agent is developed, which can accomplish multimodal-imaging-guided photothermal ablation of mouse cancers in the NIR-II bio-window. Sulfur doping extends the absorption spectra of Ni(OH)2 nanosheets from the visible to NIR-II bio-window, affording highly efficient photothermal conversion (58.20% for 1064 nm), entailing it to become an excellent contrast agent for photoacoustic imaging. Further, because of their intrinsic paramagnetic property, they can be applied for magnetic resonance imaging. Owing to the abundant defective sites in S-Ni(OH)2 nanosheets, they exhibit response to the tumor microenvironment, resulting in effective biodegradation and excretion from the body. In vivo toxicity experiments indicated that S-Ni(OH)2-BSA NSs delivered no appreciable toxicity and good biocompatibility. This work provides an avenue for the rational design of effective theranostics agents.

Aza-BODIPY Probe-Decorated Mesoporous Black TiO2 Nanoplatform for the Highly Efficient Synergistic Phototherapy

As an important noninvasive tumor treatment method, phototherapy has drawn extensive research interest. However, the requirements of separate excitation wavelengths, high degree of electron-hole recombination, and low reactive oxygen species (ROS) production capability are still the major barriers. This work reports the construction of a novel nanoplatform: design and synthesis of an aza-BODIPY (AB) probe-decorated mesoporous black titanium dioxide (TiO₂) (MT) nanoparticles (NPs) for enhanced photodynamic therapy and photothermal therapy under single-wavelength near-infrared (NIR) laser irradiation for the first time. AB probe-decorated MT NPs (abbreviated as MTAB) were synthesized through the Al reduction of mesoporous anatase TiO₂ NPs and subsequent adsorption of the AB probe. The mesoporous structure of MT ensured AB loading capacity and avoided the complicated modification and synthesis processes. Heterogeneous MTAB, which possessed staggered energy levels, were assessed for their capability for effective separation of photogenerated electrons and holes for the first time. Upon NIR laser light irradiation, MTAB exhibited sufficient ROS generation, resulting in distinct tumor cell killing and tumor tissue elimination. This unique heterogeneous nanoplatform with staggered energy levels provides a new strategy to enhance ROS generation and improve the therapeutic efficacy.

Semiconductor-to-conductor transition in 2D copper(ii) oxide nanosheets through surface sulfur-functionalization

Functionalization is a widely-used strategy to modulate and optimize the properties of materials towards various applications, including sensing, catalysis, and energy generation. While the influence of sulfur-functionalization of carbon materials and oxides like ZnO and TiO₂ has been studied, far less research has been devoted to analyzing sulfur-functionalization of CuO and other transition metal oxide nanomaterials. Here, we report sulfur-functionalization of copper(ii) oxide nanosheets synthesized by using a soft-templating procedure, with sulfur-addition based on hydrogen sulfide gas as a source. The resulting sulfur-functionalization does not change the overall crystal structure and morphology of the CuO nanosheets, but leads to a decrease in surface hydroxyl groups. Sulfur induces a semiconductor-to-conductor state transition of the CuO nanosheets, which is supported by computational modeling. The metallic transition results from shifting of the Fermi level into the valence band due to formation of Cu-S bonds on the surface of the CuO nanosheets.

Promoting Active Electronic States in LaFeO3 Thin-Films Photocathodes via Alkaline-Earth Metal Substitution

The effects of alkaline-earth metal cation (AMC; Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) substitution on the photoelectrochemical properties of phase-pure LaFeO₃ (LFO) thin-films are elucidated by X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance, and electrochemical impedance spectroscopy (EIS). XRD confirms the formation of single-phase cubic LFO thin films with a rather complex dependence on the nature of the AMC and extent of substitution. Interestingly, subtle trends in lattice constant variations observed in XRD are closely correlated with shifts in the binding energies of Fe 2p_3/2 and O 1s orbitals associated with the perovskite lattice. We establish a scaling factor between these two photoemission peaks, unveiling key correlation between Fe oxidation state and Fe-O covalency. Diffuse reflectance shows that optical transitions are little affected by AMC substitution below 10%, which are dominated by a direct bandgap transition close to 2.72 eV. Differential capacitance data obtained from EIS confirm the p-type characteristic of pristine LFO thin-films, revealing the presence of sub-bandgap electronic state (A-states) close to the valence band edge. The density of A-states is decreased upon AMC substitution, while the overall capacitance increases (increase in dopant level) and the apparent flat-band potential shifts toward more positive potentials. This behavior is consistent with the change in the valence band photoemission edge. In addition, capacitance data of cation-substituted films show the emergence of deeper states centered around 0.6 eV above the valence band edge (B-states). Photoelectrochemical responses toward the hydrogen evolution and oxygen reduction reactions in alkaline solutions show a complex dependence on alkaline-earth metal incorporation, reaching incident-photon-to-current conversion efficiency close to 20% in oxygen saturated solutions. We rationalize the photoresponses of the LFO films in terms of the effect sub-bandgap states on majority carrier mobility, charge transfer, and recombination kinetics.

Rapid Photo-Sonotherapy for Clinical Treatment of Bacterial Infected Bone Implants by Creating Oxygen Deficiency Using Sulfur Doping

Periprosthetic infection is considered the main cause of implant failure, which is expected to be solved by fabricating an antibacterial coating on the surface of the implant. Nevertheless, systemic antibiotic treatment still represents the mainstream method for preventing infection, and few antibacterial coatings are applied clinically. This is because the externally introduced traditional antibacterial coatings suffer from the risk of invalidation and tissue toxicity induced by the consumption of antibacterial agents, degradation, and shedding. In this work, we proposed a rapid photo-sonotherapy by creating an oxygen deficiency on a titanium (Ti) implant through sulfur (S)-doping (Ti-S-TiO_2-x), which endowed the implants with great sonodynamic and photothermal ability. Without introducing an external antibacterial coating, it reached a high antibacterial efficiency of 99.995% against Staphylococcus aureus under 15 min near-infrared light and ultrasound treatments. Furthermore, bone infection was successfully treated after combination treatments, and improved osseointegration was observed. Importantly, the S-doped Ti implant immersed in water for 6 months showed an unchanged structure and properties, suggesting that the Ti implant with intrinsic modification showed stable antibacterial performance under exogenous stimuli with a high antibacterial performance in vivo. This photo-sonotherapy based on sulfur doping is also promising for cancer therapy with biosafety.

A 3D Hierarchical Pancake-Like Porous Carbon Nitride for Highly Enhanced Visible-Light Photocatalytic H2 Evolution

Polymeric carbon nitride is a fascinating visible-light-response metal-free semiconductor photocatalyst in recent decades. Nevertheless, the photocatalytic H2 efficiency is unsatisfactory due to the insufficient visible-light harvesting capacity and low quantum yields caused by the bulky structure seriously limited its applications. To overcome these defects, in this research, a 3D hierarchical pancake-like porous carbon nitride (PPCN) was successfully fabricated by a facile bottom-up method. The as-prepared photocatalyst exhibit enlarged surface area, enriched reactive sites, improved charge carrier transformation and separation efficiency, and expanded bandgap with a more negative conduction band towardan enhanced reduction ability. All these features synergistically enhanced the photocatalytic H2 evolution efficiency of 3% Pt@PPCN (430 µmol g−1 h−1) under the visible light illumination (λ ≥ 420 nm), which was nine-fold higher than that of 3% Pt@bulk C3N4 (BCN) (45 µmol g−1 h−1). The improved structure and enhanced photoelectric properties were systematically investigated by different characterization techniques. This research may provide an insightful synthesis strategy for polymeric carbon nitride with excellent light-harvesting capacity and enhanced separation of charges toward remarkable photocatalytic H2 for water splitting.

In situ growth of porous TiO2 with controllable oxygen vacancies on an atomic scale for highly efficient photocatalytic water splitting

In situ regulation of oxygen vacancies of porous TiO₂ at atomic scale with promoting photocatalytic efficiency.

Promoted spatial charge separation of plasmon Ag and co-catalyst Co x P decorated mesoporous g-C3N4 nanosheet assembly for unexpected solar-driven photocatalytic performance

Plasmon Ag and co-catalyst Co _x P decorated mesoporous graphite carbon nitride nanosheet assemblies have been synthesized via a template-calcination and ball milling strategy combined with photoreduction. The obtained composites are characterized by x-ray diffraction, Fourier transmission infrared spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy. The results show that the sample assembly with mesoporous structure has specific surface area of 50.4 m² g^-1, pore size of 11.3 nm and pore volume of 0.21 cm³ g^-1. The Ag and Co _x P nanoparticles are decorated on the surface of graphite carbon nitride uniformly. Under solar light irradiation, the photocatalytic degradation rate of ceftazidime for the prepared sample assembly is up to ∼92%, and the photocatalytic reaction rate constant is about 10 times higher than that of bare graphite carbon nitride. Moreover, the sample assembly also exhibits a solar-driven photocatalytic hydrogen production rate of 96.66 μmol g^-1 h^-1. It can attributed to the surface plasmon resonance effect of Ag nanoparticles and Co _x P co-catalyst promoting the spatial charge separation and the mesoporous structure providing more surface active sites and favoring mass transfer. This special structure offers new insights for fabricating other high-performance photocatalysts with high spatial charge separation.