Ti3+ Self-Doped Blue TiO2(B) Single-Crystalline Nanorods for Efficient Solar-Driven Photocatalytic Performance

Ultra-fast green synthesis of a defective TiO2 photocatalyst towards hydrogen production

An ultra-fast green synthesis of defective titanium dioxide (TiO2) photocatalysts was conducted by the microwave-assisted method using l-ascorbic acid (l-As) as a reducing agent. Effect of l-As concentrations on the chemical-, optical- and photoelectrochemical properties as well as the photocatalytic performance towards the hydrogen (H2) production was explored. The obtained TiO2 nanoparticles (NPs) illustrated the brown fine powders with different brownness levels depending on the concentrations of l-As. A high l-As concentration provided a high brownness of TiO2 NPs with a high generation of Ti3+ defects and oxygen vacancies (Ov), which can extend the light absorption towards the visible and near-infrared regions, suppress the recombination rate of electron-hole pairs, promote the photocurrent response and minimize the interface charge transfer resistance. An appropriate quantity of generated defects and good porous properties played a crucial role in photocatalytic H2 production. Under fluorescence illumination, the sample synthesized with a TiO2 and l-As weight ratio of 1 : 0.25 (PAs0.25) exhibited the highest H2 production rate (∼162 μmol g-1 h-1 in the presence of 1 wt% Au co-catalyst) with a slight drop (∼8.2%) after the 5th use (15 h). The synthesis method proposed in this work provides a new insight to an ultra-fast synthesis of defective TiO2 NPs using an eco-friendly chemical precursor under non-severe conditions.

Coupling photocatalytic CO2 reduction and CH3OH oxidation for selective dimethoxymethane production

Currently, conventional dimethoxymethane synthesis methods are environmentally unfriendly. Here, we report a photo-redox catalysis system to generate dimethoxymethane using a silver and tungsten co-modified blue titanium dioxide catalyst (Ag.W-BTO) by coupling CO2 reduction and CH3OH oxidation under mild conditions. The Ag.W-BTO structure and its electron and hole transfer are comprehensively investigated by combining advanced characterizations and theoretical studies. Strikingly, Ag.W-BTO achieve a record photocatalytic activity of 5702.49 µmol g-1 with 92.08% dimethoxymethane selectivity in 9 h of ultraviolet-visible irradiation without sacrificial agents. Systematic isotope labeling experiments, in-situ diffuse reflectance infrared Fourier-transform analysis, and theoretical calculations reveal that the Ag and W species respectively catalyze CO2 conversion to *CH2O and CH3OH oxidation to *CH3O. Subsequently, an asymmetric carbon-oxygen coupling process between these two crucial intermediates produces dimethoxymethane. This work presents a CO2 photocatalytic reduction system for multi-carbon production to meet the objectives of sustainable economic development and carbon neutrality.

Efficient electrochemical degradation of ceftazidime by Ti3+ self-doping TiO2 nanotube-based Sb-SnO2 nanoflowers as an intermediate layer on a modified PbO2 electrode

Ceftazidime (CAZ) is an emerging organic pollutant with a long-lasting presence in the environment. Although some PbO2 materials exhibit degradation capabilities, inefficient electron transport in the substrate layer and the problem of electrode stability still limit their use. Here, an interfacial design in which TiO2 nanotube arrays generate Ti3+ self-doping oxide substrate layers and highly active 3D Sb-SnO2 nanoflowers-like interlayers was used to prepare PbO2 anodes for efficient degradation of CAZ. Interestingly, after implementing Ti3+ self-doping in the PbO2 anode base layer and introducing 3D nanoflowers-like structures, the capacity for •OH generation increased significantly. The modified electrode exhibited 5-fold greater •OH generation capacity compared to the unmodified electrode, and a 2.7-fold longer accelerated electrode lifetime. The results indicate that interfacial engineering of the base and intermediate layers of the electrodes can improve the electron transfer efficiency, promote the formation of •OH, and extend the anode lifetime of the activated CAZ system.

Highly stable and durable ZnIn2S4 nanosheets wrapped oxygen deficient blue TiO2(B) catalyst for selective CO2 photoreduction into CO and CH4

Developing new and highly stable efficient photocatalysts is crucial for achieving high performance and selective photocatalytic CO2 conversion. In this paper, we designed a one-dimensional oxygen-deficient blue TiO2(B) (BT) catalyst for improved electron mobility and visible light accessibility. In addition, hexagonal ZnIn2S4 (ZIS) nanosheets with a low bandgap and great visible light accessibility are employed to produce effective heterostructures with BT. The synthesized materials are tested for photocatalytic conversion of CO2 into solar fuels (H2, CO and CH4). The optimized composite yields 71.6 and 10.3 μmol g-1h-1 of CO and CH4, three and ten times greater than ZIS, respectively. When ZIS nanosheets are combined with a one-dimensional oxygen-deficient BT catalyst, improved electron mobility and visible light accessibility are achieved, charge carriers are effectively segregated, and the transfer process is accelerated, resulting in efficient CO2 reduction. The photocatalytic CO2 conversion activity of the constructed BT/ZIS heterostructures is very stable over a 10-day (240-hour) period, and CO and CH4 production rates increase linearly with time; however, as time goes on, the rates of H2 production decrease. Further, a five-time recycling test confirmed this, revealing essentially equal activity and selectivity throughout the experiment. As a result, CO2 to CO and CH4 conversion has high selectivity and longer durability. The band structure of the BT/ZIS composite is determined using Mott-Schottky measurement, diffuse reflectance spectroscopy, and valence band X-ray photoelectron spectroscopy. This research demonstrates a novel approach to investigating effective, stable, and selective photocatalytic CO2 reduction systems for solar-to-chemical energy conversion.

Microwave Synthesis of Pt Clusters on Black TiO2 with Abundant Oxygen Vacancies for Efficient Acidic Electrocatalytic Hydrogen Evolution

Oxygen vacancies-enriched black TiO₂ is one promising support for enhancing hydrogen evolution reaction (HER). Herein, oxygen vacancies enriched black TiO₂ supported sub-nanometer Pt clusters (Pt/TiO₂ -O_V ) with metal support interactions is designed through solvent-free microwave and following low-temperature electroless approach for the first time. High-temperature and strong reductants are not required and then can avoid the aggregation of decorated Pt species. Experimental and theoretical calculation verify that the created oxygen vacancies and Pt clusters exhibit synergistic effects for optimizing the reaction kinetics. Based on it, Pt/TiO₂ -O_V presents remarkable electrocatalytic performance with 18 mV to achieve 10 mA cm^-2 coupled with small Tafel slope of 12 mV dec^-1 . This work provides quick synthetic strategy for preparing black titanium dioxide based nanomaterials.

A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO₂ nanomaterials in the presence of H₂O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO₂ nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO₂ catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO₂ photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO₂ nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO₂ are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given.

Heterophase Polymorph of TiO2 (Anatase, Rutile, Brookite, TiO2 (B)) for Efficient Photocatalyst: Fabrication and Activity

TiO₂ exists naturally in three crystalline forms: Anatase, rutile, brookite, and TiO₂ (B). These polymorphs exhibit different properties and consequently different photocatalytic performances. This paper aims to clarify the differences between titanium dioxide polymorphs, and the differences in homophase, biphase, and triphase properties in various photocatalytic applications. However, homophase TiO₂ has various disadvantages such as high recombination rates and low adsorption capacity. Meanwhile, TiO₂ heterophase can effectively stimulate electron transfer from one phase to another causing superior photocatalytic performance. Various studies have reported the biphase of polymorph TiO₂ such as anatase/rutile, anatase/brookite, rutile/brookite, and anatase/TiO₂ (B). In addition, this paper also presents the triphase of the TiO₂ polymorph. This review is mainly focused on information regarding the heterophase of the TiO₂ polymorph, fabrication of heterophase synthesis, and its application as a photocatalyst.

Synthesis of Porous Hollow Spheres Co@TiO2-x-Carbon Composites for Highly Efficient Lithium-Ion Batteries

The hollow TiO₂ anode material has received great attention for next-generation LIBs because of its excellent stability, environmental friendly, and low volume change during lithiation/delithiation. However, there are some problems associated with the current anatase TiO₂ anode materials in practical application owing to low lithium-ion diffusivity and poor reversible theoretical capacities. The introduction of defects has been turned out to be a significant and effective method to improve electronic conductivity, especially oxygen vacancies. In this paper, a facile hydrothermal reaction and subsequent chemical vapor deposition method were successfully used to fabricate Co@TiO_2-x-carbon hollow nanospheres. These results suggest that the synthesized product exhibits good rate performance and superior cycling stability.

TiO2 nanoflower photocatalysts: Synthesis, modifications and applications in wastewater treatment for removal of emerging organic pollutants

Titanium dioxide (TiO₂) has been considered as one of the most promising photocatalysts nanomaterials and is being used in a variety of fields of energy and environment under sunlight irradiation via photocatalysis. Highly efficient photocatalytic materials require the design of the proper structure with excellent morphology, interfacial structures, optical and surface properties, etc. Which are the key points to realize effective light-harvesting for photocatalytic applications. Hierarchical TiO₂ based nanoflower structures (i.e., 3D nanostructures) possess such characteristics and have attracted much attention in recent years. The uniqueness of TiO₂ nanoflowers (NFs) with a coarse texture and arranged structures demonstrates higher photocatalytic activity. This review deals with the hydrothermal synthesis of 3D TiO₂ NFs and effect of shape/size as well as various key synthesis parameters to improve their optoelectronic and photocatalytic properties. Furthermore, to improve their photocatalytic properties, various strategies such as doping engineering and heterojunction/nanocomposite formation with other functional nanomaterials have been discussed followed by their potential applications in photocatalytic degradation of various emerging pollutants discharged into the wastewater from various sources. Importance of such 3D nanoarchitecutres and future research in other fields of current interest in environments are discussed.

N-Rich Doped Anatase TiO2 with Smart Defect Engineering as Efficient Photocatalysts for Acetaldehyde Degradation

Nitrogen (N) doping is an effective strategy for improving the solar-driven photocatalytic performance of anatase TiO2, but controllable methods for nitrogen-rich doping and associated defect engineering are highly desired. In this work, N-rich doped anatase TiO2 nanoparticles (4.2 at%) were successfully prepared via high-temperature nitridation based on thermally stable H3PO4-modified TiO2. Subsequently, the associated deep-energy-level defects such as oxygen vacancies and Ti3+ were successfully healed by smart photo-Fenton oxidation treatment. Under visible-light irradiation, the healed N-doped TiO2 exhibited a ~2-times higher activity of gas-phase acetaldehyde degradation than the non-treated one and even better than standard P25 TiO2 under UV-visible-light irradiation. The exceptional performance is attributed to the extended spectral response range from N-rich doping, the enhanced charge separation from hole capturing by N-doped species, and the healed defect levels with the proper thermodynamic ability for facilitating O2 reduction, depending on the results of ∙O2− radicals and defect measurement by electron spin resonance, X-ray photoelectron spectroscopy, atmosphere-controlled surface photovoltage spectra, etc. This work provides an easy and efficient strategy for the preparation of high-performance solar-driven TiO2 photocatalysts.

Gradient Titanium Oxide Nanowire Film: a Multifunctional Solar Energy Utilization Platform for High-Salinity Organic Sewage Treatment

The treatment of high salt organic sewage is considered to be a high energy consumption process, and it is difficult to degrade organic matter and separate salt and water simultaneously. In this study, a gradient structure titanium oxide nanowire film is developed, which can realize the thorough treatment of sewage under sunlight. Among the film, part TiO_2-x has enhanced photocatalytic properties and can completely degrade 0.02 g·L^-1 methylene blue in 90 min under 2 sun. Part Ti_nO_2n-1 has excellent photothermal conversion efficiency and can achieve 1.833 kg·m^-2·h^-1 water evaporation rate at 1 sun. Through the special structure design, salt positioning crystallization can be realized to ensure the film's stable operation for a long time. The gradient hydrophilicity of the film ensures adequate and rapid water transfer, while the water flow can induce a significant hydrovoltaic effect. The measured V_OC is positively correlated with light intensity and photothermal area and corresponds to the water evaporation rate.

One-Pot Synthesis of TiO2/Hectorite Composite and Its Photocatalytic Degradation of Methylene Blue

TiO2/hectorite composite photocatalysts with different molar ratios of lithium, magnesium, and silicon were synthesized by a one-pot hydrothermal method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherms, and ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS). When the molar ratio of lithium, magnesium, and silicon was 1.32:5.34:8 (TH-2), the composite showed the highest UV photocatalytic degradation of methylene blue (MB). The apparent rate constant of TH-2 was 0.04361 min−1, which was about 3.12 times that of EVONIK Degussa commercial TiO2 of AEROXIDE P25. The improvement of photocatalytic efficiency of the composite was mainly due to its high specific surface area, light trapping ability, and effective separation of electrons (e−) and holes (h+). At the same time, the F element of hectorite is beneficial to the formation of Ti3+ in TiO2, thus enhancing the photocatalytic activity. After five cycles, the removal rate of MB with TH-2 still reached 87.9%, indicating its excellent reusability.

TiO2/g-C3N4 photocatalyst for the purification of potassium butyl xanthate in mineral processing wastewater

In the present work, TiO₂-graphite-phase-carbon-nitride (TiO₂/g-C₃N₄) was prepared through a hydrothermal method to obtain a new photocatalytic material. This material was characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Solid-state UV-Vis diffuse reflectance spectrometry (UV-Vis-DRS) and electron paramagnetic resonance (EPR). The synthesized TiO₂/g-C₃N₄ exhibited homogeneous morphology, in which TiO₂ nanoparticles were uniformly distributed on the g-C₃N₄ nanosheets. Regarding its potential use as photocatalytic material in the treatment of mineral processing wastewater, 18% TiO₂/g-C₃N₄ showed superior photodegradation performance than TiO₂ and g-C₃N₄, to give 97.1% degradation rate under 100 min of simulated light irradiation. The experimental results showed that the successful incorporation of TiO₂ on g-C₃N₄ nanosheets enhanced the spectral response range of TiO₂/g-C₃N₄, and the photocatalytic activity was improved. In view of that, it can be considered that this kind of photocatalytic material has a good prospect in the treatment of mineral processing wastewater, which would have clearly environmental relevance.

Plasma Cu-decorated TiO2-x/CoP particle-level hierarchical heterojunctions with enhanced photocatalytic-photothermal performance

Plasma Cu-decorated TiO_2-x/CoP particle-level hierarchical heterojunction photocatalysts with surface engineering were fabricated through solvothermal and solid phase reduction strategies. The CoP nanoparticles not only serve as a cost-effective cocatalyst but also provide abundant surface active sites, which facilitate rapid transfer of photogenerated carriers. The Ti³⁺ and oxygen vacancy defects extend photoresponse from UV to visible light region, and enhance the separation efficiency of photogenerated carriers efficiently. Because of surface plasma resonance (SPR) of Cu, Cu/TiO_2-x/CoP with average particle size of 100-200 nm has significant photothermal effect, in which the temperature of Cu/TiO_2-x/CoP is increased by 76 °C with irradiation for 30 s, ~ 8 times higher than that of the original TiO₂. Cu/TiO_2-x/CoP exhibits a high photocatalytic degradation rates for highly toxic 2,4-dichlorophenol (99.2%) and 2,4,6-trichlorophenol (98.5%), which higher 7.6 and 8.9 times than the initial TiO₂, respectively. Thanks to the particle-level hierarchical heterojunction, the efficient surface engineering and SPR effect favoring the spatial charge separation, Cu/TiO_2-x/CoP shows excellent photocatalytic-photothermal Performance. This particle-level hierarchical heterojunction architectural design provides a new insight for synthesizing particulate photocatalysts with high-efficiency.

Selective growth of Ti3+/TiO2/CNT and Ti3+/TiO2/C nanocomposite for enhanced visible-light utilization to degrade organic pollutants by lowering TiO2-bandgap

A convenient route was developed for the selective preparation of two stable nanocomposites, Ti³⁺/TiO₂/CNT (labeled as TTOC-1 and TTOC-3) and Ti³⁺/TiO₂/carbon layer (labeled as TTOC-2), from the same precursor by varying the amount of single-walled carbon nanotubes used in the synthesis. TiO₂ is an effective photocatalyst; however, its wide bandgap limits its usefulness to the UV region. As a solution to this problem, our prepared nanocomposites exhibit a small bandgap and wide visible-light (VL) absorption because of the introduction of carbonaceous species and Ti³⁺ vacancies. The photocatalytic efficiency of the nanocomposites was examined via the degradation of methylene blue dye under VL. Excellent photocatalytic activity of 83%, 98%, and 93% was observed for TTOC-1, TTOC-2, and TTOC-3 nanocomposites within 25 min. In addition, the photocatalytic degradation efficiency of TTOC-2 toward methyl orange, phenol, rhodamine B, and congo red was 28%, 69%, 71%, and 91%, respectively, under similar experimental conditions after 25 min. Higher reusability and structural integrity of the as-synthesized photocatalyst were confirmed within five consecutive runs by photocatalytic test and X-ray diffraction analysis, respectively. The resulting nanocomposites provide new insights into the development of VL-active and stable photocatalysts with high efficiencies.

Oxygen vacancy-mediated sandwich-structural TiO2-x /ultrathin g-C3N4/TiO2-x direct Z-scheme heterojunction visible-light-driven photocatalyst for efficient removal of high toxic tetracycline antibiotics

A surface defect sandwich-structural TiO_2-x/ultrathin g-C₃N₄/TiO_2-x direct Z-scheme heterojunction photocatalyst is successfully constructed. The results manifest the existence of oxygen vacancies, sandwich structure and direct Z-scheme heterojunction. Noticeably, TiO_2-x/ultrathin g-C₃N₄/TiO_2-x efficiently eliminates high toxic tetracycline hydrochloride by means of·O₂^-, h⁺ and·OH, whose removal rate is 87.7% during 90 min and the pseudo-first-order rate constant reaches up to 31.7 min^-1 × 10^-3. The extraordinary performance can be attributed to the special 3D structure, Z-scheme heterojunction expediting charge transfer and promoting the generation of active species, meanwhile the oxygen vacancies enhancing the spatial separation of photo-induced carriers. Moreover, various environmental factors are systematically explored by statistics. SO₄^2-, NH₃-N and pH exhibit an obvious impact on removal rate. Meanwhile, TiO_2-x/ultrathin g-C₃N₄/TiO_2-x could also effectually remove tetracycline hydrochloride from complex actual-wastewater and exhibit high stability. Besides, the photocatalytic mechanism and degradation path of tetracycline hydrochloride are also elucidated.

Preparation, Characterization, and Photocatalytic Properties of Self-Standing Pure and Cu-Doped TiO2 Nanobelt Membranes

A traditional hydrothermal method was modified to synthesize ultra-long sodium titanate nanobelts by simultaneously stirring the solution. The ultra-long sodium titanate nanobelts were converted to hydrogen titanate nanobelts through an ion exchanging way. A method was then used to prepare self-standing flexible large-area membranes; they were then subject to post-annealing at different temperatures to obtain a self-standing TiO2 nanobelt membrane with a slight decrease in flexibility. Cu-doped TiO2 membranes were prepared by ion exchanging and post-annealing in the same manner. X-ray diffractions, scanning electron microscopy, field-emission scanning electron microscopy, field-emission transmission electron microscopy, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and UV-vis spectroscopy were used to characterize the samples. Photodegradation of methylene blue (MB) water solutions was used to evaluate the photocatalytic activity. It was seen that the pure sample presented obvious visible-light responding photocatalytic activity, possibly due to the self-sensitization of the MB molecule. The UV-induced photocatalytic activity is higher because of the photoinduced holes and electrons. It was suggested that the Cu dopant induced intra-gap states from electron traps and recombination centers, resulting in the decrease in both of the visible and UV induced photocatalysis.

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

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

Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis

Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO2-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti3+-self-doped TiO2 (Ti3+–TiO2) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti3+–TiO2 photocatalysts, where Ti3+ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti3+–TiO2 by improving their photocatalytic activity. Ti3+–TiO2 photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention.

Enhanced Hydrogen Production from Ethanol Photoreforming by Site-Specific Deposition of Au on Cu2O/TiO2 p-n Junction

Hydrogen production by photoreforming of biomass-derived ethanol is a renewable way of obtaining clean fuel. We developed a site-specific deposition strategy to construct supported Au catalysts by rationally constructing Ti3+ defects inTiO2 nanorods and Cu2O-TiO2 p-n junction across the interface of two components. The Au nanoparticles (~2.5 nm) were selectively anchored onto either TiO2 nanorods (Au@TiO2/Cu2O) or Cu2O nanocubes (Au@Cu2O/TiO2) or both TiO2 and Cu2O (Au@TiO2/Cu2O@Au) with the same Au loading. The electronic structure of supported Au species was changed by forming Au@TiO2 interface due to the adjacent Ti3+ defects and the associated oxygen vacancies while unchanged in Au@Cu2O/TiO2 catalyst. The p-n junction of TiO2/Cu2O promoted charge separation and transfer across the junction. During ethanol photoreforming, Au@TiO2/Cu2O catalyst possessing both the Au@TiO2 interface and the p-n junction showed the highest H2 production rate of 8548 μmol gcat−1 h−1 under simulated solar light, apparently superior to both Au@TiO2 and Au@Cu2O/TiO2 catalyst. The acetaldehyde was produced in liquid phase at an almost stoichiometric rate, and C−C cleavage of ethanol molecules to form CH4 or CO2 was greatly inhibited. Extensive spectroscopic results support the claim that Au adjacent to surface Ti3+ defects could be active sites for H2 production and p-n junction of TiO2/Cu2O facilitates photo-generated charge transfer and further dehydrogenation of ethanol to acetaldehyde during the photoreforming.

Liquid-Plasma Hydrogenated Synthesis of Gray Titania with Engineered Surface Defects and Superior Photocatalytic Activity

Defect engineering in photocatalysts recently exhibits promising performances in solar-energy-driven reactions. However, defect engineering techniques developed so far rely on complicated synthesis processes and harsh experimental conditions, which seriously hinder its practical applications. In this work, we demonstrated a facile mass-production approach to synthesize gray titania with engineered surface defects. This technique just requires a simple liquid-plasma treatment under low temperature and atmospheric pressure. The in situ generation of hydrogen atoms caused by liquid plasma is responsible for hydrogenation of TiO₂. Electron paramagnetic resonance (EPR) measurements confirm the existence of surface oxygen vacancies and Ti³⁺ species in gray TiO_2−x. Both kinds of defects concentrations are well controllable and increase with the output plasma power. UV–Vis diffused reflectance spectra show that the bandgap of gray TiO_2−x is 2.9 eV. Due to its extended visible-light absorption and engineered surface defects, gray TiO_2−x exhibits superior visible-light photoactivity. Rhodamine B was used to evaluate the visible-light photodegradation performance, which shows that the removal rate constant of gray TiO_2−x reaches 0.126 min⁻¹ and is 6.5 times of P25 TiO₂. The surface defects produced by liquid-plasma hydrogenation are proved stable in air and water and could be a candidate hydrogenation strategy for other photocatalysts.

Facile and Large-scale Synthesis of Defective Black TiO2−x(B) Nanosheets for Efficient Visible-light-driven Photocatalytic Hydrogen Evolution

In the work, we firstly report the facile and large-scale synthesis of defective black TiO2−x(B) nanosheets via a dual-zone NaBH4 reduction method. The structure, physico-chemical, and optical properties of TiO2−x(B) nanosheets were systematically characterized by powder X-ray diffraction, Raman spectroscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy, etc. The concentration of Ti3+ can be well tuned by NaBH4 reduction. With increasing the mass ratio of NaBH4 to TiO2(B), the generation of Ti3+ defects gives rise to the increased intensity of a broad band absorption in the visible wavelength range. It is demonstrated that the TiO2−x(B) photocatalyst synthesized with the mass ratio of NaBH4 to TiO2(B) of 3:1 exhibited an optimum photocatalytic activity and excellent photostability for hydrogen evolution under visible-light irradiation. By combining the advantages of 2D TiO2(B) nanosheets architecture with those of Ti3+ self-doping and simultaneous production of oxygen vacancy sites, the enhanced photocatalytic performance of the defective TiO2−x(B) nanosheets was achieved.

The TiO2 (B) nano-belts with excellent performance prepared via alkaline stirring hydrothermal method and its application to remove 17α-ethynylestradiol

In this work, TiO₂ (B) nano-belts were synthesized by hydrothermal method under stirring, and static conditions and preparation conditions were optimized. The prepared materials were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), photoluminescence spectroscopy (PL), and N₂ adsorption/desorption measurement. The photocatalytic performance was evaluated by removing synthetic estrogen 17α-ethynylestradiol (EE2), which is the most potent endocrine-disrupting chemical. The results show that the TiO₂ nano-belt possesses pure metastable monoclinic TiO₂ (B) and has uniform nano-belt shape with 80~120-nm diameters and 62.904 m² g^-1 of specific surface area. Under the best optimal preparation conditions (0.5 g P25, 20 mL 10 mol L^-1 NaOH, hydrothermal temperature 180 °C for 18 h under stirring, 400 °C calcination for 2 h), the TiO₂ (B) has better catalytic activity with 100.00% removal rate towards 3 mg L^-1 EE2 in 120 min. The removal rates of EE2 over catalyst which was prepared under static condition and P25 are 74.66% and 70.71%, respectively. The photocatalytic degradation rate constant of TiO₂ (B) prepared under stirring condition (0.0379 min^-1) is 4.51 times and 8.42 times than those of TiO₂ prepared under static condition (0.0084 min^-1) and P25 (0.0045 min^-1). The excellent photocatalytic activity is mainly ascribed to longer one-dimensional nano-belt structure and effective suppression of photo-produced electron-hole.

Surface-defect-rich mesoporous NH2-MIL-125 (Ti)@Bi2MoO6 core-shell heterojunction with improved charge separation and enhanced visible-light-driven photocatalytic performance

Mesoporous NH₂-MIL-125(Ti)@Bi₂MoO₆ core-shell heterojunctions with surface defects were fabricated through a facile solvothermal method. The mesoporous core-shell structure with a large relative surface area of 87.7 m² g^-1 and narrow pore size of 8.2 nm extends the photoresponse to the range of visible light due to the narrow band gap of ∼1.89 eV. The visible-light-driven photocatalytic degradation efficiency of highly toxic dichlorophen and trichlorophenol were 93.28 and 92.19%, respectively, and the corresponding rate constants were approximately 8 and 17 times higher than the rates achieved by pristine NH₂-MIL-125(Ti). The photocatalytic oxygen production rate was increased to 171.3 µmol g^-1. Recycling for several cycles indicates high stability, which is favorable for practical applications. The excellent photocatalytic performance can be ascribed to the formation of the core-shell heterojunctions and to the surface defects that favor charge separation and visible light absorption; the mesoporous structure offers an adequate number of surface active sites and mass transfer. This novel mesoporous core-shell photocatalyst will have potential applications in the environment, and this strategy offers a new insight into fabrication of other high-performance core-shell structure photocatalysts.

Synergistic effect of surface plasmon resonance, Ti3+ and oxygen vacancy defects on Ag/MoS2/TiO2-x ternary heterojunctions with enhancing photothermal catalysis for low-temperature wastewater degradation

Ag/MoS₂/TiO_2-x ternary heterojunctions are fabricated through hydrothermal and photo-deposition process combine with in-situ solid-state chemical reduction approach. The prepared materials are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, and X-ray photoelectron spectroscopy. The results show that the ternary heterojunctions doped with Ti³⁺ are formed, meanwhile, Ag nanoparticle and MoS₂ nanosheets are anchored on surface of TiO₂ nanobelts simultaneously. The photocatalytic degradation ratio of Bisphenol A in low temperature water and hydrogen production rate for Ag/MoS₂/TiO_2-x are up to 96.7% and ∼1.98 mmol h^-1 g^-1, respectively, which are several times higher than that of pristine TiO₂. Furthermore, the photothermal performance of Ag/MoS₂/TiO_2-x is also unexpected. The excellent photocatalytic activity and photothermal performance can be ascribed to the synergistic effect of the formation of heterojunctions, Ti³⁺ and surface oxygen vacancies defects and surface plasmon resonance of Ag nanoparticles, which extend the photoresponse to visible-infrared light region and favor the spatial separation of photogenerated charge carriers.

Oxygen-Deficient Dumbbell-Shaped Anatase TiO2-x Mesocrystals with Nearly 100 % Exposed {101} Facets: Synthesis, Growth Mechanism, and Photocatalytic Performance

The development of hierarchical TiO₂ superstructures with new morphologies and intriguing photoelectric properties for utilizing solar energy is known to be an effective approach to alleviate the serious problems of environmental pollution. Herein, unique oxygen-deficient dumbbell-shaped anatase TiO_2-x mesocrystals (DTMCs) enclosed by nearly 100 % {101} facets were readily synthesized by mesoscale transformation in TiCl₃ /acetic acid (HAc) mixed solution, followed by calcination under vacuum. These mesocrystals exhibited much higher photoreactivity toward removing the model pollutants methyl orange and Cr^VI than truncated tetragonal bipyramidal anatase nanocrystals (TNCs), anatase mesocrystals built from truncated tetragonal bipyramidal anatase nanocrystals (TTMCs), and anatase mesocrystals constructed by anatase nanocrystals with nearly 100 % exposed {101} facets (TMCs), revealing that both the oxidation and reduction abilities of anatase TiO₂ were simultaneously enhanced upon fabricating an oxygen-deficient mesocrystalline architecture with about 100 % exposed {101} facets. Further characterization illustrated that such an enhancement of photoreactivity was mainly due to the strengthened light absorption, boosted charge carrier separation, and nearly 100 % exposed {101} facets of the oxygen-deficient dumbbell-shaped anatase mesocrystals. This work will be useful for guiding the synthesis of oxygen-deficient ordered superstructures of metal oxides with desired morphologies and exposed facets for promising applications in environmental remediation.

Hollowsphere Nanoheterojunction of g-C3N4@TiO2 with High Visible Light Photocatalytic Property

In this work, g-C₃N₄@TiO₂ nanostructures with hollow sphere morphology, small grain size, high crystalline quality, and high surface area are successfully synthesized by the annealing method using melamine and hollowsphere precursor, which could be a universal method to synthesis hollow sphere nanoheterojunction. Excellent photocatalytic property was observed from the as-prepared g-C₃N₄@TiO₂ nanostructure with 466.43 μmol·g^-1·h^-1 hydrogen generation rate under visible light irradiation (>420 nm), which was 5.5 times as much as the control couple, nanoparticle nanoheterojunction g-C₃N₄@TiO₂. No apparent deactivation was found during the follow-up cycle performance test. The special morphology and the heterojunction construction contribute to both visible light absorption and photogenerated electron-hole pair separation efficiency and finally to the photocatalytic property. The content of g-C₃N₄ was proved to be an important parameter for the promotion of the photocatalytic property. Overlarge content may lead to lower photogenerated electron-hole pair separation efficiency.

Controllable Synthesis of Inverse Opal TiO2-x Photonic Crystals and Their Photoelectric Properties

In this study, inverse opal TiO_2-x photonic crystals (IO-TiO_2-x ) have been successfully synthesized by a two-step calcination. The whole synthesis is safe and feasible. Additionly, the reduction degree and the structure of IO-TiO_2-x can be precisely controlled. A series of IO-TiO_2-x samples with different reduction degree were prepared and characterized. The TEM images show that the obtained samples possess a 3D-ordered macroporous inverse opal structure. The reduced Ti atoms/oxygen vacancies were confirmed by Raman and XPS spectroscopy. All IO-TiO_2-x samples showed better photoelectric properties than those of common TiO₂ which indicates their great potential to be applied to photoelectric fields. The improvement of photoelectric properties is attributed to the efficient electron-hole separation efficiency induced by moderately reduced Ti atoms/oxygen vacancies. Meanwhile, the 3D-ordered macroporous inverse opal structure and the band gap are regulated to "capture" more solar energy. This new approach is proven to be a meaningful method to synthesize high-performance TiO₂ materials.

TiO2 Films Functionalized with ABDA for Enhanced Photoelectrochemical Performance

Efficient photogenerated charge separation is needed for potential solar energy conversion and storage. Herein, we present the preparation and characterization of an optically active anthracence-based molecule 4,4′-(anthracene-2,6-diylbis(azanediyl))bis(4-oxobutanoic acid) (ABDA), whose coupling with TiO2 has been proven useful in the pursuit of enhanced photoelectrochemical (PEC) performance. Ultraviolet-visible absorption spectroscopy and PEC measurements indicated that the ABDA/TiO2 composite has extended the light absorption of TiO2 to the visible region and efficiently increased the charge separation. The photocurrent of ABDA/TiO2 is 1.8 times higher than that of pristine TiO2. This study has provided a method for the development of functionalized TiO2 with enhanced PEC behaviour for energy conversion applications.

Mesoporous hollow black TiO2 with controlled lattice disorder degrees for highly efficient visible-light-driven photocatalysis

Black TiO₂ has received tremendous attention because of its lattice disorder-induced reduction in the TiO₂ bandgap, which yields excellent light absorption and photocatalytic ability. In this report, a highly efficient visible-light-driven black TiO₂ photocatalyst was synthesized with a mesoporous hollow shell structure. It provided a higher specific surface area, more reaction sites and enhanced visible light absorption capability, which significantly promoted the photocatalytic reaction. Subsequently, the mesoporous hollow black TiO₂ with different lattice disorder-engineering degrees were designed. The structure disorder in the black TiO₂ obviously increased with reduction temperature, leading to improved visible light absorption. However, their visible-light-driven photocatalytic efficiency increased first and then decreased. The highest value can be observed for the sample reduced at 350 °C, which was 2-, 1.4- and 5-fold that of the samples reduced at 320 °C, 380 °C and 400 °C, respectively. This contradiction can be ascribed to the varied functions of the surface defects with different concentrations in the black TiO₂ during the catalytic process. In particular, the defects at low concentrations boost photocatalysis but reverse photocatalysis at high concentrations when they act as charge recombination centers. This study provides significant insight for the fabrication of high-efficiency visible-light-driven catalytic black TiO₂ and the understanding of its catalysis mechanism.

Our work provides significant insights into the design of hollow black TiO₂ spheres and the mechanism accounting for their high-efficient visible-light-driven catalysis.

Facile preparation of Ti3+ self-doped TiO2 nanoparticles and their dramatic visible photocatalytic activity for the fast treatment of highly concentrated Cr(vi) effluent

An efficient visible photocatalyst which is suitable for the rapid removal of highly concentrated Cr(vi) for environmental therapy.

FeOCl/Ln (Ln = La or Y): efficient photo-Fenton catalysts for ibuprofen degradation

Doping of rare earth elements (La and Y) in FeOCl boosted the Fenton catalytic activity under sunlight.

Low temperature solution synthesis of reduced two dimensional Ti3C2 MXenes with paramagnetic behaviour

MXenes - two dimensional, 2D, early transition metal, M, carbides and nitrides, X - are the latest addition to the 2D materials' world. Herein, we report on a facile low temperature solution chemical synthesis method to reduce Ti₃C₂T_x multilayered, ML, MXenes. Using X-ray photoelectron spectroscopy, electron spin resonance, magnetization measurements and other techniques, we concluded that immersing Ti₃C₂T_x MLs in the reducing agent Li-ethylenediamine (Li-EDA) - held at temperatures varying from room to 120 °C - reduces the 2D layers creating Ti³⁺ ions and oxygen vacancies. Above a temperature (T) of ≈10 K, the magnetic susceptibilities, χ, are temperature independent, implying that the resulting powders are Pauli paramagnetic. The loss of the magnetic signal upon intercalation of Li⁺ or EDA, together with a Curie-like increase in χ at T < 10 K, is consistent with that of a disordered metal that is close to a metallic to insulator transition and proves that the magnetism is associated with the 2D flakes. This result is the first evidence of any magnetism of any MXene.

Enhanced Photoelectrochemical Properties of Ti3+ Self-Doped Branched TiO₂ Nanorod Arrays with Visible Light Absorption

A novel Ti³⁺ self-doped branched rutile TiO₂ nanorod arrays (NRAs) was successfully grown on an F-doped tin oxide (FTO) transparent conductive glass by a combined hydrothermal and magnetron sputtering method. Surface morphology, structure, optical properties, and photoelectrochemical behavior of the branched TiO₂ NRAs are determined. Using TiO₂ nanoparticles (NPs) deposited on the top of the nanorods as seeds, TiO₂ nanobranches can easily grow on the top of the nanorods. Moreover, the Ti³⁺ defects in the TiO₂ NPs and associated oxygen vacancies, and the nanobranches expend the optical absorption edge of the TiO₂ NRAs from 400 nm to 510 nm. Branched TiO₂ NRAs exhibit excellent photoelectrochemical properties compared to the pure TiO₂ NRAs, as revealed by photoelectrochemical measurements. This enhanced photoelectrochemical properties is induced by the increased surface area and expanded optical absorption range. Due to their favorable characteristics, these novel branched TiO₂ NRAs will provide a new path to the fabrication of hierarchical nanostructured materials.