Black N/H-TiO2 Nanoplates with a Flower-Like Hierarchical Architecture for Photocatalytic Hydrogen Evolution

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Atomic Layer Deposition of Defective Amorphous TiOx Thin Films with Improved Photoelectrochemical Performance

A proper control of defects in TiO2 thin films is challenging work for enhancing the photoelectrochemical (PEC) efficiency in water splitting processes. Additionally, a deep understanding of how defects affect the PEC performance of TiO2 thin films is of great interest for achieving better performance. With these aims, we prepared defective amorphous TiOx thin films at various growth temperatures by atomic layer deposition using tetrakis(dimethylamido)titanium as the Ti precursor. Careful X-ray photoelectron spectroscopy and electron spin resonance spectroscopy analyses revealed that the defect concentration in the TiOx thin films can be controlled by adjusting the growth temperature during the ALD process. We also evaluated the light absorption properties of the deposited TiOx thin films using ultraviolet-visible absorption spectroscopy. And it was found that the TiOx thin film deposited at a growth temperature of 200 °C exhibited the highest defect concentration and the highest photocurrent density of 0.051 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) compared to those of the other films. The light absorption efficiency, photogenerated charge separation efficiency, and charge transfer efficiency of defective amorphous TiOx thin films were carefully studied to understand the correlation between the defect concentration in the prepared TiOx thin film and its PEC activity. This study provides insight into the PEC properties of defective amorphous ALD-TiOx thin films.

Structural Distortion of g-C3N4 Induced by N-Defects for Enhanced Photocatalytic Hydrogen Evolution

Hydrogen evolution by photocatalytic technology has been one of the most promising and attractive solutions, and can harvest and convert the abundant solar energy into green, renewable hydrogen energy. As a new kind of photocatalytic material, graphitic carbon nitride (g-C3N4) has drawn much attention in photocataluytic H2 production due to its visible light response, ease of preparation and good stability. For a higher photocatalyic performance, N defects were introduced in to the traditional g-C3N4 in this work. The existence of N defects was proved by adequate material characterization. Significantly, a new absorption region at around 500 nm of N-deficient g-C3N4 appeared, revealing the exciting n-π* transition of lone pair electrons. The photocatalytic H2 production performance of N-deficient g-C3N4 was increased by 5.8 times. The enhanced photocatalytic performance of N-deficient g-C3N4 was attributed to the enhanced visible light absorption, as well as the promoted separation of photo-generated carries and increased specific surface area.

A review on TiO2-x-based materials for photocatalytic CO2 reduction

Photocatalytic CO₂ reduction technology has a broad potential for dealing with the issues of energy shortage and global warming. As a widely studied material used in the photocatalytic process, titanium dioxide (TiO₂) has been continuously modified and tailored for more desirable application. Recently, the defective/reduced titanium dioxide (TiO_2-x) catalyst has attracted broad attention due to its excellent photocatalytic performance for CO₂ reduction. In this perspective review, we comprehensively present the recent progress in TiO_2-x-based materials for photocatalytic CO₂ reduction. In detail, the review starts with the fundamentals of CO₂ photocatalytic reduction. Then, the synthesis of a defective TiO₂ structure is introduced for the regulation of its photocatalytic performance, especially its optical properties and dissociative adsorption properties. In addition, the current application of TiO_2-x-based photocatalysts for CO₂ reduction is also highlighted, such as metal-TiO_2-x, oxide-TiO_2-x and TiO_2-x-carbon-based photocatalysts. Finally, the existing challenges and possible scope of photocatalytic CO₂ reduction over TiO_2-x-based materials are discussed. We hope that this review can provide an effective reference for the development of more efficient and reasonable photocatalysts based on TiO_2-x.

Oxygen Vacancy-Induced Construction of CoO/h-TiO2 Z-Scheme Heterostructures for Enhanced Photocatalytic Hydrogen Evolution

Environmentally friendly catalysts with excellent performance and low cost are critical for photocatalysis. Herein, using hydrogenated TiO₂ (h-TiO₂) nanosheets with enriched oxygen vacancies as the support, two-dimensional CoO/h-TiO₂ Z-scheme heterostructures are fabricated for hydrogen production through photocatalytic water splitting. It is revealed that the oxygen vacancies in h-TiO₂ can inhibit the oxidation of Co²⁺ into high-valence Co³⁺ during the hydrothermal reaction and thermal treatment processes. A CoO/h-TiO₂ Z-scheme heterostructure possesses a space charge region and a built-in electric field at the interface, and oxygen vacancies in h-TiO₂ can provide more reactive sites, which synergistically improve the separation and transportation of photogenerated carriers. As a result, the photocatalytic hydrogen evolution rate achieves 129.75 μmol·h^-1 (with 50 mg of photocatalysts) on the optimized CoO/h-TiO₂ heterostructures. This work provides a new design idea for the preparation of excellent TiO₂-based photocatalysts.

Boosted CO2 photoreduction performance on Ru-Ti3CN MXene-TiO2 photocatalyst synthesized by non-HF Lewis acidic etching method

Photocatalytic CO₂ reduction to produce value-added products is considered a promising solution to solve the global energy crisis and the greenhouse effect. In this study, Ti₃CN MXene was synthesized using a Lewis acidic etching method without the usage of toxic hydrofluoric acid (HF). Ti₃CN MXene was then used as a support for the in situ hydrothermal growth of TiO₂ and Ru nanoparticles. In the presence of 0.5 wt% Ru, Ru-Ti₃CN-TiO₂ shows CO and CH₄ production rates of 99.58 and 8.97 μmol/g, respectively, in 5 h under Xenon lamp irradiation, more than 20.5 and 9.3 times that of commercial P25. The enhancement in photocatalytic activity was attributed to the synergy between the in-situ growth of TiO₂ on Ti₃CN MXene and Ru nanoparticles. It was proven experimentally that Ti₃CN MXene can provide abundant pathways for electron transfer. The separation and transfer of the photo-induced charge were further increased with the help of Ru and Ti₃CN MXene, leaving more electrons to participate in the subsequent CO₂ reduction reaction. We believe that this work will encourage more attention to designing environment-friendly MXene-based photocatalysts for CO₂ photoreduction using the non-HF method.

Surface plasmon-driven photoelectrochemical water splitting of a Ag/TiO2 nanoplate photoanode

A silver/titanium dioxide nanoplate (Ag/TiO₂ NP) photoelectrode was designed and fabricated from vertically aligned TiO₂ nanoplates (NP) decorated with silver nanoparticles (NPs) through a simple hydrothermal synthesis and electrodeposition route. The electrodeposition times of Ag NPs on the TiO₂ NP were crucial for surface plasmon-driven photoelectrochemical (PEC) water splitting performance. The Ag/TiO₂ NP at the optimal deposition time of 5 min with a Ag element content of 0.53 wt% demonstrated a remarkably high photocurrent density of 0.35 mA cm⁻² at 1.23 V vs. RHE under AM 1.5G illumination, which was 5 fold higher than that of the pristine TiO₂ NP. It was clear that the enhanced light absorption properties and PEC performance for Ag/TiO₂ NP could be effectively adjusted by simply controlling the loading amounts of metallic Ag NPs (average size of 10–30 nm) at different electrodeposition times. The superior PEC performance of the Ag/TiO₂ NP photoanode was attributed to the synergistic effects of the plasmonic Ag NPs and the TiO₂ nanoplate. Interestingly, the plasmonic effect of Ag NPs not only increased the visible-light response (λ_max = 570 nm) of TiO₂ but also provided hot electrons to promote photocurrent generation and suppress charge recombination. Importantly, this study offers a potentially efficient strategy for the design and fabrication of a new type of TiO₂ hybrid nanostructure with a plasmonic enhancement for PEC water splitting.

A hybrid nanostructure Ag/TiO₂ photoelectrode for PEC water splitting with a remarkable high photocurrent density, 0.35 mA cm⁻² (5 fold higher than that of the pristine TiO₂ photoeletrode) was fabricated by a facile one-pot hydrothermal and electrodeposition method.

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.

In-plasma-catalysis for NO x degradation by Ti3+ self-doped TiO2-x /γ-Al2O3 catalyst and nonthermal plasma

In an attempt to realize the efficient treatment of NO_x, a mixed catalyst of Ti³⁺ self-doped TiO_2−x and γ-Al₂O₃ was constructed by reducing commercial TiO₂. The degradation effect on NO_x was evaluated by introducing the mixed catalyst into a coaxial dual-dielectric barrier reactor. It was found that the synthesized TiO_2−x could achieve considerable degradation effects (84.84%, SIE = 401.27 J L⁻¹) in a plasma catalytic system under oxygen-rich conditions, which were better than those of TiO₂ (73.99%) or a single plasma degradation process (26.00%). The presence of Ti³⁺ and oxygen vacancies in TiO_2−x resulted in a relatively narrow band gap, which contributed to catalyzing deeply the oxidation of NO_x to NO₂⁻ and NO₃⁻ during the plasma-induced “pseudo-photocatalysis” process. Meanwhile, the TiO_2−x showed an improved discharge current and promoted discharge efficiency, explaining its significant activation effect in the reaction. Reduced TiO_2−x could achieve an impressive degradation effect in a long-time plasma-catalysis process, and still maintained its intrinsic crystal structure and morphology. This work provides a facile synthesis procedure for preparing Ti³⁺ self-doped TiO_2−x with practical and scalable production potential; moreover, the novel combination with plasma also provides new insights into the low-temperature degradation of NO_x.

TiO_2−x has a smaller forbidden band width, more abundant Ti³⁺ and oxygen vacancies, so as to obtain a better and more stable degradation effect of NO_x in plasma-catalysis process.

Orientational Alignment of Oxygen Vacancies: Electric-Field-Inducing Conductive Channels in TiO2 Film to Boost Photocatalytic Conversion of CO2 into CO

Oxide semiconductors are widely used in the photocatalytic fields, and introducing oxygen vacancies is an effective strategy to improve their photocatalytic efficiency. However, oxygen vacancies in the bulk often act as the recombination centers of electron-hole pairs, which accelerates the recombination of electron-hole pairs. In this paper, we propose a strategy of electric field treatment and apply it to a TiO₂ film with oxygen vacancies to promote the photocatalytic efficiency. After treatment by an electric field, the conductive channels consisting of oxygen vacancies are formed in the TiO₂ film, which greatly decreases the resistance by almost 6 × 10³ times. The yield of CO can reach up to 1.729 mmol g_cat^-1 h^-1, which is one of the best performances among the reported TiO₂-based catalysts. This work provides an effective and feasible way for enhancing photocatalytic activity through an electric field, and this method is promising for wide use in the field of catalysis.

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

Ultraviolet-induced Ostwald ripening strategy towards a mesoporous Ga2O3/GaOOH heterojunction composite with a controllable structure for enhanced photocatalytic hydrogen evolution

The design of efficient semiconductor oxide materials with heterojunction nanostructures for photocatalysis holds great promise in the fields of clean energy conversion and storage.

Lattice-Refined Transition-Metal Oxides via Ball Milling for Boosted Catalytic Oxidation Performance

Surface oxygen vacancy can greatly affect the properties of transition-metal oxides. However, engineering oxygen vacancy-abundant transition-metal oxides with high specific surface area (SSA) remains challenging. At present, the generation of oxygen vacancies in metal oxides is time-consuming and less environmentally friendly by chemical leaching methods that usually require additional waste treatment. Herein, a series of oxygen vacancy-abundant transition-metal oxides with high SSA are constructed via a lattice refining strategy. This strategy is realized by urea-assisted ball milling pyrolysis and is green, efficient, and universal. The oxygen vacancies promote the mobility of oxygen, leading to a boosted catalytic oxidation performance of aromatic sulfides. Such a strategy provides an efficient approach to manufacturing oxygen vacancies on transition-metal oxides, which may be beneficial for various related applications as an effective catalytic material.

Ti-rich TiO2 Tubular Nanolettuces by Electrochemical Anodization for All-Solid-State High-Rate Supercapacitor Devices

Supercapacitors store charge by ion adsorption or fast redox reactions on the surface of porous materials. One of the bottlenecks in this field is the development of biocompatible and high-rate supercapacitor devices by scalable fabrication processes. Herein, a Ti-rich anatase TiO₂ material that addresses the above-mentioned challenges is reported. Tubular nanolettuces were fabricated by a cost-effective and fast anodization process of Ti foil. They attained a large potential window of 2.5 V in a neutral electrolyte owing to the high activation energy for water splitting of the (1 0 1) facet. Aqueous and all-solid-state devices showed diffusion time constants of 46 and 1700 ms, as well as high maximum energy (power) densities of 0.844 (0.858) and 0.338 μWh cm^-2 (0.925 mW cm^-2 ), respectively. The all-solid-state device showed ultrahigh stability of 96 % in capacitance retention after 20 000 galvanostatic charge/discharge cycles. These results open an avenue to fabricate biochemically inert supercapacitor devices.

In situ formation of defect-engineered N-doped TiO2 porous mesocrystals for enhanced photo-degradation and PEC performance

N-Doped oxygen defective N/TiO_2-x mesocrystal nanocubes were successfully prepared by a facile strategy in our system. Crystal topotactic transformation from NH₄TiOF₃ mesocrystals facilitated the formation of a porous structure of TiO₂. Meanwhile, the introduction of N dopants and oxygen vacancies (OVs) was also achieved during this process. The as-prepared products exhibit much higher photoelectrochemical (PEC) and photocatalytic degradation performance under visible light illumination. It is suggested that the promising catalytic properties result from the synergistic effect of doping, OVs and the amazing porous mesocrystal structure of N/TiO_2-x .

Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO₂ under Various Atmospheres

In this report, the photocatalytic activity of P25 has been explored and the influence of thermal treatment under various atmospheres (air, vacuum and hydrogen) were discussed. The samples’ characteristics were disclosed by means of various instruments including X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and UV–vis. This study also accentuates various states of the oxygen vacancy density formed inside the samples as well as the colour turning observed in treated P25 under various atmospheres. Produced coloured TiO₂ samples were then exploited for their photocatalytic capability concerning photodegradation of methylene blue (MB) using air mass (AM) 1.5 G solar light irradiation. Our findings revealed that exceptional photocatalytic activity of P25 is related to the thermal treatment. Neither oxygen vacancy formation nor photocatalytic activity enhancement was observed in the air-treated sample. H₂-treated samples have shown better photoactivity which even could be further improved by optimizing treatment conditions to achieve the advantages of the positive role of oxygen vacancy (O-vacancy at higher concentration than optimum acts as electron trapping sites). The chemical structure and stability of the samples were also studied. There was no sign of deteriorating of O₂-vacancies inside the samples after 6 months. High stability of thermal treated samples in terms of both long and short-term time intervals is another significant feature of the produced photocatalyst.

One-step hydrothermal synthesis of N/Ti3+ co-doping multiphasic TiO2/BiOBr heterojunctions towards enhanced sonocatalytic performance

N/Ti³⁺ co-doping multiphasic TiO₂/BiOBr heterojunctions (NT-TBx) were prepared by one-step in situ hydrothermal processes. The crystal phase, morphology, component, and optical properties of the heterojunctions were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, and Ultraviolet-visible diffuse reflectance spectroscopy techniques, respectively. The as-prepared samples exhibit better sonocatalytic activity for the degradation methylene blue, Rhodamine B, and p-Nitrophenol aqueous solution compared with pristine TiO₂ and N/Ti³⁺ co-doping multiphasic TiO₂. Especially, the highest degradation ratio of methylene blue was achieved for NT-TB_0.3 up to 98.2% after 50 min under ultrasonic irradiation. The high sonocatalytic activity has been kept after four cycles with the tiny decline, indicating the excellent stability of the as-prepared samples. The improvement of sonocatalytic activity could be attributed to the formation of doping level and multiphasic TiO₂/BiOBr heterojunctions, which account for the absorption of long wavelength light and the electron-hole pair separation, respectively. Furthermore, superoxide radical (O₂^-) was demonstrated to be the main reactive species for the degradation of methylene blue under ultrasonic irradiation. This study provides a facile fabrication procedure for N/Ti³⁺ co-doping multiphasic TiO₂/BiOBr heterojunctions and demonstrates an efficient route to promote the application of TiO₂ in addressing environment-related issues.

Revealing the Relationship between Photocatalytic Properties and Structure Characteristics of TiO2 Reduced by Hydrogen and Carbon Monoxide Treatment

Reduction is considered to be an effective method to improve the photocatalytic activity of TiO₂ ; however, the underlying relationship between structure and photocatalytic performance has not been adequately unveiled to date. To obtain insights into the effect of structure on photocatalytic activity, two types of reduced TiO₂ were prepared from CO (CO-TiO₂ ) and H₂ (H-TiO₂ ). For H-TiO₂ , Ti-H bonds and oxygen vacancies are formed on the surface of H-TiO₂ , which results in a more disordered surface lattice. However, for CO-TiO₂ , more Ti-OH bonds are formed on the surface and more bulk oxygen vacancies are introduced; the disorder layer of CO-TiO₂ is relatively thin, owing to most surface vacancies being filled by Ti-OH bonds. Under simulated solar irradiation, the photocatalytic H₂ evolution rate of CO-TiO₂ reaches 7.17 mmol g^-1  h^-1 , which is 4.14 and 1.50 times those of TiO₂ and H-TiO₂ , respectively. The photocatalytic degradation rate constant of methyl orange on CO-TiO₂ is 2.45 and 6.39 times those on H-TiO₂ and TiO₂ . The superior photocatalytic activity of CO-TiO₂ is attributed to the effective separation and transfer of photogenerated electron-hole pairs, due to the synergistic effects of oxygen vacancies and surface Ti-OH bonds. This study reveals the relationship between the photocatalytic properties and structure, and provides a new method to prepare highly active TiO₂ for H₂ production and environmental treatment.

Anthracene-decorated TiO2 thin films with the enhanced photoelectrochemical performance

New insight of introducing new organic compounds for the efficient photogenerated charge separation is vitally important for the current solar energy conversion. Herein, (2Z,2'Z)-4,4'-(anthracene-2,6-diylbis(azanediyl))bis(4-oxobut-2-enoic acid) (ADA)/TiO₂ composite thin film is fabricated through the wet-impregnation strategy, which exhibits excellent photoelectrochemical performance (PEC). A combined study of ultraviolet-visible absorption spectra, scanning Kelvin probe maps, electrochemical and photoelectrochemical measurements reveals that the ADA/TiO₂ composite with narrow bandgap of 2.42 eV extends the photo response to the visible light region. The photocurrent generated by the optimal ADA/TiO₂ is 2.5 times higher than that of the pristine TiO₂. The result is attributed to the broader light absorption range and the separation of photoelectrons and holes prompted by ADA. Moreover, the high stability of the ADA/TiO₂ composite favors the practical application. The present work may offer a promising strategy for the low-cost PEC cell in the clean solar hydrogen production.

Defect-engineered TiO2 Hollow Spiny Nanocubes for Phenol Degradation under Visible Light Irradiation

Herein, we mainly report a strategy for the facile synthesis of defect-engineered F-doped well-defined TiO2 hollow spiny nanocubes, constructed from NH4TiOF3 as precursor. The topological transformation of NH4TiOF3 mesocrystal is accompanied with fluorine anion releasing, which can be used as doping source to synthesize F-doped TiO2. Our result shows that the introduction of oxygen vacancies (Vo's) and F dopant can be further achieved by a moderate photoreduction process. The as prepared sample is beneficial to improve photocatalystic degradation and Photoelectrochemical (PEC) efficiency under visible light irradiation. And this improvement in photocatalytic and photoelectrocatalytic performance can be ascribed to the significant enhancement of visible light absorption and separation of excited charges resulted from the presence of oxygen vacancies, F- ions and hollow structure of TiO2.

Controlled Synthesis of CuS/TiO2 Heterostructured Nanocomposites for Enhanced Photocatalytic Hydrogen Generation through Water Splitting

Photocatalytic hydrogen (H₂) generation through water splitting has attracted substantial attention as a clean and renewable energy generation process that has enormous potential in converting solar-to-chemical energy using suitable photocatalysts. The major bottleneck in the development of semiconductor-based photocatalysts lies in poor light absorption and fast recombination of photogenerated electron-hole pairs. Herein we report the synthesis of CuS/TiO₂ heterostructured nanocomposites with varied TiO₂ contents via simple hydrothermal and solution-based process. The morphology, crystal structure, composition, and optical properties of the as-synthesized CuS/TiO₂ hybrids are evaluated in detail. Controlling the CuS/TiO₂ ratio to an optimum value leads to the highest photocatalytic H₂ production rate of 1262 μmol h^-1 g^-1, which is 9.7 and 9.3 times higher than that of pristine TiO₂ nanospindles and CuS nanoflakes under irradiation, respectively. The enhancement in the H₂ evolution rate is attributed to increased light absorption and efficient charge separation with an optimum CuS coverage on TiO₂. The photoluminescence and photoelectrochemical measurements further confirm the efficient separation of charge carriers in the CuS/TiO₂ hybrid. The mechanism and synergistic role of CuS and TiO₂ semiconductors for enhanced photoactivity is further delineated.

Defect-mediated electron–hole separation in semiconductor photocatalysis

This review summarizes the inherent functionality of bulk, surface and interface defects, and their contributions towards mediating electron–hole separation in semiconductor photocatalysis.

Engineering the Surface/Interface Structures of Titanium Dioxide Micro and Nano Architectures towards Environmental and Electrochemical Applications

Titanium dioxide (TiO₂) materials have been intensively studied in the past years because of many varied applications. This mini review article focuses on TiO₂ micro and nano architectures with the prevalent crystal structures (anatase, rutile, brookite, and TiO₂(B)), and summarizes the major advances in the surface and interface engineering and applications in environmental and electrochemical applications. We analyze the advantages of surface/interface engineered TiO₂ micro and nano structures, and present the principles and growth mechanisms of TiO₂ nanostructures via different strategies, with an emphasis on rational control of the surface and interface structures. We further discuss the applications of TiO₂ micro and nano architectures in photocatalysis, lithium/sodium ion batteries, and Li-S batteries. Throughout the discussion, the relationship between the device performance and the surface/interface structures of TiO₂ micro and nano structures will be highlighted. Then, we discuss the phase transitions of TiO₂ nanostructures and possible strategies of improving the phase stability. The review concludes with a perspective on the current challenges and future research directions.