High Photoreactivity on a Reconstructed Anatase TiO2(001) Surface Predicted by Ab Initio Nonadiabatic Molecular Dynamics

Anatase TiO₂(001) surface with (4 × 1) reconstruction is proposed to be a highly active catalytic surface. In this work, using time-domain ab initio nonadiabatic molecular dynamics, we reveal that the ridge structure formed by anatase(001) surface reconstruction is the photoreactive site for hole migration and trapping. Moreover, the ridge structure is destroyed by low-coverage CH₃OH adsorption, leading to the suppression of its high photoreactivity. However, when the CH₃OH coverage is increased and intermolecular hydrogen bonds (H-bonds) form, the ridge structure and its high photoreactivity are restored. Furthermore, the hole trapping dynamics is strongly coherent with intermolecular proton transfer in structures with intermolecular H-bonds. Our study proves that anatase TiO₂(001)-(4 × 1) is a highly photoreactive surface where the ridge is the photoreactive site for hole trapping, which is coherent with the proton transfer process.

Adsorption and Mechanism of Glycine on the Anatase with Exposed (001) and (101) Facets

As a widely existing mineral types on Earth, semiconductor minerals play an important role in the origin of life and the material geochemical cycle. The first step of peptide formation is amino acid adsorption on the mineral surface, but the role and mechanism of different crystal facets of semiconductor minerals are not well understood. Anatase (TiO2) with exposed (001) facets was synthesized by a hydrothermal method, and then analyzed and compared with the purchased ordinary anatase (TiO2) for the adsorption of glycine, the simplest amino acid. XRD, SEM and TEM results show that the hydrothermally synthesized anatase (TiO2) has a good anatase crystal form, which is micro-nano-scale flake particles and mainly composed of (001) facets. The results of HPLC used in the adsorption experiment showed that under optimal conditions (pH 5 to 6, an adsorption time of 24 h, and an initial concentration of 0.09 mol/L), the adsorption quantity of glycine on anatase (TiO2) with exposed (001) facets may reach 10 mg/m2, which is larger than that for ordinary anatase (TiO2) with exposed (101) facets. Based on a combination of various characterizations and simulation calculations, the results proved that anatase can activate thermodynamically stable γ-glycine to β-glycine. The adsorption of glycine on anatase (TiO2) has two forms, one is the zwitterionic form in which the carboxyl group forms a bridge structure with two Ti atoms connected by surface bridging oxygen, and the dissociated form is in which the amino group forms a bond with the surface Ti atom. Among these, glycine is mainly adsorbed to anatase by dissociative molecules on the anatase (TiO2) with exposed (001) facets and by zwitterion adsorption on the anatase (TiO2) with exposed (101) facets. This research elucidates the conditions and mechanism of amino acid adsorption by semiconductor minerals in weak acidic environment, which is similar to the environmental pH that was beneficial to the formation of life on the early Earth. Therefore, these can provide a reference for the further study of the role of semiconductor minerals in the adsorption and polymerization of small biomolecules in the origin of life.

Facet-Control versus Co-Catalyst-Control in Photocatalytic H2 Evolution from Anatase TiO2 Nanocrystals

Titanium dioxide (TiO₂) and, in particular, its anatase polymorph, is widely studied for photocatalytic H₂ production. In the present work, we examine the importance of reactive facets of anatase crystallites on the photocatalytic H₂ evolution from aqueous methanol solutions. For this, we synthesized anatase TiO₂ nanocrystals with a large amount of either {001} facets, that is, nanosheets, or {101} facets, that is, octahedral nanocubes, and examined their photocatalytic H₂ evolution and then repeated this procedure with samples where Pt co‐catalyst is present on all facets. Octahedral nanocubes with abundant {101} facets produce >4 times more H₂ than nanosheets enriched in {001} facets if the reaction is carried out under co‐catalyst‐free conditions. For samples that carry Pt co‐catalyst on both {001} and {101} facets, faceting loses entirely its significance. This demonstrates that the beneficial role of faceting, namely the introduction of {101} facets that act as electron transfer mediator is relevant only for co‐catalyst‐free TiO₂ surfaces.

Selective suppression of {112} anatase facets by fluorination for enhanced TiO2 particle size and phase stability at elevated temperatures

Generally, anatase is the most desirable TiO₂ polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO₂ crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO₂ surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of ca. 35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO₂ by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO₂ synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications.

Peering into the Formation of Template-Free Hierarchical Flowerlike Nanostructures of SrTiO3

The development of efficient advanced functional materials is highly dependent on properties such as morphology, crystallinity, and surface functionality. In this work, hierarchical flowerlike nanostructures of SrTiO3 have been synthesized by a simple template-free solvothermal method involving poly(vinylpyrrolidone) (PVP). Molecular dynamics simulations supported by structural characterization have shown that PVP preferentially adsorbs on {110} facets, thereby promoting the {100} facet growth. This interaction results in the formation of hierarchical flowerlike nanostructures with assembled nanosheets. The petal morphology is strongly dependent on the presence of PVP, and the piling up of nanosheets, leading to nanocubes, is observed when PVP is removed at high temperatures. This work contributes to a better understanding of how to control the morphological properties of SrTiO3, which is fundamental to the synthesis of perovskite-type materials with tailored properties.

Hexafluorotitanic acid-assisted synthesis of large-sized, ultrathin titania nanosheets as multifunctional and high-performance photocatalysts

A fast cyclohexanol solvothermal pathway was developed to prepare highly dispersed anatase titania (TiO₂) nanosheets with an edge length of ∼800 nm and a thickness of ∼6 nm. Under the synergistic control of hexafluorotitanic acid and cyclohexanol, the exposed 001 facets reached ∼98.5% on the TiO₂ nanosheets obtained by the treatment at 180 °C for 150 min. Moreover, it was found that the phase transformation and structural development drastically occurred during the solvothermal treatment. When used as a catalyst for photodegradation of rhodamine B, the TiO₂ nanosheets exhibited a good recycling stability and a much higher photocatalytic degradation rate (nearly 99% degradation within 2.5 h) than the commercial P25 (93.6%). After being uniformly loaded with 4 wt.% of the Pt nanoparticles, the TiO₂ nanosheets displayed a photocatalytic hydrogen production rate of 2.239 mmol g^-1 h^-1 under simulated solar light, which was much higher than the pristine TiO₂ nanosheets (0.045 mmol g^-1 h^-1) as well as most of the reported TiO₂-based photocatalysts. The remarkable photocatalytic activity and good stability of the TiO₂ nanosheets with highly exposed 001 facets would make them find potential applications in both water treatment and hydrogen generation from water splitting under solar light.

Gas-Phase Photoelectrocatalytic Oxidation of NO via TiO2 Nanorod Array/FTO Photoanodes

Most photoelectrocatalytic (PEC) reactions are performed in the liquid phase for convenient electron transfer in an electrolyte solution. Herein, a novel PEC reactor involving a tandem combination of TiO₂ nanorod array/fluorine-doped tin oxide (TiO₂-NR/FTO) working electrodes and an electrochemical auxiliary cell was constructed to drive the highly efficient PEC oxidation of indoor gas (NO_x). With the aid of a low bias voltage (0.3 V), the as-formed PEC reactor exhibited an 80% removal rate for oxidizing NO (500 ppb) under light irradiation, which is much higher than that of the traditional photocatalytic (PC) process. Upon being irradiated by light, the photogenerated electrons are quickly separated from the holes and transferred to the counter electrode (Pt) owing to the applied bias voltage, leaving photogenerated holes in the TiO₂-NR/FTO electrode for oxidizing NO molecules. Moreover, both dry and humid NO could be effectively removed by the tandem TiO₂-NR/FTO-based gas-phase PEC reactor, indicating that the NO molecules could also be directly oxidized by photogenerated holes in addition to hydroxyl radicals. The presence of trace amounts of water could promote the PEC oxidation of NO owing to the formation of hydroxyl radicals induced by reactions between the water and holes, which could further oxidize NO. This PEC reactor offers an energy-saving, environmentally friendly, and efficient route to treat air polluted with low concentrations of gases (NO_x and SO_x).

Enhanced Antibacterial Property of Facet-Engineered TiO2 Nanosheet in Presence and Absence of Ultraviolet Irradiation

Titania (TiO2) has attracted much attention recently for reducing bacterial diseases by the generation of reactive oxygen species (ROS) under UV irradiation. However, demand for higher photocatalytic activity due to higher recombination of electron and hole remains. The aims of this study were to make titania with higher antibacterial property and show the mechanisms of the bactericidal effect. In this study, we hydrothermally synthesized TiO2 nanosheets (NS) with highly-oriented structures. Samples were divided into five groups, depending on the fluorine/titanium ratio in the raw material, namely NS1.0, NS1.2, NS1.5, NS1.8, and NS2.0. Facet ratio and nanosheet size increased with an increase of fluorine/titanium ratio. The photocatalytic activity of TiO2 nanosheet was assessed by the generation of ROS. Hydroxyl radicals and superoxides were generated efficiently by ultraviolet light irradiation on NS1.5 and NS1.0, respectively. Antibacterial activity against Streptococcus mutans was assessed in the presence and absence of UV irradiation; NS1.0 showed superior antibacterial properties compared to commercially available TiO2 nanoparticles, under both conditions, due to the oxidation of intracellular components and cell membrane. These results together suggested TiO2 nanosheet induced bacterial cell death by oxidation, and TiO2 facet engineering resulted in enhancement of both photocatalytic and antibacterial activities of TiO2.

Effect of Surface Chemistry and Crystallographic Parameters of TiO2 Anatase Nanocrystals on Photocatalytic Degradation of Bisphenol A

The photocatalytic activity of a series of anatase TiO2 materials with different amounts of exposed (001) facets (i.e., 12% (TiO2-1), 38% (TiO2-3), and 63% (TiO2-3)) was tested in a batch slurry reactor towards liquid-phase bisphenol A (BPA, c0(BPA) = 10 mg/L, ccat. = 125 mg/L) degradation. Photo-electrochemical and photo-luminescence measurements revealed that with the increasing amount of exposed anatase (001) facets, the catalysts generate more electron-hole pairs and OH∙ radicals that participate in the photocatalytic mineralization of pollutants dissolved in water. In the initial stages of BPA degradation, a correlation between % exposure of (001) facets and catalytic activity was developed, which was in good agreement with the findings of the photo-electrochemical and photo-luminescence measurements. TiO2-1 and TiO2-3 solids achieved 100% BPA removal after 80 min in comparison to the TiO2-2 sample. Adsorption of BPA degradation products onto the TiO2-2 catalyst surface was found to have a detrimental effect on the photocatalytic performance in the last stage of the reaction course. Consequently, the global extent of BPA mineralization decreased with the increasing exposure of anatase (001) facets. The major contribution to the enhanced reactivity of TiO2 anatase (001) surface is the Brønsted acidity resulting from dissociative chemisorption of water on a surface as indicated by FTIR, TPD, and MAS NMR analyses.

New Developments in Material Preparation Using a Combination of Ionic Liquids and Microwave Irradiation

During recent years, synthetic methods combining microwaves and ionic liquids became accepted as a promising methodology for various materials preparations because of their high efficiency and low energy consumption. Ionic liquids with high polarity are heated rapidly, volumetrically and simultaneously under microwave irradiation. Hence, combination of microwave irradiation as a heating source with ionic liquids with various roles (e.g., solvent, additive, template or reactant) opened a completely new technique in the last twenty years for nanomaterials and polymers preparation for applications in various materials science fields including polymer science. This review summarizes recent developments of some common materials syntheses using microwave-assisted ionic liquid method with a focus on inorganic nanomaterials, polymers, carbon-derived composites and biomass-based composites. After that, the mechanisms involved in microwave-assisted ionic-liquid (MAIL) are discussed briefly. This review also highlights the role of ionic liquids in the reaction and crucial issues that should be addressed in future research involving this synthesis technique.

Synthesis of mesoporous core-shell TiO2 microstructures with coexposed {001}/{101} facets: enhanced intrinsic photocatalytic performance

TiO₂ microstructures were synthesized via a facile one-step route for enhanced intrinsic photocatalytic performance. The prepared TiO₂ microstructures are featured by both mesoporous core-shell structures and coexposed {001}/{101} facets. Their intrinsic photocatalytic performance were remarkably enhanced due to their high specific surface area, coexposed {001}/{101} facets, and promoted separation of photogenerated carriers. Furthermore, the origin and detailed mechanism for diethylenetriamine (DETA) that served as a high efficient stabilizer of TiO₂ {001} facet have been theoretically investigated. Finally, a new DETA-modified Ostwald ripening mechanism was originally proposed when studying the growth mechanism of the mesoporous core-shell TiO₂ spherical microstructures with coexposed {001}/{101} facets.

Diatomite modified by TiO2 for adsorption of U(VI)

Diatomite was modified with TiO2. The synthesized materials were characterized and used for removal of U(VI) from aqueous solutions. The influences of pH, contact time and temperature on U(VI) adsorption onto TiO2@diatomite were studied by batch technique, and X-ray photoelectron spectroscopy (XPS) was employed to analyze the experimental data. We compared the adsorption of U(VI) onto natural diatomite, TiO2 and TiO2@diatomite made by sol-gel method. The dynamic process showed that the adsorption of U(VI) onto TiO2@diatomite matched the pseudo-second-order kinetics model, and the adsorption of U(VI) was significantly dependent on pH values. Through simulating the adsorption isotherms by Langmuir, Freundlich and Dubini–Radushkevich (D–R) models, respectively, it could be seen that the adsorption patterns of U(VI) onto TiO2@diatomite were mainly controlled by surface complexation, and the adsorption processes were endothermic and spontaneous. The modification of diatomite by TiO2 shows a novel material for removing U(VI) from water environment for industrialized application.

The Many "Facets" of Halide Ions in the Chemistry of Colloidal Inorganic Nanocrystals

Over the years, scientists have identified various synthetic "handles" while developing wet chemical protocols for achieving a high level of shape and compositional complexity in colloidal nanomaterials. Halide ions have emerged as one such handle which serve as important surface active species that regulate nanocrystal (NC) growth and concomitant physicochemical properties. Halide ions affect the NC growth kinetics through several means, including selective binding on crystal facets, complexation with the precursors, and oxidative etching. On the other hand, their presence on the surfaces of semiconducting NCs stimulates interesting changes in the intrinsic electronic structure and interparticle communication in the NC solids eventually assembled from them. Then again, halide ions also induce optoelectronic tunability in NCs where they form part of the core, through sheer composition variation. In this review, we describe these roles of halide ions in the growth of nanostructures and the physical changes introduced by them and thereafter demonstrate the commonality of these effects across different classes of nanomaterials.

Acidic ionic liquids: an alternative to HF for {001} reactive facet controlled synthesis of anatase titania

A HF free method for the controlled synthesis of nanosized TiO₂ with a higher percentage of {001} reactive facets.

Synergistic effect of Ti3+ doping and facet regulation over Ti3+-doped TiO2 nanosheets with enhanced photoreactivity

Ti³⁺-doped TiO₂ nanosheets with different percentages of exposed {001} facets were synthesized by aluminium (Al) reduction.

Enhanced visible light photocatalytic activity of BiOBr by in situ reactable ionic liquid modification for pollutant degradation

In this study, hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal method in the presence of imidazole ionic liquids. The resultant samples were characterized by XRD, SEM, HRTEM, PL, EPR, EIS and UV-vis absorption spectroscopy. The photoactivity of BiOBr was evaluated by the photocatalytic degradation of methyl orange (MO) and tetracycline hydrochloride. Oxygen vacancies were detected in the system and proven to be correlated with the activity of the catalyst. It was also revealed that BiOBr microspheres prepared by 1-butyl-3-methylimidazolium bromide at 433 K for 8 hours displayed a superior performance compared to the other samples in the degradation of model organic contaminants. After 4.5 hours of reaction, the highest degradation efficiency of 94.0% was achieved by BiOBr-C₄-Br. Stronger photoluminescence spectral intensities could be obtained as the cationic chain lengths of the ionic liquids reduced gradually. According to our experiments, the better performance of BiOBr-C₄-Br in the degradation of model pollutants can be attributed to the effect of oxygen vacancies. The findings of our work may have important implications for the design of BiOBr.

In this study, hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal method in the presence of imidazole ionic liquids.

Facet-Dependent Diol-Induced Density of States of Anatase TiO2 Crystal Surface

Owing to their fundamental importance and practical applications, anatase TiO2 crystals with well-defined {001} and {101} facets attracted intensive research interests. In this study, we systematically investigated solvent dependence of the photoreaction of the different coexposed crystal facets during noble metal photodeposition. By examining the deposition position in each solvent, we revealed that solvents play a pivotal role on the facet selectivity. On the basis of density functional theory calculations, the solvent molecules were found to modify both the crystal facet electronic structure and the {001}-{001} heterojunction. These modifications are not only the origin of diverse charge-carrier pathways but are also responsible for carrier accumulation at specific facets that increase their reductive power. These findings are vital for a better understanding of photocatalytic materials and an improved design for the next-generation materials.

Role of Surface Stress on the Reactivity of Anatase TiO2(001)

In contrast with theoretical predictions in which anatase TiO₂(001) and its (1 × 4) reconstructed surfaces are highly reactive, recent experimental results show this surface to be inert except for the defect sites. In this report, based on a systematic study of anatase TiO₂(001)-(1 × 4) surface using first-principles calculations, the tensile stress is shown to play a crucial role on the surface reactivity. The predicted high reactivity based on add-molecule model is due to the large surface tensile stress, which can be easily suppressed by a stress-release mechanism. We show that various surface defects can induce stress release concomitantly with surface passivation. Thus the synthesis of anatase(001) surface with few defects is essential to improve the reactivity, which can be achieved, for example, via H₂O adsorption. Our study provides a uniform interpretation of controversial experimental observations and theoretical predictions on anatase TiO₂(001) surface and further proposes new insights into the origin of surface reactivity.

A reconstructed anatase (001)-1 × 4 surface and its reactivity

Our results solve the atomic structure of anatase (001)-(1 × 4) reconstructed surface, which exhibits enhanced photocatalytic activity.

Hetero-epitaxial growth control of single-crystalline anatase TiO2 nanosheets predominantly exposing the {001} facet on oriented crystalline substrates

Well-controlled TiO₂ nanosheet growth was achieved by applying a proper crystalline orientation of substrates as a hetero-epitaxial growth strategy.

Few-layered metallic 1T-MoS2/TiO2 with exposed (001) facets: two-dimensional nanocomposites for enhanced photocatalytic activities

Titanium dioxide (TiO₂) with exposed (001) facets (TiO₂(001)) has attractive photocatalytic properties.

Direct Observation of Charge Separation on Anatase TiO2 Crystals with Selectively Etched {001} Facets

Synchronous illumination X-ray photoelectron spectroscopy (SIXPS) was employed for the first time to directly identify the photogenerated charge separation and transfer on anatase TiO2 single-crystals with selectively etched {001} facets. More specifically, for the TiO2 crystals with intact {001} and {101} facets, most of photogenerated charge carriers rapidly recombined, and no evident electron-hole separation was detected. With selectively etching on {001} facets, high efficient charge separation via hole transfer to titanium and electron to oxygen was clearly observed. However, when the {001} facets were completely etched into a hollow structure, the recombination for photogenerated electron-hole pairs would dominate again. These demonstrations clearly reveal that the appropriate corrosion on {001} facets could facilitate more efficient electron-hole separation and transfer. As expected, the optimized TiO2 microcrystals with etched {001} facets could achieve a hydrogen generation rate of 74.3 μmol/h/g, which is nearly 7 times higher than the intact-TiO2 crystals.

CNTs threaded (001) exposed TiO2 with high activity in photocatalytic NO oxidation

A microwave-ionothermal strategy was developed for in situ synthesis of CNTs threaded TiO2 single crystal with a tunable percentage of surface exposed (001) active facets. The CNTs were used as microwave antennas to create local "super hot" dots to induce Ti(3+) adsorption and hydrolysis, thereby leading to a good assembly of (001) facets exposed single crystalline TiO2 threaded by the CNTs in the presence of Hmim[BF4] ionic liquid. Due to the high percentage of the active (001) facets of single crystal TiO2 and the direct electron transfer property of the CNTs, the as-prepared CNTs-TiO2 composite showed a photocatalytic NO removal ratio of up to 76.8% under UV irradiation. In addition, with self-doped Ti(3+), the CNTs-TiO2 composite also exhibited an enhanced activity under irradiation with either solar lights or visible lights, showing good potential in practical applications for environmental remediation.

Graphene Oxide-Assisted Synthesis of Microsized Ultrathin Single-Crystalline Anatase TiO2 Nanosheets and Their Application in Dye-Sensitized Solar Cells

High-quality microsized ultrathin single-crystalline anatase TiO2 nanosheets (MS-TiO2) with exposed {001} facets were synthesized by a facile and low-cost two-step process that combines a graphene oxide (GO)-assisted hydrothermal method with calcination. Both GO and HF play an important role in the formation of well dispersed MS-TiO2. As a novel microsized (1-4 μm) ultrathin two-dimensional (2D) material, MS-TiO2 possesses much higher lateral size and aspect ratio compared to common 2D nanosized (30-60 nm) ultrathin TiO2 nanosheets (NS-TiO2), resulting in excellent electronic conductivity and superior electron transfer and diffusion properties. Here, we fabricated MS-TiO2 and NS-TiO2, both of which were incorporated with the TiO2 nanoparticles (P25) to constitute the hybrid photoanode of dye-sensitized solar cells (DSSCs), and explored the effect of the lateral size (nano- and micro-) of ultrathin TiO2 nanosheets on their electron transfer and diffusion properties. Benefiting from the faster electron transfer rate and short diffusion path of the MS-TiO2, the MS-TiO2/P25 gains the more superior performance compared to pure P25 and NS-TiO2/P25 in the application of DSSCs. Moreover, it is expected that the novel high aspect ratio MS-TiO2 may be applied in diverse fields including photocatalysis, photodetectors, lithium-ion batteries and others concerning the environment and energy.

Ultrathin anatase nanosheets with high energy facets exposed and related photocatalytic performances

Ultrathin anatase nanosheets with high energy (116) facets exposed were fabricated from exfoliated titanate nanosheets and exhibited high photocatalytic performance.

Growth and photocatalytic performance of carambola-like TiO2 consisting of nanosheets exposed {001} facets

Carambola-like TiO₂ was synthesized via a one-step solvothermal method for the first time, in which enhanced photocatalytic performance was observed.

Synthesis and hydrogenation of anatase TiO2 microspheres composed of porous single crystals for significantly improved photocatalytic activity

We developed a facile synthesis of anatase microspheres composed of porous single crystals in the absence of preseeding treatment, and examined the hydrogenation effect of porous TiO₂ on the photocatalytic activity.

Hydrothermal synthesis of the novel rutile-mixed anatase TiO2 nanosheets with dominant {001} facets for high photocatalytic activity

We introduce a hydrothermal route to synthesize rutile-mixed anatase nanosheets with dominant {001} facets for high photocatalytic activity.

Hierarchically assembled microspheres consisting of nanosheets of highly exposed (001)-facets TiO2 for dye-sensitized solar cells

Mono-dispersed 2D nanosheets of 3D microspheres nanostructure was synthesized. It shows highly exposed (001)-facets (ca. 82%) and high surface area (112.2 m² g⁻¹). 11.13%-efficient DSSC is obtained with TiO₂ microspheres working electrode.

Rational design of nanomaterials for water treatment

The ever-increasing human demand for safe and clean water is gradually pushing conventional water treatment technologies to their limits. It is now a popular perception that the solutions to the existing and future water challenges will hinge upon further developments in nanomaterial sciences. The concept of rational design emphasizes on 'design-for-purpose' and it necessitates a scientifically clear problem definition to initiate the nanomaterial design. The field of rational design of nanomaterials for water treatment has experienced a significant growth in the past decade and is poised to make its contribution in creating advanced next-generation water treatment technologies in the years to come. Within the water treatment context, this review offers a comprehensive and in-depth overview of the latest progress in rational design, synthesis and applications of nanomaterials in adsorption, chemical oxidation and reduction reactions, membrane-based separation, oil-water separation, and synergistic multifunctional all-in-one nanomaterials/nanodevices. Special attention is paid to the chemical concepts related to nanomaterial design throughout the review.

A Biomineralization Strategy for "Net"-Like Interconnected TiO2 Nanoparticles Conformably Covering Reduced Graphene Oxide with Reversible Interfacial Lithium Storage

A green and simple biomineralization-inspired method to create "net"-like interconnected TiO₂ nanoparticles conformably covering reduced graphene oxide (RGO) with high loading density is reported. This method uses polyamine as both the biomineralization agent and linker to manipulate the nucleation, growth, and crystallization of TiO₂ nanoparticles on the surface of graphene oxide. The obtained TiO₂/RGO composites demonstrate sub-10-nm TiO₂ nanoparticles with (001) facets, ultrathin thickness (10-12 nm), and a high surface area of 172 m² g^-1. When used as anode material for lithium ion batteries, the material displayed excellent rate capability and long cycle life; a capacity of 155 mAh g^-1 is obtained after 50 cycles at the rate of 5C (1C = 168 mA g^-1) and a specific capacity of 115 mAh g^-1 is retained after 2000 cycles at the rate of 25C, which is much higher than that of mechanically mixed TiO₂/graphene composites. Detailed discharge curve analysis reveals that the high rate and cycle performance are partly a result of the reversible interfacial lithium storage of materials, which might be attributed to the pores in the TiO₂ nets on the RGO and may provide a sufficient number of interfaces for accepting both electrons and lithium ions.

Selective synthesis of TiO2 single nanocrystals and titanate nanotubes: a controllable atomic arrangement approach via NH4TiOF3 mesocrystals

Nanostructured titania and titanate have been considered as very important materials used in photocatalysis, photovoltaics, gas sensing and other electronic industries. In principle, their common structural feature is that the precursor phase involving TiO6 octahedra or similar building units may be converted to any of the nanostructured titania and titanate forms in a controllable way. Based on the atomic arrangement of ionic liquid-mediated NH4TiOF3 mesocrystals, TiO2 nanocrystals and titanate nanotubes were selectively obtained in H3BO3 and NaOH media, respectively, by using a simple hydrothermal method. Interestingly, the titanate nanotubes were successfully formed by extraction of NH4(+) and F from NH4TiOF3 in a milder alkaline environment as low as 1 M NaOH, rather than conventional treatment of TiO2 in 10 M NaOH. The as-prepared TiO2 nanocrystals with exposed {001} facets exhibit a high photocatalytic activity and sedimentation rate as compared to commercial TiO2. Upon further doping or ion-exchange, the newly prepared TiO2 nanocrystals will show potential applications in the environment.

Phase stability frustration on ultra-nanosized anatase TiO2

This work sheds light on the exceptional robustness of anatase TiO2 when it is downsized to an extreme value of 4 nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000 °C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO2 converts into a complete solid solution until almost Li1TiO2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li1TiO2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content.