The continuing development of Magnéli phase titanium sub-oxides and Ebonex® electrodes

Oxygen Deficiencies in Titanium Oxide Clusters as Models for Bulk Defects

TD-DFT calculations were performed on neutral Ti_nO_2n, Ti_nO_2n-1, and Ti_nO_2n-2 clusters, where n ≤ 7. Calculations show the Ti_nO_2n clusters are closed shell systems containing empty d orbitals and that the partially filled d orbitals of the suboxide clusters have a profound effect on their structural, electronic, and topological properties. The low energy photoexcitations of Ti_nO_2n clusters are all O-2p to Ti-3d transitions, while the open-shell suboxide clusters are all characterized by d-d transitions that occur at a much smaller optical gap. Upon low energy photoabsorption, the localization of the hole is accompanied by a local bond elongation, i.e., polaron formation, whereas d-electrons are generally delocalized around the cluster. The properties of the clusters, including the oxygen binding energies and structures, were calculated to account for the variation in relative populations found in experimental cluster distributions. Several Ti_nO_2n-2 clusters contain higher symmetry which is reflected in their relative stability. In particular, the tetrahedral symmetry of Ti₄O₆ inhibits charge carrier localization and therefore exhibits higher stability.

Occurrence and removal of poly/perfluoroalkyl substances (PFAS) in municipal and industrial wastewater treatment plants

The presence of poly- and perfluoroalkyl substances (PFAS) has caused serious problems for drinking water supplies especially at intake locations close to PFAS manufacturing facilities, wastewater treatment plants (WWTPs), and sites where PFAS-containing firefighting foam was regularly used. Although monitoring is increasing, knowledge on PFAS occurrences particularly in municipal and industrial effluents is still relatively low. Even though the production of C8-based PFAS has been phased out, they are still being detected at many WWTPs. Emerging PFAS such as GenX and F-53B are also beginning to be reported in aquatic environments. This paper presents a broad review and discussion on the occurrence of PFAS in municipal and industrial wastewater which appear to be their main sources. Carbon adsorption and ion exchange are currently used treatment technologies for PFAS removal. However, these methods have been reported to be ineffective for the removal of short-chain PFAS. Several pioneering treatment technologies, such as electrooxidation, ultrasound, and plasma have been reported for PFAS degradation. Nevertheless, in-depth research should be performed for the applicability of emerging technologies for real-world applications. This paper examines different technologies and helps to understand the research needs to improve the development of treatment processes for PFAS in wastewater streams.

Inexpensive gram scale synthesis of porous Ti4O7 for high performance polymer electrolyte fuel cell electrodes

As a fuel cell catalyst support, more than 2 g of Magnéli phase Ti₄O₇ fine-particles were synthesized in a single reaction via an inexpensive route. The single-cell performance reached that of commercial carbon-supported platinum, with an excellent load cycle durability, one of the highest ever reported for oxide-supported platinum catalysts.

An electrocoagulation and electrooxidation treatment train to remove and degrade per- and polyfluoroalkyl substances in aqueous solution

This study examined the feasibility of a novel treatment train that combines electrocoagulation (EC) with electrooxidation (EO) treatment to remove and degrade per- and polyfluoroalkyl substances (PFASs) from water. Electrocoagulation with a zinc anode could effectively remove PFASs from water, and long-chain PFASs (C₇-C₁₀) tended to have a higher removal rate. Foam was generated when a relatively high current density (>1 mA cm^-2) was applied to a relatively high PFAS concentration (each PFAS > 0.1 μM) during EC, which promoted the separation of PFASs from the bulk solution, especially for long-chain PFASs. Isotherm-like adsorption results indicated that competitive adsorption on floc occurred between PFASs when no foam was produced in a solution containing 10 different PFASs. Acid dissolution methods could recover and concentrate 10 PFASs in controlled volumes from both the floc and the foam, and it was also successfully applied in groundwater collected from a contaminated site. The concentrated PFASs in the acid solutions were efficiently destructed using EO treatment with a Ti₄O₇ anode at 10 mA cm^-2, and no supplement of electrolyte was needed for the floc dissolved solution. This electrochemical-based process can economically separate, concentrate and destroy PFASs in groundwater and wastewater.

Electrochemical advanced oxidation processes coupled with membrane filtration for degrading antibiotic residues: A review on its potential applications, advances, and challenges

Antibiotic pollution is mainly caused by aquaculture wastewater and pharmaceuticals, which are frequently used by humans. Due to limited treatment efficiency or improper selection of treatment methods, these antibiotic residues may be very harmful in human drinking water and aquatic environments. The EAOPs coupling membrane technology (EAOPs-membrane) can play their own advantages, which can significantly improve the degradation efficiency and alleviate membrane pollution (electrochemical manners). In this context, this review mainly collecting researches and information on EAOPs-membrane treatment of antibiotic pollution published between 2012 and 2020. Discussed the different combinations of these two technologies, the mechanism of them in the system to improve the processing efficiency, prolong the working time, and stabilize the system structure. Mainly due to the synergistic effect of electrochemical behavior such as electric repulsion and in-situ oxidation, the membrane fouling in the system is alleviated. In this review it was summarized that the selection of different membrane electrode materials and their modifications. The paper also elaborates the existing challenges facing the EAOPs-membrane methods for antibiotic pollution treatment, and their prospects.

A tubular electrode assembly reactor for enhanced electrochemical wastewater treatment with a Magnéli-phase titanium suboxide (M-TiSO) anode and in situ utilization

The electrochemical oxidation technology has been widely used for the waste water treatment and water reuse because of its easy-to-operate nature, an effective removal of pollutants and non-secondary pollution. However, the price of electrode materials, the limitation of mass transfer and the associated effects on contaminant degradation hamper its application. Within this context, an in situ utilization tubular electrode assembly reactor (TEAR) was proposed, in which a stainless steel pipe (SSP) was used as the cathode, and a tubular Magnéli-phase titanium suboxide (M-TiSO) anode was posited in the center of that pipe. Besides the cathode and anode, an integral electrochemical system to treat water pollutants was constituted with a spiral static mixer made from three-dimensional (3D) printing. A spiral static mixer was pushed into the interspace of electrodes to minimize the adverse effect caused by inhomogeneous distribution of pollutants. Here, the effects of current density and resident time on the removal of methylene blue (MB) and total organic carbon (TOC) were investigated, the corresponding hydrodynamics was studied using computational fluid dynamics (CFD), and the long-term stability of removing MB by the reactor was discussed. The results indicated that the MB and TOC removal rate was enhanced at specific current density with a static mixer and the velocity distribution tended to be more homogeneous. Moreover, the anode surface shear force and heat transfer were increased by improving the fluid state. This study proposed an in situ utilization concept and provided a potential value for feasible and efficient water treatment.

A stainless steel pipe (SSP) was used as a cathode. A tubular Magnéli-phase titanium suboxide (M-TiSO) anode was posited in the center. A spiral static mixer was used to process intensification.

Combining Zirconia and Titanium Suboxides by Vat Photopolymerization

A recently developed multi-ceramic additive manufacturing process (multi-CAMP) and an appropriate device offer a multi-material approach by vat photopolymerization (VPP) of multi-functionalized ceramic components. However, this process is limited to ceramic powders with a certain translucency for visible light. Electrically conductive ceramic powders are therefore ruled out because of their light-absorbing behavior and dark color. The goal of the collaborative work described in the article was to develop a material combination for this multi-material approach of the additive vat photopolymerization method which allows for combining electrical conductivity and electrical insulation plus high mechanical strength in co-sintered ceramic components. As conductive component titanium suboxides are chosen, whereas zirconia forms the mechanically stable and insulation part. Since titanium suboxides cannot be used for vat photopolymerization due to their light-absorbing behavior, titania is used instead. After additive manufacturing, the two-component parts are co-sintered in a reducing atmosphere to transform the titania into its suboxides and, thus, attaining the desired property combination. The article describes the challenges of the co-processing of both materials due to the complex optical properties of titania. Furthermore, the article shows successfully co-sintered testing parts of the material combination of zirconia/titanium suboxide which are made by assembling single-material VPP components in the green state and subsequent common thermal treatment. The results of microstructural and interface investigations such as electrical measurements are discussed.

Defect Engineering on a Ti4O7 Electrode by Ce3+ Doping for the Efficient Electrooxidation of Perfluorooctanesulfonate

Defect engineering in an electrocatalyst, such as doping, has the potential to significantly enhance its catalytic activity and stability. Herein, we report the use of a defect engineering strategy to enhance the electrochemical reactivity of Ti₄O₇ through Ce³⁺ doping (1-3 at. %), resulting in the significantly accelerated interfacial charge transfer and yielding a 37-129% increase in the anodic production of the hydroxyl radical (OH^•). The Ce³⁺-doped Ti₄O₇ electrodes, [(Ti_1-xCe_x)₄O₇], also exhibited a more stable electrocatalytic activity than the pristine Ti₄O₇ electrode so as to facilitate the long-term operation. Furthermore, (Ti_1-xCe_x)₄O₇ electrodes were also shown to effectively mineralize perfluorooctanesulfonate (PFOS) in electrooxidation processes in both a trace-concentration river water sample and a simulated preconcentration waste stream sample. A 3 at. % dopant amount of Ce³⁺ resulted in a PFOS oxidation rate 2.4× greater than that of the pristine Ti₄O₇ electrode. X-ray photoelectron spectroscopy results suggest that Ce³⁺ doping created surficial oxygen vacancies that may be responsible for the enhanced electrochemical reactivity and stability of the (Ti_1-xCe_x)₄O₇ electrodes. Results of this study provide insights into the defect engineering strategy for boosting the electrochemical performance of the Ti₄O₇ electrode with a robust reactivity and stability.

Low-Cost Bipolar Plates of Ti4O7-Coated Ti for Water Electrolysis with Polymer Electrolyte Membranes

Although hydrogen is expected to play an important role in the storage of energy from renewable energy sources, technology to produce hydrogen at low cost is needed for its widespread use. The key to the low-cost production of hydrogen with a polymer electrolyte membrane (PEM) water electrolysis system, which is widely used today, is to replace the Au- or Pt-coated Ti with a low-cost material that can be manufactured from inexpensive, corrosion-resistant, and conductive components. We studied titanium suboxide (Ti₄O₇)-coated titanium (Ti) bipolar plates, which can be substituted for commonly used Pt-coated Ti bipolar plates, as an inexpensive way of producing the PEM water electrolysis system. The water electrolysis characteristics of the cell were evaluated using Ti₄O₇-sputtered Ti for the bipolar plates of the water electrolysis cell, and the applicability of Ti₄O₇-sputtered Ti was investigated. The Ti₄O₇-sputtered Ti had a very low contact resistance (4-5 mΩ cm²) before and after voltage application that was equivalent to that of gold or platinum plating. The efficiency of water electrolysis in this study was comparable to those of previous reports using bipolar plates coated with precious metals. This development opens the door for fabrication of low-cost electrolyzers as well as related electrochemical devices such as fuel cells, sensors, catalysts, and air or liquid cleaning devices.

Progress and Insights in the Application of MXenes as New 2D Nano-Materials Suitable for Biosensors and Biofuel Cell Design

Recent progress in the application of new 2D-materials-MXenes-in the design of biosensors, biofuel cells and bioelectronics is overviewed and some advances in this area are foreseen. Recent developments in the formation of a relatively new class of 2D metallically conducting MXenes opens a new avenue for the design of conducting composites with metallic conductivity and advanced sensing properties. Advantageous properties of MXenes suitable for biosensing applications are discussed. Frontiers and new insights in the area of application of MXenes in sensorics, biosensorics and in the design of some wearable electronic devices are outlined. Some disadvantages and challenges in the application of MXene based structures are critically discussed.

Insights in the Application of Stoichiometric and Non-Stoichiometric Titanium Oxides for the Design of Sensors for the Determination of Gases and VOCs (TiO2-x and TinO2n-1 vs. TiO2)

In this review article, attention is paid towards the formation of various nanostructured stoichiometric titanium dioxide (TiO2), non-stoichiometric titanium oxide (TiO2-x) and Magnéli phase (TinO2n-1)-based layers, which are suitable for the application in gas and volatile organic compound (VOC) sensors. Some aspects related to variation of sensitivity and selectivity of titanium oxide-based sensors are critically overviewed and discussed. The most promising titanium oxide-based hetero- and nano-structures are outlined. Recent research and many recently available reviews on TiO2-based sensors and some TiO2 synthesis methods are discussed. Some promising directions for the development of TiO2-based sensors, especially those that are capable to operate at relatively low temperatures, are outlined. The applicability of non-stoichiometric titanium oxides in the development of gas and VOC sensors is foreseen and transitions between various titanium oxide states are discussed. The presence of non-stoichiometric titanium oxide and Magnéli phase (TinO2n-1)-based layers in 'self-heating' sensors is predicted, and the advantages and limitations of 'self-heating' gas and VOC sensors, based on TiO2 and TiO2-x/TiO2 heterostructures, are discussed.

Coupling of Anodic Oxidation and Soil Remediation Processes: A Review

In recent years, due to industrial modernization and agricultural mechanization, several environmental consequences have been observed, which make sustainable development difficult. Soil, as an important component of ecosystem and a key resource for the survival of human and animals, has been under constant contamination from different human activities. Contaminated soils and sites require remediation not only because of the hazardous threat it possess to the environment but also due to the shortage of fresh land for both agriculture and urbanization. Combined or coupled remediation technologies are one of the efficient processes for the treatment of contaminated soils. In these technologies, two or more soil remediation techniques are applied simultaneously or sequentially, in which one technique complements the other, making the treatment very efficient. Coupling anodic oxidation (AO) and soil remediation for the treatment of soil contaminated with organics has been studied via two configurations: (i) soil remediation, ex situ AO, where AO is used as a post-treatment stage for the treatment of effluents from soil remediation process and (ii) soil remediation, in situ AO, where both processes are applied simultaneously. The former is the most widely investigated configuration of the combined processes, while the latter is less common due to the greater diffusion dependency of AO as an electrode process. In this review, the concept of soil washing (SW)/soil flushing (SF) and electrokinetic as soil remediation techniques are briefly explained followed by a discussion of different configurations of combined AO and soil remediation.

Modelling and synthesis of Magnéli Phases in ordered titanium oxide nanotubes with preserved morphology

The presence of Magnéli phases in titanium oxide nanotubes (NTs) can open up frontiers in many applications owing to their electrical and optical properties. Synthesis of NTs with Magnéli phases have posed a challenge due to the degradation and loss of morphology in NTs upon high-temperature treatments (>600 °C) in a reducing environment. This study reports on the synthesis of anodically formed NTs containing Magnéli phases through a double annealing route: oxygen (O₂) annealing followed by annealing in 2% hydrogen with a nitrogen balance (2%H₂-N₂). The nucleation, growth, and transformation of anodized amorphous NTs into crystalline phases was investigated. The NTs obtained through this route were highly ordered and composed of mixed phases of anatase, rutile, and the Magnéli phase (Ti₄O₇). Experimental results from scanning electron microscopy (SEM), X-ray diffraction (XRD), scanning transmission electron microscopy (S/TEM), and Raman spectroscopy were combined with first principle calculations to develop an understanding of the sequential phase transformations during annealing. A predictive model was developed using density functional theory (DFT) to potentially predict the titanium oxides formed and their stability with reference to the mole fraction of oxygen. The change in the density of states (DOS), band structure, optical properties, and stability of phases are also discussed using DFT simulations. The combination of experimental characterization and modelling helped to understand the nucleation of anatase and rutile and the reorganization of these phases to form Magnéli phases on the anodized amorphous NTs through annealing treatment.

Treatment train approaches for the remediation of per- and polyfluoroalkyl substances (PFAS): A critical review

Per- and polyfluoroalkyl substances (PFAS) have recently drawn great attention due to their ubiquitous presence in aquatic environments and potential toxicity to human health and the environment. A number of recent studies have demonstrated that "passive" removal approaches, such as adsorption, filtration, and reverse osmosis or "active" degradation technologies, such as enhanced photolysis, electrochemical oxidation, and sonochemical destruction, are all able to individually conduct remedial measures for PFAS contamination at some level. However, drawbacks, specifically high energy consumption, low cost-efficiency, and extreme operating conditions, are commonly observed from these studies which significantly suppress the future for commercialization of these innovative technologies. Since 2015, a new trend of PFAS remediation has emerged that uses multiple synergetic technologies simultaneously (known as treatment train processes) to effectively achieve in-situ remediation of PFAS. This paper provides new insight of the recently reported treatment train studies selected from approximately 150 different publications with regards to the remediation of PFAS and discusses their innovative designs, remediation performances, present limits, and possible improvements. Based on a comprehensive review of the current treatment train studies, this review work proposes a new design that consists of three individual technologies, namely, nanofiltration, electrochemical anodic oxidation, and electro-Fenton degradation, to maximize economic and environmental benefits of PFAS remedial measures.

Effects of chloride on electrochemical degradation of perfluorooctanesulfonate by Magnéli phase Ti4O7 and boron doped diamond anodes

This study examined the degradation of perfluorooctanesulfonate (PFOS) in an electrochemical system using Magnéli phase titanium suboxide (Ti₄O₇) as the anode. In particular, the influence of chloride on the treatment process was examined. Tests were also conducted with boron doped diamond (BDD) electrodes for comparison. Experimental data demonstrated that PFOS was effectively degraded by electrochemical oxidation on both BDD and Magnéli phase Ti₄O₇ anodes. It appeared that PFOS degradation occurred via direct electron transfer (DET) in combination with attack by hydroxyl radicals adsorbed on the anode surface (HO^•_ads) that were formed by anodic oxidation of water. The presence of Cl^- inhibited the degradation of the PFOS on Ti₄O₇ electrode by suppressing the oxidation of water, but accelerated PFOS degradation on BDD electrode, where the oxidation of Cl^- via DET occurred. Formation of chlorate and perchlorate was slower on Ti₄O₇ than on the BDD anode. The mechanisms governing the behavior of PFOS and chloride reactions on BDD and Ti₄O₇ anodes were explored by experiments in combination with density functional theory (DFT) computations.

A reverse slipping strategy for bulk-reduced TiO2−x preparation from Magnéli phase Ti4O7

Bulk-reduced TiO_2−x samples were obtained by a reverse slipping strategy forming black TiO_2−x from Ti₄O₇.

Rapid and selective electrochemical transformation of ammonia to N2 by substoichiometric TiO2-based electrochemical system

In this study, we have developed a continuous-flow electrochemical system towards the rapid and selective conversion of ammonia to N₂, based on a tubular substoichiometric titanium dioxide (Ti₄O₇) anode and a Pd–Cu co-modified Ni foam (Pd–Cu/NF) cathode, both of which are indispensable. Under the action of a suitable anode potential, the Ti₄O₇ anode enables the conversion of Cl⁻ to chloride radicals (Cl˙), which could selectively react with ammonia to produce N₂. The anodic byproducts, e.g. NO₃⁻, were further reduced to N₂ at the Pd–Cu/NF cathode. EPR and scavenger experiments confirmed the dominant role of Cl˙ in ammonia conversion. Complete transformation of 30 mg L⁻¹ ammonia could be obtained over 40 min of continuous operation under optimal conditions. The proposed electrochemical system also exhibits enhanced oxidation kinetics compared to conventional batch systems. This study provides new insights into the rational design of a high-performance electrochemical system to address the challenging issue of ammonia pollution.

A continuous-flow electrochemical system for rapid and selective conversion of ammonia to N₂ was proposed. The system consists of a tubular substoichiometric titanium dioxide (Ti₄O₇) anode and a Pd–Cu co-modified Ni foam (Pd–Cu/NF) cathode.

TiO2-x/TiO2-Structure Based 'Self-Heated' Sensor for the Determination of Some Reducing Gases

In this research we report the gas-sensing properties of TiO2-x/TiO2-based hetero-structure, which was 'self-heated' by current that at constant potential passed through the structure. Amperometric measurements were applied for the evaluation of sensor response towards ethanol, methanol, n-propanol and acetone gases/vapours. The sensitivity towards these gases was based on electrical resistance changes, which were determined by amperometric measurements of current at fixed voltage applied between Pt-based contacts/electrodes deposited on the TiO2-x/TiO2-based layer. X-ray diffraction (XRD) analysis revealed the formation of TiO2-x/TiO2-based hetero-structure, which is mainly based on Ti3O5/TiO2 formed during the hydro-thermal oxidation-based sensing-layer preparation process. Additionally, photoluminescence and time-resolved photoluminescence decay kinetics-based signals of this sensing structure revealed the presence of TiO2 mainly in the anatase phase in the TiO2-x/TiO2-based hetero-structure, which was formed at 400 °C annealing temperature. The evaluation of TiO2-x/TiO2-based gas-sensing layer was performed at several different temperatures (25 °C, 72 °C, 150 °C, 180 °C) and at these temperatures different sensitivity to the aforementioned gaseous materials was determined.

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

This study investigated the degradation of perfluorooctanesulfonate (PFOS) in a reactive electrochemical membrane (REM) system in which a porous Magnéli phase titanium suboxide ceramic membrane served simultaneously as the anode and the membrane. Near complete removal (98.30 ± 0.51%) of PFOS was achieved under a cross-flow filtration mode at the anodic potential of 3.15 V vs standard hydrogen electrode (SHE). PFOS removal efficiency during the REM operation is much greater than that of the batch operation mode under the same anodic potential. A systematic reaction rate analysis in combination with electrochemical characterizations quantitatively elucidated the enhancement of PFOS removal in REM operation in relation to the increased electroactive surface area and improved interphase mass transfer. PFOS appeared to undergo rapid mineralization to CO₂ and F^-, with only trace levels of short-chain perfluorocarboxylic acids (PFCAs, C₄-C₈) identified as intermediate products. Density functional theory (DFT) simulations and experiments involving free radical scavengers indicated that PFOS degradation was initiated by direct electron transfer (DET) on anode to yield PFOS free radicals (PFOS^•), which further react with hydroxyl radicals that were generated by water oxidation and adsorbed on the anode surface (^•OH_ads). The attack of ^•OH_ads is essential to PFOS degradation, because, otherwise, PFOS^• may react with water and revert to PFOS.

Different Reactivity of Rutile and Anatase TiO2 Nanoparticles: Synthesis and Surface States of Nanoparticles of Mixed-Valence Magnéli Oxides

Magnéli phases Ti_n O_2n-1 (3<n≤10) are mixed Ti⁴⁺ /Ti³⁺ oxides with high electrical conductivity. When used for water remediation or electrochemical energy storage and conversion, they are nanostructured and exposed to various environments. Therefore, understanding their surface reactivity is of prime importance. Such studies have been hindered by carbon contamination from syntheses. Herein, this synthetic and characterization challenge is addressed through a new approach to 50 nm carbon-free Ti₄ O₇ and Ti₆ O₁₁ nanoparticles. It takes advantage of the different reactivities of rutile and anatase TiO₂ nanoparticles towards H₂ , to use the former as precursor of Ti_n O_2n-1 and the latter as a diluting agent. This approach is combined with silica templating to restrain particle growth. The surface reactivity of the Magnéli nanoparticles under different atmospheres was then evaluated quantitatively by synchrotron-radiation-based X-ray photoelectron spectroscopy, which revealed oxidized surfaces with lower conductivity than the core. This finding sheds a new light on the charge transfer occurring in these materials.

Dismutation of Titanium Sub-oxide into TiO and TiO2 with Structural Hierarchy Assisted by Ammonium Halides

Black TiO_2-x attracts enormous attention due to its large solar absorption and improved conductivity. In this work, a novel structure of TiO_2-x with conductive TiO layer, performing full-spectrum absorption, was synthesized in one step by the unforeseen dismutation reaction of titanium sub-oxides (Ti_n O_2n-1 ) in ammonium halide atmosphere. For this new reaction, a possible mechanism of decomposition-etching-disproportionation-rehydrolysis process was proposed. The vital intermediate reactant TiCl₄ , which verifies the assumption, has been captured in the form of (NH₄ )₂ TiCl₆ , especially where Ti₂ O₃ is the reactant. Furthermore, this work not only can nominate TiO as an alternative for noble metals or carbon materials in the aim to improve the electron conductivity and solar absorption of black TiO_2-x , which are important in electrochemistry and optoelectronics fields, but also can be a new route to synthesize special structures for other multivalent transition metals.

Conductive Nanosized Magnéli-Phase Ti4O7 with a Core@Shell Structure

Magnéli-phase Ti₄O₇, known for its high electrical conductivity and corrosion resistance, is typically prepared by hydrogen reduction at high temperatures (∼1000 °C), leading to large particles. Nanosized Ti₄O₇ have been explored for application toward high specific surface area electrode materials and electrocatalyst supports; nonetheless, the particle size of Ti₄O₇ is still insufficient for utilization as a support. In this study, we have pursued a novel synthetic approach for nanosized Ti₄O₇ platelets with a length of 10-80 nm and thickness of 3-10 nm even under high-temperature conditions. We herein describe the use of SiO₂ beads as a core to obtain a SiO₂ core coated with multilayers of TiO₂ nanosheets exfoliated from layered H₂Ti₄O₇ which is subsequently subjected to high-temperature reduction to prepare a SiO₂-core@Ti₄O₇-shell structure. The pair distribution function technique has proven that the shell is transformed to single-phase Ti₄O₇. The electrical double layer capacitance of SiO₂-core@Ti₄O₇-shell was much larger than that of conventionally synthesized Ti₄O₇ particles with a micrometer size. The results show the beneficial effects of the SiO₂-core@Ti₄O₇-shell structure, and it is the first example of the synthesis for conductive Ti₄O₇ with a high specific surface area even under conditions of high-temperature synthesis.

In Vitro Cytotoxicity Evaluation of the Magnéli Phase Titanium Suboxides (TixO2x-1) on A549 Human Lung Cells

The use of titanium suboxides, known as Magnéli phase TiOx, is expected to increase in the near future due to their desirable properties. In order to use Magnéli phase TiOx nanoparticles safely, it is necessary to know how nanoparticles interact with biological systems. In this study, the cytotoxicity of three different Magnéli TiOx nanoparticles was evaluated using human lung A549 cells and the results were compared with hazard data on two different TiO₂ nanoparticles whose biological interactions have already been extensively studied. After A549 cells were exposed to nanoparticles, the metabolic activity was measured by the Resazurin assay, the amount of cellular proteins was measured by the Coomassie Blue assay, and lysosomal integrity was measured by the Neutral Red Uptake assay. In order to investigate possible modes of particle actions, intracellular Ca2+ level, reactive oxygen species (ROS) production, and photo-oxidative disruptions of lysosomal membranes were assessed. All experiments were performed in serum-containing and in serum-deprived cell culture mediums. In addition, the photocatalytic activity of Magnéli TiOx and TiO₂ nanoparticles was measured. The results show that Magnéli TiOx nanoparticles increase intracellular Ca2+ but not ROS levels. In contrast, TiO₂ nanoparticles increase ROS levels, resulting in a higher cytotoxicity. Although Magnéli TiOx nanoparticles showed a lower UV-A photocatalytic activity, the photo-stability of the lysosomal membranes was decreased by a greater extent, possibly due to particle accumulation inside lysosomes. We provide evidence that Magnéli TiOx nanoparticles have lower overall biological activity when compared with the two TiO₂ formulations. However, some unique cellular interactions were detected and should be further studied in line with possible Magnéli TiOx application. We conclude that Magnéli phase nanoparticles could be considered as low toxic material same as other forms of titanium oxide particles.

Solid-Gas Phase Photo-Catalytic Behaviour of Rutile and TiOn (1 < n < 2) Sub-Oxide Phases for Self-Cleaning Applications

The solid-gas phase photo-catalytic activities of rutile TiO₂ and TiO_n (1 < n < 2) sub-oxide phases have been evaluated. Varying concentrations of Ti³⁺ defects were introduced into the rutile polymorph of titanium dioxide through carbo-thermal reduction at temperatures ranging from 350 °C to 1300 °C. The resulting sub-oxides formed were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, impedance spectroscopy and UV-visible diffuse reflectance spectroscopy. The presence of Ti³⁺ in rutile exposed to high reduction temperatures was confirmed by X-ray diffraction. In addition, a Ti³⁺-Ti⁴⁺ system was demonstrated to enhance the photo-catalytic properties of rutile for the degradation of the air pollutants NO₂ and CO₂ under UV irradiation of wavelengths (λ) 376–387 nm and 381–392 nm. The optimum reduction temperature for photo-catalytic activity was within the range 350–400 °C and attributed to improved charge-separation. The materials that were subject to carbo-thermal reduction at temperatures of 350 °C and 400 °C exhibited electrical conductivities over one hundred times higher compared to the non-reduced rutile. The results highlight that sub-oxide phases form an important alternative approach to doping with other elements to improve the photo-catalytic performance of TiO₂. Such materials are important for applications such as self-cleaning where particles can be incorporated into surface coatings.

Formation mechanisms of interfaces between different TinO2n−1 phases prepared by carbothermal reduction reaction

The structures of two types of interfaces between different Ti_nO_2n−1 phases have been investigated based on comprehensive XRD and TEM analysis. Combined with thermodynamic calculations, the structural evolutions and formation mechanisms of these interfaces are further proposed in detail.

ElemNet: Deep Learning the Chemistry of Materials From Only Elemental Composition

Conventional machine learning approaches for predicting material properties from elemental compositions have emphasized the importance of leveraging domain knowledge when designing model inputs. Here, we demonstrate that by using a deep learning approach, we can bypass such manual feature engineering requiring domain knowledge and achieve much better results, even with only a few thousand training samples. We present the design and implementation of a deep neural network model referred to as ElemNet; it automatically captures the physical and chemical interactions and similarities between different elements using artificial intelligence which allows it to predict the materials properties with better accuracy and speed. The speed and best-in-class accuracy of ElemNet enable us to perform a fast and robust screening for new material candidates in a huge combinatorial space; where we predict hundreds of thousands of chemical systems that could contain yet-undiscovered compounds.

Switchable Intrinsic Defect Chemistry of Titania for Catalytic Applications

The energy crisis is one of the most serious issue that we confront today. Among different strategies to gain access to reliable fuel, the production of hydrogen fuel through the water-splitting reaction has emerged as the most viable alternative. Specifically, the studies on defect-rich TiO2 materials have been proved that it can perform as an efficient catalyst for electrocatalytic and photocatalytic water-splitting reactions. In this invited review, we have included a general and critical discussion on the background of titanium sub-oxides structure, defect chemistries and the consequent disorder arising in defect-rich Titania and their applications towards water-splitting reactions. We have particularly emphasized the origin of the catalytic activity in Titania-based material and its effects on the structural, optical and electronic behavior. This review article also summarizes studies on challenging issues on defect-rich Titania and new possible directions for the development of an efficient catalyst with improved catalytic performance.

Size Control of Ti4O7 Nanoparticles by Carbothermal Reduction Using a Multimode Microwave Furnace

Utilization of Ti4O7 in applications such as catalyst support calls for control over the size of the Ti4O7 nanoparticles. This can be achieved using a simple process such as carbothermal reduction. In this study, various sizes of Ti4O7 nanoparticles (25, 60, and 125 nm) were synthesized by carbothermal reduction using a multimode microwave apparatus. It was possible to produce Ti4O7 nanoparticles as small as 25 nm by precisely controlling the temperature, heating process, and holding time of the sample while taking advantage of the characteristics of microwave heating such as rapid and volumetric heating. The results show that microwave carbothermal reduction is advantageous in controlling the size of the Ti4O7 nanoparticles.

Cobalt-Doped Black TiO2 Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment

TiO₂ has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO₂ nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO₂ nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO₄ electrolyte at 10 mA cm^–2. Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (O_v) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, O_v, and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO₂ anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoO_x film on top of Co-Black electrode. The CoO_x/Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO₂ (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm^–2.

Beyond the Compositional Threshold of Nanoparticle-Based Materials

The design of inorganic nanoparticles relies strongly on the knowledge from solid-state chemistry not only for characterization techniques, but also and primarily for choosing the systems that will yield the desired properties. The range of inorganic solids reported and studied as nanoparticles is however strikingly narrow when compared to the solid-state chemistry portfolio of bulk materials. Efforts to enlarge the collection of inorganic particles are becoming increasingly important for three reasons. First, they can yield materials more performing than current ones for a range of fields including biomedicine, optics, catalysis, and energy. Second, looking outside the box of common compositions is a way to target original properties or to discover genuinely new behaviors. The third reason lies in the path followed to reach these novel nano-objects: exploration and setup of new synthetic approaches. Indeed, willingness to access original nanoparticles faces a synthetic challenge: how to reach nanoparticles of solids that originally belong to the realm of solid-state chemistry and its typical protocols at high temperature? To answer this question, alternative reaction pathways must be sought, which may in turn provide tracks for new, untargeted materials. The corresponding strategies require limiting particle growth by confinement at high temperatures or by decreasing the synthesis temperature. Both approaches, especially the latter, provide a nice playground to discover metastable solids never reported before. The aim of this Account is to raise attention to the topic of the design of new inorganic nanoparticles. To do so, we take the perspective of our own work in the field, by first describing synthetic challenges and how they are addressed by current protocols. We then use our achievements to highlight the possibilities offered by new nanomaterials and to introduce synthetic approaches that are not in the focus of recent literature but hold, in our opinion, great promise. We will span methods of low temperature "chimie douce" aqueous synthesis coupled to microwave heating, sol-gel chemistry and processing coupled to solid state reactions, and then molten salt synthesis. These protocols pave the way to metastable low valence oxyhydroxides, vanadates, perovskite oxides, boron carbon nitrides, and metal borides, all obtained at the nanoscale with structural and morphological features differing from "usual" nanomaterials. These nano-objects show original properties, from sensing, thermoelectricity, charge and spin transports, photoluminescence, and catalysis, which require advanced characterization of surface states. We then identify future trends of synthetic methodologies that will merit further attention in this burgeoning field, by emphasizing the importance of unveiling reaction mechanisms and coupling experiments with modeling.

Mineralization of organic pollutants by anodic oxidation using reactive electrochemical membrane synthesized from carbothermal reduction of TiO2

Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO₂ is used for the mineralization of biorefractory pollutants during filtration operation. The mixture of Ti₄O₇ and Ti₅O₉ Magnéli phases ensures the high reactivity of the membrane for organic compound oxidation through ^•OH mediated oxidation and direct electron transfer. In cross-flow filtration mode, convection-enhanced mass transport of pollutants can be achieved from the high membrane permeability (3300 LMH bar^-1). Mineralization efficiency of oxalic acid, paracetamol and phenol was assessed as regards to current density, transmembrane pressure and feed concentration. Unprecedented high removal rates of total organic carbon and mineralization current efficiency were achieved after a single passage through the REM, e.g. 47 g m^-2 h^-1 - 72% and 6.7 g m^-2 h^-1 - 47% for oxalic acid and paracetamol, respectively, at 15 mA cm^-2. However, two mechanisms have to be considered for optimization of the process. When the TOC flux is too high with respect to the current density, aromatic compounds polymerize in the REM layer where only direct electron transfer occurs. This phenomenon decreases the oxidation efficiency and/or increases REM fouling. Besides, O₂ bubbles sweeping at high permeate flux promotes O₂ gas generation, with adverse effect on oxidation efficiency.

Nano Titanium Monoxide Crystals and Unusual Superconductivity at 11 K

Nano TiO₂ is investigated intensely due to extraordinary photoelectric performances in photocatalysis, new-type solar cells, etc., but only very few synthesis and physical properties have been reported on nanostructured TiO or other low valent titanium-containing oxides. Here, a core-shell nanoparticle made of TiO core covered with a ≈5 nm shell of amorphous TiO_1+x is newly constructed via a controllable reduction method to synthesize nano TiO core and subsequent soft oxidation to form the shell (TiO_1+x ). The physical properties measurements of electrical transport and magnetism indicate these TiO@TiO_1+x nanocrystals are a type-ІІ superconductor of a recorded T_c^onset = 11 K in the binary Ti-O system. This unusual superconductivity could be attributed to the interfacial effect due to the nearly linear gradient of O/Ti ratio across the outer amorphous layer. This novel synthetic method and enhanced superconductivity could open up possibilities in interface superconductivity of nanostructured composites with well-controlled interfaces.

Modified Synthesis Strategies for the Stabilization of low n Tin O2n-1 Magnéli Phases

Titanium reduced oxides TiO_2-x occupy, since long time, a prominent place on the landscape of binary metal oxides because of their intriguing ability to form extended defects that affect both the formation of new superlattices and different electronic behaviours. Related to these features, a wide range of practical applications has been achieved. Moved by the conviction of the great potential of understanding the influence of the reactivity, compositional variations and size effects on their functional properties, the aim of this personal account is the optimization of a recently developed strategy for the stabilization of low n Ti_n O_2n-1 terms. In particular, we will focus on the Ti₄ O₇ composition as well as the incorporation of transition metals, like Mn, in order to deal with new reduced Magnéli phases.