High Energy Heavy Ion-Induced Structural Modifications in Binary Oxides.

The objective of this work was to determine the relation between materials properties and their effect on the structural response of binary oxides to high energy heavy ion irradiation. The Group 14 oxides offered an ideal system of study due to the gradual change in materials properties from SiO2 to PbO2, while their electronic configurations remain consistent; this series facilitated the association of specific materials properties with their effect on radiation response. SnO2 and PbO2 were investigated experimentally in order to complete the body of data for this system. For comparative purposes, Ta2O5 was investigated under the same conditions due to the contrast in physical and chemical characteristics it offers, as well as its unusually large and complicated unit cell. SnO2, PbO2, and Ta2O5 were irradiated by 2.2 GeV 197Au ions (11.1 MeV/u) at room temperature. Samples were analyzed with synchrotron X-ray diffraction, Raman spectroscopy, transmission electron microscopy, small-angle X-ray scattering, and X-ray photoelectron spectroscopy. Irradiation of SnO2 led to the formation of a crystalline SnO phase with trace quantities of metallic Sn, indicating the loss of oxygen and cation reduction during irradiation. Irradiation of PbO2 resulted in the formation of seven distinct structures with compositions of Pb2O3, Pb3O4, PbO, and Pb. Gradual cation reduction was measured. Irradiation of Ta2O5 induced amorphous ion tracks with core-shell morphologies. Oxygen loss was evidenced, increasing with fluence to an estimated final stoichiometry of Ta2O4.2. Using the Group 14 oxide system, the following relations were made: (i) increased susceptibility to amorphization has been attributed to high enthalpy of formation, bandgap, electrical resistivity, and cation electronegativity (relative to those resistant to amorphization), as well as relatively low bond ionicity and bond lengths; (ii) increased susceptibility to oxygen loss during irradiation has been attributed to relatively low bond dissociation energy, bandgap, and electrical resistivity, as well as relatively large bond lengths; (iii) increased susceptibility to cation reduction has been attributed to relatively high bond ionicity as well as low enthalpy of formation, melting temperature, resistivity, and cation electronegativity. Materials property value thresholds are presented for all properties that show correlations to each radiation effect.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113452/1/acusick_1.pd

A model for non-thermal action of microwave radiation on oxide film/semiconductor structures

A model is considered that explains mechanism of non-thermal action of microwave radiation on the thin SiO₂ (ТiO₂, Er₂O₃, Gd₂O₃) film/SiC and SiO₂/GaAs structures. It assumes that the centers of electron-hole recombination are redistributed because of resonance interaction between dislocations of certain length and microwave radiation. As a result, additional bands appear in photoluminescence (PL) spectra of the oxide film/SiC structures or intensities of some bands are redistributed in the PL spectra of the SiO₂/GaAs structure, as well as optical density of the oxide film/SiC structures changes

Magnetron sputter deposition and nitridation of Ta3N5 thin films for photo-electrochemical water splitting

The reliance of human society on fossil fuels has created significant environmental consequences, as such it is imperative that renewable and sustainable sources of energy generation are developed. Hydrogen generation via solar water splitting is a compelling method of renewable energy production and could form the basis for a future hydrogen economy. Tantalum nitride (Ta3N5) is a compelling solar water splitting material due to its appreciable band gap of 2.1 eV and redox potentials that straddle those of water, which enables Ta3N5 to absorb light in the visible spectrum and perform the overall splitting of water into oxygen and hydrogen. However, Ta3N5 self-oxidizes under water splitting conditions which suppresses its performance. This can be avoided by separating Ta3N5 from H2O under water splitting conditions, or by performing the reduction of water with Ta3N5 instead of the oxidation reaction. This thesis describes the synthesis and characterisation of Ta3N5 thin films via sputter deposition and thermal nitridation, with the aim of developing Ta3N5 as a high performance photo-electrode material through the incorporation of chromium and aluminium as acceptor dopants to drive p-type properties. Films are characterised using SEM/EDS, XRD, UV-Vis, and SIMS to determine phase, elemental composition and opto-electric properties. Photo-response and majority carrier concentration were measured using Hall effect apparatus and electrochemical techniques. In this work, films were synthesized with the goal of directly depositing Ta3N5. Several phases within the tantalum nitride phase series were observed, with the metastable TaN group of phases being the most common. Ta3N5 was synthesized from sputtered tantalum oxide films and successfully annealed to produce Ta3N5. The difficulty in depositing Ta3N5 directly is addressed by describing a mechanism for the ammonolysis of Ta2O5 to Ta3N5. Acceptor doped Ta3N5 photo-electrodes were produced and characterised using this method. Chromium doped Ta3N5 films exhibited an exsolved chromium nitride phase in XRD results, and a solubility limit for chromium in Ta3N5 was determined to be ~6 at. %. For aluminium doped films, no exsolved phase was observed and no solubility limit determined under the conditions presented. Aluminium doped Ta3N5 films demonstrated improved photocathode response relative to the standard Ta3N5 films

Tungsten-Based Composites for Nuclear Fusion Applications

This chapter provides a comprehensive knowledge about the potential role of tungsten-based composites in fusion reactors and the research work which has been done in this very important area of nuclear materials. The characteristics of tungsten, which make it the most potential candidate for plasma-facing applications, have been presented along with the shortcomings in pure tungsten. The research work that has been done so far in the field of tungsten-based composites to overcome the problems with pure tungsten has been included. The fabrication, characterization, types of reinforcements and the classes of composites have been reviewed. The behavior of tungsten-based composites under various kinds of loads (i.e. mechanical and thermal) and environments (radiations and oxidizing etc.) has been summarized

Estruturas 2D funcionais de tantalatos alcalinos para microelectrónica e aplicações relacionadas

Doutoramento em Ciência e Engenharia de MateriaisAlkali tantalates and niobates, including K(Ta / Nb)O3, Li(Ta / Nb)O3 and Na(Ta / Nb)O3, are a very promising ferroic family of lead-free compounds with perovskite-like structures. Their versatile properties make them potentially interesting for current and future application in microelectronics, photocatalysis, energy and biomedics. Among them potassium tantalate, KTaO3 (KTO), has been raising interest as an alternative for the well-known strontium titanate, SrTiO3 (STO). KTO is a perovskite oxide with a quantum paraelectric behaviour when electrically stimulated and a highly polarizable lattice, giving opportunity to tailor its properties via external or internal stimuli. However problems related with the fabrication of either bulk or 2D nanostructures makes KTO not yet a viable alternative to STO. Within this context and to contribute scientifically to the leverage tantalate based compounds applications, the main goals of this thesis are: i) to produce and characterise thin films of alkali tantalates by chemical solution deposition on rigid Si based substrates, at reduced temperatures to be compatible with Si technology, ii) to fulfil scientific knowledge gaps in these relevant functional materials related to their energetics and ii) to exploit alternative applications for alkali tantalates, as photocatalysis. In what concerns the synthesis attention was given to the understanding of the phase formation in potassium tantalate synthesized via distinct routes, to control the crystallization of desired perovskite structure and to avoid low temperature pyrochlore or K-deficient phases. The phase formation process in alkali tantalates is far from being deeply analysed, as in the case of Pb-containing perovskites, therefore the work was initially focused on the process-phase relationship to identify the driving forces responsible to regulate the synthesis. Comparison of phase formation paths in conventional solid-state reaction and sol-gel method was conducted. The structural analyses revealed that intermediate pyrochlore K2Ta2O6 structure is not formed at any stage of the reaction using conventional solid-state reaction. On the other hand in the solution based processes, as alkoxide-based route, the crystallization of the perovskite occurs through the intermediate pyrochlore phase; at low temperatures pyrochlore is dominant and it is transformed to perovskite at >800 °C. The kinetic analysis carried out by using Johnson-MehlAvrami-Kolmogorow model and quantitative X-ray diffraction (XRD) demonstrated that in sol-gel derived powders the crystallization occurs in two stages: i) at early stage of the reaction dominated by primary nucleation, the mechanism is phase-boundary controlled, and ii) at the second stage the low value of Avrami exponent, n ~ 0.3, does not follow any reported category, thus not permitting an easy identification of the mechanism. Then, in collaboration with Prof. Alexandra Navrotsky group from the University of California at Davis (USA), thermodynamic studies were conducted, using high temperature oxide melt solution calorimetry. The enthalpies of formation of three structures: pyrochlore, perovskite and tetragonal tungsten bronze K6Ta10.8O30 (TTB) were calculated. The enthalpies of formation from corresponding oxides, ∆Hfox, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -203.63 ± 2.84 kJ/mol, - 358.02 ± 3.74 kJ/mol, and -1252.34 ± 10.10 kJ/mol, respectively, whereas from elements, ∆Hfel, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -1408.96 ± 3.73 kJ/mol, -2790.82 ± 6.06 kJ/mol, and -13393.04 ± 31.15 kJ/mol, respectively. The possible decomposition reactions of K-deficient KTa2.2O6 pyrochlore to KTaO3 perovskite and Ta2O5 (reaction 1) or to TTB K6Ta10.8O30 and Ta2O5 (reaction 2) were proposed, and the enthalpies were calculated to be 308.79 ± 4.41 kJ/mol and 895.79 ± 8.64 kJ/mol for reaction 1 and reaction 2, respectively. The reactions are strongly endothermic, indicating that these decompositions are energetically unfavourable, since it is unlikely that any entropy term could override such a large positive enthalpy. The energetic studies prove that pyrochlore is energetically more stable phase than perovskite at low temperature. Thus, the local order of the amorphous precipitates drives the crystallization into the most favourable structure that is the pyrochlore one with similar local organization; the distance between nearest neighbours in the amorphous or short-range ordered phase is very close to that in pyrochlore. Taking into account the stoichiometric deviation in KTO system, the selection of the most appropriate fabrication / deposition technique in thin films technology is a key issue, especially concerning complex ferroelectric oxides. Chemical solution deposition has been widely reported as a processing method to growth KTO thin films, but classical alkoxide route allows to crystallize perovskite phase at temperatures >800 °C, while the temperature endurance of platinized Si wafers is ~700 °C. Therefore, alternative diol-based routes, with distinct potassium carboxylate precursors, was developed aiming to stabilize the precursor solution, to avoid using toxic solvents and to decrease the crystallization temperature of the perovskite phase. Studies on powders revealed that in the case of KTOac (solution based on potassium acetate), a mixture of perovskite and pyrochlore phases is detected at temperature as low as 450 °C, and gradual transformation into monophasic perovskite structure occurs as temperature increases up to 750 °C, however the desired monophasic KTaO3 perovskite phase is not achieved. In the case of KTOacac (solution with potassium acetylacetonate), a broad peak is detected at temperatures 700 °C. Infrared analysis indicated that the differences are due to a strong deformation of the carbonate-based structures upon heating. A series of thin films of alkali tantalates were spin-coated onto Si-based substrates using diol-based routes. Interestingly, monophasic perovskite KTaO3 films deposited using KTOacac solution were obtained at temperature as low as 650 °C; films were annealed in rapid thermal furnace in oxygen atmosphere for 5 min with heating rate 30 °C/sec. Other compositions of the tantalum based system as LiTaO3 (LTO) and NaTaO3 (NTO), were successfully derived as well, onto Si substrates at 650 °C as well. The ferroelectric character of LTO at room temperature was proved. Some of dielectric properties of KTO could not be measured in parallel capacitor configuration due to either substrate-film or filmelectrode interfaces. Thus, further studies have to be conducted to overcome this issue. Application-oriented studies have also been conducted; two case studies: i) photocatalytic activity of alkali tantalates and niobates for decomposition of pollutant, and ii) bioactivity of alkali tantalate ferroelectric films as functional coatings for bone regeneration. Much attention has been recently paid to develop new type of photocatalytic materials, and tantalum and niobium oxide based compositions have demonstrated to be active photocatalysts for water splitting due to high potential of the conduction bands. Thus, various powders of alkali tantalates and niobates families were tested as catalysts for methylene blue degradation. Results showed promising activities for some of the tested compounds, and KNbO3 is the most active among them, reaching over 50 % degradation of the dye after 7 h under UVA exposure. However further modifications of powders can improve the performance. In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of the cells. In lieu of this here we exploited an alternative strategy for bone implants or repairs, based on charged mediating signals for bone regeneration. This strategy includes coating metallic 316L-type stainless steel (316L-SST) substrates with charged, functionalized via electrical charging or UV-light irradiation, ferroelectric LiTaO3 layers. It was demonstrated that the formation of surface calcium phosphates and protein adsorption is considerably enhanced for 316L-SST functionalized ferroelectric coatings. Our approach can be viewed as a set of guidelines for the development of platforms electrically functionalized that can stimulate tissue regeneration promoting direct integration of the implant in the host tissue by bone ingrowth and, hence contributing ultimately to reduce implant failure.Tantalatos e niobatos alcalinos, como K(Ta / Nb)O3, Li(Ta / Nb)O3 and Na(Ta / Nb)O3, são uma família atrativa de compostos ferroeléctricos livres de chumbo com estrutura perosvquítica. As suas propriedades versáteis fazem destes potencialmente interessantes para aplicações em microelectrónica, foto catálise, energia e biomédica. Entre os compostos acima citados, os compostos de tantalato de potássio, KTaO3 (KTO), tem atraído bastante atenção como substitutos para o amplamente conhecido titanato de estrôncio, SrTiO3 (STO). KTO é um óxido perovsquítico com comportamento paraelétrico quântico, quando eletricamente estimulado, e elevada polaribilidade tornando viável engenhar as suas propriedades através de estímulos internos e externos. No entanto os problemas na sua produção, quer em macroescala quer em nanoestruturas 2D, tornam estes compostos numa alternativa pouco viável para a substituir o STO. Consequentemente, e de forma a contribuir cientificamente para aumentar o conhecimento sobre as aplicações dos tantalatos, os principais objectivos desta tese são: i) produzir e caracterizar filmes finos de tantalatos alcalinos através de deposição de solução química em substratos rígidos, à base de silício, e a baixas temperaturas de forma a serem compatíveis com a tecnologia de silício; ii) complementar o conhecimento científico sobre estes materiais funcionais relativamente às suas características termodinâmicas; iii) explorar aplicações alternativas para os tantalatos alcalinos, como a foto catálise. No que diz respeito à síntese, foi focalizada no entendimento da formação de fase no tantalato de potássio sintetizado por diferentes métodos, de modo a controlar a cristalização da estrutura perovsquítica desejada e evitar a formação da fase pirocloro a baixas temperaturas e fases deficientes em potássio. Em tantalatos alcalinos o processo de formação da fase desejada está longe de estar plenamente analisado, como é o caso das perovsquites que contêm chumbo, consequentemente o trabalho foi inicialmente focado na compreensão da relação processo-fase para identificar as forças motrizes responsáveis por regular o processo de síntese. Foi realizada um estudo comparativo da formação de fase via método convencional de reação do estado sólido e via método de sol-gel. A análise estrutural revelou que a estrutura piroclórica intermédia K2Ta2O6 não foi formada em nenhuma etapa da reação via método do estado sólido. Por outro lado em processos baseados em solução, como os baseados em alcóxidos, a cristalização perovsquítica ocorre através da indesejada fase pirocloro intermédia; a baixas temperaturas a fase pirocloro é dominante e sofre a transformação para perovsquite a >800 °C. A análise cinética efectuada usando o modelo Johnson-Mehl-Avrami-Kolmogorow e a difração de raio-X quantitativa (DRX), demonstraram que nos pós obtidos pelo método sol-gel, a cristalização ocorre em duas etapas: i) no estágio inicial a reação é denominada por nucleação primária, o mecanismo é controlado por fronteira de fase, e ii) no segundo estágio, o baixo valor do expoente de Avrami, n ~ 0.3, não segue nenhuma categoria reportada impossibilitando assim uma clara identificação do mecanismo. Posteriormente, e em colaboração com o grupo da Professora Alexandra Navrostky da Universidade da Califórnia, Davis, foram realizados estudos de termodinâmica, usando calorimetria de solução de óxidos fundidos a alta temperatura. Foram calculadas as entalpias de formação das três estruturas: pirocloro, perovsquite e tetragonal tungsténio bronze K6Ta10.8O30 (TTB). As entalpias de formação relativas aos óxidos correspondentes, ∆Hfox, para KTaO3, KTa2.2O6 e K6Ta10.8O30, são -203.63 ± 2.84 kJ/mol, 358.02 ± 3.74 kJ/mol e -1252.34 ± 10.10 kJ/mol, respectivamente; enquanto que as relativas aos elementos, ∆Hfel, para KTaO3, KTa2.2O6 e K6Ta10.8O30 são 1408.96 ± 3.73 kJ/mol, -2790.82 ± 6.06 kJ/mol e -13393.04 ± 31.15 kJ/mol, respectivamente. As possíveis reações de decomposição, de KTa2.2O6 para KTaO3 e Ta2O5 (reação 1) ou para K6Ta10.8O30 e Ta2O5 (reação 2), foram propostas e o cálculo das entalpias resultou em 308.79 ± 4.41 kJ/mol e 895.79 ± 8.64 kJ/mol, respectivamente. As reações são fortemente endotérmicas, indicando que estas decomposições são energeticamente desfavoráveis, uma vez que é improvável que qualquer termo de entropia possa sobrepor-se a uma entalpia tão positiva. Os estudos termodinâmicos provaram que o pirocloro é energeticamente mais estável que a perovsquite para temperaturas baixas. Assim, a organização local dos precipitados amorfos canaliza a cristalização para a estrutura mais favorável, que é a pirocloro com uma organização local similar; a distância entre os vizinhos mais próximos na fase amorfa, ou na fase ordenada a baixo alcance, é similar à do pirocloro. Tendo em conta a derivação estequiométrica no sistema KTO, selecionar a técnica de fabricação / deposição de filmes finos mais apropriada é uma questão-chave, especialmente no que concerne aos óxidos ferroeléctricos complexos. A deposição por solução química tem sido o método de processamento mais reportado, para crescimento de filmes finos de KTO, mas o método clássico de alcóxidos permite cristalizar a fase perovsquite a temperaturas >800 °C enquanto que a temperatura máxima de estabilidade para os substratos de silício platinizado é ~700 °C. Portanto, foi usado um processo alternativo baseado em dióis, com precursores carboxilados de potássio, com o objectivo de estabilizar os precursores em solução, evitando assim o uso de solventes tóxicos e diminuindo a temperatura de cristalização da fase perovsquite. A análise dos pós revelou que no caso de KTOac (solução baseada em acetato de potássio), uma mistura de fase perovsquite e pirocloro foi detectada a uma temperatura de apenas 450 °C, e a transformação gradual em estrutura perovsquítica monofásica ocorre quando as temperaturas sobem acima de 750 °C, no entanto a fase KTaO3 monofásica não é obtida. No caso do KTOacac (solução com acetil-acetona de potássio, cadeia alquílica longa carboxilato de metal), um amplo pico é detectado a temperaturas 700 °C. A análise de infravermelhos mostrou que estas diferenças acontecem devido à deformação da estrutura base dos carbonatos sob aquecimento. Uma série de filmes finos de tantalatos alcalinos foram depositados por spincoating em substratos de silício, usando a metodologia baseada em dióis. Filmes monofásicos de perovsquite KTaO3 depositados usando solução de KTOacac foram obtidos a uma temperatura de apenas 550 °C; os filmes foram recristralizados em fornos de aquecimento rápido em atmosfera de oxigénio durante 5 minutos com taxa de aquecimento de 30 °C/seg. Outras composições, LiTaO3 (LTO) e NaTaO3 (NTO), foram depositados com sucesso em substratos de silício a 650 °C. O carácter ferroeléctrico do LTO à temperatura ambiente foi provado. Infelizmente, não foi possível medir as propriedades eléctricas do KTO no condensador paralelo devido às interfaces filme-substrato ou filme-eléctrodo. Assim sendo, estudos futuros são necessários para compreender esta questão. Foram também conduzidos estudos com vista às possíveis aplicações; dois casos de estudo: i) estudo da atividade fotocatalítica de tantalatos e niobatos alcalinos para decomposição de poluentes, e ii) estudo de bioatividade de filmes ferroelétricos de tantalatos alcalinos como revestimento funcional para regeneração óssea. Recentemente, tem sido dedicada muita atenção ao desenvolvimento de novos materiais fotocatalíticos, e as composições à base de óxido de tântalo e nióbio tem demonstrado capacidade de fotocatálise na reação de separação da água devido ao elevado potencial das bandas de condução. Assim, várias composições das famílias dos tantalatos e niobatos alcalinos foram testadas como catalisadores para degradação do azul de metileno. Os resultados mostram valores de atividade promissores para alguns dos compostos, sendo o KNbO3 o mais ativo de entre os testados, alcançando valores acima de 50 % na degradação do pigmento após 7 h sob exposição a UVA. No entanto algumas modificações nas composições dos pós podem melhorar a sua performance. No que concerne à regeneração óssea, é importante obter plataformas que através de estímulos apropriados consigam assegurar a adesão e direcionar o crescimento, a proliferação e a diferenciação celular. Neste contexto, foi aqui explorada uma estratégia alternativa para revestimento de implantes ósseos, baseada na regeneração óssea mediada por sinais elétricos. Esta estratégia implica revestir substratos metálicos de aço inoxidável tipo 316L (316L-SST), com camadas de LiTaO3 ferroeléctrico, funcionalizadas através de polarização elétrica ou de irradiação com luz UV. Foi demonstrado que a formação de fosfato de cálcio na superfície e a adsorção de proteínas é consideravelmente melhorada quando o 316L-SST é revestido com filmes ferroelétricos funcionalizados. Esta estratégia pode ser encarada como um conjunto de orientações para o desenvolvimento de plataformas eletricamente funcionalizadas, capazes de estimular a regeneração de tecidos, promovendo a associação direta do implante com os tecidos hospedeiros, contribuindo assim para a redução de falhas na reabilitação com implantes ósseos

Development of Advanced Nanomaterials for Potential Lithium-Ion Battery Application

Lithium-ion batteries (LIBs) are promising energy storage media under serious consideration for practical applications in electric vehicle (EVs) and hybrid electric vehicles (HEVs). However, to meet the requirements for EVs and HEVs, the performance of commercially available LIBs needs to be greatly improved in terms of the energy density, cycling life, rate capability, safety and cost. It is well known that the LIB performance is highly dependent on the choice of electrode materials. Therefore, it is greatly important to develop new electrode materials as replacements for graphite/LiCoO2 used in commercial LIBs, in order to achieve high-performance LIBs desirable for EV and HEV applications. In this thesis, to achieve the above goal, efforts made in this thesis followed into two sections. The first section was to develop novel nanostructured electrode materials, which could be directly used in LIBs. The other section was to develop various surface-modification materials, which could be applied to further improve the LIB performance of electrode materials. Various advanced characterization techniques, including field-emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), high-resolution TEM (HRTEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), X-ray absorption near edge structure (XANES) spectroscopy, and electrochemical methods, have been applied to analyze the prepared nanomaterials, understand their growth mechanisms, and evaluate their battery performance. The nanostructured electrode materials included nitrogen-doped carbon nanotubes (NCNTs), phosphorus-nitrogen doped carbon nanotubes (PNCNTs), and lithium titanate (Li4Ti5O12). A scalable method, ultrasonic spray pyrolysis, was developed inhouse to produce NCNTs with tunable structure as potential anode materials. Further attempt to incorporate P element into CNTs was made, and it was successful when P and N elements were doped together. The P doping effect on the structure of NCNTs was investigated in details. Furthermore, novel nanosctuctured Li4Ti5O12 were prepared by a microwave-assisted hydrothermal method in a fast and energy-efficient way. Their electrochemical performances were evaluated, and nanoflower-like Li4Ti5O12 showed better LIB performance than nanoparticle Li4Ti5O12. Three different surface-modification materials, ZrO2, AlPO4 and LiTaO3 solid-state electrolyte, were developed by atomic layer deposition (ALD), for potential use to improve the chosen electrode materials. Deposition of these materials on different substrates, including NCNTs, graphene nanosheets, Si (100) and anodic aluminum oxide (AAO) template, showed that as-grown thin films of ZrO2, AlPO4 and LiTaO3 were precisely controllable in terms of film thickness, film crystallinity and film composition. These characteristics enabled by ALD promised ZrO2, AlPO4 and LiTaO3 great potentials as surface-modification materials. One application example of these materials was demonstrated by using ALD-ZrO2 coating to enhance the performance of nanoflower-like Li4Ti5O12

Active removal of waste dye pollutants using Ta[sub]3N[sub]5/W[sub]18O[sub]49 nanocomposite fibres

A scalable solvothermal technique is reported for the synthesis of a photocatalytic composite material consisting of orthorhombic Ta3N5 nanoparticles and WOx≤3 nanowires. Through X-ray diffraction and X-ray photoelectron spectroscopy, the as-grown tungsten(VI) sub-oxide was identified as monoclinic W18O49. The composite material catalysed the degradation of Rhodamine B at over double the rate of the Ta3N5 nanoparticles alone under illumination by white light, and continued to exhibit superior catalytic properties following recycling of the catalysts. Moreover, strong molecular adsorption of the dye to the W18O49 component of the composite resulted in near-complete decolourisation of the solution prior to light exposure. The radical species involved within the photocatalytic mechanisms were also explored through use of scavenger reagents. Our research demonstrates the exciting potential of this novel photocatalyst for the degradation of organic contaminants, and to the authors’ knowledge the material has not been investigated previously. In addition, the simplicity of the synthesis process indicates that the material is a viable candidate for the scale-up and removal of dye pollutants on a wider scale