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Summary of ROS-dependent and ROS-independent anticancer effects of Ce-based nanoparticles in the cellular environment, categorized according to materials-based and radiation-assisted effects.

Anatase thin films spin coated on soda–lime–silica (SLS) glass and unpolished (001) rutile were annealed at 200–550 °C for 8 h, followed by GAXRD, Raman, XPS, SIMS, AFM, TEM, UV–Vis, ellipsometry, and MB dye degradation. Films on SLS substrates annealed at 200–350 °C were amorphous but those annealed at 450°–550 °C consisted of anatase; the rutile substrates gave epitaxial rutile films. Annealing caused diffusion of glass ions into the films and counterdiffusion of Ti into the glass substrates. The decrease in glass ion concentrations during aqueous MB testing shows that grain boundary diffusion occurred. The AFM, TEM, and UV–Vis data were affected by the substrate topographies, where SLS was smooth and rutile was rough/uneven. Decreasing Eg in the anatase films with increasing annealing temperature was attributed to increasing crystallinity (heterogeneous nucleation) while the same effect in the rutile films was attributed to the substrate topography (homogeneous nucleation). The anatase films photocatalytically outperformed the rutile films; this was attributed to the potential to form midgap states from oxygen vacancy formation and/or Ti vacancy formation (deriving from the Ti counter-diffusion). However, the deep energy levels of these defects suggest that the performance is dominated by the crystallinity and blockage of the active sites.

Electrocatalytic activities of electrodes for water splitting generally are assessed in terms of current density normalisation on the basis of geometric area. However, this approach does not involve the effects of surface microstructure which often is rough. The present work examines this disagreement through the electrochemical characterisation of thermally treated carbon fibre paper in which the current density is normalised comparatively by geometric area, BET specific surface area and electrochemical active surface area (ECSA). The results show that the geometric area provides a nominal means of assessing the electrocatalytic activity. Since BET is effective in assessing the physical surface area, it provides a superior indication. However, ECSA provides the most discriminating means of assessment and reflects the intrinsic electrochemical activity.

Precise control over the morphology of nanomaterials is critical yet challenging. The present work reports an efficient approach to tailor the architecture of nanostructures. The process involves rapid disassembly/reassembly of an unstable metal-based coordination polymer (MCP) by controlling the kinetics of the reassembly process. The synthesis procedure delivers unprecedented polycrystalline nanostructures, e.g., holey 2D CeO2−x nanosheets, with precisely tailored thicknesses in the range of 10–100 nm, and hollow 3D pseudo-octahedra and spheres. The consequent high surface areas and pore volumes, short diffusion distances, and high defect densities of the holey 2D CeO2−x indicate significant densities of active sites. This holey architecture exhibits rapid CO conversion and outstanding solar light photocatalytic performance. This approach of directed assembly offers a template-free, controllable, and cost-effective approach to achieve engineered CeO2−x architectures, which are nearly impossible through existing approaches.

The present work reports a detailed mechanistic interpretation of the role of the solubility of dopants and resultant midgap defect energies in band gap engineering. While there is a general perception that a single dopant is associated with single solubility and defect mechanisms, in reality, the potential for multiple solubility and defect mechanisms requires a more nuanced interpretation. Similarly, Kroger–Vink defect equilibria assume that stoichiometries during substitutional and interstitial solid solubility as well as Schottky and Frenkel pair formation are compensated by the diffusion of matrix ions to the grain boundaries or surface. However, this approach does not allow the possibility that stoichiometry is uncompensated, where diffusion of the matrix ion to lattice interstices occurs, followed by charge compensation by redox of this ion. Consequently, a modified defect equilibria formalism has been developed in order to allow description of this situation. Experimental data for the structural, chemical, semiconducting, and photocatalytic properties as a function of doping level are correlated with conceptual structural models, a comprehensive energy band diagram, and the corresponding defect equilibria. These correlations reveal the complex mechanisms of the interrelated solubility and defect formation mechanisms, which change significantly and irregularly as a function of small changes in doping level. The analyses confirm that the assumption of single mechanisms of solid solubility and defect formation may be simplifications of more complex processes. The generation of (1) a matrix of complementary characterisation and analytical data, (2) the calculation of a complete energy band diagram, (3) consideration of charge compensation mechanisms and redox beyond the limitations of Kroger–Vink approaches, and (4) the development of models of corresponding structural analogies combine to create a new approach to interpret and explain experimental data. These strategies allow deconstruction of these complex issues and thus targeting of optimal and possibly unique doping levels to achieve lattice configurations that may be energetically and structurally unfavorable. These approaches then can be applied to other doped semiconducting systems.

The present work reports data for TiO2 thin films on borosilicate glass and (001) single-crystal TiO2, annealed at 200–550 °C for 8 h. Characterization included GAXRD, laser Raman microspectroscopy, AFM, UV–Vis, XPS, SIMS, TEM, ellipsometry, and methylene blue (MB) dye degradation. The substrate determined the TiO2 polymorph that formed, while the annealing temperature and boron contamination from the substrate determined most of the associated properties. The films on glass substrates were amorphous following annealing at 200 °C but were anatase at higher temperatures. The films on rutile exhibited epitaxial growth at all annealing temperatures. Annealing caused diffusion of glass component elements into the films and counterdiffusion of Ti into the glass substrates. Since aqueous MB testing caused decreased glass ion concentrations, the diffusion mechanism is via the grain boundaries. Volatilization of boron occurred during annealing at 550 °C. The morphological features dominated the optical properties; the anatase films exhibited high transmissions and low reflectances, while the rutile films exhibited the converse. The band gap decreased slightly with increasing annealing temperatures, reflecting increasing crystallinity. The refractive indices showed an anomalous trend of decrease with increasing annealing temperature and associated crystallinity; this is attributed to the effects of boron volatilization and associated air-filled pore formation. Although the anatase films outperformed the rutile films, the effect of annealing temperature is likely to have been dominant in that it determined the relative extents of crystallinity, grain size, RMS roughness, optical indirect band gap, and oxygen vacancy concentration.

Mo3+- or Mo5+-doped TiO2 sol-gel thin films (≤0.100 mol%) were spin coated on fused silica glass substrates and annealed at 450 °C for 2 h. The effect of the valence of the dopant precursor is significant to the nanostructural development and resultant properties. Mo3+ or Mo5+ doping yields converse trends with doping level, thus reflecting the competing influences of lattice distortion and destabilization (dominating Mo3+ doping) and nucleation and recrystallization (dominating Mo5+ doping). Mo doping results in oxidation of Mo3+ and reduction of Mo5+, both of which alter to Mo(5−x)+, as well as oxidation of Ti3+ to Ti(4+x)+; all of these result in V O • • annihilation. Although the absorption edges were largely indistinguishable, Mo3+ doping causes a red shift and Mo5+ doping causes a blue shift. These data suggest that the performances are controlled by the synergistic effects of crystallinity, surface area, and band gap, with the latter's exhibiting the dominant effect. This suggests that the defect structure governs the photocatalytic performance but also that the defect chemistry at these low annealing temperatures is indicative of nonequilibrium conditions, thereby explaining the significance of the dopant valence.

Mo-doped TiO2 [≤ 0.20 wt% Mo; ≤ 0.10 mol% (metal basis)] with conjugated polyvinyl alcohol (TiO2/C-PVA) composite thin films was prepared by sol–gel dip coating on polished fused SiO2 substrates, followed by annealing at 180 °C for 4 h. These conditions were sufficient for solid solubility, despite the unusually low annealing temperature. The annealed thin films consisted of homogeneously distributed individual and slightly agglomerated anatase grains in a continuous C-PVA matrix characterized by the carbon double bond formed upon conjugation. The films exhibited drying shrinkage cracks, which increased consistently in extent with increasing Mo-doping concentration, effectively increasing the number of exposed TiO2 particles. Mo addition enhanced anatase nucleation, recrystallization, and growth at lower doping concentrations (up to ≤ 0.10 wt%), thereby increasing crystallinity. However, increasing doping levels (> 0.10 wt%) appeared to exceed the solubility limit, resulting in supersaturation and significant lattice destabilization. Mo-doping also caused the Ti2p XPS peaks to shift to lower binding energies and the Mo3d peaks to shift to higher binding energies. These data are consistent with thermodynamically unstable Ti4+ → Ti3+ conversion and thermodynamically stable Mo5+ → Mo6+ conversion, which are interpreted in terms of intervalence charge transfer (IVCT), in which charge compensation is achieved through majority Ti4+ → Ti3+ reduction plus Mo5+ → Mo6+ oxidation. Ti3+ concentration also reflects a direct correlation with the Mo-doping concentration and resultant IVCT within the Mo solubility limit and a reverse effect upon supersaturation. There is a correlation with the Eg but this can be attributed to recrystallization rather than a semiconducting effect. No effect of midgap state formation from enhancement of the $$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$ concentration is expected because IVCT is a redox effect only and dissolution of Mo5+ or Mo6+ would generate Ti vacancies. The methylene blue dye degradation data exhibited the same trend but at a significant level (90.6% degradation), thus indicating that the mechanism dominating the photocatalytic performance is the recrystallization of the anatase and/or the modification of the semiconducting properties induced by Mo-doping, as indicated by the trends in band gap.

The morphologies of ceria nanocrystals play an essential role in determining their redox and catalytic performances in many applications, yet the effects of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms have not been systematised. The design of these morphologies is underpinned by a range of fundamental parameters, including crystallography, optical mineralogy, the stabilities of exposed crystallographic planes, CeO2-x stoichiometry, phase equilibria, thermodynamics, defect equilibria, and the crystal growth mechanisms. These features are formalised and the key analytical methods used for analysing defects, particularly the critical oxygen vacancies, are surveyed, with the aim of providing a source of design parameters for the synthesis of nanocrystals, specifically CeO2-x. However, the most important aspect in the design of CeO2-x nanocrystals is an understanding of the roles of the main variables used for synthesis. While there is a substantial body of data on CeO2-x morphologies fabricated using low cerium concentrations ([Ce]) under different experimental conditions, the present work fully maps the effects of the relevant variables on the resultant CeO2-x morphologies in terms of the commonly used raw materials [Ce] (and [NO3-] in Ce(NO3)3·6H2O) as feedstock, [NaOH] as precipitating agent, temperature, and time (as well as the complementary vapour pressure). Through the combination of consideration of the published literature and the generation of key experimental data to fill in the gaps, a complete mechanistic description of the development of the main CeO2-x morphologies is illustrated. Further, the mechanisms of the conversion of nanochains into the two variants of nanorods, square and hexagonal, have been elucidated through crystallographic reasoning. Other key conclusions for the crystal growth process are the critical roles of (1) the formation of Ce(OH)4 crystallite nanochains as the precursors of nanorods and (2) the disassembly of the nanorods into Ce(OH)4 crystallites and NO3--assisted reassembly into nanocubes (and nanospheres) as an unrecognised intermediate stage of crystal growth.

Metal oxide pseudocapacitors are limited by low electrical and ionic conductivities. The present work integrates defect engineering and architectural design to exhibit, for the first time, intercalation pseudocapacitance in CeO2–x. An engineered chronoamperometric electrochemical deposition is used to synthesize 2D CeO2–x nanoflakes as thin as ~12 nm. Through simultaneous regulation of intrinsic and extrinsic defect concentrations, charge transfer and charge–discharge kinetics with redox and intercalation capacitances together are optimized, where reduction increases the gravimetric capacitance by 77% to 583 F g–1, exceeding the theoretical capacitance (562 F g–1). Mo ion implantation and reduction processes increase the specific capacitance by 133%, while the capacitance retention increases from 89 to 95%. The role of ion-implanted Mo6+ is critical through its interstitial solid solubility, which is not to alter the energy band diagram but to facilitate the generation of electrons and to establish the midgap states for color centers, which facilitate electron transfer across the band gap, thus enhancing n-type semiconductivity. Critically, density functional theory simulations reveal, for the first time, that the reduction causes the formation of ordered oxygen vacancies that provide an atomic channel for ion intercalation. These channels enable intercalation pseudocapacitance but also increase electrical and ionic conductivities. In addition, the associated increased active site density enhances the redox such that the 10% of the Ce3+ available for redox (surface only) increases to 35% by oxygen vacancy channels. These findings are critical for any oxide system used for energy storage systems, as they offer both architectural design and structural engineering of materials to maximize the capacitance performance by achieving accumulative surface redox and intercalation-based redox reactions during the charge/discharge process.

CeO2 films doped with 0–9 mol% Ga/Mn were fabricated by spin coating on 3D-printed Ti6Al4V, calcined at 650 °C for 2 h, and characterised by TEM, FESEM, 3D laser scanning confocal microscopy, GAXRD, and XPS. The results depend on the roles of several factors: (1) Sol-gel precursor viscosity affected pore filling and surface coverage. (2) Lattice contraction and resultant intervalence charge transfer increased the Ce3+ concentration as a minority effect. (3) Substitutional solid solubility and associated redox charge compensation controlled the defect equilibria, which highlight the majority role of this solid solubility mechanism in decreasing the Ce3+ concentration. (4) Electronegativity played a negligible role in affecting the valences but was important in initiating intervalence charge transfer. (5) Multivalence charge transfer combined electron exchanges between film matrix, dopants, and Ti substrate. The present work provides a foundation to interpret the effects of extrinsic effects from both dopant and substrate on the properties of films.

There is growing interest in reducing the use of ordinary Portland cement (OPC) owing to its high energy consumption and CO2 emissions. An environmentally-friendly alternative is the use of geopolymers, which can potentially reduce direct CO2 emissions through the appropriate choice of raw materials, mix design, and curing regimes. In this regard geopolymer mortars are also realistic candidates for the replacement of OPC mortars in nuclear waste immobilisation applications as they provide a more durable incorporation matrix as well as suppressing the formation of radiolytic hydrogen. The advantages of geopolymers over OPC for nuclear waste immobilisation include i) lower water content as alkaline activator is the main component that drives geopolymerisation, ii) higher thermal stability (

Flat TiO2 thin films were dip coated on contact lens polymer substrates (fluorinated ethylene propylene copolymer, FEP) using a hybrid sol-gel and annealed for 12 h at ≤200 °C. The grain sizes were in the range 10–20 nm but extensive shrinkage cracking was present. The crystallinities of the films annealed at ≤150 °C increased with increasing temperature gradually but only to a limited extent, although the crystallinity at 200 °C was significant. Recrystallisation resulted in decreased transparency, increased reflectivity, and a red shift to lower band gap. The methylene blue (MB) degradation was in the order 25 °C

TiO2 thin films of varying Co and Mo individual doping levels (0.00–1.00 mol% metal basis) were fabricated on soda-lime-silica glass substrates by spin coating, followed by annealing at 450 °C for 2 h. Mineralogical analyses showed that all of the films were comprised only of anatase and suggested that both Co and Mo formed interstitial solid solutions. For the Co-doped films, the variation in anatase XRD peak intensities indicated three discrete stages of structural and nanostructural development: recrystallization (≤0.05 mol% Co), lattice distortion (0.05–0.60 mol% Co), and precipitation (≥0.60 mol% Co). For the Mo-doped films, Mo consistently enhanced nucleation, recrystallization, and lattice distortion within the solubility limit, which was not reached at 1.00 mol% Mo. Chemical analyses showed that Ti4+/Ti3+, Co3+/Co2+, and Mo5+/Mo4+ (and possibly Mo6+) were present in the films. The formation of non-equilibrium valences was considered in terms of the effects of crystal field stabilization energy (CFSE), intervalence charge transfer (IVCT), and electronegativity. Nanostructural analyses of the Co-doped films showed that, with increasing doping level, the grain size increased at the lowest level, followed by a decrease owing to changes in the structure (lattice destabilization) and nanostructure (localized liquid formation). In contrast, the grain size of the Mo-doped films increased with increasing doping level due to the maintenance of solid solubility, defect formation (and associated enhanced nucleation and recrystallization), and grain growth. Defect formation and charge compensation resulted in lattice contraction, which was confirmed by laser Raman microspectroscopy and resultant destabilization. Optical analyses showed that all of the thin films were flat, smooth, and nanostructurally homogeneous. The band gap data suggested that the governing effect derived from the lattice distortion associated with the lattice incorporation of both dopants. Photocatalytic testing showed that the lowest level of doping for both dopants (0.01 mol%) yielded maximal photocatalytic activity and that the performance decreased with increasing doping levels. This was attributed to the effects of nucleation and recrystallization, semiconducting effect, dopant size effect, and minimal lattice distortion.

The present work provides guidelines for the engineering of oxygen vacancy concentrations using morphology-maps based on the characteristics of nanoceria (CeO2−x) nanocubes, nanorods, and truncated nanooctahedra. These were characterised by XRD, TEM, BET, DLS, and XPS. The morphology maps reveal that the redox performance, particle size, and surface roughness (apparent porosity) can be optimised by engineering the oxygen vacancy concentrations, but the morphology is dominated by the reaction temperature. However, the oxygen vacancy concentration is controlled by the concentration of the NaOH precipitant/oxidant. These vacancies can be potentially located at the surface, subsurface, and bulk regions, but the subsurface vacancies provide the principal redox activity. The biological effects of nanoceria in terms of oxygen vacancies were analysed in normal and cancer cells. Nanoceria particles exhibit antioxidant and cytoprotective effects at physiological pH 7.4 but prooxidant and cytotoxic effects at tumour microenvironment pH 6.4. The relative redox performances and cytotoxicities are in the order nanocubes < nanorods < truncated nanooctahedra, which is a direct reflection of the relative oxygen vacancy concentrations. The redox performance of nanoceria has been contextualised by cellular uptake and its quantification in osteosarcoma cells.

The present work reports the rapid preparation of CeO2 nanorods by surfactant-free precipitation for the first time, which initiates a strategy for the quantitative elucidation of the importance of the exposed crystallographic planes and the oxygen vacancy concentrations of different morphologies of nanoceria. These relations are revealed through comparison of the relative surface areas of the exposed crystallographic planes. The precipitation temperature was critical in that nanooctahedra formed at the three lower temperatures and nanorods formed at the highest. The key feature to differentiate the photocatalytic performance was the morphology that the nanorods exhibit ∼200% superior performance compared to those of the nanooctahedra. The principal reason for this is the presence of exposed {110} planes in the nanorods, which are not present in nanoctahedra. This crystallographic dependence of the improved performance of the nanorods is attributed directly to the greater oxygen vacancy concentration for the calculated surface area of this morphology.

Glass-ceramics (GCs) based on titanate pyrochlores have attracted recent attention as candidate waste forms for actinide immobilization. As zirconate pyrochlore has a superior radiation resistance, it is anticipated that Zr substitution of Ti in titanate pyrochlore GCs would increase their potential for waste form applications. The concept was primarily addressed via the preparation of Gd2Ti2-xZrxO7 (x = 0.1–0.3) GCs to determine the effects of sintering temperature, Zr substitution, and pyrochlore content (50–70 wt%) on the properties of the resultant GCs. XRD and SEM analyses were used to reveal the phase assemblages and microstructures while TEM and Raman spectroscopy were used to analyze the local structures. XRD results confirmed the formation of the targeted pyrochlore as the major phase, with Gd9.33(SiO4)6O2 oxyapatite present as a minor phase. SEM analyses revealed that up to 0.2 formula units of Ti could be substituted by Zr under the processing conditions. The pyrochlore crystallite sizes were largely controlled by the sintering temperature and cooling rate and showed little sensitivity to the glass contents. This work has demonstrated successful substitutions of Ti with Zr in Gd2Ti2O7 GCs as potential waste forms for actinide wastes owing to their superior radiation resistance.

Ce-doped TiO 2 thin films were prepared by sol-gel, spin coated on glass substrates, and annealed at 450 °C for 2 h. Solid solubility of Ce in anatase at the lowest doping level (≤0.25 mol% Ce) generated point defects that enhanced nucleation and recrystallization, resulting in relatively uniform grain sizes. In contrast, at ≥0.50 mol% Ce, overdoping, precipitation at grain boundaries, and liquid formation resulted in bimodal nanostructures with decreasing sizes of both the matrix grains and agglomerates owing to the progressive hindrance of Ti diffusion. The optimal photocatalytic performance at 0.25 mol% Ce was associated with a less densely packed array of fine matrix grains, while the performance at higher doping levels was dominated by liquid formation, greater packing densities, and blockage of active sites. The occurrence of Ce ↔ Ti intervalence charge transfer and associated oxygen vacancy formation are likely causes for the observed lowering of the band gap, reduction in the recombination rate, and enhancement of radiation absorption at longer wavelengths (red shift).

The kinetics of the anorthite–Al system have been examined by exposing anorthite to pure Al at 850–1150 °C for 0.5–250 h. The interfaces were investigated by electron microscopy (SEM, EDS, EPMA, and TEM). The results showed that Si4+–Al3+ interdiffusion and associated oxygen vacancies plus Ca2+–Al3+ interdiffusion and associated calcium vacancies drove the anorthite → CA2 and the CA2 → A (alumina) transformations, respectively, at 850 and 950 °C. At 1050 and 1150 °C, increased solubilities of silicon and oxygen in the liquid Al resulted in significant formation of CA2, which, when in contact with anorthite, leads to formation of gehlenite. Si4+–Al3+ interdiffusion was identified as the controlling process of the anorthite–Al interactions and so it has been quantified in terms of the activation energy of Q = 112 kJ/mol and the diffusion coefficient pre-factor of D 0 = 4 × 10−8 m2/s.

Ceria (CeO2) nanorods have been prepared by simple short-term precipitation at room temperature for the first time using aqueous solutions based on Ce(NO3)3·6H2O and NaOH. TEM showed that (a) the two solutions alone yielded nanooctahedra of cross section ∼10 nm and (b) selective surface modification by isopropanol (IPA) played a significant role in the morphological development of approximately square nanorods of dimensions 4–5 nm width, 15–25 nm length, and [110] growth direction. DFT was used to assess surface energies and the interactions of the H2O and IPA molecules with the {111}, {110}, and {100} ceria surfaces. A growth mechanism on the basis of these adsorption energies and orientations is proposed and it depends on the favorable IPA adsorption energy. Its effect is twofold. First, it facilitates the formation of a {110} prism that alters the morphology from octahedral to spheroidal and then cuboidal. Second, the anisotropic electrostatic field in the electrical double layer, which is established by the oriented adsorption of the IPA molecule, is considered to facilitate the growth of the nanorod morphology. XPS data show that nanorods exhibit a greater concentration of Ce3+ (and associated oxygen vacancies) than do the nanooctahedra. The parameters determining the development of nanoparticle morphology are ranked in the order: packing density ≈ lattice spacing > IPA adsorption > H2O adsorption > surface energy. The present work suggests the applicability of crystallography considerations and DFT modeling to direct the crystal growth of specific morphologies.

Fe/Mo single doped and codoped TiO2 thin films were spin coated on polished fused silica substrates and annealed in air at 450 °C for 2 h. The XPS data for the anatase thin films were distinctive in showing that Fe-doping caused Ti4+ reduction, Mo-doping caused Ti4+ oxidation, and codoping did not alter the Ti valence. The XPS data also showed that the precursor valences of Fe3+ and Mo5+ were reduced upon annealing. Analysis of the potential roles of thermodynamics and intervalence charge transfer (IVCT) demonstrates that the latter drives the equilibria both in solution and during annealing. Photocatalytic performance testing indicated that Fe-doping was slightly deleterious, Mo doping had a consistent positive effect, and codoping exhibited a clear negative trend as a function of doping concentration. These results are interpreted in terms of the effect of IVCT on the matrix valence, dopant valences, and charge carrier trapping. Fe doping exhibited reduced performance because both matrix Ti(4−x)+ and dopant Fe(3−y)+ acted as electron traps. Mo doping exhibited enhanced performance because the matrix Ti(4+x)+ acted as a hole trap and the dopant Mo(5−x)+ and Mo(4−x)+ acted as electron traps, thereby promoting charge separation. Codoping exhibited a clearly detected negative trend on the performance because, while Ti4+ played no role, Fe(3−y)+, Mo(5−x)+, and Mo(4−x)+ all acted as traps for the majority charge carrier electrons.

Altres ajuts: ICN2 is supported by the CERCA Programme/Generalitat de Catalunya. Holey 2D metal oxides have shown great promise as functional materials for energy storage and catalysts. Despite impressive performance, their processing is challenged by the requirement of templates plus capping agents or high temperatures; these materials also exhibit excessive thicknesses and low yields. The present work reports a metal-based coordination polymer (MCP) strategy to synthesize polycrystalline, holey, metal oxide (MO) nanosheets with thicknesses as low as two-unit cells. The process involves rapid exfoliation of bulk-layered, MCPs (Ce-, Ti-, Zr-based) into atomically thin MCPs at room temperature, followed by transformation into holey 2D MOs upon the removal of organic linkers in aqueous solution. Further, this work represents an extra step for decorating the holey nanosheets using precursors of transition metals to engineer their band alignments, establishing a route to optimize their photocatalysis. The work introduces a simple, high-yield, room-temperature, and template-free approach to synthesize ultrathin holey nanosheets with high-level functionalities.

Proton activities of suspensions of Ti particles with added cationic polyelectrolyte as a function of acid additions have been investigated and compared in terms of the electrophoretic mobility and deposition yield. The proton activity in ethanol medium decreased with the addition of PEI polyelectrolyte and reduced further in the presence of Ti particles. The decrease in proton activity in the suspension indicates that protonation occurred on both the PEI molecules and Ti particles. It is proposed that the protonation of the amine groups of PEI and hydroxyl sites of Ti particle led to the formation of hydrogen bonding between the Ti particle and PEI molecules. Increase in the PEI and Ti with increasing acid addition translated to higher electrophoretic mobilities and deposition yield at low ranges of acetic acid addition (

V-doped, Mo-doped, and codoped anatase powders have been fabricated by hydrothermal synthesis at 150 °C for 20 h, followed by calcining at 500 °C for 4 h in air. The raw materials were titanium tetra-isopropoxide, VCl3, and MoCl5 and the doping levels were in the relatively low range of 0.02–0.08 mol% (metal basis). The samples were characterized by XRD, SEM, FESEM, BET, UV–Vis spectrophotometry, XPS, and MB degradation by UV–Vis and simulated-solar light spectrophotometry. All of the powders consisted of anatase only and the crystallinities decreased for all dopant levels. For all samples as a function of dopant level, the grain sizes were similar and in the range ∼ 1– 5 μ m , with some dense agglomerates of size up to ∼ 20 μ m , although individual grains consisted of highly agglomerated nanoscale particles. For the doped samples, the crystallite sizes generally decreased, the surface areas were consistent, and the band gaps decreased for V doping but increased for Mo doping. The codoped samples appeared to be dominated by the V doping as they exhibited similar trends. These trends were interpreted largely in terms of the effects of irregular, clustered, or homogeneous dopant distribution on the nucleation and grain growth. The XPS data revealed the presence of V 5 + , Mo 4 + , Mo 5 + , Ti 3 + , and Ti 4 + . The presence of these dopants and their variable valence states was interpreted in terms of intervalence charge transfer (IVCT) and multivalence charge transfer (MVCT) and the associated introduction of midgap states, which represent key parameters in the semiconducting behavior of these doped materials. The irregular trends in photocatalytic performance as a function of dopant level and an increasing trend for the codoped samples revealed the competition between the positive effects of decreasing crystallite size and increasing role of midgap states versus the negative effects of decreasing crystallinity for the doped samples and the dominance of the former two factors for the codoped samples.

TiO2 coatings were fabricated by anodizing unpolished and polished Ti6Al4V substrates in 1–3 M H2SO4 for 10 and 20 min at 120 V. Anatase was the principal polymorph and oxygen dissolution in the Ti6Al4V substrates caused αTi lattice contraction. Dielectric breakdown and associated heating of the insulating TiO2 promoted trace rutile formation. The surface preparation of the Ti6Al4V substrates was the principal factor that determined not only the grain and pore sizes but also the morphology and topography of the coating. Consequently, the presence of the amorphous TiO2 passivating layer (unpolished) resulted in thicker and more irregular coatings than when anodization was done on the bare metal surface (polished). Large-scale delamination steps were observed for the coatings on the unpolished substrates while localized delaminations occurred for the coatings on polished substrates; the amounts of both increased with increasing anodization time. 3D laser scanning confocal microscopy allowed distinction between the fine-scale morphology and the coarse-scale topography. These data showed that increasing time and acid concentration resulted in similar trends of increasing roughness (morphology) and unevenness (topography). The present work focusses on the effect of initial substrate surface characteristics and its modification to improve the quality of the coatings formed by anodization of titanium biomedical implants.

Photocatalytic materials are pivotal for the implementation of disruptive clean energy applications such as conversion of H$_{2}$O and CO$_{2}$ into fuels and chemicals driven by solar energy. However, efficient and cost-effective materials able to catalyze the chemical reactions of interest when exposed to visible light are scarce due to the stringent electronic conditions that they must satisfy. Chemical and nanostructuring approaches are capable of improving the catalytic performance of known photoactive compounds however the complexity of the synthesized nanomaterials and sophistication of the employed methods make systematic design of photocatalysts difficult. Here, we show by means of first-principles simulation methods that application of biaxial stress, $\eta$, on semiconductor oxide thin films can modify their optoelectronic and catalytic properties in a significant and predictable manner. In particular, we show that upon moderate tensile strains CeO$_{2}$ and TiO$_{2}$ thin films become suitable materials for photocatalytic conversion of H$_{2}$O into H$_{2}$ and CO$_{2}$ into CH$_{4}$ under sunlight. The band gap shifts induced by $\eta$ are reproduced qualitatively by a simple analytical model that depends only on structural and dielectric susceptibility changes. Thus, epitaxial strain represents a promising route for methodical screening and rational design of photocatalytic materials.

Transparent TiO2 films (~50–540 nm thick) were spin-coated in multiple cycles by sol–gel on soda-lime-silica glass and annealed at 450 °C for 2 h. Analyses included mineralogy (XRD), optics (UV–Vis), chemistry (XPS), microstructure and topography (SEM, AFM), and hydrophilicity (sessile drop). The microstructures were discontinuous (1 cycle), continuous (4–11 cycles), and damaged (13–15 cycles), with the highest quality films being those fabricated using 7–11 cycles. The thickest films were damaged as a result of shrinkage during annealing, which may have occurred from a two-stage process of dehydroxylation followed by pyrolysis. The single-crystal grain sizes were ~27 nm for the films and the roughness increased with increasing thickness. The hydrophilicity showed clear correlations with the roughness and surprisingly, not with the Ti3+, –OH, and Na+ contents. The role of the glass also was critical to the absorption/transmission of radiation as well as the wetting. That is, the discontinuous and damaged films showed high wetting angles and the continuous films showed low wetting angles. Correlation was observed between the amounts of different contaminants from glass and the free energies of formation for TiO2 to Ti2O3 under the influence of these contaminants. This relation was attributed to the driving force for oxide bond formation, where the only slightly negative free energy of reaction with Na+ allowed its relatively free diffusion through the microstructure until it achieved saturation solubility, although all of the main glass components effectively achieved saturation solubility under the modest kinetics of equilibration that were used.

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V13 O16 , which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO4 in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V13 O16 -decorated BiVO4 hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V13 O16 . A Co-Pi coating on BiVO4 -V13 O16 further increases the photocurrent to 5.0 ± 0.5 mA cm-2 at 1.23 V versus RHE, which is among the highest reported for BiVO4 -based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge-transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co-Pi/electrolyte interface limits the charge transfer.

Anodic oxidation is an electrochemical method for the production of a ceramic film on a metallic substrate. It involves the use of an electrical bias at relatively low currents while the substrate is immersed in a weak organic acid bath. The films produced are usually dense and stable, with variable microstructural features. In the present work, ceramic films of the anatase and rutile polymorphs of TiO2were formed on high-purity Ti foil (50 μm) using mixtures of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA) solutions. The experiments were carried out at varying voltages (150-350 V), times (1-10 min), and current density (10 mA.cm-2) at room temperature. The ceramic films were characterised using digital photography, glancing angle X-ray diffraction (GAXRD), and field emission scanning electron microscopy (FESEM). The thicknesses of the films on Ti were measured using focused ion beam (FIB) milling. The colour, microstructures, and thicknesses of the films were seen to be strongly dependent on the applied voltage. At bias

Using an organometallic precursor, TiO$_2$ coatings were fabricated on surfaces of quartz, zircon and rutile sands. X ray Diffraction, X ray Fluorescence, UV Vis spectroscopy and surface area measurement were used to characterise support materials. The phase composition and morphology of the coatings were characterised by laser Raman spectroscopy and SEM respectively. A packed bed reactor was used to study the inactivation of Escherichia coli in recirculating water by the supported photocatalysts. It was found that the sand grains were well coated with a homogenous layer of TiO2 and coatings were well adhered, exhibiting a mixed anatase rutile composition after firing at 850C. Photocatalytic activity was highest in coatings applied to quartz sand, although sterilisation of the recirculating water was not achieved with any of the materials investigated. The advantages of quartz as a TiO$_2$ photocatalyst support material are likely a result of this materials higher purity and optical transmittance. Potential enhancement through Si doping cannot be ruled out.

Cellulose ethers (CEs) are employed in many polymer-modified mortars, such as cement renders, masonry mortars, tile adhesives, repair mortars, skim coats, and self-levelling mortars. The addition of CEs to mortars causes the retardation of cement hydration and modifies the microstructural characteristics and the properties of these mortars. The present work attempts to provide a comprehensive review of the current state of knowledge on the effects of CEs and critically identifies gaps in the knowledge. A fundamental scientific understanding concerning the chemistry and hydration of cement, chemical natures, and relevant properties of CEs are discussed. The behaviours and mechanisms of CE adsorption on cement are assessed. The influences of CEs on the kinetics of cement hydration, mechanisms of retardation, and microstructural evolution of the mortars also are reviewed. Finally, the impact of CEs on the properties of fresh and hardened mortars as well as the approaches used to mitigate the negative impacts of CEs are discussed.

Coarse (

Fully dense anatase and rutile (TiO2) films were coated on (0001) α-quartz wafers using ultrasonic spray pyrolysis in air at 400°C for 2 h. The TiO2 films were annealed subsequently in air for 4 h at 600, 800 and 1000°C respectively. The films were characterised using X-ray diffraction (mineralogy), ultraviolet visible spectrophotometry (optical properties) and photoluminescence (structural defects). These data are interpreted in terms of phase transformation temperature, optical mean free path, refractive index and effect of heat treatment on the concentration of oxygen vacancies and/or silicon contamination.

Rutile nano-powders were suspended in a solution of acetylacetone and iodine. The suspensions were electrophoretically deposited on titanium foil at a voltage range of 5-30 V over times of 5-120 s. The dried tapes then were sintered at 800°C for 2 h in flowing argon. Both the green and fired tapes were examined by field emission scanning electron microscopy, optical microscopy, X-ray diffraction, and Raman microspectroscopy. The thickness of the films depended on the voltage and the time of deposition. The sintered microstructures depended significantly on the thickness of the film, which was a function the proximity to the Ti/TiO2 interface. The interface is critical to the microstructure because it acts as the source of defect formation, which enhances sintering, grain growth, and grain facetting.

Titanium foils were subjected to soaking in NaOH aqueous solutions in the concentration range 0.1 M to 10.0 M, followed by oxidation in the range 400°C to 800°C. The samples were characterised by glancing angle X-ray diffraction and Raman microspectroscopy. The results showed that the corrosion by NaOH solution resulted in: • Partial dissolution of the anatase passive oxidation layer • Partial dissolution of the underlying titanium foil • Formation of a TiO2-rich sodium titanate hydrogel (Na2O·mTiO2·nH2O) The subsequent oxidation of the hydrogel on the titanium substrate resulted in: • Recrystallisation of sodium titanate (Na2O·5TiO2) • Recrystallisation of the rutile polymorph of TiO2 The concentration of the NaOH solution was important in that it affected the dissolution or retention of the anatase passive oxidation layer, where lower concentrations (0.5 M and 1.0 M NaOH) resulted in a lower degree of dissolution in comparison to where higher concentrations (5.0 M and 10.0 M NaOH) were used.

Anodic oxidation has been used to make well adhered and porous (≤1 μm pore diameter) thin films of anatase on titanium using electrolytic solutions with combinations of H2SO4, H3PO4, and H2O2. The crystallinity, film thickness, and pore size and number increase with time and voltage. The voltage is limited to ~180 V by electrolysis and/or breakdown and the film thickness is ≤3 μm.

Aqueous solutions of tin (II) chloride dihydrate and oxalic acid dihydrate (both 0.04 M) were prepared and mixed by (1) dropwise addition and (2) instantaneous addition, with both involving addition of the latter to the former. Following filtering, washing, and drying, the precipitates were calcined and ground. The particle size and morphology of uncalcined and calcined tin oxalate were examined by electron microscopy and laser diffraction. The method of addition was important in that it influenced both the particle size and shape of tin oxalate. This resulted from the time effect of the ionic collision frequency and the proximity effect of the diffusion distance. As expected, ageing was important in that it caused grain growth and reduction of surface area of the tin oxalate. Although there appeared to be an effect of the method of addition on agglomeration of the tin oxide, this was a result of adsorption of atmospheric moisture, which depended on the relative humidity of the environment during grinding.

The particle size distributions of tin oxide powders produced from the calcining of precipitated tin oxalate were determined by four methods, these being two static and two dynamic light scattering techniques. Although the individual particle sizes were ~ 75 nm, all of the powders were heavily agglomerated as plates. The non-spherical shape resulted in the following interpretational problems: • None of the measurements was in agreement with any others. • There were very significant disagreements between the two light scattering methods. • The particle size distributions were multimodal. • The main peaks in the distribution curves, which were used to calculate the averages and standard deviations, were not Gaussian. The main uncertainty with these data is associated with the non-spherical agglomerates, which result in the multimodal size distributions. These probably were caused by variable-sized but large platy agglomerates.

Aqueous solutions of tin (II) chloride dihydrate and oxalic acid dihydrate were prepared and mixed using two protocols: (1) fixed former concentration and variable latter concentrations and (2) fixed latter concentration and variable former concentrations. Following filtering, washing, and drying, the precipitates were calcined and ground. The calcined powders were characterised in terms of mineralogy and the particle size and morphology of the resultant tin oxide particles and agglomerates. The morphologies of the uncalcined tin oxalate also were examined. In nine of the ten samples, the tin oxalate precipitates consisted of prismatic elongated crystals. In the remaining sample, the low concentrations of solutions probably resulted in the crystallisation of smaller equiaxed particles. Regardless of the particle size or shape of the tin oxalate, the resultant particle size of the tin oxide was ~75 nm and the morphology was consistently spherical. The consistent particle size is attributed to the low solution concentrations used. The tin oxide particles were heavily agglomerated into plates of ~0.5 μm diameter. This morphology probably resulted from the plastic deformation during grinding of the calcined tin oxide, which was likely to have been subject to surface water adsorption on the fine particles. Under the experimental conditions investigated, there were no particle or agglomerate size dependencies on the solution concentrations and mixing method.

The present work considers unresolved problems that need to be addressed for the development of photo-electrodes for photo-electrochemical generation of hydrogen from water using solar energy. The present work is focused on photo-electrodes based on oxide semiconductors, including TiO2 and TiO2-based materials, which are the most promising candidates for photo-electrodes. The properties of photo-sensitive oxide semiconductors are considered in terms of the concepts of photo-electrochemistry and the concepts of defect chemistry. The role of defect chemistry as a framework for the development of photo-electrode is considered. The effect of defect disorder on the performance-related properties of TiO2-based photo-electrodes are discussed. The major challenges in the development of materials with optimized performance are considered in terms of both collective and local properties that must be assessed and modified simultaneously.

The present work describes application of the high-temperature Kelvin probe for in situ monitoring of the charge transfer at the gas/solid interface at elevated temperatures (up to 1200 K) using work function measurements. Performance of the probe is described for the oxygen/zirconia system at elevated temperatures. The work function data for yttria-stabilized (10 mol%) zirconia during oxidation in the temperature range 298–1173 K are reported. The determined work function changes during oxidation are considered in terms of the reactivity mechanisms between oxygen and zirconia, such as oxygen incorporation and oxygen chemisorption. The effect of temperature on the oxygen chemisorption isobar is considered in terms of surface coverage of zirconia with chemisorbed oxygen species, including singly ionized atomic species and singly ionized molecular species. The respective chemisorption isobars, determined at p (O 2 )=21 kPa, exhibit maxima at ∼300 and 1000 K.