As an alternative to H 2 O 2 enzymatic biosensing devices, non-enzymatic CeO 2 -based biosensors have shown improved sensibility, robustness, and shelf lives. The redox capability in CeO 2 and rapid switching between its oxidation states facilitate the formation of structural vacancy defects that serve as active sites. This work reports a novel approach for synthesis of defect-rich CeO 2-x -based nanoflakes using a controllable electrochemical-based deposition at low temperatures (45°−65 °C) followed by low-energy ion implantation. Among the nanoflakes, Mo-implanted CeO 2-x exhibited outstanding sensitivity of 4.96 × 10 −5 A·mM −1 cm −2 within the linear range of 0.05–10 mM. Moreover, the ion-implanted samples yielded high sensing stability and electronic conductivity. The former was achieved through the multi-valence charge transfer between Ce and the implanted ions that caused the reduction of Gibbs free energies required for the formation/retention of the defects. The latter was due to the narrowing of the electronic bandgap of CeO 2-x by creation of defect-induced midgap states.

As the demand for seafood increases, so does the incidence of seafood fraud. Confirming provenance of seafood is important to combat fraudulent labelling but requires a database that contains the isotopic and elemental "fingerprints" of authentic seafood samples. Local isotopic and elemental databases can be scaled up or combined with other databases to increase the spatial and species coverage to create a larger database. This study showcases the use of isotopic and elemental fingerprints of the black tiger prawn (Penaeus monodon) to develop a database that can be used to securely store the data necessary for determining provenance. The utility of this database was tested through querying and building seven different datasets that were used to develop models to determine the provenance of P. monodon. The models built using the data retrieved from the database demonstrated that the provenance of P. monodon could be determined with >80% accuracy. As the database was developed using MySQL, it can be scaled up to include additional regions, species, or methodologies depending on the needs of the users. Combining the database with methods of determining provenance will provide regulatory bodies and the seafood industry with another provenance tool to combat fraudulent seafood labelling.

The purpose of this study was to characterize heavy metals in PM2.5 (particles with aerodynamic diameters below 2.5 µm) in two industrial estates with different activities in East and West Surabaya, Indonesia. Samples of PM2.5 were collected on Nucleopore polycarbonate filters using a low volume GENT sampler, during 2019-2020. A total of 73 samples were collected. Eighteen elements were measured to study their levels. The average mass concentration of PM2.5 in.the East and west Surabaya were 18.37±6.06 µg/m3 and 12.72±6.47 µg/m3, respectively. The samples were analyzed for black carbon (BC) using an EEL smoke reflectometer and for elemental concentrations using Ion Beam Analysis (IBA). The average concentration of black carbon in East and West Surabaya is 3.51±1.13 µg/m3 and 2.90±1.62 µg/m3, respectively. The results obtained indicate that in general the concentration of heavy metals in East Surabaya is higher than in West Surabaya. The heavy metals Mn, Fe, Zn and Pb, which are markers of the steel industry in East Surabaya have concentrations of 2.5, 1.5, 4.2, and 9.7 times greater than West Surabaya, respectively. The relatively high levels of heavy metals indicated that the area around the industry is polluted. These results can be used as an early warning and should not be neglected. At the later stage, the data from this research can be developed for the source apportionment studies and health risk assessment. These results can be used as a scientific-based reference for formulating strategies and policies for regional air quality management.

Coarse (PM10) and fine (PM2.5) aerosols were sampled from June to November 2016 at three different sites in Metro Manila Philippines (Valenzuela, NAMRIA, and MMDA). PM2.5 average levels in all sites exceeded the World Health Organization annual and daily limits, indicating that the ambient air qualities in all sites were unhealthy. Black Carbon (BC), a fingerprint of incomplete combustion, constituted 31–46% of PM2.5. Multi-element analysis of PM indicated that the sulfur, lead, and zinc had substantial contributions to PM2.5, with the highest level found in Valenzuela. Receptor modeling highlighted six important sources: vehicular emissions, biomass burning, industrials, secondary sulfur, sea spray, and fine soil. Among the sources, vehicular emission was the most dominant source, comprising 20–35% of the apportioned sources. An industrial source, predominantly with Zn and Pb, was seen in Valenzuela, contributing about 5.4% of its PM2.5. The health risks of fine aerosol, BC, and major elements were evaluated also in this study. Elements studied showed negligible potential (HQ < 1) to cause non-carcinogenic health effects and very low (<1 × 10−6) carcinogenic health effects to children and adults. The observed trend for carcinogenic risks of PM2.5 in children was Valenzuela > MMDA > NAMRIA while a medium carcinogenic risk was observed for adults at all sites (CR > 1 × 10−5). The trend for PM2.5 average HQ values in both age groups was Valenzuela > MMDA > NAMRIA. Our results showcased varying levels and sources of PM and its components that can impact the health upon exposure and should be addressed in future policies to safeguard public health.

Light absorbing carbon (LAC), also referred to as black carbon (BC) or more colloquially as soot; is generated from the partial combustion of fossil fuels and biomass. The significant research interest in BC is largely due to its aerodynamic diameter well within the 2.5 ?m size fraction (known as PM2.5), as well as its abundance being a major constituent of atmospheric particulate matter, particularly in urban regions. Accurately measuring BC is crucial for researchers and regulators for identifying root causes, monitoring emission source concentrations and input into climate change models in order to identify approaches that can best mitigate its atmospheric abundance. This paper presents results from recent studies using a BC research instrument developed by ANSTO, the Multiwavelength Absorption Black carbon Instrument (MABI). The paper describes in detail the instrument design, function and interpretation of data from measurement of filters collected from various geographical locations in Australia and Asia. This instrument measures the light absorption of LAC particles deposited on filters at seven different wavelengths ranging from 405 to 1050 nm to estimate the LAC concentration of different particle diameters in order to differentiate between LAC from high temperature fossil fuel combustion (such as diesel vehicle engines) and biomass burning. Providing a powerful tool for identifying source contributions and determining LAC content of filters using quantitative analysis.

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.

Sampling of PM2.5 has been undertaken twice per week at the Liverpool and Mascot sites (in Sydney, Australia) since 1998. Ion Beam Analysis (IBA) was applied to each sample to determine the concentrations of 21 elements from hydrogen to lead and the black carbon concentration was determined using photon transmission techniques. Sampling days that displayed high and low airborne soil concentrations were identified and three distinct sets of soil fingerprints were determined using Positive Matrix Factorisation (PMF) source apportionment techniques. A fingerprint for all sampling days (representing the average soil fingerprint for each site), a fingerprint corresponding to low soil days associated with local retrained road dust and a fingerprint for high soil days associated with agricultural activities. The ratios of key soil elements (i.e. Si, Al, Fe) displayed larger temporal variation for the high soil days, whereas lower variation was observed for low (local) soil days. Furthermore, it was found that the El Nino-Southern Oscillation (ENSO) affected the concentration of windblown soil dust in the atmosphere. The average soil fingerprint, for all data, was heavily influenced by sampling days containing higher concentrations of soil dust, thus representing the dominant soil type. However, we did observe differences in the K/Fe and Ca/Si ratios to be a distinguishing factor between the average soil fingerprint and the high soil day fingerprint. The Soil fingerprint for the low soil concentration days had a large fraction of black carbon associated with vehicle emissions, represented retrained road dust.

Uniformly codoped anatase TiO2 thin films of varying (equal) Mo and Cr concentrations (<= 1.00 mol% for each dopant) were fabricated using sol-gel spin coating and deposited on fused silica substrates. All films were annealed at 450 degrees C for 2 h to recrystallise anatase. Undoped anatase films have been subjected to dual ion implantation for the first time, using Mo, Cr, and sequential Mo thorn Cr at 1 x 10(14) atoms/cm(2). The films were characterised by GAXRD, AFM, SIMS, XPS, and UV-Vis and the performance was assessed by dye degradation. Despite the volumetric doping by sol-gel and the directional doping by ion implantation, neither method resulted in homogeneous dopant distributions. Both methods caused decreasing crystallinities and associated partial amorphisation. The XPS signal of the uniformly codoped films is dominated by undissolved dopant ions, which is not the case for the ion-implanted films. Increasing Ti valences are attributed to the fully oxidised condition of the Ti4+ ions that diffuse to the surface from Ti vacancy formation compared to the Ti valence of the bulk lattice, which contains Ti3+. Increasing O valence is attributed to the electronegativity of O2-, which is higher than that of Ti4+. Detailed structural mechanisms for the solubility and energetics mechanisms involve the initial formation of Mo and Cr interstitials that fill the two voids adjacent to the central Ti ion in the TiO6 octahedron, followed by integrated solid solubility (ISS) and intervalence/multivalence charge transfer (IVCT/MVCT). The sequential order of the last two is reversed for the two different doping methods. These two effects are likely to be the source of synergy, if any, between the two dopant ions. The photocatalytic performances of the uniformly codoped films are relatively poor and correlate well with the band gap (E-g). The performances of the ion-implanted films do not correlate with the E-g, where TiO2-Mo performs poorly but TiO2-Cr and TiO2-Mo-Cr outperform the undoped film. These results are interpreted in terms of the competition between the effects of Mo doping, which causes partial amorphisation and/or blockage of active sites, and Cr doping, which may cause Mo-Cr synergism, Cr-based heterojunction formation, and/or improved charge-carrier separation owing to the surface-deposition nature of ion implantation. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol–climate model. The study uses 1 million variants of the Hadley Centre General Environment Model version 3 (HadGEM3) that sample 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulfate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ±1σ (standard deviation) range of global annual mean direct radiative forcing (RFari) is reduced by 33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI) is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual mean aerosol–cloud radiative forcing, RFaci, the ±1σ range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by 6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined “representativeness error” associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For example, constraints using either sulfate or PM2.5 measurements individually result in RFari±1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be overconfident.

Exposure to particulate matter results in adverse health outcomes, especially in sensitive members of the community. Many communities that co-exist with industry are concerned about the perceived impact of emissions from that industry on their health. Such concerns have resulted in two studies in the Hunter Valley of New South Wales, Australia. The chemical composition of samples of particulate matter, collected over two 12-month sampling periods (2012 and 2014–2015) at six sites in the Hunter Valley and across two size fractions (PM2.5 and PM2.5–10) were input to a receptor model to determine the source of particulate matter influencing particle composition at the sites. Fourteen factors were found to contribute to particle mass. Of these, three source profiles common to all sites, size fractions, and sampling periods were sea salt, industry-aged sea salt and soil. Four source profiles were common across all sites for PM2.5 including secondary sulphate, secondary nitrate, mixed industry/vehicles, and woodsmoke. One source profile (other biomass smoke) was only identified in PM2.5 at Singleton and Muswellbrook, two source profiles (mixed industry/shipping and vehicles) were only identified in PM2.5 at Newcastle, Beresfield, Mayfield, and Stockton, and one source (primary nitrate) was only identified at Stockton in PM2.5. Three sources (bioaerosol, light absorbing particles (coal dust), and industry) were only identified in the PM2.5–10 size fraction at Mayfield and Stockton. The contribution of the soil factor to PM2.5 mass was consistent across the sites, while the fresh sea salt factor decreased with distance from the coast from 23% at Stockton to 3% at Muswellbrook, and smoke increased with distance from the coast. Primary industry was greatest at Stockton (due to the influence of ammonium nitrate emitted from a prilling tower) and lowest inland at Muswellbrook. In general, primary emissions across the sites accounted for 30% of the industry sources. The largest contribution to PM2.5 was from secondary sources at all sites except at Muswellbrook, where woodsmoke and industry sources each made an equal contribution of 40%. In general, secondary reactions accounted for approximately 70% of the industry source, although at Stockton, with the presence of the prilling tower, this split was 50% primary and 50% secondary and at Muswellbrook, the split was 20% primary and 80% secondary. These findings add to the evidence base required to inform policies and programs that will improve air quality in the Hunter Valley.

Speciated air quality data informs health studies and quantitates impacts. However, monitoring is concentrated around populated regions whilst, large remote and rural regions remain unmonitored despite risks of dust-storms or wild-fires. Sub-hourly, infrared, geostationary data, such as the 10-min data from Himawari 8, could potentially be used to quantify regional air quality continually. Monitoring of Aerosol Optical Depth (AOD) is restricted to visible spectra (i.e. daytime only), while newer quantification methods using geostationary infrared (IR) data have focused on detecting the presence, or absence, of an event. Limited attention has been given to the determination of particle size and aerosol composition (such as sulfates, black carbon, sea-salt, and mineral dust), using IR exclusively, and more appropriate methods are required to improve the understanding of source impacts. Hourly data were collected for a three-year study period (July 2015 to July 2018) across the greater Sydney region in Eastern Australia from seventeen ground-based sites that measured meteorological data and quantified ambient concentrations of NO, NO2, SO2, PM2.5, PM10, and O-3 This data was combined with source-apportioned categories (soil, sea-spray, smoke, secondary sulfates, and vehicles) from positive matrix factorization (PMF) of elemental aerosol collected on daily filters at five monitoring sites across the region. Regression analysis of five brightness temperature difference (BTD) infrared indices were used to determine a pollution index. The pollution index was shown to be related to humidity, particle size, and compositional changes. Unlike fixed thresholds, the continual index function can be aggregated spatially and temporarily. Good resolution is obtained between PM2.5 and O-3. BTD appears insensitive to concentration, and the pollution index was used to detect and identify composition prior to determining concentration.

Fine particle air pollution is a significant problem in large urbanised areas across the Asian region. With funding from the International Atomic Energy Agency (IAEA) fifteen countries in Asia have been collecting weekly samples on filters of fine and coarse particles in major cities for the past 15 years. These filters have been analysed for over 20 different chemical species from hydrogen to lead using a range of analytical techniques including accelerator based ion beam techniques such as PIXE, PIGE, PESA, RBS, as well as XRF and NAA. These data have been included into a major database, which is generally available, containing over 17,000 combined sampling days from these fifteen countries spanning an area of the globe from +/- 50 degrees latitude and from 70 degrees to 180 degrees longitude. That is, the sampling covers an area north-south from Mongolia to New Zealand and west-east from Islamabad, Pakistan to Wellington, NZ.

Sea salt is one of the major aerosols in the atmosphere in both the fine and coarse size ranges. Newly formed sea salt particles have a similar composition to seawater; including elements such as Na, Cl, Mg, S, Ca, Br and K. However, once in the atmosphere sea salt particles can undergo chemical reactions with other airborne pollutants, resulting in a loss of chlorine (whereas Na is conservative). The modified aerosol is commonly referred to as aged sea spray or aged sea salt. Fine aerosols from two sites in the Sydney Basin were analysed for source fingerprints with components that may have originated from the ocean (i.e. fresh and aged sea spray). At Lucas Heights, 18.4 km from the nearest coast, the average source fingerprint concentrations of fresh and aged sea spray were 0.47 +/- 0.02 and 1.08 +/- 0.03 mu g/m(3), respectively. At Richmond, 58 km from the coast, the average fingerprint concentrations of fresh and aged sea spray were 0.26 +/- 0.01 and 0.87 +/- 0.02 mu g/m(3), respectively. At Lucas heights, fresh and aged sea spray contributed to 11% and 21% of PM2.5, respectively. At Richmond fresh and aged sea spray contributed to 4.8 +/- 0.35 and 16 +/- 0.5% of the PM2.5, respectively. The Cl/Na ratios of aged sea spray at Lucas Heights and Richmond were 0.72 and 0.87, respectively, in comparison to 1.54 for fresh sea salt. At Richmond the corresponding Ca/Na and K/Na ratios were both 0.037 (close to that of seawater), and at Lucas Heights, the corresponding ratios were 0.038 and 0.026, respectively. Back trajectory and Radon-222 analysis demonstrated that the largest concentrations of aged sea spray occur when the air masses had travelled over regions of anthropogenic sources. This confirms an interaction between anthropogenic precursors and sea spray that liberates chlorine enabling it to contribute to other chemical reactions in the atmosphere, e.g. resulting in an increase in the formation of ozone.

This work considers the effect of chromium surface segregation for polycrystalline Cr-doped TiO2 on surface vs. bulk defect disorder. It is shown that annealing of Cr-doped TiO2 (0.04 at% Cr) in the gas phase of variable oxygen activity at 1273 K results in a gradual transition in the valence of chromium at the surface from predominantly Cr3+ species in reduced conditions, p(O2) = 10−12 Pa, to comparable concentrations of both Cr3+ and Cr6+ species in oxidising conditions, p(O2) = 105 Pa. The reported data is considered in terms of defect equilibria leading to the formation of positively and negatively charged chromium in both the cation sub-lattice and interstitial sites. The derived theoretical models represent the effect of oxygen activity on the surface charge and the resulting electric field leading to migration mechanism of charged chromium species.

Characterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM2.5 (particulate matter with aerodynamic diameters less than 2.5μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM2.5 mass concentration for the study period was (3.3±2.5)μgm-3. It is shown that automobile (44.9±0.8)%, secondary sulfate (21.4±0.9)%, smoke (12.3±0.6)%, soil (11.3±0.5)% and aged sea salt (10.1±0.4)% were the five PM2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research.

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO2-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. This work reports the effect of photoelectrochemical coupling of both pure and Cr-doped TiO2 on photocatalytic partial water oxidation. The couples are annealed in oxidising and reducing conditions, at p(O2) = 105 Pa and p(O2) = 10−10 Pa, respectively. The performance of the coupled system may be enhanced, or retarded, by the electrical potential barrier that is formed between the couple components as a result of the difference in Fermi levels. In this work, we show that the potential barrier results in the effect of synergy when the charge transport within the couple components is high enough. This is the case for the couples annealed in reducing conditions.

The imperative to protect the environment from increasingly apparent climate change imposes the urgent need to reduce the emissions of greenhouse gases to the atmosphere. This, consequently, results in intensification of research in the development of new materials and devices for the generation of energy that is environmentally clean. This work considers photosensitive oxide semiconductors for solar energy conversion by light-induced water oxidation. It has been documented that the performance of oxide semiconductors for solar-to-chemical energy conversion is determined by a range of defect-related properties, including the concentration of surface active sites, Fermi level, charge transport, electronic structure, and alignment of band edges with the energy level of the redox couple. The present work considers the research strategy in processing TiO2-based semiconductors, which are the promising candidates for a new generation of solar materials. It is shown that the performance -related properties of TiO2 and its solid solutions are determined by surface versus bulk defect disorder and the associated semiconducting properties. Therefore, the development of TiO2-based materials with enhanced performance could be based on using defect engineering for imposing optimized bulk versus surface properties. In this work, we discuss a range of defect-related properties of TiO2 and its solid solutions, such as electrical and optical properties and the related photocatalytic performance. We show that the phenomenon of segregation may be used as the technology for imposition of controlled surface versus bulk defect disorder that is required for processing the systems with optimized properties.

Health implications of air pollution vary dependent upon pollutant sources. This work determines the value, in terms of reduced mortality, of reducing ambient particulate matter (PM2.5: effective aerodynamic diameter 2.5μm or less) concentration due to different emission sources. Suva, a Pacific Island city with substantial input from combustion sources, is used as a case-study. Elemental concentration was determined, by ion beam analysis, for PM2.5 samples from Suva, spanning one year. Sources of PM2.5 have been quantified by positive matrix factorisation. A review of recent literature has been carried out to delineate the mortality risk associated with these sources. Risk factors have then been applied for Suva, to calculate the possible mortality reduction that may be achieved through reduction in pollutant levels. Higher risk ratios for black carbon and sulphur resulted in mortality predictions for PM2.5 from fossil fuel combustion, road vehicle emissions and waste burning that surpass predictions for these sources based on health risk of PM2.5 mass alone. Predicted mortality for Suva from fossil fuel smoke exceeds the national toll from road accidents in Fiji. The greatest benefit for Suva, in terms of reduced mortality, is likely to be accomplished by reducing emissions from fossil fuel combustion (diesel), vehicles and waste burning.

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO2-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface vs. bulk properties. The present work reports the effect of oxygen activity in the oxide lattice on photocatalytic activity of pure and Cr-doped TiO2 (0.04 at% Cr). Processing of specimens included annealing at 1273 K in the gas phase of controlled oxygen activity in the range 10−12 Pa < p(O2) < 105 Pa. We show that the increase of oxygen activity results initially in a decrease of photocatalytic activity, minimum around the n-p transition point, and then increase assuming maximum at p(O2) = 105 Pa. The obtained results are considered in terms of a theoretical model that explains the effect of defect disorder on the reactivity of TiO2 with water. The minimum of the photocatalytic activity corresponds to the n-p transition point. The maximum of performance at high p(O2) is determined by increased concentration of titanium vacancies forming surface active sites.