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Photocatalytic and Antimicrobial Activity of Sulfur‐Functionalized TiO2‐Containing Composite Films
Abstract
Here we report a facile sulfation of TiO2 semiconductor photocatalyst by simply grinding and calcination method using elemental sulfur from desulfurisation of petroleum. The successful sulfation of the prepared visible light active was proved by FT‐IR and XPS measurements, as well. The photocatalytic tests revealed that the S‐TiO2‐2 is the most efficient member of the samples, which has greater photocatalytic activity than TiO2 in the photodegradation of formic acid, under both UV and by visible light activation. Moreover, the improved electrokinetic and water dispersibility behaviours of the sulfur modified photocatalyst allowed the preparation of polyacrylate based photoreactive thin film with increased photocatalytic and strong antimicrobial properties and improved mechanical behavior.
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Titanium dioxide nanoparticles (TiO2 NPs) are regularly used in sunscreens because of their photoprotective capacity. The advantage of using TiO2 on the nanometer scale is due to its transparency and better UV blocking efficiency. Due to the greater surface area/volume ratio, NPs become more (bio)-reactive giving rise to concerns about their potential toxicity. To evaluate the irritation and corrosion of cosmetics, 3D skin models have been used as an alternative method to animal experimentation. However, it is not known if this model is appropriate to study skin irritation, corrosion and phototoxicity of nanomaterials such as TiO2 NPs. This systematic review (SR) proposed the following question: Can the toxicity of TiO2 nanoparticles be evaluated in a 3D skin model? This SR was conducted according to the Preliminary Report on Systematic Review and Meta-Analysis (PRISMA). The protocol was registered in CAMARADES and the ToxRTool evaluation was performed in order to increase the quality and transparency of this search. In this SR, 7 articles were selected, and it was concluded that the 3D skin model has shown to be promising to evaluate the toxicity of TiO2 NPs. However, most studies have used biological assays that have already been described as interfering with these NPs, demonstrating that misinterpretations can be obtained. This review will focus in the possible efforts that should be done in order to avoid interference of NPs with biological assays applied in 3D in vitro culture.
Transformation of coumarin (COU) and coumarin-3-carboxylic acid (3-CCA), the formation of their fluorescent hydroxylated products, (7-hydroxy-coumarin (7-HO-COU) and 7-hydroxy-3-carboxycoumarinic acid (7-HO-3-CCA)) were investigated and compared using three different advanced oxidation processes: gamma radiolysis, VUV (172 nm) photolysis and heterogeneous photocatalysis (TiO2/UV (300–400 nm)). Beside •OH (hydroxyl radical), other reactive species: H• (H-atom, in VUV irradiated aqueous solution and in gamma radiolysis with low yield) and eaq⁻ (hydrated electron, in gamma radiolysis) also contributed to the degradation.
The reaction rate constants of COU and 3-CCA with each reactive species were determined via pulse radiolysis. The values obtained were: 6.88 × 10⁹ and 4.9 × 10⁹ with •OH; 2.5 × 10⁹ and 1.3 × 10⁹ with H•; 11.4 × 10⁹ and 14.3 × 10¹⁰ mol⁻¹ dm³ s⁻¹ with eaq⁻, in the case of COU and 3-CCA, respectively. Based on the results of radiolysis it was suggested, that the formation of fluorescent products are initiated only by •OH.
The effects of dissolved O2 and •OH scavengers (MeOH and t-BuOH) were also investigated. In radiolysis dissolved O2 increased the formation rate of fluorescent products. In VUV photolysis of COU and 3-CCA solutions the inhibition effect of alcohols was more pronounced in the presence of O2 than in its absence. In heterogeneous photocatalysis both MeOH and t-BuOH decreased the transformation rate of COU, while they had no observable effect on that of 3-CCA, which is well adsorbed on TiO2 surface.
A comprehensive study on the sulfur doping of TiO2, by means of H2S treatment at 673 K, has been performed in order to highlight the role of sulfur in affecting the properties of the system, as compared to the native TiO2. The focus of this study is to find a relationship among the surface, structure, and morphology properties, by means of a detailed chemical and physical characterization of the samples. In particular, transmission electron microscopy images provide a simple tool to have a direct and immediate evidence of the effects of H2S action on the TiO2 particles structure and surface defects. Furthermore, from spectroscopy analyses, the peculiar surface, optical properties, and methylene blue photodegradation test of S-doped TiO2 samples, as compared to pure TiO2, have been investigated and explained by the effects caused by the exchange of S species with O species and by the surface defects induced by the strong H2S treatment.
Black TiO2 attracts enormous attention due to its large solar absorption and induced excellent photocatalytic activity. Herein, a new approach assisted by hydrogen plasma to synthesize unique H-doped black titania with a core/shell structure (TiO2@TiO2-xHx) is presented, superior to the high H2-pressure process (under 20 bar for five days). The black titania possesses the largest solar absorption (≈83%), far more than any other reported black titania (the record (high-pressure): ≈30%). H doping is favorable to eliminate the recombination centers of light-induced electrons and holes. High absorption and low recombination ensure the excellent photocatalytic activity for the black titania in the photo-oxidation of organic molecules in water and the production of hydrogen. The H-doped amorphous shell is proposed to play the same role as Ag or Pt loading on TiO2 nanocrystals, which induces the localized surface plasma resonance and black coloration. Photocatalytic water splitting and cleaning using TiO2-xHx is believed to have a bright future for sustainable energy sources and cleaning environment.
The transfer of energy (in the form of heat) between the building and its surroundings affects its thermal performance. When a given building system is thermally inefficient it will require that the HVAC equipment will be in permanent activity, increasing the underlying energy costs. This work evaluates the influence of using a TiO2-coated plastering mortar in the thermal performance of a building wall model. The TiO2 aqueous solution was sprayed onto the mortar surface, in its fresh state, by using an atmospheric air compressor at a distance of about 20 cm, during 30 s and the speed of the aqueous solution jet set at 100 mL/min, thus leading to a coverage rate of about 12 mg/cm2.For the first time, as far as the authors’ knowledge, this research work allowed to test the previously speculated hypothesis and verify its feasibility in the building industry context. It has been observed that the application of a TiO2-coated mortar worsens the thermal behaviour of the wall model, in 10% and 13% for the conduction thermal resistance and for thermal transmission coefficient, respectively. Furthermore, the deposition of TiO2 nanoparticles on the exterior wall surface enhances the water evaporation rate in 136%.
Heterogeneous photocatalysis has been widely applied in various fields, such as photovoltaic cell, solar water splitting, photocatalytic pollutant degradation, and so on. Therefore, the reaction mechanisms involved in these important photocatalytic processes, especially in TiO2 photocatalysis, have been extensively investigated by various surface science techniques in the past decade. In this review, we highlight the recent progress that provides fundamental insights into TiO2 photocatalysis through direct tracking the evolution of single molecule photochemistry on TiO2 single crystal surfaces using a combination of scanning tunneling microscopy (STM) and other surface science techniques. Insight into the structures of various TiO2 surfaces is discussed first, which provides a basic concept on TiO2. Afterward, the details of the single molecule photocatalysis of several important molecules (water, alcohols, and aldehydes) on the model TiO2 surfaces are presented, which are trying to probe bond cleavages and the roles of adsorption sties and adsorption states in TiO2 photocatalysis step-by-step. Last, challenges and opportunities in single molecule photocatalysis on TiO2 are discussed briefly.
TiO2 doped with nitrogen (N), silicon (Si), or selenium (Se) (N-TiO2, Si-TiO2, and Se-TiO2) were obtained by the integrated sol-gel and solvothermal method with short time of crystallization and low temperature. The UV/visible and visible light absorption and photocatalytic activity of these doped TiO2 materials were improved by a dry-co-grinding process with a short grinding time and low rotational speed (30 min at 200 rpm) to obtain N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 catalysts. The materials were characterized by XRD, Raman, BET surface area and porosity, XRF, SEM, TEM, FTIR-ATR, and UV/vis-DRS analyses. The photocatalytic activity of these materials was evaluated by the degradation of phenol under UV/visible and visible light irradiation. The integrated sol-gel and solvothermal methods with short time of crystallization (2 h) and low temperature (225 °C), and the dry-co-grinding process during 30 min at 200 rpm led to materials (N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2) with higher specific surface area, a reduction in the band gap value, and an enhancement of the absorption in the visible light spectrum. Moreover, N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 exhibited higher photocatalytic activities for degradation of phenol under UV/visible and visible light irradiation than those obtained with the doped TiO2, synthesized TiO2 or TiO2 P25.
Hydrogen (H2) production via photocatalytic water splitting is one of the most promising technologies for clean solar energy conversion to emerge in recent decades. The achievement of energy production from water splitting would mean that we could use water as a fuel for future energy need. Among the various photocatalytic materials, titanium dioxide (TiO2) is the dominant and most widely studied because of its exceptional physico-chemical characteristics. Surface decoration of metal/non-metal on TiO2 nanoparticles is an outstanding technique to revamp its electronic properties and enrich the H2 production efficiency. Metal dopants play a vital role in separation of electron-hole pairs on the TiO2 surface during UV/visible/simulated solar light irradiation. In this paper, the basic principles, photocatalytic-reactor design, kinetics, key findings, and the mechanism of metal-doped TiO2 are comprehensively reviewed. We found that Langmuir-Hinshelwood kinetic model is commonly employed by the researchers to demonstrate the rate of H2 production. Copper (Cu), gold (Au) and platinum (Pt) are the most widely studied dopants for TiO2, owing to their superior work function. The metal dopants can amplify the H2 production efficiency of TiO2 through Schottky barrier formation, surface plasmon resonance (SPR), generation of gap states by interaction with TiO2 VB states. The recent advances and important consequences of 2D materials, perovskites, and other novel photocatalysts for H2 generation have also been reviewed.
There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called Advanced Oxidation Processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.
For the first time, nitrogen-doped TiO2 was successfully synthesized by a novel single-step flame spray pyrolysis (FSP) method. Our X-ray photoelectron spectroscopy results illustrate that the nitrogen was effectively doped into the crystal structure of TiO2 in our as-synthesized N-TiO2 catalysts predominantly in the form of interstitial nitrogen (Ti–O−N) rather than substitutional nitrogen (Ti–N). The shift of the (1 0 1) plane anatase diffraction peaks to lower angles in our N-doped TiO2 catalysts compared to pristine TiO2 revealed the distortion and strain in the crystal structure instigated by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (r = 1.71 Å) compared to oxygen (r = 1.40 Å). Our single-step rapid aerosol synthesis method directs the nitrogen atoms mainly occupy interstitial positions in TiO2 lattice. The increase in the primary nitrogen content does not impact the bandgap energies (from 2.54 eV to 2.53 eV), whereas increase in the secondary source monotonically decreased (from 2.95 eV to 2.47 eV) the bandgap energies. This observed lowering of the band-gap energy for the flame made N-doped TiO2 materials implies that the nitrogen doping in TiO2 by aerosol method is highly effective in extending the optical response of TiO2 in the visible region. The nitrogen atoms incorporation into the crystal structure of titania alters the electronic band structure of TiO2, resulting to a new mid-gap energy state N 2p band formed above O 2p valance band. This occurrence narrows the band gap of TiO2 (from 3.07 to ∼2.47 eV) in our N-doped TiO2 and shifts the optical absorption to the visible region.
TiO 2 has received tremendous attention owing to its potential applications in the field of photocatalysis for solar fuel production and environmental remediation. This review mainly describes various modification strategies and potential applications of TiO 2 in efficient photocatalysis. In past few years, various strategies have been developed to improve the photocatalytic performance of TiO 2 , including noble metal deposition, elemental doping, inorganic acids modification, heterojunctions with other semiconductors, dye sensitization and metal ion implantation. The enhanced photocatalytic activities of TiO 2-based material for CO 2 conversion, water splitting and pollutants degradation are highlighted in this review.
Surface modification of photocatalytic materials to give better activity and potentially extending the response into the visible spectrum, is an area of active research. In this work, DFT modelling suggests that surface modification of rutile and anatase TiO2 with partially oxidised copper clusters can induce a red shift in the photo-action spectrum. Copper clusters were synthesised and characterised separately before TiO2 nanoparticle surface modification. Characterisation of copper clusters and photocatalysts modified with copper clusters showed that ex-situ synthesis can control the size of surface clusters. Sub-nanometre clusters of copper maintained their size and morphology upon attachment to the photocatalyst surface. The copper clusters were determined to be a mixture of Cu(0) and Cu(I), and no significant change in the oxidation state was observed following surface modification or following photoelectrochemical measurements. Experimental measurements including UV-Vis spectroscopy and valence band XPS showed a small red shift the band gap correlating to the DFT predictions. Photoelectrochemical characterisation showed an enhancement in the UV photocurrent response and a small red shift in the effective band gap for the surface modified TiO2.
Finding a photocatalyst that can utilize the full solar spectrum is paramount importance in photocatalysis. Assembling TiO2 with a narrow bandgap semiconductor to form a heterostructure which can harvest the light from UV to near-infrared (NIR) region would be ideal for photocatalysis. Here, we report the synthesis of Ag2S quantum dots (QDs)/TiO2 nanobelt heterostructures to display the UV-visible-NIR full spectrum photocatalytic property. The enhanced photocatalytic performance is ascribed to the efficient charge separation properties of the heterostructure formed by intimate contact between Ag2S and TiO2, and efficient visible and NIR harvesting of Ag2S QDs on the surface of TiO2 nanobelts.
There is always a market for cost effective methods of pollution degradation and one of the best areas to keep costs down is through synthesis techniques. This paper provides a simple technique to synthesise porous TiO2 nanoparticles with increased surface area through a scaffold template technique. Their photocatalytic activity is enhanced by incorporating sulphur as a dopant and were validated by analysing the degradation of malachite green (MG). The materials were doped at a molar ratio of 100:1 (Ti:S) and calcined at different temperatures to adjust the anatase/rutile content. Detailed characterisation of the materials was undertaken using XRD, BET, XPS, TEM and FTIR. The nanoparticles displayed a microporous structure and had an increased surface area of 115 m2 g−1 which was reduced by doping and temperature induced phase transformation. Photocatalytic testing showed that the doped materials calcined at 700 °C preformed the best in. It was observed that 20 mg l−1 of MG was decomposed in 30 min using a 40 W UV bulb at pH 9 and the results surpassed those achieved by the commercial catalyst P25 which was also tested for comparison.
Sulfur ion (S6+) was doped into the anatase TiO2 prepared by sol-gel method (SG-TiO2) using sulfur powder as a sulfur source (S-TiO2) and its photoreactivity was probed for the degradation of phenol under UV/solar light illumination. The S-TiO2 and SG-TiO2 were characterized by PXRD, UV-vis DRS, FTIR, SEM, XPS, BET and PL techniques. It was observed that S6+ ion was incorporated into the TiO2 crystal lattice at Ti4+ lattice site and the sulfur on the surface gets modified to SO42- due to the heat treatment under atmospheric conditions. The high photocatalytic activity of S-TiO2 compared to SG-TiO2 is attributed to the surface modification of sulfur as sulfate which plays a crucial role in trapping electrons. S-TiO2 shows significant increase in the surface area, reduced crystallite size, increased surface acidity, visible light absorption and prolonged lifetime of the photogenerated charge carriers. Hole scavengers like potassium iodide and tertiary butanol suggested the surface degradation mechanism rather than the bulk degradation pathway. Addition of oxidizing agents to the degradation reaction did not show any enhancement in the degradation rates since the presence of SO42- on the TiO2 surface itself acts as the efficient electron trapping centers. Both trapping and detrapping of the electron takes place more efficiently at SO42- centers. The enhanced activity of S-TiO2 is attributed to the synergistic effect between S6+ dopant with surface modified SO42-.
A simple approach to estimating the detection limits of X-ray photoelectron spectroscopy (XPS) for any element in any elemental matrix is presented, using the intensity of the background at the expected position for the photoelectron peak to be detected. The approach has been extended to estimate the detection limit for all elements from lithium to bismuth in a similar range of elemental matrices. Using a number of assumptions, it is possible to obtain a reasonable estimate of the background intensity at any electron kinetic energy in the XPS spectrum of an element. Therefore, a detection limit for an arbitrary element homogeneously distributed in that matrix can be estimated. The results show that, although most elements are detectable at about the 1 at.% to 0.1 at.% level, for heavy elements in a light element matrix, the detection limit can be better than 0.01 at.%, whereas for light elements in a heavy element matrix, detection limits above 10 at.% are not uncommon. Two charts detailing the detection limits for all combinations of trace and matrix elements from lithium (Z = 3) to bismuth (Z = 83) are provided for Al Kα and Mg Kα X-ray sources using a typical hemispherical analyser instrument which provides 106 counts eV for the Ag 3d5/2 peak from pure silver. These detection limits can be scaled to estimate the detection limits for any given instrument and operating conditions if the intensity of the Ag 3d5/2 peak from pure silver under those conditions is known. © 2014 Crown Copyright. Surface and Interface Analysis © 2014 John Wiley & Sons Ltd.
Titanium dioxide (TiO2) doped with sulfur (S) was synthesized by oxidation annealing of titanium disulfide (TiS2). According to the x-ray diffraction patterns, TiS2 turned into anatase TiO2 when annealed at 600 °C. The residual S atoms occupied O-atom sites in TiO2 to form Ti�S bonds. The S doping caused the absorption edge of TiO2 to be shifted into the lower-energy region. Based on the theoretical analyses using ab initio band calculations, mixing of the S 3p states with the valence band was found to contribute to the band gap narrowing. © 2002 American Institute of Physics.
Chemical state X-ray photoelectron spectroscopic analysis of first row transition metals and their oxides and hydroxides is challenging due to the complexity of the 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. A review of current literature shows that all values necessary for reproducible, quantitative chemical state analysis are usually not provided. This paper reports a more consistent, practical and effective approach to curve-fitting the various chemical states in a variety of Sc, Ti, V, Cu and Zn metals, oxides and hydroxides. The curve-fitting procedures proposed are based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate literature databases and/or a compilation of the literature references, and (3) specific literature references where fitting procedures are available. Binding energies, full-width at half maximum (FWHM) values, spin-orbit splitting values, asymmetric peak-shape fitting parameters, and, for Cu and Zn, Auger parameters values are presented. The quantification procedure for Cu species details the use of the shake-up satellites for Cu(II)-containing compounds and the exact binding energies of the Cu(0) and Cu(I) peaks. The use of the modified Auger parameter for Cu and Zn species allows for corroborating evidence when there is uncertainty in the binding energy assignment. These procedures can remove uncertainties in analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.
Photocatalytic oxidation of phenol was performed over sulphated TiO2 prepared by a sol–gel method. Comparison with non-sulphated TiO2 and sulphated Degussa was also made. Wide structural and surface characterisation of catalysts was carried out in order to establish a correlation between the effect of sulphation process on the TiO2 photocatalytic properties. Sulphation process clearly stabilizes TiO2 catalyst phase against sintering, maintaining anatase phase and relatively high surface area values with respect non-sulphated TiO2. In spite of sulphate loading should be higher at low temperatures, better conversion values for phenol oxidation has been obtained for samples calcined at 700 °C. For this calcination temperature, the optimisation of structural and surface area values lead to better photocatalytic performance in spite of sulphate presence and therefore acidic properties of samples should be dismissed. Sulphated TiO2 samples prepared by sol–gel presented higher photocatalytic conversions for temperatures higher than 600 °C.
Vanadia, copper and iron oxide catalysts supported on conventional TiO2, ZrO2, and sulphated-TiO2 and ZrO2 have been prepared. These catalysts were characterized by elemental analysis, N2-BET, XRD, and NH3-TPD methods. The influence of potassium oxide additives on the acidity and activity in NO selective catalytic reduction (SCR) with ammonia was studied. The absolute activity of the samples does not vary significantly depending on the nature of the active metal and the acidic properties of the support used, seem to be influenced mainly by the concentration of active metal. Loading of the catalysts with potassium leads to a considerable decrease of their catalytic activity. In the case of the traditional carriers (TiO2, ZrO2), the poisoning of the catalyst with small amounts of potassium oxide (K/metal ratio <0.5) leads to almost complete deactivation of the catalysts. The use of transition metals which reveal mainly Lewis acidity (Fe, Cu), slightly increase the resistance towards alkali poisoning in comparison with V-based catalyst. For the sulphated systems, strongly acidic surface sulphate groups represent attractive sites for hosting potassium oxide at temperatures below 400 °C. The resistance of corresponding catalysts towards poisoning correlates well with the strength of acid sites of the support used. The highest resistance was observed for the catalyst based on sulphated-ZrO2. At temperatures above 375–400 °C, potassium additives become more mobile and are no longer bonded by the sulphated groups of the carrier and potassium migration leads to its preferential localization at the active sites responsible for the SCR activity, which is followed by considerable decrease of the activity.
Visible light-activated sulfur doped TiO2 nanocrystalline films were synthesized by a sol-gel method based on the self-assembly technique with nonionic surfactant to control nanostructure and an inorganic sulfur source (i.e., H2SO4). The films were characterized by UV-vis diffuse reflectance, XRD, TEM, Raman, AFM, ESEM, XPS, FT-IR, EDX, EPR and porosimetry. The results showed that the physicochemical properties of the films, such as BET surface area, porosity, crystallite size and pore size distribution could be controlled by the calcination temperature. The highest surface area, smallest crystallite size and narrow pore size distribution were obtained for sulfur doped TiO2 films calcined at 350°C, which exhibit very smooth surface with minimal roughness (<1nm). The optical absorption edge of sulfur doped TiO2 was red shifted with indirect bandgap energy of 2.94eV. Sulfur species distributed uniformly throughout the films were identified both as S2- ions related to anionic substitutional doping of TiO2 as well as S6+/S4+ cations, attributed mainly to the presence of surface sulfate groups. EPR measurements revealed a sharp signal at g=2.004, whose intensity correlated with the sulfur content and most importantly was markedly enhanced under visible light irradiation, implying the formation of localized energy states in the TiO2 band gap due to anion doping and/or oxygen vacancies. In terms of photocatalytic activity, films calcined at 350°C were the most effective for the degradation of hepatotoxin microcystin-LR (MC-LR) under visible light irradiation, while films calcined at 400°C and 500°C degraded MC-LR to a lower extent, following the evolution of the sulfur content with calcination temperature. The photocatalytic activity of the sulfur doped TiO2 film was stable during three consecutive experiments under visible light irradiation, confirming the mechanical stability and reusability of the doped nanostructured thin film photocatalysts.
A comparative study of the photodeposition of Pt, Au and Pd under the same experimental conditions onto pre-sulphated and non-sulphated TiO2 was performed. Morphological and surface characterisation of the samples as well as photocatalytic activity for phenol photooxidation was studied. The influence of sulphate pre-treatment on the deposits size and dispersion onto the TiO2 surface, and photodeposition yields with the different metals were also analysed. The photocatalytic activity of the doped materials was then investigated, observing that catalytic behaviour can be correlated to physical characteristics of the samples determined by (XRD) X-ray diffraction, (XPS) X-ray photoelectron spectroscopy, (XRF) X-ray fluorescence spectrometry and (TEM) transmission electron microscopy. Sulphate pre-treatment was found to influence both the level of dispersion and the size of metal clusters on the TiO2 surface. Sulphation and metallisation of samples was found to produce a synergistic enhancement in photoactivity for the degradation of phenol. The photoactivity of the catalysts with respect to the doped metal species was ordered Pt > Pd > Au.
Citation
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