Anatase formation during the synthesis of mesoporous titania and its photocatalytic effect

Thermally stable mesoporous titania can be synthesized following different synthesis routes. In this paper, mesoporous titania was synthesized applying the evaporation-induced self-assembly (EISA) method. The mesostructured titania was treated with an NH(4)OH solution to increase the thermal stability. The influence of this postsynthesis treatment on the anatase formation was investigated using different initial synthesis conditions. Mesoporous titania was synthesized under both acidic and basic conditions, with hexadecylamine and cetyltrimethylammonium bromide as surfactants. The samples were investigated with FT-Raman to investigate when exactly anatase was formed during the synthesis. It will be shown that the anatase formation depends mainly on the initial synthesis conditions. This study shows that anatase can already be formed before calcination under certain circumstances. Furthermore, the accessibility of the anatase phase influenced the photocatalytic activity.     

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO₂ was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO₂ had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m²/g. The photocatalytic activity of synthesized TiO₂ was evaluated with photocatalytic H₂ production from water-splitting reaction. The photocatalytic activity of synthesized TiO₂ treated with appropriate calcination temperature was considerably higher than that of commercial TiO₂ (Ishihara ST-01). The utilization of mesoporous TiO₂ photocatalyst with high crystallinity of anatase phase promoted great H₂ production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.     

Aerosol-assisted fabrication of mesoporous titania spheres with crystallized anatase structures and investigation of their photocatalitic properties

We demonstrate practical aerosol-assisted approach to synthesize spherical mesoporous titania particles with high surface areas. Scanning electron microscopy observation of the spray-dried products clearly shows spherical morphology. To remove surfactants and enhance crystallinity, the spray-dried products are calcined under various temperatures. The crystalline structures inside the particles are carefully detected by wide-angle XRD measurements. With increase of the calcination temperatures, anatase crystal growth proceeds and transformation from anatase to rutile is occurred. The effect of various calcination temperatures on the mesostructures is also studied by using N₂ adsorption desorption isotherms. The mesoporous titania particles calcined at 350, 400, and 500 °C exhibit type IV isotherms with a capillary condensation step and shows a hysteresis loop, which is a characteristic of mesoporous materials. The reduction in the surface areas and the pore volumes is confirmed by increasing the calcination temperatures, while the average pore diameters are increased gradually. This is attributed to the distortion of the mesostructures due to the grain growth of the anatase phase and the transformation to the rutile phase during the calcination process. As a preliminary experimental photocatalytic activity, oxidative decomposition of acetaldehyde under UV irradiation is examined. The mesoporous titania calcined at 400 °C shows the highest photocatalytic activity, due to both high surface area and well-developed anatase crystalline phase.     

Influence of Pt promoter on the photo-oxidative degradation by visible-light plasmonic Pt-titania catalyst

Nanometer platinum-deposited titania particles were prepared through a soft chemical reduction method. The physico-chemical properties of the obtained products are analyzed by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectra. The as-prepared metal-TiO₂ nanohybrid was found to show excellent photocatalytic reactivity toward rhodamine-B decomposition. In the current case, chemical reduction of hydrogen hexachloroplatinate by glucose results in the intercalation of metallic platinum into the titania matrix. The deposited platinum atoms were featured by surface-plasmon resonance under visible-light excitation and electrons from platinum nanoparticles would transfer to the conduction band of titania and accelerate the formation O₂^*− to degrade dye molecule. As a consequence, platinum deposition onto TiO₂ surface is confirmed to yield a superior photocatalytic performance over the naked titania.     

Synthesis of bimodal porous structured TiO2 microsphere with high photocatalytic activity for water treatment

In this work bimodal structured titanium dioxide (TiO₂) microsphere has been prepared from commercial TiO₂ powder and nano-sized titania gel via sol–gel spray-coating technique. Crystallization and transformation behavior of titania gel were investigated. The results revealed that the crystallization and transformation of anatase particles were substantially affected by the concentration of solvent and calcination temperature. Anatase crystallite size of 10 nm was obtained at mole ratio of solvent/precursor 50/1 and calcination temperature of 450 °C. The prepared nano-sized titania gel was embedded within the core (commercial TiO₂, P25) during the spraying process. The prepared TiO₂ microsphere was characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), field emission electron microscope (FESEM) and micropore analysis. The photocatalytic activity was monitored by following the degradation of phenol with activity benchmarked against commercial P25 (Degussa). The increase of photocatalytic activity of TiO₂ microsphere was attributed to the nano-sized anatase crystallite which has been incorporated into the TiO₂ microsphere.     

Influence of N sources on the photocatalytic activity of N-doped TiO2

Influence of nitrogen precursors urea, semicarbazide and N,N’-dimethyl urea on the photocatalytic activity of the N-doped TiO₂ were studied by a simple decomposition method. The nano N-TiO₂ catalysts were synthesized via two different modified approaches by calcination at 500 °C. The synthesized samples were characterized by IR, UV-DRS, Raman, TG-DTA, XRD, EDX, XPS, SEM, TEM and BET analysis. Of the synthesized six samples of N-TiO₂ five samples showed better photocatalytic activity towards direct sunlight photo-degradation of methylene blue (MB) and rhodamine B (RhB) than Degussa P25. The catalysts obtained using semicarbazide samples F3 and F4 having large surface area of 76 and 85.8 m²/g displayed maximum photocatalytic activity. The sample F4 was 1.5 times more active than Degussa P25 for the decolourisation of MB and 1.9 times more active for the decolourisation of RhB. The presence of nitrogen, large surface area and coupling of rutile-anatase phases were found to be the main responsible factors for the enhanced photocatalytic activity. The exclusive formation of the anatase phase in the case of urea precursor is attributed to the slow evaporation of urea due to the formation of melamine derived products. The calcination temperature is the deciding factor responsible for the photocatalytic activity of the N-TiO₂ samples prepared from precursors which can potentially form the melamine and its oligomerized products on the surface of TiO₂.     

Preparation of SiO2-Pt-CdS composite photocatalyst and its photocatalytic activity for hydrogen evolution under visible light

CdS nanoparticles were prepared by the precipitation method. Pt was loaded on CdS by photodeposition. SiO₂-Pt-CdS was synthesized via hydrolysis of tetraethylorthosilicate in the presence of Pt-CdS. The samples were characterized by XRD, BET, PL and UV-Vis techniques. The photocatalytic activity of the samples for hydrogen evolution was investigated under visible light irradiation (λ ≥ 420 nm). The stability and activity of CdS was improved by coating SiO₂.     

Pt-Chitosan-TiO2 for Efficient Photocatalytic Hydrogen Evolution via Ligand-to-Metal Charge Transfer Mechanism under Visible Light

The Pt-chitosan-TiO₂ charge transfer (CT) complex was synthesized via the sol-gel and impregnation method. The synthesized photocatalysts were thoroughly characterized, and their photocatalytic activity were evaluated toward H₂ production through water reduction under visible-light irradiation. The effect of the preparation conditions of the photocatalysts (the degree of deacetylation of chitosan, addition amount of chitosan, and calcination temperature) on the photocatalytic activity was discussed. The optimal Pt-10%DD75-T200 showed a H₂ generation rate of 280.4 μmol within 3 h. The remarkable visible-light photocatalytic activity of Pt-chitosan-TiO₂ was due to the CT complex formation between chitosan and TiO₂, which extended the visible-light absorption and induced the ligand-to-metal charge transfer (LMCT). The photocatalytic mechanism of Pt-chitosan-TiO₂ was also investigated. This paper outlines a new and facile pathway for designing novel visible-light-driven photocatalysts that are based on TiO₂ modified by polysaccharide biomass wastes that are widely found in nature.     

硫和银共掺杂介孔TiO2的制备表征及光催化活性

以P123为模板,以钛酸四正丁酯、硝酸银和硫脲为原料采用模板法制备了一系列硫和银共掺杂介孔TiO2光催化材料。利用扫描电子显微镜（SEM）、X射线衍射（XRD）、BET和紫外-可见光谱（UV-Vis）等技术对其形貌、晶体结构及表面结构、光吸收特性等进行了表征。以甲基橙溶液的光催化降解为模型反应, 考察了不同掺杂量的样品在紫外和可见光下的光催化性能。结果表明：用模板法制备的共掺杂介孔TiO2光催化材料在紫外和可见光条件下较纯介孔TiO2和单掺杂介孔TiO2对甲基橙溶液具有更好的光催化降解效果, 且硫和银的掺杂量及样品焙烧温度显著影响该材料的催化性能。当硫掺杂量为2%（mol）和银掺杂量为1%（mol）,在500℃焙烧2 h所得光催化材料的催化性能最佳, 4 h即可使甲基橙的降解率达98.8%,重复使用4次仍可使甲基橙的降解率保持在87.5%以上。因此, 以该模板合成法, 通过硫和银的共掺杂有望使TiO2成为一种低或无能耗、高活性的绿色环保型催化材料。     

Pt deposited TiO2 catalyst fabricated by thermal decomposition of titanium complex for solar hydrogen production

C, N codoped TiO₂ catalyst has been synthesized by thermal decomposition of a novel water-soluble titanium complex. The structure, morphology, and optical properties of the synthesized TiO₂ catalyst were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the Pt deposited TiO₂ catalysts synthesized at different temperatures was evaluated by means of hydrogen evolution reaction under both UV–vis and visible light irradiation. The investigation results reveal that the photocatalytic H₂ evolution rate strongly depended on the crystalline grain size as well as specific surface area of the synthesized catalyst. Our studies successfully demonstrate a simple method for the synthesis of visible-light responsive Pt deposited TiO₂ catalyst for solar hydrogen production.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

A simple method to synthesize N-doped rutile titania with enhanced photocatalytic activity in sunlight

This study demonstrates a simple route for the synthesis of nanocrystalline N doped rutile titania by calcination of acidified TiCl₃ in presence of urea. Urea was used as a source of nitrogen. The N doped rutile titania was yellow in colour and showed excellent photocatalytic activity in sunlight.     

Synthesis of visible-light reactive TiO2−xNy photocatalyst by mechanochemical doping

Yellowish TiO_2−xN_y was prepared by a novel mechanochemical nitrogen-doping method. The samples were prepared by a high-energy ball milling of P25 titania with different nitrogen sources such as hexamethylenetetramine, urea or ammonium carbonate, followed by calcination in air at 400 °C. The high mechanical energy accelerated the phase transformation of anatase to rutile, while the existence of the nitrogen reagents tended to block the transformation. The calcination treatment slightly increased the crystallinity of the prepared titania. The prepared powders possessed two absorption edges at around 400 and 540 nm and showed an excellent photocatalytic ability for the oxidation of nitrogen monoxide under visible light irradiation. Under the irradiation of visible light with wavelengths of >510 nm, nitrogen monoxide could be continuously removed by the nitrogen doped titania prepared from the P25 titania-hexamethylenetetramine mixture, while the powders prepared using urea and ammonium carbonate as nitrogen sources showed lower activities. This mechanochemical technique might be widely useful for doping oxides with nonmetallic elements.     

Synthesis,characterization and evaluation of nanocrystalline anatase titania for the degradation of dibutyl phosphate

Degradation of dibutyl phosphate (DBP) in aqueous solution was successfully demonstrated in this paper using nanoparticles of anatase titania. Nanocrystalline anatase titania employed for the degradation study was synthesized in house by solgel route under stirring mode using titanium ethoxide precursor. The catalyst was characterized using XRD, DRS, BET, TEM, TG–DTA and Raman spectroscopy to establish the catalytic activity and surface morphology. A cylindrical photoreactor was used for the photocatalytic experiments. 10 mg of nano anatase titania and 0.5 mL of 30 % H₂O₂ were used as catalysts for the degradation of 1,000 mL of 240 mg/L DBP. Ion chromatographic procedure was used for following the DBP degradation. More than 95 % of DBP degradation could be in less than 45 min and the kinetics of DBP was found to follow pseudo first order. It was demonstrated that the photocatalytic efficiency of the synthesized titania was better than P-25 titania.     

Principal component analysis and response surface methodology: optimization for H2 evolution from water catalyzed adopting V–Bi under visible light

Energy generation by photocatalytic water splitting with semiconductors under visible light is an effective method for generating pollution-free energy. In this work, a highly efficient vanadium pentoxide (V₂O₅)-based composite photocatalyst was prepared by hydrothermal calcination. The preparation conditions were optimized using single factor experiments, factor analysis (FA), principal component analysis (PCA), and response surface method (Design Expert). The results showed that the optimal preparation conditions were 6% Bi₂S₃ loading, 10 h hydrothermal time, 175.0°C hydrothermal temperature, 4.0 h calcination time, and a calcination temperature of 400.0°C. The results of FA and PCA analysis showed that the hydrothermal temperature, calcination time, and calcination temperature were the three main influencing factors. According to the optimization analysis using the response surface method, the highest hydrogen production rate (590.151 μmol/(g?h)) was obtained at a hydrothermal temperature of 168.74°C, a calcination time of 3.97 h, and a calcination temperature of 390.15°C. The quantum yield of the catalyst was 27.71%.     

The effects of the crystallization rate of the mesoporous TiO2 on the stability of the mesoporous structure after reflux

A simple synthetic method was employed to prepare mesoporous titania with anatase crystalline walls and high photocatalytic activity. The properties and structures of mesoporous titania were characterized by means of low angle and wide angle X-ray diffraction (XRD), Fourier transform (FT)-IR spectra, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and N₂ adsorption–desorption. The characteristic results clearly show that crystallization rate of the mesoporous titania affects the stability of the mesoporous structure after reflux, and that the anatase crystal in the mesoporous wall of mesoporous titania can stabilize the mesoporous structure. The photocatalytic activity of titania powder was evaluated from an analysis of the photodegradation of methyl orange under UV irradiation. The results indicate that the titania powder with mesoporous structure shows the highest photocatalytic activity.     

Template synthesis of titania on polysaccharides

Template synthesis of titania was conducted in solutions of polysaccharides, xanthan and sodium hyaluronan, prepared in ethylene glycol and on cellulose fibrils placed in ethylene glycol. The process was controlled by the addition of water in amounts sufficient only for the hydration of polysaccharides. When the precursor of TiO₂, tetra(isopropyl) orthotitanate, was added, the fast reactions of hydrolysis and condensation were triggered only after its contact with water, which provided the precipitation of titania on xanthan and sodium hyaluronan macromolecules or on cellulose fibrils. The morphology of the synthesized TiO₂ samples depended on the reagent concentrations in a reaction mixture. Amorphous titania was transformed by calcination into the crystalline state. Some of the obtained TiO₂ samples have rather high photocatalytic activity comparable to that of the commercial photocatalysts.     

钴掺杂二氧化钛的光催化制氢性能

采用聚合络合法（PCM）制备出钴掺杂二氧化钛（CO/TiO₂）光催化剂.以热重-差示扫描量热同步热分析（TGA-DSC）,傅里叶变换红外（FT-IR）光谱,X射线粉末衍射（XRD）,氮气吸附-脱附,紫外-可见漫反射光谱（UV-Vis DRS）,X射线光电子能谱（XPS）等手段对材料进行了表征.采用光催化制氧作为探针反应,以氧气的产量评价材料的光催化性能结果表明:采用聚合络合法制备的样品主体成分为锐钛矿晶型的二氧化钛,钴元素呈高度分散,钴的掺杂能够明显提升二氧化钛光催化材料的光催化制氢活性,当钴钛物质的量之比为0.3%时,催化剂具有最佳的光催化制氢活性,达到2499μmol,是同等条件下制备的无掺杂二氧化钛的近六倍.还对钴离子掺杂增强机理进行了探讨.     

One-pot hydrothermal synthesis of willow branch-shaped MoS2/CdS heterojunctions for photocatalytic H2 production under visible light irradiation

Willow branch-shaped MoS₂/CdS heterojunctions are successfully synthesized for the first time by a facile one-pot hydrothermal method. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption measurements, diffuse reflectance spectroscopy, and photoelectrochemical and photoluminescence spectroscopy tests. The photocatalytic hydrogen evolution activities of the samples were evaluated under visible light irradiation. The resulting MoS₂/CdS heterojunctions exhibit a much improved photocatalytic hydrogen evolution activity than that obtained with CdS and MoS₂. In particular, the optimized MC-5 (5 at.% MoS₂/CdS) photocatalyst achieved the highest hydrogen production rate of 250.8 μmol h^-1, which is 28 times higher than that of pristine CdS. The apparent quantum efficiency (AQE) at 420 nm was 3.66%. Further detailed characterizations revealed that the enhanced photocatalytic activity of the MoS₂/CdS heterojunctions could be attributed to the efficient transfer and separation of photogenerated charge carriers resulting from the core-shell structure and the close contact between MoS₂ nanosheets and CdS single-crystal nanorods, as well as to increased visible light absorption. A tentative mechanism for photocatalytic H₂ evolution by MoS₂/CdS heterojunctions was proposed. This work will open up new opportunities for developing more efficient photocatalysts for water splitting.     

The photocatalytic properties of Ti–Mo oxides prepared by a simple sol–gel route

Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO₃, TiO₂/MoO₃ or Mo-doped TiO₂ have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO₃.