Adsorption-driven photocatalytic activity of mesoporous titanium dioxide

Titanium dioxide with a mesoporous structure, when photoactivated in water, demonstrates an unprecedented photocatalytic activity, driven strongly by an adsorption degree of molecules onto the catalyst surface, which promotes a preferential conversion of a well-adsorbed molecule. This catalyzes a selective transformation of a well-adsorbed molecule into a less-adsorbed molecule, so-labeled "stick-and-leave" transformation, which promotes a direct hydroxylation of benzene to phenol, one of the most difficult synthetic reactions, with very high selectivity (>80%) and using water as a source of oxidant.     

Structure and photocatalytic properties of materials based on titanium dioxide and silver nanoparticles

Phase composition and structure of mesostructured materials, titanium dioxide and titanium dioxide modified with silver nanoparticles, have been studied by X-ray diffraction analysis. Introduction of Ag(I) ions into the initial composition and variation of the annealing temperature over the 500–950°C range allows controlling the anatase to rutile crystal phase ratio in the samples. The photocatalytic activity of TiO₂ and TiO₂/Ag samples has been demonstrated using the methyl orange degradation reaction. The catalytic properties of the materials have been found to depend on the anatase to rutile phase ratio and on the presence of silver nanoparticles.     

Preparation and photocatalytic activity of nonmetal Co-doped titanium dioxide photocatalyst

A series of boron and sulfur co-doped titanium dioxide (TiO₂) photocatalysts were prepared by a sol-gel method using boric acid, thiourea and tetrabutyl titanate [Ti(OC₄H₉)₄] as precursors. The photoabsorbance of as-prepared photocatalysts was measured by UV–Vis diffuse reflectance spectroscopy (DRS), and its microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N₂ adsorption-desorption measurements. The prepared photocatalysts consisted of the anatase phase mainly in the form of spherical particles. The photocatalytic performance was studied by photodegradation of methyl blue (MB) in water under UV and visible light irradiation. The calcination temperature and the codoping content influenced the photoactivity. The synergistic effect of boron and sulfur co-doping played an important role in improving the photocatalytic activity. In addition, the possibility of cyclic usage of codoped TiO₂ was also confirmed, the photocatalytic activity of TiO₂ remained above 91% of that of the fresh sample after being used four times. It was shown that the co-doped TiO₂ could be activated by visible light and could thus be potentially applied for the treatment of water contaminated by organic pollutants.     

Doped titanium dioxide nanocrystalline powders with high photocatalytic activity

Doped titanium dioxide nanopowders (M:TiO₂; M=Fe, Co, Nb, Sb) with anatase structure were successfully synthesized through an hydrothermal route preceded by a precipitation doping step. Structural and morphological characterizations were performed by powder XRD and TEM. Thermodynamic stability studies allowed to conclude that the anatase structure is highly stable for all doped TiO₂ prepared compounds. The photocatalytic efficiency of the synthesized nanopowders was tested and the results showed an appreciable enhancement in the photoactivity of the Sb:TiO₂ and Nb:TiO₂, whereas no photocatalytic activity was detected for the Fe:TiO₂ and Co:TiO₂ nanopowders. These results were correlated to the doping ions oxidation states, determined by Mössbauer spectroscopy and magnetization data.     

A study of the photocatalytic activity of titanium dioxide nanopowders

Photodestruction and adsorption of dyes in aqueous suspensions of nanopowders of titanium dioxide of anatase modification was studied. The photocatalytic activity of titanium dioxide nanopowders was examined in relation to the dispersity of particles and pH of the medium.     

Exploration of silver decoration concentration to enhance photocatalytic efficiency of titanium dioxide photocatalysts

Ag decoration on TiO₂ is favorable to absorption of visible light and wider absorption range. Ag nanoparticles playing the role of electron receivers on TiO₂ surface enhance photodegradation. However, excess Ag nanoparticles caused reduced specific surface area of photocatalysts and increased probability of charge recombination, resulting in lower photocatalytic efficiency. In this study, the influence of various Ag decoration concentrations on photocatalytic activity was investigated. Surface treatment by nitric acid after Ag decoration was performed to avoid excessive Ag deposition. The extent of Ag elimination and its impacts on photocatalytic activity were also explored. An optimum Ag content in the photocatalyst was achieved and photocatalytic efficiency was obviously improved. It was found that the number of calcination times affected the crystallinity and stability of photocatalysts. Better photocatalytic efficiency could be obtained after twice calcinations.     

Gas-phase photocatalytic oxidation of benzene over titanium dioxide loaded on Bi_(12)TiO_(20)

TiO2 was prepared by sol-gel method using tetrabutyl titanate as precursor. TiO2 was loaded on Bi12TiO20. The photocatalyst with different TiO2 loading was calcined at 723 K. The photocatalytic activity of decomposition gaseous benzene was investigated in a batch reactor. The prepared photocatalyst was characterized by UV-vis diffuse reflectance. The result showed that TiO2/Bi12TiO20 absorbed much more ultraviolet light than Ti02 in the ultraviolet light region and showed red shift. The results indicated that the prepared photocatalyst can greatly promote the photocatalytic activity. The 2.0% TiO2/Bi12TiO20 system exhibited the highest photocatalytic activity.     

Synthesis and antibacterial activity of novel titanium dioxide doped with silver

Pure and silver doped nanoparticles of titanium dioxide (TiO₂) was prepared using novel, modified sol–gel method. The samples were characterized by transmission electron microscopy, X-ray diffraction, N₂ adsorption measurement, atomic absorption spectroscopy (AAS), UV–vis spectroscopy (UV–vis). The antibacterial activity of the prepared samples was indicated by minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) values according to the reference methods of Clinical and Laboratory Standards Institute for the determination of MIC of aerobic bacteria by broth microdilution. The results showed very good antibacterial activity of silver nanoforms to bacteria strains: Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumoniae. The sensitivity of the tested bacteria to silver nanoforms depends on the crystalline form of the carrier—TiO₂, its surface area, porosity, the content of silver, its particle size and oxidation state. The originality of this work is the synthesis of novel type of nanocomposites TiO₂ doped with silver and determination its excellent antibacterial activity.     

介孔TiO2粉体的合成和表征及光催化性能研究

本文以甘油为结构导向剂,运用水热合成法制备了介孔二氧化钛粉体(MT),采用抽提和焙烧两种方法除去结构导向剂.分别对合成的样品、P25和商品TiO2粉末(PT)进行了XRD、TEM、TGA、N2等温吸附-脱附等实验表征,根据TGA计算了样品的表面羟基密度.研究了样品光催化降解甲基橙效率与其表面性质的关系.结果表明,经焙烧除去结构导向剂的样品的比表面最高,达285.3m2·g-1,孔径4nm～6nm,具有良好的光催化降解甲基橙性能.     

Enhanced photocatalytic activity for titanium dioxide by co-modification with copper and iron

A copper(II) and iron(III) co-modified titanium dioxide nano material was prepared by a simple sol–gel process using titanium(IV) isopropoxide plus copper(II) and iron(III) nitrates as raw materials. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence spectra. The XRD results showed that the undoped TiO₂ nanoparticles mainly include anatase phase while the Cu, Fe-codoped TiO₂ nanoparticles showed a mixture of anatase phase with a small fraction of rutile phase displaying higher activity than the pure anatase phase. Optical characterization showed that the codoping with copper(II) and iron(III) resulted in a red shift of adsorption and lower recombination probability between electrons and holes, which were associated with high photocatalytic activity of the Cu, Fe-codoped TiO₂ nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of the samples was tested by aqueous methyl orange degradation. The capability of the codoped catalyst was much higher than that of the pure TiO₂ catalyst under visible irradiation. A mechanism is proposed in order to account for the enhanced catalytic activity.     

介孔二氧化钛的合成及其对甲基橙降解的光催化活性

以十六烷基三甲基溴化铵为模板剂,通过水解钛酸正丁酯合成了介孔二氧化钛分子筛,探讨了合成条件的影响。采用X射线粉末衍射(XRD)、红外光谱(FT-IR)、透射电子显微镜(TEM)和N2吸附-脱附等技术对介孔二氧化钛的晶相、结构、形貌、比表面积和孔径分布进行了表征。实验结果表明:得到的介孔二氧化钛分子筛的孔径为4-4.3nm,用抽提的方法去除模板剂得到的介孔二氧化钛的比表面积比焙烧的要高。以甲基橙为模型污染物,检验了所合成介孔二氧化钛的光催化性质。     

Synthesis of titanium dioxide nanoparticles with mesoporous anatase wall and high photocatalytic activity

Mesoporous titanium dioxide nanosized powder with high specific surface area and anatase wall was synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting materials were characterized by XRD, nitrogen adsorption, FESEM, TEM, and FT-IR spectroscopy. The as-synthesized mesoporous TiO2 nanoparticles have mean diameter of 17.6 nm with mean pore size of 2.1 nm. The specific surface area of the as-synthesized mesoporous nanosized TiO2 exceeded 430 m2/g and that of the samples after calcination at 600 degrees C still have 221.9 m2/g. The mesoporous TiO2 nanoparticles show significant activities on the oxidation of Rhodamine B (RB). The large surface area, small crystalline size, and well-crystallized anatase mesostructure can explain the high photocatalytic activity of mesoporous TiO2 nanoparticles calcined at 400 degrees C.     

Photoactivity of mechanochemically prepared nanoparticulate titanium dioxide investigated by EPR spectroscopy

Titanium dioxide nanopowders were prepared by mechanochemical synthesis in a high-energy ball mill using TiOSO₄·xH₂O and Na₂CO₃ followed by annealing in the temperature range 200–800 °C. The UVA photonic efficiency of radical processes on synthesized TiO₂ powders was determined by in situ EPR spectroscopy, using, as indicators, the N-oxide spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide and 5-(diisopropoxy-phosphoryl)-5-methyl-1-pyrroline N-oxide) or the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate, ABTS⁺). The results obtained by monitoring the photoinduced generation of hydroxyl radical spin adducts correlated with those found by the investigation of the photoreduction of ABTS⁺. The presence of iron and chromium ions, which were evidenced in samples milled in steel, decreased the photonic efficiency of radical processes. The presence of a sulfate salt matrix during the annealing process distinctly inhibits the transformation of anatase to rutile. The highest photocatalytic activity was shown by anatase samples which were prepared by milling in corundum and annealed at 700 °C. They were composed of crystallites with a mean size of 25–30 nm and well developed crystal faces.     

氮-硫共掺杂二氧化钛光催化剂的制备及其可见光催化活性

采用研磨煅烧法,以硫脲(TU)作为氮源和硫源,H2TiO3(HT)为TiO2的前驱体,制备了不同TU/HT比例的N,S共掺杂TiO2光催化剂(NS/TiO2);利用X射线衍射仪、透射电镜、X射线光电子能谱仪、拉曼光谱仪、紫外-可见吸收光谱仪等分析了NS/TiO2的晶体结构、显微形貌、典型元素的化学状态以及光谱性质;利用BET法测定了NS/TiO2的比表面积,同时测定了其在可见光照下催化降解罗丹明B的活性.结果表明,当TU/HT质量比为0.5时,NS/TiO2的光催化活性最佳,光照70min时的罗丹明B降解率为44.4%.氮元素以NH3形式吸附在TiO2表面,硫元素以S6+形式存在,部分S6+取代Ti 4+的位置.与此同时N,S共掺杂使得TiO2的禁带宽度减小,可见光催化活性提高.     

The photostability of wool doped with photocatalytic titanium dioxide nanoparticles

Photoyellowing of wool is a serious problem for the wool industry. This study assessed the role of photocatalytic nanocrystalline titanium dioxide (P-25) as a potential antagonist or catalyst in the photoyellowing of wool. Untreated, bleached and bleached and fluorescent-whitened wool slivers were processed into fine wool powders for the purpose of even and intimate mixing with the TiO₂ nanoparticles in the solid state. Pure wool and wool/TiO₂ mixtures were then compressed into solid discs for a photoyellowing study under simulated sunlight and under UVB and UVC radiations. Yellowness and photo-induced chemiluminescence (PICL) measurements showed that nanocrystalline TiO₂ could effectively reduce the rate of photoyellowing by inhibiting free radical generation in doped wool, and that a higher concentration of TiO₂ contributed to a lower rate of photooxidation and reduced photoyellowing. Hence nanocrystalline TiO₂ acts primarily as a UV absorber on wool in dry conditions and not as a photocatalyst.     

二氧化钛微晶结构和光催化性能关联性研究

研究了不同煅烧温度、煅烧时间的系列二氧化钛样品悬浮体系光催化降解X-3B活性艳红的催化活性。分析了晶粒尺寸、晶相、晶格畸变应力和光催化体系等诸多因素对二氧化钛光催化活性的影响。发现晶格畸变应力对空穴电子对复合速率的影响在诸因素中占主导地位,并在一定程度上决定了二氧化钛悬浮体系的光催化效能。     

溴化银/二氧化钛复合材料的可见光催化性能

将硝酸银的乙醇溶液与溶胶凝胶TiO2混合得到前驱体,随后经共沉淀-煅烧制备得到AgBr/TiO2复合材料;采用扫描电镜、X射线衍射仪、X射线光电子能谱仪分析了复合材料的形貌、晶体结构、Ag元素的价态,采用紫外-可见漫反射光谱仪测定了其光吸收性能;进而以甲基橙(MO)的可见光降解为探针反应测定了AgBr/TiO2复合材料的可见光催化性能.结果表明,当前驱体在不同温度下煅烧后,无定形TiO2颗粒逐渐增大,并逐渐转变为锐钛矿结构;担载的AgBr可明显拓展TiO2的可见光吸收范围;Ag物种主要以Ag+形式存在.当煅烧温度为300℃时,复合材料的光催化活性最高,MO的降解率在60min内达到90%以上;随着煅烧温度的增加,催化活性逐渐降低.     

Physicochemical and photocatalytic properties of nanosized titanium dioxide deposited on silicon dioxide microspheres

The synthesis of SiO₂ core-TiO₂ shell composites from a titanium dioxide sol and a suspension of microspherical silicon dioxide is described. The main factors ensuring the formation of a composite with a preset morphology are the size and charge of the TiO₂ sol particles (10–45 nm) and silicon dioxide core particles (300–700 nm), the pH values of the suspensions of the starting components and the resulting composite, and the proportions and way of mixing of the siliconand titanium-containing components. The SiO₂ core-TiO₂ shell composites show high photocatalytic activity in the degradation of Rhodamine FL-BM dye (rate constant of k = 0.0813 min⁻¹) and are much more active than precipitated TiO₂ powder (k = 0.0022 min⁻¹). The activity of the composite is determined by the calcination temperature (700–800°C), by the proportion and accessibility of the active component (TiO₂), and by the presence of a dopant (P₂O₅).