Sonochemical fabrication of fluorinated mesoporous titanium dioxide microspheres

A sonochemical-hydrothermal method for preparing fluorinated mesoporous TiO₂ microspheres was developed. Formation of mesoporous TiO₂ and doping of fluorine was achieved by sonication and then hydrothermal treatment of a solution containing titanium isopropoxide, template, and sodium fluoride. The as-synthesized TiO₂ microspheres were characterized by X-ray diffraction (XRD), Fourier translation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, photoluminescence spectroscopy (PL), and BET surface areas. The P123 template was removed completely during the hydrothermal and washing steps, which was different from the conventional calcination treatment. The as- synthesized TiO₂ microspheres had good crystallinity and high stability. Results from the photocatalytic degradation of methylene blue (MB) showed that fluorination could remarkably improve the photocatalytic activity of titanium dioxide.     

Visible light photocatalytic activity and Photoelectrochemical property of Fe-doped TiO<Subscript>2</Subscript> hollow spheres by sol–gel method

Fe-doped TiO₂ hollow spheres (Fe-THs) were synthesized by sol–gel process using carbon spheres as templates. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectrum (DRS), N₂ adsorption–desorption isotherms, Electron paramagnetic resonance (EPR) spectroscopy and Photoluminescence emission spectroscopy (PL). UV–vis spectra showed that Fe³⁺ doping could extend the absorption edge to the visible region. EPR spectra showed that Fe³⁺ was incorporated into the crystal lattice of TiO₂, which could inhibit the recombination of photo-induced electron–hole pairs and improve the photocatalytic activity. The photocatalytic activities of the prepared samples were evaluated for the degradation of dye Reactive Brilliant Red X-3B (C.I. reactive red 2) under visible light irradiation. The results indicated that Fe³⁺ doping sample showed the highest photocatalytic activity with an optimal doping concentration of 0.50 wt%. The recycle ability of the Fe-THs was also investigated. After 5 cycles, the degradation rate was still higher than 90%, decreased by only 6.36% compared to the first cycle. Moreover, in order to characterize the electron-transferring efficiency in the process of photocatalysis reaction, a photocurrent-time spectrum was examined by anodic photocurrent response.     

稀土Ce掺杂对ZnO结构和光催化性能的影响

采用共沉淀-焙烧法合成了一系列不同含量的稀土Ce掺杂的ZnO光催化剂. 利用傅里叶变换红外(FT-IR)光谱、粉末X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)光谱、光致发光(PL)谱等技术对所制备的光催化剂进行了系列表征. 以酸性橙II脱色降解为模型反应, 考察了掺杂不同含量的铈及不同焙烧温度对ZnO的物理结构和光催化脱色性能的影响. 结果表明: 掺入质量分数(w)为2%的铈可以明显改善氧化锌表面状态, 有利于产生更多的表面羟基; 同时可以抑制光生电子与光生空穴(e^-/h⁺)的复合, 显著提高光催化脱色活性和光催化稳定性; 焙烧温度对光催化剂的晶体结构、表面性能和光催化活性产生较大影响, 500 °C的焙烧处理使样品的结晶度较高, 同时催化剂颗粒粒径较细, 表面具有丰富的羟基. 但过高的焙烧温度(600-800 °C)将导致催化剂的物理结构发生恶化, 降低光催化性能.     

稀土Ce掺杂对ZnO结构和光催化性能的影响

采用共沉淀-焙烧法合成了一系列不同含量的稀土Ce掺杂的ZnO光催化剂. 利用傅里叶变换红外(FT-IR)光谱、粉末X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)光谱、光致发光(PL)谱等技术对所制备的光催化剂进行了系列表征. 以酸性橙II脱色降解为模型反应, 考察了掺杂不同含量的铈及不同焙烧温度对ZnO的物理结构和光催化脱色性能的影响. 结果表明: 掺入质量分数(w)为2%的铈可以明显改善氧化锌表面状态, 有利于产生更多的表面羟基; 同时可以抑制光生电子与光生空穴(e^-/h⁺)的复合, 显著提高光催化脱色活性和光催化稳定性; 焙烧温度对光催化剂的晶体结构、表面性能和光催化活性产生较大影响, 500 °C的焙烧处理使样品的结晶度较高, 同时催化剂颗粒粒径较细, 表面具有丰富的羟基. 但过高的焙烧温度(600-800 °C)将导致催化剂的物理结构发生恶化, 降低光催化性能.     

Preparation of Ce‐doped TiO2 Hollow Fibers and Their Photocatalytic Degradation Properties for Dye Compound

Cerium‐doped titanium dioxide (TiO₂) with a hollow fiber structure was successfully prepared using ammonium ceric nitrate and tetrabutyltitanate as precursors and cotton fiber as the template. The effects of cerium (Ce)‐doping on the crystallite sizes, crystal pattern, and optical property of the prepared catalysts were investigated by means of techniques such as scanning electron microscopy (SEM), X‐ray diffraction (XRD), BET surface area, and UV‐vis diffuse absorption spectroscopy. SEM observation showed that the prepared TiO₂ fibers possessed fibrous shape inherited from the cotton fiber and had a hollow structure. As confirmed by XRD and UV‐vis diffuse absorption spectroscopy examinations, Ce‐doping restrained the growth of grain size and extended the photoabsorption edge of TiO₂ hollow fiber into the visible light region. The present photocatalyst showed higher photocatalytic reactivity in photodegradation of highly concentrated methylene blue (MB) solutions than pure TiO₂ under UV and visible light, and the amount of Ce‐doped significantly affected the catalytic property. In the experiment condition, the photocatalytic activity of 0.5 mol% Ce‐doped TiO₂ fiber was optimal of all the prepared samples. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed. The material was easily removed by centrifugal separation. Therefore, using the template method and by doping with cerium, TiO₂ may hopefully become a low‐energy consuming, high activity and green environmentally friendly catalytic material.     

Preparation and Characterization of Bismuth Doped TiO2 Thin Films

A series of Bismuth-doped titanium oxide (Bi-doped TiO₂) thin films on glass substrates have been prepared by sol-gel dip coating process. The prepared catalysts were characterized by XRD and XPS. The photocatlytic activity of the thin film catalysts was evaluated through the photodegradation of aqueous methyl orange under UV illumination. The experiments demonstrated that the Bi-doped TiO₂ prepared was anatase phase. The doped bismuth was in the 3⁺ oxidation state. The presence of Bi significantly enhanced the photocatalytic activity of TiO₂ films. At calcination temperature of 500°C, with doping concentration of 2 wt %, Bi-doped TiO₂ thin film showed the highest photocatalyic activity.     

Sol–gel preparation and characterization of Ag and Mg co-doped nano TiO<Subscript>2</Subscript>: efficient photocatalytic degradation of C.I. Acid Red 27

In this study, we successfully prepared pure, mono-doped, and Ag, Mg co-doped TiO₂ nanoparticles using the sol–gel method, with titanium tetraisopropoxide as the Ti source. The prepared samples were characterized by X-ray powder diffraction (XRD), specific surface area and porosity (BET and BJH) measurement, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence, and energy dispersive X-ray spectroscopy techniques. The XRD data showed that the prepared nanoparticles had the same crystals structures as the pure TiO₂. Also, DRS results indicated that the band gap of co-doped photocatalyst was smaller than that of the monometallic and undoped TiO₂ and that there was a shift in the absorption band towards the visible light region. Furthermore, the photocatalytic activity of the prepared catalysts was evaluated by the degradation of C.I. Acid Red 27 in aqueous solution under visible light irradiation. The results showed that Ag (0.08 mol%), Mg (0.2 mol%) co-doped TiO₂ had the highest photoactivity among all samples under visible light. It was concluded that co-doping of the Ag and Mg can significantly improve the photocatalytic activity of the prepared photocatalysts, due to the efficient inhibition of the recombination of photogenerated electron–hole pairs. The optimum calcination temperature and time were 450 °C and 3 h, respectively.     

单斜与锐钛矿双晶相TiO2/MWNTs复合材料的制备及其可见光光催化活性

以超强耐酸碱的表面活性剂-丁基封端脂肪醇聚氧乙烯醚作为晶型调节剂,利用钛酸丁酯和氢氧化钠的水热反应制备了单斜相与锐钛矿相双晶相TiO₂/多壁碳纳米管(简称MWNTs)复合材料,并考察了复合材料的可见光光催化活性。结果显示:MWNTs的加入可调控TiO₂的晶相组成,增强TiO₂的光催化活性,其中含5%MWNTs的样品具有较高的催化降解效率;随煅烧温度的升高,样品的光催化活性大幅提升。其机理归因于(1)促进单斜相和锐钛矿相双晶相结构的形成;(2)碳纳米管优良的导电作用及碳纳米管/TiO₂间的异质结效应;(3)高温下碳纳米管分解产生的碳元素掺杂作用。     

单斜与锐钛矿双晶相TiO2/MWNTs复合材料的制备及其可见光光催化活性

以超强耐酸碱的表面活性剂-丁基封端脂肪醇聚氧乙烯醚作为晶型调节剂,利用钛酸丁酯和氢氧化钠的水热反应制备了单斜相与锐钛矿相双晶相TiO2/多壁碳纳米管(简称MWNTs)复合材料,并考察了复合材料的可见光光催化活性。结果显示:MWNTs的加入可调控TiO2的晶相组成,增强TiO2的光催化活性,其中含5%MWNTs的样品具有较高的催化降解效率;随煅烧温度的升高,样品的光催化活性大幅提升。其机理归因于(1)促进单斜相和锐钛矿相双晶相结构的形成;(2)碳纳米管优良的导电作用及碳纳米管/TiO2间的异质结效应;(3)高温下碳纳米管分解产生的碳元素掺杂作用。     

Cu?Cu2O?TiO2 Nanojunction Systems with an Unusual Electron–Hole Transportation Pathway and Enhanced Photocatalytic Properties

Multicomponent Cu? Cu₂O? TiO₂ nanojunction systems were successfully synthesized by a mild chemical process, and their structure and composition were thoroughly analyzed by X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, and X‐ray photoelectron spectroscopy. The as‐prepared Cu? Cu₂O? TiO₂ (3 and 9 h) nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of the degradation of organic compounds than those of the Cu? Cu₂O, Cu? TiO₂, and Cu₂O? TiO₂ starting materials. Moreover, time‐resolved photoluminescence spectra demonstrated that the quenching times of electrons and holes in Cu? Cu₂O? TiO₂ (3 h) is higher than that of Cu? Cu₂O? TiO₂ (9 h); this leads to a better photocatalytic performance of Cu? Cu₂O? TiO₂ (3 h). The improvement in photodegradation activity and electron–hole separation of Cu? Cu₂O? TiO₂ (3 h) can be ascribed to the rational coupling of components and dimensional control. Meanwhile, an unusual electron–hole transmission pathway for photocatalytic reactions over Cu? Cu₂O? TiO₂ nanojunctions was also identified.     

Microwave-hydrothermal synthesis and photocatalytic properties of biomass charcoal/TiO2 nanocomposites

Biomass charcoal-doped titanium dioxide (C/TiO₂) composites were proposed by microwave-hydrothermal and calcination method using tetrabutyl titanate as the titanium source and lignin as the carbon source. TiO₂ crystals with different morphologies could be successfully adsorbed onto the surface of biomass charcoal. These products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), derivative thermogravimetric (DTG), UV–vis diffuser flection spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), and Brunauer–Emmett–Teller (BET). The photocatalytic activities of the as-obtained composites were checked under visible light irradiation. The results showed that both the microwave-hydrothermal temperature and time played an important role in the microstructure and photocatalytic activity of the samples. The rapid microwave-hydrothermal with the thermal post-treatment provides a promising route for the fabrication of biomass charcoal-doped nanocomposites materials.     

Investigation of photocatalytic activity of metal-doped TiO2 nanoparticles prepared by Pechini method

M-doped TiO₂ (M = Ag²⁺, Al³⁺, Ce⁴⁺, Nb⁵⁺) with different dopant contents have been prepared by the Pechini method using titanium IV isopropoxide as precursor. The effect of doping concentration on the photocatalytic activity for methyl orange (MO) photodegradation was investigated using UV radiation. The photocatalysts were characterized by surface area, X-ray diffraction and UV–Vis diffuse reflectance spectroscopy. An increase in the photoactivity of TiO₂ nanoparticles was confirmed by MO photocatalytic degradation experiments, when the transition metal ions were incorporated into the semiconductor crystalline lattice, which could be attributed to an increase in the charge separation and reduction of e^?/h⁺ recombination as a function of the substitutional defect generated at very low levels.     

Influence of the Metal Work Function on the Photocatalytic Properties of TiO2 Layers on Metals

The photocatalytic properties of titanium dioxide (TiO₂) layers on different metal plates are investigated. The metal–semiconductor interface can be described as a Schottky contact, and is part of a depletion layer for the majority carriers in the semiconductor. Many researchers have demonstrated an increase in the photocatalytic activity, due to the formation of a metal–semiconductor contact that are obtained by deposition of small metal islands on the semiconductor. Nevertheless, the influence of a Schottky contact remains uncertain, sparking much interest in this field. The immobilization of nanoparticulate TiO₂ layers by dip‐coating on different metal substrates results in the formation of a Schottky contact. The recombination rate of photoinduced electron–hole pairs decreases at this interface provided that the thickness of the thin TiO₂ layer has a similar magnitude to the depletion layer. The degradation of dichloroacetic acid in aqueous solution and of acetaldehyde in a gas mixture is investigated to obtain information concerning the influence of the metal work function of the back contact on the efficiency of the photocatalytic process.     

Synthesis,characterization and photocatalytic application of TiO2/magnetic graphene for efficient photodegradation of crystal violet

A magnetized nano‐photocatalyst based on TiO₂/magnetic graphene was developed for efficient photodegradation of crystal violet (CV). Scanning electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and elemental mapping were used to characterize the prepared magnetic nano‐photocatalyst. The photocatalytic activity of the synthesized magnetic nano‐photocatalyst was evaluated using the decomposition of CV as a model organic pollutant under UV light irradiation. The obtained results showed that TiO₂/magnetic graphene exhibited much higher photocatalytic performance than bare TiO₂. Incorporation of graphene enhanced the activity of the prepared magnetic nano‐photocatalyst. TiO₂/magnetic graphene can be easily separated from an aqueous solution by applying an external magnetic field. Effects of pH, magnetized nano‐photocatalyst dosage, UV light irradiation time, H₂O₂ amount and initial concentration of dye on the photodegradation efficiency were evaluated and optimized. Efficient photodegradation (>98%) of the selected dye under optimized conditions using the synthesized nano‐photocatalyst under UV light irradiation was achieved in 25 min. The prepared magnetic nano‐photocatalyst can be used in a wide pH range (4–10) for degradation of CV. The effects of scavengers, namely methanol (OH^? scavenger), p‐benzoquinone (O₂^?? scavenger) and disodium ethylenediaminetetraacetate (hole scavenger), on CV photodegradation were investigated.     

Sol–gel synthesized vanadium doped TiO2 photocatalyst: physicochemical properties and visible light photocatalytic studies

Vanadium doped titanium dioxide (V–TiO₂) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N₂ adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V⁵⁺ ions were successfully incorporated into the crystal lattice of TiO₂ as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO₂, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO₂ sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO₂ powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO₂ powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (k_obs) of 5.024 × 10^?3 min^?1 which is nearly five times higher than that of pure TiO₂, as result of low band gap value, high specific surface area and a decrease in recombination rate.     

Ag‐Enhanced TiO2–x/C Composites with Metal‐Organic Frameworks as Precursors for Photodegradation of Methyl Blue

A series of Ag‐enhanced TiO_2–x/C composites (Ag/TiO_2–x/C composites) with metal‐organic frameworks (MOFs) as precursors were prepared, and their photocatalytic activities were evaluated by the UV‐light driven photodegradation behaviors of methyl blue (MB). The as‐obtained samples were characterized by several techniques such as SEM, XRD, N₂‐adsorption, XPS, UV/Vis spectrophotometry and UV/Vis diffuse‐reflectance spectra. The best photocatalytic performance was achieved in Ag/TiO_2–x/C composite pyrolyzed at 1000 °C (ATC‐P10) due to rapid capture of electrons caused by silver doping, higher density of TiO_2–x lattice oxygen vacancies for better trapping of electrons, and high surface area due to reduction and evaporation of metallic Zn. No obvious deactivation was observed after 10 cycles of UV‐light degradation of MB under the same experimental conditions. This report reveals a new approach to prepare stable and highly efficient UV‐light‐driven photocatalysts for organic pollutants in water.     

Bi‐, Y‐Codoped TiO2 for Carbon Dioxide Photocatalytic Reduction to Formic Acid under Visible Light Irradiation

Bi‐ and Y‐codoped TiO₂ photocatalysts were synthesized through a sol‐gel method, and they were applied in the photocatalytic reduction of CO₂ to formic acid under visible light irradiation. The results revealed that, after doping Bi and Y, the surface area of TiO₂ was increased from 5.4 to 93.1 m²/g when the mole fractions of doping Bi and Y were 1.0% and 0.5%, respectively, and the lattice structures of the photocatalysts changed and the oxygen vacancies on the surface of the photocatalysts formed, which would act as the electron capture centers and slow down the recombination of photo‐induced electron and hole. The photocurrent spectra also proved that the photocatalysts had better electronic transmission capacities. The HCOOH yield in CO₂ photocatalytic reduction was 747.82 μmol/g_cat by using 1% Bi‐0.5% Y‐TiO₂ as a photocatalyst. The HCOOH yield was 1.17 times higher than that by using 1% Bi‐TiO₂, and 2.23 times higher than that by using pure TiO₂. Furthermore, the 1% Bi‐0.5% Y‐TiO₂ showed the highest apparent quantum efficiency (AQE) of 4.45%.     

Zr离子掺杂TiO2可见光催化剂光催化活性的研究

本文采用溶胶-凝胶法制备了Zr离子掺杂TiO₂光催化剂。光催化降解对氯苯酚实验表明,Zr离子掺杂浓度为10%时活性最高,其紫外光、可见光催化活性分别是纯TiO₂的1.5倍和4倍。利用XRD、Raman、XPS、UV-Vis DRS、PL等技术对样品进行了表征,结果表明：Zr离子以取代式掺杂方式进入TiO₂晶格,在TiO₂导带下方形成掺杂能级,增强了可见光响应,促进了光生载流子的分离,此外Zr离子掺杂在催化剂表面引入大量表面缺陷,增加了表面羟基物种,从而使得Zr离子掺杂TiO₂光催化剂的紫外、可见光催化活性显著提高。     

The preparation and characterization of La doped TiO2 nanoparticles and their photocatalytic activity

In this paper, pure and La doped TiO₂ nanoparticles with different La content were prepared by a sol-gel process using Ti (OC₄H₉)₄ as raw material, and also were characterized by XRD, TG-DTA, TEM, XPS, DRS and Photoluminescence (PL) spectra. We mainly investigated the effects of calcining temperature and La content on the properties and the photocatalytic activity for degrading phenol of as-prepared TiO₂ samples, and also discussed the relationships between PL spectra and photocatalytic activity as well as the mechanisms of La doping on TiO₂ phase transformation. The results showed that La³⁺ did not enter into the crystal lattices of TiO₂ and was uniformly dispersed onto TiO₂ as the form of La₂O₃ particles with small size, which possibly made La dopant have a great inhibition on TiO₂ phase transformation; La dopant did not give rise to a new PL signal, but it could improve the intensity of PL spectra with a appropriate La content, which was possibly attributed to the increase in the content of surface oxygen vacancies and defects after doping La; La doped TiO₂ nanoparticles calcined at 600°C exhibited higher photocatalytic activity, indicating that 600°C was an appropriate calcination temperature. The order of photocatalytic activity of La doped TiO₂ samples with different La content was as following: 1>1.5>3>0.5>5>0 mol%, which was the same as the order of their PL intensity, namely, the stronger the PL intensity, the higher the photocatalytic activity, demonstrating that there were certain relationships between PL spectra and photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions.     

Significant effect of lanthanide doping on the texture and properties of nanocrystalline mesoporous TiO2

A systematic study of microstructure and photocatalytic properties of lanthanide doping of nanocrystalline mesoporous titanium dioxide is performed. The anatase-to-rutile (A-R) phase transformation of nanosized TiO₂ was significantly inhibited by lanthanide doping and the inhibitory effect was enhanced with the increase of the rare earth radius, i.e., La³⁺>Gd³⁺>Yb³⁺ for different lanthanide dopants. At high calcination temperatures, different texture lanthanide titanium oxides of Ln₄Ti₉O₂₄ (La³⁺, Pr³⁺, Nd³⁺), Ln₂Ti₂O₇ (Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Er³⁺), and Yb₂TiO₅ were developed, respectively, revealing that the structures of lanthanide titanium oxide developed in Ln/TiO₂ depend on the lanthanide radius. Larger radius lanthanides prefer to form higher coordination number lanthanide titanium oxide. In addition, the thermal stability of mesoporous structures of TiO₂ was remarkable improved by lanthanide doping. The photocatalytic properties were studied by employing the photodegradation of Rhodamine B (RB) as a probe reaction. The results indicate that the lanthanide doping could bring about significant improvement to the photoreactivity of TiO₂, and the improvement was sensitive to the atomic electronic configuration.