Photocatalytic activity of TiO2 doped with boron and vanadium

Boron (B)- and vanadium (V)-doped TiO(2) photocatalysts were synthesized using modified sol-gel reaction processes and characterized by X-ray diffraction (XRD), Raman spectroscopy and N(2) physisorption (BET). The photocatalytic activities were evaluated by monitoring the degradation of methylene blue (MB). The results showed that the materials possess high surface area. The addition of B favored the transformation of anatase to rutile, while in the presence of V, anatase was the only phase detected. The MB degradation on V-doped TiO(2) was significantly affected by the preparation method. In fact while the presence of V in the bulk did not influence strongly the photoreactivity under visible irradiation, an increase of surface V doping lead to improved photodegradation of MB. The degradation of MB dye indicated that the photocatalytic activities of TiO(2) increased as the boron doping increased, with high conversion efficiency for 9mol% B doping.     

太阳光下Cr~(3+)掺杂TiO_2复合微粒光催化性能研究

利用酸催化的溶胶一凝胶法成功地合成了一系列不同CP3+掺杂量(x=0.01%～10%)的TiO2复合光催化剂(Cd3+/TiO2).在太阳光条件下,以亚甲基蓝溶液的光催化降解对复合材料的光催化性能进行了表征,并考察了催化剂投加量、Cr3+掺杂量和溶液pH值等因素对光催化降解反应的影响.结果表明,亚甲基蓝溶液在复合微粒上的光催化降解反应遵循Langmuir-Hinshelwood动力学模型,在催化剂投加量为lg/L、Cr3+掺入量为0.3%和pH=7时,Cr3+/TiO2复合微粒光催化活性达最佳,测得表观反应速率常数 K为7.27×10-3 rag(L·min)-1,t1/2为95min,反应4h后亚甲基蓝的降解率可达79%,与纯的TiO2相比较,反应速率提高了2倍,降解率提高了20%.中性或碱性条件下有利于亚甲基蓝溶液的光催化降解.     

Synthesis and characterization of the N-doped TiO2 photocatalyst for the photodegradation of methylene blue and phenol

To extend the light absorption of TiO2-based photocatalysts towards the visible-light range and to eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalyst (N-doped TiO2) powder was prepared through a simple sol-gel process. The crystal phase composition, structure, and light absorption of the new photocatalyst were comprehensively examined via X-ray diffraction, ultraviolet-visible (UV-Vis) absorption spectroscopy, and atomic-absorption spectroscopy. The photo-oxidation efficiency of the photocatalyst was also evaluated in the photodegradation of methylene blue (MB) and of phenol in aqueous solutions under visible-light irradiation from a neon lamp (lambda > 400 nm). The results of the analyses that were performed in this study indicated that the N-doped TiO2 could eliminate the electron/holes recombination and could increase the light absorption in the visible range. The results of the analysis of the UV-Vis diffuse reflection and optical-absorption spectra indicated that a new energy level below 3.2 eV generated in the N-doped TiO2 promoted the optical absorption in the visible-light region and made visible-light excitation possible (E < 3.2 eV). The experiment demonstrated that the photo-oxidation efficiency of MB when N-doped TiO2 powder was used was significantly higher than that when the conventional TiO2 powders were used. The development of such photocatalyst may be considered a breakthrough in the large-scale utilization of solar energy to address the current and future environmental needs.     

流化床化学气相沉积法制备CNT/Fe-Ni/TiO2及其光催化性能研究

以Fe-Ni/TiO2为催化剂,采用流化床化学气相沉积法(FBCVD)在TiO2表面原位生长碳纳米管(CNT),得到CNT/Fe-Ni/TiO2复合光催化剂.通过SEM、XRD、UV-Vis等方法表征其结构和性能,以亚甲基蓝溶液降解为模型考察其光催化性能.结果表明:Fe-Ni/TiO2催化剂在FBCVD过程中,镍主要起到了CNT生长催化活性位的作用;在生长CNT后的复合光催化剂中,比例较低的Fe3+主要作为电子俘获剂,抑制TiO2光生电子空穴的复合;Ni和CNT共同起到将电子迅速地从TiO2中导出,从而降低光生电子空穴复合几率的作用.三者的协同作用显著改善了TiO2的光催化性能.其中Fe和Ni掺杂量分别为0.25mol%和4.75mol%样品的光催化活性较高,生长CNT后得到的复合光催化剂对亚甲基蓝的降解效率较纯TiO2提高约70%.     

Construction of hierarchical nanostructured TiO2/Bi2MoO6 heterojunction for improved visible light photocatalysis

In this study, Bi2MoO6 hollow microspheres were modified by depositing TiO2 nanoparticles through a simple hydrothermal method. The prepared TiO2/Bi2MoO6 photocatalysts were characterized by scanning and transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic performance of the heterostructured catalysts was evaluated by degradation of methylene blue (MB) under visible-light irradiation (lambda>420 nm). The photocatalysts based on nanostructured Bi2MoO6 and TiO2 exhibit much higher photocatalytic activity than the single-phase Bi2MoO6 or TiO2 and the mechanical mixture of Bi2MoO6 and TiO2 for degradation of MB under the same conditions. The results reported in this study provide insight into constructing other heterostructured photocatalysts.     

Fabrication of TiO2/Ti electrode by laser-assisted anodic oxidation and its application on photoelectrocatalytic degradation of methylene blue

A TiO2/Ti mesh electrode by laser calcination was prepared in this article. The resulting TiO2 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS), and it illuminated that the prepared electrode mainly consisted of anatase TiO2 nanoparticles on its surface and exhibited a superior photocatalytic activity. The photodegradation of methylene blue (MB) using the proposed electrode under different experimental conditions was investigated in terms of both UV absorbance at 664 nm and chemical oxygen demand (COD) removal. The electrical bias applied in photoelectrocatalytic (PEC) oxidation was also studied. The experimental results showed that under the optimal potential of +0.50 V (versus SCE), UV absorbance and COD removal during the photodegradation of MB by the proposed TiO2/Ti mesh electrode were 97.3% and 87.0%, respectively. Through the comparison between photocatalytic (PC) oxidation and photoelectrocatalytic (PEC) oxidation, it was found that PEC oxidation was a convenient and effective way to mineralize the organic matters and that laser-treated photoelectrode exceeded the oven-treated one.     

微乳液水热法制备钨酸铋光催化剂及性能研究

采用微乳液介导水热法制备Bi2WO6和Fe/Bi2WO6光催化剂,并研究水热反应温度、前驱体pH值、水相与表面活性剂的摩尔比ω值和Fe3+掺杂量对光催化剂结构、形貌和光催化活性等方面的影响.结果表明:合成的Bi2WO6为15～25 nm的纳米球状结构;当前驱体pH=1、水热温度为150℃下合成的Bi2WO6催化剂对亚甲基蓝(MB)的降解率达到93.8%;当ω=27时合成的Bi2WO6对MB光催化降解率达到了97.8%.研究发现当掺入1.03%的Fe3+的Bi2WO6比纯Bi2WO6对MB的降解率提高了2倍,达到90.2%.     

Surface modification of nanometer size TiO2 with salicylic acid for photocatalytic degradation of 4-nitrophenol

The efficiency of photocatalytic reactions was limited by the wide band-gap of TiO(2) and the high degree of electron-hole recombination inherent in photocatalytic process, as well as by the limited adsorption capability of photocatalysts. In order to increase the overall efficiency, the surface of nanometer size TiO(2) was simply and fast modified by chemical adsorption in saturated solution of salicylic acid. A stable, light yellow surface complex was formed quickly, which has obvious absorption in the region from 320 to 420 nm. Through surface modification, the adsorption efficiency of 4-nitrophenol by TiO(2) was enhanced from 42 to 84%. The photocatalytic efficiency was tested on the degradation of 4-nitrophenol. The influences of catalyst and its dosage, pH value, and 4-nitrophenol concentration on the degradation were investigated. Under such photodegradation conditions as initial pH 4.0, 4-nitrophenol 5 mg l(-1), catalyst 100 mg, and irradiation time 160 min with 160 W high-pressure mercury lamp, the degradation efficiency of 4-nitrophenol by TiO(2) was increased from 39.5 to 79.3% after surface modification, and furthermore, the degradation efficiency could be enhanced to 91.1% if the concentration of 4-nitrophenol was not more than 1 mg l(-1). Compared with the pure TiO(2), surface modification led not only to improve the surface coverage of 4-nitrophenol, but also to increase the light utilization. Both of these factors were crucial for the photocatalytic activity of heterogeneous photocatalysis, especially for photodegradation of aromatic pollutants.     

Photocatalytic reduction of NO with NH3 using Si-doped TiO2 prepared by hydrothermal method

A series of Si-doped TiO2 (Si/TiO2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000mL/min under UV irradiation (luminous flux: 1.1x10(4)lm, irradiated catalyst area: 160cm2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO2 at 323K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti-O-Si bands were formed on the surface of Si/TiO2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH3 chemisorption amount were enhanced for Si/TiO2 leading to its photocatalytic activity improvement.     

Photodegradation of methyl tert-butyl ether (MTBE) by UV/H2O2 and UV/TiO2

Two UV-based advanced oxidation processes (AOPs), UV/H2O2 and UV/TiO2, were tested in batch reactor systems to evaluate the removal efficiencies and optimal conditions for the photodegradation of methyl tert-butyl ether (MTBE). The optimal conditions at an initial MTBE concentration of 1 mM ([MTBE]0=1 mM) were acidic and 15 mM H2O2 in UV/H2O2 system, and pH 3.0 and 2.0 g/l TiO2 in UV/TiO2 suspended slurries system under 254-nm UV irradiation. Under the optimal conditions, MTBE photodegradation during the initial period of 60 min in UV/H2O2 and UV/TiO2 systems reached 98 and 80%, respectively. In both systems, MTBE photodegradation decreased with increasing [MTBE]0. While MTBE photodegradation rates increased with increasing dosage of H2O2 (5-15 mM) and TiO2 (0.5-3 g/l), further increase in the dosage of H2O2 (20 mM) or TiO2 (4 g/l) adversely reduced the MTBE photodegradation. Pseudo first-order kinetics with regard to [MTBE] can be used to describe the MTBE photodegradation in both systems. The pseudo first-order rate constants linearly increased with the increase in the molar ratio of [H2O2]0 to [MTBE]0 in UV/H2O2 system and linearly increased with the decrease in [MTBE]0 in UV/TiO2 system.     

Use of an integrated photocatalysis/hollow fiber microfiltration system for the removal of trichloroethylene in water

This work focused on the degradation of toxic organic compounds such as trichloroethylene (TCE) in water, using a combined photocatalysis/microfiltration (MF) system. The performances of the hybrid system were investigated in terms of the removal efficiency of TCE and membrane permeability, in the presence or absence of background species, such as alkalinity and humic acids. The mass balancing of the fate of TCE during photocatalytic reactions was performed in order to evaluate the feasibility of the photocatalytic membrane reactor (PMR). Greater TCE degradation (>60%) was achieved with an increase in the TiO2 dosage (up to 1.5g/L) in PMR, but a substantially large TiO2 dosage brought about a decrease in TCE degradation efficiency. The photocatalytic decomposition of TCE appeared to be more effective in acidic pH conditions than with a neutral or alkaline pH. The addition of alkalinity and humic acid into the feedwater did not have a significant effect on TCE degradation, while humic acids (whose dose was 1mg/L as TOC) in the feedwater played a part in a decline of permeability by 60%. Membrane permeability in the PMR was also affected by tangential velocities. An improvement of 60% in flux was achieved when the tangential velocity increased from 0.19 to 1.45m/s. This is because flow regimes can govern the deposition of TiO2 particles on the membrane surface.     

煅烧温度和燃烧剂及助剂用量对TiO2光催化性能的影响

为了找出自蔓燃制备TiO2光催化剂的最佳奈件,本文以TiO（NO3）2为前驱体,以前躯体用量、燃烧剂柠檬酸和硝酸铵的比例、煅烧温度为主要考查因素,通过正交试验制备TiO2并进行亚甲基蓝的光催化降解实验。结果表明,自蔓燃工艺制备的TiO2粉体具有松散、多孔的特性;正交试验选出最优制备条件为：煅烧温度在550℃,n（TiCl1）：n（柠檬酸）：n（硝酸铵）=1：1：3,最优条件下的TiO2比不采用此工艺制备的TiO2的降解率提高了13．28％;最大光降解速率比不采用此工艺制备的TiO2的速率提高了58％。     

Study on photocatalytic degradation of several volatile organic compounds

The gas-phase photolytic and photocatalytic reactions of several aromatics and chlorohydrocarbons were investigated. The experimental results revealed that chlorohydrocarbons like trichloroethylene, dichloromethane and chloroform could be degraded through either photolysis or photocatalysis under irradiation of germicidal lamp, and the elimination rate of chlorohydrocarbons through photolysis was quicker than that through photocatalysis. UV light from a germicidal lamp could directly lead to degradation of toluene but could hardly act on benzene. The photodegradation rate for these volatile organic compounds (VOCs) through photolysis followed an order: trichloroethylene>chloroform>dichloromethane>toluene>benzene>carbon tetrachloride, and through photocatalysis followed: trichloroethylene>chloroform>toluene>dichloromethane>benzene>carbon tetrachloride. Besides, a series of modified TiO2 photocatalysts were prepared by depositing noble metal, doping with transition metal ion, recombining with metal oxides and modifying with super strong acid. Activity of these catalysts was examined upon photocatalytic degradation of benzene as a typical compound that was hard to be degraded. It indicated that these modification methods could promote the activity of TiO2 catalyst to different extent. The apparent zero-order reaction rate constant for degrading benzene over SnO2/TiO2 catalyst had the highest value, which was nearly three times as that over P25 TiO2. But it simultaneously had the lowest rate for mineralizing the objective compound. In spite that Fe3+/TiO2 catalyst behaved slightly less active than SnO2/TiO2 for degradation of benzene, the mineralization rate over Fe3+/TiO2 was the highest one among the prepared catalysts.     

A new submerged membrane photocatalysis reactor (SMPR) for fulvic acid removal using a nano-structured photocatalyst

The study focuses on the degradation of fulvic acid by nano-structured TiO2 in a submerged membrane photocatalysis reactor (SMPR). It has been demonstrated that the composite TiO2 photocatalyst could be automatically settled due to its gravity and then be easily separated by MF membrane. In addition, it was more efficient to maintain high flux of membranes than that of commercial TiO2 P25. The paper describes the effects of operational parameters on the photocatalytic degradation of fulvic acid in SMPR. It was found that the photocatalyst at 0.5 g/L and airflow at 0.06 m3/h were the optimal condition for the removal of fulvic acid (FA) and the FA degradation rate was higher at acidic condition than that at alkalinous media. In order to compare the effects of different filtration duration on permeate flux rate of MF, P25 powder and nano-structured TiO2 were employed. According to the experiments, the permeate flux rate of MF is improved and thus the membrane fouling phenomenon is reduced with the addition of nano-structured TiO2 catalyst. Therefore, the submerged membrane photocatalysis reactor can be potentially applied in photocatalytic oxidation process during drinking water treatment.     

掺Ag复合改性的纳米TiO_2的制备及其光催化性能

采用溶胶-凝胶法制备了掺Ag复合改性的纳米TiO2复合材料,以提高纳米TiO2在日光下的催化活性。采用差热-热重分析法、X射线衍射、透射电子显微镜、分光光度计等测试技术分析和研究了Ag-TiO2复合材料的微观结构、组织和性能,并探讨了影响Ag-TiO2复合材料光催化性能的各种因素。研究结果表明,利用溶胶-凝胶法可以获得纳米级二氧化钛,单晶尺寸10～30nm。Ag的掺杂会降低锐钛矿相向金红石相的转变温度,掺杂最佳值为Ag/Ti(摩尔比)=0.03;在550℃下热处理1h的Ag-TiO2的光催化性能最高,日光下光照3h对甲基橙的分解率可达97%。     

An excellent Z-scheme Ag2MoO4/Bi4Ti3O12 heterojunction photocatalyst: Construction strategy and application in environmental purification

Herein we have designed an excellent type of Z-scheme Ag₂MoO₄/Bi₄Ti₃O₁₂ (AMO/BTO) heterojunction photocatalysts by immobilizing AMO particles onto rod-like BTO hierarchical architectures. The formation of Z-scheme AMO/BTO heterostructures was verified by various characterization techniques including XRD, UV–vis DR spectroscopy, SEM, TEM, XPS and FTIR spectroscopy. PL spectroscopy, photocurrent response and EIS analyses suggest that the creation of AMO/BTO heterojunctions is conducive to the efficient separation of photoexcited electron-hole pairs. The photocatalytic performances of the AMO/BTO composites were investigated by simulated-sunlight driving photodegradation of methylene blue (MB), tetrabromobisphenol A (TBBPA), tetracycline hydrochloride (TC), phenol and methyl orange (MO)/rhodamine B (RhB)/MB mixture solutions. It is demonstrated that the AMO/BTO heterojunction photocatalysts are endowed with excellent photodegradation performances much higher than that of bare AMO and BTO. For example, the photodegradation rate of MB by using 30 wt%AMO/BTO — confirmed to be the optimal composite sample — is about 17.0 and 14.7 times as high as that by using bare BTO and AMO, respectively. A Z-scheme electron transfer mechanism was proposed to elucidate the enhanced photodegradation performances of the AMO/BTO heterojunction photocatalysts.     

Photocatalytic degradation of phenol in aqueous solutions by Pr-doped TiO2 nanoparticles

Photocatalytic degradation of phenol in water was examined using Pr-doped TiO₂ nanoparticles. These photocatalysts were synthesized by an acid-peptized sol–gel method from titanium tetra-isopropoxide with different concentrations of Pr(III) dopant and calcination temperatures. Several tools such as XRD, BET surface area, SEM, and EDX, were used to evaluate particle structure, size distribution, and composition. The optical absorption properties of the prepared particles were also measured. Photocatalytic activity of the particles was studied in a batch reactor containing phenol solution with 400 W UV irradiation. Parameters affecting photocatalytic process such as the catalyst crystallinity, light absorption efficiency, the dosage of catalyst, dopant and phenol concentrations were investigated. The Pr-doped TiO₂ showed high activity for photocatalytic degradation of phenol. The presence of Pr ions in the TiO₂ particles would cause a significant absorption shift towards the visible region. The degradation process was optimized using 1 g/L Pr-doped TiO₂ with a Pr(III) concentration of 0.072 mol% after 2 h irradiation. It was shown that photodegradation followed a pseudo-first-order kinetics and the rate constant changed with phenol concentration.     

离子液体中Co掺杂介孔TiO2可见光催化剂的制备及性能研究

以离子液体([C₄MIM]BF₄)为模板剂, 采用溶胶-凝胶法制备了介孔TiO₂和Co掺杂的介孔TiO₂光催化剂。研究了Co掺杂对样品的比表面积、晶相、元素价态、吸光特性及可见光活性的影响。结果表明: 所制备的Co/TiO₂光催化剂为介孔结构的具有较大比表面积的锐钛矿相纳米颗粒; XPS分析表明: Co以Co²⁺取代Ti⁴⁺进入TiO₂晶格形成杂质能级, 降低了TiO₂带隙能, 有效拓展了TiO₂的光响应范围。以亚甲基蓝水溶液为降解对象, 在可见光 (λ>420 nm)下考察制备样品的光催化活性, 结果表明: Co掺杂的TiO₂具有可见光活性, 且0.3%Co/TiO₂的活性最高。     

Preparation, characterization and activity evaluation of TiN/F-TiO2 photocatalyst

In this paper, F-TiO(2) and TiN/F-TiO(2) nanoparticle photocatalysts were prepared by ball milling. The photocatalysts were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), terephthalic acid photoluminescence probing technique (TA-PL), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflection spectroscopy (DRS). The photocatalytic activity of the photocatalysts was evaluated by photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB). The results showed that the photocatalytic activity of the F-TiO(2) was much higher than that of TiO(2), and the photocatalytic activity of the TiN/F-TiO(2) was much higher than that of TiO(2) and F-TiO(2) under UV light irradiation. The optimum percentage of doped TiN is 0.2 wt.%. Compared with pure TiO(2), the photoabsorption wavelength range of the TiN/F-TiO(2) and F-TiO(2) photocatalysts red shifts and improves the utilization of the total spectrum. The effect of ball milling time on the photocatalytic activity of the photocatalysts was also investigated. The optimum ball milling time is 12 h. The mechanisms of influence on the photocatalytic activity of the photocatalysts were also discussed.     

New anatase-type Til-2xNbxAlxO2 solid solution nanoparticles: direct formation, phase stability, and photocatalytic performance

New anatase-type titania solid solutions co-doped with niobium and aluminum (Til-2xNbxAIlxO2 (X = 0 -0.20)) were synthesized as nanoparticles from precursor solutions of TiOSO4, NbCl5, and Al(NO3)3 under mild hydrothermal conditions at 180 degrees C for 5 h using the hydrolysis of urea. The lattice parameters a0 and c0 of anatase slightly and gradually increased, when the content of niobium and aluminum increased from X = 0 to 0.20. The crystallite size of anatase increased from 12 to 28 nm with increasing the value of X from 0 to 0.20. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The adsorptivity of TiO2 was improved by the formation of anatase-type Til-2xNbxAlxO2 solid solutions. The photocatalytic activity of anatase-type Til-2xNbxAlxO2 solid solutions was superior to that of commercially available anatase-type pure TiO2 (ST-01) and anatase-type pure TiO2 hydrothermally prepared. The new anatase phase of Til-2xNbxAlxO2 (X = 0-0.20) solid solutions existed stably up to 850 0C during heat treatment in air. In comparison with hydrothermal pure TiO2, the starting temperature of anatase-to-rutile phase transformation was delayed by the formation of Ti1-2xNbxAlxO, (X = 0-0.20) solid solutions, although its completing temperature was accelerated.