Photocatalytic activities of TiO2 loaded with NiO

A pretreated NiO-TiO₂ powder system is an active catalyst for photocatalytic decomposition of H₂O into H₂ and O₂ in aqueous alkaline solution (3 N NaOH) as well as under NaOH coating conditions.     

Preparation of Cu-doped TiO2 via refluxing of alkoxide solution and its photocatalytic properties

Cu-doped TiO₂ was prepared by the refluxing of a mixture of copper and titanium alkoxides. The refluxing improved the Cu²⁺ dispersion in the TiO₂ and formed effective Ti–O–Cu bonds. The impurity states due to the highly dispersed Cu²⁺ were presumed to trap the electrons in the conduction band of the TiO₂ and prevent charge recombination of the electrons and holes. Consequently, the prolonged charge separation duration was suggested to enhance the photocatalytic activity of the Cu-doped TiO₂. This enhancement was confirmed by the hydroxyl radical generation and organic compound degradation. The Ti–O–Cu bonds and electronic interaction between Cu and Ti should effectively promote the electron trapping. The Cu-doped TiO₂ exhibited a visible light-induced activity due to the transition from the TiO₂ valence band to the Cu²⁺ impurity states.     

Synthesis and visible light photocatalytic properties of polyoxometalate-thionine composite films immobilized on porous TiO2 microspheres

Multilayer films (PW(12)-TH)(n) (PW(12)=PW(12)O(40)(3-), TH=thionine) were immobilized on porous anatase TiO(2) microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO(2) was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO(2) template particles had a round shape with an average diameter of 250 nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW(12)-TH)(n) composite films onto TiO(2) microspheres, and the growth of PW(12)-TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW(12)-TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO(2) became weaker when immobilized (PW(12)-TH)(n). The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO(2) and PW(12) showed an excellent photocatalytic performance. Both TH sensitization and PW(12) adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW(12)-TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.     

金红石相二氧化钛纳米晶的光催化活性

以苯酚光催化氧化和铬酸根光催化还原反庆为模型反应,研究不同粒径的金红石相二氧化钛纳米晶的光催化性活性。用XRD,TEM和BET等表明超细金红石相二氧化钛的粒径为7～8nm,UV-vis谱表明其吸收带边界蓝移11nm。在上述反应中,具有量子尺寸效应的金红石相二氧化钛(7nm)均表现出很高的催化活性,催化活性随粒径增大而迅速下降。7.2nm金红石相二氧化钛的光催化活性与6.8nm的锐钛矿相二氧化钛相当。     

Synthesis of 3D hierarchical porous TiO2/InVO4 nanocomposites with enhanced visible-light photocatalytic properties

Three-dimensional (3D) hierarchical porous TiO₂/InVO₄ nanocomposites were fabricated by loading TiO₂ nanoparticles on the surface of porous InVO₄ microspheres. X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectroscopy and photoluminescence spectroscopy (PL) were adopted to analyze the structure–property relationship of samples. The results show that the surface of as-prepared TiO₂/InVO₄ nanocomposites are composed of uniformly interconnected bi-phase nanocrystals, forming a close interface between these two components, which is favorable for the highly efficient interparticle electron transfer to achieve enhanced photocatalytic properties. However, the adsorption ability is decreased due to the loading of TiO₂ nanoparticles on the surface of InVO₄. Therefore, under the joint action of these factors, the TiO₂/InVO₄ nanocomposites achieve the best photocatalytic activity when the mole ratio of In:Ti reaches 4:1, and the visible-light photocatalytic activity is about as 3.3 times high as that of pure InVO₄ without modification.     

TiO_2-CuPcTs敏化薄膜光电流及可见光光催化性能

以四磺酸酞菁铜(CuPcTs)为敏化剂,玻璃和图案化的氧化铟锡(ITO)分别作为基底,制备了敏化薄膜TiO2-CuPcTs和ITO/TiO2-CuPcTs/ITO敏化器件.以罗丹明B(RhB)的可见光光催化降解为模型反应评价敏化薄膜的光催化性能.敏化薄膜采用UV-vis和Raman技术进行表征,同时利用敏化器件的结构特性,测定其在氮气和纯水体系下的光电流.研究结果表明,TiO2-CuPcTs可以有效地将光谱响应拓宽到可见光区,一级反应速率常数为空白TiO2薄膜的3.7倍.TiO2-CuPcTs薄膜光催化降解RhB的重复性能稳定.与ITO/TiO2/ITO器件相比,敏化器件ITO/TiO2-CuPcTs/ITO具有较高的光电流信号,验证了激发态的CuPcTs能够将电子转移到TiO导带上的敏化机理.     

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.     

Photocatalytic and antifouling properties of TiO2-based photocatalytic membranes

Photocatalysis has been extensively studied due to its potential ability to avoid the excessive use of chemical reagents and reduce the energy consumption by employing solar energy. Moreover, to alleviate the reduction in the membrane permeation selectivity, separation efficiency, and membrane service life caused by the emerging micro-pollutants and membrane fouling, membrane technology is often coupled with microbial, electrochemical, and catalytic processes. However, although physical/chemical cleaning and membrane module replacement can overcome the inherent limitations caused by membrane fouling and other membrane separation processes, high operating costs limit their practical applications. In this review, common preparation methods for TiO₂ photocatalytic membranes are described in detail, and the main approaches to enhancing their photocatalytic performance are discussed. More importantly, the mechanism of the TiO₂ photocatalytic membrane antifouling process is elucidated, and some applications of photocatalytic membranes in other areas are described. This review systematically outlines future research directions in the field of photocatalytic membrane modification, including metal and non-metal doping, fabrication of heterojunction structures, control over reaction conditions, increase in hydrophilicity, and increase in membrane porosity.     

Polyacrylamide gel synthesis and photocatalytic properties of TiO2 nanoparticles

In this study, a polyacrylamide gel route was introduced to synthesize TiO₂ nanoparticles. The influence of synthesis conditions on the properties of products was investigated. It is found that the samples prepared at the calcination temperature of 400 °C crystallize majorly in the anatase phase with a minor rutile phase. The second rutile phase has a dependence on the chelating agent, which is formed more readily when using acetic acid as the chelating agent. The introduction of acrylamide and glucose to the precursor solution shows the capability of improving the particle morphology, and the resulted particles are uniformly shaped like spheres. The photocatalytic activity of the prepared TiO₂ samples was evaluated by the degradation of acid orange 7 under 254 nm ultraviolet irradiation, revealing that they exhibit a good photocatalytic activity. Ethanol was used as a ^·OH scavenger to investigate its effect on the photocatalytic efficiency as well as the ^·OH radical yields. Based on the experimental results, ^·OH radical is suggested to be the dominant active species responsible for the dye degradation.     

The photocatalytic properties of amorphous TiO2 composite films deposited by magnetron sputtering

The preparation of amorphous TiO₂ film coupled with various metal-oxide semiconductors and their photocatalytic activities evaluated by photo-degradation of methylene blue and rhodamine B aqueous solution are briefly reviewed. The proposed photoreaction mechanism of the amorphous composite semiconductor and the differences between amorphous TiO₂-based films and crystalline TiO₂ photocatalytic materials in terms of preparation and usage are addressed. The inactive intrinsic amorphous TiO₂ film coupled with various metal oxides were found to gain high photocatalytic activity. These dopants induce forming new energy levels in the band gap of TiO₂ to enhance the charge separation of the photoinduced electrons and holes and extend the light absorption of TiO₂-based photocatalytic films into the visible region. In addition, two different effects of coupling metal oxides have been proved: the introduction of oxides of W, Cr, V, Ag, and Mo can significantly increase the photo-reactivity of amorphous TiO₂ film, while the combination of oxides of Zr, Sn, Sb, Cu, Ta, Fe, and Ni cannot affect the inactivity of pure amorphous TiO₂ film.     

TiO2 anatase-based membranes with hierarchical porosity and photocatalytic properties

Taking benefit of previously obtained results, stable complex organic-inorganic hybrid suspensions are successfully prepared by mixing a polystyrene latex aqueous suspension, a titania hydrosol and a nonionic triblock copolymer. These suspensions can be then deposited as thin films on dense or porous substrates. Solvent evaporation induces the formation of spherical micelles by self-assembly of the amphiphilic molecules during the drying of the films. Two types of isolated spherical macropores (few ten nanometers) and mesopores (4-5 nm) are generated inside the layers by the thermal removal of the polystyrene particles and of the micelles, respectively. The remaining inorganic network exhibits an additional interconnected microporosity with a mean pore size of 1.5 nm, resulting from the aggregation of the anatase nanoparticles. A complete removal of the templating units at low temperature is possible using the photocatalytic properties of the anatase network. Such layers exhibit attractive properties for the design of ceramic membranes. They can be advantageously used in order to increase the permeability of the separative layer and to reduce the number of intermediate layers of these asymmetric structures.     

Photothermal and photocatalytic processes on TiO2 based materials prepared by sol-gel method

In the present work, Fe³⁺ doped TiO₂ coatings on glass substrates were prepared by dip-coating from a sol-gel solution. The influence of the dopant concentration on the structure, optical, photocatalytic and photothermal properties of the films was studied. The results obtained have shown a strong correlation between the catalytic properties and the amount of iron dopant and the temperature of the thermal treatment.     

Study of photocatalytic activity of Cd-doped mesoporous nanocrystalline TiO2 prepared at low temperature

Mesoporous nanocrystalline Cd-doped titania was firstly prepared at low temperature by a modified sol–gel method, using dodecylamine as a template. The template could be easily removed by refluxing samples in nitric acid ethanol solution. The Fourier transform infrared spectrometer (FT-IR), low-angle and wide-angle X-ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and UV–visible diffuse reflectance spectroscopy were used for the characterization of catalysts. The characteristic results clearly showed that Cd²⁺ ions were doped into the titania lattice, and the mesoporous architecture of Cd-doped TiO₂ was composed of mixed-phase crystal textures of anatase and brookite. The samples displayed high visible-light photocatalytic activity for photodegradating 2,4-dichlorophenol (2,4-DCP) solution. The high activities of samples were attributed to the bicrystalline framework, large BET surface area, small crystallite size, and Cd-doping.     

Preparation of highly photocatalytic active nano-sized TiO2 particles via ultrasonic irradiation

A novel method for preparing highly photoactive nano-sized TiO2 photocatalysts with anatase and brookite phases has been developed by hydrolysis of titanium tetraisoproproxide in pure water or a 1:1 EtOH-H2O solution under ultrasonic irradiation; the photocatalytic activity of TiO2 particles prepared by this method exceeded that of Degussa P25.     

Mesoporous TiO2/SiO2 composite nanofibers with selective photocatalytic properties

Mesoporous TiO2/SiO2 composite nanofibers with a diameter of 100-200 nm and silica shell thickness of 5-50 nm have been fabricated by a sol-gel combined two-capillary co-electrospinning method; the composite nanofibers exhibited selective photocatalytic activity based on the decomposition of Methylene Blue, Active Yellow and Disperse Red.     

Highly efficient photocatalytic dehalogenation of organic halides on TiO2 loaded with bimetallic Pd-Pt alloy nanoparticles

UV irradiation of TiO(2) loaded with bimetallic Pd-Pt alloy particles promotes highly efficient dehalogenation of organic halides with alcohol as a hydrogen source.     

N-Doped, porous TiO2 with rutile phase and visible light sensitive photocatalytic activity

Nitrogen-doped, porous rutile has been prepared by hydrothermal reaction of TiN in nitric acid, with the nitrogen atoms present in the interstitial sites and in the form of adsorbed nitrate ions. The N-rutile powder exhibits outstanding photocatalytic activity toward degradation of adsorbed methylene blue under visible light irradiation.     

Anatase TiO2 porous thin films prepared by sol-gel method using CTAB surfactant

Anatase TiO₂ porous thin films were prepared on glass substrates by sol-gel method with Cetyltrimethylammonium Bromide (CTAB) as a pore-forming agent, Tetrabutylorthotitanate as Ti precursor, ethanol as solvent and diethanolamine as chelating agent respectively. IR, TG-DSC, XRD and SEM analyzed the chemical and physical changes during sol-gel process and characteristics of the films. Effects of the amount of CTAB, alkane and water on morphology of the films were discussed and the principle of forming porous structure was proposed. It was shown that the diameter of pores was changed in the range of 30–400 nm.