Fabrication and photocatalytic property of TiO<Subscript>2</Subscript> nanofibers

TiO₂ nanofibers were prepared from tetrabutyl titanate sol precursors by using electrospun method. X-ray diffraction (XRD) and atomic force microscope (AFM) were used to characterize their crystal structure and morphology feature. The results demonstrated that TiO₂ nanofibers possessed anatase phase and the average diameter of TiO₂ nanofibers was about 150 nm. The photocatalytic property of TiO₂ nanofibers was evaluated for the photodecomposition of methyl orange solution. And TiO₂ nanofibers exhibited high photocatalytic activities with transfer efficiency about 100% after 20 min.     

Preparation and photocatalytic activity of B,Ce Co-doped TiO2 hollow fibers photocatalyst

A series of B, Ce co-doped TiO₂ (B, Ce-TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared by template method using boric acid, ammonium ceric nitrate and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500°C in an N₂ atmosphere for 2 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and UV-visible spectroscopy (UV-Vis) were employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photocatalytic performance of the samples was studied by photodegradation phenol in water under UV light irradiation. The results showed that the TiO₂ fiber materials have hollow structures, and the fiber structure materials showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light. In the experiment condition, the photocatalytic activity of B, Ce co-doped TiO₂ fibers was optimal of all the prepared samples. In addition, the possibility of cyclic usage of B, Ce co-doped TiO₂ fiber photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fibers remained above 90% of that of the fresh sample after being used four times. The material was easily removed by centrifugal separation from the medium. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Photocatalysis: Light energy conversion for the oxidation,disinfection, and decomposition of water

The results of many-year studies of the relationship between the physical properties and photocatalytic activity of TiO₂ and Pt/TiO₂ in photocatalytic purification and disinfection of air and water and water photodecomposition with oxygen evolution are presented. Recommendations are given as to finding the optimal method for platinum supporting on TiO₂ to achieve the highest possible catalytic activity. Multisite kinetic models of the gas-phase oxidation of simple organic substances are considered. Methods for regenerating the photocatalyst after its deactivation in the oxidation of sulfur-containing organic substances are suggested. New data are discussed on the acceleration of air purification by the combination of photocatalytic oxidation with atmospheric electric discharges, the addition of gaseous hydrogen peroxide, and oxidation on photocatalysts existing in the aerosol state. As compared to pure TiO₂, platinated titanium dioxide has a higher capability for disinfection and complete mineralization of microorganisms. Two promising methods for production of hydrogen from water using solar light are presented.     

TiO2 photocatalysis: Design and applications

TiO₂ photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, sterilization, hydrogen evolution, and photoelectrochemical conversion. The development of new materials, however, is strongly required to provide enhanced performances with respect to the photocatalytic properties and to find new uses for TiO₂ photocatalysis. In this review, recent developments in the area of TiO₂ photocatalysis research, in terms of new materials from a structural design perspective, have been summarized. The dimensionality associated with the structure of a TiO₂ material can affect its properties and functions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties. We provide a brief introduction to the current situation in TiO₂ photocatalysis, and describe structurally controlled TiO₂ photocatalysts which can be classified into zero-, one-, two-, and three-dimensional structures. Furthermore, novel applications of TiO₂ surfaces for the fabrication of wettability patterns and for printing are discussed.     

Preparation of Anatase Hollow TiO2 Spheres and Their Photocatalytic Activity in the Photodegradation of Chlorpyrifos

Hollow anatase titania (TiO₂) spheres were synthesized using fructose and tetrabutyl titanate (Ti(OC₄H₉)₄, TBT) as the precursors via the conventional hard template method. The morphological, structural and thermal properties of the products were characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG‐DTA), Brunauer? Emmett? Teller (BET) surface area analysis and diffuse reflectance ultraviolet visible (DR UV? Vis) spectroscopy. XRD revealed that the hollow TiO₂ prepared was in the anatase phase and the BET surface area measured was about 22 m² g^?1. The photocatalytic activity of the synthesized hollow anatase TiO₂ in the photodecomposition of chlorpyrifos was 18.67 % higher than that obtained using commercial TiO₂.     

Preparation and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst SnSx/TiO2

Visible-light-responsive composite photocatalysts SnS₂/TiO₂ and SnS/TiO₂ with different mass ratios were prepared by in-situ synthesis technology in solution with commercial TiO₂. The junction-based materials SnS_x (x=1, 2)/TiO₂ were found to have high visible-light photocatalytic performance and possess much better activity than the single-phase SnS_x or TiO₂. The greatly enhanced photocatalytic activity of the SnS_x/TiO₂ composites was mainly attributed to the matching band potentials and efficient charge transfer and separation at the tight-bonding interface between SnS_x and TiO₂. The fact was confirmed by the comparison of photocatalytic activities of the SnS₂/TiO₂ samples prepared by physical mixing method and in-situ synthesis technique.     

Stabilization of Titanium Dioxide Nanoparticles at the Surface of Carbon Nanomaterials Promoted by Microwave Heating

TiO₂ is frequently combined with carbon materials, such as reduced graphene oxide (RGO), to produce composites with improved properties, for example for photocatalytic applications. It is shown that heating conditions significantly affect the interface and photocatalytic properties of TiO₂@C, and that microwave irradiation can be advantageous for the synthesis of carbon‐based materials. Composites of TiO₂ with RGO or amorphous carbon were prepared from reaction of titanium isopropoxide with benzyl alcohol. During the synthesis of the TiO₂ nanoparticles, the carbon is involved in reactions that lead to the covalent attachment of the oxide, the extent of which depends on the carbon characteristics, heating rate, and mechanism. TiO₂ is more efficiently stabilized at the surface of RGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance.     

Surface Modifications and Optoelectronic Characterization of TiO2‐Nanoparticles: Design of New Photo‐Electronic Materials

TiO₂ nanoparticles are of great current interest for applications in photo‐electronic materials including light‐energy conversion, artificial photosynthetic systems as well as photocatalysis. The success of these applications relies on the exciton recombination dynamics and visible‐light sensitivity of the TiO₂ nanomaterials. Thus, in order to develop the highly efficient photo‐electronic materials absorbing visible light, different low dimensional TiO₂ nanostructures such as nanodiscs, nanofibers and nanochains were synthesized, and thereafter their surfaces were modified by incorporating with Sn‐porphyrins and heteropoly acid. The optoelectronic properties of the surface‐modified nanomaterials were investigated with regard to the optical properties and the surface exciton dynamics by using both steady‐state and ultrafast time‐resolved laser spectroscopic techniques including single nanoparticle photoluminescence technique. These results were correlated with the photo‐electronic properties including photocatalytic activities and solar cell efficiencies, indicating that the electron transfer mechanism in the modified nanostructures may be similar to the “Z‐scheme” of the plant photosynthetic system so that both photocatalytic activity and solar cell efficiencies were synergistically enhanced by using two color illumination.     

Modifications on reduced titanium dioxide photocatalysts: A review

A large variety of reduced titanium dioxide (TiO_2-x) materials have been reported recently. Reduced TiO₂, usually resulting from the removal of oxygen atoms or hydrogen incorporation, is proved to be efficient for achieving highly photocatalytic performance including photodegradation of organic compounds, hydrogen generation from water splitting, CO₂ reduction for CH₄ evolution, solar cells, etc. To further improve the properties and activities of TiO_2-x, a combination of the Ti³⁺ self-doping and other traditional modifications like nonmetals doping has been proposed in the past decades. This paper provides a general and critical review on the further modifications on reduced TiO₂ samples, including non-metal elements (N, B, S, F and I) doping, noble-metal (Au, Pt, Pd and Ag) and iron-group metal (Fe, Co and Ni) grafting, metal oxide compositing, carbon (nanotubes and graphene) and carbon-based-material compositing, special facets exposure (mainly dual {001}-{101} and {111}-{110} facets) of TiO_2-x and ordered structure controlling of TiO_2-x. These modifications enhance the physical and/or chemical properties of the reduced TiO₂, or create new features for the modified TiO_2-x samples, which finally leads to the enhancement of photocatalytic performance. Key examples such as N-doping, Au grafting and graphene-based compositing are discussed carefully, and the mechanisms for solar light enhancement, electron transfer and charge separation are also investigated. Finally, some challenging issues on TiO_2-x catalysts are also proposed to encourage new approaches for preparation of TiO_2-x catalysts with efficiently photocatalytic performance.     

Preparation and photocatalytic behavior of TiO2-carbon nanotube hybrid catalyst for acridine dye decomposition

A new kind of hybrid catalyst, TiO₂-carbon nanotubes, was prepared via sol-gel method for the first time. Its photocatalytic activity in the photodegradation of acridine dye aqueous solution at low concentration was tested. There was no measurable effect on the formation of crystalline phase of TiO₂ catalyst with the addition of 10 wt.% carbon nanotubes to TiO₂ samples. AFM photograph of TiO₂-carbon nanotubes sintered at 300°C showed that the carbon nanotubes were enwrapped by TiO₂, which greatly increased the adsorbing ability of the catalyst and was in favor of photocatalytic reaction. Compared with naked TiO₂ powder the hybrid catalyst prepared in this way showed high efficiency in the photodecomposition of acridine dye.     

脉冲沉积制备Cu2O/TiO2纳米管异质结的可见光光催化性能

在用阳极氧化法制备有序排列TiO₂纳米管阵列薄膜的基础上,引入脉冲沉积工艺,成功实现了均匀、弥散分布的Cu₂O纳米颗粒修饰改性TiO₂纳米管阵列,形成Cu₂O/TiO₂ 纳米管异质结复合材料. 利用场发射扫描电镜（FESEM）、场发射透射电镜（FETEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）和紫外-可见漫反射光谱（UV-Vis DRS）对样品进行表征,重点研究了Cu₂O/TiO₂ 纳米管异质结的光电化学特性和对甲基橙（MO）的可见光催化降解性能. 结果表明,Cu₂O纳米颗粒均匀附着在TiO₂纳米管阵列的管口和中部位置,所制备的Cu₂O/TiO₂ 纳米管异质结具有高效的可见光光催化性能;在浓度为0.01 mol·L^-1的CuSO₄溶液中制得的Cu₂O/TiO₂纳米管异质结表现出最好的电化学特性和光催化性能;另外,对Cu₂O纳米颗粒影响光催化活性的机理进行了讨论.     

Chemical synthesis of Ni/TiO<Subscript>2</Subscript> nanophotocatalyst for UV/visible light assisted degradation of organic dye in aqueous solution

The Ni/TiO₂ nanoparticles with different Ni dopant content were prepared by a modified sol–gel method. The structure and photoinduced charge properties of the as-prepared catalysts were determined using X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy techniques, and the photocatalytic efficiency of these catalysts was tested using an organic dye. It was shown that Ni modification could greatly enhance the photocatalytic efficiency of these nanocomposite catalysts by taking the photodegradation of methyl orange as a model reaction. With appropriate ratio of Ni and TiO₂, Ni/TiO₂ nanocomposites showed the superior photocatalytic activity than the single TiO₂ nanoparticles. Surface photovoltage spectra demonstrated that Ni modification could effectively inhibit the recombination of the photoinduced electron and holes of TiO₂. This electron–hole pair separation conditions are responsible for the higher photocatalytic performance of Ni/TiO₂ nanocomposites in the visible region of electromagnetic spectrum.     

Preparation and characterization of polyurethane based self-cleaning and antibacterial coating containing silver ion exchanged montmorillonite/TiO<Subscript>2</Subscript> nanocomposite

In order to reach an antibacterial, photocatalytic, and hydrophilic coating, commercial grade polyurethane (CPU) resin was modified with silver ion exchanged montmorillonite/TiO₂ nanocomposite in various montmorillonite to TiO₂ nanoparticle ratios. To characterize the prepared nanocomposites and coatings, X-ray diffraction patterns, FTIR and UV–Vis spectroscopy and SEM images were used. The modified commercial grade polyurethane coatings containing nanocomposites show better properties, including hydrophilicity, degradation of organic pollutants, antibacterial activity and water resistivity, compared to unmodified commercial grade polyurethane coatings. The water droplet contact angle of unmodified CPU coating was 70°, however it decreased to lower than 10° in modified CPU coatings after 24 h LED lamp irradiation. Decolorization efficiency of malachite green dye solution by the use of modified CPU coatings achieved up to 70% after 5 h LED lamp illumination, compared to less than 5% for unmodified CPU coatings. Modified CPU coatings also showed significant water resistivity and antibacterial properties.     

Cu/Ni助催化剂对TiO2光催化制取苯酚性能的影响

以TiO₂纳米粒子为主催化剂,采用"浸渍-还原法"构筑了铜、镍共负载的二氧化钛基光催化系统。以苯为起始原料,H₂O₂为氧化剂,研究了Cu/Ni助催化剂对TiO₂可见光催化制取苯酚性能的影响并对Cu/Ni助催化剂的作用机制进行了探讨。结果表明,在可见光照射下,纯TiO₂纳米粒子对苯氧化制取苯酚反应没有催化活性。铜、镍的引入可以明显地增强Ti₀₂可见光催化制取苯酚的活性。当使用负载有铜、镍的TiO₂作为催化剂时,苯酚的产率可达到18%。结果还表明Cu、Ni之间存在着很强的协同作用。在该协同作用下,Cu、Ni共负载的TiO₂纳米粒子表现出了较单一金属负载的TiO₂纳米粒子高得多的光催化活性。     

Cu/Ni助催化剂对TiO2光催化制取苯酚性能的影响

以TiO₂纳米粒子为主催化剂, 采用“浸渍-还原法”构筑了铜、镍共负载的二氧化钛基光催化系统。以苯为起始原料, H₂O₂为氧化剂, 研究了Cu/Ni助催化剂对TiO₂可见光催化制取苯酚性能的影响并对Cu/Ni助催化剂的作用机制进行了探讨。结果表明, 在可见光照射下, 纯TiO₂纳米粒子对苯氧化制取苯酚反应没有催化活性。铜、镍的引入可以明显地增强TiO₂可见光催化制取苯酚的活性。当使用负载有铜、镍的TiO₂作为催化剂时, 苯酚的产率可达到18%。结果还表明Cu、Ni之间存在着很强的协同作用。在该协同作用下, Cu、Ni共负载的TiO₂纳米粒子表现出了较单一金属负载的TiO₂纳米粒子高得多的光催化活性。     

Physical properties of nano-titania hollow fibers and their photocatalytic activity in the decomposition of phenol

A series of nano-titania (TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared using tetra-n-butyl titanate (Ti(OC₄H₉)₄) as precursor and cotton fiber as the template. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption-desorption measurements were employed to characterize the morphology, crystal structure, and surface structure of the samples. The photocatalytic activities of the samples were studied by phenol photodegradation in water under UV irradiation. The effect of calcination temperature, photocatalyst dosage, initial concentration of phenol and irradiation time on the photodegradation of phenol was studied. Results showed that the TiO₂ fiber materials have hollow structures, indicating that these materials had a large specific surface area. The fiber structure material showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light, and the sample calcined at 500°C exhibited the highest phenol photodegradation efficiency. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fiber remained ca. 90% of photocatalytic activity of the fresh sample after being used four times. Moreover, TiO₂ fiber was easily recovered by centrifugal separation from water.     

One-Pot Synthesis of Nitrogen-Doped TiO2 with Supported Copper Nanocrystalline for Photocatalytic Environment Purification under Household White LED Lamp

Developing efficient and cheap photocatalysts that are sensitive to indoor light is promising for the practical application of photocatalysis technology. Here, N-doped TiO₂ photocatalyst with loaded Cu crystalline cocatalyst is synthesized by a simple one-pot method. The structure is confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy analysis, which exhibit that Cu metal nanocrystalline is uniformly deposited on the surface of N-doped TiO₂ material. UV-Vis absorption spectra illustrate that the modified samples possess favorable visible light absorption properties and suppressed-electron hole separation. The as-fabricated Cu-loaded N-TiO₂ materials show high activity in photocatalytic decomposing isopropanol and inactivating E. coli under the irradiation of a household white LED lamp. The developed synthetic strategy and photocatalytic materials reported here are promising for indoor environment purification.     

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Titanium dioxide (TiO₂) is regarded as an important prototype photocatalytic material for several decades. The charge carrier kinetics determines the photocatalytic properties of TiO₂ materials; this is found to be greatly dependent on electronic structures. It has been revealed that the intrinsic intermediate gap states (intrinsic GSs) play a significant role in charge carrier kinetics that drive the photocatalytic processes of TiO₂ materials, which are not well summarized until now. Motivated by this thought, the purpose of this review focuses on physiochemical science of the intrinsic GSs of TiO₂ materials and their important role in charge carrier kinetics. We first give a summary on the chemical resources of the intrinsic GSs in TiO₂ and their physiochemical nature. Their general energy distribution, charge carrier population, and the associated thermodynamic properties are also elaborated from an overall viewpoint. We further carefully summarize and compare the experimental studies on the energy and the density distribution of the intrinsic GSs and discuss the associated chemical resources and charge carrier localizations. Trapping is the dominant function of intrinsic GSs in the charge carrier kinetics of TiO₂ materials. The significant effect of trapping on the transport, recombination, and interfacial transfer of charge carriers are also comprehensive summarized. Furthermore, the effects of charge carrier kinetics on photocatalytic performances are also discussed to some extents. Because of the importance of intrinsic GSs in modulating charge carrier kinetics, it is expected to increase the photocatalytic activity by engineering the intrinsic GSs, not only for TiO₂ materials, but also for the other semiconductor photocatalysts.     

Characterization of Titanium Dioxide Doped with Nitrogen and Sulfur and its Photocatalytic Appraisal for Degradation of Phenol and Methylene Blue

The degradation of organic dyes in the presence of modified TiO₂ is still under intensive investigation. We report here an evaluation of the photocatalytic activity of nitrogen‐ (N‐) and sulfur‐ (S‐) doped TiO₂ for the degradation of phenol and methylene blue (MB). N‐doped TiO₂ (N–TiO₂), S‐doped TiO₂ (S–TiO₂), and N–S‐doped TiO₂ (N–S–TiO₂) were prepared using the sol–gel method. The photocatalytic activity was evaluated in a batch reactor using phenol and MB as models of pollutants. In addition, this investigation was performed using a household lamp as the visible light source. Properties of the synthesized materials in terms of Brunauer–Emmett–Teller (BET) surface analysis, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and photocatalytic ability were examined. Our study shows that N–S–TiO₂ exhibits better photocatalytic degradation ability for all the considered dyes compared to the other doped TiO₂ materials. In conclusion, we have successfully prepared and evaluated the photocatalytic activity of N‐ and S‐doped TiO₂ for the degradation of phenol and MB using an ordinary household lamp.     

Photocatalytic TiO2 coatings on limestone

The application of photocatalytic coatings on stone has been investigated for providing surface protection and self-cleaning properties. Sol–Gel and hydrothermal processes were used to synthesise TiO₂ colloidal suspensions and coatings with enhanced photocatalytic activity without any thermal curing of the coated stone. The stone was a porous limestone (apulian sedimentary carbonatic, calcite stone). Films and powders prepared from TiO₂ sols were studied using X-ray diffraction to evaluate the microstructure and identify rutile and anatase phases. A morphological and physical characterisation was carried out on coated and uncoated stone to establish the changes of appearance, colour, water absorption by capillarity and water vapour permeability. The photocatalytic activity of the coated surface was evaluated under UV irradiation through NO _x and organics degradation tests. The performances of the synthesised TiO₂ sols were compared with commercial TiO₂ suspension. Since the coating doesn’t need temperature treatments for activating the photocatalytic properties, the nano-crystalline hydrothermal TiO₂ sols seem good candidate for coating applications on stone that cannot be annealed after the coating application.