Fabrication of carbon-modified TiO2 nanotube arrays and their photocatalytic activity

TiO₂ nanotube (TN) arrays were fabricated by an anodic oxidation process. Through a heat treatment of the as-fabricated TN arrays under a continuous Ar and acetylene flux, carbon-modified TN (C-TN) arrays were obtained. The as-fabricated catalysts were characterized by FE-SEM, HRTEM, XPS, Raman and UV-Vis spectra. Moreover, photocatalytic activity of the C-TN arrays was evaluated through the photodegradation of aqueous methyl blue. The experiments demonstrated that the C-TN arrays display an excellent photocatalytic activity. Under sunlight irradiation, the C-TN arrays are able to almost completely decompose the methylene blue pollutant of 1 × 10^− 5 M within 300 min.     

Synthesis and photocatalytic property of SnO2/TiO2 nanotubes composites

SnO2/TiO2 nanotubes composite photocatalysts with different SnO2 contents were successfully synthesized by means of a simple solvothermal process. The synthesized products were characterized physically by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The composite photocatalysts can not only make the target pollutant, methylene blue (MB), adsorbed at a high concentration level around the surface of the composites but also decrease the recombination rate of electron-hole pairs so as to achieve good photocatalytic performance. The effect of SnO2 contents on the photocatalytic activities of the composites was also investigated. The results showed that the SnO2/TiO2 nanotubes composite photocatalyst with 5 wt.% SnO2 loading had the highest photocatalytic efficiency.     

Fabrication of photocatalytic heat-mirror with TiO2/TiN/TiO2 stacked layers

The photocatalytic heat-mirror based on TiO₂/TiN/TiO₂ stacked layers is prepared by reactive magnetron sputtering on quartz substrates under substrate-heating condition. We find that the addition of a thin Ti interlayer between the TiN and the outer TiO₂ layers drastically improves the heat-insulating performance. This type of stacked layer also exhibits higher photocatalytic activity for decomposition of acetaldehyde gas, compared with a TiO₂ single layer. The optical property of the TiN in TiO₂/TiN/TiO₂ stacked layers is the key not only revealing excellent heat-insulating effect but also improving the photocatalytic performance of the outer TiO₂ layers in the stacked layers.     

Preparation of nitrogen co-doped SiO2/TiO2 thin films on ceramic with enhanced photocatalytic activity under visible-light irradiation

In this study, we have successfully deposited N-doped SiO₂/TiO₂ thin films on ceramic tile substrates by sol–gel method for auto cleaning purpose. After dip coating and annealing process the film was transparent, smooth and had a strong adhesion on the ceramic tile surface. The synthesised catalysts were then characterised by using several analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM) and UV-vis absorption spectroscopy (UV-vis). The analytical results revealed that the optical response of the synthesised N-doped SiO₂/TiO₂ thin films was shifted from the ultraviolet to the visible light region. The nitrogen substituted some of the lattice oxygen atoms. The surface area of co-doped catalyst increased, and its photocatalytic efficiency was enhanced. The photocatalytic tests indicated that nitrogen co-doped SiO₂/TiO₂ thin films demonstrated higher than of the SiO₂/TiO₂ activity in decolouring of methylene blue under visible light. The enhanced photocatalytic activity was attributed to an increasing of the surface area and a forming of more hydroxyl groups in the doped catalyst.     

Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants

Nitrogen-doped TiO₂ was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO₂ prepared by the sol–gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO₂ properties, such as absorption ability in the UV–visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO₂ with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO₂ can be arranged in the following order: TiO₂/diethanolamine > TiO₂/triethylamine > TiO₂/urea > un-doped TiO₂. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO₂ with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10⁻² min⁻¹ with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.     

Fabrication of TiO2 nanotube arrays of different dimension for photocatalytic decomposition of IPA in air streams

Abstract

TiO₂ nanotube arrays (TNTs) were fabricated by anodization under various operational conditions. Dimensions of fabricated TNTs were significantly influenced by the temperature and water content of ethylene glycol-based electrolyte prepared for anodization. TNTs of longer length, larger inner diameter, and thinner wall thickness were fabricated in electrolytes of higher temperatures. For TNTs fabricated in electrolyte containing higher water contents, the relatively fast dissolution of TiO₂ led to the formation of TNTs of shorter tube length and larger inner diameter. TNTs were fabricated under different anodization conditions (mainly the water content in ethylene glycol electrolyte and anodization time) to exhibit similar tube length and different inner diameters. Experiments conducted using TNTs of longer tube lengths and smaller inner diameters demonstrated higher photocatalytic decompositions of gaseous isopropyl alcohol (IPA); however, the photocatalytic application of TNTs is limited by the penetration of illumination.     

碳纳米管修饰LaFeO3/TiO2复合材料的光催化性能与机理

采用超声辅助溶胶凝胶法制备了LaFeO₃颗粒,进一步以碳纳米管(CNTs)为基底和钛酸丁酯为前体,通过一步水热法煅烧合成CNTs/TiO₂/LaFeO₃(CTF)三元异质结光催化复合材料。通过扫描电子显微镜(SEM)、X射线衍射分析(XRD)、氮气吸附-解吸等温线(BET)、紫外-可见分光光度计(UV-Vis)、光致发光光谱(PL)等表征手段对材料的形貌与特征结构、比表面积和孔径结构以及光学特征进行了分析,并在紫外光下通过降解活性黑五(RB5)测试样品的光催化性能。结果表明,以CNTs作为载体,能够有效提升LaFeO₃/TiO₂复合材料的光催化性能。当CNTs在复合材料中的质量占比为5%时,150 W汞灯照射下RB5的50 min去除率可达99.5%。CNTs一方面通过增加复合材料的比较面积为催化反应的进行提供了更多的活性位点,更为重要的是,CNTs作为光生载流子传输的通道加快了电荷分离效率,提升了复合材料的降解能力和催化反应动力学进程。     

Preparation and photocatalytic activity of TiO2 powders from titanium citrate complex using two-step hydrothermal treatments

White, almost carbon-free TiO₂ powders were prepared from a titanium citrate complex ((NH₄)₄[Ti₂(C₆H₄O₇)₂(O₂)₂]·4H₂O) using a two-step hydrothermal treatment. The product yield, carbon contamination, and crystalline phase of TiO₂ depended on both the temperature and pH value for each treatment. Titanium was precipitated as a solid phase (H₂Ti₂O₅·H₂O) using the first hydrothermal treatment in the basic condition (pH = 12) at temperatures less than 150 °C. Then white rutile or anatase powder was crystallized using the second hydrothermal treatment at 200 °C. By changing the pH condition of the second hydrothermal treatment, rutile and anatase were synthesized selectively. The photocatalytic decomposition activity of obtained rutile powder for gaseous 2-propanol under visible light was increased by Cu-grafting.     

Excellent visible light photocatalytic properties of novel graphene based CdLa2S4/TiO2 heterojunction nanocomposite

This paper introduced one pot method for the synthesis of hybrid CdLa₂S₄-graphene/TiO₂ nanocomposite. The surface properties seen by SEM present a characterization of the texture on CdLa₂S₄-graphene/TiO₂ composites and showed a homogenous composition in the particles. The EDX spectra for the elemental identification showed the presence of C, O and Ti with strong Cd, La and S peaks for the CdLa₂S₄-graphene/TiO₂ nanocomposite. The generation of reactive oxygen species were detected through the oxidation reaction from 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). It is found that the photocurrent density and the photocatalytic effect increase in the case with the modified CdLa₂S₄.From the photocatalytic results, the excellent activity of CdLa₂S₄-graphene/TiO₂ nanocompositefor degradation of methylene blue (MB) and Texbrite BA-L (TBA) undervisible irradiation could be attributed to both the effects between photocatalysis of the supported TiO₂ and charge transfer of the grapheme nanosheet, and the introduction of CdLa₂S₄ to enhance the photogenerated electrons.     

In-situ preparation of multi-layer TiO2 nanotube array thin films by anodic oxidation method

The multi-layer TiO₂ nanotube array thin films have been formed by anodic oxidation method via adjusting the outer voltage during oxidation process in glycerol electrolyte containing 0.3% NH₄HF₂. The diameter of the nanotube array increases with the outer voltage, and the length of nanotube in every layer increases with the anodic oxidation time. These multi-layers bring new possibilities to tailor the properties of the TiO₂ nanotube array thin films formed via anodic oxidation method. Further, such multi-layer structure provide a new approach to evaluate the growth rate of TiO₂ nanotube, which will help us to understand more deeply the formation mechanism of the TiO₂ nanotubes. The growth rate of TiO₂ nanotube array is respectively 1.2 and 3.6 μm/h under the anodic voltage of 30 V and 60 V. These multi-layer TiO₂ nanotube array thin films may exhibit lots of potential applications in photoelectrochemical fields.     

Enhanced photoelectrocatalytic activity in TiO2 nanotube arrays modified with TiO2 nanoparticles

The use of TiO₂ nanotube arrays fabricated by anode oxidation of titanium sheets as a photoelectrocatalyst is limited by low surface activity owing to passive crystallization post-treatment. We report here on a vacuum assisted filling route for modifying TiO₂ nanotube arrays using high-activity anatase TiO₂ nanoparticles as a filling. Photoelectrocatalytic degradation experiments show that a nearly 4-fold activity enhancement in photoelectrocatalysis is achieved and good photoelectrocatalytic stability is kept after the nanotube arrays are filled with the high-activity TiO₂ nanoparticles. The remarkable enhancement in photoelectrocatalysis is ascribed to the key modification of the TiO₂ nanotube arrays using the high-activity TiO₂ nanoparticles. Our findings provide an insight into designing excellent photoelectrocatalysts by filling TNAs with available high-activity TiO₂ nanoparticles.     

Synergy between surface adsorption and photocatalysis during degradation of humic acid on TiO2/activated carbon composites

A photocatalyst comprising nano-sized TiO(2) particles on granular activated carbon (GAC) was prepared by a sol-dipping-gel process. The TiO(2)/GAC composite was characterized by scanning electron microscopy (SEM), X-ray diffractiometry (XRD) and nitrogen sorptometry, and its photocatalytic activity was studied through the degradation of humic acid (HA) in a quartz glass reactor. The factors influencing photocatalysis were investigated and the GAC was found to be an ideal substrate for nano-sized TiO(2) immobilization. A 99.5% removal efficiency for HA from solution was achieved at an initial concentration of 15 mg/L in a period of 3h. It was found that degradation of HA on the TiO(2)/GAC composite was facilitated by the synergistic relationship between surface adsorption characteristics and photocatalytic potential. The fitting of experimental results with the Langmuir-Hinshelwood (L-H) model showed that the reaction rate constant and the adsorption constant values were 0.1124 mg/(L min) and 0.3402 L/mg. The latter is 1.7 times of the calculated value by fitting the adsorption equilibrium data into the Langmuir equation.     

TiO_2-Fe_3O_4/MIL-101(Cr)磁性复合光催化材料的制备及其光催化性能

采用原位水热法合成了TiO_2-Fe_3O_4/MIL-101(Cr)磁性复合光催化材料,利用XRD、SEM、UV-Vis DRS、BET和磁学测量系统对复合光催化材料的结构和性能进行了表征,并以亚甲基蓝(MB)为模拟污染物,研究了该复合光催化材料的可见光催化活性,并考察了光催化材料的稳定性。结果表明:巯基官能化的Fe_3O_4和TiO_2与MIL-101(Cr)结合成功,复合后的TiO_2-Fe_3O_4/MIL-101(Cr)光催化材料的可见光响应范围得到明显拓宽;当TiO_2的添加量为400mg时所制得的磁性复合光催化材料具有相对较好的光催化降解效果,经过120min光照后,对MB的去除率高达80%;该磁性复合光催化材料具有良好的稳定性和磁分离性能。     

Mechanical properties of TiO2-filled CNT/PMMA composites

ABSTRACT

The present study investigated the effect of TiO₂ fillers on the mechanical properties of CNT/PMMA composites. TiO₂/PMMA/CNT composites were prepared by using twin screw extruder and test samples by injection moulding. Results indicated that incorporation of CNT in PMMA causes decreases in tensile stress, elongation at break, and on impact properties. It is observed that addition of CNT and TiO₂ seems to be beneficial in increasing mechanical strength via increasing the interface dispersed phase.     

Dye-sensitized TiO2 film with bifunctionalized zones for photocatalytic degradation of 4-cholophenol

A new strategy to photocatalytic degradation of 4-cholophenol (4-CP) under visible light irradiation was described. The TiO₂ film deposited on an ordinary glass sheet was distributed into two zones. One zone was sensitized by N719 dye and fabricated to be a sandwich type cell with a similar structure of dye-sensitized solar cells. The other zone was inserted into pollutants solution for degradation. A highly oxidized overvoltage anode was achieved from the dye-sensitized zone. The bifunctionalized TiO₂ film and the anode could degrade 4-chlorophenol in two separate reactors with 97% and 96% removal of 4-CP after 5 h, respectively. The degradation efficiency could be improved by addition of FeSO₄. The as-prepared bifunctionalized TiO₂ film was comparably stable in the process of degradation.     

TiO2 hydrosols with high activity for photocatalytic degradation of formaldehyde in a gaseous phase

Two types of TiO2 hydrosols (TOSO and HTO) were prepared from titanium sulfate (TiOSO4) and metatitanic acid (H2TiO3) by a chemical precipitation-peptization method, respectively. The prepared hydrosols were characterized by means of X-ray diffraction, particle size distribution, scanning electron microscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller and Barret-Joyner-Halender methods. The results showed that the TiO2 hydrosols with an anatase crystal structure had smaller particle sizes, higher surface areas, larger pore volume, and higher transparence than Degussa P-25 suspension. The photocatalytic activity of the TiO2 hydrosols was evaluated for formaldehyde degradation under UVA illumination in a gaseous phase. The results demonstrated that the photocatalytic activity with the catalyst loading of 2mgcm(-2) was ranked as an order of HTO>TOSO>P-25. The photocatalytic activity was further studied using the HTO catalyst under different experimental conditions. The results showed that catalyst loading, relative humidity, and initial concentration could influence the efficiency of HCHO photocatalytic degradation. It was found that a catalyst loading of more than 2mgcm(-2) and a relative humidity of 55% were two essential conditions for achieving the best performance under these experimental conditions. The repeated experiments indicated that the HTO catalyst was reasonably stable and could be repeatedly used for the HCHO oxidation under UVA irradiation. This investigation would be helpful to promote the application of TiO2 photocatalytic technique for indoor air purification.     

Hydrothermal preparation and characterization of TiO2:AC composites

A new photocatalyst titania:activated carbon (TiO₂:AC) composite was prepared by impregnating anatase type TiO₂ nanoparticulates onto the activated carbon surface through a mild hydrothermal route. A varied ratio of TiO₂ to AC was considered for impregnation. As-prepared TiO₂:AC composite was characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET surface area and positron annihilation lifetime spectroscopy (PALS). Powder XRD results showed the persisting nature of anatase phase of TiO₂ deposited on the activated carbon surface. The BET, FTIR and PALS results revealed the impregnation threshold. The TiO₂ particulates were well adhered and uniformly dispersed on the carbon surface as confirmed by SEM.     

Preparation and visible-light photocatalytic activity of In2S3/TiO2 composite

A novel In₂S₃/TiO₂ composite with visible-light photocatalytic activity was prepared by a chemical precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope and UV–vis diffuse reflectance spectroscopy. Under both UV- and visible-light irradiation, the In₂S₃/TiO₂ composite shows good photocatalytic activity to degrade methyl orange, ascribed to the absorption of visible light by In₂S₃ sensitizer and enhanced separation of photoinduced electron–hole pairs in the composite semiconductors.     

Efficient mineralization of dimethyl phthalate by catalytic ozonation using TiO2/Al2O3 catalyst

The removal of dimethyl phthalate (DMP), which is a pollutant of concern in water environments, was carried out by catalytic ozonation with TiO₂/Al₂O₃ catalysts. The heterogeneous catalytic ozonation was an ozonation process combined with the catalytic and adsorptive properties of the TiO₂/Al₂O₃ catalysts to significantly accelerate the mineralization efficiency. Semi-batch ozonation was performed under various experimental conditions including the fed ozone concentration, catalyst type, catalyst dosage, and ultraviolet radiation on the degradation of DMP. The complete removal of DMP was efficiently achieved by both sole and catalytic ozonation; meanwhile, the presence of the catalysts slightly accelerated the elimination rate of DMP. On the other hand, the mineralization efficiency, in terms of total organic carbon (TOC) removal, was substantially enhanced by employing the TiO₂/Al₂O₃ catalyst. The mineralization efficiency using the TiO₂/Al₂O₃ catalyst was the highest, followed in decreasing order by the Al₂O₃ catalyst, the TiO₂ catalyst, and sole ozonation. In addition, the use of the TiO₂/Al₂O₃ catalyst would increase the utilization efficiency of the fed ozone, especially in the late ozonation period. Furthermore, the decrease in the catalytic activity of the TiO₂/Al₂O₃ catalyst after multi-run experiments can be mostly recovered by an incineration process at a high temperature.