Modified microwave method for the synthesis of visible light-responsive TiO2/MWCNTs nanocatalysts

Recently, TiO₂/multi-walled carbon nanotube (MWCNT) hybrid nanocatalysts have been a subject of high interest due to their excellent structures, large surface areas and peculiar optical properties, which enhance their photocatalytic performance. In this work, a modified microwave technique was used to rapidly synthesise a TiO₂/MWCNT nanocatalyst with a large surface area. X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller measurements were used to characterise the structure, morphology and the surface area of the sample. The photocatalytic activity of the hybrid nanocatalysts was evaluated through a comparison of the degradation of methylene blue dye under irradiation with ultraviolet and visible light. The results showed that the TiO₂/MWCNT hybrid nanocatalysts degraded 34.9% of the methylene blue (MB) under irradiation with ultraviolet light, whereas 96.3% of the MB was degraded under irradiation with visible light.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Microwave hydrothermal synthesis and photocatalytic properties of TiO2/BiVO4 composite photocatalysts

TiO₂/BiVO₄ composite photocatalysts with heterojunction structures were synthesized by the one-step microwave hydrothermal method. The physical and photophysical properties of the as-prepared photocatalysts were fully characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), UV–vis diffuse reflectance spectra, photoluminescence (PL) and BET surface area analysis. The photocatalytic activities were evaluated by the decolorization of rhodamine B under UV and simulated sun-light irradiation. The results reveal that the as-prepared TiO₂/BiVO₄ composites exhibit higher photocatalytic activities than pure BiVO₄. The 20% TiO₂/BiVO₄ sample shows the best photocatalytic activity. The enhancement of photocatalytic activity is mainly attributed to the increasing separation rate of photogenerated charge carriers. The possible photocatalytic mechanism is discussed on the basis of the calculated energy band positions.     

Photoassisted mineralization of remazole red F3B over NiO/TiO2 and CdO/TiO2 nanoparticles under simulated sunlight

In this work, a series of titania-supported NiO and CdO materials were synthesized by a modified sol-gel process. The prepared photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). The activities of titania-supported NiO and CdO photocatalysts for photocatalytic degradation of Remazole Red F3B (RR) dye, under simulated sunlight, were investigated. The photocatalytic mineralization of an RR dye solution over various NiO-x/TiO₂ and CdO-x/TiO₂ photocatalysts under simulated sunlight was investigated. It was worthy noticing that the photocatalytic activity of titania improved using the prepared catalysts. The prepared TiO₂, NiO-5/TiO₂, and CdO-2/TiO₂ photocatalysts exhibited higher photocatalytic activity under simulated sunlight than did commercial TiO₂. The prepared photocatalysts were stable after photocatalytic degradation of the dye. The observed photocatalytic mineralization of the dye was 51 and 71% over NiO-10/TiO₂ and CdO-2/TiO₂ after 180 min of irradiation, respectively. Juxtaposing a p-NiO-5/TiO₂ semiconductor provided a potential approach for decreasing charge recombination. The prepared photocatalystsNiO-5/TiO₂ and CdO-2/TiO₂ are promising composites for the solar detoxification of textile wastewater.     

Fullerene modification CdSe/TiO2 and modification of photocatalytic activity under visible light

CdSe, CdSe-TiO₂, and CdSe-C₆₀/TiO₂ composites were prepared using sol–gel method, and their photocatalytic activity was evaluated by measuring the degradation of rhodamine B solutions under visible light. The surface area, surface structure, crystal phase, and elemental identification of these composites were characterized by nitrogen adsorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and UV-visible (vis) absorption spectrophotometry. XRD showed that the CdSe-C₆₀/TiO₂ composite contained a typical single and clear anatase phase. SEM of the CdSe-C₆₀/TiO₂ composites revealed a homogenous composition in the particles. EDX revealed the presence of C and Ti with strong Cd and Se peaks in the CdSe-C₆₀/TiO₂ composite. The degradation of dye was determined by UV–vis spectrophotometry. An increase in photocatalytic activity was observed and attributed to an increase in the photoabsorption effect by fullerene and the cooperative effect of the CdSe. The repeatability of photocatalytic activity was also tested in order to investigate the stability of C₆₀ and CdS-C₆₀/TiO₂ composites.     

The dependence of the photocatalytic activity of TiO2/carbon nanotubes nanocomposites on the modification of the carbon nanotubes

Nanostructural TiO₂/modified multi-wall carbon nanotubes photocatalysts were prepared by hydrolysis of Ti(iso-OC₃H₇)₄ providing chemical bonding of anatase TiO₂ nanoparticles onto oxidized- or amino-functionalized multi-wall carbon nanotubes (MWCNT). The processes of functionalization of the MWCNT and the deposition of TiO₂ influence the photocatalytic activity of the synthesized nanocomposites. The phase composition, crystallite size, and the structural and surface properties of the obtained TiO₂/modified-MWCNT nanocomposite were analyzed from XRD, FEG-SEM, TEM/HRTEM and FTIR data, as well low temperature N₂ adsorption. In the photocatalytic study, the TiO₂/oxidized-MWCNT catalyst showed the highest and the TiO₂/amino functionalized-MWCNT catalysts somewhat lower degradation rates, indicating that the enhancement of photocatalysis was supported by the more effective electron transfer properties of the oxygen- than amino-containing functional groups, which support the efficient charge transportation and separation of the photogenerated electron-hole pairs.     

Synthesis and photocatalytic performance of PVA/TiO2/graphene‐MWCNT nanocomposites for dye removal

TiO₂/graphene‐MWCNT nanocomposite was prepared using solvothermal reaction for the effective distribution of TiO₂ nanoparticles on carbonaceous materials. TiO₂/graphene‐MWCNT nanocomposite was immobilized in poly(vinyl alcohol) (PVA) matrix for a convenient recovery after wastewater purification. MWCNT was incorporated in a nanocomposite not only to prevent the restacking of graphene but also to increase the electron transfer from TiO₂. The detailed characterization of the nanocomposite was performed using SEM, EDX, XRD, XPS, and FTIR. The photocatalytic performance of PVA/TiO₂/graphene‐MWCNT nanocomposite was investigated by UV spectroscopy on the basis of degradation of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite showed improved photocatalytic decomposition of more than 70% of residual dye left in case of using PVA/TiO₂/graphene nanocomposite due to the improved electron transfer and the higher adsorption of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite was suitable as a promising material for the recyclable photocatalytic wastewater purification system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40715.     

Recovery and reuse of TiO<Subscript>2</Subscript> photocatalyst from aqueous suspension using plant based coagulant - A green approach

Separation of TiO₂ from aqueous suspension is a major constraint in heterogeneous photocatalytic water treatment. As an alternative for existing less effective immobilization techniques, the application of plant based coagulant for the recovery and reuse of TiO₂ was investigated for the first time. Aqueous extract derived from seeds of Strychnos potatorum was found to be an effective coagulant for the sedimentation of TiO₂. Further, the potential for recovery and reuse of the sedimented photocatalysts TiO₂, was investigated by photocatalytic degradation of rhodamine B and terephthalic acid tests. The photocatalytic degradation experiments with recovered catalyst obey pseudo first-order kinetics with enhanced photocatalytic activity than that of the pure TiO₂. The investigation of recovered catalysts with XRD, BET, SEM etc., suggests that there is no change in surface and morphological properties when compared with pure TiO₂ and the recovered catalysts are highly suitable for recycle and reuse.     

Efficient photocatalytic degradation of methylene blue over BiVO4/TiO2 nanocomposites

BiVO₄/TiO₂ nanocomposites were successfully synthesized by coupling the modified sol-gel method with hydrothermal method. The samples were physically characterized X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer, Emmett and Teller (BET)-specific surface area, UV–vis diffuse reflectance spectrophotometry, zeta potential, and photoluminescence techniques. The BiVO₄/TiO₂ nanocomposites exhibited good photocatalytic activity in degradation of methylene blue under simulated solar light irradiation. The photodegradation of methylene blue demonstrated that 0.5BiVO₄/0.5TiO₂ photocatalyst exhibited much enhanced photoactivity than pure BiVO₄ and TiO₂. Based on the obtained results, the as-prepare BiVO₄/ TiO₂ nanocomposite possessed great adsorptivity of methylene blue, extended light adsorption range, and efficient charge separation properties. Overall, this work could provide new insights into the fabrication of a BiVO₄/TiO₂ composite as high performance photocatalyst and promise as a solar light photocatalyst for dye wastewater treatment.     

Graphene-supported flocculent-like TiO2 nanostructures for enhanced photoelectrochemical activity and photodegradation performance

Here, novel graphene/TiO₂ nanocomposite has been successfully prepared by loading flocculent-like titanate nanostructure in graphene sheets via hydrothermal method plus a subsequent annealing process. The as-obtained hybrid was characterized by X-ray diffraction, scanning electron microscopy with an energy dispersive spectroscope (EDS), Raman, and UV–vis diffuse reflectance spectra, respectively. The photoelectrochemical activities and photocatalytic degradation performance of methyl orange under the illumination of ultraviolet light were investigated, and the flocculent-like TiO₂/graphene composites was found to have a superior photocatalytic activity compared to flocculent-like titanate nanostructure and commercial anatase TiO₂ powder, which can be attributed to the improved light absorption and extremely efficient charge separation of the hybrid structure. The results suggest that the as-prepared flocculent-like TiO₂/graphene composite is a promising photocatalyst for photoelectrochemical hydrogen production and pollution removal.     

Facile synthesis of Cu<Subscript>x</Subscript>O (x = 1, 2)/TiO<Subscript>2</Subscript> nanotube arrays as an efficient visible-light driven photocatalysts

TiO₂ nanotube arrays (TNTs) modified with Cu_xO (x = 1, 2) were prepared by a simple impregnation-calcinations method. The obtained samples were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy , UV–Vis diffuse reflectance spectroscopy and photocurrent tests. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. Compared with pure TNTs, the Cu_xO/TNTs composite exhibited much higher photocatalytic activity under visible-light irradiation (λ > 420 nm). The photocatalytic activity of the composite was related to impregnation time of the copper nitrate solution, and an optimal time was 2 h. The activity of 2-Cu_xO/TNTs displayed 4.9 times as high as that of pure TNTs. The enhanced photocatalytic performance is mainly attributed to the synergistic effects of initiating visible-light absorption and the matched band edge positions of Cu₂O, CuO and TiO₂. Also, a possible mechanism on the Cu_xO/TNTs photocatalytic degradation of RhB is proposed. Overall, the inexpensive and environmentally friendly photocatalyst, as promising materials, could be used to remove some aquatic pollutants in the field of water purification.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Synthesis of carbon quantum dots/TiO2 nanocomposite for photo-degradation of Rhodamine B and cefradine

Pure TiO₂ and carbon quantum dots (CQDs)-doped TiO₂ nanocomposite (CQDs/TiO₂ nanocomposite) were prepared by a sol-gel approach for photocatalytic removal of Rhodamine B and cefradine. Analyses by Transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), UV–visible spectroscopy and X-ray powder diffraction (XRD) confirmed the successful formation of CQDs/TiO₂ heterostructure. The as-prepared TiO₂ and CQDs/TiO₂ composite possessed small particles, spherical-like shape, and anatase crystal form. Meanwhile, Rhodamine B and cefradine were chosen to evaluate the photocatalytic activity of TiO₂ and CQDs/TiO₂ composite. Results revealed that with the facile decoration of CQDs, the absorption of photocatalyst was extended into visible light region and photocatalytic activity was improved in comparison with pure TiO₂. Furthermore, the mechanism for the improvement of the photocatalytic performance of the composites was discussed on the basis of the results. CQDs play an important role in the photocatalytic process, due to their superior ability to extend the visible absorption and produce more electrons and electron–hole pairs for the degradation of pollutants. In all, the paper offers further insights into the development of CQDs/TiO₂ nanocomposite as photocatalyst for the degradation of antibiotics.     

Photoelectrocatalytic degradation of bisphenol A in aqueous solution using a Au–TiO2/ITO film

A series of Au–TiO₂/ITO films with nanocrystaline structure was prepared by a procedure of photo-deposition and subsequent dip-coating. The Au–TiO₂/ITO films were characterized by X-ray diffraction, scanning electronic microscopy, electron diffraction, X-ray photoelectron spectroscopy, and UV–VIS diffuse reflectance spectroscopy to examine the surface structure, chemical composition, the chemical state of metal, and the light absorption properties. The photocatalytic activity of the Au–TiO₂/ITO films was evaluated in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of bisphenol A (BPA) in aqueous solution. Compared with a TiO₂/ITO film, the degree of BPA degradation using the Au–TiO₂/ITO films was significantly higher in both the PC and PEC processes. The enhancement is attributed to the action of Au deposits on the TiO₂ surface, which play a key role by attracting conduction band photoelectrons. In the PEC process, the anodic bias externally applied on the illuminated Au–TiO₂/ITO film can further drive away the accumulated photoelectrons from the metal deposits and promote a process of interfacial charge transfer.     

Preparation of ordered TiO2 nanofibers/nanotubes by magnetic field assisted electrospinning and the study of their photocatalytic properties

Ordered-and-oriented TiO₂ nanofibers and nanotubes were prepared by magnetic field-assisted electrospinning, and photocatalytic properties of all samples were analyzed under UV–Vis shine. TiO₂ nanofibers/nanotubes prepared by magnetic field-assisted electrospinning showed better degradation effect on rhodamine B, reduced the band gap, increased the contact area of organic pollutants with the sample and higher photocatalytic activity than TiO₂ nanofibers/nanotubes prepared by classical electrospinning. The product obtained after high temperature annealing was a mixed phase of rutile phase and anatase phase and could be advantageous to the segregate of photogenic electron hole pairs and enhance the high dye absorption capacity; Surface roughness could increase more active sites and accelerate the reaction rate of photocatalytic activity; the addition of magnetic field regulated the morphology of TiO₂, and narrowed the band gap to favor photocatalytic performance. The magnetic field-assisted electrospinning study prepared in this paper was an easy-to-use and versatile method for the preparation of ordered TiO₂ nanomaterials, which could be easily extended to practical applications or other materials for photocatalysis and water cleavage.     

Mechanism of Charge Transfer in the Transition Metal Ion Doped TiO2 with Bicrystalline Framework of Anatase and Rutile: Photocatalytic and Photoelectrocatalytic Activity

The high photocatalytic activity of the Mn²⁺ doped TiO₂ with bicrystalline framework of anatase and rutile is probed for the degradation of benzene under solar light with/without applied bias. The enhanced activity is attributed to the transfer of electrons from the rutile to electron trapping/lattice trapping sites of anatase and also to the impurity level created by the dopant which favours effective charge separation. The shallow detrapping nature of Mn²⁺ dopant additionally contributes to the overall enhancement in the photocatalytic activity especially in the presence of applied electric field.     

Hollow hybrid titanate/Au@TiO2 hierarchical architecture for highly efficient photocatalytic application

Hollow hybrid titanate/Au@TiO₂ hierarchical architecture consisting of titanate and anatase titanium dioxide (TiO₂) loaded with Au nanoparticles was prepared via a sol-impregnation method combined with a hydrothermal etching process. The titanate/Au@TiO₂ architecture possesses unique hollow spherical configuration with Au nanoparticles loaded in the middle of titanate and TiO₂ shells and allows to be used as a microreactor for photocatalytic application. The hybrid titanate/Au@TiO₂ photocatalyst shows significantly enhanced photocatalytic activity on degradation of methylorange (MO) under UV light irradiation due to the lower electron–hole pairs recombination rate arisen from the synergistic effect of titanate-Au-TiO₂ in hybrid hierarchical architecture.     

ML-WO3/TiO2异质结的制备及其对罗丹明B的光催化降解

采用空间限域法制备了单层三氧化钨纳米片(ML-WO₃),然后将其与TiO₂复合得到ML-WO₃/TiO₂纳米材料,被用来在模拟太阳光下对罗丹明B进行光催化降解。ML-WO₃/TiO₂的组成和光学特性通过扫描电镜、透射电镜、高分辨透射电镜、X射线衍射、紫外-可见吸收光谱和光致发光光谱手段进行表征。结果证实,纳米ML-WO₃/TiO₂克服了纯TiO₂带隙较大的缺陷,在全波段太阳光表现出比ML-WO₃和TiO₂更强的吸收性能,ML-WO₃与TiO₂之间具有明显的协同效应。活性物种捕获实验表明.OH和.O_2^-自由基是RhB降解的主要活性物种。ML-WO₃和TiO₂之间构建的Z型异质结电荷转移路径能够保证光生载流子的高效分离和重组。在5次循环实验后ML-WO₃/TiO₂的光催化活性仍能接近80%,具有良好的光化学稳定性。通过高效液相色谱-质谱检测RhB的中间产物,推测了RhB可能的降解路径。     

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

A phase transformation of micron‐sized TiO₂ powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO₂ with high associated photocatalytic activity. Heat‐treated micron‐sized TiO₂ powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO₂ powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO₂ photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO₂ is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry