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.     

Photocatalytic oxidation of 2-propanol under visible light irradiation on TiO<Subscript>2</Subscript> thin films prepared by an RF magnetron sputtering deposition method

Visible light-responsive TiO₂ (Vis-TiO₂) thin films able to absorb UV and visible light in wavelength regions of 250–600 nm were successfully developed by applying a radio-frequency magnetron sputtering deposition method. These Vis-TiO₂ thin films exhibited high activity for the photocatalytic oxidation of 2-propanol diluted in water even under visible light irradiation (λ ≥ 450 nm). The photocatalytic activity of Vis-TiO₂ thin films was dramatically enhanced by the deposition of Pt particles on the surface. Secondary ion mass spectrometry measurements revealed that Pt particles are distributed from the top surface to the deep bulk of Vis-TiO₂ thin films with a columnar structure. The unique columnar structure of Vis-TiO₂ thin films plays an important role in the high photocatalytic performance.     

TiO<Subscript>2</Subscript>/TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanocomposite and its acetaldehyde photodecomposition ability

Nitrogen-doped titania was coupled with the commercial titania nanoparticles by mechanical milling in liquid medium. The as-prepared nanocomposites (TiO₂/TiO_2−x N _y ) were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area, UV–Vis spectroscopy, chemiluminescence, and acetaldehyde decomposition activity techniques. When a small amount of nitrogen-doped titania was added into the commercial titania, higher intensity and longer lifetime of ¹O₂ was observed, and the photocatalytic activity was efficiently improved. The TiO_2−x N _y acts as the acceptor of photoinduced holes. The recombination of the electron-hole was effectively depressed by the heterogeneous electron transfer. This could be an effective way to obtain highly active photocatalysts.     

Preparation of nanocrystalline Fe-doped TiO<Subscript>2</Subscript> powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO₂ powders were prepared using TiOSO₄, urea, and Fe(NO₃)₃ · 9H₂O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO₂, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m²/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe³⁺ and Fe²⁺ have been detected on the surface of TiO₂ powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO₂ powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO₂ was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO₂ powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.     

Synthesis and characterization of novel InVO<Subscript>4</Subscript>–TiO<Subscript>2</Subscript> thin films using the low temperature sol

The InVO₄ sol was obtained by a mild hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). Novel visible-light activated photocatalytic InVO₄–TiO₂ thin films were synthesized through a sol–gel dipping method from the composite sol, which was obtained by mixing the low temperature InVO₄ sol and TiO₂ sol. The photocatalytic activities of the new InVO₄–TiO₂ thin films under visible light irradiation were investigated by the photocatalytic discoloration of methyl orange aqueous solution. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–Vis absorption spectroscopy (UV–Vis). The results revealed that the InVO₄ doped thin films enhanced the methyl orange degradation rate under visible light irradiation, 3.0 wt% InVO₄–TiO₂ thin films reaching 80.1% after irradiated for 15 h.     

Decomposition of rhodamine 6G in the presence of titania coupling coupled with carbon source as photocatalyst under visible light excitation

Heterogeneous photocatalytic degradation of N-containing R6G dye was achieved by visible light-activated carbon doped TiO₂ (C-TiO₂) nanoparticles, synthesized by a low-temperature wet-chemical technique using glucose as carbon source. The structural and physicochemical properties of C-TiO₂ were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and FT-IR spectroscopy. Compared with the pure TiO₂, the carbon modified nanomaterials exhibited enhanced absorption in the broad visible-light region together with an apparent red shift in the optical absorption edge. The resulting carbon-doped TiO₂ catalyst was employed as an effective photocatalyst for degradation of Rhodamine 6G (R6G) in aqueous solutions under visible light irradiation (λ > 420 nm). In addition, the intrinsic mechanism of visible light-induced photocatalytic oxidation of organic compounds on the carbon-doped titania was proposed and discussed.     

N,B, Si-tridoped mesoporous TiO<Subscript>2</Subscript> with high surface area and excellent visible-light photocatalytic activity

N, B, Si-tridoped mesoporous TiO₂, together with N-doped, N, B-codoped and N, Si-codoped TiO₂, was prepared by a modified sol–gel method. The samples were characterized by wide-angle X-ray diffraction (WAXRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, UV–visible adsorbance spectra (UV–vis) and X-ray photoelectron spectra (XPS). The N, B, Si-tridoped mesoporous TiO₂ showed small crystallite size, large specific surface area (350 m²/g), uniform pore distribution (3.2 nm) and strong absorption in the visible light region. The photocatalytic activities of the samples were evaluated by the photodegradation of 2,4-dichlorophenol (2,4-DCP) aqueous solution. The N, B, Si-tridoping sample exhibited much higher photocatalytic activity compared with other synthesized photocatalysts. The high activity could be attributed to the strong absorption in the visible light region, large specific surface area, small crystallite size, large amount of surface hydroxyl groups, and mesoporosity.     

Preparation of nanocrystalline TiO<Subscript>2</Subscript> powders for photocatalytic oxidation of phenol

Nanocrystalline TiO₂ powders in the anatase, rutile, and mixed phases prepared by hydrolysis of TiCl₄ solution were of ultrafine size (<7.2 nm) with high specific surface areas in the range 167 to 388 m²/g. In the photocatalytic degradation of phenol as model reaction, the photocatalytic properties of TiO₂ nanoparticles were evaluated by use of UV–vis absorption spectroscopy and total organic carbon (TOC) content. The synthetic mixed-phase TiO₂ powder calcined at 400 °C had higher activity than pure anatase or rutile; it degraded more than 90% phenol to CO₂ (evaluated by TOC) after irradiation with near UV light for 90 min at a catalyst loading of 0.4 g/L. The TOC results indicated that rutile TiO₂ crystallites of particle size 7.2 nm resulted in much better photocatalytic performance than particles of larger size. This result suggested that some intermediates, not determined by UV–vis absorption spectroscopy, existed in the solution after the photocatalytic process over the rutile TiO₂ photocatalysts of larger crystallite size.     

Preparation and characterization of titania/tetratitanate nanocomposites

Nanocomposite titania/tetratitanate particles were prepared by utilizing the electrostatic interaction of the colloidal tetratitanate nanosheets and TiO₂ powders through dispersing TiO₂ into tetratitanate solution at pH4. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, chemical analysis, and photocatalytic activity measurement. The crystallites of Ti₄O₉^2? in the form of tetratitanate nanosheets have lateral size around 100 nm. The visible light responsive photocatalytic activity of rutile nanoparticles could be improved by forming nanocomposite with layered tetratitanate. The high specific surface area of this kind of composite and a certain amount of mesopores in nanocomposite powder could be responsible for better performance in the NO elimination.     

Application of beam irradiation in preparation of visible light responsive TiO2 films

TiO₂ films were prepared by sol-gel method. In order to improve the utilization of light, the technologies of implantation of transition metal ions (V⁺ and Cr⁺) and electron beam irradiation to deposit noble metal particles (Ag and Pt) were used. A red shift was found in the spectrum of modified TiO₂ films. The photocatalytic experiments showed that the photocatalytic ability under visible light irradiation could be improved dramatically by both the implantation of transition metal and the electron beam irradiation. __________ Translated from Chinese Journal of Catalysis, 2007, 28(1): 39–44 [译自: 催化学报]     

Efficient decomposition of liquid waste containing EDTA by advanced oxidation nanotechnology

Degradation of ethylenediaminetetraacetic acid (EDTA) present in the liquid waste was demonstrated by photocatalytic oxidation route by using nanoparticles of anatase titania. Nano sized titania photocatalyst was synthesized using sol–gel method coupled with ultrasonication mode and characterized using X-ray diffraction, transmission electron microscope, BET, Fourier transform infrared spectroscopy and TG–DTA. A cylindrical photoreactor was employed for the degradation studies. Five milligram of the nano anatase TiO₂ + 0.5 ml of 30% H₂O₂ were employed as catalysts for the degradation studies of 1,000 mg/L EDTA. EDTA degradation was followed by a complexometric titration method. Complete degradation of 1,000 mg/L EDTA could be achieved in 90 min and the photocatalytic efficiency of the synthesized titania photocatalyst was higher than that of P-25 TiO₂ for EDTA degradation. The influence of pH on the degradation of EDTA follow the order acidic > neutral > alkaline. More than ten fold increases in the decontamination factors were obtained for the chemical precipitation step for the liquid waste containing degraded EDTA compared to liquid waste without EDTA degradation.     

Simple preparation of Mn–N-codoped titania photocatalyst with visible light response

Mn–N-codoped TiO₂ nanocrystal photocatalysts responsive to visible light were synthesized for the first time by a simple hydrothermal synthesis method. X-ray powder diffraction (XRD) measurement indicated that all the photocatalysts have an anatase crystallite structure, and that increase of the doping concentration had little effect on the structure and particle size. Compared to N-doped TiO₂, a shift of the absorption edge of Mn–N-codoped TiO₂ to a lower energy and a stronger absorption in the visible light region were observed. The Mn–N-codoped TiO₂ showed higher photocatalytic reactivity than undoped TiO₂ or N-doped TiO₂ for the photodegradation of rhodamine B (RhB) under visible light irradiation. The highest photocatalytic activity was achieved on 0.4 mol% Mn–N–TiO₂ calcined at 673 K.     

Sol–gel and impregnated prepared silver TiO<Subscript>2</Subscript> semiconductors as photocatalysts for the UV decomposition of 2,4-<Emphasis Type="SmallCaps">d</Emphasis>: a comparative study of the preparation method

UV-photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-d) was studied on Silver–TiO₂ semiconductors prepared by co-gelling silver acetylacetonate and titanium butoxide (TiO₂–Ag) or by incipient impregnation with silver acetylacetonate (0.5 wt% Ag) of bare TiO₂ sol–gel and TiO₂–P25 supports. The comparative study shows that only a slight modification on the specific surface area was obtained on the TiO₂–Ag sample (60 m²/g) as compared to the TiO₂ sol–gel bare support (65 m²/g). XRD patterns of the samples show anatase as the crystalline phase present in the sol–gel TiO₂ preparations. By means of HRTEM and HAADF-STEM electron microscopy techniques, silver nanoparticles (<12.0 nm) were identified which are very small to be detected by XRD. The photocatalytic oxidation of the herbicide 2,4-d used as a model of contaminant show for the kinetic parameter t_1/2 values of 45 min for the TiO₂–Ag sample, while for the impregnated Ag/TiO₂ and Ag/P25 nanomaterials t_1/2 was 124 and 66 min, respectively. The higher photoactivity of the TiO₂–Ag photocatalyst is attributed to a combined effect of the silver nanoparticles in interaction with the titania semiconductor.     

Tuning the properties of a black TiO2-Ag visible light photocatalyst produced by a rapid one-pot chemical reduction

A highly efficient black TiO₂-Ag photocatalytic nanocomposite, active under both UV and visible light illumination, was synthesized by decorating the surface of 25 nm TiO₂ particles with Ag nanoparticles. The material was obtained via a rapid, one-pot, simple (surfactant and complexing agent free) chemical reduction method using silver nitrate and formaldehyde as a metal salt and reducing agent, respectively. The nanocomposite shows an increase of over 800% in the rate of photocatalytic methylene blue dye degradation, compared to commercial unmodified TiO_2, under UV-VIS illumination. Unlike pure TiO₂, the nanocomposite exhibits visible light activation, with a corresponding drop in optical reflectance from 100% to less than 10%. The photocatalytic properties were shown to be strongly enhanced by post-reduction annealing heat treatments in air, which were observed to decrease, rather than coarsen, silver particle size, and increase particle distribution. This, accompanied by a variation in the silver surface oxidation states, appear to dramatically affect the photocatalytic efficiency under both UV and visible light. This highly active photocatalyst could have wide ranging applications in water and air pollution remediation and solar fuel production.     

Enhanced photocatalytic activity for titanium dioxide by co-modification with copper and iron

A copper(II) and iron(III) co-modified titanium dioxide nano material was prepared by a simple sol–gel process using titanium(IV) isopropoxide plus copper(II) and iron(III) nitrates as raw materials. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence spectra. The XRD results showed that the undoped TiO₂ nanoparticles mainly include anatase phase while the Cu, Fe-codoped TiO₂ nanoparticles showed a mixture of anatase phase with a small fraction of rutile phase displaying higher activity than the pure anatase phase. Optical characterization showed that the codoping with copper(II) and iron(III) resulted in a red shift of adsorption and lower recombination probability between electrons and holes, which were associated with high photocatalytic activity of the Cu, Fe-codoped TiO₂ nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of the samples was tested by aqueous methyl orange degradation. The capability of the codoped catalyst was much higher than that of the pure TiO₂ catalyst under visible irradiation. A mechanism is proposed in order to account for the enhanced catalytic activity.     

Visible-light-driven photocatalytic degradation of microcystin-LR by Bi-doped TiO<Subscript>2</Subscript>

Bi-doped nano-crystalline TiO₂ (Bi–TiO₂) has been synthesized by sonocrystallization at low temperature. The Bi–TiO₂ materials have narrower bandgaps than pristine TiO₂, which endow them with significant visible light absorption. Accordingly, these materials had enhanced photocatalytic activity in the degradation of organic dye pollutants and the cyanotoxin microcystin-LR (MC-LR) under visible irradiation. It was found that degradation of MC-LR is rather efficient. After irradiation with visible light for 12 h the original MC-LR was removed completely, and 78% of the organic carbon was mineralized into CO₂ after irradiation for 20 h. The hydroxyl radical (·OH) is the major active species responsible for the degradation reaction. Identified intermediates primarily originate from attack of ·OH radicals on the double bonds between C4 and C5 (C6 and C7) of Adda and the ethylenic bond of Mdha in MC-LR. Some peptide bonds are also broken with longer irradiation time.     

Photocatalytic degradation of methylene blue on Fe3+-doped TiO2 nanoparticles under visible light irradiation

Fe³⁺-doped TiO₂ composite nanoparticles with different doping amounts were successfully synthesized using sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultravioletvisible spectroscopy (UV-Vis) diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of Fe³⁺/TiO₂ nanoparticles under visible light irradiation. The influence of doping amount of Fe³⁺ (ω: 0.00%–3.00%) on photocatalytic activities of TiO₂ was investigated. Results show that the size of Fe³⁺/TiO₂ particles decreases with the increase of the amount of Fe³⁺ and their absorption spectra are broaden and absorption intensities are also increased. Doping Fe³⁺ can control the conversion of TiO₂ from anatase to rutile. The doping amount of Fe³⁺ remarkably affects the activity of the catalyst, and the optimum efficiency occurs at about the doping amount of 0.3%. The appropriate doping of Fe³⁺ can markedly increase the catalytic activity of TiO₂ under visible light irradiation. __________ Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(6): 55–56 [译自: 西北师范大学学报(自然科学版)]     

Facile preparation of visible-light-sensitive sulfur–nitrogen-codoped titanium dioxide

S–N-codoped TiO₂ powders have been synthesized through a facile one-step sol–gel method by using tetrabutyltitanate and thiourea as precursors. The S–N-codoped TiO₂ treated at 500 °C showed the highest photocatalytic activity for degrading methylene blue under visible light irradiation. XRD, XPS and UV–vis studies revealed that the high visible-light photocatalytic activity of the doped TiO₂ may originate from the synergetic effect of sulfur and nitrogen codoping into TiO₂.     

Synthesis and characterization of ZnO-doped cupric oxides and evaluation of their photocatalytic performance under visible light

ZnO–CuO binary oxide photocatalysts were synthesized by the liquid phase coprecipitation method. The catalysts were characterized by X-ray diffraction, transmission electron microscopy and UV–vis spectroscopy. The photocatalytic activity of the ZnO–CuO nanocomposites was estimated on the basis of decoloration of methyl orange dye under visible light. The effects of parameters such as calcining temperature, amount of catalyst and pH on the photocatalytic degradation efficiency of methyl orange solutions were investigated in detail. The maximum photocatalytic activity was obtained on ZnO–CuO nanocomposites with a calcining temperature of 350 °C, using a catalyst amount of 0.056 g/L and a pH of 7.5. The visible light-driven capability of ZnO–CuO nanocomposites is much better than that of commercially available TiO₂ photocatalysts under comparable conditions.     

Synergistic effects of sulfation and Fe-doping on the photocatalysis of titania

Fe-doped sulfated titania photocatalysts were prepared by one-step thermal hydrolysis of industrial titanyl sulfate and characterized using XRD, FT-IR, UV–Vis DRS, and N₂ adsorption–desorption techniques. The effects of the volume ratio of pre-adding water to TiOSO₄ on the structure of the titania photocatalysts were investigated. The photocatalytic activities of Fe-doped sulfated titania samples were evaluated using the photooxidation of methylene blue in aqueous solutions under UV light irradiation. The results indicate that Fe-doping induces the red shift of the absorption edge to the visible light range. Meanwhile, sulfur species in the form of sulfate are incorporated into the network of Ti–O–Ti and coordinated to titania in bidentate models, which can effectively promote the separation of the photogenerated electrons and holes. Synergistic effects of both are beneficial for improving the photocatalytic activity of the Fe-doped sulfated titania photocatalysts.