Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

Photocatalytic TiO2 films deposited on cenosphere particles by pulse magnetron sputtering method

In the present study, TiO₂ films were deposited on the surface of cenosphere particles using the modified magnetron sputtering equipment under different working conditions. The resulting films were characterized by field emission scanning electron microscopy (FE-SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The FE-SEM and AFM results show that the grain sizes and root-mean-square (RMS) roughness values of the TiO₂ films increase with the increase in deposition time and film thickness. The XRD results indicate that the film was TiO₂ film and sputtering time is an importance condition to influence the films crystal. With the increasing of sputtering time, the crystallization of the TiO₂ film was increased. The XPS results show that only TiO₂ films existed on the surface of cenosphere particles. In addition, the photocatalytic activities of these films were investigated by degrading methyl orange under UV irradiation. The results suggest that the photocatalytic activity of cenosphere particles with anatase TiO₂ films is remarkable and this catalyst can be applicable for the photocatalytic degradation of other organic compounds under UV lights.     

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。     

Photocatalytic activity of pulsed laser deposited TiO2 thin films in N2, O2 and CH4

We report on pulsed laser deposition of TiO₂ films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO₂ lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO₂ films was red-shifted up to ∼ 480 nm from 360 nm in case of undoped ones.The photocatalytic activity of TiO₂ films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO₂ films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO₂ structures deposited in pure methane and oxygen atmosphere.     

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.     

Photocatalytic performance of very thin TiO2/SnO2 stacked-film prepared by magnetron sputtering

TiO₂/SnO₂ stacked-layers are synthesized by reactive sputter deposition on the glass substrate. Very thin TiO₂/SnO₂ bilayer-photocatalysts exhibited a very high photocatalytic activity for a degradation of gaseous acetaldehyde. Both the control of an electronic structure of TiO₂ overlayer in the near-surface region and the interfacial separation of photogenerated electrons/holes in the TiO₂/SnO₂ stacked-layer are keys to improve the photocatalytic performance.     

Visible-light photocatalysis in nitrogen-carbon-doped TiO2 films obtained by heating TiO2 gel-film in an ionized N2 gas

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO₂ films were obtained by heating a TiO₂ gel in an ionized N₂ gas. The as-synthesized TiO_2−x−yN_xC_y films have shown an improvement over titanium dioxide in optical absorption and photocatalytic activity such as photodegradation of methyl orange under visible light. The process of the oxygen atom substituted by nitrogen and carbon was discussed. Oxygen vacancy induced by the formation of Ti³⁺ species and nitrogen and carbon doped into substitution sites of TiO₂ have been proven to be indispensable for the enhance of photocatalytic activity, as assessed by UV-Vis Spectroscopy and X-ray photoemission spectroscopy.     

Photocatalytic degradation of 2,4-dichlorophenol wastewater using porphyrin/TiO2 complexes activated by visible light

The use of TiO₂ as photocatalyst to degrade the organic compounds is an effective method of oxidation process and has been widely studied in environmental engineering. However, TiO₂ absorbed the UV light which is only small part of sunlight reaching earth surface to activate photocatalytic procedure effectively is a major disadvantage. Therefore, studies on the development of new TiO₂ wherein its photocatalytic activity can be activated by visible light which is the major part of sunlight will be valuable for field application. In this study, we evaluate the photocatalytic degrading efficiency of porphyrins/TiO₂ complexes on the organic pollutants under irradiation with visible light (λ = 419 nm). The results showed that the photodecomposition efficiency of 2,4-dichlorophenol (2,4-DCP) wastewater by using porphyrin/TiO₂ irradiated under visible light for 4 h was up to 42-81% at pH 10. These evidences reveal that the system of porphyrin/TiO₂ complexes has also significantly efficiency of photocatalytic degradation for some hazardous or recalcitrant pollutants under visible light irradiation.     

Determination of photo-catalytic activity of un-doped and Mn-doped TiO2 anatase powders on acetaldehyde under UV and visible light

Titanium dioxide (TiO₂) photocatalytic powder materials doped with various levels of manganese (Mn) were synthesized to be used as additives to wall painting in combating indoor and outdoor air pollution. The heterogeneous photocatalytic degradation of gaseous acetaldehyde (CH₃CHO) on Mn-TiO₂ surfaces under ultraviolet and visible (UV/Vis) irradiation was investigated, by employing the Photochemical Static Reactor coupled with Fourier-Transformed Infrared spectroscopy (PSR/FTIR) technique. Experiments were performed by exposing acetaldehyde (~ 400 Pa) and synthetic air mixtures (~ 1.01 × 10⁵ Pa total pressure) on un-doped TiO₂ and doped with various levels of Mn (0.1-33% mole percentage) under UV and visible irradiation at room temperature. Photoactivation was initiated using either UV or visible light sources with known emission spectra. Initially, the photo-activity of CH₃CHO under the above light sources, and the physical adsorption of CH₃CHO on Mn-TiO₂ samples in the absence of light were determined prior to the photocatalytic experiments. The photocatalytic loss of CH₃CHO on un-doped TiO₂ and Mn-TiO₂ samples in the absence and presence of UV or visible irradiation was measured over a long time period (≈ 60 min), to evaluate their relative photocatalytic activity. The gaseous photocatalytic end products were also determined using absorption FTIR spectroscopy. Carbon dioxide (CO₂) was identified as the main photocatalysis product. It was found that 0.1% Mn-TiO₂ samples resulted in the highest photocatalytic loss of CH₃CHO under visible irradiation. This efficiency was drastically diminished at higher levels of Mn doping (1-33%). The CO₂ yields were the highest for 0.1% Mn-TiO₂ samples under UV irradiation, in agreement with the observed highest CH₃CHO decomposition rates. It was demonstrated that low-level (0.1%) doping of TiO₂ with Mn results in a significant increase of their photocatalytic activity in the visible range, compared to un-doped TiO₂. This elevated activity is lost at high doping levels (1-33%). Finally, the photocatalytic degradation mechanism of CH₃CHO on 0.1% Mn-TiO₂ surfaces under visible irradiation leading to low CO₂ yields is different than that under UV irradiation resulting to high CO₂ yields.     

Photocatalytic degradation of phenol in aqueous solutions by Pr-doped TiO2 nanoparticles

Photocatalytic degradation of phenol in water was examined using Pr-doped TiO₂ nanoparticles. These photocatalysts were synthesized by an acid-peptized sol–gel method from titanium tetra-isopropoxide with different concentrations of Pr(III) dopant and calcination temperatures. Several tools such as XRD, BET surface area, SEM, and EDX, were used to evaluate particle structure, size distribution, and composition. The optical absorption properties of the prepared particles were also measured. Photocatalytic activity of the particles was studied in a batch reactor containing phenol solution with 400 W UV irradiation. Parameters affecting photocatalytic process such as the catalyst crystallinity, light absorption efficiency, the dosage of catalyst, dopant and phenol concentrations were investigated. The Pr-doped TiO₂ showed high activity for photocatalytic degradation of phenol. The presence of Pr ions in the TiO₂ particles would cause a significant absorption shift towards the visible region. The degradation process was optimized using 1 g/L Pr-doped TiO₂ with a Pr(III) concentration of 0.072 mol% after 2 h irradiation. It was shown that photodegradation followed a pseudo-first-order kinetics and the rate constant changed with phenol concentration.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.     

Mn-doped TiO2 nanopowders with remarkable visible light photocatalytic activity

TiO₂ nanocrystalline powders with various Mn-doping levels were synthesized by the sol-gel process using tetrabutyl titanate and manganese nitrate as precursors. The crystal structure, morphology, doping concentration, optical absorption property, and elemental state of the obtained samples were analyzed. TEM results showed that the synthesized TiO₂ powders were anatase nanoparticles about 7 nm in size. EDX and XPS analyses proved the incorporation of Mn ions into the TiO₂ lattice. A remarkable red shift of the absorption edge was achievable by increased Mn content, leading to gigantically narrowed energy gap to permit absorption well into the infrared spectral region. The dramatic optical absorbance of the doped TiO₂ nanopowders in the visible spectral region led to strong photocatalytic activity under visible light illumination, which was observed by measuring the degradation of methylene blue. In contrast, little degradation was observed for the pure TiO₂ powder. The optimum Mn/Ti ratio was observed to be 0.2 at.% for photocatalytic applications.     

Photocatalytic degradation of dyes and organic contaminants in water using nanocrystalline anatase and rutile TiO2

Nanocrystalline TiO₂ was synthesized by controlled hydrolysis of titanium tetraisopropoxide. The anatase phase was converted to rutile phase by thermal treatment at 1023 K for 11 h. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared absorption spectrophotometry (FT-IR) and N₂ adsorption (BET) at 77 K. This study compare the photocatalytic activity of the anatase and rutile phases of nanocrystalline TiO₂ for the degradation of acetophenone, nitrobenzene, methylene blue and malachite green present in aqueous solutions. The initial rate of degradation was calculated to compare the photocatalytic activity of anatase and rutile nanocrystalline TiO₂ for the degradation of different substances under ultraviolet light irradiation. The higher photocatalytic activity was obtained in anatase phase TiO₂ for the degradation of all substances as compared with rutile phase. It is concluded that the higher photocatalytic activity in anatase TiO₂ is due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst.     

等离子体电解氧化法制备多孔TiO2/V2O5复合物膜层及其增强光催化产氢活性

较差的光催化产氢效率极大地阻碍了TiO₂光催化剂的工业化应用。为此,本文在含有NH₄VO₃的磷酸盐溶液中,采用等离子体电解氧化(PEO)法制备了多孔TiO₂/V₂O₅复合膜光催化剂,通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、X射线光电子谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)对其组成、结构及光吸收性质进行了表征,并采用气相色谱评价了薄膜催化剂的光催化产氢性能,研究了电解液中NH₄VO₃含量对膜的结构、组成和光催化产氢性能的影响。结果表明:复合膜催化剂主要由锐钛矿和金红石型TiO₂组成,具有微孔结构,V₂O₅主要以无定形形式存在于膜中,与TiO₂有很强的相互作用,影响TiO₂的晶面间距。研究发现,元素V抑制了TiO₂的结晶和金红石型TiO₂的形成,扩大了薄膜的光学吸收范围。针对Na₂S+ Na₂SO₃溶液中的光催化产氢性能的研究显示,在质量浓度为1 g/L NH₄VO₃的电解液中制备的TiO₂/V₂O₅薄膜的光催化活性最高,优于近年来报道的其他光催化剂。光催化重复实验表明,该复合膜催化剂具有较高的稳定性和较为恒定的光催化活性。     

Photocatalytic effects for the TiO2-coated phosphor materials

This study investigated the photocatalytic behavior of the coupling of TiO₂ with phosphorescent materials. A TiO₂ thin film was deposited on CaAl₂O₄:Eu²⁺,Nd³⁺ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aqueous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO₂-phosphorescent materials, two different samples of TiO₂-coated phosphor and TiO₂–Al₂O₃-coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO₂-coated phosphor powders were different from those of the pure TiO₂ and TiO₂–Al₂O₃-coated phosphor. The absorbance in a solution of the ALD TiO₂-coated phosphor decreased much faster than that of pure TiO₂ under visible irradiation. In addition, the ALD TiO₂-coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO₂–Al₂O₃-coated phosphor did. The TiO₂-coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS).     

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.     

Bactericidal effect of blue LED light irradiated TiO2/Fe3O4 particles on fish pathogen in seawater

This study uses blue LED light (λ_max = 475 nm) activated TiO₂/Fe₃O₄ particles to evaluate the particles' photocatalytic activity efficiency and bactericidal effects in seawater of variable salinities. Different TiO₂ to Fe₃O₄ mole ratios have been synthesized using sol-gel method. The synthesized particles contain mainly anatase TiO₂, Fe₃O₄ and FeTiO₃. The study has identified TiO₂/Fe₃O₄'s bactericidal effect to marine fish pathogen (Photobacterium damselae subsp. piscicida BCRC17065) in seawater. The SEM photo reveals the surface destruction in bacteria incubated with blue LED irradiated TiO₂/Fe₃O₄. The result of this study indicates that 1) TiO₂/Fe₃O₄ acquires photocatalytic activities in both the freshwater and the seawater via blue LED irradiation, 2) higher photocatalytic activities appear in solutions of higher TiO₂/Fe₃O₄ mole ratio, and 3) photocatalytic activity decreases as salinity increases. These results suggest that the energy saving blue LED light is a feasible light source to activate TiO₂/Fe₃O₄ photocatalytic activities in both freshwater and seawater.     

Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

Iron promotion of the TiO2 photosensitization process towards the photocatalytic oxidation of azo dyes under solar-simulated light irradiation

The photocatalytic oxidation of the azo dye Orange-II (Or-II) using Fe loaded TiO₂ (Fe–TiO₂) was studied under ultraviolet (UV), visible (vis) and simultaneous UV–vis irradiations using a solar light simulator. Photocatalysts were characterized by means of XRD, SEM-EDX, FTIR and DRS. Fe³⁺ species, identified in XPS analyses, were responsible of the increased absorption of visible light. Moreover, DRS analyses showed a decrease in the bandgap due to Fe³⁺ loading. Photocatalystic tests proved that Fe modification enhanced the TiO₂ photocatalytic activity towards Or-II photodegradation under simultaneous UV–vis irradiation. Even so, the performance of the Fe–TiO₂ samples towards the photodegradation of phenol, under UV irradiation, was lower than TiO₂ suggesting the recombination of the UV photogenerated electron–hole pair. Therefore, results evidence a Fe³⁺ promotion of the electron caption in the photosensitization process of TiO₂ by Or-II acting as a sensitizer. Such process leads to the Or-II photooxidation under UV–vis irradiation by losing energy in electron transferring processes to sensitize TiO₂, and, the formation of reactive oxygen species promoted by the injected electron to the TiO₂ conduction band.     

Structure and photocatalytic activity studies of TiO2-supported over Ce-modified Al-MCM-41

Ce-Al-MCM-41, TiO₂/Al-MCM-41 and TiO₂/Ce-Al-MCM-41 materials with varying contents of Ce (by impregnation) and TiO₂ loaded (by solid-state dispersion) on Al-MCM-41 support are prepared. The Ce modified and TiO₂ loaded composite systems are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS) techniques. The DRS and XPS of low Ce content (0.2-0.5 wt.%) modified Al-MCM-41 samples are showing more characteristic of Ce³⁺ species wherein cerium in interaction with Al-MCM-41 and that of high Ce (0.8, 3.0 wt.%) content modified samples are showing the characteristic of both Ce⁴⁺and Ce³⁺species. A series of Ce-modified Al-MCM-41 and TiO₂ loaded composite catalysts are evaluated for photocatalytic degradation of phenol under UV irradiation. Low Ce content in Ce³⁺ state on Al-MCM-41 is showing good photoactivity in comparison with high Ce content samples and pure ceria. The composite TiO₂/Ce-Al-MCM-41 is showing enhanced degradation activity due decreased rate of electron-hole recombination on TiO₂ surface by the redox properties of cerium. The photocatalyst TiO₂/Ce-Al-MCM-41 with an optimum of 10 wt.% TiO₂ and 0.3 wt.% Ce is showing maximum phenol degradation activity. The possible mechanism of phenol degradation on the composite photocatalyst is proposed.