Synthesis of efficient Y-Bi2WO6/G visible light photocatalysts with high stability for pollutant degradation

Environmental Science and Pollution Research - For effective photocatalytic pollutant degradation on bismuth tungstate (Bi2WO6), it is vital to enhance the photogenerated charge separation and the...     

Effect of matrix on the electrochemical characteristics of TiO2 nanotube array-based PbO2 electrode for pollutant degradation

A series of lead dioxide electrodes developed on titania nanotube arrays with different matrix were fabricated by electrodeposition. Before the deposition of PbO₂, the matrix of this anode was electrochemically reduced in (NH₄)₂SO₄ solution and/or pre-deposited with certain amounts of copper. To gain insight into these pretreatments, the PbO₂ electrodes were characterized by SEM, LSV, and XRD, and their electrocatalytic activities for pollutant degradation were compared using p-nitrophenol (p-NP) as a model. It was confirmed that the electrochemical reduction with (NH₄)₂SO₄ resulted in the partial conversion of TiO₂ into Ti₄O₇ and Ti₅O₉, which increased the conductivity of PbO₂ anode, but decreased its electrochemical activity, while the Ti/TNTs*-Cu/PbO₂ electrode with both pretreatments possessed the highest oxygen evolution overpotential of 2.5 V (vs. SCE) and low substrate resistance. After a 180-min treatment on this electrode, the removal efficiency of p-NP reached 82.5 % and the COD removal achieved 42.5 % with the energy consumption of 9.45 kWh m^?3, demonstrating the best performance among these electrodes with different matrices. Therefore, this titania nanotube array-based PbO₂ electrode has a promising application in the industrial wastewater treatment.     

Higher intrinsic photocatalytic efficiency of 2,4,6-triphenylpyrylium-based photocatalysts compared to TiO2 P-25 for the degradation of 2,4-dichlorophenol using solar simulated light

The photocatalytic efficiency of two 2,4,6-triphenylpyrylium (TP(+)) based photocatalysts (supported on silica or incorporated inside zeolite Beta, 3wt%) for the degradation of 2,4-dichlorophenol (DCP) in aqueous media has been compared with TiO(2) (Degussa P-25). It was found that the efficiency of the degradation depends on the photocatalytic setup, recirculation through a tubular reactor being highly unfavorable for the TP(+)-based photocatalysts due to the deposition of the silica or zeolite particles. In contrast, high efficiency in DCP disappearance (up to 87%) and in the total organic content decrease (up to 62%) were obtained using a discontinuous batch reactor in which the TP(+) photocatalysts were uniformly suspended. Kinetic studies were also made and DCP degradation follows a first order kinetics. The obtained kinetic constants when corrected to account for the influence of the fraction of light absorbed and the amount of active sites shows that the intrinsic activity of TP(+) adsorbed on silica or incorporated inside zeolite Beta was over one order of magnitude higher than TiO(2) activity.     

TiO2光催化涂料的制备及其降解甲醛研究

自制TiO2光催化涂料,重点对所制备的涂料在室内进行降解甲醛研究,考察了在不同分散剂、不同光催化剂以及不同甲醛初始浓度、不同光源、不同温度和不同湿度等环境因素下涂料对甲醛降解率的影响。结果表明,选用聚丙烯酸钠离子型分散剂,铜金属掺杂TiO2光催化剂制备的光催化涂料对甲醛降解率达80％以上且具有良好的耐久性,在室温（20℃左右）湿度50％日光灯照射下,甲醛初始浓度5μL时效果最佳。     

Kinetics and mechanism of TNT degradation in TiO2 photocatalysis

The photocatalytic degradation of TNT in a circular photocatalytic reactor, using a UV lamp as a light source and TiO(2) as a photocatalyst, was investigated. The effects of various parameters such as the initial TNT concentration, and the initial pH on the TNT degradation rate of TiO(2) photocatalysis were examined. In the presence of both UV light illumination and TiO(2) catalyst, TNT was more effectively degraded than with either UV or TiO(2) alone. The reaction rate was found to obey pseudo first-order kinetics represented by the Langmuir-Hinshelwood model. In the mineralization study, TNT (30 mg/l) photocatalytic degradation resulted in an approximately 80% TOC decrease after 150 min, and 10% of acetate and 57% of formate were produced as the organic intermediates, and were further degraded. NO(-)(3) NO(-)(2), and NH(+)(4) were detected as the nitrogen byproducts from photocatalysis and photolysis, and more than 50% of the total nitrogen was converted mainly to NO(-)(3)in the photocatalysis. However, NO(-)(3) did not adsorbed on the TiO(2) surface. TNT showed higher photocatalytic degradation efficiency at neutral and basic pH.     

Reaction pathways of dimethyl phthalate degradation in TiO2-UV-O2 and TiO2-UV-Fe(VI) systems

The photocatalytic degradation of dimethyl phthalate (DMP) in aqueous TiO₂ suspension under UV illumination has been investigated using oxygen (O₂) and ferrate (Fe(VI)) as electron acceptors. The experiments demonstrated that Fe(VI) was a more effective electron acceptor than O₂ for scavenging the conduction band electrons from the surface of the catalyst. Some major intermediate products from DMP degradation were identified by HPLC and GC/MS analyses. The analytical results identified dimethyl 3-hydroxyphthalate and dimethyl 2-hydroxyphthalate as the two main intermediate products from the DMP degradation in the TiO₂–UV–O₂ system, while in contrast phthalic acid was found to be the main intermediate product in the TiO₂–UV–Fe(VI) system. These findings indicate that DMP degradation in the TiO₂–UV–O₂ and TiO₂–UV–Fe(VI) systems followed different reaction pathways. An electron spin resonance analysis confirmed that hydroxyl radicals existed in the TiO₂–UV–O₂ reaction system and an unknown radical species (most likely an iron–oxo species) is suspected to exist in the TiO₂–UV–Fe(VI) reaction system. Two pathway schemes of DMP degradation in the TiO₂–UV–O₂ and TiO₂–UV–Fe(VI) reaction systems are proposed. It is believed that the radicals formed in the TiO₂–UV–O₂ reaction system preferably attack the aromatic ring of the DMP, while in contrast the radicals formed in the TiO₂–UV–Fe(VI) reaction systems attack the alkyl chain of DMP.     

N掺杂TiO_2可见光催化降解有机物机理研究

实验研究了掺杂N的TiO2光催化剂在可见光下对有机物的降解机理,研究方法有：加入自由基俘获剂探索对反应速率的影响、有机物降解过程TOC与脱色比较,化学探针法测定了实验中存在的HO.。结果表明,有机物在脱色的同时苯环也在断裂,说明有机物的降解是受无选择性的氧化剂攻击而完成;除亚甲基蓝以外,加入自由基俘获剂对可见光反应速率均有抑制现象,证明自由基的攻击是有机物可见光催化降解的主要途径。分别以二甲基亚砜和水杨酸为分子探针,实验结果证明了光催化反应系统中存在HO.物种,前者与HO.反应形成特定的偶氮结构有机物在425 nm处有吸收,后者与HO.反应生成2,3-二羟基苯甲酸和2,5-二羟基苯甲酸。亚甲基蓝、苯酚和水杨酸经5 h的可见光催化降解后,其TOC分别降低了62.8%、78.9%和96.0%,说明掺杂N的TiO2有较强的可见光催化降解有机物能力。     

TiO_2微球光催化降解腐植酸钠

以阳离子交换树脂为模板,采用溶胶-凝胶法以四氯化钛为原料制备TiO2微球,采用XRD,FTIR,SEM对样品进行了表征。微球中主要组分是锐钛矿型TiO2,同时掺杂有少量Na＋,SO24-等离子,比TiO2粉末具有更好的光催化性能,具备重复使用的能力,使用寿命较长,可作为一种有实用价值的光催化剂。在300 W高压汞灯下采用二氧化钛微球催化降解腐植酸钠,分析了催化剂投加量和反应时间对降解率的影响。腐植酸钠的光催化降解实验结果表明：初始浓度为10 mg/L的腐植酸钠在碱性条件,催化剂投加量为2.5 g/L,反应时间为3 h时最为适宜,最大降解率可达到96.51%。     

Assessment comparison of commercial TiO2 and TiO2 sol-gel on the degradation of caffeine using artificial radiation

Environmental Science and Pollution Research - The presence of endocrine disrupting compounds in water receptor bodies, such as drugs, currently has in scientific field a great focus of studies...     

Photocatalytic degradation of phenol by visible light-responsive iron-doped TiO2 and spontaneous sedimentation of the TiO2 particles

Fe-doped TiO₂ was prepared by the calcination of Fe_xTiS₂ (x = 0, 0.002, 0.005, 0.008, 0.01) and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectra. All the Fe-doped TiO₂ were composed of an anatase crystal form and showed red shifts to a longer wavelength. The activity of the Fe-doped TiO₂ for the degradation of phenol was investigated by varying the iron content during UV (365 nm) and visible light (405 nm and 436 nm) irradiation. The degradation rate depended on the Fe content and the Fe-doped TiO₂ was responsive to the visible light as well as the elevated activity toward UV light. The molar ratio of 0.005 was the optimum for both the UV and visible light irradiations. The result was discussed on the basis of the balance of the excited electron–hole trap by the doped Fe³⁺ and their charge recombination on the doped Fe³⁺ level. The Fe-doped TiO₂ (x = 0.005) was more active than P25 TiO₂ under solar light irradiation. The suspended Fe-doped TiO₂ spontaneously precipitated once the stirring of the reaction mixture was terminated.     

Photocatalytic degradation of pentachlorophenol on TiO2 sol-gel catalysts

The photocatalytic degradation of pentachlorophenol (PCP) in aqueous solution was investigated using TiO2 catalysts. The samples were prepared by the sol-gel method using different gelation pH and different calcination temperatures. The solids were characterized by specific surface area, X-ray diffraction, UV-Vis absorbance, FTIR and pentachlorophenol adsorption. The catalytic activity of the solids was evaluated in a conventional photoreactor at 298 K using 30 ppm of pentachlorophenol. It was found that the reaction follows a first-order reaction and the kinetic constant values change slightly with the pH of gelation and more significantly with the calcination temperature.     

Photocatalytic degradation of azo dyes by nitrogen-doped TiO2 nanocatalysts

This study examined the photocatalytic degradation of three azo dyes, acid orange 7 (AO7), procion red MX-5B (MX-5B) and reactive black 5 (RB5) using a new type of nitrogen-doped TiO2 nanocrystals. These newly developed doped titania nanocatalysts demonstrated high reactivity under visible light (lambda>390 nm), allowing more efficient usage of solar light. The doped titania were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experiments were conducted to compare the photocatalytic activities of nitrogen-doped TiO2 nanocatalysts and commercially available Degussa P25 powder using both UV illumination and solar light. It is shown that nitrogen-doped TiO2 after calcination had the highest photocatalytic activity among all three catalysts tested, with 95% of AO7 decolorized in 1 h under UV illumination. The doped TiO2 also exhibited substantial photocatalytic activity under direct sunlight irradiation, with 70% of the dye color removed in 1h and complete decolorization within 3 h. Degussa P25 did not cause detectable dye decolorization under identical experimental conditions using solar light. The decrease of total organic carbon (TOC) and evolution of inorganic sulfate (SO4(2-)) ions in dye solutions were measured to monitor the dye mineralization process.     

PCDD/DF formations by the heterogeneous thermal reactions of phenols and their TiO2 photocatalytic degradation by batch-recycle system

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/DFs) formation by the thermal reactions of phenols with CuCl2 under oxygen flux were carried out in relation to their formation mechanisms. To evaluate the effect of photocatalytic degradation of titanium dioxide (TiO2) thin film prepared by the sol-gel method, the photocatalysis of PCDD/DFs in acetonitrile/water solution by batch-recycle system was conducted. For the thermal reaction system of powder mixtures of 2,4,5-trichlorophenol (2,4,5-TCP) and CuCl2, the formation rates were 8.1 microg/g-2,4,5-TCP/min for total PCDD/DFs and 6.9 microg/g-2,4,5-TCP/min for PCDDs, and total PCDD/DF rate was higher by approximately 40 fold compared to phenol vapor/oxygen/CuCl2 powder system. For the system of 2,4,5-TCP, PCDDs were mainly formed via ortho-phenoxyphenols (POP) intermediate by the condensation of 2,4,5-trichlorophenate. For PCDD/DF photocatalytic degradations, most PCDD congeners photodecomposed rapidly and the rates presented more than 70% (as dechlorination rates of 76% for PCDDs) at 24 h after irradiation, using PCDD/DFs formed with 2,4,5-TCP. The rate constants were in the order of 4.8-6.1 x 10(-3) min(-1), assuming the pseudo-first-order reactions for their low levels.     

Investigation of the antibacterial effects of silver-modified TiO2 and ZnO plasmonic photocatalysts embedded in polymer thin films

Nanosilver-modified TiO₂ and ZnO photocatalysts were studied against methicillin-resistant Staphylococcus aureus on the surface and against naturally occurring airborne microorganisms. The photocatalysts/polymer nanohybrid films were prepared by spray coating technique on the surface of glass plates and on the inner surface of the reactive light source. The photoreactive surfaces were activated with visible light emitting LED light at λ?=?405 nm. The optical properties of the prepared photocatalyst/polymer nanohybrid films were characterized by diffuse reflectance measurements. The photocatalytic properties were verified with the degradation of ethanol by gas chromatography measurements. The destruction of the bacterial cell wall component was examined with transmission electron microscope. The antibacterial effect of the photocatalyst/polymer nanohybrid films was tested with different methods and with the associated standard ISO 27447:2009. With the photoreactive coatings, an extensive disinfectant film was developed and successfully prepared. The cell wall component of S. aureus was degraded after 1 h of illumination. The antibacterial effect of the nanohybrid films has been proven by measuring the decrease of the number of methicillin-resistant S. aureus on the surface and in the air as the function of illumination time. The photocatalyst/polymer nanohybrid films could inactivate 99.9 % of the investigated bacteria on different thin films after 2 h of illumination with visible light source. The reactive light source with the inner-coated photocatalyst could kill 96 % of naturally occurring airborne microorganisms after 48 h of visible light illumination in indoor air sample. The TEM results and the microbiological measurements were completed with toxicity tests carried out with Vibrio fischeri bioluminescence bacterium.     

Photocatalytic degradation of cellulose bleaching effluent by supported TiO2 and ZnO

A cellulose bleaching effluent (E1) was degraded in batch conditions by photocatalysis using TiO2 and ZnO supported on glass Raschig rings. The effluent was completely decolourised and the total phenol content was reduced by 85% after 120 min treatment with both catalysts. Partial mineralization of the organic matter was confirmed by total organic carbon (TOC) reduction, approximately 50%. The residual organic matter shows a low acute toxicity as compared to the initial values and AOX values are strongly reduced after the photocatalytic oxidation. Molecular mass distribution showed that high molecular mass compounds were almost completely degraded.     

Sonophotocatalytic degradation of alazine and gesaprim commercial herbicides in TiO2 slurry

The photocatalytic degradation of alazine and gesaprim commercial herbicides was carried out in aqueous TiO(2) suspensions under UV light (15W, 352 nm). Degradation of these herbicides was also observed by the combined effects of photocatalysis with sonolysis (sonophotocatalysis) using an ultrasound source of 20kHz. Degradation profiles were recorded by measuring the concentration of the active compounds present in the alazine (alachlor and atrazine) and gesaprim (atrazine) by HPLC as a function of irradiation time (sound and/or light). Over 90% of the active component in the gesaprim was abated and those in alazine were completely degraded. The content of total organic carbon and chemical oxygen demand was also monitored. Mineralization of the commercial herbicides was achieved. Over 80% of chemical oxygen demand abatement was attained for both herbicides with sonophotocatalysis at 150 min of irradiation time. The photocatalytic degradation of the herbicides followed a pseudo-first order kinetics and their rate constant was increased by the combined effects of sonolysis.     

介孔TiO2的制备及光催化降解有机染料的研究

以十六烷基三甲基溴化胺为模板剂,用溶胶-凝胶法制备了介孔TiO2,用x射线衍射、透射电子显微镜、热重/差热分析及氮气吸附等方法对其进行了分析表征,并用偶氮染料阳离子红X-GRL为目标污染物分析了它的光催化活性.实验结果表明,450℃热处理后的介孔TiO2是锐钛矿型的,平均孔径为18 nm.氮气吸附曲线呈典型的介孔材料Ⅳ型吸附等温线特征.由于介孔TiO2具有较大的比表面积,因此表现出比非介孔TiO2高的光催化活性.     

Photocatalytic degradation kinetics and mechanism of phenobarbital in TiO2 aqueous solution

5-Ethyl-5-phenylpyrimidine-2,4,6(1H, 3H, 5H)-trione is an anti-convulsant used to treat disorders of movement, e.g. tremors. This work deals with the transformation of phenobarbital by UV/TiO₂ heterogeneous photocatalysis, to assess the decomposition of the pharmaceutical compound, to identify intermediates, as well as to elucidate some mechanistic details of the degradation. The photocatalytic removal efficiency of 100 μm phenobarbital is about 80% within 60 min, while the degradation efficiency of phenobarbital was better in alkaline solution. The study on contribution of reactive oxidative species (ROSs) has shown that OH is responsible for the major degradation of phenobarbital, while the photohole, photoelectrons and the other ROSs have the minor contribution to the degradation. Finally, based on the identification of degradation intermediates, two main photocatalytic degradation pathways have been tentatively proposed, including the hydroxylation and cleavage of pyrimidine ring in the phenobarbital molecule respectively. Certainly, the phenobarbital can be mineralized when the photocatalytic reaction time prolongs.     

Dye decomposition and air de-pollution performance of TiO2/SiO2 and N-TiO2/SiO2 photocatalysts coated on Portland cement mortar substates

Environmental Science and Pollution Research - In this study, the newly synthesized TiO2 and N doped TiO2 clusters were added to silica sol to synthesize N-TiO2/SiO2 composites via the...