Removal of persistent tartrazine dye by photodegradation on TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge under visible light

TiO₂ nanoparticles on calcined sewage sludge (TiO₂/sludge) were prepared by the sol-gel method and were fully characterized. The photocatalytic efficiency of TiO₂/sludge was evaluated by tartrazine dye degradation by halide lamp. TiO₂/sludge exhibited a high photocatalytic oxidation efficiency (more than 90%) of tartrazine compared with naked TiO₂ (less than 20%) due to the synergy effect of sewage sludge. The optimization of experimental conditions was 0.5 g/l TiO₂/Sludge, pH 8 with 50 mg/l tartrazine dye. The addition of sewage sludge to TiO₂ improves the efficiency of dye mineralization. The prepared catalyst showed easier separation and effective reuse.     

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。     

Characterization Of C60/Bi2TiO4F2 as a Potential Visible Spectrum Photocatalyst for The Depolymerization of Lignin

Effects of a photocatalyst, C₆₀-modified Bi₂TiO₄F₂, on pine kraft lignin under visible light irradiation were investigated, along with those of Bi₂TiO₄F₂ and C₆₀/TiO₂ as references. The influences of pH, C₆₀ mass fraction, and the initial lignin concentration on lignin conversion and yields of mono-phenolic products were investigated. Seven products were determined by GC/MS, including phenol, 2-methoxyphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, vanillin, acetovanillone, and homovanillic acid. The yields of products and lignin conversion were higher by C₆₀/Bi₂TiO₄F₂ than Bi₂TiO₄F₂ and C₆₀/TiO₂. C₆₀/Bi₂TiO₄F₂ and C₆₀/TiO₂ were more stable than Bi₂TiO₄F₂ upon repetitive recycling of catalyst. The effectiveness of C₆₀/Bi₂TiO₄F₂ declines 25%, whereas that of Bi₂TiO₄F₂ declines 56.4% after being recycled five times. FTIR and HRTEM indicated that the deactivation of photocatalysts might be caused by lignin adsorbed on the surface of photocatalysts and the change in the crystal structure.     

TiO2/浮石光催化降解活性艳红X-3B的中试研究

采用TiO2/浮石悬浮态光催化剂,对活性艳红X-3B模拟废水进行了光催化降解的中试研究.考察了催化剂投加量、曝气量、溶液pH、投加助剂H2O2、污染物初始浓度对光催化效率的影响.结果表明,TiO2/浮石在中试条件下对活性艳红X-3B有较好的降解效果;催化剂最佳投加质量浓度为45g/L,增大曝气量和pH,适当投加助剂H2O2有利于光催化降解效率的提高;活性艳红X-3B的光催化降解过程符合负一级反应动力学规律,反应速率常数与活性艳红X-3B模拟废水初始浓度之间具有近似负一级的动力学关系.     

Dehydrogenation of ethylbenzene over TiO2-Fe2O3 and ZrO2-Fe2O3 mixed oxide catalysts

The mixed metal oxides TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO₂-Fe₂O₃ catalysts. However, for TiO₂-Fe₂O₃ catalysts, the surface area, the amount of acidic and basic sites and TiFe₂O₅ crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ catalyst system and also for the TiO₂-Fe₂O₃-ZrO₂ system, i.e. the activities of these catalysts can be ranked in the following order: TiO₂-Fe₂O₃-ZrO₂>TiO₂-Fe₂O₃ >ZrO₂>Fe₂O₃>TiO₂. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.     

Low temperature preparation and characterization of nanospherical anatase TiO2 and its photocatalytic activity on Congo red degradation under sunlight

Nanospherical titanium oxide with anatase structure was obtained at low temperature and normal pressure using a simple method of preparation. The dilute titanium (III) chloride solution was stirred at room temperature for several hours, and then ammonium hydroxide with hydrogen peroxide was added. A yellow gel TiO₂·xH₂O was obtained with nanodot shape and amorphous structure. Heated at 300 °C, it crystallized to pure anatase structure with nanospherical shape. The anatase particles prepared show good adsorption and photodegradation of Congo red solution under the sunlight. Materials were characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and UV spectroscopy.     

Effect of M-doping (M = Fe,V) on the photocatalytic activity of nanorod rutile TiO2 for Congo red degradation under the sunlight

Nanorods TiO₂, Fe-TiO₂ (3 and 2 at.% Fe), V-TiO₂ (5 at.% V) were prepared by a low temperature method and characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and BTE surface area analysis. The as-prepared samples were evaluated as catalysts for photodegradation of Congo red aqueous solution under the sunlight. Nanorods Fe-doped TiO₂ shows higher adsorption and also higher photocatalytic degradation of Congo red solution compared to pure nanorods TiO₂ rutile. A higher activity is obtained when the amount of doped Fe is 2 at.%, compared to 3 at.%. However, nanorods V-TiO₂ does not show neither adsorption nor photodegradation activity of Congo red solution.     

Mechanism of degradation of nitrilotriacetic acid by heterogeneous photocatalysis over TiO2 and platinized TiO2

TiO₂-heterogeneous photocatalysis of nitrilotriacetic acid (NTA) at pH 2.5 was studied to establish the kinetic regime and the reaction mechanism. Pure Degussa P-25 and Hombikat UV100 commercial samples were compared. A Langmuirian behavior was observed over P-25. Platinization of the Hombikat sample (0.5 wt.%) caused an important increase on the photocatalytic rate with a change in the kinetics from zero order in the pure precursors to first order in the platinized sample. The nature of the intermediates and their evolution with time were compared on all systems. Glycine, iminodiacetic and oxamic acids have been identified in different proportions, together with ammonium and glycolic acid, depending on the catalyst used. The rapid depletion of NTA was not accompanied by a corresponding total organic carbon (TOC) reduction, but 84% of TOC decrease was obtained on P25 after 24 h, a very reasonable result for refractory compounds. A detailed mechanism is proposed for the photocatalytic reaction, suggested to be the same over the three catalysts here tested.     

Sulfanilic acid-modified P25 TiO2 nanoparticles with improved photocatalytic degradation on Congo red under visible light

Visible-light-induced titania/sulfanilic acid nano-composite photocatalysts were prepared and characterized by FTIR, XPS, UV-vis, XRD, and SEM. The results indicate that the formation of Ti-O-S bonds after the modification of P25 TiO₂ nanoparticles with sulfanilic acid ligands extends the photoresponse of the photocatalyst from the UV to the visible range. The photocatalytic activity of the nano-composite photocatalyst was examined by degrading Congo red under visible light, in which its effecting factors such as irradiation time, catalyst dosage, solution pH and the addition of H₂O₂, were investigated in detail. The possible mechanism of photocatalytic degradation under visible irradiation has been also presented.     

Electrochemically Assisted Photocatalysis of Hybrid WO3/TiO2 Films: Effect of the WO3 Structures on Charge Separation Behavior

In this study, the photocatalysis of hybrid WO₃/TiO₂ films with different loadings of WO₃ were investigated with and without potential bias. It was clearly indicated that hybrid WO₃/TiO₂ films show less photo-reactivity under only UV-irradiation, while more effective photocatalysis under potential bias than either TiO₂ or WO₃ by themselves, their photocatalytic performance depending on the loadings of WO₃. In particular, a hybrid WO₃/TiO₂ film involving an amorphous-like WO₃ phase plays a significant role in an enhancement of the electrochemically assisted photocatalysis.     

Size Effect in Hybrid TiO2:Au Nanostars for Photocatalytic Water Remediation Applications

TiO₂:Au-based photocatalysis represents a promising alternative to remove contaminants of emerging concern (CECs) from wastewater under sunlight irradiation. However, spherical Au nanoparticles, generally used to sensitize TiO₂, still limit the photocatalytic spectral band to the 520 nm region, neglecting a high part of sun radiation. Here, a ligand-free synthesis of TiO₂:Au nanostars is reported, substantially expanding the light absorption spectral region. TiO₂:Au nanostars with different Au component sizes and branching were generated and tested in the degradation of the antibiotic ciprofloxacin. Interestingly, nanoparticles with the smallest branching showed the highest photocatalytic degradation, 83% and 89% under UV and visible radiation, together with a threshold in photocatalytic activity in the red region. The applicability of these multicomponent nanoparticles was further explored with their incorporation into a porous matrix based on PVDF-HFP to open the way for a reusable energy cost-effective system in the photodegradation of polluted waters containing CECs.     

温和条件下CoPc/TiO2光催化还原CO2

采用浸渍法制备的TiO2负载钴酞菁(CoPc/TiO2)为光催化剂,在碱性水溶液中、可见光照下,CO2可被光催化还原为产物HCOOH、CO、CH4。对催化剂的制备条件进行了考察,在m(CoPc)∶m(TiO2)=1∶100、催化剂浸渍时间12 h、浸渍溶剂为甲苯、催化剂焙烧温度200℃的条件下,还原总产物量最高可达1 075.38μmol/g-cat,其中甲酸为主产物,最高可达708.54μmol/g-cat。对催化剂进行了XRD、DRS表征,证实了CoPc在TiO2表面的负载。结果表明:用该催化剂在可见光照及常温常压下,于水溶液中就可将CO2还原。其次,实验还发现光照下可产生电子转移,实现了电荷的重新分配,以降低电子-空穴的重新结合;TiO2表面应有一定的空隙率,有利于CO2在其表面获得电子被还原。     

Photocatalytic Activity of a TiO<Subscript>2</Subscript> Photocatalyst Doped with C<Superscript>4+</Superscript> and S<Superscript>4+</Superscript> Ions Having a Rutile Phase Under Visible Light

C⁴⁺ and S⁴⁺-codoped titanium dioxide (TiO₂) having a rutile phase was prepared. By doping C⁴⁺ and S⁴⁺ ions into a TiO₂ lattice, the absorption edge of rutile TiO₂ powder was largely shifted from 400 to 700 nm. 2-Methylpyridine and methyleneblue were photocatalytically oxidized at high efficiency on C⁴⁺ and S⁴⁺-doped TiO₂ under visible light at a wavelength longer than 5 nm.     

Surface initiated graft polymerization from carbon-doped TiO2 nanoparticles under sunlight illumination

A simple and efficient method is presented for the preparation of polymer-grafted TiO₂ by a photocatalytic polymerization. PMMA chains are directly grafted from the surface of the TiO₂ nanoparticles in water under sunlight illumination. FT-IR and TEM results demonstrate that there existed strong chemical bonding at the interface of TiO₂ nanoparticles and PMMA chains. The thermal stabilities of the grafted polymer are dramatically elevated relative to that of pure PMMA according to TGA results. Moreover, the resulted polymer exhibits much higher melting temperature compared with traditional stereoregular PMMA by controlling the conformation of polymer chains growing in the highly restricted space on the surface of nanoparticles.     

The reduction behavior of Mo/TiO2-Al2O3 catalyst

The effect of TiO₂ modified Al₂O₃ surface on the reducibility of MoO₃ has been studied by TPR and XPS. The results show that Mo⁶⁺ in Mo/TiO₂-Al₂O₃ can be reduced to much lower valency, especially at low Mo loading. The influence of the calcination temperature on the reduction of Mo⁶⁺ on Al₂O₃ and TiO₂-Al₂O₃ carriers is different. The data reveals that the reducibility of Mo⁶⁺ on Al₂O₃ slightly decreased, while that on TiO₂-Al₂O₃ increased when the calcination temperature was raised. It is suggested that the stronger tetrahedral site of the Al₂O₃ surface was first occupied by TiO₂ and main octahedral Mo⁶⁺ in polymeric species-; and a small crystalline MoO₃ formed on TiO₂-Al₂O₃, whereas the formation of tetrahedral Mo⁶⁺ species and Al₂(MoO₄)₃ phase was inhibited.     

The Effects of Al2O3 Addition and WO3 Modification on Catalytic Activities of NiO/TiO2 for Acid Catalysis

NiO/Al₂O₃–TiO₂/WO₃ catalysts for acid catalysis were prepared by the addition of Al₂O₃ and the modification with WO₃. The strong acid sites were formed through the bonding between dispersed WO₃ and TiO₂. The larger the dispersed WO₃ amount, the higher both the acidity and catalytic activity. The addition of Al₂O₃ up to 5 mol% enhanced acidity and catalytic activity of NiO/Al₂O₃–TiO₂/WO₃ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond. The presence of NiO may attract reactants and enhance the local concentration of reactants near acid sites and consequently increase catalytic activity.     

Photocatalytic reaction of H2O+CO2 over pure and doped Rh/TiO2

In the photocatalytic reduction of carbon dioxide to formic acid, formaldehyde and methanol in aqueous suspensions of TiO₂ and Rh/TiO₂, the effects of doping the TiO₂ with W⁶⁺ were investigated.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

Stoichiometric photocatalytic decomposition of pure water in Pt/TiO2 aqueous suspension system

The influence of the direction of ultraviolet irradiation upon the yields of the photocatalytic decomposition of pure water has been investigated in Pt/TiO₂ aqueous suspension system. The yields of the photocatalytic decomposition irradiated from the top of the reaction cell are about 10³ times higher than those irradiated from the bottom. The difference seems due to the reverse reaction of the formed H₂ and O₂ in the suspension.