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.     

Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution

This work reports the semiconductor-assisted photochemical degradation of reactive dyes. In an oxygenated-UV-ZnO system almost total decolorization of Remazol Brilliant Blue R, Remazol Black B, Reactive Blue 221 and Reactive Blue 222 was observed in reaction times of about 60 min. Extending the photochemical treatment up to 120 min, mineralization higher than 80% for all the dyes was observed. During the same period, the residual acute toxicity was significantly reduced only for Remazol Black B. A systematic optimization study carried out by factorial design showed that for the reactive dyes tested, the ZnO semiconductor exhibits a better efficiency than that observed with anatase TiO2. A synergistic effect in the coupled TiO2-ZnO system was not observed.     

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C₁₄H₁₄N₃SO₃Na) and orange II (C₁₆H₁₁N₂SO₄Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO₂ irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H₂O₂, S₂O₈²⁻) and some ions (Cl⁻, SO₄²⁻) on the process was also studied.     

氧化铁光催化降解活性染料的研究

用NaOH和Fe(NO3)3·9H2O共沉淀法制备Fe2O3的前驱体,分别在350℃,550℃,700℃烧结得到α-Fe2O3催化剂.通过对3种活性染料的降解实验,探讨了光照和光照时间的影响,比较了不同烧结温度下所得催化剂光催化活性的大小,得出350℃烧结的催化剂光催化活性最好.     

The pH and anion effects on the heterogeneous photocatalytic degradation of o-methylbenzoic acid in TiO2 aqueous suspension

This investigation used UV light of 365 nm and titanium dioxide in aqueous suspension to study the photocatalytic reaction of o-methylbenzoic acid under the influence of pH values, anion additives and the varieties of titanium dioxide. From experimental results, under the condition of 5 g/l TiO2, pH 3 and light intensity of 2.45 mW/cm2, 0.1 mM of o-methylbenzoic acid could be completely decomposed in 2 h. The reaction was faster with lowering pH, and was found to be apparent first-order following Langmuir-Hinshelwood model. In the presence of anion additives, the inhibitive effect of chloride ions was larger than that of sulfate ions under acidic condition for Degussa brand titanium dioxide, but without influence using Janssen brand. Both brands, however, promoted the mineralization of o-methylbenzoic acid (o-MBA).     

Photocatalytic degradation of AZO dyes by supported TiO2 + UV in aqueous solution

The photocatalytic degradation performance of photocatalysts TiO2 supported on 13-X, Na-Y, 4A zeolites with different loading content was evaluated using the photocatalytic oxidation of dyes direct fast scarlet 4BS and acid red 3B in aqueous medium. The results showed that the best reaction dosage of TiO2-zeolite catalysts is about 2 g/l and the photocatalytic kinetics follows first order for all supported catalysts. The photocatalytic activity order of the three series catalysts is 13X type >Y type >4A type. The physical state of titanium dioxide on the supports is evaluated by X-ray photoelectron spectra (XPS), powder X-ray diffraction (XRD), BET, and FTIR.     

The separation of catalyst after photocatalytic reactions conducted in the presence of TiO2/FeCl3/UV

One of the problems connected with wastewater treatment by the photocatalytic method in the presence of TiO2 suspension is necessity of the later catalyst separation. The method proposed by us for this purpose, consists in the usage of coagulation of TiO2 suspension with the aid of FeCl3, particularly in the cases when addition of the salt is used in order to intensification of the photocatalytic process. The effects of the TiO2 separation were studied from the mixtures, after photocatalytic Acid Orange 7 degradation, with dosage of FeCl3 at different stages of the process. The coagulation was carried out at different pH values as well as different FeCl3 concentrations. It was stated that nearly 100% of separation and simultaneously, nearly 100% of decolouration of the examined Acid Orange 7 solutions after their illumination in the presence of TiO2/FeCl3 and coagulation which was produced only by increasing of pH of the obtained mixtures, were nearly possible.     

TiO2／SiO2催化剂可见光降解偶氮染料的研究

以多孔硅胶作载体.通过酸性溶胶法制备了TiO2/SiO2催化剂.采用X射线衍射(XRD)、热重一差热分析(TG-DTA)、扫描电镜(SEM)和BET等方法对该催化剂进行了表征.以偶氮染料酸性橙7(A07)的可见光降解作为探针反应,研究了TiO2/SiO2的催化活性.结果表明,TiO2的平均晶粒尺寸为5.1 nm,晶型为锐钛矿;TiO2/SiO2具有大的比表面积,比P-25催化剂具有更高的光催化活性和更好的沉降性能,便于回收利用.     

TiO2光催化降解有机污染物的协同效应研究

微量的强氧化剂H2O2、O3引入纳米TiO2光催化体系能够极大地提高有机污染物氧化降解效率.本文通过对这一效应促进有机物降解的相关文献综述,探讨论述了协同效应产生的机理以及影响因素,并就其将来研究与实际污染物处理应用提出了新思路.     

Heterogeneous photocatalytic degradation of picloram, dicamba, and floumeturon in aqueous suspensions of titanium dioxide

Heterogeneous photocatalytic degradation of three-selected herbicide derivatives: (1) picloram (4-Amino-3,5,6-trichloropyridine-2-carboxylic acid, (2) dicamba (2-Methoxy-3,6-dichlorobenzoic acid, and (3) floumeturon (N,N-Dimethyl-N-[3-(trifluoromethyl)phenyl]-urea) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic technique and decrease in total organic carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation of the herbicide was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO2, and in the presence of electron acceptors such as hydrogen peroxide (H2O2), potassium bromate (KBrO3), and ammonium persulphate (NH4)2S2O8 besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts in the case of dicamba (2) and floumeturon (3), whereas Hombikat UV100 was found to be better for the degradation of picloram (1). The herbicide picloram (1) was found to degrade faster as compared to dicamba (2) and floumeturon (3). The degradation products were analyzed by gas chromatography-mass spectrometry (GC/MS) technique, and plausible mechanisms for the formation of products have been proposed.     

Study on the photocatalytic degradation of glyphosate by TiO(2) photocatalyst

In this paper, the photocatalytic degradation of glyphosate selected as the deputy of organic pollutant in aqueous solution with TiO(2) powder as a photocatalyst has been studied. The effects of various parameters, such as the amount of the photocatalyst, illumination time, initial pH value, electron acceptors, metal ions, and anions on the photocatalytic degradation of glyphosate were investigated. From the studies, the best condition for the effect of the parameters on the photocatalytic degradation of glyphosate was obtained. The results show that the optimum amount of the photocatalyst used is 6.0 g l(-1) for the photocatalytic reactions. The photodegradation efficiency of glyphosate increases with the increase of the illumination time. With the addition of Fe(3+), Cu(2+), H(2)O(2), K(2)S(2)O(8) or KBrO(3), the photocatalytic degradation of glyphosate is accelerated. However, with the addition of Na(+), K(+), Mg(2+), Ca(2+), Zn(2+), Co(2+) and Ni(2+), or with the addition of trace amounts of Cl(-), Br(-), SO(4)(2-), there are no obvious effects on the reactions. Acidic or alkaline mediums are favorable for the photocatalytic degradation of glyphosate. The possible roles of the additives on the reactions and the possible mechanisms of effect were discussed.     

Photocatalytic degradation of the fungicide Fenhexamid in aqueous TiO(2) suspensions: identification of intermediates products and reaction pathways

Liquid-chromatography interfaced with time-of-flight mass spectrometry (LC-TOF/MS) was used to separate and characterize the transformation products arising from TiO₂-photocatalytic degradation of the fungicide Fenhexamid (FEX) in aqueous solution under simulated solar irradiation. Prior to identification, irradiated solutions of FEX (10 mg L⁻¹) were concentrated by solid-phase extraction. Assignments of the mass spectra ions were aided by elemental composition calculations, comparison of structural analogues and available literature, and acquired knowledge regarding mass spectrometry of related heterocyclic compounds. The primary transformation intermediates identified were hydroxyl and/or keto-derivatives. Several positional isomers are typically produced as a consequence of the non-selectivity of the OH radical attack. Moreover, products resulted from the cleavage of the amide and NHdichlorophenol bonds were formed. Finally, cyclic - benzo[d]oxazole intermediates are also formed through an intramolecular photocyclization process and cleavage of halogen - carbon bond. In the case of the hydroxy and/or keto-derivatives, the generic fragmentation scheme obtained from the interpretation of the ESI-TOF-MS data cannot be diagnostic to precisely localize the position of the entering substituent on the FEX molecule, and thus to characterize all its possible oxygenated derivatives by assigning a plausible structure with confidence. On the basis of identified products different pathways of photocatalytic degradation of FEX were proposed and discussed.     

镧负载改性TiO2太阳光催化降解微囊藻毒素的研究

考察了镧负载改性TiO2催化剂在太阳光下降解微囊藻毒素LR (MCLR)的效果及其影响因素。结果表明,镧负载改性的TiO2可显著增加MCLR在TiO2表面的吸附量,同时提高MCLR在太阳光下的降解率。随着镧负载量的增加,太阳光下MCLR降解率可从65%提高到95%,pH降低可促进MCLR的降解。改性TiO2对藻毒素的降解存在最佳投加量,实验结果表明,在pH=6,MCLR初始浓度为2 mg/L,0.001-La-TiO2的最佳投量为0.5 g/L,在3 600 μW/cm2太阳光下照射30 min,降解率可达97%。     

TiO2薄膜光催化降解双酚A的研究

采用sol-gel法制备TiO2薄膜。以该薄膜为催化剂，研究了在H2O2存在的条件下，对内分泌干扰物质双酚A的光催化降解反应。分别讨论了pH值、H2O2的加入量、双酚A的初始浓度以及光照时间对降解反应的影响。结果表明，在pH=4，30mg／L的H2O2中对初始浓度为50mg／L的双酚A溶液光照180min有较好的降解效果。     

TiO2薄膜光催化降解双酚A的研究

采用sol-gel法制备TiO2薄膜.以该薄膜为催化剂,研究了在H2O2存在的条件下,对内分泌干扰物质双酚A的光催化降解反应.分别讨论了pH值、H2O2的加入量、双酚A的初始浓度以及光照时间对降解反应的影响.结果表明,在pH=4,30 mg/L的H2O2中对初始浓度为50 mg/L的双酚A溶液光照180 min有较好的降解效果.     

TiO2 photocatalytic degradation of PCBs in soil-water systems containing fluoro surfactant

Titanium dioxide-mediated photodegradation of Polychlorinated biphenyls (PCBs) in soil/aqueous systems with added fluorinated surfactant was investigated. PCBs can bind tightly to organic matter in the soil, especially in aged, contaminated soil. Experiments showed an effective PCB photocatalytic degradation in mixed systems of soil/clay with anionic fluorinated surfactant FC-143 and TiO2. The FC-143 surfactant is stable in this photochemical process. PCB degradation rates in samples followed the order: spiked clay > spiked soil > Hudson River bank soil. The results suggest that anionic fluorinated surfactant may form semimicelles and/or admicelles on the surface of positively charged TiO2. The hydrophobic surface of TiO2 can provide a nonpolar phase that acts as a partioning medium for hydrophobic PCBs. Therefore, PCBs in soil can be released to the semimicelle and/or admicelle on the TiO2 surface and are effectively photodegraded in a dispersion containing anionic fluorinated surfactant. The combination of surfactant extraction and photooxidation forms the basis for a novel two-stage process for the removal and destruction of PCBs from soil.     

TiO2光催化处理水中苯酚的环境风险研究

利用薄膜水循环TiO2光催化反应器(TiO2-WFCPR)处理水中苯酚的实验数据,分析了不同处理条件下苯酚光催化降解过程中间产物的降解规律和出水的环境风险.研究结果表明,即使苯酚已达<污水综合排放标准>(GB 8978-1996)一级排放标准,但出水中还不同程度地存在有害的中间产物,排放时会对环境造成危害,因此应以残留苯酚及其中间产物的浓度及影响确定该工艺最终的反应时间.足够的反应时间和偏碱性条件是降低苯酚及其中间产物环境风险的关键因素.苯酚初始浓度及进水pH越高,苯酚达标的反应时间会越长,处理的经济性就越差.所以,从环境风险与经济性综合考虑,该工艺适用于处理苯酚初始质量浓度≤60.00 mg/L的水,适宜的pH为6.0～8.0.     

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。     

Enhancement of photocatalytic oxidation of humic acid in TiO2 suspensions by increasing cation strength

This study aimed at improving the photocatalytic (PC) oxidation of humic acids (HA) in TiO2 suspensions by adding cationic ion such as calcium or magnesium. A set of tests was first conducted in the dark to study the adsorption of HA onto TiO2 in suspensions at different pH and calcium concentrations. The experiment demonstrated that the adsorption of HA onto the TiO2 particles was either pH-dependent or calcium strength-dependent due to electrostatic interaction and calcium ion bridging. The photodegradation of HA in the presence of UV irradiation was investigated as a function of pH and the concentration of calcium and magnesium ions. The results showed that the adsorption behavior between HA and TiO2 played a very important role during the PC oxidation process. The PC oxidation could be enhanced at neutral pH by increasing the cation strength. The kinetics of HA PC degradation in TiO2 suspensions with different initial concentrations was also studied using the Langmuir-Hinshelwood model.