Ozone-driven photocatalyzed degradation and mineralization of pesticide,Triclopyr by Au/TiO2

Triclopyr is a widely used pesticide which is non-biodegradable and enters aquatic systems. The ozone facilitated photocatalyzed degradation and mineralization of Triclopyr using Au-loaded titania as heterogeneous catalyst is reported. The oxidative degradation activity of the hazardous pesticide was investigated at pH 7.8 under varied reaction conditions, including in presence and absence of ozone, titania alone, in presence and absence of light and with different loadings of Au on support. Photocatalysis with 2% Au/TiO₂ in the presence of ozone yielded 100% degradation of Triclopyr in 2 h. The extent of degradation of pesticide and its mineralization were confirmed by GC-MS. For 10 mg/L of Triclopyr, 0.1 g/L of catalyst was found to be the optimum for mineralization. Results show that photocatalyzed ozonation with Au/TiO₂ as catalyst is a very effective for its removal. No leaching of Au was observed in triplicate runs. Catalyst was fully recoverable and reusable with no loss of activity.     

Photocatalytic ozonation of terephthalic acid: a by-product-oriented decomposition study

Terephthalic acid (TA) is considered as a refractory model compound. For this reason, the TA degradation usually requires a prolonged reaction time to achieve mineralization. In this study, vanadium oxide (V_xO_y) supported on titanium oxide (TiO₂) served as a photocatalyst in the ozonation of the TA with light-emitting diodes (LEDs), having a bandwidth centered at 452 nm. The modified catalyst (V_xO_y/TiO₂) in combination with ozone and LEDs improved the TA degradation and its by-products. The results obtained by this system were compared with photolysis, single ozonation, catalytic ozonation, and photocatalytic ozonation of V_xO_y/TiO₂ with UV lamp. The LED-based photocatalytic ozonation showed almost the same decomposition efficiency of the TA, but it was better in comparison with the use of UV lamp. The oxalic acid accumulation, as the final product of the TA decomposition, was directly influenced by either the presence of V_xO_y or/and the LED irradiation. Several by-products formed during the TA degradation, such as muconic, fumaric, and oxalic acids, were identified. Besides, two unidentified by-products were completely removed during the observed time (60 min). It was proposed that the TA elimination in the presence of V_xO_y/TiO₂ as catalyst was carried out by the combination of different mechanisms: molecular ozone reaction, indirect mechanism conducted by ·OH, and the surface complex formation.     

氮掺杂二氧化钛可见光催化降解曙红Y溶液

采用溶胶凝胶法制备了氮掺杂二氧化钛光催化剂,用XRD、SEM、FTIR和粒度分析仪对催化剂进行了表征,并且在可见光作用下对曙红Y溶液进行了光催化降解实验。研究了催化剂的投加量、曙红Y的初始浓度、光照时间和pH对曙红Y溶液的光降解效果。结果表明,以可见光作光源,催化剂的投入量为0.4 g,曙红Y溶液的初始浓度为20 mg/L,光照时间为50 min,pH=4条件下,曙红Y溶液的降解率达98.87%。     

臭氧催化氧化降解苯胺的机理

对臭氧单独氧化和臭氧催化氧化下的苯胺降解效率进行了比较,并通过液质联机分析了氧化过程中产物变化情况。实验结果表明,催化剂MnO2-CuO-CeO2/沸石的添加能有效地提高臭氧氧化苯胺的降解率,当苯胺初始浓度为200mg/L,反应20 min后,苯胺的去除率由原来的75%提高到89%;通过LC-MS分析,臭氧催化氧化苯胺降解过程中代谢产物依次为对亚胺醌、对苯醌、马来酸和草酸,并由此推断出了臭氧催化氧化降解苯胺的途径。     

Catalytic ozonation of 2,4-Dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger

Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (k_obs ) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the k_obs value increased from 19.3 to 26 M^?1 s^?1 and 67 M^?1 s^?1 when varying the alumina dose from 1 to 2 and 4 g L^?1, respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L^?1, the k_obs values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M^?1 s^?1, respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M^?1 s^?1 were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.     

臭氧氧化法深度处理生活垃圾焚烧厂沥滤液

采用臭氧氧化法对生活垃圾焚烧厂沥滤液经生化处理后的废水(称沥滤液生化处理水)进行深度处理。实验结果表明,COD降解速率随废水pH的提高明显增加,其中pH=10.5时的COD降解速率常数约为pH=4时的5.8倍。在臭氧投量为52.92 mg/min、pH=10.5的条件下反应70 min后,UV254和COD去除率分别达到84.7%和59.3%。向反应体系投加叔丁醇后COD去除率下降了约15%,由羟自由基氧化去除的COD占总COD去除量的26.7%。毒性实验结果表明,沥滤液生化处理水的96 h-EC50为38%,经臭氧氧化进一步处理后出水的96 h-EC50为77%,表明经臭氧深度处理后沥滤液生化处理水的毒性明显降低。     

汉沙黄/TiO_2光催化剂的制备及其光催化活性

采用溶剂热合成法制备了一种新型的汉沙黄/TiO2复合物光催化剂,利用多种手段SEM、XRD、FT-IR对催化剂的样品形貌、结构进行表征。分别以罗丹明B、亚甲基蓝、中性红为目标降解物,考察了可见光下溶液pH值对催化剂的吸附性能和催化活性的影响。结果表明,敏化后的TiO2对光的响应由紫外区扩展到可见区,催化活性优于纯TiO2,对上述3种染料的吸附率分别为19.2%、29.2%和43.2%,降解率分别为98.6%、92.5%和97.8%。制备的汉沙黄/TiO2光催化剂稳定性好,重复使用率高,在印染废水处理中具有很好的应用前景。     

Photocatalytic ozonation of pesticides in a fixed bed flow through UVA-LED photoreactor

In this study, a fixed bed flow through UVA-LED photoreactor was used to compare the efficiency of ozone, photocatalysis and photocatalysis-ozone degradation, and mineralization of two pure pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), and a commercial one, Killex®. For the degradation of the parent compounds, ozone-based processes were more effective. While for mineralization, photocatalytic processes were more effective. Photocatalytic ozonation was the most efficient process for both the degradation and mineralization of the parent compounds. The degradation rates and mineralization by photocatalytic ozonation were higher than the summation of the corresponding rates by ozonation and photocatalysis, indicating a symbiotic relationship.Overall, the photocatalytic ozonation process with the fixed bed TiO₂ reduces the time needed for the degradation and mineralization of the pesticides, reduces the costs of powder catalyst separation and overcomes the reduced efficiency of immobilized catalysts, which makes the process quite attractive for practical applications.     

Photocatalytic decomposition of crotamiton over aqueous TiO(2) suspensions: determination of intermediates and the reaction pathway

The photocatalytic degradation of crotamiton in aqueous solution using TiO₂ was investigated. To investigate the effect of initial pH, the photodegradation behaviors of three types of pharmaceuticals were compared (crotamiton, clofibric acid, sulfamethoxazole). The degradation rates of crotamiton in the pH range 3-9 were nearly equal, but those of clofibric acid and sulfamethoxazole were affected by pH. At pH > 6.5, TiO₂ particles, clofibric acid and sulfamethoxazole had negative charge, therefore, the repulsive force between TiO₂ particles and anionic pharmaceuticals occurred and a low reaction rate at high pH was observed. The effect of UV intensity and TiO₂ concentration on photodegradation efficiency was also investigated. Linear and logarithmical relationships between UV intensity, TiO₂ concentration and the reaction rate constant were confirmed. Furthermore, the structures of photodegradation intermediates formed concomitantly with the disappearance of crotamiton were estimated. Seven intermediates were characterized by LC/MS/MS analyses, and it was assumed that the photocatalytic degradation of crotamiton was initiated by the attack of electrophilic hydroxyl radicals on aromatic rings and alkyl chains.     

Photocatalytic degradation of the herbicide pendimethalin using nanoparticles of BaTiO3/TiO2 prepared by gel to crystalline conversion method: A kinetic approach

Photocatalytic degradation of the herbicide, pendimethalin (PM) was investigated with BaTiO₃/TiO₂ UV light system in the presence of peroxide and persulphate species in aqueous medium. The nanoparticles of BaTiO₃ and TiO₂ were obtained by gel to crystallite conversion method. These photo catalysts are characterized by energy dispersive x-ray analysis (EDX), scanning electron microscope (SEM), x-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) adsorption isotherm and reflectance spectral studies. The quantum yields for TiO₂ and BaTiO₃ for the degradation reactions are 3.166 Einstein m^?2 s^?1 and 2.729 Einstein m^?2 s^?1 and catalytic efficiencies are 6.0444 × 10^?7 mg^?2h^?1L² and 5.403 × 10^?7 mg^?2h^?1L², respectively as calculated from experimental results. BaTiO₃ exhibited comparable photocatalytic efficiency in the degradation of pendimethalin as the most widely used TiO₂ photocatalyst. The persulphate played an important role in enhancing the rate of degradation of pendimethalin when compared to hydrogen peroxide. The degradation process of pendimethalin followed the first-order kinetics and it is in agreement with Langmuir-Hinshelwood model of surface mechanism. The reason for high stability of pendimethalin for UV-degradation even in the presence of catalyst and oxidizing agents were explored. The higher rate of degradation was observed in alkaline medium at pH 11. The degradation process was monitored by spectroscopic techniques such as ultra violet-visible (UV-Vis), infrared (IR) and gas chromatography mass spectroscopy (GC-MS). The major intermediate products identified were: N-propyl-2-nitro-6-amino-3, 4-xylidine, (2, 3-dimethyl-5-nitro-6-hydroxy amine) phenol and N-Propyl-3, 4-dimethyl-2, 6-dinitroaniline by GC-MS analysis and the probable reaction mechanism has been proposed based on these products.     

Photocatalytic degradation of gaseous toluene over Ag-doping TiO₂ nanotube powder prepared by anodization coupled with impregnation method

In this work, Ag-doping TiO₂ nanotubes were prepared and employed as the photocatalyst for the degradation of toluene. The TiO₂ nanotube powder was produced by the rapid-breakdown potentiostatic anodization of Ti foil in chloride-containing electrolytes, and then doped with Ag through an incipient wetness impregnation method. The samples were characterized by scanning electron microscope, high-resolution transmission electron microscopy, X-ray diffraction, surface photovoltage measurements, X-ray photoelectron spectroscopy and N₂ adsorption. The nanotubular TiO₂ photocatalysts showed an outer diameter of approximately 40 nm, fine mesoporous structure and high specific surface area. The photocatalytic activity of Ag-doping TiO₂ nanotube powder was evaluated through photooxidation of gaseous toluene. The results indicated that the degradation efficiency of toluene could get 98% after 4 h reaction using the Ag-doping TiO₂ nanotubes as the photocatalyst under UV light illumination, which was higher than that of the pure TiO₂ nanotubes, Ag-doping P25 or P25. Benzaldehyde species could be observed during the photocatalytic oxidation monitored by in situ FTIR, and the formed benzaldehyde intermediate during reaction would be partially oxidized into CO₂ and H₂O.     

Photocatalytic degradation of p,p′-DDT under UV and visible light using interstitial N-doped TiO2

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO₂ in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO₂ nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO₂ under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO₂ were evaluated. Results show that the N-doped TiO₂ can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min^?1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min^?1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO₂ catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO₂ under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO₂ under visible light was 0.03078 L mg^?1, and the apparent reaction rate constant (k) was 1.3941 mg L^?1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology.     

Photocatalytic oxidation of propoxur in aqueous titanium dioxide suspensions

Abstract

The photocatalytic oxidation of propoxur, a nitrogen‐containing pesticide, has been investigated using aqueous TiO₂ suspensions as catalyst in this study. The operating variables considered in the study were initial pH, temperature, [H₂O₂] and TiO₂ loading. Results showed that 1 g/l of TiO₂ was the optimum dosage for oxidizing propoxur in this system. Hydrogen peroxide can increase the oxidation rate with increasing its initial concentration. There was no obvious difference in the rate of propoxur oxidation at the initial pH of 4, 6 and 9, and the final pHs of reaction solutions were around 5.5. However, propoxur degraded slower at initial pH 2, and the pH did not vary during the period of photocatalytic reaction. The photocatalytic oxidation of propoxur using TiO₂ suspensions as the photocatalyst was reaction‐controlled as indicated by the activation energy.     

TiO2膜降解水中污染物的稳定性考察与再生方法研究

针对实际水处理中对催化剂性能的要求，以光催化降解苯酚溶液作为探针反应，考察了玻璃纤维网上负载的TiO₂膜催化剂长期使用条件下的稳定性，研究了催化剂在自来水中使用失活后的再生方法。结果表明，经过50次使用之后，膜催化剂120 min反应对苯酚的降解率从100%下降至83%，总体上看，所制催化剂还是具有相当好的稳定性；在反应器中用蒸馏水浸泡配合光催化反应对TiO₂膜催化剂进行原位再生是一种可行的再生途径。     

Studies on degradation of glyphosate by several oxidative chemical processes: Ozonation,photolysis and heterogeneous photocatalysis

Several different Advanced Oxidation Processes (AOPs) including ozonation at pH 6.5 and 10, photolysis and heterogeneous photocatalysis using TiO₂ as semiconductor and dissolved oxygen as electron acceptor were applied to study the degradation of glyphosate (N-phosphonomethyl glycine) in water. The degree of glyphosate degradation, the reactions kinetic and the formation of the major metabolite, aminomethyl phosphonic acid (AMPA), were evaluated. Ozonation at pH 10 resulted in the maximum mineralization of glyphosate. It was observed that under the experimental conditions used in this study the degradation of glyphosate followed the first-order kinetics. The half-life obtained for glyphosate degradation in the O₃/pH 10 process was 1.8 minutes.     

光催化降解模拟室内挥发性有机污染物研究

用浸渍-提拉法制备玻璃弹簧负载型TiO2薄膜催化剂,在自制的反应器中进行光催化降解由丙酮、甲苯、对二甲苯组成的模拟室内挥发性有机污染物VOCs研究.研究发现:催化剂中掺杂金属离子能影响催化剂的降解效果,降解效果依次为掺铈TiO2＞纯TiO2＞掺银TiO2;气体流量显著影响降解效果,丙酮、甲苯和对二甲苯的最佳降解流量分别为3、5、7 L/min;混合气体中非对称性的极性分子的降解效率高于对称性分子,导致丙酮、对二甲苯组分降解率降低,甲苯降解率增高.     

H4SiW12O40/TiO2/beads光催化降解亚甲基蓝的研究

以钛酸四丁酯为原料，空心微珠为载体，采用溶胶凝胶法制备TiO₂/beads光催化剂载体，然后浸渍法制备出H₄SiW₁₂O₄₀/TiO₂/beads表面负载修饰型复合光催化剂，并运用SEM、XRD、FT-IR和DRS对催化剂进行表征和分析。研究了H₄SiW₁₂O₄₀/TiO₂/beads对亚甲基蓝降解的光催化活性，考察了光强度、pH值、曝气量、底物浓度和催化剂用量等对催化效率的影响。实验结果表明，在中性条件下，H₄SiW₁₂O₄₀/TiO₂/beads催化剂的投加量为0.25 g/L，浓度为7.5 mg/L的亚甲基蓝溶液在250 W的紫外灯和600 W的可见光灯下光照60 min降解率分别可达到94.5%和55%。     

Fe/Ce/沸石负载型类芬顿催化剂制备及其特性

采用柠檬酸盐溶胶-凝胶法制备了Fe/Ce/沸石负载型芬顿催化剂,通过透射电镜(TEM)和X射线衍射(XRD)对其进行表征,并将其作为非均相类芬顿催化剂处理孔雀石绿染料溶液。研究表明,通过掺杂Ce,可提高催化剂颗粒分散度和催化剂表面的氧气含量,进而提高催化活性。在催化剂投加量3.0 g/L,H2O2投加量67 mg/L,pH=8.0的条件下,反应30 min后,浓度为150 mg/L的孔雀石绿溶液脱色率可达97.3%。     

Solar light–driven photocatalytic degradation and mineralization of beta blockers propranolol and atenolol by carbon dot/TiO2 composite

Herein improved solar light–driven photocatalytic degradation and mineralization of two emerging pollutants as well as recalcitrant beta blockers propranolol (PR) and atenolol (AT) have been demonstrated by metal-free carbon dot/TiO₂ (CDT) composite. Hydrothermally synthesized TiO₂ has been decorated with electrochemically synthesized carbon dots (CDs) and was well characterized by various analytical techniques viz. XRD, FTIR, Raman, XPS, UV–visible DRS, FESEM, and TEM. The optimized CDT composite, 2CDT (2 mL carbon dot/TiO₂), showed?~?3.45- and?~?1.75-fold enhancement in the photodegradation rate as compared to pristine TiO₂ for PR and AT respectively in 1 hour of irradiation along with complete degradation of PR and AT after 3 hours of irradiation. 2CDT exhibited 76% and 80% mineralization of PR and AT in contrast with 62% and 47% observed by pristine TiO₂. Further, the major reaction intermediates formed after degradation have been identified by HPLC/MS analysis, confirming more than 99% reduction of the parent compound for both PR and AT. Reusability of the optimized catalyst also showed successful degradation up to 3 cycles, showing reduction abilities of 97%, 95%, and 94% for 1st, 2nd, and 3rd cycle respectively. The enhanced degradation and mineralization efficiency of the 2CDT composite could be attributed to the excellent photosensitizer and electron reservoir properties of the CD along with upconverted photoluminescence behavior. The present study unlocks the possibility of using metal-free, facile CDT composite for effective degradation and mineralization of widely used beta blockers and other pharmaceuticals.

     

V2O5-TiO2-AlF3/Al2O3催化臭氧化2,4-滴丙酸的氧化效能

为了提高有机物的臭氧化降解效率,工作中利用浸渍法制备了一种新型的三组分催化剂(记为V2O5-TiO2-AlF3/Al2O3)。催化臭氧化降解2,4-滴丙酸的实验结果表明,该催化剂能有效提高臭氧化的效率,体系可能遵循羟基自由基的作用机理。利用相对法计算结果表明,与单独臭氧化相比,V2O5-TiO2-AlF3/Al2O3催化臭氧化体系具有更大的Rct值。重复实验结果表明,该催化剂具有相对较好的稳定性。以上研究结果对推广催化臭氧化技术在实际废水处理中的应用具有重要的实际意义。