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.     

Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase

The reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO2 process, including substrate adsorption, degradation, and mineralization, was studied. The theoretical maximum quantity of MCB that could be adsorbed onto TiO2 surface in aqueous phase was 0.18+/-0.04 micromol m(-2) of TiO2. In accordance with the upper limit of the relative surface coverage of MCB molecules to surface hydroxyls of TiO2 was around 2.2%, the water molecules as the major adjacent species near TiO2 surface would compete with MCB molecules. Increasing the initial substrate concentration to an appropriate value or enhancing the affinity between the MCB and the TiO2 surface by adjusting the solution pH would promote the photocatalytic degradation. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition. Generally, 90% of the total organic carbon (TOC) was mineralized after 240 min illumination time in the examined pH range except solution pH 11. The suppressed mineralization of MCB at solution pH 11 was ascribed to the lack of adsorption. A simplified 2-step consecutive kinetic model was used to simulate the mineralization.     

pH indications in aqueous organic photodecompositions with carbonyl and hydroxyl groups

A pH variation pattern during organic compound (ethylene glycol, phenol, and glucose) decomposition under UV/H2O2 of different schemes was observed. This method was successfully applied to reflect the organic carbon oxidation progress, especially the rapid chemical oxygen demand (COD) decrease timing in the later mineralization stage. The results were demonstrated in a sequential feed-batch advanced oxidation reactor, showing that pH can be used as an alternative indicator to provide complete oxidation and cycle time information.     

Photochemical behaviour of carbendazim in aqueous solution

To elucidate the photochemical behaviour of carbendazim (or MBC) in superficial waters, photolysis studies have been carried out in aqueous solutions at several pH using a UV light source (high pressure mercury arc lamp) or a solar light simulator (xenon arc lamp). The kinetics of photodecomposition of carbendazim was determined using HPLC-DAD and the identification of photoproducts was carried out with HPLC-MS (ESI negative and positive mode). According to the experimental results carbendazim is a rather stable molecule in the dark or in environmental conditions. The pH influence of the environmental medium on the photodegradation rate has been confirmed. The photochemical process can be considerably accelerated in alkaline solutions using HPK-quartz irradiation (quantum efficiency at pH 9 phi = 3.1 x 10(-3) degraded molecule per absorbed photon) while the photodegradation is not as efficient under a simulated sun irradiation (quantum efficiency in the suntest phi = 10(-4) at pH 7). Three photoproducts have been tentatively identified in pure water: 2-aminobenzimidazole, benzimidazole isocyanate and monocarbomethoxy-guanidine (issued from the cleavage of the benzimidazole ring). The last one seems very stable and could be accumulated in the environment.     

Electrochemical monitoring of methylparathion degradation in an acid aqueous medium in presence of Cu(II)

A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o,4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2-7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH < or = 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 x 10(-3) s(-1) at pH 2, 5.5 x 10(-3) s(-1) at pH 4 and 9.0 x 10(-3) s(-1) at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.     

Phenol photonitration upon UV irradiation of nitrite in aqueous solution II: effects of pH and TiO2.

Phenol photonitration and photonitrosation were studied both in homogeneous and in heterogeneous phase in the presence of TiO2 particles. The effect of pH as well as of the semiconductor particles on the kinetics and products of the reaction was observed. Formation of nitrophenols is enhanced at acidic pH, due to thermal processes initiated by nitrous acid, as well as in the presence of TiO2, due to the photocatalytic oxidation of nitrite.     

Ferric citrate-induced photodegradation of dyes in aqueous solutions

The photooxidation of dye solutions containing Fe(III)-citrate complexes was studied. The photodegradation under near-UV light of the five dyes, C. I. reactive red 2, C. I. reactive blue 4, C. I. reactive black 8, C. I. basic red 13 and C. I. basic yellow 2, in aqueous solutions at pH2.0 containing Fe(III)-citrate complexes was found to follow pseudo-first order kinetics. The photodegradation rates of the dye, C. I. reactive red 2, decreased with increasing the initial dye concentration in range of 20 – 60 mg/L . A comparatively higher photodegradation efficiency of the dye was gained under the condition of pH2.0 and the Fe(III) to citrate ratio 1:2.     

Rapid and complete dechlorination of PCP in aqueous solution using Ni-Fe nanoparticles under assistance of ultrasound

The Ni-Fe bimetallic particles have been laboratory prepared using sodium borohydride (NaBH4) as the reductant to reduce Ni2+ and Fe2+ in aqueous solution simultaneously, and characterized by TEM, XRD, BET and XPS. The particles were proved to be nanoscale amorphous alloy with an average diameter of about 30 nm and a BET surface area of 20.9 m2 g(-1). Experiments for dechlorination of pentachlorophenol (PCP) by the Ni-Fe bimetallic nanoscale particles in aqueous solutions were carried out under the enhancement of ultrasound. Major factors that influence the dechlorination efficiency, such as initial pH value, Ni content in the Ni-Fe particles, and output power of ultrasonic irradiation, were investigated. The results indicated that Ni-Fe nanoscale bimetallic particles were very effective for the dechlorination of PCP. Dechlorination efficiency was 46% in 30 min under the optimal condition without assistance of ultrasound, whereas it increased to 96% when ultrasonic irradiation was present. Initial pH value showed apparent effect on the dechlorination. As the pH varied from acidic condition to neutral condition, the dechlorination efficiency decreased dramatically. In addition, the dechlorination efficiency was improved with increased Ni/Fe ratio and ultrasonic output power. Less chlorinated phenols including tetrachlorophenol, trichlorophenol, dichlorophenol, monochlorophenol were formed during the initial reaction, and phenol was determined by GC-MS as sole product in the end of reaction.     

Removal of aqueous lead by poorly-crystalline hydroxyapatites

The use of a phosphorus amendment in altering Pb to a chemically less mobile phase is a promising strategy based on minimizing ecotoxicological risk and improving time and cost efficiency. This study evaluated crystalline and poorly-crystalline hydroxyapatite sorbents on removal of aqueous Pb in response to reaction time, solution pH, and Pb concentration. Batch experiments were conducted using a commercially-available crystalline hydroxyapatite (HA), and two poorly-crystalline hydroxyapatites synthesized from gypsum waste (CHA) and incinerated ash of poultry waste (MHA). Poorly-crystalline hydroxyapatites had greater capacity for Pb removal from a solution with a wider pH range as compared to a crystalline hydroxyapatite. The maximum sorption capacity of Pb determined by the Langmuir model was 500 mg g⁻¹ for CHA, 277 mg g⁻¹ for MHA and 145 mg g⁻¹ for HA. Removal of aqueous Pb by CHA was not dependent on solution pH, with a 98.8% reduction throughout the solution pH range of 2–9, whereas aqueous Pb removal by HA and MHA was pH-dependent with less removal in the neutral solution pH. Poorly-crystalline hydroxyapatites may provide an effective alternative to existing remediation technologies for Pb-contaminated sites.     

Photo-Fenton-assisted ozonation of p-Coumaric acid in aqueous solution

The degradation of p-Coumaric acid present in olive oil mill wastewater was investigated as a pretreatment stage to obtain more easily biodegradable molecules, with lower toxicity that facilitates subsequent anaerobic digestion. Thus, photo-Fenton-assisted ozonation has been studied and compared with ozonation at alkaline pH and conventional single ultraviolet (UV) and acid ozonation treatments. In the combined process, the overall kinetic rate constant was split into various components: direct oxidation by UV light, direct oxidation by ozone and oxidation by hydroxyl radicals. Molecular and/or radical ozone reaction was studied by conducting the reaction in the presence and absence of tert-butylalcohol at pHs 2, 7 and 9. Ozone oxidation rate increases with pH or by the addition of Fenton reagent and/or UV radiation due to generation of hydroxyl radicals, *OH. Hydrogen peroxide and ferrous ion play a double role during oxidation since at low concentrations they act as initiators of hydroxyl radicals but at high concentrations they act as radical scavengers. Finally, the additional levels of degradation by formation of hydroxyl radicals have been quantified in comparison to the conventional single processes and an equation is proposed for the reaction rate as a function of studied operating variables.     

Hydrolysis and photolysis of oxytetracycline in aqueous solution

Oxytetracycline ((2Z,4S,4aR,5S,5aR,6S,12aS)-2-(amino-hydroxy-methylidene)-4-dimethylamino-5,6,10,11,12a-pentahydroxy-6-methyl-4,4a,5,5a-tetrahydrotetracene-1,3,12-trione) is a member of tetracycline antibiotics family and is widely administered to farm animals for the purpose of therapeutical treatment and health protection. Increasing attention has been paid to the environmental fate of oxytetracycline and other veterinary antibiotics with the occurrence of these antibiotics in the environment. The hydrolysis and photolysis degradation of oxytetracycline was investigated in this study. Oxytetracycline hydrolysis was found to obey the first-order model and similar rate constant values ranging from 0.094 ± 0.001 to 0.106 ± 0.003 day^{? 1} were obtained at different initial concentration ranging from 10 to 230 μ M. Solution pH and temperature were shown to have remarked effects on oxytetracycline hydrolysis. The hydrolysis in pH neutral solution appeared to be much faster than in both acidic and alkaline solutions. Oxytetracycline half-life decreased from 1.2 × 10² to 0.15 day with the increasing temperature from 4 ± 0.8 to 60 ± 1°C. The presence of Ca^{2 +} made oxytetracycline hydrolytic degradation kinetics deviate from the simple first-order model to the availability-adjusted first-order model and greatly slowed down the hydrolysis. Oxytetracycline photolysis was found to be very fast with a degradation rate constant at 3.61 ± 0.06 day^{? 1}, which is comparable to that of hydrolysis at 60°C. The presence of Ca^{2 +} accelerated oxytetracycline photolysis, implying that oxytetracycline become more vulnerable to sunlight irradiation after chelating with Ca^{2 +}. The photolysis may be the dominant degradation pathway of oxytetracycline in shallow transparent water environment.     

废弃绿茶对水溶液中Co2+的吸附研究

利用废弃绿茶叶粉末(简称茶叶末)作为吸附剂,考察了pH、温度、时间等对水溶液中Co2+的影响。结果表明:(1)茶叶末对Co2+的吸附量随着pH的上升而上升,其中pH=5.50为最佳。茶叶末对Co2+的吸附量均随时间延长呈现上升趋势,吸附速度先快后慢,吸附最佳时间为90min。(2)不同温度下,茶叶末对Co2+的吸附较好地符合Langmuir模型。该吸附过程是化学离子交换过程,主要发生在重金属离子与羟基、氨基的氢原子之间。(3)茶叶末对Co2+的吸附是自发、放热过程,降温有利于吸附,反应时吸附界面上的混乱度增加。(4)盐酸是很好的解吸介质,解吸率为92.65%。通过灼烧(或燃烧)可以回收水溶液中绝大部分的Co2+,不仅减小了对环境的污染,而且节约了资源。     

Fresnel lens to concentrate solar energy for the photocatalytic decoloration and mineralization of orange II in aqueous solution

The decoloration and mineralization of the azo dye orange II under conditions of artificial ultraviolet light and solar energy concentrated by a Fresnel lens in the presence of hydrogen peroxide and TiO(2)-P25 was studied. A comparative study to demonstrate the viability of this solar installation was done to establish if the concentration reached in the focus of the Fresnel lens was enough to improve the photocatalytic degradation reaction. The degradation efficiency was higher when the photolysis was carried out under concentrated solar energy irradiation as compared to UV light source in the presence of an electron acceptor such us H(2)O(2) and the catalyst TiO(2). The effect of hydrogen peroxide, pH and catalyst concentration was also determined. The increase of H(2)O(2) concentration until a critical value (14.7 mM) increased both the solar and artificial UV oxidation reaction rate by generating hydroxyl radicals and inhibiting the (e(-)/h(+)) pair recombination, but the excess of hydrogen peroxide decreases the oxidation rate acting as a radical or hole scavenger and reacting with TiO(2) to form peroxo-compounds, contributing to the inhibition of the reaction. The use of the response surface methodology allowed to fit the optimal values of the parameters pH and catalyst concentration leading to the total solar degradation of orange II. The optimal pH range was 4.5-5.5 close to the zero point charge of TiO(2) depending on surface charge of catalyst and dye ionization state. Dosage of catalyst higher than 1.1 gl(-1) decreases the degradation efficiency due to a decrease of light penetration.     

Continuous flow photo-Fenton treatment of ciprofloxacin in aqueous solutions using homogeneous and magnetically recoverable catalysts

The degradation of ciprofloxacin was studied in aqueous solutions by using a continuous flow homogeneous photo-Fenton process under simulated solar light. The effect of different operating conditions on the degradation of ciprofloxacin was investigated by changing the hydrogen peroxide (0–2.50 mM) and iron(II) sulphate (0–10 mg Fe L^?1) concentrations, as well as the pH (2.8–10), irradiance (0–750 W m^?2) and residence time (0.13–3.4 min) of the process. As expected, the highest catalytic activity in steady state conditions was achieved at acidic pH (2.8), namely 85 % of ciprofloxacin conversion, when maintaining the other variables constant (i.e. 2.0 mg L^?1 of iron(II), 2.50 mM of hydrogen peroxide, 1.8 min of residence time and 500 W m^?2 of irradiance). Additionally, magnetite magnetic nanoparticles (ca. 20 nm of average particle size) were synthesized, characterized and tested as a possible catalyst for this reaction. In this case, the highest catalytic activity was achieved at natural pH, namely a 55 % average conversion of ciprofloxacin in 1.8 min of residence time and under 500 W m^?2. Some of the photocatalytic activity was attributed to Fe²⁺ leaching from the magnetic nanoparticles to the solution.     

4A沸石去除水中Pb2＋的研究

在静态条件下，研究了4A沸石对废水中Pb2＋的吸附性能，并探讨了影响吸附的因素。实验表明：当温度为30℃，废水pH为5～6，0．01g4A沸石对100mg／LPb2＋溶液10mL吸附20min，Pb2＋的去除率可达到99％以上。在实验研究条件下，4A沸石对Pb2＋的吸附符合Langmuir和Freundlich等温吸附方程，相关系数为0．9819和0．9998。经计算，4A沸石对Pb2＋的饱和吸附量为125mg／g。4A沸石吸附水中Pb2＋达到吸附平衡的时间较短；溶液pH值的变化对吸附效果影响不显著；温度从室温略微升高，Pb2＋的去除率略有增大。吸附在4A沸石上的Pb“可回收利用，处理后的4A沸石可以再生，且重复使用性能较好。     

Removal of aqueous lead by poorly-crystalline hydroxyapatites

The use of a phosphorus amendment in altering Pb to a chemically less mobile phase is a promising strategy based on minimizing ecotoxicological risk and improving time and cost efficiency. This study evaluated crystalline and poorly-crystalline hydroxyapatite sorbents on removal of aqueous Pb in response to reaction time, solution pH, and Pb concentration. Batch experiments were conducted using a commercially-available crystalline hydroxyapatite (HA), and two poorly-crystalline hydroxyapatites synthesized from gypsum waste (CHA) and incinerated ash of poultry waste (MHA). Poorly-crystalline hydroxyapatites had greater capacity for Pb removal from a solution with a wider pH range as compared to a crystalline hydroxyapatite. The maximum sorption capacity of Pb determined by the Langmuir model was 500 mg g⁻¹ for CHA, 277 mg g⁻¹ for MHA and 145 mg g⁻¹ for HA. Removal of aqueous Pb by CHA was not dependent on solution pH, with a 98.8% reduction throughout the solution pH range of 2–9, whereas aqueous Pb removal by HA and MHA was pH-dependent with less removal in the neutral solution pH. Poorly-crystalline hydroxyapatites may provide an effective alternative to existing remediation technologies for Pb-contaminated sites.     

Photodegradation of the antimicrobial triclocarban in aqueous systems under ultraviolet radiation

This work aimed to investigate the effectiveness of ultraviolet (UV) radiation on the degradation of the antimicrobial triclocarban (TCC). We investigated the effects of several operational parameters, including solution pH, initial TCC concentration, photocatalyst TiO₂ loading, presence of natural organic matter, and most common anions in surface waters (e.g., bicarbonate, nitrate, and sulfate). The results showed that UV radiation was very effective for TCC photodegradation and that the photolysis followed pseudo-first-order kinetics. The TCC photolysis rate was pH dependent and favored at high pH. A higher TCC photolysis rate was observed by direct photolysis than TiO₂ photocatalysis. The presence of the inorganic ions bicarbonate, nitrate, and sulfate hindered TCC photolysis. Negative effects on TCC photolysis were also observed by the addition of humic acid due to competitive UV absorbance. The main degradation products of TCC were tentatively identified by gas chromatograph with mass spectrometer, and a possible degradation pathway of TCC was also proposed.     

TiO2/EP光催化降解水体中微污染磺胺嘧啶的研究

制备了膨胀珍珠岩（EP）为载体的TiO2催化剂（TiO2/EP）,对使用较为广泛的抗生素磺胺嘧啶（SDZ）进行了光催化降解研究,探讨了TiO2的负载量、溶液的初始浓度、初始pH、无机离子（HCO3^-、SO4^2-和Cl^-）和腐殖酸（HA）对SDZ降解效果的影响。结果表明：SDZ的光催化降解符合一级反应动力学方程;当TiO2最佳负载量为20 wt%,SDZ浓度为5 mg/L,pH=6.7,紫外光照射强度为1 000μW/cm^2,反应时间为45 min时,SDZ的降解率达到96%;HCO3^-在低浓度时能促进SDZ的光催化降解,高浓度时促进作用不明显;SO4^2-和Cl^-对SDZ的光催化降解有轻微的抑制作用;HA对SDZ光催化降解有显著的抑制作用,浓度越高,抑制作用越强。UV-TiO2/EP是一种去除水体中微污染SDZ的有效方法。     

季铵化木屑纤维素的制备及其对水中苯酚的吸附性能研究

以3-氯-2-羟丙基三甲基氯化铵(CTA)为醚化剂，对木屑纤维素进行了改性。探讨了改性木屑纤维素用量、pH值、吸附温度、吸附时间和苯酚初始浓度等因素对静态吸附效果的影响。结果表明，木屑纤维素经改性后，对水中的苯酚的吸附过程存在化学吸附，对水中的苯酚的吸附容量得到明显提高。     

Degradation of microcystins in aqueous solution with in situ electrogenerated active chlorine

A new and efficient method for the degradation of microcystins (one family of blue algal toxins) was developed and studied. Microcystins (MCs) in water were directly and effectively removed by active chlorine transformed in situ from the naturally existing Cl- in water resource using electrochemical method. Titanium coated with RuO2 and TiO2 was used as the anode. Microcystin-RR (MCRR) and Microcystin-LR (MCLR) were chosen as the model compounds of MCs. The results suggested that 20.87 mgl(-1) MCs (12.58 mgl(-1) MCRR and 8.29 mgl(-1) MCLR) in aqueous solution with 1.85 mM Cl- could be synchronously decomposed within 15 min electrolysis under the condition of the current density 8.89 mAcm(-2), 20 degrees C and pH 7.00. The qualitative analysis showed that the heptapetide ring and the Adda group of both treated MCs were changed. The results also indicated that the removal rates of both MCs increased with the increasing of chloride concentration and applied current density, but decreased with the increasing of initial concentration of MCs and initial pH of electrolyte. In the absence of Cl-, only a small fraction of both MCs were decomposed by direct anodic oxidation, while their almost complete removals could be obtained in the case of indirect electrooxidation with in situ electrogenerated active chlorine from Cl- in water.