Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

Oxalic acid destruction at high concentrations by combined heterogeneous photocatalysis and photo-Fenton processes

Heterogeneous photocatalysis (HP) using UV/TiO₂, photo-Fenton (PF) reaction using UV/Fe/H₂O₂ and the combination UV/TiO₂/Fe/H₂O₂ (HP–PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032 M). PF reactions were generally more efficient than HP including the reaction in the absence of H₂O₂. Oppositely to previous results (e.g., with EDTA), HP–PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO₂. The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates (R₀) and time to 95% of total mineralization (TOC₉₅). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC₉₅. Addition of Fe³⁺ also affects the reaction parameters but the effect of H₂O₂ seems to be higher, at least under the present conditions. When both H₂O₂ and iron were added simultaneously, the efficiency was higher. The optimal H₂O₂:Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H₂O₂ increased R₀ until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO₂. Analogies and differences with the EDTA system are presented.     

Fe-exchanged Y zeolite as catalyst for wet peroxide oxidation of reactive azo dye Procion Marine H-EXL

This paper evaluates the degradation of a reactive azo dye, Procion Marine H-EXL, by catalytic wet hydrogen peroxide oxidation (CWHPO). The catalyst was prepared by ion-exchange, starting from a commercially available ultrastable Y zeolite. All experiments were performed on a laboratory scale set-up. The effects of different reaction parameters such as initial pH, catalyst and hydrogen peroxide concentrations on the oxidation of the dye aqueous solution were assessed. Apart from the conventional parameters, the toxic potential of the dye’s degradation products was investigated using the bioluminescence test. HPICE analysis was also performed to obtain detailed information on the resulting oxidation products (organic and inorganic anions). The results indicate that after only 10 min at 50 °C, 20 mmol/l H₂O₂ and 1g/l FeY_11.5 the color removal was as high as of 97% at pH=3 and 53% at pH=5. More than 96% removal of the dye could be attained in 30 min at pH=5, t=50 °C, 20 mmol/l H₂O₂ and 1 g/l FeY_11.5 which corresponds to about 76% reduction of the initial COD and 37% removal of the initial TOC. A preliminary study of catalytic oxidation with hydrogen peroxide of the synthetic textile wastewater containing the specific dye is also presented. Leaching tests indicate that the activity of the catalyst is not due to leached iron ions, although an amount of 0.1–4.0 ppm of iron ions was found in aqueous solution. The catalyst allows almost total elimination of the dye and a significant removal of COD and TOC without the significant leaching of Fe ions. It was also observed that by using this catalyst, it is possible to extend the range of pH values for which Fenton-type oxidation can occur and no iron hydroxide sludge is formed.     

Formation of hydrogen peroxide from coal tar as hydrogen sources using 9-mesityl-10-methylacridinium ion as an effective photocatalyst

Visible light irradiation of an O₂-saturated acetonitrile (MeCN) solution containing 9-mesityl-10-methylacridinium ion (Acr⁺–Mes) and MeCN-extracted coal tar results in formation of hydrogen peroxide (H₂O₂). Anthracene and other aromatic hydrocarbons contained in coal tar act as hydrogen sources in the photocatalytic reduction of O₂ to produce H₂O₂. The photocatalytic formation of H₂O₂ is initiated by photoexcitation of Acr⁺–Mes, which results in formation of the electron-transfer state: Acr–Mes⁺, followed by electron-transfer from coal tar to the Mes⁺ moiety and electron-transfer from the Acr moiety to O₂.     

Ag-Zn_3(VO_4)_2光催化剂催化降解甲基橙溶液

采用水热法结合高温热处理制备Ag-Zn_3(VO_4)_2光催化剂,研究催化剂在可见光下降解甲基橙溶液的性能,并考察催化剂用量、甲基橙溶液初始浓度、pH值、盐效应和H_2O_2用量对光催化性能的影响,评价Ag-Zn_3(VO_4)_2光催化剂的重复使用性能。结果表明,在催化剂用量2.0 g·L~(-1)、甲基橙溶液初始浓度20 mg·L~(-1)和溶液pH=6.2条件下光照反应5 h,甲基橙溶液脱色率可达99.18%,Na_2SO_4对光催化降解甲基橙起抑制作用,且随着溶液中盐浓度增加,抑制作用更明显。H_2O_2在一定浓度范围可促进光催化降解甲基橙,100 mL甲基橙溶液中30%H_2O_2加入量为1.0 mL时,甲基橙溶液脱色率可提高21.68个百分点。催化剂重复使用5次后,光照5 h的甲基橙溶液脱色率仍可达到75.99%。     

Fe/Fe cycling promoted by Ta3N5 under visible irradiation in Fenton degradation of organic pollutants

Ta₃N₅ was synthesized by nitridation of Ta₂O₅ under NH₃ flow at 700 °C. The catalyst was pure Ta₃N₅ according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m²/g. When Ta₃N₅ was added to Fe³⁺/H₂O₂ solution (known as Fenton-like system), most Fe³⁺ were adsorbed on the Ta₃N₅ surface and could not react with H₂O₂ in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe³⁺ ions were reduced to Fe²⁺ rapidly and Fe²⁺ were reoxidized by H₂O₂ on the Ta₃N₅ surface, thus a fast Fe³⁺/Fe²⁺ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta₃N₅/Fe³⁺/H₂O₂ system could efficiently decompose H₂O₂ to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N,N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results.     

A combination of ultrasound and oxidative enzyme: sono-biodegradation of phenol

Sonolysis, enzyme treatment, and a combination of the two processes were tested for the degradation of phenol in aqueous medium. With sonolysis alone, 423 kHz ultrasound eliminated phenol molecules through hydroxyl radical reactions. In the presence of hydrogen peroxide, the enzyme horseradish peroxidase (HRP) catalyzed the oxidation of phenol to insoluble polymers which could be separated easily from the solution. In the combined system (HRP, H₂O₂, US-423 kHz) the degradation rate was accelerated, and the color of the solution changed to dark brown without any precipitate formation. The enhancement was more significant in the presence of additives such as polyethylene glycol (PEG). The higher rate induced through the use of ultrasound leads to the reduction of HRP dose requirements, which is of importance for the economic feasibility of this method. The enzyme solution alone did not show any inactivation up to 45 min sonication at 423 kHz. Investigation of phenol removal efficiency was mainly focused on enzyme, phenol and PEG concentrations, as well as the sequence and method of addition of reagents.     

ELIMINATION OF BENZENE AND CHLOROBENZENES BY PHOTODEGRADATION AND OZONATION PROCESSES

Benzene (B) and two representative chlorobenzenes (1,4-dichlorobenzene (DCB) and 1,2,3-trichlorobenzene (TCB)) were oxidized by means of UV irradiation alone, ozone alone, and the combinations UV/H₂O₂ and O₃/H₂O₂. In the single photolytic process, the influence on the photodegradation of the pH, temperature, and type of radiation source used was established. A kinetic study was performed by evaluating the first-order rate constants and the quantum yields. The effect of the additional presence of hydrogen peroxide was pointed out in the combined process UV/H₂O₂,with the determination of the specific contribution of the radical pathway to the overall photodegradation system. In the oxidation by ozone based systems (ozone alone and the combination O₃/H₂O₂), the rate constants at 20°C for the reaction of each compound with ozone and hydroxyl radicals were determined.     

Degradation of salicylic acid by photo-assisted Fenton reaction using Fe ions on strongly acidic ion exchange resin as catalyst

The photo-assisted Fenton degradation of salicylic acid (SA) was studied by using strongly acidic ion exchange resin (SAIER) exchanged with Fe ions as catalyst in the presence of UV light (254 nm) and H₂O₂. The X-ray photoelectron spectroscopy (XPS) results revealed that the Fe ions are indeed anchored by the sulfonate groups on the surface of the SAIER and are Fe³⁺. Our results also indicate that the Fe/SAIER catalyst can significantly enhance the degradation rate of SA without remarkable Fe leaching to the solution, implying that the catalyst has photo-catalytic activity. In addition, the effects of [H₂O₂]/[SA] molar ratio, UVC light power, solution pH, catalyst loading, and initial SA concentration on the degradation of SA were investigated in detail.     

H2O2预氧化对BFA复合融雪剂性能的影响及其融雪机理

针对H₂O₂预氧化对生化黄腐酸（BFA）钙盐复合物的融雪化冰性能影响及其机理进行了研究。结果表明,在H₂O₂与BFA质量比为1.5、pH 7.5、35℃的最佳预降解条件下反应120 min,可使BFA钙盐复合物的冰点降低27%。紫外光谱、红外光谱及凝胶色谱分析结果表明,BFA经H₂O₂氧化降解后,一些复杂的芳香族有机物发生降解甚至开环、不饱和脂肪烃被氧化,产生了大量小分子羧酸、醇、酚及烯烃等有机物。它们在Ca²⁺的络合作用下形成了小分子聚合物或共聚物,在融雪化冰中起主要作用。增加BFA结构中的-COOH、-OH和ph-OH等亲水性基团含量是提高BFA钙盐复合融雪剂性能的关键。     

Hydroxyl radical-involved cancer therapy via Fenton reactions

The tumor microenvironment features over-expressed hydrogen peroxide(H₂O₂).Thus,versatile therapeutic strategies based on H₂O₂ as a reaction substrate to generate hydroxyl radical(?OH)have been used as a prospective therapeutic method to boost anticancer efficiency.However,the limited Fenton catalysts and insufficient endogenous H₂O₂ content in tumor sites greatly hinder?OH production,failing to achieve the desired therapeutic effect.Therefore,supplying Fenton catalysts and elevating H₂O₂ levels into cancer cells are effective strategies to improve?OH generation.These therapeutic strategies are systematically discussed in this review.Furthermore,the challenges and future developments of hydroxyl radical-involved cancer therapy are discussed to improve therapeutic efficacy.     

Reductive/oxidative treatment with superior performance relative to oxidative treatment during the degradation of 4-chlorophenol

This study obtained information on the effectiveness of the photo-assisted Fenton oxidation of 4-chlorophenol (4-CP) combined with zero-valent pretreatment. The kinetic rate parameters of the process as well as the operating conditions were determined. Homogeneous photo-assisted Fenton enhanced processes lead to 33% mineralization of 4-chlorophenol (1.25 mM) in solutions containing Fe-ions (2–10 mg/l) and H₂O₂ (10 mM) within 2 h under visible light irradiation. When this solution was pretreated with zero-valent Fe (14 g/70 ml) in Ar atmosphere, the mineralization attained levels of >80% after the second stage photo-assisted Fenton process. Intermediates that could be effectively degraded by photo-Fenton reactions were not attained in the absence of zero-valent Fe pretreatment. The pretreatment by zero-valent Fe under light lead to about 70% of the stoichiometric amount of chloride contained in 4-CP. Partial recovery of chloride ions indicated the formation of chloro-intermediates. These intermediates were experimentally detected by high-pressure liquid chromatograph (HPLC)–MS and the most important intermediates were identified. Fenton photo-assisted processes were effective employing very low concentrations of Fe²⁺(2–5 mg/l) after the pretreatment stage that do not need to be separated after the 4-CP degradation process. This is important for the practical application of the novel combined heterogeneous–homogeneous process. Evidence for the stable catalytic performance of the coupled process to degrade 4-CP is presented. The effect on the 4-CP degradation of Fe-ion, H₂O₂, 4-CP concentration and gas atmosphere was systematically investigated. The activation energy (E_a) of 2.66 kJ/mol was found for the abatement of 4-CP.     

O3 based advanced oxidation for ibuprofen degradation

The degradation of the anti-inflammatory ibuprofen (IBP) was evaluated by several advanced oxidation processes. IBP was treated by single ozonation and oxidation with hydrogen peroxide (H₂O₂), as well as a combination of these treatments. In order to improve the efficiency, the presence of catalysts such as original carbon nanotubes, labelled as CNT, and iron oxide supported on carbon nanotubes, named as Fe/CNT sample, was considered. The evolution of IBP degradation, mineralization and toxicity of the solutions was assessed. The formation of intermediates was also monitored. In the non-catalytic processes, IBP was faster removed by single ozonation, whereas no significant total organic carbon (TOC) removal was achieved. Oxidation with H₂O₂ did not present satisfactory results. When ozone and H₂O₂ were combined, a higher mineralization was attained (70% after 180 min of reaction). On the other hand, in the catalytic processes, this combined process allowed the fastest IBP degradation. In terms of mineralization degree, the presence of Fe/CNT increases the removal rate in the first hour of reaction, achieving a TOC removal of 85%. Four compounds were detected as by-products. All treated solutions presented lower toxicity than the initial solution, suggesting that the released intermediates during applied processes are less toxic.     

Hydrogen-storage properties of a Mg-based mixture prepared by reactive mechanical grinding with ultrafine Fe2O3 particles and Ni

The sample Mg-10 wt.% (Fe₂O₃, Ni) was prepared by grinding Mg mechanically under H₂ (reactive mechanical grinding) with ultrafine Fe₂O₃ particles and Ni particles. The sample Mg-10 wt.% (Fe₂O₃, Ni) as milled absorbed 4.24 wt.% hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished only by one hydriding–dehydriding cycle. The activated sample absorbed 4.05 wt.% hydrogen at 593K, 12 bar H₂ for 60 min and desorbed 3.05 wt.% hydrogen at 593 K, 1.0 bar H₂ for 60 min. After hydriding–dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.     

Cu/Al2O3催化剂用于H2O2分解生成羟基自由基的效率

非均相Fenton催化反应是降解废水中有机污染物的有效方法。提高H₂O₂分解生成羟基自由基（·OH）的利用率是提升废水处理效率、降低成本的关键。使用溶胶-凝胶法制备了Cu/Al₂O₃催化剂,基于·OH的生成效率,通过单因素实验发现反应温度、反应溶液pH及H₂O₂初始浓度是决定H₂O₂利用率的主要因素。通过响应面法进行实验设计,分析响应面方程,考察了H₂O₂初始浓度、溶液pH及反应温度三个因素之间的交互作用及其对反应过程的影响。以H₂O₂利用率的最大化为目标优化反应条件,当H₂O₂初始浓度、溶液pH及反应温度分别为707 mg·L^-1、5.12及59.4℃时,H₂O₂利用率可高达0.57,与实验结果相对误差仅为3.5%。所得结果对降低废水处理成本、提高降解效率具有重要的指导作用。     

H4SiW12O40-catalyzed oxidation of nitrobenzene in supercritical water: kinetic and mechanistic aspects

The catalytic effect of a heteropolyacid, H₄SiW₁₂O_40, on nitrobenzene (20 and 30 μM) oxidation in supercritical water was investigated. A capillary flow-through reactor was operated at varying temperatures (T=400–500 °C; P=30.7 MPa) and H₄SiW₁₂O₄₀ concentrations (3.5–34.8 μM) in an attempt to establish global power-law rate expressions for homogenous H₄SiW₁₂O₄₀-catalyzed and uncatalyzed supercritical water oxidation. Oxidation pathways and reaction mechanisms were further examined via primary oxidation product identification and the addition of various hydroxyl radical scavengers (2-propanol, acetone, acetone-d₆, bromide and iodide) to the reaction medium. Under our experimental conditions, nitrobenzene degradation rates were significantly enhanced in the presence of H₄SiW₁₂O₄₀. The major differences in temperature dependence observed between catalyzed and uncatalyzed nitrobenzene oxidation kinetics strongly suggest that the reaction path of H₄SiW₁₂O₄₀-catalyzed supercritical water oxidation (average activation E_a=218 kJ/mol; k=0.015–0.806 s⁻¹ energy for T=440–500 °C; E_a=134 kJ/mol for the temperature range T=470–490 °C) apparently differs from that of uncatalyzed supercritical water oxidation (E_a=212 kJ/mol; k=0.37–6.6 μM s⁻¹). Similar primary oxidation products (i.e. phenol and 2-, 3-, and 4-nitrophenol) were identified for both treatment systems. H₄SiW₁₂O₄₀-catalyzed homogenous nitrobenzene oxidation kinetics was not sensitive to the presence of OH√ scavengers.     

Oxidative leaching kinetics of molybdenum-uranium ore in H2SO4 using H2O2 as an oxidizing agent

The processing of molybdenum-uranium ore in a sulfuric acid solution using hydrogen peroxide as an oxidant has been investigated. The leaching temperature, hydrogen peroxide concentration, sulfuric acid concentration, leaching time, particle size, liquid-to-solid ratio and agitation speed all have significant effects on the process. The optimum process operating parameters were: temperature: 95°C; H₂O₂ concentration: 0.5 M; sulfuric acid concentration: 2.5 M; time: 2 h; particle size: 74 μm, liquid-to-solid ratio: 14 ∶ 1 and agitation speed: 600 rpm. Under these experimental conditions, the extraction efficiency of molybdenum was about 98.4%, and the uranium extraction efficiency was about 98.7%. The leaching kinetics of molybdenum showed that the reaction rate of the leaching process is controlled by the chemical reaction at the particle surface. The leaching process follows the kinetic model 1 ? (1?X)^1/3 = kt with an apparent activation energy of 40.40 kJ/mole. The temperature, concentrations of H₂O₂ and H₂SO₄ and the mesh size are the main factors that influence the leaching rate. The reaction order in H₂SO₄ was 1.0012 and in H₂O₂ it was 1.2544.     

Immobilized Fe(III)-HY: an efficient and stable photo-Fenton catalyst

This article presents preparation, characterization and evaluation of an efficient heterogeneous Fe(III)-HY catalyst for photo-assisted Fenton reaction. Fe(III) ions are immobilized on HY zeolite using different loadings by impregnation, calcination and the activity of the catalyst is evaluated by the degradation of phenol. To initiate a photo-Fenton reaction, suspended Fe(III)-HY in solution is irradiated using UV light to form Fe(II)-HY necessary for the reaction to go. The effect of Fe loadings, H₂O₂ concentration, pH and quenching on photo-Fenton reaction are studied. The results obtained clearly show that 0.25 wt.% Fe(III)-HY is efficient in the degradation of phenol at pH = 6. Further the efficiency of Fe(III)-HY is compared with that of a homogeneous photo-Fenton reaction and the increased rate of reaction on Fe(III)-HY highlights the synergistic role of zeolite. Heterogeneous Fe(III)-HY in photo-Fenton reaction allows a wide range of pH for reaction against the narrow pH range in homogeneous system. The system is further subjected to evaluate its stability in solid state. Firstly the reaction solution containing Fe(III)-HY catalyst on irradiation is analyzed for Fe ions with atomic absorption spectroscopy (AAS) and also by calorimetry using 1,10-phenanthroline (o-phen) to find out any Fe leaching from the catalyst and the results show insignificant leaching of Fe (<0.3 ppm) at maximum loading of Fe under experimental conditions. Secondly, the irradiated Fe(III)-HY is complexed with o-phen and it is subjected to Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS) and electron spectroscopy for chemical analysis (ESCA) studies to detect and confirm the oxidation state of Fe in solid state. Critical analysis of these studies clearly show that Fe(III)-HY on irradiation changed to Fe(II)-HY and it is intact with the surface during the course of the reaction. The DRS spectra further evidences complexation of Fe(II) with o-phen. The stability of the catalyst is established by recycling studies.     

The beneficial role of use of ultrasound in heterogeneous Fenton-like system over supported copper catalysts for degradation of p-chlorophenol

A heterogeneous sono-catalytic system with addition of hydrogen peroxide (US_H2O2+Cat.) was employed for the degradation of 200 ppm of p-chlorophenol (4-CP) at 25 °C and 100 W of ultrasound power. One thousand and six hundred parts per million of initial hydrogen peroxide (H₂O₂) concentration and 1 g/L of catalyst loading over three heterogeneous copper catalysts, CuO, Cu/Al₂O₃ (Cu/Al) and CuO·ZnO/Al₂O₃ (Cu/Zn) was used. The benefits of ultrasound in a heterogeneous catalytic system were evaluated. A considerable synergistic effect of the US_H2O2+Cat. system was only achieved with supported catalysts (Cu/Al and Cu/Zn) possibly due to good dispersion of catalysts as a result of catalyst size reduction during ultrasound irradiation. Moreover, between the two supported copper catalysts, the Cu/Al provided promising catalytic performance by giving higher 4-CP and TOC removal accompanied with efficient H₂O₂ consumption. Experiments with a homogeneous copper catalyst revealed that use of ultrasound in a homogeneous system shows an adverse effect on decomposition of 4-CP.     

Comparison of supports for the direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using a range of supported Au–Pd alloy catalysts is compared for different supports using conditions previously identified as being optimal for hydrogen peroxide synthesis, i.e. low temperature (2 °C) using a water–methanol solvent mixture and short reaction time. Five supports are compared and contrasted, namely Al₂O₃, -Fe₂O₃, TiO₂, SiO₂ and carbon. For all catalysts the addition of Pd to the Au only catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Of the materials evaluated, the carbon-supported Au–Pd alloy catalysts give the highest reactivity. The results show that the support can have an important influence on the synthesis of hydrogen peroxide from the direct reaction. The effect of the methanol–water solvent is studied in detail for the 2.5 wt% Au–2.5 wt% Pd/TiO₂ catalyst and the ratio of methanol to water is found to have a major effect on the rate of hydrogen peroxide synthesis. The optimum mixture for this solvent system is 80 vol.% methanol with 20 vol.% water. However, the use of water alone is still effective albeit at a decreased rate. The effect of catalyst mass was therefore also investigated for the water and water–methanol solvents and the observed effect on the hydrogen peroxide productivity using water as a solvent is not considered to be due to mass transfer limitations. These results are of importance with respect to the industrial application of these Au–Pd catalysts.