Presence Of Radical Scavengers Research Articles

Photocatalytic and persulfate-facilitated tetracycline degradation using NiFe2O4/carbon/polymer membranes: Activity and stability during flow-through

We synthesized NiFe2O4/carbon composite nanoparticles through a straightforward co-precipitation method, and incorporated these particles into porous polyethersulfone (PES) membranes via casting solution blending and film casting cum phase separation. The resulting photocatalytic membranes were used for the oxidative degradation of tetracycline (TC) in flow–through. We could demonstrate a higher catalytic activity in acidic conditions, a photocatalytic enhancement under visible light irradiation, and a 3x higher TC removal by persulfate (PS) in comparison to H2O2. Moreover, we observed the leaching of all Ni from the incorporated NiFe2O4 after using a membrane for 30 h in the flow-through degradation of 5 ppm TC with PS. This was accompanied by a loss of the total organic carbon removal activity, suggesting that Ni plays an important role as mineralization promoter. However, no Fe leaching occurred and the in situ formed FexOy retained the high TC conversion activity of NiFe2O4 after 30 h contact to acidic conditions, highlighting an exceptional long-term stability. We further identified that substrate desorption, catalyst complexation, and metal leaching can be facilitated by the presence of radical scavengers. This significantly contributed to their inhibitory effects, illustrating that an altered substrate-catalyst interaction may frequently be overlooked during the detection of radical species.

Development of a 3D Ni-Mn binary oxide anode for energy-efficient electro-oxidation of organic pollutants

The depletion of clean water resources and the consequent accumulation of contaminants in aquatic systems must be urgently addressed by means of innovative solutions. Electro-oxidation (EO) is considered a promising technology, prized for its versatility and eco-friendliness. However, the excessively high prices and the toxicity associated with some of the materials currently employed for EO impede its broader application. This study introduces cost-effective Ni-Mn binary oxide anodes prepared on Ni foam (NF) substrate. A scalable synthesis route that enables a 35-fold increase in the production of active material through a single optimization step has been devised. The synthesized binary oxide material underwent electrochemical characterization, and its effectiveness was assessed in an electrochemical flow-through cell, benchmarked against single Ni or Mn oxides and more conventional alternatives like boron-doped diamond (BDD) and dimensionally-stable anode (DSA). The novel binary oxide anode demonstrated exceptional performance, achieving complete removal of phenol at very low current density of 5 mA cm−2, along with an 80% of chemical oxygen demand (COD) decay within only 60 min. The NF/NiMnO3 anode outperformed the BDD and DSA when using comparable projected surface areas, owing to its high porosity and ability to produce hydroxyl radicals, as confirmed from the degradation profiles in the presence of radical scavengers. Furthermore, GC/MS analysis served to elucidate the degradation pathways of phenol.

Hydrogenation of different carbon substrates into light hydrocarbons by ball milling

The conversion of carbon-based solids, like non-recyclable plastics, biomass, and coal, into small molecules appears attractive from different points of view. However, the strong carbon–carbon bonds in these substances pose a severe obstacle, and thus—if such reactions are possible at all—high temperatures are required1–5. The Bergius process for coal conversion to hydrocarbons requires temperatures above 450 °C6, pyrolysis of different polymers to pyrolysis oil is also typically carried out at similar temperatures7,8. We have now discovered that efficient hydrogenation of different solid substrates with the carbon-based backbone to light hydrocarbons can be achieved at room temperature by ball milling. This mechanocatalytic method is surprisingly effective for a broad range of different carbon substrates, including even diamond. The reaction is found to proceed via a radical mechanism, as demonstrated by reactions in the presence of radical scavengers. This finding also adds to the currently limited knowledge in understanding mechanisms of reactions induced by ball milling. The results, guided by the insight into the mechanism, could induce more extended exploration to broaden the application scope and help to address the problem of plastic waste by a mechanocatalytic approach.

Exploring the influence of free radicals on photolytic removal of nadolol from water: Mechanism of degradation and toxicity of intermediates

β-blockers are known to have negative effects on fish and other aquatic animal species, so their removal is key for preserving aquatic ecosystems. To reduce the risks related to β-blockers, it is necessary to assess their effects and develop more effective treatments such as advanced oxidation processes. Improving sewage treatments is a critical approach to reducing β-blockers in aquatic environments. In this work, for the first time, the direct and indirect photolysis of nadolol (NAD) was investigated under different light sources (simulated solar (SS), UV-LED, and UV radiations) in ultrapure water. Indirect photolysis by H2O2 showed 1.5, 2.1, and 5.6 times higher NAD degradation efficiency than direct photolysis under mentioned irradiations. This effect was particularly pronounced in the presence of UV radiation, in which the degradation efficiency of NAD was the highest (80.2%). Computational analysis based on density functional theory calculations, together with the results of NAD photodegradation efficiency in the presence of radical scavengers (isopropanol and benzoquinone), was used to propose the NAD degradation mechanism. Sixteen degradation intermediates were proposed, along with their NMR chemical shifts. Also, this study analyzed the degree of catalase activity, lipid peroxidation, and hydroxyl radicals neutralization of NAD and its photodegradation mixtures obtained after indirect photolysis. The degree of mineralization and in vitro toxicity of NAD and its degradation intermediates obtained in the presence of UV/H2O2 were assessed.

Dark transformation from 17β-estradiol to estrone initiated by hydroxyl radical in dissolved organic matter

The occurrence and fate of 17β-estradiol (E2) in natural water have gained extensive attention owing to its high ecotoxic risk to wildlife. Dissolved organic matter (DOM) is a ubiquitous water constituent and contributes significantly to E2 removal, although the reaction mechanism is rarely clarified. The present study aims to investigate E2 transformation in water containing fresh or aged DOM surrogates at environmentally relevant concentrations in the dark. Experiments along with radical probes of benzene and furfuryl alcohol reveal that reactive radicals, particularly hydroxyl radical (·OH), formed non-photochemically at higher concentrations in aged DOM than in fresh DOM. The contribution of ·OH in E2 removal is indicated by the decreases in the removal of radical probes in the presence of E2; moreover, E2 removal is inhibited in the presence of radical scavengers. The dose-dependent inhibitive effect of substrate concentrations, including E2 and coexistent propylparaben, shows that the radical concentration is a limiting factor for E2 removal, which could be enhanced by increasing DOM concentration, dissolved oxygen, and light supply. As the main byproduct, estrone (E1) is persistent in the current DOM water in the dark, but it can be easily photodegraded when exposed to light. Theoretical analysis reveals that the initial step is ·OH-initiated H- abstraction on the hydroxyl group in the cyclopentane ring of E2. The formed singlet excited state of E2 undergoes further intramolecular rearrangement and oxidative dehydrogenation to generate E1 and the hydroperoxy radical (·HO2). Considering the universal occurrence of E2 in DOM-rich aquatic matrices, the present findings have special implications for the biogeochemical cycle and risk assessment of this pollutant in natural aquatic environments, particularly those beyond the photic zone.

Cobalt ferrite/MIL-101(Fe)/graphene oxide heterostructures coupled with peroxymonosulfate for triclosan degradation

Sulfate radical-based-advanced oxidation processes (SR-AOPs) have been recently considered for micropollutants degradation in water treatment. In the present study, cobalt ferrite (CoFe2O4), a metal-organic framework (MOFs) (MIL-101(Fe)), and graphene oxide (GO) were used to synthesize a novel heterostructure, CoFe2O4/MIL-101(Fe)/GO (C/M/G), through a hydrothermal method. The structural properties of C/M/G were determined by several characterization methods. The samples tested in the degradation of triclosan (TCS) with peroxymonosulfate (PMS), were able to activate it generating the highly active hydroxyl (HO•) and sulfate radicals (SO4•−). The effect and interaction of controlling parameters on TCS removal were investigated. Complete removal of TCS (500 μg/L) was achieved with pH 5, 0.04 g/L catalyst, and 8 μM PMS in only 30 min. The TCS removal declined obviously in the presence of radical scavengers and coexisting ions. The leachings of cobalt (Co) and iron (Fe) ions were lower than those of other CoFe2O4 composites coupled with PMS. Moreover, this process demonstrated high performance in the treatment of TCS in tap and well water. Accordingly, the C/M/G/PMS system seems to be a highly effective and environmentally compatible process for micropollutant degradation in water treatment.

Photoinduced degradation of three azole compounds from 3rd EU watchlist monitored by high-resolution higher-order mass spectrometry – Part I: A mechanistic study

• Nine new degradation and transformation products of azoles were identified. • HR-MS and HR-MS/MS revealed structures from hydroxyl radical and photo-absorption induced reactions. • Direct and indirect mechanism of degradation could be discerned. Pesticides are found in water bodies worldwide. Among them, there are azoles which are used as fungizides. Hence, tebuconazole, imazalil and penconazole have been included into the 3 rd EU watchlist to survey their presence in water bodies. Pesticides mostly enter the aquatic environment through leaching from agriculture, fruit washing or via conventional sewage water treatment plants, which are often not able to completely eliminate these pesticides. Advanced purification processes have become intensely researched. The advanced oxidation process, UVC and UVA irradiation and addition of the radical scavenger tert -butanol, was investigated using high-resolution higher-order mass spectrometry to gain kinetic and mechanistic insight. Structure elucidation of degradation and transformation products revealed fragments and also multiple hydroxylated intermediates depending on the UV source and the presence of radical scavenger. Hydroxyl radical-induced indirect degradation was found to dominate a direct photoreaction pathway induced by photo-absorption by the initial substance. The indirect mechanism did not occur during UVA irradiation due to the lack of hydroxyl radicals. The radical scavenger decelerated or prevented degradation. In total, nine new degradation and transformation products were identified. Mass spectrometry revealed product structures of the pesticides substituted with one or more hydroxyl radical groups, cyclization and substitution of chlorine by a hydroxyl radical.

ROS -mediated anticancer response of potent copper(II) drug entities derived from S, O and N, N chelating donor scaffold: Single X-ray crystal diffraction and spectroscopic studies

New Cu(II) anticancer drug entities derived from S, O, and N, N donor chelating scaffolds were synthesized and thoroughly characterized by various spectroscopic and single X-ray diffraction studies. The single X-ray crystal structure of 1 and 2 revealed a monoclinic and triclinic crystal system with space group C 2 / c and P -1, respectively. The biomolecular interaction studies of 1 and 2 with ct-DNA were carried out by employing a battery of biophysical techniques, viz., absorption, emission, circular dichroic, and electrochemical (CV) and corroborative results of these experiments demonstrated avid electrostatic binding via surface groove. The synthesized Cu(II) complexes showed high efficacy as ROS generators involving Cu(II)/Cu(I) redox-active pair as evidenced by cleavage assay in the presence of radical scavengers. The ROS generation in the presence of copper-based complexes is considered one of the most favorable cell death mechanisms for the inhibition of cancers. In vitro anticancer activity of 1 and 2 was, therefore, evaluated against a panel of five human cancer cell lines, namely MCF-7, MDA-MB-231, Hop-62, AW1356, and SiHa, and results of cytotoxicity demonstrated good anticancer response against all tested cancerous strains with GI50 value <10 µM, except by 1 against MDA-MB-231, Hop-62 and AW1356 cell lines. Interestingly, 2 has displayed considerable cytotoxicity against MCF-7, Hop-62, and SiHa cancer cell lines even better than that of standard drug adriamycin. Furthermore, computational DFT studies validated the high binding efficacy and significant cytotoxicity of complex 2, which could be attributed to high positive charge density over the Cu(II) center.

Enhanced oxidative desulfurization of liquid model fuel under microwave irradiation over W2N@C catalyst nanoarchitectonics

Oxidative desulfurization (ODS) of liquid fuel was conducted using a series of W-based catalysts like WO3/ZrO2, WO3/AC, and tungsten-nitride@porous carbon (W2N@C), under both microwave (MW) and conventional electric heating to estimate firstly the quantitative contribution of MW in ODS kinetics. At first, because of the favorable effect of MW on ODS, the most stubborn thiophenic compound, thiophene (Th), could be eliminated (97%) within only 30 min at 60 °C under MW irradiation in the presence of the W2N@C catalyst (that showed the highest ODS performance among the studied catalysts). Importantly, the activation energies of Th oxidation over the W2N@C were 22 and 38 kJ⋅mol−1 with microwave and conventional heating, respectively. Moreover, the kinetic constant of Th oxidation with MW was about 3.4 times that of the oxidation with the electric heating at the same temperature (60 °C). The rapid kinetics and low Ea under microwave irradiation might be because of the facile formation of reactive superoxide radicals (⋅O2−) (different from the conventional heating where non-radical mechanism prevails) that could be suggested from the oxidations in the presence of radical scavengers and electron spin resonance experiments. The recyclability of the catalyst, after regeneration from oxidation reactions under MW, was also secured, supporting the possible application of W2N@C in removing of thiophenics (especially under MW) from fuel. Finally, MW heating, compared with conventional electric heating, could be recommended as a highly effective strategy for ODS with rapid kinetics and low Ea because of the ready formation of active radicals.

Zeolite-assisted radiolysis of aromatic chlorides mitigating influence of coexisting ions in water matrix

We have studied zeolite-assisted radiolytic degradation of aromatic chlorides in the presence of radical scavengers. This study aims to determine whether the combined use of zeolite with ionizing radiation can reduce the influence of water matrix in the irradiation treatment of water-soluble organic compounds. A high-silica mordenite-type zeolite (HMOR) was used as the adsorbent for the aromatic chlorides. We investigated and compared the effects of HMOR on the radiation-induced degradation of three aromatic chlorides, 2-chlorophenol (2-ClPh), 2-chloroaniline (2-ClAn), and 2-chlorobenzoic acid (2-ClBA). The irradiation experiments were performed by using a Co-60 γ-ray source and bromide, nitrate and formate ions were used as the radical scavengers. In the presence of these radical scavengers, the degradation of 2-ClPh in water was inhibited, but the combined use of HMOR much improved the degradation yield. This improvement was attributed to high performance of HMOR in adsorption of 2-ClPh. Similarly, HMOR was effective for adsorption of 2-ClAn from water and facilitated the 2-ClAn degradation in the presence of formate ion. In contrast, HMOR was poor at adsorption of 2-ClBA and consistently the radiation-induced degradation of 2-ClBA in the water-HMOR mixture was inhibited by formate ion. These results demonstrate that HMOR can mitigate the influence of radical scavengers in water and facilitate the radiation-induced degradation of a molecule such as 2-ClPh and 2-ClAn, providing HMOR strongly adsorbs that molecule.

Catalytic degradation of acetaminophen by Fe and N Co-doped multi-walled carbon nanotubes

An Fe and N co-doped carbon nanotube (CNT) (Fe/N-CNT) was successfully prepared using a simple hydrothermal method. CNT, Fe doped CNTs (Fe-CNT), N doped CNTs (N-CNT), and Fe/N-CNT were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and zeta potential analysis. The catalytic activities of the materials were investigated via pharmaceutical (acetaminophen, ACT) degradation using persulfate (PS). The ACT removal rate was in the order: Fe-CNT > N-CNT > Fe-CNT > CNT, for 30 min with 10 mg/L ACT, 0.05 g/L materials, and 0.08 mM PS. The doped N existed as pyridinic-N, pyrrolic-N/N–Fe, graphitic-N, and oxidized-N, while the doped Fe existed as Fe–N, FeO/Fe3O4, and Fe2O3/FeOOH at the edge. The rates of ACT removal and PS decomposition were well correlated with pyrrolic-N/N–Fe. The ACT removal in the Fe/N-CNT + PS system was as high as >98.4% and was not significantly affected by the initial pH of 2.0–8.2 and ten consecutive uses. However, natural organic matter (NOM) inhibited ACT removal by the accumulation on Fe/N-CNT. The results of ACT removal in the presence of radical scavengers, PS decomposition, and cyclic voltammetry showed that the ACT removal was dominantly attributed to a non-radical pathway with the accelerated electron transfer from ACT to PS through the Fe/N-CNT. The results in this study strongly suggest that the Fe/N-CNT + PS system is an excellent process for the degradation of refractory organic pollutants in various water matrices with improved performance and stability attributed by non-radical pathway.

Optimization of photo-electro/Persulfate/nZVI process on 2-4 Dichlorophenoxyacetic acid degradation via central composite design: a novel combination of advanced oxidation process.

2-4 Dichlorophenoxy acetic acid is most publicly applied from chlorinated phenoxy acids herbicides. In this research, central composite design for optimization of photo-Elecro/persulfate/nZVI process to degradation and mineralization of this herbicide in aqueous solution to environment protection was applied. The initial pH (2-4), persulfate anion concentration (0.25-0.5mg/L), direct electrical (0.5-1 A), herbicide concentration (50-100mg/l), nZVI dose (0.05-1mg/L), and reaction time (50-100mg/l) are independent variables optimized. Also, the synergist effect, COD and TOC removal, the effect of radical scavengers, and by-products were investigated. The fitting of the model, suggested a quadratic model (R2 = 0.9926). F-value and P value of ANOVA were 719.81 and 0.0001 respectivelty. After optimizing the PEP/nZVI process, the proposed optimal conditions was pH = 3.4, persulfate concentration equal to 0.49mg/l, in 1 A direct current, nZVI dose equal to 0.1mg/l, in 50.05mg/l herbicide concentration as an initial concentration, in 80min reaction time. The theoretical and actual removal was evaluated 91.99% and 92%, respectively. In the optimum condition, 45.4% synergist effect indicated. 78.3% and 66.5% of initial COD and TOC were decreased. 39.02% of Cl ion was released form 2,4-D structure. The presence of radical scavengers have an adverse impact on the performance of process. The highest amount of radical scavenging was in methanol, tert-butyl alcohol and bicarbonate ions at concentrations at 50mM/l. The kinetic data was fitted via pseudo-first-order reaction (R2 = 0.99).The direct and indirect oxidation process lead to formation of several organic by-products which were confirmed by GC-MS analysis.

Sonochemical degradation of neonicotinoid pesticides in natural surface waters. Influence of operational and environmental conditions

Neonicotinoids sonochemical oxidation at high-frequency ultrasound (MHz range) has been carried out in ultrapure and natural surface-water matrices (river, reservoir and wastewater treatment plant effluent). To evaluate the influence of the operating variables, that is initial pollutant concentration, ultrasound frequency, ultrasound power, and pulse-stop time a Box-Behnken experimental design was planned. Optimal results were obtained using a frequency of 578 kHz, a power of 40 W L−1, with a pollutant concentration of 1 μM (for each pesticide), and using a pulse-stop time of 100 ms. The experimental data adjustment using the Langmuir-Hinshelwood heterogeneous kinetic model showed that neonicotinoids oxidation was carried out in the bubble-liquid interface by the attack of hydroxyl radicals. Experiments performed in the presence of radical scavengers, that is, methanol, ethanol and tert-butyl alcohol corroborated this reaction mechanism. The influence of some environmental conditions such as pH, presence of soluble inorganic species (Cl−, SO42−, NO3−, HPO42−, HCO3−) and soluble organic species (humic acids content) were established. Finally, the aqueous matrix's influence was investigated for three natural surface water cases, and the results were rationalized according to the main water physicochemical characteristics.

The degradation of paraben preservatives: Recent progress and sustainable approaches toward photocatalysis

Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products, cosmetics, and foodstuff. Their widely used field leads to increasing concentrations detected in various environmental matrices like water, soil, and sludges, even detected in human tissue, blood, and milk. Treatment techniques, including chemical advanced oxidation, biological degradation, and physical adsorption processes, have been widely used to complete mineralization or to degrade parabens into less complicated byproducts. All kinds of processes were reviewed to give a completed picture of parabens removal. In light of these treatment techniques, advanced photocatalysis, which is emerging rapidly and widely as an economical, efficient, and environmentally-friendly technique, has received considerable attention. TiO2-based and non-TiO2-based photocatalysts play an essential role in parabens degradation. The effect of experimental parameters, such as the concentration of targeted parabens, concentration of photocatalyst, reaction time, and initial solution pH, even the presence of radical scavengers, are surveyed and compared from the literature. Some representative parabens such as methylparaben, propylparaben, and benzylparaben have been successfully studied the reaction pathways and their intermediates in their degradation process. As reported in the literature, the degradation of parabens involves the production of highly reactive species, mainly hydroxyl radicals. These reactive radicals would attack the paraben preservatives, break, and finally mineralize them into simpler inorganic and nontoxic molecules. Concluding perspectives on the challenges and opportunities for photocatalysis toward parabens remediation are also intensively highlighted.

Degradation of petroleum hydrocarbons in soil via advanced oxidation process using peroxymonosulfate activated by nanoscale zero-valent iron

Recently, the use of nanoscale zero-valent iron (nZVI) for removal of organic contaminants from aqueous and soil system has increased. In this study, we employ nZVI to activate peroxymonosulfate (PMS) for the degradation of total petroleum hydrocarbons (TPHs) in aged diesel-contaminated soil. Upon PMS activation by nZVI, PMS produces more highly reactive oxygen species (ROS) in both aqueous solution and soil compared to other compounds (PMS/Co(II)), as determined by electron paramagnetic resonance spectroscopy. Thus, nZVI is an effective catalyst for PMS activation, leading to the efficient degradation of diesel oil in soil compared to other catalysts and oxidants. The optimal concentrations of PMS and nZVI were found to be 3 and 0.2%, respectively, showing the best degradation efficiency (61.2% in 2 h). The observed TPH degradation was retarded (up to 19.1–37% efficiency) in the presence of radical scavengers, such as tert-butyl alcohol, nitrobenzene, ethyl alcohol, and isopropyl alcohol. These results also demonstrate that ROS (hydroxyl and sulfate free radicals) are generated via PMS activation by nZVI. Moreover, more than 96% of TPH can be degraded by sequential applications of PMS/nZVI. Factors affecting TPH degradation, namely PMS/nZVI concentration, soil:solution ratio, soil pH, activators, and oxidants, are also analyzed. The results demonstrate that TPH is degraded to below the residential soil quality limit using PMS/nZVI based on the advanced oxidation process (AOP), which is therefore an effective option for chemical remediation of diesel-contaminated soils over a wide range of pH.

Matrix composition during ozonation of N-containing substances may influence the acute toxicity towards Daphnia magna

Micropollutants reach the aquatic environment through wastewater treatment plant effluents. Ozonation, applied in wastewater treatment for micropollutants abatement, can yield transformation products (TP), which might be of ecotoxicological concern. Previous studies on TP formation were mostly performed in ultrapure water. However, the water matrix can have a substantial influence and lead to unpredictable yields of TPs with toxicological potential.In this study the acute toxicity (immobilization) of the parent substances (isoproturon and metoprolol) and also of available TPs of isoproturon, metoprolol and diclofenac towards Daphnia magna (D. magna) were investigated. Further, the acute toxicity of TP mixtures, formed during ozonation of isoproturon, metoprolol and diclofenac was evaluated in the following systems: in the presence of radical scavengers (tert-butanol and dimethyl sulfoxide) and in the presence of hypobromous acid (HOBr), a secondary oxidant in ozonation.For all tested substances and TP standards, except 2,6-dichloroaniline (EC50 1.02 mg/L (48 h)), no immobilization of D. magna was detected. Ozonated pure water and wastewater did not show an immobilization effect either. After ozonation of diclofenac in the presence of dimethyl sulfoxide 95% (48 h) of the daphnids were immobile. Ozonation of parent substances, after the reaction with HOBr, showed no effect for isoproturon but a high effect on D. magna for diclofenac (95% immobilization (48 h)) and an even higher effect for metoprolol (100% immobilization (48 h)). These results emphasize that complex water matrices can influence the toxicity of TPs as shown in this study for D. magna.

Syntheses, structural diversities and photocatalytic properties of three nickel(II) coordination polymers based semi-bis(benzimidazole) and aromatic dicarboxylic acid ligands

Three new ternary nickel(II) coordination polymers, namely, {[Ni2(L)2(1,4-NDC)2(H2O)]·8.5H2O}n (1), {[Ni(L)(TBTA)(H2O)2]·H2O}n (2) [Ni(L)(OBA)(H2O)]n (3) (L = 1,4-bis(5,6-dimethylbenzimidazol-1-yl)-2-butylene; 1,4-H2NDC = 1,4-naphthalenedicarboxylic acid; H2TBTA = tetrabromoterephthalate; H2OBA = 4,4′-oxybis(benzoic acid)), were solvothermally synthesized and characterized. 1 exhibits an unusual 3D 3,6T13 framework. 2 and 3 both display the 2D sql networks. 1–3 have highly photocatalytic efficiency for the degradation of methylene blue by UV light irradiation. The photocatalytic mechanism was proposed, which was confirmed by trapping experiments in the presence of radical scavengers.

Ultrasonic-assisted H2O2/TiO2 process in catechol degradation: kinetic, synergistic and optimisation via response surface methodology

ABSTRACT This experimental study investigated the performance of Catechol degradation by US/TiO2/H2O2 process as an integrated advance oxidation process. In this experimental study, initial pH, dose of TiO2, initial concentration of Catechol, H2O2 concentration and reaction time parameters optimised BBD. The results suggest that US/TiO2/H2O2 process has a high efficiency in Catechol degradation. Optimum condition of US/TiO2/H2O2 process is pH = 3.43, H2O2 concentration = 130 mg/l, TiO2 dose = 0.34 g/l, Catechol concentration = 12.52 mg/l and reaction time = 70.64 min. According to predicate point, the percentage of Catechol removal in this condition was 96.2 and 92.34 as a predicated and experimental percentage of Catechol removal by this process. The kinetics of reaction follows pseudo-first-order kinetic. The synergist effect of sonolysis, TiO2 and H2O2 is 2.09 fold. 70 and 63% of initial COD and TOC were removed. Presence of radical scavenger has an adverse impact on the performance of US/TiO2/H2O2 process.

Ozone-assisted catalytic oxidation of aqueous nitrite ions on HZSM-5 zeolites

Simultaneous removal of NOx and SO2 during the wet absorption process has made it possible for nitrogen resource utilization. However, nitrites formation at high ratio in absorption solution would limit its application. In this study, the catalytic oxidation behaviors of aqueous nitrite ions assisted by ozone on HZSM-5 zeolites with different SiO2/Al2O3 ratios have been investigated. The experimental results revealed that the oxidation and disproportionation reactions of nitrite ions took place competitively, both of which were accelerated under acidic condition. Moreover, the introduction of HZSM-5 zeolites and ozone would significantly improve the nitrite oxidation rate, where the zeolites with high SiO2/Al2O3 ratios were found to be more effective owing to the enhanced adsorption of nitrite ions and ozone. Based on the results under different operating conditions (such as O3 concentration, HZSM-5 dosage, pH values and presence of radical scavengers etc.), the reaction mechanism was then proposed. The disproportionation reaction of nitrite ions mainly occurred in the bulk solution. And the catalytic oxidation of nitrite ions over zeolites proceeded via a non-radical surface reaction between the adsorbed nitrite ions and ozone/oxygen molecular.

A rapid and efficient removal approach for degradation of metformin in pharmaceutical wastewater using electro-Fenton process; optimization by response surface methodology.

Presence of emerging contaminants such as pharmaceutical products in aquatic environments has received high concern due to their undesirable effect on wildlife and human health. Current work deals with developing a treatment model based on the electro- Fenton (EF) process for efficient removal of metformin (MET) from an aqueous medium. The obtained experimental results revealed that over the reaction time of 10 min and solution pH of 3, the maximum removal efficiency of 98.57% is achieved where the value of MET initial concentration, current density, and H2O2 dosage is set at 10 mg.L-1, 6 mA.cm-2, and 250 μL.L-1, respectively, which is in satisfactory agreement with the predicted removal efficiency of 98.6% with the desirability of 0.99. The presence of radical scavengers throughout the mineralization of MET under the EF process revealed that the generation of •OH radicals, as the main oxidative species, controlled the degradation mechanism. The obtained kinetics data best fitted to the first order kinetic model with the rate constant of 0.4224 min-1 (R2 = 0.9940). The developed treatment process under response surface methodology (RSM) was employed for modeling the obtained experimental data and successfully applied for efficient removal of the MET contaminant from pharmaceutical wastewater as an adequate and cost-effective approach.