Comparison of UVC/S₂O₈ ^2- with UVC/H₂O₂ in terms of efficiency and cost for the removal of micropollutants from groundwater

This study compared the UVC/S2O82- system with the more commonly used AOP in water industry, UVC/H2O2, and examined whether the first one can be an economically feasible alternative technology. Atrazine and 4 volatile compounds (methyl tert-butyl ether, cis-dichlorethen, 1,4-dioxane and 1,1,1-trichloroethane) were chosen as model contaminants because they exhibit different susceptibility to UVC photolysis and AOPs. A collimated beam apparatus was utilized for the majority of the experiments (controlled environment, without mass transfer phenomena), while selected experiments were performed in a flow-through reactor to simulate industrial applications. Initial experiments on the activation of oxidants with a LP lamp indicated that S2O82- is photolysed about 2.3times faster than H2O2 and that the applied treatment times were not sufficient to utilize the majority of the oxidant. The effect of oxidants' concentrations were tested with atrazine alone and in the micropollutants' mixture and it was decided to use 11.8mgL-1 S2O82- and 14.9mgL-1 H2O2 for further testing since is closer to industrial applications and to minimize the residual oxidant concentration. Changes of the matrix composition of the treated water were investigated with the addition of chloride, bicarbonate and humic acids at concentrations relevant to a well-water-sample, the results showed that the system least affected was UVC/H2O2. Only when bicarbonate was used, UVC/S2O82- performed better. Overall, testing these systems with the mixture of micropollutants gave better insights to their efficiency than atrazine alone and UVC/S2O82- is recommended for selective oxidation of challenging matrices

Removal of phenol using sulphate radicals activated by natural zeolite-supported cobalt catalysts

Two Co oxide catalysts supported on natural zeolites from Indonesia (INZ) and Australia (ANZ) were prepared and used to activate peroxymonosulphate for degradation of aqueous phenol. The two catalysts were characterized by several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) and N2 adsorption. It was found that Co/INZ and Co/ANZ are effective in activation of peroxymonosulphate to produce sulphate radicals for phenol degradation. Co/INZ and Co/ANZ could remove phenol up to 100 and 70 %, respectively, at the conditions of 25 ppm phenol (500 mL), 0.2 g catalyst, 1 g oxone and 25 °C. Several parameters such as amount of catalyst loading, phenol concentration, oxidant concentration and temperature were found to be the key factors influencing phenol degradation. A pseudo first order would fit to phenol degradation kinetics, and the activation energies on Co/INZ and Co/ANZ were obtained as 52.4 and 61.3 kJ/mol,respectively

Insights into N-doping in single-walled carbon nanotubes for enhanced activation of superoxides: A mechanistic study

Emerging characteristics upon nitrogen-doping were differentiated in the activation of superoxides over single-walled carbon nanotubes. Both experimental and theoretical studies revealed that enhanced peroxymonosulfate (PMS) activation is ascribed to a nonradical process while persulfate (PS) activation is accelerated via directly oxidizing water, yet hydrogen peroxide (H2O2) activation is inert to N-doping. This study details the first insights into versatile N-doping in carbocatalysis for organic oxidation in sustainable remediation

SrCo1−xTixO3−δ perovskites as excellent catalysts for fast degradation of water contaminants in neutral and alkaline solutions

Perovskite-like oxides SrCo1−xTixO3−δ (SCTx, x = 0.1, 0.2, 0.4, 0.6) were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for phenol degradation under a wide pH range, exhibiting more rapid phenol oxidation than Co3O4 and TiO2. The SCT0.4/PMS system produced a high activity at increased initial pH, achieving optimized performance at pH  ≥ 7 in terms of total organic carbon removal, the minimum Co leaching and good catalytic stability. Kinetic studies showed that the phenol oxidation kinetics on SCT0.4/PMS system followed the pseudo-zero order kinetics and the rate on SCT0.4/PMS system decreased with increasing initial phenol concentration, decreased PMS amount, catalyst loading and solution temperature. Quenching tests using ethanol and tert-butyl alcohol demonstrated sulfate and hydroxyl radicals for phenol oxidation. This investigation suggested promising heterogeneous catalysts for organic oxidation with PMS, showing a breakthrough in the barriers of metal leaching, acidic pH, and low efficiency of heterogeneous catalysis

Synergistic effects of H\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e and S\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e8\u3c/sub\u3e\u3csup\u3e2−\u3c/sup\u3e in the gamma radiation induced degradation of congo-red dye: Kinetics and toxicities evaluation

© 2019 Elsevier B.V. Gamma radiation has received increasing attention due to their high potential in degradation of recalcitrant pollutants. Thus in the present study, gamma radiation was used for degradation of congo-red (CR) dye, a highly toxic and carcinogenic pollutant, in the presence of H2O2 and S2O82−. The CR was significantly degraded by gamma radiation (i.e., 53%), however, presence of H2O2 and S2O82− promoted degradation of CR to 98 and 87%, respectively, at 1184 Gy absorbed dose. The radical scavengers and electron spin resonance studies revealed that gamma radiation decompose H2O2 and S2O82− into [rad]OH and SO4[rad]− and both [rad]OH and SO4[rad]− caused degradation of CR. The CR showed high reactivity, i.e., 3.25 × 109 and 8.50 × 108 M−1 s−1 with [rad]OH and SO4[rad]−, respectively, and removal of CR was inhibited in the presence of [rad]OH and SO4[rad]− scavengers. The removal of CR was promoted with elevating initial concentrations of H2O2 and S2O82− and decreasing initial concentrations of CR. pH of aqueous solution also significantly influenced removal of the dye. The proposed degradation pathways of CR were established from the [rad]OH mediated degradation of CR and nature of identified degradation products. The greater mineralization of CR, formation of small molecular mass degradation product, and decline in concentration of acetate after extended treatment suggest the gamma-ray mediated peroxide based process to be a promising alternative for potential degradation of CR

A novel route for catalytic activation of peroxymonosulfate by oxygen vacancies improved bismuth-doped titania for the removal of recalcitrant organic contaminant

In this work, bismuth-doped titania (BixTiO2) with improved oxygen vacancies was synthesized by sol-gel protocol as a novel peroxymonosulfate (PMS, HSO5−) activator. HSO5− and adsorbed oxygen molecules could efficiently be transformed into their respective radicals through defect ionization to attain charge balance after their trapping on oxygen vacancies of the catalyst. XRD study of BixTiO2 with 5 wt% Bi (5BiT) revealed anatase, crystalline nature, and successful doping of Bi into TiO2 crystal lattice. The particle size obtained from BET data and SEM observations was in good agreement. PL spectra showed the formation rates of •OH by 3BiT, 7BiT, 5BiTC, and 5BiT as 0.720, 1.200, 1.489, and 2.153 μmol/h, respectively. 5BiT catalyst with high surface area (216.87 m2 g−1) and high porosity (29.81%) was observed the excellent HSO5− activator. The catalytic performance of 0BiT, 3BiT, 5BiT, and 7BiT when coupled with 2 mM HSO5− for recalcitrant flumequine (FLU) removal under dark was 10, 27, 55, and 37%, respectively. Only 5.4% decrease in catalytic efficiency was observed at the end of seventh cyclic run. Radical scavenging studies indicate that SO4•− is the dominant species that caused 62.0% degradation. Moreover, strong interaction between Bi and TiO2 through Bi-O-Ti bonds prevents Bi leaching (0.081 mg L−1) as shown by AAS. The kinetics, degradation pathways, ecotoxicity, and catalytic mechanism for recalcitrant FLU were also elucidated. Cost-efficient, environment-friendly, and high mineralization recommends this design strategy; BixTiO2/HSO5− system is a promising advanced oxidation process for the aquatic environment remediation

Degradation and mineralization of antipyrine by UV-A LED photo-Fenton reaction intensified by ferrioxalate with addition of persulfate

The intensification of the degradation of antipyrine in aqueous solution by using a UV-A-LED-photo-Fenton reaction intensified by ferrioxalate complexes and with addition of persulfate anions was studied. The efficiency of the reaction was evaluated in terms of antipyrine degradation and mineralization degree at different initial concentrations of hydrogen peroxide, ferrous ion, oxalic acid and persulfate anion. The reaction was carried out using a lab-scale photoreactor irradiated with artificial UV-A-LED light emitting at 365 nm. Artificial neural networks (NNs) were implemented for modelling the degradation process. Under optimal conditions, complete degradation of antipyrine and 93% mineralization was reached in 2.5 and 60 min, respectively. The contribution of HO radicals in this system was evaluated running the reaction in the absence and presence of appropriate quenchers such as tert-butyl alcohol and methanol. In the last step of reaction, possibly different intermediates such as 2-butenedioic acid, butanedioic acid, 4-oxo-pentanoic acid, acetate and formate can be generated which cannot be degraded by HO radicals or their reaction is very slow. This ferrioxalate-mediated system reduces the amount of H2O2 needed (100 mg L−1) for antipyrine degradation and persulfate was not necessary because it could not be activated with UV-A LED nor with Fe2+ since it is quickly converted to Fe3+ forming ferrioxalate complexes.</p