In this study the efficiency of electrochemical oxidation of aromatic pollutants, such as reactive dyes, at boron-doped diamond on silicon (Si/BDD) electrodes was investigated. The level of B/C ratio ...which is effective for the degradation and mineralization of selected aromatic pollutants, and the impact of B/C ratio on the crystalline structure, layer conductivity and relative sp3/sp2 coefficient of a BDD electrode were also studied. The thin film microcrystalline electrodes have been deposited on highly doped silicon substrates via MW PE CVD. Si/BDD electrodes were synthesized for different B/C ratios of the gas phase. Mechanical and chemical stability of the electrodes was achieved for the microcrystalline layer with relatively high sp3/sp2 band ratio. Layer morphology and crystallite size distribution were analyzed by SEM. The resistivity of BDD electrodes was studied using four-point probe measurements. The relative sp3/sp2 band ratios were determined by deconvolution of Raman and X-ray photoelectron spectra. The efficiency of degradation and mineralization of the reactive azo dye rubin F-2B was estimated based on the absorbance measurements at 545nm. The influence of commonly used electrolytes NaCl and Na2SO4 on the dye removal efficiency was also investigated. The results suggest that, in general, the oxidation occurs indirectly at the anode through generation of hydroxyl radicals •OH, which react with the dye in a very fast and non-selective manner. In NaCl electrolyte the dye was also decomposed by more selective, active chlorine species (Cl2, HOCl). However the efficiency of this process in BDD depended on the electrode's doping level. Higher amounts of dopant on the surface of BDD resulted in the higher efficiency of dye removal in both electrolytes.
•The efficiency of electrochemical oxidation of reactive azo dyes on Si/BDD electrodes was investigated.•The commonly used electrolytes NaCl and Na2SO4 influence strongly the azo dye removal.•The high doped electrode was more efficient at azo dye removal than the low level doped electrode.•Boron concentration give more significant difference in the azo removal in NaCl electrolyte.
Commonly used alkylimidazolium ionic liquids are poorly to negligibly biodegradable, and some are toxic, with the potential to poison typical biological test systems. Therefore, when ionic liquids ...are present in technological wastewaters they could break through classical wastewater treatment systems into natural waters and become potentially persistent pollutants. A recent study investigating different advanced oxidation processes found that the H
2O
2/UV system degraded dissolved imidazolium ionic liquids with the greatest efficiency. In the present study, high performance liquid chromatography was coupled with electrospray mass spectrometry to separate, analyse and identify degradation products following the treatment of ionic liquid solutions with H
2O
2 in the presence of UV irradiation. It was found that hydroxylation in short-chain entities occurred mainly within the ring moiety, whereas in the case of longer alkylated cations, oxidation of the alkyl chain yielded several products. The potential transformation products were identified structurally by MS/MS analysis and are discussed in the light of their putative toxicity and biodegradability.
The study examined the usefulness of a Fenton-like system for the degradation of ionic liquid residues in water. The ionic liquid was oxidized in a dilute aqueous solution of ...1-butyl-3-methylimidazolium chloride (bmimCl). The ionic liquid decomposes readily and rapidly in aqueous solution by chemical degradation in a Fenton-like system. Under chosen conditions the initial bmimCl solution was reduced by a factor of 0.973 within 90
min. Additional results showed that bmimCl degradations in a Fenton-like system in excess H
2O
2 could be interpreted as a combined oxidation–reduction mechanism. Preliminary investigations of the mechanism of such degradations have indicated that initial OH
radicals can attack any one of the three carbon atoms on the imidazolium ring. The intermediates of this reaction may be mono- di- or amino- carboxylic acids.
•Four cytostatic drugs were photooxidized over Bi-B co-doped TiO2 under solar light.•The photocatalytic oxidation of IF was similar effective for 3Bi-B-TiO2 and TiO2.•Photocatalytic oxidation pathway ...of IF was different over 3-Bi-BTiO2 and TiO2.•Dechlorination in contrast to mineralization was effective over 3Bi-B-TiO2.
The Bi-B co-doped TiO2 photocatalysts were prepared via a simple sol-gel method. Initially, the photocatalysts were applied to decompose ifosfamide (IF). 3Bi-B-TiO2 was found to be the most effective photocatalyst with regard to the cytostatic drug decay; it was also characterized by good sedimentation properties. For the constant concentration ratio of IF:catalyst, this photocatalyst was more effective in the removal of IF at low drug concentrations. The study employing scavengers, i.e. F− ions and isopropanol demonstrated that the modification of TiO2 with Bi and B co-dopants has a negative effect on the generation of OHfree radicals. The decomposition of the studied cytostatic drug was most likely connected to the reaction with OHads radicals generated at the catalyst surface. The quantitative and qualitative determination of IF intermediates during the photocatalytic decomposition in the presence of 3Bi-B-TiO2 showed that dechlorination was a more advanced process compared to the oxidation of organic matter.
Lastly, other cytostatic drugs such as, cyclophosphamide (CP), 5-fluorouracil (5-FU) and imatinib (IMA) decomposed in the presence of 3Bi-B-TiO2 under artificial sunlight and visible light irradiation. The rate and efficiency of photocatalytic decay of the aforementioned cytostatic drugs increased in the following order: CP≈IF<5-FU<IMA.
In this study, the electrochemical degradation process of 5-fluorouracil (5-FU) in aqueous media was performed using a continuous flow reactor in an undivided cell (system I), and in a divided cell ...with a cationic membrane (Nafion® 424) (system II). In system I, 75% of 5-FU degradation was achieved (50 mg L−1) with a applied current density japp = 150 A m−2, volumetric flow rate qv = 13 L h−1, after 6 h of electrolysis (kapp = 0.004 min−1). The removal efficiency of 5-FU was higher (95%) when the concentration was 5 mg L−1 under the same conditions. Nitrates (22% of initial amount of N), fluorides (27%) and ammonium (10%) were quantified after 6 h of electrolysis.
System II, 77% of 5-FU degradation was achieved (50 mg L−1) after 6 h of electrolysis (kapp = 0.004 min−1). The degradation rate of 5-FU was complete when the concentration was 5 mg L−1 under the same conditions. Nitrates (29% of initial amount of N), fluorides (25%) and ammonium (5%) were quantified after 6 h of electrolysis.
In addition, the main organic byproducts identified by mass spectroscopy were aliphatic compound with carbonyl and carboxyl functionalities.
Due to, the mineralization of 5-FU with acceptable efficiency of 88% found in system II (japp of 200 A m−2), this system seems to be more promising in the cytostatic drug removal. Moreover the efficiency of 5-FU removal in diluted solutions is better in system II than in system I.
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•5-FU was oxidized at BDD anode in a flow reactor with divided and undivided cell.•5-FU in the low concentration was better removed in system with divided cell.•5-FU mineralization efficiency was better in system with divided cell.•OH and SO4- radicals generated at BDD anode participated in 5-FU oxidation.
In order to rise efficiency of the wastewater treatment in a refinery plant, several oxidation experiments were done, testing their applicability as an additional pretreatment method. The influence ...of treatment with low concentrations of H
2O
2 combined with stirring and UV light on degradation of organic compounds present in the refinery wastewater was studied. Oxidation of the total petroleum hydrocarbons occurs at relatively low concentrations of H
2O
2, additional UV irradiation slightly accelerates the process due to the increased formation of hydroxyl radicals. 1,2-dichloroethane and
t-butyl methyl ether degrade in the similar manner and except for the lowest H
2O
2 concentration used (1.17
mM), the reduction after 24
h is total. The degradation rate for dichloromethane is the lowest one, depending both on hydrogen peroxide concentration and the presence of UV. Its maximum reduction of 83% was obtained using the highest applied peroxide concentration of 11.76
mM.
► The explanation influence of IL composition on electrochemical oxidation at BDD anode. ► Identification of IL oxidants in different electrolyte. ► Two pathways of ILs transformation at BDD anode. ► ...Influence of halide ions on ILs electrooxidation at BDD. ► Identification of by-products for imidazolium salts with the different anions.
The electrochemical oxidation of ionic liquids (ILs) in aqueous solutions on boron-doped diamond was investigated with the aim of explaining the influence of the IL composition Cl-,Br-,BF4-,PF6-,CF3SO3-,CH3C6H4SO3-. By keeping the cation (1-butyl-3-methylimidazolium) constant and varying the anion, a comparative study of their oxidizability could be carried out. The experimental data suggest that hydroxyl radicals were the dominant oxidant reacting with the IL ionic pair. The chloride ion enhanced imidazolium cation degradation, whereas CH3C6H4SO3- competed with the cation for anodically produced hydroxyl radicals. The nature of the background anions (Na2SO4, NaCl, NaBr) also influenced the efficiency of the electrochemical process. The addition of trace halides further decreased chemical oxygen demand (COD). The results suggest that different oxidation mechanisms prevail at different halide concentrations. However, peroxodisulphate generated at the BDD anode in a Na2SO4 supporting electrolyte did not play a significant role in imidazolium salt oxidation. The intermediates found in the single compartment reactor after 3h of electrolysis suggest that O2- also occured and governed in part the electrochemical oxidation of IL.
The effect of selected inorganic anions on the effectiveness of the Fenton advanced oxidative treatment of waters contaminated with methyl
t-butyl ether (MTBE) was examined. With respect to the ...chloride or phosphate ions used, inhibition of oxidation was clearly in evidence, whereas addition of sulfates or perchlorates influenced these rates to a much smaller extent. Anions suppress MTBE decomposition in the following sequence: ClO
4
−
<
SO
4
2−
<
Cl
−
<
H
2PO
4
−. There are very probably several mechanisms affecting oxidation. Complexation reactions with iron are likely to affect the distribution and reactivity of iron species with H
2O
2. Hydroxyl radicals may also be scavenged from less reactive inorganic radicals. Additionally, in order to explore the degradation mechanism of MTBE by Fenton's reagent in the presence of different salts, four intermediate products of MTBE oxidation were identified:
tert-butyl formate (TBF),
tert-butyl alcohol (TBA), acetone, and methyl acetate (MA).
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•Diamond anodes were revealed as an efficient electrodes in the landfill leachates oxidation.•A decrease in the sp3/sp2 ratio increased the Cl2/HOCl evolution at diamond ...anodes.•Electrochemical oxidation degraded micropollutants, such as bisphenol A.•Acidic conditions and the addition of 10mg/L of Fe2+ inhibited N-NH4 elimination.•Electrochemically pre-treaded landfill leachates were appropriate for further biological nitrogen removal.
The electrochemical oxidative treatment of landfill leachates (LLs) containing high amounts of ammonia nitrogen and organic matter was used as a promising method, prior to biological processes, to achieve the final effluent quality that would be acceptable by current regulations. The deposited boron-doped diamond electrodes (BDDs) with different boron doping concentrations (10000, 5000 and 500ppm of B) were applied as anodes. The results showed that the boron doping level influences the electrochemical activity and selectivity of electrode surface due to a decrease in the sp3/sp2 ratio of the BDD material. Special attention was paid to the oxidation efficiency of organic matter (COD=4225mg O2/L, BOD=366mg O2/L) and ammonia (2270mg N-NH4+/L) in the investigated LLs. Additionally, bisphenol A (BPA; 1539.6μg/L), a suspected endocrine disruptor, was studied as a potential indicator of the removal efficiency of micropollutants.
It was found that the oxidation of BPA and BOD are correlated with the sp3/sp2 ratio, while a decrease in the sp3/sp2 ratio of the BDD material was associated with the elevated efficiency of N-NH4+ removal. Low pH and the addition of Fe(II) salts suppressed the oxygen evolution reaction, and overcame the mass transport limitation of organics in the case of OH-mediated oxidation.
Regarding the elimination of ammonium nitrogen, lower effectiveness was generally achieved in comparison to the COD removal. The maximum removal of COD and ammonium nitrogen reached 79 and 41%, respectively. These values were much higher than those reported in the previous study involving a single-cell flow reactor. Thus, anaerobic ammonium oxidation (Anammox) processes seem to be a reasonable option as a final step of LL treatment.
Ionic liquids are widely studied as alternative solvents in organic synthesis and catalysis, in electrochemistry and the separation sciences; with their many applications they will soon be produced ...on an industrial scale. Available toxicological data of ionic liquids have already suggested initial guidelines for the conscious design of safer chemicals. In this study a new group of such redesigned ionic liquids—1-alkoxymethyl-3-hydroxypyridinium cations+acesulphamate, saccharinate and chloride anions—was assayed with respect to their inhibitory activity towards acetylcholinesterase and their cellular toxicity towards the IPC-81 rat promyelocytic leukaemia cell line: the acute biological activity of these compounds is very low. Effective concentrations lie in the millimole range, which is well above possible intracellular concentrations. Only the compounds with the longest alkoxymethyl chain inhibit the enzyme at effective concentrations that are one order of magnitude smaller. No significant differences are observed when the anion compartment in the enzymatic assay is varied. However, the cytotoxicity data show EC
50 for acesulphamates and saccharinates to be higher than the values for the chloride analogues. Also, a slight alkoxymethyl chain length effect on the overall cytotoxicity is discernible. The biodegradability of the 1-alkoxymethyl-3-hydroxypyridinium salts varies from 21% to 72% and depends on the type of anion the cation is linked with. It improves with lengthening alkyl chain, but only in the range from 4 to 11 carbon atoms.
