Enhanced chalcopyrite-catalyzed heterogeneous Fenton oxidation of diclofenac by ABTS.

The widely used 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) has gained growing attention in advanced oxidation processes (AOPs), whereas there was limited knowledge regarding the feasibility of ABTS in enhancing heterogeneous Fenton oxidation so far. Hereof, ABTS was introduced into the chalcopyrite (CuFeS2)- catalyzed heterogeneous Fenton oxidation process to degrade diclofenac (DCF), and the degradation efficiency was enhanced by 25.5% compared with CuFeS2/H2O2 process. The available reactive oxygen species (ROS) and the enhanced mechanism were elaborated. Experimental results uncovered that •OH was the dominant reactive species responsible for the DCF degradation in the CuFeS2/H2O2/ABTS process, and ABTS•+ was derived from both •OH and Fe(IV). The presence of ABTS contributed significantly to the redox cycle of surface Fe of CuFeS2, and the roles of reductive sulfur species and surface Cu(I) in promoting surface Fe cycling also could not be neglected. In addition, the effects of several influencing factors were considered, and the potential practicability of this oxidation process was examined. The results demonstrate that the CuFeS2/H2O2/ABTS process would be a promising approach for water purification. This study will contribute to the development of enhancing strategies using ABTS as a redox mediator for heterogeneous Fenton oxidation of pharmaceuticals.

Low additive peracetic acid enhanced sulfamethazine degradation by permanganate: A mechanistic study.

In this study, a novel water treatment process combining permanganate (Mn(VII)) and peracetic acid (PAA, CH3C(O)OOH) was employed to degrade sulfamethazine (SMT), a typical model contaminant. Simultaneous application of Mn(VII) and a small amount of PAA resulted in much faster oxidation of organics than a single oxidant. Interestingly, coexistent acetic acid played a crucial role in SMT degradation, while background hydrogen peroxide (H2O2) had a negligible effect. However, compared with acetic acid, PAA could better improve the oxidation performance of Mn(VII) and accelerate the removal of SMT more significantly. The mechanism of SMT degradation by Mn(VII)-PAA process was systematically evaluated. Firstly, based on the quenching experiments, electron spin resonance (EPR) results and UV-visible spectrum, singlet oxygen (1O2), Mn(III)aq and MnO2 colloids were the predominant active substances, while organic radicals (R-O•) showed negligible contribution. Then, the decay of Mn(VII) in the presence of PAA and H2O2 was investigated. It was found that the coexisting H2O2 accounted for almost all the decay of Mn(VII), PAA and acetic acid both had low reactivity toward Mn(VII). During the degradation process, acetic acid was able to acidify Mn(VII) and simultaneously acted as a ligand to form reactive complexes, while PAA mainly played a role of spontaneously decomposing to produce 1O2, they jointly promoted the mineralization of SMT. Finally, the degradation intermediates of SMT and their toxicities were analyzed. This paper reported the Mn(VII)-PAA water treatment process for the first time, which provided a promising approach for rapid decontamination of refractory organics-polluted water.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies.

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (•OH), superoxide radical (O2•-), singlet oxygen (1O2), carbonate radicals (CO3•-), and peroxymonocarbonate (HCO4-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Graphene shell-encapsulated copper-based nanoparticles (G@Cu-NPs) effectively activate peracetic acid for elimination of sulfamethazine in water under neutral condition.

In this study, a graphene shell-encapsulated copper-based nanoparticles (G@Cu-NPs) was prepared and employed for peracetic acid (PAA) activation. The characterization of G@Cu-NPs confirmed that the as-prepared material was composed of Cu0 and Cu2O inside and encapsulated by a graphene shell. Experimental results suggested that the synthesized G@Cu-NPs could activate PAA to generate free radicals for efficiently removing sulfamethazine (SMT) under neutral condition. The formation of graphene shells could strongly facilitated electron transfer from the core to the surface. Radical quenching experiments and electron spin resonance (ESR) analysis confirmed that organic radicals (R-O•) and hydroxyl radicals (•OH) were generated in the G@Cu-NPs/PAA system, and R-O• (including CH3CO3• and CH3CO2•) was the main contributor to the elimination of SMT. The possible SMT degradation pathways and mechanisms were proposed, and the toxicity of SMT and its intermediates was predicted with the quantitative structure-activity relationship (QSAR) analysis. Besides, the effects of some key parameters, common anions, and humic acid (HA) on the removal of SMT in the G@Cu-NPs/PAA system were also investigated. Finally, the applicability of G@Cu-NPs/PAA system was explored, showing that the G@Cu-NPs/PAA system possessed satisfactory adaptability to treat different water bodies with admirable reusability and stability.

In-depth exploration of toxicity mechanism of nanoscale zero-valent iron and its aging products toward Escherichia coli under aerobic and anaerobic conditions.

The bacteria toxicity of nanoscale zero-valent iron (nZVI) can be changed during its application in water treatment but the toxicity mechanism is still not well understood, particularly under anaerobic conditions. Here, the toxicity of nZVI and its aging products towards Escherichia coli (E. coli) and the mechanisms of extracellular and intracellular reactive oxygen species (ROS) damage were deeply probed in the presence and absence of oxygen in ultrapure water. Under aerobic conditions, the ROS damage primarily caused by the generation of extracellular free •OH can be a major contributor to the toxicity of nZVI to E. coli. By contrast, in anaerobic nZVI treatment system, the intracellular •OH can be quenched by benzoic acid which is a cell permeable quencher and the electron spin resonance (ESR) signals of 5,5-dimethy-1-pyrroline (DMPO)- •OH were evidently observed in system with the addition of F- which could desorb the surface •OH into solution. It indicated that the intracellular •OH adsorbed on the particle surface can also play an indispensable role in inactivating cells under anaerobic conditions. Moreover, nZVI can steeply decline the membrane potential, causing severe membrane disruption and therefore resulting in the stronger toxicity in anaerobic conditions. Furthermore, the chemical composition transformation of nZVI and generation of benign iron corrosion products (e.g., Fe3O4, γ-Fe2O3, γ-FeOOH) are mainly responsible for the reduced toxicity with the increasing aging time. These results provide insights into the extracellular and intracellular ROS damage occurred in aerobic and anaerobic nZVI treatment systems, offering more perspective to the risk assessment of nZVI application.

Insights into the correlation between different adsorption/oxidation/catalytic performance and physiochemical characteristics of Fe-Mn oxide-based composites.

Fe-Mn oxide-based composites have been widely used in the solidification of heavy metals or the removal of organic pollutants, which can not only show excellent adsorption/oxidation performance, but also show catalytic activity for common oxidants. At present, the correlation between adsorption/oxidation/catalytic performance and physicochemical characteristics of these composites, and the underlying mechanisms are still unclear. Therefore, the main purpose of this review is to disclose the internal relationship between the physicochemical properties of Fe-Mn oxide-based composites and the pollutant removal performance. From the perspective of crystal phase, the basic units of Fe-Mn oxide composites are divided into Fe-Mn binary oxide (FMBO) and spinel MnFe2O4, and the two species were discussed separately in most chapters. The selected physicochemical properties mainly include the type of Fe-Mn oxide composites, surface-to-volume ratio, pore volume, pHpzc, crystal type, surface functional groups. Because the physicochemical properties that determine how effective Fe-Mn oxide material is at removing contaminants may differ as it performs different functions, we discussed the above problems under different application scenarios (adsorption, oxidation, and advanced oxidation process). Additionally, internal factor (Fe/Mn mole ratio) and external factors (pHini, co-ions and ionic strength) were analyzed, and several common synthetic strategies of these composites were presented.

Sulfur or nitrogen-doped rGO supported Fe-Mn bimetal - organic frameworks composite as an efficient heterogeneous catalyst for degradation of sulfamethazine via peroxydisulfate activation.

In this work, sulfur/nitrogen modified reduced graphene oxide (S/N-rGO) was employed as both electron shuttle and support to fabricate Fe-Mn bimetallic organic framework@S/N-rGO hybrids (BOF@S/N-rGO) via a facile two-step solvothermal route. Compared with the transition metal ions (Fe2+/Mn2+), the classical metal oxide catalyst (Fe2O3 and Fe3O4) and nano zero-valent iron (nZVI), BOF@S/N-rGO catalyst can more effectively activate peroxydisulfate (PDS) with ultra-low concentration (0.05 mM) to degrade sulfamethazine (SMT). Quenching experiments, electron paramagnetic resonance (EPR) measurement and linear sweep voltammetry (LSV) showed that the activation pathways of PDS between the two catalysts were different. In BOF@N-rGO+PDS system, the degradation of SMT was mainly attributed to the oxidation of radicals including SO4•- and •OH, especially SO4•- . However, in BOF@S-rGO+PDS system, in addition to the radical pathway, there are also non-radical pathways, namely 1O2 and direct electron transfer. Furthermore, the applicability of BOF@S/N-rGO used in the PDS-mediated advanced oxidation processes (AOPs) was systematically investigated in terms of the effects of operating parameters and coexisting substance (anions and humic acid (HA)), the degradation of other pollutants, as well as the stability and reusability of the catalyst. This study proved that BOF@S/N-rGO was a promising activator of PDS with ultra-low concentration for the degradation of SMT.

Insights into a novel CuS/percarbonate/tetraacetylethylenediamine process for sulfamethazine degradation in alkaline medium.

This work presents a novel CuS/percarbonate/tetraacetylethylenediamine (CuS/SPC/TAED) process for the degradation of sulfamethazine (SMT). Results indicated that the CuS/SPC/TAED process enabled the efficient generation of peracetic acid (PAA), which can be efficiently activated by CuS in alkaline reaction media, and 93.6% of SMT was degraded in 30 min. Mechanism study revealed that the available reactive oxygen species (ROS) including hydroxyl radical (•OH), carbonate radical (CO3•-), superoxide radical (O2•-), singlet oxygen (1O2), and organic radicals (R-O•). Among them, R-O• (acetyloxyl radical (CH3CO2•) and acetylperoxyl radical (CH3CO3•)) were confirmed to be the primary species that contributed to SMT degradation. Simultaneously, the role of sulfur species and carbonate ions were explored. It was found that the reductive O2•- and sulfur species rendered the efficient redox of Cu species. Besides, the effects of key influencing factors including SPC/TAED mole ratio, CuS dosage, initial pH, temperature, and nontarget matrix constituents on SMT degradation were examined. Finally, the degradation intermediates of SMT was identified, and the toxicity of these products was estimated by quantitative structure-activity relationship (QSAR) analysis. Overall, this work offers a new and simple strategy for antibiotic-polluted water remediation.

Degradation of sulfamethazine in water by sulfite activated with zero-valent Fe-Cu bimetallic nanoparticles.

In this work, zero-valent Fe-Cu bimetallic nanoparticles were synthesized using a facile method, and applied to activate sulfite for the degradation of sulfamethazine (SMT) from the aqueous solution. The key factors influencing SMT degradation were investigated, namely the theoretical loading of Cu, Fe-Cu catalyst dosage, sulfite concentration and initial solution pH. The experimental results showed that the Fe-Cu/sulfite system exhibited a much better performance in SMT degradation than the bare Fe0/sulfite system. The mechanism and possible degradation pathway of SMT in Fe-Cu/sulfite system were revealed. The reactive radicals that played a dominant role in the SMT degradation process were •OH and SO4•-, while the loading of Cu induced the synergistic effect between Fe and Cu. The redox cycle between Cu(I)/Cu(II) remarkably contributed to the conversion of Fe(III) to Fe(II), greatly enhancing the catalytic performance of Fe-Cu bimetal. In real groundwater applications, the Fe-Cu/sulfite system also exhibited satisfactory SMT degradation. The 30-day aging tests of Fe-Cu particles demonstrated that the aging of catalyst was not obviously affecting the removal of SMT. Furthermore, the reusability of catalyst was evidenced by the recycling experiments. This study provides a promising application of bimetal activated sulfite for enhanced contaminant degradation in groundwater.

A comparative study on the physicochemical properties, reactivity and long-term performance of sulfidized nanoscale zerovalent iron synthesized with different kinds of sulfur precursors and procedures in simulated groundwater.

There are plentiful ways to synthesize sulfidized nanoscale zerovalent iron (S-nZVI), and this study investigated the influence of sulfur reagents (Na2S, Na2S2O3, Na2S2O4) and sulfidation sequence (co-sulfidation and post-sulfidation method) on the physicochemical properties, reactivity, and long-term performance of S-nZVI in simulated groundwater. The results suggested that the co-sulfidized nZVI (S-nZVIco) has higher reactivity (∼2-fold) than S-nZVIpost due to the stronger electron transfer capacity, deriving from the higher content of Fe0 and reductive sulfur species. However, during aging, the reactivity of S-nZVIco would be lost more rapidly than S-nZVIpost, due to the faster corrosion of Fe0 and more oxidation of reductive sulfur species. S-nZVIpost has the superior long-term performance with the degradation rate of trichloroethylene (TCE) remained at 30%∼60% even after 90 d of aging. Sulfur precursors can control the selectivity of S-nZVI by affecting the sulfur speciation on the particle surface. The proportion of reductive sulfur species on S-nZVIpost synthesized by Na2S was higher than S-nZVIpost synthesized by Na2S2O3 or Na2S2O4, resulting in a higher selectivity of the former S-nZVIpost than the latter S-nZVIpost. In addition, sulfidation procedures and sulfur precursors did not affect the degradation pathway of TCE. Nevertheless, the degradation product distribution can be affected by the different physicochemical transformation of various types of S-nZVI with the aging time. These results indicated that sulfur reagents and sulfidation procedures have crucial effects on the reactivity and long-term performance of S-nZVI, which can be designed for the specific application scenarios.

Adsorption and catalytic degradation of organic contaminants by biochar: Overlooked role of biochar's particle size.

Biochar (BC) is considered as a promising adsorbent and/or catalyst for the removal of organic contaminants. However, the relationship between the particle size of BC and its adsorption/catalysis performance is largely unclear. We therefore investigated the influence of particle size on the performance of BC pyrolyzed at 300-900 °C in trichloroethylene (TCE) adsorption and persulfate (PS) activation for sulfamethazine (SMT) degradation. The results showed that high-temperature pyrolyzed BC (BC900) presented superior adsorption capacity for TCE and excellent catalytic activity for PS activation to degrade SMT. Compared to 150-250 µm, 75-150 µm and pristine BC900, 0-75 µm BC900 showed the highest TCE adsorption efficiency, which increased by 19.5-62.3%. Similarly, SMT removal by BC900/PS systems also increased from 24.2% to 98.3% with decreasing BC particle size. However, the catalytic activity of BC after grinding was not significantly improved as expected, indicating the properties of biochar was not only controlled by size effect. Characterization measurements proved that small-sized BC tended to have larger specific surface area, more micropores, higher conductivity, rich graphitic domains and surface redox-active functional groups, thus resulting in an enhanced adsorption and catalytic ability of BC.

Multi-wavelength spectrophotometric determination of peracetic acid and the coexistent hydrogen peroxide via oxidative coloration of ABTS with the assistance of Fe2+ and KI.

In this study, a multi-wavelength spectrophotometric method for simultaneous determination of peracetic acid (PAA) and coexistent hydrogen peroxide (H2O2) was presented. This method was based on the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) with the assistance of Fe2+/KI to produce a stable green radical (ABTS●+), which could be determined at four characteristic peaks (i.e., 415 nm, 650 nm, 732 nm, and 820 nm). The absorbances of ABTS●+ at four peaks were well linear (R2 > 0.999) with concentrations of both total peroxides (PAA + H2O2) and PAA in the range of 0-40 µM under optimized conditions. The sensitivities for determining total peroxides at 415 nm, 650 nm, 732 nm and 820 nm were determined to be 4.248 × 104 M-1 cm-1, 1.682 × 104 M-1 cm-1, 2.132 × 104 M-1 cm-1, and 1.928 × 104 M-1 cm-1, respectively. For determining PAA, the corresponding sensitivities were 4.622 × 104 M-1 cm-1, 1.895 × 104 M-1 cm-1, 2.394 × 104 M-1 cm-1 and 2.153 × 104 M-1 cm-1, respectively. The concentration of coexistent H2O2 was gained by deducting PAA concentration from total peroxides concentration. The ABTS method was accurate enough to determine PAA concentration in natural water samples. Moreover, the ABTS method was successfully used to determine the changes of PAA and coexistent H2O2 and to distinguish their role on naproxen degradation in heat-activated PAA process. Overall, the ABTS method could be used as an alternative method for the convenient, rapid and sensitive determination of PAA and the coexistent H2O2 in water samples.

Hydroxylamine enhanced Fe(II)-activated peracetic acid process for diclofenac degradation: Efficiency, mechanism and effects of various parameters.

In this study, a commonly used reducing agent, hydroxylamine (HA), was introduced into Fe(II)/PAA process to improve its oxidation capacity. The HA/Fe(II)/PAA process possessed high oxidation performance for diclofenac degradation even with trace Fe(II) dosage (i.e., 1 µM) at pH of 3.0 to 6.0. Based on electron paramagnetic resonance technology, methyl phenyl sulfoxide (PMSO)-based probe experiments and alcohol quenching experiments, FeIVO2+ and carbon-centered radicals (R-O•) were considered as the primary reactive species responsible for diclofenac elimination. HA accelerated the redox cycle of Fe(III)/Fe(II) and itself was gradually decomposed to N2, N2O, NO2- and NO3-, and the environmentally friendly gas of N2 was considered as the major decomposition product of HA. Four possible degradation pathways of diclofenac were proposed based on seven detected intermediate products. Both elevated dosages of Fe(II) and PAA promoted diclofenac removal. Cl-, HCO3- and SO42- had negligible impacts on diclofenac degradation, while humic acid exhibited an inhibitory effect. The oxidation capacity of HA/Fe(II)/PAA process in natural water matrices and its application to degrade various micropollutants were also investigated. This study proposed a promising strategy for improving the Fe(II)/PAA process and highlighted its potential application in water treatment.

Efficient degradation of sulfamethazine via activation of percarbonate by chalcopyrite.

In this work, the novel application of chalcopyrite (CuFeS2) for sodium percarbonate (SPC) activation towards sulfamethazine (SMT) degradation was explored. Several key influencing factors like SPC concentration, CuFeS2 dosage, reaction temperature, pH value, anions, and humic acid (HA) were investigated. Experimental results indicated that SMT could be effectively degraded in the neutral reaction media by CuFeS2/SPC process (86.4%, 0.054 min-1 at pH = 7.1). The mechanism of SPC activation by CuFeS2 was elucidated, which was discovered to be a multiple reactive oxygen species (multi-ROS) process with the coexistence of hydroxyl radical (•OH), carbonate radical (CO3•-), superoxide radical (O2•-), and singlet oxygen (1O2), as evidenced by quenching experiments and electron spin resonance (ESR) tests. The generated •OH via the traditional heterogeneous Fenton-like process would not only react with carbonate ions to yield other ROS but also involve in SMT degradation. The abundant surface-bound Fe(II) was deemed to be the dominant catalytic active sites for SPC activation. Meanwhile, it was verified that the reductive sulfur species, the interaction between Cu(I) and Fe(III) as well as the available O2•- derived from the activation of molecular oxygen and the conversion of •OH favored the regeneration of Fe(II) on CuFeS2 surface. Furthermore, the degradation intermediates of SMT and their toxicities were evaluated. This study presents a novel strategy by integrating transition metal sulfides with percarbonate for antibiotic-contaminated water treatment.

Recent advances in waste water treatment through transition metal sulfides-based advanced oxidation processes.

With the ever-growing water pollution issues, advanced oxidation processes (AOPs) have received growing attention due to their high efficiency in the removal of refractory organic pollutants. Transition metal sulfides (TMSs), with excellent optical, electrical, and catalytical performance, are of great interest as heterogeneous catalysts. These TMSs-based heterogeneous catalysts have been demonstrated to becapable and adaptable in water purification through advanced oxidation processes. The aim of this review is to conduct an exhaustive analysis and summary of recent progress in the application of TMSs-based AOPs for water decontamination. Firstly, the commonly used tuning strategies for TMSs-based catalysts are concisely introduced, including artificial size and shape control, composition control, doping, and heterostructure manufacturing. Then, a comprehensive overview of the current state-of-the-art progress on TMSs-based AOPs (i.e., Fenton-like oxidation, photocatalytic oxidation, and electro chemical oxidation processes) for wastewater treatment is discussed in detail, with an emphasis on their catalytic performance and involved mechanism. In addition, influencing factors of water chemistry, namely, pH, temperature, dissolved oxygen, inorganic species, and natural organic matter on the catalytic performance of established AOPs are analyzed. Furthermore, the reusability and stability of TMSs-based catalysts in these AOPs are also outlined. Finally, current challenges and future perspectives related to TMSs-based catalysts and their applications for AOPs wastewater treatment are proposed. It is expected that this review would shed some light on the future development of TMSs-based AOPs towards water purification.

Surgical strategies for glottic carcinoma with a giant thyroid tumor A case report and literature review.

Description of strategies for preventing surgical complications in the treatment of laryngeal carcinomas associated with giant thyroid cancer. For this study, the clinical data of an elderly patient with laryngeal carcinoma associated with a large thyroid tumor, diabetes and hypertension were used. The patient's tumor was removed with simultaneous surgery performed by the thyroid surgery department and the laryngeal surgery department; the patient was followed for more than 3 years and the scars of tracheal granulation and laryngeal adhesions were removed with repeated laser interventions. The literature review was carried out on the Wanfang database, on the China How Net database and on the MEDLINE database via Computer. The final research keywords used for the study were "squamous cell carcinoma" and "glottis" or "larynx" / "larynx", "surgery", "thyroid cancer" and "simultaneous surgery". RESULTS: After completion of the intervention, the nasogastric tube and tracheal cannula were successfully removed, the glottis was successfully reconstituted and oral respiration, phonation and oral feeding were normally resumed. CONCLUSION: The multidisciplinary approach for the simultaneous removal of a laryngeal carcinoma associated with a bulky thyroid tumor in elderly subjects with multi-system and multi-organ damage has been successfully implemented. There are only a few such cases presented in the literature to illustrate risk prevention strategies for postoperative complications, including postoperative infection, extubation difficulties and loss of speech, which deserve to be known. KEY WORDS: Glottic carcinoma, Thyroid tumor, Laser surgery multidisciplinary, Tracheal cannula, Vocal cords.

A spectrophotometric method for measuring permanganate index (CODMn) by N,N-diethyl-p-phenylenediamine (DPD).

A new spectrophotometric method for measuring permanganate index (chemical oxygen demand using potassium permanganate (KMnO4) as oxidant, CODMn) in water was established. The method was based on the rapid oxidation of N,N-diethyl-p-phenylenediamine (DPD) by residual KMnO4 in digestion solution under neutral pH condition to form the stable pink radical (DPD●+). Only 20 s were enough to form the pink DPD●+. The generated DPD●+ could be quantitatively measured by a visible spectrophotometer at 551 nm. Stoichiometric coefficient of the reaction between KMnO4 and DPD was close to 1:5 (1:5.07). There was a well linear relationship (R2 = 0.999) between the change of the absorbance of DPD●+ at 551 nm and the concentration of CODMn in the range of 0-4.46 mg L-1. Limit of detection of the DPD method was as low as 0.02 mg L-1 CODMn. The DPD method was highly accurate for measuring CODMn in standard solutions with well recovery rates of 99.17%-102.22%, and was well tolerant to the interference of coexistent Cl- and Fe3+. The DPD method was successfully applied for measuring CODMn in real water samples, including surface water, underground water and drinking water. In comparison to the traditional titration method, the proposed DPD method was more convenient to operate, required less samples and digestion reagents (i.e., KMnO4 and H2SO4) and could be employed for online monitor.

Multi-wavelength spectrophotometric determination of hydrogen peroxide in water by oxidative coloration of ABTS via Fenton reaction.

In this study, a sensitive and low-cost multi-wavelength spectrophotometric method for the determination of hydrogen peroxide (H2O2) in water was established. The method was based on the oxidative coloration of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) via Fenton reaction, which resulted in the formation of green radical (ABTS•+) with absorbance at four different wavelengths (i.e., 415 nm, 650 nm, 732 nm, and 820 nm). Under the optimized conditions (CABTS = 2.0 mM, CFe2+ = 1.0 mM, pH = 2.60 ± 0.02, and reaction time (t) = 1 min), the absorbance of the generated ABTS•+ at 415 nm, 650 nm, 732 nm, and 820 nm were well linear with H2O2 concentrations in the range of 0-40 µM (R2 > 0.999) and the sensitivities of the proposed Fenton-ABTS method were calculated as 4.19 × 104 M-1 cm-1,1.73 × 104 M-1 cm-1, 2.18 × 104 M-1 cm-1, and 1.96 × 104 M-1 cm-1, respectively. Meanwhile, the detection limits of the Fenton-ABTS method at 415 nm, 650 nm, 732 nm, and 820 nm were respectively calculated to be 0.18 µM, 0.12 µM, 0.10 µM, and 0.11 µM. The absorbance of the generated ABTS•+ in ultrapure water, underground water, and reservoir water was quite stable within 30 min. Moreover, the proposed Fenton-ABTS method could be used for monitoring the variations of H2O2 concentration during the oxidative decolorization of RhB in alkali-activated H2O2 system.

Spectrophotometric determination of trace hydrogen peroxide via the oxidative coloration of DPD using a Fenton system.

A low-cost and environmentally-friendly spectrophotometric method for hydrogen peroxide (H2O2) determination based on the oxidative coloration reaction of N,N'-diethyl-p-phenylenediamine (DPD) via the Fenton reactions in aqueous water was established. The generated pink radical cation (DPD+) showed maximum absorption at 551 nm. Importantly, under the optimal conditions (pH 3.0, 20 mM DPD, 1.5 mM Fe(II) and reaction time of 45 s), the increase in absorbance at 551 nm for DPD+ generation was linear with respect to the addition of H2O2 (0-12 µM). The sensitivity and the detection limit of the proposed Fenton-DPD method for H2O2 determination at 551 nm were (2.55 ±â€¯0.01) × 104 M-1 cm-1 and 0.05 µM, respectively. The stoichiometric factor for the reaction of H2O2 with DPD was 1:1.18. The absorbance of the generated DPD+ was found to be stable in different types of water within 20 min. Moreover, the proposed Fenton-DPD method could be used for the analysis of the trace H2O2 in rainwater and determine the rate constants that involved H2O2 with high accuracy.

Multi-wavelength spectrophotometric determination of hydrogen peroxide in water with peroxidase-catalyzed oxidation of ABTS.

In this study, a new spectrophotometric method was proposed for the measurement of hydrogen peroxide (H2O2) in aqueous solutions. The method was based on the peroxidase (POD)-catalyzed reaction in which 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) was oxidized to form the stable green radical (ABTS+). The generated ABTS+ could be determined spectrophotometrically. The absorbance of the generated ABTS+ at 415 nm, 650 nm, 732 nm and 820 nm were linear with H2O2 concentrations in the range of 0-40 µM. The sensitivities of the proposed ABTS method for H2O2 determination at 415 nm, 650 nm, 732 nm and 820 nm were 6.29 × 104 M-1 cm-1, 2.00 × 104 M-1 cm-1, 2.54 × 104 M-1 cm-1 and 1.89 × 104 M-1 cm-1, respectively. The oxidation of ABTS to generate ABTS+ in POD-catalyzed H2O2 system at pH 6.0 was so fast that the determination time of the ABTS method was as short as 0.5 min. The stoichiometry of the reaction of H2O2 and ABTS in the presence of POD was calculated as nearly 1:2 (1:1.92). The residual absorbance of the generated ABTS+ was also found to be stable within 30 min in natural waters. Low H2O2 concentration in rainwater could be both measured by the ABTS method and the DPD method with high accuracy, however, H2O2 concentration in wastewater contained rhodamine B could only be accurately measured with the ABTS method at 732 nm. Moreover, waste solutions after H2O2 analysis with the proposed ABTS method were non-hazardous towards E. coli.