Droplet spray ionization mass spectrometry for real-time monitoring of activation of peroxymonosulfate by 1,4-benzoquinone

Investigation into the Synergistic Effect of the Zinc Peroxide/Peroxymonosulfate Double-Oxidation System for the Efficient Degradation of Tetracycline

The increasingly severe antibiotic pollution has become one of the most critical issues. In this study, a zinc peroxide/peroxymonosulfate (ZnO2/PMS) double-oxidation system was developed for tetracycline (TC) degradation. A small amount of ZnO2 (10 mg) and PMS (30 mg) could effectively degrade 82.8% of TC (100 mL, 50 mg/L), and the degradation process could be well described by the pseudo-second-order kinetic model. Meanwhile, the ZnO2/PMS double-oxidation system showed high adaptability in terms of reaction temperature (2-40 °C), initial pH value (4-12), common inorganic anions (Cl-, NO3-, SO42- and HCO3-), natural water source and organic pollutant type. The quenching experiment and electron paramagnetic resonance (EPR) characterization results confirmed that the main reactive oxygen species (ROS) was singlet oxygen (1O2). Moreover, three possible pathways of TC degradation were deduced according to the analyses of intermediates. On the basis of comparative characterization and experiment results, a synergistic activation mechanism was further proposed for the ZnO2/PMS double-oxidation system, accounting for the superior degradation performance. The released OH- and H2O2 from ZnO2 could activate PMS to produce major 1O2 and minor superoxide radicals (•O2-), respectively.

l-Cysteine and barium titanate co-modified enteromorpha biochar as effective peroxymonosulfate activator for atrazine treatment

In this study, pyrolysis and hydrothermal methods were used for Enteromorpha biochar that was co-modified with l-cysteine and barium titanate (LBCBa). It has great environmental tolerance and can remove 93.0 % of atrazine (ATZ, 10 mg·L-1) within 60 mins of ultrasonic treatment. The enhanced hydrophilicity, electron-donating capability, and piezoelectricity of LBCBa are considered to induce excellent performance. The apparent reaction rate of the LBCBa-2/PMS/ATZ system with ultrasonic was 2.87 times that without ultrasonic. The density functional theory points out that, introducing l-cysteine to carbon edges improves the adsorption of ATZ and peroxymonosulfate (PMS), making PMS easier to activate. This work offered unique insights for fabricating effective catalysts and demonstrated the combination of hydrophilic functional groups and piezoelectricity in improving catalytic performance and stability.

The debatable role of singlet oxygen in persulfate-based advanced oxidation processes

Singlet oxygen (¹O₂) attracts much attention in persulfate-based advanced oxidation processes (PS-AOPs), because of its wide pH tolerance and high selectivity toward electron-rich organics. However, there are conflicts about the ¹O₂ role in PS-AOPs on several aspects, including the formation of different key reactive oxygen species (ROS) at similar active sites, pH dependence, broad-spectrum activity, and selectivity in the elimination of organic pollutants. To a large degree, these conflicts root in the drawbacks of the methods to identify and evaluate the role of ¹O₂. For example, the quenchers of ¹O₂ have high reactivity to other ROS and persulfate as well. In addition, electron transfer process (ETP) also selectively oxidizes organics, having a misleading effect on the identification of ¹O₂. Therefore, in this review, we summarized and discussed some basic properties of ¹O₂, the debatable role of ¹O₂ in PS-AOPs on multiple aspects, and the methods and their drawbacks to identify and evaluate the role of ¹O₂. On the whole, this review aims to better understand the role of ¹O₂ in PS-AOPs and further help with its reasonable utilization.

Condensed Phase Membrane Introduction Mass Spectrometry: A Direct Alternative to Fully Exploit the Mass Spectrometry Potential in Environmental Sample Analysis

Membrane introduction mass spectrometry (MIMS) is a direct mass spectrometry technique used to monitor online chemical systems or quickly quantify trace levels of different groups of compounds in complex matrices without extensive sample preparation steps and chromatographic separation. MIMS utilizes a thin, semi-permeable, and selective membrane that directly connects the sample and the mass spectrometer. The analytes in the sample are pre-concentrated by the membrane depending on their physicochemical properties and directly transferred, using different acceptor phases (gas, liquid or vacuum) to the mass spectrometer. Condensed phase (CP) MIMS use a liquid as a medium, extending the range to new applications to less-volatile compounds that are challenging or unsuitable to gas-phase MIMS. It directly allows the rapid quantification of selected compounds in complex matrices, the online monitoring of chemical reactions (in real-time), as well as in situ measurements. CP-MIMS has expanded beyond the measurement of several organic compounds because of the use of different types of liquid acceptor phases, geometries, dimensions, and mass spectrometers. This review surveys advancements of CP-MIMS and its applications to several molecules and matrices over the past 15 years.

Evolution of Singlet Oxygen by Activating Peroxydisulfate and Peroxymonosulfate: A Review

Advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) or peroxymonosulfate (PMS) activation have attracted much research attention in the last decade for the degradation of recalcitrant organic contaminants. Sulfate (SO₄^•−) and hydroxyl (^•OH) radicals are most frequently generated from catalytic PDS/PMS decomposition by thermal, base, irradiation, transition metals and carbon materials. In addition, increasingly more recent studies have reported the involvement of singlet oxygen (¹O₂) during PDS/PMS-based AOPs. Typically, ¹O₂ can be produced either along with SO₄^•− and ^•OH or discovered as the dominant reactive oxygen species (ROSs) for pollutants degradation. This paper reviews recent advances in ¹O₂ generation during PDS/PMS activation. First, it introduces the basic chemistry of ¹O₂, its oxidation properties and detection methodologies. Furthermore, it elaborates different activation strategies/techniques, including homogeneous and heterogeneous systems, and discusses the possible reaction mechanisms to give an overview of the principle of ¹O₂ production by activating PDS/PMS. Moreover, although ¹O₂ has shown promising features such as high degradation selectivity and anti-interference capability, its production pathways and mechanisms remain controversial in the present literatures. Therefore, this study identifies the research gaps and proposes future perspectives in the aspects of novel catalysts and related mechanisms.

Degradation mechanism study of fluoroquinolones in UV/Fe2+/peroxydisulfate by on-line mass spectrometry

Antibiotics are of concern due to their prevalent detection in aquatic environment. Sulfate radical based advanced oxidation processes show a great capacity to degrade antibiotics, but the mechanisms are still unclear. In this work, the degradation mechanism of fluoroquinolones (FQs), a major group of antibiotics, in UV/Fe²⁺/PMS was deeply investigated. The degradation process was in-situ and real-time monitoring by illumination-assisted droplet spray ionization mass spectrometry. A series of reactive intermediates were captured, and further characterized by high-resolution mass spectrometry (HRMS) and tandem MS. About 50 different transformation products have been identified for ciprofloxacin and norfloxacin. More than 15 products were the first time reported. Taking into consideration of the sequential formation and intensity change of intermediates, the feasible and complete transformation pathways of FQs were proposed. Compared with the photolysis process, the defluorination of FQs was not observed in this system. This work provided abundant information of FQs degradation by persulfate advanced oxidation processes (AOPs) and meanwhile demonstrated the importance of HRMS and on-line MS in mechanism research of AOPs.

Fast determination of peroxymonosulfate by flow injection chemiluminescence using the Tb(III) ligand in micelle medium

Based on the chemiluminescence (CL) phenomenon of peroxymonosulfate (PMS) and Tb(III) enhanced by its ligand in a micelle microenvironment, a fast and sensitive flow injection CL method for PMS detection was proposed and applied to the analysis of different samples and PMS decomposition. Under the optimized conditions, a linear range was obtained from 4.0 × 10^-6  mol L^-1 to 2.0 × 10^-4  mol L^-1 with a high correlation coefficient (r = 0.9997), detection limit of 5.0 × 10^-7  mol L^-1 (S/N = 3) and relative standard deviation of 2.4% for 1.0 × 10^-5  mol L^-1 PMS (n = 9). This was successfully applied to the determination of PMS in Virkon powder, tap water, and swimming pool water samples with satisfactory recoveries from 94.8% to 104.8%. In particular, the analytical frequency could be as fast as five samples per minute because there was no reaction step before analysis and the CL phenomenon was instantaneous. Therefore, this CL method has also been successfully applied to investigate the PMS decomposition profiles in carbon material (carbon nanotubes, carbon nanofibres, activated carbon and graphene oxide) catalysis systems, which followed pseudo-first-order kinetics with good correlation coefficients (r > 0.9305). Quenching experiments and electron spin resonance spectra verified that the CL phenomenon was due to the formation of singlet oxygen, and that hydroxyl and sulfate radicals might be important in the generation of singlet oxygen. Tb(III) is the luminescent emitter according to the characteristics emission bands of the fluorescence and CL spectra in different media.

Activating peroxymonosulfate by halogenated and methylated quinones: performance and mechanism

This work describes the efficiency and mechanism of peroxymonosulfate (PMS) activation by benzoquinone with different functional groups for sulfamethoxazole degradation.