Competition between Loss of H2 versus H+H in the Fragmentation of the Fluorene Cation.

The fluorene cation is a frequently studied molecule in the context of fragmentation experiments. This is because of its potential role in interstellar chemistry, notably as a precursor of PAH cages. In this paper, we analyze H, H+ , H2 and H 2 + ${{\rm{H}}_2^ + }$ losses from the fluorene cation using the SMF (Statistical Molecular Fragmentation) model. We calculate the probabilities of all the 534 possible fragmentation channels as a function of the excitation energy, up to the loss of three hydrogens. Four different types of hydrogen atom pairings (from the same carbon, from the same ring, from different rings and across-the-bay) have been tested in order to determine which types contribute to the actual production of hydrogen molecules. The simulated breakdown curves are in very good agreement with different experimental results when same ring pairing is taken into account. It was possible to deduce from the model the locations of the emitted H, H+ , H2 and H 2 + ${{\rm{H}}_2^ + }$ species.

Study on Dynamic Column Behavior and Complexation Mechanism of DBS-Modified Crown Ether-Based Silica to 90Sr.

A crown ether-loaded hybrid adsorbent suitable for the separation and enrichment of strontium from high-level liquid waste was synthesized. 4',4'(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its modifiers dodecyl benzenesulfonic acid (DBS) and 1-dodecanol were impregnated into silica-based polymer support. The hybrid adsorbent exhibited excellent Sr(II) selectivity ability, and effective chromatographic separation and recovery of Sr(II) from simulated high-level liquid waste could be achieved with a (DtBuCH18C6 + DBS + dodec)/SiO2-P packed column. The recovery rate of Sr(II) calculated based on the mass balance was approximately 99% and over 80% for the other coexisting metal ions. An appropriate increase in the concentration of Na-DTPA eluent was favorable to improve the efficiency of the elution process because of the increased complexation capacity of [DTPA]5- to Sr(II). The developed theoretical model can simulate the dynamic breakthrough curves of the material on the basis of short column data, thereby predicting the scale-up column of the practical operation. Density functional theory calculation was used to explore the action mechanism of DBS modifiers on the Sr(II) complexation process of crown ether groups. Two Sr(II) complexation isomeric models of DtBuCH18C6 were established, and the calculation results revealed a similar complexation ability. DtBuCH18C6 could form a stable Sr(II) complexation structure with DBS coordination, which further indicated that DBS could be a ligand to promote the Sr(II) adsorption ability of crown ether materials.

"One-can" strategy for the synthesis of hydrothermal biochar modified with phosphate groups and efficient removal of uranium(VI).

Significant selectivity, reasonable surface modification and increased structural porosity were three key factors to improve the competitiveness of biochar in the adsorption field. In this study, a hydrothermal bamboo-derived biochar modified with phosphate groups (HPBC) was synthesized using "one-can" strategy. BET showed that this method could effectively increase the specific surface area (137.32 m2 g-1) and simulation of wastewater experiments indicated HPBC had an excellent selectivity for U(VI) (70.35%), which was conducive to removal of U(VI) in real and complex environments. The accurate matchings of pseudo-second-order kinetic model, thermodynamic model and Langmuir isotherm showed that at 298 K, pH = 4.0, the adsorption process dominated by chemical complexation and monolayer adsorption was spontaneous, endothermic and disordered. Saturated adsorption capacity of HPBC could reach 781.02 mg g-1 within 2 h. The introduction of phosphoric acid and citric acid by "one-can" method not only provided abundant -PO4 to assist adsorption, but also activated oxygen-containing groups on the surface of the bamboo matrix. Results showed that adsorption mechanism of U(VI) by HPBC included electrostatic action and chemical complexation involving P-O, PO and ample oxygen-containing functional groups. Therefore, HPBC with high phosphorus content, outstanding adsorption performance, excellent regeneration, remarkable selectivity and green value provided a novel solution for the field of radioactive wastewater treatment.

Radiation Resistance and Adsorption Behavior of Aluminum Hexacyanoferrate for Pd.

Irradiation resistance is important for adsorbents used in radioactive environments such as high-level liquid waste. In this work, a silica-based composite adsorbent (KAlFe(CN)6/SiO2) was synthesized and γ-irradiated from 10 to 1000 kGy. The angles of the main X-ray diffraction peaks slightly decreased with the increase in irradiation dose, and a minor decomposition of CN- occurred after irradiation to 1000 kGy, indicating that the KAlFe(CN)6/SiO2 adsorbent could preserve structural integrity with a dose below 100 kGy. In 1 to 7 M HNO3, the adsorption ability of the irradiated KAlFe(CN)6/SiO2 remained performant, with a higher Kd than 1625 cm3 g-1. The adsorption equilibrium of Pd(II) in 3 M HNO3 was attained within 45 min before and after irradiation. The maximal adsorption capacity Qe of the irradiated KAlFe(CN)6/SiO2 on Pd(II) ranged from 45.1 to 48.1 mg g-1. A 1.2% relative drop in Qe was observed after 100 kGy irradiation, showing that γ-irradiation lower than 100 kGy insignificantly affected the adsorption capacity of KAlFe(CN)6/SiO2. Calculating and comparing the structures and free energies of different adsorption products via the density functional theory (DFT) method showed that KAlFe(CN)6/SiO2 was more inclined to completely adsorb Pd(II) and spontaneously generate Pd[AlFe(CN)6]2.

Degradation of the mixed nuclear-grade cationic and anionic exchange resins using Fe2+/H+ homogeneous Fenton oxidation.

To further improve the treatment capacity of actual wastes, H+ was introduced into the homogeneous Fenton system as a co-catalyst for dissolution and degradation of the mixed nuclear-grade cationic and anionic exchange resins. The effects of acid type and concentration, catalyst type and concentration, H2O2 dosage, initial temperature, antifoaming agent and resin ratio were studied. The concentration of inorganic acid, type and concentration of catalyst had significant influence on the decomposition of mixed resins. The experimental results showed that when the mixing ratio of resins was 1:1, the initial temperature was 96 ± 1 °C, the amount of H2O2 was 200 mL, and the concentration of H+/Fe2+ was 1 M/0.1 M, complete dissolution and 79% weight reduction of mixed resins were obtained. Combined with density functional theory (DFT) calculations, cationic exchange resin and anionic exchange resin showed different reactivity in the experiment. Hydroxyl radicals (•OH) tended to attack -SO3- groups with more negative charges, and the barrier energy of -SO3- ion dissociation was 8.2 kcal/mol, which caused the cationic exchange resin to be easily destroyed. According to the characterization results, the characteristic intermediates were determined, indicating that desulfonation, valence change of nitrogen atom, and cleavage of long-chain carbon skeleton existed during the reaction, but incomplete oxidation still remained.

Adsorption of Co2+ and Sr2+ in aqueous solution by a novel fibrous chitosan biosorbent.

In this study, a novel fibrous chitosan biosorbent was prepared using LiOH/KOH/urea/H2O (4.5:7:8:80.5 by weight) as spinning solvent. The fibrous chitosan exhibited a higher adsorption capacity and a faster adsorption rate for Co2+ and Sr2+, compared with spherical chitosan due to its high specific surface area (16.9 m2 g-1), uniform fineness (24.1 µm), and good mechanical strength. The adsorption capacity of fibrous chitosan for Co2+ and Sr2+ was 31.3 mg g-1 and 20.0 mg g-1, respectively, which was higher than that of spherical chitosan (22.5 mg g-1for Co2+ and 8.9 mg g-1 for Sr2+). The coordination between -NH2/-OH of chitosan and the nuclide ions was the rate-limiting step. The improvement of adsorption performance was due to the higher specific surface area which increased the exposure degree of functional groups (adsorptive sites). This new wet-spun fibrous chitosan biosorbent showed great potential in the adsorptive removal of nuclides ions from aqueous solution.

Degradation of the mixed organic solvents of tributyl phosphate and n-dodecane by heterogeneous Fenton-like oxidation using nanoscale zero-valent iron as the catalyst.

The treatment and disposal of spent radioactive organic solvents, i.e., tributyl phosphate (TBP) and diluent (such as kerosene, n-dodecane, etc.), produced in the reprocessing of spent fuel in the closed cycle are crucial for the sustainable development of the nuclear industry. In this study, the synthesized nanoscale zero-valent iron (nZVI) was used as the heterogeneous Fenton-like catalyst to promote the generation of hydroxyl radicals (•OH) by reacting with H2O2 to degrade the mixed organic solvents of TBP and n-dodecane. nZVI was characterized by scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherms, and X-ray photoelectron spectroscopy (XPS) to investigate the micro-morphology, nano-particle size, and surface valence state. The change of Fe2+/Fe3+ concentration ratio during the reaction was measured to clarify the performance of nZVI. The effects of temperature, catalyst dosage, H2O2 dosage, and acidifier concentration on the degradation of TBP and n-dodecane were studied, and the results were complemented by the COD of the aqueous solution and the volume reduction rate of the organic phase. The mixed organic solvents of TBP and n-dodecane containing Co2+ were used to simulate the spent radioactive organic solvents and to study the distribution of nuclides after the reaction. The results showed that most of the radioactivity was in the residual solution, and the condensate contained almost no radioactivity. The degradation of TBP and n-dodecane was carried out separately, which showed that n-dodecane was more difficult to degrade. Density functional theory (DFT) calculations were applied to determine the adsorption energy of organic solvents and nZVI. According to the Fourier transform infrared spectra (FTIR) and their corresponding DFT calculations, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) of the sample after the reaction, the possible intermediates were analyzed, and the degradation mechanism was speculated.

Iron-Based Dual Active Site-Mediated Peroxymonosulfate Activation for the Degradation of Emerging Organic Pollutants.

It is still a challenge to synthesize highly efficient and stable catalysts for the Fenton-like reaction. In this study, we constructed an integrated catalyst with highly dispersed iron-based dual active sites, in which Fe2N and single-atom Fe (SA-Fe) were embedded into nitrogen- and oxygen-co-doped graphitic carbon (Fe-N-O-GC-350). Extended X-ray absorption fine structure (EXAFS) confirmed the coordination structure of iron, and line combination fitting (LCF) demonstrated the coexistence of Fe2N and SA-Fe with percentages of 75 and 25%, respectively. Iron-based dual active sites endowed Fe-N-O-GC-350 with superior catalytic activity to activate peroxymonosulfate (PMS) as evidenced by the fast degradation rate of sulfamethoxazole (SMX) (0.24 min-1) in the presence of 0.4 mM PMS and 0.1 g/L Fe-N-O-GC-350. Unlike the reported singlet oxygen and high-valent iron oxo-mediated degradation induced by the SA-Fe catalyst, both surface-bound reactive species and singlet oxygen contributed to SMX degradation, while surface-bound reactive species dominated. Density functional theory (DFT) simulation indicated that Fe2N and SA-Fe enhanced the adsorption of PMS, which played a key role in PMS activation. The Fe-N-O-GC-350/PMS system had resistance to the interference of common inorganic anions and high oxidation capacity to recalcitrant organic contaminants. This study elucidated the important role of Fe2N in PMS activation and provide a clue to design rationally catalysts with iron-based dual active sites to activate PMS for the degradation of emerging organic pollutants.

Multiple dehydrogenation of fluorene cation and neutral fluorene using the statistical molecular fragmentation model.

The statistical molecular fragmentation (SMF) model was used to analyze the 306 fragmentation channels (containing 611 different species) that result from the fluorene (C13H10+) cation losing up to three hydrogen atoms (neutral radicals and/or a proton). Breakdown curves from such analysis permit one to extract experimentally inaccessible information about the fragmentation of the fluorene cation, such as the locations of the lost hydrogen atoms (or proton), yields of the neutral fragments, electronic states of the residues, and quantification of very low probability channels that would be difficult to detect. Charge localization during the fragmentation pathways was studied to provide a qualitative understanding of the fragmentation process. Breakdown curves for both the fluorene cation and neutral fluorene were compared. The SMF results match the rise and fall of the one hydrogen loss yield experimentally measured by imaging photoelectron-photoion coincidence spectroscopy using a VUV synchrotron.

Construction of three-dimensional reduced graphene oxide wrapped nZVI doped with Al2O3 as the ternary Fenton-like catalyst: Optimization, characterization and catalytic mechanism.

The rational design and synthesis of novel nanocomposites as effective heterogeneous catalysts is meaningful for the advances in Fenton-like technology. Herein, multiple variants of three-dimensional reduced graphene oxide wrapped nZVI doped with Al2O3 (3D-RGO@nZVI/Al2O3) were prepared by three different self-assembly methods. The composites were characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, Raman spectrum analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. A series of experiments on chloramphenicol degradation at different pH values were employed to evaluate the catalytic properties of the prepared catalysts. With the systematical investigation of their morphologies, chemical components and catalytic performance, the optimal 3D-RGO@nZVI/Al2O3 catalyst was synthesized, which was favorable for inducing the Fenton-like reaction by activation of dissolved oxygen (DO) within a wide pH range. The anchored nZVI particles were the main active sites for catalytic oxidation, and doped Al3+ played a major role in buffering the pH of CAP solution. Electron spin resonance spectroscopy revealed the existence of the superoxide radicals (·O2-) and singlet oxygen (1O2), which provides a new insight into the reaction mechanism of reactive oxygen species in the Fenton-like system. This work is an essential effort to explore the promoting effect of synthesis methods on the catalytic behavior of catalysts, and to further study the Fenton-like reaction triggered by DO activation.

Nanoscale Fe0/Cu0 bimetallic catalysts for Fenton-like oxidation of the mixture of nuclear-grade cationic and anionic exchange resins.

Spent resins generated from the nuclear industrial processes are still difficult to be treated and disposed. Fenton-like processes have great application potential in the treatment of spent resins, but the Fenton reaction mechanisms and resin degradation pathways remain challenging. In this study, nanoscale Fe0/Cu0 bimetallic catalysts were prepared and characterized for the Fenton-like degradation of the mixture of cationic and anionic resins. High catalytic property of Fe0/Cu0 bimetallic nanoparticles activated by H2O2 was evaluated, according to the effects of various nanoparticles, temperature, catalyst amount, H2O2 concentration and the mixing ratio of cationic and anionic resins. Combined the shape and color changes of mixed resins with the experimental and calculated characterization results, different degradation difficulty of cationic and anionic resins and their degradation mechanisms were studied. According to the density functional theory calculations of the optimized resin molecules with the Fe0/Cu0 catalyst, the mechanisms of Fenton-like reactions and the degradation of mixed resins through the synergistic effect of Fe and Cu species were proposed. The comprehensive Fenton-like reactions and degradation mechanisms provide new insights to advance the treatment of spent resins and organic polymers by Fenton-like processes.

Reaction mechanism of chloramphenicol with hydroxyl radicals for advanced oxidation processes using DFT calculations.

The structure properties of chloramphenicol (CAP), including bond information and the Fukui function for the atoms in the main chain, were investigated computationally by density functional theory (DFT). The result shows that the chiral carbons in CAP offer the most active positions for chemical reactions, which is in good agreement with the experiment. The detailed degradation mechanism for CAP with hydroxyl radicals in advanced oxidation processes is further studied at the SMD/M06-2X/6-311 + G(d,p) level of theory. The main reaction methods, including the addition-elimination reaction, hydrogen abstract reaction, hydroxyl radical addition, and bond-breaking processes, are calculated. The results show that the nitro-elimination reaction is the most likely reaction in the first step of the degradation of CAP, and the latter two processes are more likely to be hydrogen abstract reactions. The details for the transition states, intermediate radicals, and free energy surfaces for all proposed reactions are given, which makes up for a lack of experimental knowledge.

Enhanced heterogeneous Fenton-like degradation of nuclear-grade cationic exchange resin by nanoscale zero-valent iron: experiments and DFT calculations.

Nanoscale zero-valent iron (nZVI) was prepared and used as a heterogeneous Fenton-like catalyst for the degradation of nuclear-grade cationic exchange resin. The properties of nZVI before and after reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analysis. The results showed that nZVI-H2O2 system exhibited the enhanced degradation of cationic resins, compared with Fe2+-H2O2, Cu0-H2O2, and Fe0/Cu0-H2O2 systems. The effects of initial temperature, nZVI dose, and H2O2 concentration were studied, and the higher temperature and nZVI dose with relatively low H2O2 concentration brought faster degradation rate. The degradation of cationic resins followed the pseudo-first-order kinetics with the apparent activation energy of 53.29 kJ/mol. According to the experimental and calculated infrared and UV-visible spectra, the carbon skeleton of cationic resins was broken with the detachment of benzene ring and the desulfonation of resin polymer by hydroxyl radicals (•OH), generating long-chain alkenes. These intermediates were further oxidized through the hydroxyl substitution, hydrogen abstraction, ring cleavage, or carbonylation reactions, finally forming carboxylic acids remained in solution.

A Statistical Model and DFT Study of the Fragmentation Mechanisms of Metronidazole by Advanced Oxidation Processes.

The degradation pathway of the antibiotic metronidazole (MNZ) in wastewater was investigated computationally with a physical statistical method and a quantum chemical approach. In both cases, density functional theory (DFT) at the M06-2X/6-311+G(d,p) level was used to calculate the structures and property parameters of all molecules. On one hand, decay of the isolated MNZ molecule excited at a given excitation energy was studied using the statistical molecular fragmentation (SMF) model. On the other hand, the reaction mechanisms of MNZ oxidized by hydroxyl radicals (•OH) in advanced oxidation processes (AOPs) were analyzed. Both studies show that the main reaction sites in MNZ are, by decreasing importance, -NO2, -CH2OH, and -CH2CH2OH. The main degradation reactions are (i) alcohol group oxidation including the abstraction of hydrogen on C in the -CH2OH group and oxidation of the hydroxyl group to the aldehyde and further to the carboxylic acid and (ii) addition-elimination reactions happening on the imidazole ring which finally replace the nitro by hydroxyl radicals. The results gained are in a good agreement with the available experimental data on MNZ degradation by AOPs. The structures of intermediates, transition states, and free energy surfaces are helpful in elucidating the details of the elimination mechanism, supplementing current experimental knowledge.

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles as efficient micro-electrolysis-promoted Fenton-like catalysts for metronidazole removal.

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles (3D-GN@Cu0) were synthesized using a self-assembly process of liquid-phase reduction and characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectrum analysis, and X-ray photoelectron spectroscopy. The catalytic activity of 3D-GN@Cu0 was evaluated in view of the effects of various systems, the pH value, catalyst dosage, initial metronidazole concentration and temperature, and it showed a high efficiency for removing metronidazole with saturated dissolved oxygen (without adding extra H2O2) in a wide range of pH value from 3.2 to 9.8. Combined with the results of dissolved oxygen activation, determination of reactive oxidizing species, and X-ray photoelectron spectroscopy (XPS) analysis, the surface-bounded ·OHads formed by the reaction of the in situ generation H2O2 with 3D-GN@Cu0 was mainly responsible for the removal of metronidazole. The charge distribution and electrostatic potential (ESP) of 3D-GN@Cu0 further illustrated the distribution and transfer of electrons on the catalyst surface, which predicted a micro-electrolysis-promoted Fenton-like reaction mechanism.

Mechanism of Co(II) adsorption by zero valent iron/graphene nanocomposite.

Nanoscale zero valent iron (ZVI)/graphene (GF) composite was prepared and characterized by Brunauer-Emmett-Teller (BET) surface area measurement and zeta potential determination. The adsorption isotherm of Co(II) in aqueous solution, as well as the influence of pH values and ionic strengths was studied. The mechanism of Co(II) adsorption by GF was investigated through analyzing the sorption products at initial pH of 3.0, 6.0 and 9.0 using high-resolution transmission electron microscope with energy dispersive X-ray detector (HRTEM-EDX), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), Raman spectra, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) measurement. The results indicated that Langmuir isotherm model fitted well and the adsorption capacity was 131.58 mg g(-1) at 30°C. Adsorption capacity was not significantly influenced by ionic strength and kept high at pH 4.0∼9.0. The detail information of GF-Co interaction at different initial pH values was obtained using XAFS analysis combined with other characterization methods. Coordination numbers (CN) and interatomic distances (R) of both Fe and Co were given. At pH 3.0 and pH 6.0, the Co-substituted iron oxides transformed to CoFe2O4-like structure, while at pH 9.0 they changed to green rust-like phases. Co occupied preferentially in the octahedral sites in acid solution. The adsorption mechanism of Co(II) was attributed to inner-sphere complexation and dissolution/re-precipitation of the substituted metal oxides.

Degradation of 4-Chloro-3,5-Dimethylphenol by a Heterogeneous Fenton-Like Reaction Using Nanoscale Zero-Valent Iron Catalysts.

Degradation of 4-chloro-3,5-dimethylphenol (PCMX) by a heterogeneous Fenton-like process using nanoparticulate zero-valent iron (nZVI) and hydrogen peroxide (H2O2) at pH 6.3 was investigated. Interactive effects of three factors-initial PCMX concentration, nZVI dosage, and H2O2 concentration-were investigated using the response surface method based on the Box-Behnken design. Experimental results showed that complete decomposition of PCMX and 65% of total organic carbon removal were observed after 30 min of reaction at neutral pH under recommended reaction conditions: nZVI, 1.0 g/L; H2O2, 18 mM; and initial PCMX concentration, 0.15 g/L. Based on the effects of scavengers n-butanol and KI, removal of PCMX was mainly attributed to the attack of •OH, especially the surface-bonded •OH. A possible degradation pathway of PCMX was proposed.

Magnetic nanoscaled Fe3O4/CeO2 composite as an efficient Fenton-like heterogeneous catalyst for degradation of 4-chlorophenol.

Magnetic nanoscaled Fe(3)O(4)/CeO(2) composite was prepared by the impregnation method and characterized as a heterogeneous Fenton-like catalyst for 4-chlorophenol (4-CP) degradation. The catalytic activity was evaluated in view of the effects of various processes, pH value, catalyst addition, hydrogen peroxide (H(2)O(2)) concentration, and temperature, and the pseudo-first-order kinetic constant of 0.11 min(-1) was obtained for 4-CP degradation at 30 °C and pH 3.0 with 30 mM H(2)O(2), 2.0 g L(-1) Fe(3)O(4)/CeO(2), and 0.78 mM 4-CP. The high utilization efficiency of H(2)O(2), calculated as 79.2%, showed a promising application of the catalyst in the oxidative degradation of organic pollutants. The reusability of Fe(3)O(4)/CeO(2) composite was also investigated after six successive runs. On the basis of the results of metal leaching, the effects of radical scavengers, intermediates determination, and X-ray photoelectron spectroscopic (XPS) analysis, the dissolution of Fe(3)O(4) facilitated by CeO(2) played a significant role, and 4-CP was decomposed mainly by the attack of hydroxyl radicals (•OH), including surface-bound •OH(ads) generated by the reaction of Fe(2+) and Ce(3+) species with H(2)O(2) on the catalyst surface, and •OH(free) in the bulk solution mainly attributed to the leaching of Fe.

A heterogeneous Fenton-like system with nanoparticulate zero-valent iron for removal of 4-chloro-3-methyl phenol.

The removal of biocide 4-chloro-3-methyl phenol (CMP) was investigated by heterogeneous Fenton-like system using nanoparticulate zero-valent iron (nZVI) as catalyst. The properties of nZVI before and after reaction were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of pH value, initial concentration of CMP, nZVI dose and hydrogen peroxide (H(2)O(2)) concentration were determined. The experimental results showed that lower pH value and CMP concentration brought faster degradation rate. With the initial pH value of 6.1 and initial CMP concentration of 0.7 mM, the optimal dosage of reagents were 0.5 g nZVI/L and 3.0 mM H(2)O(2). At pH 6.1, the degradation of CMP followed two-stage first-order kinetic that composed of an induction period (first-stage) and a followed rapid degradation stage (second-stage). According to the effects of scavengers n-butanol and KI, hydroxyl radicals (OH), especially the surface-bounded •OH, had a dominant role in the oxidation of CMP. The degradation intermediates, carboxylic acids and chloride ion produced during the reaction process were monitored by high performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS) and ion chromatography (IC). On the basis of these findings, the possible mechanistic steps of CMP degradation were proposed.