Addition Of Tert-butyl Alcohol Research Articles

Degradation and mineralization of anti-cancer drugs Capecitabine, Bicalutamide and Irinotecan by UV-irradiation and ozone

The degradation of three anti-cancer drugs (ADs), Capecitabine (CAP), Bicalutamide (BIC) and Irinotecan (IRI), in ultrapure water by ozonation and UV-irradiation was tested in a bench-scale reactor and AD concentrations were measured through ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). A low-pressure mercury UV (LP-UV) lamp was used and degradation by UV (λ = 254 nm) followed pseudo-first order kinetics. Incident radiation in the reactor was measured via chemical actinometry using uridine. The quantum yields (φ) for the degradation of CAP, BIC and IRI were 0.012, 0.0020 and 0.0045 mol Einstein−1, respectively. Ozone experiments with CAP and IRI were conducted by adding ozone stock solution to the reactor either with or without addition of tert-butanol (t-BuOH) as radical quencher. Using this experimental arrangement, no degradation of BIC was observed, so a semi-batch setup was employed for the ozone degradation experiments of BIC. Without t-BuOH, apparent second order reaction rate constants for the reaction of the ADs with molecular ozone were determined to be 3.5 ± 0.8 ∙ 103 L mol−1 s−1 (CAP), 7.9 ± 2.1 ∙ 10−1 L mol−1 s−1 (BIC) and 1.0 ± 0.3 ∙ 103 L mol−1 s−1 (IRI). When OH-radicals (∙OH) were quenched, rate constants were virtually the same for CAP and IRI. For BIC, a significantly lower constant of 1.0 ± 0.5 ∙ 10−1 L mol−1 s−1 was determined. Of the tested substances, BIC was the most recalcitrant, with the slowest degradation during both ozonation and UV-irradiation. The extent of mineralization was also determined for both processes. UV irradiation was able to fully degrade up to 80% of DOC, ozonation up to 30%. Toxicity tests with Daphnia magna (D. magna) did not find toxicity for fully degraded solutions of the three ADs at environmentally relevant concentrations.

A microwave-induced plasma jet for efficient degradation of methomyl in aqueous solution.

As a typical carbamate pesticide, methomyl was once widely used in agriculture for its excellent broad-spectrum insecticidal effect. However, due to its high toxicity, long half-life, and difficult degradation properties, it poses a serious challenge to water environment pollution. In this study, an electrode-free discharge microwave-induced plasma technology was used to rapidly and efficiently degrade methomyl in aqueous solution. In this experiment, the statistical design of experiments (DOE) was adopted to optimize the plasma degradation parameters. Under the optimized parameters (P = 140 W, D = 0mm, R = 0.5 L/min), 78.4% removal of 50mg/L of methomyl was achieved after 8min. The optical emission spectrometry and free radical detection experiments showed that the active substances generated by the collision reaction between plasma and water molecules occurring at the gas-liquid interface were the key factors to exert the degradation effect. The degradation rate of methomyl decreased by 73.2% after the addition of tert-butanol (OH burster), while it decreased by only about 12.0% after the addition of peroxidase. These implied that ∙OH was largely responsible for methomyl degradation. In addition, based on the detected intermediates, possible degradation mechanisms and pathways were analyzed.

Experimental study on the treatment of dye wastewater by plasma coupled biotechnology

In this experiment, a gas-liquid two-phase discharge water treatment inverse device was designed independently to treat the actual workshop intermediate dye wastewater from a chemical plant. Firstly, the effects of initial concentration of wastewater, initial pH, circulation flow rate of solution, content of Fe2+, content of H2O2, and addition of tert-butanol on the organic removal rate and decolorization rate of dye wastewater treatment were investigated. The results showed that Fe2+ and tert-butanol would react with the active particles (H2O2, ·OH) and inhibit the degradation of the dye wastewater, resulting in the decrease of both organic matter degradation rate and decolorization rate. The experimentally degraded dye wastewater mainly contained benzoic acid and its derivatives in addition to dye molecules, thus the degradation mechanism of benzoic acid was mainly analyzed. Then, the actual dye wastewater treated by low-temperature plasma was combined with the traditional biological treatment technology. The biochemical properties of the wastewater treated by low-temperature plasma technology were greatly improved, and the B/C was increased from the initial 0.17 to 0.33. The effluent after the combined biological method could meet the effluent discharge standard, and the final CODcr reached 198mg/L, BOD5 reached 65mg/L, and pH and chromaticity reached 6.39 and 50, respectively.

Preparation of Mn-FeOX/ZSM-5 by high-gravity method for heterogeneous catalytic ozonation of nitrobenzene

Mn-FeOX/ZSM-5 is a good catalyst for wastewater treatment, but the conventional methods for preparing Mn-FeOX/ZSM-5 have the problems of non-uniform dispersion of active components and long preparation time. As the liquid-solid mass transfer process could be effectively increased in a high-gravity field, Mn-FeOX/ZSM-5 was prepared by high-gravity method in this study, and its properties were characterized by XRD, FTIR and SEM. The stability of Mn-FeOX/ZSM-5 and the loss of active components were investigated, and the mechanism of Mn-FeOX/ZSM-5 catalyzed the ozonation of nitrobenzene (NB) was also discussed. The results show that the specific surface area of Mn-FeOX/ZSM-5-h is 292.103 m2/g and the active components are well dispersed. Mn-FeOX/ZSM-5-h has the best catalytic activity under the conditions of precursor solution concentration = 0.3 mol/L, liquid flow rate = 60 L/h, and high gravity factor β = 30, and the removal efficiency of TOC reaches 87.5% within 25 min. The catalyst has good stability and only 1.10% of Mn and 0.63% of Fe are lost on average after 5 cycles. However, the removal rate of NB is significantly reduced with the addition of tert-butyl alcohol (TBA), implying that ·OH plays a dominant role in catalytic ozonation of NB by Mn-FeOX/ZSM-5. The electron paramagnetic resonance results confirm that ·OH is produced in the degradation process. In conclusion, Mn-FeOX/ZSM-5-h prepared by high-gravity method is a good catalyst for catalytic ozonation of NB because of its high catalytic activity and stability.

Treatment of Phenol-Containing Coal Chemical Biochemical Tailwater by Catalytic Ozonation Using Mn-Ce/γ-Al2O3

In this study, a Mn-Ce/γ-Al2O3 catalyst with multiple active components was prepared through the doping–calcination method for advanced treatment of coal chemical biochemical treatment effluent and characterized by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, and BET analysis. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. The Mn-Ce/γ-Al2O3 catalyst significantly enhanced COD and total phenol removal in reaction with ozone. The characterization results suggested that the pore structure of the optimized Mn-Ce/γ-Al2O3 catalyst was significantly improved. After calcination, the metallic elements Mn and Ce existed in the form of the oxides MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 30 min, (2) initial pH of 9, (3) ozone dosage of 3.0 g/h, and (4) catalyst dosage of 30 g/L. The removal efficiency of COD and total phenol from coal chemical biochemical tail water was reduced with the addition of tert-butanol, which proves that hydroxyl radicals (•OH) played a leading role in the Mn-Ce/γ-Al2O3 catalytic ozonation treatment process of biochemical tailwater. Ultraviolet absorption spectroscopy analysis indicated that some conjugated structures and benzene ring structures of organics in coal chemical biochemical tail water were destroyed. This work proposes the utilization of the easily available Mn-Ce/γ-Al2O3 catalyst and exhibits application prospects for the advanced treatment of coal chemical biochemical tailwater.

SN2 versus E2 reactions in a complex microsolvated environment: theoretical analysis of the equilibrium and activation steps of a nucleophilic fluorination.

The reactivity of the fluoride ion towards alkyl halides is highly dependent on the solvating environment. In polar aprotic solvents with large counter-ions is highly reactive and produces substantial E2 product, whereas in polar protic solvents leads to slow kinetics and high selectivity for SN2 reactions. The use of a more complex environment with stoichiometric addition of tert-butanol to acetonitrile solvent is able to module the reactivity and selectivity of tetrabutylammonium fluoride (TBAF). In the present work, we have performed a detailed theoretical analysis of this complex reaction system by density functional theory, continuum solvation model, and including explicit tert-butanol molecules. A kinetic model based on the free energy profile was also used to predict the reactivity and selectivity. The results indicated that the TBAF(tert-butanol) complex plays the key role to increase the SN2 selectivity, whereas higher aggregates are not relevant. The E2 product is formed exclusively via free TBAF, because the solvating tert-butanol in the TBAF(tert-butanol) complex inhibits the E2 pathway. Our analysis suggests that diols or tetraols could produce an improved selectivity.

Development of a Continuous Photo-catalytic/Ozonation System: Application on Amido Black Removal from Water

ABSTRACT A continuous system for photo-catalytic/ozonation was designed at laboratory scale and evaluated for water treatment using Amido Black 10B dye (AB) as a pollutant model. The effect of single ozonation (O3), photolytic ozonation (UV/O3) and combined photocatalytic/ozonation treatment (UV/O3/TiO2) were investigated. TiO2 nanocatalysts films were coated on stainless steel grids (AISI 304) by Atomic Layer Deposition technique (ALD) at 350 °C. An experimental hydrodynamic study of the designed reactor was conducted based on dry and total pressure drop. Three flow regimes were observed by increasing the total pressure drop against gas load factor (Fs). Depollution experiments conducted on the developed reactor showed that reaction rates and efficiency of studied processes were dependent on the studied operational parameters (initial dye concentration, ozone dose, pH). The maximum AB dye ([AB]0 = 100 mg. L−1) conversion efficiency, using the designed (UV/O3/TiO2) system, was about 40.3% of initial TOC and 100% AB color removal was achieved within 10 min at an optimal ozone dose of 132 mg. L−1. A significant improvement in AB removal using UV/TiO2/O3 process (koverall = 0.056 min−1, 40.3%) compared to O3 alone (koverall = 0.032 min−1, 26.87). Results shows also that the addition of tert-butanol (TB), as radical scavenger ([TB] = 0.2 M and 0.4 M), greatly affects the reaction mechanisms of a photocatalytic ozonation process within 5 min of reaction, by decreasing the Amido Black conversion from 99.67% ([TB] = 0 M) to 74.63% and 31.35%, respectively, in presence of 0.2 M and 0.4 M of tert-butanol. The remarkable decrease in AB removal rate observed in the presence of a radical scavenger expresses that there was an obvious enhancement of hydroxyl radical OH• generation due to the synergetic effect between ozone and photocatalytic processes.

Evaluation of nZVI for the degradation of atrazine in heterogeneous Fenton-like systems at circumneutral pH

The requirement of acidification for the successful of the Fenton processes in water treatment has promoted the search for new strategies to work at pH close to neutrality. With this objective, in this work the use of nZVI has been evaluated for the oxidative elimination of 10 mg L−1 of atrazine at circumneutral pH with nZVI/UVA, nZVI/H2O2, and nZVI/H2O2/UVA systems. While UVA irradiation of sole nZVI was ineffective for degrading the herbicide, the addition of H2O2 boosted up the reaction, with the nZVI/H2O2/UVA system attaining the highest degradation rate. The inhibition of the reaction upon addition of tert-butanol as scavenger pointed out the significant role of hydroxyl radicals in the atrazine oxidation. The characterization of fresh and spent samples, carried out by XRD, SEM, TEM, and nitrogen adsorption-desorption experiments, confirmed the presence of ferric oxidized compounds responsible of the heterogeneous photo-Fenton-like reactions. On the basis of the degradation products determined by high performance liquid chromatography (HPLC), a scheme of atrazine degradation pathways in the ZVI/H2O2/UVA system was proposed in which the reaction is mainly initiated by alkylic oxidation rather than dechlorination. Finally, the effect on the atrazine oxidation rate of the water constituent species was analyzed in different water matrices (pure, supply, simulated and secondary effluent real water). Considered individually, Cl−, SO42−, HCO3−, and DOC, showed a moderate inhibitory effect on atrazine degradation kinetics, but their combination could explain the significant decrease of efficiency detected in the real secondary effluent water compared to less complex matrices.

Mechanisms for removal of gaseous toluene in headspace using sonophysical and sonochemical effects at the gas–liquid interface

We developed a new method for removing gaseous substances by using high frequency (200 kHz) ultrasonic irradiation of water, and the effects of ultrasonic irradiation on gas-phase toluene were evaluated quantitatively for the first time. The removal ratio of gaseous toluene increased with increasing ultrasonic power, but the reaction was inhibited by the addition of radical scavengers, indicating that ultrasonic irradiation not only accelerated the dissolution of gaseous toluene but also induced toluene decomposition. The contribution made by OH radicals to the decomposition of gaseous toluene at the gas–liquid interface was confirmed by the difference in removal ratios between addition of KI and addition of tert-butyl alcohol. The toluene removal mechanism was investigated by studying the logarithmic plots for toluene concentration at specified times. The results of this study clearly showed the promotion of gaseous toluene dissolution and the reaction via OH radicals at the gas–liquid interface by sonophysical and sonochemical effects with both effects contributing to the removal of gaseous toluene. Furthermore, the total organic carbon concentration in the aqueous phase increased with increasing reaction time, indicating that the toluene degradation products were trapped and decomposed into low-molecular-weight organic compounds in the aqueous phase.

Optimization of heterogeneous Fenton-like process with Cu-Fe@CTS as catalyst for degradation of organic matter in leachate concentrate and degradation mechanism research

The heterogeneous Fenton-like process with bimetallic chelated magnetic chitosan aerogel (Cu-Fe@CTS) as catalyst was applied to treat pre-coagulated leachate nanofiltration concentrate. The process conditions were optimized by Box-Behnken Design (BBD) and the maximum UV254 removal reached 96.06% under the conditions of temperature 87.62 °C, oxidant dosage 0.2395 mol/L and catalyst dosage 1 g/L. The TOC concentration was reduced from 847.5 to 99.7 mg/L and COD concentration was reduced from 1625 to 464 mg/L. The three-dimensional (3D) fluorescence analysis showed that most of Fulvic acid-like (FA-like) was removed. The adsorption experiment showed that the catalyst reached the adsorption balanced after 60 min and the corresponding FA adsorption removal reached 14.1%. The addition of Tert-butanol (TBA) reduced the FA removal by 59.4%, indicating that the hydroxyl radicals (OH) was the main active species. Experiments of the OH capture at different pH showed that the Fenton-like system produced more OH at pH of 4, at which the maximum FA removal was 96.61%, while the FA removal still reached 94.26% at pH of 7. The OH capture at different temperature showed that the Fenton-like system produced more OH at 90 °C. KI and TBA shielding experiments showed that OH was produced on the catalyst surface rather than being produced by catalysis of free metal ions in the solution.

Fenton-like degradation of sulfathiazole using copper-modified MgFe-CO3 layered double hydroxide

The catalytic activity of layered double hydroxides, with and without insertion of copper, was evaluated in a heterogeneous Fenton process for degradation of the antibiotic sulfathiazole (STZ). The characterizations with different techniques revealed lamellar structures formed by stacking of layers containing magnesium, iron, and copper cations. The insertion of copper in the lamellar structure increased the specific area of the material and the degradation kinetics, achieving complete STZ removal after 90 min. X-ray photoelectron spectroscopy analysis showed the presence of Cu(II) and Cu(I) surface sites, which contributed to the generation of hydroxyl and hydroperoxyl/superoxide radicals. It also indicated an increase of Cu(I) content after use. For both materials, but specially for LDH without copper, addition of tert-butyl alcohol and p-benzoquinone hindered STZ degradation, indicating the importance of hydroxyl and hydroperoxyl/superoxide radicals in the degradation process, respectively. These results demonstrated the potential of copper-modified MgFe-CO3 as a catalyst for the degradation of emerging contaminants, offering the benefits of easy preparation and high efficiency in the Fenton process.

The Effect of Thermal Treatment on the Physicochemical Properties of Minerals Applied to Heterogeneous Catalytic Ozonation

In order to enhance the efficiency of heterogeneous catalytic ozonation, the effect of thermal treatment on three commonly used and inexpensive minerals, i.e., zeolite, talc and kaolin (clay), which present different physicochemical properties as potential catalysts, has been examined for the removal of para-chlorobenzoic acid (p-CBA). p-CBA is considered a typical micro-pollutant, usually serving as an indicator (model compound) to evaluate the production of hydroxyl radicals in ozonation systems. The catalytic activity of selected solid catalysts was studied for different pH values (6, 7 and 8) and different temperatures (15 °C, 25 °C and 35 °C). The mechanism of radicals’ production was also verified by the addition of tert-butyl alcohol (TBA). The respective thermal behavior study showed that the point of zero charge (PZC) of these minerals increased with the increase of applied treatment temperature, as it removed crystalline water and hydroxyls, thus improving their hydrophobicity. Circa-neutral surface charge and the presence of hydrophobicity were found to favor the affinity of ozone with solid/catalytic surfaces and the subsequent production of hydroxyl radicals. Therefore, zeolite and talc, presenting PZC 7.2 and 6.5 respectively, showed higher catalytic activity after thermal treatment, while kaolin with PZC equal to 3.1 showed zero to moderate catalytic efficiency. The degradation level of p-CBA by oxidation was favored at 25 °C, while the pH value exerted positive effects when it was increased up to 8.

Antibacterial Activity of Nitrogen-Doped Carbon Dots Enhanced by Atomic Dispersion of Copper.

Antibiotic resistance is an imminent threat to human health, requiring the development of effective alternate antibacterial agents. One such alternative includes nanoparticle (photo)catalysts that are good at producing reactive oxygen species (ROS). Herein, we report the design and preparation of nitrogen-doped carbon dots functionalized with atomically dispersed copper centers by Cu-N coordination (Cu/NCD) that exhibit apparent antibacterial activity toward Gram-negative Escherichia coli (E. coli) under photoirradiation. The growth of E. coli cells is found to be markedly inhibited by Cu/NCD under 365 nm photoirradiation, whereas no apparent inhibition is observed in the dark or with the copper-free carbon dots alone. This is ascribed to the prolonged photoluminescence lifetime of Cu/NCD that facilitates the separation of photogenerated electron-hole pairs and ROS formation. The addition of tert-butyl alcohol is found to completely diminish the antimicrobial activity, suggesting that hydroxyl radicals are responsible for microbial death. Consistent results are obtained from fluorescence microscopic studies using CellROX green as the probe. Similar bactericidal behaviors are observed with Gram-positive Staphylococcus epidermidis (S. epidermidis). The copper content within the carbon material is optimized at a low loading of 1.09 wt %, reducing the possibility of toxic copper-ion leaching. Results from this study highlight the significance of carbon-based nanocomposites with isolated metal species as potent antimicrobial reagents.

Degradation of phenanthrene by peroxymonosulfate activated with bimetallic metal-organic frameworks: Kinetics, mechanisms, and degradation products

In this study, bimetallic metal-organic frameworks (FeCo-BDC) containing the (BDC = 1,4-benzenedicarboxylic acid) metalloligand unit, linked by Fe(II) and Co(II) cations, were synthesized successfully with different stoichiometric ratio of precursors. FeCo-BDC were investigated by XRD, FT-IR, SEM, XPS, ICP-MS, BET, and TEM techniques. Effects of stoichiometric ratio of precursors, peroxymonosulfate (PMS) concentrations, catalyst dosages, and initial pH on the phenanthrene degradation were evaluated. The results indicated that 99.0% of phenanthrene removal efficiency was achieved at pH 3.15, 50 mg/L FeCo-BDC-2, 0.6 mM PMS, 1.0 mg/L phenanthrene and 30 min reaction time. Based on the scavenger experiments and electron paramagnetic resonance (EPR) analyses, SO4−, OH, and O2− were identified as the dominant Reactive Oxygen Species (ROS) and responsible for the phenanthrene degradation. It was interesting to find that the signals of DMPO-OH/SO4− transformed to DMPOX with the addition of tert butyl alcohol (TBA). The intermediate products of phenanthrene were identified by GC–MS and the possible degradation pathway was proposed, whereas two intermediates containing sulfur atom were detected for the first time in the Sulfate Radicals-based Advanced Oxidation Processes (SR-AOPs). These interesting findings will guide the development of metal-organic frameworks as catalysts of PMS and enrich our understanding of the SR-AOPs for wastewater treatment.

Enhanced degradation of atrazine in water by VUV/UV/Fe process: Role of the in situ generated H2O2

Vacuum ultraviolet/ultraviolet/Fe (VUV/UV/Fe) has been regarded as a new advanced oxidation process (AOP), but its kinetics and mechanism for pollutant degradation remain largely unknown. This work investigates the degradation of a typical pesticide, i.e. atrazine (ATZ), by VUV/UV/Fe. The results show that ATZ was efficiently degraded by VUV/UV/Fe and the pseudo first-order rate constant (ka) reached 1.01 min−1, which was 1.7 times as high as the sum of those by UV/Fe and VUV/UV. This synergistic effect observed during the VUV/UV/Fe process was attributed to effective utilization of the H2O2, which was generated in situ by VUV photolysis of water, via the Fenton-like reaction. The apparent production rate of H2O2 was 0.19 mM min−1 in VUV/UV process, but decreased dramatically to 0.07 mM min−1 with addition of 1.0 mM Fe3+, which confirms the consumption of H2O2 by the Fenton-like reaction. The addition of tert-butanol and 1,4-benzoquinone proves that HO2 generated via the Fenton-like reaction played an important role, albeit not as much as HO, in the degradation of ATZ by VUV/UV/Fe. The application of Fe3+ as the iron source was much more effective than that of Fe2+ for the degradation of ATZ by VUV/UV/Fe. ka was a concave function of the solution pH and reached the optimal value at pH 3.5. The four selected inorganic anions inhibited the ATZ degradation by VUV/UV/Fe in an order of SO42− < HCO3− < NO3− < Cl−. The release of Cl− caused by the substitute reaction of chlorine atom with reactive oxygen species accounted for only 17.8% of the removed ATZ. It demonstrates that VUV/UV/Fe is a promising treatment process for pollutant removal from water.

Enhanced degradation and mineralization of sulfamethoxazole by integrating gamma radiation with Fenton-like processes

Degradation of sulfamethoxazole (SMX) by ionizing radiation combined with goethite (α-FeOOH) catalyzed Fenton-like process were studied under various conditions. The results showed that SMX could be degraded completely at 2 kGy with or without the addition of goethite. This process followed pseudo first-order kinetics model. The presence of goethite promoted the mineralization of SMX, and the mineralization ratio increased with the increase of goethite dosage. The decomposition of SMX in goethite/ionizing radiation system exhibited high activity at pH ranging from about 3.0 to 11.0. Acidic condition was more preferable than alkaline condition for the degradation of SMX. The presence of humic acid inhibited SMX degradation, due to the competition of hydroxyl radical with SMX molecules. The addition of tert butyl alcohol (TBA) resulted in the decrease of SMX removal efficiency, indicating that hydroxyl radical played the main role in this system. This investigation demonstrated that goethite combined with ionizing radiation has potential for enhancing the mineralization of toxic organic pollutants in water and wastewater.

Mixed industrial wastewater treatment by combined electrochemical advanced oxidation and biological processes

Nowadays, because the quality and quantity of mixed industrial wastewater keep fluctuating in recent times, the treatment of mixed industrial wastewater has gained more attention. The main target of this study is to degrade the wastewater through a combination of electrochemical advanced oxidation processes (EAOPs) and biological treatment. To enhance the biodegradability of the wastewater, Electro-Fenton process, along with external persulphate addition, was applied before the biological treatment. The effect of voltage, catalyst concentration and persulphate dosage was studied. The optimized conditions selected for the experiments were pH-3, effective area-25 cm2, electrode spacing-1 cm while voltage-10 V, persulphate dosage-200 mg L−1, and catalyst dosage-10 mg L−1 were optimized during the experiments leading towards 60% of COD removal efficiency in course of 1 h of electrolysis. Addition of tert-butyl alcohol and ethanol revealed the existence of sulphate and hydroxyl radicals as the major oxidants that help in pollutant degradation by combining EAOPs and biological treatment. Overall 94% COD removal efficiency was achieved. Therefore, for the organic pollutant degradation, combined process serves to be an efficient and effective treatment option.

Degradation of Sulfamethoxazole Using Iron-Doped Titania and Simulated Solar Radiation

This work examined the photocatalytic destruction of sulfamethoxazole (SMX), a widely used antibiotic, under simulated solar radiation using iron-doped titanium dioxide as the photocatalyst. Amongst the various iron/titania ratios examined (in the range 0%–2%), the catalyst at 0.04% Fe/TiO2 molar ratio exhibited the highest photocatalytic efficiency. The reaction rate followed pseudo-first-order kinetics, where the apparent kinetic constant was reduced as the initial concentration of SMX or humic acid increased. The photodecomposition of SMX was favored in natural pH but retarded at alkaline conditions. Unexpectedly, the presence of bicarbonates (in the range of 0.125–2 g/L) improved the removal of SMX, however, experiments conducted in real environmental matrices showed that process efficiency decreased as the complexity of the water matrix increased. The presence of sodium persulfate as an electron acceptor enhanced the reaction rate. However, only a small synergy was observed between the two individual processes. On the contrary, the addition of tert-butanol, a well-known hydroxyl radical scavenger, hindered the reaction, indicating the significant contribution of these radicals to the photocatalytic degradation of SMX. The photocatalyst retained half of its initial activity after five successive experiments.

NDMA formation from 4,4'-hexamethylenebis (HDMS) during ozonation: influencing factors and mechanisms.

N-nitrosodimethylamine (NDMA), a toxic disinfection byproduct commonly associated with chloramination, has recently been found to form from an anti-yellowing agent (4,4'-hexamethylenebis (1,1-dimethylsemicarbazide) (HDMS)) during ozonation but the mechanisms are unclear. In this paper, the potential roles of molecular ozone (O3) and hydroxyl radical (∙OH) on NDMA formation from HDMS were investigated under various oxidation conditions (ozone dosages, pH) and different components in water (bromide ion (Br-), bicarbonate ion (HCO3-), sulfate ion (SO42-), and humic acid (HA), as well as natural organic matter (NOM) from a lake). Moreover, HDMS transformation pathways by ozonation were determined. The results indicated that the formation of NDMA was enhanced through the combined effect of O3 and ∙OH compared to that by O3 alone (addition of tert-butyl alcohol (tBA) as ∙OH scavenger). ∙OH itself cannot generate NDMA directly; however, it can transform HDMS to intermediates with higher NDMA yield than parent compound. The NDMA generation was affected (small dosages promoted but high dosages inhibited) by HA or Br- no matter with or without tBA. The presence of SO42- and HCO3- ions lowered NDMA formation through ∙OH scavenging effect. Increasing pH not only increased degradation rate constant by enhancing ∙OH generation but also affected HDMS dissociation ratio, reaching the maximum NDMA formation at pH 7-8. Natural constituents in selected water matrix inhibited NDMA formation. Impacts of these influencing factors on NDMA formation by only O3 however were significantly less pronounced over that by the joint roles of O3 and ∙OH. Based on the result of Q-TOF, LC/MS/MS, and GC/MS, the possible transformation pathways of HDMS by ozonation were proposed. The NDMA enhancement mechanism by the combined effect of O3 and ∙OH can be attributed to greater amounts of intermediates with higher NDMA yield (such as unsymmetrical dimethylhydrazine (UDMH)) produced. These findings provide new understanding of NDMA formation upon ozonation of typical amine-based compounds.

Preparation of Mn-Co/Ceramic Honeycomb Catalyst and Its Performance on Catalytic Ozonation of Hydroquinone

In order to improve the activity and working life of metal catalysts in the heterogeneous catalytic ozonation of organic wastewater, four kinds of Mn-Co/ceramic honeycomb (CH) catalysts with different mass ratios of Mn and Co were prepared by coating method using cobalt nitrate hexahydrate [Co(NO3)2·6H2O] and manganese nitrate [Mn(NO3)2] as precursors, respectively, and CH as the carrier. The structure of the catalysts was analyzed via X-ray diffraction (XRD), N2 adsorption/desorption, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The mechanical properties of the catalysts were studied. The reaction kinetics model of O3 alone and catalytic ozonation of the hydroquinone were established and catalytic ozonation performance of catalysts was investigated. The results showed that the crystal phase of Mn0Co1/CH belonged to CoAl2O4 and that the crystal phase of the Mn-Co/CH catalyst (Mn1Co1, Mn2Co1, and Mn3Co1) mainly belonged to Mn3O4 and CoO. In particular, the Mn1Co1/CH catalyst had a large specific surface area of 190 m2·g-1, high pore volume of 0.25 cm3·g-1, and pore size of 4.8 nm. The highest catalytic activity was obtained when Mn∶Co was 1∶1 (Mn1Co1/CH catalyst). The catalytic activity of the Mn1Co1/CH catalyst was the highest, and removal efficiencies of hydroquinone and COD were 78% and 54%, respectively, using Mn1Co1/CH catalytic ozonation. The Mn-Co/CH catalyst had a high compressive strength (15.89-16.94 MPa). The degradation efficiency of hydroquinone decreased significantly after the addition of tert-butanol, which indicated that·OH played an important role in the Mn1Co1/CH catalytic ozonation. The catalytic ozonation process fitted the first-order kinetic model. The apparent rate constant k for O3 alone was only 0.0306. Furthermore, the Mn1Co1/CH catalyst had the highest rate, with an apparent rate constant k of 0.0535 min-1. The Mn-Co/CH catalyst was easy to industrialize owing to its lower consumption, excellent catalytic characteristics, and long working life.