Formation Of Organic By-products Research Articles

Heterobimetallic CoCeOx derived from cobalt partially-substituted Ce-UiO-66 for chlorobenzene efficient catalytic destruction

Here, a metal–organic framework (MOF)-templated strategy was applied to synthesize the CoCeOx bimetallic catalysts by calcining Co partially-substituted Ce-UiO-66. It is indicated that the substituted Co limited Ce cations in Ce-UiO-66 framework, which affects its growth and structure crystallinity to some extent. After pyrolysis treatment, the derived bimetallic oxide (CoCeOx-M) can basically keep the octahedral structure and the surface area is much higher than the bulk metal composite oxide (CoCeOx-B) prepared by traditional coprecipitation. Results reveal that CoCeOx-M performs the best chlorobenzene degradation capacity, superior stability and vapor tolerance compared with those of CeO2-M (derived from Ce-UiO-66) and CoCeOx-B. At the same time, it is favorable to inhibit the formation of CO during the oxidation reaction. The superior catalytic performance of CoCeOx-M is attributed to a good dispersion of metal cations, high surface area and active oxygen concentration, and good redox property. Moreover, the formation of organic byproducts especially chlorinated organics can be obviously prohibited over CoCeOx-M compared with that of CeO2-M. Mechanism study reveals that chlorobenzene dissociates on the surface of CoCeOx-M to form carboxylates such as acetate species, maleate and phenolate before finally oxidized into CO2, H2O, and HCl. The present work poses new insights into the fabrication of efficient catalysts for industrial CVOC purification.

Synergistic Modification of PVC with Nitrogen-Containing Heterocycle and Tung-Oil Based Derivative for Enhanced Heat Stabilization and Plasticization Behavior

The additives present in polyvinyl chloride (PVC) materials are the major source of organic by-products during PVC degradation. The thermal stabilizer and plasticizer are the main additives that endow PVC with the required properties during its processing. However, these two additives easily migrate when samples are obtained by physical mixing of the additives with PVC. This causes the reduction of PVC sample efficacy and the increase in the formation of organic by-products in the radiolysis process. In this work, two kinds of grafted PVC samples (tung-oil derivative grafted PVC and Atz grafted PVC, abbreviated as P-GT4 and P-AZ3) were synthesized by chemical grafting of 3-amino-1,2,4-triazole (Atz) and tung-oil derivative on PVC, respectively. These two PVC samples were then blended at different mass ratios to obtain hybrid PVC materials with excellent plasticization, thermal stability and migration resistance ability. Differential scanning calorimetry (DSC), discoloration, Congo red test and thermogravimetric analysis (TGA) showed that when the mass ratio of P-GT4 to P-AZ3 in the mixed PVC resin was 1:3, the resulting P1:3-GT4-AZ3 (P4) presented the best plasticization and thermal stability. The kinetics of thermal decomposition showed that the activation energy of P4 was much higher than that of the reference material [PVC/DOTP/CaSt2/ZnSt2, PVC/CZ41 for short] at mass loss α = 20% and 80%. In addition, the leaching test showed that P4 material possessed excellent migration resistance ability.

Plasma-enhanced catalytic oxidation of ethylene oxide over Fe–Mn based ternary catalysts

In this work, Fe–Mn based ternary catalysts (Fe–Mn-X, X = Ce, Co and Cu) were evaluated in the plasma-catalytic oxidation of ethylene oxide (EO) using a cylindrical dielectric barrier discharge (DBD) reactor. The addition of transition metal dopants to the Fe–Mn catalyst significantly improved the performance of plasma-catalyzed EO oxidation compared to the reaction using plasma only and the Fe–Mn catalyst. The highest EO conversion (91.9%) and CO2 selectivity (78.9%) were obtained over the Fe–Mn–Co catalyst at a specific energy input (SEI) of 730.2 J l−1. Moreover, the presence of water vapor improved EO conversion and CO2 selectivity in the relative humidity (RH) range of 0–60%, while further increasing the RH to 80% reduced EO conversion. The interactions between Fe, Mn and dopants increased the specific surface area and pore volume of the Fe–Mn-X catalyst, while maintaining the crystalline structure of the catalysts. The presence of the dopants enhanced the reducibility of the Fe–Mn-X catalysts and produced more surface adsorbed oxygen (Oads) on the catalyst surfaces. Moreover, the interactive effects among the Fe, Mn and dopants facilitated the plasma-catalytic oxidation reactions via enhanced surface reactions. The coupling of plasma with the Fe–Mn–Co catalyst reduced the formation of organic by-products in the plasma-catalyzed oxidation of EO.

Bromine Radical (Br• and Br2•-) Reactivity with Dissolved Organic Matter and Brominated Organic Byproduct Formation.

Dissolved organic matter (DOM) is a major scavenger of bromine radicals (e.g., Br• and Br2•-) in sunlit surface waters and during oxidative processes used in water treatment. However, the literature lacks quantitative measurements of reaction rate constants between bromine radicals and DOM and lacks information on the extent to which these reactions form brominated organic byproducts. Based on transient kinetic analysis with different fractions and sources of DOM, we determined reaction rate constants for DOM with Br• ranging from <5.0 × 107 to (4.2 ± 1.3) × 108 MC-1 s-1, which are comparable with those of HO• but higher than those with Br2•- (k = (9.0 ± 2.0) × 104 to (12.4 ± 2.1) × 105 MC-1 s-1). Br• and Br2•- attack the aromatic and antioxidant moieties of DOM via the electron transfer mechanism, resulting in Br- release with minimal substitution of bromine into DOM. For example, the total organic bromine was less than 0.25 μM (as Br) at environmentally relevant bromine radicals' exposures of ∼10-9 M·s. The results give robust evidence that the scavenging of bromine radicals by DOM is a crucial step to prevent inorganic bromine radical chemistry from producing free bromine (HOBr/OBr-) and subsequent brominated byproducts.

Objective Findings on the K-Doped g-C3N4 Photocatalysts: The Presence and Influence of Organic Byproducts on K-Doped g-C3N4 Photocatalysis

The thermal-condensation method is widely used for the synthesis of K-doped g-C3N4 photocatalysts, but the presence of organic byproducts in the resultant products is often overlooked in previous reports. Here, we demonstrated the universal presence of organic byproducts in K-doped g-C3N4 synthesized by typical thermal condensation of KOH/melamine, KOH/dicyandiamide, or KOH/urea. Taking the K-doped g-C3N4 photocatalysis for the degradation of dimethyl phthalate as an example, the negative influence of the organic byproducts on K-doped g-C3N4 photocatalysis was confirmed. Specifically, the organic byproducts can be gradually dissolved into the photocatalytic system of K-doped g-C3N4 as new and stable pollutants. Based on the solubility investigations on the byproducts in several solvents, hot-water washing was demonstrated to be a relatively effective approach to remove the organic byproducts from K-doped g-C3N4. The formation of organic byproducts during the synthesis of K-doped g-C3N4 could be ascribed to the fact that the presence of K salts in melamine, dicyandiamide, or urea molecules results in their insufficient thermal condensation into expected g-C3N4. The present work provides objective information about the K-doped g-C3N4 photocatalysts and reminds researchers about the influence of the organic byproducts on the applications of the other impurity-doped g-C3N4 photocatalysts.

Tubular Membrane-Like Catalysts for the Oxidative Decomposition of Low-Concentrated Toluene in Air by Periodic Short-Term Plasma Discharge

A porous membrane-like alumina (MA) tube was employed as a catalyst to improve the energy efficiency of the oxidative decomposition of low-concentrated toluene in air by periodic short-term plasma discharge. The raw MA tube prepared by anodizing an aluminum tube had a relatively small surface area and toluene adsorption capacity, but they were remarkably increased by silica coating. Introducing the silica-coated catalyst into the dielectric-barrier discharge plasma generated for 5 s every 1 min resulted in a 3.6-fold increase in the rate of the toluene decomposition in a closed-circulating reaction system, suggesting that the toluene molecules were condensed by adsorption onto the catalyst surface and then decomposed by plasma. The energy efficiency was 14 g kWh−1, which was 9.3 times larger than that for the non-catalytic oxidation of toluene by continuous plasma irradiation. Palladium loading onto the catalyst slightly degraded the decomposition rate, but it suppressed the formation of organic by-products. These results clearly indicate the effectiveness of using a membrane-like catalyst in periodically-irradiated plasma reactors for VOC decompositions.

Quantification of low molecular weight oxidation byproducts produced from real filtered water after catalytic ozonation with different pathways

Catalytic ozonation was suggested to be effective for micropollutant removal during water treatment. However, research on organic byproduct formation from catalytic ozonation of real filtered water in water treatment plants was lacking. In this work, two synthesized catalysts, α-FeOOH and CeO2, were applied to catalyze ozonation of real filtered water at different ozone dosages, and the byproducts were quantified. Results showed that the α-FeOOH enhanced hydroxyl radical production, while the CeO2 did not. Both catalysts further reduced dissolved organic carbon (DOC) and UV254 of the filtered water during the catalytic oxidation processes. The O3/CeO2 improved the removal of low molecular weight compounds, especially the refractory compounds such as ketoacids and carboxylic acids, compared to ozonation alone. While the O3/α-FeOOH generated higher concentrations of carboxylic acids than that of ozonation. Thus, in light of DOC and low molecular weight compound reductions, CeO2 was the superior catalyst for micropollutant removal in real filtered water.

Phosphorus pentoxide for amide and peptide bond formation with minimal by-products

Phosphorus pentoxide and DMAP are used for amide bond formation from carboxylic acids and amines. Dipeptides and amides have been synthesized using this reagent in 42–77% yields and >99% ees. The protocol is attractive as it occurs at ambient temperature, the formation of organic by-products is minimal and the reagent can be readily quenched using water. Furthermore, excellent enantioselectivities are observed without the use of harsh triazole based additives.

Implications of Byproduct Chemistry in Nanoparticle Synthesis

Byproducts in metal nanoparticle synthesis can interfere with nanomaterial formation and self-assembly, as well as the perceived nanomaterial properties. Such syntheses go through a complicated series of intermediates, making it difficult to predict byproduct chemistry and challenging to determine experimentally. By a combined experimental and theoretical approach, the formation of organic byproducts is mapped out for the synthesis of gold nanoparticles with Good’s buffer 2-(N-morpholino)ethanesulfonic acid. Comprehensive nuclear magnetic resonance studies supported by mass spectrometry, ultraviolet–visible spectroscopy, and density functional theory reveal a number of previously unidentified byproducts formed by oxidation, C–N bond cleavage, and C–C bond formation. A reaction mechanism involving up to four consecutive oxidations is proposed. Oligomeric products with electronic transitions in the visible range are suggested. This approach can be extended broadly and lead to a more informed synthesis desig...

Application of proton transfer reaction mass spectrometry for the assessment of toluene removal in a nonthermal plasma reactor.

Proton transfer reaction mass spectrometry (PTR-MS) is a mature technique for the real-time measurement and monitoring of volatile organic compounds in the atmosphere. In this paper, a modified quantification method for PTR-MS was used to assess the performance of nonthermal plasma (NTP) reactor for the removal of toluene which was widely used in industrial production processes. Toluene and 11 corresponding organic by-products were tentatively identified and quantified by a proton transfer reaction time-of-flight mass spectrometer. The degradation dynamics of toluene and the formation of organic by-products were monitored in real-time (resolution=1second) under "plasma off" and "plasma on" conditions. We conclude that initial concentration and gas flow rate were the key parameters in the health risk assessment of NTP for the removal of toluene. The toluene removal efficiency and CO2 selectivity decreased with increasing upstream toluene concentration or gas flow rate, whereas the health risk influence index increased with increasing upstream toluene concentration or gas flow rate. The highest removal efficiency of toluene (100%), CO2 selectivity (53.2%), and the best health risk influence index for organic by-products (0.11) were achieved when the toluene concentration was kept at 105ppmv and flow rate at 0.4L/minute. The results demonstrate that PTR-MS is a promising tool to improve the practical applications of volatile organic compound removal by NTP because it can be used to optimize the NTP working conditions by providing a precise, fast, and clear health risk assessment for organic by-products based on their real-time analysis.

Pd-Catalyzed Regioselective Asymmetric Addition Reaction of Unprotected Pyrimidines to Alkoxyallene.

Catalytic asymmetric synthesis of N-heterocyclic glycosides free of protecting and directing groups is reported. The key reaction is highlighted by the atom-efficient and regioselective addition of unprotected pyrimidines to highly functionalized alkoxyallene. Numerous acyclic and cyclic N-heterocyclic glycosides are accessed with minimal formation of organic byproducts. The synthetic utility of the reaction is demonstrated by the first catalytic asymmetric synthesis of anticancer pharmaceutical (-)-Tegafur and stereoselective synthesis of an oxepane nucleoside derivative.

Toxic Byproduct Formation during Electrochemical Treatment of Latrine Wastewater.

Electrochemical systems are an attractive option for onsite latrine wastewater treatment due to their high efficiency and small footprint. While concerns remain over formation of toxic byproducts during treatment, rigorous studies examining byproduct formation are lacking. Experiments treating authentic latrine wastewater over variable treatment times, current densities, chloride concentrations, and anode materials were conducted to characterize byproducts and identify conditions that minimize their formation. Production of inorganic byproducts (chlorate and perchlorate) and indicator organic byproducts (haloacetic acids and trihalomethanes) during electrolysis dramatically exceeded recommendations for drinking water after one treatment cycle (∼10–30 000 times), raising concerns for contamination of downstream water supplies. Stopping the reaction after ammonium was removed (i.e., the chlorination breakpoint) was a promising method to minimize byproduct formation without compromising disinfection and nutrient removal. Though treatment was accelerated at increased chloride concentrations and current densities, byproduct concentrations remained similar near the breakpoint. On TiO2/IrO2 anodes, haloacetic acids (up to ∼50 μM) and chlorate (up to ∼2 μM) were of most concern. Although boron-doped diamond anodes mineralized haloacetic acids after formation, high production rates of chlorate and perchlorate (up to ∼4 and 25 μM) made them inferior to TiO2/IrO2 anodes in terms of toxic byproduct formation. Organic byproduct formation was similar during chemical chlorination and electrolysis of wastewater, suggesting that organic byproducts are formed by similar pathways in both cases (i.e., reactions with chloramines and free chlorine).

Mesostructured Cu–Mn–Ce–O composites with homogeneous bulk composition for chlorobenzene removal: Catalytic performance and microactivation course

Cu–Mn–Ce–O composites with enhanced surface area and developed mesoporosity were synthesized using a homogeneous coprecipitation (hcp) method, and were tested in the catalytic destruction of chlorobenzene (CB). X-ray diffraction (XRD), N2 adsorption/desorption, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), temperature programmed desorption of CB/O2 (CB/O2-TPD), and diffuse reflectance ultraviolet visible spectroscopy (DRUV-Vis) were used to characterize the structure and textural properties of catalysts. Mn and Cu enter CeO2 matrix with a fluorite-like structure, and produce large amounts of oxygen vacancies. Addition of manganese promotes the formation of reduced copper phase, and the presence of large numbers of high valence Mn4+ ions strongly enhances the redox couple of Cu+–Cu2+ in the composites. Both the synthesis protocol and metal doping amount significantly affect the catalyst reducibility, surface state and oxygen density. Cu0.15Mn0.15Ce0.85Ox synthesized via the hcp method exhibits the highest catalytic activity with 90% of chlorobenzene destructed at 255 °C (CO2 selectivity > 99.5%). Enriched surface oxygen, excellent active oxygen mobility and CB adsorption ability guarantee the superior activity and stability of Cu–Mn–Ce–O composite catalysts. Nucleophilic and electrophilic substitutions happen in sequence during chlorobenzene destruction, and the adsorbed Cl can be finally removed in the form of Cl2 via the Deacon reaction. Furthermore, the incorporation of CuO and MnOx phases can inhibit the formation of organic byproducts, such as phenolates, maleates, and o-benzoquinone-type species, especially at elevated reaction temperatures.

Chlorobenzene Destruction over Mesostructured CuO and MnO x Co-Modified CeO2 Catalyst: Activity and Activation Route

Mesostructured CuMnCeO x catalysts were prepared and tested in chlorobenzene destruction. Mn and Cu phases enter CeO2 matrix with a fluorite-like structure to form Cu–Mn–O–Ce solid solution. Both synthesis protocol and metal-doping content affect the metal state, reducibility, and oxygen distribution of composites. The c0.15c0.15c0.7 sample exhibits the highest activity with 90 % of chlorobenzene oxidized at around 250 °C. Enhanced oxygen concentration and mobility, and abundant oxygen vacancy promote the desorption of adsorbed Cl, which guarantees the superior stability of CuMnCeO x . Incorporation of CuO and MnO x effectively inhibits the formation of organic byproducts, such as phenolates, maleates, and o-benzoquinone, especially at elevated temperatures.

Limits of UV disinfection: UV/electrolysis hybrid technology as a promising alternative for direct reuse of biologically treated wastewater

Although UV irradiation represents an energy efficient disinfection method, bacterial regrowth in UV irradiated secondary effluents is a serious problem for their direct reuse (e.g., for domestic or irrigation purposes). The decrease of the lethal UV fluence caused by coverings (scaling and biofouling) on quartz sleeves of UV lamps and/or fluctuating specific water parameters (suspended solids, transmittance or turbidity) results in a reversible inactivation of faecal coliforms ( Escherichia coli ). The reactivation of E. coli is increased with rising light intensity (≥470 Lux) and rising temperature (≥20 °C). The supplementation of UV disinfection with an electrolysis compartment ensures a reliable, sustained bacterial reduction and prevents reactivation of E. coli in UV irradiated (H = 138–140 J m−2) wastewater at a concentration of total oxidants of 0.5 mg L−1. The electric charge input of 0.012 Ah L−1 was lowest on MOX (mixed oxide) electrodes compared to particle BDD (boron-doped diamond) and thin film BDD electrodes. The formation of organic by-products (adsorbable organically bound halogens, trihalomethanes) ranged from marginal to moderate. In contrast to BDD electrodes, no chlorite, chlorate and perchlorate were observed on MOX electrodes. The energy consumption of the UV/electrolysis hybrid reactor was 0.17 kWh m−3.

Hydrogen Formation via Steam Reforming of Ethanol Over Cu/ZnO Catalyst Modified with Nickel, Cobalt and Manganese

The greatest influence of nickel, cobalt and manganese modifiers of CuZn-based catalyst is observed at low temperatures of the ethanol steam reforming. Below 480 °C the most advantageous effects are: a decrease in the methane formation and an increase in the hydrogen selectivity, yield and its productivity. At 480 °C the formation of organic by-products (methane excluding) is almost completely depressed. However, significant lowering in the methane selectivity and a high production of hydrogen require higher temperatures of the process.

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60–80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.

Factors Affecting the Formation of Organic By-Products During Water Chlorination: A Bench-Scale Study

The formation of chlorination by-products (CBPs) was investigated through bench-scale chlorination experiments with river water. The compounds selected for analysis belonged to the groups of trihalomethanes, haloacetic acids, haloketones and haloacetonitriles. Trihalomethanes and haloacetic acids were the major species formed during chlorination, while haloketones and haloacetonitriles occurred at lower levels. The factors affecting the formation of these compounds were examined by two sets of experiments; the first with varying pH and reaction time, and the second with varying chlorine dose and temperature. Different effects of these factors were observed for different categories of CBPs, and in many cases, these effects were compound-specific, as confirmed by statistical analysis. Optimization of chlorination conditions in water treatment plants is a critical issue that should take into account the influence of chlorination parameters on the formation of individual CBPs.

Sonochemical degradation of aromatic organic pollutants

This work examines the use of ultrasound to mineralize 4-chlorophenol, 2,4-dichlorophenol, [aryl- 2H 3]2,4-dichlorophenol, 4-chloro-3,5-dimethylphenol, 4-fluorophenol, 2,4,6-trinitrotoluene, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene in dilute aqueous solution. Mineralization rates were determined as a function of substrate structure and concentration, bulk phase temperature, pH and the presence of co-solutes such as detergents and humic acids. All substrates were found to degrade sonochemically, as evidenced by the release of Cl − and NO 3 −, respectively. Product analyses by GC–MS, HPLC, and micellar electrokinetic capillary chromatography (MECC) indicated mineralization with little formation of organic byproducts, a significant advantage over other remediation methods. Chloride release from chlorophenols was approximately proportional to substrate total chlorine content, irrespective of structural differences, and reached 80% of the theoretical limit. Fluoride release from 4-fluorophenol was ca. 10-fold lower than that of chloride from 4-chlorophenol. Changes in the bulk phase temperature from 9.5 to 34 °C, and 12.5 to 30 °C, respectively, were of little consequence to observed mineralization rates for nitroaromatics and chlorophenols. A significant mineralization rate increase resulted from sonication of 4-chlorophenol in acidified media. Additions of amphiphilic co-solutes resulted in modest, but statistically significant, sonolysis enhancements.

Formation of organic by-products during chlorination of natural waters

Natural water from six sources in Mytilene, Greece, was chlorinated in order to identify and quantify some of the organic by-products formed. The compounds examined were trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, chloral hydrate and chloropicrin. The factors tested were time and chlorine dose. The presence of bromide ion in some of the waters studied resulted in significant changes in the by-product speciation, with enhanced brominated species formation. In addition, UV absorbance, measured at three wavelengths, led to correlation of organic matter content with the concentrations of by-products produced. The species formed, varying among different water sources, increased with increasing chlorine dose. Most of the species also increased with increasing contact time, although there were some exceptions due to hydrolysis reactions.