Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways

TiO2, ZrO2 and a series of TiO2-ZrO2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO2 (3CT), 3 wt% Co/ZrO2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO2 (CO2-ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C2H4 yield, C2H6 conversion and CO2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV-vis diffuse reflectance spectra (UV-vis DRS), H2 temperature-programmed reduction (H2-TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.

Enhanced biomethane production with a low carbon footprint via anaerobic co-digestion of swine wastewater with rice husk

An electricity-assisted anaerobic co-digestion (EAAD) process was developed and compared with conventional anaerobic co-digestion (AD) using piggery wastewater and rice husk as feedstocks. Various methodologies, including kinetic models, microbial community analyses, life-cycle carbon footprints, and preliminary economic analysis, were integrated to comprehensively evaluate the performance of the two processes. The results demonstrated that EAAD exhibited a positive improvement of 2.6 % to 14.5 % in biogas production compared to AD. The suitable wastewater-to-husk ratio for EAAD was found to be 3:1, which corresponded to a carbon-to‑nitrogen ratio of approximately 14. This ratio demonstrated positive co-digestion effects and electrical enhancements in the process. According to the modified Gompertz kinetics, the biogas production rate in EAAD ranged from 1.87 to 5.23 mL/g-VS/d, significantly higher than the range of 1.19 to 3.74 mL/g-VS/d observed in AD. The study also investigated the contributions of acetoclastic and hydrogenotrophic methanogens to biomethane formation, revealing that acetoclastic methanogens accounted for 56.6 % ± 0.6 % of the methane production, while hydrogenotrophic methanogens contributed to 43.4 % ± 0.6 %. No significant difference in the methanogenic reaction pathways was observed between AD and EAAD, indicating that the introduction of an external electric field did not alter the predominant pathways (p > 0.05, two-sample t-test). Furthermore, retrofitting existing AD plants with EAAD units can reduce the carbon intensity of piggery wastewater treatment by 17.6 % to 21.7 %. The preliminary economic analysis indicated a benefit-cost ratio of 1.33 for EAAD, confirming the feasibility of implementing EAAD for wastewater treatment while simultaneously producing bioenergy. Overall, this study provides valuable insights into upgrading the performance of existing AD plants by introducing an external electric field. It demonstrates that EAAD can achieve higher and cost-effective biogas production with a lower life-cycle carbon footprint, thus enhancing the sustainability and efficiency of the biogas production process.

Advanced oxidation and a metrological strategy based on CLC-MS for the removal of pharmaceuticals from pore & surface water

In this work, it is studied the photolysis, electrolysis, and photo-electrolysis of a mixture of pharmaceutics (sulfadiazine, naproxen, diclofenac, ketoprofen and ibuprofen) contained in two very different types of real water matrices (obtained from surface and porewater reservoirs), trying to clarify the role of the matrix on the degradation of the pollutants. To do this, a new metrological approach was also developed for screening of pharmaceuticals in waters by capillary liquid chromatography mass spectrometry (CLC-MS). This allows the detection at concentrations lower than 10 ng mL^-1. Results obtained in the degradation tests demonstrate that inorganic composition of the water matrix directly influences on the efficiency of the drugs removal by the different EAOPs and better degradation results were obtained for experiments carried out with surface water. The most recalcitrant drug studied was ibuprofen for all processes evaluated, while diclofenac and ketoprofen were found to be the easiest drugs for being degraded. Photo-electrolysis was found to be more efficient than photolysis and electrolysis, and the increase in the current density was found to attain a slight improvement in the removal although with an associated huge increase in the energy consumption. The main reaction pathways for each drug and technology were also proposed.

Degradation of Bisphonel AF (BPAF) by zero-valent iron activated persulfate: Kinetics, mechanisms, theoretical calculations, and effect of co-existing chloride

The removal of Bisphonel AF (BPAF) by zero-valent iron activated persulfate (Fe⁰/PS) system was systematically evaluated in this work. 30.0 μM BPAF was removed by 94.4% in 60 min of treatment under optimal conditions of pH = 3.0 and [PS] = [Fe⁰] = 3.0 mM. Cl^- significantly accelerated the removal of BPAF, resulting from accelerated Fe²⁺ release and reactive chlorine species (RCS) formation. Liquid chromatography-time-of-flight-mass spectrometry identified thirteen degradation products, and bond breaking, coupling reactions, hydroxylation and sulfate addition were considered as the major transformation pathways. When Cl^- was present, six new chlorinated byproducts were also generated. Based on density functional theory (DFT) calculations, the occurrence of radical addition reactions was verified and the preferential reaction channels were determined. Significantly BPAF degradation products were less toxic, according to toxicity assessment by the ECOSAR program. Moreover, a high removal efficiency of BPAF (>90%) was also obtained in the three actual water matrixes. The present work demonstrates the feasibility of Fe⁰/PS system for treating BPAF, which could also provide new insights into the influence of coexisting Cl^- on the environmental fate of organic pollutants in sulfate radicals based advanced oxidation processes.

The efficient degradation of diclofenac by ferrate and peroxymonosulfate: performances, mechanisms, and toxicity assessment

In this study, the degradation efficiency and reaction mechanisms of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, by the combination of ferrate (Fe(VI) and peroxymonosulfate (PMS) (Fe(VI)/PMS) were systematically investigated. The higher degradation efficiency of DCF in Fe(VI)/PMS system can be obtained than that in alone persulfate (PS), Fe(VI), PMS, or the Fe(VI)/PS process at pH 6.0. DCF was efficiently removed in Fe(VI)/PMS process within a wide range of pH values from 4.0 to 8.0, with higher degradation efficiency in acidic conditions. The increasing reaction temperature (10 to 30 ℃), Fe(VI) dose (6.25 to 100 µM), or PMS concentration (50 to 1000 µM) significantly enhanced the DCF degradation. The existences of HCO₃¯, Cl¯, and humic acid (HA) obviously inhibited the DCF removal. Electron paramagnetic resonance (EPR), free radical quenching, and probing experiments confirmed the existence of sulfate radicals (SO₄^•¯), hydroxyl radicals (^•OH), and Fe(V)/ Fe(IV), which are responsible for DCF degradation in Fe(VI)/PMS system. The variations of TOC removal ratio reveal that the adsorption of organics with ferric particles, formed in the reduction of Fe(VI), also were functioned in the removal process. Sixteen DCF transformation byproducts were identified by UPLC-QTOF/MS, and the toxicity variation was evaluated. Consequently, eight reaction pathways for DCF degradation were proposed. This study provides theoretical basis for the utilization of Fe(VI)/PMS process.

Effects of environmental factors on the fleroxacin photodegradation with the identification of reaction pathways

The abuse of fluoroquinolones (FQs) antibiotics leads to bacterial resistance and environmental pollution, so it is of great significance to verify the decomposition mechanism for eliminating antibiotic efficiently and conveniently. The effects of various environmental factors and the fleroxacin (FLE) photodegradation mechanisms were investigated by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS), UV-Vis absorption spectroscopy, fluorescence spectroscopy and quantum chemical calculation. Six possible photodegradation reaction paths on T₁ (excited triplet state) were proposed and simulated. The departure of the piperazine ring and the substitution of F atom at C-6 position by OH group were determined as the main reactions based on the reaction rates and energy barriers of each path. The multi-pathway reactions resulted in the fastest photodegradation rates of FLE at pH 6-7 than other pH conditions. NaN₃ would promote FLE photodegradation by inhibiting the reverse reaction of the separation process of F atom at C-8 and the generation of biphenyl molecules, which was a novel and distinctive phenomenon in this report. ·OH would rapidly combine with the free radicals generated in photolysis processes and made a great contribution to FLE photodegradation. Ca²⁺, Mg²⁺ and Ba²⁺ could stabilize the carboxyl group to impede the photo-competitive process of the decarboxylation reaction, while NO₃^- could generate reactive oxygen species to promote photodegradation.

Experimental and theoretical study on Fe(VI) oxidative degradation of dichlorophen in water: Kinetics and reaction mechanisms

Dichlorophenol (DCP), a commonly used fungicide and insecticide, is widely found in waters and wastewaters. Herein, the degradation of DCP by Ferrate (Fe(VI)) in different matrices was comprehensively investigated. In pure water, a complete removal of DCP was achieved in 300 s at [Fe(VI)]:[DCP] molar ratio of 2:1. The presence of HA (10 mg L^-1) inhibited DCP degradation to a certain extent. A total of twenty degradation products were identified by HPLC/MS analysis. Based on these products, reaction pathways including the cleavage of C-C bridge bond, hydroxylation, and radical coupling were proposed. These reaction mechanisms were further rationalized by theoretical calculations. The analyses of Wiberg bond orders and transition state indicated that C₇-C₈ bond was the most vulnerable site for cleavage, and C₁₂ site was the most likely site for hydroxyl addition. Mulliken atomic spin densities distribution suggested that self-coupling products was easily generated via C-O-C coupling ways. Finally, the feasibility of applying Fe(VI) to degrade DCP (20 μM) in a municipal wastewater effluent and a lake water was evaluated and verified. The findings in this study are of relevance in designing Fe(VI)-based treatment strategy for chlorine-containing persistent pesticides.

Chemical kinetic investigation on NOx emission of SI engine fueled with gasoline-ethanol fuel blends

Understanding the nitrogen oxide (NOx) formation chemical kinetic mechanism and analyzing the effect of relevant influence parameters are the effective strategy for NOx emission control. Based on the essential role of ethanol-gasoline blends among oxygenate alternative fuel, the experiments in a GDI (gasoline direct injection) SI (spark ignition) engine and the chemical kinetic simulation were carried out. According to the validated model, seven NO contributing reactions and three reaction pathways were observed. Besides the thermal NO formation pathway, two other pathways with N₂O and NNH through NH-HNO-NO have nonnegligible places in the high engine speed condition. As for the parameters, initial temperature aggravates NO emission, initial pressure and ethanol fraction inhibit NO, which influence it through thermal NO pathway and have slight impact on the other two pathways. While with the increase of equivalence ratio (ER) from 0.5 to 1.0, ER promotes first and then resists NO formation, getting highest emission when ER equals to 0.85. In a lean burn condition, the thermal pathway is highly inhibited and the N₂O pathway is sharply accelerated. Through current work, NOx producing mechanism under high-speed condition is investigated comprehensively, which not only completes the total NO formation pathways from atmospheric N₂ but also provides reference for the designing and modification of low harmful NOx emitting gasoline-ethanol engines.

Oily sludge treatment in subcritical and supercritical water: A review

Oily sludge, an inherent byproduct of the petroleum industry, presents dual characteristics of petroleum resources and hazardous waste. Owing to the unique physicochemical properties of sub-/supercritical water, hydrothermal technologies have been increasingly used for oily sludge treatment. This review is the first to focus on oily sludge treatment using sub-/supercritical water. Eight hydrothermal technologies used for different purposes are summarized herein: pressurized hot water extraction (PHWE) for hydrocarbon separation, thermal hydrolysis (TH) for dewaterability improvement, hydrothermal carbonization (HTC) for hydrochar production, wet air oxidation (WAO) for biodegradability improvement, hydrothermal liquefaction (HTL) for bio-oil production, supercritical water upgrading (SCWU) for light oil production, supercritical water oxidation (SCWO) for complete degradation, and supercritical water gasification (SCWG) for H₂-rich syngas production. Moreover, a general reaction pathway for sub-/supercritical water treatment of oily sludge is presented, with a particular focus on the chemical mechanism at temperatures above 350 °C. Lastly, two reaction maps are included to illustrate the reaction pathways of two groups of identifiable model compounds in oily sludge: aliphatic and aromatic hydrocarbons. This review provides detailed information that can promote a better understanding of various hydrothermal technologies, a guideline for selecting the suitable hydrothermal process for a particular oily sludge, and recommendations for further researches.

A pilot study for enhanced transformation of a metabolite 3,5-dichloroaniline derived from dicarboximide fungicides through immobilized laccase mediator system

This pilot investigation aimed to evaluate the removal efficiency and the underlying biocatalytic pathways of immobilized fungal laccase during the oxidative biotransformation of a non-phenolic metabolite, 3,5-dichloroaniline (3,5-DCA) derived from dicarboximide fungicides. The maximum loading of laccase on the microporous support surfaces could reach 36.4 mg/g. The immobilized laccase on the microporous support surfaces exhibited excellent thermal stability, pH adaptability, storage stability, and reusability compared to free laccase. The ILMS assay indicated that the immobilized laccase efficiently removed studied 3,5-DCA (99-100%) in the aqueous medium, within 72 h in the presence of catechol. In this study, we identified three coupling reaction products during the removal of 3,5-DCA through an ILMS assay. Based on the identified coupling reaction products, we proposed the reaction pathway for the biotransformation of 3,5-DCA by immobilized laccase, which was shown to be potentially useful in the sustainable environmental remediation of aniline metabolite (i.e., 3,5-DCA) derived from dicarboximide fungicides.

Photochemical transformation of hexachlorobenzene (HCB) in solid-water system: Kinetics, mechanism and toxicity evaluation

As one of the first batch of persistent organic pollutants (POPs) included in Stockholm Convention, hexachlorobenzene (HCB) has attracted great attention because of its wide occurrence and great environmental risks. Considering the easy adsorption of HCB on solids and the complexity of natural particles, we systematically investigated the photodegradation of HCB on the surface of silica gel (SG) in aqueous solution in this work to reveal its fate in natural waters. Under mercury lamp irradiation, more than 90% of HCB loaded on SG could be removed after 240 min. Moreover, the effects of solution pH and water constituents were examined, and results showed that the presence of NO₂^-, NO₃^-, Fe³⁺ and humic acid (HA) significantly inhibited the reaction due to the scavenging of ROS and/or competitive absorption of light. According to radical quenching experiments and electron paramagnetic resonance (EPR) spectra, hydroxyl radicals and singlet oxygen generated on the surface of SG could participate in the transformation of HCB, but •OH played a dominant role. Based on products identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), two main pathways were proposed for the removal of HCB, including dechlorination and hydroxylation which represent direct and indirect photodegradation, respectively, and the occurrence of these two reactions was further supported by density functional theory (DFT) calculations. From the quantitative analysis of penta-chlorobenzene, it was estimated that dechlorination and hydroxylation contributed to approximately 44.4% and 55.6% of initial HCB degradation, respectively. Furthermore, toxicity predictions by the ecological structure-activity relationship model (ECOSAR) suggested that the toxicity of HCB was decreased in the photodegradation process. This study would provide important information for understanding the photochemical transformation mechanism of HCB at the solid/water interface.

Changes in levels of N-nitrosamine formed from amine-containing compounds during chloramination via photocatalytic pretreatment with immobilized TiO2: Effect of source water and pH

We investigated the effectiveness of photocatalytic pretreatment (PCP) of precursors in minimizing the formation potentials (FPs) of carcinogenic nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodiethanolamine (NDELA), during water chloramination. A steel mesh substrate with immobilized TiO₂ was highly efficient at mitigating nitrosamine formation and removing targeted precursors such as ranitidine, nizatidine, trimebutine, triethanolamine, and metoclopramide. Compared to UVC/H₂O₂, PCP under UVA irradiation (intensity of 0.67 mW cm^-2) was more effective for reducing nitrosamine-FPs during post-chloramination. However, the PCP efficacies varied with the water source, pretreatment pH, and irradiation time. For example, PCP of eutrophic water increased the NDMA-FPs, but produced notable reductions (up to 99%) for NDELA- and NDEA-FPs. Shorter irradiation times, up to 15 min, increased the NDELA-FP in triethanolamine, and the NDMA-FP in nizatidine and trimebutine. However, the nitrosamine-FP decreased by > 50% after PCP at a pH > 5.6, following irradiation for 120 min. Oxygen addition, N-de(m)ethylation, and N-dealkylation were responsible for decreasing nitrosamine-FPs via the destruction of key moieties; this has been elucidated by mass spectroscopy. This study suggests that PCP could be used as an alternative strategy for minimizing nitrosamine-FPs during water treatment.

Oxidation of chloroquine drug by ferrate: Kinetics, reaction mechanism and antibacterial activity

Chloroquine (CLQ) is required to manufacture on a larger scale to combat COVID-19. The wastewater containing CLQ will be discharged into the natural water, which was resistant to environmental degradation. Herein, the degradation of CLQ by ferrate (Fe(VI)) was investigated, and the biodegradability of the oxidation products was examined to evaluate the potential application in natural water treatment. The reaction between CLQ and Fe(VI) was pH-dependent and followed second-order kinetics. The species-specific rate constant of protonated Fe(VI) species (HFeO₄ ^-) was higher than that of the FeO₄ ^2- species. Moreover, increasing the reaction temperature could increase the degradation rate of CLQ. Besides, HCO₃ ^- had positive effect on CLQ removal, while HA had negative effect on CLQ removal. But the experiments shows Fe(VI) could be used as an efficient technique to degrade co-existing CLQ in natural waters. During the oxidation, Fe(VI) attack could lead to aromatic ring dealkylation and chloride ion substitution to form seven intermediate products by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) determination. Finally, a pure culture test showed that the oxidation of CLQ by Fe(VI) could slightly increase the antimicrobial effect towards Escherichia coli (E.coli) and reduce the toxicity risk of intermediates. These findings might provide helpful information for the environmental elimination of CLQ.

Unravelling caramelization and Maillard reactions in glucose and glucose + leucine model cakes: Formation and degradation kinetics of precursors, α-dicarbonyl intermediates and furanic compounds during baking

Understanding the mechanisms leading to the multitude of newly-formed compounds generated during the thermal processing of food is important for the reasoned construction of quality. Thanks to a solid food model with a structure and technological history comparable to that of a real sponge cake and containing only known amounts of precursors (glucose with or without leucine), an adapted reaction scheme unravelling Maillard and caramelization reactions was built and then compared to experimental kinetic data measured on numerous reaction markers (precursors, α-dicarbonyl intermediates and furanic compounds). For caramelization, this study showed that glucose mainly formed 1,2-enediol and then fructose rather than glucosone and glyoxal. 5-hydroxymethylfurfural started to form when there were sufficient quantities of fructose, and 3,4-dideoxyoglucosone was not generated until after this step. Furfural was mainly formed via 3-deoxyglucosone. The involvement of leucine tended to accelerate the breakdown of sugars as more degradation pathways (via enaminols) were added.

Treatment-driven removal efficiency, product formation, and toxicity evolution of antineoplastic agents: Current status and implications for water safety assessment

Antineoplastic compounds, designed for chemotherapeutic anticancer therapy, have become emerging contaminants of global concern over the past decade due to their ubiquitous occurrence, environmental persistence, and multiple adverse effects on aquatic ecosystems. Increasing efforts have been devoted to developing efficient strategies for remediating water containing these micropollutants. In this study, the physicochemical properties, natural attenuation, and chemical reactivity with aqueous oxidizing species of five antineoplastic drugs with the highest environmental prevalence (i.e., tamoxifen, cyclophosphamide, ifosfamide, 5-fluorouracil, and methotrexate) were summarized. The removal performance, transformation products (TPs) of varying structures, overall reaction pathways, and toxicity evolution during different treatments were evaluated and discussed. Additionally, the biodegradability and multi-endpoint toxicity of each TP were predicted using in silico QSAR software. Depending on their distinct inherent structures, the reactivity of the antineoplastics with oxidizing species varied, with hydroxyl radicals exhibiting unparalleled merits in rapid oxidation. Complete elimination of these contaminants was observed during oxidative treatments, but with inadequate mineralization. Notably, the increase in toxicity within multiple processes was determined based on both experimental bioassays and theoretical predictions. This may be attributed to the adverse effects induced by the large number of identified and unknown TPs individually and in combination. Together with the environmental persistence and low biodegradability of most TPs, these results necessitate the application of efficient post-treatments in conjunction with a more thorough water safety evaluation (e.g., using high-throughput screening) of the mixtures of treated water and wastewater.

A kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion

Pressurized oxy-combustion is an emerging and more efficient technology for carbon capture, utilization, and storage than the first generation (atmospheric) oxy-combustion. NO_x is a major conventional pollutant produced in pressurized oxy-combustion. In pressurized oxy-combustion, the utilization of latent heat from moisture and removal of acid gases (NOx and SOx) are mainly conducted in an integrated direct-contact wash column. Recent studies have shown that NOx particular inlet concentration should be maintained before direct contact wash column to remove NOx and SOx efficiently. As a result, minimizing NOx for environmental reasons, avoiding corrosion in carbon capture, utilization, and storage, and achieving effective NOx and SOx removal in direct contact wash columns are crucial. Reburning is a capable and affordable technology for NO_x reduction; however, this process is still less studied at elevated pressure, particularly in pressurized oxy-combustion. In this paper, the kinetic evaluation and optimization study on NO_x reduction by reburning under pressurized oxy-combustion was conducted. First, the most suitable mechanism was selected by comparing the results of different kinetic models with the experimental data in literature at atmospheric and elevated pressures. Based on the validated mechanism, a variety of parameters were studied at high pressure, i.e., comparing the effects of oxy and the air environment, different reburning fuels, residence time, H₂O concentration, CH₄/NO ratio, and equivalence ratio on the NO reduction. The results show that de-NOx efficiency in an oxy environment is significantly enhanced compared to the air environment. Improvement in the de-NOx efficiency is considerably higher with a pressure increase of up to 10 atm, but the effect is less prominent above 10 atm. The formation of HCN is significantly reduced while the N₂ formation is enhanced as the pressure increases from 1 to 10 atm. The residence time required for the maximum NO reduction decreases as the pressure increases from 1 atm to 15 atm. At the higher pressure, the NO reduction rises prominently when the ratio of CH₄/NO increases from 1 to 2; however, the effect fades after that. At higher pressure, the NO reduction by CH₄ reburning decreases as the H₂O concentration increases from 0 to 35%. The optimum equivalence ratio and high pressure for maximum NO reduction are 1.5 and 10 atm, respectively. This study could provide guidance for designing and optimizing a pressurized reburning process for NOx reduction in POC systems.

Effective degradation of 2,4-dihydroxybenzophenone by zero-valent iron powder (Fe0)-activated persulfate in aqueous solution: Kinetic study, product identification and theoretical calculations

2,4-Dihydroxybenzophenone (BP-1), a typically known derivative of the benzophenone-type UV filter, has been frequently detected in aqueous environments and poses a potential risk to human health and the entire ecosystem. In this study, an effective advanced oxidation technique using zero-valent iron powder (Fe⁰)-activated persulfate (PS) was used for the degradation of BP-1. The effects of several experimental parameters, including Fe⁰ dosages, PS dosages, pH, and common natural water constituents, were systematically investigated. The BP-1 degradation efficiency was enhanced by increasing the Fe⁰ and PS dosages and decreasing the solution pH. The presence of different concentrations of humic acid (HA) could inhibit BP-1 removal, while the addition of various cations and anions had different effects on the degradation. Moreover, the degradation of BP-1 in five water matrices was also compared, and the removal rates followed the order of ultrapure water > tap water > secondary clarifier effluent > river water > synthetic water. Thirteen oxidation products were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, and five possible degradation pathways were proposed. The addition reactions initiated by HO and SO₄^-, as well as single-electron coupling reactions and ring-closing reactions, were further supported by density functional theory (DFT) calculations. Assessment of toxicity of intermediates of the oxidation of BP-1 suggested decreased toxicity from the parent contaminant. The present work illustrates that BP-1 could be efficiently degraded in the Fe⁰/PS system, which may provide new insights into the removal of benzophenones in water and wastewater.

Impacts of solvation on photo-damage of polypeptides: Modulation and biological implications

We investigate the photon/matter interactions between soft X-rays and three selected polypeptides, poly-glycine (poly-Gly), poly-L-arginine (poly-Arg), and poly-l-lysine (poly-Lys), where the effects of molecular packing under the influence of solvent, e.g., water, substrates (Au foil or Si wafer) and X-ray irradiation under different durations were systematically investigated. Compared with negligible photo-damage on bare polypeptide powders, significantly enhanced degradation in pre-solvated polypeptides was observed likely because of the formation photo-generated radicals. X-ray photoemission spectroscopy (XPS) were employed as the analysis means to identify and quantify the chemical changes, especially the high-resolution photoemission spectra of C 1s, O 1s, N 1s and their evolution under continuous X-ray irradiation. The photo-degradation was found to preferentially occur on the CO entity in poly-Gly and the guanidinium group in poly-Arg. In poly-Arg, deprotonation occurs via the switch from zwittterionic to a neutral configuration, whereas poly-Lys deprotonates by directly losing the corresponding amine. The critical role of the interactions between amino acids, the building blocks of protein and almost all forms of biological activities, and the free-radical-generating living environment under irradiation was critically analyzed. The present study found that the preparation history of a sample, especially its inadvertent exposure to the sources of H₂O, O₂ and OH, could significantly alter the outcome of a radiation-related chemical process. Implications on the non-destructive probe of biologically important systems using physical methods involving X-rays were discussed as well.

Analysis of reaction pathways and catalytic sites on metal-free porous biochar for persulfate activation process

To develop a metal-free biochar with high and inherent catalytic activity towards refractory and highly toxic contaminants in advanced oxidation processes, it is necessary to explore its reaction pathways and responsible catalytic sites. Herein, a metal-free biochar derived from corn cob (CCBC) was prepared and used for reaction pathway analysis during peroxydisulfate (PDS) activation. The pyrolysis temperature played an important role for regulating the biochar structure and properties, and CCBC obtained at 800 °C showed the best adsorption capacity and catalytic activity towards five typical organic pollutants, including 2, 4-dichlorophenol, Tetracycline hydrochloride, Ciprofloxacin, Methyl orange and Rhodamine B, due to its richer pore and defect structure. Further treatment of pharmaceutical wastewater demonstrated the good efficiency and potential of this metal-free catalyst for practical application. Radical (58% contribution) and non-radical (42% contribution) pathways were both found in CCBC/PDS system. More importantly, further redox experiments manifested that the carbon framework (defects, sp²-hybrid carbon, etc.) only made a contribution to the free radical pathway, while the ketone group (CO) of CCBC was proved to be mainly responsible for the non-radical pathway, namely the generation of singlet oxygen (¹O₂).

Tailored photocatalysts and revealed reaction pathways for photodegradation of polycyclic aromatic hydrocarbons (PAHs) in water, soil and other sources

Polycyclic aromatic hydrocarbons (PAHs), which are in the class of persistent organic pollutants, are considered as hazardous pollutants. To date, these compounds were detected globally in soil, sludge, water, and other contamination sources. A variety of treatment methods have been used in recent years to degrade PAHs in the environment. Photocatalysis, among advanced techniques, is proposed as the most effective method for the treatment of PAHs. In this context, we introduce the classification of PAHs, summarize, and highlight the recent studies on photodegradation of various types of PAHs. A series of efficient photocatalysts, including TiO₂-, Ag₃PO₄-, ZnO-, MHCFs-based, and others, have been reported with the potential result for photodegradation of PAHs. Focus is also placed on revealing several possible reaction pathways for different types of PAHs that have been proposed in the literature. Particular attention to current status, challenges, and prospects in the future for enhanced photodegradation of PAHs are also discussed.

Efficient removal of triclosan via peroxymonosulfate activated by a ppb level dosage of Co(II) in water: Reaction kinetics, mechanisms and detoxification

Triclosan (TCS), an extensively used broad-spectrum antimicrobial agent, has raised significant environmental concerns regarding its widespread occurrence in waters. In this study, the removal of TCS in aqueous solution via peroxymonosulfate (PMS) activated by an extremely low-level Co²⁺ (0.02 μM) was systematically investigated. During preliminary test, TCS (10 μM) was totally degraded in 30 min by using 0.1 μM Co²⁺ and 40 μM PMS at pH 7.0 with a degradation rate constant of 0.1219 min^-1. A first-order apparent degradation rate of TCS was found with respect to the PMS concentrations. At extremely low dosage of Co²⁺ (0.02 μM), the presence of NO₃^-, HCO₃^-, PLFA, and SRHA within test concentrations significantly inhibited TCS removal, while a dual effect of Cl^- on the degradation rate of TCS was observed. The quenching experiments verified that SO₄^- was the dominant reactive oxygen species (ROS) rather than OH. Six major intermediates were identified using TOF-LC-MS, based on which we proposed three associated reaction pathways including hydroxylation, ether bond breakage, and dechlorination. Toxicity predictions by ECOSAR software exhibited aquatic toxicity reduction of TCS after Co²⁺/PMS treatment. We outlook these findings to advance the feasibility of organic contaminants removal via Co²⁺/PMS system with Co²⁺ at extremely low levels.

In-situ treatment of herbicide-contaminated groundwater-Feasibility study for the cases atrazine and bromacil using two novel nanoremediation-type materials

Two injectable reactive and sorption-active particle types were evaluated for their applicability in permeable reaction zones for in-situ removal of herbicides ("nanoremediation"). As model substances, atrazine and bromacil were used, two herbicides frequently occurring in groundwater. In order to provide recommendations for best use, particle performance was assessed regarding herbicide degradation and detoxification. For chemical reduction, Carbo-Iron® was studied, a composite material consisting of zerovalent iron and colloidal activated carbon. Carbo-Iron reduced bromacil with increased activity compared to nanoscale zerovalent iron (nZVI). The sole reaction product, 3-sec-butyl-6-methyluracil, showed 500-fold increase in half-maximal-effect concentration (EC₅₀) towards the chlorophyte Scendesmus vacuolatus compared to the parent compound. The detoxification based on dehalogenation confirmed the dependency of the specific mode-of-action on the carbon-halide bond. For atrazine, neither nZVI nor Carbo-Iron showed significant degradation under the conditions applied. As novel subsurface treatment option, Trap-Ox® zeolite FeBEA35 was studied for generation of in-situ permeable oxidation barriers. Both adsorbed atrazine and bromacil underwent fast unselective oxidation. The transformation products of the Fenton-like reaction were identified, and oxidation pathways derived. For atrazine, a 300-fold increase in EC₅₀ for S. vacuolatus was found over the duration of the reaction, and a loss of phytotoxicity to non-detectable levels for bromacil.

Clopyralid degradation by AOPs enhanced with zero valent iron

Four different technologies have been compared (photolysis, ZVI + photolysis, electrolysis and ZVI + electrolysis) regarding the: (1) degradation of clopyralid, (2) extent of its mineralization, (3) formation of by-products and main reaction pathways. Results show that photolysis is the less efficient treatment and it only attains 5 % removal of the pollutant, much less than ZVI, which reaches 45 % removal and that electrolysis, which attains complete removal and 78 % mineralization within 4 h. When ZVI is used as pre-treatment of electrolysis, it was obtained the most efficient technology. The identification of transformation products was carried out for each treatment by LCMS. In total, ten products were identified. Tentative pathways for preferential clopyralid degradation for all processes were proposed. This work draws attention of the synergisms caused by the coupling of techniques involving the treatment of chlorinated compound and sheds light on how the preferential mechanisms of each treatment evaluated occurred.

Oxidation of flumequine in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

The degradation of flumequine (FLU) in aqueous solution by ultraviolet (UV)-activated peroxymonosulfate (PMS) was investigated in this work. Under the conditions of [PMS]₀:[FLU]₀ = 1:1, T = 25 ± 2 °C, pH = 7.0 ± 0.1, nearly complete removal of FLU was achieved after 60 min. The effects of various operating parameters, including oxidant doses, pH, the presence of typical ions (NH₄⁺、Mg²⁺、Fe³⁺、Cl^-、NO₃^-、HCO₃^-) and humic acid were evaluated. It was found that the pseudo-first-order rate constants of FLU degradation increased with increasing PMS dosage and decreasing solution pH. The presence of Mg²⁺ could accelerate FLU removal, while Fe³⁺, HCO₃^-, NO₃^- and HA inhibited the reaction. Moreover, the degradation of FLU in different water matrices were also explored, and the removal followed the order of Tap water > Ultrapure water > River water > Secondary clarifier effluent. According to the control and radical quenching experiment results, direct photolysis and reactive radicals (SO₄^- and HO) contributed mainly to FLU degradation in the UV/PMS system. Initial FLU molecule underwent reactions such as hydroxylation, hydroxyl substitution, demethylation, decarboxylation/decarbonylation and ring opening, leading to the formation of nineteen oxidation products. The effective degradation by UV/PMS suggests a feasible technology for treating FLU in waters and wastewaters.

Removal, potential reaction pathways, and overall cost analysis of various pollution parameters and toxic odor compounds from the effluents of turkey processing plant using TiO2-assisted UV/O3 process

In the present study, removal of hazardous toxic odor compounds with color, COD and turbidity were concurrently investigated for the effluents of a turkey processing plant located in Bolu, Turkey. A hybrid TiO₂-assisted photo-ozonation (UV/TiO₂/O₃) process was set to address this issue. Subsequently, a comprehensive GC/MS method was developed for quantification of odor compounds. Finally, a complete overall cost analysis was incorporated with the findings of the study to demonstrate an economic analysis of the process. Descriptive results showed that the effluents had high pollution content in terms of color (0.374 IU; b = -0.06), COD (146 mg/L O₂) and turbidity (15.52 NTU). Moreover, dimethyl silanediol (DS, 34.3%), acetic acid (AA, 20.5%), and diisobutyl phthalate (DP, 32.5%) were determined as major odor compounds of the effluents. After UV/TiO₂/O₃ process, DS, AA, and DP were reduced to 12.4%, 12.0%, and 8.4%, respectively under the operating conditions of ozone dose of 16 mg/L, initial pH of 7.5, reaction time of 25 min, and catalyst dose of 3 g/L TiO₂. At the same conditions removal efficiencies of color, COD and turbidity were obtained %99, %85, and 78%, respectively. These values demonstrated the accuracy of UV/TiO₂/O₃ process in terms of removal of hazardous odor compounds and the other pollution parameters. Studies on reaction mechanism showed that main degradation mechanism occurred in three ways: formation of long-chained cyclic compounds from DS (1), formation of acetamide and ammonium acetate from AA (2), and formation of phthallic acid from DP (3). Finally, overall cost analysis showed that the current process costed 0.014 $ per 1 L of treated effluent and this value showed that the current process met the economic criteria in terms of feasibility.

Enhanced Cu(II)-mediated fenton-like oxidation of antimicrobials in bicarbonate aqueous solution: Kinetics, mechanism and toxicity evaluation

Increasing attention has been attracted in developing new technologies to remove chlorofene (CF) and dichlorofene (DCF), which were active agents in antimicrobials for general cleaning and disinfecting. This study investigated the significant influences of bicarbonate (HCO₃^-) on the degradation of CF and DCF in the Cu(II)-mediated Fenton-like system Cu²⁺/H₂O₂. Our results indicate that HCO₃^- may play a dual role to act 1) as a ligand to stabilize Cu(II), forming soluble [Cu^II(HCO₃^-)(S)]⁺ species to catalyze H₂O₂ producing hydroxyl radical (OH) and superoxide ion (O₂^-) and 2) as a OH scavenger. Furthermore, the reaction kinetics, mechanisms, and intermediates of CF and DCF were assessed. The apparent rate constants of CF and DCF were enhanced by a factor of 8.5 and 5.5, respectively, in the presence of HCO₃^- at the optimized concentration of 4 mM. Based on the intermediate identification and frontier electron densities (FEDs) calculations, the associated reaction pathways were tentatively proposed, including C-C scission, single or multiple hydroxylation, and coupling reaction. In addition, significant reduction in the aquatic toxicity of CF and DCF was observed after treatment with Cu²⁺/H₂O₂-HCO₃^- system, evaluated by Ecological Structure Activity Relationships (ECOSAR) program. These findings provide new insights into Cu(II)-mediated reactions to better understand the environmental fate of organic contaminants in carbonate-rich waters.

Volume-conserving photoisomerization of a nonplanar GFP chromophore derivative: Nonadiabatic dynamics simulation

Nonadiabatic dynamics of a nonplanar green fluorescent protein (GFP) chromophore derivative was examined theoretically by trajectory surface hopping approach at the CASSCF level based on Zhu-Nakamura theory. The geometry optimizations show that there are four ground-state minima and four conical intersections between the ground (S₀) and first excited (S₁) states. Four S₁-state minima were found at a perpendicularly twisted conformation around the imidazolinone-bridged bond. Upon excitation to S₁ state, the main decay pathways of four isomers involve different S₀/S₁ potential energy surface conical intersections. The dominant excited-state relaxation mechanism of this GFP chromophore derivative is the twists of two bridging bonds and the methyl group in the bridge combined with the pyramidalization character of the central carbon atom. Further twists of two bridging bonds and the methyl group occur sequentially in the S₀ state. It is worth to mention that the special volume-conserving motion of this molecule is attributed to twists of two bridging bonds in the same direction during the whole photoisomerization processes. The theoretical investigation presented herein provides important insights into the volume-conserving photoisomerization mechanisms of a nonplanar GFP chromophore derivative. We believe that the present work can benefit the design of the photochromic molecule devices in confined media.

Hydrothermal liquefaction of cellulose in ammonia/water

In order to obtain the N-containing organics from cellulose under mild conditions, hydrothermal liquefaction of cellulose in the presence of ammonia was conducted in this study. The results showed that the increasing reaction temperature and prolonging time facilitated the conversion of cellulose in hydrothermal liquefaction (HTL) with NH₃·H₂O and decreased the amount of solid residue. Reaction temperature showed more influence than reaction time on solid residue formation. The components of bio-oil were significantly affected by reaction temperature and reaction time. Electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry (ESI FT-ICR MS) provided an insight for understanding the distribution of the different kinds of N-heterocycle compounds in the bio-oil. The possible reaction pathway of N-heterocycle compounds formation from cellulose during hydrothermal liquefaction with NH₃·H₂O was proposed.

Ferrate(VI) oxidation of polychlorinated diphenyl sulfides: Kinetics, degradation, and oxidized products

This paper presents oxidation of polychlorinated diphenyl sulfides (PCDPSs), dioxin-like compounds, by ferrate(VI) (Fe^VIO₄^2-, Fe(VI)). Kinetics of the reactions of Fe(VI) with seventeen PCDPSs, differ in number and positions of chlorine atoms (from 2 to 7), were investigated at pH 8.0. The second-order rate constants (k, M^-1 s^-1) of the reactions varied with the numbers and positions of chlorine atoms and appeared to be related with standard Gibbs free energy of formation (Δ_fG⁰) of PCDPSs. Degradation experiments in the presence of ions and humic acid demonstrated complete removal of PeCDPS by Fe(VI) in minutes. Pathways of the reaction were investigated by identifying oxidized products (OPs) of the reaction between Fe(VI) and 2,2',3',4,5-pentachlorodiphenyl sulfide (PeCDPS) at pH 8.0. Pathways of oxidation involved major pathway of attack on sulfur(II) by Fe(VI) in steps to yield sulfoxide type products, and subsequent breakage of C-S bond with the formation of sulfonic acid-containing trichloro compound. Minor pathways were hydroxylation of benzene ring and substitution of chlorine atom with hydroxyl group. Estimation of toxicity of OPs of the oxidation of PeCDPS by Fe(VI) suggested the decreased toxicity from the parent contaminant.

Impact of O3 or O3/H2O2 treatment via a membrane contacting system on the composition and characteristics of the natural organic matter of surface waters

The present study aims to evaluate changes in the structure-composition of natural organic matter (NOM) that occur after the application of bubbleless ozonation or peroxone treatment of surface waters. The oxidation experiments (using 0.5-2 mg O3/mg DOC, or 2:1 O₃:H₂O₂ molar ratio) were performed in a continuous mode, using a tubular ceramic membrane contactor. Fluorescence spectroscopy (emission-excitation matrix) and liquid chromatography-organic carbon detection (LC-OCD) were mainly used for the detailed DOC characterization. In brief, the application of single ozonation resulted to high reduction of humic-like peak fluorescence intensities (50-85%) and also to the formation of two new peaks in the region of protein-like components. The co-addition of H₂O₂ did not present the anticipated increase in the reduction of fluorescence intensity; however, it resulted to the further oxidation of protein-like fluorophores. LC-OCD measurements confirmed the decrease of average molecular weight of NOM during ozone treatment, due to the gradual degradation of biopolymers (14-23%) and humic substances (11-17%) towards building blocks and low molecular weight (LMW) neutrals. Advanced oxidation process (AOP) treatment by the mixture O₃/H₂O₂ resulted in the simultaneous decrease of building blocks and LMW neutral concentrations. Conventional batch ozonation and AOP experiments were conducted using ozone-saturated solutions to investigate the effect of different contacting patterns. The results revealed that the different reaction pathways followed during bubbleless and conventional batch experiments may also influence the formation of NOM oxidation intermediates.

Polycyclic aromatic hydrocarbon formation during the gasification of sewage sludge in sub- and supercritical water: Effect of reaction parameters and reaction pathways

The formation of polycyclic aromatic hydrocarbon is a widespread issue during the supercritical water gasification of sewage sludge, which directly reduces the gasification efficiency and restricts the technology practical application. The changes of the concentrations and forms as well as the synthesis rate of polycyclic aromatic hydrocarbons in the residues from supercritical water gasification of dewatered sewage sludge were investigated to understand influence factors and the reaction pathways. Results showed that the increase of reaction temperature during the heating period favours directly concentration of polycyclic aromatic hydrocarbon (especially higher-molecular-weight), especially when it raise above 300 °C. Lower heating and cooling rate essentially extend the total reaction time. Higher polycyclic aromatic hydrocarbon concentration and higher number of rings were generally promoted by lower heating and cooling rate, longer reaction time and higher reaction temperature. The lower-molecular-weight polycyclic aromatic hydrocarbons can be directly generated through the decomposition of aromatic-containing compounds in sewage sludge, as well as 3-ring and 4-ring polycyclic aromatic hydrocarbons can be formed by aromatization of steroids. Possible mechanisms of reaction pathways of supercritical water gasification of sewage sludge were also proposed.

Solid surface-mediated photochemical transformation of decabromodiphenyl ether (BDE-209) in aqueous solution

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants which have received considerable attention due to their global distribution, bioaccumulation potential, environmental persistence, and possible toxic effects. In this work, the photodegradation of decabromodiphenyl ether (BDE-209) in aqueous system was investigated by preloading it on the surface of various solid matrices. After 6 h of Xe lamp irradiation, almost complete degradation of BDE-209 was observed on silica gel (SG), with much slower degradation occurring in other adsorbents. The degradation of BDE-209 on SG sample followed pseudo-first-order kinetics, and the observed reaction rate constant was decreased by lowering pH, adding humic acid and increasing the initial BDE-209 concentration. In addition to direct photolysis, BDE-209 could be oxidized by hydroxyl radicals generated from SG, as confirmed by the electron paramagnetic resonance (EPR) technology. Product analysis showed that BDE-209 was mainly decomposed into lower brominated PBDEs, polybrominated dibenzofurans (PBDFs), hydroxylated PBDEs (OH-PBDEs), hydroxylated PBDFs (OH-PBDFs), bromophenols and bromide ions. Thus, consecutive debromination, intramolecular elimination of HBr, hydroxyl addition and the cleavage of ether bond were proposed as the degradation pathways. This study may help understanding the photochemical transformation of solid surface adsorbed BDE-209 in natural surface waters, which is important to evaluate the environmental fate of PBDEs.

Exploring ozonation as treatment alternative for methiocarb and formed transformation products abatement

Despite the high toxicity and resistance to conventional water treatments exhibited by methiocarb (MC), there are no reports regarding the degradation of this priority pesticide by means of alternative purification technologies. In this work, the removal of MC by means of ozonation was studied for the first time, employing a multi-reactor methodology and neutral pH conditions. The second-order rate constants of MC reaction with molecular ozone (O₃) and formed hydroxyl radicals (OH·) were determined to be 1.7·10⁶ and 8.2·10⁹ M^-1 s^-1, respectively. During degradation experiments, direct ozone reaction was observed to effectively remove MC, but not its formed intermediates, whereas OH· could oxidize all species. The major identified TPs were methiocarb sulfoxide (MCX), methiocarb sulfoxide phenol (MCXP) and methiocarb sulfone phenol (MCNP), all of them formed through MC oxidation by O₃ or OH· in combination with hydrolysis. A toxicity assessment evidenced a strong dependence on MCX concentration, even at very low values. Despite the OH· capability to degrade MC and its main metabolites, the relative resistance of TPs towards ozone attack enlarged the oxidant dosage (2.5 mg O₃/mg DOC) necessary to achieve a relatively low toxicity of the medium. Even though ozonation could be a suitable technique for MC removal from water compartments, strategies aimed to further promote the indirect contribution of hydroxyl radicals during this process should be explored.

Supercritical water oxidation of oil-based drill cuttings

Oil-based drill cuttings (OBDC) are a typical hazardous solid waste that arises from drilling operations in oil and gas fields. The supercritical water oxidation (SCWO) of OBDC was comprehensively investigated in a batch reactor under the conditions of various oxygen coefficients (OC, 1.5-3.5), temperatures (T, 400-500°C) and reaction times (t, 0.5-10min). Preheating experiments indicated that most of the organic compounds in the initial OBDC sample were distributed within gaseous, oil, aqueous and solid phases, with no more than 9.8% of organic compounds converted into inorganic carbon. All tested variables, i.e., OC, T and t, positively affect the transformation of carbon compounds from the oil and solid phases to the aqueous phase and, ultimately, to CO₂. Carbon monoxide is the primary stable intermediate. The total organic carbon (TOC) removal efficiency can reach up to 89.2% within 10min at 500°C. Analysis of the reaction pathways suggests both homogeneous and heterogeneous reactions exist in the reactor. The homogeneous reaction is a typical SCWO reaction that is governed by a free radical mechanism, and the heterogeneous reaction is dominated by mass transfer. The information obtained in this study is useful for further investigation and development of hydrothermal treatment procedures for OBDC.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m²/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500μg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

Calcium-catalyzed pyrolysis of lignocellulosic biomass components

The present study examines the effect of calcium pretreatment on pyrolysis of individual lignocellulosic compounds. Previous work has demonstrated that the incorporation of calcium compounds with the feedstock prior to pyrolysis has a significant effect on the oxygen content and stability of the resulting oil. The aim of this work was to further explore the chemistry of calcium-catalyzed pyrolysis. Bench-scale pyrolysis of biomass constituents, including lignin, cellulose and xylan is performed and compared to the oils produced from pyrolysis of the same components after calcium pretreatment. The resulting oils were analyzed by quantitative GC-MS and SEC. These analyses, together with data collected from previous work provide evidence which was used to develop proposed reaction pathways for pyrolysis of calcium-pretreatment biomass.

Investigation of PAA/PVDF-NZVI hybrids for metronidazole removal: synthesis, characterization, and reactivity characteristics

For the first time, the removal process of metronidazole (MNZ) from aqueous solutions over nano zerovalent iron (NZVI) encapsulated within poly(acrylic acid) (PAA)/poly(vinylidene fluoride) (PVDF) membranes was reported. The resultant composite (PPN) demonstrated high reactivity, excellent stability and reusability over the reaction course. Such excellent performance might be attributed to the presence of the charged carboxyl groups in PVDF membrane support, which could enhance NZVI dispersion and improve its longevity. Results showed that a lower initial concentration and higher reaction temperature facilitated the removal of MNZ by PPN, and that the acidic and neutral conditions generally exhibited more favorable effect on MNZ removal than the alkaline ones. Kinetics of the MNZ removal by PPN was found to follow a two-parameter pseudo-first-order decay model well, and the activation energy of the MNZ degradation by PPN was determined to be 30.49kJ/mol. The presence of chloride ions slightly enhanced the reactivity of PPN with MNZ, whereas sulfate ions inhibited its reactivity. In addition, MNZ degradation pathways by PPN were proposed based on the identified intermediates. This study suggests that PPN composite possessing excellent performance may be a promising functional material to pretreat antibiotic wastewaters.