Identification Of Intermediates Research Articles

In situ Reaction Monitoring in Photocatalytic Organic Synthesis

AbstractVisible‐light photocatalysis provides numerous useful methodologies for synthetic organic chemistry. However, the mechanisms of these reactions are often not fully understood. Common mechanistic experiments mainly aim to characterize excited state properties of photocatalysts and their interaction with other species. Recently, in situ reaction monitoring using dedicated techniques was shown to be well‐suited for the identification of intermediates and to obtain kinetic insights, thereby providing more holistic pictures of the reactions of interest. This minireview surveys these technologies and discusses selected examples where reaction monitoring was used to elucidate the mechanism of photocatalytic reactions.

Investigation of hybrid plasma-catalytic degradation of toluene over FeOOH/γ-Al2O3 catalysts

In the present study, FeOOH/γ-Al2O3 catalyst was first introduced into dielectric barrier discharge (DBD) plasma-catalysis system for toluene degradation, and its catalytic performance and mechanism were studied. It was found that the toluene degradation efficiency, energy yield (EY), and COx selectivity were significantly improved in the plasma-FeOOH/γ-Al2O3 system by comparison to the plasma-only process. The ozone concentration detected in this study decreased significantly in plasma-FeOOH/γ-Al2O3 system, which could be concluded that the ozone catalytic process played an important role in the plasma-FeOOH/γ-Al2O3 system for toluene degradation. The toluene and intermediates adsorbed on the surface FeOOH catalysts could react with O* from O3 decomposition and Oads derived from oxygen vacancies, which was conducive to an improved degradation and mineralization performance. Besides, the transformation of O3 to·OH on FeOOH surface was considered as one of the main mechanisms for enhancing toluene degradation when the relative humidity of the background gas was increased from 30% to 50%. The key process parameters, including specific energy input (SEI), catalyst loading, and oxygen content of the background gas, were optimized by response surface methodology (RSM) integrated Box-Behnken design (BBD). The results showed that oxygen content of the background gas was the most significant factor affecting the degradation efficiency of toluene, while energy yield was mainly determined by SEI. The possible toluene degradation pathways in plasma-FeOOH/γ-Al2O3 system were proposed according to the identification of intermediates using GC-MS.

Decreasing dissolved oxygen enhances in situ curtailment of intermediate Cr(VI) during photo-oxidative decomplexation of Cr(III)-EDTA

Cr(III)-organic complexes are stably presented in tanning, electroplating, and other industrial wastewaters, and their safe and efficient removal remains a current challenge. Available oxidation processes can remove Cr(III) complexes but readily result in highly toxic Cr(VI) accumulation. Herein, negligible Cr(VI) accumulation was achieved during photo-oxidation of Cr(III) complexes using a simple strategy of decreasing dissolved oxygen (DO). At the DO concentration of 5.0 mg·L-1 or less, the in-process formation of intermediate Cr(VI) was totally abated by in situ formed reductive species, and total Cr was reduced from 9.0-11.0 mg·L-1 to below 1.0 mg·L-1. A complete curtailment of Cr(VI) was observed after 30-60 min at pH 6.0-9.0. Increasing Cr(III)-EDTA concentration and decreasing pH value facilitated the in situ reduction of intermediate Cr(VI). Based on the identification of intermediates and additional Cr(II) and quenching experiments, the possible key species involved in intermediate Cr(VI) reduction were the photogenerated Cr(II) and some C-centered radicals from Cr(III)-EDTA decomplexation, and the possible mechanisms of Cr(III)-EDTA decomplexation and intermediate Cr(VI) reduction were thus proposed. The process also showed efficient treatment on other Cr(III) complexes (citrate, oxalate, and tartrate) and realistic Cr(III) complexed wastewater. This study would provide an insignificant Cr(VI)-accumulated alternative for efficient and safe removal of Cr(III) complexes from contaminated water.

Waste self-heating bag derived iron-based composite with abundant oxygen vacancies for highly efficient Fenton-like degradation of micropollutants

In this study, iron-rich waste self-heating bag was reutilized as the raw material to prepare oxygen vacancies (OV) functionalized iron-based composite (iron oxide (Fe3O4)-carbon-vermiculite, viz. OV-ICV), which exhibited excellent performance in the Fenton-like degradation of micropollutants via peroxydisulfate (PDS) activation. Above 95% of 1.0 mg/L carbaryl (CB) was efficiently eliminated in the presence of 0.1 g/L of OV-ICV and 0.5 mmol/L of PDS over a wide pH range of 3–10 within 30 min. Besides, OV-ICV also showed acceptable adaptability, stability, and renewability. Imbedding OV into Fe3O4 structure significantly generated more active iron sites and localized electrons, promoted the charge transfer ability, and assisted the redox cycle of ≡Fe(III)/≡Fe(II) for PDS activation. Mechanism investigation demonstrated that superoxide radicals (O2•−) derived from the activation of molecular oxygen mediated the generation of H2O2, and both of them further enhanced the formation of more sulfate radicals (SO4•−) and hydroxyl radicals (•OH), which led to the efficient degradation and mineralization of CB. Furthermore, the degradation pathways of CB were proposed based on the intermediates identification. This work lays a foundation for the rational reutilization of iron-containing wastes modified with defect engineering in heterogeneous Fenton-like catalysis for the remediation of micropollutants wastewater.

Catalyst Complexity in a Highly Active and Selective Wacker-Type Markovnikov Oxidation of Olefins with a Bioinspired Iron Complex

Palladium-catalyzed Wacker-type reactions occupy a central place in organic synthesis with important implications in industry. Pursuing more benign protocols by replacing palladium with first-row transition metals allowed the identification of iron as a privileged one in the last few years. Although the anti-Markovnikov selectivity for iron catalysts is well developed, the Markovnikov-selective reactions still afford significant quantities of alcohol side-products, and identification of reaction intermediates has remained elusive so far. Herein, we present an iron catalyst that affords Markovnikov ketone products from (hetero)aromatic and aliphatic olefins in up to 99% selectivity under ambient conditions with 190,000 turnover numbers and turnover frequencies of 74 h–1 at 50 °C. The catalyst design is based on the promiscuous activity encountered in the family of the cytochromes P-450 enzymes, and it enables the formation of iron-hydride species under catalytically relevant reaction conditions. Substrate scope assessment and mechanistic investigations suggest that the Markovnikov-selective catalytic cycle competes with unprecedented three additional catalytic cycles (alcohol formation, hydrogenation, and reductive homo-coupling) depending on the nature of the olefin and the reaction conditions.

Identification of Intermediates in the Reaction Pathway of SO2 on the CaO Surface: From Physisorption to Sulfite to Sulfate.

The interaction of CaO and Ca(OH)2 with solvated or gaseous SO2 plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO2 from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO2 with a CaO(001) single crystal. First, the surface chemistry of SO2 was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO2 solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas.

Insight into micropollutant abatement during ultraviolet light-emitting diode combined electrochemical process: Reaction mechanism, contributions of reactive species and degradation routes

Electrochemical process coupling with ultraviolet light-emitting diode for micropollutant abatement was evaluated in the treatment of wastewater containing Cl−. Four representative micropollutants, atrazine, primidone, ibuprofen and carbamazepine, were selected as target compounds. The impacts of operating conditions and water matrix on micropollutant degradation were investigated. Fluorescence excitation-emission matrix spectroscopy spectra and high performance size exclusion chromatography were employed to characterize the transformation of effluent organic matter in treatment. The degradation efficiencies of atrazine, primidone, ibuprofen and carbamazepine are 83.6 %, 80.6 %, 68.7 % and 99.8 % after 15 min treatment, respectively. The increment of current, Cl− concentration and ultraviolet irradiance promote the micropollutant degradation. However, the presence of bicarbonate and humic acid inhibit micropollutant degradation. The mechanism of micropollutant abatement was elaborated based on reactive species contributions, density functional theory calculation and degradation routes. Free radicals (HO•, Cl•, ClO• and Cl2•-) could be generated by chlorine photolysis and subsequent propagation reactions. The concentrations of HO• and Cl• are 1.14 × 10−13 M and 2.0 × 10−14 M in optimal condition, respectively, and the total contributions of HO• and Cl• for the degradation of atrazine, primidone, ibuprofen and carbamazepine are 24 %, 48 %, 70 % and 43 %, respectively. The degradation routes of four micropollutants are elucidated based on intermediate identification, Fukui function and frontier orbital theory. Micropollutants can be effectively degraded in actual wastewater effluent, and the small molecule compound proportion increases during effluent organic matter evolution. Compared with photolysis and electrolysis, the coupling of the two processes has potential for energy saving in micropollutant degradation, which shed light on the prospects of ultraviolet light-emitting diode coupling with electrochemical process for effluent treatment.

Photochemical degradation of perfluorooctanoic acid under UV irradiation in the presence of Fe (III)-saturated montmorillonite

Perfluorooctanoic acid (PFOA) has attracted worldwide attention owing to its widespread distribution and potential ecological risks. Developing low-cost, green-chemical and highly efficient treatment approaches is significant for treating PFOA caused environmental issues. Herein, we propose a feasible PFOA degradation strategy under UV irradiation by adding Fe (III)-saturated montmorillonite (Fe-MMT), and the Fe-MMT could be regenerated after reaction. In our system consisting of 1 g L−1 Fe-MMT and 24 μM PFOA, nearly 90 % initial PFOA could be decomposed within 48 h. The enhanced PFOA decomposition could be explained by the ligand-to-metal charge transfer mechanism based on the generated reactive oxygen species (ROSs) and the transformation of iron species in the MMT layers. Moreover, the special PFOA degradation pathway was revealed according to the intermediate identification and the density functional theory calculation. Further experiments demonstrated that even in the presence of co-existing natural organic natter (NOM) and inorganic ions, efficient PFOA removal could still be obtained in UV/Fe-MMT system. This study offers a green-chemical strategy for PFOA removal from contaminated waters.

Photodegradation of Ciprofloxacin and Levofloxacin by Au@ZnONPs-MoS2-rGO Nanocomposites

This study aimed to investigate the photocatalytic performance of diverse zinc oxide catalysts containing gold nanoparticles (AuNPs), molybdenum disulfide (MoS2), and reduced graphene oxide (rGO) toward the degradation of the antibiotics levofloxacin (LFX) and ciprofloxacin (CFX) in aqueous solutions. The obtained results demonstrate that LFX is more resistant to degradation when compared with CFX and that the principal route of degradation under visible light is the formation of hydroxyl radicals. Photoluminescence (PL) measurements were employed to verify the inhibitory effect of electron–hole recombination when AuNPs, MoS2, and rGO are integrated into a semiconductor. The catalyst that achieved the highest percentage of CFX degradation was 1%Au@ZnONPs-3%MoS2-1%rGO, exhibiting a degradation efficiency of 96%, while the catalyst that exhibited the highest percentage of LFX degradation was 5%Au@ZnONPs-3%MoS2-1%rGO, displaying a degradation efficiency of 99.8%. A gas chromatography–mass spectrometry (GC-MS) analysis enabled the identification of reaction intermediates, facilitating the determination of a potential degradation pathway for both antibiotics. Additionally, recyclability assessments showed that the synthesized catalysts maintained stable photocatalytic efficiencies after 15 cycles, indicating that the heterostructures have the potential for further usage and may be tested with other organic contaminants as well.

Bimetal-organic framework MIL-53(Fe,Ni) stimulates peroxydisulfate to degrade rhodamine B: Properties and degradation mechanism

Metal-organic frameworks with high porosity have received much attention in environmental pollutant treatment. This study presented a simple single-pot solvent thermal method for the preparation of a bimetal-organic framework MIL-53(Fe,Ni), further used for activated peroxydisulfate to degrade rhodamine B (RhB). The morphology and structure of the sample were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, photoelectron spectroscopy, fourier transform infrared spectroscopy, and thermogravimetric analysis. The results showed that MIL-53(Fe,Ni) was successfully synthesized by the simple reaction, with high thermal stability and high specific surface area. The effects of pH value, co-existing ions, temperature, humic acid and different real water samples on RhB degradation were systematically investigated. Under optimized conditions, 93.9% of RhB was degraded within 180 min, together with excellent reusability. Quenching experiments and electron paramagnetic resonance showed that both free radicals (∙OH, SO4∙- and O2∙-) and non-free radicals (1O2 and direct charge transfer) were responsible for the RhB degradation. In addition, the identification of intermediates by high-resolution mass spectrometer and reaction site prediction calculations (electrostatic potential, Fukui function and molecular orbit analysis), proposing a possible degradation pathway of RhB. The work highlights the broad applications of bimetal-organic frameworks in advanced oxidation processes.

Microwave electrodeless UV light source combine ozone generation with photocatalytic simultaneous degradation of norfloxacin

This work designed a microwave electrodeless UV light source device integrating ozone generation and photocatalysis (O3 + UV254/TiO2), norfloxacin was selected to evaluate the degradation performance of the device. The degradation and mineralization efficiencies obtained for norfloxacin (10 mg/L, 5 L) treated by the O3 + UV254/TiO2 system for 30 min and 60 min were 82.12% ± 2.84%, 97.00% ± 2.55% and 67.93 ± 0.46%, 75.77 ± 0.26%, respectively, and the highest energy yield obtained at 5 min was 465.53 ± 67.99 mg/kWh. The experiments compared the degradation effects of O3, O3 + UV254 and O3+ UV254/TiO2 treatment of NOR solutions, and the degradation efficiencies obtained at 40 min were 74.51± 2.61%, 77.09 ± 2.12% and 91.63 ± 2.62%, respectively, which showed that O3+ UV254/TiO2 exhibited the best degradation effect. In addition, the effect of coexisting inorganic salts on the degradation efficiency of norfloxacin was investigated. The identification of intermediates by HPLC-Q-TOF-MS proposed four possible degradation pathways. The ring opening of the quinolone group represents a decrease in the antibacterial activity of the norfloxacin drug, indicating that the microwave electrodeless UV light device is a promising alternative strategy for treating effluent containing norfloxacin.

Construction of Cu7 S4 @CuCo2 O4 Yolk-Shell Microspheres Composite and Elucidation of Its Enhanced Photocatalytic Activity, Mechanism, and Pathway for Carbamazepine Degradation.

Water pollution caused by the massive use of medicines has caused significant environmental problems. This work first reports the synthesis and characterization of the Cu7 S4 /CuCo2 O4 (CS/CCO) yolk-shell microspheres via hydrothermal and annealing methods, and then investigates their photocatalytic performance in removing organic water pollutants. The 10-CS/CCO composite with yolk-shell microspheres exhibits the highest photodegradation rate of carbamazepine (CBZ), reaching 96.3% within 2h. The 10-CS/CCO also demonstrates more than two times higher photodegradation rates than the pure (Cu7 S4 ) CS and (CuCo2 O4 ) CCO. This outstanding photocatalytic performance can be attributed to the unique yolk-shell structure and the Z-scheme charge transfer pathway, reducing multiple reflections of the acting light. These factors enhance the light absorption efficiency and efficiently transfer photoexcited charge carriers. In-depth, photocatalytic degradation pathways of CBZ are systematically evaluated via the identification of degradation intermediates with Fukui index calculation. The insights gained from this work can serve as a guideline for developing low-cost and efficient Z-scheme photocatalyst composites with the yolk-shell structure.

Photocatalytic Degradation of Organic and Inorganic Pollutants to Harmless End Products: Assessment of Practical Application Potential for Water and Air Cleaning

It is well-documented that large-scale pollution generated by human activity has a dramatic impact on ecosystems. In this context, removing harmful chemicals via photocatalysis has tremendous potential as a depollution method, utilizing freely available solar light and catalytic materials with low or negligible ecotoxicity. The main drawbacks, which aren’t often addressed in the available literature, are the formation of harmful intermediate products, low reaction rates, limited catalyst stability, and difficult catalyst recovery. In most cases, published works assess the efficiency of tested photocatalysts from pollutant degradation studies, whereas identifying and quantifying by-products is not often conducted. This review summarizes the recent advances reported for the photocatalytic removal of some organic (e.g., alcohols, carboxylic acids, volatile organic compounds, phenol) and inorganic (e.g., NO3−) contaminants. The efficiency of various UV- and visible-light active photocatalysts and the reaction degradation pathways were explained, emphasizing the main factors contributing to their mineralization. The reaction mechanisms, the identification and quantification of degradation intermediates, and the implication of reactive active species (ROS) were discussed and analyzed for each category of model target pollutant. Additionally, the actual challenges and future photocatalytic approaches to improve environmental remediation were presented.

In Situ Probing and Identification of Electrochemical Reaction Intermediates by Floating Electrolytic Electrospray Mass Spectrometry

AbstractThe in‐depth study of electrochemical (EC) synthesis can require a powerful mass spectrometry (MS) analytical platform which can discover and identify fleeting intermediates in EC reactions. Here we report a floating electrolytic electrospray ionization (FE‐ESI) strategy that can perform EC processes in a floating electrolytic cell and monitor intermediates by high‐resolution MS. Compared with previous EC‐MS methods, a significant advantage of FE‐ESI‐MS is that it allows one to modulate the electrolytic and electrospray process individually, ensuring its high sensitivity in discovering intermediates and universality to investigate redox reactions in different scenarios. This powerful platform has been successfully used to investigate the EC reductive coupling of p‐tolylboronic acid and p‐nitrotoluene. A series of nitrene intermediates were discovered and identified by FE‐ESI‐MS, indicating that a hidden mechanism involving nitrene formation might play a key role in EC reductive coupling process.

In Situ Probing and Identification of Electrochemical Reaction Intermediates by Floating Electrolytic Electrospray Mass Spectrometry.

The in-depth study of electrochemical (EC) synthesis can require a powerful mass spectrometry (MS) analytical platform which can discover and identify fleeting intermediates in EC reactions. Here we report a floating electrolytic electrospray ionization (FE-ESI) strategy that can perform EC processes in a floating electrolytic cell and monitor intermediates by high-resolution MS. Compared with previous EC-MS methods, a significant advantage of FE-ESI-MS is that it allows one to modulate the electrolytic and electrospray process individually, ensuring its high sensitivity in discovering intermediates and universality to investigate redox reactions in different scenarios. This powerful platform has been successfully used to investigate the EC reductive coupling of p-tolylboronic acid and p-nitrotoluene. A series of nitrene intermediates were discovered and identified by FE-ESI-MS, indicating that a hidden mechanism involving nitrene formation might play a key role in EC reductive coupling process.

Visible light and iodate/iodide mediated degradation of bisphenol A by self-assembly 3D hierarchical BiOIO3/Bi5O7I Z-scheme heterojunction: Intermediates identification, radical mechanism and DFT calculation

Broadening the light absorption and inhibiting carrier's recombination are vital to the improvement of photocatalytic performance. Herein, self-assembly 3D hierarchical microsphere BiOIO3/Bi5O7I Z-scheme heterojunction with carrier transfer channel was firstly fabricated by in-situ solvothermal method. The degradation efficiency for bisphenol A (BPA) reached 98.9 % within 60 min visible light irradiation. The enhanced photocatalytic activity was benefited from the Z-scheme system assisted by iodate/iodide (IO3-/I-) as carrier transfer channel that not only accelerated the interfacial charge separation, but also provided massive reactive centers for obtaining high redox capacity. The vulnerable sites and the degradation pathways of BPA were identified by density functional theory calculations and liquid chromatography-mass spectrometry analyses. The toxicity of BPA and its intermediates were predicted by ECOlogical Structure Activity Relationship (ECOSAR) and the results demonstrated that BPA was eventually mineralized to harmless products. The Z-scheme charge transfer mechanism was deeply elucidated based on the role of active species (·O2-, ·OH and h+), band structure and carrier separation efficiency. This study provides a promising strategy for the photoactivity enhancement of bismuth based heterojunction in environment purification.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process.

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe2+ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80mM, the Fe2+ concentration of 5mM, the ultrasonic power of 180W, the ultrasonic frequency of 20-25kHz, the temperature of 39℃, the reaction time of 30min, and the COD removal rate reached 81.15%, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na<BQ<t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21mg/L, and the COD value decreased to 80.83mg/L after 60min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Free radical mechanism of toxic organic compound formations from o-chlorophenol.

Organic free radical intermediates are pivotal to our understanding of toxic chemicals formation from chlorophenols that widely exist in thermal processes. However, in most cases, multiple free radical intermediates exist and produce complex spectra that are hard to deconvolute. Identification of free radical intermediates is the current difficulty for detailed formation mechanisms of toxic products from chlorophenols. In this study, a universal bottom-up method was developed to identify the organic free radical intermediates. Candidate organic free radicals were firstly speculated according to the critical parameters obtained from experimental electron paramagnetic resonance (EPR) spectra and the calculated bond dissociation energies of precursors. Their theoretical spectra were then used retrospectively to justify the accordance with the experimental EPR spectra. Identification of the organic free radicals provides straightforward evidence for the formation pathways of pollutants from chlorophenol. Internal factors influencing formation of radical intermediates and the toxic products were also studied, including the ortho effect of the precursor, spin densities of the organic free radical intermediates, and steric hindrance effects of the molecular intermediates. In combination of the experimental results and theoretical calculations, detailed formation mechanisms of toxic pollutants intermediating by organic free radicals from thermal oxidation of chlorophenol were strongly evidenced.

Heterojunction of (P, S) co-doped g-C3N4 and 2D TiO2 for improved carbamazepine and acetaminophen photocatalytic degradation

Novel photocatalysts of phosphorus and sulfur co-doped graphitic carbon nitride incorporated in 2D TiO2 structure were successfully fabricated and applied for solar-driven degradation of emerging pollutants from the group of pharmaceuticals not susceptible to biodegradation. The hybrid photocatalysts with different loadings of (P, S)-doped g-C3N4 were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy (DR/UV–vis), photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The optimum (P, S)-doped g-C3N4/TiO2 (5 %) composite revealed improved photocatalytic activity towards the degradation of carbamazepine and acetaminophen. For CBZ, about 100 % degradation was achieved in less than 30 min of photodegradation, whereas for ACT, the complete removal was observed in 60 min of irradiation under simulated solar light. The multi-anion doped g-C3N4/2D TiO2 composite demonstrated an excellent synergy towards the degradation of CBZ and ACT with a synergy index of 1.35 and 1.62. Moreover, the mineralization efficiency measured as TOC removal was 76 % and 40 % for CBZ and ACT, respectively. The reactive oxygen species responsible for the degradation of selected pharmaceuticals are superoxide (O2–) and hydroxyl radicals (HO), and the kinetics of reactions proved to fit the first-order kinetics with a rate constant of 0.21 min−1 for CBZ degradation and 0.074 min−1 for ACT degradation. Our results suggest that (P, S)-doped g-C3N4/ 2D TiO2 heterostructure is a Z-scheme heterojunction, which can effectively separate photogenerated charge carriers. The emissions and decay times analyzed for single components and the optimal (P, S)-doped g-C3N4/ 2D TiO2 (5 %) composite confirmed interfacial charge transfer between TiO2 nanosheets and (P, S)-g-C3N4 and more effective separation of electron-hole pairs. Identification of carbamazepine and acetaminophen intermediates was performed using LC-MS analysis in combination with additional DFT calculations of the possible by-products formation. Regarding reusability, the photocatalytic activity of (P, S)-doped g-C3N4/ 2D TiO2 (5 %) was stable after subsequent cycles of carbamazepine and acetaminophen degradation.

Adaptation of bacterial community in maize rhizosphere for enhancing dissipation of phthalic acid esters in agricultural soil.

Rhizospheric degradation is a green and in situ strategy to accelerate dissipation of organic pollutants in soils. However, the mechanism on microbial degradation of phthalic acid esters (PAEs) in rhizosphere is still unclear. Here, the bacterial community and function genes in bulk and rhizospheric soils of maize (Zea mays L.) exposed to gradient concentrations of di-(2-ethylhexyl) phthalate (DEHP) were analyzed with 16S rRNA, metagenomic sequencing and quantitative PCR (qPCR). Maize rhizosphere significantly increased the dissipation of DEHP by 4.02-11.5% in comparison with bulk soils. Bacterial community in rhizosphere exhibited more intensive response and shaped its beneficial structure and functions to DEHP stress than that in bulk soils. Both rhizospheric and pollution effects enriched more PAE-degrading bacteria (e.g., Bacillus and Rhizobium) and function genes in rhizosphere than in bulk soil, which played important roles in degradation of PAEs in rhizosphere. The PAE-degrading bacteria (including genera Sphingomonas, Sphingopyxis and Lysobacter) identified as keystone species participated in DEHP biodegradation. Identification of PAE intermediates and metagenomic reconstruction of PAE degradation pathways demonstrated that PAE-degrading bacteria degraded PAEs through cooperation with PAE-degrading and non-PAE-degrading bacteria. This study provides a comprehensive knowledge for the microbial mechanism on the superior dissipation of PAEs in rhizosphere.