Catalytic activity and mechanism of F- and Cl-doped graphene for peroxymonosulfate activation to remove tetracycline hydrochloride.

Highly active catalysts with salt and acid/alkali resistance are desired in peroxymonosulfate (PMS) activation processes and marine environment applications. F- and Cl-doped graphene (F-GN and Cl-GN) were prepared via electronegative and atom radius adjustment for tetracycline hydrochloride (TCH) pollution removal to satisfy these requirements. The introduction of special F and Cl functionalities into graphene exhibits superior electron transfer properties for PMS activation, considering the experimental and density functional theory (DFT) calculation results. The TCH degradation efficiency reached up to 80% under various pH and salt disturbance conditions with F-GN and Cl-GN. Cl-GN exhibited an activity superior to F-GN due to the higher electron polarization effect of C atoms adjacent to Cl atoms. The presence of more positive charged C sites in Cl-GN (around Cl doping) is more favorable for PMS attachment and sequence radical generation than F-GN. In addition, the main active species functionalized during reaction included ·OH and SO4-·, and the stability of F-GN and Cl-GN was confirmed to be over 60% by recycle test. Final research results provide an effective strategy for designing and preparing PMS activators resistant to salt, acid, and alkali, thereby expanding their application potential.

Elucidating the roles of Ni ions and crosslinking heteroatoms in Ni3(BHT)2/2GO as electron shuttles for electrocatalytic oxidation of tetracycline hydrochloride.

As a hot candidate for marine pollution control, electrocatalytic oxidation strongly depends on the characteristics of anode materials. Even though emerging 2D metal-organic frameworks (2D-MOFs)/graphene oxide (GO) complex has satisfied the conductive and tunable requirements of anode, electrocatalytic efficiency still needs to be improved by maximizing the electron carriers or shuttles. Herein, we capitalized upon crosslinking heteroatoms as pointcut to adjust the electron distribution, mobility, and transfer orientation in 2D-MOFs/GO. As a result, Ni3(BHT)2/2GO (metal centers: Ni; crosslinking heteroatoms: S), which was much higher than materials with metal centers of Cu or crosslinking heteroatoms of N, achieved superior conductivity and 100% tetracycline hydrochloride removal within 12 min. In Ni3(BHT)2/2GO, Ni ions and S atoms cooperated as electron shutters rather than isolated active center and granted accelerated electron transfer from 2D-MOFs to GO layers. Furthermore, Ni sites and S crosslinking heteroatoms exhibited superior activity for ⋅O2- and ⋅OH generation, whereas 1O2 depended more on C and O substrates. All experiments, theory calculations, and application expanding approved the practice feasibility of 2D-MOFs/GO in electrocatalytic oxidation by adjusting crosslinking heteroatoms. All these results provided new perspectives on the micro-molecular regulation for improving electrocatalytic efficiency.

Modulating Cu valence state in Cu and graphene oxide composites for electrocatalytic tetracycline hydrochloride degradation.

Cu and graphene oxide composites (Cu-GO) were designed by anchoring Cu+ via oxygen groups in GO based on the heavy co-relationships of copper (Cu) anode electrocatalytic activity with Cu valence state. With the consumption of oxygen groups under various pyrolysis temperatures, the Cu valence state changed from Cu ions (as CuCl2 and CuCl) to Cu oxide (CuO and Cu2O) and the final metallic Cu. In which the Cu+ in CuCl was more favorable for electrocatalytic oxidation than other Cu valence states. Due to the dramatic contribution of 1O2 and active chlorine, 100% degradation efficiency was achieved using tetracycline hydrochloride (TCH) as the target pollutant. Cu+ showed a selective preference for 1O2 and active chlorine triggering, rather than metallic Cu. Under the attack of 1O2 and active chlorine, the degradation intermediates of TCH were then provided by LC-MS results. The final results not only prove the feasibility of the Cu-GO/electrocatalysis system for pollution control but also shed light on the anode design via Cu valence state modulation.

Cu3(hexaamino triphenylhexane)2/reduced graphene oxide composites with boosting electron-transfer properties for acetaminophen electrocatalytic degradation.

Electron-transfer properties, as great contributors for electrocatalytic oxidation on the anode, are crucial to pollution degradation. The strong relationship between electron-transfer properties and active species (such as radicals) generation of anode catalysts suggests a new strategy for pollution-degradation efficiency improvement. In this study, a novel composite of Cu3(hexaamino triphenylhexane)2 [Cu3(HITP)2] and reduced graphene oxide (RGO) was synthesized to construct electron-transfer pathways between the two layers. Benefiting from the connection formed through RGO-O-N-Cu, the electron transfer from RGO to Cu3(HITP)2 was accelerated. The resettled charge distribution led the C atoms in the RGO layer, and the Cu and C atoms in Cu3(HITP)2 layer acted as the main surface active sites. O2•-, 1O2, and reactive chlorine were then triggered to boost the degradation of acetaminophen. The source of O2•- and 1O2 was more likely from surface oxygen groups rather than dissolved O2. Overall, this research provided a perspective proof of conductive Cu3(HITP)2/RGO composite construction with 2D/2D structure for electrocatalytic-oxidation improvement.

Mechanism exploration of highly conductive Ni-metal organic frameworks/reduced graphene oxide heterostructure for electrocatalytic degradation of paracetamol: Functions of metal sites, organic ligands, and rGO basement.

The highly conductive Ni-metal-organic framework/reduced graphene oxide (Ni-MOG/rGO) heterostructure shows an excellent catalytic activity through the modification of active sites, considerably enabling the electron transfer between rGO and Ni-MOF. However, the detailed mechanisms, i.e., the functions of separate metal sites and organic ligands and electron transfer orientation between Ni-MOFs and rGO, remain to be discussed. Here, the electrocatalytic mechanism of Ni-MOF/rGO was experimentally analyzed on the basis of the density functional theory. The dominant active sites of radical and nonradical generation were determined. Findings indicated that radicals (O2•- and •OH) and nonradicals (1O2 and active chlorine) contributed to paracetamol (APAP) degradation. Moreover, metal sites (Ni) were favorable to generate O2•- and partly •OH to initiate the reaction. By contrast, organic frameworks in Ni-MOF and rGO basement favored to generate •OH and nonradicals (1O2 and active chlorine). In this case, N sites (in Ni-MOF), which seized electrons from Ni sites, acted as the primary bonding bridge to accelerate the electron transfer from rGO to Ni-MOF. This study provided essential information to decipher the mechanism of Ni-MOF/rGO heterostructure applicable to the electrocatalytic system.

Mechanism and efficiency research of P- and N-codoped graphene for enhanced paracetamol electrocatalytic degradation.

Electrocatalytic oxidation is an effective technology for treatment of refractory organic pollutants, and its performance strongly depends on anode materials. Among all anode materials, graphene (GN) owns the advantages of high stability and lack of secondary pollution. The catalytic performance of GN can be further improved through heteroatom doping. Here, P/N-codoped graphene (PN-GN) materials were optimized and used as an anode material for 4-acetamidophenol (APAP) electrocatalytic degradation. Result indicated that PN-GN had lower internal resistance, larger specific surface area, and higher electrochemical activity than single-doped graphene materials. The catalytic activity of GN was greatly improved by P/N codoping. When PN-GN (P8.4%-N7.6%-500 °C) was used as catalyst (current of 20 mA, initial pH of 7, reaction time of 60 min), the degradation efficiency of APAP reached 98.2% ± 1.8%, which was 17.9% ± 3.6% higher than P-codoped graphene (P-GN), 14.7% ± 4.6% higher than N-codoped graphene (N-GN), and 54.0% ± 5.2% higher than GN. After 180 min of reaction, the degradation efficiency of total organic carbon (TOC) was 78.5%. The reaction conditions were optimized and the degradation pathway of APAP was estimated to elucidate the catalytic mechanism. The main active substances generated in the system were identified as active chlorine and O2•-.

Paracetamol degradation via electrocatalysis with B and N co-doped reduced graphene oxide: Insight into the mechanism on catalyst surface and in solution.

This paper presents the use of B and N co-doped reduced graphene oxide (BN-GN) as an electrode for paracetamol electrochemical degradation. The reaction mechanism, focused on active sites in the atom level and dominant radical species generated through the reaction, was analyzed by characterization, density functional theory (DFT) calculation, quenching experiments, and electron paramagnetic resonance analysis. The characterization results indicated that the introduction of N and B functionalities into GN improved catalytic activity due to the generation of new surface defects, active sites, and improvement of conductivity. Results of experiments and DFT showed that co-doping of B and N greatly improved the catalytic activity, and the B atoms in C-N-B groups were identified as main active sites. The main active substances of BN-GN generated in the electrocatalytic oxidation of paracetamol in the solution were O2•- and active chlorine. The influence of O2•- and active chlorine on the efficiency/path of catalytic oxidation and the proposed mechanism were also determined for paracetamol degradation. This study provides an in-depth understanding of the mechanism of BN-GN catalysis and suggests possibilities for practical applications.

Facilely Prepared Cl-Doped Graphene as an Efficient Anode for the Electrochemical Catalytic Degradation of Acetaminophen.

The application of electrochemical catalytic oxidation in wastewater treatment with powerful Cldoped graphene as an anode has been discussed as a novel approach to degrade acetaminophen effectively. The characteristics of Cl-doped graphene that were related to Cl loading content and microscopic morphology were analyzed by using several instruments, and the defects created by Cl doping were identified. Quenching experiments and electron paramagnetic resonance detection were proposed to clarify the mechanism underlying the production of active free radicals by Cldopedgraphene. The degradation results indicated that efficiency increased with the percentage of Cl atoms doped into the graphene. The best degradation efficiency of acetaminophen could reach 98% when Cl-GN-12 was used. In the process of electrocatalytic oxidation, O•-2, and active chlorine, as the main active species, persistently attacked acetaminophen into open-ring intermediates, such as 4-chlororesorcinol, and finally into CO2 and H²O.

[Degradation of RBK5 by High Crystallinity Mn-Fe LDH Catalyst Activating Peroxymonosulfate].

High crystallinity Mn-Fe LDH was synthesized by improved co-precipitation combined with the hydrothermal method and was utilized as a catalyst for peroxymonosulfate (PMS) activation to degrade reactive black 5. The high crystal purity and clear lamellar structure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The operating parameters such as Mn/Fe molar ratio, catalyst dosage, PMS concentration, and initial pH value on the absorption efficiency, catalytic degradation, and reaction kinetics of RBK5 were also investigated. The results demonstrated that high crystallinity Mn-Fe LDH has good adsorption capacity and high catalytic efficiency. The degradation efficiency of RBK5 (20 mg·L-1) could reach 86% within 90 min when the Mn/Fe molar ratio was 1, the catalyst dosage was 0.2 g·L-1, the PMS concentration was 1 mmol·L-1, and the initial pH value was 7.0. The reaction process follows pseudo-first-order reaction kinetics (R2>0.9). In addition, the quenching experiment indicated that SO4-·and·OH were the main active species that degraded RBK5 from the Mn-Fe LDH/PMS system. The XPS analysis of the catalyst before and after the reaction confirmed the synergistic effect between Mn and Fe. The charge balance between Mn(Ⅱ) and Fe(Ⅲ) on the LDH surface and CO32- in layers stabilized the structure, thus promoting the synergistic effect of Mn and Fe on the lamellar surface and improving the activation efficiency of PMS by Mn-Fe LDH. Three-dimensional fluorescence and the UV-Vis scanning spectral analysis were preliminarily discussed to understand the degradation process of RBK5.

Sulfur doped-graphene for enhanced acetaminophen degradation via electro-catalytic activation: Efficiency and mechanism.

Although graphene exhibited excellent performance, its capability of electrochemical catalytic oxidation would significantly improve by modification via sulfur (S)-doping. However, due to the complicated doping species of heteroatoms, the detailed mechanism was still remained open for discussion. Thus, this first-attempt study tended to decipher such mechanism behind the direct and indirect oxidation by analyzing S species in S-graphene. The density functional theory (DFT) was adopted for reactive center calculation and confirmation of secondary active species, to discuss the degradation pathway. As the experimental and calculation results, the thiophene structure S was more favorable for electron acceptation in direct oxidation. Chloride reactive species, as the most effective secondary functionalities (rather than •OH), were favorably generated on the edge doped S position than thiophene structured S in defects, to further trigger the indirect oxidation. However, the extensive contents of reactive functionalities could act as trap for self-annihilation of chloride reactive species, resulting in poor electrocatalytic degradation of the pollutants. This study deepened the understanding of heteroatoms doping for electrochemical catalytic oxidation.

Preparation of Pt/TiO2/Graphene/Polyethylene Sheets via a Facile Molding Process for Azo Dye Electrodegradation.

As the characterizations of electrode are meaningful for electric catalytic efficiency and mechanism, the improvement of electrode have raised considerable public concern in recent decades. However, the metal electrode have the drawbacks of high price and easy for toxicity, nano electrode restricted by difficulties for electrode coating, possibility of agglomeration, and abscission during reactions. Focus on those defects, the proposed study is going to establish a useful technique for polymer combined nano-electrode preparation. The morphology, functional groups, and other characterization of the Pt/TiO2/graphene particles and organic composite nano Pt/TiO2/graphene sheets were analyzed by transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), electrochemical impedance spectroscopy (EIS). To identify the stability of self-prepared electrodes, parameters such as catalysts dosage, current density and pH will be analyzed by using RBK5 as target pollutions. The results shows that after treatment for 50 min under optimized conditions (20 mA, 1 g/L NaCl), the degradation rate of acetaminophen almost reached 100%. After five times recycle, the self-prepared electrode could still maintained a high removal rate of 90%.

[Degradation of RBk5 with Peroxymonosulfate Efficiently Activated by N-Doped Graphene].

The large loss of catalysts and secondary pollution problems are bottlenecks for the utilization of persulfate advanced oxidation processes. Thus, a modified Hummers method combined with a hydrothermal method was used to prepare N-doped graphene as a catalyst for peroxymonosulfate (PMS) activation. The produced sulfate radical (SO4-·) and hydroxyl radical (·OH) were able to degrade RBk5. N-doped graphene was characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The influences of vital parameters (i. e., initial pH, catalyst dosage, and PMS dosage) on RBk5 removal were investigated systematically to examine the catalytic performance. The results showed that the N element doping can effectively improve the catalytic activity of graphene, and the activity is greatly affected by the N doping ratio. The initial pH of the wastewater had no significant effect on the degradation efficiency. Under the condition of 1.5 g·L-1 catalyst dosage and 0.3 g·L-1 PMS dosage, the removal rate of RBk5 dye reached 99% after 25 min of reaction. The reaction process accorded with first-order reaction kinetics. Radical quenching experiments were done and indicated that the degradation of RBk5 in N-doped graphene/PMS systems was a surface reaction, and SO4-· and ·OH were identified as the main radical species. The catalyst exhibited excellent stability over five successive degradation cycles.

Catalytic performance and mechanism of graphene electrode doped with S and N heteroatoms for N-(4-hydroxyphenyl)ethanamide electrochemical degradation.

As operation performance of electro-oxidation is strongly influenced by feature of anode materials, apparently oriented preparation of electrode materials to maximize stable degradation efficiency would be top-priority consideration for system optimization. Recently, heteroatoms hybrid graphene is well known as one of major matrices popularly constructed onto anode modification due to its excellent electronic properties and long-term operation stability. The novelty focused on the first proposed competitive interactions between N and S species on graphene edges for improving operation efficiency. Due to the complicated characteristics of heteroatoms hybrid graphene, the mechanism of synergistic or antagonistic interactions of different heteroatoms was still open to be explored. To clarify the functions of S and N heteroatoms on graphene electrode, N and S co-doped graphene were prepared by hydrothermal method. Analyses upon characterization of materials, dominant radical species reacted through reaction, density functional theory (DFT) calculation, N-(4-hydroxyphenyl)ethanamide degradation pathway and the influence of heteroatom species on the efficiency/path of electrocatalytic oxidation and proposed mechanism were determined. The findings indicated that S doped graphene had more promising electrocatalytic activity than N, and that the co-existence of S and N converted the N species from pyrrolic N (the N species with the highest activity) into graphitic N (the N species with the least activity). Apparently, the activity of S was also repressed. With S and N co-doping, active sites for direct electrocatalytic oxidation was possibly properly placed at carbon atoms with S or hydroxyl group. Moreover, the S species and hydroxyl groups are more favorable for indirect electrocatalytic oxidation via HO• and active chlorine species generation. The analysis in-depth with the proposed mechanism was suggested as guideline for optimal design of functional electrodes.

Kinetic study of Reactive Black 5 degradation by Fe2+/S2O82- process via interactive model-based response surface methodology.

This study aimed to kinetically discover optimal conditions on characteristics of Reactive Black 5 decolorization/degradation via ferrous (Fe2+)-activated potassium persulfate (PS). Monod-like kinetics and interactive model-based response surface methodology (RSM) were applied to fitting and predict optimize treatment. Biodegradability of the intermediates was also tested by shaking culture with two species (Proteus hauseri ZMd44 and Shewanella sp. WLP72). Results showed that the optimal degradation efficiency was predicted (through RSM) as pH 3.72, (PS) = 0.39 mM, and (Fe2+) = 0.29 mM. The transformation products (dl-4-hydroxymandelic acid, benzoic acid, benzene, formic acid, oxalic acid and acetic acid) were less toxic than the original dye solution. According to those results, clean-up of dye pollutants by the Fe2+/S2O82- process is feasible as a pre-processing for the biodegradation, and the predicted optimal conditions are meaningful for further industry utilization.

Mechanism and toxicity research of benzalkonium chloride oxidation in aqueous solution by H2O2/Fe(2+) process.

As widely used disinfectants, the pollution caused by benzalkonium chloride (BAC) has attracted a lot of attention in recent years. Since it is not suitable for biodegradation, BAC was degraded firstly by Fenton advanced oxidation technologies (AOTs) in this research to enhance the biodegradability of the pollutions. The result revealed that the optimal molar ratio of H2O2/Fe(2+) for BAC degradation was 10:1, and the COD removal rate was 32 %. To clarify the pathway of degradation, the technique of GC-MS was implemented herein to identify intermediates and the toxicity of those BAC intermediates were also novelty tested through microbial fuel cells (MFC). The findings indicated that ten transformation products including benzyl dimethyl amine and dodecane were formed during the H2O2/Fe(2+) processes, which means the degradation pathway of BAC was initiated both on the hydrophobic (alkyl chain) and hydrophilic (benzyl and ammonium moiety) region of the surfactant. The toxicity of BAC before and after treated by Fenton process was monitored through MFC system. The electricity generation was improved 337 % after BAC was treated by H2O2/Fe(2+) oxidation processes which indicated that the toxicity of those intermediates were much lower than BAC. The mechanism and toxicity research in this paper could provide the in-depth understanding to the pathway of BAC degradation and proved the possibility of AOTs for the pretreatment of a biodegradation process.

Unraveling characteristics of nutrient removal and microbial community in a novel aerated landscape - Activated sludge ecological system.

In this study, a novel landscape-activated sludge ecological system (LASeM) was constructed with the advantages of promising treatment, less land need and significant landscape services. Compared to literature, this study provided promising integrated wastewater treatment and landscape for wastewater treatment. This first-attempt study clearly deciphered interactive effect of aeration rate (AR) on nutrient removal and microbial community structure in LASeM. When AR was 0.016m(3)h(-1), the most appropriate removal of COD, NH4(+)-N and TP were 96%, 97% and 74% with the effluent of 14.3, 1.7 and 0.7mgL(-1), respectively, which showed satisfactory capabilities for rural domestic wastewater treatment. According to clone library analysis, Proteobacteria (71%), Bacteroidetes (17%) were found to be the dominant bacterial phylums present in LASeM for biodegradation. In particular, the incorporation of plants altered the microbial community and strengthened capability for the nutrients removal likely due to synergistic interactions among species in the ecosystem.

Comparative isocline analysis upon microbial decolorization in immobilized cell bioreactor using biocarriers.

This study used various biocarriers (e.g., porites corals, Biolite™, porous ceramic filter media (PCFM)) to immobilize cells in fixed bed bioreactor (FBB) for wastewater decolorization. As prior studies proposed, an innovative graphical method of constant-slope isoclines to determine maximal allowable treatment capacity (MATC) was used as screening criteria for feasibility of packing matrices of immobilized cell systems (ICSs). Moreover, detailed inspection upon physical and chemical characteristics of packing matrices was also carried out to confirm the consistency of MTAC. The result of isocline analysis was in parallel with physical characteristics of biocarriers (i.e., porites coral>Biolite™>PCFM). This first-attempt study successfully provided perspective in general terms to assess how the selected supporting materials were suitable to be packing matrices of ICSs for industrial applications (e.g., wastewater treatment).