Nitrogen-Doped Reduced Graphene Oxide as a Bifunctional Material for Removing Bisphenols: Synergistic Effect between Adsorption and Catalysis

Facile synthesis of amine-functional reduced graphene oxides as modified quick, easy, cheap, effective, rugged and safe adsorbent for multi-pesticide residues analysis of tea

Amine-functional reduced graphene oxide (amine-rGO) with different carbon chain length amino groups were successfully synthesized. The graphene oxides (GO) reduction as well as amino grafting were achieved simultaneously in one step via a facile solvothermal synthetic strategy. The obtained materials were characterized by X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy to confirm the modification of GO with different amino groups. The adsorption performance of catechins and caffeine from tea acetonitrile extracts on different amine functional rGO samples were evaluated. It was found that tributylamine-functional rGO (tri-BuA-rGO) exhibited the highest adsorption ability for catechins and caffeine compared to GO and other amino group functional rGO samples. It was worth to note that the adsorption capacity of catechins on tri-BuA-rGO was 11 times higher than that of GO (203.7mgg^-1 vs 18.7mgg^-1). Electrostatic interaction, π-π interaction and surface hydrophilic-hydrophobic properties of tri-BuA-rGO played important roles in the adsorption of catechins as well as caffeine. The gravimetric analysis confirmed that the tri-BuA-rGO achieved the highest efficient cleanup preformance compared with traditional dispersive solid phase extraction (dSPE) adsorbents like primary-secondary amine (PSA), graphitized carbon black (GCB) or C18. A multi-pesticides analysis method based on tri-BuA-rGO is validated on 33 representative pesticides in tea using gas chromatography coupled to tandem mass spectrometry or high-performance liquid chromatography coupled with tandem mass spectrometry. The analysis method gave a high coefficient of determination (r²>0.99) for each pesticide and satisfactory recoveries in a range of 72.1-120.5%. Our study demonstrated that amine functional rGO as a new type of QuEChERS adsorbent is expected to be widely applied for analysis of pesticides at trace levels.

Unveiling Adsorption Mechanisms of Organic Pollutants onto Carbon Nanomaterials by Density Functional Theory Computations and Linear Free Energy Relationship Modeling

Predicting adsorption of organic pollutants onto carbon nanomaterials (CNMs) and understanding the adsorption mechanisms are of great importance to assess the environmental behavior and ecological risks of organic pollutants and CNMs. By means of density functional theory (DFT) computations, we investigated the adsorption of 38 organic molecules (aliphatic hydrocarbons, benzene and its derivatives, and polycyclic aromatic hydrocarbons) onto pristine graphene in both gaseous and aqueous phases. Polyparameter linear free energy relationships (pp-LFERs) were developed, which can be employed to predict adsorption energies of aliphatic and aromatic hydrocarbons on graphene. Based on the pp-LFERs, contributions of different interactions to the overall adsorption were estimated. As suggested by the pp-LFERs, the gaseous adsorption energies are mainly governed by dispersion and electrostatic interactions, while the aqueous adsorption energies are mainly determined by dispersion and hydrophobic interactions. It was also revealed that curvature of single-walled carbon nanotubes (SWNTs) exhibits more significant effects than the electronic properties (metallic or semiconducting) on gaseous adsorption energies, and graphene has stronger adsorption abilities than SWNTs. The developed models may pave a promising way for predicting adsorption of environmental chemicals onto CNMs with in silico techniques.

Natural magnetic pyrrhotite as a high-Efficient persulfate activator for micropollutants degradation: Radicals identification and toxicity evaluation

This study discusses the SO₄^- based process mediated by natural magnetic pyrrhotite (NP) for the degradation of refractory organic micropollutants. Complete degradation of 20μM phenol in distilled water (DW) was obtained within 20min using NP/PS (persulfate) system. Electron paramagnetic resonance spectra indicated aerobic and acidic conditions favored the generation of both SO₄^- and OH species, but only OH signal was survived at alkaline condition. The leaked Fe²⁺ and Fe(II) of NP collectively work to activate PS and generate surface and bulk SO₄^- and OH simultaneously. The identified intermediates indicate the transformation of benzene ring is the key step for phenol degradation by NP/PS system. Moreover, phenol degradation was greatly inhibited in surface water (SW, 29%) and wastewater (WW, 1%), but 25.9% and 17.5% of TOC removal were obtained in the SW and WW during NP/PS treatment, respectively. Additionally, the acute toxicity tests for NP/PS process exhibited a fluctuating trend depending on the water matrix, while the genotoxic activity analysis indicated that the treated phenol solutions were not genotoxic but cytotoxic. Overall, this study provides a solution to abate refractory organic micropollutants in water systems.

Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation

Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol^-1). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

In situ synthesis of cobalt ferrites-embedded hollow N-doped carbon as an outstanding catalyst for elimination of organic pollutants

Using polydopamine-metal ions complex as precursor, hollow mesoporous N-doped carbon microspheres encapsulating spinel ferrites nanocrystals (HM-NC/CoFe₂O₄) were facilely prepared with the aim of creating a novel heterogeneous catalyst for sulfate radical-based oxidation of organic contaminants. The surface morphology, structure and composition of HM-NC/CoFe₂O₄ catalyst were thoroughly investigated. The applicability of the catalyst was systematically assessed through numerous controlled trials, several operating parameters, as well as different model pollutants by means of peroxymonosulfate (PMS) activation. Outstanding efficiency and excellent reusability were achieved due to the unique structure and composition of HM-NC/CoFe₂O₄. The HM-NC scaffold with high porosity and surface area not only stabilizes the CoFe₂O₄ nanoparticles but also greatly facilitates the accessibility and adsorption of substrates to the active sites. In addition, both HM-NC and CoFe₂O₄ on the material surface can act as active sites. Sulfate radicals and hydroxyl radicals are identified as main active species and a possible enhancement mechanism of catalytic performance is also proposed. Due to the simple synthesis method, low-cost precursors, unique structure and excellent catalytic activity and stability, this novel composite have great potential as new strategic materials for remediation of water pollution.

Non-photochemical production of singlet oxygen via activation of persulfate by carbon nanotubes

The reaction between persulfate (PS) and carbon nanotubes (CNTs) for the degradation of 2,4-dichlorophenol (2,4-DCP) was investigated. It was demonstrated that CNTs could efficiently activate PS for the degradation of 2,4-DCP. Results suggested that the neither hydroxyl radical (OH) nor sulfate radical (SO₄^-) was produced therein. For the first time, the generation of singlet oxygen (¹O₂) was proved by several methods including electron paramagnetic resonance spectrometry (EPR) and liquid chromatography mass spectrometry measurements. Moreover, the generation of the superoxide radical as a precursor of the singlet oxygen was also confirmed by using certain scavengers and EPR measurement, in which the presence of molecular oxygen was not required as a precursor of ¹O₂. The efficient generation of ¹O₂ using the PS/CNTs system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral conditions with the mineralization and toxicity evaluated. A kinetic model was developed to theoretically evaluate the adsorption and oxidation of 2,4-DCP on the CNTs. Accordingly, a catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PS and CNTs, and the subsequent decomposition of this intermediate into ¹O₂.

Visible Light Assisted Heterogeneous Fenton-Like Degradation of Organic Pollutant via α-FeOOH/Mesoporous Carbon Composites

A novel α-FeOOH/mesoporous carbon (α-FeOOH/MesoC) composite prepared by in situ crystallization of adsorbed ferric ions within carboxyl functionalized mesoporous carbon was developed as a novel visible light assisted heterogeneous Fenton-like catalyst. The visible light active α-FeOOH nanocrystals were encapsulated in the mesoporous frameworks accompanying with surface attached large α-FeOOH microcrystals via C-O-Fe bonding. Assisting with visible light irradiation on α-FeOOH/MesoC, the mineralization efficiency increased owing to the photocatalytic promoted catalyzing H₂O₂ beyond the photothermal effect. The synergistic effect between α-FeOOH and MesoC in α-FeOOH/MesoC composite improved the mineralization efficiency than the mixture catalyst of α-FeOOH and MesoC. The iron leaching is greatly suppressed on the α-FeOOH/MesoC composite. Interestingly, the reused α-FeOOH/MesoC composites showed much higher phenol oxidation and mineralization efficiencies than the fresh catalyst and homogeneous Fenton system (FeSO₄/H₂O₂). The XPS, XRD, FTIR, and textural property results reveal that the great enhancement comes from the interfacial emerged oxygen containing groups between α-FeOOH and MesoC after the first heterogeneous Fenton-like reaction. In summary, visible light induced photocatalysis assisted heterogeneous Fenton-like process in the α-FeOOH/MesoC composite system improved the HO• production efficiency and Fe(III)/Fe(II) cycle and further activated the interfacial catalytic sites, which finally realize an extraordinary higher degradation and mineralization efficiency.

Activation of persulfates by natural magnetic pyrrhotite for water disinfection: Efficiency, mechanisms, and stability

This study introduces natural occurring magnetic pyrrhotite (NP) as an environmentally friendly, easy available, and cost-effective alternative catalyst to activate persulfate (PS) of controlling microbial water contaminants. The E. coli K-12 inactivation kinetics observed in batch experiments was well described with first-order reaction. The optimum inactivation rate (k = 0.47 log/min) attained at a NP dose of 1 g/L and a PS dose of 1 mM, corresponding to total inactivation of 7 log₁₀ cfu/mL cells within 15 min. Measured k increased > 2-fold when temperature increased from 20 to 50 °C; and > 4-fold when pH decreased from 9 to 3. Aerobic conditions were more beneficial to cell inactivation than anaerobic conditions due to more reactive oxygen species (ROS) generated. ROS responsible for the inactivation were identified to be SO₄^- > OH > H₂O₂ based on a positive scavenging test and in situ ROS determination. In situ characterization suggested that PS effectively bind to NP surface was likely to form charge transfer complex (≡Fe(II)⋯O₃SOOSO₃^-), which mediated ROS generation and E. coli K-12 oxidation. The increased cell-envelope lesions consequently aggravated intracellular protein depletion and genome damage to cause definite bacterial death. The NP still maintained good physiochemical structure and stable activity even after 4 cycle. Moreover, NP/PS system also exhibited good E. coli K-12 inactivation efficiency in authentic water matrices like surface water and effluents of secondary wastewater.

Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide

Interaction of phenol and naphthol with reduced graphene oxide (rGO), and their competitive behavior on rGO were examined by batch experiments, spectroscopic analysis and theoretical calculations. The batch sorption showed that the removal percentage of phenol or naphthol on rGO in bisolute systems was significantly lower than those of phenol or naphthol in single-solute systems. However, the overall sorption capacity of rGO in bisolute system was higher than single-solute system, indicating that the rGO was a very suitable material for the simultaneous elimination of organic pollutants from aqueous solutions. The interaction mechanism was mainly π-π interactions and hydrogen bonds, which was evidenced by FTIR, Raman and theoretical calculation. FTIR and Raman showed that a blue shift of C═C and -OH stretching modes and the enhanced intensity ratios of I_D/I_G after phenols sorption. The theoretical calculation indicated that the total hydrogen bond numbers, diffusion constant and solvent accessible surface area of naphthol were higher than those of phenol, indicating higher sorption affinity of rGO for naphthol as compared to phenol. These findings were valuable for elucidating the interaction mechanisms between phenols and graphene-based materials, and provided an essential start in simultaneous removal of organics from wastewater.

Iron encapsulated in 3D N-doped carbon nanotube/porous carbon hybrid from waste biomass for enhanced oxidative activity

Novel iron encapsulated in nitrogen-doped carbon nanotubes (CNTs) supported on porous carbon (Fe@N-C) 3D structured materials for degrading organic pollutants were fabricated from a renewable, low-cost biomass, melamine, and iron salt as the precursors. SEM and TEM micrographs show that iron encapsulated bamboo shaped CNTs are vertically standing on carbon sheets, and thus, a 3D hybrid was formed. The catalytic activities of the prepared samples were thoroughly evaluated by activation of peroxymonosulfate for catalytic oxidation of Orange II solutions. The influences of some reaction conditions (pH, temperature, and concentrations of reactants, peroxymonosulfate, and dye) were extensively evaluated. It was revealed that the adsorption could enrich the pollutant which was then rapidly degraded by the catalytically generated radicals, accelerating the continuous adsorption of residual pollutant. Remarkable carbon structure, introduction of CNTs, and N/Fe doping result in promoted adsorption capability and catalytic performances. Due to the simple synthetic process and cheap carbon precursor, Fe@N-C 3D hybrid can be easily scaled up and promote the development of Fenton-like catalysts.

A 2D-g-C3N4 nanosheet as an eco-friendly adsorbent for various environmental pollutants in water

A novel graphitic carbon nitride (g-C₃N₄) nanosheet adsorbent with a large surface area, remarkable hydrophilicity and high adsorption capacity, was presented for the removal of cadmium ions (Cd²⁺) and methylene blue (MB) from aqueous solution. Adsorption measurements were conducted systematically to study the influences of the contact time, initial concentrations of Cd²⁺ and MB, temperature, and pH value. The maximum adsorption capacities of g-C₃N₄ towards Cd²⁺ and MB were 94.4 and 42.1 mg g^-1, respectively, at 318.5 K when the initial concentrations of Cd²⁺ and MB were 200 and 20 mg L^-1, respectively. The adsorption kinetics fit a pseudo-second-order model. The high adsorption performance of the g-C₃N₄ adsorbent can be attributed to the multiple adsorption sites on g-C₃N₄, including the π-π conjugate interactions and electrostatic attractions with pollutants in water. In addition, it is significant to achieve high adsorption performance of g-C₃N₄ nanosheets by efficiently exposing the adsorption sites by adjusting the microstructure surface properties and dispersity in solution.

Adsorptive removal of bisphenol A (BPA) from aqueous solution: A review

Endocrine-disrupting compounds (EDCs) are an important class of emerging contaminants that have been detected (and are still being detected) in aquatic environments such as surface waters, groundwater, wastewater, runoff, and landfill leachates. Bisphenol A (BPA) is a known endocrine disruptor that is acutely toxic to the living organisms. BPA has been widely used in the manufacture of sunscreen lotions, nail polish, body wash/lotions, bar soaps, shampoo, conditioners, shaving creams, and face lotions/cleanser, besides its other industrial applications. In the present review, an overview of the recent research studies dealing with the BPA removal from water by adsorption method is presented. We have reviewed various conventional and non-conventional adsorbents which have been used for BPA removal from water. It is evident from the literature reviewed that modified adsorbents and composite materials have shown promising results for BPA removal from water. Literature has been extensively discussed in terms of adsorption capacities, fitted isotherm and kinetic models and thermodynamic aspects.

Heterogeneous activation of peroxymonosulfate by amorphous boron for degradation of bisphenol S

Recently, tremendous efforts have been devoted to developing carbon-based metal-free catalysts as an alternative to metal-based catalysts for remediation of emerging contaminants. However, further investigations have demonstrated that the durability of carbocatalysts is poor. Therefore, it is extremely desirable to seek a novel metal-free catalyst with high efficiency and superb stability. Herein, we first discovered that amorphous boron (A-boron) can be used as a metal-free catalyst for peroxymonosulfate (PMS) activation to produce free radicals for effective degradation of bisphenol S (BPS), which is a newly-occurring estrogenic endocrine-disrupting chemical. It exhibited outstanding catalytic activity and superior stability as comparing to metal-based and metal-free carbon-based catalysts. Moreover, many other typical organic pollutants in water such as bisphenol F, sulfamethoxazole, rhodamine B and methyl orange can also be effectively decomposed in A-boron/PMS oxidative system. The effects of reaction parameters on BPS degradation were systematically investigated. The catalytic oxidation mechanism was proposed. The intriguing catalytic feature of A-boron discovered in this study will provide new opportunities for the future development of A-boron based materials with promising applications in water remediation.

Fe/Fe3C@N-doped porous carbon hybrids derived from nano-scale MOFs: robust and enhanced heterogeneous catalyst for peroxymonosulfate activation

Fe/Fe₃C@N-doped porous carbon hybrids were synthesized as a robust and enhanced heterogeneous catalyst for peroxymonosulfate activation.

New insights into the activity of a biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions

To gain insight into the mechanism of p-nitrophenol removal using the biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions, batch experiments and models were conducted.

Substitution Boosts Charge Separation for High Solar-Driven Photocatalytic Performance

Bandgap engineering of photocatalysts is a common approach to achieving high effective utilization of solar resource. However, the difficulty in achieving bandgap narrowing and high activity simultaneously seems to be irreconcilable via the traditional modification pathway. Herein, we have substituted iodine for a fraction of bromine atoms in BiOBr to overcome this restriction and provided some deep-seated insights into how the substitution boosts the photocatalytic properties. The substituted BiOBr_0.75I_0.25 exhibited exceptional photoactivity, with photon-to-current conversion efficiency approximately 6 times greater than TiO₂ in UV region, and more than 10 times higher than BiOBr or BiOI in visible-light region. We found that the substitution narrowed the bandgap, facilitated the diffusion of electron with small effective mass, as well as induced oxygen vacancies on [Bi₂O₂]²⁺ layers. By virtue of the stronger dipole moments produced, the enhancement of intrinsic electric fields between [Bi₂O₂]²⁺ and halogen slabs was achieved in BiOBr_0.75I_0.25; thereby the distance the photogenerated electron could diffuse was sufficient to inhibit the recombination. Our findings not only shed light on the potential properties of hybrid-halide photocatalysts but also provide a strategy for developing high efficiency catalysts.

Iron encapsulated in boron and nitrogen codoped carbon nanotubes as synergistic catalysts for Fenton-like reaction

Iron nanoparticles (NPs) encapsulated in B, N-codoped carbon nanotubes (Fe@C-BN) as heterogeneous Fenton-like catalysts were obtained by a simple and scalable pyrolysis method, and their performances were examined in the oxidative degradation of various organics in the presence of the different oxidants. The results showed that organic dyes can be effectively degraded by Fe@C-BN in the presence of peroxymonosulfate. Calcination temperature and mass of iron salt significantly affected the structures and performances of the catalysts. The effects of several reaction conditions, such as initial dye concentration, oxidant type (peroxymonosulfate, peroxydisulfate, and H2O2) and dosage, initial pH, inorganic anions, reaction temperature and dye types on oxidation as well as the stability of the composite were extensively evaluated in view of the practical applications. Through the investigation of reaction processes, HO(·) and SO4(·-) radicals were identified using quenching experiments. Owing to the synergistic effects between the iron NPs and B, N-doped carbon, Fe@C-BN catalysts intrinsically display an excellent catalytic activity for Fenton-like reaction. This study gives new insights into the design and preparation of iron NPs encapsulated in B, N-codoped carbon nanotubes as an effective strategy to enhance the overall catalytic activity.

Mussel-inspired approach to constructing robust cobalt-embedded N-doped carbon nanosheet toward enhanced sulphate radical-based oxidation

Heterogeneous sulphate radical based advanced oxidation processes (SR-AOPs) have lately been raised as a promising candidate for water treatment. Despite the progress made, either the stability or the performance of the current catalysts is still far from satisfactory for practical applications. Herein, using polydopamine-cobalt ion complex that inspired by mussel proteins as medium, we facilely fabricate a robust SR-AOPs catalyst with cobalt nanoparticles (NPs) embedded in nitrogen-doped reduced graphene oxide matrix (NRGO@Co). The NRGO scaffold with high porosity and surface area not only stabilizes the NPs but also greatly facilitates the accessibility and adsorption of substrates to the active sites. With the synergistic effect arising from the NRGO and Co NPs, the NRGO@Co hybrid catalyst exhibits enhanced catalytic activity for activation of peroxymonosulfate (PMS) to degrade organic pollutants in water. Furthermore, taking advantage of the favorable magnetic properties, the catalyst can be easily recycled and reused for at least 4 runs with negligible loss of activity. Coupled with systematic investigation in terms of influential factors, mineralization, and radicals identification, make the catalyst hold significant potential for application in remediation of organic pollutants in water.

Activated carbon fiber for heterogeneous activation of persulfate: implication for the decolorization of azo dye

Activated carbon fiber (ACF) was used as a green catalyst to activate persulfate (PS) for oxidative decolorization of azo dye. ACF demonstrated a higher activity than activated carbon (AC) to activate PS to decolorize Orange G (OG). The decolorization efficiency of OG increased as ACF loading, PS dosage, and temperature increased. OG decolorization followed a pseudo first-order kinetics, and the activation energy was 40.902 kJ/mol. pH had no apparent effect on OG decolorization. Radical quenching experiments with various radical scavengers (e.g., alcohols, phenol) showed that radical-induced decolorization of OG took place on the surface of ACF, and both SO4 (·-) and HO· were responsible for OG decolorization. The impact of inorganic salts was also evaluated because they are important compositions of dye wastewater. Cl(-) and SO4 (2-) exhibited a promoting effect on OG decolorization, and the accelerating rate increased with elevating dosage of ions. Addition of Cl(-) and SO4 (2-) could increase the adsorption of OG on ACF surface, thus favorable for OG decolorization caused by the surface-bound SO4 (·-) and HO·. Conversely, HCO3 (-) and humic acid (HA) slightly inhibited OG decolorization. The azo band and naphthalene ring on OG were remarkably destructed to other intermediates and finally mineralized to CO2 and H2O.

Fe, Co, Ni nanocrystals encapsulated in nitrogen-doped carbon nanotubes as Fenton-like catalysts for organic pollutant removal

Magnetic metal M (M=Fe, Co, Ni) nanocrystals encapsulated in nitrogen-doped carbon nanotubes (M@N-C) were fabricated conveniently using dicyandiamide as a C/N precursor, and exhibited varying activities toward Fenton-like reaction. The surface morphology and structure of the M@N-C catalysts were characterized and an efficient catalytic degradation performance, high stability, and excellent reusability were observed. In addition, several operational factors, such as initial dye concentration, oxidant type (peroxymonosulfate, peroxydisulfate and H2O2) and dosage, reaction temperature, and dye type as well as stability of the composite were extensively evaluated in view of the practical applications. The results showed that various transition metals M significantly affected the structures and performances of the catalysts, and specially, their activity followed the order of Co>Fe>Ni in the presence of peroxymonosulfate. Moreover, HO⁡ and SO4(-) radicals participating in the process were evidenced using quenching experiments, and a rational mechanism was proposed based on a non-radical process and the free radical process. Control experiments revealed that the enhanced active sites were mainly ascribed to the synergistic effects between the metal nanocrystals and nitrogen-doped carbon. The findings of this study elucidated that encapsulation of nanocrystals in nitrogen-doped carbon nanotubes was an effective strategy to enhance the overall catalytic activity.

Metal-free catalysis of persulfate activation and organic-pollutant degradation by nitrogen-doped graphene and aminated graphene

We evaluated three types of functionalized, graphene-based materials for activating persulfate (PS) and removing (i.e., sorption and oxidation) sulfamethoxazole (SMX) as a model emerging contaminant. Although advanced oxidative water treatment requires PS activation, activation requires energy or chemical inputs, and toxic substances are contained in many catalysts. Graphene-based materials were examined herein as an alternative to metal-based catalysts. Results show that nitrogen-doped graphene (N-GP) and aminated graphene (NH2-GP) can effectively activate PS. Overall, PS activation by graphene oxide was not observed in this study. N-GP (50 mg L(-1)) can rapidly activate PS (1 mM) to remove >99.9% SMX within 3 h, and NH2-GP (50 mg L(-1)) activated PS (1 mM) can also remove 50% SMX within 10 h. SMX sorption and total removal was greater for N-GP, which suggests oxidation was enhanced by increasing proximity to PS activation sites. Increasing pH enhanced the N-GP catalytic ability, and >99.9% SMX removal time decreased from 3 h to 1 h when pH increased from 3 to 9. However, the PS catalytic ability was inhibited at pH 9 for NH2-GP. Increases in ionic strength (100 mM NaCl or Na2SO4) and addition of radical scavengers (500 mM ethanol) both had negligible impacts on SMX removal. With bicarbonate addition (100 mM), while the catalytic ability of N-GP remained unaltered, NH2-GP catalytic ability was inhibited completely. Humic acid (250 mg L(-1)) was partially effective in inhibiting SMX removal in both N-GP and NH2-GP systems. These results have implications for elucidating oxidant catalysis mechanisms, and they quantify the ability of functionalization of graphene with hetero-atom doping to effectively catalyze PS for water treatment of organic pollutants including emerging contaminants.

The mechanism of degradation of bisphenol A using the magnetically separable CuFe2O4/peroxymonosulfate heterogeneous oxidation process

The removal of bisphenol A (BPA) in aqueous solution by an oxidation process involving peroxymonosulfate (PMS) activated by CuFe2O4 magnetic nanoparticles (MNPs) is reported herein. The effects of PMS concentration, CuFe2O4 dosage, initial pH, initial BPA concentration, catalyst addition mode, and anions (Cl(-), F(-), ClO4(-) and H2PO4(-)) on BPA degradation were investigated. Results indicate that nearly complete removal of BPA (50 mg/L) within 60 min and 84.0% TOC removal in 120 min could be achieved at neutral pH by using 0.6 g/L CuFe2O4 MNPs and 0.3 g/L PMS. The generation of reactive radicals (mainly hydroxyl radicals) was confirmed using electron paramagnetic resonance (EPR). Possible mechanisms on the radical generation from CuFe2O4/PMS system are proposed based on the results of radical identification tests and XPS analysis. The lack of inhibition of the reaction by free radical scavengers such as methanol and tert-butyl alcohol suggests that these species may not be generated in the bulk solution, and methylene blue probe experiments confirm that this process does not involve free radical generation. Surface-bound, rather than free radicals generated by a surface catalyzed-redox cycle involving both Fe(III) and Cu(II), are postulated to be responsible for the mineralization of bisphenol A.

Nitrogen- and Sulfur-Codoped Hierarchically Porous Carbon for Adsorptive and Oxidative Removal of Pharmaceutical Contaminants

Heteroatom (nitrogen and sulfur)-codoped porous carbons (N-S-PCs) with high surface areas and hierarchically porous structures were successfully synthesized via direct pyrolysis of a mixture of glucose, sodium bicarbonate, and thiourea. The resulting N-S-PCs exhibit excellent adsorption abilities and are highly efficient for potassium persulfate activation when employed as catalysts for the oxidative degradation of sulfachloropyridazine (SCP) solutions. The adsorption capacities of N-S-PC-2 (which contains 4.51 atom % nitrogen and 0.22 atom % sulfur and exhibits SBET of 1608 m(2) g(-1)) are 73, 7, and 3 times higher than those of graphene oxide, reduced graphene oxide, and commercial single-walled carbon nanotube, respectively. For oxidation, the reaction rate constant of N-S-PC-2 is 0.28 min(-1). This approach not only contributes to the large-scale production and application of high-quality catalysts in water remediation but also provides an innovative strategy for the production of heteroatom-doped PCs for energy applications.

Biotransformations of bisphenols mediated by a novel Arthrobacter sp. strain YC-RL1

Arthrobacter sp. strain YC-RL1, capable of utilizing bisphenol A (BPA) as sole carbon source for growth, was isolated from petroleum contaminated soil. YC-RL1 could rapidly degrade BPA in a wide range of pH (5.0-9.0) and temperature (20-40 °C). Substrate analysis found that YC-RL1 could also degrade bisphenol F (BPF) and tetrabromobisphenol A (TBBPA). The maximum and minimum concentrations of BPA (0.2-600 mg/L), BPF (0.2-600 mg/L), and TBBPA (0.2-300 mg/L) for efficient biodegradation were detected. The released bromide ion and metabolic intermediates of BPF and BPA/TBBPA were detected, as well as the degradation pathways for BPF and BPA/TBBPA were deduced tentatively. The present study provides important information for the investigation of BPs degrading mechanism and the application of microbial remediation in BP-contaminated environment. This study is the first report about a genus Arthrobacter bacterium which could simultaneously degrade BPA, BPF, and TBBPA.