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

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Reduced graphene oxide-metal nanoparticle composite membranes for environmental separation and chloro-organic remediation

This study explores the integration of separation performance of rGO membrane with heterogeneous oxidation reactions for remediation of organic contaminants from water. Herein, an approach was introduced based on layer-by-layer assembly for functionalizing rGO membranes with polyacrylic acid and then by in situ synthesis of Fe based reactive nanoparticles. TEM characterization of the cross-section lamella of the membranes showed a high density of nanoparticles (12% Fe) in the functionalized domain, signifying the importance of polyacrylic acid for in situ synthesis of nanoparticles. The membranes exhibited a pure water permeability of 1.9 LMH bar⁻¹. The membranes had low to moderate salt retention, and more than 90% neutral red retention (organic probe molecule, size: 1.2 nm). The membranes also exhibited high retention of humic acids (80%), preventing these organics from entering the reactive domain, and thus potentially reducing the formation of undesired by-products. A persulfate mediated oxidative pathway was employed to demonstrate the reactive removal of organic contaminants. The membranes achieved >95% conversion by convectively passing 2 mM persulfate feed at a transmembrane pressure of 0.4 bar. Successful degradation of TCE (up to 61%) was achieved in a single pass by convective flowing of the feed solution through the membrane, generating up to 80% of the theoretical maximum chloride as one of the byproducts. Elevated temperatures significantly enhanced persulfate mediated TCE oxidation extent from 24% at 23 °C to 54% at 40 °C under batch operating conditions.

This study explores the integration of separation performance was achieved in a loose nanofiltration regime with heterogeneous oxidation reactions for remediation of organic contaminants from water.

Carbon-based magnetic nanocomposite as catalyst for persulfate activation: a critical review

The activation of persulfate to produce active radicals has been attracting wide attention in environmental remediation fields. Among various catalysts, non-metal carbocatalysts and carbon-based composites have shown attractive prospects given that they are environmental-friendly, highly efficient, abundant, and diverse. In this paper, the use of carbon-based magnetic nanocomposites as catalysts for persulfate activation was reviewed and discussed. The preparation methods of carbon-based magnetic nanocomposites were first briefly summarized. Subsequently, the use of activated carbon, carbon nanotubes, graphene oxide, biochar, and nanodiamond-based magnetic composites to activate persulfate was discussed, respectively. A synergetic effect between carbon materials and magnetic nanoparticles facilitated the activation process because of the increased electron transfer capacity, good dispersity of magnetic nanoparticles, and good repeatability and separability. Both radical and non-radical pathways were detected in the activation processes, but the specific mechanisms were greatly influenced by the components of the catalyst and solution conditions. And fundamental studies were needed to clarify the inner mechanisms of the process. In the end, strategies for enhancing the catalytic performances of carbon-based magnetic nanocomposites were suggested. It is expected that this review will provide some inspirations for developing highly efficient and green catalyst, as well as sulfate radical-based advanced oxidation technology for the remediation water environment.

A Critical Review on Energy Conversion and Environmental Remediation of Photocatalysts with Remodeling Crystal Lattice, Surface, and Interface

Solar energy is a renewable resource that can supply our energy needs in the long term. A semiconductor photocatalysis that is capable of utilizing solar energy has appealed to considerable interests for recent decades, owing to the ability to aim at environmental problems and produce renewal energy. Much effort has been put into the synthesis of a highly efficient semiconductor photocatalyst to promote its real application potential. Hence, we reviewed the most advanced methods and strategies in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e^--h⁺) recombination, while these three processes could be influenced by remodeling the crystal lattice, surface, and interface. Additionally, we individually examined their current applications in energy conversion (i.e., hydrogen evolution, CO₂ reduction, nitrogen fixation, and oriented synthesis) and environmental remediation (i.e., air purification and wastewater treatment). Overall, in this review, we particularly focused on advanced photocatalytic activity with simultaneous wastewater decontamination and energy conversion and further enriched the mechanism by proposing the electron flow and substance conversion. Finally, this review offers the prospects of semiconductor photocatalysts in the following three vital (distinct) aspects: (i) the large-scale preparation of highly efficient photocatalysts, (ii) the development of sustainable photocatalysis systems, and (iii) the optimization of the photocatalytic process for practical application.

Synergetic mediation of reduced graphene oxide and Cu(II) on the oxidation of 2-naphthol in water

Reduced graphene oxide (rGO) is one of the most widely used carbon nanomaterials. When it is released into the environment, rGO can markedly affect the transformation of many pollutants, and change their fate and risk. In this work, the synergetic effects of rGO and Cu(II) on the oxidation of 2-naphthol were examined in water in the dark. It was found that the coexistence of rGO and Cu(II) significantly promoted the oxidation of 2-naphthol. Corresponding products were identified as the coupling oligomers of 2-naphthol (dimer, trimer and tetramer) and hydroxylated compounds (OH-2-naphthol, OH-dimer, di-OH-dimer and naphthoquinone derivatives). In the oxidation reaction, rGO played dual roles, i.e. adsorbent and electron-transfer mediator. rGO firstly adsorbed Cu(II) and 2-naphthol on its surface, and then transferred electrons from 2-naphthol to Cu(II) to yield 2-naphthol radicals and Cu(I). 2-Naphthol radicals coupled to each other to form different oligomers of 2-naphthol. Cu(I) was re-oxidized back to Cu(II) by dissolved oxygen, which sustained the continuous oxidation of 2-naphthol. During the autoxidation of Cu(I), reactive oxygen species were generated, which further reacted with 2-naphthol to form hydroxylated products. These findings provide new insights into the risk assessment of rGO and 2-naphthol in aquatic environments.

A novel graphene oxide-carbon nanotubes anchored α-FeOOH hybrid activated persulfate system for enhanced degradation of Orange II

Persulfate activation has been applied as one of the efficient advanced oxidation processes (AOPs) to remediate polluted environments. In this study, a novel α-FeOOH anchored by graphene oxide (GO)-carbon nanotubes (CNTs) aerogel (α-FeOOH@GCA) nanocomposite activated persulfate system (α-FeOOH@GCA + K₂S₂O₈) was applied for decolorization of Orange II (OII). The decolorization of OII was remarkably enhanced to a level of ~99% in this system compared with that of pristine α-FeOOH (~44%) or GO-CNTs (~18%). The enhanced catalytic activity of α-FeOOH@GCA was due to the formation of a heterojunction by α-FeOOH and GO-CNTs as confirmed by the presence of Fe-O-C chemical bonds. The degradation intermediates of OII were comprehensively identified. The proposed degradation pathway of OII begins with the destruction of the conjugated structures of OII by the dominant reactive oxygen species, surface-bound SO₄^•-. The decolorization efficiency of OII by the α-FeOOH@GCA activated persulfate system decreased from the first to third cycle of recycling. Ultraviolet (UV) irradiation or introduction of a small amount of Fe²⁺ could restore the activation of this system. The results show that the α-FeOOH@GCA persulfate activation system promises to be a highly efficient environmental remediation method for organic pollutants.

Sunflower stalk-derived biochar enhanced thermal activation of persulfate for high efficient oxidation of p-nitrophenol

Sunflower stalk-derived biochars (BC) were prepared at various temperatures (i.e., 500, 650, and 1000 °C) and demonstrated as a highly efficient catalyst in persulfate (PS) activation for the oxidation of p-nitrophenol (PNP) at 60 °C. The apparent PNP oxidation rate constant in the BC500 (0.1543 L mol^-1 S^-1), BC650 (0.6062 L mol^-1 S^-1), or BC1000 (2.1379 L mol^-1 S^-1) containing PS system was about 2, 8 and 28 times higher than that in PS/PNP (0.0751 L mol^-1 S^-1) system, respectively. The effect of reaction temperature on PNP oxidation was also investigated. Furthermore, the radical quenching tests and electron paramagnetic resonance spectroscopy (EPR) were employed to investigate the sulfate and hydroxyl radicals for PNP oxidation. The Raman results suggested that the defective sites on biochars possess vital role for oxidation of PNP in PS system. The possible activation pathway of PS/BC was proposed that the defective sites on BC were involved for weakening the O-O bond in PS and subsequently cleaving O-O bond by heat to generate sulfate radical. The oxidation of PNP at low concentration (below 100 μg L^-1) was completely removed in urban wastewater by PS/BC system within 30 min. This work would provide new insights into PS activation by BC catalyst and afford a promising method for organic pollutant removal in high-temperature wastewater.

One-step synthesis of nitrogen-doped sludge carbon as a bifunctional material for the adsorption and catalytic oxidation of organic pollutants

Nitrogen-doped carbon (NC) materials have been extensively investigated for their great potential applications in adsorption, catalysis, etc. Herein, we report a facile one-step pyrolysis process for NC synthesis using abundant bio-waste of excess sludge as carbon source and cheap precursor of urea as nitrogen source. The developed materials were evaluated for organic pollutants removal through adsorption and catalytic oxidation by peroxymonosulfate (PMS) activation. Experimental results demonstrated that nitrogen doping significantly affected the elemental composition and microstructure of NC, leading to improved adsorption capability as well as PMS activation activity for methylene blue (MB) removal. The adsorption capacity for MB reached 35.831 mg g^-1 over NC-700 sample (NC prepared at 700 °C). In MB catalytic oxidation experiments, effects of sample calcination temperature, catalyst dosage, PMS loading, and co-existing ions were investigated. Under optimal reaction conditions, 98.70% of MB could be removed in 20 min. Through radical quenching and electron spin resonance (ESR) tests, it was confirmed that singlet oxygen (¹O₂) was the main reactive species for MB degradation. Additionally, NC-700 performed well in recycle studies without significant efficiency loss. Other typical organic pollutants including malachite green (MG), methyl orange (MO), bisphenol A (BPA), phenol (PE), and sulfamethoxazole (SMX) could also be removed using NC-700 as adsorbent and catalyst. These features manifest that excess sludge-derived NC could be a promising material for organic pollutants remediation.

Electrochemical activation of peroxymonosulfate with ACF cathode: Kinetics, influencing factors, mechanism, and application potential

The combination of peroxymonosulfate (PMS) and electrolysis with an activated carbon fiber (ACF) as cathode (E-ACF-PMS) was systematically investigated. A synergistic effect was observed in the E-ACF-PMS process. Compared with the E-ACF-PDS process, the E-ACF-PMS process spent one-third as much energy for elimination of carbamazepine (CBZ). Increased PMS concentration, current density, and pH value significantly enhanced CBZ elimination. It was also noted that the presence of phosphate (PO₄^3-), bicarbonate (HCO₃^-), and humic acid (HA) inhibited CBZ removal, while the presence of chloride ion (Cl^-) accelerated it. According to radical scavenging experiments and the estimation of relative contribution, reactive oxygen species oxidation (including OH, SO₄^•-, and ¹O₂) played an important role in CBZ degradation, accounting for 75.67%. We systematically explored the production mechanism for ¹O₂ and the results demonstrated that ¹O₂ was mainly generated on the cathode, rather than generated by O₂^•- or O₂ reported by other researchers. Possible degradation pathways for CBZ in E-ACF-PMS process were also proposed. Finally, the potential for practical applications was explored and compared with E-ACF-PDS. The results of SEM images, BET, and nitrogen adsorption isotherm before and after ACF reuse for 50 times suggested that ACF could maintain its adsorption capacity and catalytic ability in the E-ACF-PMS process. Testing also suggested that the protection of ACF in electrochemical oxidation was based on its relatively high current intensity and removal efficiency. The removal efficiencies of other organic pollutants, including nitrobenzene (NB), sulfamethoxazole (SMX), diclofenac (DC), and tetracycline (TC) were also evaluated. In addition, experiments were conducted to study the effects of different water matrices and toxicology implications and results demonstrated that substituting PMS for PDS in an E-ACF system could create a more efficient, sustainable, and with less secondary toxicity process for wastewater treatment.

Development of Fe-doped g-C3N4/graphite mediated peroxymonosulfate activation for degradation of aromatic pollutants via nonradical pathway

A new composite catalyst, i.e., Fe doped g-C₃N₄/graphite (Fe-CN/G), was successfully constructed to activate peroxymonosulfate (PMS) for efficient phenolic compounds (i.e., p-chlorophenol, 4-CP) degradation in the pH range of 3-10. The optimized Fe-CN/G, i.e., Fe_3.75-CN/G_5.0, was fabricated at the dosage of 3.75 mmol FeCl₃·6H₂O, 5.0 g dicyandiamide, and 5.0 mmol glucose. Fe complexed in the nitrogen pots of Fe_3.75-CN/G_5.0 was demonstrated to be the primary active site for PMS activation, and the introduction of graphite favored the exposure of more accessible active sites in Fe_3.75-CN/G_5.0, suggesting a synergistic effect between the Fe and graphite of Fe_3.75-CN/G_5.0 on 4-CP degradation. Multiple experiments confirmed that sulfate radical (SO₄^-), hydroxyl radical (HO), singlet oxygen (¹O₂) and superoxide radical (O₂^-) exerted negligible contribution on 4-CP degradation. The in-situ Fe K-edge X-ray absorption near-edge structure (XANEX) analysis revealed a redox cycle of Fe in PMS/Fe_3.75-CN/G_5.0, suggesting the formation of high-valent iron-oxo species (Fe^IVO) was responsible for 4-CP degradation. In addition, PMS/Fe_3.75-CN/G_5.0 exhibited acceptable degradation of 4-CP in the presence of coexisting anions and natural organic matters (NOM). We believe this study provides new insights into the design and development of Fe-based heterogeneous catalysts for PMS-based wastewater treatment.

Insights into the oxidation of organic contaminants by iron nanoparticles encapsulated within boron and nitrogen co-doped carbon nanoshell: Catalyzed Fenton-like reaction at natural pH

Iron nanoparticles encapsulated within boron and nitrogen co-doped carbon nanoshell (B/N-C@Fe) were synthesized through a novel and green pyrolysis process using melamine, boric acid, and ferric nitrate as the precursors. The surface morphology, structure, and composition of the B/N-C@Fe materials were thoroughly investigated. The materials were employed as novel catalysts for the activation of potassium monopersulfate triple salt (PMS) for the degradation of levofloxacin (LFX). Linear sweep voltammograms and quenching experiments were used to identify the mechanisms of PMS activation and LFX oxidation by B/N-C@Fe, where SO₄^- as well as HO were proved to be the main radicals for the reaction processes. This study also discussed how the fluvic acid and inorganic anions in the aqueous solutions affected the degradation of LFX and use this method to simulate the degradation in the real wastewater. The synthesized materials showed a high efficiency (85.5% of LFX was degraded), outstanding stability, and excellent reusability (77.7% of LFX was degraded in the 5th run) in the Fenton-like reaction of LFX. In view of these advantages, B/N-C@Fe have great potentials as novel strategic materials for environmental catalysis.

Insights into the mechanism of nonradical reactions of persulfate activated by carbon nanotubes: Activation performance and structure-function relationship

This study aimed to elucidate the intrinsic mechanisms of PS activation by carbon nanotubes (CNTs). Singlet oxygen generation (¹O₂) and direct CNTs-mediated electron transfer were hypothesized to be two major pathways of the oxidation of 2,4-dichlorophenol (2,4-DCP) by PS in the presence of both unmodified and modified CNTs. For the first time, roles of CNT active sites responsible for PS activation were determined using CNT derivatization and structural characterization. By selectively deactivating the carbonyl, hydroxyl or carboxylic groups on CNTs surface and linear sweep voltammetry (LSV) analysis, CO groups were determined to be the main active sites contributing to the direct electron transfer oxidation, while singlet oxygen was generated at CNTs defects. Subsequent UV irradiation was shown to cause the recovery of surface defects with I_D/I_G of CNTs increasing by 21%. This resulted in the regeneration of the performance for the coupled system and allowed for multi-cycle activation of PS by CNTs. These results suggest that CNTs/PS system combined with regeneration based on UV irradiation can be used as an effective alternative process for continuous degradation of recalcitrant aqueous contaminants through the non-radical mechanism.

Cow manure-derived biochar: Its catalytic properties and influential factors

The conversion of waste biomass into biochar is considered as a waste disposal alternative, especially because biochar is a low-cost adsorbent for soil contaminants. However, a risk of desorption of contaminants from biochar may lead to secondary pollution. This study investigated the degradation behavior of soil fumigant, 1,3-dichloropropne (1,3-D), on cow manure-derived biochar (CMB) pyrolyzed at five different temperatures from 300 to 700 °C (termed as C-300 to C-700). Results showed that 1,3-D degradation rate was U-shape related to biochar pyrolysis temperature. Four degradation byproducts (NH₂CH₂CH₂CH₃OH, CH₃CH₂NH₂, NH₂COCONH₂, OHCH₂COOH) were identified by headspace GC-MS. When biochar humidity improved from 0 to 50% or incubation temperature increased from 20 to 40 °C, the degradation of cis-1,3-D on C-300 improved 24.26% and 35.48%, respectively. The OH concentrations, detected by the terephthalic acid method, were considerably higher for C-300 than that for C-700. Pyrolysis temperature (300-700 ° C) governed biochar physicochemical properties and further affected 1,3-D degradation mechanisms (pH-controlled substitution or OH-restricted oxidation reaction). All these findings showed that CMB can adsorb and degrade 1,3-D, thereby reduce its desorption risk, indicative of the conversion of cow manure into biochar as an effective waste management practice.

A nonradical reaction-dominated phenol degradation with peroxydisulfate catalyzed by nitrogen-doped graphene

Nitrogen doping is a common approach for functionalization of graphene to generate active sites for catalytic reactions. However, the effect of nitrogen content and species within nitrogen-doped graphene (NG) on catalytic phenol oxidation remains largely unaddressed, especially for the peroxidisulfate (PDS) system. In this work, graphene (G), NH₃•H₂O-reduced graphene (NG-NH₃), and N₂H₄-reduced graphene (NG-N₂H₄) with different nitrogen contents were synthesized, and their catalytic abilities in inducing PDS was evaluated. The degradation results indicated that nitrogen doping improved the catalytic ability of G and NG-NH₃ shows a higher catalytic ability than NG-N₂H₄, even though they have similar nitrogen contents. Based on the XPS spectra, among all the doped nitrogen species, the graphitic N made the greatest contribution to the catalytic activity. The scavenger and electron paramagnetic resonance results imply a major contribution of a nonradical mechanism in the NG-PDS-phenol reaction system. Finally, the hydroquinone and p-hydroxybenzoic acid were identified as two intermediate products during the degradation. The decrease in total organic carbon concentration (TOC) after reaction confirmed that phenol was mineralized partially in CO₂. These findings will guide the applications of NG as a catalyst and enrich our understanding of the PDS-phenol reaction system.

Insights into Heteroatom-Doped Graphene for Catalytic Ozonation: Active Centers, Reactive Oxygen Species Evolution, and Catalytic Mechanism

To guide the design of novel graphene-based catalysts in catalytic ozonation for micropollutant degradation, the mechanism of catalytic ozonation with heteroatom-doped graphene was clarified. Reduced graphene oxide doped with nitrogen, phosphorus, boron, and sulfur atoms (N-, P-, B-, and S-rGO) were synthesized, and their catalytic ozonation performances were evaluated in the degradation of refractory organics and bromate elimination simultaneously. Doping with heteroatoms, except sulfur, significantly improved the catalytic ozonation activity of graphene. Introducing sulfur atoms destroyed the stability of graphene during ozonation, with the observed partial performance improvement caused by surface adsorption. Degradation pathways for selected refractory organics were proposed based on the intermediates identified using high-resolution Orbitrap mass spectroscopy and gas chromatographic-mass spectroscopy. Three and six new unopened intermediates were identified in benzotriazole and p-chlorobenzoic acid degradation, respectively. Roles of chemical functional groups, doped atoms, free electron, and delocalized π electron of heteroatom-doped graphene in catalytic ozonation were identified, and contributions of these active centers to the formation of reactive oxygen species (ROS), including hydroxyl radicals, superoxide radicals, singlet oxygen, and H₂O₂, were evaluated. A mechanism for catalytic ozonation by heteroatom-doped graphene was proposed for the first time.

Magnetic nitrogen-doped reduced graphene oxide as a novel magnetic solid-phase extraction adsorbent for the separation of bisphenol endocrine disruptors in carbonated beverages

A novel magnetic nitrogen-doped reduced graphene oxide (Fe₃O₄@N-RGO) had been fabricated for the first time on the basis of a simple solvothermal method and then was successfully applied to extract four bisphenol endocrine disruptors (bisphenol A, bisphenol B, bisphenol F and bisphenol AP) in carbonated beverages coupled with high performance liquid chromatography (HPLC). The as-prepared Fe₃O₄@N-RGO was characterized by transmission electron microscopy (TEM), Brunner-Emmet-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS) and vibrating sample magnetometer (VSM). The introduction of nitrogen atoms not only made the wrinkle level of N-RGO increased, but also retarded the irreversible aggregation of graphene sheets. Compared with Fe₃O₄@RGO, Fe₃O₄@N-RGO owned larger specific surface area and more adsorption sites. Hence, Fe₃O₄@N-RGO showed excellent extraction efficiency toward bisphenol endocrine disruptors. The analytical parameters influencing the extraction efficiency were optimized in detail. Under the optimal conditions, a satisfactory performance was obtained. The calibration lines were linear over the concentration in the range of 0.4-1000 μg L^-1 with determination coefficients (r²) between 0.9976 and 0.9996. The limits of detection (LOD) ranged from 0.1 μg L^-1 to 0.2 μg L^-1. The recoveries varied from 86.52% to 101.47% with relative standard deviations (RSDs) less than 8.59%. Overall, the proposed method was an efficient pretreatment and enrichment procedure and could be successfully applied for selective extraction and determination of bisphenol endocrine disruptors in complex matrices.

Efficient degradation of drug ibuprofen through catalytic activation of peroxymonosulfate by Fe3C embedded on carbon

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is becoming an important member of pharmaceuticals and personal care products (PPCPs) as emerging pollutants. To degrade IBU, magnetic Fe₃C nanoparticles embedded on N-doped carbon (Fe₃C/NC) were prepared as a catalyst by a sol-gel combustion method. As characterized, the Fe₃C/NC nanoparticles were composed of a NC nano-sheet and capsulated Fe₃C particles on the sheet. The Fe₃C/NC nanoparticles were confirmed an efficient catalyst for peroxymonosulfate (PMS) activation to generate sulfate radicals (SO₄^•-), single oxygen (¹O₂) and hydroxyl radicals (•OH) toward the degradation of IBU. The added IBU (10 mg/L) was almost completely removed in 30 min by using 0.1 g/L Fe₃C/NC and 2 g/L PMS. The catalyst was confirmed to have good ability and excellent reusability through leaching measurements and cycle experiments. A catalytic mechanism was proposed for the catalytic activation of PMS on Fe₃C/NC, which involves both Fe₃C reactive sites and N-doped carbon matrix as reactive sites in Fe₃C/NC. Moreover, the degradation pathway of IBU in the Fe₃C/NC-PMS system was proposed according to the detections of degradation intermediates.

Adsorption mechanisms of five bisphenol analogues on PVC microplastics

Polyvinyl chloride (PVC) plastics are easily embrittled and decomposed to microplastics in an aquatic environment. The plasticizers such as bisphenol A (BPA), bisphenol S (BPS) and their analogues might be released and adsorbed by the PVC microplastics causing consequential pollution to the ecosystem. Herein, a systematic study was performed to determine the adsorption mechanisms of five bisphenol analogues (BPA, BPS, BPF, BPB and BPAF) on PVC microplastics. The maximum adsorption efficiency reached 0.19 ± 0.02 mg·g^-1 (BPA), 0.15 ± 0.01 mg·g^-1 (BPS), 0.16 ± 0.01 mg·g^-1 (BPF), 0.22 ± 0.01 mg·g^-1 (BPB), and 0.24 ± 0.02 mg·g^-1 (BPAF) at PVC dosage of 1.5 g·L^-1. The kinetics study shows that the adsorption processes can be divided into three stages including external mass transport, intraparticle diffusion and dynamic equilibrium. The isotherm modeling shows a better fit of the adsorption results to the Freundlich isotherm compared to the Langmuir model. The thermodynamic study indicates the adsorption of all bisphenols as exothermic processes. Furthermore, the adsorption mechanisms of bisphenols were explicated intensively, with respect to hydrophobic interactions, electrostatic forces, and noncovalent bonds. A positive effect of hydrophobic interactions was identified for bisphenols adsorption on PVC microplastics, but an obvious inhibition by electrostatic repulsions was revealed for BPF due to its ionization in the neutral solution. In addition, noncovalent bonds (hydrogen and halogen bonds) may promote the adsorption of bisphenols on PVC microplastics. Finally, the desorption and competitive adsorption of five bisphenol analogues on the microplastics were provided together with a perspective for future works.

Application of nickel foam-supported Co3O4-Bi2O3 as a heterogeneous catalyst for BPA removal by peroxymonosulfate activation

Nickel foam (NF)-functionalized Co₃O₄-Bi₂O₃ nanoparticles (CBO@NF) synthesized using a facile one-step microwave-assistant method were employed as catalysts to activate peroxymonosulfate (PMS) with bisphenol A (BPA) as the target pollutant. The crystallinity, morphology, and chemical valence state of the synthesized CBO@NF were analyzed using XRD, SEM, and XPS, respectively. Moreover, effects of the preparation parameters, including the calcination temperature and calcination time as well as the loading dosage, were evaluated in detail. A degradation efficiency of 95.6% was achieved within 30 min with the optimal degradation system. The CBO@NF/PMS system shows great catalytic activity in a pH range from 3.0 to 11.0. The stability and reusability of the CBO@NF supported catalyst was evaluated through a recycling experiment. In addition, the possible degradation mechanism was also explored using a quenching experiment and electron paramagnetic resonance (EPR) detection. The result shows that both the surface-bound SO₄^- and OH play significant roles during the degradation process, where the electron transfer of Co²⁺/Co³⁺, Bi³⁺/Bi⁵⁺, and Ni²⁺/Ni³⁺ realizes the sustained regeneration of the active radicals. This work provides new insight for the practical applications of sulfate radical-based advanced oxidation processes (SR-AOPs) in wastewater treatment.

A versatile strategy to fabricate magnetic dummy molecularly imprinted mesoporous silica particles for specific magnetic separation of bisphenol A

m-DMIMSP showed an ordered mesoporous structure, favorable magnetic property, good accessibility and affinity, and excellent binding selectivity towards BPA.

Facile one-pot synthesis of a porphyrin-based hydrophilic porous organic polymer and application as recyclable absorbent for selective separation of methylene blue

With the development of dye production and printing industry, dyes wastewater has increased dramatically. The resulting environmental pollution problem is increasing seriously. In the present work, a porphyrin-based porous organic polymer (PPOPs-OH) was synthesized by using pyrrole and 2,6-dihydroxynaphthalene-1,5-dicarbaldehyde (DHNDA) as basic building block in situ. This method was cost- and time-efficient, without the participation of metal catalysts. Further reaction of PPOPs-OH with chlorosulfonic acid, a new sulfonic acid functional material (PPOPs-SO₃H) was obtained with the increasing electronegativity and hydrophilicity. PPOPs-SO₃H exhibit good adsorption capacity for methylene blue (MB) from water (980.4 mg g^-1) and excellent selectivity for MB in the present of rhodamine B (RhB) and methyl orange (MO). Mechanism investigation revealed that electrostatic in comparison with π-π interaction is the prominent force in the absorption process. Recycling experiments found the absorption properties of PPOPs-SO₃H did not reduce significantly after several cycles. As a consequence, our findings highlight an appealing opportunities for covalent organic polymers with their potential application as high-efficiency and robust adsorbents for pollutants removal and environmental protection.

Fabrication of graphene-oxide/β-Bi2O3/TiO2/Bi2Ti2O7 heterojuncted nanocomposite and its sonocatalytic degradation for selected pharmaceuticals

A graphene-oxide (GO)/β-Bi₂O₃/TiO₂/Bi₂Ti₂O₇ heterojuncted nanocomposite, designated as GBT, was synthesized via a two-step hydrothermal process. The sonocatalytic activity of the GBT was evaluated at several frequencies (28, 580, and 970 kHz) and compared with Bi-doped GO (GB) and Ti-doped GO (GT). Transmission electron microscopy images showed heterojuncted crystal structures of Bi and Ti on GO, and X-ray diffraction patterns verified that the crystal structures consisted of β-Bi₂O₃, TiO₂, and Bi₂Ti₂O₇ nanocomposites. Energy-dispersive X-ray spectroscopy revealed a higher proportion of metal on GBT surfaces compared with GB and GT surfaces. The energy band gaps of GT, GB, and GBT were 3.0, 2.8, and 2.5 eV, respectively. Two pharmaceuticals (PhACs; carbamazepine [CBZ] and acetaminophen [ACE]) were selected and treated under sonolytic conditions at frequencies of 28, 580, and 970 kHz at a power level of 180 W L^-1. The selected pharmaceuticals, present at initial concentrations of 20 μM, were reduced by over 99% by ultrasonic irradiation in the presence of GBT. The 580 kHz treatment achieved the most rapid organic removal among the frequencies tested. The removal kinetic of CBZ was higher than that of ACE owing to its relatively high hydrophobicity. High sonocatalytic activity of GBT was observed through measurement of H₂O₂ in solution. Because of its low band gaps and high surface activity, GBT exhibited higher sonolytic activity in removing selected PhACs than GT or GB.

Optimization of the catalytic activity of a ZnCo2O4 catalyst in peroxymonosulfate activation for bisphenol A removal using response surface methodology

An effective peroxymonosulfate activator, ZnCo₂O₄, was synthesized through a microwave-assisted method. According to response surface methodology (RSM) using Box-Behnken design (BBD), the effects of four parameters, microwave temperature, microwave time, calcination time and calcination temperature, were investigated, and the results show that both the microwave temperature and calcination temperature have a great influence on the catalytic activity during the preparation process. In addition, a quadratic model is valid for computing and predicting the observed responses. The characteristics of the synthesized ZnCo₂O₄ catalyst were analyzed with various equipments. The results show that the ZnCo₂O₄ nanosheets are cubic crystals with a spinel structure and a high surface area of 105.90 m²‧g^-1. Under the conditions of [ZnCo₂O₄] = 0.2 g‧L^-1 and [PMS]/[BPA]_molar = 2.0, the bisphenol A degradation efficiency reaches 99.28% within 5 min in the ZnCo₂O₄/PMS system. ZnCo₂O₄ possesses great stability and reusability according to recycling experiments. In addition, the possible active radical species were confirmed through quenching experiments and EPR detection, indicating that surface-bound SO₄^- and OH play vital roles during the degradation process.

Co3O4 nanocrystals/3D nitrogen-doped graphene aerogel: A synergistic hybrid for peroxymonosulfate activation toward the degradation of organic pollutants

3D porous Co₃O₄/nitrogen-doped graphene aerogel (NGA) hybrid for heterogeneous activation of peroxymonosulfate (PMS) was prepared by feasible hydrothermal and freeze-drying methods. The morphology, crystal structure and chemical composition of the catalyst were investigated by scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, Raman spectra and Fourier transform infrared spectroscopy. Co₃O₄/NGA at a high N doping level of 7.6% (in atomic percentage) exhibited excellent catalytic performance for acid orange 7 (AO7) degradation, with almost complete removal within 30 min. Moderate PMS content, higher temperature and lower solution pH conditions would facilitate the decomposition of AO7. The catalyst possesses excellent long-term stability and recycling performance with simple separation and post-treatment approaches. Kinetic model was developed to simulate the transformation of main active radical species and the AO7 oxidation profiles, considering effects of coexisting ions (Cl^- and HCO₃^-). Based on results of electron spin resonance, typical quenching tests and kinetic calculation, sulfate radicals play dominate role in AO7 degradation. Co₃O₄ nanocrystals and the new active sites created by nitrogen doping into graphene honeycomb network should synergistically contribute to the high degradation efficiency. This work has expanded the possibility of recyclable catalysts design for heterogeneous activation of PMS, with a dual catalytically active center and desirable stability.

Oxidative degradation of Bisphenol A by carbocatalytic activation of persulfate and peroxymonosulfate with reduced graphene oxide

In the present study, novel metal-free activation of persulfate (PS) and peroxymonosulfate with reduced graphene oxide (rGO) was investigated to degrade Bisphenol A (BPA), one of the most important endocrine disrupting compounds, from different aqueous matrices, namely distilled water (DW) and municipal wastewater treatment plant effluent (TWW). The home-made rGO was characterize and the effect of oxidant (PS and PMS) and catalyst (rGO) concentrations on BPA degradation rates in DW and TWW samples was examined. Complete BPA degradation occurred in DW and TWW with the PS/rGO treatment system after 10 min and 30 min, respectively, whereas 94% (DW) and 83% (TWW) BPA removals were obtained with PMS/rGO for the same treatment period (BPA = 2 mg/L; rGO = 0.02 g/L; PS = 0.25 mM; PMS = 0.5 mM). The radical quenching experiments demonstrated that the SO₄^- predominated in the activation of PS and PMS with rGO for BPA removal, however, HO contributed to the catalytic oxidation process but to a lower extend. The reusability test results, where the catalyst was deactivated seriously just after second cycle, highlighted the need for further studies to enhance the stability of rGO. This study represented an environmentally benign and efficient oxidative treatment of BPA along with insights into the rGO activated PS or PMS processes.

Degradation of aqueous 2,4,4'-Trihydroxybenzophenone by persulfate activated with nitrogen doped carbonaceous materials and the formation of dimer products

In this work, we systematically investigated the persulfate (PS) activation potential of a series of nitrogen doped carbonaceous materials for the degradation of 2,4,4'-trihydroxybenzophenone (2,4,4'-HBP), an additive in polyvinyl acetate films and personal care products. Nitrogen originating from urea, NH₄NO₃, indole and polyaniline was doped into carbonaceous materials, including hydroxylated multi-walled carbon nanotubes (CNT-OH), large-inner thin-walled carboxylated carbon nanotubes (CNT-COOH) and graphite oxide (GO), to examine the catalytic effect. The NH₄NO₃-CNT-OH catalyst, which showed the best catalytic performance in 2,4,4'-HBP removal, was characterized by SEM, TEM, FT-IR, Raman, BET surface area, XRD and XPS, and pyrrolic nitrogen was found to play a highly important role in the activation of PS. Under the conditions of [2,4,4'-HBP]₀: [PS]₀ = 1: 500, T = 25 °C, pH₀ = 7.0, concentration of catalyst = 100 mg L^-1, 43.48 μM 2,4,4'-HBP was completely removed in 2 h. According to electron paramagnetic resonance (EPR) spectra and radical quenching experiments, hydroxyl and sulfate radicals on the surface of the catalyst contributed to the substrate oxidation. Cleavage of C-C bridge bond, hydroxylation and polymerization were mainly involved in the oxidation process, leading to the formation of 10 intermediates (e.g., dimers), as detected by the MS/MS spectra. To the best of our knowledge, this report is the first to describe the transformation mechanism of 2,4,4'-HBP in nitrogen doped carbonaceous materials catalyzed PS system.

Preparation and application of magnetic nitrogen-doped rGO for persulfate activation

A heterogeneous catalyst (M-N-rGO) composed of stability enhanced magnetic iron oxide nanoparticles and nitrogen-doped reduced graphene oxide was synthesized and characterized by SEM, XRD, BET, and XPS. It showed excellent catalytic degradation properties in advanced oxidation technology. In the presence of 200 mg/L catalyst and 135 mg/L persulfate at pH 5, 95% of 10-20 mg/L methylene blue could be degraded in 90 min with the TOC removal efficiency of 50%. The rate constant based on pseudo-first-order kinetics ranged from 0.0227 to 0.0488/min in the temperature range of 15 to 32 °C, and the activation energy was 32.5 kJ/mol. Under the optimal operation conditions, 20 mg/L of 2,4-dichlorophneol (2,4-DCP) could be removed almost completely. EPR analysis showed that sulfate and hydroxyl radicals were responsible for degradation of pollutants, and radical quenching experiments indicated that nonradical pathway also played a role in pollutant removal. And a mechanism for M-N-rGO and persulfate system was elucidated. This catalyst was easy for preparation, low-cost, highly effective, convenient for separation, and could be used effectively for four times through 0.1 mol/L H₂SO₄ regeneration. It provided a choice for wastewater treatment in practice.

Oxidation of Rhodamine B by persulfate activated with porous carbon aerogel through a non-radical mechanism

In this study, porous carbon aerogel (CA) was synthesized with D-glucose, ammonium persulfate and aniline by a hydrothermal carbonization method. It was reported for the first time as an excellent catalyst for activating persulfate (PS) to degrade rhodamine B (RhB). The morphology of CA was characterized, exhibiting microporous and mesoporous structures. The solution pH of 3, 5, 7 and 9 showed slight impact on the degradation of RhB; however, when the pH increased to 11, the removal of RhB decreased. The PS concentration and CA dosage played a key role in the RhB degradation, and the activation energy was calculated to be 22.11 kJ/mol. Electron paramagnetic resonance (EPR) spectra suggested that neither sulfate radical (SO4^-) nor hydroxyl radical (OH) was generated from the PS activation. The radical quenching experiments also confirmed that CA activated PS in a non-radical pathway. It was indicated that PS bonded with CC in the sp² hybridized system could directly degrade RhB. The defective edges at the boundary of CA also facilitated the RhB removal. This work presented a green material with both excellent catalytic performance and high regeneration possibility in the heterogeneous metal-free PS activation, providing a new strategy in water treatment.

Catalytic performance of quinone and graphene-modified polyurethane foam on the decolorization of azo dye Acid Red 18 by Shewanella sp. RQs-106

Quinone-modified graphene powder is not reusable in bio-treatment systems, and the roles of quinone and graphene during extracellular electron-transfer processes remain unclear. In this study, we prepared anthraquinone-2-sulfonate and reduced graphene-oxide-modified polyurethane foam (AQS-rGO-PUF) and found that AQS-rGO-PUF exhibited higher catalytic performance on Acid Red 18 (AR 18) bio-decolorization compared with AQS-PUF and rGO-PUF. We observed a significant synergistic effect between AQS and rGO in AQS-rGO-PUF-mediated system in the presence of 50 μM AQS and 1.63 mg/L rGO. The synergistic effect was mainly attributed to electron transfer from AQS to rGO either directly or via flavins secreted by strain RQs-106, and ultimately to AR 18, accounting for ∼33.47% of AR 18 removal during AQS-rGO-PUF-mediated decolorization. Additionally, AQS-rGO-PUF exhibited good mechanical properties and maintained its macroporous structure. Furthermore, after eight rounds of experiments using AQS-rGO-PUF, the bio-decolorization efficiency of AR 18 retained >98.18% of its original value. These results indicate that the combination of AQS-rGO-PUF and Shewanella strains show potential efficacy for enhancing the treatment of azo-dye-containing wastewater.

Catalytic Removal of Aqueous Contaminants on N-Doped Graphitic Biochars: Inherent Roles of Adsorption and Nonradical Mechanisms

Environmentally friendly and low-cost catalysts are important for the rapid mineralization of organic contaminants in powerful advanced oxidation processes (AOPs). In this study, we reported N-doped graphitic biochars (N-BCs) as low-cost and efficient catalysts for peroxydisulfate (PDS) activation and the degradation of diverse organic pollutants in water treatment, including Orange G, phenol, sulfamethoxazole, and bisphenol A. The biochars at high annealing temperatures (>700 °C) presented highly graphitic nanosheets, large specific surface areas (SSAs), and rich doped nitrogen. In particular, N-BC derived at 900 °C (N-BC900) exhibited the highest degradation rate, which was 39-fold and 6.5-fold of that on N-BC400 and pristine biochar, respectively, and the N-BC900 surpassed most popular metal or nanocarbon catalysts. Different from the radical-based oxidation in N-BC400/PDS via the persistent free radicals (PFRs), singlet oxygen and nonradical pathways (surface-confined activated persulfate-carbon complexes) were discovered to dominate the oxidation processes in N-BC900/PDS. Moreover, the adsorption of organics was determined to be the key step determining reaction rate, revealing that the pre-adsorption of reactants significantly accelerated the nonradical oxidation pathway. This study not only provides robust and cheap carbonaceous materials for environmental remediation but also enables the first insight into the graphitic biochar-based nonradical catalysis.

Persistent free radicals in carbon-based materials on transformation of refractory organic contaminants (ROCs) in water: A critical review

With the increased concentrations and kinds of refractory organic contaminants (ROCs) in aquatic environments, many previous reviews systematically summarized the applications of carbon-based materials in the adsorption and catalytic degradation of ROCs for their economically viable and environmentally friendly behavior. Interestingly, recent studies indicated that carbon-based materials in natural environment can also mediate the transformation of ROCs directly or indirectly due to their abundant persistent free radicals (PFRs). Understanding the formation mechanisms of PFRs in carbo-based materials and their interactions with ROCs is essential to develop their further applications in environment remediation. However, there is no comprehensive review so far about the direct and indirect removal of ROCs mediated by PFRs in amorphous, porous and crystalline carbon-based materials. The review aims to evaluate the formation mechanisms of PFRs in carbon-based materials synthesized through pyrolysis and hydrothermal carbonization processes. The influence of synthesis conditions (temperature and time) and carbon sources on the types as well as the concentrations of PFRs in carbon-based materials are also discussed. In particular, the effects of metals on the concentrations and types of PFRs in carbon-based materials are highlighted because they are considered as the catalysts for the formation of PFRs. The formation mechanisms of reactive species and the further transformation mechanisms of ROCs are briefly summarized, and the surface properties of carbon-based materials including surface area, types and number of functional groups, etc. are found to be the key parameters controlling their activities. However, due to diversity and complexity of carbon-based materials, the exact relationships between the activities of carbon-based materials and PFRs are still uncertain. Finally, the existing problems and current challenges for the ROCs transformation with carbon-based materials are also pointed out.

Magnetic solid-phase extraction for the analysis of bisphenol A, naproxen and triclosan in wastewater samples

Magnetic Fe₃O₄ graphene oxide nanocomposite was synthesized by chemical coprecipitation method and characterized by scanning electron microscopy, Fourier transform infrared spectra and X-ray diffraction. A simple, rapid, convenient and environmentally friendly method was developed for separation and pre-concentration of trace amounts of bisphenol A, naproxen and triclosan in wastewater samples by high performance liquid chromatography with magnetic Fe₃O₄ graphene oxide nanocomposite as the adsorbent for magnetic solid-phase extraction. Various parameters possibly influencing the extraction performance such as amount of the adsorbent, extraction time, sample pH and elution conditions were optimized. Under the optimal working conditions, the developed method showed good linearity (R > 0.9997) in the range of 1-200 μg/L, and the limits of detection are between 0.5 and 0.8 μg/L. The enrichment factors are in the range of 81-89. The repeatability of the method, expressed as relative standard deviation, is 3.36-4.26%.

Adsorption of VOCs on reduced graphene oxide

A modified Hummer's method was adopted for the synthesis of graphene oxide (GO) and reduced graphene oxide (rGO). It was revealed that the modified method is effective for the production of GO and rGO from graphite. Transmission electron microscopy (TEM) images of GO and rGO showed a sheet-like morphology. Because of the presence of oxygenated functional groups on the carbon surface, the interlayer spacing of the prepared GO was higher than that of rGO. The presence of OH and CO groups in the Fourier transform infrared spectra (FTIR) spectrum and G-mode and 2D-mode in Raman spectra confirmed the synthesis of GO and rGO. rGO (292.6m²/g) showed higher surface area than that of GO (236.4m²/g). The prepared rGO was used as an adsorbent for benzene and toluene (model pollutants of volatile organic compounds (VOCs)) under dynamic adsorption/desorption conditions. rGO showed higher adsorption capacity and breakthrough times than GO. The adsorption capacity of rGO for benzene and toluene was 276.4 and 304.4mg/g, respectively. Desorption experiments showed that the spent rGO can be successfully regenerated by heating at 150.0°C. Its excellent adsorption/desorption performance for benzene and toluene makes rGO a potential adsorbent for VOC adsorption.

Metal-Free Carbocatalysis in Advanced Oxidation Reactions

Catalytic processes have remarkably boosted the rapid industrializations in chemical production, energy conversion, and environmental remediation. As one of the emerging applications of carbocatalysis, metal-free nanocarbons have demonstrated promise as catalysts for green remediation technologies to overcome the poor stability and undesirable metal leaching in metal-based advanced oxidation processes (AOPs). Since our reports of heterogeneous activation of persulfates with low-dimensional nanocarbons, the novel oxidative system has raised tremendous interest for degradation of organic contaminants in wastewater without secondary contamination. In this Account, we showcase our recent contributions to metal-free catalysis in advanced oxidation, including design of nanocarbon catalysts, exploration of intrinsic active sites, and identification of reactive species and reaction pathways, and we offer perspectives on carbocatalysis for future environmental applications. The journey starts with the discovery of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by graphene-based materials. With the systematic investigations on most carbon allotropes, for the first time the carbocatalysis for PMS or PDS activation was correlated with the pristine carbon configuration, oxygen functionality (ketonic groups), defect degree (exposed edge sites and vacancies), and dimensional structure. Moreover, an intrinsic difference in catalytic oxidation does exist between PMS and PDS activation. For example, the PMS/carbon reaction is dominated by free radicals, while PDS/carbon catalysis was unveiled as a singlet oxygen- or nonradical-based process in which the surface-activated PDS complex directly degrades the organic pollutants without relying on the generation of free radicals. Nitrogen doping significantly enhances the carbocatalysis because of the positively charged carbon domains, which strongly bind with persulfates to form reactive intermediates toward organic reactions. More importantly, N doping substantially alters the catalytic oxidation from a radical process to a nonradical pathway in PMS activation. Codoping of sulfur or boron with nitrogen at a rational level will synergistically promote the catalysis as a result of the formation of more catalytic centers by improved charge/spin redistribution of the carbon framework. Furthermore, a structure-performance relationship was established for annealed nanodiamonds with a characteristic sp³/sp² (core/shell) hybridization, where the catalytic pathways were intimately dependent on the thickness of the graphitic shells. Interestingly, the introduction of structural defects and N dopants into the well-defined graphitic carbon framework and alteration of graphene/diamond hybrids can transform the persulfate/carbon system from a radical oxidation pathway to a nonradical pathway. Encapsulation of metal nanoparticles within carbon layers further modulates the electronic states of the interacting carbon via charge transport to increase the electron density. Overall, this Account contributes to unveiling the mist of carbocatalysis in AOPs and to summarizing the achievements of metal-free remediation. We also present future research directions on underpinning the knowledge base to facilitate the applications of nanocarbons in sustainable catalysis and environmental chemistry.

New insights into bisphenols removal by nitrogen-rich nanocarbons: Synergistic effect between adsorption and oxidative degradation

In this work, nitrogen-rich graphene-like carbon sheets (N-GLCS) with high specific surface area (488.4m²/g), narrow pore distribution and high N-doping (18.4 at%) were prepared and applied as both adsorbent and catalyst for the removal of bisphenols. Adsorption experiments demonstrated the high adsorption capacities of the N-GLCS toward bisphenol F (BPF) (222.9mg/g), bisphenol A (BPA) (317.8mg/g), and bisphenol C (BPC) (540.4mg/g). Results showed that about 98.6% of BPA (70mg/L) was removed at pH 7.0 within 80min after the adsorption-catalytic degradation process. The N-GLCS also showed a superb reusability for the catalytic oxidative degradation of BPA (70mg/L) with the removal percentage maintains over 83% after 5 cycles. With the synergistic combination of the excellent adsorption and catalytic properties of the N-GLCS, trace amount of pollutants can be preconcentrated and immobilized at the surface of N-GLCs, at the same time, active radicals were also produced at the surface of the N-GLCS by the activation of peroxydisulfate (PS), and finally the pollutants can be degraded in-situ by the active radicals. These findings provide a new avenue towards the efficient removal of trace-level EDCs from water solution by using the coupled adsorption-advanced oxidation processes.

N-doping effectively enhances the adsorption capacity of biochar for heavy metal ions from aqueous solution

N-doping was successfully employed to improve the adsorption capacity of biochar (BC) for Cu²⁺ and Cd²⁺ by direct annealing of crop straws in NH₃. The surface N content of BC increased more than 20 times by N-doping; meanwhile the content of oxidized-N was gradually diminished but graphitic-N was formed and increased with increasing annealing temperature and duration time. After N-doping, a high graphitic-N percentage (46.4%) and S_BET (418.7 m²/g) can be achieved for BC. As a result, the N-doped BC exhibited an excellent adsorption capacity for Cu²⁺ (1.63 mmol g^-1) and Cd²⁺ (1.76 mmol g^-1), which was up to 4.0 times higher than that of the original BC. Furthermore, the adsorption performance of the N-doped BC remained stable even at acidic conditions. A positive correlation can be found between adsorption capacity with the graphitic N content on BC surface. The surface chemistry of N-doped BC before and after the heavy metal ions adsorption was carefully examined by XPS and FTIR techniques, which indicated that the adsorption mechanisms mainly included cation-π bonding and complexation with graphitic-N and hydroxyl groups of carbon surfaces.

Synthesis of cobalt-impregnated carbon composite derived from a renewable resource: Characterization and catalytic performance evaluation

A novel nitrogen-doped biochar embedded with cobalt (Co-NB) was fabricated via pyrolysis of glucose pretreated with melamine (N donor) and Co(II). The Co-NB showed high catalytic capability by converting p-nitrophenol (PNP) into p-aminophenol (PAP) by NaBH₄. The analyses of FE-SEM, TEM, BET, XRD, Raman, and X-ray photoelectron spectroscopy XPS of the Co-NB showed hierarchical porous structure (BET 326.5m²g^-1 and pore volume: 0.2403cm³g^-1) with well-dispersed Co nanoparticles (20-60nm) on the N-doped graphitic biochar surface. The Co-NB showed higher PNP reduction capability compared to the Co-biochar without N-doping, achieving 94.3% removal within 4min at 0.24gL^-1 catalyst dose and initial concentration of 0.35mM PNP. Further conversion experiments under varying environmental conditions (e.g., NaBH₄ concentration (7.5-30mM), biochar dosage (0.12-1.0gL^-1), initial PNP concentration (0.08-0.17mM)) were conducted in batch mode. The reusability of Co-NB was validated by the repetitive conversion experiments (5cycles). The overall results demonstrated biochar potential as catalysts for environmental applications if properly designed.

Synergistic effect of adsorption coupled with catalysis based on graphene-supported MOF hybrid aerogel for promoted removal of dyes

A three-dimensional MIL-100(Fe)/graphene hybrid aerogel (MG-HA) was fabricated via in situ decoration of graphene oxide with MIL-100(Fe) nanoparticles. The resulting MG-HA with interconnected pore structure was applied as both adsorbent and catalyst for the removal of methylene blue (MB) from aqueous solutions. The result shows that the saturation adsorption capacity of the MG-HA was as high as 333.33 mg g⁻¹, exceeding that of both the corresponding pristine graphene aerogel and MIL-100(Fe) nanoparticles. In the presence of hydrogen peroxide, MG-HA further exhibited catalytic degradation ability. The dual functions achieved a synergistic effect leading to the quick and complete removal of MB. The benefit was revealed in the treatment of high concentration of pollutants without leaving secondary pollution. The merit was intuitively demonstrated in the instant removal of MB through a model separation device in comparison with a series of common adsorbents. A feasible mathematic model was built based on the synergistic adsorption/catalysis process, which perfectly fitted the experimental data. A pseudo-second-order adsorption process and pseudo-first-order catalytic degradation kinetics were revealed. Additionally, the MG-HA was able to retain 93.4% of its initial removal efficiency after 5 cycles of application. The macro-material body can be easily separated and reused without a time-consuming and high-cost recycling process.

A three-dimensional MIL-100(Fe)/graphene hybrid aerogel was fabricated for highly efficient removal of dye pollutants via synergistic adsorption and degradation.

Atomic-level design of CoOH+–hydroxyapatite@C catalysts for superfast degradation of organics via peroxymonosulfate activation

In situ formation of CoOH⁺–hydroxyapatite@C via ion exchange between Ca and Co realises the simultaneous adsorption of Co²⁺ and catalytic peroxymonosulfate oxidation for superfast oxidative degradation of organic contaminants.