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.

•Ni embedded in N-doped CNTs supported on porous carbon was prepared via pyrolysis.•Ni0 catalyzed the growth of intertwined CNTs on carbon layer affording 3D materials.•Ni@N-C displayed catalytic capability for removal of organics and toxic CrVI.•Ni@N-C maintained good structure and stable activity even after several cycles.•Remarkable carbon structure and N/Ni-doping promoted catalytic activity.Novel “sea urchin”-like Ni nanoparticles embedded in N-doped carbon nanotubes (CNTs) supported on porous carbon (Ni@N-C) 3D materials derived from waste biomass were prepared via pyrolysis and employed as an environmentally friendly, easy available and cost-effective catalyst for removal of toxic pollutants. The characterizations indicated that Ni0 catalyzed the growth of intertwined CNTs on carbon layers, affording abundant porous structures and larger specific surface area. With the synergistic effect of embedded Ni0 nanoparticles, nitrogen doping, hierarchical micro-mesopores, and interconnected CNTs, Ni@N-C displayed a superior catalytic capability for the oxidation of organic pollutants using peroxymonosulfate as an oxidant, and catalytic reduction of toxic CrVI to nontoxic CrIII by formic acid as a reducing agent. It was found that pyrolysis temperatures affected the compositions, morphologies, and catalytic properties of Ni@N-C. Inactive oxidized N species have transformed to the highly active graphitic N, pyridinic-N, and Ni-O-N clusters, thereby improving the catalytic activity. Moreover, Ni@N-C maintained good physicochemical structure and stable activity even after several cycles of reactions. The simple synthetic strategies, 3D structure, and remarkable performance of Ni@N-C composites make them serve as alternative environmentally friendly catalysts for removal of pollutants.Download high-res image (299KB)Download full-size image

•NSC-Fe-X@PVDF catalytic membranes were fabricated by phase inversion technique.•Hierarchical structures are formed by anchoring NSC-Fe-X NPs on PVDF membranes.•Catalytic performance of NSC-Fe-X@PVDF was affected by several key parameters.•Sulfate and hydroxyl radicals are responsible for this persulfate-driven oxidation.•Morphological and structural features of membrane enhance catalytic activity.Iron nanoparticles (NPs) embedded in S, N-codoped carbon were prepared by one-step pyrolysis of a homogeneous mixture consisting of Fe, S, N, C precursors, and then immobilized in poly (vinylidene fluoride) membranes as a multifunctional catalytic system (NSC-Fe@PVDF) to effectively activate peroxymonosulfate (PMS) and oxidize organic compounds in water. The NSC-Fe@PVDF membranes effectively decolorized organic pollutants at a wide pH range (2.05-10.85), due to the synergistic effects between the S, N-doped carbon and iron NPs. The efficiency depended on the doping types, amount of metal, PMS dosages, reaction temperatures, solution pHs, and organic substrates. In-situ electron spin resonance spectroscopy and sacrificial-reagent incorporated catalysis indicate radical intermediates such as sulfate and hydroxyl radicals are mainly responsible for this persulfate-driven oxidation of organic compounds. Membrane’s porous structure and high internal surface area not only minimize the NPs agglomeration, but also allow the facile transport of catalytic reactants to the active surface of metal catalysts. The results demonstrate the morphological and structural features of catalytic membranes enhance the overall catalytic activity.

Magnetic ZnFe2O4–C3N4 hybrids were successfully synthesized through a simple reflux treatment of ZnFe2O4 nanoparticles (NPs) (ca. 19.1 nm) with graphitic C3N4 sheets in methanol at 90 °C, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. Also, the catalytic activities of heterogeneous ZnFe2O4–C3N4 catalysts were evaluated in photo-Fenton discoloration toward Orange II using H2O2 as an oxidant under visible light (λ > 420 nm) irradiation. The reaction kinetics, degradation mechanism, and catalyst stability, as well as the roles of ZnFe2O4 and C3N4 in photoreaction, were comprehensively studied. It was found that the ZnFe2O4–C3N4 photocatalysts presented remarkable catalytic ability at neutral conditions, which is a great advantage over the traditional Fenton system (Fe2+/H2O2). The ZnFe2O4–C3N4 hybrid (mass ratio of ZnFe2O4/g-C3N4 = 2:3) exhibits the highest degradation rate of 0.012 min–1, which is nearly 2.4 times higher than that of the simple mixture of g-C3N4 and ZnFe2O4 NPs. g-C3N4 acted as not only a p-conjugated material for the heterojunction formation with ZnFe2O4, but also a catalyst for the decomposition of H2O2 to ·OH radicals. The heterogeneous ZnFe2O4–C3N4 hybrid exhibited stable performance without losing activity after five successive runs, showing a promising application for the photo-oxidative degradation of organic contaminants.

A magnetic ZnFe2O4–reduced graphene oxide (rGO) hybrid was successfully developed as a heterogeneous catalyst for photo-Fenton-like decolorization of various dyes using peroxymonosulfate (PMS) as an oxidant under visible light irradiation. Through an in situ chemical deposition and reduction, ZnFe2O4 nanoparticles (NPs) with an average size of 23.7 nm were anchored uniformly on rGO sheets to form a ZnFe2O4–rGO hybrid. The catalytic activities in oxidative decomposition of organic dyes were evaluated. The reaction kinetics, effect of ion species and strength, catalytic stability, degradation mechanism, as well as the roles of ZnFe2O4 and graphene were also studied. ZnFe2O4–rGO showed to be a promising photocatalyst with magnetism for the oxidative degradation of aqueous organic pollutants and simple separation. The combination of ZnFe2O4 NPs with graphene sheets leads to a much higher catalytic activity than pure ZnFe2O4. Graphene acted as not only a support and stabilizer for ZnFe2O4 to prevent them from aggregation, largely improving the charge separation in the hybrid material, but also a catalyst for activating PMS to produce sulfate radicals at the same time. The ZnFe2O4–rGO hybrid exhibited stable performance without losing activity after five successive runs.

•Co(OH)2–reduced graphene oxide (rGO) was synthesized by a one-pot hydrothermal method.•Phenol degradation rate of Co(OH)2–rGO using peroxymonosulfate was faster than Co(OH)2.•Kinetics of phenol degradation on Co(OH)2–rGO follows a first-order model.•A mechanism for phenol degradation was presented.A cobalt hydroxide (Co(OH)2) nanoflake-reduced graphene oxide (rGO) hybrid was synthesized by a one-pot hydrothermal method using glucose as a reducing agent for graphene oxide (GO) reduction. The structural and surface properties of the material were investigated by scanning and transmission electron microscopies, energy-dispersive X-ray spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Catalytic activities of GO, rGO, Co(OH)2 and Co(OH)2–rGO in aqueous phenol degradation using peroxymonosulfate as an oxidant were compared. A synergetic effect on the catalytic activity was found on the Co(OH)2–rGO hybrid. Although rGO has weak catalytic activity, Co(OH)2–rGO hybrid showed a higher catalytic activity than Co(OH)2. The phenol degradation on Co(OH)2–rGO was extremely fast and took around 10 min for 100% phenol removal. The degradation was found to follow the first order kinetics and a mechanism for phenol degradation was presented.Graphical abstract

Magnetic cobalt nanoparticles (NPs) at a size of approximately 29.9 nm anchored on graphene sheets were prepared and tested for heterogeneous oxidation of a dyeing pollutant, Orange II, with peroxymonosulfate (PMS) in aqueous solutions. The physicochemical properties of Co–graphene hybrids were investigated by various characterization techniques, such as powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The incorporation of Co NPs and graphene sheets produces much higher catalytic activity of Orange II degradation than pure Co. The Orange II decomposition rate increases with increasing temperature (25–45 °C), pH (4–10), and PMS dosage (0.04–0.60 g/L) but decreases with its increased concentration (30–120 mg/L). Kinetic studies show decomposition of Orange II on Co–graphene can be described by a pseudo-first-order kinetic model with activation energy of 49.5 kJ/mol.

Mn3O4–reduced graphene oxide (rGO) hybrids were synthesized, and their catalytic performance in heterogeneous activation of peroxymonosulfate (PMS) to oxidize a target pollutant, Orange II, in aqueous solutions was investigated. The surface morphology and structure of the Mn3O4–rGO hybrids were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Through an in situ chemical deposition and reduction, Mn3O4–rGO hybrids with Mn3O4 nanoparticles at an average size of 29.2 nm were produced. The catalytic activity in Orange II oxidative decomposition was evaluated in view of the effects of various processes, pH, PMS concentration, Orange II concentration, and temperature. The combination of Mn3O4 nanoparticles with graphene sheets leads to a much higher catalytic activity than that of pure Mn3O4 or rGO. Graphene was found to play an important role in Mn3O4 dispersion and decomposition of Orange II. Typically, 30 mg/L of Orange II could be completely oxidized in 120 min at 25 °C and 0.05 g/L of Mn3O4–rGO hybrids, showing a promising application of the catalyst in the oxidative degradation of aqueous organic pollutants. The efficiency of Orange II decomposition increased with increasing temperature (25–55 °C), pH (4.0–11.0), and PMS dosage (0.25–1.5 g/L), but it decreased with increasing initial Orange II concentration (30–90 mg/L). Mn3O4–rGO hybrids exhibited stable performance without losing activity after four successive runs.

Amino-functionalized Fe3O4/SiO2 core/shell nanoparticles were synthesized by reacting Fe3O4 nanoparticles with tetraethyl orthosilicate and (3-aminopropyl) triethoxysilane to introduce amino groups on the surface. The amino groups on the Fe3O4/SiO2 were reacted with the carboxylic groups of graphene oxide (GO) with the aid of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinnimide to form Fe3O4/SiO2GO nanoparticles. The structural, surface, and magnetic characteristics of the material were investigated by scanning and transmission electron microscopy, energy-dispersive X-ray spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Adsorption equilibrium and kinetics of methylene blue on the Fe3O4/SiO2GO were studied in a batch system. The maximum adsorption capacities were found to be 97.0, 102.6, and 111.1 mg g−1 at 25, 45, and 60 °C, respectively. A second-order kinetic equation could best describe the sorption kinetics. Thermodynamic parameters indicated that the adsorption of methylene blue onto the material was thermodynamically feasible and could occur spontaneously.Graphical abstractHighlights► Nanoparticles were developed by immobilizing Fe3O4@SiO2 on graphene oxide. ► Adsorption properties toward methylene blue in aqueous solution were investigated. ► The maximum adsorption capacities were found to be 111.1 mg/g at 60 °C.

This paper reports the synthesis of magnetic CoFe2O4–reduced graphene oxide (rGO) hybrids and the catalytic performance in heterogeneous activation of peroxymonosulfate (PMS) for decomposition of phenol. The surface morphologies and structures of the CoFe2O4–rGO hybrids were investigated by field emission scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), transmission electron microscopies(TEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption–desorption isotherm, and thermogravimetric analysis (TGA). Through an in situ chemical deposition and reduction, CoFe2O4–rGO hybrids with CoFe2O4 nanoparticles of 23.8 nm were produced. Catalytic testing showed CoFe2O4–rGO hybrids exhibited much better catalytic activity than CoFe2O4, which suggests rGO plays an important role in CoFe2O4–rGO hybrids for the decomposition of phenol. Moreover, the hybrid catalyst presents good magnetism and could be separated from solution by a magnet.

This paper reports the synthesis of Co3O4–reduced graphene oxide (rGO) hybrids and the catalytic performance in heterogeneous activation of peroxymonosulfate (PMS) for the decomposition of phenol. The surface morphologies and structures of the Co3O4–rGO hybrids were investigated by field emission scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Through an in situ chemical deposition and reduction, Co3O4–rGO hybrids with Co3O4 nanoparticles at an average size of 33 nm were produced. Catalytic testing showed that 20 mg/L of phenol could be completely oxidized in 20 min at 25 °C on Co3O4–rGO hybrids, which is mostly attributed to the generation of sulfate radicals through Co3O4-mediated activation of PMS. Phenol oxidation was fitted by a pseudo-zero-order kinetic model. The rate constant was found to increase with increasing temperature and PMS dosage, but to decrease with increasing initial phenol concentration. The combination of Co3O4 nanoparticles with graphene sheets leads to much higher catalytic activity than pure Co3O4. rGO plays an important role in Co3O4 dispersion and decomposition of phenol.