Yunjin Yao

Sulfate radicals induced from peroxymonosulfate by cobalt manganese oxides (CoxMn3−xO4) for Fenton-Like reaction in water

A series of CoxMn3-xO4 particles as Fenton-like solid catalysts were synthesized, and their catalytic performance in oxidative degradation of organic dye compounds in water was investigated. The surface morphology and structure of the CoxMn3-xO4 catalysts were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that, as an oxide composite of Co and Mn elements, CoMn2O4 showed much stronger catalytic activity in peroxymonosulfate (PMS) oxidation than Co3O4, Mn2O3, and their physical mixture. Typically, the uses of 0.02 g/dm(3) CoMn2O4 and 0.2 g/dm(3) PMS yielded a nearly complete removal of Rhodamine B (0.03 g/dm(3)) in 80 min at 25 °C. The efficiency of Rhodamine B decomposition increased with increasing temperature (15-55 °C), but decreased with the increase of fulvic acid concentration (0-0.08 g/dm(3)). Furthermore, CoMn2O4 could maintain its catalytic activity in the repeated batch experiments. Moreover, HO· and SO4(·-) radicals participating in the process were evidenced using quenching experiments, and a rational mechanism was proposed. PMS oxidation with CoMn2O4 is an efficient technique for remediation of organic contaminants in wastewater.

One-pot approach for synthesis of N-doped TiO2/ZnFe2O4 hybrid as an efficient photocatalyst for degradation of aqueous organic pollutants

N-doped TiO2/ZnFe2O4 catalysts were successfully prepared by coupling nitrogen modified TiO2 with ZnFe2O4 via a one-pot vapor-thermal method. The physicochemical properties of the as-prepared catalysts have been characterized using various spectroscopic and microscopic techniques. The UV-vis-light-driven photocatalytic activities of the hybrids were evaluated and the effects of the amount of photocatalyst, different types of dyes, catalyst stability on photodegradation of organic dyes were investigated. Moreover, degradation kinetics and mechanism as well as the roles of N doping, ZnFe2O4 and TiO2 have been analyzed. It was revealed that N-doped TiO2/ZnFe2O4 exhibited an improved performance compared with TiO2/ZnFe2O4 or ZnFe2O4 because of the formation of a heterostructure at the interface as well as the introduction of N species. Active species such as holes, electrons, hydroxyl radicals, and superoxide radicals involved in the photodegradation process were detected by using different types of scavengers. Because of ZnFe2O4 in the hybrid, the catalyst shows ferromagnetism, and thus, the hybrid catalyst is easily isolated from the reaction mixture after the photocatalytic experiments. This work not only offers a simple method for the fabrication of N doped TiO2/ZnFe2O4 hybrids, but also provides an effective and conveniently recyclable photocatalyst for the purification of water.

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, HOu2061 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.

Enhanced photo-Fenton-like process over Z-scheme CoFe2O4/g-C3N4 Heterostructures under natural indoor light.

Low-cost catalysts with high activity and stability toward producing strongly oxidative species are extremely desirable, but their development still remains a big challenge. Here, we report a novel strategy for the synthesis of a magnetic CoFe2O4/C3N4 hybrid via a simple self-assembly method. The CoFe2O4/C3N4 was utilized as a photo-Fenton-like catalyst for degradation of organic dyes in the presence of H2O2 under natural indoor light irradiation, a green and energy-saving approach for environmental cleaning. It was found the CoFe2O4/C3N4 hybrid with a CoFe2O4: g-C3N4 mass ratio of 2:1 can completely degrade Rhodamine B nearly 100xa0% within 210xa0min under room-light irradiation. The effects of the amount of H2O2 (0.01–0.5xa0M), initial dye concentration (5–20xa0mg/L), solution pH (3.08-10.09), fulvic acid concentration (5–50xa0mg/L), different dyes and catalyst stability on the organic dye degradation were investigated. The introduction of CoFe2O4 on g-C3N4 produced an enhanced separation efficiency of photogenerated electronxa0−xa0hole pairs by a Z-scheme mechanism between the interfaces of g-C3N4 and CoFe2O4, leading to an excellent activity as compared with either g-C3N4 or CoFe2O4 and their mixture. This study demonstrates an efficient way to construct the low-cost magnetic CoFe2O4/C3N4 heterojunction as a typical Z-scheme system in environmental remediation.

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.

Heteroatoms doped metal iron–polyvinylidene fluoride (PVDF) membrane for enhancing oxidation of organic contaminants

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. Membranes 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.

Modulation of rectifying behaviour by oxygen contents in La0.5Sr0.5CoO3−δ/0.7 wt% Nb-doped SrTiO3 heterojunctions

Heterojunctions composed of La0.5Sr0.5CoO3−δ and 0.7 wt% Nb-doped SrTiO3 were deposited at different oxygen partial pressures and display opposite rectifying shapes: the junctions fabricated at a lower oxygen pressure show a backward shape and they gradually display a forward shape by tuning up the oxygen partial pressures. The former tends to form degenerate p–n junctions due to oxygen deficiency, which is responsible for the backward rectifying shape. The latter, however, can be viewed as a Schottky-type diode. The oxygen contents for the junctions can be estimated from their x-ray diffraction patterns, and are also confirmed from their resistance and magnetization measurements.

Activation of persulfates by catalytic nickel nanoparticles supported on N-doped carbon nanofibers for degradation of organic pollutants in water

An N-doped carbon nanofiber cloth (CC) with anchored nickel nanoparticles (Ni@N-CC) was synthesized from a facile pyrolysis process and employed as a catalyst to oxidize target contaminants using peroxydisulfate (PDS) as both radical precursors and electron acceptors. An effective strategy was developed to control the porous structures and catalytic performances by optimizing the precursor weights and pyrolysis temperatures for Ni@N-CC preparation. The optimal temperature was 700u202f°C, and the best dicyanodiamine mass was 1.0u202fg. Ni@N-CC was found to be superior for PDS activation to CC and nickel nanoparticles (NPs), ascribing to highly active sites, intimate connection between the nickel NPs and highly conductive N-doped CC, as well as the formed three-dimensional architecture. The oxidation rates were influenced by the oxidant loading (0.185-1.11u202fmM), initial organics concentration (10-50u202fmg/L), temperature (5-45u202f°C), pH (2.65-10.47), and inorganic anions. Furthermore, mechanistic investigations using various probe reagents and spin trapping technique identified the generation of several active species for oxidation. The reaction was found to proceed via the electron transfer mediation from organics to PDS on N-doped CC and one electron reduction of PDS on Ni0 NPs. This study highlights the design of highly active and reusable heterogeneous carbon/metal hybrids for more efficient PDS activation in environmental remediation.