Shengtao Xing

Synthesis of MnFe2O4@Mn–Co oxide core–shell nanoparticles and their excellent performance for heavy metal removal

Magnetic nanomaterials that can be easily separated and recycled due to their magnetic properties have received considerable attention in the field of water treatment. However, these nanomaterials usually tend to aggregate and alter their properties. Herein, we report an economical and environmentally friendly method for the synthesis of magnetic nanoparticles with core-shell structure. MnFe2O4 nanoparticles have been successfully coated with amorphous Mn-Co oxide shells. The synthesized MnFe2O4@Mn-Co oxide nanoparticles have highly negatively charged surface in aqueous solution over a wide pH range, thus preventing their aggregation and enhancing their performance for heavy metal cation removal. The adsorption isotherms are well fitted to a Langmuir adsorption model, and the maximal adsorption capacities of Pb(II), Cu(II) and Cd(II) on MnFe2O4@Mn-Co oxide are 481.2, 386.2 and 345.5 mg g(-1), respectively. All the metal ions can be completely removed from the mixed metal ion solutions in a short time. Desorption studies confirm that the adsorbent can be effectively regenerated and reused.

Fabrication of magnetic core–shell nanocomposites with superior performance for water treatment

Magnetic core–shell nanocomposites were synthesized by an economical and environmentally friendly method. The shell materials with the desired composition can be obtained through simple manipulation of precursor adsorption, which can modify their performance for water treatment. The composite containing appropriate amounts of Fe, Mn, and Co oxides exhibits excellent adsorption capability and catalytic activity for removing heavy metal ions and organic pollutants in water. The results suggest that the chemical modification of the shell material is promising for the optimization of pollutants removal by core–shell nanocomposites.

Catalytic ozonation of sulfosalicylic acid over manganese oxide supported on mesoporous ceria.

Manganese oxide supported on mesoporous ceria was prepared and used as catalyst for catalytic ozonation of sulfosalicylic acid (SA). Characterization results indicated that the manganese oxide was mostly incorporated into the pores of ceria. The synthesized catalyst exhibited high activity and stability for the mineralization of SA in aqueous solution by ozone, and more than 95% of total organic carbon was removed in 30 min under various conditions. Mechanism studies indicated that SA was mainly degraded by ozone molecules, and hydroxyl radical reaction played an important role for the degradation of its ozonation products (small molecular organic acids). The manganese oxide in the pores of CeO2 improved the adsorption of small molecular organic acids and the generation of hydroxyl radicals from ozone decomposition, resulting in high TOC removal efficiency.

Synthesis of porous MnO2 hierarchical structures through controlled precursor adsorption

Complex MnO2 nanostructures were prepared through controlled precursor adsorption. The preferential adsorption of a precursor ion leads to the anisotropic growth of crystals, and even produces crystals of different crystal structures. The thus produced primary anisotropic crystals assemble into porous spherical hierarchical 3D architectures.

Characterization and reactivity of Mn–Ce–O composites for catalytic ozonation of antipyrine

Mn–Ce–O composites were prepared by a redox-precipitation method and used as a catalyst for ozonation of antipyrine (AP) in aqueous solution. The phase composition, surface area and electron transfer ability of the products are dependent on the molar ratio of precursors. Mn–Ce–O(8/2) exhibited the highest activity for the degradation and mineralization of AP with ozone, which can be attributed to its high electron transfer ability. The decomposition of ozone into ˙OH can be accelerated through the electron transfer between ozone and catalyst. The refractory intermediates in ozonation and catalytic ozonation were identified and the catalytic performances of Mn–Ce–O(8/2) for these intermediates were also investigated. The hydroxyl radical reaction played an important role in the degradation of the refractory intermediates, and the contribution of surface reactions was strengthened with decreasing pH. A possible mechanism for the catalytic ozonation of AP was proposed.

Mechanism for catalytic ozonation of p-nitrophenol in water with titanate nanotube supported manganese oxide

Manganese oxide supported on titanate nanotubes (TNT) was prepared by an impregnation method and used as a catalyst for ozonation of p-nitrophenol (PNP) in an aqueous solution. Characterization results indicated that the manganese oxide was highly dispersed on the surface of TNT. The synthesized catalyst exhibited high activity for the mineralization of PNP with ozone, and about 95% of the total organic carbon was removed at 45 min. The degradation of PNP was mainly due to the oxidative process in solution, and the hydroxyl radical reaction played an important role for the degradation of its ozonation products (formic acid and oxalic acid). The negatively charged surface and surface acid sites of the support favored the adsorption of ozone, while the highly dispersed MnOx accelerated the decomposition of adsorbed ozone into hydroxyl radicals. A possible mechanism for the catalytic ozonation of PNP was proposed.

Influence of precursor pH on the structure and photo-Fenton performance of Fe/hydrochar

Fe/hydrochar was one-pot synthesized by a hydrothermal method under different pH conditions. The structure, composition and chemical state of the obtained samples were analyzed by different characterization methods. It was found that the precursor pH affected the morphology, surface area, surface Fe content and organic groups of the products. The catalytic performance of the samples for the photo-Fenton decolorization of Orange II with visible light irradiation and the role of dissolved Fe in this process were investigated. The result indicated that the Fe/hydrochar prepared at pH 2 exhibited the highest catalytic activity because of its strong visible light adsorption, high surface Fe content, and rich oxygen-containing groups. The light irradiation accelerated the leaching of Fe and regeneration of Fe2+, and the contribution of homogeneous reactions increased dramatically with reaction time, thus promoting the formation of ˙OH in solution. A possible mechanism for the Fe3+/Fe2+ cycle at the catalyst/water interface was proposed.

FACILE SYNTHESIS OF VARIOUS MANGANESE OXIDES NANO/MICRO-CRYSTALS BY A LIGNOSULFANATE-MEDIATED HYDROTHERMAL PROCESS: EFFECT OF THE REACTANT CONCENTRATION AND SOLUTION MEDIA

Various manganese oxides nano/micro-crystals, including Mn3O4 octahedrons, hierarchical flower-like K-δ-MnO2 microspheres, multi-branch and strip-shaped γ-MnOOH, have been prepared by a lignosulfanate (LSN)-mediated hydrothermal process. The effect of LSN on the structure and morphology has been thoroughly investigated by X-ray powder diffraction and scanning electron microscopy (SEM). The results indicated that stepwise reduction and Ostwalds ripening occurred simultaneously in this hydrothermal process, and LSN could serve as both reducing agent and growth modifier. The appropriate reducing capacity and selective absorption ability of LSN played an important role for the formation of various manganese oxides nano/micro-crystals. The catalytic performance of the products for the oxidation of o-xylene has been also investigated. The result showed that the MnO2 crystals prepared with LSN exhibited the highest catalytic activity.

Comparative study of Cu-based bimetallic oxides for Fenton-like degradation of organic pollutants

In order to provide useful information for the rational design of effective Fenton-like catalyst, a series of Cu-based bimetallic oxides were synthesized and their Fenton-like performances for the degradation of Orange II and ciprofloxacin were compared. The structure, chemical oxidation state, surface charge property and redox ability of the catalysts were also investigated by different characterization techniques. Among them, NiCu exhibited the highest adsorption capacity towards Orange II and the highest activity for the production of OH from H2O2 decomposition, which could be attributed to its high surface area and highly positively charged surface. However, FeCu exhibited the highest activity for the degradation of Orange II. The reason might be that FeCu has more unpaired electrons and higher redox ability, thus promoting the activation of adsorbed Orange II through the electron transfer process. By contrast, NiCu exhibited the highest activity for the removal of ciprofloxacin because ciprofloxacin was mainly degraded by OH. Finally, the main degradation intermediates of Orange II and ciprofloxacin were determined by liquid chromatography-mass spectrometry.

Lignosulfonate-assisted Hydrothermal Synthesis of Mesoporous MnFe2O4 and Fe3O4 for Pb(II) Removal

The development of efficient magnetic adsorbents is highly desirable for water treatment. In this work, MnFe2O4 and Fe3O4 were prepared by a lignosulfonate-assisted hydrothermal method. The structu...