Zichuan Ma

Efficient disinfection of Escherichia coli in water by silver loaded alumina

Abstract The catalytic inactivation of Escherichia coli (E. coli) in water by silver loaded alumina as catalyst was investigated. Ag/Al2O3 and AgCl/Al2O3 catalysts exhibited high bactericidal activity at room temperature in water with no need for any light or electrical power input. Dissolved oxygen which can be catalyzed to reactive oxygen species (ROS) was found to be essential for the strong bactericidal activities of the catalysts. Decomposition of the cell wall leading to leakage of the intracellular component and the complete lysis of the whole cell were directly observed by transmission electron microscopy (TEM). The resultant change in cell permeability was confirmed by potassium ion leakage. The different morphological changes between E. coli cells treated with the catalysts and Ag+ were also observed. The formation of ROS involved in the bactericidal process by AgCl/Al2O3 was confirmed by addition of catalase and OH scavenger. Higher temperature and pH value were found to have positive effect on the bactericidal activity of AgCl/Al2O3. All these results indicated that the bactericidal effect of the catalyst was a synergic action of ROS and Ag+, not an additive one. A possible mechanism is proposed.

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.

Removal of heavy metal ions from aqueous solution using red loess as an adsorbent

The adsorption behaviors of heavy metals onto novel low-cost adsorbent, red loess, were investigated. Red loess was characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectra. The results indicated that red loess mainly consisted of silicate, ferric and aluminum oxides. Solution pH, adsorbent dosage, initial metal concentration, contact time and temperature significantly influenced the efficiency of heavy metals removal. The adsorption reached equilibrium at 4 hr, and the experimental equilibrium data were fitted to Langmuir monolayer adsorption model. The adsorption of Cu(II) and Zn(II) onto red loess was endothermic, while the adsorption of Pb(II) was exothermic. The maximum adsorption capacities of red loess for Pb(II), Cu(II) and Zn(II) were estimated to be 113.6, 34.2 and 17.5 mg/g, respectively at 25 degrees C and pH 6. The maximum removal efficiencies were 100% for Pb(II) at pH 7, 100% for Cu(II) at pH 8, and 80% for Zn(II) at pH 8. The used adsorbents were readily regenerated using dilute HCl solution, indicating that red loess has a high reusability. All the above results demonstrated that red loess could be used as a possible alternative low-cost adsorbent for the removal of heavy metals from aqueous solution.

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.

Removal of bromate ion using powdered activated carbon.

Bromate ion (BrO3-) removal from drinking water by powdered activated carbons (PACs) in bath mode was evaluated under various operational conditions. Six kinds of PACs, including wood-based carbon, fruit-based carbon, coal-based carbon, and these three carbons thermally deoxidized in a nitrogen atmosphere, were selected to investigate their capacity on BrO3- removal. With the highest zeta potential value and being richly mesoporous, coal-based carbon had a high and an excellent BrO3- adsorption efficiency. The removal content of BrO3- by per gram of coal-based carbon was 0.45 mg within 5 hr in 100 microg/L bromate solution. The surface characteristics of PACs and bromide formation revealed that both physical and chemical PACs properties simultaneously affected the adsorption-reduction process. Under acidic conditions, PACs possessed high zeta value and adequate basic groups and exhibited neutral or positive charges, promoting BrO3- adsorption-reduction on the carbon surface. Interestingly, the PACs thermally deoxidized in N2 atmosphere optimized their properties, e.g. increasing their zeta values and decreasing the oxygen content which accelerated the BrO3- removal rate. The maximum adsorption capacity of fruit-based carbon was the highest among all tested carbons (99.6 mg/g), possibly due to its highest pore volume. Remarkably, the thermal regeneration of PACs in N2 atmosphere could completely recover the adsorption capacity of PACs. The kinetic data obtained from carbons was analyzed using pseudo second-order and intraparticle diffusion models, with results showing that the intraparticle diffusion was the more applicable model to describe adsorption of BrO3- onto PACs.

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.

Vesicle–tube–ribbon evolution via spontaneous fusion in a self-correcting supramolecular tissue

A real-time reversible fusion pathway from vesicles to fibres, passing through several types of intermediates such as fused vesicles and short and long tubes, was monitored in a cholesterol-based assembly. The mechanism of the structural evolution via a gelation process was studied by means of electronic microscopy, small-angle X-ray scattering and powder X-ray diffraction. The fibres of the gel tissue could be switched by sonication and mechanical shaking to tubes and broken fibres, respectively, and reversed by thermal treatment or aging for a certain period via a fusion process. The destroyed fibres could match with each other in the healing process, showing the self-healing and self-correcting character of the self-assembly. This complete investigation of the reversible vesicle–tube–ribbon transition is of great significance in the design and synthesis of new nano/microstructures, especially stimulus-responsive aggregates through a “bottom-up” strategy.

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.