| The removal of organic dyes has got increased attention due to their highly stable andcomplex chemical structures, which makes them difficult to degrade by conventionalmethods. Above all, most of them with deeply colored, mutagenic nature and weakpurification capacities would cause harm not only where they are produced and used, butglobally. So far, adsorption and photocatalysis have been became the main techniques for thetreatment of dye-containing effluents. However, using the sole method is generally costly,less efficient, and cause seriously secondary pollution to environment in practical application.Therefore, in this paper, we devoted to fabricate a series of new materials which areeconomic, efficient and environmentally friendly for the treatment of dye effluents.Meanwhile, the obtained products were characterized by varies characterization means toknow more about their physical and chemical properties.(1) The opposite zeta-potentials of P25-TiO2nanoparticles (guest particles) and yeasts (cores,host particles) were achieved by tuning pH of their own aqueous suspensions. Then theTiO2@yeast hybrid micro-spheres with raspberry-like structure were prepared by electrostaticinteraction-driven self-assembly. Results from characterizations indicated: the resultingsamples retains ellipsoid shape, with the uniform size (length3.6±0.25μm, width2.4±0.15μm) and good dispersity; the main crystal structure of as-synthesized TiO2@yeastmicrosphere is consisted of anatase and rutile; the obtained samples have a good respondingto UV light; the possible formation mechanisms of TiO2@yeast hybrid micro-spheres, whichcan be interpreted by the one-step electrostatic attraction self-assembly. There into, the uniquesurface traits of the primitive yeast and TiO2nanoparticles are responsible for the fabricationsof TiO2@yeast hybrid microspheres. The settling ability of particles indicates the compositecatalysts are good for recycle and reuse. They also exhibited a high photocatalytic activity forthe degradation of Congo red dye aqueous solutions.(2) The raspberry-like TiO2@yeast hybrid microspheres were fabricated by electrostaticinteraction driven self-assembly heterocoagulation. The obtained microspheres were used as adsorbents for removal of cationic dye MB in aqueous solutions. Adsorption performancewas investigated by analyzing the influences of factors such as the initial pH, contact time,and temperature at different initial concentrations. Equilibrium data were described by theLangmuir, Freundlich and Dubinin–Radushkevich isotherm models. It was found thatequilibrium data was best represented by Langmuir isotherm model. The kinetic regressionresults manifested that the adsorption kinetic was more accurately represented by a pseudosecond-order model and the intraparticle diffusion was not the only rate controlling step. Thethermodynamic studies indicated that adsorption process was spontaneous, entropy gainedand endothermic nature within the studied temperature range. Moreover, the dye-loadedTiO2@yeast could be effectively regenerated in situ exploiting the structural advantages ofitself.(3) Phosphotungstic acid (HPW)-impregnated yeast hybrid micro-spheres were prepared byimpregnation–adsorption technique through tuning pH of the aqueous yeasts(cores)suspensions. Results from characterizations indicated: the HPW has been effectivelyintroduced onto the surface of yeast, and the resulting samples retain ellipsoid shape, with theuniform size (length4.5±0.2μm, width3.0±0.3μm) and good mono-dispersion; the maincrystal structure of as-synthesized HPW@yeast microsphere is Keggin structure; the HPW incomposites has better thermal stability than pure HPW; the functional groups or chemicalbonds inherited from the pristine yeast cell were critical to the assembling of the composites;the obtained samples have a good responding to UV light. The settling ability indicates thehybrid microspheres possess an excellent suspension performance. In the test of catalyticactivity, the HPW@yeast microsphere exhibits a high photocatalytic activity for thedecoloration of Methylene blue and Congo red dye aqueous solutions, and there are a littleactivity losses after four cycles of uses.(4) BiVO4@yeastmicrospheres have been successfully fabricated using spherical yeasts ascores via an environmental-friendly way. Results from the characterization show: thediameter of the BiVO4@yeast microspheres varying between3μm to5μm and the yeastswere well coated with BiVO4; the absorption edge of samples as-prepared is estimated about525nm with a band gap of2.3eV. Moreover, the photocatalytic performances of the as-obtained BiVO4@yeast microspheres were investigated by the decomposition of AuramineO under visible-light irradiation. The BiVO4@yeast-products exhibited a better photo-catalytic activity due to its excellent suspension property which is not only beneficial to theadsorption of dye molecules but also made it possible for BiVO4to get the utmost out of lightsource to realize oxidizing organic pollutants by photo catalytic degradation.In this article, three kinds of new composite microspheres were fabricated which haveintegrated the surface characteristics from microrganizm with the photocatalytic functionexerted by the catalytic materials effectively. And the synthesis techniques have manyobvious advantages such as environmental friendly, easy operation, mild reaction and costinexpensive. The obtained products have the high decolorization efficiency for dye-stuffwasterwater and no secondary pollution which could be effectively to treat the waste waterand could realize the goal of improving environment and utilizing resources. This paper hasmade some attempts in the multidiscipline among biosorption, nano-sized photocatalysismaterial and heteropoly acid catalysts and thus greatly enrich the species of compositesmaterials. Morover, it may be of reference value to the application of other microorganism ascores to related new composites in the area of treating dye wastewater. |
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