Double-Shelled Metal Oxide Nanocomposite For Photodegradation Pollutants In Water

Compositing and restructuring of nanosized metal oxide will bring novel structure and excellent optical performance and then it can play an important role in the photocatalytic degradation of organic pollutants in water.After orderly combination metal oxides with noble metal,catalytic substrate can be quickly and efficiently adsorbed on the surface defect sites of metal oxide hollow nanospheres.Both active site of metal oxides and metal-oxide crystal interface can improve catalytic active of nanocomposite.According to the requirement of sample pretreatment for the determination of COD and TOC and wastewater treatment,this paler was focus on two key problems,including high recombination of electron and hole of photocatalyst and easily inactivation.We designed the structure of nanocomposite,synthesized successfully of double-shelled and multifunctional hollow nanospheres.The dispersity,morphology,size and lattice of hollow nanospheres was tested with scanning electron microscope（SEM）and transmission electron microscopy（TEM）.Analyse the phase and purity of sample was characterized with electron energy loss spectroscopy and X-ray diffraction analysis（XRD）.1.Double-shelled WO₃@TiO₂hollow spheres for photodegradation of anionic and cationic aromatic pollutantsWithin a certain p H range,if the difference in isoelectric points between nano metal oxides M_xO and N_yO was large enough,the inner and outer shell of double-shelled M_xO@N_yO hollow spheres were positively and negatively charged,respectively.Namely we can innovative prepared double-shelled hollow nanospheres with surface both positive and negative charged.We use nano metal oxide WO₃and TiO₂as verification model,shell-shell composite.The nanoparticles of WO₃and TiO₂were coated successively onto the functionalized polystyrene（PS）template spheres,the resulted PS@WO₃@TiO₂nanocomposites were calcined at elevated temperature,and then double-shelled WO₃@TiO₂hollow spheres were obtained.The hollow nanospheres were composite by independent shell of WO₃and TiO₂,with uniform dispersion,size of 470 nm,the maximum absorption wavelength is 480 nm.The specific surface area and the average pore diameter of these hollow spheres were 53.04 m²/g and 8.042 nm,respectively.With the p H range of 2-5,the surface of shell WO₃and TiO₂were negative and positive,respectively,so the hollow nanospheres could efficiently adsorb cationic aromatic pollutants（rhodamine B,methyl violet,4-nitroaniline）and anionic aromatic pollutants（methyl orange,acid violet 43,trimesic acid）;The photocatalytic activity for the degradation of cationic and anionic aromatic pollutants was in the order of double-shelled hollow spheres WO₃@TiO₂>single-shelled WO₃-TiO₂>P25,i.e.,coupling TiO₂and WO₃can not only adsorb anionic and cationic ionic contaminants,but also have a synergistic effect on the photocatalytic performance.2.Double-shelled TiO₂@WO₃/Au hollow spheres for adsorption and photodegradation of rhodamine BThe noble metal Au nanoparticles were introduced into nano WO₃shell for the preparation of TiO₂@WO₃/Au hollow nanospheres.The nanoparticles of TiO₂,WO₃and Au NPs were coated successively onto PS template spheres.The resulted PS@TiO₂@WO₃/Au nanocomposites were calcined at elevated temperature,and then double-shelled TiO₂@WO₃/Au hollow spheres were obtained.The presence of TiO₂hollow sphere and WO₃/Au shell was confirmed by electron energy loss mapping analysis and X-ray diffraction analysis（XRD）,with uniform dispersion,and its maximum absorption wavelength is 475nm.The specific surface area and average pore diameter of TiO₂@WO₃/Au hollow spheres were 45.62 m²/g and 8.916 nm,respectively.The photodegradation activity for rhodamine B was in the declining order of TiO₂@WO₃/Au>TiO₂-WO₃>P25.Under visible-light irradiation,the photodegradation rate of 94.44%was achieved for TiO₂@WO₃/Au,which exhibited an increase of 62.16%compared with P25.The optimal hollow sphere size for TiO₂@WO₃/Au was 450 nm.The synergistic effect of coupling TiO₂hollow spheres with WO₃shell and Au NPs on photocatalytic performance was proved by us.The photoexcited electrons from WO₃could be captured by TiO₂and Au NPs,and then the electron-hole separation was improved.Moreover,the visible light absorption of TiO₂hollow spheres was increased by the coexistence of WO₃and Au and unique hierarchical mesoporous architectures of TiO₂@WO₃/Au.Because the surface charge of TiO₂@WO₃/Au and rhodamine B was negative and positive,respectively,the affinity between them could be improved by electrical attractions,and then the major obstacle of heterogeneous photocatalysis（i.e.,the poor surface coverage of pollutants on the photocatalyst）could be resolved.3.Double-shelled TiO₂@CeO₂hollow spheres for photodegradation of methyl orangeThe nanoparticles of TiO₂and CeO₂were coated successively onto PS template beads.The resulted PS@TiO₂@CeO₂nanocomposites were calcined at elevated temperature,and then double-shelled TiO₂@CeO₂hollow spheres were obtained,composited by independent shell of TiO₂and CeO₂,with uniform dispersion,which maximum absorption wavelength is480 nm.The photodegradation activity for methyl orange was in the declining order of TiO₂@CeO₂>CeO₂>P25.Under visible-light irradiation,the photodegradation rate of79.37%was achieved for TiO₂@CeO₂,which exhibited an increase of 47.56%compared with P25.The photoexcited electrons from CeO₂could be captured by TiO₂,and then the electron-hole separation was improved.Moreover,the visible light absorption of TiO₂hollow spheres was increased by the coexistence of CeO₂.Therefore,the synergistic effect of coupling TiO₂hollow spheres with CeO₂shell on photocatalytic performance was proved.