Fabrication And Photocatalytic Properties Of Nanocomposite Materials With Hierarchical Structures

Environmental pollution and shortage of energy are two problems confronted withword in the21century. Titanium dioxide has shown great potential in solvingevironmental pollution and energy crisis, which has been widely used in waterpurification and H2production by water splitting. Nevertheless, the performance of mostphotocatalysts required to be further enhanced in part due to its narrow light-responserange as well as its low quantum efficiency. Thus, the design and fabrication of TiO2photocatalyst with highly light-harvesting and photocatalytic efficiency is the mosturgent problem. Inspired by nature, the biomaterials with unique optical functionality areused as template to generate photocatalytic nanocomposite materials. Then we analyzedthe couple effect of hierarchical structure and muti-component composition, which couldprovide us new insights and models for the exploration of photocatalytic materials. Themain contents and results are as follows:1. Inspired by the hierarchical porous structures of butterfly wings with highlight-harvesting capability, the biomorphic TiO2is synthesized by a solvothermalsoakage procedure combined subsequent calcination treatment, on the basis of thebutterfly wings (Papilio Paris Linnaeus) as the template. As-prepared biomorphic TiO2inherits the hierarchical structure of butterfly wings from nano-to macro-scales. UnderUV-light irradiation, the decomposition rate of the biomorphic TiO2is about two times ofthe rate of the contrasting sample, and five times of the rate of the commercial titania.The higher photocatalytic activity of the biomorphic TiO2is probably attributed to thebeehive structure, which could improve light-harvesting efficiency of TiO2, and thusfurther improve the photocatalytic efficiency.2. The Au/TiO2nanocomposites with hierarchical porous structure are successfullyprepared through a sol-gel technique in ethanol/water medium followed deposition-precipitation process, by introducing butterfly wings (Papilio Paris) as the template.Thereinto, Au nanoparticles are deposited uniformly on the surface of the TiO2substrate.As-prepared biomorphic Au/TiO2inherits the hierachical porous structure of butterflywings. The highest activity is observed at biomorphic8.0wt%Au/TiO2, and about100% of methyl orange is degraded after80min reaction under visible light, while54%forbiomorphic TiO2, which is far above the results of the contrasting TiO2(37%) and P25(56%). The superior photocatalytic activity should be ascribed to the hierarchical porousstructures and the presence of Au nanoparticles. The hierarchical porous structurespossess the larger specific surface area,which could offer more absorption and reactionsites for the photocatalytic reaction. Moreover, the beehive structures could takeadvantage of light by increasing the path length. Furthermore, the Au particles on theTiO2substrate can act as electron traps facilitating the electron-hole separation, leading toenhanced quantum efficiency. After three recycles for the photodegradation of methylorange, the activity of the biomorphic8wt%Au/TiO2does not exhibit any significantloss, indicating that the catalysts are relatively stable during the photocatalytic process.3. To expand the light response of TiO2, we contrive an ternary system by using CdSas sensitizer for the high efficiency of H2-production rate, on the basis of noble modifiedtitanium dioxide with hierarchical porous structure. The biomorphic CdS/Pt-TiO2(PPL)is successfully prepared through a sol-gel technique combined with photoreduction andchemical bath deposition method, on the basis of the butterfly wings (Papilio ParisLinnaeus) as the template. Thereinto, Pt and CdS nanoparticles are well deposited on thesurface of the TiO2substrate. The visible-light driven photocatalytic activity of theas-prepared samples was evaluated by photocatalytic H2production from Na2SO3andNa2S aqueous solution under visible1ight irradiation. It was shown that nophotocatalytic H2-production activity was generated on the TiO2(PPL) and Pt-TiO2(PPL)under visible1ight irradiation. Depositing CdS nanoparticles on Pt-TiO2(PPL) caused asignificant enhancement of the visible-ight photocatalytic H2production rates. TheCdS/Pt-TiO2(PPL) show the highest photocatalytic activity(12.7%apparent quantumefficiency obtained at420nm)，exceeding that CdS sensitized Pt/TiO2nanoparticles(1.20%)。The superior average rate of hydrogen evolution should be attributed tosynergetic effect of the hierarchical porous structures and CdS/Pt-TiO2ternary hybrid.4. The leaves of Zea Mays Linn contain abundant nitrogen source and exhibit anextremely high light-harvesting efficiency due to its hierarchy internal structures.Inspired by these, Au/N-TiO2photocatalyst with the hierarchical structure of leaves issuccessfully prepared through soakage procedure combined with thedeposition-precipitation method, on the basis of the Zea Mays Linn leaves as the template. Thereinto, nitrogen is introduced into anatase TiO2in the form of substitutional andinterstitial nitrogen, and Au nanoparticles are well deposited on the surface of N-TiO2.The average decomposition rate of templated5wt%Au/N-TiO2under solar light is0.045min-1, while0.032min-1for templated N-TiO2and0.029min-1for P25, which ispreponderant than the non-template N-TiO2(0.012min-1) and the TiO2(0.002min-1). Thesuperior photocatalytic activity of templated Au/N-TiO2should be attributed to thesynergy effects of muti-component composition and the unique hierarchical structure.Moreover, after three recycles for the photodegradation of R6G, templated5wt%Au/N-TiO2does not exhibit any significant loss of activity, indicating that thephotcatalysts are stable during the photocatalytic oxidation of the pollutant molecules.5. The blue wing of butterfly Euploea mulcibe presents an optical response due toits3D submicrostructures. Inspired by this, the blue wing of butterfly Euploea mulciberis used as a template to generate3D periodic structures Ag/TiO2nanocomposites. TheTiO2with3D periodic structures is firstly to be fabricated by a sol-gel techniquefollowed by subsequent calcination, and then Ag nanoparticles would be assembled onthe surface of the TiO2matrix with a chemical reduction method. The templated Ag/TiO2preserves the3D periodic structures of the butterfly Euploea mulcibe (blue wings). Theobtained templated Ag/TiO2shows superior detection sensitivity, and the enhancementfactor(EF)is estimated to be about1.1×105. Moreover, the templated Ag/TiO2showsgood reproducibility with a relative standard deviation (RSD)8.5%, which is comparableto commercial counterpart. Apart from the function of SERS detection, the templatedAg/TiO2also shows the superior photocatalytic activity. Therefore, compared with otherconventional SERS substrates, the high sensitive, reproducible, superior catalyticproperties and cost-effective templated Ag/TiO2could become an ideal substrate for boththe detection and degradation of organic pollutants.This research provides new method for the synthesis of hierarchical photocatalyticmaterials and brings in new insights for the structural design and compositionaloptimization of good photocatalytic materials.