Investigation On Silver Doped Oxides Sol-gel System

Nanomaterials have different properties from the normal materials duo to the characteristics of volume effect,surface effect,quantum dimensional effect and quantum channeling effect.The metal nanoparticles have the unique physical and chemical properties,such as surface plasma resonance(SPR),three order nonlinear optical property etc.The particular optical and electrical performance can be obtained when the silver nanoparticles doped in the different matrix.Noble metal nanoparticles doped oxides semiconductor can change the properties of semiconductor,such as the photocatalyst performance,electrical characteristics.In our study,we investigated the sol gel process of noble metal doped oxide materials and adopted silver as the doping metal,titanium oxide(TiO₂)and zinc oxide(ZnO)as the oxide matrix,because silver(Ag)is a kind of comparatively cheap noble metal with good chemical stability and excellent conductivity.The broad band gap semiconductors TiO₂ and ZnO have good performance in many fields.The results of our work can be applied in the studies of noble metal doped oxide materials.In this paper,we study sol gel preparation process of Ag/TiO₂ composite material with tetrabutyl titanate and silver nitrate as the titania and silver source.The influences of the addition agents,sol aging time and other factors on the form changes of silver in the sols and films are discussed systematically.The results indicated the Ag colloid nanoparticles can be obtained in the sol with diethanolamine(DEA)as addition agent.The nanoparticle growth process can be indicated by UV-visible spectra method.It shows Ag nanoparticles grow slowly during the aging period.The reason is that the complex reactions between DEA and Ag⁺,as well as DEA and titanate occurred in the sol simultaneously.The resulting macromolecule organic complex compound around Ag colloid nanoparticle acted as the enclosure layer which can inhibit the reduction process of silver nitrate.The steric effect makes the Ag nanoparticles grow gradually.Whereas,Ag colloid nanoparticles can not be obtained in the sol with nitrate as addition agent.That means DEA act as the reductant in the sol gel process.The XRD results of the films with DEA display the diffraction peaks corresponding to rutile phase,but the films with nitrate as addition agent do not.From the comparison of the XRD results,it can be deduced that DEA can promote the phase transformation of titanium oxide from anatase to rutile phase.In addition,the Ag nanoparticles in the films with DEA are smaller than that with nitrate.The differences of reduction process account for the different results.One is complexing reduction;the other is heat decomposition of silver nitrate to get the silver particles.With Ag doping volume content increasing,the electrical resistivity of the films with DEA reduces rapidly because of channeling effect of silver nanoparticles with excellent conductivity.The resistivity decreased to the lowest value of 4^* 10⁴Ωcm when the doping volume ratio is 0.16.Furthermore,we study sol gel preparation process of Ag/ZnO composite material with zinc acetate dihydrate as the zinc oxide source.Ag ions can be reduced into Ag⁰ in the sol with the reductant effect of the DEA,which increased the absorption intensity of the sols in the range of 300-550nm.The results of XRD indicated the lattice of Ag/ZnO films swell duo to the substituting of Ag for the Zn in the ZnO crystal lattice when the doping volume ratio is less than 0.1,but the lattice parameters do not change when the doping volume ratio is more than 0.1.Ag nanoparticles are liable to aggregate into big particles on the film surface,so Ag particles about 150nm in diameter appeared on the surface of the films after heat treatment at 500℃.When the temperature increased to 600℃,the Ag diffraction peaks and Ag particles don't appear in the XRD patterns and corresponding SEM photographs of the film surface,because some Ag element evaporated,some Ag fused with the ZnO in the grain boundary of ZnO and Ag nanoparticles of small size formed.When heat treatment was conducted on the films at 500℃and 600℃,Uv-vis spectra displayed the absorption peaks at around 500nm and 410nm,respectively,which attributed to surface plasma resonance of Ag nanoparticles,The fluorescent light(PL)spectra showed the PL peaks at around 400nm and 470nm of the film heat treated at 500℃,which can be attributed to deficiencies caused by Ag doped in the films.The PL peak of the film heat treated at 600℃appeared at around 380nm,which can be attributed to free excitons recombination of ZnO.Ag nanoparticles can also improve the electrical conductivity of the Ag/ZnO films and the resistivity of the films decreased to the lowest value of 10⁴Ωcm when the doped volume ratio is 0.1.