Investigation On The Synthesis, Optical And Photocatalytic Properties Of ZnSe Nanomaterials

ZnSe is an important semiconductor material (AII-BVI group) with widedirect band gap (2.67eV) at room temperature and large exciton binding energy(21meV). ZnSe has attracted much more attention recently due to their greatpotential for fundamental research and practical applications. The ZnSenanomaterials have the wide-ranging optoelectronic applications including bluelight-emitting diodes, photodetectors, room-temperature excitonic devices,full-color displays. Furthermore, due to their low toxicity (without heavy metalions), ZnSe nanomaterials are potential blue fluorescent biological labels.Although attempts have been tried, the photodegradation in presence of ZnSenanomaterials has seldom been reported. ZnSe nanomaterials have beensuccessfully synthesized via various methods, such as CVD, electrodepositionmethod, sol-gel, coprecipitation method, MBE. The solvothermal method hasbeen most widely used because it requires a relatively low temperature, cheapprecursors of low toxicity, which is simple and easy to operate.In this paper, the ZnSe quantum dots, nanosheets and nanoparticles wereobtained by a solvothermal method. The structure, morphologies, opticalproperties and photocatalytic activity have been investigated in detail by themethods of X-ray Diffraction (XRD), transmission electron microscope (TEM),energy dispersive x-ray analysis (EDAX), UV Raman and fluorescencespectrometer and UV-Vis. The major achievement obtained is as follow:(1) ZnSe quantum dots and nanoparticles were obtained by annealing the precursors which were prepared by a solvothermal method. The ZnSequantum dots were about3.5nm, while the ZnSe nanoparticles wereabout21nm, as observed using TEM. The growth mechanisms for thetwo samples with different structures were discussed. The ZnSe quantumdots with the wurtzite structure exhibited a strong near band-edgeemission (NBE) peak centered at422nm which was blue-shifted incomparison with that of the bulk ZnSe, which mainly caused by thequantum confinement effect. However, the zinc blende ZnSenanoparticles exhibited near-band-edge luminescence peak centered at472nm. The Raman spectrum of the ZnSe quantum dots with wurtzitestructure and nanoparticles with cubic structure were studied. The LO andTO phonon peaks of the ZnSe quantum dots and nanoparticles wereshifted towards the lower frequency. Large broadening of Raman spectrawere observed in the ZnSe quantum dots.(2) ZnSe nanocrystals with different morpholygies were obtained byannealing the precursors prepared via a solvothermal process withdifferent volume ratio of ethylenediamine and water. When the volumeratio increased from1:1to5:1, the morphologies changed from theisotropic nanoparticles to the highly anisotropic nanosheets. The X-raydiffraction (XRD) results showed both the ZnSe nanoparticles andnanosheets were metastable wurtzite crystal phase. The results of TEMfound that the nanoparticles were uniform and the average size was about7nm, while the large-scale nanosheets with length up to4μm and widthup to3μm had the single crystalline nature. By investigating the growthmechanism of the ZnSe nanosheets, the nanocrystal unit was assembledin a parallel orientation into the sheet morphology due to the solventcoordination molecular template effect of the EN. The nanoparticles andnanosheets exhibited the NBE peak centered at422nm, which wasblue-shifted compared with the PL spectra of bulk WZ ZnSe. Theinvestigation of the photocatalytic activity for the ZnSe nanoparticles andnanosheets showed that the nanosheets were more suitable for thedegradation of Rhodamine B under UV radiation.(3) ZnSe nanoparticles with cubic structure were obtained by using differentsolvents. ZnSe nanoparticles with different sizes were successfully prepared using EDTA by a hydrothermal method. The effect of reactiontime on the sizes and optical properties of ZnSe nanoparticles wereinvestigated. The position of near-band-edge emission peak in theroom-temperature PL spectra showed a red-shift ranging from472nm to479nm with particle size decreasing from21nm to7nm, while the lowdefect-related emission band became broader and stronger. Using theethanediol or triethanolamine as the solvent, the optical properties and thephotocatalytic activity of the ZnSe nanomaterials obtained by usingdifferent solvents were studied. The investigation of the photocatalyticactivity showed that the ZnSe obtained by using triethanolamine had highphotocatalytic activity. The factors which influenced the photocatalyticactivities of ZnSe nanomaterials were studied.