Synthesis, Surface Modification And Property Of Silicon Quantum Dots

Silicon quantum dots（Si QDs） have features of non-toxic, raw materialsabundance, fluorescent controllable and good biocompatibility. In the biomedical fieldand the field of energy and environment, nano-structure semiconducting materialshave attracted so many researchers because of their special properties[1]. As a newtype of semiconduct nano-materials, silicon nanomaterials, due to their special opticalproperties based on the particle size and different hydrophobicity&biocompatibilitycharacteristics based on the surface modification, more and more researchers begin toexplore their synthesis methods, surface modification, biological applications andphotocatalytic properties[2-5].This article discusses the preparation, surface modification and performanceresearch of silicon quantum dots as three aspects as follows:Firstly, preparation of silicon quantum dots: there are three distinct methodswhich are called restore silane method, high-energy ball milling method andelectrochemical etching method, respectively. In this article, the advantages anddisadvantages of these three preparation methods will be discussed and comparedwith each other. The silicon quantum dots prepared by restore silane method havegood characteristics of uniform particle size, excellent dispersion and less susceptibleto oxidation. However，these silicon quantum dots’ shortcomings are also apparent,e.g. the reducing agent used in this method is dangerous, it is not suitable for masspreparation and it is difficult to prepare the silicon nanocrystals with full spectrumlight. By contrast, by using the high-energy ball milling method, silicon quantum dotscan be large-scale prepared and the synthesis processing is relatively safety. But at thesame time, this method have a higher energy consumption, longer preparation time aswell as difficult to control the particle size. And then, silicon quantum dots preparedby electrochemical etching method have the advantages of uniform particle size, rapidpreparation and particularly, attribute to the presence of Si-H bond on the surface, theprepared silicon quantum dots can be easily modified functional molecules.Still, inthis process, there are some disadvantages such as that hydrofluoric acid which isfamous for toxicity must be used in this method and the particles made byelectrochemical etching method have worth uniformity than the particles made by therestore silane method.Secondly, the modification of silicon quantum dots, according to the differentway of preparation, two methods of modification are mentioned in this article. Theyare one-step direct modification and two-steps indirect modification. When the siliconquantum dots are prepared by the restore silane method, trichlorosilane are often usedto introduce modified functional groups to modify the silicon quantum dots directly. And when the silicon quantum dots are made by using the high-energy ball millingmethod, silicon free radicals will form on the cross-section of silicon during themilling processing. The silicon quantum dots can be modified through the reaction ofsilicon free radicals and C=C bonds directly. Also, when using electrochemicaletching method for preparation, the surface modification of silicon quantum dots canbe carried on by using the Si-H bonds on the surface of silicon quantum dots.Thirdly, the performance of silicon quantum dots are discussed as followed threeaspects: using of silicon quantum dots as biomarkers by fluorescence properties,reduction of carbon dioxide by using the photocatalytic properties of silicon quantumdots, preparation of new composite nanomaterials by using the reduction properties ofsilicon quantum dots. About the imaging applications of silicon quantum dots, theundecenol-modified silicon quantum dots prepared by electrochemical etchingmethod have been used for confocal imaging of Hela cells, the results show thatsilicon quantum dots can be used as fluorescent contrast agent well and almostnontoxicity; In photocatalytic applications, the silicon quantum dots prepared by thehigh energy ball milling method are used for the photocatalytic reduction of carbondioxide. The results show that carbon dioxide can be photocatalytic reduced toformaldehyde by milling prepared silicon quantum dots. This is the first reported thatsilicon quantum dots prepared by ball milling method are used in photocatalyticreduction of carbon dioxide. This is very forefront and novel. In the synthesis of newcomposite nanomaterials, mainly by using electrochemical etching prepared siliconquantum dots with the surface of the silicon hydrogen as a reducing agent, thesilicon-gold nanocomposites are prepared by restoring the chlorine acid.