Preparations Of Nanoparticles Of Ag And Ni, Silicon Quantum Dots And Silicon Nanotubes On Silicon Substrates And Their Applications

Silicon nano materials with their unique physical and chemical properties have received intensive interests in recent years. Porous silicon(PSi) materials can be applied in preparation of catalysts because of their large specific surface areas. Silicon quantum dots(SiQDs) can be used in fluorescent biolabelings of biomolecules and cell fluorescence imagings due to their easy modifications, low toxicities, biocompatibilities and fluorescence properties.Herein we focused on preparing nanoparticles(NPs) of silver and nickel, silicon quantum dots(SiQDs) and silicon nanotubes(SiNTs) on silicon substrates. The loaded Ag or Ni NPs were applied in catalytic reduction of nitroaromatic compounds in the presence of sodium borohydride(NaBH4). Chemical modifications on SiQDs had potential applications in anchoring biomolecules and realizing fluorescent biolabeling of biomolecules.First, porous silicon(PSi) chips were prepared using electroless chemical etching method. Then the chips with Ag or Ni NPs were obtained respectively(denoted with AgNPs/PSi and NiNPs/PSi respectively). The AgNPs/PSi or NiNPs/PSi chip performed catalytic capabilities in reduction of nitroaromatic compounds in the presence of NaBH4. The PSi chip could also be used in obtaining SiQDs and SiNTs by the successive chemical etching. SiQDs were then modified to construct preferable interfaces for binding biomolecules. The details are listed as following.(1) AgNPs could be deposited on a PSi chip by reducing silver ions with surface Si-Hx(x = 1, 2 and 3) species. The images of scanning electron microscope(SEM) showed that the AgNPs dispersed homogeneously on the PSi chip. The AgNPs/PSi chip was applied in catalytic reduction of nitroaromatic compounds. The experimental results indicated that the AgNPs/PSi chip had excellent catalyses on reducing p-nitroaniline, sodium m-nitrobenzenesulfonate, p-nitrophenol and p-nitroacetophenone in the presence of Na BH4. The apparent activation energies of reducing sodium m-nitrobenzenesulfonate were calculated to be 27.13 kJ/mol. This showed high catalytic activities of the AgNPs/PSi chip.(2) When the PSi chip was immersed in a mixture of ammonium fluoride(NH4F) and Ni2+ for 15 min, the NiNPs were generated on the PSi chip due to the strong reducibility of the surface Si-Hx species. The NiNPs/PSi chip exhibited catalytic effect on the reduction of p-nitroaniline and sodium m-nitrobenzenesulfonate, which was similar with the catalysis of the AgNPs/PSi chip. The apparent activation energies of the catalytic reducing p-nitroaniline were obtained by the relationship between absorbance of ultraviolet-visible spectra and reaction time. The calculated value of 17.38 kJ / mol demonstrated the high catalytic activity of the NiNPs/PSi chip.(3) A facile method of preparing fluorescent SiQDs on PSi surface(SiQDs/PSi) was also introduced. The obtained SiQDs were proved by the images of transmission electron microscopy and fluorescence spectra. The SiQDs/PSi chip was modified with 10-undecylenic acid(UA) and successively with N-hydroxysuccinimide(NHS). The terminal NHS esters were so active in combining with primary amino groups of biomolecules. The successes of stepwise modifications were proved by both infrared(IR) and X-ray photoelectron spectra(XPS). n-Octylamine was chosen as a model compound to imitate the reaction of surface NHS esters of SiQDs and biomolecules. It was found that there are no significant changes of the photofluorescence during the chemical modifications. Such an approach provided an easy way of labeling biomolecues with SiQDs.(4) Grafted polymer brushes of poly(poly(ethylene glycol) monomethacrylate)(P(PEGMA)) could be constructed on surfaces of SiQDs. Surface hydroxyls of SiQDs could be initiated by 2-bromo-2-methyl bromide. Therefore grafted polymer brushes of P(PEGMA) were constructed on surface of SiQDs by virtue of surface-initiated atom transform radical polymerization. The side hydroxyls of the polymer brushes could be changed into carboxyls and successively into NHS esters. The stepwise modifications on SiQDs were monitored by IR and XPS. The photoluminescence of the SiQDs and their derivatives were remained during the chemical modifications. The fluorescent stability of the SiQDs with surface grafted polymer brushes was also investigated in phosphate buffer solution at pH = 7.4.(5) The PSi chip could also be used as a substrate for preparing SiNTs. When such a chip was immersed in the aqueous solutions of NH4 F and Co2+ for 20 min, the SiNTs were generated on the silicon substrate. The concentration of F- and etching time were the most important factors, which were supported by the SEM images and electrochemical analyses. A possible mechanism was put forward to explain formation of the SiNTs.