Synthesis Of Fluorescent Porous Silicon And Its Application In The Detection Of Metal Ions And Organic Molecules

Porous Silicon(PS) with obvious light-induced fluorescence, ultrahigh specific surface area(>500m2/cm3), varied microstructure and excellent biocompatibily leading to possess special physicochemical properties. In view of this, PS has been an attractive frontier of porous materials research, widely used in the solar cells, electron devices, environmental monitor, biochemical analysis etc. In recent years, PS has been an attractive frontier of silicon materials research, greatly promoting the high speed development of various fields. However, the simple and environment-friendly synthesis method of PS must continue to be further developed to obtain PS with stable fluorescenceand specific function. To achieve this objective, we have systematically studied the synthesis of PS with simple and inexpensive as well as their applications in the detection of metal ions and organic molecules. These optical sensing systems have the advantage of good specificity and high sensitivity, the main contents of this work can be concluded as follows:1. Preparation of fluorescent porous silicon by Chemical etching Method and Its Application in Ag+ DetectionA facile preparation of orange fluorescent porous silicon(PS) has been reported using a simple chemical etching method at 45℃. The prepared PS samples were characterized by scanning electron microscope(SEM), Fourier Translation Infrared spectrum(FT-IR) and specific surface area(BET). The results showed that the PS emitted strong orange fluorescence possessing excellent photostability. Moreover, the fluorescence of PS can be effectively quenched by silver ions(Ag+) at room temperature. This method showed a good linear relationship within the Ag+ in the range of 4.5×10-8~6.6×10—7 mol/L, with the detection limit was 2.2×10-8 mol/L, and the correlation coefficient R2=0.9914. The Ag+-sensing mechanism of this method was further explained. Furthermore, the fluorescent Ag+ sensor could be readily applied to Ag+ detection in environmental water samples, and satisfactory results were obtained.2. Electrochemical Preparation of Porous Silicon Wafers for the Applications in the Detection of Picric AcidIn this study, a facile preparation of highly fluorescent PS has been developed using electrochemical method. In this method, HF and C2H5 OH composed the electroyle solution, graphite rod was used as cathode and silicon wafer used as anode. The prepared PS samples were characterized by scanning electron microscope(SEM), Fourier Translation Infrared Spectrum(FT-IR), Atomic Force Microscope(AFM) and specific surface area(BET). The results showed that the PS had uniform holes and emitted strong orange-red fluorescence with excellent poto-stability. Research showed that the fluorophore could be oxidized by picric acid and leading to fluorescence quenching efficiently. By virtue of the specific response, a new, simple selective and sensitive fluorescent method for detecting PA has been developed based on PS. In the optimized condition, this method showed a good linear relationship within the concentration range of 6.5 ×10-9 mol/L~1.5×10-7 mol/L, the detection limit was 5.0×10-9mol/L and R2=0.9921(3σ, σ=S0/S). The study showed that the PS had excellent properties, such as low detection limit, wide linear range and good selectivity, in making sensors for detecting PA. Real water samples were analyzed with satisfactory results, which suggested its potential for real detection analysis.3. Amino-modified porous silicon for chemical sensor of Fe3+In this study, PS-NH2 was prepared simply by coupling reagent of APTES and surfactant of methylbenzene under 80℃ conditions. The prepared PS-NH2 samples were characterized by SEM, FT-IR, XPS and fluorescence spectrometer. The results showed that PS-NH2 emitted stable orange fluorescence under UV-light and has obvious pore structure. Moreover, the amino has been modified on the PS surface successfully. Research showed the fluorescence from PS-NH2 can be efficiently quenched by Fe3+ for photoinduced electron transfer of amino. By virtue of the specific response, a new, fast and sensitive fluorescent method for detecting Fe3+ has been developed. Under optimum conditions, the fluorescence recovery is linearly proportional to the concentration of Fe3+ between 1.0×10-9mol/L and 1.0×10-6mol/L and the detection limit is as low as 8.6×10-10mol/L, the correlation coefficient R2=0.9938.