The Preparation Of Controllable Gold, Silver Nanoparticles And The Studies Of Their Applications In Rapid Detection Of Chromium Ions

In recent years, with the rapid development of industrialization, water environment in Chinawas subject to varying degrees of pollution. Especially heavy metal pollution of drinkingwater resulted in frequent heavy metal poisoning. Mining, metal smelting chemical wasteproduction and waste water contain a large number of heavy metal, the heavy metal is toxic, noteasy to be broken down, and can be enriched through the food chain with biological amplification,which seriously affects the aquatic life and human health, causing high importance by manyscholars and people. Most of the existing test methods of heavy metal need large instruments, forexample, inductively coupled plasma emission spectrometry （ICP-AES）, plasma massspectrometer （ICP-MS） and electrochemical workstation, which are expensive and can not be usedon real time and field test. So, exploring a rapid, timely, field testing method for heavy metals inaqueous systems in real time is of great value in practical applications such as environmentalmonitoring, sewage treatment, air quality analysis.Gold and silver nanomaterials, due to its special optics, electricity, magnetism, and thethermodynamic properties, have been widely used in superconducting, photoelectric, antibacterial,Catalysis and surface-enhanced Raman scattering and other fields. In addition, the change of theconcentration, morphology and particle size of gold and silver nanoparticles will cause thesolution changes on color and surface plasmon resonance absorption peaks. Exploiting thisproperty, gold and silver nano-materials has been widely applied in the field of medical testing andanalysis in recent years. This paper intends to colorimetric detect heavy metal ions （chromiumions） by using the prepared nano-gold and silver sol, with simpleness, high sensitivity andselectivity. Specific study content contains the following four major components:1) Spherical silver nanoparticles were successfully prepared by using seed preparation methodwith controlled morphology and uniform size. Ultraviolet-visible spectrophotometer （UV–visspectroscopy）, transmission electron microscope （TEM）, x-ray diffraction （XRD） were used to character the prepared spherical silver nanoparticles, which show that the prepared silvernano-particles are spherical, with uniform particle size distribution, and the average particle size is10nm.2) Silver nanoparticles with different morphologies （such as spherical, hexahedral, polyhedral）were prepared through green chemical method at room temperature, with glucose as the reducingagent, water-soluble starch as a protective agent. Scanning electron microscope （SEM）,transmission electron microscope （TEM） were used to character the silver nano-particles, whichshow that the prepared spherical silver nanoparticles have an average size of8nM, hexahedralsilver nano-particles200-300nm, polyhedral silver nanoparticles have good dispersion anduniform size.3) Tripolyphosphate modified gold nanoparticles were successfully prepared at roomtemperature using sodium borohydride as the reducing agent, sodium polyphosphate as protectingagent. Ultilizing the complexing reaction mechanism between Cr³⁺and polyphosphate modifiedgold nanoparticles, under the optimization conditions,（the concentration of sodium polyphosphateis0.8mM, pH value of solution is3.25）, we can detect trace Cr³⁺fast and easily. The results showthat we can observe10^-7M of Cr³⁺directly using the naked eye, with high sensitivity and goodselectivity.4) Silver core gold shell nanoparticles （Agcore-Aushellnanoparticles） were successfully preparedat room temperature using seed-mediated growth method. The optimal pH value usingAgcore-Aushellnanoparticles is determined to be2.00and the concentration of CTAB is0.2M. Under the optimized conditions, the recognization of Cr （VI） based on the factthat Cr （VI） can accelerate the etching rate of Agcore-Aushellnanoparticles by bromideions in hexadecyl trimethyl ammonium bromide （CTAB）, has a detection limit of1.0×10^-7M by the naked eye. The linear relationship of the quantitative analysis forCr （VI） concentrations ranges from8.0×10^-6M to1.0×10^-8M. This work exhibitsvery high sensitivity and excellent selectivity in the detection of Cr （VI） in aqueoussolutions.