Indium Oxide And Silver Nanostructure Materials: Synthesis And Their Application In Chlorophenol And Mercury Sensing

This paper is focused on the controlled synthesis of indium oxide nanostructures through liquid-phase chemistry routes.Investigations are based on three aspects: controlled synthesis,formation mechanism,properties and applications.The contents mainly include metastable corundum-type In₂O₃ of hierarchical nanostructured preparation,size-controlling,formation mechanism and gas-sensing properties, morphosynthesis of Ag nanoparticles and Hg²⁺ Recognition in Aqueous Media, intending to study the intrinsic controlling mechanism of the nanocrystal formation and their effects on the devices' applications.1.Catanionic-surfactant-controlled morphosynthesis and gas-sensing properties of corundum-type In₂O₃InCl₃-4H₂O was dissolved in heptane,oleic acid and laurylamine were used as the additives.After the solution was heated at 220℃for a setting time,orthorhombic InOOH is separated by centrifugation,indium oxyhydroxide dehydrated to form indium oxides hierarchical nanostructure upon heating.On the basis of the reaction conditions,it is believed that the InOOH wire-bundles in this study are formed mainly via the following sequence.At the initial stage,catanionic-surfactant was obtained by mixing laurylamine and oleic acid,which can induce bilayers due to the electrostatic and hydrophobic interactions.With the increased temperature and pressure,nucleation and growth of the InOOH crystals occur under solvothermal conditions.The surfactants will interact strongly with InOOH crystals by forming hydrogen bonds along the[001]direction,which in turn help one-dimentional growth and prevent side-ripening.Thus,with the assistance of catanionic-surfactant,bundle-like morphology based on nanowires was obtained.Finally,dumbbell-like hierarchical InOOH nanostructures were generated through the outward bending the nanowires by secondary nucleation and growth of new nanowires in each space among the as-grown bundle-like nanostructures.The results suggested that laurylamine alone had no effect on the crystal morphologies of InOOH,possibly due to the weak interaction between laurylamine and growing InOOH crystals.But laurylamine provided the necessary alkaline environment for the hydrolyzing of In³⁺ as well as promote the preferential growth of different crystal planes with the coexistence of oleic acid.Novel gas sensors based on the corundum-type In₂O₃ hierarchical nanostructures exhibited high response and selectivity to 2-chlorophenol at 280℃with a detection limit of about 5 ppm.The response of the sensor to other gases,such as benzene, toluene,CHCl₃,CH₂Cl₂,and ammonia under the operating temperature of 280℃was totally insensitive.So the sensor based on corundum-type In₂O₃ hierarchical structures shows an obvious advantage in selective detection of 2-chlorophenol.2.Synthesis of Ag Nanoparticles and Hg²⁺ Recognition in Aqueous MediaThe silver nanoparticles were obtained through a reduction reaction of silver nitrate with NaBH₄ in the presence of starch.It showed a characteristic peak centered at 400 nm in the visible light area.Calculated according to the Lambert-Beer's law,the extinction coefficients of the as-prepared silver nanoparticles is about 1.39104 M^-1 cm^-1(at 400 nm),which can meet the demand of colorimetric sensing detection.The sensitivity of silver nanoparticles toward Hg²⁺ was identified by UV-vis absorption spectra in this work.The sensing begins by adding an aliquot of an aqueous solution of Hg²⁺ at a designated concentration to a solution of the Ag nanoparticles at room temperature.Various concentrations of Hg²⁺ from one stock solution were tested.The absorbance peak of the Ag nanoparticles could be depressed with the increased concentration of Hg²⁺ ion.A linear relationship(y=1.41-5.75×10^-4x,R²=0.9984),stands between the absorbance intensity of the Ag nanoparticles and concentration of Hg²⁺ ion over the range from 10 ppb to 1 ppm at the absorption of 390 nm.The limit of quantification,at a signal-to noise ratio of 3,was down to 5 ppb.the selectivity of this system for Hg²⁺ has been evaluated through testing the response of the assay to various environmentally relevant metal ions,including Hg²⁺,Na⁺,K⁺,Ba²⁺,Mg²⁺,Ca²⁺, Fe³⁺ at a concentration of 10^-4 M.Only the Hg²⁺ sample shows a significant fading relative to that of the blank.The facile synthesis,high stability and high water solubility of the starch-stabilized Ag nanoparticle probes allow a reliable assay performed in aqueous environments.3.Hollow Ag/TiO₂ Nanocomposites with Enhanced Photocatalytic ActivityCarbonaceous microspheres,which serve as the templates,are first prepared from saccharide starting materials by dehydration under hydrothermal conditions.The surface of the spheres is hydrophilic,being functionalized with C=O groups,silver were loaded onto their surfaces by room-temperature surface reduction.The polysaccharide-like hydrophilic surface of the spheres,bearing hydroxyl roups(-OH), favored the hydrolysis of tetrabutyltitanate.Thus,a shell of TiO₂ precursor formed on the surface.The Fermi level of silver is lower than TiO₂,so a Schottky barrier formed at the metal-semiconductor interface.Investigation dicated that optimized amount of Ag deposits not only acted as electron sinks to enhance the eparation of photoinduced electrons from holes,but also elevated the amount of the surface hydroxyl,leading o the formation of more hydroxyl radicals(·OH) and then the higher photodegradation efficiency to MB solutions.