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α-Fe_2O_3, γAl_2O_3, SiO_2 nanoparticles mixed system of single and chemical behavior of the interface

Author: LiuJia
Tutor: SunZhongXi
School: Jinan University
Course: Inorganic Chemistry
Keywords: nano-mixed system surface acid-base property surface complexation inorganic anion alkali ion
CLC: TB383.1
Type: Master's thesis
Year: 2010
Downloads: 70
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Abstract


Fe2O3、Al2O3 and SiO2 are common substances in soil. The physical, chemical reactions occurring on the surfaces of Fe2O3, Al2O3 and SiO2 such as acid-base, adsorption, desorption, complexation, precipitation, dissolution, flocculation, and others largely determine the destination of pollutants in water and soil. However, the impurities, contained in a multi-component system such as soil vary from region to region, taking natural soil as the object to study the fundamental properties of the solid-liquid interface is lacking of representitive characterestic. Synthetic silica, iron oxide, alumina nano-materials are pure and their composition, structure can be controlled. Characteristics of their micro structure and composition can change their metal ions adsorption capacities and selectivities. Therefore, study of adsorption properties of synthetic Fe2O3, Al2O3 and SiO2 can provide better data on the adsorption of complex systems and the basic theories for rational use of industrial waste.In this paper,α-Fe2O3,γ-Al2O3 and SiO2 nano-particles were prepared from the precursors of TEOS, aluminum nitrate, ferric nitrate by sol– gel and precipitation methods, and in some cases in combination with using templates. The synthetic samples were characterized by TEM, XRD, N2 adsorption/desorption and IR methods. The results showed that the preparedα-Fe2O3,γ-Al2O3 and SiO2 all have large specific surface areas.Fe2O3 were prepared from the precursors of Fe3+ nitrate, chloride and sulfate. The zero-valent iron was synthesized by the reduction of iron （Ⅱ） salts using NaBH4. The nano-iron oxides were synthesized by the reaction of nano zero-valent iron with hydroxide of alkali metal （LiOH, NaOH, KOH）. The products were characterized by advanced XRD, BET, IR, TEM techniques. The result shows that the surface area of iron oxide prepared using nitrate, chlorate and sulfate salts as precursor are in the order of NO3- > Cl- >SO42-.respectively, i.e. the anti-sintering property is in the same order. According to solution chemistry reaction, the testing results and reaction mechanism of samples were evaluated using Medusa software;as Li+, Na+, K+ radius increases, the corresponding surface area of Fe2O3 prepared is increasing gradually.At length, the surface acid-base and complexation behaviors of heavy metal ions as well as concerning equilibrium constants in the aqueous suspensions ofα-Fe2O3,γ-Al2O3,SiO2 and their mixed systems were systematically studied by potentiometric titration technique in combination with computer calculation using constant capacitance model （CCM）. The experimental results and calculations revealed that the surface chemical reactions in the mixed system were not the same as the sum of their individual single system but possessing complicated mutual interaction among them. The surface chemical reaction models and relevant equilibrium constants in the mixed system were established as follows: forα-Fe2O3/γ-Al2O3 mixed system≡XOH+H+≡XOH2+ log K1=4.04≡XOH≡XO-+H+ log K2=-9.20 forα-Fe2O3/γ-Al2O3/SiO2 mixed system≡XOH+H+≡XOH2+ log K1=4.23≡XOH≡XO-+H+ logK2=-8.41The surface complexation models and constants of Cu2+、Pb2+、Zn2+ in the mixed system can be well described by following reaction: inα-Fe2O3/γ-Al2O3 mixed system≡XOH+M2+≡XOM++H+ with log K of -2.50, -2.25, -3.75 where M represents Cu2+, Pb2+, Zn2+ respectively. inα-Fe2O3/γ-Al2O3/SiO2 mixed system≡XOH+M2+≡XOM++H+ with log K of -2.20, -1.90, -3.20 where M represents Cu2+, Pb2+, Zn2+ respectively.

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