졸-겔법에 의한 TiO<sub>2</sub> 미분할 합성과 반응메카니즘(II):Titanium n-propoxide의 가수분해

명중재; 박진구; 정용선; 경진범; 김호건

Journal of the Korean Industrial and Engineering Chemistry, Vol.8, No.5, 777-783, October, 1997

Export Citation

졸-겔법에 의한 TiO₂ 미분할 합성과 반응메카니즘(II):Titanium n-propoxide의 가수분해

Synthesis of TiO₂ Fine Powder by Sol-Gel Process and Reaction Mechanism(II) : Hydrolysis of Titanium n-Propoxide

명중재, 박진구, 정용선, 경진범, 김호건

초록

n-propanol 용매내에서 titanium n-propoxide(Ti(OⁿPr)₄)의 가수분해반응에 의하여 TiO₂미분말을 합성하였고, 가수분해속도를 자외선 분광법에 의하여 측정하였다. 분말합성은 water/alkoxide의 농도비가 약 300정도에서 실시하였으며, 물농도, 반응온도, 반응시간 및 반응용액의 산·염기효과에 의한 합성조건을 조사하였다. 반응은 Ti(OⁿPr)₄의 농도에 비하여 물농도를 과량으로 하여 유사일차반응으로 진행시켰고, 반응속도상수를 Guggenheim method로 계산하였다. 또한 물의 동위원소효과(D₂O)를 측정하여 반응에 관여하는 물분자의 촉매성을 확인하였다. 실험결과 중성 및 염기성 용액 조건에서 TiO₂미분말이 합성되었고, 미세구조 관찰로부터 TiO₂입자는 직경 0.4-0.7㎛정도의 구형입자로 확인되었으며, 물의 농도와 반응온도가 증가할수록, 반응시간이 감소할수록 입자크기는 작아지는 경향을 보였다. 물의 동위원소효과로부터, 물분자는 nucleophilic catalysis로 작용하고 있으며, 반응속도로부터 전이상태에 참여하는 n-value와 열역학적 파라미터를 계산한 결과, Ti(OⁿPr)₄의 가수분해반응은 이분자 반응인 associative S_N2 mechanism으로 진행하는 것으로 추정되었다.

TiO₂ powders were synthesized via hydrolysis reaction of titanium n-propoxide in n-propanol solvent and the reaction rates were studied by use of UV-vis spectroscopic method. Concentration of water, reaction temperature, reaction time and acid-base effects of the solution were investigated to determine the optimum conditions for TiO₂ powder synthesis. The reaction were controlled to proceed to pseudo-first orders reaction in the presence of excess water in n-propanol solvent. The rate constants which varied with temperature and concentration of water were calculated by Guggenheim method. Reaction using D₂O was also carried out to determine the catalytic character of water. TiO₂ powders were synthesized only in the neutral and basic solution and those were almost spheric forms having average particle size of 0.4-0.7㎛ diameter. Particle size decreased with increasing concentration of water and reaction temperature, however, increased with increasing reaction time. Associative S_N2 mechanism for the hydrolysis was proposed from the data of n-value in the transition state and thermodynamic parameter. D₂O solvent isotope effect showed that H₂O molecules reacted as nucleophilic catalysis.

[References]

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[1] Bradley DC, "Metal Alkoxides, Advances in Chemistry Series," 23, 10 (1959)

[2] Bradley DC, Mehrotra RC, Gaur DP, Academic Press, 19 (1978)

[3] Mehrotra RC, J. Non-Cryst. Solids, 100, 1 (1988)

[4] Livage J, Henry M, Sanchez C, "Sol-Gel Chemistry of Transition Metal Oxide, Progress in Solid State Chemistry," 18, 259 (1988)

[5] Pohl ER, Osterholtz FD, "Molecular Characterization of Composite Interfaces," Plenum, New York, 157 (1985)

[6] Iler RK, "The Chemistry of Silica," John Wiley & Sons, N.Y. (1979)

[7] Keefer KD, "Better Ceramics through Chemistry," Eds. C.J. Brinker, D.E. Clark, and D.R. Ulrich, North-Holland, N.Y., 15 (1984)

[8] Timms RE, J. Chem. Soc., 1969 (1971)

[9] Okkerse C, "Physical and Chemical Aspects of Adsirbents and Catalysts," Academic Press, New York (1978)

[10] Uhlmann DR, Jelinski BJ, Wrek GE, "Better Ceramics through Chemistry," New York, 59 (1984)

[11] Swain CG, Esteve RM, Jones RH, J. Am. Chem. Soc., 11, 965 (1989)

[12] Myung JJ, Chung YS, Kyong JB, Kim HK, J. Korean Ind. Eng. Chem., 7(4), 794 (1996)

[13] Guggenheim EA, Phil. Mag., 2, 538 (1926)

[14] Bacon JR, Demos JN, Anal. Chem., 55, 653 (1983)

[15] Ikemoto T, Uematsu K, Mizutani N, Kato M, 窯業協會紙, 93, 261 (1985)

[16] Jean JH, Goy DM, Ring TA, Am. Ceram. Soc. Bull., 66(10), 1517 (1987)

[17] Keefer KD, "Better Ceramics through Chemistry," eds. C.J. Brinker, D.E. Clark and D.R. Ulrich, North-Holland, N.Y., 15 (1984)

[18] Kingery WD, Bowen HK, Uhlmann DR, "Introduction to Ceramics," 2nd, John Wiley & Sons, New York, 95 (1960)

[19] Williams CE, May RP, Guinier A, "Material Science and Technology," ed. R.W. Cahn, D. Haasen and E.J. Kramer, 2B, VCH, New York, 611 (1993)

[20] Fedor LR, Bruice TC, J. Am. Chem. Soc., 87, 4138 (1965)

[21] Bunton CA, Shiner VJ, J. Am. Chem. Soc., 83, 3207 (1961)

[22] Gopalakrishnan G, Hogg JL, J. Org. Chem., 46, 4959 (1981)

[23] Kivinen A, Acta Chem. Scand., 19, 845 (1965)

[24] Hudson RF, Ber. Bunsenges Phys. Chem., 68, 215 (1964)

[25] Alder RW, Baker R, Brown JM, "Mechanism in Organic Chemistry," Chap. 3, Wiley-Interscience, London (1971)

[26] Tashma R, Rappoport Z, J. Am. Chem. Soc., 99, 1845 (1977)