Synthesis and Characterization of Nano-Aerogels

9.4. The Synthesis Parameters of Direct Sol-Gel Process in CO₂

During the aerogel synthesis processes, important parameters include: the temperature, pressure, concentrations of the reactants, scCO₂ wash, and flow rate of CO₂.

In this study, the temperature and pressure’s effect on TEOS conversion was studied by using the in situ IR spectrometry. It was found that a higher temperature and a lower pressure facilitate the consumption of Si-OEt. Surprisingly, in the range of 40-70 °C and 2000-7000 psig, there was no detectable effect of temperature and pressure on the TiO₂ morphology. However, the reactants’ concentrations, especially the acid/alkoxide ratio, had a significant effect on the resulting oxide nanomaterials. In the case of SiO₂, high concentrations of starting materials resulted in badly agglomerated micron-size particles. In the case of TiO₂, different acid ratios resulted in different morphologies, i.e. fibers or spheres. In the case of zirconia, high concentrations of starting materials resulted in formation of mesoporous monolith, and low concentrations resulted in formation of spherical nanoparticles.

The CO₂ flow rate during the extraction and venting step is also important to maintain the microstructure and a large surface area of the resulting materials. For example, when the reactor was less than 100 ml, a CO₂ flow rate less than 1 ml/min was necessary.

9.5. Future Work Recommendation

Recommendations for future work include:

1. Study the effect of temperature and pressure on the kinetics of sol-gel synthesizing TiO₂ and ZrO₂ in CO₂ using the in situ ATR-FTIR technique, which was not studied in this research.

2. Study the solubility of the precursors, e.g. TIP and ZBO in CO₂ under various temperatures and pressures. Use the experimental data and empirical equations to estimate various important physical properties such as the critical points of metal alkoxides, which are useful for stringent thermodynamic studies.

3. Synthesis of other oxides or hybrid oxides using the direct sol-gel process in CO₂. The successful synthesis of the oxide nanomaterials in this research is encouraging to extend the method for synthesizing other oxides, such as Al₂O₃, ZnO, and Fe₂O₃ and the hybrid materials.

4. Besides acetic acid, other carboxylic acids and polycarboxylic acids may also have potential to be used as polycondensation agents. Different molecular structures of the polycondensation agents may result in the formation of nanomaterials with different morphologies.

Bibliography

1. Niederberger, M.; Garnweitner, G.; Buha, J.; Polleux, J.; Ba, J.; Pinna, N., Nonaqueous synthesis of metal oxide nanoparticles: Review and indium oxide as case study for the dependence of particle morphology on precursors and solvents. Journal of Sol-Gel Science and Technology 2006, 40, 259-266.

2. Oskam, G., Metal oxide nanoparticles: synthesis, characterization and application. Journal of Sol-Gel Science and Technology 2006, 37, 161-164.

3. Raveendran, P.; Fu, J.; Wallen, S. L., A simple and " green " method for the synthesis of Au, Ag, and Au-Ag alloy nanoparticles. Green Chemistry 2006, 8, 34-38.

4. Schultz, E., Fully Exploiting the Potential of the Periodic Table through Pattern Recognition. J Chem Educ 2005, 82, 1649.

5. Walcarius, A.; Mandler, D.; Cox, J. A.; Collinson, M.; Lev, O., Exciting new directions in the intersection of functionalized sol-gel materials with electrochemistry. Journal of Materials Chemistry 2005, 15, 3663-3689.

6. Gupta, G.; Shah, P. S.; Zhang, X.; Saunders, A. E.; Korgel, B. A.; Johnston, K. P., Enhanced Infusion of Gold Nanocrystals into Mesoporous Silica with Supercritical Carbon Dioxide. Chem Mater 2005, 17, 6728-6738.

7. Do, T.-O., Nano - particles: potential applications in catalysis and nanotechnology. Recent Research Developments in Chemistry 2004, 2.

8. Tarascon, J.-M.; Grugeon, S.; Laruelle, S.; Larcher, D.; Poizot, P., The key role of nanoparticles in reactivity of 3d metal oxides toward lithium. Lithium Batteries 2004, 220-246.

9. Martin, C. R.; Kohli, P., The emerging field of nanotube biotechnology. Nat Rev Drug Discovery 2003, 2, 29-37.

10. Zhou, S.; Wu, L.; Xiong, M.; He, Q.; Chen, G., Dispersion and UV-VIS properties of nanoparticles in coatings. Journal of Dispersion Science and Technology 2004, 25, 417-433.

11. Pena, J.; Vallet-Regi, M.; San Roman, J., TiO2-polymer composites for biomedical applications. J Biomed Mater Res 1997, 35, 129-134.

12. Gangopadhyay, R.; De, A., Conducting Polymer Nanocomposites: A Brief Overview. Chem Mater 2000, 12, 608-622.

13. Min, B. K.; Santra, A. K.; Goodman, D. W., Understanding silica-supported metal catalysts: Pd/silica as a case study. Catalysis Today (2003), 2003, 85, 113-124.

14. Somorjai, G. A.; Rioux, R. M., High technology catalysts towards 100% selectivity: Fabrication, characterization and reaction studies. Catalysis Today 2005, 100, 201.

15. Zhang, S.-W.; Zhou, S.-X.; Weng, Y.-M.; Wu, L.-M., Synthesis of SiO₂/Polystyrene Nanocomposite Particles via Miniemulsion Polymerization. Langmuir 2005, 21, 2124-2128.

16. Ahn, J.-H.; Wang, G. X.; Liu, H. K.; Dou, S. X., Nanoparticle-dispersed PEO polymer electrolytes for Li batteries. J Power Sources 2003, 119-121, 422-426.

17. Buck, S. M.; Koo, Y.-E. L.; Park, E.; Xu, H.; Philbert, M. A.; Brasuel, M. A.; Kopelman, R., Optochemical nanosensor PEBBLEs: photonic explorers for bioanalysis with biologically localized embedding. Current Opinion in Chemical Biology 2004, 8, 540.

18. Brongersma, M. L., Nanoscale photonics: Nanoshells: gifts in a gold wrapper. Nature Materials 2003, 2, 296-297.

19. Barbé, C.; Bartlett, J.; Kong, L.; Finnie, K.; Lin, H. Q.; Larkin, M.; Calleja, S.; Bush, A.; Calleja, G., Silica Particles: A Novel Drug-Delivery System. Advanced Materials 2004, 16, 1959-1966.

20. Schneider, M.; Baiker, A., Titania-Based Aerogels. Catal Today 1997, 35, 339-365.

21. Gratzel, M., Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells. Inorg Chem 2005, 44, 6841-6851.

22. Mor, G. K.; Shankar, K.; Paulose, M.; Varghese, O. K.; Grimes, C. A., Use of Highly-Ordered TiO₂ Nanotube Arrays in Dye-Sensitized Solar Cells. Nano Lett 2005.

23. Bisquert, J.; Cahen, D.; Hodes, G.; Ruhle, S.; Zaban, A., Physical Chemical Principles of Photovoltaic Conversion with Nanoparticulate, Mesoporous Dye-Sensitized Soalr Cells. J. Phys. Chem. B 2003, 108, 8106-8118.

24. Akbar, S.; Yoo, S., Ceramic nano-structure for chemical sensing. Chemical Sensors 2004, 20, 30-31.

25. Wang, R.; Hashimoto, K.; Fujishima, A.; Chikuni, M.; Kojima, E.; Kitamura, A.; Shimohigoshi, M.; Watanabe, T., Light-induced amphiphilic surfaces. Nature 1997, 388, 431-432.

26. Yu, D.-G.; An, J. H.; Bae, J. Y.; Ahn, S. D.; Kang, S.-Y.; Suh, K. S., Preparation of Titanium dioxide/poly(methyl methacrylate-co-n-butyl acrylate-co-methacrylic acid) hybrid composite particles via emulsion polymerization. J Appl Poym Sci 2005, 97, 72-79.

27. Petrella, A.; Tamborra, M.; Curri, M. L.; Cosma, P.; Striccoli, M.; Cozzoli, P. D.; Agostiano, A., Colloidal TiO₂ Nanocrystals/MEH-PPV Nanocomposites: Photoelectrochemical Study. J Phys Chem B 2005, 109, 1554-1562.

28. Hu, Q.; Marand, E., In situ formation of nanosized TiO₂ domains within poly(amide-imide) by a sol-gel process. Polymer 1999, 40, 4833-4943.

29. Fernandez-Garcia, M.; Martinez-Arias, A.; Hanson, J. C.; Rodriguez, J. A., Nanostructured Oxides in Chemistry: Characterization and Properties. Chem Rev 2004, 104, 4063-4104.

30. Cimino, S.; Pirone, R.; Lisi, L., Zirconia supported LaMnO3 monoliths for the catalytic combustion of methane. Appl Catal B-Environ 2002, 35, 243-254.

31. Bahamonde, A.; Campuzano, S.; Yates, M.; Salerno, P.; Mendioroz, S., Influence of zirconia raw materials on the development of DeNOx monolithic catalysts. Appl Catal B-Environ 2003, 44, 333-346.

32. Diamant, Y.; Chappel, S.; Chen, S. G.; Melamed, O.; Zaban, A., Core-shell nanoporous electrode for dye sensitized solar cells: the effect of shell characteristics on the electronic properties of the electrode. Coordination Chemistry Reviews 2004, 248, 1271.

33. Yamahara, K.; Sholklapper, T. Z.; Jacobson, C. P.; Visco, S. J.; De Jonghe, L. C., Ionic conductivity of stabilized zirconia networks in composite SOFC electrodes. Solid State Ionics 2005, 176, 1359.

34. Morita, Y.; Nakata, K.; Kim, Y.-H.; Sekino, T.; Niihara, K.; Ikeuchi, K., Wear properties of alumina/zirconia composite ceramics for joint prostheses measured with an end-face apparatus. Bio-Medical Materials and Engineering 2004, 14, 263-270.

35. Fendler, J. H., Self-Assembled Nanostructured Materials. Chem Mater 1996, 8, 1616-1624.

36. Lin, J.; Lin, Y.; Liu, P.; Meziani, M. J.; Allard, L. F.; Sun, Y. P., Hot-Fluid Annealing for Crystalline Titanium Dioxide Nanoparticles in Stable Suspension. J Am Chem Soc 2002, 124, 11514-11518.

37. Chen, H.; Dai, K.; Peng, T.; Yang, H.; Zhao, D., Synthesis of thermally stable mesoporous titania nanoparticles via amine surfactant-mediated templating method. Mater Chem Phys 2006, 96, 176.

38. Oh, C. W.; Seong, G.-D. L.; Park, S.; Ju, C.-S.; Hong, S.-S., Synthesis of nanosized TiO₂ particles via ultrasonic irradiation and their photocatalytic activity. Reaction Kinetics and Catalysis Letters 2005, 85, 261.

39. Cushing, B. L.; Kolesnichenko, V. L.; O'Connor, C. J., Recent Advances in the Liquid-Phase Syntheses of Inorganic Nanoparticles. Chem Rev 2004, 104, 3893-3946.

40. Moran, P. D.; Bartlett, J. R.; Bowmaker, G. A.; Woolfrey, J. L.; Cooney, R. P., Formation of TiO₂ sols, gels and nanopowders from hydrolysis of Ti(OiPr)₄ in AOT reverse micelles. Journal of Sol-Gel Science and Technology 1999, 15, 251-262.

41. Li, D.; Xia, Y., Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning. Nano Lett 2004, 4, 933-938.

42. Li, D.; Xia, Y., Fabrication of titania nanofibers by electrospinning. Nano Lett 2003, 3, 555-560.

43. Shao, C.; Guan, H.; Liu, Y.; Gong, J.; Yu, N.; Yang, X., A novel method for making ZrO₂ nanofibres via an electrospinning technique. J Cryst Growth 2004, 267, 380-384.

44. Kim, C. S.; Okuyama, K.; Nakaso, K.; Shimada, M., Direct measurement of nucleation and growth modes in titania nanoparticles generation by a CVD method. J Chem Eng Jpn 2004, 37, 1379.

45. Nakaso, K.; Okuyama, K.; Shimada, M.; Pratsinis, S. E., Effect of reaction temperature on CVD-made TiO₂ primary particle diameter. Chemical Engineering Science 2003, 58, 3327.

46. Sudarshan, T. S. In Coated powders - new horizons and applications, Advances in Surface Treatment: Research & Applications (ASTRA), Proceedings of the International Conference, Hyderabad, India, 2003; Hyderabad, India, 2003; pp 412-422.

47. Kim, C.; Nakaso, K.; Xia, B.; Okuyama, K.; Shimada, M., A new observation on the phase transformation of TiO₂ nanoparticles produced by a CVD method. Aerosol Sci Tech 2005, 39, 104-112.

48. Mueller, R.; Jossen, R.; Pratsinis, S. E.; Watson, M.; Akhtar, M. K., Zirconia nanoparticles made in spray flames at high production rates. J Am Ceram Soc 2004, 87, 197-202.

49. Liang, C.; Shimizu, Y.; Sasaki, T.; Koshizaki, N., Synthesis, characterization, and phase stability of ultrafine TiO₂ nanoparticles by pulsed laser ablation in liquid media. J Mater Res 2004, 19, 1551-1557.

50. Kim, T. H.; Kang, J. P.; Kwon, Y. K., Synthesis and characterization of hollow titania nanospheres using a cationic colloidal particle as a template. Polymer Preprints 2005, 46, 566-567.

51. Li, X.; Lau, K. H. A.; Kim, D. H.; Knoll, W., High-Density Arrays of Titania Nanoparticles Using Monolayer Micellar Films of Diblock Copolymers as Templates. Langmuir 2005, 21, 5212-5217.

52. Iwasaki, M.; Davis, S. A.; Mann, S., Spongelike Macroporous TiO₂ Monoliths Prepared from Starch Gel Template. J Sol-Gel Sci Techn 2004, 32, 99-105.

53. Lim, K. T.; Hwang, H. S.; Ryoo, W.; Johnston, K. P., Synthesis of TiO₂ Nanoparticles Utilizing Hydrated Reverse Micelles in CO₂. Langmuir 2004, 20, 2466-2471.

54. Pierre, A. C.; Pajonk, G. M., Chemistry of Aerogels and Their Application. Chem Rev 2002, 102, 4243-4265.

55. Jessop, P.; Leitner, W., Chemical Synthesis Using Supercritical Fluids. Weinheim: Wiley-VCH: 1999.

56. McHugh, M. A.; Krukonis, V. J., Supercritical Fluid Extraction: Principles and Practice. Second ed.; Butterworth-Heinemann: Boston, 1994.

57. Sun, Y.-P., Supercritical fluid technology in materials science and engineering: syntheses, properties, and applications. Marcel Dekker: New York, 2002; p ix, 582 p.

58. Massey, B. S.; Ward-Smith, A. J., Mechanics of fluids. 8th ed.; Taylor & Francis: London; New York, 2006; p x, 696 p.

59. Fenghour, A.; Wakeham, W. A.; Vesovic, V., The Viscosity of Carbon Dioxide. Journal of Physical and Chemical Reference Data 1998, 27, 31-44.

60. NIST Chemistry WebBook: Thermophysical Properties of Fluid Systems. In National Institute of Standards and Technology: 2007.

61. White, H. E., Modern college physics. 4th ed.; Van Nostrand: Princeton, N. J., 1966; p 755 p.

62. Hahne, E.; Grigull, U., Heat transfer in boiling. Academic Press: New York, 1977; p xiv, 486 p.

63. Ye, X.; Wai, C. M., Making Nanomaterials in Supercritical Fluids: A Review. J. Chem. Ed. 2003, 80, 198-203.

64. Tan, H. S.; Borsadia, S., Particle Formation Using Supercritical Fluids: Pharmaceutical Applicatons. Exp. Opin. Ther. Patents 2001, 11, 861-872.

65. Krukonis, V. In Supercritical Fluid Nucleation of Difficult to Comminute Solids, AIChE annual meeting, San Francisco, November, 1984; San Francisco, 1984; p paper 140 f.

66. Matson, D. W.; Norton, K. A.; R.D.Smith, Chemtech 1989, 19, 480.

67. Petersen, R. C.; Matson, D. W.; Smith, R. D., Polym Eng Sci 1987, 27, 1693.

68. Reverchon, E., Supercritical antisolvent precipitation of micro- and nanoparticles. J. of Supercrit. Fluids. 1999, 15, 1-21.

69. DeSimone, J. M.; Maury, E. E.; Menceloglu, Y. Z.; McClain, J. B.; Romack, T. J.; Combes, J. R., Dispersion Polymerizations in Supercritical Carbon Dioxide. Science 1994, 265, 356-359.

70. Shaffer, K. A.; DeSimone, J. M., Chain Polymerizations in Inert Near and Supercritical Fluids. Trends in Polymer Science 1995, 3, 146-153.

71. Super, M.; Berluche, E.; Costello, C.; E., B., Copolymerization of 1,2-Epoxycyclohexane and Carbon Dioxide Using Carbon Dioxide as Both Reactant and Solvent. Macromolecules 1997, 30, 368-372.

72. Quadir, M. A.; DeSimone, J. M.; van Herk, A. M.; German, A. L., Pulsed_Laser Polymerization of Methyl Methacrylate in Liquid and Supercritical Carbon Dioxide. Macromolecules 1998, 31, 6481-6485.

73. Charpentier, P. A.; Kennedy, K.; DeSimone, J. M.; Roberts, G. W., Continuous Polymerizations in Supercritical Carbon Dioxide:Chain-Growth Precipitation Polymerizations. Macromolecules 1999, 32, 5973-5975.

74. Musie, G.; Wei, M.; Subramaniam, B.; Busch, D. H., Catalytic oxidations in carbon dioxide-based reaction media, including novel CO₂ -expanded phases. Coordination Chemistry Reviews 2001, 219-221, 789-820.

75. Tacke, T.; Wieland, S.; Panster, P., Selective and complete hydrogenation of vegetable oils and free fatty acids in supercritical fluids. Green Chemistry Using Liquid and Supercritical Carbon Dioxide 2003, 228-240.

76. Matsuda, T.; Watanabe, K.; Harada, T.; Nakamura, K., Enzymatic reactions in supercritical CO₂: carboxylation, asymmetric reduction and esterification. Catalysis Today 2004, 96, 103.

77. Loy, D. A.; Russick, E. M.; Yamanaka, S. A.; Baugher, B. M., Direct Formation of Aerogels by Sol-gel Polymerizations of Alkoxides in Supercritical Carbon Dioxide. Chem Mater 1997, 9, 2264-2268.

78. Moner-Girona, M.; Roig, A.; Molins, E., Sol-gel Route to Direct Formation of Silica Aerogel Microparticles Using Supercritical Solvents. J Sol-Gel Sci Techn 2003, 26, 645-649.

79. Aymonier, C.; Loppinet-Serani, A.; Reveron, H.; Garrabos, Y.; Cansell, F., Review of supercritical fluids in inorganic materials science. Journal of Supercritical Fluids 2006, 38, 242-251.

80. van Eldik, R.; Asano, T.; LeNoble, W. J., Activation and Reaction Volumes in Solution. 2. Chem. Rev. 1989, 89, 549-688.

81. Savage, P. E.; Gopalan, S.; Mizan, T. I.; Martino, C. J.; Brock, E. E., Reactions at Supercritical Conditions: Application and Fundamentals. AIChE J 1995, 41, 1723-1778.

82. Ellington, J. B.; Park, K. M.; Brennecke, J. F., Effect of local composition enhancements on the esterification of phthalic anhydride with methanol in supercritical carbon dioxide. Ind. Eng. Chem. Res. 1994, 33, 965-974.

83. Johnston, K. P.; Haynes, C., Extreme solvent effects on reaction rate constants at supercritical fluid conditions. AIChE J 1987, 33, 2017-2026.

84. Peng, D.-Y.; Robinson, D. B., A new two-constant equation of state. Ind Eng Chem Fundam 1976, 15, 59-64.

85. Johnston, K. P., Safer solutions for chemists. Nature 1994, 368, 187-188.

86. Turner, C. H.; Gubbins, K. E., Effects of supercritical clustering and selective confinement on reaction equilibrium: A molecular simulation study of the esterification reaction. J Chem Phys 2003, 119, 6057-6067.

87. Ellington, J. B.; Brennecke, J. F., Pressure effect on the esterification of phthalic anhydride in supercritical carbon dioxide. Chemical Communications 1993, 13, 1094-5.

88. Karen, A. K.; George, W. R.; Joseph, M. D., Heterogeneous Polymerization of Fluoroolefins in Supercritical Carbon Dioxide. 2005; p 329.

89. Woods, H. M.; Silva, M. M. C. G.; Nouvel, C.; Shakesheff, K. M.; Howdle, S. M., Material Processing in Supercritical Carbon Dioxide: Surfactants, Polymers and Biomaterials. J Mater Chem 2004, 14, 1663-1678.

90. O'Neil, A.; Watkins, J. J., Green chemistry in the microelectronics industry. Green Chem 2004, 6, 363-368.

91. King, J. W.; Williams, L. L., Utilization of critical fluids in processing semiconductors and their related materials. Curr Opin Solid ST M 2003, 7, 413-424.

92. Charpentier, P. A.; DeSimone, J. M.; Roberts, G. W., Continuous polymerizations in supercritical carbon dioxide. ACS Symposium Series 2002, 819, 113-135.

93. McHugh, M. A.; Krukonis, V. J., Supercritical Fluid Extraction:

Principles and Practice. Second ed.; Butterworth-Heinemann: Boston, 1994.

94. Darr, J. A.; Poliakoff, M., New Directions in Inorganic and Metal-Organic Coordination Chemistry in Supercritical Fluids. Chem Rev 1999, 99, 495-541.

95. Pierre, A. C.; Pajonk, G. M., Chemistry of Aerogels and Their Application. Chem. Rev. 2002, 102, 4243-4265.

96. Yoda, S.; Otake, K.; Takebayashi, Y.; Sugeta, T.; Sato, T., Effect of Supercritical Impregnation Conditions on the Properties of Silica-Titania Aerogels. J Non-Cryst Solids 2001, 285, 8-12.

97. Stallings, W. E.; Lamb, H. H., Synthesis of Nanostructured Titania Powders via Hydrolysis of Titanium Isopropoxide in Supercritical Carbon Dioxide. Langmuir 2003, 19, 2989-2994.

98. Suh, D. J.; Park, T.-J., Synthesis of High-Surface-Area Zirconia Aerogels with a Well-Developed Mesoporous Texture Using CO2 Supercritical Drying. Chem. Mater. 2002, 14, 1452-1454.

99. Pai, R. A.; Humayun, R.; Schulberg, M. T.; Sengupta, A.; Sun, J.-N.; Watkins, J. J., Mesoporous Silicates Prepared Using Preorganized Templates in Supercritical Fluids. Science 2004, 303, 507-510.

100. Hanrahan, J. P.; Copley, M. P.; Ryan, K. M.; Spalding, T. R.; Morris, M. A.; Holmes, J. D., Pore Expansion in Mesoprous Silicas Using Supercritical Carbon Dioxide. Chem. Mater. 2004, 16, 424-427.

101. Rathke, J. W.; Klingler, R. J.; Krause, T. R., Propylene hydroformylation in supercritical carbon dioxide. Organometallics 1991, 10, 1350-1355.

102. Reid, C.; Prausnitz, J. M.; Poling, B. E., The properties of gases and liquids. McGraw-Hill: New York, 1985.

103. Hench, L. L.; West, J. K., The sol-gel process. Chemical Reviews 1990, 90, 33-72.

104. Brinker, C. J.; Scherer, G. W., Sol-Gel Science:The Physics and Chemistry of Sol-Gel Processing. Academic Press: New York, 1990.

105. Brinker, C. J.; Scherer, G. W., Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing. Academic Press: New York, 1990.

106. Cansell, F.; Aymonier, C.; Loppinet-Serani, A., Review on materials science and supercritical fluids. Current Opinion in Solid State and Materials Science 2003, 7, 331.

107. Gesser, H. D.; Goswami, P. C., Aerogels and related porous materials. Chem. Rev. 1989, 89, 765-788.

108. Ebelmen, Untersuchungen uber die Verbindung der Borsaure und Kieselsaure mit. Aether Ann. Chim. Phys., 1846, Ser. 3, 319-55.

109. Kistler, S. S., J. Phys. Chem. 1932, 36, 52-64.

110. Lev, O.; Wu, Z.; Bharathi, S.; Glezer, V.; Modestov, A.; Gun, J.; Rabinovich, L.; Sampath, S., Sol-Gel Materials in Electrochemistry. Chem Mater 1997, 9, 2354-2375.

111. Roy, R., Ceramics by the Solution-Sol-Gel Route. Science 1987, 238, 1664-1669.

112. Schmidt, M.; Schwertfeger, F., Applications for silica aerogel products. J. Non-Cryst. Solids 1998, 225, 364-368.

113. Gesser, H. D.; Goswami, P. C., Aerogels and related porous materials. Chem Rev 1989, 89, 765-788.

114. Campbell, L. K.; Na, B. K.; Ko, E. I., Chem. Mater. 1992, 4, 1329-1333.

115. Brinker, C. J.; Scherer, G. W., Sol-Gel Science. Academic Press, New York: 1990.

116. Loy, D. A.; Russick, E. M.; Yamanaka, S. A.; Baugher, B. M., Direct Formation of Aerogels by Sol-gel Polymerizations of Alkoxides in Supercritical Carbon Dioxide. Chem. Mater. 1997, 9, 2264-2268.

117. Chhor, K.; Bocquet, J. F.; Pommier, C., Syntheses of submicron TiO₂ powders in vapor, liquid and supercritical phases, a comparative study. Materials Chemistry and Physics 1992, 32, 249.

118. Courtecuisse, V. G.; Bocquet, J. F.; Chhor, K.; Pommier, C., Modeling of a continuous reactor for TiO₂ powder synthesis in a supercritical fluid - experimental validation. The Journal of Supercritical Fluids 1996, 9, 222-226.

119. Brasseur-Tilmant, J.; Chhor, K.; Jestin, P.; Pommier, C., Ceramic membrane elaboration using supercritical fluid. Materials Research Bulletin 1999, 34, 2013.

120. Znaidi, L.; Chhor, K.; Pommier, C., Batch and semi-continuous synthesis of magnesium oxide powders from hydrolysis and supercritical treatment of Mg(OCH3)2. Materials Research Bulletin 1996, 31, 1527.

121. Chhor, K.; Bocquet, J. F.; Pommier, C., Syntheses of submicron magnesium oxide powders. Materials Chemistry and Physics 1995, 40, 63.

122. Bocquet, J. F.; Chhor, K.; Pommier, C., Barium titanate powders synthesis from solvothermal reaction and supercritical treatment. Materials Chemistry and Physics 1999, 57, 273.

123. Hu, M. Z. C.; Harris, M. T.; Byers, C. H., Nucleation and Growth for Synthesis of Nanometric Zirconia Particles by Forced Hydrolysis. Journal of Colloid and Interface Science 1998, 198, 87.

124. Zeng, J.; Zhang, M.; Song, Z.; Wang, L.; Li, J.; Li, K.; Lin, C., Lead-zirconate-titanate thin films deposited on silicon using a novel technique at low temperature. Applied Surface Science 1999, 148, 137.

125. Zeng, J.; Lin, C.; Li, J.; Li, K., Preparation of highly oriented Pb(Zr_0.52Ti_0.48)O₃ thin films by sol -gel -hydrothermal process. Journal of Materials Research 1999, 14, 2712-2715.

126. Zeng, J.; Lin, C.; Song, Z.; Li, K.; Li, J., Sol-gel-hydrothermal growth of oxide thin films at low temperatures. Philosophical Magazine Letters 2000, 80, 119-124.

127. Shen, J.; Zhang, Q.; Wang, J.; Yang, T.; Deng, Z.; Zhou, B.; Chen, L., Sol - gel processing of zirconia coating for HR mirrors with high laser damage threshold. Journal of Sol-Gel Science and Technology 2000, 19, 271-274.

128. Zhang, Q.; Shen, J.; Wang, J.; Wu, G.; Chen, L., Sol-gel derived ZrO₂-SiO₂ highly reflective coatings. International Journal of Inorganic Materials 2000, 2, 319.

129. Zhao, J.; Fan, W.; Wu, D.; Sun, Y., Stable nanocrystalline zirconia sols prepared by a novel method: alcohol thermal synthesis. Journal of Materials Research 2000, 15, 402-406.

130. Hayashi, H.; Torii, K., Hydrothermal synthesis of titania photocatalyst under subcritical and supercritical water conditions. J Mater Chem 2002, 12, 3671-3676.

131. Yang, J.; Mei, S.; Ferreira, J. M. F., Hydrothermal synthesis of well-dispersed TiO₂ nano -crystals. J Mater Res 2002, 17, 2197-2200.

132. Parvulescu, V.; Parvulescu, V. I.; Alifanti, M.; Jung, S. M.; Grange, P., One pot synthesis of mesoporous ternary V₂O₅-TiO₂-SiO₂ catalysts. Studies in Surface Science and Catalysis 2003, 146.

133. Tai, C. Y.; Hsiao, B.-Y.; Chiu, H.-Y., Preparation of spherical hydrous-zirconia nanoparticles by low temperature hydrolysis in a reverse microemulsion. Colloids and Surfaces, A: Physicochemical and Engineering Aspects 2004, 237, 105.

134. Corradi, A. B.; Bondioli, F.; Focher, B.; Ferrari, A. M.; Grippo, C.; Mariani, E.; Villa, C., Conventional and Microwave-Hydrothermal Synthesis of TiO₂ Nanopowders. Journal of the American Ceramic Society 2005, 88, 2639-2641.

135. Kang, M.; Ko, Y.-R.; Jeon, M.-K.; Lee, S.-C.; Choung, S.-J.; Park, J.-Y.; Kim, S.; Choi, S.-H., Characterization of Bi/TiO₂ nanometer sized particle synthesized by solvothermal method and CH₃CHO decomposition in a plasma-photocatalytic system. J Photochem Photobiol, A 2005, 173, 128.

136. Tadros, M. E. A., Carol L. J.; Russick, Edward M.; Youngman, Michael P., Synthesis of titanium dioxide particle in supercritical CO₂. J Supercrit Fluids 1996, 9, 172-176.

137. Hong, S.-S.; Lee, M. S.; Lee, G.-D.; Lim, K. T.; Ha, B.-J., Synthesis of titanium dioxides in water-in-carbon dioxide microemulsion and their photocatalytic activity. Mater Lett 2003, 57, 2975.

138. Reverchon, E.; Caputo, G.; Correra, S.; Cesti, P., Synthesis of titanium hydroxide nanoparticles in supercritical carbon dioxide on the pilot scale. The Journal of Supercritical Fluids 2003, 26, 253.

139. Yoda, S.; Sakurai, Y.; Endo, A.; Miyata, T.; Yanagishita, H.; Otake, K.; Tsuchiya, T., Synthesis of titania-pillared montmorillonite via intercalation of titanium alkoxide dissolved in supercritical carbon dioxide. J Mater Chem 2004, 14, 2763-2767.

140. Sun, D.; Liu, Z.; He, J.; Han, B.; Zhang, J.; Huang, Y., Surface sol-gel modification of mesoporous silica molecular sieve SBA-15 with TiO₂ in supercritical CO₂. Microporous and Mesoporous Materials 2005, 80, 165.

141. Yamashita, H.; Kawasaki, S.; Ichihashi, Y.; Harada, M.; Takeuchi, M.; Anpo, M.; Stewart, G.; Fox, M. A.; Louis, C.; Che, M., Characterization of Titanium-Silicon Binary Oxide Catalysts Prepared by the Sol-Gel Method and Their Photocatalytic Reactivity for the Liquid-Phase Oxidation of 1-Octanol. Journal of Physical Chemistry B 1998, 102, 5870-5875.

142. Jensen, H.; Joensen, K. D.; Iversen, S. B.; Sogaard, E. G., Low Temperature Synthesis of Metal Oxides by a Supercritical Seed Enhanced Crystallization (SSEC) Process. Ind Eng Chem Res 2006, ASAP.

143. Jensen, H.; Bremholm, M.; Nielsen, R. P.; Joensen, K. D.; S, P. J.; Birkedal, H.; Chen, Y.-S.; Almer, J.; Sogaard, E. G.; Iversen, S. B.; Iversen, B. B., In situ high-energy synchrotron radiation study of sol-gel nanoparticle formation in supercritical fluids. Angewandte Chemie, International Edition 2007, 46, 1113-1116.

144. Cabanas, A.; Enciso, E.; Carbajo, M. C.; Torralvo, M. J.; Pando, C.; Renuncio, J. A. R., Synthesis of SiO2-Aerogel Inverse Opals in Supercritical Carbon Dioxide. Chem Mater 2005, 17, 6137-6145.

145. Cabanas, A.; Enciso, E.; Carmen Carbajo, M.; Torralvo, M. J.; Pando, C.; Renuncio, J. A. R., Studies on the porosity of SiO₂-aerogel inverse opals synthesised in supercritical CO₂. Microporous and Mesoporous Materials 2007, 99, 23.

146. Levit, N.; Tepper, G., Supercritical CO₂-assisted electrospinning. J Supercrit Fluids 2004, 31, 329-333.

147. Lazzaroni, M. J.; Bush, D.; Jones, R.; Hallett, J. P.; Liotta, C. L.; Eckert, C. A., High-pressure phase equilibria of some carbon dioxide-organic-water systems. Fluid Phase Equilibria 2004, 224, 143-154.

148. Schneider, M. S.; Grunwaldt, J.-D.; Burgi, T.; Baiker, A., High pressure view-cell for simultaneous in situ infrared spectroscopy and phase behavior monitoring of multiphase chemical reactions. Rev Sci Instrum 2003, 74, 4121-4128.

149. Feng, L.; Berglund, K. A., ATR FTIR for determination optimal cooling curves for batch crystallization of succinic acid. J. of Crystal Growth 2002, 2, 449-452.

150. Lewiner, F.; F`evotte, G.; Klein, J. P.; Puel, F., Improving Batch Cooling Seeded Crystallization of an Organic Weed-Killer Using On-Line ATR FTIR Measurement of Supersaturation. J. of Crystal Growth 2001, 226, 348-362.

151. Burns, D. A.; Ciurczak, E. W., Handbook of near-infrared analysis. 2nd ed.; Dekker: New York, 2001; p xv, 814 p.

152. Newbury, D. E.; Williams, D. B., The electron microscope: the materials characterization tool of the millennium. Acta Materialia 2000, 48, 323-346.

153. Van der Mast, K. D., Ultramicrosc 1996, 64, 1.

154. Horiuchi, S., Fundamentals of high-resolution transmission electron microscopy. North-Holland: Amsterdam; New York, 1994; p xv, 342 p.

155. Zaefferer, S., Investigation of the correlation between texture and microstructure on a submicrometer scale in the TEM. Adv Eng Mater 2003, 5, 745-752.

156. Egerton, R. F.; Li, P.; Malac, M., Radiation damage in the TEM and SEM. Micron 2004, 35, 399-409.

157. Zhang, H.; Banfield, J. F., Understanding Polymorphic Phase transformation Behavior during Growth of Nanocrystalline Aggregates: Insights from TiO2. J Phys Chem B 2000, 104, 3481-3487.

158. MATTER, U. m. s. d., Unit Cell. In The University of Liverpool: 2000.

159. Huang, J. Y.; Park, B. H.; Jan, D.; Pan, X. Q.; Zhu, Y. T.; Jia, Q. X., High-resolution Transmission Electron Microscopy Study of Defects and Interfaces in Epitaxial TiO₂ Films on Sapphire and LaAlO₃. Philos Mag A 2002, 82, 735-749.

160. Mittemeijer, E. J.; Scardi, P., Diffraction analysis of the microstructure of materials. Springer: Berlin; New York, 2004; p xxv, 549 p.

161. Brunauer, S.; Emmett, P. H.; Teller, E., Adsorption of Gases in Multimolecular Layers. J Am Chem Soc 1938, 60, 309-319.

162. Rouquerol, J.; Avnir, D.; Fairbridge, C. W.; Evertt, D. H.; Haynes, J. H.; Pernicone, N.; Ramsay, J. D. F.; Sing, K. S. W.; Unger, K. K., Recommendations for the characterization of porous solids. Pure Appl Chem 1994, 66, 1739.

163. Barrett, E. P.; Joyner, L. G.; Halenda, P. P., The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. J Am Chem Soc 1951, 73, 373-380.

164. Gregg, S. J.; Sing, K. S. W., Adsorption, surface area, and porosity. 2nd ed.; Academic Press: London; Toronto, 1982; p xi, 303 p.

165. Liu, H.; Zhang, L.; Seaton, N. A., Sorption hysteresis as a probe of pore structure. Langmuir 1993, 9, 2576-2582.

166. Salmas, C. E.; Androutsopoulos, G. P., Rigid Sphere Molecular Model Enables an Assessment of the Pore Curvature Effect upon Realistic Evaluations of Surface Areas of Mesoporous and Microporous Materials. Langmuir 2005, 21, 11146-11160.

167. Libby, B.; Monson, P. A., Adsorption/Desorption Hysteresis in Inkbottle Pores: A Density Functional Theory and Monte Carlo Simulation Study. Langmuir 2004, 20, 4289-4294.

168. Kikkinides, E. S.; Kainourgiakis, M. E.; Stubos, A. K., Origin of Hysteresis of Gas Adsorption in Disordered Porous Media: Lattice Gas Model versus Percolation Theory. Langmuir 2003, 19, 3338-3344.

169. Lukens, W. W.; Schmidt-Winkel, P.; Zhao, D.; Feng, J.; Stucky, G. D., Evaluating Pore Sizes in Mesoporous Materials: A Simplified Standard Adsorption Method and a Simplified Broekhoff-de Boer Method. Langmuir 1999, 15, 5403-5409.

170. Dean, J. A., Analytical Chemistry Handbook. Academic Press, New York: 1995.

171. Sui, R.; Rizkalla, A. S.; Charpentier, P. A., Synthesis and Formation of Silica Aerogel Particles By a Novel Sol-Gel Route in Supercritical Carbon Dioxide. J Phys Chem B 2004, 108, 11886-11892.

172. Ye, S., A New Electrocatalyst Consisting of a Molecularly Homogeneous Platinum-Aerogel Nanocomposite. Can. J. Chem. 1997, 75, 1666-1673.

173. Hair, L. M.; al., e., Local, Nano- and Micro-Structures of Mixed Metal Oxide Aerogels for Catalyst Applications. J. Non-Cryst. Solids 1995, 186, 168-176.

174. Hrubesh, L. W., Aerogel applications. J. Non-Cryst. Solids 1998, 225, 335-342.

175. Kistler, S. S., Coherent Expanded Aerogels and Jellies. Nature 1931, 127, 741.

176. Cooper, A. I., Polymer synthesis and processing using supercritical carbon dioxide. J. Mater. Chem. 2000, 10, 207-234.

177. Loy, D. A.; Russick, E. M.; Yamanaka, S. A.; Baugher, B. M., Chem. Mater. 1997, 749.

178. Moner-Girona, M.; Roig, A.; Molins, E.; Llibre, J., J. Sol-Gel Sci. 2003, 26, 645-649.

179. Tohge, N.; Moore, G. S.; Mackenzie, J. D., Structural Developments During the Gel to Glass Transition. J Non-Cryst Solids 1984, 63, 95-103.

180. Pouxviel, J. C.; Boilot, J. P.; Beloeil, J. C.; Lalleman, J. Y., NMR Study of the Sol/Gel Polymerization. J. Non-Cryst. Solids 1987, 89, 345-360.

181. Odian, G., Principles of Polymerization. 3rd ed.; John Wiley & Sons, Inc.: New York, 1991.

182. Ota, T.; Imaeda, M.; Takase, H.; Kobayashi, M.; Kinoshita, N.; Hirashita, T.; Miyazaki, H.; Hikichi, Y., Porous titania ceramic prepared by mimicking silicified wood. J am Ceram Soc 2000, 83, 1521-1523.

183. Yoshida, K.; Tanagawa, M.; Atsuta, M., Effects of filler composition and surface treatment on the characteristics of opaque resin composites. J Biomed Mater Res 2001, 58, 525-530.

184. Suzuki, H.; Taira, M.; Wakasa, K.; Yamaki, M., Refractive-index-adjustable fillers for visible-light-cured dental resin composites: preparation of TiO2-SiO2 glass powder by the sol-gel process. J Dent Res 1991, 70, 883-888.

185. Taruta, S.; Itou, Y.; Tausagawa, N.; Okada, K.; Otsuka, N., Influence of aluminum titanate formation on sintering of bimodal size-distributed alumina powder mixtures. J am Ceram Soc 1997, 80, 551-556.

186. Takaba, H.; Way, J. D., Separation of Isomeric Xylenes Using Cyclodextrin-Modified Ceramic Membranes. Ind. Eng. Chem. Res. 2003, 42, 5697-5701.

187. Tani, K.; Suzuki, Y., Investigation of the ion-exchange behavior of titania. Application as a packing material for ion chromatography. Chromatographia 1997, 46, 623-627.

188. Lin, H.-M.; Kao, S.-T.; Lin, K.-M.; Chang, J.-R.; Shyu, S.-G., Grafting TiO2 on MCM-41 as a TiO2 support for vanadia for catalytic oxidation of ethanol-EXAFS and XANES analyses of vanadium. J Catal 2004, 224, 156-163.

189. Rainone, F.; Kiwi-Minsker, L.; Bulushev, D. A.; Buffat, P. A.; Renken, A., Structural and catalytic properties of vanadia-based fibrous catalysts in toluene partial oxidation. Appl Catal A-Gen 2003, 244, 251-263.

190. Herrmann, J. M., Electronic effects in strong metal-support interactions on titania deposited metal catalysts. J Catal 1984, 89, 404-412.

191. Anpo, M.; Takeuchi, M., The design and development of highly reactive titanium oxide photocatalysts operating under visible light irradiation. J Catal 2003, 216, 505-516.

192. Martyanov, I. N.; Klabunde, K. J., Comparative study of TiO2 particles in powder form and as a thin nanostructured film on quartz. J Catal 2004, 225, 408-416.

193. Lukaski, A. C.; Muggli, D. S., Photocatalytic oxidation of methyl formate on TiO2: a transient DRIFTS study. J Catal 2004, 223, 250-261.

194. Tseng, I.-H.; Wu, J. C. S.; Chou, H.-Y., Effects of sol-gel procedures on the photocatalysis of Cu/TiO2 in CO2 photoreduction. J Catal 2004, 221, 432-440.

195. Yeung, K. L.; Yau, S. T.; Maira, A. J.; Coronado, J. M.; Soria, J.; Yue, P. L., The influence of surface properties on the photocatalytic activity of nanostructured TiO2. J Catal 2003, 219, 107-116.

196. Bach, U.; Lupo, D.; Comte, P.; Moser, J., E; Weissortel, F.; Salbeck, J.; Spreitzer, H.; Gratzel, M., Solid-State Dye-Sensitized Mesoporous TiO2 Solar Cells with High Photon-to-Electron Conversion Efficiencies. Nature 1998, 395, 583-585.

197. Bando, K. K.; Mitsuzuka, Y.; Sugino, M.; Sugihara, H.; Sayama, K.; Arakawa, H., Attachment of an Organic dye on a TiO2 Substrate in Supercritical CO2: Application to a Solar Cell. Chemistry Letters 1999, 853-854.

198. Schumacher, B.; Denkwitz, Y.; Plzak, V.; Kinne, M.; Behm, R. J., Kinetics, mechanism, and the influence of H2 on the CO oxidation reaction on a Au/TiO2 catalyst. J Catal 2004, 224, 449-462.

199. Nelson, B. P.; Candal, R.; Corn, R. M.; Anderson, M. A., Control of Surface and z Potentials on Nanoporous TiO2 Films by Potential-Determining and Specifically Adsorbed Ions. Langmuir 2000, 16, 6094-6101.

200. Sakai, N.; Ebina, Y.; Takada, K.; Sasaki, T., Electronic Band Structure of Titania Semiconductor Nanosheets Revealed by Electrochemical and Photoelectrochemical Studies. J Am Chem Soc 2004, 126, 5851-5858.

201. Navio, J.; Colon, G.; Macias, M.; Real, C.; Litter, M. I., Iron-doped titania semiconductor powders prepared by a sol-gel method. Part I. Synthesis and characterization. Appl Catal A-Gen 1999, 177, 111-120.

202. Yoko, T.; Yuasa, A.; Kamiya, K.; Sakka, S., Sol-gel-derived titanium dioxide film semiconductor electrode for photocleavage of water. Preparation and effects of postheating treatment on the photoelectrochemical behavior. J Electrochem Soc 1991, 138, 2279-2285.

203. Fujishima, A.; Honda, K., Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37-8.

204. Elder, S. H.; Cot, F. M.; Su, Y.; Heald, S. M.; Tyryshkin, A. M.; Bowman, M. K.; Gao, Y.; Joly, A. G.; Balmer, M. L.; Kolwaite, A. C.; Magrini, K. A.; Blake, D. M., The Discovery and Study of Nanocrystalline TiO₂-(MoO₃) Core-Shell Materials. J Am Chem Soc 2000, 122, 5138-5146.

205. Choi, W.; Termin, A.; Hoffmann, M. R., The Role of Metal Ion Dopants in Quantum-Sized TiO₂: Correlation between Photoreactivity and Charge Carrier Recombination Dynamics. J Phys Chem 1994, 98, 13669-13679.

206. Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y., Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxide. Science 2001, 293, 269-271.

207. Jung, H. S.; Lee, J. K.; Nastasi, M.; Lee, S. W.; Kim, J. Y.; Park, J. S.; Hong, K. S.; Shin, H., Preparation of Nanoporous MgO-Coated TiO₂ Nanoparticles and Their Application to the Electrode of Dye-Sensitized Solar Cells. Langmuir 2005, 21, 10332-10335.

208. Lee, S.; Jeon, C.; Park, Y., Fabrication of TiO₂ Tubules by Template Synthesis and Hydrolysis with Water Vapor. Chem Mater 2004, 16, 4292-4295.

209. Bosc, F.; Ayral, A.; Albouy, P. A.; Guizard, C., A Simple Route for Low-Temperature Synthesis of Mesoporous and Nanocrystalline Anatase Thin Films. Chem Mater 2003, 15, 2463-2468.

210. Joo, J.; Kwon, S. G.; Yu, T.; Cho, M.; Lee, J.; Yoon, J.; Hyeon, T., Large-Scale Synthesis of TiO₂ Nanorods via Nonhydrolytic Sol-Gel Ester Elimination Reaction and Their Application to Photocatalytic Inactivation of E. coli. J Phys Chem B 2005, 109, 15297-15302.

211. Li, G.; Li, L.; Boerio-Goates, J.; Woodfield, B. F., High Purity Anatase TiO₂ Nanocrystals: Near Room-Temperature Synthesis, Grain Growth Kinetics, and Surface Hydration Chemistry. J Am Chem Soc 2005, 127, 8659-8666.

212. Baerns, M., Basic Principles in Applied Catalysis. Springer: New York, 2004.

213. Yang, P.; Zhao, D.; Margolese, D. I.; Chmelka, B. F.; Stucky, G. D., Generalized Syntheses of Large-pore mesoporous Metal Oxides with Semicrystalline Frameworks. Nature 1998, 396, 152-155.

214. Imhof, A.; Pine, D. J., Ordered Macroporous Materials by Emulsion Templating. Nature 1997, 389, 948-951.

215. Li, D.; Zhou, H.; Honma, I., Design and Synthesis of Self-ordered Mesoporous Nanocomposite through Controlled in-situ Crystallization. Nature Materials 2004, 3, 65-72.

216. Yun, H.-S.; Miyazawa, K.; Zhou, H.; Honma, I.; Kuwabara, M., Synthesis of Mesoporous Thin TiO2 Films with Hexagonal Pore Structures Using Triblock Copolymer Templates. Adv Mater 2001, 13, 1377-1380.

217. Liu, C.; Fu, L.; Economy, J., A Simple, Template-Free Route for the Synthesis of Mesoporous Titanium Dioxide Materials. J Mater Chem 2004, 14, 11887-1187.

218. Madhugiri, S.; Sun, B.; Smirniotis, P. G.; Ferraris, J. P.; Balkus Jr., K. J., Electrospun Mesoporous Titanium Dioxide Fibers. Microporous and Mesoporous Materials 2004, 69, 77-83.

219. Bansal, V.; Rautaray, D.; Ahmad, A.; Sastry, M., Biosynthesis of zirconia nanoparticles using the fungus Fusarium oxysporum. J Mater Chem 2004, 14, 3303-3305.

220. Flood, R. U.; Fitzmaurice, D., Preparation, Characterization, and Potential-Dependent Optical Adsorption Spectroscopy of Unsupported Large-Area Transparent Nanocrystalline TiO2 Membranes. J Phys Chem 1995, 99, 8954-8958.

221. Yao, B.; Zhang, L., Preparation and characterization of mesoporous titania gel-monolith. J Mater Chem 1999, 34, 5983-5987.

222. Krstic, V. D., Fracture of brittle solids in the presence of thermoelastic stresses. J Am Ceram Soc 1984, 67, 589-593.

223. Hosono, H.; Sakai, Y.; Fasano, M.; Abe, Y., Preparation of monolithic porous titania-silica ceramics. J am Ceram Soc 1990, 73, 2536-2538.

224. Maurer, S. M.; Ng, D.; Ko, E. I., Catal Today 1993, 16, 319.

225. Suh, D. J.; Park, T.-J., Effect of aging conditions on the pore structural properties of titania aerogels. J Mater Sci Lett 1997, 16, 490.

226. Campbell, L. K.; Na, B. K.; Ko, E. I., Synthesis and Characterization of Titania Aerogels. Chem Mater 1992, 4, 1329-1333.

227. Boyle, T. J.; Tyner, R. P.; Alam, T. M.; Scott, B. L.; Ziller, J. W.; Potter, B. G., Jr., Implications for the Thin-Film Densification of TiO2 from Carboxylic Acid-Modified Titanium Alkoxides. Syntheses, Characterizations, X-ray Structures of Ti3(3-O)(O2CH)2(ONep)8, Ti3(3-O)(O2CMe)2(ONep)8, Ti6(3-O)6(O2CCHMe2)6(ONep)6, [Ti(-O2CCMe3)(ONep)3]2, and Ti3(3-O)(O2CCH2CMe3)2(ONep)8 (ONep = OCH2CMe3)1. J Am Chem Soc 1999, 121, 12104-12112.

228. Perrin, F. X.; Nguyen, V.; Vernet, J. L., FT-IR Spectroscopy of Acid-Modified Titanium Alkoxides: Investigations on the Nature of Carboxylate Coordination and Degree of Complexation. J Sol-Gel Sci Techn 2003, 28, 205-215.

229. Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds. A Wiley-Interscience Publication: New York, 1997; Vol. Part B, p 59-62.

230. Deacon, G. B.; Phillips, R. J., Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination. Coord Chem Rev 1980, 33, 227-50.

231. Rammal, A.; Brisach, F.; Henry, M., Hydrothermal synthesis of TiO₂ anatase nanocrystals using hexaprismatic-shaped oxo-carboxylate complexes. Comptes Rendus Chimie 2002, 5, 59-66.

232. Doeuff, S.; Dromzee, Y.; Taulelle, F.; Sanchez, C., Synthesis and solid- and liquid-state characterization of a hexameric cluster of titanium(IV): Ti₆(m2-O)₂(m3-O)₂(m2-OC₄H₉)₂(OC₄H₉)₆(OCOCH₃)₈. Inorg Chem 1989, 28, 4439-45.

233. Papiernik, R.; Hubert-Pfalzgraf, L. G.; Vaissermann, J.; Goncalves, M. C. H. B., Synthesis and characterization of new titanium hexanuclear oxo carboxylato alkoxides. Molecular structure of [Ti6(m3-O)6(m-O2CC6H4OPh)6(OEt)6]. J Chem Soc, Dalton Trans 1998, 14, 2285-2288.

234. Sui, R.; Charpentier, P. A.; Rizkalla, A. S.; Jennings, M. C., Hexakis(m -acetato-k 2O,O')hexaisopropoxyhexa-m 3-oxo-hexatitanium. Acta Crystallogr 2006, E62, m373-m375.

235. Wu, P.-G.; Ma, C.-H.; Shang, J. K., Effects of nitrogen doping on optical properties of TiO₂ thin films. Appl Phys A 2005, 81, 1411-1417.

236. Zhang, H.; Banfield, J. F., J. Mater Chem 1998, 8, 2073-2076.

237. Zhang, H.; Banfield, J. F., Thermodynamic Analysis of Phase Stability of Nanocrystalline Titania. J Mater Chem 1998, 8, 2073-2076.

238. Doeuff, S.; Henry, C.; Sanchez, C.; Livage, J., Hydrolysis of titanium alkoxides: modification of the molecular precursor by acetic acid. J Non-Cryst Solids 1987, 8, 206-216.

239. Fink, R.; Hancu, D.; Valentine, R.; Beckman, E. J., Toward the Development of “CO2-philic” Hydrocarbons. 1. Used of side-Chain Functionalization to Lower the Miscibility Pressure of Polydimethylsiloxanes in CO2. J. Phys. Chem. B 1999, 103, 6441-6444.

240. Raveendran, P.; Wallen, S. L., Sugar Acetates as Novel, Renewable CO2-philes. J. Am. Chem. Soc., 2002, 124, 7274-7275.

241. Mu, T.; Han, B.; Zhang, J.; Li, Z.; Liu, Z.; Du, J.; Liu, D., Hydrogen bonding of acetic acid in CO₂ + n-pentane mixed fluids in the critical region. J Supercrit Fluids 2004, 30, 17-24.

242. Yamamoto, M.; Iwai, Y.; Nakajima, T.; Arai, Y., Fourier Transform Infrared Study on Hydrogen Bonding Species of Carboxylic Acids in Supercritical Carbon Dioxide with Ethanol. J Phys Chem A 1999, 103, 3525-3529.

243. Liu, J.; Shi, J.; He, D.; Zhang, Q.; Wu, X.; Liang, Y.; Zhu, Q., Surface Active Structure of Ultra-fine Cu/ZrO2 Catalysts Used for the CO2+H2 to Methanol Reaction. Appl Catal A-Gen 2001, 218, 113-119.

244. Koppel, R. A.; Stocker, C.; Baiker, A., Copper- and silver-zirconia aerogels: preparation, structural properties and catalytic behavior in methanol synthesis from carbon dioxide. J Catal 1998, 179, 515-527.

245. Kalies, H.; Pinto, N.; Pajonk, G. M.; Bianchi, D., Hydrogenation of Formate Species Formed by CO Chemisorption on a Zirconia Aerogel in the Presence of Platinum. Appl Catal A-Gen 2000, 202, 197-205.

246. Bahamonde, A.; Mohino, F.; Rebollar, M.; Yates, M. A., P.; Mendioroz, S., Pillared clay and zirconia-based monolithic catalysts for selective catalytic reduction of nitric oxide by methane. Catal Today 2001, 69, 233-239.

247. Pacheco, G.; Zhao, E.; Garcia, A.; Sklyarov, A.; Fripiat, J. J., Synthesis of Mesoporous Zirconia with Anionic Surfactants. J. Mater. Chem. 1998, 8, 219-226.

248. Crepaldi, E. L.; de A.A. Soler-Illia, G. J.; Grosso, D.; Albouy, P.-A.; Sanchez, C., Design and Post-functionalisation of Ordered Mesoporous Zirconia Thin Films. Chem. Commun. 2001, 1582-1583.

249. Suh, D. J.; Park, T.-J., Synthesis of High-Surface-Area Zirconia Aerogels with a Well-Developed Mesoporous Texture Using CO₂ Supercritical Drying. Chem Mater 2002, 14, 1452-1454.

250. Somiya, S.; Yamamoto, N.; H. Yanagina, Science and Technology of Zirconia III. American Ceramic Society: Westerville, OH, 1988; Vol. 24A and 24B.

251. Li, G.; Li, W.; Zhang, M.; Tao, K., Characterization and catalytic application of homogeneous nano-composite oxides ZrO2-Al2O3. Catal Today 2004, 93-95, 595-601.

252. Kong, Y.-M.; Bae, C.-J.; Lee, S.-H.; Kim, H.-W.; Kim, H.-E., Improvement in biocompatibility of ZrO2-Al2O3 nano-composite by addition of HA. Biomaterials 2005, 26, 509-517.

253. Badwal, S. P. S.; Ciacchi, F. T.; Giampietro, K. M., Analysis of the conductivity of commercial easy sintering grade 3 mol% Y₂O₃-ZrO₂ materials. Solid State Ionics 2005, 176, 169.

254. Shukla, S.; Seal, S.; Vanfleet, R., Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia. J Sol-Gel Sci Techn 2003, 27, 119-136.

255. Willert, M.; Rothe, R.; Landfester, K.; Antonietti, M., Synthesis of Inorganic and Metallic Nanoparticles by Miniemulsification of Molten Salts and Metals. Chem Mater 2001, 13, 4681-4685.

256. Limaye, A. U.; Helble, J. J., Morphological control of zirconia nanoparticles through combustion aerosol synthesis. J Am Ceram Soc 2002, 85, 1127-1132.

257. Mondal, A.; Ram, S., Monolithic t-ZrO2 nanopowder through a ZrO(OH)2×xH2O polymer precursor. J Am Ceram Soc 2004, 87, 2187-2194.

258. TORAYA, H., Whole-powder-pattern fitting without reference to a structural model: application to X-ray powder diffraction data. J Appl Cryst 1986, 19, 440-447.

259. Rojas-Cervantes, M. L.; -Aranda, R. M. M.; -Peinado, A. J. L.; -Gonzalez, J. D. D. L., ZrO2 obtained by the sol-gel method: influence of synthesis parameters on physical and structural characteristics. Journal of Materials Science 1994, V29, 3743.

260. Ward, D. A.; Ko, E. I., Synthesis and Structural Transformation of Zirconia Aerogels. Chem Mater 1993, 5, 956-969.

261. Gregg, S. J.; Sing, K. S. W., Adsorption, Surface Area and Porosity. Academic Press: 1982.

262. Phalippou, J.; Woignier, T.; Zarzycki, J., In Ultrastructure processing of ceramics, glasses, and composites, Hench, L. L.; Ulrich, D. R., Eds. Wiley: New York, 1984; pp 70-87.

263. Weibel, A.; Bouchet, R.; Boulc'h, F.; Knauth, P., The Big Problem of Small Particles: A Comparison of Methods for Determination of Particle Size in Nanocrystalline Anatase Powders. Chem Mater 2005, 7, 2378-2385.

264. Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds. A Wiley-Interscience Publication: New York, 1997.

265. Conley, R. T., Infrared spectroscopy. Allyn and Bacon: Boston, 1966; p ix, 293 p.

266. Yi, G.; Sayer, M., An acetic acid/water based sol-gel PZT process. II: Formation of a water based solution. J Sol-Gel Sci Techn 1996, 6, 75-82.

267. Sharp, K. G., A two-component, non-aqueous route to silica gel. J Sol-Gel Sci Techn 1994, 2, 35-41.

268. Kickelbick, G.; Holzinger, D.; Brick, C.; Trimmel, G.; Moons, E., Hybrid Inorganic-Organic Core-Shell Nanoparticles from Surface-Functionalized Titanium, Zirconium, and Vanadium Oxo Clusters. Chem Mater 2002, 14, 4382-4389.

269. Kickelbick, G.; Schubert, U., Oxozirconium methacrylate clusters. Zr₆(OH)₄O₄(OMc)₁₂ and Zr₄O₂(OMc)₁₂ (OMc = methacrylate). Chem Ber/Recl 1997, 130, 473-477.

270. Kickelbick, G.; Wiede, P.; Schubert, U., Variations in capping the Zr₆O₄(OH)₄ cluster core: X-ray structure analyses of [Zr₆(OH)₄O₄(OOC-CH=CH₂)₁₀]₂([mu]-OOC-CH=CH₂)₄ and Zr₆(OH)₄O₄(OOCR)₁₂(PrOH) (R = Ph, CMe = CH₂). Inorganica Chimica Acta 1999, 284, 1.

271. Brown, S. D.; Sum, S. T.; Despagne, F.; Lavine, B. K., Chemometrics. Anal Chem 1996, 68, 21-62.

272. Windig, W.; Guilment, J., Interactive self-modeling mixture analysis. Analytical Chemistry 1991, 63, 1425-32.

273. Jung, Y. M.; Noda, I., New approaches to generalized two-dimensional correlation spectroscopy and its applications. Applied Spectroscopy Reviews 2006, 41, 515-547.

274. Jiang, J.-H.; Liang, Y.; Ozaki, Y., Principles and methodologies in self-modeling curve resolution. Chemometrics and Intelligent Laboratory Systems 2004, 71, 1-12.

275. Wallace, R. M., Analysis of Absorption Spectra of Multicomponent Systems. J Phys Chem 1960, 64, 899-901.

276. Windig, W.; Stephenson, D. A., Self-modeling mixture analysis of second-derivative near-infrared spectral data using the SIMPLISMA approach. Analytical Chemistry 1992, 64, 2735-42.

277. Sasic, S.; Amari, T.; Siesler, H. W.; Ozaki, Y., Polycondensation Reaction of Bis(hydroxyethylterephthalate)Self Modeling Curve Resolution Analysis of On-Line ATR/FT-IR Spectra. Applied Spectroscopy 2001, 55, 1181.

278. Du, Y.; Jiang, J.; Liang, Y.; Amari, T.; Ozaki, Y., Chemometric resolution of ATR-IR spectra data for polycondensation reaction of bis(hydroxyethyl terephthalate) with a combination of self-modeling curve resolution (SMCR) and local rank analysis. Analyst 2003, 128, 1320-1325.

279. Tummers, P. H. G.; Houben, E. J. E.; Jansen, J. F. G. A.; Wienke, D., Evaluation of advanced data analysis techniques on time resolved FT-IR spectroscopy data of photo-copolymerization reactions. Vibrational Spectroscopy 2007, 43, 116-124.

280. Dupuy, N.; Batonneau, Y., Reliability of the contribution profiles obtained through the SIMPLISMA approach and used as reference in a calibration process: Application to Raman micro-analysis of dust particles. Analytica Chimica Acta 2003, 495, 205.

281. Batonneau, Y.; Bremard, C.; Laureyns, J.; Merlin, J. C.; Windig, W., Polarization Effects of Confocal Raman Microspectrometry of Crystal Powders Using Interactive Self-Modeling Analysis. J Phys Chem B 2003, 107, 1502-1513.

282. Chew, W.; Widjaja, E.; Garland, M., Band-Target Entropy Minimization (BTEM): An Advanced Method for Recovering Unknown Pure Component Spectra. Application to the FTIR Spectra of Unstable Organometallic Mixtures. Organometallics 2002, 21, 1982-1990.

283. Windig, W.; Antalek, B.; Lippert, J. L.; Batonneau, Y.; Bremard, C., Combined Use of Conventional and Second-Derivative Data in the SIMPLISMA Self-Modeling Mixture Analysis Approach. Anal Chem 2002, 74, 1371-1379.

284. Rauch, P. J.; Harrington, P. d.; Davis, D. M., Chemometric Resolution of Mixture Components by Cleardown Rates. Anal Chem 1998, 70, 716-723.

285. Wasim, M.; Hassan, M. S.; Brereton, R. G., Evaluation of chemometric methods for determining the number and position of components in high-performance liquid chromatography detected by diode array detector and on-flow 1H nuclear magnetic resonance spectroscopy. Analyst 2003, 128, 1082-1090.

286. Bu, D.; Brown, C. W., Self-Modeling Mixture Analysis by Interactive Principal Component Analysis. Applied Spectroscopy 2000, 54, 1214.

287. O'Haver, T. C.; Green, G. L., Numerical error analysis of derivative spectrometry for the quantitative analysis of mixtures. Anal Chem 1976, 48, 312-318.

288. Guan, Z.; Combes, J. R.; Menceloglu, Y. Z.; DeSimone, J. M., Homogeneous Free Radical Polymerizations in Supercritical Carbon Dioxide: 2. Thermal Decomposition of 2,2'-Azobis(isobutyronitrile). Macromolecules 1993, 26, 2663-2669.

289. Kazarian, S. G.; Vincent, M. F.; Bright, F. V.; Liotta, C. L.; Eckert, C. A., Specific Intermolecular Interaction of Carbon Dioxide with Polymers. J Am Chem Soc 1996, 118, 1729-1736.

290. Raveendran, P.; Wallen, S. L., Cooperative C-H---O Hydrogen Bonding in CO₂-Lewis Base Complexes: Implications for Solvation in Supercritical CO₂. J Am Chem Soc 2002, 124, 12590-12599.

291. Yukihide, S.; Daisuke, A.; Naoki, T., pH-dependent color change of colloidal dispersions of gold nanoclusters: Effect of stabilizer. The European Physical Journal E - Soft Matter 2002, V8, 377.

292. Sanchez, C.; Livage, J.; Henry, M.; Babonneau, F., Chemical modification of alkoxide precursors. J Non-Cryst Solids 1988, 100, 65-76.

293. Xu, J.; Yan, J.; Wang, X.; Yu, H.; Milliken, T., Photochemical Reaction of Chrysene in Acetonitrile/Water. Polycyclic Aromatic Compounds 2004, 24, 249 - 256.

294. Meredith, J. C.; Johnston, K. P.; Seminario, J. M.; Kazarian, S. G.; Eckert, C. A., Quantitative Equilibrium Constants between CO₂ and Lewis Bases from FTIR Spectroscopy. J Phys Chem 1996, 100, 10837-10848.

295. Blatchford, M. A.; Raveendran, P.; Wallen, S. L., Spectroscopic Studies of Model Carbonyl Compounds in CO₂: Evidence for Cooperative C-H---O Interactions. J Phys Chem A 2003, 107, 10311-10323.

296. Nelson, M. R.; Borkman, R. F., Ab Initio Calculations on CO₂ Binding to Carbonyl Groups. J Phys Chem A 1998, 102, 7860-7863.

297. Meredith, J. C.; Johnston, K. P.; Seminario, J. M.; Kazarian, S. G.; Eckert, C. A., Quantitative Equilibrium Constants between CO₂ and Lewis Bases from FTIR Spectroscopy. J. Phys. Chem. 1996, 100, 10837-10848.

298. Dobrowolski, J. C.; Jamroz, M. H., Infrared evidence for carbon dioxide electron donor-acceptor complexes. Journal of Molecular Structure 1992.

299. Krevelen, D. W. v., Properties of polymers: their correlation with chemical structure, their numerical estimation and prediction from additive group contributions. 3rd, completely rev. ed.; Elsevier: Amsterdam; New York, 1990; p xxii, 875 p.

300. Williams, L. L.; Rubin, J. B.; Edwards, H. W., Calculation of Hansen Solubility Parameter Values for a Range of Pressure and Temperature Conditions, Including the Supercritical Fluid Region. Ind Eng Chem Res 2004, 43, 4967-4972.

301. Lagalante, A. F.; Hansen, B. N.; Bruno, T. J.; Sievers, R. E., Solubilities of Copper(II) and Chromium(III).beta.-Diketonates in Supercritical Carbon Dioxide. Inorg Chem 1995, 34, 5781-5785.

302. Yazdi, A. V.; Beckman, E. J., Design, Synthesis, and Evaluation of Novel, Highly CO2-Soluble Chelating Agents for Removal of Metals. Ind Eng Chem Res 1996, 35, 3644-3652.

303. Allada, S. R., Solubility Parameters of Supercritical Fluids. Ind Eng Chem Process Des Dev 1984, 23, 344-348.

304. Guigard, S. E.; Stiver, W. H., A Density-Dependent Solute Solubility Parameter for Correlating Solubilities in Supercritical Fluids. Ind Eng Chem Res 1998, 37, 3786-3792.

305. Fedors, R. F., Method for estimating both the solubility parameters and molar volumes of liquids. Polymer Engineering and Science 1974, 14, 147-54.

306. Wade, L. G., Organic chemistry. 6th ed.; Pearson Prentice Hall: Upper Saddle River, N.J., 2006; p xli, 1262, 7, 1, 14 p.

307. Elmali, A.; Zeyrek, C. T.; Elerman, Y., Crystal structure, magnetic properties and molecular orbital calculations of a binuclear copper(II) complex bridged by an alkoxo-oxygen atom and an acetate ion. Journal of Molecular Structure 2004, 693, 225.

308. Delfs, C. D.; Stranger, R., Oxidation State Dependence of the Geometry, Electronic Structure, and Magnetic Coupling in Mixed Oxo- and Carboxylato-Bridged Manganese Dimers. Inorg Chem 2001, 40, 3061-3076.

309. Hay, P. J.; Thibeault, J. C.; Hoffmann, R., Orbital interactions in metal dimer complexes. Journal of the American Chemical Society 1975, 97, 4884-99.

310. Norman Jr., J. G.; Kolari, H. J.; Gray, H. B.; Trogler, W. C., Electronic structure of dimolybdenum tetraformate, dimolybdenum(4+) ion, and dimolybdenum. Inorg Chem 1997, 16, 987-993.

311. Acho, J. A.; Ren, T.; Yun, J. W.; Lippard, S. J., Dimolybdenum(II) Calixarene Complexes: Synthesis, Structure, Raman Spectroscopy, and Bonding. Inorganic Chemistry 1995, 34, 5226-33.

312. Giddings, J. C.; Myers, M. N.; McLaren, L.; Keller, R. A., High pressure gas chromatography of nonvolatile species. Compressed gas is used to cause migration of intractable solutes. Science 1968, 162, 67-73.

313. Fried, J. R., Polymer science and technology. 2nd ed.; Prentice Hall Professional Technical Reference: Upper Saddle River, NJ, 2003; p xvii, 582 p.

314. Bradley, D. C., Alkoxo and aryloxo derivatives of metals. Academic Press: San Diego, 2001; p ix, 704 p.

315. Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P., Metal alkoxides. Academic Press: London; New York, 1978; p viii, 411 p.

316. Galia, A.; Argentino, A.; Scialdone, O.; Filardo, G., A new simple static method for the determination of solubilities of condensed compounds in supercritical fluids. The Journal of Supercritical Fluids 2002, 24, 7.

317. Agrawal, A.; Saran, A. D.; Rath, S. S.; Khanna, A., Constrained nonlinear optimization for solubility parameters of poly(lactic acid) and poly(glycolic acid)-validation and comparison. Polymer 2004, 45, 8603-8612.

318. Martini, L. G.; Avontuur, P.; George, A.; Willson, R. J.; Crowley, P. J., Solubility parameter and oral absorption. European Journal of Pharmaceutics and Biopharmaceutics 1999, 48, 259-263.

319. Fedors, R. F., Method for estimating both the solubility parameters and molar volumes of liquids. Addendum. Polymer Engineering and Science. Polymer Engineering and Science 1974, 14, 472.

320. Sui, R.; Rizkalla, A. S.; Charpentier, P. A., FTIR Study on the Formation of TiO₂ Nanostructures in Supercritical CO₂. J Phys Chem B 2006, 110, 16212-16218.

321. Barton, A. F. M., CRC handbook of solubility parameters and other cohesion parameters. CRC Press: Boca Raton, Fla., 1983; p 594 p.

322. Gordon, L. J.; Scott, R. L., Enhanced Solubility in Solvent Mixtures. I. The System Phenanthrene-Cyclohexane-Methylene Iodide. J Am Chem Soc 1952, 74, 4138-4140.

323. Yazdi, A. V.; Beckman, E. J., Design of Highly CO2-Soluble Chelating Agents. 2. Effect of Chelate Structure and Process Parameters on Extraction Efficiency. Ind Eng Chem Res 1997, 36, 2368-2374.

324. Johnston, K. P.; Shah, P. S., Making Nanoscale Materials with Supercritical Fluids. Science 2004, 303, 482-483.