Solvothermal synthesis of soluble, surface modified metal oxide nanocrystals Peter Dunne 1 , Christian Heinekamp 1,2,3 , Clodagh R. Nerney 1 , Aoife Kavanagh 1,4 , Andrew S. Bathe 1 , Adrián Sanz Arjona 1,5 , Annie Regan 1,4 , Nicola Pinna 3 1 Trinity College Dublin, Ireland, 2BAM Federal Institute for Materials Research and Testing, Germany, 3 Institut für Chemie, Humboldt Universität zu Berlin, Germany, 4 CDT ACM, Trinity College Dublin, Ireland, 5 Department of Chemistry, University of Copenhagen,Denmark Metal oxides, such as titanium and tin oxide, exhibit an array of properties which have made them integral to many applications, from the mundane, to the exotic. Both titanium oxide and tin oxide have long been exploited as pigments, for example, later becoming known as the prototypical photocatalytic and gas-sensing materials, respectively. They also find extensive use in glass-coatings for energy efficient and self-cleaning windows, and as components in photovoltaic devices, batteries, and more. While many of their applications require these materials to be in the form of coatings or thin films, as with many oxides titanium and tin oxide are generally intractable solids, requiring the development of sometimes complex and/or expensive deposition methods, such as CVD or PVD for the generation of coatings. Alternative approaches such as sol-gel methods are generally cheaper and more robust, but come with a lack of control. An increasingly popular alternative to these methods is the generation of solution processable metal oxide nanoparticles. 2 Here we report the production of highly dispersible (doped) titanium and tin oxide nanocrystals by post‑synthetic modification of hydrous oxide precursors by solvothermal treatment with trifluoroacetic acid. Solvothermal treatment of amorphous titania in trifluoroacetic acid yields highly dispersible surface modified anatase phase nanoparticles. 3,4,5 The incorporation of dopant metals does not compromise the particle properties, making this procedure very promising for the many applications in which the use of solution processable nanoparticles with tuneable optoelectronic properties are critical. Interestingly, while applying this approach to tin oxide also yields dispersible nanocrystals, it has been found that extended solvothermal treatment of hydrous tin oxide in trifluoroacetic acid leads to the emergence of an apparently new tin oxide phase, exhibiting a diffraction pattern consistent with the braking of the 4 2 screw axis symmetry of the rutile structure. This new modification of the rutile structure is tentatively attributed to fluorination of the tin oxide nanocrystals under solvothermal conditions.
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2. T. Arita, Y. Ueda, K. Minami, T. Naka and T. Adschiri, Ind. Eng. Chem. Res., 2010, 49, 1947-1952. 3. J. S. McManus, P. D. Cunningham, L. B. Regan and P. W. Dunne, Chem. Commun., 2012, 48, 7453-7455. 4. J. S. McManus, P. D. Cunningham, L. B. Regan, A. Smith, D. W. McGrath and P. W. Dunne, Cryst. Growth Des., 2014, 14, 4819-4826. 5. A. S. Bathe, A. Sanz Arjona, A. Regan, C. Wallace, C. R. Nerney, N. O'Donoghue, J. M. Crosland, T. Simonian, R. I. Walton and P. W. Dunne, Nanoscale Advances, 2022, 4, 5343-5354.
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