Chemically Binding Carboxylic Acids onto TiO_ Nanoparticles with Adjustable Coverage by Solvothermal Strategy

摘要

This paper presents a solvothermal strategy for chemical modification of TiO_2 nanoparticles with carboxylic acids. Solvothermal reaction between the TiO_2 nanoparticles and carboxylic acid molecules in an autoclave at 100 °C provides carboxylic acid-modified TiO_2 particles with a modification efficiency much higher than the conventional immersion method. TiO_2 nanoparticles were prepared by hydrolysis of titanium isopropoxide in nitric acid solution; the modified nanoparticles were characterized by powder X-ray diffraction pattern, scanning electron microscopy, absorption and Fourier transform infrared spectra, and thermogravimetric analysis. Results show that the binding form of the modifier molecules on TiO2 surface is in a bidentate chelating mode, the crystalline phase composition and morphological structure of the preformed TiO_2 nanoparticles are not affected by the solvothermal reaction, and the surface coverage of the modifier molecules can be adjusted by the weight ratio of modifer/TiO_2 during feeding. It is evident that the reaction processes in the solvothermal strategy involve the formation of double hydrogen bondings between carboxylic acid molecule and TiO_2 at the same Ti site and the coordination at solvothermal temperature by dehydration from the hydrogen bondings. The solvothermal strategy for modifying TiO_2 nanoparticles is expected to find potential applications in many fields; for example, our results demonstrate that the photovoltaic performance of the TiO_2 nanoparticles can be improved by the solvothermal modification even with an insulating modifier and controlled by the modifier coverage.