Solvothermal synthesis of nanostructured energy storage materials

Background and Experimental Preparations The ability of some metal oxides to undergo reversible intercalation of Li+ under an applied potential makes these materials appealing for such devices as Li-ion batteries and asymmetric supercapacitors. Solvothermal synthesis encompasses a growing number of materials chemistry techniques employed to control particle size, shape, morphology, and structure, the basis of which is the reaction of organic or inorganic precursors in a suitable solvent under a controlled thermal environment.([1]) Depending on the precursors and desired materials properties, solvents can be aqueous, organic or room temperature ionic liquids (RTILs) and the method of energy transfer can be via convection or even microwave irradiation. Importantly, the chosen conditions must be compatible with the precursor-solvent interactions with dielectric and strong ionic mediums such as RTILs, which are able to impart considerable influence under an induced microwave field. Indeed, sonochemical treatment under these conditions has also proved effective for inducing secondary reactions and self-assembly processes.([2]) As an illustration, anatase TiO2 nanoparticles were prepared by hydrothermal treatment that gives controlled growth via Ostwald ripening,([3]) whereas rutile TiO2 nanotubes were prepared according to a modified procedure of Zhang et al.([4]) Briefly, amorphous TiO2 phase was prepared from the controlled hydrolysis of a solution of tetraisopropyl orthotitanate in 1: 1 v/v isopropanol immersed in an ice-water bath. Dehydration of the colloidal precipitate at 50 degrees C gave a finely divided powder that was further treated by dispersion of the dry TiO2 (2 g) in a concentrated NaOH solution (15 M, 80 mL) in a sealed polytetrafluoroethylene (PTFE)-lined vessel. The vessel was heated to 130 degrees C for 72 h, cooled, filtered, rinsed with deionized water, then stirred in HCl (1 M, 300 mL) overnight before further filtration, washing, and drying in air, then calcination at 400 degrees C in air for 4 h.