Development of bifunctional microencapsulated phase change materials with crystalline titanium dioxide shell for latent-heat storage and photocatalytic effectiveness

Abstract

A sort of novel bifunctional microencapsulated phase change material (PCM) was designed by encapsulating n-eicosane into a crystalline titanium dioxide (TiO2) shell and, then, was successfully synthesized through in-situ polycondensation in the sol–gel process using tetrabutyl titanate as a titania precursor. The resultant microcapsule samples were characterized by Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to determine their chemical compositions and structures. Furthermore, the crystallinity of the TiO2 shell was verified by powder X-ray diffraction patterns. It was confirmed that the fluorinions could induce the phase transition from the amorphous TiO2 to the brookite-form crystals during the sol–gel process, thus resulting in a crystalline TiO2 shell for the microencapsulated n-eicosane. The scanning and transmission electron microscopy investigations indicated that all of the resultant microcapsules presented a perfect spherical shape with a uniform particle size of 1.5–2μm, and they also exhibited a well-defined core–shell structure as well as a smooth and compact shell. The crystalline TiO2 shell made the resultant microcapsules a photocatalytic activity, and therefore, these microcapsules demonstrated a good photocatalytic effect for the chemical degradation and an antimicrobial function for some of the Gram-negative bacteria. Most of all, all of the microencapsulated n-eicosane samples indicated good phase-change performance and high thermal reliability for latent-heat storage and release, and moreover, they achieved a high encapsulation efficiency and a high thermal-storage capability. The bifunctional microencapsulated n-eicosane synthesized in this study will be a potential candidate for the applications of waste heat recovery and treatment, intelligent textiles or fabrics for the warmth underwear and medical protective clothing, preservation and sterilization of foods, and solar energy storage and recovery, etc.