Thesis (M. Eng.) - Asian Institute of Technology, 2022

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Nanotechnology

With the increasing human population, the number of human-made architectures increases along with the people. The architectures release heat slower than natural infrastructures and destroy the heat cycle leading to the collected heat, especially in the city. This occurrence is called the urban heat island effect. Along with many solutions of city design, green infrastructures, and policies, the near-infrared (NIR) reflective structures are promising solutions to the issue. Coating with NIR reflective pigments, human-made architectures can obtain the cooling effect where the absorbed heat is decreased. TiO2 is one of the most popular materials that provide high NIR reflectance to the pigments. This work reports core-shell nanostructures of metal oxides-TiO2 since the core-shell structures prevent the nanoparticles' agglomeration and enhance the pigments' NIR reflectivity. The possible metal oxides cores are Cr2O3, Al2O3, and Fe2O3 nanoparticles, which are commercially available. In addition, sol-gel synthesis of the NIR reflective pigments is a simple, low-cost, and environmentally friendly approach. The possible factors that affect the NIR reflectance of the nanoparticles are investigated, such as the thickness of the TiO2 shell, nanoparticle sizes, and fabrication conditions. The synthesized nanoparticles are then be analyzed with characterization tools, such as transmission electron microscopy, UV-vis-NIR spectrophotometer, etc., to study the properties and the cooling effect obtained from the coating of these pigments.