Surface Solar Cooling with Photo-Responsive Nanocomposites

The low-cost sepiolite, a fibrous and white phyllosilicate clay of high moisture sorption ability, was studied for the evaporative cooling of its surface in comparison to concrete. Initially, the material was characterized through techniques like elemental analysis, x-ray diffraction and thermal analysis. Afterwards, some of the basic relations between the composition and the structure of sepiolite and the sorption rate and capacity of moisture for the proposed application were determined. First order sorption rates of less than 100 hours were observed with capacities up to 30 % at high relative humidity. Moreover, the water evaporation rate, the water/moisture sorption-desorption under simulated solar radiation and the associated surface temperature reductions were determined in a specially developed chamber (wind tunnel) with controllable environmental conditions and multi-sensors data acquisition. Surface temperature reductions of more than 5 °C were obtained. Moreover, titania in its anatase form was built on the sepiolite structure, characterized and tested for surface cooling. In the sorption experiments, the water vapor equilibrium and kinetics of the nanocomposite were only slightly reduced. Therefore, the nanocomposite could be potentially used for air pollutants photodegradation in addition to solar cooling.