Surface solar cooling through water vapor desorption from photo-responsive sepiolite 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, sorption rate and moisture capacity of the raw sepiolite were investigated based on its composition and structure for the proposed application. First order sorption rates of less than 100 h were observed with capacities more than 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 nanocomposites were only slightly reduced. In addition, photodegradation measurements of methyl orange demonstrated the photocatalytic activity of the prepared materials. Therefore, the nanocomposites could be potentially used for combined processes like pollutants photodegradation in addition to solar cooling.