Core-shell-embedded Mesoporous Silica Capsules for Atmospheric Water Harvesting

Abstract

A one-step ultrasonic mechanical method was used to synthesize a kind of atmospheric water harvesting material with high water harvesting performance in a wide relative humidity (RH) range, especially at low RH (RH < 40%), namely, mesoporous silica capsule (MSC) with core-shell structure. Transmission electron microscopy (TEM), nitrogen adsorption and other characterization techniques were used to study the formation process of nano-microspheres. A new mechanism of self-adaptive concentration gradient regulation of silicon migration and recombination core-shell structure was proposed to explain the formation of a cavity in the MSC system. The core-shell design can enhance the specific surface area and pore volume while maintaining the monodispersity and mesoporous size. To study the water harvesting performance of MSC, solid silica nanoparticles (SSN) and mesoporous silica nanoparticles (MSN) were prepared. In a small atmospheric water collection test (25 °C, 40% RH), the water vapour adsorption and desorption kinetics of MSC, SSN, MSN and a commercial silica gel (CSG) were compared and analyzed. The results show that the MSC with mesoporous channels and core-shell structure can provide about 0.324 g _water/g _adsorbent, 79% higher than the CSG(0.181 g _water /g _adsorbent). It is 25.1% higher than that of 0.259 g _water /g _adsorbent of un-hollowed MSN and 980% higher than that of 0.03 g _water /g _adsorbent of un-hollowed SSN. The material has a large specific surface area and pore volume, simple preparation method and low cost, which provides a feasible idea for realising atmospheric water collection in arid and semi-arid regions.

Keywords

mesoporous silica nanocapsules / core-shell structure / atmospheric water harvesting / adsorption performance