Deliquescent behavior of calcium phosphate materials synthesized by sol–gel technique

Water storage and purification, as well as dehydration processes, are a cause of concern for many healthy and industrial issues. In this work, calcium phosphate (CaP) materials with high water capture performance were prepared by sol–gel synthesis. After their structural characterization by several techniques, they were used in water capture tests performed in temperatures ranging from 25 to 45 °C using a climatic chamber kept at a relative humidity of 60%. The CaP samples showed a higher water uptake capacity than a commercial silica sample commonly used as a water adsorbent, despite the low surface area and pore volume displayed by the former. Moreover, different from the silica adsorbent, the studied CaP materials were submerged by the captured water after the first day, which suggests a deliquescent behavior. The CaP mass uptakes reached around 350% when tested at 25 °C and the materials release the adsorbed water quickly when heated at 100 °C. It was also demonstrated that the materials prepared here maintained their structural integrity even after the deliquescence step, which could allow their use for many cycles.