Toward new low-temperature thermochemical heat storage materials: Investigation of hydration/dehydration behaviors of MgSO4/Hydroxyapatite composite

A new two-component (composite) water sorbent MgSO4/Hydroxyapatite has been developed for sorption-based solar heat storage. The matrix of the composite is a hydroxyapatite (HAP) material with ordered structure, high surface area of 111.3 m2/g and mesopore dimensions centered at 45 nm. The composites, prepared by wet-impregnation of HAP with MgSO4, have lower specific surface area and similar mesopore dimensions as the matrix. The maximum water sorption capacity of HAP is 0.039 g/g, while the composite (20-MgSO4/HAP) possesses 3.7 times higher maximum water sorption capacity due to the presence of the salt in the matrix. The HAP composite containing 20% MgSO4 achieved the highest heat of hydration 464 J/g. A long-term cycling (dehydration at 150 and hydration at 30 °C at a relative humidity of 60%) confirms a comparatively good stability of the composite.