Smart thermo-regulating inorganic microcapsules of sodium thiosulfate pentahydrate using nanosilica from rice hull ash for climate resilient structures

Abstract This study synthesized microcapsules of sodium thiosulfate pentahydrate (STP) using hybrid shells composed of tetraethylorthosilicate (TEOS) and nanosilica (nS) derived from rice hull ash (RHA). Despite its suitability as a cost-effective Phase Change Material (PCM), STP has been primarily used unencapsulated in many applications. Microencapsulation techniques for inorganic hydrates predominantly rely on TEOS, an alkoxysilane, as a precursor for forming the protective shell. Here, STP was microencapsulated with hybrid nS:TEOS shells at 25, 50, 75, and 100 mol% nS. Each substitution achieved varying levels of success, wherein the 75 %nS shell formulation exhibited the most desirable result. Microcapsules formed from the formulation had a latent heat of melting of 76.44 J/g, a latent heat of solidification of -43.19 J/g, and an encapsulation efficiency of 36.74 %. The heterogeneity of the hybrid shell mitigated the fragility associated with pure TEOS and the supercooling issues found in mPCMs with 100 %nS shells. The resulting mPCMs offer a sustainable passive thermal regulation solution in many applications, including climate-responsive materials. The use of nS derived from RHA not only lowers environmental impact and material costs but also directly supports circular economy and key Sustainable Development Goals (SDGs), specifically 7, 12, & 13.