High-performance humidity control coatings prepared from inorganic wastes

Valorization of industrial wastes in an economic and environmental-friendly way is important. In the present study, the preparation of humidity control coatings (HCCs), which is an energy-saving method to regulate indoor humidity, are developed by recycling inorganic sludges (i.e., enhancement silica fume (ESF) and spent fluid catalytic cracking catalysts (sFCCC)). Bassanite, kaolin, sodium silicates and acrylic resins are combined with ESF and sFCCC in different amounts to prepare HCCs. Experimentally, moisture adsorption–desorption performance of the HCCs increases as ESF increases. Moreover, the humidity control performance can be enhanced in the range of medium relative humidity (50–75%) upon the addition of sFCCC which results in the formation of more micropores in the HCCs. However, excessive amounts of sFCCC could reduce the moisture adsorbed capacities in the humidity range of 50–90% relative humidity due to the decrease of mesopore volume. As a result, the HCCs with 38% of ESF and 10% of sFCCC have the optima ratios of mesoporous and microporous structure showing the moisture adsorbed value and content of 309 g m⁻² and 27.0%, respectively, which are much better than commercial coatings (58.7 g m⁻² and 11.4%). Moreover, the prepared HCCs can reach the coating benchmark of level 2 (based on Japanese Industrial Standards (JIS A 1470-1)) at medium relative humidity range (50–75%). In the simulation tests with variable temperatures, the HCCs exhibit a narrow amplitude change of moisture (7% relative humidity) which is smaller than commercial coatings (11–13% relative humidity). Most importantly, the HCCs have good film hardness, 99.99% of antimicrobial efficacy and environmental friendliness according to the pencil, antibacterial activity and toxicity characteristic leaching procedure (TCLP) tests, respectively.