Synthesis and progress of thermosensitive adsorbents in heat and humidity treatment: A review

The primary objective of this paper is to provide a comprehensive overview of recent developments in thermosensitive adsorbents, directing at synthesis, applications and discussion of equilibrium and dynamic adsorption/desorption properties, operation modes and regeneration methods. Synthesis methods are categorized into two mains (free radical polymerization method and the combination of RAFT with “click” chemistry) and their advantages and disadvantages are summarized. Applications of these adsorbents in the areas of dehumidification, air water harvesting, passive cooling, wastewater treatment, temperature sensors, flow control and drilling fluid fields are summed up. Regeneration methods including solar irradiation, electro-osmotic flow regeneration, electrical heaters, waste heat regeneration, microwave energy applications, and ultrasonic technology are analyzed. Equilibrium adsorption quantities of hygroscopic salt based thermosensitive adsorbents can be as high as 1.6 g/g to 3.8 g/g at 20–30 °C and 80–90 % RH. The thermosensitive property of PNIPAM can markedly diminish the energy demands associated with desorption, resulting in fast desorption rate. Adsorption kinetics needs further improvement, especially for applications with rapid switching of adsorption and regeneration processes. Solar irradiation is rated as one of the most promising ways of regeneration. This review identifies strategies for future research to boost thermosensitive composites' energy efficiency.