MXene-enabled adsorption-photothermal synergy in starch-PEG/CaCl2 composite hydrogel: A low-cost high-efficiency sorbent for atmospheric water harvesting

Sorption-based atmospheric water harvesting (SAWH) offers a solution to global freshwater shortages that is not restricted by geographical conditions. However, in the current research, there are still problems such as the excessively high cost of adsorbents and the fact that photothermal materials only increase the desorption temperature during the desorption stage, without playing a role in the adsorption stage or even having a negative impact on it. This paper choses to use low-cost materials: renewable polysaccharides, potato starch (PS), bulk polymers, polyethylene glycol (PEG) as the framework, low-cost hygroscopic agent (CaCl 2 ) was employed as the moisture sorbing component, and MXene as the photothermal component to prepare high-performance sorbents materials (PPMC) through freeze-drying. MXene integration enabled dual functionality. During adsorption, it simultaneously enhanced kinetics and saturated capacity PPMC. Compared to PPC without MXene, PPMC's initial adsorption rate increased from 6.2 mg/g·min to 13.93 mg/g·min, representing an increase of 125 %, its saturated adsorption capacity increased substantially from 0.93 g/g to 1.47 g/g (59 % enhancement). During desorption, MXene's surface plasmon resonance confers exceptional photothermal conversion capability. Under 0.5 sun illumination (500 W/m 2 ), the material reaches 47 °C within 10 min and stabilizes at 71.1 °C after 2.5 h, enabling rapid vapor liberation. Water production validation using a compact system in arid environments (avg. 34.78 % RH, 19.7 °C) demonstrates successful freshwater harvesting. Post-collection analysis confirms compliance with WHO drinking water standards, which establish a cost-effective strategy for atmospheric water harvesting in resource-constrained scenarios.