Application of a reversible thermochromic Co-MOF in smart windows

Metal–organic frameworks (MOFs) are promising candidates for thermochromic materials. In this study, a hydrogen-bonded 3D porous metal–organic framework, Co-BTC (Co3(BTC)2·12H2O, BTC = 1,3,5-benzenetricarboxylate), exhibited a pink color at room temperature, attributed to the d–d transition of Co2+ ions within the framework, and displayed reversible thermochromic behavior due to alterations in the coordination environment of Co2+ ions. Additionally, Co-BTC/PVB thermochromic film was successfully designed and fabricated as a smart window with a monolayer structure. The window exhibited reversible thermochromic behavior comparable to Co-BTC, with visible transmittance modulation of 10.73%, near-infrared transmittance modulation of 25.87%, and solar transmittance modulation of 12.63%. Compared to a pure PVB window, the smart window reduced indoor temperatures by 5.7 °C in field tests, indicating a significant energy-saving effect. This research presents a potential application for the rational design of MOFs in the development of advanced smart windows.