Green sustainable photothermal materials by spent coffee grounds

Abstract

BackgroundSpent coffee grounds (SCG) contain a variety of active compounds. In this work, we try to demonstrate the diversity of SCG reuse and report a novel application of SCGs as photothermal materials. MethodsFirst, SCGs were dispersed in water, followed by irradiation an 808-nm near-infrared (NIR) laser. By monitoring the changes in the water temperature, the photothermal properties and photothermal conversion efficiency of SCGs were analyzed. Next, SCGs with different contents were further incorporated into the thermally responsive poly(N-isopropylacrylamide) (polyNIPAM) hydrogels. During laser irradiation, the shrinking ratio and bending angle of the hydrogels were tested. Significant findingsThe results obtained herein suggest that SCGs possess photothermal properties under NIR irradiation without any carbonization treatment; furthermore, to the best of our knowledge, this is the first study to report that SCGs possess a usable photothermal conversion efficiency (24.8%). The SCG-incorporated polyNIPAM hydrogels exhibited thermal shrinkage and bending characteristics under NIR irradiation, and thus, they can be considered as a photothermal actuator. When more SCGs were added, the crosslinking density of the hydrogels was low, and the degree of shrinkage and bending was high. We believe that this work will provide novel insights for the recycling and reuse of SCGs.