Green sustainable photothermal materials by spent coffee grounds

Background: Spent 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. Methods: First, 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 findings: The 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. (c) 2022 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study discovered that spent coffee grounds (SCG) possess photothermal properties under near-infrared laser irradiation, making them suitable for applications as photothermal materials. Additionally, when incorporated into polyNIPAM hydrogels, SCGs can induce thermal shrinkage and bending, indicating their potential as photothermal actuators. These findings provide new insights for the recycling and reuse of SCGs.