Generation of Near-UV Absorption Band at Extremely Alkaline Ph in Colloidal Coffee

Abstract

Coffee and its primary ingredient, caffeine, have been used as solar absorbers and also to increase the thermal stability and efficiency of perovskite solar cells. In this work, we have reported the generation of an optical absorption band in the near-UV region in colloidal coffee solution at extremely alkaline pH values. This generation of absorption band could be explained by the orientation of various induced dipole-dipole interactions arising from varying pH. The said generation is due to narrowing of direct as well as indirect bandgaps from 4 eV→2.8 eV & 3.4 eV→2.5 eV, respectively. Additionally, we have estimated the changes in optical energy storage efficiency, inferring it to be highest for pH 11 having the highest intensity of the generated absorption band (λ abs ≈360 nm). With these observations and further deductions, the work reported in this paper would be of immense interest to the researchers working in the field of development of novel UV absorbers and also in the development of chemical pH sensors.