Coffee-based colloids for direct solar absorption

Abstract

Despite their promising thermo-physical properties for direct solar absorption, carbon-based nanocolloids present some drawbacks, among which the unpleasant property of being potentially cytotoxic and harmful to the environment. In this work, a sustainable, stable and inexpensive colloid based on coffee is synthesized and its photo-thermal properties investigated. The proposed colloid consists of distilled water, Arabica coffee, glycerol and copper sulphate, which provide enhanced properties along with biocompatibility. The photo-thermal performance of the proposed fluid for direct solar absorption is analysed for different dilutions and compared with that of a traditional flat-plate collector. Tailor-made collectors, opportunely designed and realized via 3D-printing technique, were used for the experimental tests. The results obtained in field conditions, in good agreement with two different proposed models, show similar performance of the volumetric absorption using the proposed coffee-based colloids as compared to the classical systems based on a highly-absorbing surface. These results may encourage further investigations on simple, biocompatible and inexpensive colloids for direct solar absorption.

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

“…We have also estimated the absorptive optical energy storage efficiency by first normalizing the transmittance values, T=e -a λ l ) (a λ : wavelengthdependent absorption coefficient), from 0 to 1. After normalizing, the transmittance values have been subsequently put into the following relationship that yields the energy storage efficiency [4] shown in equation 2:…”

“…Recently, coffee and its ingredient caffeine have garnered attention of researchers working in the field of photovoltaics. Colloidal solution of coffee has been shown to be useful as a material for direct solar absorption 4 whereas caffeine has been used to improve the performance and thermal stability of perovskite solar cells 5 . Recently, an alternative way to sense extremely alkaline pH using the shape of hydrophobe-water interfaces was reported 6 .…”

Generation of Optical Absorption Band in Colloidal Coffee at Extremely Alkaline pH

“…We also estimated the absorptive optical energy storage efficiency by first normalizing the transmittance values, = −  (  : wavelength-dependent absorption coefficient), from 0 to 1. After normalizing, the transmittance values have been subsequently put into the following relationship that yields the energy storage efficiency [4] shown in equation 2:…”

Design and optimization of solar steam generation system for water purification and energy utilization: A review

“…A large number of photothermal materials have been explored in recent years, including metal nanoparticles, semiconductor materials and carbon-based materials. Photothermal conversion is caused by the strongly driven the electromagnetic field of solar radiation in the carrier of the solar absorber, so that the carrier produces heat [47,48]. According to the properties of photothermal materials, there are three types of photothermal conversion mechanisms.…”

“…For practical applications, environmentally benign photothermal material is a key factor that will determine the competitiveness of solar steam generation [94]. Interestingly, Asinari's group synthesized coffee-based colloids, which consists of distilled water, Arabica coffee, glycerol and copper sulphate [47]. The coffee-based colloids not only provide enhanced properties along with biocompatibility but also may encourage increasing environmentally benign photothermal material apply to state-ofthe-art solar evaporation systems.…”