Waste Coffee Ground Biochar: A Material for Humidity Sensors

Abstract

Worldwide consumption of coffee exceeds 11 billion tons/year. Used coffee grounds end up as landfill. However, the unique structural properties of its porous surface make coffee grounds popular for the adsorption of gaseous molecules. In the present work, we demonstrate the use of coffee grounds as a potential and cheap source for biochar carbon. The produced coffee ground biochar (CGB) was investigated as a sensing material for developing humidity sensors. CGB was fully characterized by using laser granulometry, X-ray diffraction (XRD), Raman spectroscopy, field emission-scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and the Brunnauer Emmett Teller (BET) technique in order to acquire a complete understanding of its structural and surface properties and composition. Subsequently humidity sensors were screen printed using an ink-containing CGB with polyvinyl butyral (PVB) acting as a temporary binder and ethylene glycol monobutyral ether, Emflow, as an organic vehicle so that the proper rheological characteristics were achieved. Screen-printed films were the heated at 300℃ in air. Humidity tests were performed under a flow of 1.7 L/min in the relative humidity range 0–100% at room temperature. The initial impedance of the film was 25.2 0.15 MΩ which changes to 12.3 MΩ under 98% humidity exposure. A sensor response was observed above 20 % relative humidity (RH). Both the response and recovery times were reasonably fast (less than 2 min).

Preparation and Characterization of UV-LED Curable Acrylic Films Containing Biochar and/or Multiwalled Carbon Nanotubes: Effect of the Filler Loading on the Rheological, Thermal and Optical Properties

“…It was collected from Bar Katia (Turin, Italy) supplied by Vergnano Spa (Torino, Italy) and corresponds to an Arabica mixture. The exhausted coffee was collected and dried at 105 • C for 72 h. Coffee samples (100 g) were pyrolyzed using a vertical furnace and a quartz reactor (heating rate: 15 • C/min) and kept at 800 • C for 30 min in argon atmosphere [19][20][21].…”

Phytic Acid and Biochar: An Effective All Bio-Sourced Flame Retardant Formulation for Cotton Fabrics

“…Exhausted coffee powder collected from Bar Katia (Turin, Italy) and supplied by Vergnano Spa (Torino, Italy) as an Arabica mixture was employed as raw material for the preparation of Biochar. More specifically, the exhausted coffee was collected and dried at 105 • C for 72 h. Coffee samples (100 g) were pyrolyzed using a vertical furnace and a quartz reactor (heating rate: 15 • C/min) and kept at 800 • C for 30 min in argon atmosphere [19,20].…”

“…In particular, here we take advantage from a new flame retardant "green" recipe that exploits the combination of phytic acid, a naturally occurring molecule, extracted from different plant tissues (e.g., oil seeds, soy beans and cereal grains [16]) and bearing six phosphate groups (28 wt.% of phosphorus based on molecular weight), with biochar, a carbon-rich solid product obtained from the thermo-chemical conversion of biomasses in an oxygen-limited environment [19,20].…”

A Review of Non-Soil Biochar Applications

“…The authors clearly showed the onset of the response, with a relative humidity of 5% varying the impedance of two orders of magnitude when humidity reached 100%. Similarly, Jagdale et al [342] used spent coffee grounds to realize a relative humidity sensor with a starting response at 20% humidity. Further studies showed the use of biochar-based materials for the detection of ions (i.e., lead [343], copper [344], and zinc [345]) at concentrations of nmol/L and for organic materials in mmol/L concentrations [346,347].…”