Waste Coffee Ground Biochar: A Material for Humidity Sensors

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 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)

Biochar/Zinc Oxide Composites as Effective Catalysts for Electrochemical CO2 Reduction

Novel electrocatalysts based on zinc oxide (ZnO) and biochars are prepared through a simple and scalable route and are proposed for the electrocatalytic reduction of CO₂ (CO₂RR). Materials with different weight ratios of ZnO to biochars, namely, pyrolyzed chitosan (CTO) and pyrolyzed brewed waste coffee (CBC), are synthesized and thoroughly characterized. The physicochemical properties of the materials are correlated with the CO₂RR to CO performance in a comprehensive study. Both the type and weight percentage of biochar significantly influence the catalytic performance of the composite. CTO, which has pyridinic- and pyridone-N species in its structure, outperforms CBC as a carbon matrix for ZnO particles, as evidenced by a higher CO selectivity and an enhanced current density at the ZnO_CTO electrode under the same conditions. The study on various ZnO to CTO weight ratios shows that the composite with 40.6 wt % of biochar shows the best performance, with the CO selectivity peaked at 85.8% at −1.1 V versus the reversible hydrogen electrode (RHE) and a CO partial current density of 75.6 mA cm–² at −1.3 V versus RHE. It also demonstrates good stability during the long-term CO₂ electrolysis, showing high retention in both CO selectivity and electrode activity

DEPOSITED Bi2O3 THIN FILMS ON SINTERED SILICA FOR PHOTOCATALYTIC WATER TREATMENT

Bismuth oxide (Bi2O3) thin films were deposited on sintered silica surface by the spray pyrolysis method using bismuth acetate as the precursor salt. Spray pyrolysis enables uniform film distribution on sintered silica. The films were characterized by X-ray diffraction (XRD) to investigate the obtained Bi2O3 phase, UV-vis diffuse reflectance spectroscopy (DRS) to obtain the energy band gap, and Field Emission Scanning Electron Microscopy (FESEM) to study the morphological structure. XRD pattern revealed that obtained phase of films is tetragonal β- Bi2O3, by using DRS results the calculated energy band gap is 2.4eV and FESEM images show porous flowery structures. Furthermore the heterogeneous photocatalytic activity of the films was investigated by introducing the deposited silica filters into organic dyes solution and irradiating in UV and visible light for photocatalyst activation. Bi2O3 thin films shown good photocatalytic activity showing that (i) spray pyrolysis is a promising deposition method and that (ii) deposited silica filters are suitable support to promote effective interaction of photocatalyst with dye molecules while avoiding the problem of photocatalyst powders suspension in dye solution. Improved photocatalytic activity in visible light proves Bi2O3 thin films for sustainable water treatment and related applications

New cementitious composite building material with enhanced toughness

In the present work, carbon nano/micro-particles obtained by chemical vapor depostion (CVD) process and controlled pyrolysis from polyethylene beads (CNBs) and coconuts choir (CCNs) are presented. These materials were characterized by Raman spectroscopy, thermogravimetry and field emission-scanning electron microscopy (FE-SEM). FE-SEM observations evidenced that CNBs particles proved to be spherical and interconnected, while the CCNs were irregular in shape, as the result of the grinding step. When added to cement paste, up to 0.08 wt%, both materials were effective in increasing the cement matrix compressive strength and toughness. From FE-SEM observations it is evident that the presence of these small particles disturb the propagation of microcracks that have to deviate from their trajectory and have to follow the carbon nano/micro-particles contour. This mechanism increases strongly the fracture surface during the test performed by imposing the monotonic increment of crack opening. The crack and crack pinning are the mechanisms which can explain the increase of toughness in the composite sample