Foams are mainly composed of dispersed gas trapped in a liquid or solid phase making them lightweight and thermally insulating materials. Additionally, they are applicable for large surfaces, which makes them attractive for thermal insulation. State-of-the-art thermally insulating foams are made of synthetic polymeric materials such as polystyrene. This work focuses on generating foam from surfactants and renewable lignocellulosic materials for thermally insulating stealth material. The effect of two surfactants (sodium dodecyl sulphate (SDS) and polysorbate (T80)), two cellulosic materials (bleached pulp and nanocellulose), and lignin on the foaming and stability of foam was investigated using experimental design and response surface methodology. The volume-optimized foams determined using experimental design were further studied with optical microscopy and infrared imaging. The results of experimental design, bubble structure of foams, and observations of their thermal conductivity showed that bleached pulp foam made using SDS as surfactant produced the highest foam volume, best stability, and good thermal insulation. Lignin did not improve the foaming or thermal insulation properties of the foam, but it was found to improve the structural stability of foam and brought natural brown color to the foam. Both wet and dry lignocellulosic foams provided thermal insulation comparable to dry polystyrene foam. Graphical abstract
Electrochemical methods for preparing functional surfaces typically use optimized solutions where competing reactions do not need to be considered. However, with the increased demand for resource efficiency, selective deposition methods that can make use of more complex solutions are gaining importance. In this study, we show how gold recovery as nanoparticles from Au-Cu-Cl solutions can be assisted by electrochemically generated Cu 1+ species. In the electrochemically assisted reduction (EAR) method, a low-energy electrochemical step is employed, followed by spontaneous gold reduction onto the electrode. The studied solutions mimic challenging hydrometallurgical process solutions where the ratio of gold (5 ppm) to copper (20 g/L) is low. In addition to selective gold recovery, by controlling the electrochemical pulse parameters, the loss of deposits due to corrosion could be minimized, current efficiency improved from ∼0 to >10%, and relatively narrow particle size distributions achieved (43 ± 10 nm), and this can be done even at a high (4.5 M) NaCl concentration.
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