Soak-and-Squeeze Deposition of Graphene Oxide on Open-Cell Foams for Detergent Removal

This study investigates the deposition of graphene oxide (GO) coatings on open-cell polyurethane foams through a soak-and-squeeze process for detergent removal. GO dispersions between 0.25 and 4 g/L were rheologically characterised to relate apparent viscosity to coating deposition. A first rationalisation of the squeeze-coating process was proposed by estimating the characteristic shear rates during squeezing, obtaining values of 12.2 s−1 and 50.4 s−1 for 20 and 60 PPI foams, respectively. Multiple deposition cycles were performed, achieving GO loads up to 12.7 wt% for both types of foam. The adsorption behaviour of GO powder toward a commercial detergent solution containing linear alkylbenzene sulphonate (LAS) was investigated at 25, 40 and 60 °C. UV-Vis spectroscopy was used to monitor concentration changes, while conductivity analyses investigated the temperature-dependent aggregation behaviour of the detergent system. The adsorption kinetics were well described by the Elovich model, suggesting adsorption on heterogeneous GO surfaces. Filtration tests using GO-coated foams showed a decrease in conductivity during flow-through experiments, whereas UV-Vis measurements indicated limited LAS removal under dynamic conditions, likely due to insufficient contact time between the detergent and the coated surface. Static contact tests performed for 1 h at 25 °C showed a reproducible detergent concentration decrease of approximately 16–18%. This value was further increased up to 65% under optimised conditions by modifying the GO-to-detergent ratio and foam configuration. The results demonstrate that the soak-and-squeeze approach is a simple and effective method for producing reproducible GO coatings on open-cell foams, while indicating that sufficient contact time is required to promote detergent removal.