Green Protein Hydrogels and Non-dry Aerogels in Water Purification

Abstract: Having access to clean water is not a certainty for every human being. Today, there are major problems with polluted water that not just affect us humans, but also the ecosystem around us. In recent years, research into making aerogels from protein nanofibrils (PNF) has increased. What is interesting about these gels is their properties of adsorbing contaminants in the water, such as organic molecules and metal ions. In this report, hydrogels and non-dry aerogels (called “non-dry” due to there being one additional heat-treatment step that can be performed to “dry” the aerogel to make it sturdier and more water-proof), have been produced by whey protein isolate (WPI), which is extracted from the dairy industry. This is a sustainable, cheap, and renewable raw material. The goals are thus: (1) to examine if there is a difference in adsorption capacity between hydrogels and non-dry aerogels in a static setup and (2) to understand and examine which product parameters give the gels the best adsorption efficiency. To achieve these goals, eight different gels were synthesized with eight different contents. The parameters have varied from the following; dialyzed or non-dialyzed WPI solution, straight or curly seeds and whether or not salt had been added to the gels. The samples’ adsorption efficiency was analyzed by micro equilibrium dialysis (MED) and UV-VIS spectroscopy. For hydrogels, the dialyzed solution with salt and curly seeds was the variant with the highest binding capacity for ThT at 34% of the initial ThT concentration. For non-dry aerogels the dialyzed solution with curly seeds and no added salt was the best variant for binding ThT, at 84% of initial ThT content bound. It was also seen that the gels that have non-dialyzed WPI solution or that the solutions contained salt increased the adsorption capacity. The conclusions drawn were that salt has a positive effect on the adsorption capacity of the gels that have formed a matrix, and a negative effect on the adsorption of loose fibrils as well as that the solutions may not need to be dialyzed. The type of seeds or fibrils effect on adsorption capacity was inconclusive. The adsorption capacity for non-dry aerogels was three times higher compared to hydrogels.