Porous inorganic polymer (IP) monoliths were synthesised using a modified bauxite residue (BR) as the reactive fraction with the objective of using them as adsorbents for methylene blue (MB) from synthetic wastewater. First, unreactive, as-produced BR was transformed into a suitable glassy precursor material for IPs by blending BR with minor quantities of C and CaSiO3, thermally treating it at 1200 °C for 2 h, and quenching in water. The alkaline activation of this slag in combination with a pore foaming agent led to the formation of a highly porous microstructure with up to 85% in total porosity. The synthesised porous monoliths demonstrated high MB uptake (up to 17 mg of MB/g of IP with an initial MB concentration of 75 mg/L). A higher porosity of the monoliths, a higher pH, an increasing initial MB concentration as well as stirring of the testing solution have a positive effect on the adsorption capacity, while an optimum solution volume for adsorption was identified. Furthermore, the reuse of these novel monolithic adsorbents was demonstrated by repeating adsorption tests up to five cycles (adsorption-desorption), with a decrease in adsorption capacity of approximately 30%, but a promising cumulative uptake of about 40 mg of MB per g IP.

In this investigation cork was used as a low density aggregate in the production of ultra-lightweight and low thermal conductivity inorganic polymer (geopolymer) composites. This novel and highly sustainable material, synthesised at room temperature (23 °C), may decrease the energy losses inside buildings, thus contributing to the United Nations development goals regarding energy and climate change. The ultra-low density (260 kg/m3) and low thermal conductivity (72 mW/m K) shown by the cork-composites are the second lowest ever reported for inorganic polymer composites, only being surpassed by that of polystyrene-inorganic polymer composites. However, cork is a fully renewable and sustainable resource, while polystyrene is manufactured from non-renewable fossil fuels, and for that reason our strategy has an additional sustainability advantage. Moreover, the cork-inorganic polymer composites do not release any toxic fume when under fire conditions, which is a major advantage over polymeric-based foams.