Multifunctional granulated blast furnace slag-based inorganic membrane for highly efficient separation of oil and dye from wastewater

Superhydrophilic and underwater superoleophobic metal-based mesh membranes exhibit high flux, high separation efficiency, low energy consumption, and facile continuous oil/water separation. However, their separation performance for oil/water emulsions and organic pollutants is very poor. In this study, graphene oxide (GO)-modified granulated blast furnace slag (GBFS)-based geopolymer paste was coated onto a stainless-steel mesh to prepare an inorganic geopolymer membrane (GO/GBFSGM). A sample containing 0.25 % GO (0.25GO/GBFSGM) demonstrated the highest flux of 10,520.25 kg·m−2·h−1 and high separation efficiencies (>98 %) for various oil/water mixtures and oil-in-water emulsions under gravity-driven conditions. In addition, the 0.25GO/GBFSGM sample possessed excellent pollution resistance, cycling stability, mechanical stability, and alkali, salt, and heat resistances. Importantly, it exhibited unique physical rejection and electrostatic adsorption properties for organic dye molecules owing to the three-dimensional network gelling structure of the geopolymer. The adsorption rate of a 10 mg/L methylene blue solution by 0.25GO/GBFSGM exceeded 91 % within 4 h. This study proposes a "treating waste with waste" concept, i.e., the utilization of GBFS solid waste for the preparation of multifunctional inorganic membranes that can effectively separate oil and dye from wastewater with tremendous economic, environmental, and social benefits.