Coal fly ash-based porous geopolymers prepared by a combined foaming process: adsorption mechanism analysis and...

In this work, coal fly ash, a widely available industrial solid waste in Xinjiang, China, was utilized as the aluminosilicate source to synthesize coal fly ash-based porous geopolymers via a novel foaming strategy combining saponification and hydrogen peroxide. This method enabled the formation of coal fly ash-based porous geopolymers with a maximum porosity of 61.63%. Methylene blue and Pb²⁺ were selected as representative contaminants to evaluate the adsorption behavior of coal fly ash-based porous geopolymers under optimized conditions, with maximum adsorption capacities of 65.85 mg/g for methylene blue and 264.55 mg/g for Pb²⁺. The isotherm and kinetic model fitting results suggested that both adsorption processes follow a combined chemical-physical mechanism. FT-IR and XPS further revealed the relationship between structural features and adsorption behavior, highlighting the combined effect of pore architecture, surface functional groups, and amorphous gel in governing adsorption behavior. Life cycle assessment using openLCA indicated relatively low environmental impacts, largely attributed to the utilization of coal fly ash as a waste-derived raw material. Using decarbonized electricity and low-toxicity reagents is the direction for subsequent research optimization. Also, the cost of coal fly ash-based porous geopolymers is only $0.154 kg^-1. This work provides theoretical support for design of efficient, green, and cost-effective adsorbents.