Geopolymers as a Sustainable Chemical Platform: From Building Materials to Advanced Functional Applications

Geopolymers are aluminosilicate inorganic polymers traditionally investigated as sustainable alternatives to ordinary cement. This review rethinks geopolymers not merely as sustainable binders but as a versatile chemical platform whose properties arise from controllable dissolution–condensation pathways, nanoscale structural disorder, and activator chemistry. We critically analyze the sustainability considering life-cycle assessments and discuss how activator production and curing conditions challenge oversimplified green claims in recent literature. The transition from bulk construction materials to nanoengineered and hybrid systems is examined, highlighting the role of nanofillers and interfacial engineering strategies. A particular focus is devoted to halloysite-based systems, tracing their evolution from early nanoarchitectural surface modification of fly ash particles to recent developments in self-assembled inorganic films with tunable morphology at a mesoscopic length scale. These systems demonstrate that geopolymerization can act as a structural converter across nano-, meso-, and macroscales, enabling applications in barrier, adsorption, CO2 capture, and environmental remediation. We conclude by outlining design principles for future geopolymer research, emphasizing activation chemistry, structural control, and morphological programmability as key aspects in developing sustainable functional materials for advanced applications. Future efforts will need to identify sustainable activation strategies for construction applications and to develop chemically adaptable systems for high-performance functional uses.