Fig. 2: The catalysis of α-Fe₂O₃, δ-MnO₂, and γ-Al(OH)₃ on geopolymerization of organic molecules.

a The efficiencies of geopolymerization are quantified as the mean percentage increase of geopolymers production under mineral catalysis relative to the catalyst-free control. Statistical significance was assessed by two-tailed Student’s t-tests comparing each mineral treatment to the control. Solid points represent the statistically significant effects (p < 0.05), while hollow points indicate non-significant effects. Error bars represent standard deviation, n = 3 independent replicates. b The mean percentage increase of the geopolymers’ electron transfer capacity (ETC) generated with different phenolic compounds in the Fe + Mn + Al treatment relative to the catalyst-free control. Error bars represent standard deviation, n = 3 independent replicates. c The mean effective diameter of geopolymers generated with resorcinol as a representative phenolic compound in the Fe, Mn, Al oxides treatments and the catalyst-free control (CK). Error bars represent the standard deviation, n = 3 independent replicates. d The mean CO₂ production during geopolymerization with resorcinol as a representative phenolic compound in the Fe, Mn, Al oxides treatments and the catalyst-free control (CK). Error bars represent the standard deviation, n = 3 independent replicates. e The mean generation of free radicals (•OH) with resorcinol as a representative phenolic compound in Fe, Al, and Fe + Al treatments. Error bars represent standard deviation, n = 3 independent replicates. ND, not detected. *p < 0.05; **p < 0.01; *** p < 0.001; ns, not significant (ANOVA).