Pozzolan-based eco-adsorbents were synthesized by geopolymerization with addition of hydrogen peroxide (H2O2) with mass ratios 0% (GP0) and 1% (GP1) and the products used to sorb cationic methylene blue (MB) dye from water. The chemical composition, textural properties, mineral composition, surface functions, as well as morphology and internal structure of these samples were determined by the X-ray fluorescence, adsorption of nitrogen by the B.E.T (Bruamer Emmet Teller) method, X-ray diffraction, Fourier Transformed Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. The effects of contact time, dye initial concentration, adsorbent dosage, pH and temperature were examined and are herein reported. Incorporation of 1% H2O2 increased the specific surface area from 4.344 to 5.610 m2/g representing ~ 29% increase in surface area. This translated an increase in the MB adsorption capacity by 15 orders of magnitude from 24.4 to 366.2 mg/g for GP0 and GP1, respectively. The adsorption rates of methylene blue on the two geopolymers were best described by the pseudo-second order kinetic model. The adsorption equilibrium data were best described by the Sips and Freundlich isotherms models for GP0 and GP1, respectively. Thermodynamically, it was determined that the adsorption of methylene blue onto GP0 and GP1 is a physical and endothermic process. The results show that incorporation of low amount of hydrogen peroxide into pozzolan-based geopolymers increases their adsorption capacity for methylene blue dye stupendously while preserving the surface chemistry.