“…The use of spheres promotes higher (30.1 mg/g) [149] dye uptake in the 1st adsorption cycle in comparison with the use of cylindrical discs ((15.4 mg/g) [87] and (17.3 mg/g) [169]). The methylene blue uptake shown by the geopolymer spheres (30.1 mg/g) is superior to several other geopolymer powders: 0.7 mg/g [170], 2.7 mg/g [171], 3.0 mg/g [172], 14.8 mg/g [173,174], 19.7 mg/g [175], 24.6 mg/g [176], 25.6 mg/g [177]; it was slightly inferior to others [137,178], and roughly 1.7 times lower than that reported by Liu et al [144]. However, the bulk-type samples (spheres and membranes) can be easily retrieved and regenerated multiple times, leading to cumulative uptakes several times superior to those obtained with powdered geopolymers.…”