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This study investigates the importance of washing process in the quantitative improvement of both porosity and specific surface area of geopolymers. To this end, geopolymers were synthesized using natural kaolinite clay via alkaline activation. The characterization of both unwashed (UW-GP) and washed (W-GP) geopolymers, involved several techniques: X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Thermal Gravimetric Analysis (TGA), specific surface area, pore distribution, pore volume and Scanning Electron Microscopy (SEM). After the washing process, both specific surface area (SBET) and pore volume (Vp) of geopolymers have increased considerably: SBET = 0.59 m2/g and Vp = 0.001 cm3/g (UW-GP) versus SBET = 78.80 m2/g and Vp = 0.104 cm3/g (W-GP)) respectively. Also, the adsorption test was conducted using methylene blue molecules dissolved in water, and the results for our geopolymers were obtained as follows: Qads (UW-GP) = 52.2 mg/g and Qads (W-GP) = 55.6 mg/g. These values demonstrate that the washing process has a minimal effect on the adsorption capacity of geopolymers. Hence, the washing process allows the increasing of the surface reactivity of geopolymers through the elimination of excess of unreacted alkaline solution which is responsible of the efflorescence. [ABSTRACT FROM AUTHOR]

In the present study, hierarchically ordered macro-mesoporous γ-alumina with a grainy wall structure was synthesized, for the first time, through a facile route from aluminum-tri-sec-butoxide as an aluminum precursor and polystyrene spheres as a template. This macro-mesoporous alumina possesses a highly ordered porous structure with a grainy wall of nanoparticles (ca. 45 nm), a high surface area (ca. 213 m/g), and a large pore volume (ca. 0.45 cm/g). By simply controlling the ratio of water in the washing process during the synthesis of macro-mesoporous γ-aluminum oxide, pseudoboehmite nanoparticles were found as an intermediate substance. Subsequent calcination at 600 °C induced the formation of hierarchically ordered macro-mesoporous γ-alumina with a grainy wall. This material is expected to be a good candidate for a catalyst, adsorbent, and composite material, due to the uniform macro-mesoporous structure, larger surface area, and grainy wall, which could improve the accessibility of large molecules to the active sites. [ABSTRACT FROM AUTHOR]