Role of washing process in the improvement of surface properties of porous geopolymers

Abstract

This study investigates the importance of washing process in the quantitative improvement of both porosity and specific surface area of geopolymer. To this end, geopolymer was synthesized using natural kaolinite clay via alkaline activation. Depending on both unwashed and washed geopolymers, the following characterization techniques were achieved: 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 (unwashed) versus SBET = 78.80 m2/g and Vp = 0.104 cm3/g (washed) respectively. Hence, the washing process allows increasing of the surface reactivity of geopolymers through the elimination among others of excess of unreacted alkaline solution which is responsible of the efflorescence.