Removal of Methylene Blue from Aqueous Solutions with Fly Ash Based Geopolymer Foam

Abstract

Geopolymers are ceramic like materials synthesized by alkali activation of aluminosilicate powder at relatively low temperatures. Geopolymers have excellent properties such as high mechanical strength, high acid resistance, and high fire resistance. Depending on the properties of geopolymers, they have many application fields like adsorption, waste encapsulation, and construction industry. Adsorption is one of the remarkable application areas of geopolymers. Due to the increasing demand for clean water resources, the need for developments in water treatment is also increasing. Geopolymers offer cost effective and environmentally friendly alternatives to adsorbent materials. Many waste materials including fly ash and blast furnace slag can be used to synthesize geopolymeric materials. In this experimental study fly ash was used as raw material and geopolymer foam was produced by using 4 M sodium hydroxide and sodium silicate. Hydrogen peroxide was utilized to obtain foamed material. Fresh geopolymer paste cured at 80°C for 4 hours and then aged at laboratory conditions. Samples aged for 28 days were used in methylene blue removal from an aqueous solution. Adsorption experiments were carried out at laboratory conditions under normal light and under UV lamp in the presence of TiO2. The concentration of the solution obtained at the end of the adsorption contact time was determined by UV/VIS spectrophotometer at 665 nm. The effect of adsorbent ratio and temperature on removal efficiency and adsorption capacity were investigated. The highest removal efficiency values were obtained as 92% and 83% under UV lamp and normal light, respectively. The results indicated that geopolymers are very promising materials that can be used in methylene blue removal.