Design of novel alkali activated materials exhibiting adsorption performance and photocatalytic activity

Abstract

Alkali activated materials (AAMs) are environmentally friendly alternatives to traditional cement binders with their comparable mechanical properties. Geopolymers are a subcategory of of AAMs and synthesized from aluminosilicate sources. The main motivation of this thesis is to understand the methylene blue (MB) adsorption and photocatalytic activity of AAMs and geopolymers by utilizing diffraction and microscopy techniques to establish an structure-performance relationship. Firstly, an industrial waste red mud together with metakaolin were used as raw materials and anatase amount in the geopolymer paste was varied to obtain a photocatalytically active geopolymer (RMGP) to remove MB dye from wastewaters. Findings implied that surface Ti species were responsible for the photocatalytic MB removal and 3.7 wt% addition of anatase was found to result in a tripled rate constant compared to that of pure anatase, due to synergistic effect of adsorption and photocatalysis processes. Secondly, novel and new Sep-based AAMs (Sep-AAM) as adsorbents for MB removal was introduced. Results showed that Sep-AAM has an enhanced MB adsorption capacity of 99.9 mg g-1 , adsorption occurs via chemical adsorption, and is slightly endothermic. MB adsorption performance of monolith-formed Sep-AAMs and metakaolin based counterparts (MKGP) with varying porosities were studied in the third part of this thesis. Outcomes of this part showed that it is possible to tune the MB adsorption performance and compressive strength by adjusting the porosity levels, and both of these monoliths can be regenerated up to four cycles. In the last part, MB adsorption performance of RMGP from part one was significantly enhanced by incorporating urea-based graphitic carbon nitride. The findings of this thesis demonstrate that AAMs and geopolymers with their economical and environmentally-friendly synthesis procedures offer high mechanical strength, enhanced adsorption and photocatalytic performance towards MB, and sustainable alternatives for wastewater treatment applications.