Modified zeolite from metakaolin and fly ash as efficient adsorbent for cationic methylene blue dye removal

Abstract

Effective textile dye removal from aquatic wastewater is essential, as this effluent is harmful to human health, biodiversity, and natural environments. This study investigates the synthesis of zeolitic materials for dye removal from wastewater using metakaolin and fly ash as starting materials. In the first synthesis step, the starting materials are blended at various metakaolin-to-fly ash ratios and treated with a 3 M sodium hydroxide solution under stirring. The solid-to-liquid ratio of the precursor gel is 1:8 (w/v). The suspensions are then subjected to hydrothermal treatment at 120 °C for 6 h. In the second step, an impregnation method is used to obtain titanium dioxide (TiO2)-containing zeolite, and the effect of the TiO2 content on the zeolite adsorption performance is investigated. The synthesized products are characterized using X-ray diffraction, scanning electron microscopy, particle size analysis, surface area measurement, and ultraviolet-visible spectrophotometry. From the results, a metakaolin-to-fly ash weight ratio of 4:1 is optimal and yields sodalite and zeolite A. For 20-ppm methylene blue solution, the adsorption efficiencies of freshly synthesized zeolite and TiO2-containing zeolite are found to be 87.63% and 99.87%, respectively. In addition, the adsorption performance of the reused product is similar to that of the freshly synthesized product. Thus, the synthesized modified zeolite is an efficient adsorbent for methylene blue removal.