Geopolymer/Zeolite composite materials with adsorptive and photocatalytic properties for dye removal.

This study investigated the adsorption capacities and photocatalytic activities of geopolymer-zeolite composite materials by incorporating different amounts of zeolite and TiO2 in a geopolymer matrix for dye removal. Geopolymers with SiO2/Al2O3 molar ratio of 2.5 were synthesized from metakaolin. The geopolymers containing zeolite and TiO2-doped zeolite exhibited similar behavior in terms of mineral compositions, microstructures and chemical frameworks. The compressive strength of geopolymer-zeolite composite materials decreased with increasing amount of zeolite and TiO2-doped zeolite (0-40 wt%) because of the increase in the porosity of composite materials. The maximum methylene blue adsorption capacity and photocatalytic efficiency of the powdered geopolymer composites with 40 wt% TiO2-doped zeolite was 99.1% and was higher than that of the composites with 40 wt% zeolite without TiO2-doping (92.5%). In addition, the geopolymer composites with TiO2-doped zeolite exhibited excellent stability after repeated usage as photocatalysts. The adsorption capacity and photocatalytic activity of pelletized geopolymer composites decreased because of the reduction in their specific surface area.

Synthesis of zeolite phases from combustion by-products.

Synthesis of zeolites from combustion by-products, including fly ash, bottom ash and rice husk ash, was studied. A molar ratio of SiO2/Al2O3 of 1.5 was used for the syntheses. Refluxing and hydrothermal methods were also used for synthesis for comparison. The reaction temperatures of refluxing and hydrothermal methods were 100 degrees C and 130 degrees C, respectively. Sodalite, phillipsite-K, and zeolite P1 with analcime were obtained when fly ash, bottom ash and rice husk ash were used as starting materials, respectively. With rice husk ash as a starting material, zeolite P1 was produced. This result had advantages over previous studies as there was no prior activation required for the synthesis. The concentrations and types of alkaline used in the synthesis also determined the zeolite type. The different zeolites obtained from three systems were measured for specific surface area and pore size by using BET and Hg-porosimetry, respectively. Ammonium exchange capacities of the synthesised powders containing zeolites, sodalite, zeolite P1 and phillipsite-K were 38.5, 65.0 and 154.7 meq 100 g(-1), respectively.

Workability and strength of lignite bottom ash geopolymer mortar.

In this paper, the waste lignite bottom ash from power station was used as a source material for making geopolymer. Sodium silicate and sodium hydroxide (NaOH) were used as liquid for the mixture and heat curing was used to activate the geopolymerization. The fineness of bottom ash, the liquid alkaline/ash ratio, the sodium silicate/NaOH ratio and the NaOH concentration were studied. The effects of the additions of water, NaOH and napthalene-based superplasticizer on the workability and strength of the geopolymer mortar were also studied. Relatively high strength geopolymer mortars of 24.0-58.0 MPa were obtained with the use of ground bottom ash with 3% retained on sieve no. 325 and mean particle size of 15.7 microm, using liquid alkaline/ash ratios of 0.429-0.709, the sodium silicate/NaOH ratios of 0.67-1.5 and 7.5-12.5M NaOH. The incorporation of water improved the workability of geopolymer mortar more effectively than the use of napthalene-based superplasticizer with similar slight reduction in strengths. The addition of NaOH solution slightly improves the workability of the mix while maintaining the strength of the geopolymer mortars.