NaOH activation of soils is an affordable and promising way to improve mechanical properties of earthen bricks. If for well-activated geopolymers, the hard polymeric network limits the influence of water on mechanical...NaOH activation of soils is an affordable and promising way to improve mechanical properties of earthen bricks. If for well-activated geopolymers, the hard polymeric network limits the influence of water on mechanical properties, for the weakly activated one, as non-calcined raw clayey soils, the influence of water on these properties would be more critical. This work aims to determine the effect of sodium hydroxide concentration on the drying kinetics of bricks made with raw clayey soils, and to model this kinetics. The results show that the drying kinetics is governed by the diffusion of water due to the absence of free water. The drying duration increases linearly with the increasing of NaOH content, while the volumetric shrinkage decreases, probably thanks to the reduction of the material porosity during the formation of the zeolitic structures. Besides, the drying duration is strongly and negatively correlated with the initial drying rate (−0.97) and bricks did not show visible cracks. Among the five parametric models tested, the Khazaei’s model is the best in terms of all statistical criteria considered. For all models used, the coefficient of determination is ranged from 0.993 to 0.999, and the evolution of the models’ parameters is in accordance with that of the drying kinetics observed.展开更多
The geopolymer synthesized by alkali-activated fly ash was firstly used as a novel photocatalyst for degradation of methylene blue （MB） dye from wastewater. The geopolymer is composed of nanoparticulates with an ave...The geopolymer synthesized by alkali-activated fly ash was firstly used as a novel photocatalyst for degradation of methylene blue （MB） dye from wastewater. The geopolymer is composed of nanoparticulates with an average particle size of about 50 nm, More than 90% of pore volume in the fly ash-based geopolymet predominately centralized on the pore size in the range of 17-700 nm. The degradation efficiency of MB dye by fly ash-based geopolymer catalyst was up to 92.79% under UV irradiation due to the synergistic effect of adsorption and semiconductor photocatalysis. The pseudo-first-order and pseudo-second-order rate equations as well as intra-particle diffusion rate equation were employed to correlate analysis for the adsorption kinetics of MB dye, The experimental data agreed well with pseudo-second-order rate equation in both cases of with UV and without UV irradiations. The intra-particle diffusion process is not the rate determining step. The photocatalytic degradation of MB dye in solution obeys third-order reaction kinetics.展开更多
文摘NaOH activation of soils is an affordable and promising way to improve mechanical properties of earthen bricks. If for well-activated geopolymers, the hard polymeric network limits the influence of water on mechanical properties, for the weakly activated one, as non-calcined raw clayey soils, the influence of water on these properties would be more critical. This work aims to determine the effect of sodium hydroxide concentration on the drying kinetics of bricks made with raw clayey soils, and to model this kinetics. The results show that the drying kinetics is governed by the diffusion of water due to the absence of free water. The drying duration increases linearly with the increasing of NaOH content, while the volumetric shrinkage decreases, probably thanks to the reduction of the material porosity during the formation of the zeolitic structures. Besides, the drying duration is strongly and negatively correlated with the initial drying rate (−0.97) and bricks did not show visible cracks. Among the five parametric models tested, the Khazaei’s model is the best in terms of all statistical criteria considered. For all models used, the coefficient of determination is ranged from 0.993 to 0.999, and the evolution of the models’ parameters is in accordance with that of the drying kinetics observed.
基金financially supported by Industrial Key Project of Shaanxi Province(No.2010K01-080)Open Fund of State Key Laboratory of Architecture Science and Technology in West China(XAUAT)+1 种基金Xi'an University of Architecture and Technology(No.10KF05)Scientific Research Program Funded by Shaanxi Provincial Education Department(No.12JK0579)
文摘The geopolymer synthesized by alkali-activated fly ash was firstly used as a novel photocatalyst for degradation of methylene blue （MB） dye from wastewater. The geopolymer is composed of nanoparticulates with an average particle size of about 50 nm, More than 90% of pore volume in the fly ash-based geopolymet predominately centralized on the pore size in the range of 17-700 nm. The degradation efficiency of MB dye by fly ash-based geopolymer catalyst was up to 92.79% under UV irradiation due to the synergistic effect of adsorption and semiconductor photocatalysis. The pseudo-first-order and pseudo-second-order rate equations as well as intra-particle diffusion rate equation were employed to correlate analysis for the adsorption kinetics of MB dye, The experimental data agreed well with pseudo-second-order rate equation in both cases of with UV and without UV irradiations. The intra-particle diffusion process is not the rate determining step. The photocatalytic degradation of MB dye in solution obeys third-order reaction kinetics.
