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Bai H.,Tianjin Polytechnic University | Bai H.,Tianjin Normal University | Zhang Q.,Tianjin Polytechnic University | He T.,Tianjin Polytechnic University | And 4 more authors.
Applied Clay Science | Year: 2016

To investigate diffusion model and adsorption mechanism of hydrogel for the removal of anionic dye Amaranth from aqueous solution, poly(N-isopropylacrylamide)(abbreviated as PNIPAm)/clay lithium magnesium silicate hydrate (abbreviated as LMSH) nanocomposite hydrogels with various clay percentage of LMSH/NIPAm (named as NPX hydrogel) were prepared. Adsorption kinetics of NPX samples were investigated under different experimental conditions (including solution pH, initial concentration of Amaranth dye solution and clay percentage of LMSH/NIPAm). Based on the adsorption experiments, adsorption dynamics, diffusion mechanisms and adsorption isotherms of NPX samples in Amaranth solution were analyzed through pseudo first-order model, pseudo second-order model, film diffusion model, intra-particle diffusion model and different isotherm models. The adsorption kinetics showed that in acidic (pH = 2) Amaranth solution NPX nanocomposite hydrogel was more effective for the removal of Amaranth dye. With increasing clay percentage of LMSH/NIPAm from 5 to 40 wt.%, adsorption capacity of Amaranth dye onto NPX samples decreased due to shrunk pore effect of NPX nanocomposite hydrogels and enhanced electrostatic repulsive interactions between NPX samples and Amaranth molecules. Adsorption dynamics indicated pseudo second-order model was more suitable for the investigated adsorption process. The adsorption rate-controlling step mainly came from film diffusion, but not the only factor. Adsorption isotherm indicated the adsorption process from monolayer adsorption to multilayer adsorption. According to Dubinin-Radushkevich isotherm model (abbreviated as D-R model), the calculated mean free energy implied chemisorption nature between NPX nanocomposite hydrogel and Amaranth. Based on adsorption mechanism of NPX nanocomposite hydrogel on Amaranth established, the conclusion confirms the prospect of NPX nanocomposite hydrogel as effective adsorbent to dispose real dyeing wastewater. © 2016 Elsevier B.V. Source

Bai H.H.,Tianjin Polytechnic University | Bai H.H.,Tianjin Normal University | Jin R.,Tianjin Normal University | Zhang Q.S.,Tianjin Polytechnic University | And 2 more authors.
Materials Science Forum | Year: 2015

In this study, different appearances, structures and morphologies of macro-clay G105-Polymer grade montmorillonite (PMMT) and nano-clay Lithium magnesium silicate (LMSH) were compared and analyzed, which were used in different conditions of non-adsorption and adsorption of crystal violent(CV). Adsorption kinetics and properties of the macro/nano-clay in CV solution were studied, and adsorption time, dye concentration and environmental pH were the main factors on the inspection in this work. The adsorption mechanisms of the macro-/nano-clay on CV were investigated. The results showed that adsorption actions of PMMT and LMSH on CV were some similar, such as time-dependent, linear growth of adsorbed CV amount with increasing CV concentration, adsorption capacity of macro-/nano-clay declined firstly and then increased in 10mg/L CV solution along with increasing pH value. But the adsorption differences in two systems of PMMT-CV and LMSH-CV were obvious. Adsorption behavior of LMSH-CV system showed two adsorption phenomena. Under neutral conditions, adsorbed CV amount in 0.5g LMSH was 1.69 times that of PMMT. Adsorption amount of LMSH was more significant to be affected by dye concentration and pH conditions. The research achievements further showed that adsorption mechanism was the root cause of the following difference. The adsorption of PMMT- CV relied mainly on iron-exchange effect of layers replaceable cations and surface adsorbed ions with CV cations, while the significant adsorption of LMSH- CV was mainly due to the electrostatic interaction from layers negative charge distribution and CV cationic properties in the solution, partly surface ions exchanges also existed in the adsorption process of LMSH-CV. © (2015) Trans Tech Publications, Switzerland. Source

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