Study On Intercalation Of Layered Double Hydroxides And Its Sorptive Characteristics

Layered double hydroxides （LDH） is a naturally born anionic clay with exchangeableinterlayer anions and adjustable composition of host layer. LDH has been widely used indifferent fields including environmental protection, agriculture and industry production. Inthis work the effects of charge density of LDH on its adsorption behavior towards anionicdyes were systematically examined, and the differences between adsorption of indigo carminedye （IC） on MgFe-LDH and LDO （calcined product of MgFe-LDH） were investigated. Inaddition, the sorption capacity of organo-LDH with different surfactant content towardorganic compounds was investigated, and the kinetics and thermodynamic parameters werecalculated. The main original conclusions of this work are as follows:（1） The adsorption capacity of LDH toward anionic dyes is found to be revsersely relatedto its charge density. The adsorption of alizarin red on LDH was determined to be192.6mg/Lat Mg/Al=4, and was decreased to155.3mg/L and118.5mg/L as Mg/Al was increased to3and2, respectively. It could be ascribed to the difficulty in replacing CO32-which was betterabsorbed through electrostatic interactions for LDH with higher charge density. Theadsorption of acidic dyes on synthesized CO₃^2--LDH could be accounted by the mechanismsof surface adsorption and anion exchange.（2） The adsorptive characteristics of carmine dye （IC） on MgFe-LDH and calcined formLDO are found to be quite different. BET results showed the structure of LDO had changed incomparison to LDH, specific surface area got larger from102.55m²/g to52.31m²/g. Theadsorption isotherms were shown to be Langmuir-type and the adsorption kinetics followedpseudo second order equation. In addition, the adsorption capacities of the regeneratedmaterials decreased with increasing adsorption cycles. However, after four times regenerationcycles LDO remains well adsorption effect.（3） The sorption of nitrobenzene on the organo-LDH is an entropy-driven process, andthe organic carbon content normalized sorption coefficient of nitrobenzene(K_oc) was shown toremain relatively constant. The intercalated DS-was consistent with a paraffin bilayersarrangement within the interlayer space of DS-at high loading level. The linear model fits thenitrobenzene sorption isotherms on LDH-DS well, implying a partitioning sorption process.K_dvalues of nitrobenzene rise from39.5mL/g to73mL/g, and Kocremain relatively constant（200mL/g） as the DS-loading amount increase. The adsorption could be described as apseudo-second order model and was endothermic in nature of the process with the increasingof temperature, the free energy decreased and the spontaneity increased.