| Layered double hydroxides (LDHs) are a kind of functional materials with apermanent positive charge and have hydrotalcite layered crystal structure. Due totheirs unique electrical properties, layered structure and the exchangeablecharacteristic of interlayer anions, LDHs are increasingly used in many fields, suchas chemical industry, industrial catalysis, medicine and environmental sciences. Sofar, hydrotalcites with permanent positive charge have not been found for industrialapplication, and the preparations of such materials are relatively easy. So, theresearch about properties and application of hydrotalcites is one of the topics forhuman beings.Electroplating wastewater is complex system with heavy metal ions, anionicsurfactants, refractory organic matters and so many kinds of pollutants coexist. It isdifficult to remove a variety of pollutants effectively and simultaneously. Accordingto the idea of using waste treat waste, the heavy metal cations and organic matters inthe electroplating wastewater were used to synthetic multiple organic LDHs byadding different kinds and different quantity anionic surfactant by means of thecoprecipitation. Simultaneously the organic LDHs were used to sorption organiccontaminants by its special organic phase structure between the layers to achieve theremoval of a variety of pollutants and the self-purification of wastewater. The factors,such as the physicochemical properties of organic pollutants, the type and quantity ofanionic surfactant in the actual wastewater should be regulated and controlled tooptimize the microstructures of multiple organic LDH, focusing on themicrostructure control promoting the formation of multiple organic LDH,optimization the sorption performance of the organic pollutants and the soptionmechanisms. This study not only dealed with the recycling of heavy metal ions andorganic matters in the electroplating waste water and obtained a kind of effectivesorption materials. The specific experiments are as follows: 1. The synthesis of multiple LDHs in the electroplanting wastewater and theapplication on sorption and photocatalytic on the organic pollutantsHeavy metal ions and organic contaminants can be effectively removed fromelectroplating wastewaters through self-assembly formation of multiple organiclayered double hydroxides by adding simulation washing wastewater (SDBS andSDS). The organic LDHs were characterized by XRD, FT-IR, TOC, EA, et al. Thesynthetic products were used to remove dye wastewater (Congo red) and nonionicorganic matter (nitrobenzene) to survey the performance of organic LDHs. Theresults show that the removal rate of Zn2+and Fe3+can reached99%and the residualconcentration of Cr3+and Fe3+were less than1mg/L, which was accord with thenational standard. The removal of organic compounds can reach the maximum of95%. The obtained organic materials were used to adsorb azoic dye Congo red, withthe maximum adsorption amount of42.5mg/g. The sorption of nitrobenzene showeda linear sorption, which suggested a partition mechanism. Through photocatalyticperformance study of the multiple organic LDHs, it was found that it and its calcinedproduct have a high light degradation rate of Congo red under the visible light.2. Sorption of Aqueous Organic Contaminants onto Dodecyl Sulfate IntercalatedMagnesium Iron Layered Double HydroxideThe DS-Mg/Fe LDH was characterized by the means of X-ray diffraction(XRD), Fourier infrared (FT-IR), Total Organic Carbon analysis (TOC),themogravimetric and differential thermal analysis (TG-DTA) and surfacecharacteristics analysis (BET-N2). The sorption characteristics and mechanisms ofhydrophobic organic contaminants (naphthalene, nitrobenzene, acetophenone) andhydrophilic contaminant (aniline) on DS-Mg/Fe LDH were investigated, and weresubsequently compared with that on the inorganic magnesium iron layered doublehydroxides (CO3-Mg/Fe LDH and NO3-Mg/Fe LDH). The properties of organicmatter (polarization properties and water solubility) were studied to know theinfluence of sorption. The results showed that the greater sorption amount of organic contaminants on DS-Mg/Fe LDH than on CO3-Mg/Fe LDH and NO3-Mg/Fe LDHindicated that organic modified LDHs were potential sorbents for the abatement oforganic contaminants. The uptake curves of naphthalene, nitrobenzene andacetophenone on DS-Mg/Fe LDH were linear, and sorption capacities for threehydrophobic compounds were in the sequence of their hydrophobicity with partitionmechanism. After eliminating the influence of the hydrophobicity, the polarcompounds (nitrobenzene and acetophenone) exhibited higher affinity to DS-Mg/FeLDH than nonpolar compound (naphthalene), which demonstrated that both thehydrophobicity and polarity benefited the sorption of hydrophobic compounds onorganic LDHs. For hydrophilic compound, aniline, its uptake curve was nonlinear.The sorption process of aniline was the cooperation of the adsorption on hydroxidesurface through forming the hydrogen bonding and the weak partition to theinterlayer organic phase. |
