Intercalation Of Kaolinite With Long-Chain Organic Compounds And Its Formation Mechanism

Based on clay mineralogy,crystallography,crystal chemistry and other theoretical knowledges,the method for preparation of methoxy-modified kaolinite was improved.The effect of reaction temperature on intercalating and morphological evolution of octyltrimethylammonium chloride into kaolinite was characterized.Short-chain quaternary ammonium salts were intercalated into kaolinite by solid-solid reaction,and its formation mechanism and effect factors were investigated.Additionally,a series of kaolinite/fatty acids intercalation compounds were synthesized,and its corresponding products and formation mechanism were carefully analyzed.The time required for preparation of methoxy-modified kaolinite was shortened by utilizing kaolinite/dimethyl sulfoxide intercalation compounds an intermediary.The obtained samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy,and further displacement intercalation with butyl trimethylammonium chloride was also carried out.Results showed that the time required for the methoxy-modified kaolinite preparation was drastically shortened by at least 50%.Reducing the solid-to-liquid ratio?kaolinite/dimethyl sulfoxide intercalation compounds:methanol?can help the elastic deformation of kaolinite and remove the intercalators,which accelerated the grafting of methanol onto kaolinite interlayer.The excellent intercalation effect could be obtained at the mass ratio of 1:50.The obtained products showed the d_00l0l value of methoxy-modified kaolinite could be arbitrary values between 0.86 and 1.08 nm,which were caused by the methanol and water molecules between the interlayer spaces of methoxy-modified kaolinite.Methanol molecules confined in the interlayer space were sourced from solvent,while water molecules were adsorbed form the air.Results showed that the methanol and water molecules were bonded with the layer of kaolinite by weak hydrogen bonds.And the the methanol and water molecules in the interlayer have no obvious effect on the subsequent intercalation reaction.Thestructuralproperty,thermalbehavior,andmorphologyof octyltrimethylammonium chloride–kaolinite compounds prepared at different reaction temperatures were studied by X-ray diffraction,Fourier transform infrared spectroscopy,thermogravimetry–differential scanning calorimetry,and scanning electron microscopy.The arrangement model of quaternary ammonium cations was studied by combining X-ray diffraction and the molecular structure of octyltrimethylammonium chloride.The present study demonstrated that the arrangement model of octyltrimethylammonium cations within the kaolinite interlayer space was independent of reaction temperature.The alkyl chains adopted a similar rigid paraffin-bilayer arrangement with different tilted angles.Fourier transform infrared spectroscopy was used to investigated the conformation.Results showed that the alkyl chains within the Kaol interlayers mainly arranged in the all-trans conformation,and the molecular environment of the alkyl chains still behaved like solid-like.The decomposition of organoclays were separated into four stages,and the hydrophobicity,thermal stability and the surfactant packing density were analysized.Scanning electron microscopy showed the yield of nanoscrolls of the organic complexes was strongly dependent on the reaction temperature,which was related to the surfactant packing density.Most of the transformed nanoscrolls were found in the products prepared at 70°C.Solid-solid reactions have been utilized to study the formation and intercalation mechanism of organoammonium-kaolinite formed from quaternary ammonium salt and kaolinite by using a methoxy-modified kaolinite as an intermediate.Results showed that butyl trimethylammonium and hexyl trimethylammonium ions were successfully intercalated into the silicate layers,while the larger ions(C_nH_2n+1N?CH₃?³⁺,n?8)were not.This was due to the alkylammonium ions were introduced by ion-dipole intercalation,while the interaction among the longer alkyl chains may exert a geometrical constraint?or steric hindrance?on the solid-solid intercalation of larger alkylammonium ions.In solid-solid reactions,the adsorbed water molecules played an important role,while,in solution method,the pH value of the mixed solution and the charge distribution at the external surfaces may also contributed to the intercaltion.FTIR results showed that much more water molecules were adsorbed on the product obtained by conventional method.In addition,a smiliar structural model and thermal behavior in the products obtained by both methods was also revealed.By using methoxy-modified kaolinite as the precursor,kaolinite was intercalated with dodecanoic,tetradecanoic,hexadecanoic,octadecanoic and octacosanoic acids.It is shown that a linear relationship was recognized between the basal spacing and the number of carbon atoms.The basal spacing increased up to the largest value?7.61 nm?reported so far when octacosanoic acid was used.Based on stereochemical calculation,the intercalated guest species should be arranged in the form of paraffin-type bilayer in the interlayer space.Furthermore,carboxylic acid molecules were coexisted with carboxylate anions within silicate layers.During intercalation,carboxylate anions were intercalated by ion-dipole intercalation,and carboxylic acid molecules may be simultaneously introduced by entraining reaction.the intercalation process could be easily affected by the pH value of the system,which could be related to the ratio of acidic species.The carboxyl groups in fatty aicd should be mainly interact with the inner surface hydroxyl groups of kaolinite,which was supported by ²⁹Si MAS NMR analysis.Thus,the morphologies of fatty acid intercalated kaolinite remained its lamellar structure,which may be caused by the arrangement model of intercalated guest species and its flexibility.