Preparation Of Magnetic Montmorillonite And Its Mechanism Of Phenol Removal

The phenolic pollutions became a global critic problem due to aromatic rings,stable structure and high biological toxicity.Thus,an effective treatment approach urgently developed for the removal of phenol.At present,adsorption technologies in physical methods and Fenton oxidation technology in chemical methods are widely used in the treatment of actual phenolic wastewater.But it is a difficult problem to develop cheap and efficient adsorption materials and catalytic materials.Thus,in this paper,Fe₃O₄@cetyltrimethylammonium bromide/erucic acid amide-montmorillonite（Fe₃O₄@C/E-MMT）nanocomposite was synthesized by one-step coprecipitation method and Fe₃O₄@silica pillared montmorillonite（Fe₃O₄@SPC）was synthesized by one-step interlayer formwork method,respectively.The adsorption and heterogeneous Fenton like catalytic degradation of phenol by the two materials were studied.The mechanism of adsorption and oxidation was explored.The main research contents are as follows:（1）Fe₃O₄@C/E-MMT was synthesized by one-step coprecipitation method.By X-ray Diffraction（XRD）and Fourier Transform Infrared Spectroscopy（FTIR）,Cetyltrimethylammonium bromide（CTAB）and erucic acid amide（EA）were successfully intercalated into Ca-MMT,the interlayer spacing of cetyltrimethylammonium bromide/erucic acid amide-montmorillonite（C/E-MMT）increased from 1.51 nm to 4.26 nm,the interlayer spacing of Fe₃O₄@C/E-MMT reduced to 3.78 nm.Combined with Scanning Electronic Microscopy（SEM）,it was found that Fe₃O₄@C/E-MMT retained the lamellar structure of Ca-MMT and most Fe₃O₄was loaded on the surface of Ca-MMT.By N₂adsorption-desorption method（BET）,Ca-MMT and Fe₃O₄@C/E-MMT belonged to type IV adsorption-desorption isotherm and had typical H3 hysteresis loops.The pore volume of Fe₃O₄@C/E-MMT increased obviously so that it was helpful to improve the adsorption performance.The results of adsorption experiments showed that Fe₃O₄@C/E-MMT had good adsorption performance for phenol.The optimal adsorption conditions are as follows:25℃,p H 7,120 min,0.08 g Fe₃O₄@C/E-MMT was added to the 30 m L initial concentration of 100mg·L^-1phenol,the removal rate of phenol was 85.46%,and the removal capacity was 31.45mg·g^-1.The experimental adsorption data followed a pseudo-second-order kinetic model and the adsorption process was controlled by surface adsorption and intra particle diffusion.The experimental adsorption data followed Langmuir isothermal adsorption model and the maximum adsorption capacity of phenol was 42.39 mg·g^-1.X-ray Photoelectron Spectroscopy（XPS）and FTIR of Fe₃O₄@C/E-MMT suggested the adsorption mechanism:the hydrogen bond between nitrogen atom on Fe₃O₄@C/E-MMT and hydroxyl hydrogen atom on phenol formed chemisorption.（2）Fe₃O₄was loaded on SPC by one-step interlayer formwork method to synthesize Fe₃O₄@SPC.By XRD and FTIR,the interlayer spacing of silica pillared montmorillonite（SPC）increased from 1.51 nm to 3.56 nm,the interlayer spacing Fe₃O₄@SPC was 3.30 nm.Combined with SEM,it was found that most of Fe₃O₄particles were dispersed on the surface of SPC.By BET,N₂adsorption-desorption isotherm of Fe₃O₄@SPC belonged to mixed type of type I and type IV and had typical H4 hysteresis loops.The increase of pore volume could effectively enhance the adsorption capacity of Fe₃O₄@C/E-MMT for phenol,and improved the catalytic efficiency.According to the free radical scavenging activity test of tert butyl alcohol,it was confirmed that·OH played a major role in the catalytic oxidation of phenol.The optimal catalytic conditions were as follows:120 min,p H 3.5,the dosage of Fe₃O₄@SPC of 0.5 g·L^-1,the dosage of H₂O₂of 20 mmol·L^-1,the initial concentration of 100 mg·L^-1,the degradation rate of phenol was 100%.The intermediate products of phenol degradation were analyzed by Gas Chromatograph-Mass Spectroscopy（GC-MS）,the degradation process was speculated:the ortho and para positions of phenol were attacked by·OH to form o/p-hydroquinone.Due to the oxidative dehydrogenation,o/p-hydroquinone were oxidized to o/p-benzoquinone respectively.Then,the benzene ring was broken to form maleic acid and fumaric acid,a series of small molecular acids were formed by decarboxylation reaction,and finally oxidized to H₂O and CO₂.Through five repeatability experiment,the removal rate of phenol was still up to 90%,which supposed that Fe₃O₄@SPC had good reusability.The iron ion dissolution experiment and the result of XPS showed that Fe₃O₄@SPC had excellent catalytic activity and stability.