Surface Silanization Of Heat-activated Montmorillonite For Removing Methyl Orange From Aqueous Solution

Methyl orange is the main pollutant in dye wastewater at present,which is not easy to degrade,strong enrichment,easy to cause carcinogenic mutation and other hazards.Its treatment has become one of the difficult problems urgently needed to be solved.In order to achieve efficient degradation of methyl orange and other azo dyes,montmorillonite as raw material was prepared by thermal activation and surface modification of 3-aminopropyl triethoxysilane（APTES）.The changes of montmorillonite morphology,structure and surface groups during the modification process were analyzed by X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,thermal analysis（TG）and nuclear magnetic resonance（NMR）.The removal effect,adsorption process and mechanism of methyl orange by modified montmorillonite were explored through batch experiments.The main achievements of this paper are as below:（1）After calcined at high temperature,montmorillonite was removed by interlayer adsorption water under 200℃,and its structure did not change.At about 600℃,the hydroxy structure begins to be removed.At 800℃,the montmorillonite structure has been completely destroyed.When the temperature reaches 900℃,Si O₂ becomes amorphous free state.At 200℃,more silicon groups are formed on the surface and border of montmorillonite,which increases the activity of hydroxyl groups on the surface of montmorillonite,which provides an experimental basis for the organic modification of montmorillonite.（2）There are three main sites for grafting modification of montmorillonite:interlayer,outer surface and fracture edge.In the system of absolute toluene and absolute ethanol,organosilane can only react with the hydroxyl group on the outer surface of montmorillonite.In the ethanol/water system,organosilane can be hydrolyzed to form silicon hydroxyl group,dehydrate and condense with the hydroxyl group on the inner surface of montmorillonite to form covalent bond,and oligomerization reaction will occur between silicon hydroxyl groups;The non-polar solvent system was favorable for the grafting reaction and the silane grafting amount was higher.The increase of water content in ethanol/water system can promote the hydrolysis and condensation of APTES and increase its silane grafting amount and modification effect.（3）p H has a great influence on the adsorption performance of modified montmorillonite.The adsorption equilibrium can be reached at p H=2.0 for 30 min,and equilibrium adsorption capacity is 69.55 mg/g.The adsorption kinetics conforms to the quasi second-order kinetic model,and the adsorption thermodynamics conforms to the Langmuir adsorption model.The adsorption reaction is a spontaneous,exothermic and entropy decreasing process.The adsorption process includes physical adsorption and chemical adsorption.The effect of different ions on methyl orange removal was Mg²⁺>Ca²⁺>Na⁺>Fe³⁺>K⁺,modified montmorillonite has strong anti-interference to coexisting ions;As a desorption agent,anhydrous ethanol has the best desorption effect.After five times of recycling,the adsorption efficiency can still reach 65%.