Study On Adsorption Properties And Mechanism Of Modified Montmorillonite Composites For Salvianolic Acids

Objective Salvianolic acid A(SAA),salvianolic acid B(SAB)and rosmarinic acid(RA)are a class of phenolic acid compounds with similar structure in Salvia miltiorrhiza Bge,which are widely used in the treatment of cardiovascular and cerebrovascular diseases,liver fibrosis,diabetes and complications,tumors and other diseases.In this paper,modified montmorillonite composite was designed and synthesized to achieve efficient adsorption and separation of three salvianolic acids from Salvia miltiorrhiza Bge.through multiple interactions.Methods 1.Sodium montmorillonite(Na-MMT)was used as matrix material.Branched polyethylenimide(b-PEI)was used as intercalator to expand the layer distance of Na-MMT and introduce amino groups.4-carboxyphenylboric acid monomer was added as functional group via amidation reacrtion with the help of 1ethyl-3-(3-dimethylaminopropyl)-carbonized diimide hydrochloride(EDC)and Nhydroxysuccinimide(NHS)to obtain the modified montmorillonite composite(PAPIM).2.The materials were characterized by scanning electron microscopy(SEM),Xray photoelectron spectroscopy(XPS),dynamic light scatterer(DLS),automatic specific surface and porosity analyzer(BET),Fourier infrared spectrometer(FT-IR),Xray diffractometer(XRD),energy dispersive X-ray spectrometer(EDX).3.The influences of adsorbent dosage,pH on salvianolic acid adsorption were investigated.Adsorption kinetics,adsorption isotherm,adsorption thermodynamics and adsorption selectivity of three kinds of salvianolic acid adsorbed by the material were studied as well.4.Adsorption-desorption cycles for three kinds of salvianolic acid were studied.FT-IR characterization of materials before and after adsorption was carried out to investigate the desorption and recycling regeneration of PAPIM.5.Extracting Salvia miltiorrhiza Bge.to obtain the water extract and study the adsorption properties of materials in the real water extract of Salvia miltiorrhiza for three kinds of salvianolic acid.6.Model fitting of adsorption kinetics,adsorption isotherm and adsorption thermodynamics data was carried out.And the changes of material structure and properties before and after adsorption were characterized by XPS,FT-IR and other means to study the adsorption mechanism of three salvianolic acids by PAPIM.The adsorption energy of three salvianolic acids was calculated by density functional theory(DFT).Results 1.The results of SEM,XRD,FT-IR,DLS and XPS proved the successful preparation of PAPIM.The modified montmorillonite was observed by scanning electron microscopy(SEM),and the layer spacing was enlarged,and the specific surface area were reduced and average pore size were increased.It was proved that bPEI and 4-carboxyphenylboric acid were successfully inserted into the Na-MMT interlayer.2.The optimal dosage of adsorbent is 1.0 g/L.When the pH value was 3,the adsorption effect of the material on the three salvianolic acids was good.The adsorption of three salvianolic acids followed a pseudo-second-order kinetic model,and the adsorption equilibrium was reached within 30 min at 298.15 K.The adsorption isotherm of the material for the three phenolic acids conforms to the Langmuir model.It was predicted that the maximum adsorption capacity of SAA was 1.285 mmol/g(635.2 mg/g),the maximum adsorption capacity of SAB was 0.692 mmol/g(497.1 mg/g)and the maximum adsorption capacity of RA was 1.154 mmol/g(415.9 mg/g).3.After 5 cycles,the adsorption efficiency of three salvianolic acids by PAPIM decreased slightly,but remained above 80%,indicating that the material has good reusability.4.In the aqueous extract of Salvia miltiorrhiza Bge at 1-6 mg/mL,the adsorption efficiency of SAA by PAPIM was close to 100%within 2h,while the adsorption efficiency of SAB and RA decreased with the increase of concentration.5.The adsorption process of materials on three kinds of salvianolic acids involves chemical adsorption and physical adsorption.Based on model fitting and relevant experimental results,the adsorption mechanism of the three salvianolic acids was deduced,including covalent bond,π-π stacking,electrostatic interaction and hydrogen bond.By density functional theory calculation,the binding energy for the adsorption of SAA by phenylboric acid functionalized polyvinylimide was-57.53kcal/mol,the adsorption energy for SAB was-15.94kcal/mol,and the adsorption energy for RA was-18.36kcal/mol.Conclusion PEI intercalated montmorillonite composite modified with 4carboxyphenylboric acid functionalized has the characteristics of fast kinetics,large capacity and relatively selective adsorption of salvianolic acid compounds.It provides a new idea for the effective adsorption of other phenolic acids.