Three-dimensional Magnetic Graphene Oxide Polyvinyl Alcohol Novel Composites-immobilized Enzymes

Petrochemical energy is non-renewable and limited in quantity,which severely restricts the sustainable development of the economy.The emergence of biodiesel has effectively redu-ced the use of petrochemical energy while reducing the pollution to the environment.In this experiment,biodiesel was prepared by immobilized enzyme to catalytic soybean oil.The design and preparation of an immobilized carrier having unique characteristics have a great effect on the good catalytic activity of the enzyme.Two-dimensional graphene oxide?2D-GO?is easily agglomerated by van der Waals forces and changes back to graphite oxide,thereby losing a large number of active sites.In this experiment,three-dimensional graphene oxide with a large specific surface area was designed and prepared,and Fe3O4 nanoparticles?Fe3O4NPs?with large magnetic properties are loaded to prepare three-dimensional magnetic graphene oxide?3D-GO/PVA/Fe3O4?nanocomposites,and are used to immobilize carriers and catalyze the preparation of biodiesel from soybean oil.First,GO was prepared by modified Hummers method,and Fe3O4 NPs were prepared by solvothermal method.Secondly,GO was hydrogenated by polyvinyl alcohol?PVA?,and Fe3O4 NPs were added to prepare 3D-GO/PVA/Fe3O4.Thirdly,in this experiment,three-dimensional magnetic graphene oxide-magnetite PVA?3D-GO/PVA/Fe3O4?nanoco-mposites were successfully prepared.The morphology of the composites was characterized and analyzed by scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.X-ray powder diffraction?XPS?,Fourier transform infrared?FT-IR?and X-ray diffraction?XRD?spectra were used to investigate the chemical structure and crystal structure.The magnetic properties of the composites were investigated by vibrating sample magnetometers?VSM?.The specific surface area and average pore size of the composites were determined by Brunauer-Emmett-Teller?BET?and Barrett-Joyner-Halenda?BJH?calculations.The specific surface area and average pore size of 3D-GO/PVA/Fe3O4nanocomposites were calculated to be 388.87 m²g^-1 and 9.6 nm,respectively.The higher specific surface area indicates that the three-dimensional framework structure of the composites avoid the problem of the aggregation of two-dimensional GO sheets.The nanocomposite's saturation magnetization?Ms?of 30.5 emu/g allows the nanocomposites to be easily recovered with the help of an external magnetic field.3D-GO/PVA/Fe3O4 nanocomposites exhibited better performance of immobilized Porcine pancreas lipase?PPL?.The composites and lipase were combined by physical adsorption.The maximum immobilization efficiency was 91%,and relative enzyme activity up to 90%.After 10 cycles,the immobilized enzyme activity remained at about 70.8%of the initial activity.The stability test showed that the activity of the immobilized enzyme was maintained at 71.1%for 56 days at 4?.The immobilized enzyme was used as a catalyst to catalyze the reaction of soybean oil to biodiesel.The optimal reaction conditions of soybean oil and methanol were determined by single factor method.The molar ratio of methanol to soybean oil was 6:1,the optimum temperature was 45?,and the reaction time was 10 h.The immobilized enzyme showed good catalytic activity,the ester conversion rate reached 85.3%,and the ester conversion rate reached 49.1%after repeated use 10 times.