| Cassava residue is the dregs of cassava after the production of starch and alcohol.Because it contains a lot of starch and cellulose,it is an ideal material for the preparation of magnetic polymer microspheres.Magnetic polymer microspheres are widely used in the field of water treatment because of its advantages such as magnetic responsiveness,large specific surface area,biocompatibility and non pollution.Firstly,modified starches(cationic starch?phosphate starch?distarch phosphate?oxidized starch and urea starch)with different functional groups were used as adsorbent,and the ultraviolet spectrophotometry was used to measure the concentration of Cu2+.What's more,the adsorption properties and kinetics of above modified starches on Cu2+ were investigated.Then the acrylic acid(AA)with carboxyl groups?acrylamide(AM)with amide groups and cassava residue were used to prepare AA/AM magnetic cassava residue microsphere by inverse phase emulsion polymerization.Effects of reaction temperature?reaction time?volume ratio of oil to water and mass ratio of initiator?crosslinking agent?AA?MCR to monomer were investigated.Scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize the structure of microspheres.And methyl methacrylate(MMA)was introduced into the AA/AM magnetic cassava residue microsphere system for the preparation of MMA/AA/AM magnetic microspheres with better dispersion.Scanning electron microscopy?Fourier transform infrared spectroscopy?vibrating sample magnetometer?particle sizer and zeta potential analyzer were used to characterize the structure of MMA/AA/AM magnetic microspheres.Effects of mass ratio of MMA?initiator and crosslinking agent to monomer were investigated.Furthermore,the isotherms,kinetics and thermodynamics of MMA/AA/AM magnetic microspheres on Cu2+ were also studied.The main experimental results is following:(1)The saturated adsorption capacity of cationic starch?phosphate starch?distarch phosphate?oxidized starch?urea starch and raw cassava starch are 40.5 mg·g-1?50.7 mg·g-1?43.8 mg·g-1?42.8 mg·g-1?47.7 mg·g-1 and 16.6 mg·g-1.The grafted group on the modified starch had the adsorption effect on Cu2+.Adsorption kinetic studies showed that the adsorption isotherm data of these modified starches match with the Freundlich isotherm model.The adsorption data of cationic starch is in accord with pseudo-second order kinetic model,and the others‘adsorption data more coincide with pseudo-first order kinetic model.(2)When reaction temperature is 323.2 K,reaction time is 3 h,volume ratio of oil to water is 10,and mass ratio of initiator?crosslinking agent?AA?MCR to monomer are 2.12%?0.45%?75%?0.2 respectively,the AA/AM magnetic cassava residue microspheres has the maximum adsorption capacity which can reach 98.2 mg·g-1,it is better than modified starches.The microsphere has the advantages of uniform size,smooth surface,regular shape,good ballability and disadvantages of bonding.(3)When mass ratio of MMA?initiator and crosslinking agent to monomer are 0.75%/2.12%and 0.5%,the MMA/AA/AM magnetic cassava residue microspheres has the maximum adsorption capacity which can reach 110.5 mg·g-1,it is better than AA/AM magnetic cassava residue microspheres.The microspheres have smooth surface?uniform size?good dispersion and excellent reusability,its average particle size?PDI?saturation magnetization are 206 nm?0.18?11.9 emu·g-1 respectively.The adsorption process in accord with pseudo-second order adsorption kinetic model and Freundlich isothermal adsorption model.When the temperature is in the range of 283.2-323.2 K,the adsorption process is spontaneous and endothermic process.According to the thermodynamics of adsorption and ?H(47.12 kJ·mol-1),the adsorption process is mainly based on chemical adsorption. |
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