Preparation And Adsorption Properties For Cr(Ⅵ) Of New Functional Starch Microspheres

The functional starch microspheres with spherical shape, homogeneous particles sizedistribution and interior pore distribution were prepared by inverse emulsion polymerizationunder the protection of nitrogen, using soluble starch,2,3-epoxypropyl trimethylammonium chloride （GTA） and acrylamide （AM） as major materials, kerosene as oilphase, N,N’-methylene-bis-acrylamide （MBAA） as crosslinking agent, potassium persulfate–sodium hydrogen sulfite （K₂S₄O₈-NaHSO₃） oxidation-reduction system as initiator,Span80as emulsifier. The adsorption behavior for simulation Cr（Ⅵ） wastewater wasinvestigated using the functional starch microspheres as adsorbent.Firstly, the cationic starch microspheres were successfully synthesized by inverseemulsion polymerization, using soluble starch as raw materials and GTA as cationiteprovides quaternary ammonium functional group. The effects of the stirring speed,water-oil ratio, material proportioning, et, al. on the particle size and monodispersity ofmicrospheres were discussed and optimized. The result showed that the obtainedmicrospheres have small particle size and narrow size distribution when the water-oil ratio8:1,material proportioning15:3, K₂S₄O₈-NaHSO₃0.3g，MBAA1g，Span807.5g，stirring speed400r/min，temperature50℃and polymerization3h. The cationic starch microspheres wereobserved and characterized by scanning electron microscope（SEM）, Fourier transforminfrared（FT-IR） and X-ray diffraction （XRD）, SEM pictures showed spherical shape, theaverage particle size is about20μm; FT-IR confirmed that crosslinking reaction occurred andcationic groups were grafted; XRD patterns revealed that microspheres were of amorphousstructure mostly; dissolubility experiment found that the dissolubility and swelling degree ofcationic starch microspheres decreased because of crosslinking action.Secondly, the starch-AM graft copolymer microspheres were successfully synthesized byinverse emulsion polymerization, using soluble starch as raw materials and AM as graftingmonomer. The optimum reaction conditions were determined: AM2.5g，Span807g，water-oil ratio7:1，MBAA1g，stirring speed350r/min，temperature55℃。The morphologies,structure and performance of prepared starch graft copolymer microspheres werecharacterized by SEM、FT-IR、XRD. The result showed that they had perfect sphericity andthe average particle size was about28μm; Crosslinking reaction occurred between the starchand MBAA, the functional monomer-AM was grafted; amorphous area of obtained microspheres is larger than original starch; they have low dissolubility and the swellingdegree is lower than the cationic starch microspheres, it revealed that the interior crosslinkingdegree of starch-AM graft copolymer microspheres is greater than the cationic starchmicrospheres.Finally, the adsorption behavior for Cr（Ⅵ） was investigated using the functional starchmicrospheres as adsorbent. The result showed that the maximum adsorption capacity of thecationic starch microspheres and starch-AM graft copolymer microspheres can be43.68mg/gand37.45mg/g when the adsorption temperature is20℃, adsorbent dosage is20mg, pH≤6,initial chromium concentration is separate90mg/L and70mg/L, and adsorption time is40-60min. The adsorption behavior follows Langmuir isotherm much better. The adsorptionkinetic analysis found that the adsorption behavior follows the pseudo-second-order kineticequation.