| In this paper,corn porous starch(CPS)prepared by common corn starch enzymatic method was used as raw material,citric acid was used as crosslinker and sodium hypochlorite was oxidizing agent,and the physical and chemical properties of modified CPS were investigated and the adsorption performance of ammonium ion was studied by modified CPS as adsorbent.Preparation of citric acid crosslinked corn porous starch(CCPS)was by dry method,the results showed that the substitution degree of citric acid(DS)and methylene blue adsorption capacity were 1.78,19.87 mg/g,respectively,under the condition of pH 3.5,citric acid addition amount 0.6,reaction temperature 130 ? and reaction time 4 h,respectively.SEM observation showed that CCPS granules were slightly depressed.FTIR infrared spectroscopy showed that 1735 cm-1 new C=O absorption peak appeared in CCPS,while the DSC absorption peak and XRD peak disappeared,possibly due to cross-linking reaction to destroy the crystallization area of starch.Then,the oxidized corn porous starch(OCPS)prepared by using sodium hypochlorite under basic conditions was studied.The results showed that the oxidized corn porous starch had higher carboxyl group content and methylene blue adsorption capacity,respectively 0.92 and 22.66 mg/g under the conditions of reaction temperature 45 ?,sodium hypochlorite addition 5%,reaction time 3 h,reaction pH 10.SEM showed that the surface of the CPS granules became rough,and the FTIR showed that the OCPS had no new absorption peak.The initial gelatinization temperature,peak temperature,termination of gelatinization temperature and enthalpy of OCPS are all lower than that of CPS,but the crystal form of OCPS is still the same as that of CPS.In order to study the effect of compound modification on the carboxyl content and the adsorption amount of methylene blue,the cross-linked oxidized corn porous starch was prepared with OCPS under different citric acid additions.It was found that with the increase of citric acid content,the content of carboxyl group and methylene blue adsorption increased first and then decreased,when the amount of citric acid was 0.2,the content of carboxyl group and methylene blue reached 4.91% and 26.34 mg/g,respectively.With the increase of the cross-linking degree of cross-linked oxidized corn porous starch,it was found that the surface of the particles showed the concave phenomenon.FTIR showed that all cross-linked oxidized corn porous starch appeared new peak at 1739 cm-1 and found the intensity of the new absorption peak is consistent with the carboxyl content.With the increase of the proportion of citric acid,the DSC absorption peak of crosslinked oxidized corn porous starch gradually weakened to disappear,and XRD also found that the peak intensity of the spikes decreased with the increase of the degree of crosslinking.In the end,the effect of crosslinked oxidized corn porous starch on the adsorption capacity of ammonium ions with different pH value,temperature,time,ion concentration and adsorbent content was studied.It was found that the maximum adsorption capacity of ammonium ions was 7.93 mg/g.In addition,the adsorption of ammonium ions by cross-linking oxidized corn porous starch is exothermic,and the adsorption process is in accordance with Freundlich adsorption isothermal equation and pseudo-second order kinetic model. |
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