Iron-loaded Modification Of Esterified Sugar Beet Fiber And Its Adsorption And Catalytic Mechanism

In this study,sugar beet pulp?SBP?was used as the main raw material,de–pectinated sugar beet pulp fiber?DSBP?was obtained by removing pectin from sugar beet pulp by acid extraction.DSBP was modified with citric acid to introduce carboxylic groups through an industrialized pad–dry–cure process to obtain an esterified modified sugar beet pulp fiber?CDSBP?.Subsequently,the obtained citric acid-esterification sugar beet pulp fiber?CDSBP?was coordinated with Fe³⁺ions to produce carboxylic fiber iron complex?CDSBP-Fe?.Finally,the complex was hydrolyzed by mixing with alkaline media to form the iron modified sugar beet pulp fiber?FCDSBP?which is extremely stable and has a red brown color.The adsorption performance and mechanism of two modified materials?CDSBP and FCDSBP?from de–pectinated pulp to sugar decalcification(Ca²⁺)and heavy metal ions(Cu²⁺and Pb²⁺)adsorption in aqueous solutions were studied.The catalytic performance and mechanism of CDSBP-Fe was evaluated as heterogeneous light Fenton catalysts for oxidative degradation of reactive red195.The preparation conditions and technological process of CDSBP and CDSBP-Fe were optimized.The surface morphology and chemical structure of three modified products were characterized by FT-IR,XRD and SEM.The main conclusions of the study were presented:?1?The esterification modification processes were optimized with the content of carboxyl functional groups in the adsorbent as index,the optimum modification conditions of CDSBP were ascertained:the concentration of citric acid is 2.0 mol/L,temperature of 90?and time of 0.5 h,which yielded 3.78 mmol/g of carboxyl content in CDSBP.FT-IR and XRD analysis indicated that the carboxyl groups have been introduced into surface structure of sugar beet pulp by ester linkage with citric acid and citric acid treated samples have higher degree of crystallinity;SEM analysis shows that after the treatment with citric acid,the surface of the CDSBP became smooth and many small wrinkles were found.?2?The preparation conditions of CDSBP-Fe is as follows:CDSBP with Q_COOH value?approximately 2.1 mmol/g?,the concentration of FeCl₃ is 0.1 mol/L,temperature of 50?and time of 2 h,which obtained CDSBP-Fe 0.87 mmol/g of the Fe content in CDSBP-Fe.FT-IR and SEM results suggested that Fe³⁺ions coordinated with the carboxyl groups of CDSBP.Under the condition of light radiation,CDSBP-Fe could promote the degradation of azo dyes.The degradation rate was up to 95.6%after 25 min of reaction.CDSBP-Fe showed good activity at pH range from 3 to 9.Additionally,the activity of CDSBP-Fe was not decreased after five successive runs.It also found that Reactive Red 195 degradation efficiency was clearly improved by introducing Ascorbic acid and Cysteine to Fenton system.?3?Batch experiments about adsorption of metal ions by CDSBP and FCDSBP were conducted.The adsorption capacity increased firstly and then leveled off with the increase of metal ion concentration and adsorption time.The best treatment pH values of sugar decalcification and heavy metal ions adsorption were 6 and 4.5,respectively.The obtained experimental data of adsorption on metal ions(Ca²⁺,Cu²⁺and Pb²⁺)by the CDSBP and FCDSBP fitted the Langmuir isotherm model well,and the pseudo second order kinetic model could be used to describe adsorption process.According to the calculated thermodynamic parameters,the metal ions adsorption process was endothermic and spontaneous in nature.CDSBP had good recycling performance and the adsorption capacity could be regeneratedby0.1 mol/L NaCl.?4?The adsorption capacity of modified sugar beet pulp fiber biosorbents to remove metal ions were greatly improved.The maximum adsorption capacity of FCDSBP for Ca²⁺,Cu²⁺and Pb²⁺was 77.40,97.08 and 205.76 mg/g,which was approximately 3 times that of CDSBP?24.27,30.71 and 75.36 mg/g?.The main adsorption mechanism of CDSBP to remove metal ions was metal–ligand complexation,and the functional groups?–COOH?on the surface of CDSBP played an important role.FT-IR and XRD analysis indicated that amorphous iron formations and hydroxylated oxide located at the surface of FCDSBP.These formations on external surfaces of fiber positively affected the adsorption capacity of metal ions and had an more important contribution to the adsorption of metal ions than complexation.