Modification Of Chitosan Derivatives With Different Functional Groups And The Capabilities Of Heavy Metal Ions Adsorptive Removal

Nowadays,the toxic heavy metal contained wastewater discharged from industrial and agricultural processes has caused serious ecological problems.Therefore,removal of heavy metal contaminants from wastewater before being discharged into the environment is necessary for the natural environmental protection.Being one of the promising technologies for the contaminant removal,the use of low-cost,high-efficiency and environmental-friendly adsorbent in the adsorption engineering practice has become a key issue for the technology development.Bing one of the natural polymers,chitosan?CS?and its derivatives have many unique characteristics,such as non-toxic,low cost,abundant reserve,and containing a large number of?NH₂ and?OH functional groups in their matrix,which have wide application prospects in many fields.Consequently,it is possible to obtain some novel CS based adsorbents through functional groups modification with the aim of expanding the environmental applications of chitosan derivatives,and the adsorbents were proposed had the capabilities for heavy metal ions removal from wastewater.Based on our previous research results,in this study,we optimized the chitosan derivatives modification procedure and then introduced modifiers including polyamine-co-thiourea?T-CS,T-EDA-CS,T-TETA-CS,andT-TEPA-CS?and thiosemicarbazide?TCCS?into the structure of CS in a one-pot reaction method by using formaldehyde as linkage.And a thiocarbohydrazide-chitosan modified magnetic biochar composite?TMBC?was also prepared in the same reaction.All the prepared samples were characterized by SEM,elemental analysis,XRD,XPS,and FT-IR.Batch adsorption experiments were conducted to examine the properties of as-prepared adsorbents in the removal of Hg???,Cr???and Cd???ions from aqueous solutions at various aqueous pH,contact time,metal ion initial concentration.Furthermore,the contaminant desorption,the adsorbent reusability,and the contaminant adsorption mechanism were also investigated,respectively.The main findings and conclusions of this study are summarized as follows:?1?The modifiers like ethylenediamine?EDA?,triethylenetetramine?TETA?,tetraethylenepentamine?TEPA?,and thiourea?T?were successfully introduced into the structure of CS in this study.In comparison with CS,the modification enhanced the Hg???adsorption onto T-CS,T-EDA-CS,T-TETA-CS,and T-TEPA-CS.Hg???adsorption amounts for all adsorbents increased gradually and reached maxima at pH above 4.0.The adsorption of Hg???achieved an equilibrium state within 12 h with the process well described by the pseudo-second-order kinetic model.The concentration of NaNO₃ in solution had no remarkable inhibition effect on Hg???adsorption.The maximum Hg???adsorption capacities of the four adsorbents obtained from Langmuir model were in order of T-EDA-CS?217.10mg/g?>T-CS?164.85 mg/g?>T-TETA-CS?149.74 mg/g?>T-TEPA-CS?140.63 mg/g?at room temperature,respectively.Although the Hg???adsorption capacities of the four adsorbents were strongly related to the modifier types and the length of the incorporating amino ligands in this study,all the adsorbents could be readily regenerated and had great reusability potential in Hg???ions capture from aqueous solution.The further investigation implied that Hg???ion adsorption mechanism was controlled by a complexation reaction process.?2?Introducing of Thiocarbohydrazide?TC?into the structure of CS promoted the formation of Thiocarbohydrazide modified CS hydrogel derivative?TCCS?and endows TCCS more S and N containing groups than CS.The adsorption experiments showed that TCCS could be used as a potential adsorbent for the Cd???and Cr???removal from aqueous solutions.Cd???ion adsorption amount increased gradually with the increase of solution pH value and reached maxima at pH 6.0,while Cr???ion adsorption decreased with the increase of solution pH value and exhibited maxima Cr???removal rate at pH 3.0.Both of Cd???and Cr???adsorption achieved equilibrium states within 90 min with the process well described by the pseudo-second-order kinetic model.The adsorption isotherms of Cd???and Cr???adsorption onto TCCS could be well described by Langmuir model with the maximum adsorption capacities were 81.26 and 144.68 mg/g at 298 K,respectively.TCCS could be regenerated and reused in Cd???and Cr???ions removal process.The Cd???ion adsorption mechanism was dominated by a complexation reaction process,while the Cr???adsorption was governed by multiple mechanisms including electrostatic attraction,reduction,and complexation process.?3?An aminothiourea-chitosan modified magnetic biochar composite?TMBC?can also be successfully prepared for the efficient removal of Cd???from wastewater.The obtained TMBC not only had acceptable environmental stability but also had a high adsorption affinity for Cd???than that of MBC,BC,and other carbon-based adsorbents reported.The optimized pH value for Cd???adsorption was 5.98,and the Cd???adsorption reached equilibrium within 6 h with the process could be described by the pseudo-second-order kinetic model.The further adsorption isotherm modeling showed the maximum adsorption capacity was 93.72mg/g at 298K in Langmuir model.TMBC had great reusability in Cd???ions adsorptive removal and could be easily separated and recovered from wastewater with the help of a magnet.The acceptable efficiency TMCB on heavy metal ion removal makes it as a promising adsorbent for the treatment of heavy metal contaminated wastewater.