Construction Of Polysaccharide-functionalized Iron-based Nanomaterials And Research On The Removal Of Arsenic And Antimony

Arsenic and antimony are prevalent toxic heavy metals in the environment,which are highly mobile,and exist in complex forms.They are extremely hazardous to the environment and human health.The nanoscale zero-valent iron(n Z?I)with core-shell structure shows good application prospects for the removal of arsenic and antimony due to its advantages of environmental friendliness,low cost and high removal efficiency.However,it has a strong tendency to agglomerate due to its inherent magnetic properties and van der Waals interactions,which can reduce the removal efficiency of arsenic and antimony.In this paper,natural polysaccharide chitosan(CS)was firstly used to modify n Z?I based on ligand interaction to promote its dispersion and sufficient aging of the shell layer,thus improving the removal efficiency of arsenic and antimony.However,the post-collection treatment of CS-modified iron-based nanomaterials is still a major challenge.Therefore,in this study,a thin film nanocomposite membrane containing a sodium alginate(SA)selective layer was fabricated by loading the modified post-iron-based nanomaterial into the matrix film.The removal performance and mechanism of arsenic and antimony by the as-prepared nanocomposites and nanocomposite membranes were also investigated,respectively.The details are as follows.(1)CS was used as a ligand to modify the zero-valent iron nanoparticles.The amino(-NH₂)and hydroxyl(-OH)groups of CS were used to complex with Fe²⁺to improve its dispersibility,and then sodium borohydride(Na BH₄)was added to reduce the modified Fe²⁺to obtain CS-functionalized iron-based nanomaterials.The presence of dissolved oxygen also promoted the aging of the n Z?I shell layer,and finally the iron-based nanocomposites with good dispersion,high specific surface and fully aged shell layer were obtained.The as-prepared CS/Fe nanocomposite had a maximum specific surface area of 111.81 m²·g^-1,and it exhibited high removal capacities for As(?)and Sb(?)of 108.6 and 138.8 mg·g^-1,respectively.Meanwhile,the nanocomposite exhibited high selective and cycling performance.The interfering ions such as SO₄^2-,CO₃^2-,Si O₃^2-,PO₄^3-and humic acid(HA)almost had no significant effect on the removal of Sb(?),while Si O₃^2-,PO₄^3-and HA with high concentrations slightly inhibited the removal of As(?).In addition,the removal of As(?)and Sb(?)was almost independent on p H values and ionic strength.After four cycles,the removal rates of Sb(?)and As(?)were still maintained above 85%and 50%,respectively.The high removal performance of As(?)and Sb(?)by CS/Fe nanocomposites is mainly based on the synergistic effect of hydrogen bonding and inner sphere complexation.(2)To improve the practicality of CS/Fe nanocomposites,a hybrid matrix membrane(CIM membrane)was prepared by incorporating it into a polysulfone(PSF)matrix membrane.Then a thin film nanocomposite membrane(SA-CIM membrane)was prepared by coating a thin SA dense layer on the surface of the matrix membrane based on electrostatic self-assembly.The CIM membrane with 20%nanofiller loading exhibited a better removal performance for Sb,and exhibiting removal capacities for Sb(?)and Sb(?)of 16.51 and 13.62 mg·g^-1,respectively.The SA-CIM membrane had good retention and removal ability for Sb,and had a retention rate of nearly 80%at low concentration levels.The retention mechanism involved the synergy of steric hindrance,electrostatic repulsion and adsorption.