Fabrication And Adsorption Properties Of Tannin/polysaccharide Composites

Polysaccharide materials,such as chitosan and cellulose are potentially used in the environmental and energy fields because of the low-cost and abundant in nature.As a kind of polyphenols,tannins can combine with heavy metal ions and canatic dye by electrostatic action.However,tannin is a water-soluble substance,which limits it is a kind of adsorbent alone.In this paper,Tannin/Cellulose(T/Cellulose)microspheres,Tannin/Chitosan(T/Chitosan)microspheres and Tannin-immobilized microfibrillated cellulose(TM)were successfully prepared for water treatment.Fourier infrared(FTIR),Scanning electron microscope(SEM)and Transmission electron microscope(TEM)were employed to characterize the structures and morphologies of the adsorbed materials.Tannin/cellulose microspheres(T/Cellulose)were successfully prepared by a facile homogeneous reaction in W/O emulsion for Pb(II)removal from aqueous solution.The structures of the microspheres were characterized by scanning electron microscope(SEM),Fourier transform infrared(FTIR)and Zeta potentials test.The effects of p H,adsorbent dosage,contact time and temperature on adsorption ability were investigated.The results showed that tannins immobilized on cellulose could combined Pb(II)ions by electrostatic attraction.Adsorption kinetics could be better described by the pseudo-second-order kinetic model.The adsorption behaviors were in agreement with Langmuir adsorption isotherm model.The maximum adsorption capacity was 23.75 mg/g from the Langmuir isotherm evaluation at 308 K with initial p H 5.The results suggested that tannin/cellulose microspheres could be a low-cost and efficient adsorbent for removing Pb(II)ions from aqueous solution.T/Chitosan microspheres showed the similar structure with T/Cellulose microspheres,but showed a higher efficiency on the removal of Pb(II)because of the excellent adsorption ability to Pb(II).When the Pb(II)initial concentration was 100 mg/l,p H=5 and the contact time was 2h,the adsorption capacity for Pb(II)of T/Cellulose microspheres was 25.88 mg/g.The results showed that the adsorption process for Pb(II)of microspheres can be described by Langmuir model and pseudo-second-order model by adsorption equilibrium and adsorption kinetic test.Further study was about the removal of Cr(VI)by T/Chitosan microspheres.The results showed a conversion from Cr(VI)to Cr(III)exists during the adsorption process,owing to the reducibility of tannins on microspheres.Tannin-immobilized microfibrillated cellulose(TM)fibers were fancily and successfully prepared for removing cationic dye from aqueous solution.SEM,FTIR and zeta potentials of TM fibers were applied for characterizing the structure and properties of TM fibers.The adsorption behaviors and ability of TM fibers were evaluated by adsorption test with Methlyene Blue(MB)as a cationic dye model.An attractive adsorption results owing to the tannins immobilization on cellulose as adsorbent sites and network structure provided by cellulose microfibers.The pseudo-second-order model and Langmuir isotherm could better describe the adsorption behaviors of TM fibers.The adsorption ability of TM fibers was no significant loss after five adsorption-desorption cycles.This work provided a new idea and pathway to design tannin-immobilized adsorbents for water treatment.