Removal Of Heavy Metals From Liquid Food With Chitosan Gel Beads

In recent years,heavy metal contamination has become more serious and has become a global issue.Heavy metal is highly poisonous in relatively low concentrations.It could accumulate in human body and pose a serious threat to human health.Therefore,the removal of heavy metal from food is very necessary for protecting food safety and public health.Liquid foods,such as tea beverage and fruit juice,are widely favored by consumers.However,due to the influence of raw materials,production process and other factors,there are heavy metal residues in liquid foods.Chitosan is a biodegradable abundant naturally polysaccharide.And it has abundant amino and carboxyl groups,that can bind effectively to heavy metals.However,the poor acid stability and low mechanical strength of chitosan restrict its applications.Modified methods usually been applied to improve chitosan's performance as an adsorbent.In this paper,macromolecular polysaccharide,low-molecular-weight organic acid and inorganic nano-materials were used to modified chitosan and prepared chitosan-based gel beads.These prepared chitosan-based gel beads were utilized to remove heavy metals from liquid foods such as tea beverages and fruit juices.The main results are as follows:(1)Macromolecular polysaccharide(pectin)functionalized chitosan gel beads(CPBs)were fabricated to remove Cu(II),Cd(II),Hg(II)and Pb(II)from drinking water.The structures of CPBs were characterized by SEM,Texture Analyzer,FTIR,acid stability analysis and porous structure analysis.It was found that the addition of pectin not only increased the specific surface area,mechanical strength and acid stability,but also increased adsorption capacity of heavy metals.The effect of p H,adsorption kinetics,adsorption isotherms and adsorption thermodynamics and adsorption mechanism were systematically investigated.Cu(II),Cd(II),Hg(II)and Pb(II)can be effectively adsorbed under the wide p H conditions.The chemisorption was the main rate-controlling step in uptake of heavy metals by CPBs.The maximum adsorption capacities of CPBs for Cu(II),Cd(II),Hg(II)and Pb(II)were 169.4,177.6,208.5 and266.5 mg/g,respectively.The XPS and FTIR analysis of adsorbents concluded that the complexation with functional groups(i.e.,carboxyl,hydroxyl,amine and amide)was the major interaction between heavy metals and CPBs.(2)Low-molecular-weight organic acid(tartaric acid)functionalized chitosan gel beads(CTBs)were synthesized to remove Cu(II)and Cd(II)from tea beverage.The structures of CTBs were characterized by acid stability analysis,SEM,Texture Analyzer,FTIR and porous structure analysis.It was found that tartaric acid not only not created a stable and porous structure,but also increased the specific surface area and the adsorption performance.The effect of p H,adsorption kinetics,adsorption isotherms and adsorption thermodynamics and adsorption mechanism were systematically investigated.Cu(II)and Cd(II)can be effectively adsorbed under the wide p H conditions.The chemisorption was the main rate-controlling step in uptake of Cu(II)and Cd(II)by CTBs.The maximum adsorption capacities of CTBs for Cu(II)and Cd(II)were 192.5 and 194.5 mg/g,respectively.The XPS and FTIR analysis of adsorbents concluded that the chelation or coordination interaction with the functional groups(O and N-containing groups)was the major interaction between Cu(II),Cd(II)and CTBs.The removal efficiency of CTBs for Cu(II)and Cd(II)from tea beverage was up to 90%.And the adsorption treatment had no significant effect on taste,odor and caffeine content of tea beverage.(3)Inorganic nano-materials(nano selenium)functionalized chitosan gel beads(Nano Se@CBs)were prepared for Hg(II)removal from apple juice.The structures of Nano Se@CBs were characterized by SEM,FTIR and XRD.It was found that the addition of nano selenium increased the surface roughness.The effect of p H,adsorption kinetics,adsorption isotherms and adsorption thermodynamics and adsorption mechanism were systematically investigated.Hg(II)can be effectively adsorbed under the wide p H conditions.The chemisorption was the main rate-controlling step in uptake of Hg(II)by Nano Se@CBs.The maximum adsorption capacity of Nano Se@CBs for Hg(II)was 376.5 mg/g.The XPS analysis of Nano Se@CBs concluded that the complexation with selenium and amino was the major interaction between Hg(II)and Nano Se@CBs.The removal efficiency of Nano Se@CBs for Hg(II)apple juice was up to 80%.And the adsorption treatment had no significant effect on taste,odor,organic acid content,°Brix,total sugar,titratable acidity and clarity of apple juice.