Synthesis Of Cellulose-Based Functional Materials And Study On Adsorption Properties Of Heavy Metal Ions

The quality of water directly affects our life quality and health.However,due to the rapid development of human activities and industry,a large number of industrial wastewater containing copper,zinc,chromium,manganese,lead,cadmium and other heavy metals are discharged into natural water without effective treatment,resulting in the content of various metal ions in water exceeding the standard.Compared with other technologies,adsorption has the advantages of simple operation,low treatment cost and high treatment efficiency,so it has become a mainstream method for removing heavy metal ions.At present,many researchers have focused on the design and synthesis of green,low-cost and efficient adsorbents.As the most abundant natural organic polymer material in nature,cellulose mainly derived from discarded crop straw,which has the characteristics of wide source,renewable,biodegradable and cheap.The preparation of cellulose-based adsorption materials can not only effectively treat wastewater containing heavy metal ions,but also provide the new mentality for the utilization of agricultural waste.In this paper,two kinds of cellulose-based materials with high swelling degree,high specific surface area and multiple active groups were designed,and the adsorption effect and possible adsorption mechanism of heavy metal ions were investigated.The main research contents and conclusions are as follows:(1)Sodium sulfonate group(-SO₃Na)was grafted onto carboxymethyl cellulose(CMC)by free radical polymerization to form hydrogel adsorbents for the adsorption of poisonous metals including Cu²⁺and Zn²⁺from water.Cellulose-based hydrogels(CMC-g-P(AA-co-SS))were prepared using acrylic acid(AA)and sodium styrene sulfonate(SS).This method solves the problems of equipment corrosion and secondary pollution caused by the introduction of sulfonic acid group(-SO₃^-)by the sulfonation method with concentrated sulfuric acid.SEM,FTIR,XPS,element analysis,swelling degree test and Zeta potential measurement were employed to analyze the surface morphology and structure of CMC-g-P(AA-co-SS).The results revealed that AA and SS were successfully grafted onto CMC,which made the surface of hydrogel appear fold and swelling degree increased.Moreover,the existence of-SO₃Na and carboxylate groups(-COO^-)led to the negative charge on the surface of the hydorgel in an acidic environment(pH=1.5?7.0),which was conducive to the adsorption of heavy metal ions.The synthetic method of CMC-g-P(AA-co-SS)adsorbent is simple,green,pollution-free and has good adsorption performance.The results of adsorption experiments showed that H-6 hydrogel had the strongest adsorption performance for Cu²⁺and Zn²⁺when pH=5.0 and water temperature was about 40?.The adsorption isotherm model and adsorption kinetic model indicated that the monolayer chemical adsorption dominated in the process,and the maximum adsorption amounts of Cu²⁺and Zn²⁺were260.74 mg/g and 257.95 mg/g.After 5 cycles,the adsorption activity of CMC-g-P(AA-co-SS)remained high,with the adsorption capacity for Cu²⁺and Zn²⁺being 93.3%and 78.3%of the original,respectively.The possible adsorption mechanism is the coordination and electrostatic attraction between Cu²⁺,Zn²⁺and oxygen-containing groups.(2)A novel polymer with high specific surface area(PDVB-NH₂)was linked with cellulose nanocrystals(CNC)to prepare CNC/PDVB-NH₂ for the removal of Cr⁶⁺and Mn⁷⁺(Mn O₄^-)from water.The CNC/PDVB-NH₂ composites were characterized by SEM,elemental analysis,FTIR,XPS,Zeta potential measurement,specific surface area and pore size distribution measurement.The results showed that there were nanopores on the surface of CNC/PDVB-NH₂ composites,and the specific surface area was 238.3 m~2/g.The isoelectric point of CNC/PDVB-NH₂ composites was 2.4,the surface of the material was positively charged in the range of pH 1.5 to 2.4,and the surface of the material had a large number of negative charges when the pH was higher than 2.4.The results of adsorption experiments indicated that the optimum conditions were pH=2.0and 40?,and the adsorption capacity for Cr⁶⁺reached equilibrium in about 180 min,while that of Mn⁷⁺only needed 10 min.The adsorption process of Cr⁶⁺and Mn⁷⁺by CNC/PDVB-NH₂composite was spontaneous and endothermic,and follows Langmuir adsorption isotherm model and pseudo-second-order kinetic model.The theoretical maximum adsorption capacity for Cr⁶⁺and Mn⁷⁺was 130.39 mg/g and 308.94 mg/g.After 5 cycles of adsorption experiments,the adsorption capacity of Cr⁶⁺and Mn⁷⁺was 67.1%and 72.5%of the initial adsorption capacity,respectively.The possible mechanism of adsorption of Cr⁶⁺and Mn⁷⁺by CNC/PDVB-NH₂composite are positive and negative electrostatic attraction,redox reaction and coordination.