Preparation And Directional Adsorption Properties Of Adsorbents For Heavy Metal Ions Based On The Wood Nanocellulose

With the continuous development of economy,the awareness of environmental protection of human is more and more intense.In recent years,with the development of industries,such as heavy metal smelting,mining,leather and lead storage battery,heavy metal pollution is more and more serious,which is endangering the sustainable development of social economy and human's health.How to remove and recycle heavy metal ions effectively is widely studied at home and abroad.Adsorption is widely studied compared to many other methods.At the same time,how to obtain new renewable,green,and efficient adsorbent is also one of the hot research fields about the heavy metal remove.This paper summarized the current situation and harm of heavy metal pollution in water,and the purification treatment methods commonly used to remove heavy metals.Combining the concept of green and environmental protection,in this thesis,the eco-friendly and renewable cellulose was used as raw material.And the surface charged cellulose nanofibrils(CNFs)were prepared by sulfuric acid hydrolysis and high pressure homogeneous processing.The adsorbents were prepared using these CNFs by chemical graft copolymerization.The adsorption behavior of the CNFs adsorbents for Cu2+?Pb2+and industry sewage were systemic studied.The main conclusions are as follow:(1)The pulp fiber was easy to reunite and deposited after only acid hydrolysis.While the cellulose treated by acid hydrolysis and high pressure homogeneous formed stable milky suspension.When the concentration of sulfuric acid was higher,the size of obtained CNFs was smaller.The CNFs had negative charged surface after sulfuric acid hydrolysis.And the value of negative charge of CNFs increased with the increasing concentration of sulfuric acid and the increasing of hydrolysis time.The sulfuric acid hydrolysis did not change the crystal forms of CNFs,crystallinity increased firstly,and then decreased.FTIR results showed that C-O-SO3 was introduced to the surface of CNFs.However,CNFs prepared by hydrochloric acid hydrolysis had higher intramolecular hydrogen bonding(HBI).(2)The aerogel prepared by pulp fiber cross-linked acrylic acid(WP-AA)and cellulose nanofibrils cross-linked acrylic acid(CNFs-AA)had porous network structure.Cu2+and Pb2+ were absorbed by CNFs-AA adsorbent.The pH of solution affected the adsorption of Cu2+and Pb2+significantly,the adsorption capacity of Cu2+and Pb2+ for CNFs-AA was much higher than WP-AA.The adsorption kinetics and isothermal adsorption model showed that both Pb2+ and Cu2+inferred from the Pseudo-second-order kinetics model and Langmuir isothermal model.The functional groups,including COO-,-COON,and-OH in CNFs-AA adsorbent,led to electrostatic interaction,ion exchange between the adsorbent and metal ions.(3)Aerogels prepared by CNFs-PVA-AA(CPA),and CPA adsorbed Pb2+(CPA-Pb2+),Cu2+(CPA-Cu2+)had cross-linked porous network structure.When the pH value of solution were 5.0 and 6.0,the adsorption capacity for Pb2+ and Cu2+of CPA adsorbent were the highest,which were 117.19mg/g,131.28mg/g and 129.1 mg/g respectively for Pb2+and 36.66mg/g,29.87mg/g and 42.99mg/g respectively for Cu2+.The adsorption kinetics and isothermal adsorption model showed that both Pb2+and Cu2+inferred from the Pseudo-second-order kinetics model and Fredunlich isothermal model.FTIR results showed that carboxyl group was the mainly adsorption sites of heavy metal ions,network structure of CPA aerogel adsorbent can also significantly improve the adsorption of heavy metal ions.(4)CPA adsorbent could adsorb various ions in industrial sewage,and the adsorption capacity for Pb2+,Cu2+,Cd2+and Zn2+ were different,which showed the order of Pb2+>Cd2+>Cu2+>Zn2+,showing the directional selectivity adsorption.During formation of CPA gel,cellulose provided abundant reactive hydroxyl,and cross-linked with PVA first.Then polyacrylic acid was formed by the polymerization of acrylic acid.The polyacrylic acid cross-linked with PVA,forming the cross-linking hydrogel.The functional groups,including COO-,-COOH,and-OH in CPA adsorbent,led to electrostatic interaction,ion exchange between the adsorbent and metal ions.Due to excellent and robust porous structure in CPA adsorbent,further physical absorption was convinced to accelerate ions adsorption.The combination of chemical adsorption and physical adsorption,making CPA adsorbent possesses better adsorption for heavy metal ions.