Preparation Of Nanocellulose Aerogel And Its Adsorption Behavior For Heavy Metals And Dyes In Water

The water pollution caused by the enrichment of heavy metal ions and chemical dyes remains a major challenge to water pollution.Adsorption method is widely recognized as a key technology for wastewater pollutant treatment due to its high efficiency,economy,multi-purpose,and easy control.Among them,biomass adsorbents have become a research hotspot for domestic and foreign scholars due to their environmentally friendly advantages.Cellulose,as the largest biomass material in the world,has broad application prospects.In this paper,tetrabutylammonium hydroxide(TBAOH)pretreatment was used to prepare high-performance nanocellulose.On this basis,polyvinyl alcohol(PVA),tannin(TA)were introduced to prepare nanocellulose aerogel.The adsorption behavior and mechanism of nanocellulose aerogel for heavy metal ions and chemical dyes were studied.Firstly,a three factor and three level orthogonal experiment was designed with pre-treatment time,TBAOH concentration,and pre-treatment temperature as factors to study the process conditions of TBAOH pretreatment assisted mechanical preparation of nanocellulose.The results showed that the concentration of TBAOH aqueous solution was 40%,the pre-treatment time was 240 minutes,and the pre-treatment temperature was 40 ℃.The effect of pre-treatment assisted mechanical preparation of nanocellulose was the best.The prepared nanocellulose was characterized by SEM,FT-IR,XRD,and thermogravimetric analysis.The results showed that the nanocellulose obtained in the experiment had good dispersibility,and TBAOH pretreatment had a promoting effect on the swelling of cellulose;The nano cellulose obtained from the experiment has a high hydroxyl content,and its crystallinity and thermal stability have decreased compared to the raw fiber.A study on the reuse of TBAOH ionic liquids for pretreatment was conducted,and the results showed that TBAOH ionic liquids have good reusability.Then,PVA/CNF aerogel was prepared by using the prepared nano cellulose and polyvinyl alcohol(PVA),and the effects of PVA addition on the N2 adsorption capacity,pore diameter,specific surface area,porosity,swelling rate and compression strength of nano cellulose aerogel were investigated.PVA/CNF aerogel with 1% PVA addition was selected to carry out the adsorption experiments of cadmium(II),lead(II),copper(II),methylene blue and acid orange II.The adsorption capacity increases with the initial concentration of heavy metals,reaching a peak at p H=6,reaching141.643 mg/g,151.285 mg/g,and 109.890 mg/g,respectively;The maximum adsorption capacity of PVA/CNF aerogel(1% PVA)was 109.28 mg/g and 113.636mg/g,respectively.The kinetic and thermodynamic fitting results show that the kinetic model of the adsorption model of heavy metals,cadmium(II),lead(II),copper(II),methylene blue and acid orange II on PVA/CNF aerogel conforms to the quasi first order kinetics,and the thermodynamic model conforms to the Langmuir model.At the same time,PVA/CNF aerogel still has good adsorption capacity for heavy metals and organic dyes after five repeated tests.Finally,PVA/CNF aerogel and tannin(TA)were used to prepare TA/CNF/PVA aerogel with low density,large specific surface area,high adsorption capacity and good thermal stability.The maximum N2 adsorption capacity of TA/CNF/PVA aerogel is 71.022 cm3/g.The study on its adsorption behavior shows that its adsorption kinetics for cadmium(II),lead(II),copper(II),methylene blue and acid orange II all conform to the quasi second order kinetic model,and the thermodynamics conforms to the Langmuir isotherm model.The maximum adsorption capacities for cadmium(II),lead(II),and copper(II)reached 196.850mg/g,181.488 mg/g,and 151.515 mg/g,respectively;The maximum adsorption capacities for methylene blue and acid orange II reached 162.337 mg/g and 170.940mg/g,respectively,indicating that they have good pollutant adsorption energy.CNF/TA/PVA aerogel has good reusability and still has good adsorption capacity for heavy metals and organic dyes after five repeated tests.