Adsorption Of Heavy Metals And Dyes By Modified Hydroxypropyl Methyl Cellulose From Aqueous Solutions

Water pollution is a major environmental problem in the world,and industrial wastewater usually contains a variety of heavy metals and dyes.Heavy metals are“highly toxic and low-density chemical constituents”.They are non-biodegradable and widely distributed,causing serious harm to human health and the environment.Among all the heavy metals,the damage of Pb²⁺,Cu²⁺and Ni²⁺to human cannot be ignored.The three heavy metals can stimulate the human central nervous system,reduce intelligence quotient,damage the kidney and liver,and reduce the growth of bones.Synthetic dyes are widely used in textile,printing,plastic,leather and food industries.These compounds have stable conjugated aromatic structures and toxicity.With the rapid development of industrialization,heavy metals and synthetic dyes pollute water more and more seriously.Wastewater pollution ha s become a global environmental problem.At present,there are many ways to remove heavy metals and synthetic dyes from wastewater,including chemical precipitation,flocculation and coagulation,photocatalytic degradation,ion exchange,biological oxidati on,membrane filtration and adsorption and so on.Among them,the adsorption method is a promising technology because of its high efficiency,simple design,convenient operation and insensitivity to toxic pollutants.In the adsorption method,the acquisition of the adsorbent material has been a problem to be solved.In recent years,cellulose materials have attracted wide attention from researchers because of their low cost,wide range of sources,low toxicity and good adsorption.In this thesis,hydroxypropyl methyl cellulose was used as the basic material,and diethylenetriamine was used to modify it.Then,the modified material is discussed deeply,and its role in the treatment of wastewater is also studied.The specific contents of the study are as follows:?1?Using a chemical modification method to modify hydroxypropyl methylcellulose under the combined action of epichlorohydrin,dimethylformamide?DMF?and diethylenetriamine,as a result,a new adsorbent was obtained.In order to study the physicochemical properties of the new adsorbents,the surface morphology and special functional groups were characterized by scanning electron microscopy?SEM?and Fourier transform infrared spectroscopy?FT-IR?.The results showed that the unmodified hydroxypropyl methylcellulose surface was smooth and dense,showing a cellulose tubular structure,while the modified hydroxypropyl methylcellulose material had many pores and wrinkles,the surface was very rough.From the analysis of the infrared spectrum,the amine grou p has been successfully introduced into the modified hydroxypropyl methyl cellulose material.Rough morphology and nitrogen-containing functional groups can greatly promote the adsorption of heavy metals and dyes by modified adsorbent materials.?2?The removal rate of Pb²⁺,Cu²⁺and Ni²⁺by modified hydroxypropyl methyl cellulose was studied.The effects of adsorption time,amount of adsorbent,initial concentration and pH on adsorption performance were investigated.The experimental results show that the optimal adsorbent times of Pb²⁺,Cu²⁺and Ni²⁺are 300 min,500 min and 500 min,respectively,and the optimum adsorbent dosages are 0.7 g,0.8 g and 0.8 g,respectively.Under the conditions of optimal adsorbent time and optimum adsorbent dosage,when the initial concentration of three heavy metal ions is 100 mg/L and the pH value of the solution is 6,6.5,6.5,respectively,the adsorption performance of modified hydroxypropyl methylcellulose can reach a better level,and the removal rates of adsorbents a re 98.12%,67.59%and 61.32%,respectively.In addition,the equilibrium isotherms,kinetic and thermodynamic models for the removal of three metal ions(Pb²⁺,Cu²⁺and Ni²⁺)have been studied.The results show that the adsorption process is in good agreem ent with the quasi-second order kinetic model,the Langmuir isothermal adsorption model and the Freundlich isothermal adsorption model,indicating that the adsorption process of modified adsorbents for Pb²⁺,Cu²⁺and Ni²⁺is very complex and is mainly controlled by chemisorption.From the experimental data of adsorption thermodynamics,it can be concluded that the adsorption of three metal ions by this new adsorbent is endothermic and spontaneous.?3?The adsorption removal rate of methyl orange dye in wate r by modified hydroxypropyl methyl cellulose was investigated.The effects of adsorption parameters,such as adsorption time,amount of adsorbent,initial concentration of solution and pH on the adsorption process were studied.The experimental results show that the optimal adsorbent time of methyl orange is 30 min,and the optimum adsorbent dosage is 0.3 g.When the initial concentration of methyl orange dye is about 50 mg/L,and the pH of the solution is 2,the adsorption performance of modified hydroxypropyl methyl cellulose can reach a better level under the conditions of optimum adsorbent time and dosage of adsorbent,and the removal rate of adsorbent can reach 99.51%.In addition,the equilibrium isotherms,kinetic and thermodynamic models of the adsorption process were studied.The results show that the quasi-second-order kinetic model and the Langmuir isothermal adsorption model can better describe the adsorption process,which indicates that the adsorption of methyl orange by modified adsorption materials is mainly controlled by chemical action,and that due to Gibbs free energy change?G<0,enthalpy change?H>0,it can be concluded that the adsorption of methyl orange dye by this new adsorbent is spontaneous and endothermic.In summary,the preparation process of modified adsorbent was discussed in this paper,and the synthetic modified adsorbent was obtained.The adsorption properties of chemically modified adsorbent materials were explored by Pb²⁺,Cu²⁺and Ni²⁺and methyl orange,which provided new ideas and methods for wastewater treatment.