Study On The Preparation And Performance Of Oxidized Micro-crystalline Cellulose And Its Derivatives

Heavy metal ions are known to be toxic and carcinogenic to living organisms.Their presence in the aquatic environment has been of great concern because of their toxicity and non biodegradable nature.Some metal ions are cumulative poisons,capable of being assimilated and stored in the tissues of organisms,causing noticeable adverse physiological effects.The removal of toxic metal ions from water is a very difficult task due to the high cost of treatment methods.There are various methods for the removal of toxic metal ions from aqueous solutions: reverse osmosis,ion exchange,precipitation,electrodialysis,adsorption,etc.Among these methods,adsorption is by far the most versatile and widely used for the removal of different pollutants.In addition,the preparation of cellulose-based sorbent is low cost,wide source of raw materials;And the product has some excellent performances,such as high adsorption capacity,biodegradable and recyclable,etc.It had a central issue in the field of scientific research today.In this paper,three kinds of multi-amine oxidized cellulose were prepared from microcrystalline cellulose,which were applied to the treatment of heavy metal ions in wastewater.And also the impact of the ether reaction system for preparation of ethylene cellulose and the different oxidation solvent system under different oxidation method for preparing of oxidized cellulose were discussed.Firstly,etherification reaction of the alkali-treated microcrystalline cellulose was carried out in different solvent systems,and the heterogeneous?NaOH,N,Ndimethylformamide?DMF?and sodium ethoxide/ethanol solution?and homogeneous?urea/NaOH solution?solvent system were adopted.The products were characterized by the epoxy value measurement.The results showed that 15% NaOH solution was the optimal epoxidation system and the epoxy value was up to 0.6765 mmol/gSecondly,the epoxidation cellulose was further oxidized by various oxidizing agents after etherification reaction.Two oxidation methods,containing chemical oxidation and electrochemical oxidation,were applied.Meanwhile,the homogeneous and heterogeneous oxidation system and different oxidants were used in this research.the results showed that the chemical oxidation was superior to electrochemical oxidation,and the content of carbonyl group was up to 0.1376 mmol/g.Besides,the sequence of oxidation ability of various oxidizing agents was NaIO₄> NaClO> H₂O₂.And thus NaIO₄ aqueous system of chemical oxidation cellulose is the best.And the100% dosage of NaIO₄ lead to the highest content of carbonyl group in oxidized fibers.Thirdly,the oxidized cellulose was further amined by various kinds of multi-amino monomer,such as triethylenetetramine,amino acids and chitosan.The products were characterized by Fourier transform infrared spectroscopy?FTIR?,environmental scanning electron microscopy?SEM?,X-ray diffraction?XRD?and amine content.The results showed that amino was successfully grafted onto the oxidized cellulose,and the surfaces structure of cellulose great changed after modified.The surfaces become rougher and lamellar distribution,which increased the contact sites of metal ions.The amine content of triethylenetetramine modified products?EDC-TA?was up to3.689mmol/g,which is highest for the three products,so that EDC-TA was used to the next metal ion adsorption experiments.Finally,the adsorption performances of EDC-TA for copper and lead was investigated.The impact of various factors on the adsorption properties of EDC-TA was studied,which contained the pH,time and temperature and other factors.At the same time,the adsorption behavior of EDC-TA was investigated by Kinetic model and Thermodynamic model.The results showed that the adsorption behavior of EDC-TA for metal ions greatly influenced by pH,and its positive linear correlation with adsorption capacity.It has a better adsorption performance for lead than copper.The optimum pH value is 5.5.Moreover,the adsorption behaviors of EDC-TA for copper and lead were conformed to the pseudo-second order adsorption kinetics model and Langmuir adsorption isotherm model.And the largest adsorption capacities of EDC-TA for copper and lead were 66.8 mg/g and 153.8 mg/g,respectively.