Papers by Author: Yu Jie Wang

Abstract: Choosing the basis of 6-311++G (d. p) with chitosan as its model, we use the density functional B3LYP method to optimize the structure and calculate the energy for the chitosan and sulfate. We study the adsorption for the sulfate from different adsorption point (amidogen, hydroxide and carbon-ring) with or without the protonation of chitosan amidogen. Through a comparative analysis of the bond-lengths, bond-angles, charges and binding energies before and after the interaction of chitosan and sulfate, we find that the adsorption of chitosan for sulfate is mainly the adsorption of amidogen after protonation. The adsorption mode is the combination of sulfate with two amidogens after protonation.

Abstract: In this study, chitosan was modified by acrylamide and acrylonitrile when NaHSO₃-K₂S₂O₈ as initiator under N₂. Chitosan-acrylamide-acrylonitrile ternary graft copolymer was synthesized on the use of radical polymerization mechanism. The optimal experimental conditions for the preparation are obtained by orthogonal experiments: the reaction temperature 65°C, the reaction time 6.5h, the concentration of NaHSO₃ 3mmol/L, the concentration of K₂S₂O₈ 4.5mmol/L, and the ratio of m(chitosan):m(acrylamide):m(acrylonitrile) was 1:6:4. Under such conditions, the average graft ratio and the graft efficiency could achieve 852.455% and 85.260% respectively. Chitosan and chitosan-acrylamide-acrylonitrile ternary graft copolymer were then characterized by means of XRD and SEM, and the graft mechanism was explored preliminary as well. The results showed that chitosan was modified successfully by graft polymerization, and the surface property and the strength of the product were also improved obviously.

Abstract: Investigated the sorption kinetics of methylene blue on spherical chitosan resin. Studied the influences of ionic strength, pH， initial concentration on the adsorption process. The adsorption of methylene blue increases with the decreasing ionic strength and the increasing pH and the initial concentration of the system. Furthermore, the adsorption process correspondes with Lagergren pseudo-second kinetic equation and the finess (R²) of the model was above 0.99.

Abstract: The density functional theory (DFT) calculations explored the structural optimization and the frequency of N-carboxymethyl chitosan (N-CMCS) and O-carboxymethyl chitosan (O-CMCS). For the isomers, the calculations comparatively were performed. The charge distribution and frontier molecular orbit were analyzed by using the natural bond orbital (NBO) method. The results showed: the two rotational isomers a and b can stably exist, with the stability order a>b; N-carboxymethyl chitosan reaction active sites are concentrated in -OH and -NHCH2COOH, while O-carboxymethyl chitosan reaction active sites are concentrated in -NH2 and -CH2COOH; The water-soluble mechanism of carboxymethyl chitosan was investigated deeply, on the one hand, the presence of carboxymethyl of carboxymethyl chitosan had a tendency to ionize H+, on the other hand the carboxymethyl increased the distance and weakened the hydrogen bonds between molecules, even though Einstein shift H-bond is formed in the carboxymethyl chitosan molecules.

Abstract: In this study, the graft copolymerization of acryalmide and acrylonitrile onto chitosan with K2S2O8-NaHSO3 initiator under N2 interaction is studied and the mechanism is discussed. Compared to the chitosan graft of acrylamide or acrylonitrile, the graft yield and graft efficiency of ternary polymerization increase significantly. The stability and reproducibility are also improved obviously. To be specific, the reaction time, the reaction temperature, the effect of the amount of materials, the concentration of K2S2O8, and the concentration of NaHSO3 on the graft yield and graft efficiency is investigated respectively. The C=C of acrylamide and the acrylonitrile react respectively with -NH2 and C6-OH of chitosan initiated by SO4-•. The experimental results show that the optimal synthesis conditions are given as follows: the reaction time is 6h, the reaction temperature is 60°C, the ratio of m(chitosan):m(acrylamide):m(acrylonitrile) is 1:7:5, the concentration of K2S2O8 is 4.5mmol/L, and the concentration of NaHSO3 is about 2.6mmol/L. Under such conditions the graft yield and graft efficiency can be up to 839.52% and 70.00%, respectively.

Abstract: With chitosan as the raw material, a new type of resin material is synthesized through formaldehyde crosslinking. The effects of the reactant ratio, the reaction temperature, the reaction time, the stirring rate and the system pH on the cross-linking rate are studied in detail. The resin material is then characterized by means of IR. The experimental results show that the reaction occurs mainly on the amino and the hydroxyl of chitosan. The chitosan-based resin material with good properties of sphericity and acidresistivity can be prepared under the optimal experimental conditions, which are found to be 1:5 for the ratio of chitosan and formaldehyde, 60°C for the temperature, 1 h for the reaction time, 440r/min for the stirring rate and 10 for the pH.

Abstract: The adsorption of cadmium in simulated wastewater by chitosan was investigated. The influence of temperature, contact time and pH on adsorption efficiency of cadmium was examined. Some related mathematical models were used in the fitting of experimental data. The results showed that at room temperature, the optimum pH of adsorption is between 4 and 7. At lower pH values, a strong competition existed between cadmium ions and protons for sorption sites and the sorption efficiency was decreased. After 60 minutes the adsorption equilibrium can be achieved. Chitosan is very effective at removing cadmium with the maximum adsorption capacity is 112.05mg•g-1. The adsorption kinetic curves agree with the pseudo-second-order adsorption kinetic equations and the adsorption isotherms could be well described by Langmuir isotherm equations.

Abstract: The structural optimization and the frequency for chitosan monomer, chitobiose and chitotriose with the quantum chemistry abinitio HF and the density functional B3LYP method by choosing 6-311 + G (d, p) as the basis set were calculated and studied. For its three rotational isomers, gauche-trans (gt), gauche - gauche (gg), and trans-gauche (tg), the calculations comparatively were performed respectively. The charge distribution and frontier molecular orbit were analyzed by using the method of natural bond orbital (NBO). The calculated IR spectrum was compared with the experimental data. The results showed that the three rotational isomers gt, gg, and tg can stably existed in chitosan with the stability order gg﹥gt﹥tg. Its highest occupied molecular orbital (HOMO) was provided primarily by nitrogen atom and its lowest unoccupied molecular orbital (LUMO) was provided mainly by the oxygen atom; Its reaction active sites were concentrated in -NH2 and –OH. The calculated infrared spectra were in good agreement with the experimental values.

Abstract: The method of wettability of solid-liquid interface is used to examine the differences of the liquid membranes formed by hydrophilic or hydrophobic membranes with different size and different materials, the influence of the characteristics of membrane modules in the process of desulfurization is studied. The method of accelerating the renewing rate of liquid membrane is proposed. The results show that the hydrophobic liquid membrane leads to higher renewing rate and absorption efficiency of sulfur dioxide and the hollow fiber membrane of polypropylene has higher adsorption efficiency. The dynamic contact angle of the same hollow fiber membrane is increasing with the number of the fibers leading to the increase of the diffusing resistance of liquid between the fibers. In order to accelerate the renewing rate of the liquid membrane, the concentration of the medium should be decreased under the condition of high absorption capacity.