| Having good antibacterial property and excellent biocompatibility, chitosan is a naturally renewable polymers which is mainly extracted from shrimp and crab shell during processing cycle. There are two problems to limit practical applications of chitosan. One is that the chitosan is insoluble in water, and anther is its poor thermal stability. In order to solve these two problems, this thesis established new technologies and new methods of chitosan based materials doped by inorganic nano materials, expanding the application of chitosan in antibacterial materials, catalytic materials, conductive materials, drug carrier and other areas, to carry out the following work: 1. Synthesis optimization of quaternized chitosan and its action as reducing and stabilizing agent for gold nanoparticlesThe optimal conditions for synthesizing quaternized chitosan(QCS) with via microwave irradiation were explored. When microwave temperature was 90°C, time was 60 min, power was 1000 W, mole ratio between chitosan and 2,3-epoxypropyltrimethyl ammonium chloride(ETA) was 5:1, volume ratio between isopropanol and water was 1:2, and p H value of the reaction system was 10, the degree of substitution(DS) reached its maximum of 90.2%. At last, QCS acted as a reducing and stabilizing agent to greenly synthesize gold nanoparticles without adding any other chemical reagent 2. Quaternized chitosan/rectorite/Ag NP nanocomposite catalyst for reduction of 4-nitrophenolThis section investigated a one-step green fabrication of exfoliated quaternized chitosan/rectorite/Ag NP nanocomposites under microwave radiation method. The results showed that the quaternary ammonium groups owned the reducing capacity, and the macromolecular chain of QCS could wrap around and stabilize Ag NP. In the preparation of Ag NP, rectorite was peeled off completely at the same time, and the exfoliated rectorite layers became a growth template of Ag NP. Therefore, the content of rectorite and DS of quaternary ammonium groups both had an important influence on the formation of Ag NPs. When the ratio of quaternized chitosan, rectorite and silver nitrate was 100 mg: 10 mg: 2 mmol, the Ag NP content reached the maximum of 2.73%. Then, the quaternized chitosan/rectorite/Ag NP nanocomposite was fabricated as a film, which was used in the catalytic reduction from 4-nitrophenol to 4-aminophenol by Na BH4. The film showed excellent catalytic efficiency with an activation energy of 29.76 k J mol-1 and outstanding reusable performance even after catalysis for 10 times. 3. Novel antibacterial paper based on quaternized carboxymethyl chitosan/organic montmorillonite/Ag NP nanocompositesAg NP-loaded quaternized carboxymethyl chitosan/organic montmorillonite(QAOM) nanocomposite was prepared after the reduction of Ag NP, which was reduced by quaternized carboxymethyl chitosan(QCMC) and stabilized by organic montmorillonite(OMMT). Finished papers with QAOM nanocomposites were prepared by performing surface coating and internal additive methods. The results revealed that Ag NP remained spherical in dry QAOM nanocomposites with uniform size and good dispersion. The presence of QAOM nanocomposites positively affected the tensile, tear, and bursting strengths of the finished paper and the paper prepared by using surface coating performed better than that produced by using the internal additive method. Moreover, the finished paper with QAOM nanocomposites showed an excellent antimicrobial capacity. Antibacterial paper prepared by using surface coating with only 0.01% QAOM owned an antibacterial circle of 14.6 mm, which fully meets the antibacterial needs of daily life. Therefore, this section provides basic data for an efficient and safe antibacterial agent that can be applied in the paper industry. 4. Multifunctional cellulosic paper based on quaternized chitosan and gold nanoparticle-reduced graphene oxideviaelectrostatic selfassemblyThe surface of a negatively charged paperfiber was coated with quaternized chitosan(QCS) by electrostatic self-assembly to form a homogeneous positive coating due to the highly positive charge and excellentfilmforming properties of QCS. Au NP-reduced graphene oxide/QCS/cellulose composite paper(Au NP-r GO/QCS/cellulose) was fabricated after the decoration of Au NP on graphene oxide surface. The XRD, Raman spectra, XPS and FE-SEM results of the composite papers showed that the electrostatic self-assembly caused the graphene oxide sheets to tightly wrap the paperfibers, and that the graphene oxide was reduced, thus being beneficial to the formation of a superior graphene conductive network. Notably, Au NP–r GO/QCS/cellulose composite paper possessed a conductivity of 853.4 S/m1, which is the highest among the reported conducted graphene-based cellulosic paper, to the best of our knowledge. Besides, this composite paper also presented an excellent performance in photothermal conversion and catalysis of nitrophenol reduction. This type of paper may have promising applications in electric devices, sensors and catalysts. 5. Green frabrication of graphene composite reduced by chitosan derivatives and its controlled release behavior in regard to fluorescein sodiumGraphene oxide was reduced and stabilized by chitosan derivates greenly in aqueous medium. After reduction, the quaternized carboxymethyl chitosan and graphene matrix(QCMC-r GO) with sodium alginate was added into calcium chloride solution order to prepare microspheres. Fluorescein sodium with the molecular weight of 376 was selected as the model molecule to explore the microspheres’ drug-loading rate and release behavior in the PBS solution with a p H of 7.4 and the HCl solution with a p H of 1.2, respectively. Results showed that the microspheres were p H dependent. In the neutral environment, the release time can be up to 126 hours with the release rate of 69.1%, while in the acidic environment of the p H=1.2, the release time was only 20 hours with the release rate of 82.3%. This method of reducing graphene provides the feasible basis for the application of graphene in the field of medicine. |
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