Preparation Of Chitosan Grafted Polyacrylamide/Graphene Oxide Composite Hydrogel And And Study Of Its Properties

As we all know, traditional adsorbents, including activated carbon, saw dust and starch, have some drawbacks of low adsorption rate, thermal instability, temperature and pH insensitivity and non-reusability. Due to these disadvantages, a hydrogel with unique three-dimensional network structure has been introduced as a new adsorbent into wastewater treatment industry because of its excellent properties of water adsorption and retention. However, the lower strength makes it difficult to collect for recycling when dispersed in water. Additionally, the hydrogel usually has effective adsorption towards only one specific kind of dye. All these mentioned above has limited its application in wastewater treatment. In this paper, with graphene oxide (GO) and N, N’-methylenebisacrylamide as co-crosslinking agent, the chitosan grafted polyacralamide organic/inorganic nanocomposite hydrogel with semi-interpenetrating polymer network was prepared by in situ polymerization in solution. After the investigation, the results showed that physical crosslinking agent GO and the chemical crosslinking agent BIS interacted with each other, forming a super network which dramatically improved the mechanical properties of the composite hydrogel. Moreover, the large number of amino groups and carboxyl groups on the hydrogel enhanced adsorption towards metal ions, cationic and anionic dyes through chelation, ion exchange and electrostatic interaction.Through experiments, conclusions can be expressed detailedly as follows:(1) FT-IR, SEM, XRD, DSC, TG tests showed that the hydrogel had a semi-IPN three-dimensional network structure. Graphene oxide combined with CS and PAM chain through hydrogen bonding, Van der Waals’ force and electrostatic interaction, improving the compactness of the network structure and its thermal stability. Swelling tests indicated that a small amount of GO (0.3wt%) not only could introduce-COOH,-OH and some other hydrophilic groups, but also acted as crosslinking points, improving the swelling ratio of the composite gel (2009%, an increasement of twenty percent). As a consequence of solvation, the initial swelling process of the gel in deionized water was fitted to non-Fickian diffusion and the extended swelling process accorded with the second order kinetics equation. In addition, the swelling property of the gel varies with the hydrogel component and some external factors, such as temperature, pH and ionic strength because of the3D network structure and polar groups in it.(2) The rheological results further demonstrated the presence of the network structure and enhancement of GO on the composite gel, making it possible for heavy metal ions and organic dyes to be stored and diffused in the gel. Adsorption experiments indicated that the maximum adsorption amount of Pb2+and Cu2+was144.7mg/g and57.3mg/g respectively. The adsorption sequences were Pb2+>Cu2+>Zn2+concordantly with their affective ionic charges. What’s more, GO and BIS acted as physical and chemical crosslinking points respectively, improving the mechanical properties of the gel. Therefore, the prepared gel could meet the strength requirement for recycling as an absorbent.(3) Furthermore, it also had better adsorption effects on the acidic dye congo red and basic dye crystal violet. At ambient temperature, the maximum adsorption capacity of congo red was205mg/g with0.6wt%GO at pH3, the capacity of crystal violet306mg/g with1.2wt%GO at pH11, increased by52%and216%respectively. As the result of the heterogeneous surface, the adsorption kinetics and isotherm was fitted to the presudo second order kinetics equation and Freundlich model respectively. The initial adsorption stage was the big pore diffusion and subsequently intraparticle diffusion. The adsorption thermodynamic study indicated that the adsorption process was exothermic and spontaneous. In addition, recycling tests showed that the prepared hydrogel also had good adsorption ability after recycling5times.As a result, the hydrogel could be used directly and circularly in practice, leading to a cost reduction.