Study On Preparation And Adsorption Properties Of The Porous Modified Cellulose Gel Beads

The cellulose gel bead is an important morphological structure of cellulose gel. It has a wide application prospect in chromatographic fractionation, adsorption treatment of pollutants, protein immobilization, catalyst loading and drug sustained release, etc. Furthermore, it possesses not only characteristics of common cellulose gel with green and environmental protection and nano-scale pore structure, but also advantage of high structural stability and low fluid resistance as a filling materials. Considering the shortcoming of common cellulose gel beads generated depend on dropping procedures, a new droplet-suspension gelation process was put forward based on the cellulose-NaOH/urea aqueous system in this article. And the cellulose gel beads from bamboo fiber and cheap pulp were prepared successfully, then a series of sphere cellulose hydrogel and aerogel materials with high specificity and adsorptive property were prepared successfully through cellulose molecules blend with other natural polymer, surface modification and in-situ growth of nano-particles in gel system.(1) Take NaOH/urea aqueous system as solvent, acidic chloroform-ethyl acetate as coagulating bath, then uniform-sized cellulose hydrogel and aerogel beads from bamboo fiber, eucalyptus pulp, reed pulp and microcrystalline were prepared through droplet-suspension gelation process. The results showed that these gel beads products prepared by this method exhibited higher mechanical strength compared with common cellulose gel. And the products possessed layered structure of core shell, the surface was dense shell structure generated from cellulose molecules, the interior was disordered three-dimensional network structure generated from gathering and intertwining of cellulose chains. The gel beads prepared from different concentration of cellulose solution and different cellulosic materials exhibited high specific surface area and abundant pore volume. And the specific surface area of sample SCA-3 was 209.9 m2/g, the mesoporous volume was 1.183cm3/g.(2) Take sodium alginate as function parts, the sphere sodium/alginate cellulose composite hydrogel was prepared successfully through solution mixing and suspension gelation process. The results showed that the cellulose hydrogel kept a stable spherical structure with sodium alga acid≤50%, the interior exhibited filamentous and intersectional porous structure with three dimensional network. It also exhibited high adsorbing capacity to methylene blue, rhodamine 6G and auramine O in the process of cationic dye adsorption. The adsorbing capacity and removal rate was 44.50 mg/g and 89% in 50mg/L methylene blue aqueous solution, respectively. In addition, the adsorption process of composite hydrogel to methylene blue dye was suitable under neutral or weak alkali condition. The adsorption process conformed to the Freundlich adsorption model, pseudo-second order kinetic equation and intra-particle diffusion model. After the adsorption process, the adsorbent can be desorbed by 0.1 M HCl solution. And it could still keep 81% adsorbing capacity of the initial value after 5 times of adsorption-desorption.(3) Take chitin as function parts, the uniform-sized chitin/cellulose complex hydrogel beads were prepared successfully through solution mixing and suspension gelation process. The results showed that the hydrogel beads kept a stable spherical structure with chitin≤50%, the interior exhibited filamentous and intersectional porous structure with three dimensional network. The specific surface area and mesoporous volume was 328.1 m2/g and 1.642 cm3/g, respectively. The complex hydrogel beads possessed high adsorbing capacity and structure stability during the process of Pb2+ adsorption. Its saturation adsorption stability was 0.712 mmol/L at the condition of 1mmol/L Pb2+ aqueous solution. And the adsorption process conformed to Freundlich adsorption model and pseudo-second order kinetic equation well, it was homogeneous monolayer chemical adsorption based on the complexation between amidogen and Pb2+. In the experiment of desorption-reusing, the hydrogel beads still could keep 70% adsorbing capacity of the initial value after 5 times of adsorption-desorption.(4) The carboxyl was introduced into cellulose gel beads through selective catalytic oxidation process of TEMPO. The results showed that the cellulose hydrogel reserved intrinsic spherical structure and high content of carboxyl (1.25mmol/g) after 12h oxidizing reaction. Also the surface density of gel beads was reduced greatly, the fibrillation of interior network was enhanced, the specific surface area and mesoporous volume got increased. The chemically modified cellulose gel beads exhibited well adsorptive property to both cationic dye and metal cation. The adsorbing capacity to auramine O solution was 0.83 mmol/g. The adsorbability to several metal cations was as follows:Cu2+>Cd2+, Pd2+, Ni2+>Zn2+, and the adsorbing capacity of them was all above 0.44 mmol/g.(5) The nanoparticles Ag2O were introduced into the network of cellulose hydrogel beads successfully through in-situ synthesis method. The results showed that both the pre- and post-modification of the hydrogel sample presented homogeneous sphere. The nanoparticles Ag2O distributed evenly on the skeleton of cellulose. And the interior kept intrinsic three-dimensional network structure. The Ag2O/cellulose gel beads possessed well physical and chemical adsorption to I2 steam in the adsorption experiment, and the adsorbing capacity reached up to 87.8 mg/g.(6) Take cellulose aerogel beads as matrix, octadecyltrichlorosilane (OTS) as hydrophobic modifier, the ultralight, multihole and hydrophobic cellulose aerogel beads were prepared fleetly using surface of silicon alkylation reaction. The results showed that the OTS caused no change to microscopic feature and crystalline structure of original regenerated cellulose aerogel, but shielding the hydrophilic hydroxyl of cellulose surface to be with well hydrophobic nature. The performance density and total pore volume of the cellulose aerogel beads was 17.6 mg/cm3 and 56.11 cm3/g, respectively. The cellulose aerogel beads possessed well adsorptive selectivity in the test of oil adsorption, the adsorbing capacity to several greases was in the range of 30-60 g/g. Besides the cellulose aerogel beads also possessed well reusability, the adsorbing capacity to methylbenzene was stable in 40g/g in 5 times of adsorption-desorption, and maintained high structure stability.(7) Take chitosan as function parts, the chitosan/cellulose aerogel beads with internal network of chitosan were prepared successfully through suspension gelation and acetic acid post-processing. The results showed that chitosan network inside the aerogel beads combined with cellulose network tightly by physical interaction such as hydrogen bond to form more intensive net structure. The specific surface area and mesoporous volume got increased enormously, which was 1350.7 m2/g and 4.511 cm3/g, respectively. The chemical combination of azomethine and schiff base was formed between primary amine and formaldehyde molecule in this aerogel beads. The adsorbing capacity reached up to 1.99 mmol/g which was far greater than coconut shell activated carbon material with same dosage.