Xylan Functionalized Magnetic Hydrogels:Synthesis,Properties And Applications

Nanocomposite hydrogels is endowed with novel features through a combination of the unique properties of hydrogels and the excellent properties of nanomaterials,which are widely used in drug release,catalysis and biomaterials.The addition of iron oxide nanomaterials,especially magnetic iron oxide nanomaterials,not only provides hydrogel with magnetic properties,but also contributes to improve the strength of hydrogels.When the size is smaller than 30 nm,Fe3O4 nanoparticles could exhibit superparamagnetic property.Moreover,the magnetite nanoparticles could be widely used to oxidize organic contaminants in the treatment of wastewater,or used as detection tools instead of natural peroxidases due to their intrinsic enzyme mimetic activity.Hemicellulose as a promising natural polymer is second to cellulose in abundance and it is rich,non-toxic,and biodegradable,consisting of various different sugar units with short-branched chains.Hydroxyl and carboxyl groups on the chain of xylan could be easily modified by chemical or biological modification.In order to realize the high value-added utilization of xylan,different xylan derivatives were applied to prepare the smart magnetic hydorgels followed by the introduction of Fe3O4 magnetic nanoparticles via in-situ chemical coprecipitation method.The intelligent and functional hydrogels were achieved through adjusting the reaction conditions.The main researches are described as follows: 1.Preparation of acylated xylan-based magnetic hydrogels and its application in H2O2 detectionIn order to improve the reactivity of xylan,aylated xylan possessing easily polymerized groups(C=C)was prepared by the acylation.Acylated xylan-based hydrogels were prepared by using acylated xylan as the material and acrylamide(AM)and N-isopropylacrylamide(NIPAM)as the monomers under the ultraviolet radiation.Then Fe3O4 nanoparticles were introduced into the three-dimensional network structure of hydrogel by coprecipitation method to form the acylated xylan-based magnetic nanocomposite hydrogel with uniform and ordered pore size.The effects of crosslinking agent concentration on the properties of Fe3O4 nanoparticles and hydrogels were investigated.The catalytic performance on H2O2 detection was also studied.The results showed that the prepared hydrogel exhibited a uniform three-dimensional network structure.When the concentration of crosslinking agent was 10.0 wt%,hydrogels with pore size of about 500 nm were obtained.The hydrogels displayed great mechanical properties(at 50% strain,compressive stress of 95 kPa,and compression modulus of 530 kPa).It was also found that the crosslinking density and swelling ability of hydrogels had an important effect on the growth size,morphology and loading capacity of Fe3O4.When the concentration of crosslinking agent was 7.5 wt%,the magnetic composite hydrogels with high catalytic activity could be achieved.In the presence of H2O2,the hydrogels could react with tetramethylbenzidine(TMB)which could be observed from the color change,and they showed sensitive detection ability for H2O2,and the detection concentration was as low as 5 × 10-6 mol/L.2.Preparation of temperature fast-responsive magnetic hydrogel with carboxymethyl xylan as a pore-forming agent and its photothermal conversion performanceCarboxymethyl xylan was prepared to endow xylan with the anion groups.Then the temperature fast-responsive hydrogels were synthesized through the grafting crosslinking reaction using NIPAM and AM as monomer,carboxymethyl xylan as a pore-forming agent and the NaCl solution as the reaction medium.Subsequenly,Fe3O4 nanoparticles were introduced into the as-prepared hydrogels via in situ chemical coprecipitation method to form a macroporous temperature rapid-responsive magnetic hydrogel.The photothermal property and swelling/deswelling behaviours were investigated as well as the photothermal conversion performance of the hydrogel.The results revealsed heterogeneous hydrogels possessing the uniform and macroporous characteristic were fabricated in the coordination with NaCl and CMX.NaCl played a role in the phase separation,meanwhile NaCl was used as the electrolyte to shield carboxymethyl xylan molecular chain.The obtained hydrogels exhibited a fast temperature responsive behavior and the water retention was less than 15% for 1 min under 60 oC when the concentration of NaCl was above 0.2 mol/L.Due to the presence of Fe3O4 particles,the as-prepared hydrogels showed enhanced mechanical properties and magnetic properties of the hydrogels(the maximum compressive stress of 180 kPa and the maximum compressive deformation of 66%).In addition,the LCST of hydrogels could be in the range of 35-39 oC by adjusting the amount of the hydrophilic monomer such as AM.It was found that the magnetic thermosensitive hydrogel had the attractive photothermal conversion ability and could be heated to above 40 oC within 2 min,to 59 oC within 7 min under NIR irradiation.Excellent photothermal properties,rapid temperature response and magnetically controllable behavior could further expand the application of magnetic composite hydrogels.3.Preparation of quaternized xylan/nanocellulose reinforced magnetic hydrogel and its adsorption performanceThe high-intensity magnetic hydrogels with multiple network structure were prepared by graft crosslinking methods and in situ synthesis methods.AM as the monomer was applied under a low crosslinking agent concentration,and the ionization of quaternized xylan and nano-cellulose was used to form ionic crosslinking network in the hydrogel.The mechanical properties and the adsorption properties of the as-prepared hydrogels were investigated.Results showed that prepared hydrogels displayed multiple interpenetrating network structure under the interaction of PAM and quaternized xylan and nanocellulose.Moreover,the compressive curve of hydrogel was J-type.The compressive stress of the hydrogel increased rapidly to the limit of the measurement(2.5 MPa)when the compressive strain of hydrogel reached to 85% with a 0.05 wt% crosslinking agent dosage.The compress strain showed an increase slightly with the increase of compression times.Moreover,the hydrogel could maintain 90% original strength after compression for 4 times.In addition,the maximum tensile elongation of the hydrogel was 2875% and the breaking tensile strength was 73.86 kPa.Moreover,when the compression strain reached to 85% and the tensile strain of 1500% was obtained,the hydrogel could revert to its original shape after 30 times cyclic compression/tensile tests.In addition,the strength hydrogel could be enhanced by increasing the quaternized xylan or nanocellulose contents due to the ionic crosslinking bonds.The hydrogels also had the magnetic properties and could be controlled by external magnetic field.The adsorption order(Pb2+>Cu2+>Zn2+>Cd2+)was observed in the experiments of competitive adsorption of heavy metals by prepared hydrogels.