Preparation And Property Studies Of Chitosan/Metal-Organic Framework Composites

The development of renewable resources and high-value utilization are important means to solve the depletion of limited resources on the earth and environmental pollution,which has gradually attracted the care of researchers.In recent years,due to the weaknesses of a single type of adsorbent,such as the lack of a wide range of sources,poor mechanical properties,low adsorption efficiency,and poor regeneration performance,the pursuit of an excellent adsorbent has been unable to meet.Organic-inorganic composite materials have received widespread attention because they have the superior properties of organic and inorganic materials and overcome many of their disadvantages.Chitosan is a typical representative of natural organic materials.Extensive research has been conducted on it due to its abundant sources,cheap availability and less environmental pollution.The combination of chitosan and emerging porous materials metal organic frameworks?MOFs?through chemical methods to prepare composite materials has brought new ideas for solving this problem.This composite material has good adsorption and separation properties,mechanical properties,and is easy to process.At the same time,it has excellent biocompatibility.Therefore,the use of chitosan/MOFs composite materials as a new adsorbent has good development prospects.In this paper,a series of chitosan/MOFs composite materials were prepared by a simple and rapid synthesis method,and their adsorption,separation and catalytic properties were studied.The specific research work is as follows:?1?Chitosan?CS?/ZIF-8 composite monolithic beads with a loading of up to 60wt%were prepared by in situ growth method to remove U???,which was easy to remove after use.It has a high adsorption capacity of 629 mg·g^-1 for U???at p H=3,the maximum adsorption capacity for uranium is higher than that of most MOF-based composite adsorbents,and in at least four adsorption/desorption cycles,good recyclability was shown.X-ray photoelectron spectroscopy?XPS?was used to study the adsorption mechanism of uranium and adsorbents,and the chelation of uranium ions with imidazole,hydroxyl and amino groups was revealed.Studies have shown that CS/ZIF-8 composite can be used as an effective adsorbent for uranium extraction in aqueous solution.?2?A light weight CS/ZIF-8 composite sponge having a bulk density of 0.18 g/cm³was prepared by an in-situ method.The composite sponge has a three-dimensional porous structure with rich chelation sites,and can effectively and selectively remove Congo red?CR?from an aqueous solution.The kinetic parameters are in accordance with the quasi-second order equation,indicating that the adsorption rate is mainly controlled by the chemical adsorption process.The adsorption isotherm data can fit well with the Langmuir isotherm model,indicating that the adsorption of CR by CS/ZIF-8is a single-layer adsorption.The maximum adsorption capacity?934 mg/g?is higher than most chitosan-based adsorbents.In addition,after five cycles,more than 90%of the adsorption capacity was retained.According to the spectroscopic characterization of the system,the main role in the excellent selective adsorption performance is that the Ph-NH₂ group on CR forms a hydrogen bond with chitosan and interacts with Zn???on ZIF-8.At the same time,there is a?-?stacking interaction between the benzene ring in CR and the imidazole ring in ZIF-8.In addition,the-SO₃-group on CR can coordinate with Zn?II?through Lewis acid-base interaction.?3?Using chitosan as the carrier,in-situ growth of Zn/Co-ZIF-67,further pyrolysis and carbonization to prepare a series of different CS/Zn Co catalysts,electrocatalysis studies have shown that the catalyst prepared under pyrolysis at 800?for 3h CS/Zn Co-5-800 has the best effect,the obvious reduction peak is about 0.82 V,and the initial potential is 0.940 V,compared with the positive half-wave potential(E_1/2)of Pt/C is 0.846 V?P?0.957 V,half-wave potential?0.832 V?.Moreover,compared with the rest of the samples,the diffusion limit current density of the CS/Zn Co-5-800 sample is relatively large,which indicates that there are a large number of active sites in CS/Zn Co-5-800,and the electron transfer is close to 4 electrons.Completely,at the same time,CS/Zn Co-5-800 also exhibited excellent electrochemical stability.After continuous operation for 30000 s,about 96.4%of the current density was retained.