Preparation Of Graphite Oxide/carboxymethyl Cellulose Aerogel And Study Of Its Uranium Adsorption Performanc

The large amount of radioactive uranium-containing wastewater generated during the nuclear fuel cycle poses a serious threat to the ecological environment and human health.Therefore,it is of great significance to treat uranium-containing wastewater efficiently and greenly.This study focuses on the functionalized modification of graphite oxide into aerogel composite materials,which exhibit excellent uranium adsorption performance,selective adsorption,and recyclability.The main research contents of this study are as follows:Graphite oxide powder（GOP）was used as raw material.Due to the strong van der Waals effect between GOP layers,it is easy to cause agglomeration,reduce the specific surface area and decrease the uranium adsorption performance.GOP was functionalized by NaOH/ultrasonic treatment to prepare graphite oxide nanosheets（GONs）uranium adsorption material.Through NaOH/ultrasonic treatment,we conducted functionalized modification on GOP and successfully prepared uranium adsorbent materials in the form of graphite oxide nanosheets（GONs）.After treatment,the specific surface area of GOP increased from 0.24 m²·g^-1 to 137.04 m²·g^-1,and the content of surface carboxyl and hydroxyl groups significantly increased as well.When the concentration of NaOH exceeded 2.0 mol·L^-1,the uranium adsorption capacity no longer increased.The optimal pH for GONs adsorption is 5.0,and equilibrium adsorption can be achieved within 120minutes,with a maximum adsorption capacity of 578.03 mg·g^-1.Adsorption kinetics,adsorption isotherms,and adsorption thermodynamics studies show that the process of GONs adsorbing U（Ⅵ）is a spontaneous,endothermic,monolayer adsorption mainly based on chemical adsorption.The coordination interaction between the lone pair electrons on oxygen in carboxyl and hydroxyl groups and U（Ⅵ）is the main adsorption mechanism of GONs.The functionalized modification greatly enhanced the adsorption performance of GOP.However,the macroscopic morphology of the GONs still appeared as a powdery form,posing challenges for their practical application in terms of separation,recycling,and reusability.Hence,GONs/CMC aerogels（CGNC）were prepared using a one-step method,utilizing GOP and carboxymethyl cellulose（CMC）as raw materials.The preparation involved NaOH/ultrasonic treatment and subsequent crosslinking with epichlorohydrin.The unique three-dimensional network porous structure of CGNC aerogels facilitates the contact between U（Ⅵ）and adsorption sites,while also allowing for easy recovery in uranium solutions.Based on experimental results from tests evaluating tensile properties,compressive properties,and adsorption performance,it was found that GNGC exhibited the best overall performance when the GONs content was20%.Furthermore,compared to pure carboxymethyl cellulose aerogel（CC）and CMC/GO aerogel（PCG）bonded by hydrogen bonds,GNGC demonstrated superior mechanical properties and uranium adsorption performance.Systematic uranium adsorption experiments demonstrated that the optimal pH for CGNC to adsorb U（Ⅵ）was5.5.Equilibrium adsorption was reached within 90 minutes,and the maximum adsorption capacity at 298 K was determined to be 621.12 mg·g^-1.Based on the analysis of adsorption kinetics,adsorption isotherm and adsorption thermodynamics,it is confirmed that the adsorption process is a spontaneous endothermic chemical adsorption,which conforms to the monolayer adsorption mechanism.At the same time,CGNC has excellent adsorption selectivity for U（Ⅵ）,and its distribution coefficient is as high as 10215.30m L·g^-1.After 7 cycles of adsorption-desorption,it can still maintain more than 80%of the adsorption efficiency,demonstrating good cyclic regeneration.The research results on the adsorption mechanism indicate that during the removal process of U（Ⅵ）by CGNC,both the carboxyl and hydroxyl active groups on its surface coordinate with U（Ⅵ）,and oxidation-reduction takes place.CGNC reduces U（Ⅵ）from the hexavalent state to the tetravalent state.