Preparation,Adsorption Properties And Mechanism Of Graphene Oxide Materials

The carbon atoms layer of graphite are stacked in parallel with each oth er and the short-range van der Waals force is connected to form a relatively loose interlayer domain.The delocalized large π bond in the structure layer has properties of metal bonds.Therefore,it has good intercalable,oxidizable and peelable properties.How easily the degree of oxidation,reaction rate and conditions,and the choice of chemical reagents in the graphite oxidation process directly or indirectly affect the type and content of the functional groups of the oxidized graphite,which in turn affect the structure and cation exchange performance.GO,which can be controled the preparation of specific functional groups,it is not only own was excellent adsorbent material but also can provide better material selection for the application of GOs func tional materials in the adsorption field.In this thesis,H₂SO₄ and KMnO₄ were used as reaction system.GO was prepared by modified Hummers method,and the process of preparing GO was studied in different stages.The GO with different oxidation degree can be obtained by controllable preparation.The structure characteristics,functional groups content and types were characterized.Cation exchange capacity（CEC）of GO of different oxidation degree was measured accurately using the stiasny method,a variety of analytical methods were used to compare the drying and wetting conditions of GO and products of cation exchange process,the regularity of the influence on GO structure development and cation exchange mechanism was found.Based on the study of the preparation,structure and physicochemical properties of GO,the adsorption performance and mechanism of the peeled GO,that is,monolayer graphene oxide（GOs）on MB was further studied.First,The reaction times at low temperature（0⁴°C）and medium temperature（37°C）were discussed under sufficient conditions of oxidant（KMnO₄）,respectively,as well as the effect of the increase in the temperature of the reaction system due to the addition of water in the obtained primordial graphite oxide（PGO）.The optimal reaction time was 180 min in the low temperature stage,the reaction time in the middle temperature stage was about 120 min,and the temperature control in the high tempe rature reaction stage was 65⁷5°C.Finally,GO-n（n = 0,0.4,1⁶）was obtained with different oxidation degree by controlling KMnO₄ dose.The structure characteristics,functional groups content and types were characterized,the change rule of the maximum basal spacing of graphite crystal face（002）with KMnO₄ dose was found out,and the relative content of hydroxyl group on GO structure layer was higher when the degree of oxidation was low,and the content of epoxy group and carbonyl group was higher in high oxidation degree,Suggesting that the structure and physical and chemical properties of GO also has changed significantly.And then the real-time sampling and monitoring of the oxidation process of graphite were carried out with high magnification optical microscope.The chemical reaction mechanism of graphite oxidation process at differe nt stages was discussed.The results showed that the intercalation reaction was not carried out when only graphite and concentrated H₂SO₄ were mixed,KMnO₄ is a sufficient condition for intercalation and oxidation of graphite,edge or defect of the cabbon layer is oxidized firstly,and the oxidation process of the graphite gradually extends from the edge of the structure to the inside.Functional groups type and content of GO with different oxidation degree showed great difference.The results showed that C EC was not increased with the increase of oxidation degree,but was related to the content of hydroxyl groups and carboxyl groups in the structure by the stiasny method.Controllable oxidation process makes GO-4 samples of CEC reached the maximum value of 541.81 mmol?（100g）-1,continue to increase the degree of oxidation,the CEC reduced.conversely.After NH4+ and Ca2+ exchange processes,GO still maintained a stable lamellar structure.NH4+ and Ca2+ were mainly in the form of exchangeable cations in the interlayer space of GO,and formed a hydrated cation layer with water molecules,part of the containing [NH 4（H₂O）6]+ or [Ca（H₂O）6]2+ formed near the edge of the structural layer,balancing the negative charges originating from hydrolysis of the carboxyl grou ps of the GO structural layer.The negative value of GO structure layer and open interlayer environment make the CEC value was 5⁶ times of montmorillonite.Stripped GO（GOs-n,n=2,3,4）,the maximum saturated adsorption capacity of MB+ was 728.44,965.63 and 807.29 mg·g-1,respectively.Pseudo-second-order kinetic model could better describe the dynamic process of adsorption,which based on GOs structure on the most abundant hydroxyl and carboxyl as the main active sites with MB+ occur single molecular layer,exothermic and chemical speed control process.And adsorption mechanism is dominated by ion exchange adsorption.Adsorption performance was positively correlated with the total amount of C-Oand-COO-in GOs structure.Effects of epoxy groups and car bonyl groups on the adsorption capacity of MB by hydrogen bonding become prominent with increasing the extent of oxidation.