Effect Of GO Oxidation Degree On Adsorption Properties Of GO/PVA Aerogels

Graphene oxide has large specific surface area,and its surface contains electronegative oxygen-containing functional groups,which can provide adsorption active sites.Different oxidation degree of GO has different amounts of oxygen-containing functional groups,thus affect the adsorption of organic dyes and heavy metal ions.The oxygen functional groups in GO make it easier to disperse in water to form a homogeneous and stable dispersing solution,but it will also lead to the difficulty of separation from the solution after the adsorption is completed.The surface of polyvinyl alcohol contains a large number of hydroxyl groups.On one hand,it may have a stabilizing and separating effect on the GO network structure.On the other hand,it possibly compensate the negative effect on the adsorption efficiency caused by the physical coverage of PVA chains on GO layers.GO/PVA aerogel combines the excellent properties of GO and PVA,such as light weight,high mechanical strength,porous structure,etc,making it the best candidate for wastewater treatment.We firstly use the improved Hummers oxidation method to prepare three kinds of GO with different oxidation degree by changing the amount of oxidant KMnO₄.The PVA was added to the GO aqueous solution,and PVA-supported GO aerogels are obtained through the environmentally friendly freeze drying process.The effect of PVA concentration and the ratio of GO and PVA on the pore structure and mechanical properties of the composite aerogel was studied.Then,GO/PVA aerogels（GO/PVA-1,GO/PVA-2 and GO/PVA-3）were prepared by using three kinds of GO with different degrees of oxidation,and their structure and properties were characterized.Three GO/PVA aerogels were applied to the adsorption of MB,and the effects of aerogel dosage,pH,adsorption time,initial concentration and temperature on the adsorption efficiency of MB were systematically investigated.The adsorption mechanism was studied by kinetic model,isothermal adsorption model and thermodynamics.GO/PVA aerogels were also applied to adsorb heavy metals Cd²⁺、Cu²⁺,and the effects of aerogel dosage,pH,adsorption time and ionic strength were systematically studied.The adsorption-desorption experiment was used to evaluate the regeneration performance of GO/PVA aerogels.The main experimental results are as follows:1、The improved Hummers method was used to prepare GO.With the increase of the amount of oxidant KMnO₄,the oxidation degree of GO（GO-1,GO-2,GO-3）increased,and the corresponding C/O ratio was 2.23,1.74 and 1.69 respectively.2、The concentration of PVA and the ratio of GO to PVA have an effect on the size and mechanical strength of aerogels.When the PVA concentration is 6%,GO:PVA=15:1,the aerogel prepared has the best effect and the compression modulus is 0.73129 MPa.3、MB solution was used to simulate organic dye wastewater.The adsorption capacities of MB on GO1–GO3 were 70.17,90.33,93.68 mg/g,respectively,at a temperature of298.15K,a pH of 10 and with an initial MB concentration of 150 mg/L.And the adsorption process both met the pseudo-second-order kinetic model and the Langmuir isotherm model.Recycling adsorption-desorption experiments revealed that GO/PVA aerogel shown 74.3%for MB adsorption efficiency after the fifth regeneration cycle process.GO/PVA showed potential application as recyclable adsorbent for organic dyes.4、GO/PVA composite aerogels also had good adsorption effect on MG and CR.The maximum removal rates were 96%and 84.96%,respectively,and the adsorption process conformed to the Langmuir isotherm model.5、Cd²⁺、Cu²⁺solution was used to simulate heavy metal wastewater.The adsorption capacities of Cd²⁺on GO/PVA-1–GO/PVA-3 were 8.51,9.53,9.79 mg/g,respectively,at a temperature of 298.15K,a pH of 5 and with an initial Cd²⁺concentration of 50 mg/L.The adsorption capacities of Cu²⁺on GO/PVA-1–GO/PVA-3 were28.76、37.08、38.33 mg/g,respectively,at a temperature of 298.15K,a pH of 6 and with an initial Cu²⁺concentration of80 mg/L.6、The concentration of HCl had a great effect on the adsorption of Cd²⁺and Cu²⁺by aerogels,and the desorption rate increased with the increase of HCl concentration.When the concentration of HCl is 1 mol/L,the maximum desorption rate is 90.3%and 97.1%respectively.Recycling adsorption-desorption experiments revealed that GO/PVA aerogel shown 48.74%、69.81%for Cd²⁺、Cu²⁺adsorption efficiency after the fifth regeneration cycle process.7、In this study,the adsorption effect of aerogels is closely related to the oxidation degree of GO.With the increase of GO oxidation degree,the equilibrium adsorption capacity of GO/PVA aerogels on MB,Cd²⁺and Cu²⁺increases significantly.