Research On Adsorption Of Hexavalent Chromium And Congo Red In Aqueous Solutions Onto Modified Graphene/Pyrrole Composite Materials

Hexavalent chromium?Cr????is one of the most harmful heavy metals to the human body,and it is a kind of priority control pollutant.Congo red?CR?not only affects the aquatic ecological environment but also has“triple effect”on the human body.Therefore,proper treatment of Cr???and Congo red in waste water is an urgent environmental problem.Graphene has a large specific surface area and can be used as a good carrier for other adsorption materials,it has been widely studied for the treatment of industrial wastewater.Polypyrrole contains a large amount of amino groups in the molecule and has a certain degree of reduction.However,graphene and pyrrole particles are easy to stack and agglomerate,reducing their specific surface area and active sites,and limiting their practical application.Therefore,the modification of graphene and polypyrrole to increase their specific surface area is an important problem that must be solved to achieve effective utilization.In this study,natural graphite powder,pyrrole monomer and tetraethylorthosilicate were used as raw materials.SiO₂ was inserted into the graphene layer through hydrolysis to form a graphene/silica composite material?GS?.And then,polypyrrole particles weredispersed on the surface of graphene uniformly,which reduced the agglomeration of polypyrrole particles and graphene,forming graphene/silica@polypyrrole composite?GS-PPy?.The morphological structure of GS-PPy nanocomposite was studied by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,fourier transform infrared spectroscopy?FTIR?,and X-ray diffraction?XRD?.And GS-PPy was used to remove Cr???and Congo Red,the effects of various factors such as solution pH,reaction time,solution concentration,and temperature on the adsorption effect were investigated.The pollutant removal mechanisms and the regeneration performance of the adsorbent were also investigated.The results show that rod-like SiO₂ was successfully inserted the layers of graphene to form a transparent graphene sheet layer.The spherical polypyrrole particles were uniformly dispersed on the surface of graphene,increasing the specific surface area of polypyrrole particles.Graphene,silica and polypyrrole particles were organically combined and the GS-PPy composites were successfully prepared.GS-PPy was used to remove Cr???from the solution.At pH=2.0,the adsorption effect was the best.The adsorption process can be fittedwith the pseudo-second-order kinetic model and the Langmuir isotherm model.The adsorption reaction was a spontaneous and endothermic reaction.Cr???removal by GS-PPy has good anti-interference ability,and the adsorbent has good recycling ability.The mechanisms of removing Cr???by GS-PPy mainly include electrostatic attraction,ion exchange and redox.GS-PPy was used to remove CR from the solution.At pH=4.0,the adsorption effect was the best.The adsorption process can be fitted with the pseudo-second-order kinetic model and the Langmuir isotherm model.As the temperature increased,the saturated adsorption capacity of GS-PPy gradually increased.At 298 K,the saturated adsorption capacity of GS-PPy to Congo red is 298.9 mg/g.The removal mechanisms may be weak electrostatic attraction,?-?interaction and hydrogen bonding.GS-PPy nanocomposites have high adsorption capacity for Cr???and Congo red,andis a potential candidate for the removal of Cr???and Congo red from the industrial waste water.