| Nowadays,the discharge of dye wastewater is increasing with the development of industrial industry,and the environmental problems brought by it are getting more and more serious.Wastewater is highly toxic,difficult to degrade,and have high chromaticity.They not only affect the growth of aquatic organisms,but also threaten human health.Therefore,the treatment of dyes has become a challenging problem for researchers and the scientific community.A large number of adsorbents and catalysts have been applied to the removal of dyes in wastewater.Among these,polydopamine（PDA）contains a variety of functional groups,such as catechols,amines and imines which can not only serve as ideal covalent modification sites for dye molecules,but also can be further modified with transition metal ions to enhance its reduction ability in the degradation of dye.Based on the above advantages,polydopamine is widely used as a coating material in the removal of organic pollutants.Therefore,this article aims to design effective polydopamine materials that are simple to use,has good adsorption and catalytic properties.The main work is listed as follows.1.Preparation of polydopamine encapsulated magnetic nanomaterials and its application in the removal of methylene blue（MB）.We first prepared Fe3O4 magnetic nanoparticles using FeCl3·6H2O as iron source by hydrothermal method.Then,PDA was coated on the surface of it.In order to achieve the decomposition of H2O2,silver and cobalt was conjugated on PDA surface step by step through the interaction between polydopamine and metal ions.The prepared magnetic nanoparticles was characterized by X-ray diffraction（XRD）,transmission electron microscope（TEM）,Fourier transform infrared spectrum（FT-IR）,EDS（Energy dispersive spectrometer,EDS）,etc.We also studied the effect of hydrogen peroxide concentration,pH value,reaction time and temperature on the removal of dyes.Results showed that the material has a good effect on MB removal in a wide range of pH and temperature.99.68%of MB could be removed within 2 minutes,Under the condition of standing for 2 min,it can reach 91.5%2.We then investigated the possible mechanism and found that singlet oxygen,one of the products of H2O2,is the main reactive oxygen species that degrades methylene blue.Liquid-mass spectrometry indicated that the possible degradation products are mainly C6H7NSO3,C6H6O3,and C6H6O.3.Preparation of graphene-polydopamine（PDA-GO）hydrogels and its application in the removal of MB.Using graphene oxide as carbon source and dopamine as reducing agent and crosslinking agent,a hydrogel material was prepared.The structure of graphene-ploydopamine hydrogel was analyzed by scanning electron microscopy,and it was found that the surface of PDA-GO hydrogel had a large specific surface area and large amount of pores.Both of then are beneficial to the adsorption of dye molecules.Subsequently,we optimized the synthesis conditions of PDA-GO hydrogel.When the concentration ratio between graphene and dopamine was 2 to 1,the concentration of graphene is from 0.8 to 1.2 mg/m L,and the mixture was reacted at80℃ for 12 h,we can obtain solid hydrogel material.UV-Vis spectrophotometry indicated that the hydrogel material has a good adsorption effect on MB.95%of MB could be removed in 8 h and the ratio could reach 99%after 12 hours.However,the removal rate is far slower than the above magnetic material although the hydrogel in this work is easier to be recycled.Therefore,we further deposited silver and cobalt nanoparticles on hydrogel based on the same intereaction between PDA and metal ions.Results indicted the removal rate was accelerated significantly and the ratio can reach72.3%after 60 minutes in the presence of hydrogen peroxide. |
