Adsorption Behavior Of Microplastics To Organic Dyes And Its Effect On Flotation Removal

Microplastics widely existing in the environment could cause certain pollution and harm to water and coastal ecology.Organic dyes in water are easy to adsorb on the surface of microplastics,and then form composite pollutants with higher toxicity.To scientifically evaluate the complex environmental behavior between microplastics and organic dye pollutants,and examine their ability as a carrier to migrate pollutants.The adsorption behavior of Rhodamine B(Rh B)and methylene blue(MB)on different microplastics were systematically studied.The effects of p H,salinity,humic acid(HA),particle size,and temperature on the adsorption were investigated.Foam plastics were used to remove microplastics,and the effect of microplastics adsorbed organic dyes on flotation was studied.The adsorption process of oxanthracene dyes Rh B on polyvinyl chloride(PVC),polystyrene(PS),and polyethylene terephthalate(PET)was fitted by the second-order and Langmuir model,showing that the adsorption was monolayer chemical adsorption.The maximum adsorption capacity of Rh B on microplastics was: PVC(4.598 mg/g)> PS(2.482mg/g)> PET(1.778 mg/g)from Langmuir model.The difference in specific surface area(SSA),functional groups,crystallinity,and polarity of microplastics was the main factor leading to the difference in adsorption capacity for organic dyes.At low p H,Rh B molecules were not easy to agglomerate,which conducive to the adsorption of Rh B by microplastics.Na Cl and HA could compete with Rh B for the adsorption sites on the surface of microplastics and inhibit the adsorption of Rh B.With increased temperatures,the internal chain distance of microplastic increased,conducive to the diffusion of Rh B on PVC.However,the hydrogen bond between Rh B and microplastics could be destroyed at high temperatures,which had an adverse effect on the adsorption of Rh B in PS and PET.The adsorption of Rh B by microplastics was affected by electrostatic interaction.The halogen bond and polar interaction promoted the adsorption of Rh B on PVC.The adsorption of Rh B by PS and PET was affected by the π-π interaction.When the foaming agent was 16.2 mg/L,PVC,PS,and PET could be removed 100% by flotation.With increasing Rh B concentration,the microplastics adsorbed Rh B had a certain negative impact on its flotation removal.When Rh B was 25 mg/L,the removal rates of PVC,PS,and PET adsorbed Rh B could reach 76.98%,97.34%,and99.10%.The adsorption process of azo dyes MB on polymethyl methacrylate(PMMA),PVC,and PS accorded with the second-order and Langmuir model.The maximum adsorption capacity of microplastics for MB was PMMA(4.407 mg/g)> PVC(3.721 mg/g)> PS(2.379 mg/g)from Langmuir model.PMMA containing ester group on the branched chain had the largest adsorption capacity for MB.Unlike Rh B,alkaline conditions were conducive to the adsorption of MB by microplastics.Na Cl and HA had the same effect on the adsorption as Rh B,and inhibited the adsorption of MB by microplastics.The increase in temperature was conducive to the adsorption of MB by PMMA and PVC,but unfavorable to the adsorption of MB in PS which was greatly affected by hydrogen bond.Electrostatic interaction played a key role in the adsorption of MB by microplastics.Due to different functional groups,there was a polar effect between PMMA and PVC and MB.The adsorption of MB by PVC was affected by halogen bond,and there was π-π interaction between PS and MB.With increasing MB concentration,the microplastics adsorbed MB had a negative impact on its flotation removal.When MB was 20 mg/L,the removal rates of PMMA,PVC,and PS adsorbed MB could reach 98.42%,76.65%,and81.63%.