Study On Adsorption/Desorption Behavior Of Polyethylene Microbeads For Tricloson

As a new environmental pollutant,microbeads(particle size no more than 1 mm)which are often added to personal care products have been paid more attention for its ecological effects.One of the most type of microbeads used in cosmetics is polyethylene.At present,studies on the microbeads were still in the initial stage,mainly focusing on the investigation of pollution,and few studies on the adsorption/desorption mechanism of microbeads.However,the adsorption/desorption mechanism of the microbeads was considered as the key to the harmful ecological effects,and should be paid more attention.In this study,PE beads which are the most widely used in cosmetics were selected as adsorbents,Triclosan(TCS),an anti-bacterium component commonly used in cosmetics,was selected as the target pollutant.Then,a method for isolation and quantitation of polyethylene microbeads in cosmetics was developed,and a method for detection TCS in different media was built.In a word,This study showed environmental behaviors of microbeads by exploring adsorption/desorption mechanism.The main conclusions are as follows:1.A double-density separation method was developed by using the difference of relative density between PE microbeads and two kinds of separation solutions.The PE microbeads were stably separated from 14 kinds of commercial cosmetic samples labeled with microbeads.The contents were from 0.11%to 7.76%,and size ranged from 100 ?m to 200 ?m.The morphology of isolated polyethylene microbeads were mostly regular,and color were mainly blue and white.The recoveries were from 93.2%to 98.2%,and the relative standard deviations varied in the range from 0.16%to 2.81%.2.The detection method of TCS in both solid and liquid media was built.The separation column was ZORBAX SB-C18(4.6 mm x 150 mm,5 pm);The moving phase was methanol-water(80-20);The qualitative indexes were retention time and ultraviolet spectrum,and quantative index was peak area at 280nm with DAD detector.At the same time,according to the adsorption experiment requirements,a standard curve was made in the range of 0.1-100 mg/L with a correlation coefficient of 0.9996;the detection limit of the method was 0.04 mg/L,the lower limit of quantification was 0.13 mg/L,and the precision was from 2.95%to 6.69%,which met the analysis requirements.Finally,the minimum amount of methanol used as a cosolvent in the sorption system was 1%;solid phase could be detected directly after digesting 15 minutes with 450C.40 bar conditions;the pre-treatment conditions of liquid phase was diluted with methanol making the final concentration of methanol to 50%.3.The adsorption kinetics of TCS by P-PE and E-PE beads could be described by the quasi-second-order kinetic model with the determination coefficient R2 were within the scope of 0.964?0.995 and equilibrium time about 24 h.It shew that the adsorption kinetics mechanism was chemical adsorption containing physical adsorption at the initial stage.At the same time,the internal particle diffusion model fitting results showed that the adsorption process had solute diffusion.In a word,the adsorption mechanism was chemical adsorption with particle diffusion.4.The adsorption process of TCS by P-PE and E-PE beads were both could be well described by Freundlich adsorption-distribution composite model with the determination coefficients R2 were 1,respectively.It shew that the adsorption behaviour was the superposition of the distribution and surface adsorption mechanism.The surface adsorption was multi-layer.The contribution rate in total adsorbing capacity of distribution and surface adsorption mechanism was about 49%and 51%,respectively.5.According to Gibbs free energy formula and adsorption thermodynamics experiments,?G and ?H of the two kinds of microbeads were both less than 0 indicating that the adsorption process belonged to the exothermic reaction,spontaneously.6.The desorption lag cofficient of TCS on two kinds of P-PE beads were more than 0 indicating that the adsorption process have desorption lag phenomenon and indicating that adsorption and desorption processes were not reversible.