Construction of self-assembled graphene oxide/polyelectrolyte multilayers film for application in heavy metal enrichment and detection:In-situ QCM-D experiment
Soil and groundwater pollution threats to water safety and people's health.The quartz crystal microbalance(QCM)can be used to build a technique for quick,in situ evaluation of contaminants in the soil-groundwater system.This study created self-assembled graphene oxide-polyelectrolyte multilayers coated on QCM sensors to improve their sensitivity and selectivity,as well as investigating the effects of ionic strength and pH on the heavy metal adsorption.Polyelectrolyte multilayers were fabricated by electrostatic layer-by-layer self-assembly of polyethyleneimine(PEI)and carboxymethyl Chitosan(CMC),two water-soluble polymers,and the mass and viscoelasticity real-time dynamics during multilayers growth can be detected based on frequency and dissipation monitoring using QCM.The film mass increased exponentially,whereas the film viscoelasticity varied in an"oscillation mode,"indicating that the conformation alternated throughout multilayers creation.GO was built on the membrane surface to boost heavy metal ion adsorption capability and multilayers stability.It was discovered that the positively charged PEI surface was more favorable to GO assembly than the negatively charged CMC surface,and GO deposition increased with the number of membrane layers.GO deposited on the surface of polyelectrolyte multilayers as monolayer flakes in a flat orientation and multilayer flakes in numerous orientations,displaying a cross-linked rough surface as shown by scanning electron microscope and atomic force microscope.Cu2+adsorption capacity was impacted by membrane layers.While the 3-layer(GO-PEI/CMC/PEI)had the largest enrichment capacity,it required a longer equilibrium period and cannot achieve adsorption equilibrium within 80 min.The GO-PEI/CMC/PEI film had an effective enrichment effect on different concentrations of Cu2+,Zn2+,and Cd2+respectively.Cu2+might form reversible adsorption by electrostatic attraction and irreversible adsorption via complexation,with the latter dominating as ionic strength increases.A reduction in pH could lead to the swelling of multilayers due to enhances the electrostatic repulsion between molecules,raising the number of adsorption sites and Cu2+adsorption capabilities in the multilayers.The findings of this study demonstrated that GO-polyelectrolyte multilayers coating could improve the heavy metal ion adsorption capacity of QCM sensors.however,it could also be affected by ionic strength and pH,and the influence of solution properties should be taken into consideration in pollutant enrichment-detection based on modified QCM sensor chips.
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