Adsorption behavior of UV aged microplastics on the heavy metals Pb(II) and Cu(II) in aqueous solutions.

As the "vector" of heavy metals in the aquatic environment, microplastics (MPs) have a great influence on the migration and transformation of heavy metals. In this study, the adsorption of polypropylene (PP), polyethylene (PE) and polystyrene (PS) on two models of heavy metals after UV aging and environmental variables (ionic coexistence, pH, salinity, and fulvic acid) were comprehensively explored on adsorption. The results show that new oxidation functional groups are formed and their hydrophilicity is enhanced after MPs aging. As a result, the adsorption experiments showed that the adsorption of contaminants by UV aged MPs exceeds that of pristine MPs. The adsorption amounts of Pb(II) and Cu(II) by PP, PE and PS increased by 1.45, 1.46, 1.25 and 1.63, 1.39, 1.22 times, respectively. Adsorption kinetic data were more consistent with the pseudo-second-order kinetic model, proving chemisorption to be the mechanism governing the interaction between metal ions and MPs. The Freundlich model could accurately predict the heavy metal adsorption isotherms on MPs, showing that non-homogeneous multilayer adsorption dominates the process. In Pb(II)-Cu(II) binary composite system, metal ion adsorption capacity on MPs is less than that of the single system adsorption capacity, which proves that there is a specific inhibitory effect between coexisting ions. Additionally, external factors like pH, salinity, and fulvic acid content have a big impact on adsorption behavior. According to mechanism analysis, the adsorption process mainly relies on electrostatic interaction, surface complexation, and van der Waals force.

UV and chemical aging alter the adsorption behavior of microplastics for tetracycline.

This study evaluates the "vector" effects of different microplastics (MPs) on coexisting pollutants. The adsorption of tetracycline was studied on biodegradable plastics poly(butylene adipate-co-terephthalate) (PBAT) and non-biodegradable plastics polystyrene (PS), polypropylene (PP), and polyethylene (PE) after UV aging and chemical aging. The physicochemical properties of PBAT changed more obviously after UV radiation and chemical aging comparing to PS, PP and PE. Pores and cracks appear on the surface of aged PBAT. The crystallinity increased from 29.2% to 52.62%. In adsorption experiments, pristine and aged PBAT had strong vector effects on the adsorption of tetracycline than PS, PP and PE. The adsorption capacity of tetracycline on PBAT was increased from 0.7980 mg g-1 to 1.2669 mg g-1 after chemical aging. The adsorption mechanism indicated that electrostatic interactions and hydrogen bonds contribute to the adsorption process. In addition, for the adsorption of tetracycline on PS, π-π interaction was the main cause, and the adsorption mechanism was not considerably changed by aging. In conclusion, this study demonstrates that biodegradable plastics have substantial vector effect on coexisting pollutants at the end of their life cycle, this contributes to assessment of the risk from microplastic pollution.

Experimental and modeling investigation of organic modified montmorillonite with octyl quaternary ammonium salt.

The sodium montmorillonite was organic modified with three kinds of quaternary ammonium salts containing 1 to 3 octyl chains, and then the organic montmorillonite was studied by FT-IR, XRD, and TG characterization as well as Monte Carlo simulations, to explore the influence of the number of octyl chains and the loading of intercalated cations on the basal spacing (d001) of the modified montmorillonite complexes. According to the distribution of intercalated quaternary ammonium cations and the energy change of the montmorillonite complexes, a reasonable explanation was given for the enlargement of the interlayer space. The results of experimental characterization and Monte Carlo simulations show that all the three intercalation agents can enlarge the interlayer space of montmorillonite complexes. The more the number of octyl chains in the salt, the more significant expanding effect on the interlayer space. The three intercalation cations exhibited a distribution arranged from mono-layered to multi-layered structure as the loading of intercalated cations increases.

Organic Aluminum Hypophosphite/Graphitic Carbon Nitride Hybrids as Halogen-Free Flame Retardants for Polyamide 6.

The novel organic aluminum hypophosphite (ALCPA) and its hybrid (CNALCPA) with graphitic carbon nitride (g-C3N4) were successfully synthesized and applied as halogen-free flame retardants in polyamide 6 (PA6). Their structures, morphology, thermal stability, and fire properties were characterized. Results showed that both ALCPA and CNALCPA had good flame retardancy. PA6/CNALCPA composites achieved a high limited-oxygen-index (LOI) value of 38.3% and a V-0 rating for UL94 at 20 wt % loading, while PA6/ALCPA composites could reach a V-1 rating for UL94. The flame-retardant mechanism was also studied. On the one hand, the incorporation of g-C3N4 produced more gas-phase products, which indicated a gas-phase mechanism. On the other hand, g-C3N4 could catalyze the thermal degradation of ALCPA and PA6 to form a compact char layer that was evidence for a solid-phase mechanism. The tensile test of the PA6 composites also displayed good mechanical properties.

Photoelectric effect accelerated electrochemical corrosion and nanoimprint processes on gallium arsenide wafers.

Here we report photoelectric-effect-enhanced interfacial charge transfer reactions. The electrochemical corrosion rate of n-type gallium arsenide (n-GaAs) induced by the contact potential at platinum (Pt) and GaAs boundaries can be accelerated by the photoelectric effect of n-GaAs. When a GaAs wafer is illuminated with a xenon light source, the electrons in the valence band of GaAs will be excited to the conduction band and then move to the Pt boundaries due to the different work functions of the two materials. This results in an enhanced contact electric field as well as an enlarged Pt/GaAs contact potential. Consequently, in the presence of electrolyte solution, the polarizations of both the Pt/solution interface and the GaAs/solution interface at the Pt/GaAs/solution 3-phase boundary are enhanced. If the accumulated electrons on the Pt side are removed by electron acceptors in the solution, anodic corrosion of GaAs will be accelerated strictly along the Pt/GaAs/solution 3-phase boundary. This photo-enhanced electrochemical phenomenon can increase the corrosion rate of GaAs and accelerate the process of electrochemical nanoimprint lithography (ECNL) on GaAs. The method opens an innovative, highly efficient, low-cost nanoimprint technique performed directly on semiconductors, and it has prospective applications in the semiconductor industry.

Liquid crystalline and shear-induced properties of an aqueous solution of graphene oxide sheets.

We demonstrated here the lyotropic liquid crystalline behavior of an aqueous solution of graphene oxide (GO) sheets. Scanning electron microscope experiments revealed GO sheets self-assembled into fiber-like or sheet-like structures at different concentrations under flow conditions. As a result, the solution viscosity decreased dramatically with increasing shear stress.