Ting Lü

A facile method for emulsified oil-water separation by using polyethylenimine-coated magnetic nanoparticles

AbstractOil spills and oily wastewater discharges from ships and industrial activities have serious impacts on the environment and human health. In this study, a class of easy-to-synthesize polyethylenimine (PEI)-coated Fe3O4 magnetic nanoparticles (MNPs) was successfully synthesized via a one-step coprecipitation method. The synthesized PEI-coated Fe3O4 MNPs were characterized by using multiple technologies and applied in emulsified oil-water separation for the first time. It was found that the PEI effectively tuned the surface charge and wettability of MNPs. As a result, the PEI-coated MNPs could successfully assemble at the oil-water interface and promote the coalescence of oil droplets, thereby facilitating the subsequent magnetic separation. Results showed that the oil-water separation performance was superior and enhanced with the increase of ionic strength. Recycling experiment indicated that the PEI-coated MNPs could be reused up to six times without showing a significant decrease in separation efficiency. All of these results suggested that the PEI-coated MNP could potentially be used as a class of promising nanomaterials for emulsified oil-water separation. Graphical abstractSchematic illustration of the emulsified oil-water separation process by using PEI-coated Fe3O4 MNPs.

Enhanced demulsification from aqueous media by using magnetic chitosan-based flocculant

A series of quaternized chitosan (QC)-grafted magnetic nanoparticles (MNPs) were successfully synthesized for demulsification from aqueous environments. Fe3O4 MNPs were synthesized by using a coprecipitation method, followed by surface coating with silica and aminopropyl to form a surface for further grafting of QC molecular chains. The synthetic magnetic flocculants were characterized by various technologies and their demulsification performances were evaluated in detail as a function of dosage, QC grafting ratio (Gq), pH and magnetic field. Results showed that pH did not significantly affect oil-water separation performance and MNPs with high Gq exhibited enhanced separation efficiency. The separation capacity was estimated to be >105 mg of diesel oil/mg of magnetic flocculant. Recycling experiment indicated the magnetic flocculant could be recycled up to at least 7 cycles at various pH levels. The grafted QC layer endowed the hybrid MNPs with permanent positive surface charges, thus allowing them to flocculate negatively charged oil droplets via electrostatic patching. The magnetic field could not only accelerate the separation of resulting flocs, but also remove the MNPs-coated dispersed oil droplets. In conclusion, QC-grafted MNPs provide a potentially new technique for developing environmentally friendly and highly efficient magnetic flocculant for practical demulsification applications.

Effect of hydrophobic monomer on the aqueous dispersion polymerization of acrylamide with quaternary ammonium cationic monomer

Aqueous dispersion polymerization has been considered as a promising green technology for preparing water-soluble polymers such as cationic polyacrylamide (CPAM). Dispersion copolymerization of acrylamide and 2-methylacryloylxyethyl trimethyl ammonium chloride was generally carried out in aqueous ammonium sulfate solution with poly(2-methylacryloylxyethyl trimethyl ammonium chloride) as the stabilizer. In this study, we reported the potential influence of a small amount of hydrophobic monomer, methyl methacrylate (MMA), on the above-mentioned aqueous dispersion polymerization system. It was found that MMA could play an important role in the polymerization process by significantly affecting the particle formation and stabilization, as well as the viscosity evolution of the reaction mixture during polymerization. With the addition of a small amount of MMA, the particle formation was accelerated and the viscosity of the polymerization system decreased significantly. With the increase in MMA addition, the final copolymer particle size was reduced and its size distribution became narrower; meanwhile, the particle morphology tended to be spherical. Moreover, it was found that the addition of MMA could favor the production of CPAM with high charge density. The flocculation performance of the resulting CPAM dispersion was also examined in detail and it was found that the introduction of MMA unit into CPAM molecular chain could improve its flocculation efficiency.

Application of hydrotalcite in soil immobilization of iodate (IO3

Radioactive iodine is quite mobile in soil and poses threats to human health and the ecosystem. Many materials, including layered double hydroxides (LDH), have been synthesized to successfully capture iodine from aqueous environments. However, limited information is available on the application of LDH in soil to immobilize iodine species. In the present study, the feasibility of using Mg–Al–NO3 LDH for retention of soil iodate (IO3−) in both batch and column systems was analyzed. The 2 : 1 Mg–Al–NO3 LDH exhibited the greatest removal efficiency of IO3− from aqueous solution, compared with 3 : 1 and 4 : 1 Mg–Al–NO3 LDH. The Mg2–Al–NO3 LDH demonstrated a strong affinity for IO3−, with a high sorption capacity of 149 528 mg kg−1 and a Freundlich affinity constant KF of 21 380 L kg−1. The addition of Mg2–Al–NO3 LDH in soil resulted in significant retention of IO3− in both the batch and column experiments. The affinity parameter KF of soil with the addition of 1.33% Mg2–Al–NO3 LDH was 136 L kg−1, which was 28.6 times higher than soil without LDH added. Moreover, the eluted iodate percentage was only 12.9% in the soil column with the 1.33% Mg2–Al–NO3 LDH addition, whereas almost 43.5% iodate was washed out in the soil column without LDH addition. The results suggested that Mg2–Al–NO3 LDH could effectively immobilize iodate in soil without obvious interference.

One-Step Synthesis of Polyethylenimine-Coated Magnetic Nanoparticles and its Demulsification Performance in Surfactant-Stabilized Oil-in-Water Emulsion

Abstract In this study, polyethylenimine (PEI)-coated Fe3O4 magnetic nanoparticles (MNPs) were successfully synthesized via a one-step, solvo-thermal method. The synthetic PEI-coated MNPs were characterized by using multiple techniques and their demulsification efficiencies were evaluated in surfactant-stabilized, oil-in-water emulsions. The results showed that the synthesized MNPs successfully adsorbed to the emulsion’s O/W interfaces and, consequently, the oil droplets could be rapidly destabilized under an applied magnetic field. It was found that the demulsification efficiency was enhanced with the increased particle dosage. The opposite effect was found with the increase in pH value and surfactant concentration. The presence of electrolytes facilitated oil removal, presumably by reduction of the electrostatic repulsion or by altering the hydrophobicity of the MNPs. Recovery experiments at various pH levels indicated that the PEI-coated MNPs could be reused for up to ten times without significant reduction in demulsification efficiency. Altogether, the results suggested that the PEI-coated MNPs could provide a simple but powerful tool to remove emulsified oil from aqueous systems. Graphical Abstract