Hongting Zhao

Flocculation performance and mechanism of chitosan-based flocculants in the treatment of emulsified oily wastewater

ABSTRACT Chitosan (CS)-based flocculants, denoted as CS-g-PAM and CS-g-PDBC, were successfully prepared via graft copolymerization of CS with acrylamide (AM) or dimethyl acryloyloxyethyl benzyl ammonium chloride (DBC). The grafting was confirmed by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The flocculation performance of CS-g-PAM and CS-g-PDBC, as well as flocculants such as cationic polyacrylamide (CPAM), polyaluminum chloride (PAC), and CS, was evaluated and compared for treating emulsified oil wastewater. It was found that CS-g-PDBC exhibited excellent flocculation performance under both acidic and neutral conditions, while CS showed better flocculation ability under alkaline condition. The flocculation mechanism of CS and CS-g-PDBC was investigated via zeta potential measurements. Results showed that different flocculation mechanisms were involved at various pH levels. As regarding CS, the flocculation mechanism is mainly charge neutralization, patching, and sweep floc under acidic, neutral, and alkaline conditions, respectively, while for CS-g-PDBC, patching was the dominant mechanism under both acidic and neutral conditions. GRAPHICAL ABSTRACT

Size regulation and prediction of the SiO2 nanoparticles prepared via Stöber process

ABSTRACT In this study, monodispersed SiO2 nanoparticles with controllable size ranging from 20 to 100 nm have been successfully prepared by using a Stöber sol-gel process. The particle size, distribution, and morphology were examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In order to accurately regulate the particle size, the effects of various reaction parameters on the particle size and morphology of SiO2 nanoparticles were systematically investigated. It was found that, to some extent, the SiO2 particle size increased linearly with the increase of ammonia or water content, as well as the decrease of reaction temperature, while nearly kept constant with the increase of tetraethyl orthosilicate (TEOS). Based upon the results, an empirical formula has been developed to model/predict the particle size of the SiO2 nanoparticles over a wide range of various reaction conditions. GRAPHICAL ABSTRACT

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.

Neurological responses of embryo-larval zebrafish to short-term sediment exposure to decabromodiphenylethane

Decabromodiphenylethane (DBDPE) has been widely used as an alternative flame retardant due to the restriction or phase-out of traditional polybrominated diphenyl ethers (PBDEs), and is of increasing concern regarding its ubiquity, persistence, and potential adverse effects. In the present study, the toxicological effects of DBDPE were evaluated using zebrafish as an in vivo model. Upon being exposed to DBDPE-polluted sediments for a short term, it was found that the mortality and malformation of zebrafish (including edema, bent notochord, and bent tail) were not affected even at the highest concentration tested (1000.0 μg/kg dry sediment). Regarding behavioral responses, it was found that zebrafish larvae of 48 hours post fertilization (hpf) in all groups escaped successfully with a touch to the dorsal fin. However, when exposed to the highest DBDPE concentration, the larvae of 120 hpf exhibited significantly smaller distances as compared to the control. Moreover, the results of the acetylcholinesterase (AChE) activity, the expression levels of two important nerve-related genes, and the cell apoptosis all indicated that DBDPE posed low neurotoxicity in embryo-larval zebrafish. The results in this study shed some light on the potential risks of DBDPE in the real environment and highlight the application of the sediment exposure route in the future.中文概要目的评估底泥中的十溴二苯乙烷(DBDPE)对斑马鱼 早期发育阶段的胚胎毒性和神经行为毒性,并探 索其潜在影响机制。创新点底泥暴露能更真实地反应DBDPE 等强疏水性污 染物在实际环境中的暴露情况,有利于污染物生 态风险评估的科学性和准确性。方法将受精后4 小时(4 hpf)的斑马鱼胚胎置于对照 底泥和染毒底泥(DBDPE 系列浓度)中进行短 期暴露,观察不同发育阶段的存活率、孵化率、 畸形率以及行为(包括触碰反应和自由泳动)效 应;并通过斑马鱼幼鱼的乙酰胆碱酶活性、神经 系统的相关基因(α1-tubulin和gap43)的转录水 平以及斑马鱼整体组织的细胞凋亡情况的检测 探讨其神经毒性的潜在机制。结论DBDPE 从4 hpf 处理至120 hpf,各浓度组的斑马 鱼均未出现明显的畸形和死亡。在72 hpf 时,最 低浓度组(62.5 μg/kg)DBDPE 轻微加快了斑马 鱼的孵化,而最高浓度组(1000.0 μg/kg)DBDPE 轻微延迟斑马鱼的孵化。所有浓度组的DBDPE 对48 hpf 时斑马鱼的触碰反应没有任何影响,最 高浓度组(1000.0 μg/kg)DBDPE 对120 hpf 时斑 马鱼的自由泳动总距离有显著的抑制作用 (P<0.05)。但是,斑马鱼的乙酰胆碱酶活性、 α1-tubulin 和gap43 的转录水平未发生显著变化, 所有浓度组的DBDPE 亦均未诱发斑马鱼整体组 织的细胞凋亡。

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