Abstract
The large-scale production and usage of zinc oxide nanoparticles (ZnO NPs) may lead to their post-release into the aquatic environment. In this study, the effect of hydrophobic/hydrophilic organic ligands on sorption and sedimentation of ZnO NPs has been systematically investigated. In addition, the coagulation efficiency of ZnO NPs, Zn2+, dissolved organic carbon (DOC), and UV254 with varying ferric chloride (FC) dosages in synthetic waters were also evaluated. The results showed that the higher concentration of organic ligands, i.e., humic acid (HA), salicylic acid (SA), and L-cysteine (L-cys) reduced the ζ-potential and hydrodynamic diameter (HDD) of particles, which enhanced the NPs stability. The adsorption of organic ligands onto ZnO NPs was fitted with the Langmuir model, with maximum adsorption capacities of 143, 40.47, and 66.05 mg/g for HA, SA and L-cys respectively. Removal of up to 95% of ZnO NPs and Zn2+ was achieved in studied waters at the effective coagulation zone (ECR), above which excess charge induced by coagulant restabilized the NPs in suspension. Moreover, the removal rate of DOC and UV254 were found to be higher in hydrophobic waters than hydrophilic waters. The width of ECR strongly depends on the characteristics of source water. The waters with hydrophobic ligand and higher UV254 values require more coagulant than hydrophilic waters to achieve the similar ZnO NPs and Zn2+ removal. The results of Fourier transform infrared (FT-IR) analysis of ZnO NPs composite contaminant flocs indicated that the combined effect of enmeshment and charge neutralization might be a possible removal mechanism. These findings may facilitate the prediction of fate, transport, and removal of ZnO NPs in the natural waters, and might contribute to risk assessment, as well as decision making about engineered nanoparticles (ENPs) in aquatic systems.
Highlights
The engineered nanoparticles (ENPs) are extensively used in commercial products, with applications in industrial processes, electronics, agricultural and environmental sciences, mainly because of their unique structural properties compared to conventional bulk materials [1,2]
DLS measurement indicated that the majority of NPs were well dispersed in the water, and the hydrodynamic diameter (HDD) was in the range of
We systematically investigated the effect of organic ligand types such as hydrophobic/hydrophilic, and their effects on zinc oxide nanoparticles (ZnO NPs) stability and removal by ferric chloride (FC) coagulant from synthetic waters
Summary
The engineered nanoparticles (ENPs) are extensively used in commercial products, with applications in industrial processes, electronics, agricultural and environmental sciences, mainly because of their unique structural properties compared to conventional bulk materials [1,2]. Of the globally-produced ENPs are released into the aquatic system, which leads to the high possibility of their co-presence in natural water sources [3]. A recent study suggested that around 8–20% of the annual production of ZnO NPs (31,500–34,000 t/y) may inevitably enter into the water environment [5]. There is growing concern regarding the likelihood of the occurrence of these NPs in drinking water sources, and the potential increased risk of exposure to humans as well as the aquatic environment
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