Removal of ZnO Nanoparticles from Natural Waters by Coagulation-Flocculation Process: Influence of Surfactant Type on Aggregation, Dissolution and Colloidal Stability

Abstract

The zinc oxide nanoparticles (ZnO NPs) and surfactants that are widely used in commercial and industrial products lead to the likelihood of their co-occurrence in natural water, making it essential to investigate the effect of surfactants on the fate and mobility of ZnO NPs. The present study seeks to elucidate the effect of an anionic sodium dodecyl sulfate (SDS) and a nonionic nonylphenol ethoxylate (NPEO), on ZnO NPs adsorption, aggregation, dissolution, and removal by the coagulation process. The results indicate that the presence of SDS in ZnO NPs suspension significantly reduced the ζ-potential and hydrodynamic diameter (HDD), while the effect of NPEO was found not to be significant. The sorption of SDS and NPEO by ZnO NPs were fitted with Langmuir model, but the Freundlich isotherm was more suitable for SDS at pH 9.0. Moreover, the adsorption was strongly pH-dependent due to the formation of mono-bilayer patches onto the NPs. The SDS remarkably affect the dissolution and aggregation phenomena of ZnO NPs in natural waters as compared to NPEO. Finally, the coagulation results showed that the removal efficiency of ZnO, Zn2+ and the surfactant in synthetic and wastewaters at optimum ferric chloride (FC) dosage reached around 85–98% and 20–50%, respectively. Coagulation mechanism investigation demonstrated that the cooperation of charge neutralization and adsorptive micellar flocculation (AMF) might play an important role. In summary, this study may provide new insight into the environmental behavior of coexisting ZnO NPs and surfactants in water treatment processes, and it may facilitate their sustainable use in commercial products and processes.

Interaction between Persistent Organic Pollutants and ZnO NPs in Synthetic and Natural Waters

“…Figure 1A shows the FT-IR spectroscopy of pristine ZnO powder, which reveals the broad band at 556 cm −1 corresponding to the stretching vibration of Zn–O bonds [25]. Moreover, the peaks observed at 1378, 1629, and 3402 cm −1 are attributed to the OH groups and displacement of weakly adsorbed water molecules on the NPs surface.…”

“…Figure 5B shows the FT-IR spectra of ZnO NPs before and after interactions with BDPE-47 and BDPE-209. The peaks at ~3294, ~2968, and ~2330 cm −1 that appear in ZnO–PBDPEs complex correspond to the stretching vibrations of OH, and symmetric stretching vibration of aliphatic C–H and C=O, respectively [19,25]. In comparison to the pristine ZnO NPs, a new band was observed at ~1346–1358 cm −1 , which is attributed to the adsorption of PBDPEs onto ZnO NPs surface via aromatic ether (-O-) groups [27,42] Furthermore, Figure 5C,D, indicate the XPS analysis of PBDPEs before and after the interaction with ZnO NPs, which further confirm the attachment of Br (present in BDPE-47 and BDPE-209) onto the ZnO NPs surface [43,44] Therefore, it can be inferred that surface Zn-OH groups (donor) of the NP and ether (-O-) groups in PBDPEs (acceptor), or induced dipole, might be responsible for the strong interaction between PBDPEs and ZnO NPs.…”

“…The stock solution of ZnO NPs was prepared by adding 100 mg of ZnO powder in 1 L of DI water. The detailed procedure can be found in our previous study [25]. Stock solutions (500 mg/L) of BDPE-47 and BDPE-209 were prepared in anhydrous ethanol and dimethyl sulfoxide (DMSO, purity > 99.5%), respectively, by continuous mixing with a magnetic stirrer for 2 h. The ZnO–PBDPEs suspensions were prepared with a lower ratio of 1:20 (solvent:water) to reduce the effect of solvent during experiments, and further diluted to achieve the desired concentration.…”

Firms’ Sustainability: Does Economic Policy Uncertainty Affect Internal Control?

“…Furthermore, sustainability means maintaining development trends even when facing unpredictable environmental shocks. Because the sustainability concept is quite wide, the research on sustainability is diverse and challenging, but mainly includes sustainable urban and rural development [78], sustainable use of the environment and resources [79], energy sustainability, the economy [80], business and management aspects of sustainability [81], etc. This study is included in a branch of research that considers business and management aspects of sustainability, focusing on firms' sustainability.…”

Fibrous adsorbent derived from sulfonation of cotton waste: application for removal of cadmium sulfide nanoparticles from aquatic media

“…Several methods such as phytoremediation, coagulation and flocculation, membrane filtration, and adsorption have been assessed to find suitable methods for removing metal-containing NPs from water and wastewater [20][21][22][23][24][25][26]. Because of the drawbacks of other methods including fouling in membrane filtration and high volume of sludge in coagulation and flocculation process, the adsorption process has been reported as the most efficient and economical method [27].…”