Magnetic Fe3O4/ZIF-8 optimization by Box-Behnken design and its Cd(II)-adsorption properties and mechanism

Immobilization of cadmium in river sediments by different modified nanoscale zero-valent iron: performance, mechanisms, and Fe dissolution

Modified nanoscale zero-valent iron (NZVI) exhibited great potential for the remediation of heavy metal contaminated river sediments, but its mechanisms and environmental risks are still unclear. This study systematically discussed the performance and the mechanisms of modified NZVI materials, i.e., sodium alginate-coated NZVI (SNZVI), rhamnolipid-coated NZVI (RNZVI), and graphene oxide-loaded NZVI (GNZVI), for the stabilization of Cd in sediment, with the exploration of their stability to Cd at various pH values and Fe dissolution rate. Compared with the control, the toxicity characteristic leaching procedure (TCLP) leachable Cd decreased by 52.66-96.28%, and the physiologically based extraction test (PBET) extractable Cd decreased by 44.68-70.21% after 56 days of incubation with the immobilization efficiency varying according to GNZVI > RNZVI > SNZVI > NZVI. Besides, the adsorption behavior of Cd on materials was fitted with the Freundlich model and classified as an endothermic, spontaneous, and chemical adsorption process. SEM-EDX, XRD, and FTIR results verified that the stabilization mechanisms of Cd were principally based on the adsorption, complexation of Cd2+ with secondary Fe minerals (including Fe2O3, γ-Fe2O3, and γ-FeOOH) and precipitation (Cd(OH)2). From the risk assessment results, it was observed that the materials were favorable for Cd stabilization at a pH range from 7 to 11, meanwhile, the leaching concentration of Fe in the overlying water was detected below the limit value. These findings pave the way to developing an effective strategy to remediate Cd contaminated river sediments.

ZIF-67-modified magnetic nanoparticles for extraction of phenoxy carboxylic acid herbicides

Phenoxy carboxylic acid (PCA) herbicides are commonly used herbicides that can easily accumulate in soil, groundwater, crops, and vegetable surfaces. Thus, they pose a serious risk to human health. Accurate detection of trace amounts of PCAs in various matrixes is crucial. Herein, ZIF-67-modified magnetic nanoparticles (MNPs, ZIF-67@Fe3O4) were prepared by growing ZIF-67 on the surface of Fe3O4 MNPs. The introduction of ZIF-67 improved the dispersion of Fe3O4 nanoparticles in water and enhanced their extraction performance for PCAs. When an eluent consisting of ammonia water and acetonitrile (5% : 95%; v/v) was employed, 10 mg of ZIF-67@Fe3O4 displayed optimal extraction performance for PCAs in a 20 mL sample solution at a pH of 3. We achieved a limit of detection ranging from 0.014 μg L-1 to 0.056 μg L-1 for four types of PCA herbicides by using the newly developed method. Notably, the values were considerably lower than the maximum concentration levels of PCAs in drinking water set by the Environmental Protection Agency. The relative recovery rate of PCAs using ZIF-67@Fe3O4 ranged from 83.75% to 117.07% when applied to river water and apple samples. These results demonstrate the great potential of ZIF-67@Fe3O4 in determining the residues of organic pesticides in real samples.

Removal of Hg2+ in wastewater by grafting nitrogen/sulfur-containing molecule onto Uio-66-NH2: from synthesis to adsorption studies

The remediation of heavy metal deserves to be on the agenda, with the adsorbent design bearing the brunt of it. In this study, the molecule (4, 6-diamino-2-mercaptopyrimidine, DMP) containing thiol (-SH) and amino (-NH₂) functional groups was grafted onto Uio-66-NH₂, and a composite metal-organic framework nanomaterial (Zr(NH₂)-DMP) was synthesized via a facile post-modification scheme. The morphological characteristics and structural features of the modified adsorbent were characterized by XRD, FT-IR, FE-SEM, EDS, BET, and XPS. The characterization results verified that the post-modification scheme was successfully achieved. The adsorption experiments were carried out to investigate the removal performance of the Zr(NH₂)-DMP towards Hg²⁺ under different influencing parameters. The maximum adsorption capacity of 389.4 mg/g was obtained, and the adsorption equilibrium was achieved within 30 min at pH 6 at room temperature. Adsorption thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The Zr(NH₂)-DMP exhibited excellent selectivity for Hg²⁺, and also has the potential to remove Cu²⁺, Fe²⁺, and Zn²⁺ ions. The introduction of Cl^- inhibited the removal of Hg²⁺ due to the formation of mercuric chlorides (removal efficiency reduced from 97.8 to 95.6%). The removal efficiency of up to 86.7% was obtained after four cycles. The Langmuir isotherm and Pseudo-second kinetic were more suitable for fitting the adsorption process of Hg²⁺ by Zr(NH₂)-DMP. The main removal mechanism could be attributed to the chelation between Hg²⁺ (soft acid) and nitrogen/sulfur (soft base) elements. These findings convinced that the successful synthesis of Zr(NH₂)-DMP provides an option for Hg²⁺ removal from wastewater.

Insight into different adsorption behaviors of two fluoroquinolone antibiotics by sediment aggregation fractions

Sediment, consisting of different aggregation fractions, is a hotspot site for transport and transformation of various pollutants including antibiotics. However, the fate of different antibiotics in aquatic sediments mediated by sediment aggregation fraction adsorption and the mechanism behinds are still unclear. In this study, we investigated the adsorption behavior of two fluoroquinolone antibiotics (ciprofloxacin and ofloxacin) on four aggregation fractions separated from the sediment of Taihu Lake, a typical lake contaminated by antibiotics in China. The results showed that the adsorption of ciprofloxacin and ofloxacin fitted the Freundlich model, irrespective of sediment aggregation size. The adsorption of ciprofloxacin and ofloxacin was depended on the size of sediment aggregation fractions, and the macroaggregation (> 200 μm) exhibited the strongest capacity, followed by large microaggregation (63-200 μm), medium microaggregation (20-63 μm), and small and primary microaggregation (< 20 μm). This fraction size-dependent effects of sediment aggregations on antibiotic adsorption might be closely related to the differences in their specific surface areas, organic matter contents, and surface functional groups. The adsorption of ciprofloxacin and ofloxacin by sediment aggregation fractions was characterized by a combination of chemical and physical adsorptions, with the former being the dominant process. Compared with ofloxacin, ciprofloxacin could be more rapidly and easily absorbed by four sediment aggregation fractions, and more readily complexed with carboxyl groups on macroaggregation surface. The adsorption of two antibiotics by extracellular polymeric substance showed that tryptophan and tyrosine protein-like, humic-like substance on the surface of sediment could bind to both antibiotics through a complexation reaction. The π-π electron donor-acceptor interaction and hydrogen bonds were responsible for the antibiotic adsorption by sediment aggregation.