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

Adsorption optimization and modeling of Hg2+ ions from aqueous solutions using response surface methodology by SNPs-CS bionanocomposite produced from rice husk agro-industrial waste as a novel environmentally-friendly bionanoadsorbent

In the present research, extraction of silica (SiO2) from rice husk (RH) was optimized and silica nanoparticles (SNPs) was produced using it and functionalized by chitosan (CS) functional groups to obtain CS functionalized SNPs (SNPs-CS) bionanocomposite for the first time. The physical and chemical characteristics of the produced materials were examined using structural analyses. The results of structural analyses confirmed the fine structure of the produced materials. The SNPs-CS bionanocomposite was applied to effectively remove Hg2+ ions from aqueous solutions as an environmentally-friendly bionanoadsorbent and optimization and modeling of the adsorption conditions was explored using designed experiments by Design-Expert software with central composite design (CCD) and response surface methodology (RSM). Optimum adsorption conditions were obtained as solution pH of 6, SNPs-CS dosage of 0.1 g L-1 and Hg2+ ions concentration of 100 mg L-1 by removal efficiency of 85% and desirability function of 0.876. The results of adsorption kinetic showed a better fit of the pseudo-second-order model with experimental data, indicating the chemisorption of the adsorption process. The better fit of the Langmuir model with experimental data was confirmed by the results of adsorption isotherms, demonstrating monolayer adsorption on the homogeneous surface. The adsorption thermodynamic results illustrated the exothermicity and spontaneity of the adsorption reaction. The results of SNPs-CS recovery depicted its excellent recovery ability of removal efficiency with more than 90% after five consecutive adsorption and desorption cycles, which proved high potential of the produced bionanocomposite for industrial applications.

Isolation of Sensing Units and Adsorption Groups Based on MOF-on-MOF Hierarchical Structure for Both Highly Sensitive Detection and Removal of Hg2

Bifunctional materials have attracted ongoing interest in the field of detection and removal of contaminants because of their integration of two functions, but they exhibit commonly exceptional performance in only one of these two aspects. The interaction between the two functional units of the bifunctional materials may compromise their sensing and adsorption abilities. Guided by the concept of domain building blocks (DBBs), a hierarchical metal-organic framework (MOF)-on-MOF hybrid was designed by growing gold nanoclusters (AuNCs)-embedded zeolitic imidazolate framework 8 (AuNCs/ZIF-8) on the surface of Zr-MOF (UiO-66-NH2) for the simultaneous detection and removal of Hg2+. In the hybrid, the amino groups (-NH2) and AuNCs─which were the adsorption groups and sensing units, respectively, were isolated from each other. Specifically, the adsorption groups (-NH2) were assembled in the inner UiO-66-NH2 layer, while the sensing units (AuNCs) were confined in the outer ZIF-8 layer. This hierarchical structure not only spatially hindered the electron transfer between these two units but also triggered the aggregation-induced emission of AuNCs because of the confinement of ZIF-8 on the AuNCs, thus changing the fluorescence of AuNCs from quenching to enhancement. The newly prepared UiO-66-NH2@AuNCs/ZIF-8 hybrid, as expected, showed an ultralow detection limit (0.42 ppb) and a high adsorption capacity (129.9 mg·g-1) for Hg2+. Overall, this work provides a feasible approach to improve the integrated performance of MOF-based composites based on DBBs.

An Aryl-ether-linked Covalent Organic Framework Modified with Thioamide Groups for Selective Extraction of Palladium from Strong Acid Solutions

Efficient adsorption of palladium ions from acid nuclear waste solution is crucial for ensuring the safety of vitrification process for radioactive waste. However, the limited stability and selectivity of most current adsorbents hinder their practical applications under strong acid and intense radiation conditions. Herein, to address these limitations, we designed and synthesized an aryl-ether-linked covalent organic framework (COF-316-DM) grafted dimethylthiocarbamoyl groups on the pore walls. This unique structure endows COF-316-DM with high stability and exceptional palladium capture capacity. The robust polyarylether linkage enables COF-316-DM to withstand irradiation doses of 200 or 400 kGy of β/γ ray. Furthermore, COF-316-DM demonstrates fast adsorption kinetics, high adsorption capacity (147 mg g-1 ), and excellent reusability in 4 M nitric acid. Moreover, COF-316-DM exhibits remarkable selectivity for palladium ions in the presence of 17 interference ions, simulating high level liquid waste scenario. The superior adsorption performance can be attributed to the strong binding affinity between the thioamide groups and Pd2+ ions, as confirmed by the comprehensive analysis of FT-IR and XPS spectra. Our findings highlight the potential of COFs with robust linkers and tailored functional groups for efficient and selective capture of metal ions, even in harsh environmental conditions.