Preparation of phosphorylated iron-doped ZIF-8 and their adsorption application for U(VI)

Bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI): Enhanced adsorption capacity from the synergistic effect

Uranium and thorium of symbiotic relationship commonly appear in one kind of raw or spent ore. The simultaneous enrichment toward both metals in the first step is essential during many hydrometallurgy processing. Therefore bifunctional solid-state ionic liquid supported amidoxime chitosan (ACS) adsorbents were developed to simultaneously adsorb the two metal from the aqueous solution. The adsorption capacity of the bifunctional adsorbents toward uranium and thorium were significantly superior to the ionic liquid-free amidoxime chitosan, obviously proving the synergistic effect. For both uranium and thorium, the adsorption capacity in the consequence of ACS-[N4444][DEHP], ACS-[N4444][EHEHP], ACS-[N1888][DEHP] and ACS-[N1888][EHEHP] prove the steric effect and PO bonding played important roles in the adsorption. Study on isotherms and kinetics demonstrated the adsorption of ionic liquid-ACS adopted monolayer and chemical way. The ΔGo of very small negative values highlighted ionic liquid-ACS were prone to adsorb uranium and thorium. The study showed feasibility of bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI).

Zeolitic Imidazole Framework (ZIF)-Sponge Composite for Highly Efficient U(VI) Elimination

Herein, a zeolitic imidazole framework (ZIF-67) composite was prepared by a rapid, simple and inexpensive situ hybridization technique applying polyurethane sponge (PU) as support, which was designated as ZIF-67-PU. The ZIF-67 nanoparticle was successfully supported on the surface of sponge skeletons mainly through electrostatic attraction as well as probable π-π stacking interactions with PAM modification of the sponge. The resultant ZIF-67-PU exhibited a remarkably enhanced U(VI) elimination capacity of 150.86 mg∙g-1 on the basis of the Langmuir isotherm model, in comparison to pristine sponge. Additionally, the mechanism for U(VI) elimination was mainly achieved through the complex reaction between C-N(H)/-OH groups in ZIF-67 and U(VI), based on XPS investigations. ZIF-67-PU represents a simple, feasible and low-cost disposal option for preparing ZIF-coated sponges of any shape that can enhance the U(VI) elimination capacity. Furthermore, this approach can be widely applied to the preparation of various kinds of MOF-sponges through this situ hybridization technique.

Recyclable Fe/S co-doped nanocarbon derived from metal-organic framework as a peroxymonosulfate activator for efficient removal of 2,4-dichlorophenol

In this study, a recyclable Fe/S co-doped nanocarbon (Fe/S-NC) was successfully prepared by the pyrolysis of ZIF-8 confined with Fe(II) and added S. Characterization showed that a highly graphitized carbon-based material co-doped with sulfur and iron was successfully prepared. This Fe/S-NC can efficiently activate PMS to remove organic pollutants in water. The effect of different synthesis conditions on the degradation efficiency of 2,4-DCP was studied by orthogonal experiments. The optimized Fe/S-NC/PMS system exhibited excellent catalytic performance and could degrade more than 99.7% of 2,4-DCP within 30 min. Even after 5 cycles, the degradation efficiency could still be maintained above 96.3%, which proved that the catalytic system had good cycle performance. In addition, the effect of pH on catalytic performance showed that the degradation rate of 2,4-DCP exceeds 96.7% in the pH range of groundwater (pH = 5-9). We had confirmed that the free radicals that caused 2,4-DCP degradation were SO₄^·-, ·OH, O₂^·-, and ¹O₂, which played important roles in degrading organic pollutants. These research results show that the Fe/S-NC/PMS system can be used as an efficient, stable, and environmentally friendly system to treat organic pollutants in groundwater.

Adsorption performance and optimization by response surface methodology on tetracycline using Fe-doped ZIF-8-loaded multi-walled carbon nanotubes

Herein, an iron-doped ZIF-8-loaded multi-walled carbon nanotube (FZM) was synthesized and its adsorption performance on tetracycline (TC) was investigated. The experimental conditions (solution pH, temperature, adsorbent dose) were optimized by Box-Behnken design (BBD) in response surface methodology (RSM). The results show that the adsorption effect of TC by FZM is optimal under the conditions of temperature = 298 K, pH = 6, and contact time = 360 min. The adsorption processes of TC by FZM follow the pseudo-second-order (PSO) kinetic and Freundlich isotherm models, indicating that chemisorption is the dominant factor and the adsorption reaction is multi-layer, with a theoretical maximum saturation capacity of 1111.11 mg/g at 298 K. The adsorption thermodynamic results indicate that the adsorption of TC by FZM is a spontaneous and endothermic process. The mechanism of TC adsorption by FZM possibly occurs through hydrogen bonding, surface complexation, π-π interaction, and electrostatic interaction. From the statistical results, the optimal adsorption capacity of TC by FZM is 599.78 mg/g at a pH of 7.1, a temperature of 312.5 K, and an adsorbent dose of 64.43 mg/L, with a deviation of 1.73% from the actual value. Furthermore, regeneration experiments demonstrate that FZM has excellent reusability with a 15% loss of adsorption capacity after four cycles. This study provides some insights to study the adsorption behavior of TC by MOFs and the optimization of the adsorption experimental conditions, and also shows the potential of FZM for TC removal.

A Combined Experimental and Computational Study on the Adsorption Sites of Zinc-Based MOFs for Efficient Ammonia Capture

Ammonia (NH₃) is a common pollutant mostly derived from pig manure composting under humid conditions, and it is absolutely necessary to develop materials for ammonia removal with high stability and efficiency. To this end, metal–organic frameworks (MOFs) have received special attention because of their high selectivity of harmful gases in the air, resulting from their large surface area and high density of active sites, which can be tailored by appropriate modifications. Herein, two synthetic metal–organic frameworks (MOFs), 2-methylimidazole zinc salt (ZIF-8) and zinc-trimesic acid (ZnBTC), were selected for ammonia removal under humid conditions during composting. The two MOFs, with different organic linkers, exhibit fairly distinctive ammonia absorption behaviors under the same conditions. For the ZnBTC framework, the ammonia intake is 11.37 mmol/g at 298 K, nine times higher than that of the ZIF-8 framework (1.26 mmol/g). In combination with theoretical calculations, powder XRD patterns, FTIR, and BET surface area tests were conducted to reveal the absorption mechanisms of ammonia for the two materials. The adsorption of ammonia on the ZnBTC framework can be attributed to both physical and chemical adsorption. A strong coordination interaction exists between the nitrogen atom from the ammonia molecule and the zinc atom in the ZnBTC framework. In contrast, the absorption of ammonia in the ZIF-8 framework is mainly physical. The weak interaction between the ammonia molecule and the ZIF-8 framework mainly results from the inherent severely steric hindrance, which is related to the coordination mode of the imidazole ligands and the zinc atom of this framework. Therefore, this study provides a method for designing promising MOFs with appropriate organic linkers for the selective capture of ammonia during manure composting.

Prospective application of phosphorylated carbon nanofibers with a high adsorption capacity for the sequestration of uranium from ground water

In this study carbon nanofibers (CNF) were phosphorylated by using ortho-phosphoric acid and applied for adsorptive remediation of uranium from water. The phosphorylated carbon nanofibers (PCNF) showed 96% removal of uranium as compared to 79% by CNF. The adsorption data from batch adsorption studies fitted well with the Langmuir model and a maximum adsorption capacity of 512.8 mg g⁻¹ was obtained at pH 6.0 while the adsorption followed pseudo second order kinetics. A detailed characterisation of the adsorbent has been carried out using various analytical and spectroscopic tools. The application of the adsorbent to ground water samples exhibited promising results even in the presence of other interfering cations and anions which is imperative considering the toxic effects of uranium in ground water.

Adsorption of uranium at pH 6.0 using phosphorylated carbon nanofibers.

Adsorption of Phenol onto Aluminum Oxide Nanoparticles: Performance Evaluation, Mechanism Exploration, and Principal Component Analysis (PCA) of Thermodynamics

The removal of phenolic compounds from aqueous solutions using novel adsorption techniques becomes a key research item. Of those, nanoparticles in particular, the low-cost and the high-strength aluminum oxide nanoparticles showed promising results in pollutant uptake and increase in the adsorption efficiency. This study examined various physicochemical process parameters such as temperature, pH, initial phenol concentration, and adsorbent doses, in addition to the impact of those parameters on the adsorption removal mechanism of phenol. The results highlighted that aluminum oxide nanoparticles successfully exhibited superior phenol removal from an aqueous solution in addition to a high potential regeneration of the consumed nanoparticles by HCl. For the adsorbent mass of 0.5 g, phenol adsorption uptake reached 92%. Kinetic studies performed using several models demonstrated the data best fitting with a pseudo-second-order kinetic model. Examining equilibrium studies of various isotherms, the adsorption data of phenol into aluminum oxide nanoparticles was confirmed to be controlled by film diffusion and best represented by the Langmuir isotherm. The maximum capacity of adsorption was 16.97 mg/g. For thermodynamics studies, the results indicated that the adsorption process can vary between endothermic and exothermic reactions. Such relative differences in heat generation and spontaneity in adsorption processes were demonstrated and confirmed by principal component analysis (PCA). This evidence is key for future investigations for the efficiency of adsorption conditions concerning the contaminant type and adsorbate compounds.