Construction of an ultra-sensitive electrochemical sensor based on polyoxometalates decorated with CNTs and AuCo nanoparticles for the voltammetric simultaneous determination of dopamine and uric acid.

A composite modified electrode was prepared based on α-K7P2VW17O62·18H2O (P2W17V), CNTs and AuCo nanoparticles (AuCo NPs), and used as a structurally stable and highly sensitive electrochemical sensor for simultaneous determination of dopamine (DA) and uric acid (UA). The combination of three active components endows the electrode with large specific surface area, high electrical conductivity, and excellent electrochemical activity. The as-prepared modified electrode exhibited impressive electrocatalytic oxidation performance of DA and UA at an optimum working potential (0.172 V vs. Ag/AgCl for DA and 0.288 V vs. Ag/AgCl for UA) with linear detection range from 1.25 × 10-6 to 2.81 × 10-4 M and 0.75 × 10-6 to 1.66 × 10-4 M and the detection limit of 0.15 and 0.25 µM (S/N = 3) for DA and UA, respectively. Additionally, the peak-to-peak separation signals in DPV are 116 mV. The influence of several possible co-existing substances was investigated. The applicability of the method for real samples analysis was tested by determination of DA and UA in human serums. This new sensor holds great promise for sensitive determination of DA and UA in real application. Graphical abstract.

Water-locking molecule-assisted fabrication of nature-inspired Mg(OH)2 for highly efficient and economical uranium capture.

With the depletion of uranium terrestrial deposits, researchers have focused on the development of adsorbents to extract radioactive uranium from seawater/wastewater. However, the artificial manipulation of adsorbents for the cost-effective extraction of radioactive uranium from large numbers of water samples is still significantly challenging. Herein, a facile yet versatile stepwise strategy has been reported for the fabrication of adsorbents. Magnesium hydroxide (Mg(OH)2) was fabricated via the in situ conversion of a natural ore powder (magnesite), whose unique internal pore structure is highly suitable for the development of highly efficient sorbents. The coordination interaction of the synthesized adsorbent with uranium was enhanced by further introducing inexpensive molecules with water-locking properties, which resulted in superior extraction capacity and low production cost. After careful calculation, the cost per kilogram of the adsorbent was found to be about $0.21. The adsorption behaviors of the synthesized adsorbent CMC-PAM/Mg(OH)2 were investigated by batch adsorption, flow-through column adsorption (in laboratory), and field adsorption experiments in natural seawater and river. Representatively, CMC-PAM/Mg(OH)2 was exceptional in extracting uranium not only at high concentrations with sufficient capacities in a wide pH range (1584.67 mg g-1 and 454.55 mg g-1 at pH = 5 and pH = 8, respectively), but also in trace quantities including uranium in a flow-through column (55.68 mg g-1), natural seawater (8.6 mg g-1), and river (6.7 mg g-1). Inspired by this excellent performance, the effects of competitive ions on the selective adsorption of uranium by CMC-PAM/Mg(OH)2 in simulated wastewater and seawater environments were further studied. Using a combination of FTIR spectroscopic and XPS studies, it was revealed that the amine and hydroxyl groups enhanced the overall uranyl affinity of the CMC-PAM/Mg(OH)2 composite.

Anti-Biofouling and Water-Stable Balanced Charged Metal Organic Framework-Based Polyelectrolyte Hydrogels for Extracting Uranium from Seawater.

Metal-organic frameworks (MOFs) are diffusely defined as a promising class of porous material for uranium extraction from seawater, but there are still challenges in their stability and anti-biofouling performance. Herein, a water-stable and anti-biofouling ZIF-67/SAP0.45 composite hydrogel was reported by the sequential processes of electrostatic interactions between the oppositely charged polymer, ionic gelation, and template growth of ZIF-67 crystals. Entanglement of positively charged polyethyleneimine (PEI) and negatively charged sodium alginate (SA) polymer chains provided external porosities, anti-biofouling properties, and mechanical support for the hydrogels and further reduced the possibility of ZIF-67 aggregation. The neutral composite hydrogel possessed the least Nitzschia on the surface after 7 days contact, which endows the adsorbent with a high uranium uptake capacity of 2107.87 ± 41.64 µg g-1 at 1 mg L-1 uranium-containing seawater with 8.6 × 105 mL-1 Nitzschia. Additionally, this adsorbent showed water stability with an uranium uptake capacity of 232.88 ± 8.02 mg g-1 even after five adsorption-desorption cycles because of the excellent preparation method. Benefitting from the distinctive hierarchical structure and large accessible surface area, the resultant adsorbent achieved a high uranium capacity of 6.99 ± 0.26 mg g-1 in real seawater. This flexible and scalable approach made the MOF/SAP composite hydrogel a highly desirable uranium adsorbent.

Mussel-inspired anti-biofouling and robust hybrid nanocomposite hydrogel for uranium extraction from seawater.

A major challenge of uranium extraction from seawater (UES) is to effectively block the biofouling without destroying the ecological balance, especially prevent the attachment of macroalgae on the surface of the adsorbent. Herein, a robust montmorillonite-polydopamine/polyacrylamide nanocomposite hydrogel is reported by a two-step method, including PDA intercalation MMT and further free radical polymerization with AM monomers. The interpenetrating structure of hydrogel lead to high water permeability with the swelling ratio of 51, which could fully facilitate the internal accessible sites exposure and increase the uranium diffusion. As a result, a high adsorption capacity of 44 mg g-1 was achieved in lab-scale dynamic adsorption. Most importantly, the prepared anti-biofouling hydrogel adsorbents display excellent anti-adhesion ability towards Nitzschia after 8 days contact. The adsorption capacity of uranium can reach 2130 µg g-1 in algae-contained simulated seawater. This hydrogel also exhibited a long service life of acceptable mechanical strength and adsorption capacity after at least 6 adsorption-desorption cycles. This new anti-biofouling nanocomposite hydrogel shows great potential as a new generation adsorbent for UES.

Benzimidazole-containing aramid nanofiber for naked-eye detection of heavy metal ions.

The rapid detection of heavy metal ions in wastewater has received significant attention in modern society. Herein, we report the exploration of benzimidazole-containing aramid fibers (B-ANF) for the naked-eye detection of heavy metal ions in aqueous solution. Firstly, B-ANF was prepared by hydroxylation from benzimidazole-containing aramid fiber. The unique benzimidazole unit endows the nanofiber with the ability to coordinate with multiple kinds of heavy metal ions. When B-ANF comes in contact with trace heavy metal ions in solution, the coordination interaction induces rapid aggregation, which can be detected by the naked eye within 2 minutes. Therefore, it provides an easy and time-saving strategy for the detection of heavy metal ions. In addition, B-ANF could be used for the rapid detection of total concentration of heavy metals ions in the presence of multiple kinds of heavy metal ions, which makes up for the shortage of traditional methods and shows prospects for broad application. Lastly, it was noticed that B-ANF, after the detection of heavy metal ions, could be readily recycled by an HCl/NaOH treatment, with the detection efficiency being completely preserved after the recycling process. It is believed that B-ANF integrates the advantages of low cost, easy transportation and naked-eye detection of heavy metal ions, and could be used as promising recyclable detector for heavy metal ions.