Mo3 S13 2- Intercalated Layered Double Hydroxide: Highly Selective Removal of Heavy Metals and Simultaneous Reduction of Ag+ Ions to Metallic Ag0 Ribbons.

We demonstrate a new material by intercalating Mo3 S13 2- into Mg/Al layered double hydroxide (abbr. Mo3 S13 -LDH), exhibiting excellent capture capability for toxic Hg2+ and noble metal silver (Ag). The as-prepared Mo3 S13 -LDH displays ultra-high selectivity of Ag+ , Hg2+ and Cu2+ in the presence of various competitive ions, with the order of Ag+ >Hg2+ >Cu2+ >Pb2+ ≥Co2+ , Ni2+ , Zn2+ , Cd2+ . For Ag+ and Hg2+ , extremely fast adsorption rates (≈90 % within 10 min, >99 % in 1 h) are observed. Much high selectivity is present for Ag+ and Cu2+ , especially for trace amounts of Ag+ (≈1 ppm), achieving a large separation factor (SFAg/Cu ) of ≈8000 at the large Cu/Ag ratio of 520. The overwhelming adsorption capacities for Ag+ (qm Ag =1073 mg g-1 ) and Hg2+ (qm Hg =594 mg g-1 ) place the Mo3 S13 -LDH at the top of performing sorbent materials. Most importantly, Mo3 S13 -LDH captures Ag+ via two paths: a) formation of Ag2 S due to Ag-S complexation and precipitation, and b) reduction of Ag+ to metallic silver (Ag0 ). The Mo3 S13 -LDH is a promising material to extract low-grade silver from copper-rich minerals and trap highly toxic Hg2+ from polluted water.

Polypyrrole-Mo3S13: An Efficient Sorbent for the Capture of Hg2+ and Highly Selective Extraction of Ag+ over Cu2.

The new material Polypyrrole-Mo3S13 (abbr. Mo3S13-Ppy) is a new material prepared by ion-exchange between Ppy-NO3 and (NH4)2Mo3S13. The Mo3S13-Ppy was designed to exhibit strong selectivity for Ag+ and highly toxic Hg2+ in mixtures with other ions. It displays an apparent selectivity ranking of Hg2+ > Ag+ ≥ Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+. The strong affinity of Mo3S13-Ppy for Ag+ and Hg2+ was confirmed with extremely high distribution coefficients (Kd) (∼107 mL/g) and remarkable removal efficiencies (>99.99%), resulting in <1 ppb concentrations of these ions. Furthermore, Mo3S13-Ppy achieved excellent separation selectivity for Ag+ from Cu2+ (even at a high Cu2+/Ag+ ratio, the molar ratio of 867 and mass ratio of 500) because of the special structure of Mo3S132- and its component Mo4+ and (S2)2-. This is promising for the direct extraction of low-grade silver from copper-rich minerals. The maximum Ag uptake capacity of 408 mg/g is redox-based and surprisingly involves the deposition of large, millimeter sized, metallic silver (Ag0) crystals on the surface of Mo3S13-Ppy.

Hierarchical microsphere assembled by nanoplates embedded with MoS2 and (NiFe)S x nanoparticles as low-cost electrocatalyst for hydrogen evolution reaction.

The development of low-cost electrocatalysts with high performance is important to provide sustainable hydrogen energy. In this work, via one-step sulfuration of [Formula: see text] intercalated NiFe-layered double hydroxide (abbr. NiFe-MoO4-LDH), hierarchical microspheres are assembled by intersecting nanoplates (15-30 nm in thickness) which are then decorated with MoS2 and (NiFe)S x nanoparticles (∼25 nm in size). The NiFe-MoO4-LDH is synthesized beforehand by a one-pot hydrothermal reaction. Under sulfuration at 300 °C, 400 °C and 600 °C, the NiFe-MoO4-LDH transforms into multi-metal sulfides of NiFeMoS-T (T is applied temperature). During sulfuration, the confinement effect of LDH limits the growth of metal sulfides, causing formation of nanoparticles of MoS2 and (NiFe)S x to expose more catalytic active sites. In an alkaline medium, NiFeMoS-400 depicts superior performance for hydrogen evolution reaction (HER), giving an overpotential of 210 mV at 10 mA cm-2. A Tafel slope of 88 mV dec-1 indicates a mixed Volmer-Heyrovsky rate-determining step. The electrode also maintains long-term electrochemical durability during 15 h electrolysis at 25 mA cm-2. The NiFe-MoO4-LDH precursor owns three metal elements (Ni, Fe and Mo), which ensure the formation of polymetallic sulfides, and maximum utilization of the LDH layer and interlayer metals contributes to the optimal electrocatalytic activity. The NiFeMoS nanoassembly is a potential low-cost and high-efficiency electrocatalyst.

Hierarchical Nanoassembly of MoS2/Co9S8/Ni3S2/Ni as a Highly Efficient Electrocatalyst for Overall Water Splitting in a Wide pH Range.

The design of low-cost yet high-efficiency electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) over a wide pH range is highly challenging. We now report a hierarchical co-assembly of interacting MoS2 and Co9S8 nanosheets attached on Ni3S2 nanorod arrays which are supported on nickel foam (NF). This tiered structure endows high performance toward HER and OER over a very broad pH range. By adjusting the molar ratio of the Co:Mo precursors, we have created CoMoNiS-NF- xy composites ( x: y means Co:Mo molar ratios ranging from 5:1 to 1:3) with controllable morphology and composition. The three-dimensional composites have an abundance of active sites capable of universal pH catalytic HER and OER activity. The CoMoNiS-NF-31 demonstrates the best electrocatalytic activity, giving ultralow overpotentials (113, 103, and 117 mV for HER and 166, 228, and 405 mV for OER) to achieve a current density of 10 mA cm-2 in alkaline, acidic, and neutral electrolytes, respectively. It also shows a remarkable balance between electrocatalytic activity and stability. Based on the distinguished catalytic performance of CoMoNiS-NF-31 toward HER and OER, we demonstrate a two-electrode electrolyzer performing water electrolysis over a wide pH range, with low cell voltages of 1.54, 1.45, and 1.80 V at 10 mA cm-2 in alkaline, acidic, and neutral media, respectively. First-principles calculations suggest that the high OER activity arises from electron transfer from Co9S8 to MoS2 at the interface, which alters the binding energies of adsorbed species and decreases overpotentials. Our results demonstrate that hierarchical metal sulfides can serve as highly efficient all-pH (pH = 0-14) electrocatalysts for overall water splitting.

Highly efficient capture of uranium from seawater by layered double hydroxide composite with benzamidoxime.

Through swelling/restoration reaction, benzamidoxime (BAO) is introduced into MgAl-LDH interlayers to assemble a new composite of MgAl-BAO-LDH (abbr. BAO-LDH). Wet samples of the BAO-LDH obtained by washing with diverse solvents are present in colloidal state, which facilitates the fabrication of thin film adsorbents convenient for actual application. After drying, the assembled sample exhibits floral morphology composed of thin nanosheets, much different from hexagonal morphology of NO3- intercalated MgAl-LDH precursor (NO3-LDH), demonstrating a phenomenon rarely found in swelling/restoration. The BAO-LDH depicts an extremely large maximum sorption capacity (qmU) of 327 mg·g-1 and ultra-high selectivity for U. At low U concentrations (5-10 ppm), nearly complete capture (~100%) is achieved in a wide pH range of 3-11, while at high U concentrations (110 ppm), quite high U removals (≥93.0%) are obtained at pH = 6-8, meaning perfect suitability for trapping U from seawater. For natural seawater containing trace amounts of U (3.93 ppb) coexisting with high concentration of competitive ions, the BAO-LDH displays significantly high U removal (87%). Complexation between interlayer BAO (N and O as ligands) with UO22+ and synergistic interactions of LDH layer hydroxyls with UO22+ contribute to the highly effective uranium capture. All results demonstrate the BAO-LDH is a promising adsorbent applied in seawater uranium extraction and nuclear wastewater disposal.

SDC/OS-LDH composite for highly sensitive fluorescence detection of Fe3+ at a much lower concentration.

In this work, we demonstrate the tunable luminescence of newly synthesized SDC/OS Mg/Al-LDH composites (SDC is 4,4'-stilbenedicarboxylic acid; OS is 1-octanesulfonic acid sodium; LDH is layered double hydroxide) and their application in fluorescence sensing to detect Fe(iii) ions. Through an ion-exchange method, the SDC2- and OS- anions with changed molar ratios are intercalated into the LDH interlayers to obtain composites of SDCxOS1-x-LDH (x = 0.02, 0.05, and 0.10). In the solid state, the optimized SDC0.05OS0.95-LDH exhibits a blue emission (441 nm) with a 54 nm blue-shift compared with SDC-Na solid salt (495 nm). In a delaminated state, the colloidal suspension of SDC0.05OS0.95-LDH in formamide (FM) also gives a blue emission at 444 nm in comparison to the 451/468 nm emissions of the FM solution of free SDC2- anions, and the luminescence intensity of the exfoliated composite is ∼28 times higher than that of the SDC2- anions. The SDC0.05OS0.95-LDH composite could be utilized in chemical fluorescence sensing for detecting Fe3+ ions. In aqueous solutions with extremely low Fe3+ concentrations of 0.18-1.78 µM (0.01-0.1 ppm), the composite gives a large quenching constant of 2.34 × 105 M-1, and an ultralow detection limit of 6.12 × 10-8 M. This work may provide a highly effective while simple method for the detection of Fe3+ in a small concentration range.

Layered rare-earth hydroxide (LRH, R = Tb, Y) composites with fluorescein: delamination, tunable luminescence and application in chemosensoring for detecting Fe(iii) ions.

We demonstrate a novel example of tunable luminescence and the application of the delaminated FLN/OS-LRH composites (LRHs are layered rare-earth hydroxides, R = Tb, Y; FLN is the fluorescein named 2-(6-hydroxy-3-oxo-(3H)-xanthen-9-yl)benzoic acid; OS is the anionic surfactant 1-octane sulfonic acid sodium) in detecting Fe(iii) ions. The FLNxOS1-x species (x = 0.02, 0.05, 0.10, and 0.20) are intercalated into the LTbyY1-yH layers (y = 1, 0.9, 0.7, 0.5, 0.3, 0.1 and 0) by ion exchange reactions to yield the composites FLNxOS1-x-LTbyY1-yH. In the solid state, the LYH composites display green emission (564 nm) arising from the organic FLN, while in LTbH composites, the luminescence of the Tb3+ in the layers (545 nm) and the FLN in the interlayers is co-quenched. In the delaminated state in formamide (FM), FLNxOS1-x-LTbH composites display green to yellowish-green luminescence (540-574 nm) following the increasing FLN/OS ratio; while the FLN0.02OS0.98-LTbyY1-yH composites show green emission at ∼540 nm. The fluorescence lifetimes of the composites (4.22-4.63 ns) are comparable to the free FLN-Na, and the quantum yields (31.62-78.70%) of the composites especially that (78.70%) of the FLN0.02OS0.98-LYH are much higher than that (28.40%) of free FLN-Na. The recognition ability of the FLN0.02OS0.98-LYH composite for metal cations is researched. The delaminated FLN0.02OS0.98-LYH colloidal suspension exhibits high selectivity for Fe3+ over other ions (Mg2+, Al3+, Ni2+, Co2+, Cu2+, Zn2+, Mn2+, Pb2+, and Cd2+) with fluorescence quenching, which can work as a kind of turn-off fluorescence sensor for the detection of Fe3+. The detection limit of Fe3+ is determined to be 2.58 × 10-8 M and the quenching constant (Ksv) is 1.70 × 103 M-1. This is the first work on LRH materials working as a chemosensor for recognising metal cations. It provides a new approach for the design of LRH materials to be applied in fluorescence chemosensing.