Ag clusters and nanoparticles have attracted much attention in the fields of environmental catalysis and pollutant removal. It is a common strategy to fabricate highly dispersed Ag nanoparticles in porous scaffolds via in situ growth. Here, anionic metal–organic frameworks (MOFs) have been employed to provide robust supports for Ag species. Ag nanoparticles with well-defined sizes are observed in MOFs when internal NH2Me2+ is exchanged with extrinsic Ag+ ions. The extended X-ray absorption fine structure and X-ray photoelectron spectroscopy spectra confirm that about 20% of Ag+ are reduced into Ag0, while the rest 80% are still Ag+ species. The comparison of Ag loading into anionic and neutral Cu-BTC MOFs suggests that the exchangeable cations facilitate Ag+ migration into the interior of MOFs and thus alleviate its aggregation and spontaneous reduction. Besides, the adsorption tests verify that all the Ag species in MOFs are accessible to iodine vapor to form AgI. The charge transfer from frameworks to trapped iodine and the water in the air promote the formation of iodide ions, which react with Ag+ to produce AgI. The iodine adsorption performance of MOF beads was also evaluated using the pore diffusion model. This work provides insights into the evolution of Ag species in MOFs and potential Ag-based adsorbents for radioiodine capture. 

Silver Ion-Exchanged Anionic Metal–Organic Frameworks for Iodine Adsorption: Silver Species Evolution from Ions to Nanoparticles

Interest in functional silver has rapidly grown over the years due to significant advances in separation, sensing, catalysis, and biomedical applications. Here we developed a new strategy to load single atomic silver species in the rigid and open unit of the fully conjugated benzimidazole-linked polymers (BILPs). Due to the well-defined chelating units of N-heterocycles, the Ag+ ion species can be coordinated by N ligands and stabilized in the atomic level without aggregating into nanoscale Ag clusters and nanoparticles. The obtained Ag+-BILP-101 exhibits a selective binding property of Ag+ ions from solutions. The ultrastable structure and the property of taking up metal species, endow BILPs with the advantages of functionalizing metal species. After the reduction by NaBH4, the Ag+ ions were transferred into Ag nanoparticles. The substantial and intrinsic porosity of BILPs also gives excellent accessibility to Ag species loaded in the frameworks. The plentiful N-heterocycles and loaded Ag species show a synergistic/coadsorption effect for iodine vapor, and the charge transfer from frameworks promotes the formation of iodide ions. The iodine capture capacities of Ag+-BILP-101 and Ag0-BILP-101 reach 3.3 g/g and 3.7 g/g at 80 ℃, and still maintain 3.2 g/g and 3.5 g/g at 150 ℃, respectively. After ethanol elution, the residual iodine/Ag molar ratios in Ag+/Ag0-BILP-101 samples are still more than one (about 1.5), suggesting their strong affinity toward iodine. This work highlights the excellent selective Ag+ ion binding and Ag species supporting properties of BILPs, which can extend to other porous organic framework platforms for various applications based on silver species-skeleton interactions. 

High-efficient Ag(I) Ion Binding, Ag(0) Nanoparticle Loading, and Iodine Trapping in Ultrastable Benzimidazole-linked Polymers

Metal–organic structures have great potential for practical applications in many areas. However, their widespread use is often hindered by time-consuming and expensive synthesis procedures that often involve hazardous solvents and, therefore, generate wastes that need to be remediated and/or recycled. The development of cleaner, safer, and more sustainable synthesis methods is extremely important and is needed in the context of green chemistry. In this work, a facile mechanochemical method involving water-assisted ball milling was used for the synthesis of MOF-303. The obtained MOF-303 exhibited a high specific surface area of 1180 m2/g and showed an excellent CO2 adsorption capacity of 9.5 mmol/g at 0 °C and under 1 bar. 

Mechanochemical Synthesis of MOF-303 and Its CO2 Adsorption at Ambient Conditions

Under a facile one-step hydrothermal reaction by changing thiourea dosage to regulate sulfidation degree of nickel foam (NF), a variety of nickel sulfide composites of n-NixSy/NF (1-Ni3S2/NF, 3-Ni3S2 and 6-Ni3S2/Ni9S8) were prepared and utilized to capture iodine for the first time. The compositions and structures of the composites and their influence on iodine adsorption performance were elaborated in detail. During adsorption, Ni0 in NF and Ni0/S2− in Ni3S2/Ni9S8 both served as reducing agents to achieve the chemisorption for iodine, where the Ni0 and S2− were oxidized to Ni2+ and elemental S0 (S8), and the I2 molecules were reduced to I− which then reacted with the Ni2+ to form NiI2. The 1-Ni3S2/NF, 3-Ni3S2 and 6-Ni3S2/Ni9S8 exhibited different iodine adsorption capacities (qmI) of 1442, 1109 and 420 mg/g for iodine vapor, and 1191, 869 and 296 mg/g for iodine in solutions, respectively, giving the largest qmI of 1442 (for I2 vapor) and 1191 mg/g (for I2 in solution) by 1-Ni3S2/NF. The capture mechanism for iodine in solution was mainly by chemisorption, while for iodine vapor, profiting from the three-dimensional skeleton of NF, besides the chemisorption, physical sorption also played a role. After γ irradiation, the structures of n-NixSy/NF were well-maintained and iodine adsorption performance did not deteriorate, indicating the good radiation resistance. This work provides an important reference for tailoring new kinds of cost-effective sorbents to trap iodine from radioactive nuclear wastes. 

NixSy/NF composites assembled by sulfidation of nickel foam (NF) for highly effective capture of iodine

Locating high active metal species into idea support surface to form spatially integrated nanostructure is essential for the adsorption and excitation process of water molecules. In this work, we proposed a spatial confinement strategy through incorporating Au nanoparticles into metal-organic framework (MOF) to realize low humidity sensing detection. We found the porous nature of MOF-303 morphology can provide confined room to induce Au species accumulation around the high active hydrophilic pocket (composed by three μ2-OH groups and two N(H)). In-situ Raman results further indicate the spatially-close Au species and hydrophilic pocket sites could synergistically promote chemical adsorption of water molecules and proton transfer processes. The as-fabricated Au@MOF-303 humidity sensor exhibits ultra-high response at low humidity condition (4345 Hz to 3.39 % RH), low humidity hysteresis (0.18 % RH), excellent repeatability and selectivity. Furthermore, the Au@MOF-303 sensor enables real-time monitoring of breathing signals attached to the surgical mask and the proximity of the fingertips. 

Incorporating Au nanoparticles into metal-organic framework for low humidity sensors

Cu-loaded MOF-303 for Iodine Adsorption: The Roles of Cu Species and Pyrazole Ligands

Non-evaporable getter films are essential to obtain the ultra-high vacuum environments for the modern accelerators. However, regular thermal activation of the NEG films is required to maintain their pumping capacity. The thermal activation rises the risk of deteriorating the film/substrate adhesion, which, unfortunately, has been overlooked. In the present work, ternary Ti-Zr-V films were deposited by DC magnetron sputtering on oxygen free copper (OFC) and Si substrates. The effect of thermal cycling on the microstructure and adhesion strength of the thin films were characterized. The results indicate that thermal cycling induce an increased surface roughness due to coarsening of the particle size. Contrary effect is imposed on the adhesion strength of the NEG film deposited on the OFC substrate as compared with that on the Si substrate. After thermal cycling, the scratching critical load of the Ti-Zr-V film on OFC decreases from 0.14 N to 0.06 N while those on Si substrate increased by tenfold from 0.56 N to 5.79 N. The current work is insightful on long-term maintenance of the NEG coated chambers from an angle different from the commonly emphasized pumping capabilities. 

Effect of thermal cycling on microstructure and adhesion properties of Ti-Zr-V thin films

Manipulating the mechanical strength and thermal conductivity of a Mg-4Zn-0.6Zr alloy through Ca addition

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Cu-loaded MOF-303 for Iodine Adsorption: The Roles of Cu Species and Pyrazole Ligands

Effect of thermal cycling on microstructure and adhesion properties of Ti-Zr-V thin films

Manipulating the mechanical strength and thermal conductivity of a Mg-4Zn-0.6Zr alloy through Ca addition