A new approach for ultra-high adsorption of cationic methylene blue in a Zr-sulfonic-based metal-organic framework

Enhanced photoreduction efficiency of Cr(VI) driven by visible light in a new Zr-based metal-organic framework modified by hydroxyl groups

While metal-organic framework (MOF) photocatalysts have demonstrated a unique Cr(VI) photoreduction capability in recent decades, their performance is still insufficient for practical applications because of their low Cr(VI) uptake and poor visible light response. To cope with these drawbacks, a new OH-modified Zr-based MOF, termed HCMUE-1, was successfully prepared via a solvothermal method in this work. The complete characterization of HCMUE-1 was performed through various techniques, including powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared (FT-IR), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), scanning electron microscopy combined with energy-dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). The obtained data exhibited the excellent Cr(VI) photoreduction efficiency of HCMUE-1, reaching up to 98% after 90 min and almost 100% after 120 min under visible light illumination in a low acidic medium. Noteworthily, HCMUE-1 retained the same Cr(VI) removal rate for at least seven cycles without considerable loss. Further experimental investigations demonstrated that the structural stability and surface morphology of HCMUE-1 were retained after photoreduction. Moreover, the photocatalytic reduction mechanism of Cr(VI) to Cr(III) was interpreted through a series of systematic experimental measurements. These results indicate that HCMUE-1 possesses potential as an efficient photocatalyst for reducing toxic Cr(VI) species from wastewater in real-life conditions.

Influence of ZIF-9 and ZIF-12 structure on the formation of a series of new Co/N-doped porous carbon composites as anode electrodes for high-performance lithium-ion batteries

A series of new Co/N-doped porous carbon composites, denoted as Co/CZIF-9 and Co/CZIF-12, containing Co nanoparticles encapsulated in nitrogen-doped carbon matrices were prepared by annealing Co-based zeolite imidazolate framework materials, ZIF-9 and ZIF-12, as the efficient precursors at different temperatures. The structural features of the as-synthesized composites at 900 °C were determined by analytical methods with high reliability. Consequently, Co/CZIF-12_900 exhibits a high first specific discharge capacity of 971.0 mA h g^-1 at a current density of 0.1 A g^-1. Notably, the specific discharge/charge capacity of Co/CZIF-12_900 reaches about 508.8 mA h g^-1 at 0.1 A g^-1 after 100 cycles. The outstanding behaviors can be accounted for by the efficient incorporation of hetero-nitrogen doping and the Co nanoparticles within the layered structure of porous carbon, enhancing electrical conductivity and structural stability and limiting volume change during the intercalation/deintercalation of Li⁺ ions. These findings suggest that the Co/CZIF-12_900 material could be employed as a promising anode electrode for energy storage products.

Metal-Organic Framework-Based Materials for Wastewater Treatment: Superior Adsorbent Materials for the Removal of Hazardous Pollutants

In previous years, different pollutants, for example, organic dyes, antibiotics, heavy metals, pharmaceuticals, and agricultural pollutants, have been of note to the water enterprise due to their insufficient reduction during standard water and wastewater processing methods. MOFs have been found to have potential toward wastewater management. This Review focused on the synthesis process (such as traditional, electrochemical, microwave, sonochemical, mechanochemical, and continuous-flow spray-drying method) of MOF materials. Moreover, the properties of the MOF materials have been discussed in detail. Further, MOF materials' applications for wastewater treatment (such as the removal of antibiotics, organic dyes, heavy metal ions, and agricultural waste) have been discussed. Additionally, we have compared the performances of some typical MOFs-based materials with those of other commonly used materials. Finally, the study's current challenges, future prospects, and outlook have been highlighted.

Enhanced Methylene Blue Adsorption by Cu-BTC Metal-Organic Frameworks with Engineered Particle Size Using Surfactant Modulators

Metal–organic frameworks (MOFs) featuring porous structures and large specific surface areas have shown great potential in removing organic pollutants from wastewater via adsorption processes. Although the particle size of MOFs determines the adsorption performance (something known as the size-dependent effect), engineering it into desirable dimensions for enhancing the adsorption performance is a great challenge. Here, we develop a practical and facile approach to regulate the particle size of copper benzene-1,3,5-tricarboxylate (Cu-BTC) adsorbents with high tunability by screening the functional modulator of various surfactants adding in hydrothermal synthesis procedure. The effect of surfactant type and concentration on the particle size of Cu-BTC was systematically investigated. The results show that the nonionic surfactant polyvinylpyrrolidone (PVP) demonstrated the greatest ability to control the particle size of Cu-BTC among other counterparts (e.g., N, N, N-trimethyl-1-dodecanaminium bromide (DTAB), polyethylene glycol (PEG1000), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and hexadecyl trimethyl ammonium bromide (CTAB)). By increasing the PVP concentration to 0.14 mmol L−1, the average particle size of Cu-BTC could be correspondingly reduced by more than ten times, reaching to a comparative smaller value of 2.4 μm as compared with the reported counterparts. In addition, the PVP allowed a large increase of the surface area of Cu-BTC according to porosity analysis, resulting in a great enhancement of methylene blue (MB) adsorption. The PVP-modulated Cu-BTC showed fast adsorption kinetics for MB removal accompanied with a maximum adsorption capacity of 169.2 mg g−1, which was considerably competitive with most of the analogs reported. Therefore, our study may inspire concepts for engineering the particle size of Cu-BTCs with improved properties for more practical applications.

Enhancing the remarkable adsorption of Pb2+ in a series of sulfonic-functionalized Zr-based MOFs: a combined theoretical and experimental study for elucidating the adsorption mechanism

A series of Zr-based metal-organic frameworks was prepared via the solvothermal route using sulfonic-rich linkers for the efficient capture of Pb²⁺ ions from aqueous medium. The factors affecting adsorption such as the solution pH, adsorbent dosage, contact time, adsorption isotherms, and mechanism were studied. Consequently, the maximum adsorption capacity of Pb²⁺ on the acidified VNU-23 was determined to be 617.3 mg g^-1, which is much higher than that of previously reported adsorbents and MOF materials. Furthermore, the adsorption isotherms and kinetics of the Pb²⁺ ion are in good accordance with the Langmuir and pseudo-second-order kinetic model, suggesting that the uptake of Pb²⁺ is a chemisorption process. The reusability experiments demonstrated the facile recovery of the H⁺⊂VNU-23 material through immersion in an HNO₃ solution (pH = 3), where its Pb²⁺ adsorption efficiency still remained at about 90% of the initial uptake over seven cycles. Remarkably, the adsorption mechanism was elucidated through a combined theoretical and experimental investigation. Accordingly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy connected to energy-dispersive X-ray mapping (SEM-EDX-mapping), and X-ray photoelectron spectroscopy (XPS) analysis of the Pb⊂VNU-23 sample and comparison with H⁺⊂VNU-23 confirmed that the electrostatic interaction occurs via the interaction between the SO₃^- moieties in the framework and the Pb²⁺ ion, leading to the formation of a Pb-O bond. In addition, the density functional theory (DFT) calculations showed the effective affinity of the MOF adsorbent toward the Pb²⁺ ion via the strong driving force mentioned in the experimental studies. Thus, these findings illustrate that H⁺⊂VNU-23 can be employed as a potential adsorbent to eliminate Pb²⁺ ions from wastewater.

A confinement of N-heterocyclic molecules in a metal–organic framework for enhancing significant proton conductivity

A series of N-heterocyclic⊂VNU-23 materials have been prepared via the impregnation procedure of N-heterocyclic molecules into VNU-23. Their structural characterizations, PXRD, FT-IR, Raman, TGA, ¹H-NMR, SEM-EDX, and EA, confirmed that N-heterocyclic molecules presented within the pores of parent VNU-23, leading to a remarkable enhancement in proton conductivity. Accordingly, the composite with the highest loading of imidazole, Im_13.5⊂VNU-23, displays a maximum proton conductivity value of 1.58 × 10⁻² S cm⁻¹ (85% RH and 70 °C), which is ∼4476-fold higher than H⁺⊂VNU-23 under the same conditions. Remarkably, the proton conductivity of Im_13.5⊂VNU-23 exceeds the values at 85% RH for several of the reported high-performing MOF materials. Furthermore, Im_13.5⊂VNU-23 can retain a stable proton conductivity for more than 96 h, as evidenced by FT-IR and PXRD analyses. These results prove that this hybrid material possesses potential applications as a commercial proton exchange membrane fuel cell.

A series of N-heterocyclic⊂VNU-23 materials have been prepared via the impregnation procedure of N-heterocyclic molecules into VNU-23.

A new porphyrinic vanadium-based MOF constructed from infinite V(OH)O4 chains: syntheses, characterization and photoabsorption properties

A new porphyrinic vanadium-based metal–organic framework (MOF), namely V-MOF-10 [V2(OH)2(H2TCPP)], constructed from {V(OH)O4}∞ chains and 4-tetracarboxyphenylporphyrin linkers, was synthesized by a solvothermal procedure.

Engineering of appropriate pore size combined with sulfonic functionalization in a Zr-MOF with reo topology for the ultra-high removal of cationic malachite green dye from an aqueous medium

A Zr-based metal–organic framework with reo topology, denoted as Reo-MOF-1, was fabricated through a solvothermal method capable of efficiently removing the cationic MG dye from an aqueous medium.