Facile Upcycling of Hazardous Cr-Containing Electroplating Sludge into Value-Added MetalOrganic Frameworks for Efficient Adsorptive Desulfurization

The recycling of heavy metals from solid wastes and transforming these metals into useful materials, such as metal oxides, nanocomposites, and metal–organic frameworks (MOFs), are beneficial for both sustainable development and environmental protection. MOFs are promising for adsorptive desulfurization, owing to their extremely high surface areas and tunable structures. In this paper, for the first time, MIL-53(Cr) was successfully fabricated from electroplating sludge (EPS) as a metal source through a facile hydrothermal method with and without HF. Our synthetic method is novel, green, scalable, and time-efficient. The obtained MIL-53(Cr) was employed as an adsorbent for adsorptive dibenzothiophene removal from liquid fuel. MIL-53(Cr) with HF exhibits a higher desulfurization capacity (40.11 mg g–1) than that of MIL-53(Cr) without HF (32.80 mg g–1). The improved adsorption performance of MIL-53(Cr) with HF is attributed to adding a small amount of HF, which produces highly crystalline and relativity pure MIL-53(Cr) microrods with a high surface area and porosity, and is due to a robust metal–sulfur interaction. Furthermore, the regenerated adsorbent can retain 94% of its initial sulfur adsorption capability even after 5 cycles, implying that MIL-53(Cr) prepared from Cr-EPS is an efficient adsorbent for fuel desulfurization. This study provides new insight for the production of high-value-added MOF materials from solid wastes following the principle of “resource reuse”

Facile Upcycling of Hazardous Cr-Containing Electroplating Sludge into Value-Added Metal–Organic Frameworks for Efficient Adsorptive Desulfurization

The recycling of heavy metals from solid wastes and transforming these metals into useful materials, such as metal oxides, nanocomposites, and metal–organic frameworks (MOFs), are beneficial for both sustainable development and environmental protection. MOFs are promising for adsorptive desulfurization, owing to their extremely high surface areas and tunable structures. In this paper, for the first time, MIL-53(Cr) was successfully fabricated from electroplating sludge (EPS) as a metal source through a facile hydrothermal method with and without HF. Our synthetic method is novel, green, scalable, and time-efficient. The obtained MIL-53(Cr) was employed as an adsorbent for adsorptive dibenzothiophene removal from liquid fuel. MIL-53(Cr) with HF exhibits a higher desulfurization capacity (40.11 mg g–1) than that of MIL-53(Cr) without HF (32.80 mg g–1). The improved adsorption performance of MIL-53(Cr) with HF is attributed to adding a small amount of HF, which produces highly crystalline and relativity pure MIL-53(Cr) microrods with a high surface area and porosity, and is due to a robust metal–sulfur interaction. Furthermore, the regenerated adsorbent can retain 94% of its initial sulfur adsorption capability even after 5 cycles, implying that MIL-53(Cr) prepared from Cr-EPS is an efficient adsorbent for fuel desulfurization. This study provides new insight for the production of high-value-added MOF materials from solid wastes following the principle of “resource reuse”

Designing of technological scheme for conversion of Cr-rich electroplating sludge into the black ceramic pigments of consistent composition, following the principles of circular economy

Development of method for the complete conversion of Cr-containing electroplating sludge (ES) into the black inorganic pigment was presented. Difficulties related to the ES complex, variable composition and inhomogeneity, where the dominant presence of Cr was followed by: Fe, P, Zn, Ni, Cu, etc., can be overcome by determination of the precise amount of Fe2O3 necessary to be added in order to firmly embed all the heavy metals into the pigment structure (i.e. the Fe0.7Cr1.3O3/FePO4 nanocomposite), taking care not only about weight/molar ratios, but also about average particle size, apparent densities, and volume fraction of the starting materials. As a source of Fe2O3, commercial (p.a.) Fe2O3 and two different Fe-wastes were used, thus completely fulfilling the principles of the circular economy. The obtained black inorganic pigments have consistent composition, no leaching of toxic metals, color (CIE L-a-b-values) comparable with those of commercial pigments and thus have the potential commercial large scale application. © 2021 Elsevier Ltd

Optimized scalable synthesis and granulation of MIL-88B(Fe) for efficient arsenate removal

Arsenic contamination has adverse health effects on human, and metal-organic frameworks (MOFs) are suitable adsorbents for its removal. The small-scale synthesis and high cost hindered the application of MOFs in arsenic removal. The challenge resulted from the strict synthesis conditions, like harsh temperature or pressure and the use of toxic organic solvents such as N, N-Dimethylformamide, etc. We reported herein an optimized method for scalable synthesis of MIL-88B(Fe) in innocuous ethanol solvent under benign conditions (low temperature, normal pressure, and no pretreatment of reactants). Synthetic parameters, such as the ratio of reactants, temperature, reaction time, and purification process, were optimized to achieve scalable preparation of the product. The scale-up produced MIL-88B(Fe) presents extraordinary adsorption capacity (128.99 mg/g) towards toxic arsenate in water. Furthermore, we shaped the MOFs powder into millimeter-scale granules by using the bio-compatible binding agents and flash freezing treatment. The composite also outperforms in arsenate adsorption capacity than that of commercially available products. Additionally, a 250-hours dynamic column adsorption operation proves that the composite can guarantee a safe concentration level of arsenate effluent. The well-shaped porous structure of composite facilitates its application and avoids secondary pollution in real scenarios, demonstrating applicable prospects as filters for water purification

Exploring UiO-66(Zr) frameworks as nanotraps for highly efficient removal of EDTA-complexed heavy metals from water

Metal-organic frameworks (MOFs), an exciting class of porous crystalline materials, are suitable for adsorptive removal of toxic heavy metal-ethylenediaminetetraacetic acid (M-EDTA) complexes from wastewater. In this paper, water-stable UiO-66(Zr) with well-defined morphology was successfully synthesized through a facile microwave-assisted solvothermal method and employed as nanotraps for the efficient capture of the three M-EDTA complexes, Cu-EDTA, Pb-EDTA, and Ni-EDTA. The adsorption behaviors, effects of solution pH and co-existing anions, as well as the eluant and desorption were investigated. The obtained UiO-66(Zr) showed good stability and excellent uptake capacity of M-EDTA in a wide pH range (3.0-10.0). UiO-66(Zr) exhibited a higher removal efficiency of Cu-EDTA (57.56 mg/g), Pb-EDTA (120.6 mg/g), and Ni-EDTA (54.27 mg/g). Based on the overall analysis results, our findings show that EDTA-metal complex ions can be adsorbed inside UiO-66(Zr) mainly through the Lewis-acid/-base interactions and possible anion-πinteraction with strong binding energies. Size-matching EDTA-metal complexes confined in the UiO-66(Zr) with flexible geometry would also contribute to the fast adsorption kinetics as well as the selective adsorption of different M-EDTA complexes. © 2020 Elsevier Ltd

Metal-Organic Frameworks Derived Catalyst for High-Performance Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is one of the most promising technologies for grid-scale energy storage applications because of its numerous attractive features. In this study, metal-organic frameworks (MOF)-derived catalysts (MDC) are fabricated using carbonization techniques at different sintering temperatures. Zirconium-based MOF-derived catalyst annealed at 900 °C exhibits the best electrochemical activity toward VO2+/VO2+ redox couple among all samples. Furthermore, the charge-discharge test confirms that the energy efficiency (EE) of the VRFB assembled with MOF-derived catalyst modified graphite felt (MDC-GF-900) is 3.9% more efficient than the VRFB using the pristine graphite felt at 100 mA cm−2. Moreover, MDC-GF-900 reveals 31% and 107% higher capacity than the pristine GF at 80 and 100 mA cm−2, respectively. The excellent performance of MDC-GF-900 results from the existence of oxygen-containing groups active sites, graphite structure with high conductivity embedded with zirconium oxide, and high specific surface area, which are critical points for promoting the vanadium redox reactions. Because of these advantages, MDC-GF-900 also possesses superior stability performance, which shows no decline of EE even after 100 cycles at 100 mA cm−2

Ta₂O₅‑Nanoparticle-Modified Graphite Felt As a High-Performance Electrode for a Vanadium Redox Flow Battery

To increase the electrocatalytic activity of graphite felt (GF) electrodes in vanadium redox flow batteries (VRFBs) toward the VO₂⁺/VO²⁺ redox couple, we prepared a stable, high catalytic activity and uniformly distributed hexagonal Ta₂O₅ nanoparticles on the surface of GF by varying the Ta₂O₅ content. Scanning electron microscopy (SEM) revealed the amount and distribution uniformity of the electrocatalyst on the surface of GF. It was found that the optimum amount and uniformly immobilized Ta₂O₅ nanoparticles on the GF surface provided the active sites, enhanced hydrophilicity, and electrolyte accessibility, thus remarkably improved electrochemical performance of GF. In particular, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that the Ta₂O₅-GF nanocomposite electrode with a weight percentage of 0.75 wt % of Ta₂O₅ to GF exhibited the best electrochemical activity and reversibility toward the VO₂⁺/VO²⁺ redox reaction, when compared with the other electrodes. The corresponding energy efficiency was enhanced by ∼9% at a current density of 80 mA cm^–2, as compared with untreated GF. Furthermore, the charge–discharge stability test with a 0.75 wt % Ta₂O₅-GF electrode at 80 mA cm^–2 showed that, after 100 cycles, there was no obvious attenuation of efficiencies signifying the best stability of Ta₂O₅ nanoparticles, which strongly adhered on the GF surface