Thiophene Separation with Silver-Doped Cu-BTC Metal–Organic Framework for Deep Desulfurization

Leveraging lewis acid and π-complexation to boost desulfurization efficiency in bimetallic Al/Cu(I)-MOF

The combustion of thiophene sulfides in fuel leads to the release of sulfur oxides (SOx), which pose significant threats to both ecological systems and human health. Adsorption desulfurization has gained considerable attention from researchers due to its mild operating conditions, low production costs, and minimal impact on octane number. This study investigates the use of Cu-BTC as a platform for developing a novel adsorbent aimed at efficiently removing thiophenic compounds from fuel. Aluminum atoms were incorporated into the framework of Cu-BTC to create micro/mesoporous Al/Cu-BTC. Subsequently, the π-complexation adsorbent Al/Cu(I)-BTC, featuring Lewis acid sites, was synthesized through the in-situ reduction of Al/Cu-BTC using sodium thiosulfate. The adsorption properties of Al/Cu(I)-BTC for thiophene were assessed through both batch and breakthrough experiments. Al/Cu(I)-BTC-0.10(0.28) demonstrated exceptional adsorption performance. The static and dynamic adsorption capacities of thiophene at 500 and 200 ppm were 18.54 mg S/g and 9.49 mg S/g, respectively. Importantly, the adsorption capacity of Al/Cu(I)-BTC-0.10 (0.28) for thiophene in fuel containing 500 ppm sulfur remained at 15.45 mg S/g after six regeneration cycles. In the competitive adsorption of toluene, the adsorption capacity of the adsorbent for thiophene in the fuel containing 200 ppm sulfur was 7.84 mg S/g.

Selective Separation of Thiophene Derivatives Using Metal-Organic Frameworks-Based Membranes

The removal of sulfur compounds, particularly thiophene derivatives, from oil is crucial due to concerns about environmental issues. Therefore, the deep desulfurization of transportation fuels is currently an urgent problem, and numerous attempts have been made in this direction. Membrane-based desulfurization can be a good alternative to the traditional hydrodesulfurization method, which has several limitations. In this work, the use of membranes containing a metal-organic framework, MOF-5, doped with transition metals (Ag, Cu, Ni), in the adsorptive desulfurization process was studied. The efficiency of membranes was evaluated based on selective removal of thiophene and dibenzothiophene from model oil. Characterization techniques, including scanning electron microscopic (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), confirmed the successful synthesis and incorporation of metal-organic frameworks (MOFs) into mixed matrix membranes (MMMs). Desulfurization experiments showed that MOF-5/Ag exhibited the highest thiophene adsorption efficiency (86.8%), outperforming MOF-5/Cu and MOF-5/Ni. The enhanced performance is attributed to the strong interaction between silver and sulfur. These findings demonstrate the potential of MOF-based MMMs for efficient and selective desulfurization, offering a viable alternative to traditional hydrodesulfurization (HDS) methods.

Fabrication of Unique Mixed-Valent CoICoII and CuICuII Metal-Organic Frameworks (MOFs) for Desulfurization of Fuels: A Combined Experimental and Theoretical Approach toward Green Fuel

Herein, metal-organic framework (MOF)-based adsorbents are designed with distinct hard and soft metal building units, namely, [Co2ICoII(PD)2(BP)] (Co_PD-BP) and [Cu2ICuII(PD)2(BP)] (Cu_PD-BP), where H2PD = pyrazine-1,4-diide-2,3-dicarboxylic acid and BP = 4,4'-bipyridine. The designed MOFs were characterized via spectral and SCXRD techniques, which confirm the mixed-valent states (+1 and +2) of the metal ions. Topological analysis revealed the rare ths and gwg topologies for Co MOF, while Cu-MOF exhibits a unique 8T21 topology in the 8-c net (point symbol for net: {424·64}). Moreover, severe environmental issues can be resolved by effectively removing heterocyclic organosulfur compounds from fuels via adsorptive desulfurization. Further, the developed MOFs were investigated for sulfur removal via adsorptive desulfurization from a model fuel consisting of dibenzothiophene (DBT), benzothiophene (BT), and thiophene (T) in the liquid phase using n-octane as a solvent. The findings revealed that Cu_PD-BP effectively removes the DBT with a removal efficiency of 86% at 300 ppm and an operating temperature of 25 °C, with a recyclability of up to four cycles. The adsorption kinetic analysis showed that the pseudo-first-order model could fit better with the experimental data indicating the physisorption process. Further, the studies revealed that adsorption capacity increased with the increasing initial DBT concentration with a remarkable capacity of 70.5 mg/g, and the adsorption process was well described by the Langmuir isotherm. The plausible reason behind the enhanced removal efficiency shown by Cu_PD-BP as compared to Co_PD-BP could be the soft-soft interactions between soft sulfur and soft Cu metal centers. Interestingly, density functional theory (DFT) studies were done in order to predict the mechanism of binding of thiophenic compounds with Cu_PD-BP, which further ascertained that along with other interactions, the S···π and S···Cu interactions predominate, resulting in a high uptake of DBT as compared to others. In essence, Cu_PD-BP turns out to be a promising adsorbent in the field of fuel desulfurization for the benefit of mankind.

Enhanced Desulfurization Performance of ZIF-8/PEG MMMs: Effect of ZIF-8 Particle Size

Constructing efficient and continuous transport pathways in membranes is a promising and challenging way to achieve the desired performance in the pervaporation process. The incorporation of various metal-organic frameworks (MOFs) into polymer membranes provided selective and fast transport channels and enhanced the separation performance of polymeric membranes. Particle size and surface properties are strongly related to the random distribution and possible agglomeration of MOFs particles, which may lead to poor connectivity between adjacent MOFs-based nanoparticles and result in low-efficiency molecular transport in the membrane. In this work, ZIF-8 particles with different particle sizes were physically filled into PEG to fabricate mixed matrix membranes (MMMs) for desulfurization via pervaporation. The micro-structures and physi-/chemical properties of different ZIF-8 particles, along with their corresponding MMMs, were systematically characterized by SEM, FT-IR, XRD, BET, etc. It was found that ZIF-8 with different particle sizes showed similar crystalline structures and surface areas, while larger ZIF-8 particles possessed more micro-pores and fewer meso-/macro-pores than did the smaller particles. ZIF-8 showed preferential adsorption for thiophene rather than n-heptane molecules, and the diffusion coefficient of thiophene was larger than that of thiophene in ZIF-8, based on molecular simulation. PEG MMMs with larger ZIF-8 particles showed a higher sulfur enrichment factor, but a lower permeation flux than that found with smaller particles. This might be ascribed to the fact that larger ZIF-8 particles provided more and longer selective transport channels in one single particle. Moreover, the number of ZIF-8-L particles in MMMs was smaller than the number of smaller ones with the same particle loading, which might weaken the connectivity between adjacent ZIF-8-L nanoparticles and result in low-efficiency molecular transport in the membrane. Moreover, the surface area available for mass transport was smaller for MMMs with ZIF-8-L particles due to the smaller specific surface area of the ZIF-8-L particles, which might also result in lower permeability in ZIF-8-L/PEG MMMs. The ZIF-8-L/PEG MMMs exhibited enhanced pervaporation performance, with a sulfur enrichment factor of 22.5 and a permeation flux of 183.2 g/(m^-2·h^-1), increasing by 57% and 389% compared with the results for pure PEG membrane, respectively. The effects of ZIF-8 loading, feed temperature, and concentration on desulfurization performance were also studied. This work might provide some new insights into the effect of particle size on desulfurization performance and the transport mechanism in MMMs.

Ag-exchanged mesoporous chromium terephthalate with sulfonate for removing radioactive methyl iodide at extremely low concentrations in humid environments

The development of efficient adsorbents to remove radioactive methyl iodide (CH₃I) in humid environments is crucial for air purification after pollution by nuclear power plant waste. In this work, we successfully prepared a post-synthetic covalent modified MIL-101 with a sulfonate group followed by the ion-exchange of Ag (I), which is well characterized by diffuse reflectance FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and the hydrophobic index (HI). After modification of the MOFs, we applied functionalized MIL-101 obtained by either one-pot synthesis (MIL-101-SO₃Ag) or a post-synthetic modification process (MIL-101-RSO₃Ag, R = NH(CH₂)₃) to remove the CH₃I at an extremely low concentration (0.31 ppm) in an environment with very high relative humidity (RH 95%). Enhanced hydrophobicity of the surface-modified MIL-101 was evaluated by examining the HI with the competitive adsorption of water and cyclohexane vapor, with a high surface area maintained, as confirmed by Ar physisorption. Interestingly, the post-synthetically modified MIL-101-RSO₃Ag showed exceptional adsorption performance as determined by its decontamination factor (DF = 195,350) at 303 K and RH 95%. This performance was in comparison to Ag (I)-exchanged 13X zeolite and MIL-101-SO₃Ag, which include much higher amounts of Ag. Furthermore, MIL-101-RSO₃Ag retained ~94-100% of its fresh adsorbent performance during five cycle repetitions.

Bimetallic Ag–Cu-trimesate metal–organic framework for hydrogen sulfide removal

Bimetallic Ag-Cu-trimesate metal-organic framework was fabricated for H2S mineralization. The MOF was partially regenerated using H2O2 solution for five cycles.

High-Efficiency Separation of Aromatic Sulfide from Liquid Hydrocarbon Fuel in Conjugated Porous Organic Framework with Polycarbazole Unit

We synthesized three conjugated polycarbazole porous organic frameworks named o-Cz-POF, m-Cz-POF, and p-Cz-POF for hydrocarbon fuels' adsorptive desulfurization. The carbazole building blocks possessed ortho, meta, and para steric configuration, which resulted in POFs exhibiting adjustable specific surface area and pore structure. Adsorption kinetics experiments and DFT calculations were carried out to understand the competitive adsorption of 3-methylthiophene and octane in the Cz-POF. The instantaneous adsorption rate and adsorption energy calculation analyses gave a convincing demonstration on preferential selective adsorption of 3-methylthiophene in Cz-POFs. Furthermore, the fixed bed breakthrough experiment demonstrated that the Cz-POFs can selectively adsorb 3-methylthiophene efficiently, and hydrocarbon fuel with sulfide content close to 0 ppm was obtained. The features of high stability and high desulfurization efficiency of Cz-POFs make them hold the promise as a new type of porous adsorbent for ultradeep adsorption desulfurization.

Dual-Purpose 3D Pillared Metal-Organic Framework with Excellent Properties for Catalysis of Oxidative Desulfurization and Energy Storage in Asymmetric Supercapacitor

This study proposes an approach for improving catalysis of oxidative desulfurization (ODS) of diesel fuel under mild reaction conditions and enhancing supercapacitor (SC) properties for storage of a high amount of charge. Our approach takes advantage of a novel dual-purpose cobalt(II)-based metal-organic framework (MOF), [Co(2-ATA)₂(4-bpdb)₄] _n (2-ATA: 2-aminoterephthalic acid and 4-bpdb: N, N-bis-pyridin-4-ylmethylene-hydrazine as the pillar spacer), which is called NH₂-TMU-53. Due to the stability of the used compound, we decided to evaluate the capability of this compound as a novel electrode material for storing energy in supercapacitors, and also to investigate its catalytic capabilities. It is demonstrated that the addition of H₂O₂ as an oxidant enhances the efficiency of sulfur removal, which indicates that NH₂-TMU-53 can efficiently catalyze the ODS reaction. According to the kinetics results, the catalyzed process follows pseudo-first-order kinetics and exhibits 15.57 kJ mol^-1 activation energy. Moreover, with respect to the radical scavenging evaluations, the process is governed by direct catalytic oxidation rather than indirect oxidative attack of radicals. Furthermore, NH₂-TMU-53 was applied as an electrode material for energy storage in SCs. This material is used in the three-electrode system and shows a specific capacitance of 325 F g^-1 at 5 A g^-1 current density. The asymmetric supercapacitor of NH₂-TMU-53//activated carbon evaluates the further electrochemical activity in real applications, delivers the high power density (2.31 kW kg^-1), high energy density (50.30 Wh kg^-1), and long cycle life after 6000 cycles (90.7%). Also, the asymmetric supercapacitor practical application was demonstrated by a glowing red light-emitting diode and driving a mini-rotating motor. These results demonstrate that the fabricated device presents a good capacity for energy storage without pyrolyzing the MOF structures. These findings can guide the development of high-performance SCs toward a new direction to improve their practical applications and motivate application of MOFs without pyrolysis or calcination.