Recovery of HMF from aqueous solution by zeolitic imidazolate frameworks

Recovery of 2,3-Butanediol from Fermentation Broth by Zeolitic Imidazolate Frameworks

The efficient separation of the 2,3-butanediol (2,3-BDO) intermediate from fermentation broth is an important issue in the production of biofuels from biomass-derived intermediates. Two zeolitic imidazolate frameworks ZIF-8 and ZIF-71 were investigated for the adsorption of 2,3-butanediol (2,3-BDO) from fermentation broth via liquid breakthrough adsorption measurements. While both ZIF materials initially show high separation performance, ZIF-71 retains robust separation performance even after aging in ethanol for two years, whereas the capacity of ZIF-8 decreases significantly. The robustness and stability of ZIF-71 are further confirmed with cyclic fixed bed adsorption measurements. The uptake of 2,3-BDO on ZIF-71 reaches >100 g/kg with negligible uptakes of sugars, organic acids, and other alcohols present in the fermentation broth. Excellent selectivity toward 2,3-BDO over water is also achieved. The 2,3-BDO-loaded ZIF-71 can be regenerated efficiently with ethanol as desorbent. These findings indicate that ZIF-71 shows considerable promise as an adsorbent to recover and purify diols from fermentation broths.

Mn-doped bimetallic synergistic catalysis boosts for enzymatic phosphorylation of N-Acetylglucosamine/ N-Acetylgalactosamine and their derivatives

Metal-organic frameworks (MOFs), as advanced enzyme immobilization platforms for improving biocatalysis and protein biophysics, are rarely investigated as solid supports in the enzymatic synthesis of carbohydrate and derivatives, which can be attributed to the complex biochemical reaction mechanisms and the adverse interactions between the high polarity of substrate sugars, glycoenzymes and traditional MOFs. Here, we introduced divalent metal ion Mn²⁺ into MOF to prepare bimetallic MOF microreactor that encapsulated N-acetylhexosamine 1-Kinase (NahK), a critical anomeric kinase involved in the enzymatic synthesis of sugar nucleotide. The introduced Mn ions not only adjusted the microstructure of MOFs, but also participated in the enzymatic catalysis as cofactor, thus facilitated the N-acetylglucosamine/ N-acetylgalactosamine (GlcNAc/GalNAc) phosphorylation. The Mn-doped NahK@Zn-metal organic material (MOM), integrated with high catalytic activity, high stability, and high recoverability, solved the issues of immobilization related to glucokinase activity. These features significantly improved the operability and reduced the processing cost, assuring industrial application prospects for sugar nucleotides synthesis.

Produced Water Treatment with Conventional Adsorbents and MOF as an Alternative: A Review

A large volume of produced water (PW) has been produced as a result of extensive industrialization and rising energy demands. PW comprises organic and inorganic pollutants, such as oil, heavy metals, aliphatic hydrocarbons, and radioactive materials. The increase in PW volume globally may result in irreversible environmental damage due to the pollutants' complex nature. Several conventional treatment methods, including physical, chemical, and biological methods, are available for produced water treatment that can reduce the environmental damages. Studies have shown that adsorption is a useful technique for PW treatment and may be more effective than conventional techniques. However, the application of adsorption when treating PW is not well recorded. In the current review, the removal efficiencies of adsorbents in PW treatment are critically analyzed. An overview is provided on the merits and demerits of the adsorption techniques, focusing on overall water composition, regulatory discharge limits, and the hazardous effects of the pollutants. Moreover, this review highlights a potential alternative to conventional technologies, namely, porous adsorbent materials known as metal-organic frameworks (MOFs), demonstrating their significance and efficiency in removing contaminants. This study suggests ways to overcome the existing limitations of conventional adsorbents, which include low surface area and issues with reuse and regeneration. Moreover, it is concluded that there is a need to develop highly porous, efficient, eco-friendly, cost-effective, mechanically stable, and sustainable MOF hybrids for produced water treatment.

Synthesize optimization, characterization, and application of ZIF-8 adsorbent for elimination of olive oil from aqueous solution

In view of the importance of water quality and environmental aspect, zeolitic imidazolate framework-8 (ZIF-8) adsorbent was synthesized via a solvothermal approach for oil removal from water. Response surface methodology-central composite design approach (RSM-CCD) using a statistical software (Design expert, version 8.0.6) was employed to identify the influence of three independent variables of ZIF-8 synthesis procedure including ligand/salt molar ratio, solvent/salt molar ratio, and synthesis temperature on the oil adsorption capacity and yield of adsorbent as RSM responses. The optimum conditions for preparing ZIF-8 were found as follows: ligand/salt molar ratio of 10.4, solvent/salt ratio of 702.7, and temperature of 52.9 °C, which resulted in 1120 mg/g of olive oil uptake and 43% of ZIF-8 yield. Morphological and structural properties of the prepared adsorbent were characterized by N₂ adsorption-desorption, XRD, FE-SEM, and FTIR analyses. Batch equilibrium adsorption experiments were conducted under varied system parameters expected to affect the ZIF-8 adsorption capacity including oil concentration, ZIF-8 dosage, contact time, and temperature. The isotherm and kinetic of olive oil adsorption onto ZIF-8 followed the Freundlich and pseudo-first-order models, respectively. The evaluation of thermodynamic parameters demonstrated that olive oil adsorption onto optimized ZIF-8 was spontaneous and exothermic in nature. In addition, the used ZIF-8 can be recovered effectively using a simple ethanol-washing method. Based on experimental results, the ZIF-8 prepared in this study can be successfully used in oil/water emulsion separation.

Tuning of Delicate Host-Guest Interactions in Hydrated MIL-53 and Functional Variants for Furfural Capture from Aqueous Solution

Capture of high-boiling-point furfural from diluted aqueous solution is a critical but challenging step in sustainable bio-refinery processes, but conventional separation methods such as distillation and liquid-liquid extraction requires prohibitive energy consumption. We report control over the microenvironment of hydrated MIL-53 and isoreticular variants with diversified functional terephthalic acid linkers for the purpose of preferential binding of furfural through delicate host-guest interactions. Methyl-bounded MIL-53 with improved binding energy in the hydrated form results in highly efficient capture ratio (ca. 98 %) in the extremely low concentration of furfural solution (0.5-3 wt %) and 100 % furfural specificity over xylose. The distinct hydrogen bonding sites and multiple Van de Wall interactions for furfural adsorption was testified by computational modeling. Furthermore, the recovery ratio of furfural reaches ca. 93 % in desorption.

Adsorption isotherm, kinetics simulation and breakthrough analysis of 5-hydroxymethylfurfural adsorption/desorption behavior of a novel polar-modified post-cross-linked poly (divinylbenzene-co-ethyleneglycoldimethacrylate) resin

A polar modified post-cross-linked poly (divinylbenzene-co-ethyleneglycol-dimethacrylate) (PCL-PDE) resin was synthesized by suspension polymerization of ethylene glycol dimethacrylate (EGDMA) and divinylbenzene (DVB), and a post-cross-linked reaction. After characterization, the adsorption behaviors of 5-hydroxymethylfurfural (5-HMF) on PCL-PDE resin were determined in comparison with the starting copolymers PDE resin. The equilibrium adsorption capacity of 5-HMF on PCL-PDE resin was much larger than PDE resin and the increase rate was greater than 52.6%. The equilibrium data of 5-HMF onto PCL-PDE resin were found to be better fitted by the Langmuir isotherm model. The kinetic data shows that the adsorption reached equilibrium in a short time (less than 20 min) can be fitted by the pore diffusion model (PDM) at various operating conditions. The effective pore diffusion coefficient was dependent upon adsorption temperature, and were 6.706 × 10^-10, 8.958 × 10^-10, 1.136 × 10^-9 and 1.429 × 10^-9 m² s^-1 at 288, 298, 308 and 318 K, respectively. Furthermore, the effects of feed flow rate (Q_f = 0.6, 1.5, 3.0 and 6.0 mL min^-1) and initial 5-HMF concentration (c_f = 0.52, 1.02, 2.00 and 4.96 g L^-1) on the adsorption were investigated systematically. Besides, a general rate model (GRM) was used to predict adsorption breakthrough curves of 5-HMF. The simulation results are highly consistent with the experimental data, indicating that the GRM can successfully simulate this process. In the desorption process, the desorption capacity reaches 99.6% of adsorbed capacity, suggesting that the PCL-PDE resin exhibited good reusability. Therefore, it could be suggested that the PCL-PDE resin has a potential application in the separation and purification of 5-HMF.

A Simple Step toward Enhancing Hydrothermal Stability of ZIF-8

ZIF-8 is a flexible zeolitic imidazole-based metal-organic framework and has been extensively studied because of its high structural stability. However, ZIF-8 is hydrolyzed in water at higher temperature, resulting in degradation of its crystalline and porous structure. In order to prevent ZIF-8 from structural collapse due to the hydrolysis reaction of the metal-ligand bond and/or ligand substitution reaction, it is effective to shield the metal-ligand bond from the attack of water molecules. This work reports on the thermal and hydrothermal stability of mechanochemically synthesized ZIF-8 and presents an incredibly simple step to modify the outermost surface of ZIF-8, improving the hydrothermal stability. The partial carbonization resulting in the formation of a carbon-rich outermost layer endowed ZIF-8 with not only high hydrothermal stability but also a high adsorption rate on liquid phase adsorption.

Deep oxidative desulfurization of model fuels catalysed by immobilized ionic liquid on MIL-100(Fe)

Deep desulfurization of fossil fuels has become urgently required because of the serious pollution by the large-scale use of fossil fuels. In this study, [PrSO₃HMIm]HSO₄@MIL-100(Fe) was synthesized by wet-impregnation of the ionic liquid (IL) of [PrSO₃HMIm]HSO₄ on MIL-100(Fe). The construction of [PrSO₃HMIm]HSO₄@MIL-100(Fe) was then confirmed by X-ray powder diffraction, N₂ adsorption-desorption experiments, infrared spectroscopy and elemental analysis, and then applied in the oxidative desulfurization of model fuels. In comparison with the corresponding IL, [PrSO₃HMIm]HSO₄@MIL-100(Fe) showed an enhanced performance in the desulfurization rate of model fuels due to the increase of the mass transfer rate. Under the optimized conditions (oxidant to sulphur ratio = 25, oil to acetonitrile ratio = 1, and temperature = 60 °C), a sulphur removal rate of 99.3% was observed (initial sulphur concentration = 50 ppm). The sulphur removal of three sulphur compounds by catalytic oxidation and extraction followed the order of dibenzothiophene (DBT) > thiophene (T) > benzothiophene (BT).

Upconversion of Cellulosic Waste Into a Potential "Drop in Fuel" via Novel Catalyst Generated Using Desulfovibrio desulfuricans and a Consortium of Acidophilic Sulfidogens

Biogas-energy is marginally profitable against the "parasitic" energy demands of processing biomass. Biogas involves microbial fermentation of feedstock hydrolyzate generated enzymatically or thermochemically. The latter also produces 5-hydroxymethyl furfural (5-HMF) which can be catalytically upgraded to 2, 5-dimethyl furan (DMF), a "drop in fuel." An integrated process is proposed with side-stream upgrading into DMF to mitigate the "parasitic" energy demand. 5-HMF was upgraded using bacterially-supported Pd/Ru catalysts. Purpose-growth of bacteria adds additional process costs; Pd/Ru catalysts biofabricated using the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans were compared to those generated from a waste consortium of acidophilic sulfidogens (CAS). Methyl tetrahydrofuran (MTHF) was used as the extraction-reaction solvent to compare the use of bio-metallic Pd/Ru catalysts to upgrade 5-HMF to DMF from starch and cellulose hydrolyzates. MTHF extracted up to 65% of the 5-HMF, delivering solutions, respectively, containing 8.8 and 2.2 g 5-HMF/L MTHF. Commercial 5% (wt/wt) Ru-carbon catalyst upgraded 5-HMF from pure solution but it was ineffective against the hydrolyzates. Both types of bacterial catalyst (5wt%Pd/3-5wt% Ru) achieved this, bio-Pd/Ru on the CAS delivering the highest conversion yields. The yield of 5-HMF from starch-cellulose thermal treatment to 2,5 DMF was 224 and 127 g DMF/kg extracted 5-HMF, respectively, for CAS and D. desulfuricans catalysts, which would provide additional energy of 2.1 and 1.2 kWh/kg extracted 5-HMF. The CAS comprised a mixed population with three patterns of metallic nanoparticle (NP) deposition. Types I and II showed cell surface-localization of the Pd/Ru while type III localized NPs throughout the cell surface and cytoplasm. No metallic patterning in the NPs was shown via elemental mapping using energy dispersive X-ray microanalysis but co-localization with sulfur was observed. Analysis of the cell surfaces of the bulk populations by X-ray photoelectron spectroscopy confirmed the higher S content of the CAS bacteria as compared to D. desulfuricans and also the presence of Pd-S as well as Ru-S compounds and hence a mixed deposit of PdS, Pd(0), and Ru in the form of various +3, +4, and +6 oxidation states. The results are discussed in the context of recently-reported controlled palladium sulfide ensembles for an improved hydrogenation catalyst.

Vapor- and Liquid-Phase Adsorption of Alcohol and Water in Silicalite-1 Synthesized in Fluoride Media

In this work, batch-adsorption experiments and molecular simulations are employed to probe the adsorption of binary mixtures containing ethanol or a linear alkane-1,n-diol solvated in water or ethanol onto silicate-1. Since the batch-adsorption experiments require an additional relationship to determine the amount of solute (and solvent adsorbed, as only the bulk liquid reservoir can be probed directly, molecular simulations are used to provide a relationship between solute and solvent adsorption for input to the experimental bulk measurements. The combination of bulk experimental measurements and simulated solute-solvent relationship yields solvent and solute loadings that are self-consistent with simulation alone, and allow for an assessment of the various assumptions made in literature. At low solution concentrations, the solute loading calculated is independent of the assumption made. At high concentrations, a negligent choice of assumption can lead to systematic overestimation or underestimation of calculated solute loading.

A combined experimental-computational investigation on water adsorption in various ZIFs with the SOD and RHO topologies

Our results demonstrated that the contribution of vdW interactions is negligible and the contribution of electrostatic interactions plays a dominant role in the water adsorption in ZIFs.

Ionic Liquid/Metal-Organic Framework Composites: From Synthesis to Applications

Metal-organic frameworks (MOFs) have been widely studied for different applications owing to their fascinating properties such as large surface areas, high porosities, tunable pore sizes, and acceptable thermal and chemical stabilities. Ionic liquids (ILs) have been recently incorporated into the pores of MOFs as cavity occupants to change the physicochemical properties and gas affinities of MOFs. Several recent studies have shown that IL/MOF composites show superior performances compared with pristine MOFs in various fields, such as gas storage, adsorption and membrane-based gas separation, catalysis, and ionic conductivity. In this review, we address the recent advances in syntheses of IL/MOF composites and provide a comprehensive overview of their applications. Opportunities and challenges of using IL/MOF composites in many applications are reviewed and the requirements for the utilization of these composite materials in real industrial processes are discussed to define the future directions in this field.

Adsorptive removal of phenol from aqueous solution with zeolitic imidazolate framework-67

ZIF-67(zinc-methylimidazolate framework-67), one of the zeolitic imidazolate frameworks (ZIFs), was used for the removal of phenol from aqueous solutions via adsorption and shows high adsorption capacity for phenol. The thermodynamic and kinetic adsorption behavior of ZIF-67 for phenol in water with concentration ranging from 50 to 300 ppm were investigated in a batch reactor and a ZIF-67 packed column, respectively. The effects of pH, contact time, zeta potential of the adsorbent and temperature on the adsorption behavior were evaluated, and the results demonstrated that the adsorption is primarily brought about by a specific favorable interaction (electrostatic interaction) between phenol and ZIF-67 surface. The suitability of the Langmuir adsorption model to the equilibrium data was investigated for each phenol-adsorbent system, which the results showed that the equilibrium data for all the phenol-sorbent systems fitted the Langmuir model. Thermodynamic parameters such as Gibbs free energy are calculated from the experimental data at different temperatures. The adsorbent could be perfectly regenerated at 120 °C with little loss in the adsorption ability.

Applications of water stable metal–organic frameworks

A comprehensive review is given on the applications of water stable metal–organic frameworks in areas of adsorption, membrane separation, sensing, catalysis, and proton conduction.

Superior removal of arsenic from water with zirconium metal-organic framework UiO-66

In this study, water stable zirconium metal-organic framework (UiO-66) has been synthesized and for the first time applied as an adsorbent to remove aquatic arsenic contamination. The as-synthesized UiO-66 adsorbent functions excellently across a broad pH range of 1 to 10, and achieves a remarkable arsenate uptake capacity of 303 mg/g at the optimal pH, i.e., pH = 2. To the best of our knowledge, this is the highest arsenate As(V) adsorption capacity ever reported, much higher than that of currently available adsorbents (5-280 mg/g, generally less than 100 mg/g). The superior arsenic uptake performance of UiO-66 adsorbent could be attributed to the highly porous crystalline structure containing zirconium oxide clusters, which provides a large contact area and plenty of active sites in unit space. Two binding sites within the adsorbent framework are proposed for arsenic species, i.e., hydroxyl group and benzenedicarboxylate ligand. At equilibrium, seven equivalent arsenic species can be captured by one Zr6 cluster through the formation of Zr-O-As coordination bonds.