In-situ growing ZIF-8 on cellulose nanofibers to form gas separation membrane for CO2 separation

Ce-MOF-based superhydrophobic nancellulose composite membrane with rapid photocatalytic properties and continuous oil-water separation

The discharge of oily wastewater and sewage in industry and life was increasing, seriously affecting the sustainability of the environment and ecosystem. In this work, a multifunctional superhydrophobic nanocellulose-based membrane was prepared by spraying Ce-MOF nanoparticles onto the nanocellulose membrane, which had a hydrostatic contact angle of up to 170°: (i) Resistance to harsh conditions (including high temperatures, abrasion, ultraviolet light exposure, bending, and self-cleaning); (ii) Achieve efficient separation of mixed oil and water. It has shown commendable efficacy in separating wastewater containing mixed oils. The separation flux of mixed oil wastewater was 179 L·m-2·h-1 (n-hexane and chloroform/water), and the separation efficiency was >94 % (n-hexane and chloroform/water); (iii) Efficient and rapid photocatalytic removal of pollutants, which is a useful property to prevent organic pollution; (iv) Effectively prevent biological pollutants adhesion, reducing the amount of microbial adhesion by 67.74 %. In many fields, such as industrial production and urban sewage treatment, wastewater treatment in harsh environments as well as the durability of materials has always been an issue. The appearance of this new material provides a feasible solution to this problem.

MIL-125@ZIF-8 based solid phase microextraction coating for sensitive determination of organophosphate esters in aqueous environments

A novel MOF-on-MOF heterostructure (MIL-125@ZIF-8) was synthesized and utilized as a coating material for solid-phase microextraction (SPME), which was subsequently coupled with gas chromatography (GC) for the sensitive determination of organophosphate esters (OPEs) in water samples. Compared to commercial fiber, the MIL-125@ZIF-8 coated fiber (MIL-125@ZIF-8-F) demonstrated superior extraction performance for medium-polar or non-polar compounds due to multiple interactions such as hydrophobic interaction, π-π stacking, and hydrogen bonding. The synergistic effect of MIL-125 and ZIF-8 endowed the MIL-125@ZIF-8-F with high efficiency and excellent stability under extreme conditions. Specifically, the developed MIL-125@ZIF-8-F could withstand 80 conditioning cycles without significant loss of extraction capacity. Moreover, the established method exhibited a wide linear range (10-1000 μg L-1), low detection limits (0.03-0.20 μg L-1), and excellent reproducibility under optimized condition. Finally, this proposed method provided a promising approach for the efficient enrichment of trace OPEs in actual environmental water samples.

Advances in CO2 separation from the landscape of porous aromatic framework-based engineered membranes

Uncontrolled carbon emission contributes significantly towards global warming and climate change necessitating an urgent and effective remedy. CO2 is one of the major constituents of the greenhouse gas family. The main sources that contribute to CO2 emission are industries, transports, etc., where CO2 gets emitted with other gases. Before released into the environment, effective separation of CO2 from mixture gases can lessen its direct environmental exposure. Traditional techniques for CO2 separation include adsorption, absorption, cryogenic distillation, and membrane separation. Membrane technology is advantageous in CO2 separation due to its excellent properties like energy efficiency, affordability, durability, scalability, processing simplicity, and high separation efficiency. Advancements in membrane materials have introduced various advanced materials among which porous aromatic frameworks (PAFs) are proven highly applicable in gas separation. PAFs are a branch of engineered porous materials that offer excellent porosity, substantial surface area, homogeneous pore size, room for structural modification, and anti-aging properties. PAF-based membranes are widely used in various CO2 separation applications; mostly in natural gas purification and flue gas treatment. This review article has discussed synthetic routes of PAFs, structural modification techniques, membrane applications, and mechanisms in the context of CO2 separation. The current status of PAF-based membranes is briefly highlighted from an economic and industrial point of view. Future directions for PAF-based membranes such as functionalization or integration of PAFs with other materials/nanomaterials to create hybrid materials with greater CO2-phillicity are discussed. Moreover, potential aspects to consider in the near future associated with PAF syntheses are also highlighted.

In situ growth of defective ZIF-8 on TEMPO-oxidized cellulose nanofibrils for rapid response release of curcumin in food preservation

Uncontrolled release of active agents in active packaging reduces antimicrobial efficacy, hindering the effective protection of perishable products from microbial infection. Herein, a novel defective engineering was proposed to design defective and hollow ZIF-8 structures grown on TEMPO oxidized cellulose nanofibrils (TOCNFs) and use them as fast-reacting nanocarriers for loading and controlled release curcumin (Cur) in sodium alginate (SA) active packaging systems (CZT-Cur-SA). By employing stable chelation between tannic acid (TA) and ZIF-8 zinc ions, the connections between zinc ions and imidazole ligands were severed to form a loose and hollow structure, which facilitates the rapid reaction and release of active ingredients triggered by pH changes in the microenvironment. Kinetic tests showed CZT-Cur-SA films released 65.68 % of Cur at pH 6.0 within 24 h, compared to 28.26 % at pH 7.0. These films demonstrated exhibited excellent mechanical properties, antioxidation capacity (82.59 %), reinforced moisture (0.51 × 10-10 g m-1 s-1 Pa-1) and satisfied antimicrobial effects on E. coli (1.69 %) and S. aureus (0.88 %). The optimized CZT-Cur-SA film extended strawberry shelf life to at least 7 days under ambient conditions. Our findings introduce a promising approach to designing responsive, biodegradable active packaging for enhanced food safety.

Nanocellulose composites based on embedded europium-containing coordination polymers for the detection of antibiotics

Developing sensitive and reliable methods for detecting antibiotics in water solutions is essential for protecting public health and the environment. Here, we report a novel fluorescent film with superior mechanical properties and detection response to ciprofloxacin (CIP), achieved through the in-situ growth of europium-based metal-organic frameworks on TEMPO-oxidized cellulose nanofibrils (TOCNF). Firstly, Eu(III) and 2,6-pyridinedicarboxylic acid (DPA) served as precursors, and a simple self-assembly strategy was employed to grow the composite film material (Eu-DPA@TOCNF) in situ on TOCNF, which exhibited characteristic emission peaks. Benefiting from the growth balance and control of Eu-DPA by TOCNF, the sensor based on Eu-DPA@TOCNF showed higher stability and practicability, allowing sensitive and selective detection of CIP, with a good linear relationship in the range of 0-200 μM, showing an inverse relationship between the fluorescence intensity at 619 nm and CIP concentration. The quenching mechanism of CIP on Eu-DPA@TOCNF could be attributed to the combined effects of both static and dynamic quenching processes. Consequently, the Eu-DPA@TOCNF fluorescent film provides a novel strategy for developing pollutant detection sensors based on fluorescent specificity.

Promoted electrochemical performance by MOF on MOF composite catalyst of microbial fuel cell: CuCo-MOF@ZIF-8 and the comparison between two-step hydrothermal method and dual-solution method

The microbial fuel cell (MFC) is a device that simultaneously achieves electricity generation and sewage degradation. In this study, a novel cathode catalyst metal-organic frameworks (MOFs) have been fabricated by two-step hydrothermal and dual-solution method (CuCo-MOF@ZIF-8). The synthesized trimetal MOFs exhibited a 3D badminton-like structure morphology and porosity. The results of the characterizations showed that CuCo-MOF@ZIF-8 possesses greater surface area porosity and novel functional groups. The Trimetal MOF-on-MOF mode not only demonstrated the stability of the structure but also enhanced its mechanism. Molecular mechanism analysis revealed changes in the organic ligand and metal binding site due to the transformation of Cu2+ to Cu+, Co2+ to Co3+, and Zn-N to Zn-O organic connection. Furthermore, differences between the two fabrication methods were compared. The solid-state single preparation (CuCo-MOF@ZIF-8-1), was synthesized using the two-step hydrothermal method; the liquid mixed preparation material (CuCo-MOF@ZIF-8-2), was synthesized using the dual-solution method; they exhibited completely different chemical structures and morphologies during material testing and characterization. The maximum output power density of CuCo-MOF@ZIF-8-2-MFC was 246.38 mW/m2, about 2.49 times of ZIF-8 (98.72 mW/m2). The output voltage of CuCo-MOF@ZIF-8-1-MFC was measured at 357 mV over 10 d, while that of CuCo-MOF@ZIF-8-2-MFC reached 365 mV over 12 d.

Hydrophobic ZIF-8 nanoparticles loaded on chitosan for improved methanol adsorption from fermented wine

Metal-organic frameworks (MOFs) have great potential for the adsorption of minor molecular alcohols in the vapor phase. However, the drawbacks of powdered MOFs, including low recyclability and problematic separation, limit their application in fermented wine. Chitosan (CS) is a low-cost, eco-friendly, moldable matrix used in the food industry. In this study, a novel CS@ZIF-8 adsorbent with excellent microporous surface area was successfully synthesized by incorporating hydrophobic ZIF-8 into CS. The results showed that CS@ZIF-8 beads had a high adsorption affinity for methanol at a Zn2+/2-methylimidazole molar ratio of 1:5. The adsorption mechanism of methanol on CS@ZIF-8 beads was systematically studied by X-ray photoelectron spectroscopy, isotherms, and kinetics. The Langmuir model calculated the maximum adsorption of methanol to 56.8 mg/g. Adsorption kinetics are consistent with pseudo-second-order models. Furthermore, CS@ZIF-8 beads presented excellent recyclability for removing methanol for five consecutive cycles. It could treat 60 bed volumes of Chinese yellow wine in column filtration experiments to make the concentration below 50 mg/L. In summary, the highly efficient CS@ZIF-8 adsorbent has great potential for methanol adsorption from fermented wines. PRACTICAL APPLICATION: Methanol will exhibit adverse symptoms such as weakness and headaches after it is ingested. Therefore, methanol control is an important safety factor in the production of fermented wine. The adsorption method is recognized as a widely used technique due to its high efficiency and selectivity. The CS@ZIF-8 adsorbent synthesized in this paper provides a new idea for methanol removal.

Recent development towards the novel applications and future prospects for cellulose-metal organic framework hybrid materials: a review

The hybrid material created by combining cellulose and MOF is highly promising and possesses a wide range of useful properties. Cellulose-based metal-organic frameworks (CelloMOFs) combine the inherent biocompatibility and sustainability of cellulose with the tunable porosity and diverse metal coordination chemistry of MOFs. Cellulose-MOF hybrids have countless applications in various fields, such as energy storage, water treatment, air filtration, gas adsorption, catalysis, and biomedicine. They are particularly remarkable as adsorbents that can eliminate pollutants from wastewater, including metals, oils, dyes, antibiotics, and drugs, and act as catalysts for oxidation and reduction reactions. Furthermore, they are highly efficient air filters, able to remove carbon dioxide, particulate matter, and volatile organic compounds. When it comes to energy storage, these hybrids have demonstrated exceptional results. They are also highly versatile in the realm of biomedicine, with applications such as antibacterial and drug delivery. This article provides an in-depth look at the fabrication methods, advanced applications of cellulose-MOF hybrids, and existing and future challenges.

Novel polyarylether nitrile/layered bimetallic oxide/2-Methylimidazole composite membrane for efficient synergistic adsorption and degradation of organic pollutants under visible light

The difficulty of recycling and the finite photocatalytic performance of primitive nano-photocatalysts restrict their application in wastewater purification. In this study, a multifunctional membrane with efficient synergistic adsorption and degradation performance was constructed. The nano-photocatalyst layered bimetallic oxide (LDO) was combined with the matrix membrane polyarylether nitrile (PEN) by delayed phase transition technology. The introduced 2-Methylimidazole (2-MeIm) provided a virtual electron transfer pathway between PEN and LDO and enhanced the photocatalytic performance. The results suggested that PEN/LDO/2-MeIm has outstanding removal performance to organic dyes methylene blue (MB). After three consecutive cycles, the reacted membrane can be readily recovered from the system. The MB removal rate remained high at 89.38%, suggesting that the functional membrane is eligible for recycling and reuse. Finally, based on liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations, the mechanism and pathway of MB photodegradation by the PEN/LDO/2-MeIm system were proposed. Therefore, constructing PEN/LDO/2-MeIm membranes in this study may offer a novel perspective on creating eco-friendly and functional PEN-based membranes for practical use in wastewater purification.

Fabrication of a ZIF-8/PVA Membrane on PVDF Fiber by Spray for the Highly Efficient Separation of Oil-in-Water Emulsions

In human life and production, excessive oily wastewaters containing detergents are produced and discharged, causing severe environmental pollution and water resource problems. A metal-organic framework (MOF)-based membrane is an economical and environmentally friendly tool for emulsion separation but is limited by a complex preparation process and poor flexibility. Herein, we developed a simple method to synthesize a MOF-based mixed-matrix membrane (MMM) by spray and fabricated the membrane on poly(vinylidene fluoride) (PVDF) fibers via postdeposition and in situ growth manners. The prepared ZIF-8/PVA MMMs have uniform distribution of ZIF-8 particles and poly(vinyl alcohol) (PVA) on the PVDF fibers. PVA improved the adhesion between the ZIF-8 particles and between the MOF layer and PVDF fiber, endowing the separation membrane with high flexibility and bendability. The prepared ZIF-8/PVA membrane exhibited hydrophilicity and underwater superoleophobicity, which showed high separation efficiency and considerable water flux for emulsions, emulsion containing dye, and surfactant-stabilized emulsion. In addition, the fabricated ZIF-8/PVA/PVDF fibers exhibited good antifouling property and flexibility and can maintain stable separation efficiency after working several times and even under bending, demonstrating the stability and potentiality of the ZIF-8/PVA/PVDF fibers in practical applications. This work paves a new avenue for the synthesis and application of MOF-based MMMs.

The p-diethanolaminomethylcalix[4]arene-incorporated polyacrylonitrile-based facilitated-transport-nanofiber mat for O2/N2 separation

Separation of gases from air mixture is one of the most challenging and laborious separations due to the remarkably uniform molecular size of gas molecules. Therefore, the present study aimed to synthesize polyacrylonitrile-based nanofibers mat(NM) impregnated with p-diethanolaminomethylcalix[4]arene (PAN/p-DEAC4 NM) for the separation of two crucial gases O2 and N2. The affinity of the prepared PAN/p-DEAC4 NM for O2 was examined by optimizing the loading concentration of p-DEAC4 in the range from 5% to 20% (w/v). The results showed remarkable performance of the PAN/p-DEAC4 NM for O2/N2 separation with a superior O2/N2 selectivity of 12.75 and excellent permeance of 10.2 GPU for O2 and 0.8 GPU for N2 at 2 bar. The PAN/p-DEAC4 NM followed a facilitated transport mechanism for the separation of gases and it was revealed that the p-DEAC4 platform in the PAN NM is facilitating the transport of O2 due to its greater affinity towards O2. BET analysis revealed that the prepared NM possesses non-porous morphology with a surface area of 12.69 m2 g-1. SEM micrographs also confirmed the formation of defect-free NM. Thus, this study presents a unique perspective and direction for fabricating highly permeable nanofiber mats for O2/N2 separation.

Recent advancements in polyurethane-based membranes for gas separation

Gas separation membranes are critical in a variety of environmental research and industrial applications. These membranes are designed to selectively allow some gases to flow while blocking others, allowing for the separation and purification of gases for a variety of applications. Therefore, the demand for fast and energy-efficient gas separation techniques is of central interest for many chemical and energy production diligences due to the intensified levels of greenhouse and industrial gases. This encourages the researchers to innovate techniques for capturing and separating these gases, including membrane separation techniques. Polymeric membranes play a significant role in gas separations by capturing gases from the fuel combustion process, purifying chemical raw material used for plastic production, and isolating pure and noncombustible gases. Polyurethane-based membrane technology offers an excellent knack for gas separation applications and has also been considered more energy-efficient than conventional phase change separation methodologies. This review article reveals a thorough delineation of the current developments and efforts made for PU membranes. It further explains its uses for the separation of valuable gases such as carbon dioxide (CO2), hydrogen (H2), nitrogen (N2), methane (CH4), or a mixture of gases from a variety of gas spillages. Polyurethane (PU) is an excellent choice of material and a leading candidate for producing gas-separating membranes because of its outstanding chemical chemistry, good mechanical abilities, higher permeability, and variable microstructure. The presence of PU improves several characteristics of gas-separating membranes. Selectivity and separation efficiency of PU-centered membranes are enhanced through modifications such as blending with other polymers, use of nanoparticles (silica, metal oxides, alumina, zeolite), and interpenetrating polymer networks (IPNs) formation. This manuscript critically analyzes the various gas transport methods and selection criteria for the fabrication of PU membranes. It also covers the challenges facing the development of PU-membrane-based separation procedures.

Recent progress on CO2 separation membranes

Presently, excessive carbon dioxide emissions represent a critical environmental challenge. Thus, urgent efforts are required to develop environmentally friendly and low-energy technologies for carbon dioxide treatment. In this case, membrane separation technology stands out as a promising avenue for CO2 separation, with selective membrane materials of high permeability playing a pivotal role in this process. Herein, we categorize CO2 separation membranes into three groups: inorganic membranes, organic membranes, and emerging membranes. Moreover, representative high-performance membranes are introduced and their synthesis methods, gas separation performances, and applications are examined. Furthermore, a brief analysis of the challenges encountered by carbon dioxide separation membrane materials is provided together with a discussion on the future research direction. It is expected that this review will provide some potential insights and guidance for the future development of CO2 separation membranes, which can promote their development.

Biopolymeric Nanocomposites for CO2 Capture

Carbon dioxide (CO2) impacts the greenhouse effect significantly and results in global warming, prompting urgent attention to climate change concerns. In response, CO2 capture has emerged as a crucial process to capture carbon produced in industrial and power processes before its release into the atmosphere. The main aim of CO2 capture is to mitigate the emissions of greenhouse gas and reduce the anthropogenic impact on climate change. Biopolymer nanocomposites offer a promising avenue for CO2 capture due to their renewable nature. These composites consist of biopolymers derived from biological sources and nanofillers like nanoparticles and nanotubes, enhancing the properties of the composite. Various biopolymers like chitosan, cellulose, carrageenan, and others, possessing unique functional groups, can interact with CO2 molecules. Nanofillers are incorporated to improve mechanical, thermal, and sorption properties, with materials such as graphene, carbon nanotubes, and metallic nanoparticles enhancing surface area and porosity. The CO2 capture mechanism within biopolymer nanocomposites involves physical absorption, chemisorption, and physisorption, driven by functional groups like amino and hydroxyl groups in the biopolymer matrix. The integration of nanofillers further boosts CO2 adsorption capacity by increasing surface area and porosity. Numerous advanced materials, including biopolymeric derivatives like cellulose, alginate, and chitosan, are developed for CO2 capture technology, offering accessibility and cost-effectiveness. This semi-systematic literature review focuses on recent studies involving biopolymer-based materials for CO2 capture, providing an overview of composite materials enriched with nanomaterials, specifically based on cellulose, alginate, chitosan, and carrageenan; the choice of these biopolymers is dictated by the lack of a literature perspective focused on a currently relevant topic such as these biorenewable resources in the framework of carbon capture. The production and efficacy of biopolymer-based adsorbents and membranes are examined, shedding light on potential trends in global CO2 capture technology enhancement.

Universal Strategy for Inorganic Nanoparticle Incorporation into Mesoporous Liquid Crystal Polymer Particles

Developing inorganic-organic composite polymers necessitates a new strategy for effectively controlling shape and optical properties while accommodating guest materials, as conventional polymers primarily act as  carriers that transport inorganic substances. Here, a universal approach is introduced utilizing mesoporous liquid crystal polymer particles (MLPs) to fabricate inorganic-organic composites. By leveraging the liquid crystal phase, morphology and optical properties are precisely controlled through the molecular-level arrangement of the host, here monomers. The controlled host material allows the synthesis of inorganic particles within the matrix or accommodation of presynthesized nano-inorganic particles, all while preserving the intrinsic properties of the host material. This composite material surpasses the functional capabilities of the polymer alone by sequentially integrating one or more inorganic materials, allowing for the incorporation of multiple functionalities within a single polymer particle. Furthermore, this approach effectively mitigates the drawbacks associated with guest materials resulting in a substantial enhancement of composite performance. The presented approach is anticipated to hold immense potential for various applications in optoelectronics, catalysis, and biosensing, addressing the evolving demands of the society.

Application and prospects of metal–organic frameworks in photocatalytic self-cleaning membranes for wastewater treatment

By loading photocatalytic MOF onto the separation membrane, the self-cleaning function of the membrane can be realized. This paper discusses the structure, synthesis, and properties of photocatalytic MOFs.

Self-supported MOF/cellulose-nanocrystals materials designed from ultrafiltration

Metal-organic-frameworks (MOFs) are promising materials for addressing critical issues such as petrochemical separation, water purification, energy storage and drug delivery. Their large-scale deployment, however, is hampered by a limited processability due to their powdery nature. Recently, the hybridization of MOFs with biopolymers has emerged as a greener, biocompatible strategy to shape MOFs composites into more processable membranes, films, and porous materials. In this work, cellulose nanocrystals (CNCs) were used in combination with ZIF-8 (a widely used synthetic zeolite) to produce hybrid composites through ultrafiltration. Results showed that small quantities of CNCs (1 to 20 CNC:ZIF-8 volume ratio) were sufficient to form a self-supported, dense deposit with high ZIF-8 loadings. Compared to classical MOF in situ growth strategies, this approach allowed the tuning of the composition of the final nanocomposite by controlling the nature and quantities of particles in the suspension. The fabrication of the deposit was strongly dependent on the physiochemical properties of the suspension, which were fully characterized with a set of complementary techniques, including in situ SAXS. This technique was employed to investigate the filtration process, which exhibited a homogeneous deposition of ZIF-8 particles mediated by CNC self-assembly. Finally, the available pore volume and integrity of the internal porosity of ZIF-8 were characterized by water porosimetry, demonstrating that the presence of CNCs did not alter the properties of the supported ZIF-8.

Magnetic Adsorbent Fe3O4/ZnO/LC for the Removal of Tetracycline and Congo Red from Aqueous Solution

Zeolitic imidazolate frameworks (ZIFs) can be used as an adsorbent to efficiently adsorb organic pollutants. However, ZIF nanoparticles are easy to form aggregates, hampering the effective and practical application in practical adsorption. In this study, the ZIF-8 was successfully loaded onto lignocellulose (LC) to further produce ZnO/LC by in situ growth method and hydrothermal treatment, and then Fe3O4 nanoparticles (Fe3O4 NPs) were loaded onto ZnO/LC to prepare magnetic Fe3O4/ZnO/LC adsorbent for removing tetracycline (TC) and congo red (CR) pollutants from aqueous solution. The adsorption properties of the adsorbent were systematically analyzed for different conditions, such as adsorbent dosage, solution pH, contact time, temperature and initial concentration. The experimental data were fitted using adsorption kinetic and isotherm models. The results showed that the pseudo-second-order model and Sips model were well fitted to the adsorption kinetic and adsorption isotherm, respectively. The adsorption capacities of TC and CR reached the maximum value of 383.4 mg/g and 409.1 mg/g in experimental conditions. The mechanism of the removal mainly includes electrostatic interaction, hydrogen bonding and π-π stacking. This novel adsorbent could be rapidly separated from the aqueous solution, suggesting its high potential to remove pollutants in wastewater.

Synthesis and antibacterial activities of Ag-TiO2/ZIF-8

In recent years, massive bacterial infections have led to human illness and death, reminding us of the urgent need to develop effective and long-lasting antimicrobial materials. In this paper, Ag-TiO2/ZIF-8 with good environmental friendliness and biological antibacterial activity was prepared by solvothermal method. The structure and morphology of the synthesized materials were characterized by XRD, FT-IR, SEM-EDS, TEM, XPS, and BET. To investigate the antibacterial activity of the synthesized samples, Escherichia coli and Bacillus subtilis were used as target bacteria for experimental studies of zone of inhibition, bacterial growth curves, minimum bactericidal concentration and antibacterial durability. The results demonstrated that 20 wt.%Ag-TiO2/ZIF-8 had the best bacteriostatic effect on E. coli and B. subtilis under dark and UV conditions compared to TiO2 and ZIF-8. Under the same conditions, the diameter of the inhibition circle of 20 wt% Ag-TiO2/ZIF-8 is 8.5-11.5 mm larger than that of its constituent material 4 wt% Ag-TiO2, with more obvious antibacterial effect and better antibacterial performance. It is also proposed that the excellent antibacterial activity of Ag-TiO2/ZIF-8 is due to the synergistic effect of Ag-TiO2 and ZIF-8 under UV light. In addition, the prepared material has good stability and durability with effective antimicrobial activity for more than 5 months.

Functionalized nanofibers in gas sorption process: a critical review on the challenges and prospective research

Air pollution has become the most important environmental and human health threat as it is accounting for about 7 million deaths across the globe every year. Particulate matter (PM) derived from the combustion of fossil fuels, biomass, and other agricultural residues pollutes the atmospheric air which affects the quality of the environment and poses a great threat to human health. Ecological imbalance, climatic variation, and cardiovascular and respiratory problems among humans are significant extortions due to PM pollution. Scientific approaches were initiated to limit the levels of PM in the atmospheric air and the use of nanofiber mats has received wide attention as these possess versatile properties including nanoscale-sized pore structure, homogeneity in their size distribution with high specific surface area, and low basis weight. To exploit their filtration potential towards wide classes of pollutants and also to enhance the capturing efficacy, functionalized nanofibers are currently in practice with tailor-made modifications on the surface. The present review provides a comprehensive report on the different fabrication processes of functionalized nanofibers along with the controlling factors affecting the efficacy of the gas separation process. Also, it provides technical insights on the mass transfer aspects of PM filtration by elucidation their mechanism which can provide vital information on the rate-controlling diffusive flux(es). Conclusively, the practical challenges encountered in the large-scale air filtration systems such as filter cleaning, flow-rate regulation, pressure drop, and extent of reusability are discussed, and the review has identified potential gaps in the current research and can be considered for the prospective research in the area of PM separation process.

Acoustomicrofluidic Defect Engineering and Ligand Exchange in ZIF-8 Metal-Organic Frameworks

A way through which the properties of metal-organic frameworks (MOFs) can be tuned is by engineering defects into the crystal structure. Given its intrinsic stability and rigidity, however, it is difficult to introduce defects into zeolitic imidazolate frameworks (ZIFs)-and ZIF-8, in particular-without compromising crystal integrity. In this work, it is shown that the acoustic radiation pressure as well as the hydrodynamic stresses arising from the oscillatory flow generated by coupling high frequency (MHz-order) hybrid surface and bulk acoustic waves into a suspension of ZIF-8 crystals in a liquid pressure transmitting medium is capable of driving permanent structural changes in their crystal lattice structure. Over time, the enhancement in the diffusive transport of guest molecules into the material's pores as a consequence is shown to lead to expansion of the pore framework, and subsequently, the creation of dangling-linker and missing-linker defects, therefore offering the possibility of tuning the type and extent of defects engineered into the MOF through the acoustic exposure time. Additionally, the practical utility of the technology is demonstrated for one-pot, simultaneous solvent-assisted ligand exchange under ambient conditions, for sub-micron-dimension ZIF-8 crystals and relatively large ligands-more specifically 2-aminobenzimidazole-without compromising the framework porosity or overall crystal structure.

A harsh environment resistant robust Co(OH)2@stearic acid nanocellulose-based membrane for oil-water separation and wastewater purification

Traditional membranes are inefficient in treating highly toxic organic pollutants and oily wastewater in harsh environments, which is difficult to meet the growing demand for green development. Herein, the Co(OH)₂@stearic acid nanocellulose-based membrane was prepared by depositing Co(OH)₂ on the nanocellulose-based membrane (NBM) through chemical soaking method, which enables efficient oil/water mixtures separation and degradation of pollutants by photocatalysis in harsh environments. The Co(OH)₂@stearic acid nanocellulose-based membrane (Co(OH)₂@stearic acid NBM) shows good photocatalytic degradation performance for methylene blue pollutants in harsh environment, and has significant degradation rate (93.66%). At the same time, the Co(OH)₂@stearic acid NBM with superhydrophobicity and superoleophilicity also exhibits respectable oil/water mixtures separation performance (n-Hexane, dimethyl carbonate, chloroform and toluene) under harsh environment (strong acid/strong alkali), which has an excellent oil-water mixtures separation flux of 87 L·m^-2·h^-1 (n-Hexane/water) and oil-water mixture separation efficiency of over 93% (n-Hexane/water). In addition, this robust Co(OH)₂@stearic acid NBM shows good self-cleaning and recycling performance. Even though seven oil-water separation tests have been carried out under harsh environment, it can still maintain respectable oil-water mixture separation rate and flux. The multifunctional membrane has excellent resistance to harsh environments, oil-water separation and pollutant degradation can be performed even in harsh environments, which provides a convenient way to treat sewage under harsh conditions efficiently and has great potential in practical application.

High-performance carboxymethyl cellulose-based composite film tailored by versatile zeolitic imidazolate framework

Robust biopolymer-based composite film with multifunctional performances significantly contributes to the packaging field. Herein, we proposed a sort of carboxymethyl cellulose (CMC) based composite film via incorporating versatile zeolitic imidazolate framework (ZIF) materials. Compared to pristine CMC film, the OTR, WVTR, and tensile strength of CMC/ZIF composite film with 1 wt ‰ Zn/Co-ZIF were improved from 64.89 cm³*μm/(m²*d*kPa), 1579.21 g/(m²*24h) and 16.9 MPa to 20.79 cm³*μm/(m²*d*kPa), 1209.58 g/(m²*24h) and 70.1 MPa, respectively. Notably, owing to the reduced band gap and intrinsic chemical and thermal stability of Zn/Co-ZIF, the fabricated Zn/Co-ZIF/CMC composite film presented well UV protection capability within the whole UV region and excellent UV-blocking durability after being exposed to UV-light at 365 nm for 12 h. In practice, the photocatalytic degradation of RhB solutions under UV light could be effectively suppressed when using Zn/Co-ZIF/CMC film as UV protection layer. Our findings proposed the potential application of these versatile ZIF materials as functional nanofiller within biopolymer substances for UV protection and transparent packaging area.

Collaboration of two-star nanomaterials: The applications of nanocellulose-based metal organic frameworks composites

Nanocellulose, as the star nanomaterial in carbohydrate polymers, has excellent mechanical properties, biodegradability, and easy chemical modification. However, further practical applications of nanocellulose are limited by their inadequate functionalization. Metal-organic frameworks (MOFs), as the star nanomaterial in functional polymers, have a large surface area, high porosity, and adjustable structure. The collaboration of nanocellulose and MOFs is a desirable strategy to make composites especially interesting for multifunctional and multi-field applications. What sparks will be produced by the collaboration of two-star nanomaterials? In this review article, we highlight an up-to-date overview of nanocellulose-based MOFs composites. The sewage treatment, gas separation, energy storage, and biomedical applications are mainly summarized. Finally, the challenges and research trends of nanocellulose-based MOFs composites are prospected. We hope this review may provide a valuable reference for the development and applications of carbohydrate polymer composites soon.

Application of bacterial nanocellulose decorated with zeolitic imidazolate framework (ZIF-L) as a platform for food freshness monitoring

Recently, the food freshness indicator (FFI) has garnered great interest from consumers and food producers. A novel FFI based on bacterial nanocellulose (BNC)/zeolitic imidazolate framework-L (ZIF-L) and grape anthocyanins was developed and characterized using field emission scanning electron microscopy, Fourier-transform infrared, X-ray diffraction, water contact angle, and BET techniques. The results confirmed that the BNC fibrils were decorated by in situ growth of ZIF-L, with a 3D flower-shaped structure and randomly multiple sharp-edged petals, and hydroxyl and oxygenated heterocycle aromatic ring functional groups on its surface. The reversibility, color stability performance, and moisture sorption of FFI were studied and its applicability in a two-layer arrangement as a visual freshness monitoring of shrimp and minced beef was evaluated. The FFI was able to distinguish (ΔE > 5) the fresh, medium fresh, and spoiled minced meat and shrimp visually during 10 and 4 days of storage at 4 °C, respectively. Also, monitoring of food chemical and microbiological parameters approved the correlation of food spoilage with the color parameters of FFI. These results confirmed the function of ZIF-L in the fabrication of highly pH-sensitive food intelligent packaging material.

Preparation of Zeolitic Imidazolate Framework-8-Based Nanofiber Composites for Carbon Dioxide Adsorption

In this study, polyacrylonitrile (PAN)-based activated nanofiber composites, which were embedded inside zeolitic imidazolate framework-8 (ZIF-8) crystals or ZIF-8-derived carbons (ZDC-850), were fabricated using an electrospinning process, to serve as CO2 adsorbents. The adsorbents were characterized using various techniques. The degree of crystallinity of ZDC-850 totally changed compared to that of ZIF-8. For nanofiber composites, the timing of the ligand decomposition of ZIF-8 significantly affected the material properties. The Zn metals in the ZIF-8/PAN or ZDC-850/PAN could be embedded and protected by the PAN fibers from excess volatilization in the following treatments: ZIF-8 had significant pore volumes in the range of 0.9−1.3 nm, but ZDC-850 and ZIF-8/PAN exhibited a distinct peak at approximately 0.5 nm. The CO2 adsorption capacities at 25 °C and 1 atm followed the order: ZIF-8/PAN (4.20 mmol/g) > ZDC-850 (3.50 mmol/g) > ZDC-850/PAN (3.38 mmol/g) > PAN (2.91 mmol/g) > ZIF-8 (0.88 mmol/g). The slope in the log−linear plot of isosteric heat of adsorption was highly associated with CO2 adsorption performance. Under 1 atm at 25 °C, for Zn metal active sites inside the pores, the pores at approximately 0.5 nm and in C-N (amines) groups could promote CO2 adsorption. At low CO2 pressures, for a good CO2 adsorbent, the carbon content in the adsorbent should be higher than a threshold value. Under this condition, the percentage of ultra-micropore and micropore volumes, as well as the functional groups, such as the quaternary or protonated N (amines), N=C (imines or pyridine-type N), C-OH, and -COOH groups, should be considered as significant factors for CO2 adsorption.

Facile preparation of nanocellulose/Zn-MOF-based catalytic filter for water purification by oxidation process

Sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs) have recently attracted much attention due to their potential in degrading organic pollutants. Metal-organic frameworks (MOFs) have been reported as effective materials to generate SO₄^•-. However, it is challenging to separate and recover the dispersed MOF particles from the reaction solution when MOFs are used alone. We used cellulose nanofibers (CNFs) as a porous filter template to immobilize Zn-based MOF, zeolitic imidazolate framework-8 (ZIF-8), and obtained a catalytic composite membrane having peroxymonosulfate (PMS) activating function to produce SO₄^•-. The CNF was effective in holding ZIF-8 nanoparticle and making a durable porous filter. The activated PMS-produced ^•OH and SO₄^•- radicals from ZIF-8 play an important role in the catalytic reaction. More than 90% of methylene blue and rhodamine B was degraded by ZIF-8/CNFs composite membrane in the PMS environment within 60 min. The ZIF-8/CNFs catalytic filters can be used several times without performance reduction for organic dye degradation. The results show that ZIF-8/CNFs catalytic membrane can be separated from organic pollution system quickly and used for the efficient separation and recovery of MOF particle-based catalytic materials. Therefore, this study provides a new perspective for fabricating the MOFs particles-immobilized catalytic filter by biomass nanocellulose-based materials for water purification. This method can be used for facile fabrication of the cellulose-based porous functional filter and open diverse applications.

Methyl Orange-Doped Polypyrrole Promoting Growth of ZIF-8 on Cellulose Fiber with Tunable Tribopolarity for Triboelectric Nanogenerator

Cellulose fiber (CelF) is a biodegradable and renewable material with excellent performance but negligible triboelectric polarizability. Methods to enhance and rationally tune the triboelectric properties of CelF are needed to further its application for energy harvesting. In this work, methyl-orange-doped polypyrrole (MO-PPy) was in situ coated on CelF as a mediating layer to promote the growth of metal–organic framework ZIF-8 and to construct a cellulose-based triboelectric nanogenerator (TENG). The results showed that a small amount of MO-PPy generated in situ significantly promoted the growth of ZIF-8 on CelF, and the ZIF-8 deposition ratio was able to increase from 7.8% (ZIF-8/CelF) to 31.8% (ZIF-8/MO-PPy@CelF). ZIF-8/MO-PPy@CelF remained electrically conductive and became triboelectrically positive, and the triboelectricity’s positivity was improved with the increase in the ZIF-8 deposition ratio. The cellulose-based TENG constructed with ZIF-8/MO-PPy@CelF (31.8% ZIF-8 deposition ratio) and polytetrafluoroethylene (PTFE) could generate a transfer charge of 47.4 nC, open-circuit voltage of 129 V and short-circuit current of 6.8 μA—about 4 times higher than those of ZIF-8/CelF (7.8% ZIF-8 deposition ratio)—and had excellent cycling stability (open-circuit voltage remained almost constant after 10,000 cycles). MO-PPy not only greatly facilitated the growth of ZIF-8 on CelF, but also acted as an electrode active phase for TENG. The novel TENG based on ZIF-8/MO-PPy@CelF composite has cheerful prospects in many applications, such as self-powered supercapacitors, sensors and monitors, smart pianos, ping-pong tables, floor mats, etc.

Application of polysaccharide-based metal organic framework membranes in separation science

Polysaccharide/MOF composite membranes have captured the interests of many researchers during decontamination of polluted environments. Their popularity can be attributed to the relatively high chemical and thermal stabilities of these composite membranes. Chitosan is among the polysaccharides extensively used during the synthesis of hybrid membranes with MOFs. The applications of chitosan/MOF composite membranes in separation science are explored in detail in this paper. Researchers have also synthesised mixed matrix membranes of MOFs with cellulose and cyclodextrin that have proved to be effective during separation of a variety of materials. The uses of cellulose/MOF and cyclodextrin/MOF membranes for the removal of environmental pollutants are discussed in this review. In addition, the challenges associated with the use of these mixed matrix membranes are explored in this current paper.

Hybrid Metal-Organic Framework-Cellulose Materials Retaining High Porosity: ZIF-8@Cellulose Nanofibrils

Metal-organic frameworks have attracted a great deal of attention for future applications in numerous areas, including gas adsorption. However, in order for them to reach their full potential a substrate to provide an anchor may be needed. Ideally, this substrate should be environmentally friendly and renewable. Cellulose nanofibrils show potential in this area. Here we present a hybrid material created from the self-assembly of zeolitic imidazolate framework (ZIF-8) nanocrystals on cellulose nanofibrils (CNF) in aqueous medium. The CNF/ZIF-8 was freeze dried and formed free standing materials suitable for gas adsorption. A BET area of 1014 m2 g−1 was achieved for the CNF/ZIF-8 hybrid materials ZIF-8@cellulose which is comparable with reported values for free standing ZIF-8 materials, 1600 m2 g−1, considering the dilution with cellulose, and a considerable enhancement compared to CNF on its own, 32 m2 g−1.

A review on the emerging applications of cellulose, cellulose derivatives and nanocellulose in carbon capture

Carbon capture can be implemented at a large scale only if the CO₂ selective materials are abundantly available at low cost. Since the sustainable requirement also elevated, the low-cost and biodegradable cellulosic materials are developed into CO₂ selective adsorbent and membranes recently. The applications of cellulose, cellulosic derivatives and nanocellulose as CO₂ selective adsorbents and membranes are reviewed here. The fabrication and modification strategies are discussed besides comparing their CO₂ separation performance. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) isolated from cellulose possess a big surface area for mechanical enhancement and a great number of hydroxyl groups for modification. Nanocellulose aerogels with the large surface area were chemically modified to improve their selectivity towards CO₂. Even with the reduction of surface area, amino-functionalized nanocellulose aerogels exhibited the satisfactory chemisorption of CO₂ with a capacity of more than 2 mmol/g was recorded. Inorganic fillers such as silica, zeolite and MOFs were further incorporated into nanocellulose aerogels to enhance the physisorption of CO₂ by increasing the surface area. Although CO₂ adsorbents developed from cellulose and cellulose derivatives were less reported, their applications as the building blocks of CO₂ separation membranes had been long studied. Cellulose acetate membranes were commercialized for CO₂ separation, but their separation performance could be further improved with silane or inorganic filler. CNCs and CNFs enhanced the CO₂ selectivity and permeance through polyvinyl alcohol coating on membranes, but only CNF membranes incorporated with MOFs were explored so far. Although some of these membranes surpassed the upper-bound of Robeson plot, their stability should be further investigated.