Metal organic frameworks as potent treatment media for odorants and volatiles in air

Agri-food waste biosorbents for volatile organic compounds removal from air and industrial gases - A review

Approximately 1.3 billion metric tons of agricultural and food waste is produced annually, highlighting the need for appropriate processing and management strategies. This paper provides an exhaustive overview of the utilization of agri-food waste as a biosorbents for the elimination of volatile organic compounds (VOCs) from gaseous streams. The review paper underscores the critical role of waste management in the context of a circular economy, wherein waste is not viewed as a final product, but rather as a valuable resource for innovative processes. This perspective is consistent with the principles of resource efficiency and sustainability. Various types of waste have been described as effective biosorbents, and methods for biosorbents preparation have been discussed, including thermal treatment, surface activation, and doping with nitrogen, phosphorus, and sulfur atoms. This review further investigates the applications of these biosorbents in adsorbing VOCs from gaseous streams and elucidates the primary mechanisms governing the adsorption process. Additionally, this study sheds light on methods of biosorbents regeneration, which is a key aspect of practical applications. The paper concludes with a critical commentary and discussion of future perspectives in this field, emphasizing the need for more research and innovation in waste management to fully realize the potential of a circular economy. This review serves as a valuable resource for researchers and practitioners interested in the potential use of agri-food waste biosorbents for VOCs removal, marking a significant first step toward considering these aspects together.

A comprehensive review and perspective research in technology integration for the treatment of gaseous volatile organic compounds

Volatile organic compounds (VOCs) are harmful pollutants emitted from industrial processes. They pose a risk to human health and ecosystems, even at low concentrations. Controlling VOCs is crucial for good air quality. This review aims to provide a comprehensive understanding of the various methods used for controlling VOC abatement. The advancement of mono-functional treatment techniques, including recovery such as absorption, adsorption, condensation, and membrane separation, and destruction-based methods such as natural degradation methods, advanced oxidation processes, and reduction methods were discussed. Among these methods, advanced oxidation processes are considered the most effective for removing toxic VOCs, despite some drawbacks such as costly chemicals, rigorous reaction conditions, and the formation of secondary chemicals. Standalone technologies are generally not sufficient and do not perform satisfactorily for the removal of hazardous air pollutants due to the generation of innocuous end products. However, every integration technique complements superiority and overcomes the challenges of standalone technologies. For instance, by using catalytic oxidation, catalytic ozonation, non-thermal plasma, and photocatalysis pretreatments, the amount of bioaerosols released from the bioreactor can be significantly reduced, leading to effective conversion rates for non-polar compounds, and opening new perspectives towards promising techniques with countless benefits. Interestingly, the three-stage processes have shown efficient decomposition performance for polar VOCs, excellent recoverability for nonpolar VOCs, and promising potential applications in atmospheric purification. Furthermore, the review also reports on the evolution of mathematical and artificial neural network modeling for VOC removal performance. The article critically analyzes the synergistic effects and advantages of integration. The authors hope that this article will be helpful in deciding on the appropriate strategy for controlling interested VOCs.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

Adsorption and membrane separation for removal and recovery of volatile organic compounds

Volatile organic compounds (VOCs) are a crucial kind of pollutants in the environment due to their obvious features of severe toxicity, high volatility, and poor degradability. It is particularly urgent to control the emission of VOCs due to the persistent increase of concentration and the stringent regulations. In China, clear directions and requirements for reduction of VOCs have been given in the "national plan on environmental improvement for the 13th Five-Year Plan period". Therefore, the development of efficient technologies for removal and recovery of VOCs is of great significance. Recovery technologies are favored by researchers due to their advantages in both recycling VOCs and reducing carbon emissions. Among them, adsorption and membrane separation processes have been extensively studied due to their remarkable industrial prospects. This overview was to provide an up-to-date progress of adsorption and membrane separation for removal and recovery of VOCs. Firstly, adsorption and membrane separation were found to be the research hotspots through bibliometric analysis. Then, a comprehensive understanding of their mechanisms, factors, and current application statuses was discussed. Finally, the challenges and perspectives in this emerging field were briefly highlighted.

Comparison of three different structures of zeolites prepared by template-free hydrothermal method and its CO2 adsorption properties

In this study, zeolite sodalite SOD (50NaO₂:Al₂O₃:5SiO₂), zeolite LTA (2NaO₂:Al₂O₃:1.926SiO₂) and zeolite FAU (16NaO₂:Al₂O₃:4SiO₂) of different structures were synthesized successfully through simple conventional hydrothermal crystallization technique without using any template agent. Morphological analysis of three different types of zeolites revealed that the samples exhibit three different shapes such as the "Raspberry-like", "Dice" cube like and "Octahedral" shaped morphology respectively. The thermal stability was found to be about 4.8%, 14.6% and 20.5% for the synthesized zeolites SOD, LTA and FAU respectively. From the N₂ adsorption-desorption studies, it was observed that adsorption types IV and I correspond to the synthesized samples. CO₂ adsorption by the synthesized zeolite SOD, LTA and FAU were examined in the pressure range from 0 to 101.325 kPa at a constant temperature of 297.15 K. The highest adsorption capacity of 3.7 mmol/g was obtained for zeolite FAU. The synthesized zeolite was studied using a nonlinear regression curve fit to determine the adsorption isotherm model using Langmuir and Freundlich isotherm model. It has been found that the synthesized zeolites have a large electric field gradient due to which they can strongly adsorb quadrupole of CO₂ molecules.

Applications of Metal-Organic Frameworks in Water Treatment: A Review

The ever-expanding scale of industry and agriculture has led to the gradual increase of pollutants (e.g., heavy metal ions, synthetic dyes, and antibiotics) in water resources, and the ecology and wastewater are grave problems that need to be solved urgently and has attracted widespread attention from the research community and industry in recent years. Metal-organic frameworks (MOFs) are a type of organic-inorganic hybrid material with a distinctive 3D network crystal structure. Lately, MOFs have made striking progress in the fields of adsorption, catalytic degradation, and biomedicine on account of their large specific surface and well-developed pore structure. This review summarizes the latest research achievements in the preparation of pristine MOFs, MOF composites, and MOF derivatives for various applications including the removal of heavy metal ions, organic dyes, and other harmful substances in sewage. Furthermore, the working mechanisms of utilizing adsorption, photocatalytic degradation, and membrane separation technologies are also briefly described for specific pollutants removal from sewage. It is expected that this review will provide inspiration and references for the synthesis of pristine MOFs as well as their composites and derivatives with excellent water treatment performance.

UiO-66 Selective Enrichment Integrated with Thermal Desorption GC-MS for Detection of Benzene Homologues in Ambient Air

In this study, UiO-66 was selected as sorbent media packed in the tube to selectively enrich trace levels of benzene homologues such as benzene, toluene, and xylene (BTX) in ambient air prior to thermal desorption (TD)-GC-MS determination. A series of experiments were conducted to obtain the optimal TD conditions. The results indicated that the optimal TD parameters were as follows: desorption temperature of 180°C, desorption flow rate of 50 mL min^-1, and desorption time of 30 min. Furthermore, the method based on UiO-66 enrichment integrated with TD-GC-MS for trace levels of BTX was successfully developed. It exhibited a good linearity (R ² > 0.99) in the range of 50-1000 ng, except for p, m-xylene in the range of 100-2000 ng, and achieved the recovery of 69.4-101.3%, and the relative standard deviation of 3.8-6.4%. The detection limits of BTX were 1.6-4.0 ng; according to 10 L of sampling volume, the method detection limits would be in the range of 0.16-0.40 µg m^-3. Additionally, the method was successfully applied to determine BTX in indoor air and showed good selectivity and sensitivity. In summary, the findings in this work revealed that UiO-66 was an attractive adsorbent for selective enrichment trace levels of BTX compounds in ambient air, which was favorable for the subsequent detection by TD-GC-MS.

Influence of Alkalinization Over Metal Organic Frameworks MIL-100(Fe) for Enhanced Volatile Organic Compounds (VOCs) Adsorbents

Substantial attempts have been undertaken for the improvement of the air quality over decades; and Volatile Organic Compounds (VOCs) from the chemical and textile industries are truly listed as severe issue to be controlled. To come up with modus operandi for this issue, a novel composite of metal organic frameworks (MOFs) MIL-100(Fe) with salient tuned features of natrite was designed by a green and facile method. Mineralized composite MOFs exhibited enhanced crystallinity than pure MIL-100(Fe) as well showcased a higher surface area of 1300 m² g^-1. Through dynamic acetone pressure swing adsorption setup, MIL-0.05Na (MIL-100(Fe) synthesized with 0.05 mM Na₂CO₃ solution) revealed an enhanced acetone adsorption of 210 mg g ¹ at room temperature. Gas phase adsorption isotherms confirmed the mono layer adsorption behavior. The kinetics models evaluated that the external mass transfer was the rate limiting step for surface adsorption. The thermodynamic study manifested that the adsorption reaction was spontaneous and exothermic. The proposed mechanism of adsorption was the act of physisorption which enriched the adsorbents reusability. This research work provides a futuristic vista to design mineralized Fe-MOFs composites for an energy saving adsorbents for VOCs removal.

Application of zeolitic imidazolate framework for hexavalent chromium removal: A feasibility and mechanism study

The mechanisms and effectiveness of using zeolitic imidazolate framework (ZIF-8) [a sub-family of metal-organic framework (MOF)] particles on hexavalent chromium [Cr(VI)] removal were evaluated. The ultrasonic mixing method was applied for the preparation of ZIF-8, and chemicals used for ZIF-8 synthesis included ammonium hydroxide, zinc nitrate hexahydrate, and 2-methylimidazole. ZIF-8 particle had a clear rhombic dodecahedron morphology shape and a strong peak intensity with high crystallinity. The adsorption capacity (AC) of ZIF-8 was 30.3 mg of Cr(VI)/g of ZIF-8 [Cr(VI) = 50 mg/L]. The AC of Cr(VI) raised to 34.3 mg/g under acidic conditions (pH = 5), and the AC dropped to below 13.7 mg/g with a pH range from 7 to 11. It could be because of the competitive effects between CrO₄ ^2- and hydroxide ions for adsorption locations of ZIF-8. Cr(VI) removal relied on the amount of Cr(VI) adsorbed on the particles of ZIF-8, and the mechanisms of Cr(VI) adsorption by ZIF-8 included chemical/physical processes and the rate-limiting step was the chemical adsorption. A fraction of sorbed Cr(VI) was reduced to Cr(III), and thus, ZIF-8 could serve as a reducing agent during Cr(VI) reduction. Cr(VI) was removed effectively from the water phase by ZIF-8 via adsorption and reduction mechanisms. PRACTITIONER POINTS: ZIF-8 particles had an adsorption capacity of 30.33 mg of Cr(VI)/g of ZIF-8. Cr(VI) sorption by ZIF-8 has chemical (rate-limiting step) and physical processes. ZIF-8 can serve as a reducing agent for Cr(VI) reduction. Cr(VI) can be removed by ZIF-8 via the adsorption and reduction mechanisms.

Potential applications of porous organic polymers as adsorbent for the adsorption of volatile organic compounds

Volatile organic compounds (VOCs) with high toxicity and carcinogenicity are emitted from kinds of industries, which endanger human health and the environment. Adsorption is a promising method for the treatment of VOCs due to its low cost and high efficiency. In recent years, activated carbons, zeolites, and mesoporous materials are widely used to remove VOCs because of their high specific surface area and abundant porosity. However, the hydrophilic nature and low desorption rate of those materials limit their commercial application. Furthermore, the adsorption capacities of VOCs still need to be improved. Porous organic polymers (POPs) with extremely high porosity, structural diversity, and hydrophobic have been considered as one of the most promising candidates for VOCs adsorption. This review generalized the superiority of POPs for VOCs adsorption compared to other porous materials and summarized the studies of VOCs adsorption on different types of POPs. Moreover, the mechanism of competitive adsorption between water and VOCs on the POPs was discussed. Finally, a concise outlook for utilizing POPs for VOCs adsorption was discussed, noting areas in which further work is needed to develop the next-generation POPs for practical applications.

Vertical macro-channel modification of a flexible adsorption board with in-situ thermal regeneration for indoor gas purification to increase effective adsorption capacity

Adsorption has been used widely to remove indoor volatile organic compounds (VOCs). However, the large diffusion resistance inside traditional granular adsorbents renders a low VOC adsorption rate. This study proposes a modified method to achieve the rapid diffusion into the adsorbent during the initial adsorption period. A thin and flexible adsorption board with a layer of adsorbent coated on a heating film was prepared for in-situ adsorption and regeneration. Then, regular, vertical macro-channels through the adsorption board were fabricated by laser drilling to enhance mass transfer inside the board. Experimental results demonstrated that after modification, the penetration times for formaldehyde and xylene extended from 3.8 to 6.2 h, and from 62 to 99 h, respectively. The effective adsorption capacity of the modified board had increased by a multiple of two for formaldehyde and 1.8 for xylene. A mathematical model was developed and experimentally validated to evaluate the modification effect for more adsorbent-pollutant pairs. The results showed that the amplification of effective adsorption capacity was positively correlated with the Da/(K·De) parameter; this is the diffusion resistance ratio prior to and following the modification. A spectrogram of adsorbent-pollutant pairs was plotted to guide the modification. This simple macro-channel modification of the adsorption board may be used as an alternative design for adsorption applications in indoor air purification.

A Critical Review on Metal-Organic Frameworks and Their Composites as Advanced Materials for Adsorption and Photocatalytic Degradation of Emerging Organic Pollutants from Wastewater

Water-borne emerging pollutants are among the greatest concern of our modern society. Many of these pollutants are categorized as endocrine disruptors due to their environmental toxicities. They are harmful to humans, aquatic animals, and plants, to the larger extent, destroying the ecosystem. Thus, effective environmental remediations of these pollutants became necessary. Among the various remediation techniques, adsorption and photocatalytic degradation have been single out as the most promising. This review is devoted to the compilations and analysis of the role of metal-organic frameworks (MOFs) and their composites as potential materials for such applications. Emerging organic pollutants, like dyes, herbicides, pesticides, pharmaceutical products, phenols, polycyclic aromatic hydrocarbons, and perfluorinated alkyl substances, have been extensively studied. Important parameters that affect these processes, such as surface area, bandgap, percentage removal, equilibrium time, adsorption capacity, and recyclability, are documented. Finally, we paint the current scenario and challenges that need to be addressed for MOFs and their composites to be exploited for commercial applications.

Heavy metal elimination based on metal organic framework highly loaded on flexible nanofibers

Efficient adsorbents for removal heavy metals are extensively urgent in modern society. Metal-organic frameworks (MOFs) with abundant porosity and tunable structure make it potential to access the advantages of high permeability and adsorbability in water pollutant control. However, MOFs nanoparticles inconvenient to recycle in solution hinder its application in water pollutant treatment. Herein, we report an in-situ growth and large-scalable manufacturing method to fabricate ZIF-8 nanoparticles on electrospun polyacrylonitrile (PAN) nanofibers membrane (ZIF-8/PAN NF) by hot pressing. Consequently, the prepared ZIF-8/PAN NF possesses high loading, uniform dispersion and large-scalable area as well as good flexibility. The fabricated ZIF-8/PAN NF exhibits excellent performance with fast flux (12,000 L/(m²h)) and high filtration efficiency (96.5%) for Cu²⁺ in dynamic adsorption. Additionally, adsorption and electrochemistry are introduced simultaneously. The Cu²⁺ removal rate of ZIF-8/PAN NF reaches 34.1% in 4 min with combination of adsorption and electrochemistry. While it is 29.2% for Cu²⁺ elimination in adsorption. Given the outstanding performance and easy manufacture, this study might bring MOFs powder to eliminate water pollution into practical application.

MOFs-carbon hybrid nanocomposites in environmental protection applications

The demand for green engineering environmentally friendly nanomaterials had made carbon nanotube a suitable material to keep metal-organic frameworks (MOFs) in the application of wastewater treatment and air pollution monitoring systems. This review summarizes many of the recent research accomplishments in the synthesis of MOFs and MOFs-carbon hybrid nanocomposites for various applications such as wastewater treatment and removal of hazardous gases (CO, SO₂, H₂S and NH₃) with emphasis on MOF/CNTs composites. This review focuses on the efficient removal of pollutants from the environment using adsorption techniques. Another important application of MOFs composite discussed in this review is sensor materials for environmental pollution.

Potential applications of graphene-based nanomaterials as adsorbent for removal of volatile organic compounds

In recent years, graphene-based materials (GBMs) have been regarded as the core technology in diverse research fields. Consequently, the demand for large-scale synthesis of GBMs has been increasing continuously for various fields of industry. These materials have become a competitive adsorbent for the removal of environmental pollutants with improved adsorption capacity and cost effectiveness through hybridization or fabrication of various functionalities on their large surface. In particular, their applicability opens up new avenues for the adsorptive removal of volatile organic compounds (VOCs) (e.g., through the build-up of efficient air purification systems). This review explored the basic knowledge and synthesis approaches for GBMs and their performances as adsorbent for VOC removal. Moreover, the mechanisms associated with the VOC removal were explained in detail. The performance of GBMs has also been evaluated along with their present limitations and future perspectives.

Novel Approaches Utilizing Metal-Organic Framework Composites for the Extraction of Organic Compounds and Metal Traces from Fish and Seafood

The determination of organic and inorganic pollutants in fish samples is a complex and demanding process, due to their high protein and fat content. Various novel sorbents including graphene, graphene oxide, molecular imprinted polymers, carbon nanotubes and metal-organic frameworks (MOFs) have been reported for the extraction and preconcentration of a wide range of contaminants from fish tissue. MOFs are crystalline porous materials that are composed of metal ions or clusters coordinated with organic linkers. Those materials exhibit extraordinary properties including high surface area, tunable pore size as well as good thermal and chemical stability. Therefore, metal-organic frameworks have been recently used in many fields of analytical chemistry including sample pretreatment, fabrication of stationary phases and chiral separations. Various MOFs, and especially their composites or hybrids, have been successfully utilized for the sample preparation of fish samples for the determination of organic (i.e., antibiotics, antimicrobial compounds, polycyclic aromatic hydrocarbons, etc.) and inorganic pollutants (i.e., mercury, palladium, cadmium, lead, etc.) as such or after functionalization with organic compounds.

Outdoor air monitoring: Performance evaluation of a gas sensor to assess episodic nuisance/odorous events using active multi-sorbent bed tube sampling coupled to TD-GC/MS analysis

In order to evaluate the performance of a commercially available metal oxide semiconductor gas sensor (TGS 2602, Figaro Engineering Inc.) for activating a monitoring system when a nuisance/odorous pollution episode of volatile organic compounds (VOCs) occur, a widely used active sampling methodology based on multi-sorbent bed tubes (Carbotrap, Carbopack X and Carboxen 569) and analysis through automatic thermal desorption-gas chromatography/mass spectrometry was used. Daily 24 h samples of multi-sorbent bed tubes were taken over a period of 14 days using an air collector pump sampler specially designed in the LCMA-UPC laboratory. Simultaneously, daily episodic samples were taken according to the activation of another LCMA-UPC sampler by the metal oxide semiconductor gas sensor. Sampling was done throughout January-February 2019 at El Morell (Tarragona, Spain), near the petrochemical area. All episode samples present higher concentrations of VOCs than 24 h samples, with an average ratio of 3.5 times for Total VOCs. VOC familial distributions present very similar values in 24 h and episode samples (r² = 0.7466), correlating significatively (F-Snedecor, p < 0.05). A higher level of VOCs in the atmosphere in general, not derived from a specific compound or a VOC/s family/ies, seems to be the trigger of the activation of the sampler by the sensor. On the other hand, no significant correlations are observed between alcohols concentrations and relative humidity (F-Snedecor, p < 0.05). Additionally, Total VOCs concentrations in episode samples are in agreement with higher percentages of NE-SSE wind directions, coming from the petrochemical complex. Hence, these aspects validate the use of the evaluated sensor for its application for the activation of samplers in air quality evaluations when episodic events occur, an interesting and innovative technique. Thus, this study is an important contribution to the understanding of the performance of gas sensors and proposes an expansion of their field of use.

Three-Dimensional-Printed Core-Shell Structured MFI-Type Zeolite Monoliths for Volatile Organic Compound Capture under Humid Conditions

Crystalline aluminosilicate zeolites with high sorption capacity and low production cost have been recognized as a promising adsorbent for volatile organic compound (VOC) capture. However, the ubiquitous water vapor in the VOC streams may compete with VOCs during the practical separation process because of the hydrophilic property of aluminosilicate zeolites. Herein, a self-supporting core-shell structured MFI-type zeolite monolith was fabricated by 3D-printing aluminosilicate ZSM-5 zeolites as the core, followed by coating silicalite-1 zeolites as a hydrophobic shell via post-hydrothermal crystallization. Natural sepiolite nanofibers (SNFs) were employed as printing ink additives for reinforcing the mechanical stability of 3D-printed ZSM-5 monoliths. Colloidal silica was also introduced into the printing inks, affording continuous growth of silicalite-1 layers (with a thickness of ∼200 nm) over ZSM-5 crystals. Such core-shell structured MFI-type zeolite monoliths exhibited superior dynamic adsorption performance for toluene at 298 K under humid conditions (relative humidity: 50%), with a saturated adsorption capacity of 44.3 mg/g. This work provides a facile strategy for designing self-supporting zeolite monoliths with core-shell architectures for adsorption/separation and other advanced applications.

Removal of toluene using ozone at room temperature over mesoporous Mn/Al2O3 catalysts

The catalytic oxidation of toluene with ozone at room temperature was carried out over hierarchically ordered mesoporous catalysts (CeO₂ (meso), Mn₂O₃ (meso), ZrO₂ (meso), and γ-Al₂O₃ (meso)) and Al₂O₃ with various textural properties and phases (γ-Al₂O₃ (meso), γ-Al₂O₃ (13 nm), and α-Al₂O₃) to examine the effects of the nature of the catalyst on the catalytic activity. The catalysts were characterized by N₂-physisorption measurements, powder X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy. Among the ordered mesoporous catalysts, γ-Al₂O₃ (meso) had the highest toluene removal efficiency because of its highest surface area and pore volume, which in turn was selected for further investigation. Manganese (Mn) was introduced to various Al₂O₃ to improve the toluene removal efficiency. Comparing the Mn-loaded catalysts supported on various Al₂O₃ with different crystalline phases or pore structures, Mn/γ-Al₂O₃ (meso), had the highest catalytic activity as well as the highest CO₂/CO ratio. The higher activity was attributed to the larger surface area, weaker interaction between Mn and Al₂O₃, and larger portion of Mn₂O₃ phase. The increase in ozone concentration led to an improvement in the carbon balance but this enhancement was insufficient due to the deposition of by-products on the catalyst. After long term tests at room temperature, the reaction intermediates and carbonaceous deposits of the used catalysts were identified.