Catalytic oxidation of toluene using a facile synthesized Ag nanoparticle supported on UiO-66 derivative

A review of non-thermal plasma -catalysis: The mutual influence and sources of synergetic effect for boosting volatile organic compounds removal

This review is aimed at researchers in air pollution control seeking to understand the latest advancements in volatile organic compound (VOC) removal. Implementing of plasma-catalysis technology for the removal of volatile organic compounds (VOCs) led to a significant boost in terms of degradation yield and mineralization rate with low by-product formation. The plasma-catalysis combination can be used in two distinct ways: (I) the catalyst is positioned downstream of the plasma discharge, known as the "post plasma catalysis configuration" (PPC), and (II) the catalyst is located in the plasma zone and exposed directly to the discharge, called "in plasma catalysis configuration" (IPC). Coupling these two technologies, especially for VOCs elimination has attracted the interest of many researchers in recent years. The term "synergy" is widely reported in their works and associated with the positive effect of the plasma catalysis combination. This review paper investigates the state of the art of newly published papers about catalysis, photocatalysis, non-thermal plasma, and their combination for VOC removal application. The focus is on understanding different synergy sources operating mutually between plasma and catalysis discussed and classified into two main parts: the effect of the plasma discharge on the catalyst and the effect of the catalyst on plasma discharge. This approach has the potential for application in air purification systems for industrial processes or indoor environments.

Toluene Oxidation: CO2 vs Benzaldehyde: Current Status and Future Perspectives

Toluene is a common and significant volatile organic compound (VOC). Although it finds extensive application in various industrial processes (chemical manufacturing, paint and adhesive production, and as a solvent), it creates a huge environmental impact when emitted freely into the atmosphere. Two solutions were found to mitigate the emission of this pollutant: the total oxidation to CO2 and H2O and the selective oxidation into benzaldehyde. This review discusses the two main alternatives for tackling this problem: converting the toluene into carbon dioxide by total oxidation or into benzaldehyde by selective oxidation. It presents new catalytic advances, new trends, and the advantages and disadvantages of both methods.

A facile cellulose finishing strategy through in-situ growth of sliver-doped manganese dioxide assisted by amine-quinone for improving indoor living quality

Nowadays, various harmful indoor pollutants especially including bacteria and residual formaldehyde (HCHO) seriously threaten human health and reduce the quality of public life. Herein, a universal substrate-independence finishing approach for efficiently solving these hybrid indoor threats is demonstrated, in which amine-quinone network (AQN) was employed as reduction agent to guide in-situ growth of Ag@MnO2 particles, and also acted as an adhesion interlayer to firmly anchor nanoparticles onto diverse textiles, especially for cotton fabrics. In contrast with traditional hydrothermal or calcine methods, the highly reactive AQN ensures the efficient generation of functional nanoparticles under mild conditions without any additional catalysts. During the AQN-guided reduction, the doping of Ag atoms onto cellulose fiber surface optimized the crystallinity and oxygen vacancy of MnO2, providing cotton efficient antibacterial efficiency over 90 % after 30 min of contact, companying with encouraging UV-shielding and indoor HCHO purification properties. Besides, even after 30 cycles of standard washing, the Ag@MnO2-decorated textiles can effectively degrade HCHO while well-maintaining their inherent properties. In summary, the presented AQN-mediated strategy of efficiently guiding the deposition of functional particles on fibers has broad application prospects in the green and sustainable functionalization of textiles.

Insight into modified CeMn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Monolithic Catalysts Supported by Emulsion-Templated Porous Polydivinylbenzene for Continuous Reduction of 4-Nitrophenol

A monolithic catalyst was fabricated through an emulsion-templating method, postpolymerization modification, and in situ loading of active constituents. To achieve a high specific surface area, divinylbenzene (DVB) was solely employed as the monomer, while the porous structure was adjusted with the porogen content and the types of initiators. Then, anchor points were introduced on the pore wall through nitration and amination of the polymeric scaffold. Using a controlled "silver mirror reaction", monolithic catalysts were obtained after loading of silver nanoparticles (Ag NPs), which was verified from morphological and crystallinity characteristics. The catalytic performance of the resultant monolithic catalyst was determined with the model reduction of 4-nitrophenol (4-NP). In static catalysis, the monolithic catalyst was proved to have a reactively high apparent rate constant and a good reusability. Furthermore, a flow reactor was fabricated with the monolithic catalyst, showing a high efficiency and long-term durability for the continuous reduction of 4-NP. This work broadened the adjustment of porous structures and the subsequent application for emulsion-templated monoliths.

G-C3N4-Ag composite mediated photocatalytic degradation of phenanthrene - A remedy for environmental pollution

In recent years, g-C3N4-Ag nanocomposite synthesis has gained considerable attention for its potential to treat polycyclic aromatic hydrocarbons (PAHs) and to act against bacteria and fungi. In this study, we present a novel approach to the synthesis of g-C3N4-Ag nanocomposite and evaluate its efficiency in both PAH removal and antimicrobial activity. The synthesis process involved the preparation of g-C3N4 by thermal polycondensation of melamine. The factors that affect the adsorption process of PAHs, like time, pH, irradiation type, and adsorbent dosage, were also evaluated. Isotherm models like Langmuir and Freundlich determined the adsorption capability of g-C3N4-Ag. In simulated models, phenanthrene was degraded to a maximum of 85% at lower concentrations of catalyst. The adsorption profile of phenanthrene obeys the pseudo-second-order and Freundlich isotherms pattern. The g-C3N4-Ag nanocomposite also exhibited antimicrobial activity against bacteria (Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Klebsiella pneumoniae) and fungi (Candida albicans). The present study is the first report stating the dual application of g-C3N4-Ag nanocomposite in reducing the concentration of PAH and killing bacterial and fungal pathogens. The higher adsorption capability proclaimed by g-C3N4-Ag nanocomposite shows the fabricated nanomaterial with great potential to remediate organic pollutants from the ecosystem.

Preparation of Fe3O4@UiO-66(Zr)@Ag NPs core-shell-satellite structured SERS substrate for trace detection of organophosphorus pesticides residues

Surface-enhanced Raman spectroscopy (SERS) technology has been revived and developed with the introduction of metal-organic frameworks (MOFs), while more valuable properties of MOFs for SERS substrates remain largely unexplored. This work constructed a new SERS substrate Fe₃O₄@UiO-66(Zr)@Ag nanoparticles (FUAs) with excellent SERS detection sensitivity, uniformity, reproducibility and stability, exhibiting a high Raman enhancement factor (5.62 × 10⁶), low limit of detection (LOD, 2.11 × 10^-11 M) and RSD (12.41 %) for 4-NBT, and maintaining 81 % SERS activity within 60 days. The FUAs took full advantage of the strong affinity of UiO-66(Zr) for organophosphorus pesticides (OPs) to realize trace OPs detection. The LODs of phoxim, triazophos and methyl parathion in apple juice were 0.041, 0.021 and 0.0031 mg/L, respectively, with good linearities ranging from 0.02 or 0.1-50 mg/L, meeting the requirements of the food control standards, indicating that the potentials and prospects of the FUAs SERS substrate for trace detecting OPs in foods.

Surfactant-Tunable Nanoparticle Assembly via a Template-Directed Strategy

Nanoparticle (NP) self-assembly from suspension evaporation has been a topic of interest in recent times to fabricate a solid-state structure with diverse functions. We present a simple and facile evaporation-induced strategy for the formation of NP arrays on a flat substrate utilizing a template-directed sandwich system. The lithographic features assist the assembly of the typical nanoparticles (NPs), including SiO₂, QDs@PS FMs, and QDs, on the top into circle, stripe, triangle, or square geometries with a fixed width of 2 μm. Additionally, an anionic surfactant, sodium dodecyl sulfonate (SDS), is incorporated into a negatively charged, hydrophilic SiO₂ dispersion to govern the aggregation and self-assembly of NPs, fine tuning the morphologies of the residual structures on the substrate. SDS is attributed to modify the nature of SiO₂ NPs to be hydrophobic, increase the hydrophobic attraction, dominating particle-particle and particle-interface interactions, and strengthen the particle-particle repulsive electrostatic force that results in the reduction of SiO₂ NPs trapped in the separated colloidal suspension drop. Thus, using the SDS surfactant with the concentration ranging from 0 to 1 wt %, the obtained well-ordered SiO₂ NP pattern packing on the substrate varies from six layers to one layer.

Recent advances of metal-organic framework-based and derivative materials in the heterogeneous catalytic removal of volatile organic compounds

Since the environmental hazards of volatile organic compounds (VOCs) are well known, heterogeneous catalysis has become one of the most popular methods to treat VOCs due to its environmental friendliness and simplicity of operation. Although a large number of reports have reviewed the application of catalytic oxidation for the degradation of VOCs, relatively few reports are based on this direction of metal organic frameworks (MOFs) and MOF derivatives. Herein, this paper reviews the recent applications of heterogeneous catalytic technologies in the degradation of VOCs, including photocatalysis, thermal catalysis and other catalytic approaches. The applications of MOFs and their derivatives in VOCs degradation, such as the progress of MOF-derived metal oxides in the treatment of toluene, were highlighted. The mechanisms of VOCs degradation by different catalytic approaches were systematically presented. Finally, we presented the views and directions of VOCs treatment technology development. We hope that this reaction type-oriented review will provide important insights into MOFs and MOF-derived materials for VOCs pollution control.

Yeast—As Bioremediator of Silver-Containing Synthetic Effluents

Yeast Saccharomyces cerevisiae may be regarded as a cost-effective and environmentally friendly biosorbent for complex effluent treatment. The effect of pH, contact time, temperature, and silver concentration on metal removal from silver-containing synthetic effluents using Saccharomyces cerevisiae was examined. The biosorbent before and after biosorption process was analysed using Fourier-transform infrared spectroscopy, scanning electron microscopy, and neutron activation analysis. Maximum removal of silver ions, which constituted 94–99%, was attained at the pH 3.0, contact time 60 min, and temperature 20 °C. High removal of copper, zinc, and nickel ions (63–100%) was obtained at pH 3.0–6.0. The equilibrium results were described using Langmuir and Freundlich isotherm, while pseudo-first-order and pseudo-second-order models were applied to explain the kinetics of the biosorption. The Langmuir isotherm model and the pseudo-second-order model fitted better experimental data with maximum adsorption capacity in the range of 43.6–108 mg/g. The negative Gibbs energy values pointed at the feasibility and spontaneous character of the biosorption process. The possible mechanisms of metal ions removal were discussed. Saccharomyces cerevisiae have all necessary characteristics to be applied to the development of the technology of silver-containing effluents treatment.

Combining the Potent Reducing Properties of Pecan Nutshell with a Solvent-Free Mechanochemical Approach for Synthesizing High Ag0 Content-Silver Nanoparticles: An Eco-Friendly Route to an Efficient Multifunctional Photocatalytic, Antibacterial, and Antioxidant Material

A straightforward, low-cost, and scalable solid-state mechanochemical protocol for the synthesis of silver nanoparticles (AgNP) based on the use of the highly reducing agri-food by-product pecan nutshell (PNS) is reported herein. Under optimized conditions (180 min, 800 rpm, PNS/AgNO₃ ratio = 55/45 w/w), a complete reduction in silver ions was achieved, leading to a material containing ca. 36% w/w Ag⁰ (X-ray diffraction analysis). Dynamic light scattering and microscopic analysis showed a uniform size distribution (15-35 nm average diameter) of the spherical AgNP. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay revealed lower-although still absolutely high (EC₅₀ = 5.8 ± 0.5 mg/mL)-antioxidant properties for PNS for the further incorporation of AgNP, supporting the efficient reduction of Ag⁺ ions by PNS phenolic compounds. Photocatalytic experiments indicated that AgNP-PNS (0.4 mg/mL) was able to induce the >90% degradation of methylene blue after 120 min visible light irradiation, with good recycling stability. Finally, AgNP-PNS demonstrated high biocompatibility and significantly light-enhanced growth inhibition properties against Pseudomonas aeruginosa and Streptococcus mutans at concentrations as low as 250 μg/mL, also eliciting an antibiofilm effect at 1000 μg/mL. Overall, the adopted approach allowed to reuse a cheap and abundant agri-food by-product and required no toxic or noxious chemicals, making AgNP-PNS a sustainable and easy-to-access multifunctional material.

Microorganisms@aMIL-125 (Ti): An Amorphous Metal-Organic Framework Induced by Microorganisms and Their Applications

Amorphous metal-organic framework (aMOF)-based materials have attracted considerable attention as an emerging class of nanomaterials. Herein, novel microorganisms@aMIL-125 (Ti) composites including yeast@aMIL-125 (Ti), PCC 6803@aMIL-125 (Ti), and Escherichia coli@aMIL-125 (Ti) composites were respectively synthesized by self-assembling aMOFs on the microorganisms' surface. The functional groups on the microorganisms' surface induced structural defects and participated in the formation of aMIL-125 (Ti) composites. Finally, the application of microorganisms@aMIL-125 (Ti) composites for the removal of glyphosate from aqueous solution was selected as a model reaction to illustrate their potential for environmental protection. The present method is not only economical but also has other advantages including ease of operation, environmentally friendly assay, and high adsorption. The maximum adsorption capacity of aMIL-125 (Ti) was 1096.25 mg g^-1, which was 1.74 times that of crystalline MIL-125 (Ti). Therefore, the microorganisms@aMOFs composites will have broad application prospects in energy storage, drug delivery, catalysis, adsorbing toxic substances, sensing, encapsulating and delivering enzymes, and in other fields.

Close-Contact Oxygen Vacancies Synthesized by FSP Promote the Supplement of Active Oxygen Species To Improve the Catalytic Combustion Performance of Toluene

Catalytic combustion is an important means to reduce toluene pollution, and improving the performance of catalytic combustion catalysts is of great significance for practical applications. The study of oxygen vacancies is one of the key steps to improve catalyst performance. Here, two different oxygen vacancy structures were well-defined and controllably synthesized by flame spray pyrolysis (FSP) to evaluate their effect on the catalytic combustion performance of toluene. The closely contacted oxygen vacancies (c-Vo) enhance the oxygen activation capacity of the catalyst, and the temperature of the first oxygen desorption peak and hydrogen reduction peak is 56 and 37 °C lower than the separated oxygen vacancy (s-Vo) sample, respectively. The oxygen activation energy barrier on the c-Vo is calculated to be negligible of only 0.04 eV. Both in situ DRIFT and DFT calculations indicate that the c-Vo structure accelerates the catalytic oxidation of p-toluene molecules. Moreover, due to the unique characteristics of high-temperature synthesis and rapid quenching, FSP brings excellent water resistance and high-temperature stability to the catalyst. In conclusion, utilizing the FSP in situ reduction strategy can create more c-Vo to improve the catalytic combustion performance of toluene.

In situ DRIFTS FT-IR and DFT study on Fe-V-W/Ti removal of NOx and VOCs

Nitrogen oxides (NO_X) and volatile organic compounds (VOCs) are generated during the coal-fired power plant's combustion. They can be simultaneously removed in SCR (selective catalytic reduction) region. Herein, the performance of V-W/Ti and Fe-V-W/Ti synthesized by wet impregnation in removing NO_X and VOCs was evaluated. XPS (X-ray photoelectron spectroscopy) result indicated that a redox cycle of Fe²⁺  + V⁵⁺  ⇌ Fe³⁺  + V⁴⁺ could form electron vacancy through electron transfer. Besides, the mechanisms of NH₃-SCR and VOCs catalytic oxidation were explored with in situ DRIFTS experience and DFT calculation. On Fe-V-W/Ti, in situ DRIFTS study found more absorption sites of NH₃, and different intermediates during simultaneously removal process. DFT calculation demonstrated that absorption energy of O₂ was decreased and O = O bond was lengthened with Fe doped. Both V-W/Ti and Fe-V-W/Ti followed the L-H mechanism and shared a common NH₃-SCR pathway: [Formula: see text]. However, the bidentate nitrate and monodentate nitrate were also revealed on Fe-V-W/Ti, which combined with NH₄⁺ and decomposed into N₂ and H₂O, or N₂O and H₂O, respectively. The detected NH₂ species combined with NO on the Fe-V-W/Ti, following the E-R mechanism. As for VOCs, the intermediates of benzene and toluene were revealed by in situ DRIFTS study, and detailed Mars-van Krevelen mechanism was discovered.

Preparation of Ni@UiO-66 incorporated polyethersulfone (PES) membrane by magnetic field assisted strategy to improve permeability and photocatalytic self-cleaning ability

Metal-organic frameworks (MOFs) have been considered as promising nanofillers to fabricate mixed matrix membranes for water treatment. However, manipulating distribution of MOFs nanoparticles in the membrane matrix remains a great challenge. In this study, UiO-66 was firstly coated by magnetic Ni via an in-situ reduction reaction, and then incorporated into polyethersulfone (PES) membrane matrix to prepare PES-Ni@UiO-66 membrane. The magnetic Ni allowed to manipulate the distribution of magnetic Ni@UiO-66 in the phase-inversion process by an external magnetic field. The hydrophilic Ni@UiO-66 can be pulled onto membrane surface by the magnetic force, endowing the prepared membrane with rather higher hydrophilicity. The prepared membrane exhibited superior water permeability with a pure water flux of 611.5 ± 19.8 L·m^-2·h^-1 and improved antifouling performance. Moreover, benifiting from photocatalytic activity of the exposed Ni@UiO-66 on membrane surface, the obtained PES-Ni@UiO-66 membrane demonstrated excellent photocatalytic self-cleaning ability with a flux recovery rate (FRR) higher than 95% under UV irradiation. Analyzing by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory indicated that the improved antifouling performance could be attributed to less attractive or even repulsive interaction between the prepared membrane and pollutants. This work provided valuable guidance for structural regulation and development of high-performance MOFs-based membranes for water treatment.

Improvement of anti-corrosion performance of an epoxy coating using hybrid UiO-66-NH2/carbon nanotubes nanocomposite

In this study, a porous nanocontainer from UiO-66-NH₂/CNTs nanocomposite with an excellent barrier characteristics was constructed through amine-functionalized Zr-based metal organic framework. The characterization of the prepared nano-materials were performed using different analyses such as FTIR, XRD, SEM, EDS, TEM, and BET and the results proved the successful synthesize of UiO-66-NH₂/CNTs nanocomposite. The corrosion protection performance of the coated panels was investigated by electrochemical impedance spectroscopy (EIS), salt spray, and contact angle measurement. The EIS results revealed that unmodified and UiO-66-NH₂ containing coating in 3.5 wt.% NaCl electrolyte were failed after 45 days but the corrosion was negligible in UiO-66-NH₂/CNTs coating due to high pore resistance values even after 45 days. Salt spray and contact angle measurements confirmed that UiO-66-NH₂/CNTs containing coating acts as an efficient barrier against wet saline environment even at long exposure times. This is attributed to uniform dispersion in the epoxy matrix and formation of a uniform nanocomposite coating.

Normal temperature catalytic degradation of toluene over Pt/TiO2

Normal temperature catalytic ozonation is an effective method for the removal of volatile organic compounds (VOCs). A series of TiO₂-supported noble metal catalysts were synthesized by a facile impregnation method. The as-prepared catalysts were evaluated for the catalytic oxidation of toluene. It was determined that the 1 wt%Pt/TiO₂ exhibited outstanding performance that 65% conversion of toluene was achieved with the space velocity of 30,000 h^-1 even at room temperature (25°C). The structure-activity relationship of various catalysts was investigated via BET, XRD, SEM, TEM as well as XPS. The results indicated that the uniform dispersion of Pt nanoparticles, abundant surface adsorbed oxygen species as well as the strong interaction between Pt and TiO₂ favoured toluene degradation at normal temperature. Based on FT-IR, a simplified reaction scheme was proposed: toluene was first oxidized to benzoate species then alcohol species, ketones, carboxyl acids, which was finally degraded into CO₂ and H₂O. The low activation energy of 1 wt%Pt/TiO₂ determined to be 47 kJ mol^-1 also benefited for toluene degradation at ambient temperature.

Uniform platinum nanoparticles loaded on Universitetet i Oslo-66 (UiO-66): Active and stable catalysts for gas toluene combustion

Highly dispersed Pt nanoparticles supported UiO-66 catalysts were successfully prepared by the incipient wetness impregnation method. Their thermal catalytic performances were evaluated by toluene degradation. The physicochemical properties of the samples were characterized using a series of characterization methods. The catalytic activity of catalysts remained essentially unchanged in the high weight hourly space velocity, stability and water resistance test, which also indicated good catalytic performance. In the reusability test, the catalytic performance was found to be enhanced after the reaction, because of the catalyst might follow a Pt⁰-PtO synergistic catalytic mechanism (similar to Mars-van Krevelen mechanism) and there was a phase transition between Pt⁰ and PtO during the reaction. Firstly, the toluene adsorbed on the catalyst surface was oxidized by the activated lattice oxygen of the PtO. Then, consumption of oxygen atoms led to formation of oxygen vacancies, and finally the molecular oxygen adsorbed by Pt⁰ was activated and passed to the PtO to supplement the oxygen vacancies, forming a redox cycle. In addition, the possible catalytic oxidation mechanism of toluene was also revealed.

Amorphous zirconium metal-organic frameworks assembled from mixed porphyrins as solvent-free catalysts for Knoevenagel condensation

Three mixed porphyrins, icpp (1–3) were synthesized via the reactions of 4-formylbenzoic acid and 4-imidazolecarboxaldehyde in different proportions, and then five amorphous or crystalline Zr-MOFs—SPUZ (1–5) were obtained from icpp...

Construction of UiO-66/Bi4O5Br2 Type-II Heterojunction to Boost Charge Transfer for Promoting Photocatalytic CO2 Reduction Performance

One of the basic challenges of CO₂ photoreduction is to develop efficient photocatalysts, and the construction of heterostructure photocatalysts with intimate interfaces is an effective strategy to enhance interfacial charge transfer for realizing high photocatalytic activity. Herein, a novel UiO-66/Bi₄O₅Br₂ heterostructure photocatalyst was constructed by depositing UiO-66 nanoparticles with octahedral morphology over the Bi₄O₅Br₂ nanoflowers assembled from the Bi₄O₅Br₂ nanosheets via an electrostatic self-assembly method. A tight contact interface and a built-in electric field were formed between the UiO-66 and the Bi₄O₅Br₂, which was conducive to the photo-electrons transfer from the Bi₄O₅Br₂ to the UiO-66 and the formation of a type-II heterojunction with highly efficient charge separation. As a result, the UiO-66/Bi₄O₅Br₂ exhibited improved photocatalytic CO₂ reduction performance with a CO generation rate of 8.35 μmol h⁻¹ g⁻¹ without using any sacrificial agents or noble co-catalysts. This work illustrates an applicable tactic to develop potent photocatalysts for clean energy conversion.

Recent Progress in Metal-Organic Framework-Derived Nanostructures in the Removal of Volatile Organic Compounds

Air is the most crucial and life-supporting input from nature to the living beings of the planet. The composition and quality of air significantly affects human health, either directly or indirectly. The presence of some industrially released gases, small particles of anthropogenic origin, and the deviation from the normal composition of air from the natural condition causes air pollution. Volatile organic compounds (VOCs) are common contaminants found as indoor as well as outdoor pollutants. Such pollutants represent acute or chronic health hazards to the human physiological system. In the environment, such polluted gases may cause chemical or photochemical smog, leading to detrimental effects such as acid rain, global warming, and environmental pollution through different routes. Ultimately, this will propagate into the food web and affect the ecosystem. In this context, the efficient removal of volatile organic compounds (VOCs) from the environment remains a major threat globally, yet satisfactory strategies and auxiliary materials are far from being in place. Metal–organic frameworks (MOFs) are known as an advanced class of porous coordination polymers, a smart material constructed from the covalently bonded and highly ordered arrangements of metal nodes and polyfunctional organic linkers with an organic–inorganic hybrid nature, high porosities and surface areas, abundant metal/organic species, large pore volumes, and elegant tunability of structures and compositions, making them ideal candidates for the removal of unwanted VOCs from air. This review summarizes the fundamentals of MOFs and VOCs with recent research progress on MOF-derived nanostructures/porous materials and their composites for the efficient removal of VOCs in the air, the remaining challenges, and some prospective for future efforts.

Metal organic framework-templated fabrication of exposed surface defect-enriched Co3O4 catalysts for efficient toluene oxidation

Exposed surface defect-enriched Co₃O₄ catalysts derived from metal organic framework (MOF) were fabricated by the promotion of surface Mn species for toluene oxidation. The incorporation of Mn species into Co₃O₄ surface lattice could give rise to the local lattice distortion in spinel structure, resulting in highly exposed surface defect rather than bulk defect. More Co³⁺ species were also exposed on the surface of MnO_x/Co₃O₄ samples owing to the electron transfer from Co to Mn species by the occupation of surface Mn in octahedral Co³⁺ sites. Accordingly, the low-temperature reducibility and high mobility of lattice oxygen were significantly improved in virtue of the highly exposed surface defect and predominately surface Co³⁺ sites, thus promoting the catalytic activity and stability for toluene oxidation. Moreover, the toluene conversion decreased with the increase of weight hourly space velocity (WHSV). In situ DRIFTS results confirmed the continuous oxidation process for toluene degradation, and the conversion of benzoate into maleic anhydride should be the rate-controlling step.

Toxicity and photosynthetic inhibition of metal-organic framework MOF-199 to pea seedlings

Metal-organic framework (MOF) materials are star materials with unique structures and properties. To ensure safe production and applications, the toxicity and environmental hazards of MOF materials should be thoroughly investigated. However, the environmental impact of MOF materials on plants is completely unknown. Herein, we reported the toxicity and photosynthetic inhibitory properties of MOF-199 to pea plants (Pisum sativum L.). MOF-199 was synthesized by hydrothermal method. MOF-199 was copper containing double-pyramid of high surface area (668 m2/g). MOF-199 accelerated the germination of pea seeds, but the total germination rates were unchanged. MOF-199 inhibited the seedling growth at high concentrations. The net photosynthetic rate increased, while the total photosynthesis capability decreased. Damage to the acceptor side of photosystem II was evidenced by chlorophyll fluorescence. Mechanistically, MOF-199 released Cu2+ in the nutrient solution, led to Cu2+ accumulations in seedlings, and promoted oxidative stress. In addition, the photosynthetic inhibitions of MOF-199 were stronger than equivalent concentrations of Cu(NO3)2, implying that MOF-199 particles also contributed to the environmental hazards. Our results highlighted the potential threat of MOF materials to plant growth and photosynthesis.

Mechanochemical Synthesis of Nickel-Modified Metal–Organic Frameworks for Reduction Reactions

In this work, we report the incorporation of nickel oxide nanoparticles into a metal–organic framework (MOF) structure by a solvent-free mechanochemical strategy. In particular, the zirconium-based MOF UiO-66 was modified with different Ni loadings and characterized using complementary techniques including X-ray diffraction (XRD), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The catalytic potential of the as-prepared Ni/UiO-66 materials in the hydrogenation reaction of methyl levulinate using 2-propanol as hydrogen donor solvent has been investigated under flow conditions. Under optimized conditions, the 5%Ni/UiO-66 led to the best catalytic performance (70% yield, 100% selectivity to gamma-valerolactone), which could be attributed to the higher content of the Ni species within the MOF structure. The obtained results are promising and contribute to highlighting the great potential of MOFs in biomass upgrading processes, opening the path to the sustainable development of the chemical industry.

Boosting benzene combustion by engineering oxygen vacancy-mediated Ag/CeO2-Co3O4 catalyst via interfacial electron transfer

Oxygen vacancy (O_v) engineering is a widely accepted effective strategy to manipulate the catalytic activity for volatile organic compounds (VOCs) abatement. Herein, we report the oxygen vacancy-mediated Ag/CeO₂-Co₃O₄ catalyst to boost benzene combustion. The incorporation of Ag species in Ag/CeO₂-Co₃O₄ induces the predominately exposed surface Co³⁺ sites and structural distortion of Co₃O₄ as well as rich oxygen vacancy owing to the improved interfacial electron transfer, which promote the adsorption of benzene and the dissociation of oxygen. The low-temperature reducibility and mobility of oxygen species are also improved due to the generation of oxygen vacancy. The isotopic ¹⁸O₂ exchange experiments demonstrate that abundant oxygen vacancies contribute to the rapid generation of active oxygen species, and the consumed oxygen vacancies can be compensated steadily during benzene oxidation. In-situ DRIFTS results reveal that benzene oxidation is a continuous oxidation process, and active oxygen species plays a crucial role in the deep oxidation of benzene by engineering oxygen vacancy. This work provides an efficient strategy for designing high-performance environmental catalysts for VOCs abatement.

Efficient catalytic degradation of toluene at a readily prepared Mn-Cu catalyst: Catalytic performance and reaction pathway

Fabricating of economical transitional metal oxide-based materials with satisfied low-temperature catalytic performance and application perspective is still a challenge in deep degradation of VOCs. Here, Mn-Cu bimetallic oxides were facilely prepared by one-step hydrothermal-redox method, which displayed much higher catalytic activity in toluene oxidation than those synthesized by hydrolysis-driven redox-precipitation or co-precipitation approach. It is shown that the lattice defect and oxygen vacancy concentration over prepared materials can be tuned by controlling Cu/Mn molar ratio. Amongst, spinel structured MnCu_0.5 exhibited the highest catalytic activity, superior durability and water resistance in toluene total oxidation owing to abundant surface adsorbed oxygen species, excellent low-temperature reducibility, and high amounts of Cu⁺ and Mn³⁺. In detail, the reaction rate of MnCu_0.5 was over 9.0 times higher than that of MnCu_0.75, MnCu_0.75-P and MnCu_0.75-H₂O₂ at relative low temperature of 210 °C. The cyclic redox process with easier oxygen species mobility played a key role in the catalytic oxidation of toluene. Typical reaction intermediates as benzyl alcohol, benzaldehyde, benzene, phenol, and benzoquinone could be detected by PTR-MS, which further decomposed to acetone, ethanol, ketone, acetic acid, methanol, formaldehyde and acetaldehyde species by ring opening before total mineralization.

MOF based engineered materials in water remediation: Recent trends

The significant upsurge in the demand for freshwater has prompted various developments towards water sustainability. In this context, several materials have gained remarkable interest for the removal of emerging contaminants from various freshwater sources. Among the currently investigated materials for water treatment, metal organic frameworks (MOFs), a developing class of porous materials, have provided excellent platforms for the separation of several pollutants from water. The structural modularity and the striking chemical/physical properties of MOFs have provided more room for target-specific environmental applications. However, MOFs limit their practical applications in water treatment due to poor processability issues of the intrinsically fragile and powdered crystalline forms. Nevertheless, growing efforts are recognized to impart macroscopic shapability to render easy handling shapes for real-time industrial applications. Furthermore, efforts have been devoted to improve the stabilities of MOFs that are subjected to fragile collapse in aqueous environments expanding their use in water treatment. Advances made in MOF based material design have headed towards the use of MOF based aerogels/hydrogels, MOF derived carbons (MDCs), hydrophobic MOFs and magnetic framework composites (MFCs) to remediate water from contaminants and for the separation of oils from water. This review is intended to highlight some of the recent trends followed in MOF based material engineering towards effective water regeneration.

Catalytic mechanism and pathways of 1, 2-dichloropropane oxidation over LaMnO3 perovskite: An experimental and DFT study

The rational comprehension on the catalytic mechanism and pathways of chlorinated volatile organic compounds (CVOCs) oxidation is meaningful for the design of high performance catalytic materials. Herein, we attempted to elucidate the catalytic mechanism and pathways of 1, 2-dichloropropane (1, 2-DCP) oxidation over LaMnO₃ perovskite from experimental and theoretical studies. Experimental results indicate that the initial dechlorination of 1, 2-DCP into allyl chloride (AC) can be readily achieved over LaMnO₃, while the further decomposition of AC is more vulnerable to be affected by the reaction conditions and strongly dependent on the surface active oxygen species. Density functional theory (DFT) calculation reveals that the heterogeneous conversion of 1, 2-DCP initiates with the chemisorption on the Mn site, followed by the formation of AC via a synergistic mechanism. AC decomposition is considered as the rate-determining step under an inert condition, while the dechlorination of adsorbed 1, 2-DCP dominates the whole reaction under an oxygen atmosphere.

Polyhedral cobalt oxide supported Pt nanoparticles with enhanced performance for toluene catalytic oxidation

Polyhedral CoO_x was synthesized by calcination of Co-based metal-organic framework ZIF-67 and highly dispersed Pt nanoparticles were successfully loaded on CoO_x. The catalytic results showed that Pt_nano/CoO_x had the best activity and stability. As compared with conventional Co₃O₄, polyhedral CoO_x showed more excellent catalytic oxidation performance of toluene, which was related to enhanced oxygen mobility, defective structure and rich active oxygen species provided by Polyhedral CoO_x. Moreover, Pt-CoO_x metal-support interaction enhanced the dispersion of Pt species and showed more Pt⁰ ratio. It was reasonable that the gaseous O₂ can be activated directly or moved into the catalyst's surface to form oxygen cycle.

Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Anatase/rutile titanium dioxide (TiO₂) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m² g^-1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O₂/Ar at the temperature of 600 °C (M-O-600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO₂. The weight fractions of rutile and anatase TiO₂ of M-O-600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M-O-600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O₂^-) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H₂O and CO₂. Gas chromatography-mass spectrometry (GC-MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M-O-600 during photocatalysis.