Manganese-cerium composite oxide pyrolyzed from metal organic framework supporting palladium nanoparticles for efficient toluene oxidation

Controllable deposition of dispersed Pd nanoparticles on ZnO for Suzuki-Miyaura cross-coupling reactions

Palladium nanoparticles find extensive applications in catalysis in both homogeneously and heterogeneously catalyzed processes. Supporting metal nanoparticles enhances their stability as compared to their unsupported counterparts. The role of catalytic support is increasingly recognized as crucial in determining the behaviour of these materials. However, controlling the deposition and anchoring of palladium nanoparticles remains a significant challenge. This contribution discusses the preparation of straight lines of palladium particles on zinc oxide by wet impregnation. This phenomenon is attributed to the highly stepped morphology of the employed ZnO that created steric anchoring sites to stabilize the metal particles. Palladium-based catalysts were evaluated for the valuable Suzuki-Miyaura cross-coupling reaction. The dispersed Pd/ZnO catalyst achieved a conversion rate of 86% with 100% selectivity, remarkably superior to that of the Pd/Al2O3 and Pd/TiO2 counterparts.

Selective and controlled H2 generation upon additive-free HCOOH dehydrogenation over a Pd/NCS nanocatalyst

Although sodium formate is widely used as a conventional additive to enhance selective H2 evolution from HCOOH dehydrogenation, this leads to a waste of resources and an increase in the cost of H2 production. For this reason, N-doped carbon nanospheres with abundant graphitic C/N have been designed to enrich the electron cloud density of the Pd atom for improving its catalytic activity in H2 generation upon additive-free HCOOH dehydrogenation. Herein, we have synthesized N-doped carbon nanosphere-stabilized Pd nanoparticles (Pd/NCSs) as high-efficiency nano-catalysts, via fixation of Pd nanoparticles onto N-doped carbon nanospheres (NCSs), for selective and controlled H2 generation upon additive-free HCOOH dehydrogenation. Pd/NCS-800 (1640 h-1) provided a 12 times larger TOF than commercial Pd/C (134 h-1) in H2 generation upon additive-free HCOOH dehydrogenation. It seemed that graphitic N/C of NCS-800 enriched the electron cloud density of the Pd atom, which was favorable for the cleavage of C-H bonds in HCOOH dehydrogenation. In addition, the selective H2 evolution from additive-free HCOOH dehydrogenation over Pd/NCS-800 is successfully controlled by adjusting the pH.

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.

The important role of the interaction between manganese minerals and metals in environmental remediation: a review

With illegal discharge of wastewater containing inorganic and organic pollutants, combined pollution is common and needs urgent attention. Understanding the migration and transformation laws of pollutants in the environment has important guiding significance for environmental remediation. Due to the characteristics of adsorption, oxidation, and catalysis, manganese minerals play important role in the environment fate of pollutants. This review summarizes the forms of interaction between manganese minerals and metals, the environmental importance of the interaction between manganese minerals and metals, and the contribution of this interaction in improving performance of Mn-based composite for environmental remediation. The literatures have indicated that the interactions between manganese minerals and metals involve in surface adsorption, lattice replacement, and formation of association minerals. The interaction between manganese minerals and metals plays an important role in environmental behavior of element and environmental significance of manganese minerals. The synergistic or antagonistic effect resulted from the interaction influence the purification of heavy metal and organism pollutant. The synergistic effect benefited from the coordination of adsorption and oxidation, convenient electron transfer, abundant oxygen vacancies, and fast migration of lattice oxygen. Based on the synergy, Mn-based composites have been widely used for environmental remediation. The synthesize methods of Mn-based composites mainly include homogeneous coprecipitation, chemical etching route, hydrothermal, homogeneous chelating sol-gel, and ethylene glycol reduction strategy. This review is helpful to fully understand the migration and transformation process of pollutants in the environment, expand the resource utilization of manganese minerals for environmental remediation.

Surface Modification by Amino Group Inducing for Highly Efficient Catalytic Oxidation of Toluene over a Pd/KIT-6 Catalyst

Toluene is one of the typical volatile organic compounds in industry, particularly in energy and fuels production processes, which is required to be eliminated effectively to protect the environment. Catalytic oxidation of toluene is widely studied for its high efficiency, and rational design and synthesis of metal catalysts are keys for toluene oxidation. In this study, an efficient catalyst was designed and synthesized by introducing -NH₂ groups on the ordered mesoporous silica (KIT-6) surface to anchor and disperse Pd species, leading to Pd nanoparticles being highly dispersed with uniform particle size distribution. Meanwhile, it was found that the introduction of -NH₂ made Pd centers present an electron-rich state, and the active Pd centers could activate O₂ molecules to generate more reactive oxygen species and promote the conversion of toluene, which was verified by in situ XPS and O₂-TPD characterization. Compared with the catalysts prepared by an impregnation method, the catalytic performance of the Pd/NH₂-KIT-6 (0.5 wt %) catalyst was significantly improved. A conversion of 90% for toluene (2400 ppm, 24,000 mL·g^-1·h^-1) was achieved at 171 °C, and the toluene conversion was maintained above 90% for 900 min, displaying the excellent activity and stability of the Pd/NH₂-KIT-6 catalyst.

Pd/δ-MnO2 nanoflower arrays cordierite monolithic catalyst toward toluene and o-xylene combustion

Exploring high-efficiency and stable monolithic structured catalysts is vital for catalytic combustion of volatile organic compounds. Herein, we prepared a series of Pd/δ-MnO₂ nanoflower arrays monolithic integrated catalysts (0.01–0.07 wt% theoretical Pd loading) via the hydrothermal growth of δ-MnO₂ nanoflowers onto the honeycomb cordierite, which subsequently served as the carrier for loading the Pd nanoparticles (NPs) through the electroless plating route. Moreover, we characterized the resulting monolithic integrated catalysts in detail and evaluated their catalytic activities for toluene combustion, in comparison to the controlled samples including only Pd NPs loading and the δ-MnO₂ nanoflower arrays. Amongst all the monolithic samples, the Pd/δ-MnO₂ nanoflower arrays monolithic catalyst with 0.05 wt% theoretical Pd loading delivered the best catalytic performance, reaching 90% toluene conversion at 221°C at a gas hourly space velocity (GHSV) of 10,000 h⁻¹. Moreover, this sample displayed superior catalytic activity for o-xylene combustion under a GHSV of 10,000 h⁻¹. The monolithic sample with optimal catalytic activity also displayed excellent catalytic stability after 30 h constant reaction at 210 and 221°C.

Advances in Matrix-Supported Palladium Nanocatalysts for Water Treatment

Advanced catalysts are crucial for a wide range of chemical, pharmaceutical, energy, and environmental applications. They can reduce energy barriers and increase reaction rates for desirable transformations, making many critical large-scale processes feasible, eco-friendly, energy-efficient, and affordable. Advances in nanotechnology have ushered in a new era for heterogeneous catalysis. Nanoscale catalytic materials are known to surpass their conventional macro-sized counterparts in performance and precision, owing it to their ultra-high surface activities and unique size-dependent quantum properties. In water treatment, nanocatalysts can offer significant promise for novel and ecofriendly pollutant degradation technologies that can be tailored for customer-specific needs. In particular, nano-palladium catalysts have shown promise in degrading larger molecules, making them attractive for mitigating emerging contaminants. However, the applicability of nanomaterials, including nanocatalysts, in practical deployable and ecofriendly devices, is severely limited due to their easy proliferation into the service environment, which raises concerns of toxicity, material retrieval, reusability, and related cost and safety issues. To overcome this limitation, matrix-supported hybrid nanostructures, where nanocatalysts are integrated with other solids for stability and durability, can be employed. The interaction between the support and nanocatalysts becomes important in these materials and needs to be well investigated to better understand their physical, chemical, and catalytic behavior. This review paper presents an overview of recent studies on matrix-supported Pd-nanocatalysts and highlights some of the novel emerging concepts. The focus is on suitable approaches to integrate nanocatalysts in water treatment applications to mitigate emerging contaminants including halogenated molecules. The state-of-the-art supports for palladium nanocatalysts that can be deployed in water treatment systems are reviewed. In addition, research opportunities are emphasized to design robust, reusable, and ecofriendly nanocatalyst architecture.

Revealing the mechanism of high water resistant and excellent active of CuMn oxide catalyst derived from Bimetal-Organic framework for acetone catalytic oxidation

Environmental H₂O is an influential factor in the low-temperature catalytic oxidation of volatile organic compounds (VOCs), and it significantly impacts the reaction process and mechanism. Here, a series of rod-like Cu-Mn oxides were synthesised by pyrolysing Cu/Mn-BTC for acetone oxidation. The results confirm that the formation of multiphase interfaces have more excellent catalytic performance compared to single-phase catalysis. This phenomenon can be attributed to the formation of multiphase interfaces, which resulted in the synthesized catalysts with more active oxygen species and defective sites. The CuMn₂O_x catalyst exhibited superior catalytic performance (T₉₀ = 150 °C), high water resistance and long-term stability. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy and thermal desorption-gas chromatography-mass spectrometry results indicated that the degradation pathway of acetone was as follows: acetone ((CH₃)₂CO*) → enolate complexes ((CH₂) = C(CH₃) O*) → acetaldehyde ((CH₃CHO*) → acetate (CH₃COO*) → formate (HCOO*) → CO₂ and H₂O. At a low-temperature, water vapour dissociated a large number of activated hydroxyl groups on the multiphase interface, which promoted the dissociation of enolate complexes and acetaldehyde species. This composite oxide is a promising catalyst for removing oxygenated VOCs at high humidity.

Constructing a Pt/YMn2O5 Interface to Form Multiple Active Centers to Improve the Hydrothermal Stability of NO Oxidation

The hydrothermal stability of NO oxidation is the key to the practical application of diesel oxidation catalysts in diesel engines, which in the laboratory requires that NO activity does not decrease after aging for 10 h with 10% H₂O/air at 800 °C. On the one hand, the construction of a metal/oxide interface can lead to abundant oxygen vacancies (O_v), which compensate for the loss of activity caused by the aggregation of Pt particles after aging. On the other hand, YMn₂O₅ (YMO) has excellent thermal stability and NO oxidation capacity. Therefore, a Pt/YMn₂O₅-La-Al₂O₃ (Pt/YMO-LA) catalyst was prepared by the impregnation method. The support of the catalyst, YMn₂O₅-La-Al₂O₃ (YMO-LA), was obtained by mixing high specific surface LA and YMO ball-milling. Under laboratory-simulated diesel exhaust flow, the NO oxidation performance of Pt/YMO-LA did not decrease after hydrothermal aging. Combining high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and oxygen temperature-programmed desorption (O₂-TPD), the Pt/YMn₂O₅ interface was formed after hydrothermal aging, and the increased O_v can provide reactive oxygen to Pt and YMO. The cooperative catalysis of multiple active centers composed of Pt, YMO, and O_v is the crucial factor to maintain the NO oxidation performance. In addition, in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) show that an increase in O_v is beneficial to the adsorption and desorption of more nitrate and nitrite intermediates, thus achieving the hydrothermal stability of NO oxidation.

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.

Insight into the potential application of CuOx/CeO2 catalysts for NO removal by CO: a perspective from the morphology and crystal-plane of CeO2

A series of CuOx/CeO2-X were fabricated and employed as the NO + CO reaction catalysts.

Graphitic carbon nitride/NH2-MIL-101(Fe) composite for environmental remediation: Visible-light-assisted photocatalytic degradation of acetaminophen and reduction of hexavalent chromium

Herein, an efficient photocatalyst composed of graphitic carbon nitrate and iron-based metal-organic framework (g-C₃N₄/NH₂-MIL-101(Fe)) composite was fabricated by a solvothermal method for the degradation of acetaminophen (AAP) and reduction of Cr(VI) under sunlight illumination. The composite was confirmed by X-ray diffraction. UV-visible spectra showed that the bare g-C₃N₄, pure Fe-MOF, and composite harvest solar light effectively. The photocatalytic experiment indicated that the composite exhibited superior reduction efficiency of Cr(VI) (66%) compared to the bare g-C₃N₄ (35%) and pure Fe-MOF (51%) at pH 7. As the pH decreases from 9 to 2, the reduction efficiency increased. The highest Cr(VI) reduction (91%) was observed at pH 2. On the other hand, the catalyst degraded 94% of AAP at pH 7 compared to the bare g-C₃N₄ (42%) and pure Fe-MOF (60%) in the presence of hydrogen peroxide. A radical scavenger experiment endorsed that the generation of superoxide radicals was the main reason for the AAP degradation. The cyclic stability test indicated that there was no substantial decrease in the degradation efficiency of AAP after ten repeated cycles. The kinetic studies showed that the photodegradation of AAP and reduction Cr(VI) was well-fitted to the first-order kinetics. Gas chromatography-mass spectrometry analysis showed that hydroquinone, aliphatic carboxylic acids, monohydroxy, and dihydroxy paracetamol were the main products formed as a result of such degradation process. Therefore, the iron-based MOF and their composites can be used as effective photocatalysts for pollutants degradation.

Rapid reduction of real-time industry effluent using novel CuO/MIL composite

In this study, a series of novel metal organic framework based composite materials was synthesized using a facile combustion synthesis method. The synthesized materials were characterized using standard analytical techniques for crystallite size, surface functional groups, surface area, porosity, optical properties, and particle size. The increase in the amount of CuO in the composite material resulted decrease in surface area and pore volume. The band-gap energy of the synthesized composites reduced with increase in the amount of CuO. Among the composite, 0.9 CuO:0.1 MIL displayed least emission intensity indicating lower electron-hole recombination and thereby superior charge separation of the material. The increase in the amount of CuO NPs in the composite resulted in increase in the average particle size and decrease in the zeta potential. As an application, the NaBH₄-mediated reduction of Methyl orange dye was studied using the synthesized materials. The increased amount of CuO in the composite resulted in the higher activity of the material. Highest activity was observed with the composite containing 9:1 ratio of CuO and MIL, and this material was further used to investigate the reduction of methylene blue, Rhodamine B, 4-nitrophenol, 2-nitrophenol, and 2, 4-dichlorophenol. The material exhibited excellent activity for all the selected organic pollutants. Finally, the composite containing 9:1 ratio of CuO and MIL was employed for the reduction of a real-time industry effluent and the observed results were encouraging. The reusability aspect of the synthesized material was investigated. Based on the LC-MS analysis, a possible reduction mechanism is proposed.

Preparation of novel and highly active magnetic ternary structures (metal-organic framework/cobalt ferrite/graphene oxide) for effective visible-light-driven photocatalytic and photo-Fenton-like degradation of organic contaminants

Herein, MIL-101(Fe), CoFe₂O₄, novel binary (MIL-101(Fe)/CoFe₂O₄, MIL-101(Fe)/GO and CoFe₂O₄/GO), and ternary (MIL-101(Fe)/CoFe₂O₄/(3%)GO and MIL-101(Fe)/CoFe₂O₄/(7%)GO) magnetic composites based upon the MIL-101(Fe) were synthesized. The XRD, FESEM, TEM, EDX, BET-BJH, FTIR, VSM, DRS, PL, EIS and other electrochemical analyses were applied to characterize samples. The MIL/CoFe₂O₄/(3%)GO demonstrated the best performance compared to other samples for visible light photocatalytic and photo-Fenton-like degradation of Direct Red 23 (DtR-23), Reactive Red 198 (ReR-198) dyes as well as Tetracycline Hydrochloride (TC-H) antibiotic. Degradation of dyes using the ternary composite after 70 min of visible light irradiation was greater than that of 99%. The presence of the optimum GO as a strong electron acceptor in MIL/CoFe₂O₄/(3%)GO not only led to the effective separation of charge carriers and thus reduction of their recombination but also increased the absorption of visible light. The composite possessed good durability in terms of stability and reusability. The PL, EIS and electrochemical analyses indicated that the MIL/CoFe₂O₄/(3%)GO improved the optical properties and photocatalytic performance.

Simultaneous removal of Zn2+ and p-nitrophenol from wastewater using nanocomposites of montmorillonite with alkyl-ammonium and complexant

Three types of alkyl-ammonium with different branching chains and three complexants with different functional groups were used to prepare alkyl-ammonium or complexant intercalated montmorillonite nanocomposite (A-Mt or C-Mt). In addition, synergistic intercalated montmorillonite nanocomposites (A/C-Mt) with alkyl-ammonium along with complexant were also prepared. The adsorption performance of the various nanocomposites toward Zn²⁺ and p-nitrophenol (PNP) from simulated binary wastewater containing both Zn²⁺ and PNP were systematically investigated. Characterization of Mt nanocomposites showed that both alkyl-ammoniums and complexants were successfully intercalated into the interlayers of Mt. The surfactant loading amounts of the various nanocomposites were also determined and correlated with the resulting expansion of the interlayer spacing. It was found that intercalation of alkane (OTAC) and -SH (CSH) were conducive to the adsorption of Zn²⁺ while -C₂H₄NH (TETA) and all alkyl-ammoniums were beneficial for PNP adsorption. The extent of adsorption was found to be controlled primarily by pH, i.e., the higher pH had a good effect on the adsorption of both Zn²⁺ and PNP. The adsorption process of Zn²⁺ onto Mt nanocomposites was more in line with the Freundlich model (R² = 0.99), while the Langmuir model described the adsorption of PNP well (R² = 0.99). The adsorption kinetics could be well described by the Elovich equation (R² = 0.98) and the double-constant model (R² = 0.89). Chemical adsorption was determined to be the dominant process between the contaminant and Mt nanocomposite surfaces.

Comprehensive evaluation of ionic liquid [Bmim][PF6] for absorbing toluene and acetone

Absorption is an eminent technology for volatile organic compounds (VOCs) elimination with the merits of high efficiency and low cost. Absorbent plays a critical role in the absorption process, and the thermal stability, saturation capacity, and regeneration performance should be concerned. As a kind of green and eco-friendly solvent, ionic liquid (IL) is expected to be a substitute for the conventional VOCs absorbent. In this study, 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) is employed to absorb the modeling VOCs (toluene and acetone). Moreover, the used [Bmim][PF₆] is recovered by thermal distillation and the reusability is then conducted by consecutive batch experiments. Based on that, the thermal stability of [Bmim][PF₆] is comprehensively examined, in which the kinetic and thermodynamic parameters are also calculated. Results reveal that [Bmim][PF₆] owned promising toluene absorption performance with inlet concentration of 3000 mg/m³ and flow rate of 300 mL/min at 20 °C, it possesses the saturated adsorption capacity of 5.16 mg/g. [Bmim][PF₆] also shows satisfying thermal stability up to 610 K. In addition, thermal distillation is proved to be a reliable regeneration route on account of the recovered [Bmim][PF₆] remained satisfying capacity even after five cycles.

Process optimization for the synthesis of ceramsites in terms of mechanical strength and phosphate adsorption capacity

Red mud (RM), an industrial waste of bauxite refinery, shows great potential in adsorptive phosphate immobilization but granulation of RM enables the ease for field application. Red-mud-based ceramsites with 12 compositions that blended Korean red mud, American red mud, ocher, and bentonite were synthesized through firing process (600-1000 °C). The porosity, bulk density, mechanical strength, mineralogical composition, and phosphate adsorption capacity of granulated RM were characterized and analyzed. The crystallization of plagioclases, nepheline and gehlenite was observed in the ceramsites with high alkali flux content, which enhanced both porosity and phosphate adsorption capacity. The characteristics of the ceramsites without phase transition were highly correlated with porosity. The mechanical strength of ceramsites was governed by crack population, describable by the Weibull distribution model, and thus the maximal tensile stress correlated negatively with porosity. Results showed that 32 wt % of KRREM and USREM treated at 1000 and 900 °C, respectively, yielded the best performing ceramites in terms of mechanical strength and phosphate adsorption capacity. Ultimately, the phosphate adsorption capacity, as affected by initial phosphate concentration, contact time, and temperature, of the optimized ceramsites was studied.

Insights into ferulic acid detoxification mechanism by using a novel adsorbent, AEPA250: The microinteraction of ferulic acid with AEPA250 and Saccharomyces cerevisiae

In this study, a novel adsorbent, Air Environment-prepared Adsorbent at 250 ℃ (AEPA₂₅₀), was used to detoxify the main fermentation inhibitor (ferulic acid) present in the alkali-pretreated hydrolysate. AEPA₂₅₀ reduced the effective concentration of ferulic acid by its adsorption, thereby decreasing the possible interaction of ferulic acid with Saccharomyces cerevisiae. The results indicated that AEPA₂₅₀ functionalized with hydroxyl, carboxyl, and amino groups under acidic conditions with higher binding energies (-45.667, -27.046, and -11.008 kcal mol^-1, respectively) and electronic cloud overlap and shorter bond distances (1.015, 1.010, and 2.094 Å, respectively) than those under the other pH conditions. These differences revealed that the electrostatic interaction dominated ferulic acid adsorption on AEPA₂₅₀. Additionally, under acidic conditions and for carboxyl group functionalized AEPA₂₅₀, energy band gap values of Eg1 were higher than those of Eg2, indicating that ferulic acid provided the π-electrons for the π-π electron donor-acceptor interactions with AEPA₂₅₀. Furthermore, ferulic acid detoxification after AEPA₂₅₀ adsorption caused the regulation of YDR316W-B and YPR137C-B genes of S. cerevisiae. These results might contribute to the development of other more efficient adsorbents and pretreatment methods and allow yeast engineering for improving the scale-up and self-sufficient production of bioethanol in the future.

Effect of Cr doping in promoting the catalytic oxidation of dichloromethane (CH2Cl2) over Cr-Co@Z catalysts

A core-shell catalyst which consists of a Co₃O₄ core and ZSM-5 shell, was prepared by microwave hydrothermal method and subjected for dichloromethane (DCM) oxidation. Chromium, cerium, niobium, and manganese species were separately introduced into the core-shell catalyst using the wet precipitation method and denoted as M-Co@Z (M = Cr, Ce, Nb, Mn). The catalytic activity of the Cr-Co@Z catalyst was significantly increased due to the interaction between Cr₂O₃ and Co₃O₄. The results of Raman spectra indicated the incorporation of chromium into the Co₃O₄ lattice and revealed the existence of the interaction between Cr₂O₃ and Co₃O₄. The synergistic effect between Cr₂O₃ and Co₃O₄ might be conducive to the generation of highly defective structure and increase the ratio of Co³⁺/Co²⁺ of the sample, leading to its better oxygen mobility. The dechlorination ability of Cr-Co@Z was also promoted due to the enhanced mobility of lattice oxygen. Based on in situ DRIFT studies, a possible reaction route of CH₂Cl₂ oxidation over Cr-Co@Z catalyst was proposed.

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.

Boron nitride nanosheets decorated MIL-53(Fe) for efficient synergistic ibuprofen photocatalytic degradation by persulfate activation

In this study, based on one-step hydrothermal method, boron nitride nanosheets (BNNs) and MIL-53(Fe) composites (BNFe-X) were successfully prepared and the catalytic performance of BNFe-X on persulfate (PS) activation for ibuprofen (IBP) photodegradation was investigated. The introduction of BNNs changed the morphology of MIL-53(Fe) to be a unique prism-like structure and enhanced the degradation efficiency of IBP, which followed the pseudo-first-order rate kinetics. Among the prepared composites, BNFe-3 (3% BNNs) exhibited the highest IBP degradation activity and possessed strong stability after four cycles. Over 99% IBP removal was achieved at the irradiation time of 60 min. The promoted decomposition rate of IBP could be ascribed to be the activation of PS and the enhanced electrons transfer efficiency between BNNs and MIL-53(Fe). The scavenger studies and electron spin-resonance spectroscopy (ESR) demonstrated the generation of SO₂^-, OH and O₂^-, and all these radicals had the different contributions in IBP degradation. Based on the LC-MS-MS and TOC results, the possible decomposition pathways of IBP in BNFe-3/PS system were proposed. This work suggested that the BNNs/Fe-based MOFs composites and PS system had great potential in organic pollutants degradation in aqueous solution.

Synthesis and characterization of defective UiO-66 for efficient co-immobilization of arsenate and fluoride from single/binary solutions

Here, we aimed to synthesize UiO-66 architected fumaric acid mediated lanthanum (La-fum), zirconium (Zr-fum), and cerium (Ce-fum) metal-organic frameworks (MOFs) for co-immobilizations of both arsenate and fluoride from both single and binary systems. The crystalline behavior of Zr-fum MOF was the lowest compared to the other two forms, due to the fact that it required a modulator support as the nucleus growth nature of zirconium moiety is different. The Langmuir maximum adsorption densities of arsenate (fluoride) were 2.689 (4.240), 1.666 (2.255), and 2.174 (4.155) mmol/g for La-fum, Zr-fum, and Ce-fum, respectively and these adsorption densities were found to have record-high values compared with the existing materials in the literature. The arsenate and fluoride adsorption on the MOF materials were confirmed by XPS, PXRD and FTIR studies. The arsenate adsorption mechanism on La-fum and Ce-fum through monodentate complexation confirmed using the distinguished K-edge shell distance in EXAFS studies. The arsenate and fluoride-sorbed materials were recycled using 0.01 M HNO₃ and were further utilized for six consecutive cycles for both arsenate and fluoride adsorption indicated the feasibility of the materials. This kind of facile and easy solvothermal synthesized MOFs could pave a way towards the removal of toxins in a practical wastewater as these have superior adsorption properties, stability and reusability.

Effect of Cu/Co ratio in CuaCo1-aOx (a = 0.1, 0.2, 0.4, 0.6) flower structure on its surface properties and catalytic performance for toluene oxidation

Catalytic oxidation is considered a high-efficient method to minimize efficiently toluene emission. It is still a challenge to improve the catalytic performance for toluene oxidation by modifying the surface properties to enhance the oxidation ability of catalyst. Herein, a series of Cu_aCo_1-aO_x (a = 0.1, 0.2, 0.4, 0.6) catalysts were synthesized via solvothermal method and applied for toluene oxidation. The effects of the Cu/Co ratio on the texture structure, morphology, redox property and surface properties were investigated by various characterization technologies. The Cu_0.4Co_0.6O_x catalyst with dumbbell-shaped flower structure exhibited much lower temperature of 50% and 100% toluene conversion and far higher reaction rate (13.96 × 10^-2 μmol·g^-1·s^-1) at 220 °C than the Co based oxides in previous reports. It is found that the good activity can be attributed to the fact that the proper Cu/Co ratio can significantly improve the formation of more surface adsorbed oxygen and Co³⁺ species, leading to the much higher oxidation ability came from the strong interaction between Cu and Co oxides. It is suggested that toluene should be oxidized more rapidly to CO₂ and H₂O over the Cu_0.4Co_0.6O_x catalyst than Co₃O₄ based on the results of in situ DRIFTS.

Unraveling the effects of potassium incorporation routes and positions on toluene oxidation over α-MnO2 nanorods: Based on experimental and density functional theory (DFT) studies

Alkali metal potassium is conducive to structure promotion and electronic modulation in metal oxides. Here, K species was successfully introduced into α-MnO₂via in situ synthesis (Pre-K/MnO₂) and hydrothermal impregnation method (Post-K/MnO₂) with target to boost the low-temperature reactivity and deep destruction efficiency for toluene oxidation. Results reveal that Post-K/MnO₂ possesses the highest catalytic activity with toluene (1000 ppm) totally mineralized at just 258 °C, achieving over 70 °C of temperature reduction than that of Pre-K/MnO₂. K specie shows obvious charge transfer balance ability in MnO₂, forming MnO₆-K-MnO₆ bridging bond and leading to more uniform energy of Mn-O bonds. High electron density of K⁺ can promote the activation of oxygen molecules, resulting in a better catalytic performance of toluene. Abundant Brønsted acid sites are beneficial for toluene adsorption and regeneration of hydroxyl on the surface, which promote the degradation of intermediates during toluene oxidation. Moreover, Post-K/MnO₂ shows satisfied catalytic performance under different space velocities and initial concentrations and humid condition. Density functional theory (DFT) calculation revealed the situation of oxygen vacancy and toluene/oxygen adsorption energy in catalysts with different K doping locations. Results showed that the adsorption energy is stronger when K located in large tunnel (0.46 × 0.46 nm), and it is easier to form oxygen vacancy while K entered the small tunnel (0.33 × 0.33 nm). The present work paves new insights into the designing of efficient transition metal oxide catalyst for VOC deep purification.

Unique MIL-53(Fe)/PDI Supermolecule Composites: Z-Scheme Heterojunction and Covalent Bonds for Uprating Photocatalytic Performance

It is important to find an effective way to enhance the photocatalytic efficiency of metal-organic frameworks. In this work, an organic supermolecule perylene diimide (PDI) semiconductor with a carboxyl terminal was added into the synthesis process of MIL-53(Fe) crystals. The PDI/MIL-53(Fe) (PM) composite photocatalyst was first obtained. The TC-H photodegradation rate of the most efficient 5PM was nearly 94.08% within 30 min, whose apparent reaction rate constant (k) is 4 times that of PDI and 33 times that of MIL-53(Fe), respectively. By investigation and characterization, it has been found that PDI nanofibers were dispersed and fixed in MIL-53(Fe) and bonded to each other by covalent bonds. The radical trap experiments and electron spin resonance analysis illustrated that hydroxyl radical (·OH), superoxide radical (·O₂^-), and photogenerated holes (h⁺) were active species. Combined with the band structure of PDI and MIL-53(Fe), it is proposed that the PM photocatalyst was a Z-scheme heterojunction mechanism. Therefore, PM photocatalysts showed excellent charge separation and transfer ability. The performance improvement of 5PM is due to enhanced visible light absorption, efficient charge separation, and excellent redox potential. Five cyclic photocatalytic tests and experiments further demonstrate that the 5PM photocatalyst has a promising future for pollutant removal.

Cobalt ferrite supported platinum nanoparticles: Superb catalytic activity and outstanding reusability in hydrogen generation from the hydrolysis of ammonia borane

In this work, platinum(0) nanoparticles are deposited on the surface of magnetic cobalt ferrite forming magnetically separable Pt⁰/CoFe₂O₄ nanoparticles, which are efficient catalysts in H₂ generation from the hydrolysis of ammonia borane. Catalytic activity of Pt⁰/CoFe₂O₄ nanoparticles decreases with the increasing platinum loading, parallel to the average particle size. Pt⁰/CoFe₂O₄ (0.23% wt. Pt) nanoparticles have an average diameter of 2.30 ± 0.47 nm and show an extraordinary turnover frequency of 3628 min^-1 in releasing 3.0 equivalent H₂ per mole of ammonia borane from the hydrolysis at 25.0 °C. Moreover, the magnetically separable Pt⁰/CoFe₂O₄ nanoparticles possess high reusability retaining 100% of their initial catalytic activity even after ten runs of hydrolysis. The superb catalytic activity and outstanding reusability make the Pt⁰/CoFe₂O₄ nanoparticles very attractive catalysts for the hydrogen generation systems in portable and stationary fuel cell applications.

Highly efficient microwave-assisted Fenton degradation bisphenol A using iron oxide modified double perovskite intercalated montmorillonite composite nanomaterial as catalyst

In this work, perovskite intercalated montmorillonite (MMT) composite catalyst loaded by different mass fraction iron oxide, xFe₂O₃/LaCu_0.5Co_0.5O₃-MMT_0.2 (x was the mass fraction of Fe₂O₃ and x = 0.02, 0.04, 0.06), were prepared by impregnation method, and their catalytic activity were evaluated by microwave induced catalytic degradation of bisphenol A (BPA). Fe₂O₃ had a certain absorption effect on microwave, which could enhance the absorption property of composite material, improve the catalytic activity of catalyst. XRD, SEM, XPS and vector network analysis were used to analysis the structure, morphology, surface element composition and microwave absorption performance of the composite catalyst. The results indicated that the sample had uniform structure, a larger specific surface, a higher ratio of O_ads/O_lat and excellent microwave absorption performance. The effects of microwave power, pH value and H₂O₂ dosage on the catalytic degradation performance were studied, and 0.04Fe₂O₃/LCCOM_0.2 had the most obvious effect on the removal of BPA. The possible reaction mechanisms were discussed by characterization and experimental results of free radical capture. The surface active sites of the catalyst could be excited by microwave to generate oxidative free radicals, which could degrade BPA through electron hole transport. Response surface methodology (RSM) was used to optimize the operation parameters for the 0.04Fe₂O₃/LCCOM_0.2-BPA microwave degradation system.