Photocatalytic oxidation of formaldehyde under visible light using BiVO4-TiO2 synthesized via ultrasonic blending

Formaldehyde (HCHO) is one of the primary indoor air pollutants, and efficiently eliminating it, especially at low concentrations, remains challenging. In this study, BiVO4-TiO2 catalyst was developed using ultrasonic blending technology for the photocatalytic oxidation of low-level indoor HCHO. The crystal structure, surface morphology, element distribution, and active oxidation species of the catalyst were examined using XRD, SEM, TEM, UV-Vis, EDS, and ESR techniques. Our results demonstrated that the BiVO4-TiO2 catalyst, prepared by ultrasonic blending, exhibited good oxidation performance and stability. The HCHO concentration reduced from 1.050 to 0.030 mg/m3 within 48 h, achieving a removal rate of 97.1%. The synergy between BiVO4 and TiO2 enhanced the efficiency of separating photogenerated carriers and minimized the likelihood of recombination between photogenerated electrons and holes. Additionally, this synergy significantly enhanced the presence of hydroxyl radicals (·OH) on the catalyst, resulting in an oxidation performance superior to that of either BiVO4 or TiO2. Our research offers valuable insights for the development of new photocatalysts to address HCHO pollution.

Magnetically separable Co0.6Fe2.4O4/MIL-101-NH2 adsorbent for Congo red efficient removal

The development of effective and practical adsorbents for eliminating pollutants still remains a significant challenge. Herein, we synthesized a novel magnetically separable composite, Co0.6Fe2.4O4/MIL-101-NH2, through the in-situ growth of MIL-101-NH2 on magnetic nanoparticles, designed specifically for the removal of Congo red (CR) from aqueous solutions. MIL-101-NH2 possessed high BET surface area (240.485 m2•g-1) and facile magnetic separation function and can be swiftly separated (within 30 s) through an external magnetic field post-adsorption. The investigation systematically explored the influence of crucial parameters, including adsorbent dosage, pH, adsorption duration, temperature, and the presence of interfering ions, on CR adsorption performance. Findings indicate that CR adsorption adheres to the pseudo-second-order (PSO) kinetic model and the Langmuir isotherm model. Thermodynamic analysis reveals the spontaneity, endothermic nature, and orderly progression of the adsorption process. Remarkably, the adsorbent with 0.1 g•L-1 boasts an impressive maximum adsorption capacity of 1756.19 mg•g-1 for CR at 298.15 K, establishing its competitive advantage. The reuse of the adsorbent over 5 cycles remains 78% of the initial adsorption. The CR adsorption mechanisms were elucidated, emphasizing the roles of π-π interactions, electrostatic forces, hydrogen bonding, and metal coordination. Comparison with other dyes, such as methylene blue (MB) and methyl orange (MO), and exploration of adsorption performance in binary dye systems, demonstrates the superior capacity and selectivity of this adsorbent for CR. In conclusion, our magnetically separable metal-organic framework (MOF)based composite presents a versatile and effective solution for CR removal, with promising applications in water treatment and environmental remediation.

Principles of Design and Synthesis of Metal Derivatives from MOFs

Materials derived from metal-organic frameworks (MOFs) have demonstrated exceptional structural variety and complexity and can be synthesized using low-cost scalable methods. Although the inherent instability and low electrical conductivity of MOFs are largely responsible for their low uptake for catalysis and energy storage, a superior alternative is MOF-derived metal-based derivatives (MDs) as these can retain the complex nanostructures of MOFs while exhibiting stability and electrical conductivities of several orders of magnitude higher. The present work comprehensively reviews MDs in terms of synthesis and their nanostructural design, including oxides, sulfides, phosphides, nitrides, carbides, transition metals, and other minor species. The focal point of the approach is the identification and rationalization of the design parameters that lead to the generation of optimal compositions, structures, nanostructures, and resultant performance parameters. The aim of this approach is to provide an inclusive platform for the strategies to design and process these materials for specific applications. This work is complemented by detailed figures that both summarize the design and processing approaches that have been reported and indicate potential trajectories for development. The work is also supported by comprehensive and up-to-date tabular coverage of the reported studies.

Freestanding MOF-Derived Honeycomb-Shape Porous MnOC@CC as an Electrocatalyst for Reversible LiOH Chemistry in Li-O2 Batteries

In rechargeable Li-O₂ batteries, the electrolyte and the electrode are prone to be attacked by aggressive intermediates (O₂^- and LiO₂) and products (Li₂O₂), resulting in low energy efficiency. It has been reported that in the presence of water, the formation of low-activity LiOH is more stable for electrolyte and electrode, effectively reducing the production of parasitic products. However, the reversible formation and decomposition of LiOH catalyzed by solid catalysts is still a challenge. Here, a freestanding metal-organic framework (MOF)-derived honeycomb-shape porous MnOC@CC cathode was prepared for Li-O₂ batteries by in situ growth of urchin-like Mn-MOFs on carbon cloth (CC) and carbonization. The battery with the MnOC@CC cathode exhibits an ultrahigh practical discharge specific capacity of 22,838 mAh g^-1 at 200 mA g^-1, high-rate capability, and more stable cycling, which is superior to the MnOC powder cathode. X-ray diffraction and Fourier transform infrared results identify that the discharge product of the batteries is LiOH rather than highly active Li₂O₂, and no parasitic products were found during operation. The MnOC@CC cathode can induce the formation of flower-like LiOH in the presence of water due to its unique porous structure and directional alignment of Mn-O centers. This work achieves the reversible formation and decomposition of LiOH in the presence of water, offering some insights into the practical application of semiopen Li-O₂ batteries.

Unraveling the Reaction Mechanism of HCHO Catalytic Oxidation on Pristine Co3O4 (110) Surface: A Theoretical Study

Various reaction mechanisms for the catalytic degradation of formaldehyde (HCHO) remain to be debated. Density functional theory (DFT) was applied to investigate whether the catalytic oxidation of HCHO on pristine Co3O4 (110) surface follows the Mars-van Krevelen (MvK) mechanism or the Langmuir–Hinshelwood (L-H) mechanism. Firstly, HCHO and O2 co-adsorb on the surface and two H atoms from HCHO are peculiarly prone to transfer to O2, forming CO and HOOH. For the MvK mechanism, CO2 is generated through CO grabbing a lattice oxygen. Meanwhile, the O–O bond of HOOH is broken into two OH groups. One OH fills the oxygen vacancy and its H atom moves to another OH group for H2O formation. For the L-H mechanism, CO directly obtains one OH group to generate COOH. Subsequently, the H atom of COOH transfers to another OH group along with CO2 and H2O generation. Both two mechanisms exhibit a similar maximum activation barrier. The lattice oxygen in the MvK mechanism and the surface-absorbed OH group in the L-H mechanism are the key reactive oxygen species. The small difference in energetic span further suggests that the catalytic cycle through the two mechanisms is feasible. This theoretical study provides new insight into the catalytic reaction path of HCHO oxidation on pristine Co3O4 surface.

Enhanced sequestration of tetracycline by Mn(II) encapsulated mesoporous silica nanoparticles: Synergistic sorption and mechanism

A novel Mn(II) encapsulated mesoporous silica nanoparticles (Mn-MSNs) was developed for efficiently removing antibiotic tetracycline from aqueous solutions. The material has a well-ordered, hexagonal mesopore structure with a large specific surface area (720 m²/g) and maximum sorption capacity (229 mg/g) that is about an order of magnitude higher than that of mesoporous silica nanoparticles without Mn-encapsulated, or encapsulated with other transition metal cations Fe³⁺ and Cu²⁺. Sorption results showed that the materials can sequestrate tetracycline within a large concentration range (5 μg/L-450 mg/L). Batch sorption experiment, spectroscopic analysis and density functional theory calculation collectively indicated that Mn-O complexation was the dominant mechanism for the tetracycline sorption. Electrostatic attraction and cation-π interaction also contributed to tetracycline sorption with their contribution levels varying with pH in a synergetic way with the Mn-O complexation. The Mn(II) encapsulated MSNs exhibited a good regeneration property over five repeated sorption-desorption cycles, demonstrating its promising potential in the cost-effective applications of sequestrating tetracycline from wastewater, drinking water, and contaminated solutions.

Surface Lattice Oxygen Activation by Nitrogen-Doped Manganese Dioxide as an Effective and Longevous Catalyst for Indoor HCHO Decomposition

Oxygen vacancy plays an important role in catalytic oxidation of formaldehyde (HCHO), but the inherent drawback of its thermodynamic instability causes the deactivation of catalysts. Hence, improving the thermodynamic stability of oxygen vacancy is a crux during HCHO oxidation. Here, a novel and simple nitrogen doping of MnO₂/C catalyst is designed for HCHO oxidation at room temperature. The surface lattice oxygen of MnO₂ will be activated by nitrogen-doping, which acts as active sites for HCHO oxidation and solves the thermodynamic instability issue of oxygen vacancy. Furthermore, carbon is doped with nitrogen to promote electron transfer and accelerate the HCHO oxidation process. Therefore, the catalytic activity and stability of the catalyst can be significantly promoted, which can completely remove ∼1 ppm HCHO in the tank within 3 h, and remains highly active after 5 cycles at room temperature (RH = 55%). In addition, the excellent removal performance over the prepared catalyst is also attributed to abundant surface oxygen species, amorphous crystallinity, and low reduction temperature. In situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) and density functional theory (DFT) calculations reveal the reaction mechanism of HCHO. This strategy provides crucial enlightenment for designing novel Mn-based catalysts for application in the HCHO oxidation field.

Improved oxygen activation over metal-organic-frameworks derived and zinc-modulated Co@NC catalyst for boosting indoor gaseous formaldehyde oxidation at room temperature

The indoor low-concentration formaldehyde (HCHO) removal in cobalt-based catalysts is still a "hot potato". In this work, metal-organic-frameworks (MOF)-derived and Zinc (Zn)-modulated new cobalt nanoparticles catalyst (CZ-Co@NC-800) was designed and prepared. The CZ-Co@NC-800 performed outstanding elimination activities for ~1 ppm HCHO at 25 °C. In the static test condition, it achieves complete HCHO removal in 3 h at a relative humidity (RH) of ~55%. Moreover, 90.18% HCHO removal ratio is held after five recycle tests. In the dynamic test condition, it remains the characteristic to eliminate around 95.89% of HCHO within 8 h under an RH of ~55% and a gas hourly space velocity (GHSV) of ~150,000 mL·h^-1g^-1. Such advanced results should be ascribed to large specific surface area bringing about more cobalt active sites; and it is also because residual Zn metal affects the electronic structure of CZ-Co@NC-800 and enhance the surface charge transfer rate, thus the activation and dissociation ability of oxygen is promoted. Besides, a short HCHO reaction path over CZ-Co@NC-800 which was clarified by the In situ DRIFTs is also a reason for excellent catalytic performance. This work represents a crucial addition to expand the family of cobalt-based catalysts for indoor HCHO elimination.

A novel high-performance CeO2-CuMn2O4 catalyst for toluene degradation

A series of spinel CuM₂O₄ (M = Mn, Fe, and Al) was used as the catalyst to investigate the effective degradation of toluene, and then CuMn₂O₄ with better catalytic activity was selected as the research object to study its activity at different ratios of Cu and Mn. Meanwhile, CeO₂ was introduced to modify CuMn bimetallic oxide to improve its catalytic performance. The structure, morphology, and valence states of surface elements of as-prepared catalysts were characterized by XRD, TEM, SEM, N₂ adsorption-desorption, XPS, and H₂-TPR. Using toluene as a probe molecule, the catalytic activity of the catalyst was tested and the results showed that the conversion rate of toluene catalyzed by CeO₂-CuMn₂O₄ catalyst can reach 90% at 200 °C (T₉₀) and 100% at 240 °C (T₁₀₀). The CO₂ yield can also reach 100% at 248 °C. Moreover, the possible catalytic mechanism for toluene by the CeO₂-CuMn₂O₄ was briefly explored. The catalytic oxidation of toluene over the oxide follows the Mars-van Krevelen mechanism.

Leveraging Cu/CuFe2O4-Catalyzed Biomass-Derived Furfural Hydrodeoxygenation: A Nanoscale Metal-Organic-Framework Template Is the Prime Key

Enormous efforts have been initiated in the production of biobased fuels and value-added chemicals via biorefinery owing to the scarcity of fossil resources and huge environmental synchronization. Herein, non-noble metal-based metal/mixed metal oxide supported on carbon employing a metal-organic framework as a sacrificial template is demonstrated for the first time in the selective hydrodeoxygenation (HDO) of biomass-derived furfural (FFR) to 2-methyl furan (MF). The aforementioned catalyst (referred to as Cu/CuFe₂O₄@C-A) exhibited extraordinary catalytic proficiency (100% selectivity toward MF) compared with the conventional Cu/CuFe₂O₄@C-B catalyst which was prepared by the wet impregnation method. High-resolution transmission electron microscopy and synchrotron X-ray diffraction studies evidenced the existence of both metal (Cu) and mixed metal oxide (CuFe₂O₄) phases, in which the metal could help in hydrogenation to alcohol and metal oxide could assist in the hydroxyl group removal step during HDO reaction. The stabilization of encapsulated metal/metal oxide nanoparticles in the carbon matrix, modulation of the electronic structure, and regulation of geometric effects in the Cu/CuFe₂O₄@C-A are thought to play an important role in its excellent catalytic performance, confirmed by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigations. Furthermore, the structure and activity interconnection was confirmed by in situ attenuated total reflection-IR studies, which manifested the strong interfacial interaction between FFR and the Cu/CuFe₂O₄@C-A catalyst. This finding was further supported by NH₃ temperature-programmed desorption analysis, which suggested that the presence of more Lewis/weak acidic sites in this catalyst was beneficial for the hydrogenolysis step in HDO reaction. Additionally, H₂ temperature-programmed reduction studies revealed that the adsorption of H₂ was stronger on the Cu/CuFe₂O₄@C-A than that over the conventional Cu/CuFe₂O₄@C-B catalyst; thus, the former catalyst promoted activation of H₂. A detailed kinetic analysis which demonstrated the lower activation energy barrier along with dual active sites attributed for the activation of the two separate reactions in the HDO process on the Cu/CuFe₂O₄@C-A catalyst. This work has great implication in developing a highly stable catalyst for the selective upgradation of biomass without deactivation of metal sites in extended catalytic cycles and opens the door of opportunity for developing a sustainably viable catalyst in biomass refinery industries.

Porous Mn-based oxides for complete ethanol and toluene catalytic oxidation: the relationship between structure and performance

SmMn₂O₅ exhibited a higher catalytic activity for catalytic oxidation of ethanol and toluene than SmMnO₃, Mn₃O₄ and Mn₂O₃. Mn³⁺–Mn³⁺ dimers facilitate C–C bond cleavage.