Mesoporous Silica-Confined Manganese Oxide Nanoparticles as Highly Efficient Catalysts for the Low-Temperature Elimination of Formaldehyde

Catalytic oxidation of lignite by Pt/TiO2 can enhance cadmium adsorption capacity

Addressing global warming necessitates innovative strategies in fossil fuel management. This study evaluates lignite, a low-rank coal with limited calorific value, exploring applications beyond its use as fuel. Utilizing Pt/TiO2 catalytic oxidation, the research aims to enhance the cadmium adsorption capacity of lignite in wastewater. Lignite, treated with 0.5% Pt/TiO2 at 125 °C for 2 h, demonstrated a threefold increase in cadmium adsorption capacity. Characterization using TGA-DSC confirmed the modification process as exothermic and self-sustainable. Spectroscopic analysis and Boehm titration revealed significant alterations in pore structure, surface area, and oxygen-containing functional groups, emphasizing the effectiveness of catalytic oxidation. Adsorption mechanisms such as complexation, cation exchange, and cation-π interactions were identified, enhancing Cd adsorption. Techniques, including the d-band model, H2-TPR, and O2-TPD, indicated that dissociative adsorption of molecular O2 and the subsequent generation of reactive oxygen species introduced additional oxygen-containing functional groups on the lignite surface. These findings provide essential strategies for the alternative use of lignite in environmental remediation, promoting sustainable resource utilization and enhancing cost-effectiveness in remediation processes. ENVIRONMENTAL IMPLICATION: This study innovates in using lignite to reduce cadmium (Cd) contamination in wastewater. Employing Pt/TiO2 catalytic oxidation, lignite is transformed, enhancing its cadmium adsorption capacity. This process, being exothermic, contributes to decreased energy consumption. The approach not only mitigates the hazardous impacts of cadmium but also aligns with sustainability by reducing greenhouse gas emissions and energy use, showcasing a multifaceted environmental advancement.

Enhanced formaldehyde oxidation over MnO2 and doped manganese-based catalysts: Experimental and theoretical Insights into mechanism and performance

Thermal catalytic degradation of formaldehyde (HCHO) over manganese-based catalysts is garnering significant attention. In this study, both theoretical simulations and experimental methods were employed to elucidate the primary reaction pathways of HCHO on the MnO2(110) surface. Specifically, the effects of doping MnO2 with elements such as Fe, Ce, Ni, Co, and Cu on the HCHO oxidation properties were evaluated. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS), were employed to discern the physical properties and chemical states of the active components on the catalyst surface. The comprehensive oxidation pathway of HCHO on the MnO2(110) surface includes O2 adsorption and dissociation, HCHO adsorption and dehydrogenation, CO2 desorption, H2O formation and desorption, oxygen vacancy supplementation, and other elementary reactions. The pivotal rate-determining step was identified as the hydrogen migration process, characterized by an energy barrier of 234.19 kJ mol-1. Notably, HCHOO and *CHOO emerged as crucial intermediates during the reaction. Among the doped catalysts, Fe-doped MnO2 outperformed its counterparts doped with Ce, Ni, Co, and Cu. The optimal degradation rate and selectivity were achieved at a molar ratio of Fe: Mn = 0.1. The superior performance of the Fe-doped MnO2 can be ascribed to its large specific surface area, conducive pore structure for HCHO molecular transport, rich surface-adsorbed oxygen species, and a significant presence of oxygen vacancies.

Chitosan-Coated MIL-100(Fe) as an Anticancer Drug Carrier: Theoretical and Experimental Investigation

MIL-100(Fe) was synthesized under biofriendly conditions at room temperature and pressure using iron(II) chloride as the source of iron, and it was coated with chitosan (CS), a natural polysaccharide. In this study, we used a computational technique to predict the amount of drug loading in MIL-100(Fe) and MIL-100(Fe)/CS with molecular dynamics software LAMMPS. Powder X-ray diffraction analysis was conducted to characterize the chitosan-coated MIL-100(Fe) loaded with cyclophosphamide (MIL-100(Fe)/CS/CP). The drug loading and release processes were quantified using UV spectroscopy at 193 nm. The toxic effect of MIL-100(Fe)/CS/CP was determined on human breast cancer (MCF-7) cells. In vivo images and H&E analysis show inhibition properties of MIL-100(Fe)/CS/CP on tumor cells. The conducted research indicates that computational calculation provides a unique insight into the drug adsorption since a proper understanding of the atomic interaction of MIL-100(Fe)/CS with anticancer drugs is important for developing experimental investigations. The biocompatibility and anticancer properties of chitosan molecules enhanced the tumor inhibitory effect of the particles compared with the MIL-100(Fe)/CP and free cyclophosphamide treatments.

Transition metal ions-modified birnessite toward highly efficiency photocatalytic formaldehyde oxidation under visible light irradiation

Accelerating the interfacial charge transfer process (ICTS) of the catalysts can immensely improve the photocatalytic efficiency. Doping transition metal ions not only promote the ICTS, but also boost multielectron reduction reactions of oxygen. Herein, birnessite-type MnO₂ have been modified by different transition metal ions (TM = Zn²⁺, Cu²⁺, and Fe³⁺) in this work. Post-doping, Fe-Birnessite was featured by the highest photocatalytic HCHO oxidation activity with 80 ppm of HCHO which presented complete removal of HCHO for 80 min, while K-, Cu-, and Zn-Birnessite took 105, 135, and 170 min, respectively. In detail, the photoexcited electrons were caught by Fe (III) and then generated Fe (II),which could continue to capture photoexcited electrons to produce Fe (I) under visible light; on the other hand, the Fe (I) could be oxidized by O₂ to obtain Fe (II) and then recover to Fe (III). This process tremendously improved the ICTS.

Mn-vacancy birnessite for photo-assisted elimination of formaldehyde at ambient condition

Visible light-assisted catalysis has recently attracted considerable attention because it is efficient, cost effective, and does not cause indoor air pollution. Several birnessite-type MnO₂ catalysts with different numbers of manganese vacancies (MVs) were synthesized in this study and used for photo-assisted catalytic oxidation of HCHO. Under visible light irradiation, MVs act as trapping centers to accelerate electrons transport and produce abundant reactive radicals to boost the activation of molecular oxygen, thereby improving the catalytic HCHO oxidation. The birnessite with the highest number of MVs exhibits remarkable oxidation activity with 80 ppm of HCHO (42% HCHO conversion was attained at ambient temperature) and a corresponding gas hourly space velocity (GHSV) of 60 L/(g·h) in a dynamic experiment. Moreover, it mineralizes 80 ppm of HCHO within 160 min in a static experiment, whereas it only takes 90 min under the same conditions with the visible light irradiation. The activity factor of birnessite with the highest MV content under visible light irradiation is 2.2 times that observed under dark conditions. Overall, this study elucidates the photothermal catalytic oxidation of HCHO, and concludes that the birnessite comprising MVs is a promising material for air purification applications.

Formaldehyde Total Oxidation on Manganese-Doped Hydroxyapatite: The Effect of Mn Content

An aqueous impregnation method using manganese (II) nitrate precursor, followed by calcination at 400 °C, was carried out for the preparation of manganese doped hydroxyapatite catalysts (MnxHap; x = Mn wt.%: 2.5, 5.0, 10, 20, and 30 based on MnO2). Methods of characterization including inductively coupled plasma spectroscopy (ICP), N2 physisorption, X-ray Diffraction (XRD), Fourier-Transform Transmission Infrared (FT-IR), Raman, and Thermal gravimetric analysis (TGA/MS) analysis were used for the identification of Mn species and its surrounding environment. Raman spectroscopy indicated the presence of the ε-MnO2 phase for Mn20Hap and Mn30Hap in agreement with the XRD results and the presence of β-MnOOH species for Mn5Hap and Mn10Hap. The formaldehyde total oxidation was investigated on these catalysts and it was shown that Mn5Hap was the most active catalyst, achieving a normalized rate of formaldehyde (HCHO) conversion into CO2 per mole of Mn of 0.042 h−1 at a temperature of 145 °C. The well dispersed oxidized manganese species on Hap with a medium Mn AOS (average oxidation state) were mainly responsible for this performance. Since HCHO was retained on the surface of all catalysts during the catalytic test, the combined Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT) experiment at room temperature and thermodesorption (TD)-FTIR identified formate species as their oxidation consumed surface OH groups. A stability test and moisture effect study showed that the presence of water vapor has a beneficial effect on the performances of the catalyst.

A TiO2/C catalyst having biomimetic channels and extremely low Pt loading for formaldehyde oxidation

This study presents a TiO2/C hybrid material with biomimetic channels fabricated using a wood template. Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by calcination at 400-600 °C for 4 hours under a nitrogen atmosphere. The generated TiO2 nanocrystals were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst loading (0.04-0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO2 and H2O even under room temperature (conv. ∼100%). Wood acted as both a structural template and reduction agent for Pt catalyst generation in sintering. Therefore, no post H2 reduction treatment for catalyst activation was required. The hierarchal channel structures, including 2-10 nm mesopores and 20 μm diameter channels, could be controlled by calcination temperature and atmosphere, which was confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.

Controllable synthesis of hierarchical nanoporous ε-MnO2 crystals for the highly effective oxidation removal of formaldehyde

Hierarchical nanoporous ε-MnO₂ crystals were prepared through thermal decomposition of hydrothermally-synthesized MnCO₃ precursors without any external templates or surfactants.

Surface Characterization of Mesoporous CoOx/SBA-15 Catalyst upon 1,2-Dichloropropane Oxidation

The active combustion catalyst that is based on 30 wt % cobalt oxide on mesoporous SBA-15 has been tested in 1,2-dichloropropane oxidation and is characterized by means of FT-IR (Fourier transform infrared spectroscopy) and ammonia-TPD (temperature-programmed desorption). In this work, we report the spectroscopic evidence for the role of surface acidity in chloroalkane conversion. Both Lewis acidity and weakly acidic silanol groups from SBA support are involved in the adsorption and initial conversion steps. Moreover, total oxidation reaction results in the formation of new Bronsted acidic sites, which are likely associated with the generation of HCl at high temperature and its adsorption at the catalyst surface. Highly dispersed Co oxide on the mesoporous support and Co-chloride or oxychloride particles, together with the presence of several families of acidic sites originated from the conditioning effect of reaction products may explain the good activity of this catalyst in the oxidation of Chlorinated Volatile Organic Compounds.

High-surface area mesoporous Pt/TiO₂ hollow chains for efficient formaldehyde decomposition at ambient temperature

Room-temperature catalytic decomposition of formaldehyde (HCHO) is considered as one of the most main methods for the removal of indoor HCHO due to its facile reaction conditions. Herein, high-surface area mesoporous Pt/TiO2 hollow chains were synthesized in high yield by using a simple microwave-hydrothermal route, followed by a combined NaOH-assisted NaBH4-reduction deposition of Pt nanoparticles on the as-obtained TiO2 surface. The catalytic activity for HCHO decomposition was evaluated at room temperature. The prepared Pt/TiO2 hollow chains with an optimal Pt loading of 0.5 wt.% exhibited high catalytic activity and recyclability. The apparent reaction rate constant of HCHO oxidation over this catalyst was approximately 1.42×10(-3) ppm(-1) min(-1), exceeding that of the commercial Degussa P25 TiO2 with equal Pt content (k=5.36×10(-4) ppm(-1) min(-1)) by a factor of approximately 2.65. The high catalytic activity of the Pt/TiO2 hollow chains could be mainly attributed to the hollow chain-like structure, high specific surface area, numerous mesopores, and high pore volume of TiO2 support. Consequently, the catalysts exhibited high adsorption capacity for HCHO, fast diffusion and transport of gas molecules, and good contact between gases and active sites. These characteristics enhanced the catalytic activity.

Capture of formaldehyde by adsorption on nanoporous materials

The aim of this work is to assess the capability of a series of nanoporous materials to capture gaseous formaldehyde by adsorption in order to develop air treatment process and gas detection in workspaces or housings. Adsorption-desorption isotherms have been accurately measured at room temperature by TGA under very low pressure (p<2 hPa) on various adsorbents, such as zeolites, mesoporous silica (SBA15), activated carbon (AC NORIT RB3) and metal organic framework (MOF, Ga-MIL-53), exhibiting a wide range of pore sizes and surface properties. Results reveal that the NaX, NaY and CuX faujasite (FAU) zeolites are materials which show strong adsorption capacity and high affinity toward formaldehyde. In addition, these materials can be completely regenerated by heating at 200°C under vacuum. These cationic zeolites are therefore promising candidates as adsorbents for the design of air depollution process or gas sensing applications.

Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Three-dimensional TiO2/CeO2 nanowire composite for efficient formaldehyde oxidation at low temperature

TiO₂/CeO₂ nanowires exhibited superior catalytic activity that could convert 60.2% of HCHO to CO₂ and H₂O at a low temperature of 60 °C, and also showed a good catalytic activity toward toluene oxidation.

Highly efficient formaldehyde elimination over meso-structured M/CeO2 (M = Pd, Pt, Au and Ag) catalyst under ambient conditions

A series of mesoporous CeO₂ supported noble metal (Pt, Pd, Au and Ag) catalysts, fabricated through a facial pyrolysis and in situ reduction protocol, were used for formaldehyde elimination under ambient conditions.

Layered manganese oxides for formaldehyde-oxidation at room temperature: the effect of interlayer cations

A series of K-, Mg-, Ca-, and Fe-containing birnessites were prepared by a facile comproportionation reaction of Mn²⁺ and MnO₄⁻ in the presence of different metal cations.