Mesoporous Mn Research Articles

Mixed N,O-donor Directed Blue Emissive Nano-dispersed Mesoporous Mn(II)-MOF: Dual Sensing Probe for Recyclable and Ultrasensitive ppb-Level Recognition of TNP and Cr(VI)-Oxoanions.

A new mesoporous Mn(II)-MOF [Mn2(phen)2(nia)2]∞ with 4-c uninodal net topology and reiterating rectangular channels in its cargo-net like extension was synthesized using π-conjugated phenanthroline (phen) and syn-syn bridging 5-nitroisopthalic acid (nia) linkers. The MOF (1) exhibited phase purity, uniform morphology, photo and thermal stability, and robustness; duly triggered by the exceptional framework rigidity via intermolecular H-bonding and interlayer π-π stacking interactions. The bright-blue luminescence of the MOF nano-dispersion was explored for sensitive, specific and ultrafast detection of trinitrophenol (TNP) with extremely low LOD (90.62 nM), high KSV (18.27×104 M-1) and Kq (4×1014 M-1s-1). The vapor-phase TNP sensing was also accomplished. Additionally, 1 served towards discriminatory, aqueous-phase monitoring of Cr(VI)-oxoanions, depicting LODs: 36.08 and 35.70 ppb; KSV: 3.46×104 and 4.87×104 M-1; Kq: 3.26×1013 M-1s-1 and 4.31×1013 M-1s-1; and response time: 32 and 40s for CrO4 2- and Cr2O7 2- respectively. The quenching mechanisms (i. e., RET, PET, IFE, weak interactions, collisional quenching and π⋅⋅⋅π stacking) was explained from several experimental investigations and theoretical DFT calculations. The recyclable sensing events and quantification from complex environmental matrices with admirable recovery rates and high KSV (13.02-22.44×104; ~6.31-10.98×104 and ~6.60-11.42×104 M-1 for TNP, CrO4 2- and Cr2O7 2-) undoubtedly advocated the consistency of the probe.

Stable immobilization of lithium polysulfides using three‐dimensional ordered mesoporous Mn2O3 as the host material in lithium–sulfur batteries

AbstractLithium–sulfur batteries (LSBs) have drawn significant attention owing to their high theoretical discharge capacity and energy density. However, the dissolution of long‐chain polysulfides into the electrolyte during the charge and discharge process (“shuttle effect”) results in fast capacity fading and inferior electrochemical performance. In this study, Mn2O3 with an ordered mesoporous structure (OM‐Mn2O3) was designed as a cathode host for LSBs via KIT‐6 hard templating, to effectively inhibit the polysulfide shuttle effect. OM‐Mn2O3 offers numerous pores to confine sulfur and tightly anchor the dissolved polysulfides through the combined effects of strong polar–polar interactions, polysulfides, and sulfur chain catenation. The OM‐Mn2O3/S composite electrode delivered a discharge capacity of 561 mA h g−1 after 250 cycles at 0.5 C owing to the excellent performance of OM‐Mn2O3. Furthermore, it retained a discharge capacity of 628 mA h g−1 even at a rate of 2 C, which was significantly higher than that of a pristine sulfur electrode (206 mA h g−1). These findings provide a prospective strategy for designing cathode materials for high‐performance LSBs.

Low-Temperature controlled synthesis of nanocast mixed metal oxide spinels for enhanced OER activity

The controlled cation substitution is an effective strategy for optimizing the density of states and enhancing the electrocatalytic activity of transition metal oxide catalysts for water splitting. However, achieving tailored mesoporosity while maintaining elemental homogeneity and phase purity remains a significant challenge, especially when aiming for complex multi-metal oxides. In this study, we utilized a one-step impregnation nanocasting method for synthesizing mesoporous Mn-, Fe-, and Ni-substituted cobalt spinel oxide (Mn0.1Fe0.1Ni0.3Co2.5O4, MFNCO) and demonstrate the benefits of low-temperature calcination within a semi-sealed container at 150–200 °C. The comprehensive discussion of calcination temperature effects on porosity, particle size, surface chemistry and catalytic performance for the alkaline oxygen evolution reaction (OER) highlights the importance of humidity, which was modulated by a pre-drying step. The catalyst calcined at 170 °C exhibited the lowest overpotential (335 mV at 10 mA cm−2), highest current density (433 mA cm−2 at 1.7 V vs. RHE, reversible hydrogen electrode) and further displayed excellent stability over 22 h (at 10 mA cm−2). Furthermore, we successfully adapted this method to utilize cheap, commercially available silica gel as a hard template, yielding comparable OER performance. Our results represent a significant progress in the cost-efficient large-scale preparation of complex multi-metal oxides for catalytic applications.

Mixed-ligand based water-stable Mn(II)-MOF for quick, sensitive, and reusable IFE-PET-RET facilitated detection of formaldehyde and Cr(VI)-oxoanions in real-field samples like food and industrial water: experimental and theoretical insights.

We report the luminescence-based detection of Group-1 carcinogen formaldehyde (FA) and Cr(VI)-oxoanions with a mesoporous Mn(II)-MOF (1), featuring a uninodal 4-c net topology and linear 1D square channels forming a polymeric 2D network. The Mn-MOF i.e., [Mn(phen)(hia)(H2O)]∞ was solvothermally constructed using π-conjugated, chelating phenanthroline (phen) and µ3-η2:η1 binding 5-hydroxyisophthalic acid (hia) ligands. The 2D rod-like crystallites of 1 demonstrated excellent phase purity, high thermal and photostability, and robustness under harsh conditions. The SCXRD and XPS studies established the structural framework and elemental composition, while the Hirshfeld surface analysis and NCI-RDG plot confirmed the presence of π-π stacking and weak interactions in 1. We explored the bright-blue emission of 1 for recyclable and fast-responsive (∼70 s) 'turn-off' detection of FA, with a low limit of detection (LOD) of 8.49 µM. Based on this, a 04-input-03-output molecular logic gate was proposed, which can be useful as a molecular switch for future applications. Furthermore, a unique experimental setup using the MOF film demonstrated ∼57% quenching upon exposure to FA vapor (an indoor VOC). Additionally, 1 exemplified itself as an efficient probe towards Cr(VI)-oxyanions, depicting LODs of 79 and 170 ppb, Stern-Volmer constants (KSV) of 16.13 × 104 and 12.73 × 104 M-1, and response times of ∼48 and ∼40 s for CrO42- and Cr2O72-, respectively. DFT calculations and specific wet-chemical investigations elucidated the FA detection to be triggered by photo-induced electron transfer (PET), while the Cr(VI)-sensing involved a combination of PET, the inner-filter effect (IFE), resonance energy transfer (RET), and electrostatic H-bonding interactions. The FA detection was validated using food samples (fish and meat) and wastewater specimens, achieving excellent recovery rates of ∼92-95%. Furthermore, the MOF's efficacy in recognizing the Cr(VI)-species in complex matrices (coal mine wastewater, sewage, and tap water) was investigated to yield high KSV values (3.10-5.17 × 104 and 2.16-7.03 × 104 M-1 for CrO42- and Cr2O72-), which demonstrated the probe's consistency and reliability.

Oxygen vacancy enabled mesoporous Mn–Co oxide material for high-performance formaldehyde sensor worked at room temperature

In recent years, the exploration of hazardous gases at room temperature (RT) has remained one of the key focuses in the research field of the semiconductor gas sensors. Herein, mesoporous manganese-cobalt (Mn–Co) oxides with abundant oxygen vacancies were synthesized by the combustion method assisted with the green reducing agent l-Ascorbic acid (LA). The synthesized Mn–Co oxides were performed by X-ray spectroscopy (XPS) and Raman spectrometer to research their chemical state of surface elements. The results manifested that the Mn–Co oxides with LA adding during preparation possessed abundant oxygen vacancies. Additionally, the gas sensitivity tests indicated that the Mn–Co oxides with a mole ratio of LA to metal elements (MCO-0.3L) exhibited best formaldehyde sensing properties compared to other prepared Mn–Co oxides in the concentration of 0.25–30 ppm at RT. Notably, its response to 5 ppm formaldehyde at RT was more than 7 times of that of the Mn–Co oxides prepared without LA adding (8.1 vs 1.1). The MCO-0.3L sensor has a limit of detection (LOD) as low as 5.2 ppb. It also showed good selectivity and reliability. The improved formaldehyde sensitivity of the Mn–Co oxides sensors is supposed as the synergistic action of the abundant oxygen vacancies and the mesoporous structure.

Mesoporous Mn–Fe oxyhydroxides for oxygen evolution

Mesoporous Mn–Fe oxyhydroxides exhibit excellent OER performance with overpotential of 275 mV, where the surface doping of Fe onto the MnOOH can favorably destabilize the surface bridge O atoms and promote the formation of surface oxygen vacancies.

Vitamin C-Assisted Synthesized Mn–Co Oxides with Improved Oxygen Vacancy Concentration: Boosting Lattice Oxygen Activity for the Air-Oxidation of 5-(Hydroxymethyl)furfural

The catalytic oxidation of biomass-derived 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a promising route to produce bioplastic monomers. Developing budget non-noble-metal catalysts for the efficient air-oxidation of HMF to FDCA is highly demanded but challenging. In this contribution, we present a facile and green vitamin C (VC)-assisted solid-state grinding method for synthesizing mesoporous Mn–Co spinel oxides with improved oxygen vacancy (Ov) concentration, which could offer a satisfactory FDCA yield of 96% using air as the oxygen source (130 °C, 1.5 MPa air, 3 h). Remarkably, Mn3Co2Ox–0.3VC offered an outstanding FDCA formation rate of 2611 μmolFDCA·gcat–1·h–1, which is the highest value achieved so far among ever-described Mn-based catalysts. Based on experimental studies, the catalytic performance of Mn–Co oxides for the oxidation of HMF corresponds well with their Mn–O bond intensities. The catalyst with a higher Ov concentration exhibits a weaker Mn–O bond intensity, which brings about a higher lattice oxygen (OL) reactivity. More importantly, density functional theory (DFT) calculations also demonstrate that increasing the Ov amount not only boosts the OL reactivity of the catalyst by reducing the formation energy of Ov but also contributes to the adsorption and activation of O2 over the catalyst by significantly cutting down the O2 adsorption energy, thus leading to an enhanced catalytic activity for the oxidation of HMF. Besides, the catalyst with a higher Ov concentration provides a stronger substrate adsorption ability, which may also promote the HMF oxidation reactions. This work provides insights into the role of Ov over Mn-based oxides in oxidation catalysis by a Mars–van Krevelen mechanism.

Rationally Tailored Redox Properties of a Mesoporous Mn–Fe Spinel Nanostructure for Boosting Low-Temperature Selective Catalytic Reduction of NOx with NH3

Mn–Fe spinel oxides are considered as promising catalysts for low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR), but the operation temperature window severely suffers from the...

Preparation of Mesoporous Mn-Ce-Ti-O Aerogels by a One-Pot Sol-Gel Method for Selective Catalytic Reduction of NO with NH3.

Novel Mn–Ce–Ti–O composite aerogels with large mesopore size were prepared via a one-pot sol–gel method by using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent. The effect of calcination temperature (400, 500, 600, and 700 °C) on the NH3–selective catalytic reduction (SCR) performance of the obtained Mn–Ce–Ti–O composite aerogels was investigated. The results show that the Mn–Ce–Ti–O catalyst calcined at 600 °C exhibits the highest NH3–SCR activity and lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility. The NO conversion of the MCTO-600 catalyst maintains 100% at 200 °C in the presence of 100 ppm SO2, showing the superior resistance to SO2 poisoning as compared with the MnOx–CeO2–TiO2 catalysts reported the literature. This should be mainly attributed to its large mesopore sizes with an average pore size of 32 nm and abundant Lewis acid sites. The former fact facilitates the decomposition of NH4HSO4, and the latter fact reduces vapor pressure of NH3. The NH3–SCR process on the MCTO-600 catalyst follows both the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism.

Investigation of electrochemical performance of a high surface area mesoporous Mn doped TiO2 nanoparticle for a supercapacitor

In the present study, mesoporous Mn doped TiO2 (Mn-TiO2) was synthesised by a simple sol–gel followed by solvothermal method. Brownish white powder is further characterised to confirm the synthesis of 40–50 nm sized high surface area mesoporous Mn-TiO2 nanoparticle. The electrochemical study by using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) revealed nearly 2-fold enhancement of capacitance and the carrier density compared to the pure TiO2 nanoparticle. This enhanced electrochemical property could be mainly ascribed to larger surface area, mesoporous structure and appropriate concentration of Mn doping that altered the optoelectronic properties of wide band gap TiO2.

Green oxidation of alkylaromatics using molecular oxygen over mesoporous manganese silicate catalysts.

A very green catalytic method has been introduced for the synthesis of alkylaromatic ketones by solvent-free benzylic oxidation of alkylaromatics with molecular oxygen (O2) over hexagonally mesostructured MnSBA-15 catalysts synthesized with a variety of manganese (Mn) contents using a pH-adjusting direct hydrothermal (pH-aDH) method. For example, the solvent-free oxidation of ethylbenzene (EB) over different mesoporous MnSBA-15 catalysts and uniform pore sized MnMCM-41(31) prepared by an alkaline hydrothermal method has been systematically evaluated. Washed MnSBA-15(4) (W-MnSBA-15(4)) or green mesoporous MnSBA-15(4) obtained after the removal of the non-framework octahedral Mn2O3 species deposited on the active surface of MnSBA-15(4) using a promising chemical treatment method is used for this reaction to evaluate its catalytic activity. Meanwhile the recyclability and hot-filtration experiments for this reaction have been also studied. The catalytic activities obtained from the above catalytic results prove that the W-MnSBA-15(4) has higher EB conversion and AP[double bond, length as m-dash]O selectivity than the other mesoporous catalysts used in this reaction. Therefore, in order to find the optimal reaction parameters for this reaction, various reaction parameters with W-MnSBA-15(4) have been thoroughly evaluated. Using W-MnSBA-15(4), the catalytic results obtained with different oxidants used in this reaction have also been discussed clearly. The catalytic results of solvent-free benzylic oxidations with W-MnSBA-15(4) conducted with different alkylaromatic molecules have been obviously discussed. All the mesoporous catalysts used in this reaction have been characterized using several instrumental techniques to confirm them as the standard mesoporous catalysts. The plausible reaction mechanism for the solvent-free oxidation of EB has been successfully reported based on the characterization results of the catalyst and catalytic results. The ESR and UV-vis DRS results of the W-MnSBA-15 catalyst used in these reactions corroborate that the disordered octahedral divalent (Mn2+) and tetrahedral trivalent (Mn3+)-species have been successfully incorporated on the silica surface of the catalysts. Based on the catalytic results, it is noteworthy to observe that mesoporous W-MnSBA-15(4) is a highly active, green and promising heterogeneous catalyst for the selective synthesis of alkylaromatic ketones, since the catalyst produces the best catalytic activity among the other mesoporous Mn silicate catalysts.

Unique electron reservoir properties of manganese in Mn(II)-doped CeO2 for reversible electron transfer and enhanced Fenton-like catalytic performance

Developing high-performance heterogeneous Fenton-like catalyst and understanding its intrinsic catalytic properties are of fundamental and practical significance. In this work, a mesoporous Mn(II)-doped CeO2 (MCO) with monodisperse spherical morphology and large surface area (141.8 m2 g−1) was fabricated through a simple hydrothermal–calcination process, and further utilized as the heterogeneous catalyst for oxidative degradation of organic pollutants in the presence of H2O2. The density functional theory (DFT) simulations were carried out to study the H2O2 decomposition process on the MCO surface. It was revealed that the Mn(II) doping in the CeO2 could significantly promote the complex of the surface Ce sites and H2O2 molecules. More importantly, the manganese dopants could serve as electron reservoirs, capable of reversibly donating and accepting electrons, which facilitated the electron transfer between Ce and H2O2. Owing to the electron reservoir properties of manganese, this MCO showed significantly enhanced catalytic efficiency in comparison to pure CeO2. Moreover, the catalytic activity of MCO almost kept unchanged after reuse several times, demonstrating its long-circulating characteristics. This study provides new and important insights into the electron transfer pathway involved in the heterogeneous Fenton-like process.

Graphene-Anchored Mesoporous Mn–Co Oxide Battery-like Materials for Ultrahigh Performance Hybrid Supercapacitors

The energy storage mechanism of hybrid supercapacitors originates mainly from Faradaic charge transfer generated on/near the surface of Faradaic pseudocapacitive materials. Therefore, the developme...

Templated Solid-State Fabrication of Quadrangled Mn–Co Mesoporous Oxides for Degradation of Methylene Blue in Water

Abstract By using soft reactive grinding route, mesoporous Mn–Co oxides were fabricated in the presence or absence of polyvinylpyrrolidone (PVP), respectively. Physicochemical properties of samples...

Electrospun Mesoporous Mn–V–O@C Nanofibers for High-Performance Asymmetric Supercapacitor Devices with High Stability

Supercapacitors (SCs) are being considered the next-generation power storage devices due to the many favorable properties. In this regard, mesoporous nanostructures are excellent supercapacitor ele...

Controlled Synthesis of Spinel-Type Mesoporous Mn–Co Rods for SCR of NOx with NH3 at Low Temperature

In this work, a series of Mn–Co rod-like layered catalysts self-assembled from porous rod aggregates were fabricated by a simple solvothermal approach. Compared with Mn–Co particles, Mn–Co rods exhibited a much better SCR performance (achieving >93% NOx conversion at 75 °C) and high N2 selectivity. The outstanding catalytic performance was mainly attributed to the large specific surface area and unique rod-like mesoporous structures, which could provide more active sites and reaction centers for the reaction gas to further promote the de-NOx performance of the catalyst. In addition, the high atomic ratio of Mn4+/Mn on the catalyst surface, strong acid strength, and large acidity amount also had positive effects on its catalytic activity. Moreover, Mn–Co rods possessed a better catalytic cycle performance and more surface acid sites due to the synergistic effect between Co and Mn species.

Visible light driven mesoporous Mn and S co-doped TiO2 nano material: Characterization and applications in photocatalytic degradation of indigocarmine dye and antibacterial activity

The present study explored the Photocatalytic & antibacterial activity of Mesoporous Mn and S co-doped TiO2 nano material synthesized by sol-gel method. As prepared samples were characterized by X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), Scanning electron microscopy (SEM), Energy dispersive X-ray Spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), UV–vis Diffused Reflectance Spectroscopy (UV–vis-DRS), Transmission electron Microscopy (TEM), Brunauer-Emmett-Teller (BET) and Photoluminescence (PL). The Characterization results revealed that all the co-doped and undoped samples shows anatase phase. The Frequency shift of Ti-O-Ti in the catalyst samples was observed in FT-IR due to substitutional doping of Mn and S by replacing Ti and O, Further the catalyst shows smooth spherically shaped small particle size (7.6 nm) with high surface area (155.87 m2/g) and having less band gap energy (2.58 eV). The most reactive •OH are produced during the progress of reaction was determined by using Photo luminescence (PL) technique. The photocatalytic efficiency and antibacterial activity was evaluated by degradation of Indigo carmine(IC), Bacillus coagulans and klebsiella pneumonia respectively. The complete degradation of IC was achieved at optimum reaction parameters such as 0.150 g of the catalyst dosage, solution pH = 4 and initial dye concentration 20 ppm with the catalyst of 1.0 Wt% of Mn-0.25 Wt% of S co-doped Titania with in 90 min. The zone of inhibition bacterial growth was observed (24 mm and 23 mm) compared to control value (Chloramphenicol) 25 mm and 24 mm.

Bromate Inhibition during Ozonation of Bromide-Containing Water by the Presence of Mn Incorporated MCM-41

The mesoporous Mn incorporated MCM-41 was employed to inhibit bromate formation during catalytic ozonation of bromide-containing water, Mn-MCM-41 was synthesized via hydrothermal method and the influences of temperature ramping rate (0.5, 1 and 2 K min-1) during calcination were investigated. It was characterized by XRD, TEM, SEM, XPS and H2-TPR, indicating that temperature ramping rate could affect the valence states of active Mn species, the dispersion of Mn on the surface of catalyst and the formation of oxygen vacancies, which could increase surface hydroxyl groups on Mn-MCM-41 and accelerated ozone decomposition to generate oxygen species. Compared with 0.5 K min-1 and 2 K min-1, Mn-MCM-41 with 1 K min-1 showed much better performance in bromate inhibition process, Mn100-MCM-41 (molar ratio of Si/Mn=100) achieved 96.7% inhibition efficiency at pH 6.5, which was attributed to higher fraction of Mn(II)/Mn(III) and oxygen vacancies. The influence of pH, TBA and intermediate HOBr/OBr- were explored to investigate the mechanism. The results showed that more H2O2 generation and decreased O3 exposure to Br- in Mn-MCM-41 catalytic ozonation process, the oxidative transformation from Br- to HOBr/OBr- was blocked, resulting to less bromate formation. Highlights: • Temperature ramping rate during calcination of Mn-MCM-41 was crucial. • Oxygen vacancy and variation Mn state are responsible for catalytic performance. • Mn-MCM-41 achieved high bromate inhibition efficiency (96.7%) at pH 6.5. • Mn-MCM-41 inhibited BrO3 - by reducing HOBr/OBr-.

Mesoporous Mn promoted Co3O4 oxides as an efficient and stable catalyst for low temperature oxidation of CO

Mesoporous Mn-doped Co3O4 catalysts were successfully prepared via a dry soft reactive grinding method based on solid state reaction, and their catalytic performances on CO oxidation were evaluated at a high space velocity of 49,500 mL g−1 h−1. A significant promoted effect was observed once the atomic ratios of Mn/(Co+Mn) were lower than 10%, for instance, the temperature for 50% conversion decreased to about −60 °C, showing superior catalytic performance compared to the single metal oxide. Especially, the Mn-promoted Co3O4 catalyst with a Mn/(Co+Mn) molar ratio of 10% could convert 100% CO after 3000 min of time-on-steam without any deactivation at room temperature. As prepared catalysts were characterized by XRD, N2-adsorption/desorption, TEM, H2-TPR, O2-TPD and CO-titration analysis. The significant enhancement of performance for oxidation of CO over Mn-Co-O mixed oxides was associated with the high active oxygen species concentrations formed during the pretreatment in O2 atmosphere.

Mesoporous Mn2O3/reduced graphene oxide (rGO) composite with enhanced electrochemical performance for Li-ion battery.

Transition metal oxides are the most promising candidates in low-cost and eco-friendly energy storage/conversion applications. Herein, bare Mn2O3 and a Mn2O3/reduced graphene oxide (rGO) composite have been synthesized by a facile chemical co-precipitation and subsequent annealing procedure. The synthesized Mn2O3/rGO composite exhibits a porous microcube structure formed with several interconnected particles. The porous Mn2O3/rGO composite, with high surface area and increased conductivity, facilited the charge transfer to enhance the overall electrochemical performance when applied as an anode material in Li-ion batteries. The porous Mn2O3/rGO composite exhibits a highly reversible lithium storage capacity of 1015 mA h g-1 at a rate of 0.5 C (230 mA g-1) during 130 cycles with excellent cycling stability and rate capability. The superior electrochemical performance results mainly due to the combined effect of rGO and Mn2O3, which offers high conductivity, faster Li+ ion transfer, and enhanced structural stability. The material synthesis strategy presented in this study is simple, cost-effective and scalable, which can open new avenues for large-scale applications of composites of graphene and other transition metal oxides.