Pure MnO2 Research Articles

Design of MnO2/g-C3N4 heterojunction composite photocatalysts for augmented charge separation and photocatalytic degradation performance with superior antibacterial activity

The development of advanced photocatalysts is critical for addressing environmental pollution and enhancing water purification processes. Our study has effectively developed a novel MnO2/g-C3N4 (MGC) heterojunction composite photocatalyst exhibiting superior photo-degradation under visible-light (VL) conditions and also established antibacterial activities. Comprehensive characterization was acquired using XRD, FT-IR, FE-SEM with EDX-associated mapping images, TEM, UV–Vis DRS and PL investigations, indicating the successful formation of well-dispersed MnO2 nanoparticles (NPs) over the g-C3N4 catalyst. The MGC composite heterojunction photocatalyst demonstrated increased photocatalytic degradation activity of 77.2 % in aqueous crystal violet (CV) under VL within 120 min, significantly outperforming pure g-C3N4 and MnO2 by 3.02 and 2.37 times, respectively. The MGC composite demonstrates remarkable stability and reusability, retaining 73.7 % of its efficiency after five consecutive cycles. Additionally, the as-synthesised composite endows potent antibacterial action against various pathogenic bacteria including K. pneumonia, S. aureus, E. coli and B. cereus. The active species analysis indicates that the composite photocatalyst facilitates charge transfer, while effectively preventing the recombination of photo-produced carriers via an effective Z-scheme mechanism, and the synergistic things among MnO2 and g-C3N4 are accredited to the boosted photocatalytic and antibacterial activities. This research describes a photocatalytic approach for efficiently eliminating various contaminants from water bodies, which has significant implications for the future development of photocatalytic technology for wastewater handling.

Structure dependence of the enhanced sulfur tolerance of core–shell CoMn oxides for benzene oxidation: Discrepant sulfur species and less affected reactant activation

Effective reduction of VOCs emissions in practical gas requires low-temperature catalysts with remarkable SO2 tolerance. Here via simply mixing CoCO3 into the precursors of α-MnO2, a core–shell CoMn composite was developed. The leading one with CoCO3 addition of 3 g (Co3Mn) achieved 100 % C6H6-to-CO2 conversion at ≥250 °C under 120 L/g/h, and still the CO2 yield over the sulfurized Co3Mn (simulated by H2SO3 vapor pretreatment) was maintained 100 %. However, with respect to the case of fresh MnO2, the CO2 production at 250 and 300 °C over the sulfurized MnO2 was decreased by 26 % and 8 %, respectively, and in the meantime, a larger amount of CO was detected. The dominant formation of abundant MnSO4 species due to sulfur poisoning led to the deactivation of pure MnO2, while over Co3Mn the formation of MnSO4 was significantly inhibited because of (i) the electron transfer from Co2+ to Mn4+ restraining that from S4+ to Mn4+ and (ii) the stronger alkalinity of Co species making the acidic H2SO3 preferentially anchor on Co as CoSO4. Along with the sacrificial role, another way cobalt alleviated sulfate toxicity was through transiting the aggregated sulfate deposition into scattered state. Investigations conducted primarily with UV–vis DRS and temperature-programmed techniques further reveal that neither MnO2 nor Co3Mn could escape from the sulfur-induced adversity on activation of O2 and benzene, but the sulfurized Co3Mn was much less affected, thus sustaining the deep benzene oxidation. Finally, reaction routes were unraveled according to the phenol, benzoquinone, maleic acid and acetic acid intermediates.

Characterization of Mn3O4/(x)Nb2O5 thin films as a promising material for supercapacitors

The thin films of Mn3O4/(x)Nb2O5 oxides (x = 0, 2, 4, and 6 %) were prepared by the electron beam evaporation method and then annealed at 400 °C. The structural analysis showed a tetragonal phase of Mn3O4, according to X-ray diffraction results. The quantitative elemental analysis of films confirms the stoichiometry of the Mn3O4, while the Nb2O5 couldn’t be recognized using energy dispersive X-ray fluorescence. The chemical speciation of the films was investigated using X-ray photoelectron spectroscopy. Three oxidation states of Mn were recognized at average binding energies of 645.70±0.35, 642.99±0.40, and 641.58±0.48 eV that correlated to Mn4+, Mn3+, and Mn2+, respectively. As the Nb2O5 increases, a slight decrease in the binding energy of Mn4+ is recognized, whereas it is nearly constant for the deconvoluted Mn3+ and Mn2+. Two electronic transitions (Eg1 and Eg2) of the optical band gap showed an increase with increasing Nb2O5 dopant from 2 % to 6 %. The optical parameters such as Eosc, the single oscillator energy, Edis, the dispersion energy, both moments (M−1) and (M−3), the ratio of carrier concentration/effective mass (N/m*), and the lattice dielectric constant (εL) were determined. From electrochemical measurements of pure Mn3O4 films, it is found that the voltammetric current density is directly proportional to the scan rates of cyclic voltammetry CV, with good cyclic stability, and by increasing the scan rates, the values of specific capacitance decrease while the values of specific power increase. In doped thin films, no potential drop is observed in the discharging process, which indicates good interfacial contact between the active material and the substrate during the charge/discharge process. These results suggest that the obtained Mn3O4 nanoparticles are a better candidate for supercapacitor applications.

Enhanced photocatalytic removal of methyl orange dye employing SiO2/Mn2O3 based nanocatalyst under visible light

Surface water contamination by dye pollutants is a global environmental concern. The treatment of effluent from textile waste using metal oxide-based photocatalysts is a widely employed approach owing to its efficacy and simplicity. Herein, the synthesis and fabrication of novel visible radiation receptive manganese oxide and mesoporous silica nanocomposites (Mn2O3/SiO2) is described. Surface morphology of nanocomposites using scanning electron microscopy (SEM) displayed spherical shaped agglomerated structure. The chemical composition of nanocomposites was examined by using energy dispersive x-ray (EDX) analysis respectively indicating the presence of respective elements. Structural analysis was carried out by using XRD spectroscopy, while optical properties were evaluated by employing UV–visible spectroscopy. The photocatalytic activity of pure Mn2O3 and SiO2 nanoparticles as well as their nanocomposites with two different ratios Mn2O3/SiO2 (1:3) and Mn2O3/SiO2 (3:1) were evaluated by using methyl orange (MO) as a model dye. The band gap energy of Mn2O3/SiO2 (1:3) and Mn2O3/SiO2 (3:1) nanocomposite was 2.39 eV and 1.69 eV respectively. The nanocomposites exhibited improved photocatalytic efficiency as compared to pure nanoparticles as a function of pH and mixing ratio. For instance, at pH 7.0, Mn2O3/SiO2 (1:3) nanocomposite has depicted maximum degradation efficiency of 68 % for degradation of MO as compared to Mn3O4/SiO2 (3:1) nanocomposite, Mn3O4 and SiO2 nanoparticles. However, at pH 2.0 Mn2O3/SiO2 (3:1) nanocomposite had shown maximum degradation efficiency of 99 % as compared to Mn2O3/SiO2 (1:3), Mn2O3 and SiO2 nanoparticles. The degradation reaction followed pseudo first order kinetics. At pH 7.0, the rate constant values of nanocomposites i.e. Mn2O3/SiO2(1:3) and Mn2O3/SiO2(3:1) comes out to be 4.68 × 10−3 min−1 and 2.49 × 10−3 min−1 respectively. At pH 2.0, the rate constant values calculated for Mn2O3/SiO2(1:3) nanocomposite and Mn2O3/SiO2(3:1) nanocomposite was 4.91 × 10−3 min−1 and 1.24 × 10−2 min−1 respectively. The easy fabrication of these nanocomposites coupled with facile tuning of their properties make them suitable contenders for efficient dye degradation in wastewater treatment.

Stabilization of Cuδ+ Sites Within MnO2 for Superior Urea Electro-Synthesis.

Electrocatalytic C-N coupling between NO3 - and CO2 has emerged as a sustainable route for urea production. However, identifying catalytic active sites and designing efficient electrocatalysts remain significant challenges. Herein, the synthesis of Cu-doped MnO2 nanotube (denoted as Cu-MnO2) with stable Cuδ+-oxygen vacancies (Ovs)-Mn3+ dual sites is reported. Compared with pure MnO2, Cuδ+ doping can effectively enhance urea production performance in the co-reduction of CO2 and NO3 -. Thus, Cu-MnO2 catalyst exhibits a maximum Faradaic efficiency (FE) of 54.7% and the highest yield rate of 116.7mmolh-1gcat. -1 in a flow cell. Remarkably, the urea yield rate remains over 78mmolh-1gcat. -1 across a wide potential range. Further experimental and theoretical results elucidate the unique role of Cu-MnO2 solid-solution for stabilizing Cuδ+ sites in Cuδ+-Ovs-Mn3+, endowing the catalyst with superior structural and electrochemical stabilities. This thermodynamically promotes urea formation and kinetically lowers the energy barrier of C-N coupling.

Study of an enhanced photocatalytic hybrid MnO2@SnO2 core-shell Z-scheme nano heterojunction for efficient H2 production

The usage of non-renewable carbon-base fuel energy have created multiple issues such as global warming, environmental degradations etc. Replacing these non-renewable sources of energy with renewable energy (photocatalytic H2 production) is a hot topic for researchers due to its sustainability and eco-friendliness. In this work MnO2, SnO2 and their nanocomposites have been synthesized through simple hydrothermal and co-precipitation methods. The purpose of such nanocomposite fabrication is to synthesize a suitable heterostructure for maximum solar energy harvesting in water splitting. All the prepared samples of pure MnO2, SnO2, and nanocomposites have been characterized through various techniques, which confirm the structure, functional groups, absorbance, morphology, elemental compositions, chemical compositions, and increase in photo-induced current as well as the photostability of such nanocomposites. The highest apparent quantum yield of the optimized MnO2@SnO2 (first time reported as photocatalyst for H2 production) were 21.7% at wavelength 420 nm, which is the highest ever reported for such (MnO2@SnO2) nanocomposite. The enhanced photocatalytic behavior for H2 production has been observed which is 3.67 times greater than pristine MnO2. Such an enhancement is due to the synergistic effect of SnO2 NPs decorated on the NTs of MnO2. The present work provides a novel approach to produce hydrogen with high performance as efficient solar harvesting.

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Origins of enhanced oxygen reduction activity of transition metal nitrides.

Transition metal nitride (TMN-) based materials have recently emerged as promising non-precious-metal-containing electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. However, the lack of fundamental understanding of the oxide surface has limited insights into structure-(re)activity relationships and rational catalyst design. Here we demonstrate how a well-defined TMN can dictate/control the as-formed oxide surface and the resulting ORR electrocatalytic activity. Structural characterization of MnN nanocuboids revealed that an electrocatalytically active Mn3O4 shell grew epitaxially on the MnN core, with an expansive strain along the [010] direction to the surface Mn3O4. The strained Mn3O4 shell on the MnN core exhibited an intrinsic activity that was over 300% higher than that of pure Mn3O4. A combined electrochemical and computational investigation indicated/suggested that the enhancement probably originates from a more hydroxylated oxide surface resulting from the expansive strain. This work establishes a clear and definitive atomistic picture of the nitride/oxide interface and provides a comprehensive mechanistic understanding of the structure-reactivity relationship in TMNs, critical for other catalytic interfaces for different electrochemical processes.

Electronic Structure Modification of MnO2 Nanosheet Arrays with Enhanced Water Oxidation Activity and Stability by Nitrogen Plasma.

The strategic design of catalysts for the oxygen evolution reaction (OER) is crucial in tackling the substantial energy demands associated with hydrogen production in electrolytic water splitting. Despite extensive research on birnessite (δ-MnO2) manganese oxides to enhance catalytic activity by modulating Mn3+ species, the ongoing challenge is to simultaneously stabilize Mn3+ while improving overall activity. Herein, oxygen (O) vacancies and nitrogen (N) doping have been simultaneously introduced into the MnO2 through a simple nitrogen plasma approach, resulting in efficient OER performance. The optimized N-MnO2v electrocatalyst exhibits outstanding OER activity in alkaline electrolyte, reducing the overpotential by nearly 160 mV compared to pure pristine MnO2 (from 476 to 312 mV) at 10 mA cm-2, and a small Tafel slope of 89 mV dec-1. Moreover, it demonstrates excellent durability over a 122 h stability test. The introduction of O vacancies and incorporation of N not only fine-tune the electronic structure of MnO2, increasing the Mn3+ content to enhance overall activity, but also play a crucial role in stabilizing Mn3+, thereby leading to exceptional stability over time. Subsequently, density functional theory calculations validate the optimized electronic structure of MnO2 achieved through the two engineering methods, effectively lowering the intermediate adsorption free energy barrier. Our synergistic approach, utilizing nitrogen plasma treatment, opens a pathway to concurrently enhance the activity and stability of OER electrocatalysts, applicable not only to Mn-based but also to other transition metal oxides.

High-Performance Battery-Type Supercapacitors Based on Self-Oriented Growth of Nanorods/Nanospheres Composite Assembled on Self-Standing Conductive GO/CNF Frameworks.

MnOx-based materials have limited capacity and poor conductivity over various voltages, hampering their potential for energy storage applications. This work proposes a novel approach to address these challenges. A self-oriented multiple-electronic structure of a 1D-MnO2-nanorod/2D-Mn2O3-nanosphere composite was assembled on 2D-graphene oxide nanosheet/1D-carbon nanofiber (GO/CNF) hybrids. Aided by K+ ions, the MnO2 nanorods were partially converted to Mn2O3 nanospheres, while the GO nanosheets were combined with CNF through hydrogen bonds resulting in a unique double binary 1D-2D mixed morphology of MnO2/Mn2O3-GO/CNF hybrid, having a novel mechanism of multiple Mn ion redox reactions facilitated by the interconnected 3D network. The morphology of the MnO2 nanorods was controlled by regulating the potassium ion content through a rinsing strategy. Interestingly, pure MnO2 nanorods undergo air-annealing to form a mixture of nanorods and nanospheres (MnO2/Mn2O3) with a distinct morphology indicating pseudocapacitive surface redox reactions involving Mn2+, Mn3+, and Mn4+. In the presence of the GO/CNF framework, the charge storage properties of the MnO2/Mn2O3-GO/CNF composite electrode show dominant battery-type behavior because of the unique mesoporous structure with a crumpled morphology that provides relatively large voids and cavities with smaller diffusion paths to facilitate the accumulation/intercalation of charges at the inner electroactive sites for the diffusion-controlled process. The corresponding specific capacity of 800 C g-1 or 222.2 mAh g-1 at 1 A g-1 and remarkable cycling stability (95%) over 5000 cycles at 3 A g-1 were considerably higher than those of the reported electrodes of similar materials. Moreover, a hybrid supercapacitor device is assembled using MnO2/Mn2O3-GO/CNF as the positive electrode and activated carbon as the negative electrode, which exhibits a superior maximum energy density (∼25 Wh kg-1) and maximum power density (∼4.0 kW kg-1). Therefore, the as-synthesized composite highlights the development of highly active low-cost materials for next-generation energy storage applications.

Phase evolution of nanocrystalline Mn-based oxides screened under different calcination temperatures using different precursors for proficient application in near infrared pigmentation

We examined how different calcination temperatures and precursors affect the formation of Mn-based oxides. The formation of these oxides was influenced by both the temperature (400–––1000 °C) and the type of precursors used (MnCl2·4H2O, MnCO3, MnO2, and KMnO4). When MnCl2·4H2O was calcined at 800 and 1000 °C/3h, we obtained pure tetragonal Mn3O4 phase materials. Calcining MnCO3 at 600 and 1000 °C resulted in cubic Mn2O3 and tetragonal Mn3O4 phase materials, respectively. Heating commercial MnO2 powder at 600 and 800 °C transformed it into cubic Mn2O3 phase materials. At 400 °C, the tetragonal MnO2 phase remained, but at 1000 °C, mixed Mn3O4 and Mn2O3 phases formed. Calcining KMnO4 at 1000 °C/3h led to the formation of δ-MnO2 materials. The morphological features of Mn2O3 and Mn3O4 materials exhibited different sizes and shapes, including nanostone-like, nanorod-like, and nanoflakes morphologies. The thermal analysis revealed significant differences in weight loss and thermal events, including exo and endothermic peaks. The Raman spectra and UV–Vis DRS measurements data support the formation of Mn-based oxides. The highest NIR reflectance for the various synthesized materials of Mn3O4 phase indicates a reflectance of 68 % in the solar region and 91 % in the color pigment region.

Nickel-hydroxide decorated trimanganese-tetroxide nanorods supported on graphene as bifunctional electrocatalyst for metal–air batteries

Manganese oxide, such as Mn3O4, is one of promising material as electrocatalyst in air–cathode for metal–air battery due to low cost, high catalytic activity and good stability. Although pure Mn3O4 material exhibits excellent catalytic activity to ORR, it is severely limited by its intrinsically low conductivity and high over-potential toward OER. In this work, the hybrid materials of nickel-hydroxide-decorated nanorods of trimanganese-tetroxide supported on reduced-graphene have been prepared by one-step hydrothermal method. The composite materials are used as bifunctional cathode catalysts to ORR/OER, and investigated by the technologies of rotating disk electrode and metal–air batteries. The results indicate that the hybrid material of Mn-Ni/rGO use as catalyst in air–cathode for Al/Zn–air battery has good catalytic activity. Based on analysis of scanning electron microscope and X-ray photoelectron spectroscopy, the composite material shows good performance owing to the improvement of conductivity supported on graphene, more Mn4+ on the surface of hybrid material, the coexistence of Mn3+/Mn4+ redox couple, and the synergism between nickel-hydroxide and graphene.

Interfacial structuring of Mn[sbnd]N and Mn[sbnd]C bonds by defect engineering for high-performance Zn-Mn battery

Zinc‑manganese batteries (ZMBs), with their non-flammable aqueous electrolyte and lower electrode material costs, offer a safer and more economical solution to the problem of energy intermittency. However, current ZMBs still face significant challenges, such as the presence of low electrical conductivity and poor structural stability of the manganese-based cathode, as well as unclear mechanisms of structural changes during charge storage. Here, we present a strategy to construct MnO2 containing MnC and MnN bonds (PAMO) by defect engineering and interface bonding design. This strategy benefits from the fact that MnN and MnC bonds can stabilize the structure and promote the interfacial dynamics of MnO2, thus effectively mitigating manganese dissolution. Meanwhile, the oxygen defects generated by interfacial bonding increase the electrical conductivity of MnO2. In addition, in terms of morphology and structure, the leafy vein-like secondary compartmentalized structure formed by PAMO provides more reactive sites for the redox reaction of MnO2, accelerating charge transfer and ion diffusion. The experimental results show that compared with pure MnO2 (326.8 mAh g−1), the capacity of PAMO material is enhanced by 30.1% (426.6 mAh g−1), and the battery still has 85.4% residual capacity (144.2–123.1 mAh g−1) after 6000 cycles, and coulombic efficiency is always maintained above 99.5%. This heterostructure design strategy of C- and N-doped MnO2 provides high electronic conductivity while playing an important role in improving structural stability.

Potential in-vitro antioxidant and anti-inflammatory activity of Martynia annua extract mediated Phytosynthesis of MnO2 nanoparticles

The present research work describes the phyto-synthesis of Manganese dioxide nanoparticles (MnO2NPs) from the reduction of potassium permanganate using Martynia annua (M.annua) plant extract. From the literature review, we clearly understood the M.annua plant has anti-inflammatory activity. Manganese dioxides are important materials due to their wide range of applications. Their increased surface area gives them distinct capabilities, as it increases their mechanical, magnetic, optical, and catalytic qualities, allowing them to be used in more pharmaceutical applications. A detailed review of literature highlighting the issues related to this present work and its knowledge gap that none of the inflammatory activities had been done by MnO2 NPs synthesized from M.annua plant extract. So we selected this study. The product MnO2 NPs showed the wavelength centre at 370 nm and was monitored by UV–Vis spectra. The wave number around 600 cm−1 has to the occurrence of O–Mn–O bonds of pure MnO2 confirmed by FTIR spectroscopy. Transmission electron microscopy images showed the morphology of MnO2 NPs as spherical-shaped particles with average sizes at 7.5 nm. The selected area electron diffraction analysis exhibits the crystalline nature of MnO2 NPs. The obtained MnO2 NPs showed potential antioxidant and anti-inflammatory activity was compared to the plant extract. The synthesized MnO2 NPs have a large number of potential applications in the field of pharmaceutical industries. In the future, we isolate the phytocompounds present in the M.annua plant extract and conduct a study against corona virus. MnO2 produces manganese (III) oxide and oxygen, which increases fire hazard. But further research is required to understand their environmental behaviour and safety.

One-step hydrothermal synthesis of Fe3+-doped sheet-like δ-MnO2 for high-performance hybrid supercapacitors

KMnO4 was the Mn source, FeCl3·6H2O was the Fe source, and Fe3+-doped δ-MnO2 was prepared by a one-step hydrothermal method. The effects of different addition amounts of FeCl3·6H2O on the morphology, crystal structure and electrochemical properties of MnO2 were studied. The results show that pure phase MnO2 has a sheet morphology. The doping of Fe3+ decreases the size of sheet MnO2 and increases the specific surface area of MnO2, but XRD shows that MnO2 still retains the δ-type. At the same time, the doping of Fe3+ causes MnO2 to expose high-energy crystal faces, which enhances the electrochemical activity of MnO2. Further studies found that Fe3+ of FeCl3·6H2O plays an important role, while Cl− has nothing to do with it. The electrochemical test results show that when 3 mmol Fe3+ is added, the specific capacitance of MnO2–0.3 reaches the maximum value (196 F g−1), which is much higher than that of pure MnO2 (123.4 F g−1). Finally, the hybrid supercapacitor assembled from MnO2–0.3 and activated carbon has an energy density of 19.9 Wh kg−1, which can maintain 83.3 % of the initial value after 20,000 cycles. This work provides us with a new way to control the structure of electrode materials.

Investigations on Chemically Synthesized Pure and Doped Manganese Dioxide Nanoparticles for Dye Removal and Photocatalytic Applications.

Pure and Mg2+, Ni2+, Cd2+ doped MnO2 nanoparticles were synthesized by chemical co-precipitation method. These samples were characterised by PXRD, SEM, EDX, FTIR, UV-Vis-NIR, PL, Antibacterial, Cyclic Voltammetry, Dye Degradation and Photocatalytic studies. From the powder XRD studies, the crystallite size of the particle was calculated using Scherer formula and found that the synthesized nanoparticles were in the range from 10 to 12nm. The morphology of all the synthesized samples was viewed from SEM micrograph. The composition and purity of the samples were identified from EDX studies. In FTIR spectra metal-oxygen stretching and bending modes of vibrations were observed. From the absorption spectra of UV-Vis optical analysis values of absorption coefficient, extinction coefficient, refractive index, real and imaginary part of optical dielectric constant and optical conductivity were compared. The band gap energy obtained from Tauc's plot varies from 1.21 to 1.51eV exhibits semiconducting behaviour of all the synthesized samples. Investigations on photoluminecsence spectrum reveals blue shift in wavelength for doped nanooxides compared to pure MnO2. Antimicrobial activity of synthesised samples against gram positive and gram negative bacteria was determined. The obtained results reveal very high bacterial resistance in Cd2+ doped MnO2 nanoparticles with higher activity towards bacterial resistance compared to standard drug. The specific capacitance values were determined from Cyclic Voltammetry studies. Using the batch method of dye removing technique the percentage of malachite green dye removal was calculated. Also the photocatalytic efficiency of all the synthesized MnO2 samples in removing malachite green dye was studied by exposing to sunlight for different dosage and contact time. Ni2+ doped MnO2 shows relatively higher % of dye degradation capacity about 93% for 0.1g of dosage of photocatalysts.

Unveiling the future of environmental solutions: S-g-C3N4/Te-doped metal oxides (ZnO, Mn3O4 & SnO2) as game-changers in photocatalytic and antibacterial technologies

Researchers aim to develop photoactive systems to address critical environmental challenges, presenting a significant ongoing challenge. This study emphasizes the construction of pure metal oxide NPs (ZnO, Mn3O4, and SnO2), tellurium-doped metal oxides, and composite materials of graphitic carbon nitride/tellurium-doped metal oxides to enhance photocatalytic performance in methylene blue (MB) degradation under natural sunlight. Various characterization techniques, XRD, EDX, SEM, FTIR and UV–Vis Spectroscopy, were employed to analyze the structure, shape, and optical features of the materials. The photocatalytic degradation order for MB was determined to be pure and doped ZnO > pure & doped SnO2 > pure & doped Mn3O4. ZnO NPs exhibited the highest photocatalytic degradation at 98 %, accredited to their higher crystallinity, insignificant surface area and reduced particle dimension. Pure and doped ZnO NPs demonstrated the maximum zone of inhibition, reaching 39.5 mm. Consequently, S-g-C3N4/Te-ZnO emerges as the most promising material, serving as both a photocatalytic and antibacterial agent.

Tunable Zn2+ de-solvation behavior in MnO2 cathodes via self-assembled phytic acid monolayers for stable aqueous Zn-ion batteries.

Sluggish ion diffusion kinetics at the electrode/electrolyte interface leads to insufficient rate capability and poor structural reversibility, which are mainly attributed to the hydrated Zn2+ migration process being inhibited due to its huge de-solvation energy barriers. Herein, a self-assembly method is proposed in which a multifunctional monolayer with phytic acid (PA) is coated on the surface of MnO2 strongly attaching to the substrate with the formation of chemical bonding to effectively prevent the dissolution of PA in the electrolyte. Due to the negative charge and inherent ultra-hydrophilicity of PA, modified MnO2 demonstrates stronger adsorption of positive ions and captures reactive water molecules, easily accelerating the de-solvation process of interfacial hydrated Zn2+, efficiently achieving reversible Zn2+ insertion/extraction. Meanwhile, the coating layers can protect the substrate from attack by active water molecules, thus inhibiting cathode dissolution during battery cycling. Experimental characterization studies reveal that the protected MnO2 cathode exhibits a remarkable specific capacity of 273 mA h g-1 with a zinc intercalation capacity contribution of more than 60% at a current density of 0.1 A g-1. Additionally, even at a high current density of 1 A g-1, it maintains a capacity of 197 mA h g-1, far exceeding that of pure MnO2. Furthermore, the Zn-ion pouch cell, serving as a proof of concept, achieves an impressive energy density of 300 W h kg-1 and exhibits remarkable capacity retention of 77% even after 100 cycles. This work offers a universal strategy for expediting the de-solvation process of hydrated Zn2+ on the surface of manganese-based cathodes in aqueous zinc-ion batteries.

(Invited) Effect of Carbonaceous Materials on the Performance of Supercapacitors

Carbonaceous materials such as carbon blacks, activated carbons, multi walled/single walled carbon nanotubes (CNTs), graphene oxide (GO), reduced graphene oxide (rGO), and biochar are found to be useful for energy storage applications because of their large specific surface area, high conductivity, high mechanical strength, good thermal stability, and low cost.In order to optimize the concentration of MWCNT in MnO2/MWCNT nanocomposite, we have synthesized MnO2/MWCNT nanocomposite with varying concentration of MWCNT such as pure MnO2, 1mg/ml, 4 mg/ml, and 10 mg/ml MWCNT in reaction mixture. The samples were identified as MnO2, M-CNT 100, M-CNT 400, and M-CNT 1000. From cyclic voltammetric studies at various scan rate, we plotted a graph between peak current () versus the scanning rate () and found that the slope of anodic (cathodic) peak for MnO2, M-CNT 100, M-CNT 400, and M-CNT 1000 were found to be 0.48 (0.42), 0.70 (0.61), 0.60 (0.54), and 0.52 (0.47), respectively. We also found that at a current density of 0.5 A/g, pure MnO2 has a specific capacitance of 124 F/g. The addition of MWCNT initially increases the specific capacitance to 145 F/g for M-CNT 100 nanocomposite; however, at the 400-mg and 1000-mg concentrations the specific capacitance decreases to 135 F/g and 102 F/g, respectively.Besides this, we have also studied the effect of binder on capacitive performance of MnO2/CuS/rGO samples and found that the specific capacitance of the composite materials increased upon decreasing the binder. The detailed results of our recent investigations on carbonaceous materials for supercapacitor applications will be presented at 244th ECS meeting.

Engineering Mn–O strength in manganese oxide catalyst to enhance propane catalytic oxidation

Developing highly active and thermally stable transition-metal-oxide catalysts for light alkane catalytic oxidation is of great importance but very challenging. In the work, the catalytic performance for propane deep oxidation was significantly enhanced on the Mn1NixOy solid solution catalyst by weakening the Mn–O bond strength of manganese oxide. The characterization results combined with DFT calculations demonstrated that the introduction of Ni could create additional defect sites, resulting in a significant improvement of the adsorption and the activation of both propane and oxygen molecules. The optimal Mn1Ni0.15Oy catalyst exhibits abundant oxygen vacancies with low MnO bond strength, high redox ability and oxygen mobility, which account for its superior activity. Specifically, the specific reaction rate on Mn1Ni0.15Oy is three times higher than that on pure Mn2O3. Moreover, a Mn1Ni0.15Oy/cordierite monolithic catalyst was made by wash-coating method, and exhibited remarkable catalytic performance and stability on catalytic oxidation of propane during the 45 days (1080 h) on stream, even after tens of high temperature thermal shocks (up to 650 ℃), which declared to be satisfied for practical industrial applications. This work will shed light on designing high-efficiency and long-life environmental catalyst for VOCs elimination.