MnO2 Surface Research Articles

Atomic-level mechanism and microkinetics of HCHO oxidation over K-doped MnO2 catalysts

K-doped MnO2 is regarded as an efficient catalyst for HCHO oxidation. A combined study of density functional theory (DFT) and microkinetic modeling was implemented to investigate the role of potassium doping in the catalytic reactivity of MnO2 towards HCHO oxidation. The DFT-derived thermodynamic stability analysis indicates that the K-doped MnO2 surface is more stable than the pristine MnO2 surface under the practical experimental conditions. The introduction of K ion is energetically beneficial to the adsorption of HCHO and O2 by charge transfer from potassium to the catalyst surface. The HCHO oxidation paths show that the rate-determining step is the second dehydrogenation reaction. The best catalytic activity of MnO2@K-1 is associated with the abundant Mn atom with a high chemical valence on the catalyst surface. Specially, K doping has little effect on the adsorption of water, but promotes the production of OH group by reducing the energy barrier of hydrolysis. The hydroxylated surface is favorable for the two-step cleavage of the C-H bond. The overall reaction rate of HCHO oxidation on the K-doped MnO2 catalyst is much higher than that on the pristine MnO2. At low temperatures, the reaction rate is relatively insensitive to the pressure change, while the oxidation rate gradually rises with the increasing of pressure at high temperatures. K doping is conducive to boosting the reaction rate of HCHO oxidation, which is associated with the stronger interaction of reactants with K-doped catalysts.

Degradation of Sulfamethoxazole by Manganese(IV) Oxide in the Presence of Humic Acid: Role of Stabilized Semiquinone Radicals.

In this work, we demonstrate for the first time the abatement of sulfamethoxazole (SMX) induced by stabilized ortho-semiquinone radicals (o-SQ•-) in the MnO2-mediated system in the presence of humic acid. To evaluate the performance of different MnO2/mediator systems, 16 mediators are examined for their effects on MnO2 reactions with SMX. The key role of the bidentate Mn(II)-o-SQ• complex and MnO2 surface in stabilizing SQ•- is revealed. To illustrate the formation of the Mn(II)-o-SQ• complex, electron spin resonance, cyclic voltammetry, and mass spectra were used. To demonstrate the presence of o-SQ• on the MnO2 surface, EDTA was used to quench Mn(II)-o-SQ•. The high stability of o-SQ•- on the MnO2 surface is attributed to the higher potential of o-SQ•- (0.9643 V) than the MnO2 surface (0.8598 V) at pH 7.0. The SMX removal rate constant by different stabilized o-SQ• at pH 7.0 ranges from 0.0098 to 0.2252 min-1. The favorable model is the rate constant ln (kobs,7.0) = 6.002EHOMO(o-Qred) + 33.744(ELUMO(o-Q) - EHOMO(o-Qred)) - 32.800, whose parameters represent the generation and reactivity of o-SQ•, respectively. Moreover, aniline and cystine are competitive substrates for SMX in coupling o-SQ•-. Due to the abundance of humic constituents in aquatic environments, this finding sheds light on the low-oxidant-demand, low-carbon, and highly selective removal of sulfonamide antibiotics.

Enhancing water resistance of α-MnO2 catalyst for efficient airborne benzene oxidation at mild temperatures via facile Ag incorporation

Facile structural modification of α-MnO2via single incorporation of Ag element was applied to achieve high-efficiency oxidation removal of benzene, particularly under wet gas. Ag+ ions could enter the MnO2 structure by partially replacing the tunnel K+ ions, leading to lower crystallinity, smaller crystallite and distorted lattice arrangement. Due to electron transfer from Ag+ to lattice oxygen, Ag decoration weakened Mn-O bonds and the bulk lattice oxygen became more mobile to migrate towards the Ag-MnO2 surface, resulting in the larger number of surface lattice oxygen. Along with the abundance of oxygen species, the reactivity of surface adsorbed oxygen and lattice oxygen was significantly improved as well by Ag modification. All these factors were favorable to the complete C6H6-to-CO2 conversion. Gaseous benzene could be directly oxidized by oxygen species over the pristine MnO2 catalyst, while the adsorptive activation of gaseous benzene was required for the Ag-MnO2 before further oxidation. As to the Ag-MnO2’s endurability of moisture-aroused inactivation, Ag species oppressed water adsorption in the form of strong adsorbate, thus preventing structural damage of the catalyst during humid benzene oxidation. Moreover, water molecules could enhance the “Ag-MnO2vs. adsorbed benzene” interaction, which increased the oxidation efficiency of adsorbed benzene. However, the strong binding of water vapor with the MnO2 surface would cause strong restriction of gaseous benzene from approaching the surface oxygen species, resulting in much less benzene being oxidized under wet gas.

Facile fabrication of three-dimensional MnO2 for trichloroethylene degradation by plasma catalysis

Non-thermal plasma (NTP) coupled with catalyst is a cutting-edge technique for the abatement of chlorinated volatile organic compounds (Cl-VOCs), which are typically chemically stable, highly toxic and non-biodegradable. In this study, different morphologies of 3D MnO2 catalysts were fabricated facilely through a hydrothermal method and coupled with NTP for trichloroethylene (TCE) degradation. Among the various catalysts tested, MnO2 IV exhibited the highest TCE degradation performance, with removal efficiency, mineralization and energy yield ranging from 44.3% to 94.8%, 28.9% to 90.1% and 5.76 to 2.31 g/kWh, respectively, at voltage levels between 7 and 11 kV. The relationship between the physicochemical properties of the catalysts and their degradation performance was established through various characterization methods. The exceptional catalytic efficiency of MnO2 IV can be ascribed to its hierarchical flower-like structure, the greatest specific surface area (120 m2/g), the weakest Mn-O bonds, increased lattice defects and oxygen vacancies, and lower H2 reduction temperature. These characteristics facilitate enhanced transfer, adsorption, and utilization of reactive oxygen species in NTP on the surface of MnO2 IV, promoting the deep oxidation of TCE. The optimization of operational parameters was achieved using response surface methodology, with results indicating that the applied voltage exerted the greatest influence on both the mineralization rate and energy yield. The optimal operating conditions were determined, with initial TCE concentration, applied voltage, and gas flow rate values identified as 393 ppm, 7.3 kV, and 0.83 L/min, respectively. Lastly, the TCE degradation mechanism in the NTP-MnO2 catalyst system was hypothesized based on the identification of various plasma reactive species and organic intermediates. This study provides new insights for the improvement of the VOCs oxidation performance in plasma catalytic system.

Ferroelectric-Enhanced cathode kinetics toward High-Performance aqueous Zinc-Ion batteries

Rechargeable aqueous zinc ion batteries (AZIBs) offer promising potential for large-scale energy storage systems due to their high affordability and safety. However, their practical applications are hindered by the undesired rate capability and cycling stability of the used cathode, attributed to sluggish ions kinetics during charge–discharge process. Herein, we propose an electric field balancing strategy to regulate the electrolyte ions behavior by constructing a ferroelectric interface on the cathode surface using a prototypical of MnO2-based cathode. An appropriate thickness coating of ferroelectric materials coating (i.e., β-PVDF) on the MnO2 surface is theoretically and experimentally demonstrated to enhance the ion kinetics due to the optimized electrical distribution during electrochemical operations. Further comprehensive electrochemical mechanism studies reveal that the ferroelectric interface on the MnO2@β-PVDF not only promotes the diffusion of Zn2+ but also reduces the electrochemical overpotential (17.6 mV), resulting in improved electrochemical reversibility and capacity performance. The resultant MnO2@β-PVDF cathode exhibits the highest capacity of 277.6 mAh g−1 (at 0.1 A g−1) and capacity retention of 68.6% after 120 cycles, surpassing both the pristine MnO2 and non-ferroelectric materials coated MnO2 electrodes. This success presents a new approach to enhance the overall electrochemical performance of the cathodes for the practical application of AZIBs.

Novel Application of MnO2–H2O2 System for Highly Efficient Arsenic Adsorption and Oxidation

A novel manganese dioxide–hydrogen peroxide (MnO2–H2O2) system was developed for effective Arsenic (As) removal. Under the specified conditions of no external mechanical stirring, a trace H2O2 concentration of 0.015 wt%, and a MnO2 concentration of 25 mg/L, high removal efficiency (88%) of As (100 µg/L) was achieved by the MnO2–H2O2 system within 30 min, which differs from conventional adsorption processes that require external mechanical stirring and conventional arsenite (As (III)) oxidation–adsorption processes that require high quantities of oxidants (such as ozone) and specially synthesized adsorbents/catalysts. The high removal efficiency of As (III) by the MnO2–H2O2 system was attributed to the turbulent conditions precipitated by the extensively generated oxygen (O2) from the catalytic decomposition of H2O2, the efficient adsorption of As on the surface of MnO2, and the effective generation of reactive radicals including hydroxyl and superoxide radicals (•OH and •O2−). Moreover, the MnO2 adsorbents before and after As removal were characterized systematically, and the generated radicals were verified using electron spin resonance (ESR). The results showed that the formation of inner-sphere surface complexes by the surface hydroxyl groups of MnO2 particles and As was responsible for the effective As adsorption process, and the oxidation of As (III) to arsenate (As (V)) was achieved via the generated radicals. The influences of representative environmental factors on As removal performance and the application of the MnO2–H2O2 system in river water and ground water were further studied and tested. In conclusion, the MnO2–H2O2 system offers several advantages, including low cost, ease of operation, and strong environmental adaptability, making it highly promising for practical water treatment applications.

Effects of impure ions in precursors on the formation of active oxygen in MnO2 for promoting VOCs oxidation

Impure ions in the precursor can cause the structural transition of prepared MnO2 catalysts and influence their activity in toluene catalytic oxidation. Here, the effects of K+ and SO42- on the catalytic activity of MnO2 are examined. Removing absorbed SO42- by repeating water washing facilitates the exposure of active sites on the surface of MnO2. The temperature for toluene conversion reaches 90% (T90) of catalysts decreases from 247 ºC to 238 ºC. While the loss of K+ during the water washing leads to the inferior performance of MnO2. Re-impregnating of K+ can stimulate the generation of active oxygen species on the surface of catalysts (K/MnO2), which showed elevated catalytic activity in toluene conversion (T90, 229 ºC). In addition, K/MnO2 performs good stability for toluene combustion in long-term operation. Density Function Theory calculations reveal that the formation energy of oxygen vacancy and the adsorption energy of toluene on the surface of catalyst decrease from 6.996 eV and − 0.079 to 5.482 eV and − 0.468 eV as the introduction of K+, respectively. Our results provide a complete understanding of the effects of impurity ions on the performance of manganese oxide for catalytic oxidation of toluene.

Effect of Manganese Distribution on Sensor Properties of SnO2/MnOx Nanocomposites.

Nanocomposites SnO2/MnOx with various manganese content (up to [Mn]/[Sn] = 10 mol. %) and different manganese distribution were prepared by wet chemical technique and characterized by X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and mapping, IR and Raman spectroscopy, total reflection X-ray fluorescence, mass-spectrometry with inductive-coupled plasma (ICP-MS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy. A different distribution of manganese between the volume and the surface of the SnO2 crystallites was revealed depending on the total Mn concentration. Furthermore, the identification of surface MnO2 segregation was performed via Raman spectroscopy. There is a strong dependence of the sensor signal toward CO and, especially, NO) on the presence of MnO2 surface segregation. However, manganese ions intruding the SnO2 crystal structure were shown to not almost effect on sensor properties of the material.

Theoretical insight into the influence of SO2 on the adsorption and oxidation of mercury over the MnO2 surface

The inferior sulfur resistance is a major technical bottleneck of Mn-based catalysts to be employed as low-temperature selective catalytic reduction (SCR) catalyst for elemental mercury (Hg0) oxidation. The first-principle calculation based on density functional theory was adopted to investigate the influence of SO2 on mercury adsorption and oxidation over the MnO2 surface. The results indicated that Hg0 preferred to adsorb at the hollow and Obr bridge sites on the surface, and the adsorption of HgO was a strong chemisorption behavior. SO2 could be retained on the MnO2 surface through chemisorption. The adsorbed SO2 generated inhibition on Hg0 adsorption by the competitive and repulsive effects, while the effect of SO2 on HgO adsorption was negligible. SO2 showed almost no impact on the adsorption and dissociation of O2. Hg0 adsorption and oxidation at the active sites adjacent to the adsorbed SO2 was apparently restrained on the SO2-covered surface, and the desorption of generated HgO became easier compared to that on the clean surface. By contrast, Hg0 oxidation at the nonadjacent sites to SO2 was little influenced by the adsorbed SO2. The study results would offer guidance for impairing the inhibitory effect of SO2 and improving the SO2 resistance of Mn-based catalysts.

Adsorption–desorption behavior of malachite green by potassium permanganate pre-oxidation polyvinyl chloride microplastics

Microplastics (MPs) and the typical hydrophilic organic pollutant Malachite green (MG) are frequently detected in sewage treatment plants. Potassium permanganate (KMnO4) pre-oxidation is an economical and effective technology in wastewater treatment. It is important to study the surface physicochemical characteristics of MPs and understand their fate in wastewater treatment plants after pre-oxidation. In this study, Polyvinyl chloride (PVC) MPs were treated by single and composite KMnO4 pre-oxidation with different pH values. After the pre-oxidation treatment, the appearance of OMn spectra and surface nanoparticles indicated the oxides (MnO2) were produced on the MPs surface. Moreover, the adhesion of MnO2 is helpful to improve the hydrophilicity and adsorption capacity of MG. The adsorption capacity of pristine PVC for MG was 2.6 mg/g. But the adsorption capacity increased to 7.0 mg/g for single oxidation and 140.7 mg/g for composite oxidation, respectively. The desorption experiment results indicate the pre-oxidation process could reduce the release efficiency of MG from the PVC MPs due to the better binding of surface MnO2 nanoparticles to MG. However, the total desorption capacity is still high. which illustrates that there is a high potential risk of MG which can transfer from the surface of the PVC MPs to the gastrointestinal fluids.

Ag nanoparticle-loaded to MnO2 with rich oxygen vacancies and Mn3+ for the synergistically enhanced oxygen reduction reaction

MnO2 is considered to be one of the most promising electrocatalysts for oxygen reduction reactions (ORR) in alkaline media and can be applied to various electrochemical energy conversion and storage devices. However, it is limited by the relatively slow kinetics of the cathodic electrochemical reactions. In addition, it is difficult to control the presence state of Ag during the modification of MnO2. To this end, an efficient ORR electrocatalyst of Ag nanoparticles supported by MnO2 nanorods was successfully synthesized by using NH3·H2O as a complexing agent to inhibit the Ag+ intercalating into the tunnels of MnO2. The half-wave potential (E1/2) and limiting current density (Jlim) of the obtained Ag/MnO2 electrocatalysts are 0.81 V and −5.6 mA cm−2, respectively, showing comparable ORR catalytic activity to commercial Pt/C catalysts. The excellent catalytic performances can be attributed to the presence of abundant oxygen vacancies and Mn3+ species on the MnO2 surface, as well as the synergistic effect between MnO2 substrates and Ag nanoparticles. Among them, oxygen vacancies enhances the adsorption of O2, Mn3+ facilitates the displacement of O22−/OH−, MnO2 inhibits the accumulation of peroxide species to improving the oxygen environment on the Ag surface and Ag accelerates the electron transfer in the whole process. This work provides a useful guide for the design of efficient Mn-based ORR electrocatalysts.

Hollow carbon dual-decorated with MnO2 shielding layer and carbon nanotube as a sulfur host for Li-S batteries

The shuttle effect of polysulfides and sluggish reaction kinetics have been the main obstacles for the practical applications of lithium-sulfur (Li-S) batteries. Herein, we report a rationally designed sulfur cathode (DLHC/S@MnO2-ACNT) based on double-layered hollow carbon sphere (DLHC) decorated with manganese dioxide (MnO2) shielding layer and carbon nanotube conductive network (ACNT). The Ultramicrotome technique demonstrates that S and MnO2 nanosheets are mainly located into the interlayer of the DLHC. In the elaborate nanostructured protocol, the interlayer MnO2 nanosheets catalyze the conversion of polysulfides and the surface MnO2 nanosheets effectively adsorb polysulfides to suppress the shuttle effect. Additionally, the ACNT conductive network facilitates electrons/ions transport. Benefiting from the hierarchical confinement, Li-S batteries with DLHC/S@MnO2-ACNT composite cathodes exhibit a high reversible capacity of 1051 mAh g−1 at 0.5 C and a remarkable cycling stability over 500 cycles at 1 C. Even at a high sulfur loading of 4 mg cm−2, the cell delivers a superior areal capacity of 4.47 mAh cm−2. This work provides a new route to the design of hierarchical confinement sulfur hosts for high-performance Li-S batteries.

Evaluation of DFT+U and HSE Frameworks for Strongly Correlated Iron Oxide

AbstractFor strongly correlated metal oxides, several density functional theories have been used to describe the electronic structure of bulk iron oxide (α‐Fe2O3) and corresponding surfaces, including GGA+U and hybrid functionals (HSE), but the accuracy of these methods is unclear for these metal oxides. In the present study, first‐principles simulations were carried out to examine the effects of a hybrid density functional on α‐Fe2O3 bulk and surface slabs. Further, by using GGA+U, van der Waals corrections and O2 over binding corrections were also examined. It has been found that HSE functionals with 17.5 % Fock exchange predict better properties than those with 12 % or 25 % exchange. Methodological studies indicate that GGA+U predicted zero‐bandgap surface slabs become semiconducting slabs at HSE, and that calculated bandgaps are dependent on the actual exchange addition percentage. Our studies also show that the surface energy and relative stability of different Fe2O3 terminations are less sensitive to the inclusion of dispersion terms. However, when accounting for the GGA‐error in O2 over‐binding, significant changes occur in the computed surface energies. Additionally, HSE06 functional was tested on MnO2(0001) and MnO2(110) surfaces. Both surfaces were identified as metallic by a PBE+U calculation, and an HSE06 analysis revealed a nonzero band gap.

Kinetic Study of the Influence of Humic Acids on the Oxidation of As(III) by Acid Birnessite

Dissolved arsenic (As) in natural environments is controlled by sorption onto metal oxide surfaces; its speciation is principally influenced by biogenic manganese oxides and natural organic matter (NOM). Manganese (III/IV) oxides are strong oxidants that are ubiquitous in soils and sediments, and humic acids (HA) are typical substances found in the dissolved fraction of NOM. However, the mechanism of As(III) oxidation by MnO2 in the presence of NOM remains poorly understood. Here, we investigate how HA impact the oxidation of As(III) by a synthetic manganese oxide, i.e., acid birnessite (MnO2). We find that the reaction kinetics of As with HA and MnO2 are controlled by the formation of surface complexes. The main observed effect is a decrease of the overall oxidation rate in the presence of HA. In addition, pre-exposure of MnO2 to HA for 24 h further decreases the reaction rate, which is attributed to the occupation of MnO2 surface active sites, thus causing surface passivation. Our results demonstrate that HA influence the reaction mechanism of As(III) oxidation by MnO2 via sorption onto active surface sites and the formation of aqueous complexes.

Strong Electronic Interaction between Amorphous MnO2 Nanosheets and Ultrafine Pd Nanoparticles toward Enhanced Oxygen Reduction and Ethylene Glycol Oxidation Reactions

AbstractStrengthening the interface interaction between metal and support is an efficient strategy to improve the intrinsic activity and reduce the amount of noble metal. Amorphization of support is an effective approach for enhancing the metal‐support interaction due to the numerous surface defects in amorphous structure. In this work, a Pd/a‐MnO2 electrocatalyst containing ultrafine and well‐dispersive Pd nanoparticles and amorphous MnO2 nanosheets is successfully synthesized via a simple and rapid wet chemical method. Differing from the crystal counterpart (Pd/c‐MnO2), the flexible structure of amorphous support can be more favorable to electron transfer and further enhance the metal‐support interaction. The synergism between Pd and amorphous MnO2 results in the downshift of the d‐band center, which is beneficial for the desorption of critical intermediates both in oxygen reduction reaction (ORR) and in ethylene glycol oxidation (EGOR). Due to the lower *.OH desorption energy of Pd/a‐MnO2 surface, the rapid dissociation of *OH from Pd facilitates the formation of H2O in ORR, thus demonstrating superior ORR performance comparable to Pt/C. For EGOR, the presence of amorphous MnO2 promotes the formation of adsorbed OH species, which accelerates the desorption of intermediate CO from Pd sites, and thus exhibits excellent EGOR activity and stability.

Improving lithium polysulfides adsorption by oxygen-vacancy defects: By first-principles calculation

The serial interaction of lithium polysulfides (LiPSs) intermediates that possibly occurred on the surface of vacancy-defective manganese oxides have been investigated by First-principles calculation. Vacancy defects will cause the adjustment of micro regional electron density and produce stronger polarization for polar materials MnO2. The investigation of the stable adsorption site of LiPSs on defective MnO2 surface shows that oxygen-vacancy traps are beneficial for capturing LiPSs. Due to the existence of unpaired electrons, the interaction between vacancy-defective manganese oxide and Li2Sn molecules become stronger than pristine manganese oxide, which are propitious to decrease the adsorption energy for Li2Sn (n = 1, 2, 4, 6, 8) molecules. That is to say, vacancy defects can supply an effective nucleation sites that effectively enhance the affinity for Li2S and catalyze the conversion of LiPSs, which improve the shuttle effect and increase the utilization of active materials.

Improved bioelectrochemical performance of MnO2 nanorods modified cathode in microbial fuel cell.

The property of cathode in the microbial fuel cell (MFC) was one of the key factors limiting its output performance. MnO2 nanorods were prepared by a simple hydrothermal method as cathode catalysts for MFCs. There were a number of typical characteristic crystal planes of MnO2 nanorods like (110), (310), (121), and (501). Additionally, there were great many hydroxyl groups on the surface of nanorod-like MnO2, which provided a rich set of active adsorption sites. The maximum power density (Pmax) of MnO2-MFC was 180 mW/m2, which was 1.51 times that of hydrothermally synthesized MnO2 (119.07 mW/m2), 4.28 times that of naturally synthesized MnO2 (42.05 mW/m2), and 5.61 times that of the bare cathode (32.11 mW/m2). The maximum voltage was 234mV and the maximum stabilization time was 4days. The characteristics of MnO2, including rod-like structure, high specific surface area, and high conductivity, were conducive to providing more active sites for oxygen reduction reaction (ORR). Therefore, the air cathode modified by MnO2 nanorods was a kind of fuel cell electrode with great application potential.

Poly-thymine DNA templated MnO2 biomineralization as a high-affinity anchoring enabling tumor targeting delivery

Manganese oxide nanomaterials (MONs) are emerging as a type of highly promising nanomaterials for diseases diagnosis, and surface modification is the basis for colloidal stability and targeting delivery of the nanomaterials. Here, we report the in-situ functionalization of MnO2 with DNA through a biomineralization process. Using adsorption-oxidation method, DNA templated Mn2+ precursor to biomineralize into nano-cubic seed, followed by the growth of MnO2 to form cube/nanosheet hybrid nanostructure. Among four types of DNA homopolymers, poly-thymine (poly-T) was found to stably attach on MnO2 surface to resist various biological displacements (phosphate, serum, and complementary DNA). Capitalized on this finding, a di-block DNA was rationally designed, in which the poly-T block stably anchored on MnO2 surface, while the AS1411 aptamer block was not only an active ligand for tumor targeting delivery, but also a carrier for photosensitizer (Ce6) loading. Upon targeting delivery into tumor cells, the MnO2 acted as catalase-mimic nanozyme for oxygenation to sensitize photodynamic therapy, and the released Mn2+ triggered chemodynamic therapy via Fenton-like reaction, achieving synergistic anti-tumor effect with full biocompatibility. This work provides a simple yet robust strategy to functionalize metal oxides nanomaterials for biological applications via DNA-templated biomineralization.

Functional surface modification of P2-type layered Mn-based oxide cathode by thin layer of NASICON for sodium-ion batteries

P2-type layered manganese-based oxides, as promising high-energy-density and low-cost cathodes, have been triggered considerable attentions in sodium ion batteries (SIBs). Nevertheless, P2-type manganese-based oxides still suffer from the sluggish kinetics and unfavorable Jahn-Teller effect. Herein, motivated by the high ionic conductivity and rigid three-dimension framework of NASICON-type materials, the well-known Na3Zr2Si2PO12 thin layer was coated on P2-type Na0.612K0.056MnO2 surface to modify electrochemical sodium storage and structural stability. The optimal Na0.612K0.056MnO2@Na3Zr2Si2PO12 exhibited a high discharge capacity of 203 mA h g−1 within 1.8 − 4.3 V at a low current density of 10 mA g−1. When the current density enhances into 500 mA g−1, it delivers a high initial discharge capacity of 145.7 mA h g−1 within 1.8 − 4.3 V at 500 mA g−1 and maintains 69% capacity retention after 100 cycles. Besides, at low temperature of −20 °C, it offers 100.1 mA h g−1 after 100 cycles within 1.8 − 4.3 V at 100 mA g−1, which is much higher than that of NKMO (65.2 mA h g−1). The Na3Zr2Si2PO12 can decrease Mn3+ content and avoid the Jahn-Teller effect of Na0.612K0.056MnO2 in structural level, enabling the enhanced Na+ diffusion coefficient of Na0.612K0.056MnO2. Such strategy NASICON coating on cathode would pave a new pathway on rational design of high-performance cathode for SIBs.

Highly-efficient synthesis of heavy metal adsorbents by using spent lithium-ion battery anode graphite via one-step mechanochemistry process

Resource recycling has taken center stage of global carbon neutrality. In this study, we reclaimed spent graphite (SG) from retired lithium-ion batteries (LIBs) and introduced potassium permanganate powder to prepare amorphous MnO2 loaded graphite oxide (AMO@GO) via one-step mechanochemical method for heavy metals adsorption. The synthesized AMO@GO was characterized by X-ray diffraction (XRD), Raman spectra, X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller Method (BET), Fourier Transform Infrared Spectrometer (FTIR), and Scanning Electron Microscope (SEM), which illustrated AMO@GO had richer pore structure, ample active groups, strong surface ion exchange activity. These properties made AMO@GO a highly potential adsorbent for aqueous heavy metal contamination. The results showed the adsorption capacities of AMO@GO for Cu2+, Pb2+ and Cd2+ in the water body can reach 233.99 mg/g, 353.13 mg/g and 257.95 mg/g respectively (calculated by Langmuir isotherm model), significantly higher than similar graphite-based adsorbents. Through in-depth studies of the adsorption mechanism, we found that the ion exchange of heavy metals with active groups on the surface of graphite oxide and amorphous MnO2 was the main source of sample adsorption capacity.