Manganese Sites Research Articles

Low-valent manganese active sites: Insight into reinforced interaction with sulfonated anthraquinone dye and kinetic adsorption studies over iron-modified cryptomelane

This study presents a facial co-precipitation method to enrich low-valent manganese sites for iron-doped cryptomelane. Fourier-transform infrared spectroscopy exhibits a noticeable enhancement of both vibrations at 1041 and 1116 cm-1 ascribed to Mn3+-OH bond over as-prepared materials. X-ray diffraction, scanning electron microscopy, Raman spectroscopy, the temperature-programmed desorption of oxygen and inductively coupled plasma-mass spectrometry results all verify the increase in oxygen vacancies on iron-doped cryptomelane. The vital role of Mn3+-OH sites for adsorptive removal of acid blue 62 (AB62) was experimentally evident when adsorption capacity (Qe, mgAB62/gadsorbent) increased from 54 ± 1.3 mg/g (for non-doped cryptomelane) to 161 ± 6.7 mg/g (for Fe-0.15) at initial pH 5.7. The decrease of Qe from 313 mg/g (for initial pH 3.70) to 67 mg/g (for initial pH 9.95) over Fe-0.15 suggests protonation in acid media and deprotonation in basic media, reflecting efficient Mn3+-OH sites for reinforced interaction with sulfonate groups. The disappearance of sharp bands at 1041 and 1116 cm-1 after adsorption and the replenishment of a broad band at ∼1250 cm-1 over Fe-0.15 demonstrate the displacement of sulfonate groups by -OH species (from Mn3+-OH sites). Moreover, the deterioration of two stretching modes for O=S=O at 1187 and 1230 cm-1 after adsorption reveals the formation of a monodentate or bidentate complex. Kinetic studies confirm the compatibility of AB62 chemisorption over Fe-0.15 with the pseudo-second-order kinetic, Elovich, and Langmuir isotherm models. The current findings first support evidences for the AB62 chemisorption on iron-doped cryptomelane and a Fe-0.15-feasible adsorbent for removal of sulfonated anthraquinone dye.

Chemical pressure induced spin reorientation in the magnetic structure of Ca3Mn2−xSnxO7 ( x=0,0.03,0.05 )

The effect of partially substituting Tin (Sn) at the Manganese (Mn) site of Ca3Mn2O7 , viz. Ca3Mn2−xSnxO7 with x=0.03,0.05 , on its structural and magnetic properties have been investigated using synchrotron diffraction, neutron diffraction, and bulk magnetization measurements. It is observed that with a substitution of x=0.03 , the minor (≈8%) tetragonal ( I4/mmm ) structural phase that is present in the predominantly orthorhombic ( Cmc21 ) undoped Ca3Mn2O7 , completely disappears. The compounds order antiferromagnetically, the ordering temperature decreases with increasing Sn-content, indicating a weakening of the antiferromagnetic exchange interactions. Interestingly, in the ordered state, the spin magnetic moments which were aligned along the a-axis of the unit cell in the undoped compound, are observed to have reoriented with their major components lying in the b − c plane in the Sn-doped compounds. The above influence of Sn-doping is seen to be stemming from a significant modification of the octahedral rotation and tilt mode geometry in the unit cell, that is known to be responsible for driving ferroelectricity in these compounds.

Ultralong Lifespan Zero‐Cobalt/Nickel Prussian Blue Analogs Cathode Realized by Solid Solution Reaction Sodium Storage Mechanism

AbstractDespite their low cost and high specific capacity, the practical use of monoclinic Mn‐based Prussian blue analogs (Mn‐PBAs) is limited by poor cycling stability, primarily due to the structural degradation caused by the multiple phase transitions and Jahn–Teller effect associated with Mn3+ ions throughout the entire cycle. Herein, by synergistic incorporation of low‐cost Cu and Fe into the manganese sites of Mn‐PBAs, the ternary PBAs (T‐PBAs) achieve solid solution reaction of Na+ extraction and insertion, successfully eliminating the inherent multi‐phase transition from the sodium storage mechanism of T‐PBAs. Ex situ analysis and density functional theory calculations are employed to confirm that T‐PBAs consistently maintain a cubic phase with smaller lattice distortion rather than occur in conventional three‐phase transition during the charging and discharging processes, forcefully inhibiting the structural degradation of T‐PBAs. Therefore, the T‐PBAs showcase unprecedented cycling stability at both room temperature (10 000 cycles at 1 A g−1) and −20 °C (over 3000 h, 4200 cycles at 0.2 A g−1 without distinct capacity degradation), More importantly, when paired with commercial hard carbon, the T‐PBAs based sodium‐ion batteries exhibit excellent capacity retention (2000 cycles 76.8%), showcasing their immense potential in practical applications.

Enhanced photocatalytic performance of gadolinium-doped lithium manganese oxide (Li4Mn5O12) by conventional ball milling method

Abstract Current research aims to improve the characteristics of lithium manganese oxide (LiMn2O4), a highly prospective for waste water treatment applications, by incorporating gadolinium (Gd-0.25 %) into the manganese position. This integration, achieved via conventional ball milling, aims to improve the structural, morphological, and electrical characteristics of Li4Mn5O12. A range of analytical methods, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and impedance testing, were utilized to evaluate the influence of Gd-0.25 % on Li4Mn5O12. The results indicate that the inclusion of Gd at the manganese sites enhances the thermal conductivity of Li4Mn5O12 (Li4Mn4.75Gd0.25O12), leading to improved conductivity compared to undoped Li4Mn5O12. Additionally, the enhanced material exhibits promising potential as an efficient photocatalyst, demonstrated by its degradation of methylene blue (MB) dye.

Design and synthesis of new water-soluble dinuclear manganese(II) complexes as monosaccharide binding models

The present article describes the design, synthesis, physicochemical characterization and monosaccharide binding events of two new water-soluble dinuclear manganese(II) complexes [Mn2(phpda)(µ-Cl)]·2H2O (1) and [Mn2(phpda)(µ-OAc)]·2H2O (2) of carboxylate and pyridyl-functionalized multidentate ligand, H3phpda (H3phpda = N,N′-bis[2-pyridylmethyl]-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid). FTIR, UV–Vis, ESI-MS, microanalysis, molar conductivity, cyclic voltammetry and room-temperature magnetic data establish their compositions. Structural features of 1 and 2 obtained from theoretical calculations indicate a self-assembled and well-packed array with average Mn···Mn separation of 2.952 Å. Both 1 and 2 have been studied towards 1:1 binding interactions with biologically important monosaccharides, such as d-glucose, d-xylose and d-glucosamine by employing UV–Vis spectroscopy and DFT computation. The binding constant values of monosaccharide-bound manganese(II) complexes evaluated from UV–Vis titration data are 2.145 x 103 M−1, 2.156 x 103 M−1, 2.652 x 103 M−1, 1.388 x 103 M−1, 1.793 x 103 M−1 and 2.146 x 103 M−1 for 1/d-glucose, 1/d-xylose, 1/d-glucosamine, 2/d-glucose, 2/d-xylose and 2/d-glucosamine assemblies, respectively. The possible metal centers engaged in the binding events have been ascertained by calculating the Fukui functions (fk+) on the manganese sites, including HOMOs and LUMOs. A comparative assessment of sugar-binding properties, in particular, suggests that the order of binding ability of monosaccharides with 1 and 2 is found to be d-glucosamine > d-xylose > d-glucose.

Understanding the charge transfer effects of single atoms for boosting the performance of Na-S batteries.

The effective flow of electrons through bulk electrodes is crucial for achieving high-performance batteries, although the poor conductivity of homocyclic sulfur molecules results in high barriers against the passage of electrons through electrode structures. This phenomenon causes incomplete reactions and the formation of metastable products. To enhance the performance of the electrode, it is important to place substitutable electrification units to accelerate the cleavage of sulfur molecules and increase the selectivity of stable products during charging and discharging. Herein, we develop a single-atom-charging strategy to address the electron transport issues in bulk sulfur electrodes. The establishment of the synergistic interaction between the adsorption model and electronic transfer helps us achieve a high level of selectivity towards the desirable short-chain sodium polysulfides during the practical battery test. These finding indicates that the atomic manganese sites have an enhanced ability to capture and donate electrons. Additionally, the charge transfer process facilitates the rearrangement of sodium ions, thereby accelerating the kinetics of the sodium ions through the electrostatic force. These combined effects improve pathway selectivity and conversion to stable products during the redox process, leading to superior electrochemical performance for room temperature sodium-sulfur batteries.

Evidence of a Large Refrigerant Capacity in Nb-Modified La1.4Sr1.6Mn2−xNbxO7 (0.0 ≤ x ≤ 0.15) Layered Perovskites

In this work, evidence of isothermal magnetic entropy change (∆SM) over a broad temperature region is presented in a series of La1.4Sr1.6Mn2−xNbxO7 Ruddlesden–Popper compounds with niobium modification (Nb) (0.0 ≤ x ≤ 0.15) at the manganese (Mn) site. The ceramic samples were obtained through a solid-state sintering method in optimized conditions. All compounds predominantly possessed Ruddlesden–Popper phase while a few additional reflections were resolved in Nb-doped compounds which indicates the separation of structural phases. These peaks are assigned to a separate layered perovskite and single perovskite with tetragonal symmetry and hexagonal symmetry, respectively. The microstructure of the pure sample reveals uniform grain morphology but in Nb-doped specimens chiefly three types of grains were found. It was assumed that the inter-connected large particles were of R-P phase which is dominant in both parent and x = 0.05 compounds, while the hexagonal and polygonal morphology of grains in higher concentrations of dopants directly corroborates with the symmetry of single perovskite and additional layered perovskite phases, respectively. The parent compound exhibits a single ∆SM curve, whereas all Nb-substituted samples display bifurcated ∆SM curves. This indicated two transition regions with multiple magnetic components, attributed to distinct structural phases. The highest ∆SM values obtained for components corresponding to the R-P phase are 2.32 Jkg−1k−1, 0.75 Jkg−1k−1, 0.58 Jkg−1k−1 and 0.43 Jkg−1k−1 and for the second component located around room temperature are 0.0 Jkg−1k−1, 0.2 Jkg−1k−1, 0.28 Jkg−1k−1 and 0.35 Jkg−1k−1 for x = 0.0, 0.05, 0.10 and 0.15 compositions, respectively, at 2.5 T. Due to the collective participation of both components the ∆SM was expanded through a broad temperature range upon Nb doping.

Mechanically treated Mn2O3 triggers peracetic acid activation for superior non-radical oxidation of micropollutants: Identification of reactive complexes

This study used a simple mechanical ball milling strategy to significantly improve the ability of Mn2O3 to activate peracetic acid (PAA) for sustainable and efficient degradation of organic micropollutant (like bisphenol A, BPA). BPA was successfully removed and detoxified via PAA activation by the bm-Mn2O3 within 30 min under neutral environment, with the BPA degradation kinetic rate improved by 3.4 times. Satisfactory BPA removal efficiency can still be achieved over a wide pH range, in actual water and after reuse of bm-Mn2O3 for four cycles. The change in hydrophilicity of Mn2O3 after ball milling evidently elevated the affinity of Mn2O3 for binding to PAA, while the reduction in particle size exposed more active sites contributing partially to catalytic oxidation. Further analysis revealed that BPA oxidation in the ball mill-treated Mn2O3 (bm-Mn2O3)/PAA process mainly depends on the bm-Mn2O3-PAA complex (i.e., Mn(III)−OO(O)CCH3) mediated non-radical pathway rather than R-O• and Mn(IV). Especially, the existence of the Mn(III)-PAA complex was definitely verified by in situ Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Simultaneously, density functional theory calculations determined that PAA adsorbs readily on manganese sites thereby favoring the formation of Mn(III)−OO(O)CCH3 complexes. This study advances an in-depth understanding of the underlying mechanisms involved in the manganese oxide-catalyzed activation of PAA for superior non-radical oxidation of micropollutants.

Ti-Doped Co-Free Li1.2Mn0.6Ni0.2O2 Cathode Materials with Enhanced Electrochemical Performance for Lithium-Ion Batteries

Cobalt-free manganese-based lithium-rich layered oxides (LLOs) have garnered research attention as prospective lithium-ion cathode materials owing to their large specific capacity and low price. However, their large-scale application is hindered by their low Coulombic efficiency, poor cycling performance, voltage attenuation, and structural phase transition. To address these issues, the LLO structure is modified via Ti doping at the manganese site herein. Ti-doped Li1.2Mn0.6−xTixNi0.2O2 (x = 0, 0.03, 0.05, 0.10, and 0.15) is prepared using the high-temperature solid-state method. The Ti-doped Li1.2Mn0.6Ni0.2O2 is calculated via first principles. The results show that Ti4+ doping improves the cycle stability and rate performance of Li1.2Mn0.6Ni0.2O2. Electrochemical test results show that the sample exhibits enhanced electrochemical performance when the Ti doping amount is 0.05. The discharge specific capacity at 0.1C is 210.4 mAh·g−1, which reaches 191.1 mAh·g−1 after 100 cycles, with a capacity retention rate of 90.7%. This study proves the feasibility of using cheap cobalt-free LLOs as cathode materials for LIBs and provides a novel system for exploiting low-cost and high-performance cathode materials.

Insights into dynamic structural evolution and its sodium storage mechanisms of P2/P3 composite cathode materials for sodium-ion batteries.

Cobalt substitution for manganese sites in Na0.44MnO2 initiates a dynamic structural evolution process, yielding a composite cathode material comprising intergrown P2 and P3 phases. The novel P2/P3 composite cathode exhibits a reversible phase transition process during Na+ extraction/insertion, showcasing its attractive battery performance in sodium-ion batteries.

Tungstic acid integrated metal–organic frameworks for efficient oxygen evolution reaction

Mimicking the isolated and encapsulated active manganese sites within proteins in nature through the integration of NiFe sites and tungstic acid nanoparticles in an ordered open framework in an isolated manner.

Double coordination shell modulation of nitrogen-free atomic manganese sites for enhancing oxygen reduction performance.

The rational design and fabrication of the active sites of single-atom catalysts (SACs) remains the main breakthrough for efficient electrocatalytic oxygen reduction reaction (ORR). Although metal-nitrogen-carbon (M-N-C) materials have been reported to exhibit good ORR performance, the M-N bond is prone to oxidation and subsequent destruction in Fenton-like reactions. Here, we report a nitrogen-free Mn-based SAC (Mn-S1O4G-600) anchored on a nitrogen-free graphene substrate, where manganese is bound to four oxygen atoms and one sulfur atom across two different coordination shells. In 0.1 M KOH, the Mn-S1O4G-600 demonstrates a half-wave potential of 0.86 V and a high kinetic current density of 10.3 mA cm-2 at 0.6 V. Due to the lack of nitrogen coordination, the Mn-S1O4G-600 has good anti-Fenton reaction properties. Notably, the Mn-S1O4G-600-based zinc-air battery displays an open circuit voltage of 1.46 V and outstanding cycle stability, which is superior to Pt/C. Theoretical calculations reveal that the introduction of the second S-coordination layer increases the charge density of the manganese center and decreases the energy barrier. This work identifies a novel active coordination configuration model for the ORR, paving the way for innovative design and synthesis of efficient SACs.

Modelling the dispersion of particulate matter (PM10) via wind erosion from opencast mining-Moldova Nouă tailings ponds, Romania.

Historically, Romania is known as a mining site of mineral substances, including gold, silver, copper, lead, zin, uranium, manganese, salt, and coal, whereby their long periods of exploitation and extraction affected human health and the environment in various ways. In Moldova Nouă southwest region of Romania, we investigated the environmental impacts of mining activities on air quality over 2021. We quantified PM10 emission rates through in situ monitoring, dispersion modelling, and horizontal and vertical fluxes. Statistical metrics, including the fraction within factor 2 (FAC2), mean bias (MB), mean gross error (MGE), normalized mean bias (NMB), normalized mean gross error (NMGE), coefficient of efficiency (COE), index of agreements (IOAs), and Taylor diagram signifying standards deviation (SD), root mean squared error (RMSE), and correlation coefficient (R), were used to evaluate the reliability of modelling results against observation. Results conclude that PM10 dispersion agrees with MB, MGE, NMB, NMGE, COE, IOA, and Taylor diagram and moderately with FAC2 metrics. PM10 hotspot was investigated in the vicinity of the tailings ponds of 115.5µgm-3 annual mean, 563.7µgm-3 daily mean, 63.3µgm-2s-1 annual horizontal flux, and 3.0µgm-2s-1 annual vertical flux. PM10 dispersion was identified to expand to Moldova Nouă City and nearby country Serbia. Findings concluded that a windy air mass accumulation across the overburdened dumps and ponds causes the increase of PM10 in the air, resulting in the region's pollution. Therefore, results recommend adopting a strategic mitigation measure for residents, policymakers, stakeholders, and urban planners.

Enhancing the electrochemical properties of Na2Mn2P3O9N by partial substitution at Mn site: A first-principles study

Nitridophosphate materials have recently emerged as promising cathode materials for Na-ion batteries due to their excellent ionic conductivity, but their low electronic conductivity has limited their practical applications. In this study, the electrochemical properties of Na2Mn2P3O9N, a nitridophosphate material containing manganese was examined for the first time and the prevalent issue of low electronic conductivity in nitridophosphate-based materials was addressed through partial substitution of transition metal (TM) at the Mn site. The present work aims at improving the electronic conductivity of this material while maintaining desirable properties such as ionic conductivity, voltage, and structural stability. The study employed density functional theory (DFT) calculations to explore the role of TM substitutions in electronic conductivity and electrochemical properties. From the partial substitution of different electrochemical active and inactive elements at the Mn site, we found that the Cu/Ag substitutions improve the electronic conductivity while retaining other desirable electrochemical properties. The electronic and electrochemical properties of these materials were further studied in detail to reveal the redox mechanisms. Our DFT-assisted studies prove that the parent and Ag-substituted materials exhibit a stable O network even under a high state of charge. Furthermore, our nudged elastic band calculations revealed that Na2Mn2P3O9N, along with the Cu/Ag substituted variants, exhibit favourable Na-ion diffusion. The parent and Ag-substituted materials demonstrate exceptional ionic conductivities comparable to existing commercial cathodes used in Li-ion batteries. These findings suggest that partial substitution of copper/silver at the manganese site could be a promising strategy for improving the electronic conductivity of nitridophosphate materials without compromising their beneficial properties to use in higher energy density Na-ion batteries.

Motivating Inert Strontium Manganate with Iridium Dopants as Efficient Electrocatalysts for Oxygen Evolution in Acidic Electrolyte.

The search for high-performance and low-cost electrocatalysts in acid conditions still remains a challenging target. Herein, iridium (Ir) doped strontium manganate (named as Irx -SMO) is proposed as an efficient and durable low-iridium electrocatalyst for water oxidation in acidic media. The Ir0.1 -SMO with 75% less iridium in comparison to that of iridium dioxide (IrO2 ) exhibits excellent performance for oxygen evolution reaction (OER), which is even better than most of the iridium-based oxide electrocatalysts. The theoretical outcomes confirm the activation of the inert manganese sites in strontium manganate by the incorporation of iridium dopants. This work reveals the boosted effect of the iridium dopants on the OER activity of strontium manganate, providing a strategy to tune the activity of manganese-based perovskites in electrocatalysis.

Preparation of magnesium carbonate and manganese carbonate composite materials doped at manganese site by hydrothermal method and study of Co doping effect

Preparation of magnesium carbonate and manganese carbonate composite materials doped at manganese site by hydrothermal method and study of Co doping effect

Cu-substituted Prussian white with low crystal defects as high-energy cathode materials for sodium-ion batteries

Prussian white (PW) has emerged as a promising cathode material for high-energy sodium-ion batteries owing to its high working voltage, high specific capacity, and cost-effectiveness. Nonetheless, its practical utilization is impeded by challenges related to insufficient cycling stability, primarily stemming from poor structural stability due to large defects in the lattice structures and irreversible phase transitions. In this study, we propose a novel strategy to overcome these challenges by substituting the manganese sites of PW with 10 mol% copper. During the synthesis process, substitution with Cu enabled the formation of fewer defects and interstitial water. Cu has no electrochemical redox reactions during the charge-discharge process; so, it showed an initial lower capacity(120 mAh g-1 at 0.1C). However, Cu substitution resulted in a significant improvement in the long-term cycling stability(67.6% at 10C after 500 cycles) by relieving structural stress due to the reversible rhombohedral-to-cubic phase transition. Moreover, the pouch cell (PW-Cu10/hard carbon) exhibits a discharge capacity of 85.4 mAh g−1 and stable cycling retention of 80% at 1.0C after 250 cycles. This work demonstrates a feasible strategy for designing practical Prussian white cathode materials for sodium-ion batteries.

Efficient olefin epoxidation with high turnover rates over ordered mesoporous silica nanoparticles with uniform manganese sites

Olefin epoxidation has been studied over a series of mesoporous manganese silicate nanoparticles and tBuOOH. Partial substitution of Si by Mn in silica framework leads to highly dispersed, distorted Mn(III) sites, confirmed by various physicochemical analyses. High conversion and stable styrene oxide, stilbene oxide and epoxy cyclohexane yield have been achieved with MS75 with 1:1.5 ratio of olefin: oxidant. However, at faster reaction rates lower styrene oxide yield is observed at lower Mn-containing catalyst (MS100). High TON, TOF over manganese sites shows accessible monomeric Mn sites. Attributed to high reactant density at redox-active Mn silicate sites due to facile diffusion across shallow pore depth channels of nanoparticulate om-MSx and surface hydrophobic characteristics. The catalysts were found to be stable under recycling and filtration experiments. The excellent stability against leaching of active manganese species indicates stable sites and good textural properties in om-MSx, essential for extended activity.

Phosphatase and Pseudo-Phosphatase Functions of Phosphatase of Regenerating Liver 3 (PRL-3) Are Insensitive to Divalent Metals In Vitro.

Phosphatase of regenerating liver 3 (PRL-3) is associated with cancer metastasis and has been shown to interact with the cyclin and CBS domain divalent metal cation transport mediator (CNNM) family of proteins to regulate the intracellular concentration of magnesium and other divalent metals. Despite PRL-3's importance in cancer, factors that regulate PRL-3's phosphatase activity and its interactions with CNNM proteins remain unknown. Here, we show that divalent metal ions, including magnesium, calcium, and manganese, have no impact on PRL-3's structure, stability, phosphatase activity, or CNNM binding capacity, indicating that PRL-3 does not act as a metal sensor, despite its interaction with CNNM metal transporters. In vitro approaches found that PRL-3 is a broad but not indiscriminate phosphatase, with activity toward di- and tri-nucleotides, phosphoinositols, and NADPH but not other common metabolites. Although calcium, magnesium, manganese, and zinc-binding sites were predicted near the PRL-3 active site, these divalent metals did not specifically alter PRL-3's phosphatase activity toward a generic substrate, its transition from an inactive phospho-cysteine intermediate state, or its direct binding with the CBS domain of CNNM. PRL-3's insensitivity to metal cations negates the possibility of its role as an intracellular metal content sensor for regulating CNNM activity. Further investigation is warranted to define the regulatory mechanisms governing PRL-3's phosphatase activity and CNNM interactions, as these findings could hold potential therapeutic implications in cancer treatment.

Study on the properties of the MgCO3@2Mn1−xMxCO3 carbonate composite material as a cathode electrode in the aqueous zinc-ion battery and the effect of Ag ion doping at the manganese site

With the international background of advocating green environmental protection and sustainable development, the aqueous zinc ion battery has attracted researchers’ attention because of its many advantages. The application of a manganese-based material as a positive electrode in the aqueous zinc ion battery has broad development prospect. In this paper, the composite materials of manganese carbonate and magnesium carbonate were synthesized by the hydrothermal method. Metal ions were doped at the manganese site of the composite materials to synthesize MgCO3@2Mn1−xMxCO3 materials. By comparing the electrochemical performance test results, it can be seen that the MgCO3@2Mn0.995Ag0.005CO3 material showed better magnification performance and its capacity can reach 282.6 mAh/g at 50 mA/g current density. Moreover, its electrochemical performance is also better than that of other doped materials. Through the scanning electron microscopy image analysis of the material, it can be seen that the material is mainly in a cubic structure of different sizes and the small cube structures are crosslinked together to form a sheet structure, which can further increase the closeness of the particle connection. By energy dispersive spectroscopy and x-ray photoelectron spectroscopy analysis, it can be found that the corresponding valence states of Mn, C, O, and Mg elements in the material are consistent with those in the MgCO3@2Mn0.995Ag0.005CO3 material. In the XRD test, the crystallinity of the material is good, and no obvious impurity peak is found.