Doping Sites Research Articles

Modification of Lithium‐Rich Manganese Oxide Materials: Coating, Doping and Single Crystallization

AbstractThe increasing demand for portable electronics, electric vehicles and energy storage devices has spurred enormous research efforts to develop high‐energy‐density advanced lithium‐ion batteries (LIBs). Lithium‐rich manganese oxide (LRMO) is considered as one of the most promising cathode materials because of its high specific discharge capacity (>250 mAh g−1), low cost, and environmental friendliness, all of which are expected to propel the commercialization of lithium‐ion batteries. However, practical applications of LRMO are still limited by low coulombic efficiency, significant capacity and voltage decay, slow reaction kinetics, and poor rate performance. This review focus on recent advancements in the modification methods of LRMO materials, systematically summarizing surface coating with different physical properties (e. g., oxides, metal phosphates, metal fluorides, carbon, conductive polymers, lithium compound coatings, etc.), ion doping with different doping sites (Li sites, TM sites, O sites, etc.), and single crystal structures. Finally, the current states and issues, key challenges of the modification of LRMO are discussed, and the perspectives on the future development trend base on the viewpoint of the commercialization of LRMO are also provided.

Facile fabrication of sulfur-doped porous carbon from waste sugarcane bagasse for high performance supercapacitors

Our research has led to a significant breakthrough in the field of energy storage. For the first time, we have prepared a series of highly porous sulfur-doped activated carbon derived from natural biomass sugarcane bagasse. The sulfur-doped waste sugarcane bagasse-derived activated carbon (WSC/S) possess a unique properties of large specific surface area (SSA) with high mesoporosity, better wettability, and numerous redox active dopant sites. These unique properties of WSC/S significantly enhance supercapacitor functionality. There are a large number of mesopores on the WSC/S, which shorten the ion diffusion path length and make their ion transport efficient. As the results of that the WSC/S achieved a high specific capacitance of 282.25 Fg−1 with a current density of 0.1 Ag−1 and excellent cycling stability with >96 % capacitance retention after 10,000 cycles in 6 M KOH electrolyte. We explored WSC/S as an anode material to fabricate an asymmetric supercapacitor (ASC) device, where activated carbon cloth was used as a cathode. The ASC device showed an energy density of 43.26 Wh kg−1 with a power density of 0.1 kW kg−1 at a current density of 0.1 Ag−1, which is superior to that obtained for symmetric WSC/S//WSC/S supercapacitor. These performances indicate the potential of the WSC/S for high-performance energy storage systems.

Bringing Molecules Together: Synergistic Coadsorption at Dopant Sites of Single Atom Alloys.

Bringing molecules together on a catalytic surface is a prerequisite for bimolecular and recombination reactions. However, in the absence of attractive interactions between reactants, such as hydrogen bonds, this poses a challenge. In contrast, based on density functional theory, we show that coadsorption at active sites of single-atom alloys (SAAs) is favored and that coadsorption is a general phenomenon observed for catalytically relevant adsorbates on a broad range of SAAs under temperature and pressure conditions commonly employed for catalysis. Dopants located in both terrace sites and in step edge defects exhibit a preference for coadsorption, displaying similar periodic trends. Using kinetic Monte Carlo simulations, we compare the reactivity of a model reaction on both a pure metal and an SAA and show that the preference for coadsorption significantly alters the overall reaction energy profile, even when the barriers for the rate-determining elementary step are identical. In our models, the coadsorption preference enhances the catalytic activity of the SAA surface by several orders of magnitude compared to the pure metal. We also report infrared (IR) spectroscopic signatures of coadsorption, which facilitate experimental detection. Analysis reveals that in these systems repulsive lateral interactions between nearby molecules are more than compensated for by the enhanced binding at dopant sites. Among the broad range of systems considered, SAAs containing early transition metals (TMs) exhibit the strongest coadsorption preference, which can be rationalized by assuming the existence of an optimal number of electrons involved in binding. The strong coadsorption preference, together with facile product desorption from early TMs, renders these systems attractive candidates for catalysis. Moreover, these SAAs could open new routes for reduction reactions because coadsorption with hydrogen is favored.

Local electronic structure modulation via S substitution enables fast-discharging capability for Li-rich Mn-based oxides cathodes

Anionic and cationic redox reaction contribute to the ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LMNC). However, the irreversible oxygen evolution and sluggish kinetics result in the continuous capacity decay and poor rate performance, which limited its application as cathode material in lithium-ion batteries. Herein, the local electronic structure of LMNC is appropriately modulated via S2− doping to alleviate oxygen release, stabilize the crystal structure stability, and facilitate Li+ diffusion via facile surface defect engineering. The effect of S2− doping site on the systematically energy is investigated by DFT. Under the guidance of this result, LNMC-S is prepared by co-precipitation and high-temperature solid-phase reaction method. The effect of doping concentration on electrochemical property of LMNC was systematically investigated. The results exhibit that S2− doping can effectively suppress the electronic insulation of Li2MnO3, enhance the transport dynamics of lithium ion and inhibit the phase transition of LMNC sample during charge-discharge process. Thereby, the modified sample exhibits superior electrochemical property, such as the 200th discharge capacity is 184.3 mAh·g−1 under 1C, with a capacity retention rate of 87.6 %. This paper is beneficial for enriching the existing theoretical findings and discoveries, providing theoretical guidance for the preparation of high-performance material.

Development of an efficient bifunctional electrocatalyst based on Co/CoSe2 nanoparticles embedded in N, Se co-doped carbon for AEMFC and rechargeable Zn-air battery

We suggest a hollow-structured N, Se dual-doped carbon framework embedded with Co/CoSe2 nanoparticles (Co/CoSe2@NSeC) as highly efficient bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The prepared electrocatalyst exhibits high electrochemical active surface area attributed to its unique hollow/porous structure and defective heteroatom doping sites. Furthermore, the strongly coupled heterojunction between Co and CoSe2 species not only provides abundant and highly active sites but also generates built-in electric field, thereby promoting electron transfer during the electrocatalytic reaction. Based on the above considerations, the prepared catalyst shows excellent bifunctional electrocatalytic performance. Leveraging the excellent ORR activity of Co/CoSe2@NSeC, alkaline exchange membrane fuel cells (AEMFC) with the Co/CoSe2@NSeC as air cathode exhibits high power density of 171.23 mW cm2. Furthermore, the rechargeable Zn-air battery employing the Co/CoSe2@NSeC shows high specific capacity (729.4 mAh gZn−1), peak power density (192.88 mW cm2), and sustained stability over 300 cycles.

Revealing Gliding-Induced Structural Distortion in High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries.

After charging to a high state-of-charge (SoC), layered oxide cathodes exhibit high capacities but suffer from gliding-induced structural distortions caused by deep Li depletion within alkali metal (AM) layers, especially for high-nickel candidates. In this study, we identify the essential structure of the detrimental H3 phase formed at high SoC to be an intergrowth structure characterized by random sequences of the O3 and O1 slabs, where the O3 slabs represent Li-rich layers and the O1 slabs denote Li-depleted (or empty) layers that glide from the O3 slabs. Moreover, we adopt two doping strategies targeting different doping sites to eliminate the formation of Li-vacant O1 slabs. First, we introduce direct transition metal (TM) pillars between TMO2 slabs achieved through dopants (e.g., Nb) positioned within AM layers, significantly improving the cycling stability. Second, we introduce indirect Li pillars achieved through dopants located at TM layers to adjust the Li-O bond strength. While this strategy can regulate the uniformity of Li at the slab level, it results in an uneven Li distribution at the particle scale, ultimately failing to enhance the electrochemical performance. Our established research strategy facilitates the realization of diverse pillars between TMO2 slabs through doping, thereby offering guidance for stabilizing high-capacity layered oxide cathodes at high SoC.

Electrochemical aspects of Li[Ni0.6Co0.2Mn0.2]O2 cathode materials doped by various ionic radius cations

The capacity of Li[Ni0.6Co0.2Mn0.2]O2 cathode materials decreases rapidly due to layer structure degradation, grain cracking, and electrolyte side reaction during cycling. In this paper, metal ions with different ionic radius (W6+= 0.62 Å, Mg2+= 0.72 Å, Y3+= 0.90 Å) were doped into single crystal Li[Ni0.6Co0.2Mn0.2]O2, which were synthesized by high-temperature solid-phase technology. X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) were employed to characterize various samples doped with different ionic radius. The results reveal that the radius of the doped ions plays a crucial role in improving the stability of material structure. It is attributed to the incorporation of metal ions into the Li+ or Ni2+ site, thus maintaining the integrity of the layer and reducing cation mixing. However, it is also detrimental to the performance of single crystal Li[Ni0.6Co0.2Mn0.2]O2 because of lattice distortion caused by the ionic radius of the doped metal being much greater than that of the doped site. These results show superior capability and reveal the performance trend of Li[Ni0.6Co0.2Mn0.2]O2 with metal ions of different radius. The initial discharge capacity at 0.1 C for the undoped sample was 183.8 mAh/g, compared with 189.9, 192.3 and 199.8 mAh/g for NCM622-W, NCM622-Mg, and NCM622-Y, respectively. After 100 cycles, NCM, NCM-W, NCM-Mg, and NCM-Y delivered retentions of 90.88 %, 98.16 %, 97.13 %, 94.37 %, respectively. The defect model is mainly responsible for the improvement in electrochemical performance.

First-Principles Investigation on Ru-Doped Janus WSSe Monolayer for Adsorption of Dissolved Gases in Transformer Oil: A Novel Sensing Candidate Exploration.

Using first-principles theory, this work purposes Ru-doped Janus WSSe (Ru-WSSe) monolayer as a potential gas sensor for detection of three typical gas species (CO, C2H2, and C2H4), in order to evaluate the operation status of the oil-immersed transformers. The Ru-doping behavior on the WSSe surface is analyzed, giving rise to the preferred doping site by the replacement of a Se atom with the formation energy of 0.01 eV. The gas adsorption of three gas species onto the Ru-WSSe monolayer is conducted, and chemisorption is identified for all three gas systems with the adsorption energy following the order: CO (-2.22 eV) > C2H2 (-2.01 eV) > C2H4 (-1.70 eV). Also, the modulated electronic properties and the frontier molecular orbital are investigated to uncover the sensing mechanism of Ru-WSSe monolayer upon three typical gases. Results reveal that the sensing responses of the Ru-WSSe monolayer, based on the variation of energy gap, to CO, C2H2, and C2H4 molecules are calculated to be 1.67 × 106, 2.10 × 105, and 9.61 × 103, respectively. Finally, the impact of the existence of O2 molecule for gas adsorption and sensing is also analyzed to uncover the potential of Ru-WSSe monolayer for practical application in the air atmosphere. The obtained high electrical responses manifest strong potential as a resistive sensor for detection of three gases. The findings hold practical implications for the development of novel gas sensing materials based on Janus WSSe monolayer. We anticipate that our results will inspire further research in this domain, particularly for applications in electrical engineering where the reliable detection of fault gases is paramount for maintaining the integrity and safety of power systems.

Electronic and magnetic properties of Janus ZrSSe monolayer doped with V impurity and VX3(X = C, N, O, and F) clusters

In this work, doping with V impurity and VX3 (X = C, N, O, and F) clusters is proposed to modify the electronic and magnetic properties of Janus ZrSSe monolayer. Pristine ZrSSe monolayer is an indirect-gap semiconductor two-dimensional (2D) material with energy gap of 0.73 eV. This value is reduced to 0.13 eV under effects of single Zr vacancy, which corresponds to the reduction of the order of 82.19%. V impurity magnetizes significantly ZrSSe monolayer, inducing feature-rich magnetic semiconductor nature. Herein, the magnetism with a total magnetic moment of 1.00 μ B is produced mainly by V-3d orbital. Investigations indicate that the antiferromagnetic state with zero total magnetic moment is stable when V impurities are located close to each other. Further separating impurities causes the antiferromagnetic-to-ferromagnetic state transition, such that a total magnetic moment of 2.00 μ B is obtained. ZrSSe monolayer is metallized by doping with VC3, VN3 and VF3 clusters. In the first two cases, the non-magnetic nature is preserved. Meanwhile, significant magnetization with a total magnetic moment of 3.00 μ B is achieved by VF3 cluster substitution. Similarly, VO3 cluster induces significant magnetic properties in ZrSSe monolayer with a total magnetic moment of 1.00 μ B , which are originated mainly from the antiparallel spin orientation between V atom and Se atoms closest to the doping sites. Herein, VO3 cluster substitution in ZrSSe monolayer makes new magnetic semiconductor 2D material. The Bader charge analysis indicates that all four clusters attract charge from the host monolayer. Our work may introduce efficient approaches to modify the ZrSSe monolayer electronic and magnetic properties towards spintronic and optoelectronics applications.

Fixed-Point Atomic Regulation Engineered Low-Thickness Wideband Microwave Absorption.

Atomic doping is widely employed to fine-tune crystal structures, energy band structures, and the corresponding electrical properties. However, due to the difficulty in precisely regulating doping sites and concentrations, establishing a relationship between electricity properties and doping becomes a huge challenge. In this work, a modulation strategy on A-site cation dopant into spinel-phase metal sulfide Co9S8 lattice via Fe and Ni elements is developed to improve the microwave absorption (MA) properties. At the atomic scale, accurately controlling doped sites can introduce local lattice distortions and strain concentration. Tunned electron energy redistribution of the doped Co9S8 strengthens electron interactions, ultimately enhancing the high-frequency dielectric polarization (ɛ' from 10.5 to 12.5 at 12GHz). For the Fe-doped Co9S8, the effective absorption bandwidth (EAB) at 1.7mm increases by 5%, and the minimum reflection loss (RLmin) improves by 26% (EAB = 5.8GHz, RLmin = -46dB). The methodology of atomic-scale fixed-point doping presents a promising avenue for customizing the dielectric properties of nanomaterials, imparting invaluable insights for the design of cutting-edge high-performance microwave absorption materials.

Uncovering and preventing polytellurides dissolution enables stable sodium-ion storage: A case study of SnTe

Metal tellurides (MTes) have emerged as promising candidates for high-specific energy sodium-ion batteries owing to their superior volumetric capacity and exceptional intrinsic conductivity. Nevertheless, their practical application faces challenges associated with pronounced capacity degradation associated with unclear decay mechanisms. In this study, we uncover, for the first time, that the dissolution and shuttling of intermediates (NaxTey) are responsible for the rapid capacity decay in alloy- and conversion-type MTe anodes. Based on this discovery, we propose a novel structural engineering strategy that involves confining ultrafine SnTe nanoparticles within a fibrous carbon matrix, facilitating the smooth immobilization and highly reversible conversion of NaxTey. State-of-the-art in-/ex-situ tests and density functional theory calculations elucidate the evolution and shuttling mechanisms of NaxTey, highlighting the van der Waals barrier of the carbon matrix and the remarkable chemisorption of N and S dopant sites towards Na2Te2 and Na2Te intermediates. Significantly, the chemisorption capacity of NaxTey is enhanced through the optimization of doping content and bonding type of N and S, resulting in excellent stability of SnTe embedded in a high-content N and S co-doped carbon fiber matrix (SnTe@SHNC). The elaborate SnTe@SHNC composites demonstrate exceptional performance, enduring over 1000 cycles at 1.0 A g−1 with an ultraslow capacity decay rate of 0.028 % per cycle. This work provides valuable insight into the pivotal role of controlling NaxTey in the design of durable MTe anodes for advanced SIBs.

Dopant site occupancies and iron valence states in SrZnxFe18−xO27 W-type hexaferrites using site-selective X-ray/electron spectroscopy

Zn-doped W-type Sr hexaferrite (SrZnxFe18−xO27; SrZnx-WHF) is an anticipated rare-earth-free hard magnetic material with strong magnetocrystalline anisotropy and saturation magnetization. To examine the origin of its high magnetic performance, the site distribution of Zn over seven crystallographically inequivalent Fe sites and the site-dependent valence states of Fe were investigated using site-selective elemental/chemical analysis techniques. The dominant occupation of Zn2+ at the 4etet(S) and 4ftet(S) tetrahedral sites was determined quantitatively using high-angular-resolution electron-channeling X-ray spectroscopy and statistical data analysis. The combined application of high-angular-resolution electron channeling electron spectroscopy and atomic-column resolution scanning transmission electron microscopy–electron energy-loss spectroscopy helped unambiguously clarify that most of the Fe2+ ions existed at the 6goct(S-S) octahedral site. Density functional theory calculations have shown that Zn doping leads to a redistribution of the charges toward Fe ions at this site. This redistribution preserves the local charge balance and amplifies the total number of parallel spins. Hence, the enhanced magnetocrystalline anisotropy and saturation magnetization in SrZnx-WHF can be inferred to originate from the charge redistribution at the 6goct(S-S) site, which is influenced by the presence of nonmagnetic Zn.

Nonmetal Doping Modulates Fe Single-Atom Catalysts for Enhancement in Peroxidase Mimicking via Symmetry Disruption, Distortion, and Charge Transfer.

Developing biomimetic catalysts with excellent peroxidase (POD)-like activity has been a long-standing goal for researchers. Doping nonmetallic atoms with different electronegativity to boost the POD-like activity of Fe-N-C single-atom catalysts (SACs) has been successfully realized. However, the introduction of heteroatoms to regulate the coordination environment of the central Fe atom and thus influence the activation of the H2O2 molecule in the POD-like reaction has not been extensively explored. Herein, the effect of different doping sites and numbers of heteroatoms (P, S, B, and N) on the adsorption and activation of H2O2 molecules of Fe-N sites is thoroughly investigated by density functional theory (DFT) calculations. In general, alternation in the catalytic efficiency directly depends on the transfer of electrons and the geometrical shifts near the Fe-N site. First, the symmetry disruption of the Fe-N4 site by P, S, and B doping is beneficial to the activation of H2O2 due to a significant reduction in the adsorption energies. In some cases, without Fe-N4 site disruption, the configurations fail to modulate the adsorption behavior of H2O2. Second, Fe-N-P/S configurations exhibit a stronger affinity for H2O2 molecules due to the significant out-of-plane distortions induced by larger atomic radii of P and S. Moreover, the synergistic effects of Fe and doping atoms P, S, and B with weaker electronegativity than that of N atoms promote electron donation to generated oxygen-containing intermediates, thus facilitating subsequent electron transfer with other substrates. This work demonstrates the critical role of tuning the coordinating environment of Fe-N active centers by heteroatom doping and provides theoretical guidance for controlling the types by breaking the symmetry of SACs to achieve optimal POD-like catalytic activity and selectivity.

Precision Control of Amphoteric Doping in Cu x Bi2Se3 Nanoplates.

Copper-doped Bi2Se3 (Cu x Bi2Se3) is of considerable interest for tailoring its electronic properties and inducing exotic charge correlations while retaining the unique Dirac surface states. However, the copper dopants in Cu x Bi2Se3 display complex electronic behaviors and may function as either electron donors or acceptors depending on their concentration and atomic sites within the Bi2Se3 crystal lattice. Thus, a precise understanding and control of the doping concentration and sites is of both fundamental and practical significance. Herein, we report a solution-based one-pot synthesis of Cu x Bi2Se3 nanoplates with systematically tunable Cu doping concentrations and doping sites. Our studies reveal a gradual evolution from intercalative sites to substitutional sites with increasing Cu concentrations. The Cu atoms at intercalative sites function as electron donors while those at the substitutional sites function as electron acceptors, producing distinct effects on the electronic properties of the resulting materials. We further show that Cu0.18Bi2Se3 exhibits superconducting behavior, which is not present in Bi2Se3, highlighting the essential role of Cu doping in tailoring exotic quantum properties. This study establishes an efficient methodology for precise synthesis of Cu x Bi2Se3 with tailored doping concentrations, doping sites, and electronic properties.

Copper doping induced band structure and morphology transformation in CaTiO3 for textile dye photodegradation applications

Semiconductor metal oxides with a wide bandgap like CaTiO3 can be exploited into an efficient visible light photocatalyst via cation doping. The type of dopant and the site of doping is known to greatly influence the photocatalytic activity of a material. Based on the intricacies of the density functional theory electronic structure study, we delve into the optimization of one-pot solvothermal synthesis to obtain Cu doped CaTiO3 nanocuboids. Doping of copper not only resulted in change in the electronic structure of the material but also led to change in the morphology. The uneven nanostep architecture resulted in increase in the surface area of the catalyst, which led to more active sites for the adsorption of the dyes and subsequent degradation. The reduced band gap and decreased recombination of charge carriers made the copper doped calcium titanate an efficient photocatalyst for degradation of both cationic (99.7% degradation of MV dye in 120 minutes) and anionic (99.8% degradation of RB in 45 minutes) dyes.

Harnessing true capacitive activity of nitrogen-doped MXene through hydrogel assembly and theoretical understanding of the role of dopant sites

Heteroatom nitrogen (N) doping in MXene can significantly push its energy storage metric. However, translating the intrinsic improvement of individual sheets into macroscopic electrodes is challenging due to the blockage of dopant sites by restacking. Here, we report the development of restack-controlled N-doped MXene hydrogel through speedy interfacial assembly methods to keep the dopant sites electrochemically accessible. Application of a small voltage between two zinc plates in an aqueous dispersion of N-doped MXene leads to the rapid development of doped hydrogel over the positive zinc plate via electrophoretic drag and linking by interfacial released zinc ions. As-developed hydrogels having continuous porosity and quasi-oriented sheet arrangement preserve ion transporting channels, thus allowing the surface dopant sites to participate in the supercapacitive energy storage actively. N-doped hydrogel displays a high capacitance of 488 F g−1 at 5 mV s−1 much higher as compared to compact film. The N-doped MXene hydrogels display excellent rate performance with retention over 88 % at 1000 mV s−1 and cyclic stability of 87 % over 10000 cycles. The detailed density functional theory (DFT) calculation reveals a major pseudocapacitive contribution from the surface adsorption and functional group substitution type N dopant sites as compared to another dopant site, namely, lattice substitution.

Ultrathin Protection Layer via Rapid Sputtering Strategy for Stable Aqueous Zinc Ion Batteries

AbstractSurface side reactions and time‐consuming modification methods hinder the practical application of zinc‐ion batteries. This study introduces an ultrathin protection layer for the Zn anode via a rapid sputtering method. The dopants on the CN10@Zn anode create surface dipoles and local variations in charge distribution, facilitating zinc ion migration to pyrrolic nitrogen dopant sites with reduced adsorption barriers. Additionally, hydroxyl oxygen dopants enhance the hydrophilicity of the sputtering layer, forming a strong adhesion with the zinc anode and improving ion accessibility. This results in dense nucleation sites for uniform zinc deposition. Consequently, the sputtered layer achieves a Coulombic efficiency of 99.8% over 2,700 cycles in Cu||Zn cells and a lifespan of up to 2,100 h in zinc symmetric cells. When paired with Na0.65Mn2O4 cathodes, the sputtered layer retains 89% capacity over 1,000 cycles at 1 A g−1. This study presents a promising method for rapidly fabricating ultrathin electrode materials.

Modulating the Structure of Interlayer/Layer Matrix on δ‐MnO2 via Cerium Doping‐Engineering toward High‐Performance Aqueous Zinc Ion Batteries

Abstractδ‐MnO2 has been vigorously developed as an ideal cathode material for rechargeable aqueous zinc‐ion batteries (AZIBs) due to its spacious layer spacing suitable for ion storage. However, poor intrinsic conductivity, structural collapse, and sluggish reaction kinetics are major limitations restricting their battery performance. Doping engineering has been proven to be an effective strategy for modifying the structure, conductivity, and electronic properties of Mn‐based oxides. Here, a series of δ‐MnO2 hierarchical flowers with different cerium‐doped sites are proposed as high‐performance cathodes for AZIBs, revealing the effects of various Ce doping sites on the MnO2 layer‐by‐layer structure and battery performance. Chemical analysis and theoretical calculations indicate that δ‐MnO2 with both in‐layer and interlayer Ce doping (Cein/inter‐MnO2) allows for sufficient Zn2+ storage sites, higher conductivity, and enhanced reaction kinetics due to enlarged interlayer spacing, increased oxygen defects, and reduced Coulombic repulsion between zinc ions and manganese oxide hosts. As a result, Cein/inter‐MnO2 with extended ion transfer channels and sturdy structure delivers a superior capacity of 348.8 mAh g−1 at a current density of 300 mA g−1 over 100 cycles, and a high retention rate of ≈100% at a current density of 3000 mA g−1 over 2000 cycles.

Dilution of helical antiferromagnetic matrix of CaMn7O12 under nonmagnetic Ga[formula omitted] doping

The work reports dilution studies on antiferromagnetic CaMn7O12. Introduction of nonmagnetic ion in an antiferromagnetic matrix changes the magnetic properties in an interesting way. The study becomes significant due to the fact that remarkable increase in magnetization is observed as a result of substitution of a few of the magnetic Mn ions with the nonmagnetic Ga ion. For 5% doping of Ga, the magnetization value becomes nearly thrice of the un-doped CaMn7O12. A sequential decrease in antiferromagnetic ordering transition temperature is also observed with increasing Ga percentage in the parent compound. The solid solubility limit of Ga in the matrix is found to be nearly 5%, above which it start showing impurity peaks. Experimental results are well complemented with the Density functional theory (DFT) based calculations. Theoretical calculations are carried out on (CaMn7O12)3 unit cell with one Ga atom doped at different Mn sites resulting around 5% doping concentration. Besides identifying the most favourable doping site for Ga, results indicate a reduction of bulk band gap and significant increase in magnetization, both of which are in agreement with the experimental results.

Tailoring local electron density and molecular oxygen activation behavior via potassium/halogen co-tuned graphitic carbon nitride for enhanced photocatalytic activity

Graphite carbon nitride (g-C3N4) is a promising photocatalyst,but its inadequate reactive sites, weak visible light responsiveness, and sluggish separation of photogenerated carriers hamperthe improvement of photodegradation efficiency. In this work, potassium (K) and halogen atoms co-modified g-C3N4 photocatalysts (CN-KX, X = F, Cl, Br, I) were constructed to adjust the electrical and band structure for enhanced generation of reactive oxygen species. Through an integration of theoretical calculation and experimental exploration, the doping sites of halogen atoms as well as the evolution of crystal, band, and electronic structures were investigated. The results show that a covalent bond is formed between the F atom and the C atom, substitution of the N atom occurs with a Cl atom, and doping of Br, I, or K atoms takes place at the interstitial site. CN-KX photocatalysts exhibits lower band gap, faster photogenerated electron migration, and enhanced photocatalytic activity. Specifically, the CN-KI photocatalyst exhibits the highest photodegradation efficiency because of its smaller interplanar spacing, formation of the midgap state, and adjustable local electron density. Equally, the doping of I atom not only provides a stable adsorption site for oxygen (O2) but also facilitates electron transfer, promoting the production of superoxide radicals (O2−) and contributing to the process of photodegradation.