Metal Doping Research Articles

Tuning of physicochemical and electronic characteristics of Cu-doped NiCo2O4 ternary inverse spinel oxides for effective electrocatalytic hydrogen evolution reaction

The paper reports the development of Cu-doped NiCo2O4 ternary inverse spinel oxides through microwave-assisted hydrothermal method as effective catalysts for alkaline hydrogen evolution reaction (HER). The effective and controlled doping of Cu to NiCo2O4 lattice by the partial replacement of Ni2+/Ni3+ with Cu+/Cu2+ results in the fine-tuning of structural, morphological, and electronic characteristics, favourable for electrocatalytic HER. The study effectively correlates the influence of variation in the percentages of Cu-doping on the material properties and thereby the electrocatalytic characteristics. The experimental results indicate that Cu0.10Ni0.90Co2O4 electrode having optimum Cu-doping (10%) as the best electrocatalyst with the lowest onset potential for hydrogen evolution (242.7 mV) and reduced overpotential (72.5 mV) values by following a Volmer – Heyrovsky mechanism during HER. The improvement in HER performance after Cu-doping is due to the generation of greater number of active sites and reduction in electronic band gap. The present work advantageously utilises the scope of microwave-assisted transition metal doping strategy to fine tune the physicochemical and electronic characteristics, favourable for electrocatalytic HER, and this may pave a new way for tuning the electrochemical properties of metal oxides for various applications.

Synergies of Mn modified Fe-based MOF enhanced catalytic ozonation: charge transfer and multiple sites mechanism

The conjoint improvement of catalytic ozonation activity and stability for MOFs materials has always been an urgent challenge. Metal doping offers a viable approach to inspire the interaction between active components and O3 due to the optimization of electronic structure and introduction of surface-active sites. In this work, 88A-Mn catalyst derived from MIL-88A was prepared by loading Mn to MIL-88A with a simple pyrolysis method. The structure and physical characterizations confirmed the coexistence of Fe and Mn in the catalyst. The 88A1-Mn1-350 exhibited the efficient degradation of ibuprofen in catalytic ozonation system, with its degradation rate showing 3.6 times and 2.6 times higher than those of the O3 system and the 88A-T/O3 system, respectively. Mechanism analysis indicated the synergistic effect among Fe/Mn interaction, surface hydroxyl group, and O-C=O group promoted the continuous generation of ROS, including ·OH and ·O2-. Specifically, the regeneration of Fe2+ derived from the Mn doping contributed to the recovery of catalytic activity and played an indispensable role in maintaining high efficiency. In addition, 88A1-Mn1-350 possessed outstanding stability in a wide range of pH (3-11) and the coexistence of anions. It also exhibited the superiority compared with traditional catalysts. This finding provides a feasible modification approach to enhance the property of MOFs materials, and achieves the efficient remove of refractory organics in catalytic ozonation system.

Role of Metal Dopants in Hydrogen Dissociation on Cu:CeO2 and Fe:CeO2 Surfaces Studied by Ambient-Pressure X-ray Absorption Spectroscopy

Role of Metal Dopants in Hydrogen Dissociation on Cu:CeO₂ and Fe:CeO₂ Surfaces Studied by Ambient-Pressure X-ray Absorption Spectroscopy

A Brief Review of Recent Theoretical Advances in Fe-Based Catalysts for CO2 Hydrogenation.

Catalytic hydrogenation presents a promising approach for converting CO2 into valuable chemicals and fuels, crucial for climate change mitigation. Iron-based catalysts have emerged as key contributors, particularly in driving the reverse water-gas shift and Fischer-Tropsch synthesis reactions. Recent research has focused on enhancing the efficiency and selectivity of these catalysts by incorporating alkali metal promoters or transition metal dopants, enabling precise adjustments to their composition and properties. This review synthesizes recent theoretical advancements in CO2 hydrogenation with iron-based catalysts, employing density functional theory and microkinetic modeling. By elucidating the underlying mechanisms involving metallic iron, iron oxides, and iron carbides, we address current challenges and provide insights for future sustainable CO2 hydrogenation developments.

Unveiling Nanogranular Advancements in Nickel-Doped Tungsten Oxide for Superior Electrochromic Performance

Electrochromic materials allow for precise control of their optical properties by applying an electric field, which has led to recent developments in energy-saving and indoor temperature control systems like smart windows. The selective incorporation of metal dopants is an effective technique for generating highly advanced semiconducting metal oxides with precisely customized physicochemical characteristics. In this report, we employed a one-step electrodeposition process to fabricate nickel-doped tungsten oxide (W–Ni) thin films, systematically probing the impact of nickel (Ni) doping on the collective material characteristics. Comprehensive X-ray diffraction research revealed significant changes in diffraction patterns, suggesting slight modifications in the structure caused by Ni doping. The scanning electron microscopy showed complex differences in the microstructure of the film, such as a dense surface, porosity, and clustering of nanogranules. The WNi-3% thin film doped at 3 wt. % exhibited excellent electrochromic performance by efficiently handling lithium ions and displaying favorable electrochromic properties. The improved electrode, WNi-3%, showed a maximum optical modulation of 81.90%, exceptional reversibility of 99.4%, and a high coloration efficiency of 75.12 cm2/C. These findings underscore the efficacy of Ni-doping in tailoring the electrochromic properties of nickel-doped tungsten oxide thin films, thereby advancing the frontiers of high-performance electrochromic materials for energy-efficient applications.

Modeling the Zigzag Curves of Transition Metal Ions' Charge Transition Levels in Crystals.

Predicting the defect levels of transition metal (TM) dopants in the band gap of crystals is critical in determining the charge states of TM dopants and explaining their electronic and optical properties. By analyzing the calculated charge transition levels and the crystal-field strengths of all the 3d-TM ions in several insulators, we demonstrate that the variation trend of the 3d-TM dopants in a crystal is a scaling of the variation of 3d-electron binding energies (ionization potential) of the free TM ions corrected by adding the contribution of the 3d-orbital's crystal-field splitting. We therefore develop a model to predict the relative location of TM ions' defect levels in the band gap from the defect level and crystal-field splitting of a reference TM ion in the host of concern. The model is applied to predict the defect levels of the series of TM ions in β-Ga2O3 and ZnO, which have moderate to small band gaps, making some of the levels fall into the conduction or valence bands. These results show that the model may serve as a quick reference for related material design and optimization.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications.

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

Facile synthesis of Gd/Ru-doped fluorescent carbon dots for fluorescent/MR bimodal imaging and tumor therapy

Functional metal doping endows fluorescent carbon dots with richer physical and chemical properties, greatly expanding their potential in the biomedical field. Nonetheless, fabricating carbon dots with integrated functionality for diagnostic and therapeutic modalities remains challenging. Herein, we develop a simple strategy to prepare Gd/Ru bimetallic doped fluorescent carbon dots (Gd/Ru-CDs) via a one-step microwave-assisted method with Ru(dcbpy)3Cl2, citric acid, polyethyleneimine, and GdCl3 as precursors. Multiple techniques were employed to characterize the morphology and properties of the obtained carbon dots. The Gd/Ru-CDs are high mono-dispersity, uniform spherical nanoparticles with an average diameter of 4.2 nm. Moreover, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) confirmed the composition and surface properties of the carbon dots. In particular, the successful doping of Gd/Ru enables the carbon dots not only show considerable magnetic resonance imaging (MRI) performance but also obtain better fluorescence (FL) properties, especially in the red emission area. More impressively, it has low cytotoxicity, excellent biocompatibility, and efficient reactive oxygen species (ROS) generation ability, making it an effective imaging-guided tumor treatment reagent. In vivo experiments have revealed that Gd/Ru-CDs can achieve light-induced tumor suppression and non-invasive fluorescence/magnetic resonance bimodal imaging reagents to monitor the treatment process of mouse tumor models. Thus, this simple and efficient carbon dot manufacturing strategy by doping functional metals has expanded avenues for the development and application of multifunctional all-in-one theranostics.

Review on Structural Adjustment Strategies of Titanium‐Based Metal Oxide Dimensionally Stable Anodes in Electrochemical Advanced Oxidation Technology

Emerging organic pollutants and refractory pollutants in water bodies have caused severe harm to the ecological environment and human health. Electrochemical advanced oxidation processes (EAOPs) are currently one of the most effective oxidation methods to deal with refractory organic pollutants. Electrode materials serve as the most critical component in influencing the EAOP performance. Dimensionally stable anodes (DSAs) have the advantages of dimensional stability, structural diversity, chemical stability, low oxygen evolution potential and long service life, etc. Herein, several types of Ti‐based metal oxide DSAs (Ti/MOx DSAs) commonly used in EAOPs in the past 5 years, including Ti/IrO2, Ti/RuO2, Ti/PbO2, Ti/Sb–SnO2, and Ti/TiO2, are introduced. The modification methods including metal doping, composition adjustment, nanostructure construction, introduction of intermediate layers, compositing with carbon materials, and formation of 3D structures as well as the applications of these modified Ti‐based DSAs in EAOP for the rapid degradation of various organic pollutants are summarized and their advantages and current shortcomings of electrodes are pointed out. Finally, the Ti‐based DSA's current limitations and future development prospects are concluded.

Li+(3)Mg−: A new alkaline earthide with large nonlinear optical response

Alkali metal doping has been identified as a vital step in facilitating an increase in the first hyperpolarizability(β0). To further explore this concept, we utilized Calix (Zhang et al., 2018) [3]pyrrole (3), Calix (Ma et al., 2017) [4]pyrrole (4), and Calix (Aloraini et al., 2022) [5]pyrrole (5) as our three ligands in this study. The choice of these ligands was based on their ability to undergo alkali metal doping, which ultimately led to an enhancement in the first hyperpolarizability. By doping alkali metal lithium, three new compounds Li@3, Li@4 and Li@5 were theoretically designed. Then the alkaline earthide Mg was doped onto the Li@3, and a new alkaline earthide compound Li+(3)Mg− was designed. The geometric structure and nonlinear optical properties of the molecules were studied using the CAM-B3LYP functional. The results show that Li+(3)Mg− has a considerable first-order hyperpolarizability, β0 = 21401 au, The β0 value for the 3 system is merely 37 au, whereas for the Li@3 system, it reaches a high of 12257 au Li+(3)Mg− exhibits a β0 value that is over 500 times greater than that of 3. It is evident that the electronic structure and nonlinear optical properties are significantly affected by the presence of alkali metal and alkaline earthide atoms doped in 3. The excess electron derived from alkali metal atoms and alkaline earthide atoms are significant contributors to the sudden increase in the β0 within Li+(3)Mg−. We sincerely hope that the development and production of materials with nonlinear optical properties in this study can provide new ideas and methods for the innovation of electride.

Manipulating the Intrinsic Defect of MnS by Surface Sulfidation for Inverted Sb2(S,Se)3 Planar‐Heterojunction Solar Cells

For the emerging Sb2(S,Se)3 solar cells, most high‐efficiency devices employ a standard structure based on the heterojunction of weak n‐type Sb2(S,Se)3 and heavily n‐doped cadmium sulfide (CdS), and the sunlight is incident from the n‐type CdS side in either superstrate or substrate structure. The weak carrier extraction ability of the n–n heterojunction as well as the parasitic absorption and toxicity from CdS further limit the efficiency improvement and practical applications. Herein, for the first time, a strategy of treating manganese sulfide (MnS) with thioacetamide to enhance its p‐type conductivity is demonstrated, and a solar cell with inverted structure is constructed by forming a heterojunction with n‐type Sb2(S,Se)3. This inverted structure well overcomes the light absorption loss and toxicity elements in the standard structure. This post‐treatment effectively passivates the sulfur vacancy defects of MnS and in turn enables greater band bending in the heterojunctions for suppressed nonradiative recombination. Ultimately, the hole extraction ability of MnS shows essential improvement and enables a power conversion efficiency of 5.22% for the inverted Sb2(S,Se)3 solar cell. This study provides a proof‐of‐concept device structure for the preparation of high‐efficiency Sb2(S,Se)3 solar cells and offers new perspectives to achieve effective intrinsic doping of metal chalcogenides.

Metal-Organic Frameworks Based Sensor Platforms for Rapid Detection of Contaminants in Wastewater.

Metal-organic frameworks (MOFs) are a type of multifunctional material with organic-inorganic doped metal complexes that have a lot of unsaturated metal sites and a consistent network structure. MOFs work has great performance for enhancing the mass transfer, signal, and sensitivity as well as analyte enrichment. This study highlights the recent advancements of MOFs-based sensors for pollutant detection in a water environment and summarizes the effect of various synthetic materials on the performance of MOFs-based sensors. The related challenges and optimization techniques have been discussed. Then the research results of various MOFs sensors in the detection of wastewater pollutants are analyzed. Finally, the challenges facing MOFs-based water sensor development and the outlook for future research are discussed.

First-principles study of the effect of alkaline-earth metal doping on the intrinsic MoSe2 photovoltaic properties

In this study, the effect of alkaline-earth metal element doping on the photoelectric properties of intrinsic MoSe2 is systematically investigated based on the first-principles approach, and it is believed that the findings of this work will give some theoretical guidance for future research on MoSe2 doping modification. The results show that all the doping systems exhibit good stability, and Be atom doping has the lowest formation energy value, making the doping easier to produce. The doping of alkaline-earth metal elements resulted in some lattice distortion of MoSe2. Intrinsic MoSe2 is a semiconductor with a direct bandgap of 1.498[Formula: see text]eV, and the doping of alkaline-earth metal elements causes the bandgap value to decrease in each system, and the bandgap is the smallest when Be is doped. All doped systems exhibit P-type conducting properties. Compared with the intrinsic MoSe2, all doped systems have their conduction band fraction moved to the low-energy direction overall, and new density of states peaks appear near the Fermi energy level. These state density peaks mainly originate from the results contributed by the s-orbitals of each doping system Mo-4d, Se-4p, and each dopant atom. The analysis of the work function reveals that the work function of each doped system is smaller than the intrinsic MoSe2, then the energy required for the occurrence of electron leaps is reduced, which improves the electron mobility of the doped system. The Mulliken Population analysis shows that stable chemical bonds are formed between the doped alkaline-earth metal elements and the surrounding Se atoms. The examination of the optical characteristics demonstrated that, in comparison to the intrinsic MoSe2, all doped systems’ greatest dielectric absorption peaks were attenuated and moved toward the low-energy region; the doping of alkaline-earth metal elements broadened the light absorption edge of the intrinsic MoSe2. The absorption peaks of each doping system are shifted toward the low-energy region with the red-shift phenomenon, and the light absorption is good in the ultraviolet region.

Preparation of Solid Superacid SO42-/ZrO2 and SO42-/ZrO2-MxOy (M=Ce, Co, Mn, and Zn) and Its Application in Toluene Nitration.

The nitration reaction of aromatic compounds is one of the extensively studied chemical reactions that result in the manufacturing of various industrial products applied in pharmaceuticals, dyes, perfumes, and explosives. A series of modified sulfated zirconia (SZ) catalysts SO42-/ZrO2-MxOy (M=Ce, Co, Mn, Zn, and M/SZ) doped with different metal elements by a coprecipitation method were investigated in the toluene nitration reaction. Various characterization techniques (X-ray diffraction, Brunauer-Emmett-Teller, thermogravimetric analysis, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia) indicated that doping metal elements in SZ led to excellent catalytic properties, increasing the specific surface area of the catalyst and facilitating the formation of a stable tetragonal zirconia phase. Doping zinc and cobalt in SZ enhanced the acidity of the catalyst and formed stronger acidic sites, promoting the generation of nitronium ions and providing more active sites for the toluene nitration reaction. Additionally, it reduced the loss of sulfate ions in the catalytic system that helped in improving the stability of the catalyst. Under the same conditions, the catalytic activity of toluene nitration reaction demonstrated the following order: Zn/SZ > Ce/SZ > Co/SZ > Mn/SZ > SZ, with the zinc-doped SZ catalyst exhibiting the best catalytic performance, achieving a toluene conversion rate of 78.58% and a para/ortho nitrotoluene ratio of 0.67.

Effect of tantalum doping on the Fe2O3 toward photoelectrochemical water oxidation

Metal doping is an effective method to increase the photogenerated carrier concentration and improve the carrier transport performance of Fe2O3 for photoelectrochemical water oxidation. This work synthesized a series of Ta-doped Fe2O3 nanoparticles on FTO glasses using a hydrothermal-pyrolysis method. The XPS, XRD, and Raman spectra demonstrated that the Ta5+ dopants occupy the Fe3+ sites. The Ta-doped Fe2O3 photoanodes show noticeable improvement in photoelectrochemical water oxidation via enhanced electron separation and transfer competence. Doping Ta into Fe2O3 forces the Fermi level of Fe2O3 to move to the conduction band, leading to the decrease of charge transfer resistance in Fe2O3 and water oxidation on the surface. Moreover, the carrier concentration was increased. Whereas, to maintain the charge neutrality of the system, the Ta doping inhibits the formation of oxygen vacancies, which act as the effective defects. Consequently, 2%Ta-Fe2O3 performed the optimum enhanced photoelectrochemical water oxidation activity.

Review on the Solar-Driven Photocathodic Protection of Metals in the Marine Environment

Photocathodic protection (PCP) technology has gained wide attention in the field of corrosion due to its green, environmentally friendly, and sustainable characteristics, and has become a protection technology with broad development prospects in the future marine environment. By investigating recent research results, the mainstream photoanode materials are TiO2, BiVO4, g-C3N4, ZnO, In2O3, SrTiO3 and other materials. Among them, TiO2 is an ideal photoanode material for PCP because of its efficient photochemical corrosion resistance, remarkable reaction stability, and excellent photoelectric properties. However, TiO2 itself has more drawbacks, such as limited utilization of visible light and low photogenerated electron-hole separation efficiency. These defects limit the wide application of TiO2 in PCP. Through modification methods, the reaction efficiency can be substantially improved and the availability of TiO2 can be increased. This paper lists the research progress of modifying TiO2 materials using metal and non-metal doping modification, semiconductor compounding technology, and energy storage materials for application in PCP, and introduces several new types of photoanode materials. This paper suggests new ideas for the design of more efficient photoanodes.

Alkali metal promotion on Fe-Co-Ni trimetallic catalysts for CO2 hydrogenation to light olefins

The catalyst obtained by calcination of the precursor Fe-Co-Ni trimetallic MOFs has exhibited great CO2 hydrogenation performance. To further improve the selectivity of target product light olefins and the catalyst stability, alkali metal doping is used to modify the Fe-Co-Ni trimetallic catalyst, and the effects of different types of alkali metals and different doping methods are also studied. After alkali metal doping, the increased electron concentration around Fe atoms, the enhanced alkalinity of the catalyst surface and the weakened H2 activation can improve CO2 uptake while decreasing H2 affinity, thereby inhibiting the alkane formation. Among all the catalysts doped by alkali metal, FCN-K(a) obtained by potassium citrate impregnation after calcining has the largest specific surface area, the highest microporosity and the most alkaline sites on its surface, showing the best CO2 hydrogenation performance with a CO2 conversion of 47.5 % and selectivity of light olefins 46.8 %. Meanwhile, the catalyst stability is greatly improved after alkali metal doping during ∼ 50 h test. The characterization results of spent catalysts show that FCN-K(a) has the largest amount of active phase Fe5C2 for C–C coupling. Doping with a proper amount of K can promote the carbonization of Fe and improve the stability of the active phases.

La-doped Porous Fe2O3 Nanorods as Advanced Anodes for Lithium/Sodium Ion Batteries and Sulfur Host for Li-Sulfur Batteries.

Transition metal oxides are investigated as electrochemically active anodes for several years due to the merits of high specific capacity, low cost, abundant resources and controllable synthesis. But the poor cycle performances have hindered their further wide application. Herein, porous La-doped FeOOH nanorods have been synthesized through a facile hydrothermal method, which could be transformed into porous La-doped Fe2O3 (Fe2O3-La) via a simple heating process. Compared with the undoped Fe2O3, the Fe2O3-La showed larger surface area, higher specific capacities and more stable cycle performances for lithium/sodium ion batteries. In addition, as an advanced sulfur host for lithium-sulfur batteries, the Fe2O3-La also displayed much more excellent cycle and rate performances than the undoped Fe2O3. The superior electrochemical performances of the Fe2O3-La may could be attributed to the doping of La, which could induce more porous morphology and offer more reactive sites. The positive effects of La-doping for electrochemical performances of porous Fe2O3 nanorods provide novel insights for further applications of rare earth metal doping.

Catalytic mechanism of sulfur-nitrogen doping metal single-atom graphene-based catalysts for the conversion of CO2 to CH4: A computational study

The conversion of CO2 into renewable fuel (CH4) has significant environmental and economic benefits. Graphene-supported single-atom catalysts (SACs) show promise as electrocatalysts for the carbon dioxide reduction reaction (CO2RR). In this study, using spin-polarized density functional theory (DFT) calculations, we investigate the potential for converting CO2 to CH4 on the representative SACs, specifically graphene-supported TM-N-S (transition metal-nitrogen-sulfur). The results show that TM-N-S can break the scaling relationship between the adsorption energy of *CHO and *OCH2. The free energy profiles indicate that among the candidate TM-N-S SACs, Fe, Co, and Ni-N-S stand out with low overpotentials of 0.23, 0.40, and 0.39 V, respectively. Compared with the competing hydrogen evolution reaction (HER), they exhibit higher CO2 selectivity and catalytic activity. Analysis of electronic structure and charge variations reveals the origin of CO2RR activity and the binding strength between catalyst and intermediate. This work uncovers the potential mechanism of CO2RR, providing valuable insights into the conversion of CO2 to CH4 via TM-N-S catalysis and offering novel perspectives for the design and screening of efficient SACs for CO2RR.

Co–O bond covalency change in PrCoO3 by substituting Cu, Mn, and Nb

We investigated the effects of various transition metal dopants on the changes in B-site ion-oxygen (B–O) bonding characteristics and the subsequent effects on the electrochemical properties of PrCoO3 (PCMe, PrCo0.9Me0.1O3-δ, Me = Cu, Mn, Nb). The lattice constants of Mn, Cu, and Nb-doped PrCoO3 were increased compared with that of pure PrCoO3 (PCO), and the B–O–B bond angles were determined to be 163.709°, 167.323°, 165.149°, and 161.765° for PCO, PCCu, PCMn, and PCNb, respectively, by Rietveld refinement. The pre-edge peak of the O K-edge shifted to 0.7 eV of lower energy in PCCu as compared with PCO, and to 0.2 eV of lower energy in PCMn. By contrast, PCNb shifted to 0.3 eV of higher energy. Considering the B–O–B bond angle and pre-edge peak shift, the overlap between B 3d and O 2p orbitals can be expected to be the largest in PCCu, indicating the strongest covalency, whereas PCNb has the weakest covalency. The polarization resistance, as an indicator of the ORR activity, was 7.63, 6.67, 8.05, and 9.56 Ω cm2 in PCO, PCCu, PCMn and PCNb, respectively.