Effect Of Metal Doping Research Articles

Adsorption of Bromonitromethane over Graphene‐Based Substrates: A Density Functional Theory Analysis

AbstractDisinfection by‐products (DBPs) are present ubiquitously in drinking water. These are the by‐products of the water disinfection process and are a matter of great concern, as they affect human health. In this work, the adsorption of a model DBP, bromonitromethane (BNM), on pristine graphene, graphene oxide and Ni/Pd/Pt‐doped graphene systems has been investigated using density functional theory (DFT) studies. Two adsorption modes have been considered, based on the interaction of BNM with graphene surfaces via the Br atom and the NO2 functional group. While adsorption of BNM on the pristine graphene is purely physisorption, it has been found that the adsorption capacity of pristine graphene and graphene oxide can be significantly enhanced by doping with Ni/Pd/Pt metals. Particularly, for Ni, the graphene oxide substrate gets involved in H‐bonding with the adsorbed BNM. As a result, effective and favorable adsorption occurs. Partial density of states (PDOS) plots reveal the effect of metal doping on the band gap and reactivity of different substrates. Electron density difference plots give insights into the adsorption behavior of BNM.

Micro-structural, Morphological and Optical Properties of Pure and Metal (Mn & Mg) Doped ZnO Thin Films by Low Cost SILAR Method

Pure and metals (Mn & Mg) doped zinc oxide (ZnO, ZnO/Mn and ZnO/Mg) thin films have been successfully grown onto a glass substrates by low cost SILAR method. The structural, morphological, compositional, functional group and optical properties of the prepared films were studied using X-ray diffraction, scanning electron microscope and EDAX, FTIR and UV-visible spectrophotometer, respectively. The structure of the films were found to be hexagonal with polycrystalline in nature with preferential orientation along (002) plane. From Fourier Transform Infrared spectroscopy, the presence of functional groups and its corresponding molecular vibrations were assessed. In UV-visible spectroscopy, the obtained direct optical band gap values 3.46, 3.56 and 3.7 eV for pure, Mn and Mg doped ZnO thin films, respectively. Morphological results showed that the remarkable changes in morphology due to the effect of metal doping. EDAX studies showed that the presence of zinc and oxygen content and also a doping metal ions.

Dissolved gas analysis in transformer oil using Pd catalyst decorated MoSe2 monolayer: A first-principles theory

Dissolved gas analysis (DGA) by high-sensitive gas sensors is an effective manner to estimate the operation status of electrical transformers. In this paper, based on first-principles calculations, a novel 2D material, Pd-doped MoSe2 (Pd-MoSe2) monolayer, is explored as gas sensor or scavenger for detection or removal of typical gases in transformer oil, including H2, CO and C2H2, to guarantee the safety operation for the transformers. Adsorption configuration, density of state (DOS), recovery property, band structure and frontier molecular orbital theory are used to fully investigate the adsorption and desorption behaviors for Pd-MoSe2/gas systems. It is found that Pd-MoSe2 monolayer possesses strong adsorption performance towards CO molecule, thus allowing the removal of such pollutant to guarantee the safety operation of transformers. Besides, Pd-MoSe2 monolayer would be a promising candidate for C2H2 sensing due to the desirable adsorption and desorption behaviors. However, the poor adsorption behavior of Pd-MoSe2 monolayer upon H2 molecule even at ambient temperature reveals its unsuitability for H2 detector. Our results not only expound the transition metal doping effect on pure MoSe2 monolayer, but also provide a first insight into the potential application of Pd-MoSe2 monolayer in the field of electrical engineering.

Effect of Cu, Ni and Pb doping on the photo-electrochemical activity of ZnO thin films.

In the present study, the effects of metallic doping on the photoelectron\\chemical properties of zinc oxide thin films have been studied. All films have been deposited using the spray pyrolysis technique at a constant doping level of 3 wt% whereby Cu, Ni, and Pb were used as dopants. The structure of all films was studied by X-ray diffraction which showed the grain size of all doped films to be 50 nm. The energy band gap of all films was estimated using optical transmission spectroscopy. The Ni, Cu, and Pb-doped ZnO photoelectrodes were applied for the photoelectrochemical (PEC) H2 generation from H2O. Pb doping leads to the highest photocurrent of the ZnO photoelectrodes. The current density–potential characteristics were measured under white light and monochromatic illumination. The stability of the electrode was quantified as a function of the number of H2 production runs and exposure time. Finally, the incident photon-to-current conversion efficiency, IPCE, and applied bias photon-to-current efficiency, ABPE, were calculated. The optimum IPCE at 390 nm was ∼30% whereas the ABPE was 0.636 at 0.5 V.

Effect of single metal doping on the thermoelectric properties of SnTe

SnTe, a lead-free chalcogenide-based material, shows potential to achieve high thermoelectric performance.

DFT study of the effects of Al[sbnd]P pair doping on the structural and electronic properties of stanene nanosheets

Density functional theory calculations were carried out to investigate the band gap variations in stanene, and the effects of metal and nonmetal doping on the structural and electronic properties of stanene were examined in detail. Various metal and nonmetals were considered to be substituted into the tin vacancy of stanene. The results suggest that AlP codoped stanene shows a sizeable band gap of about 0.07 eV, while the pristine stanene is a gapless material. Moreover, codoping of aluminum and phosphorous atoms into stanene monolayer opens up a wider band gap in comparison with the individual aluminum-doped and phosphorous-doped systems. Band structure calculations were performed to further investigate the band gap tuning in stanene. In Al-doped stanene, the Fermi level is shifted to the valence band edge, indicating that Al-doped stanene is a metallic system. In contrast, in P-doped system, the Fermi level shifts to the conduction band edge. Formation energy calculations indicate that AlP codoping is energetically more favorable than P-doping than Al-doping. Charge analysis based on Mulliken charges indicates that the Al atoms were positively charged, whereas P atoms negatively charged. Total electron density distribution plots show the charge accumulation on the surface, and consequently formation of chemical bonds between the dopants and tin atoms. Based on the obtained results, we found that AlP-codoped stanene exhibits a semiconductor characteristics, whereas mon-doping of Al or P atoms provides a metallic system. Our results thus suggest a theory basis for AlP-codoped stanene monolayer for application in next-generation nanoelectronic devices.

Nanostructured device based on coated ZnO layer as a window in solar cell applications

Abstract This work highlights some physical properties related to the influence of aluminum, tin and copper incorporation on nanostructured zinc oxide (ZnO:M; M:Al, Sn and Cu) thin films prepared by ultrasonic spray pyrolysis technique (USP) on glass substrate at 350±5 °C. For the as-grown layers, M- to Zn-ratio was fixed at 1.5 %. The effects of metal doping on structural, morphological, optical and electrical properties were investigated. X-ray diffraction pattern revealed that the as-prepared thin films crystallized in hexagonal structure with (0 0 2) preferred orientation. The surface topography of the films was performed by atomic force microscopy. AFM images revealed inhibition of grain growth due to the doping elements incorporation into ZnO matrix, which induced the formation of ZnO nanoparticles. Optical measurements showed a high transparency around 90 % in visible range. Some optical parameters, such as optical band gap, Urbach energy, refractive index, extinction coeffi-cient and dielectric constant were studied in terms of doping element. Particularly, dispersion of refractive index was discussed in terms of both Cauchy and single oscillator model proposed by Wemple and DiDomenico. Cauchy parameters and single oscillator energy E0 as well as dispersion energy Ed were calculated. Finally, electrical properties were investigated by means of electrical conductivity and Hall effect measurements. The measurements confirmed n type conductivity of the prepared thin films and a good agreement between the resistivity values and the oxidation number of doping element. The main aim of this work was the selection of the best candidate for doping ZnO for optoelectronics applications. The comparative study of M doped ZnO (M:Al, Sn and Cu) was performed. High rectifying efficiency of the Al/n-ZnO/p-Si/Al device was achieved and non-ideal behavior was revealed with n > 4.

Effect of alkaline earth metal doping on the catalytic performance of cobalt-based spinel composite metal oxides in N2O decomposition

A series of cobalt-based spinel composite metal oxides doped with alkaline earth metals, viz., MxCo3-xO4 (M = Mg, Ca, Sr and Ba; x = 0, 0.1, 0.3, 0.5, 0.7 and 0.9), were prepared by the coprecipitation method and characterized by XRD, SEM, nitrogen sorption, H2-TPR, O2-TPD-MS and XPS; the effect of alkaline earth metal doping on the catalytic performance of MxCo3-xO4 composites in N2O decomposition was investigated in a fixed bed micro-reactor. The results showed that after doping with the alkaline earth metals, the particle size of MxCo3-xO4 catalysts is decreased, accompanying with an increase in the specific surface area and the amount of surface adsorbed oxygen and Co2+ species. Meanwhile, the redox performance and catalytic activity of MxCo3-xO4 in N2O decomposition are also greatly enhanced. Under the conditions of 0.68% N2O, 3% O2 and Ar as balance gas, the Sr0.7Co2.3O4 catalyst doped with Sr (x = 0.7) exhibits highest activity in N2O decomposition; the reaction temperatures where the N2O conversion reaches 10% and 95% are as low as 312 and 451°C, respectively.

Hydrogen Oxidation on Ni-Based Electrocatalysts: The Effect of Metal Doping

Carbon supported nanoparticles of monometallic Ni catalyst and binary Ni-Transition Metal (Ni-TM/C) electrocatalytic composites were synthesized via the chemical reduction method, where TM stands for the doping elements Fe, Co, and Cu. The chemical composition, structure and morphology of the Ni-TM/C materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical properties towards hydrogen oxidation reaction in alkaline medium were studied using the rotating disc electrode and cycling voltammetry methods. A significant role of the TM dopants in the promotion of the hydrogen electrooxidation kinetics of the binary Ni-TM/C materials was revealed. A record-high in exchange current density value of 0.060 mA cm2Ni was measured for Ni3Fe1/C, whereas the monometallic Ni/C counterpart has only shown 0.039 mA cm2Ni. In order to predict the feasibility of the electrocatalysts for hydrogen chemisorption, density functional theory was applied to calculate the hydrogen binding energy and hydroxide binding energy values for bare Ni and Ni3TM1.

Effect of metal doping on carbon monoxide adsorption on phosphorene: A first-principles study

The effects of metal dopings on the carbon monoxide (CO) adsorption of phosphorene were investigated by the first-principles calculations. Base on the analysis of CO adsorption energy, Barder charge and density of states, it is found that six metal (Li, Al, Ni, Pd, Pt, and Au) dopings can improve the adsorption strength of CO. After CO adsorption, Li and Al doped phosphorene (bP-Li and bP-Al) undergo the indirect-to-direct bandgap transitions, while Ni and Au doped phosphorene (bP-Ni and bP-Au) undergo the magnetic-to-nonmagnetic transitions. These results imply that these six metal doped phosphorenes could be candidate materials for removing and detecting toxic CO.

Fe5C2 nanoparticles as low-cost HER electrocatalyst: the importance of Co substitution

Constructing and understanding the doping effect of secondary metal in transition metal carbide (TMC) catalysts is pivotal for the design of low-cost hydrogen evolution reaction (HER) electrocatalysts. In this work, we developed a wet-chemistry strategy for synthesizing Co-modified Fe5C2 nanoparticles ((Fe1−xCox)5C2 NPs) as highly active HER electrocatalysts in basic solution. The structure of (Fe1−xCox)5C2 NPs was characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure spectra (EXAFS) and scanning/transmission electron microscopy (S/TEM), indicating that the isomorphous substitution of cobalt in the lattice of Fe5C2. (Fe0.75Co0.25)5C2 exhibited the best HER activity (174 mV for j = −10 mA/cm2). Computational calculation results indicate that Co provides the most active site for HER. X-ray adsorption spectra (XAS) studies further suggested that the electron transfer in Fe–C bonds are enhanced by the substitution of Co, which modulates the hydrogen adsorption on the adjacent electronic-enriched carbon, and therefore promotes HER activity. Our results affirm the design of low-cost bimetallic TMCs based HER catalysts.

Methanol-to-olefin conversion on 3D-printed ZSM-5 monolith catalysts: Effects of metal doping, mesoporosity and acid strength

Abstract In this study, activity and selectivity in methanol-to-olefins (MTO) reaction of Cr, Cu, Ga, La, Mg, Y, and Zn-doped 3D-printed ZSM-5 zeolite monoliths were evaluated and the appropriate dopants were screened through various analysis. These 3D-printed ZSM-5 zeolite monoliths were doped with the above metals by direct addition of metal nitrate precursors into the 3D printing paste thus the metal doping procedure was integrated with the 3D printing fabrication. The effect of dopants on physical and chemical characteristics of the doped monoliths was studied through XRD, XRF, N2 physisorption, FTIR, SEM-EDX, H2-TPR, and NH3-TPD. The performance of these printed metal–doped zeolite monoliths in MTO reaction was systematically evaluated and compared with their non-doped counterparts at 673 K for 24 h of reaction time. It was found that doping of Cr, Mg, and Y into 3D-printed ZSM-5 zeolite monoliths leads to enhanced methanol conversion, whereas doping of Ce, Cu, Ga and Y has little or no effect on catalysts reactivity. The olefins selectivity followed the sequence Zn > Mg > La > Y > Cr > Cu > Ga at 10 wt% dopant contents, in line with the relative amount of moderated acid sites in the monoliths. The results indicated that among all the investigated metal dopants, 3D-printed ZSM-5 zeolite monolith doped with 10 wt% Mg exhibited the favorable effect on the light olefins production and showed ethylene and propylene selectivity of 24% and 33%, respectively with methanol conversion approaching 95% at 673 K. The increased selectivity towards ethylene and propylene was correlated to the presence of moderate Bronsted acidity which inhibited the formation of paraffins and aromatics, consistent with the NH3-TPD results whereby moderate Bronsted acid sites were observed after Mg addition to 3D-printed ZSM-5 zeolite monoliths. The occupation of Mg dopant in the micropores, which is assigned to the cages of the ZSM-5 framework, took up the space for perspective aromatics, which are regarded to be coke precursors, and therefore reduced the coke formation.

Promoting effect of unreducible metal doping on OMS-2 catalysts for gas-phase selective oxidation of ethanol

Various unreducible-metal cations can be successfully doped into the tunnel of manganese octahedral molecular sieve (OMS-2) by using “one-pot” refluxing method to tune the acid-base and redox properties. The resulting M-OMS-2 materials were used as efficient catalysts for gas-phase aerobic oxidation of ethanol to acetaldehyde. The activity of the M-OMS-2 catalysts was demonstrated to be proportional to the surface basicity. Na-OMS-2 exhibited the highest catalytic activity at 200 °C, which is higher than and comparable to the previously reported preferred Fe-OMS-2 and Ag-OMS-2 catalysts, respectively. The beneficial effect of Na+-doping is related to the enhancement of surface oxygen vacancies, basicity and reducibility, which also result in better catalytic stability. Kinetic studies indicate that reaction rates depend weakly on the concentration of O2 and ethanol. Ethanol OH and α-CH bond cleavages are both kinetically-relevant, with the latter being the more difficult step. O2 is the most efficient oxidant and is thought to be activated at oxygen vacancies of Mn2+/Mn3+ species to form superoxide-type O2− and lattice-oxygen-type O2− species, which act as dual active sites for the rate-controlling ethanol activation steps.

Doping of BiFeO3 : A comprehensive study on substitutional doping

The authors investigate the effects of substitutional metal doping on BiFeO${}_{3}$ by accurate first-principles calculations. In a high-throughput fashion, they screen large parts of the periodic table, providing a unique view on site preference, doping type, and oxidation states, enabling doping strategies for future multifunctional oxide electronics.

A thorough study on electrochromic properties of metal doped tungsten trioxide film prepared by a facile solution process

In this research, we investigate the effect of metal doping on the electrochromic (EC) performance of tungsten trioxide (WO3) films. These films were prepared by a novel method involving solution processing and thermal annealing. In this procedure, ammonium tetrathiotungstate ((NH4)2WS4) was dissolved in dimethylformamide at a high concentration ratio (200 mg mL−1) to obtain a homogeneous solution and then spin-coated onto the indium thin oxide (ITO) substrate for use as a working electrode. Subsequently, the film was annealed at the different temperatures (200, 300, 400, and 500 °C) to form a crystal structure of WO3. X-ray diffraction, Raman, and X-ray photoelectron spectroscopic results confirm the crystal formation of WO3. Moreover, in order to improve the electrochromic performance, different concentrations (10, 20, 30, and 40 mM) of different metal chlorides such as PtCl4, PdCl2, AuCl3, AgCl, CuCl2, NiCl2, NaCl, and KCl were added into the (NH4)2WS4 precursor and the mixture was coated on the ITO substrate and annealed at 500 °C. The results indicate that the performance of the Au-doped WO3 film was better than those with other dopants, likely as a result of the plasmonic effect. Therefore, the proposed method and Au-doped WO3 films are great candidates for the development of smart windows with high EC performance.

Effect of metal doping in the photocatalytic properties of carbon xerogel-Nb2O5 composite towards visible light degradation of methylene blue

This study explores the development of metal doped hybrid Nb2O5/carbon xerogel photocatalysts. The materials were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, dispersive energy spectroscopy and X-ray diffraction. The X-ray diffractograms of the materials are characteristic of amorphous carbon. The palladium doped composite also exhibits the hexagonal phase of the niobium oxide. The chemical elements are evenly distributed on the materials, confirming the dispersion of the doping metals in the material matrix. All composite materials absorb radiation in the visible light region. All composites exhibited photocatalytic activity under visible radiation, except for the iron doped material. The palladium doped material showed superior efficiency in the degradation of methylene blue, due to its lower band gap and higher absorption of visible light.

Structural properties of tungsten-doped cobalt molybdate and its application in electrochemical oxygen evolution reaction

New tungsten-doped CoMoO4 (W-CoMoO4) was successfully synthesized by a simple co-precipitation method and investigated for a possible application in oxygen evolution reaction (OER). The effect of W6+ doping on structure, morphology, and chemical compositions was investigated by X-ray diffraction spectroscopy, scanning electron microscopy, Fourier transform spectroscopy, Brunauer–Emmet–Teller surface area measurement, and X-ray photoelectron spectroscopy. Linear sweep voltammetry indicates that doping CoMoO4 with an optimum W6+ amount of 21 wt% provides higher current density at lower overpotential than other catalysts. Compared to undoped CoMoO4, the 21 wt% W-CoMoO4 also shows a remarkable activity and excellent long-term stability in alkaline media. This superior activity is ascribed to the synergistic effect of increased oxygen vacancy, enhanced surface area, and possibly improved electrical conductivity upon W6+ doping. The significances of this work are that the potential OER application of Co–W–Mo tertiary oxide, which has never been studied before, and the effect of non-3d high-valency metal (W) doping on OER activity enhancement are now being recognized.

Effect of rare-earth element modification on the performance of Cu/ZnAl catalysts derived from hydrotalcite precursor in methanol steam reforming

Zn-Al layered double hydroxides (ZnAl-LDHs) were prepared on γ-Al2O3 by an in-situ synthesis method; with ZnAl-LDHs as the supports, a series of rare-earth element M (M = Y, La, Ce, Sm and Gd) doped M/Cu/ZnAl catalysts were then obtained through sequential wet impregnation method and used in the methanol steam reforming to produce hydrogen. The M/Cu/ZnAl catalysts were characterized by XRD, SEM-EDS, N2 sorption, H2-TPR, XPS and N2O titration and the effect of rare-earth metal doping on their catalytic performance in the methanol steam reforming was then investigated. The results showed that the activity of Cu/ZnAl catalyst is closely related to the copper surface area and the reducibility; larger copper surface area and lower reduction temperature lead to a higher catalytic activity in methanol steam reforming. The addition of rare-earth elements including Ce, Sm and Gd can improve the copper dispersion, surface copper area and the catalyst reducibility, which is helpful to enhance the activity of M/Cu/ZnAl catalysts. Especially, the Ce/Cu/ZnAl catalyst exhibits the highest activity; over it, the methanol conversion is 100% (about 40% higher than that over the Cu/ZnAl catalyst) and the CO concentration in the product is only 0.39%, for the methanol steam reforming at 250°C.

Effect of metal doping on the visible light absorption, electronic structure and mechanical properties of non-toxic metal halide CsGeCl3.

Non-toxic metal halide perovskites have become forefront for commercialization of the perovskite solar cells and optoelectronic devices. In the present study, for the first time we show that particular metal doping in CsGeCl3 halide can considerably enhance the absorbance both in the visible and ultraviolet light energy range. We have carried out DFT based first principles calculations on Mn-doped and Ni-doped CsGeCl3 halide. We investigate the detailed structural, optical, electronic and mechanical properties of all the doped compositions theoretically. The study of the optical properties shows that the absorption edge of both Ni and Mn-doped CsGeCl3 is shifted toward the low energy region (red shift) relative to the pristine one. An additional peak is observed for both doped profiles in the visible light energy region. The study of the mechanical properties demonstrates that both the doped samples are mechanically stable and ductile as the pristine CsGeCl3. The study of the electronic properties shows that the excitation of photoelectrons is easier due to the formation of intermediate states in Mn-doped CsGeCl3. As a result Mn-doped CsGeCl3 exhibits higher absorptivity in the visible region than the Ni-doped counterpart. A combinational analysis indicates that CsGe1−xMnxCl3 is the best lead free candidate among the inorganic perovskite materials for solar cell and optoelectronic applications.

The promoting effect of noble metal (Rh, Ru, Pt, Pd) doping on the performances of MnOx–CeO2/graphene catalysts for the selective catalytic reduction of NO with NH3at low temperatures

Rh, Ru, Pt or Pd doping on MnOx–CeO2/graphene catalysts increased the amount of chemisorbed oxygen and surface acid sites.