Effect Of Co-doping Research Articles

In Situ Construction of Co-MoS2/Pd Nanosheets on Polypyrrole-Derived Nitrogen-Doped Carbon Microtubes as Multifunctional Catalysts with Enhanced Catalytic Performance.

The structural design of multiple functional components could integrate synergistic effects to enhance the catalytic performance of MoS2-based composites for catalytic applications. Herein, one-dimensional (1D) Co-MoS2/Pd@NCMTs composites were designed to prepare Co-doped MoS2/Pd nanosheets (NSs) on N-doped carbon microtubes (NCMTs) from tubular polypyrrole (PPy) as multifunctional catalysts. The Co-MoS2/Pd@NCMTs composites integrated the synergistic effects of Co-doping, a 1D tubular structure, and noble-metal Pd decoration. Thus, a higher catalytic activity was observed in 4-nitrophenol (4-NP) reduction and peroxidase-like catalysis than other components, such as MoS2, MoS2@NCMTs, and Co-MoS2@NCMTs. Remarkably, the results indicated that the dissolution, diffusion, and redistribution led to the dissolution of MoO3@ZIF-67 cores and generation of Co-doped MoS2 NSs. Benefiting from the synergistic effect from these components, Co-MoS2/Pd@NCMTs were considered as a facile colorimetric sensing platform for detecting tannic acid. Moreover, outstanding performance was realized in the reduction of 4-NP with the composites. Thus, we provide a simple synthetic strategy for simultaneously integrating electronic engineering and structural advantages to develop an efficient MoS2-based multifunctional catalyst.

Effects of co-doping in semiconductors: CdTe

Co-doping is an important method to improve doping properties in semiconductors, which is expected to lower the defect formation energy through the Coulomb interaction or covalent coupling between co-dopants and reduce the transition energy level through the level repulsions. However, the effectiveness of co-doping is sensitive to the type of co-dopants, and in some cases, negative effects can exist. Here, using $p$-type doping in CdTe as an example, we systematically investigate different dopant combinations based on first-principles hybrid functional calculations. We show that the complex of one donor + one double acceptor, e.g., ${\mathrm{Cl}}_{\mathrm{Te}}+{\mathrm{V}}_{\mathrm{Cd}}$, can cause a decrease in defect formation energy and a reduction in acceptor level, thus improving the dopability, especially when the Cl treatment is done at low temperature. The combination of two acceptors + one donor, e.g., ${\mathrm{Cl}}_{\mathrm{Te}}+2{\mathrm{Cu}}_{\mathrm{Cd}}$, has little or even negative effects because of the coexistence of the acceptor-acceptor and donor-acceptor coupling. More importantly, we show that the combination of one deep acceptor + one shallow acceptor, e.g., ${\mathrm{Sb}}_{\mathrm{Te}}+{\mathrm{P}}_{\mathrm{Te}}$, produces a much deeper acceptor level because the nominal deep acceptor ${\mathrm{Sb}}_{\mathrm{Te}}$ acts as a donor with respect to the shallow one, and then the deep acceptor state will be pushed even deeper due to the level repulsion. Thus, we should avoid this type of acceptor-acceptor co-doping to achieve high hole concentration. Our general understanding of the co-doping approach, therefore, provides a guideline for the future design of shallow defect complexes in CdTe and other semiconductors.

Effect of co doping on the electric and dielectric properties of Bi3.8−xEr0.2YbxTi3O12 lead-free ceramics

The development of novel lead-free materials operating at high temperature and able to replace lead-based compounds and their derivatives in different devices is currently a remarkable challenge. In spite of having a high Curie temperature, the ferroelectric Bi4Ti3O12 is rarely used as a piezoelectric due to its high conductivity. In this work, Bi ions in Bi4Ti3O12 were partially replaced with Yb and Er aiming to compensate oxygen vacancies and improve others physical properties. In particular, Bi3.8−xEr0.2YbxTi3O12 compounds with x = 0.05, 0.1, and 0.2 were prepared by a low-cost solid-solid state reaction process, and their structural, optical and electrical properties were investigated. It was observed that, at low temperatures, the conductivity, impedance and permittivity are mainly governed by grain effects, and by grain boundaries and grains effects at high temperatures. The electrical conductivity at 700 K decreases with Yb content and shows a minimum for x = 0.2. The relative permittivity at high temperatures is colossal while the tangent loss is negligible. High permittivities accompanied with low loss factor were obtained for Bi3.6 Er0.2Yb0.2Ti3O12. These results open a wide application domain for this particular compound.

Band gap narrowing of TiO2 nanoparticles: A passivated Co-doping approach for enhanced photocatalytic activity

In anatase TiO2, various passivated co-dopants such as (V–N), (Mo–C), (Nb–N), (Ta–N), and (F–N) are of significant interest due to their enhanced photocatalytic activities under visible light. Unlike the bulk phase, the effect of co-dopants in TiO2nanoparticles still lacks fundamental exploration. To understand this, we perform density-functional-theory calculations within the PBE generalized gradient approximation with corrections for the on-site Coulomb interaction (PBE + U) as well as hybrid functional (HSE06) approaches to investigate potential co-doping species and their locations in TiO2 nanoparticles that could be suitable for applications as antibacterial agents or for the degradation of organic pollutants. To allow an effective comparison with experiments, the criteria are set based on the experimentally measured band edge positions of TiO2 nanoparticles and the redox potentials of the reactive oxygen species of interest. Based on the analysis of donor and acceptor levels derived from thirty co-dopants, we find that the vanadium-nitrogen (VTi–NO) pair in the T2 configuration is the most suitable passivated co-dopant for enhanced photocatalytic activity as it can reduce the band gap of TiO2 nanoparticles while still providing a thermodynamic driving force for redox reactions to generate reactive oxygen species.

Effects of Bi and Mn codoping on the physical properties of barium titanate: investigation via DFT method

Effects of Bi and Mn codoping on the physical properties of barium titanate: investigation via DFT method

Crystal Structure, Rietveld Refinement and Improved Dielectric and Magnetic Properties of Ti Doped Bi0.90Pr0.10Fe1- x Ti x O3 Multiferroic Ceramics

Multiferroics Bi0.90Pr0.10Fe1- x Ti x O3 were synthesized to study the effect of Pr and Ti co-doping on crystal structure, dielectric and magnetic properties. Co-doping leads to the disappearance of impurity phases. Rietveld refinement confirms structural phase transition from pure R3c phase to mixed phases (P1 + R3c). Dielectric constant and loss exhibit dispersion in low-frequency region and become constant in the high-frequency region. Dielectric constant decreases with increasing Ti concentration and shows comparatively stable behavior by virtue of concealed oxygen vacancies. The magnetic investigation reveals that samples are weakly ferromagnetic.

Effect of (Zn, Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe1-2xZnxMnxO3 (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO3 (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10−6 A/cm2) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm2 was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm2. The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.

Effect of co-dopants on the spectral property of Yb3+ doped silica glasses at 1018 nm

To enhance the laser performance of Yb3+-doped silica fiber for 1018-nm tandem-pumped technology, three series of Yb–Al, Yb-Al-P, and Yb–P co-doped silica glasses with a large size, high homogeneity, and precise composition control were prepared using a sol-gel method combined with high-temperature sintering technology. In addition, the effects of Al3+ and P5+ co-dopants on the absorption and emission properties of Yb3+-doped silica glasses at 1018 nm were investigated systematically. The normalized spectral characteristics of the glass samples with different doping series at 1018 nm were compared horizontally, and the results showed that the normalized emission intensity of the Yb-P-doped silica glass series samples at 1018 nm was significantly better than that of the other series. The emission subpeak was located near 1018 nm when the content of doped P was 5 mol%, and the position of the subpeak gradually blue-shifted as the content of the doped P increased. Using Raman spectroscopy combined with ultra-low temperature electron paramagnetic resonance (4K), the coordination environment of Yb3+ was accurately resolved at the atomic scale. In Yb3+-doped silica glasses, the coordination environment of Yb3+ was extremely different from the introduction of Al3+ and P5+, which is consistent with the influence of Al3+ and P5+ on the spectral properties of Yb3+ at 1018 nm.

Surface strain and co-doping effect on Sm and Y co-doped BaCeO3 in proton conducting solid oxide fuel cells

Although promising, regulating the surface strain is still immature for enhance the performance of proton-conducting materials and no clear law has been found. In this work, surface strain and co-doping effect on dopant segregation, hydration reaction and proton transport of Sm and Y co-doped BaCeO3 (BCYS) in proton-conducting solid oxide fuel cells (P-SOFC) was investigated. We found that although the dopant segregation trend is reduced as the surface strain increase from −2% to 2%, which means that a large tensile strain is beneficial to enhance structural stability, oxygen vacancy formation energy and proton binding energy near the BCYS surface do not change monotonously with the surface strain. We found that the fewer electrons around the oxygen atoms before hydrogen adsorption, the more stable the proton. It is worth noting that 1% tensile strain is most favorable for enhancing the degree of surface hydration and proton transport in our calculation results, which helps to weaken the negative effects of the space charge layer formed by the accumulation of positive charges on the surface. The collocation of Sm and Y has a synergistic effect, which means Sm facilitates oxygen vacancy formation, while Y promotes hydration reaction. Moreover, the introduction of Sm and Y can hardly change the electronic conductivity of BCYS, which is conducive to the open circuit voltage of P-SOFC.

Low dielectric loss ceramics in the Mg4Nb2O9-ZnAl2O4-TiO2 ternary system

This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2 ternary system. Crystalline phases and microstructure of Mg4Nb2O9-ZnAl2O4-TiO2 dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti4+ substituted Nb5+ in the Mg4Nb2O9 structure, which promoted the decomposition of Mg4Nb2O9 to form the second phase, Mg5Nb4O15, during sintering. The synergistic effect of ZnAl2O4-TiO2 co-doping promoted the Mg4Nb2O9 ceramic densification. The sample (0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2) with x = 0.15−0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl2O4, Mg4Nb2O9 and Mg5Nb4O15, due to the NbO6 octahedra distortion resulting from the substitution of Al3+/Ti4+ for Nb5+ in Mg4Nb2O9 and Mg5Nb4O15. The long-range order of the NbO6 octahedra was enhanced by co-doping ZnAl2O4 and TiO2, thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τf of −60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg4Nb2O9-0.15ZnAl2O4-0.15TiO2. These results show that 0.7Mg4Nb2O9-0.15 ZnAl2O4-0.15TiO2 ceramic is a good candidate for microwave electronic device applications.

Effect of Sr and Co co-doping on the TiO2-diluted magnetic semiconductor for spintronic applications

Effect of Sr and Co co-doping on the TiO2-diluted magnetic semiconductor for spintronic applications

The effect of Sr and Sb co-doping on structural, morphological and thermoelectric properties of BaSnO3 perovskite material

BaSnO3 (BSO) is one of the promising perovskite materials for high temperature thermoelectric applications. The pure BSO, Sr and Sb co-doped BSO materials were prepared by the polymerization complex method and annealed at 1473 K. The X-ray diffraction patterns confirmed the cubic structure of pure BSO and Sr-Sb co-doped BSO. The addition of Sr and Sb changed the morphology of BSO from microstructures to the layered and polygonal shaped nanostructure. The valence states of each elements of the samples were confirmed by the X-ray photoelectron spectroscopy. The addition of Sb5+ atom in Sn4+ site modified the electronic band structure thereby enhanced electrical conductivity. The highest power factor of 25.3 μW/(m K2) was achieved for the SrSb5(Sr: 5 mM and Sb: 5 mM in the polymerization complex method) at 578 K. The reduced thermal conductivity and increased power factor in SrSb5 resulted in the higher figure of merit of 2.1 × 10−3 at 578 K.

Ce and Y Co-Doping Effects for (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Lead-Free Ceramics

CeO2 and Y2O3 were co-doped to (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics and sintered by conventional solid-state reaction process to form x wt.% CeO2-y wt.% Y2O3 doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (CexYy-BCZT) ceramics. The effects of different contents of CeO2-Y2O3 dopants to the (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 composition were analyzed by studying the phase, surface microstructure, piezoelectric and ferroelectric properties of BCZT ceramics. In this study, we have shown that co-doping a small amount of CeO2 and Y2O3 will not change the phase structure of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics. However, the proper introduction of CeO2 and Y2O3 can improve the piezoelectric constant and electromechanical coupling coefficient of BCZT ceramic samples. Moreover, these dopants can promote the grain growth process in (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 ceramics. C0.04Y0.02 doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramic has the best piezoelectric properties compared with other composition, the results are as follows: Relative density = 96.9%, Kp = 0.583, and d33 = 678 pC/N, V = 8.9 V. It means that this Ce0.04Y0.02 doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramic is a desired material in the application of lead-free ceramics.

Effects of Co and Si co-doping on magnetostructural transformation and magnetocaloric effect in Ni-Mn-Sn based alloys

The remarkable magnetocaloric effect demonstrated in Ni-Mn-based multi-functional alloys benefits a lot from large magnetization difference ΔM and low thermal hysteresis ΔHhys upon the magnetostructural transformation. Here, we present the effective manipulation of the magnetostructural transformation as well as the related magnetocaloric effect through simultaneously introducing Co and Si to ternary Ni-Mn-Sn alloys. Such co-doping method allows not only large magnetization difference but also low thermal hysteresis, yielding giant inverse magnetocaloric effect in a Ni39Co9Mn42Sn9Si1 alloy. Under the magnetic field change of 5T, the field-induced entropy change ΔSM up to 23.5 Jkg−1 K−1 and the reversible ΔSM of 23.4 Jkg−1 K−1 are obtained. Moreover, giant refrigeration capacity up to 402 Jkg−1 is also achieved, being much higher than those reported previously. Furthermore, large field-induced adiabatic temperature change ΔTad up to −4.0 K and reversible ΔTad of −1.8 K are demonstrated through the direct measurements under a low magnetic field change of 1.5 T. Thus, multi-component alloying could be employed as an effective route towards the design of high-performance Heusler-type magnetocaloric materials.

Effect of Co-doping on the performance of nanosheet-like ZnO ethanol gas sensor

Effect of Co-doping on the performance of nanosheet-like ZnO ethanol gas sensor

Effect of silver co-doping on luminescence of the Pr3+-doped lithium tetraborate glass

Spectroscopic and luminescent properties of the Pr-doped and Pr–Ag co-doped borate glasses with Li2B4O7 (Li2O–2B2O3) composition are studied and discussed. Experimental and theoretical oscillator strengths (fexp and ftheor), phenomenological parameters (Ω2, Ω4, Ω6), radiative properties (Arad, β, τrad), and quantum efficiencies (η) of the Pr3+ luminescence were calculated basing on the obtained experimental results and Judd–Ofelt theory. Most intense band of the Pr3+ luminescence is peaked at 601 nm (1D2 → 3H4 transition). Presence of the isolated Ag+ (4d10, 1S0) ions, small non-plasmonic Ag aggregates (Agmn+ nanoclusters), and plasmonic Ag metallic nanoparticles in the Li2B4O7:Pr,Ag glass was proposed basing on analysis of the photoluminescence and optical absorption spectra. Observed enhancement of luminescence intensity and increasing of stimulated emission cross-section and quantum efficiency of luminescence in the Li2B4O7:Pr,Ag glass is explained by energy transfer from Ag species to the Pr3+ ions as wells local-field effect induced by Ag nanoparticles.

Synergistic effect and mechanism of FeOx and CeOx co-doping on the superior catalytic performance and SO2 tolerance of Mn-Fe-Ce/ACN catalyst in low-temperature NH3-SCR of NOx

Developing alternative NH3-SCR catalysts with high SO2 tolerance is of great significance for NOx emission control at low temperature. For further improving the catalytic performance and SO2 tolerance of nitric acid modified activated carbon (ACN) loaded MnOx catalyst (Mn/ACN), FeOx and CeOx were co-doped by impregnation. FeOx and CeOx co-doped Mn-Fe(0.4)-Ce(0.4)/ACN exhibited improved catalytic activity, N2 selectivity, and SO2 tolerance. The NOx conversion of Mn-Fe(0.4)-Ce(0.4)/ACN was higher than 95% in 100–250 °C and remained around 91% after 32 h reaction under 100 ppm SO2 and 10 vol% H2O at 175 °C. Co-doping FeOx and CeOx greatly enhanced the surface acidity, redox properties, and surface chemisorbed oxygen of Mn-Fe(0.4)-Ce(0.4)/ACN through the interaction among Mnn+, Fen+, and Cen+, resulting in significantly promoted NH3-SCR performance. The stronger surface acidity and promoted catalytic activity effectively inhibited the adsorption of SO2 and the reaction between SO2 and adsorbed NH3, respectively. Meanwhile, the adsorbed SO2 was preferentially induced to react with CeOx, preventing MnOx and FeOx from being sulfated. Finally, the synergistic mechanism of FeOx and CeOx co-doping on better SO2 tolerance for Mn-Fe(0.4)-Ce(0.4)/ACN catalyst was proposed.

An integrated strategy based on Schiff base reactions to construct unique two-dimensional nanostructures for intrinsic pseudocapacitive sodium/lithium storage

Combining electrode materials with low-dimensional carbonaceous materials such as graphene is an effective way to improve the electrochemical performance of sodium/lithium-ion batteries (SIBs/LIBs). A common drawback of these recombinant hybrids is the weak interaction between the active component and graphene, resulting in poor structural stability and high resistance to diffusion of Na+/Li+ and electrons diffusing between phase boundaries during charging and discharging, thus leading to capacity decay and low rate capability of these hybrids. Here, a facile integrated construction strategy based on Schiff base reactions is developed to build a nitrogen and sulfur co-doped flexible lotus-leaf-like carbon and FeS nanosheets (FeS@N,S-CNSs). This structure takes full advantage of the high conductivity and mechanical flexibility of carbon nanosheets, and the high theoretical capacity of FeS. Together with the co-doping effects, the nanoscale size of FeS, and the robust connection between the in-situ generated FeS nanocrystals and carbon nanosheets, the FeS@N,S-CNSs outputs excellent electrochemical performance in both of SIBs and LIBs. Impressively, experimental results and Density functional theory (DFT) calculations indicate that the charging/discharging process is essentially dominated by pseudocapacitive behavior, this intrinsic feature gives FeS@N,S-CNSs electrode exceptional rate capability (∼50% capacity retention even at 100 A g−1 in SIBs).

Synergistic effect of Ag and Cu co-doping on the structural, optical, and photocatalytic performance of BiVO4

In this work, Ag- or/and Cu-doped BiVO4 samples have been prepared successfully via hydrothermal and photoreduction method. Ag/Cu co-doped BiVO4 exhibited high photocatalytic degradation efficiency in the degradation of methylene blue (MB) and displayed a significantly superior property compared to pure BiVO4, as well as only Ag- or Cu-doped BiVO4 upon exposure to visible light source. Interestingly, we found that enhanced photocatalytic activity of Ag/Cu co-doped BiVO4 arises from the synergistic effect between the Ag and Cu co-doped BiVO4 with smaller crystalline size, improved photocatalytic reaction sites, improved lifetime, and enhanced separation of photogenerated charge carriers which are confirmed using different characterization techniques. The degradation of MB was mainly indicated by superoxide radical species as confirmed by the trapping experiment. Based on the collective results obtained, an excellent photocatalytic activity in Ag/Cu co-doped BiVO4 has been confirmed.

Synergistic effect of La and Mo co-doping on the enhanced photocatalytic activity of Bi2WO6

We modified Bi2WO6 with co-doping of La and Mo ions for improving photocatalytic performance depending on the variations in physicochemical properties. The results of XRD and XPS suggest the substitutional replacement of Bi and W sites by La and Mo ions in the Bi2WO6. Also, the incorporation of La and Mo into Bi2WO6 is confirmed by the changes of particle size and lattice spacing, and band gap energy of (La, Mo) co-doped Bi2WO6 from TEM and UV–Vis spectra, respectively. From photodegradation testing of methylene blue (MB), the co-dopants of La and Mo ions with the concentration of 0.25 mol% La and 0.25 mol% Mo exhibit the highest photocatalytic activity. The increased photocatalytic activity on the co-doped Bi2WO6 is attributed to absorption to longer wavelength, the separation of electron-hole pairs, the reduction of particle size, and increasing specific surface area. By using different scavengers to examine the photodegradation process, the electrons are discovered to be the main active species.