Homogeneous Doping Research Articles

Homogeneous boron doping in a TiO2 shell supported on a TiB2 core for enhanced photocatalytic water oxidation

Photocatalytic water oxidation for O2 evolution is known as a bottle neck in water splitting. Various strategies have been conducted to keep the energetics of photogenerated holes or to create more holes in the bulk to reach the surface for efficient photocatalytic water oxidation. Our previous study demonstrated the effectiveness of interstitial boron doping in improving photocatalytic water oxidation by lowering the valence band maximum of TiO2 with a concentration gradient of boron. In this study, homogeneous doping of interstitial boron was realized in a TiO2 shell with mixed anatase/rutile phases that was produced by the gaseous hydrolysis of the surface layer of TiB2 crystals in a moist argon atmosphere. Consequently, the homogeneous doping and lowered valence band maximum improved the energetics of holes for efficient photocatalytic water oxidation.

Robocasting of MgO‐doped alumina using alginic acid slurries

AbstractThe benefits of MgO doping of alumina for maintaining a homogeneous grain structure have long been established. Therefore in this work a bespoke ink for Robocasting of alumina is developed based on the gelation of alginic acid using magnesium ions, thereby ensuring homogeneous MgO doping of the alumina green body. The shear thinning behavior of alginic acid based solutions was paired with the rheological properties of a partially coagulated colloidal suspension to allow high solid loading inks (up to 50 vol%) with good extrusion behavior. Shear thinning coefficients of n ~ 0.2 were recorded, with yield stresses of 250 Pa and stiffness values in the range 100‐1000 kPa. The printed alumina bars reached densities of >98% and unpolished strengths reached up to 326 ± 16 MPa after sintering at 0.4 mol/L magnesium chloride and 45 vol% alumina.

Octadecyl‐silica—PVDF membrane of superior MD desalination performance

ABSTRACTDespite its widespread industrial and residential uses for production of potable water, the reverse osmosis (RO) desalination process has some drawbacks by discharging harmful concentrated saline water as reject stream. A hydrophobic porous membrane can treat such environmentally unfriendly RO reject stream via Membrane Distillation (MD) process. Here, we describe preparation of superior polyvinylidenefluoride (PVDF) membrane modified with superhydrophobic silica nanoparticles for desalination application. Superhydrophobicity (contact angle of 151°) of silica nanoparticles of 7 nm sizes was achieved by reaction of the silica particles with octadecyltrichlorosilane in toluene to form SiOSi links with C18 alkyl chain. A homogeneous polymer dope mixture containing a desired amount of modified silica colloids suspended in toluene was used for the membrane preparation. The PVDF membrane with optimal silica content exhibited excellent flux with >99% salt rejection efficiency when used for MD at room temperature from the saline water feed of 3.5 wt % NaCl. The prepared hydrophobic PVDF membrane has the potential for MD application in treating the RO reject stream and other aqueous industrial effluents. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46043.

In Situ Carbon Homogeneous Doping on Ultrathin Bismuth Molybdate: A Dual‐Purpose Strategy for Efficient Molecular Oxygen Activation

AbstractSolar‐driven activation of molecular oxygen, which harnesses light to produce reactive oxygen species for the removal of pollutants, is the most green and low‐cost approach for environmental remediation. The energy coupling between photons, excitons, and oxygen is the crucial step in this reaction and still remains a challenge. In this study, a dual‐purpose strategy for enhanced molecular oxygen activation is established by in situ carbon homogeneous doping on ultrathin Bi2MoO6 nanosheets for the first time. The C‐doped ultrathin 2D material exhibits an enlarged bandgap straddling the electrochemical potential of O2 /•O2− and H2O /•OH, without any attenuation of light absorption. An internal electric field and shortened carrier‐transportation distance are also found in the longitude orientation of the nanosheets ([001] axis), leading to a higher density of effective photogenerated carriers localized on the exposed {001} surface. As applied for the nitric oxide removal, the reactive rate over the ultrathin C‐doped Bi2MoO6 nanosheets is 4.3 times higher than that over the bulk counterparts as a result of the increasing reactive oxygen species. This new proof‐of‐concept strategy not only realizes the band structure engineering and charge transportation regulation but also paves a new way to construct highly efficient photocatalytic materials.

Enhance luminescence property of Er in Bi0.5Na0.5TiO3 ceramics by gradient permeation method

A method of core–shell-like gradient permeation of Er3+ on the surface of grain was used to prepare xEr3+-Bi0.5Na0.5TiO3 ceramics. The structure and photoluminescence properties were investigated both on the gradient and homogenous doping. The XRD patterns exhibited a single rhombohedra phase. The photoluminescence measurements showed a maximum value at x = 1.5 wt% for the gradient xEr3+-Bi0.5Na0.5TiO3 ceramics, and a maximum value at x = 2.0 wt% for the homogenous one, also critical concentrations of elimination of segregation of large strip grains. Significantly, an enhanced efficiency of bright green emission at about 550 nm was observed in the gradient Er3+-Bi0.5Na0.5TiO3 ceramics. In structure a critical concentration of elimination of segregation of large strip grains corresponds to the highest PL peak. The possible mechanism was discussed that concentration quenching effect is supposed due to the degeneration effect of multi-rare earth ions to allow energy transfer accompany with non-radiative loss. Gradient concentration will cause gradient overlapping energy levels to restrict energy transfer to enhance luminescence effect.

Organic-inorganic hybrids-directed ternary NiFeMoS anemone-like nanorods with scaly surface supported on nickel foam for efficient overall water splitting

Utilizing pluronic P123 and MoO42− as morphology directing reagents, the ternary NiFeMoS anemones-like nanorods with scaly surface supported on nickel foam (NiFeMoS/NF-P) have been synthesized through a two-step method. Firstly, Ni-Fe hydroxides film has been electrodeposited on the surface of NF, leading to a homogeneous doping of NiFe. Then, the anemones-like nanorods with scaly surface have been prepared though a facile hydrothermal sulfuration with co-adding of P123 and MoO42−. SEM and TEM images confirm the NiFeMoS/NF-P has anemones-like nanorods morphology with scale-like surface composed of many nanosheets. With the absence of P123 or MoO42−, scaly surface of NiFeMoS nanorods can’t be obtained, implying the role of P123 and MoO42− as organic-inorganic hybrids directing reagents. The detailed influence of P123 and MoO42− on NiFeMoS nanostructure and electrocatalytic activity for water splitting has been investigated. NiFeMoS/NF-P as bifunctional electrocatalyst exhibit excellent electrocatalytic performance in 1M KOH, producing a current density of 150mAcm−2 at a overpotential of 280mV for OER and a overpotential of 100mV at 10mAcm−2 for HER. Moreover, in the same system for overall water-splitting, NiFeMoS/NF-P present remarkable performance with a current density of 100mAcm−2 at a low cell voltage of 1.52V.

Broccoli-shaped biosensor hierarchy for electrochemical screening of noradrenaline in living cells

Monitoring and determination of ultra-trace concentrations of monoamine neurotransmitter such as noradrenaline (NA) in living cells with simple, sensitive and selective assays are significantly interesting. We design NA-electrode sensing system based on C-, N-doped NiO broccoli-like hierarchy (CNNB). The spherical broccoli-head umbrella architectures associated with nano-tubular arrangements enabled to tailor NA biosensor design. The homogenous doping and anisotropic dispersion of CN nanospheres along the entire NB head nanotubes lead to creating of abundant electroactive sites in the interior tubular vessels and outer surfaces for ultrasensitive detection of NA in living cells such as PC12. The CNNB biosensor electrodes showed efficient electrocatalytic activity, enhanced kinetics for electrooxidation of NA, and fast electron-transfer between electrode–electrolyte interface surfaces, enabling synergistic enhancement in sensitivity, and selectivity at a low-detectable concentration of ∼ 6nM and reproducibility of broccoli-shaped NA-electrodes. The integrated CNNB biosensor electrodes showed evidence of monitoring and screening of NA released from PC12 cells under K+ ion-extracellular stimulation process. The unique features of CNNB in terms of NA-selectivity among multi-competitive components, long-term stability during the detection of NA may open their practical, in-vitro application for extracellular monoamine neurotransmitters detection in living cells.

Solid-state reaction route to synthesis of ordered mesoporous β-Zn2SiO4:Mn-SiO2 composites with ultraviolet and yellow emission

Ordered mesoporous Mn-doped β-Zn2SiO4-SiO2 composites are synthesized by solid state reaction at 800 °C using mesoporous silica as assisted template and silicon source. The formation temperature of β-Zn2SiO4 doped with Mn2+ is much lower than that of conventional solid state reaction, which is ascribed to the high reactivity of mesoporous silica with large surface area and porous structure. Mn-doped β-Zn2SiO4 crystals disperse in the mesoporous silica frameworks which play roles in supporting the mesoporous structure and restraining the phase transformation from β- to α-Zn2SiO4, contributing to enhancing the stability of composites. Excitation spectra of the composites show the zinc silicate absorption around 210 nm and the charge transfer band around 245 nm. Mn-doped β-Zn2SiO4-SiO2 composites exhibit an ultraviolet emission at 390 nm attributed to silica and a strong yellow emission around 575 nm driven by 4T1 to 6A1 radiative transition of Mn2+. No obvious concentration quenching is observed at high doping level of 0.08, proving the homogeneous doping of Mn2+ in the composites. This route exhibits a significant advantage of lowering the reaction temperature, facilitating easy doping and preventing concentration quenching.

Vertical Charge Transport and Negative Transconductance in Multilayer Molybdenum Disulfides.

Negative transconductance (NTC) devices have been heavily investigated for their potential in low power logical circuit, memory, oscillating, and high-speed switching applications. Previous NTC devices are largely attributed to two working mechanisms: quantum mechanical tunneling, and mobility degradation at high electrical field. Herein we report a systematic investigation of charge transport in multilayer two-dimensional semiconductors (2DSCs) with optimized van der Waals contact and for the first time demonstrate NTC and antibipolar characteristics in multilayer 2DSCs (such as MoS2, WSe2). By varying the measurement temperature, bias voltage, and body thickness, we found the NTC behavior can be attributed to a vertical potential barrier in the multilayer 2DSCs and the competing mechanisms between intralayer lateral transport and interlayer vertical transport, thus representing a new working mechanism for NTC operation. Importantly, this vertical potential barrier arises from inhomogeneous carrier distribution in 2DSC from the near-substrate region to the bulk region, which is in contrast to conventional semiconductors with homogeneous doping defined by bulk dopants. We further show that the unique NTC behavior can be explored for creating frequency doublers and phase shift keying circuits with only one transistor, greatly simplifying the circuit design compared to conventional technology.

Metal-Organic Framework-Derived FeCo-N-Doped Hollow Porous Carbon Nanocubes for Electrocatalysis in Acidic and Alkaline Media.

Metal-organic frameworks (MOFs) are ideal precursors/ templates for porous carbons with homogeneous doping of active components for energy storage and conversion applications. Herein, metalloporphyrinic MOFs, PCN-224-FeCo, with adjustable molar ratio of FeII /CoII alternatively residing inside the porphyrin center, were employed as precursors to afford FeCo-N-doped porous carbon (denoted as FeCo-NPC) by pyrolysis. Thanks to the hollow porous structure, the synergetic effect between highly dispersed FeNx and CoNx active sites accompanied with a high degree of graphitization, the optimized FeCo2 -NPC-900 obtained by pyrolysis at 900 °C exhibits more positive half-wave potential, higher diffusion-limited current density, and better stability than the state-of-the-art Pt/C, under both alkaline and acidic media. More importantly, the current synthetic approach based on MOFs offers a rational strategy to structure- and composition-controlled porous carbons for efficient electrocatalysis.

Fabrication and characterization of highly transparent Er:Y2O3 ceramics with ZrO2 and La2O3 additives

Abstract In this study, we report highly transparent Er:Y2O3 ceramics (0–10 at% Er) fabricated by a vacuum sintering method using compound sintering additives of ZrO2 and La2O3. The transmittance, microstructure, thermal conductivity and mechanical properties of the Er:Y2O3 ceramics were evaluated. The in-line transmittance of all of the Er:Y2O3 ceramics (1.2 mm thick) exceeds 83% at 1100 nm and 81% at 600 nm. With an increase in the Er doping concentration from 0 to 10 at%, the average grain size, microhardness and fracture toughness remain nearly unchanged, while the thermal conductivity decreases slightly from 5.55 to 4.89 W/m K. A nearly homogeneous doping level of the laser activator Er up to 10 at% in macro-and nanoscale was measured along the radial direction from the center to the edge of a disk specimen, which is the prominent advantage of polycrystalline over single-crystal materials. Based on the finding of excellent optical and mechanical properties, the compound sintering additives of ZrO2 and La2O3 are demonstrated to be effective for the fabrication of transparent Y2O3 ceramics. These results may provide a guideline for the application of transparent Er:Y2O3 laser ceramics.

Rare-earth-doped tungsten oxide microspheres with highly enhanced photocatalytic activites

Abstract Rare-earth-doped WO 2.72 microspheres (RE-WO 2.72 MSs) have been successfully synthesized by using a facile solvothermal route with tungsten salt as precursor, RE (RE=Ce, La, and Y) metal salts as dopants, and ethanol as solvent. Results of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and energy dispersive spectroscopy (EDS) showed that the solvothermal process allowed for the homogeneous doping of WO 2.72 while maintaining the original crystal structure. The RE doping could effectively engineer the bandgap of WO 2.72 , which could not only enhance the light-harvesting ability but also deduce up-shift of both the conduction band and valence band. Compared to the undoped WO 2.72 nanorods (NRs), the RE-WO 2.72 MSs exhibited highly enhanced photocatalytic properties for the degradation of methylene blue (MB) under full spectrum light irradiation. This work provides a versatile strategy for the synthesis of RE-doped tungsten oxides and can be extended to the doping of other oxide semiconductors.

Growth of P-type 4H–SiC single crystals by physical vapor transport using aluminum and nitrogen co-doping

P-type 4H–silicon carbide (SiC) crystal growth has been achieved by physical vapor transport using aluminum and nitrogen co-doping. Aluminum carbide with a two-zone heating furnace was used for p-type doping, and yielded homogenous aluminum doping during SiC crystal growth by physical vapor transport. The 4H–SiC polytype with high-aluminum doping was unstable, but aluminum–nitrogen co-doping improved its stability. We grew p-type 4H–SiC bulk crystals of less than 90mΩcm by using co-doping. Secondary-ion mass spectrometry and Raman spectroscopy showed that the crystal growth of highly doped p-type SiC can be achieved by using the physical vapor transport method.

Co-N-doped MoO2 nanowires as efficient electrocatalysts for the oxygen reduction reaction and hydrogen evolution reaction

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are traditionally carried out with noble metals (such as Pt) as catalysts, respectively. Herein, Co-N-doped MoO2 nanowires catalysts were synthesized by employing MoO2 nanowires as templates and conductive substrates. The effect of nanowire structure and non-metal/metal doping on ORR and HER performance were scientific discussed. The most active Co-N-MoO2 (Co-N-doped MoO2) exhibited high ORR catalytic activity (an onset potential of +0.87V vs. RHE, n values of 3.56 and 3.68, excellent electrochemical stability) and outstanding HER performance with a low overpotential (69mV vs. RHE), high electrochemical area and robust stability in 0.1M KOH, which are associated with the defined nanowires structure, and homogeneous doping of Co/N into MoO2 with numerous active sites.

Bottom-Up Fabrication of Sulfur-Doped Graphene Films Derived from Sulfur-Annulated Nanographene for Ultrahigh Volumetric Capacitance Micro-Supercapacitors.

Heteroatom doping of nanocarbon films can efficiently boost the pseudocapacitance of micro-supercapacitors (MSCs); however, wafer-scale fabrication of sulfur-doped graphene films with a tailored thickness and homogeneous doping for MSCs remains a great challenge. Here we demonstrate the bottom-up fabrication of continuous, uniform, and ultrathin sulfur-doped graphene (SG) films, derived from the peripherical trisulfur-annulated hexa-peri-hexabenzocoronene (SHBC), for ultrahigh-rate MSCs (SG-MSCs) with landmark volumetric capacitance. The SG film was prepared by thermal annealing of the spray-coated SHBC-based film, with assistance of a thin Au protecting layer, at 800 °C for 30 min. SHBC with 12 phenylthio groups decorated at the periphery is critical as a precursor for the formation of the continuous and ultrathin SG film, with a uniform thickness of ∼10.0 nm. Notably, the as-produced all-solid-state planar SG-MSCs exhibited a highly stable pseudocapacitive behavior with a volumetric capacitance of ∼582 F cm-3 at 10 mV s-1, excellent rate capability with a remarkable capacitance of 8.1 F cm-3 even at an ultrahigh rate of 2000 V s-1, ultrafast frequency response with a short time constant of 0.26 ms, and ultrahigh power density of ∼1191 W cm-3. It is noteworthy that these values obtained are among the best values for carbon-based MSCs reported to date.

Is the Metallic Phosphorus Carbide (β0-PC) Monolayer Stable? An Answer from a Theoretical Perspective.

Phosphorus carbide (PC) has been the subject of major research efforts in recent years. In this regard, very recently, a stoichiometric metallic phosphorus carbide (β0-PC) monolayer has been proposed as locally stable with one lone nonbonding electron in each C atom. Therefore, the ambiguity of coexistence of a nonbonding electron with metallic properties for β0-PC is reported and hence deserves further explanation. Herein, using first-principles calculations, we have explored the stability and electronic properties of β0-PC to resolve this ambiguity. The metallic behavior of β0-PC is explained on the basis of electron delocalization involving P and C atoms along a zigzag chain of β0-PC. We have also explored the possibility of getting a β0-PC monolayer via homogeneous doping of C (P) into phosphorene (graphene) and layer exfoliation of 3D bulk PC with β-InS-like structure, which has been experimentally synthesized.

Functionalization of Scanning Probe Tips with Epitaxial Semiconductor Layers

Functionalized scanning probe tips hold great promise for the controlled delivery of signals from and to selected nanoscale volumes. Here, a new nanotechnological approach for the functionalization of scanning probe tips is presented, targeting the transfer of the optical, electrical, thermal, or chemical properties of precisely characterized epitaxial semiconductor layers to the nanoscale probe tip. Homogeneously doped, strain‐relaxed heteroepitaxial germanium layers, several micrometers thick, are first grown on silicon wafers by low‐energy plasma‐enhanced chemical vapor deposition and then employed to functionalize the probe apex. This choice of materials and growth technique enables the future scalability of the tip functionalization process toward high production volumes. The fabricated probe tips are investigated in a transmission electron microscope, revealing that the crystal structure and the homogeneous doping level of the epitaxial layers are unchanged after the probe‐tip functionalization process. These doped‐germanium tips are also tested as nanoemitters of light at telecom wavelengths (1.55 µm) and applied as scattering probes for near‐field mid‐infrared microscopy. The reported combination of heteroepitaxial growth and a nanofabrication approach can be extended to a variety of epitaxial materials, thus enabling a new generation of scanning probes for the investigation of nanostructured materials and devices.

Nd:AlN polycrystalline ceramics: A candidate media for tunable, high energy, near IR lasers

We present processing and characterization of Nd-doped aluminum nitride (Nd:AlN) polycrystalline ceramics. We compare ceramics with significant segregation of Nd to those exhibiting minimal segregation. Spatially resolved photoluminescence maps reveal a strong correlation between homogeneous Nd doping and spatially homogeneous light emission. The spectroscopically resolved light emission lines show excellent agreement with the expected Nd electronic transitions. Notably, the lines are significantly broadened, producing near IR emission (∼1077 nm) with a remarkable ∼100 nm bandwidth at room temperature. We attribute the broadened lines to a combination of effects: multiple Nd-sites, anisotropy of AlN and phonon broadening. These broadened, overlapping lines in a media with excellent thermal conductivity have potential for Nd-based, tunable lasers with high average power.

Effect of charge mixture preparation technology on the physicochemical and optical properties of LiNbO3:Mg crystals

LiNbO3:MgO crystals, representing important materials for nonlinear optics, laser optics, integrated optics, and optical electronics owing to their high resistance with respect to optical damage, are studied. The crystals of LiNbO3:MgO were grown from a granulated charge mixture of lithium niobate synthesized using homogeneously doped Nb2O5:Mg precursors of different origin. The effect of organic substances used in the technology of lithium niobate charge mixture on the properties of LiNbO3:MgO single crystals is studied. It is found that the physicochemical and optical characteristics of LiNbO3:MgO crystals grown from charge mixtures synthesized from Nb2O5:Mg precursors obtained using organic solvents and without them differ to a considerable extent. It is suggested that the difference in the properties of LiNbO3:MgО crystals of different origin is caused by change in the structure of the ion complexes in the melt owing to the presence of traces of organic impurities. Change in the structure of ion complexes in the melt leads to change in crystallization mechanisms and, accordingly, in the chemical composition and the properties of LiNbO3:MgO crystals. Furthermore, it is shown that the use of homogeneous doping methods as opposed to the method of direct doping provides the distribution coefficient K eef > 1. That is, the method of homogeneous doping allows one to introduce a substantially greater concentration of an impurity element in the LiNbO3:MgO crystal compared with the direct method for doping the charge mixture at the same impurity concentration in the starting material.

Solution Combustion Synthesis of Transition Metal Oxide-Carbon Composite for Li Ion Battery Anode

Lithium ion batteries (LIBs) have attracted attentions as one of the most promising power sources for application in portable electronic devices and electric vehicles because of their high energy density and long life span. As for the pursuit of the next generation high-capacity LIBs, transition metal oxides (MOx, M = Fe, Mn, etc.) have been investigated as improved negative materials because of their higher theoretical capacities (>700 mA h g-1) than commercial graphite (372 mAh g-1). However, practical application of MOx in LIBs has been hindered by the poor cycling performance and low rate capability owing to its poor electrical conductivity and large volume expansion/shrinkage during the Li insertion/extraction processes. Compositing of the nanosized oxide with carbon materials can effectively enhance the cycling performance. The carbon matrix could effectively enhance the electrical conductivity of oxides and alleviate the change in volume arising from lithium insertion/extraction. Solution combustion synthesis (SCS) is a highly exothermic and self-sustaining reaction process by heating a solution mixture of aqueous metal nitrates and organic fuels. A variety of functional oxides, such as perovskite oxide catalysts and cathode oxide materials for LIBs has been synthesized by this method. This method offers several benefits, such as (1) the utilization of an exothermic reaction requiring no additional energy during the combustion process, (2) larger surface areas of nanosized or porous products, (3) homogeneous doping of trace amounts of various elements in a single step. By controlling the combustion reaction conditions to avoid the complete combustion of the carbonaceous material, the remaining carbon material and metal oxides can form composites for advanced LIB anode materials. This can be achieved by (1) adding excess amount of fuel and (2) adding carbon additives and performing the SCS under inert atmosphere. In this study, we present the facile production of MOx/carbon composites by SCS. The composition, phase structure and morphology of the composites are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning and transmission electron microscopy. The results indicate that MOx nanocrystals are uniformly embedded in the carbon matrix. The composite materials exhibit high discharge/charge capacities, superior cycling performance, and good rate capability. The easy production and superior electrochemical properties enable the composites to be promising candidates as anode alternatives for high-performance LIBs.