Papers by Keyword: Co-Doping

Abstract: Ni_1-2xMg_xCu_xO and Ni_1-2xMg_xRu_xO nanoparticles (x = 0.005, 0.01, 0.02, 0.04, 0.08) were synthesized by the chemical co-precipitation method using salt chloride precursor and EDTA as a capping agent.The present work compares the impact of (Mg, Cu) and (Mg, Ru) co-dopants on the dielectric properties of NiO within a frequency range 0.1 -8 MHz and various dopant concentrations x = 0, 0.005, 0.01, 0.02, 0.04, 0.08. The dielectric properties and phase formation were investigated via an impedance analyser and XRD, respectively. X-ray diffraction patterns confirm the successful synthesis and crystallization of all Ni_1-2xMg_xCu_xO and Ni_1-2xMg_xRu_xO nanoparticles in the fcc structure except for Ni_0.92Mg_0.04Ru_0.04O and Ni_0.84Mg_0.08Ru_0.08O nanoparticles confirming a secondary RuO₂ pahse. Observed and calculated data from the impedance analyzer showed higher dielectric constants, ac conductivity, energy loss, and refractive index values for Ni_1-2xMg_xCu_xO than for Ni_1-2xMg_xRu_xO nanoparticles. However, the impedance values of (Mg, Ru) dual-doped NiO nanoparticles were higher compared with (Mg, Cu) dual-doped NiO nanoparticles. Both samples showed a decrease in dielectric constants, impedance, loss tangent, and refractive index as frequency increased (0.1-7.5MHz), with a vice versa behavior as dopant concentration rose, except for the impedance. Hence, Ni_1-2xMg_xCu_xO and Ni_1-2xMg_xRu_xO nanoparticles are good candidates for electrical and optical applications.

Abstract: Continuous emissions of carbon dioxide (CO₂) into the atmosphere brought several environmental problems. Photoconversion of CO₂ not only can produce value-added products (i.e. methanol) but also aim to reduce the environmental problems caused by CO₂. The present work demonstrates the preparation of N-Bi co-doped carbon quantum dots/titanium dioxide (N-Bi co-doped CQDs/TiO₂) as a visible-light driven photocatalyst for the photoconversion of CO₂ to methanol. Hydrothermal-synthesized N-Bi co-doped CQDs were incorporated into TiO₂ nanoparticles through facile mixing method. The loading of CQDs in TiO₂ matrix resulted in a decrease of band gap to 2.75 and 2.65 eV for N-CQDs and N-Bi CQDs, respectively. Gas chromatography equipped with flame-ionization detection (GC-FID) analysis showed a methanol yield of 17 µmol/gcat from the photoconversion experiment using N-Bi-CQDs/TiO₂ photocatalyst composite. The performance of composite was assigned to the loading of N-Bi co-doped CQDs, which reduced the electron-hole recombination in TiO₂. Doping of N-Bi played an important role in localizing the photogenerated electron-holes, essentially enhancing the electron transfer at the CQDs/TiO₂ interface. Thus, our work could provide insight into the application of CQDs-based photocatalysts in the visible-light driven photocatalytic conversion of CO₂ to value-added products.

Abstract: In this study, Aluminum (Al) and Manganese (Mn) co-doped ZnO thin films were successfully synthesized into glass substrates by the sol-gel dip-coating method with different Al concentrations (1%, 3%, and 5%). The structural, morphological, and optical properties of the obtained thin films were characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and UV–VIS spectroscopy. XRD pattern revealed that the films have a polycrystalline hexagonal structure with a preferred orientation along (101) for undoped ZnO thin films, further the co-doped ZnO thin films show a shift in the preferred orientation to (002) direction without any Mn or Al related phases. The morphological analysis showed that the films have a uniform and dense ZnO grains, without any voids and cracks, and it was found that the surface roughness (RMS) increases from 8,27 to 14,43 nm when the Al doping concentration increased from 1% to 3%; however, when Al doping concentration is 5%, the RMS value decreased to 2,80 nm. From the optical analysis, the higher average transmittance was found to be corresponding to 5% Al doping concentration.

Abstract: Photoelectrocatalysis has emerged as a promising technology to degrade recalcitrant pollutants such as textile dyes in wastewater completely. Titanium dioxide is typically used as a photocatalyst, but its wide bandgap constrains its use to the use of ultraviolet light. To extend its use to the visible-light region, we doped titanium dioxide nanotubes with iron and sulfur. We used them as a photoelectrode for the photoelectrocatalytic degradation of a model pollutant – phenol red. Response surface methodology using a Box-Behnken design of experiments was used to investigate the effects of initial dye concentration, applied potential, and dopant loading on phenol red degradation kinetics. Statistical analysis showed that our reduced cubic model adequately correlates these parameters. The fastest dye degradation rate was achieved at the optimized conditions: initial phenol red concentration = 5.0326 mg L^-1, applied voltage = 29.9686 V, and dopant loading = 1.2244 wt.%. Complete degradation of phenol red may be achieved after 11.77 hours of treatment under the optimized conditions in a batch reactor. Our model's robustness enables it to be used for process modeling and a basis for designing scaled-up photoelectrocatalytic reactors.

Abstract: Photoelectrocatalysis is a rapidly developing technology for degrading recalcitrant organic compounds in wastewater due to its ability to overcome electron-hole recombination. Herein, we synthesized Fe/S co-doped TiO₂ nanotubes through an in-situ anodization technique. We developed a simple reduced quadratic model based on response surface modeling which can be used to adequately correlate the operating parameters with the photoelectrocatalytic performance of Fe/S-TiNTs in degrading phenol red. Predicted maximum dye degradation of 54.78% was achieved by the generated model using the optimized parameters: initial phenol red concentration = 5.22 mg L^-1, applied voltage = 27.4 V, and dopant loading = 2.97 wt.%. Upon validation, experimental maximum phenol degradation of 53.24% was obtained, which agrees well with the predicted value within statistical significance. Overall, our model can be potentially used for process optimization within the design space studied.

Abstract: Zinc oxide (ZnO) has gained worldwide attention due to its direct wide band gap and large exciton binding energy, which are important properties in the application of emerging optoelectronic devices. By doping ZnO with donor elements, a combination of good n-type conductivity and good transparency in the visible and near UV range can be achieved. Co-doping ZnO with several types of dopants is also beneficial in improving the electronic properties of ZnO films. To the best of our knowledge, the fundamental properties of gallium-tin (Ga-Sn) co-doped ZnO (GSZO) films were rarely explored. In this work, we attempt to coat GSZO films on glass substrates via sol-gel spin-coating method. The Ga-Sn co-doping ratio was fixed at 1:1 and the concentration of the dopants was varied at 0.5, 1.0, 1.5, and 2 at.% with respect to the precursor. The AFM image show granular features on the morphology of all GSZO films. All samples also exhibit a preferential c-axis orientation as detected by XRD. The XRD indicates higher crystal quality and larger crystallite size on GSZO thin films at 2.0 at.% and agrees well with the AFM results. However, the transparency and optical band-gap of the GSZO thin films degrade with higher co-doping concentration. The best electrical properties were achieved at co-doping concentration of 1 at.% with conductivity and carrier density of 7.50 × 10^-2 S/cm and 1.37 × 10¹⁶ cm^-3, respectively. At 1.0 at.% co-doping concentration, optimal optical transmittance and electrical properties were achieved, making it promising in the application of optoelectronics.

Abstract: A compact layer of TiO₂, between FTO and mesoporous TiO₂ layer of DSSC anode, has the ability to reduce the electron recombination while mesoporous TiO₂ layer functions to collect and transport electrons injected by the photoexcited dye. In enhancing the desired functions of compact and mesoporous TiO₂, we study the effects of co-doping it with Mg, Eu, and La. MgLa co-doped TiO₂ as compact layer has demonstrated higher efficiency due to its increased oxygen vacancies and smaller particle size which results reduced recombination. The combination of pure and co-doped TiO₂ nanoparticles to be selected as either compact or mesoporous layer of DSSC anode depends on their respective properties, as demonstrated in this paper.

Abstract: The growth of n-type 4H-SiC crystal was performed by physical vapor transport (PVT) growth method by using nitrogen and aluminum (N-Al) co-doping. Resistivity of N-Al co-doped 4H-SiC was as low as 5.8 mΩcm. The dislocation densities of N-Al co-doped substrates were evaluated by synchrotron radiation X-ray topography (SXRT). In addition, epitaxial growth was performed on the N-Al co-doped substrates by chemical vapor deposition (CVD). No double Shockley type stacking fault was observed in the epitaxial layer.

Abstract: The aim of this work was to obtain Pb_0.92(La_0.08)(Zr_0.65Ti_0.35)_0.98O₃ materials co-doped with two different lanthanide ions (Ln³⁺) and characterization how they influence on the physical properties of prepared 8/65/35 PLZT: Ln³⁺ ceramics. As a co-dopant, praseodymium (Pr³⁺) and neodymium (Nd³⁺) ions were used at the concentration of 0.0 and 0.5 wt.% respectively. The ceramic powders of 8/65/35 PLZT, PLZT:Pr³⁺ as well PLZT:Nd³⁺ were synthesized by conventional ceramic route, from high purity raw oxide materials (>99,9%). All compositions of the ceramic samples were sintered via single time process at T_s=1200°C/3h, by the hot uniaxial pressing method. Performed measurements have shown dependence of used dopant on structure, microstructure, and dielectric as well optical properties of the fabricated 8/65/35 PLZT: Ln³⁺ materials.

Abstract: Low resistivity p-type SiC bulk crystals were grown by the sublimation method with using aluminum and nitrogen co-doping. In the sublimation growth of 4H-SiC, to obtain low-resistive p-type crystals are not easy because of the instability of 4H-SiC polytype with highly Al-doping. We have grown < 90 mΩcm p-type 4H-SiC bulk crystals with the co-doping condition. The results of SIMS and Raman spectroscopy show that high concentration of nitrogen co-doping could be effective to the stabilization of 4H polytype with p-type SiC growth.