Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Investigations on structural, electronic and optical properties of ZnO in two-dimensional configurations by first-principles calculations

The electronic structures and optical properties of two-dimensional (2D) ZnO monolayers in a series of configurations were systematically investigated by first-principles calculations with HubbardUevaluated by the linear response approach. Three types of 2D ZnO monolayers, as planer hexagonal-honeycomb (Plan), double-layer honeycomb (Dlhc), and corrugated tetragonal (Tile) structures, show a mechanical and dynamical stability, while the Dlhc-ZnO is the most energetically stable configuration and Plan-ZnO is the second one. Each 2D ZnO monolayer behaves as a semiconductor with that Plan-, Dlhc-ZnO have a direct band gap of 1.81 eV and 1.85 eV at theΓpoint, respectively, while Tile-ZnO has an indirect band gap of 2.03 eV. Interestingly, the 2D ZnO monolayers all show a typical near-free-electron character for the bottom conduction band with a small effective mass, leading to a tremendous optical absorption in the whole visible and ultraviolet window, and this origination was further confirmed by the transition dipole moment. Our investigations suggest a potential candidate in the photoelectric field and provide a theoretical guidance for the exploration of wide-band-gap 2D semiconductors.

Designing and Understanding the Outstanding Tri-Iodide Reduction of N-Coordinated Magnetic Metal Modified Defect-Rich Carbon Dodecahedrons in Photovoltaics

Nitrogen-coordinated metal-modified carbon is regarded as a novel frontier electrocatalyst in energy conversion devices. However, the construction of intrinsic defects in a carbon matrix remains a great challenge. Herein, N-coordinated magnetic metal (Fe, Co) modified porous carbon dodecahedrons (Fe/Co-NPCD) with a large surface area, rich intrinsic defects, and evenly distributed metal-N_x species are successfully synthesized via the rational design of iron precursor and the bimetallic-organic frameworks. Because of a synergistic effect between N-coordinated dual magnetic metal active sites, the Fe/Co-NPCD exhibits exceptional electrocatalytic activity and electrochemical stability. A solar cell fabricates with the Fe/Co-NPCD yields an impressive power conversion efficiency of 8.35% in dye-sensitized solar cells, superior to that of mono-metal-doped carbon-based cells and conventional Pt-based cells. Furthermore, density functional theory calculations illustrate that Fe, Co, and N doping are in favor of improving the adsorption capacity of the catalyst for I₃ ^- species by optimizing the magnetic momentum between the magnetic metal atoms, thereby upgrading its catalytic activity. This work develops a general strategy for synthesizing a high-performance defect-rich carbon-based catalyst, and offers valuable insight into the role of magnetic metals in catalysis, which can be used to guide the design of high-performance catalysts in the energy field.

Effect of aluminum loading on structural and morphological characteristics of ZnO nanoparticles for heavy metal ion elimination

The aim of this work consists on the synthesis of a nanomaterial for heavy metal ion removal from aqueous solutions. Al-doped ZnO (ZnO:Alx%) nanopowders with 0 to 5% Al content are prepared via an amended sol-gel method. The morphology and microstructure of the prepared ZnO:Alx% are probed by means of scanning electron microscopy (SEM), X-ray particles diffraction (XRD) analysis, energy dispersive X-ray spectroscopy (EDS) and elemental mapping. The findings reveal the prevalence of the hexagonal wurtzite ZnO structure with increasing crystallite size (45 to 60 nm) as a result of Al doping. SEM images show nearly spherical nanoparticles with considerable aggregation. EDS and elemental mapping analysis confirm the incorporation of Al within ZnO host lattice. The relatively large surface area as estimated from N₂ adsorption makes the nanopowders very favorable for the uptake Cd(II), Cr (IV), Co (II) and Ni(II) from aqueous solution. The ZnO:Alx% with 1 wt% Al exhibits the highest uptake rate of heavy metal ions. The adsorption process has been found to be spontaneous and endothermic and obey Langmuir adsorption model. The high tendency of the prepared nanoparticles to eliminate heavy metal ions renders them suitable candidates for environmental remediation. Desorption studies with 0.1 M NaOH indicate that ZnO:Alx% can be regenerated effectively.

CO2 sensing properties of electro-spun Ca-doped ZnO fibres

The availability of low-cost, high-performing sensors for carbon dioxide detection in the environment may play a crucial role for reducing CO₂ emissions and limiting global warming. In this study, calcium-doped zinc oxide nanofibres with different Ca to Zn loading ratios (1:40 or 1:20) are synthesised via electro-spinning, thoroughly characterised and, for the first time, tested as an active material for the detection of carbon dioxide. The results of their characterisation show that the highly porous fibres consist of interconnected grains of oxide with the hexagonal wurtzite structure of zincite. Depending on the Ca:Zn loading ratio, calcium fully or partly segregates to form calcite on the fibre surface. The high response of the sensor based on the fibres with the highest Ca-doping level can be attributed to the synergy between the fibre morphology and the basicity of Ca-ion sites, which favour the diffusion of the gas molecules within the sensing layer and the CO₂ adsorption, respectively.

A chemical approach to perovskite solar cells: control of electron-transporting mesoporous TiO2and utilization of nanocarbon materials

This Perspective highlights recent chemical approaches to perovskite solar cells, including the control of electron-transporting mesoporous TiO₂and the utilization of nanocarbon materials.

Pt-free counter electrode for dye-sensitized solar cells with high efficiency

Dye-sensitized solar cells (DSSCs) have attracted widespread attention in recent years as potential cost-effective alternatives to silicon-based and thin-film solar cells. Within typical DSSCs, the counter electrode (CE) is vital to collect electrons from the external circuit and catalyze the I3- reduction in the electrolyte. Careful design of the CEs can improve the catalytic activity and chemical stability associated with the liquid redox electrolyte used in most cells. In this Progress Report, advances made by our groups in the development of CEs for DSSCs are reviewed, highlighting important contributions that promise low-cost, efficient, and robust DSSC systems. Specifically, we focus on the design of novel Pt-free CE catalytic materials, including design ideas, fabrication approaches, characterization techniques, first-principle density functional theory (DFT) calculations, ab-initio Car-Parrinello molecular dynamics (CPMD) simulations, and stability evaluations, that serve as practical alternatives to conventional noble metal Pt electrodes. We stress the merits and demerits of well-designed Pt-free CEs, such as carbon materials, conductive polymers, transition metal compounds (TMCs) and their corresponding hybrids. Also, the prospects and challenges of alternative Pt catalysts for their applications in new-type DSSCs and other catalytic fields are discussed.

Enhanced performance of supported HfO2 counter electrodes for redox couples used in dye-sensitized solar cells

Mesoporous-graphitic-carbon-supported HfO2 (HfO2 -MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2 -MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2 -MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application.