F-doping of nanostructured ZnO: a way to modify structural, electronic, and surface properties

Star anise (Illicium verum Hook. F.) polysaccharides: Potential therapeutic management for obesity, hypertension, and diabetes

This study explores the extraction of polysaccharides from star anise (Illicium verum Hook. f.) with its anti-obesity, antihypertensive, antidiabetic, and antioxidant properties. The aim is to optimize the extraction conditions of star anise polysaccharides (SAP) utilizing propane alcohols-based deep eutectic solvents and microwave-assisted methods. The optimized conditions resulted in an extraction yield of 5.14%. The characteristics of acidic pectin-like SAP, including high viscosity (44.86 mPa s), high oil-holding capacity (14.39%), a high degree of esterification (72.53%), gel-like properties, highly amorphous, a high galacturonic acid concentration, and a highly branching size polysaccharide structure, significantly contribute to their potent inhibition of pancreatic lipase (86.67%), angiotensin-converting enzyme (73.47%), and α-glucosidase (82.33%) activities as well as to their antioxidant properties of azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, 34.94%) and ferric ion reducing antioxidant power (FRAP, 0.56 mM FeSO4). Therefore, SAP could be used as a potential therapeutic agent for obesity, hypertension, and diabetes mellitus management.

Studies of NiO/Ag/NiO transparent conducting electrodes on NiO and ZnO Schottky diodes

A nickel oxide (NiO)/silver (Ag)/NiO (NAN) transparent conducting electrode (TCE) was deposited on NiO and zinc oxide (ZnO) to fabricate Schottky diodes (SDs). The physical and electrical properties of NAN/NiO and NAN/ZnO SDs were studied. In addition, conventional Au/ZnO SDs were fabricated for comparison. The prepared NAN TCE was of n-type, with more than 40% transmittance and a low sheet resistance of 6.5 Ω sq.-1, indicating that NAN is an exceptional TCE. Secondary ion mass spectrometry revealed that Ag atoms diffused into NiO and ZnO in the NAN/NiO and NAN/ZnO SDs, respectively. Owing to the large number of defects on the ZnO surface, the current-voltage (I-V) characteristics of the Au/ZnO SDs followed a linear curve. However, the reduced number of defects and a large barrier height at the NAN/ZnO interface led to a rectifying I-V curve in NAN/ZnO SDs. In contrast, a near homojunction at the NAN/NiO interface caused a linear I-V curve and a large leakage current in NAN/NiO SDs. These issues resulted in a lower ideality factor (5.32) in NAN/ZnO SDs than that in NAN/NiO SDs (15.14). The NAN/ZnO SDs exhibited a higher barrier height (0.91 eV) than the NAN/NiO SDs (0.55 eV). The mechanism of carrier transport was investigated using a ln(I) versus ln(V) plot. The NAN/NiO SDs only exhibited one region of ohmic conduction. However, two distinct regions were observed in the NAN/ZnO SDs. For V ≤ 0.7 V, the space-charge-limited current dominated; however, the diffusion-recombination model controlled carrier transport at V ≥ 0.7 V. Band diagrams were proposed to elucidate the carrier transport mechanism in NAN/NiO and NAN/ZnO SDs.

Role of Electronegativity in Environmentally Persistent Free Radicals (EPFRs) Formation on ZnO

Environmentally persistent free radicals (EPFRs), a group of emerging pollutants, have significantly longer lifetimes than typical free radicals. EPFRs form by the adsorption of organic precursors on a transition metal oxide (TMO) surface involving electron charge transfer between the organic and TMO. In this paper, dihalogenated benzenes were incorporated to study the role of electronegativity in the electron transfer process to obtain a fundamental knowledge of EPFR formation mechanism on ZnO. Upon chemisorption on ZnO nanoparticles at 250 °C, electron paramagnetic resonance (EPR) confirms the formation of oxygen adjacent carbon-centered organic free radicals with concentrations between 1016 and 1017 spins/g. The radical concentrations show a trend of 1,2-dibromobenzene (DBB) > 1,2-dichlorobenzene (DCB) > 1,2-difluorobenzene (DFB) illustrating the role of electronegativity on the amount of radical formation. X-ray absorption spectroscopy (XAS) confirms the reduction of the Zn2+ metal center, contrasting previous experimental evidence of an oxidative mechanism for ZnO single crystal EPFR formation. The extent of Zn reduction for the different organics (DBB > DCB > DFB) also correlates to their polarity. DFT calculations provide theoretical evidence of ZnO surface reduction and exhibit a similar trend of degree of reduction for different organics, further building on the experimental findings. The lifetimes of the EPFRs formed confirm a noteworthy persistency.

Site-Selective Adsorption on ZnF2/Ag Coated Zn for Advanced Aqueous Zinc-Metal Batteries at Low Temperature

Metallic Zn as a promising anode material of aqueous batteries suffers from severe parasitic reactions and notorious dendrite growth. To address these issues, the desolvation and nucleation processes need to be carefully regulated. Herein, Zn foils coated by ZnF₂-Ag nanoparticles (ZnF₂-Ag@Zn) are used as a model to modulate the desolvation and nucleation processes by hybrid surfaces, where Ag has a strong affinity to Zn adatoms and ZnF₂ shows an intense adsorption to H₂O. This selective adsorption of different species on ZnF₂ and Ag reduces the mutual interference between two species. Therefore, ZnF₂-Ag@Zn exhibits the electrochemical performance much better than ZnF₂@Zn or Ag@Zn. Even at -40 °C, the full cells using ZnF₂-Ag@Zn demonstrate an ultralong lifespan of 5000 cycles with a capacity retention of almost 100%. This work provides new insights to improve the performance of Zn metal batteries, especially at low temperatures.

F-doped ZnO nano- and meso-crystals with enhanced photocatalytic activity in diclofenac degradation

Diclofenac (DCF), a non-steroidal anti-inflammatory drug, is considered one of the most widespread emerging contaminants. Its incidence in water can favor the growth of drug-resistant bacteria and harm aquatic organisms endangering both the human health and the ecosystem. Advanced oxidation processes (AOPs) based on the action of reactive oxygen species are very effective technologies for the removal of this contaminant from water. In this context, ZnO is one of the most studied semiconductors for photocatalytic water treatment. In this work, the photocatalytic activity of fluorine-doped ZnO nano- and meso-crystals synthesized by a hydrothermal approach is reported, exploring the role of a low F atomic concentration (0.25, 0.5 and 1 at. %) on the degradation of DCF in comparison with bare ZnO. All doped samples show high rates of DCF degradation and mineralization, which were realized primarily thanks to their high efficiency in the generation of hydroxyl radicals (OH). The property-structure-function relationships of the materials are investigated by complementary techniques, such as SEM, XRD, EPR, UV-vis DRS and PL, with the aim to evaluate the role of fluorine in determining their morphological, electronic and optical properties.