New insight into zinc oxide doped with iron and its exploitation to pollutants abatement

Natural solar activation of modified zinc oxides with rare earth elements (Ce, Yb) and Fe for the simultaneous disinfection and decontamination of urban wastewater

This study investigates the capability of modified zinc oxides (ZnO) with Ce, Yb and Fe towards the simultaneous inactivation of pathogenic bacteria (Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa) and Contaminants of Emerging Concern (CECs, Diclofenac, Sulfamethoxazole and Trimethoprim) under natural sunlight. Several catalyst loads (from 0 to 500 mg/L) were assessed as proof-of principle in isotonic solution followed by the evaluation of organic matter effect in simulated and actual urban wastewater (UWW), using bare TiO₂-P25 as reference. The order of photocatalysts efficiency for both bacterial and CECs removal was: ZnO-Ce ≅ TiO₂-P25 > ZnO-Yb > ZnO-Fe > photolysis > darkness in all water matrices. The best photocatalytic performance for water disinfection and decontamination was obtained with 500 mg/L of ZnO-Ce: 80% of ∑CECs removal after 45 min (4.4 kJ/L of accumulated solar UV-A energy (Q_UV)) and the total inactivation of bacteria (Detection Limit of 2 CFU/mL) after 120 min (14 kJ/L of Q_UV) in UWW. The microbial and CECs abatement mechanism was described based on the generation of hydroxyl radicals, which was experimentally demonstrated for ZnO-Ce. Additionally, no significant release of Zn²⁺ and Ce was detected after the solar exposure. These results point out for the first time the capability of ZnO-Ce for the simultaneous UWW disinfection and decontamination under natural sunlight.

Comparison of Advanced Oxidation Processes for the Degradation of Maprotiline in Water—Kinetics, Degradation Products and Potential Ecotoxicity

The impact of different oxidation processes on the maprotiline degradation pathways was investigated by liquid chromatography-high resolution mass spectrometry (LC/HRMS) experiments. The in-house SPIX software was used to process HRMS data allowing to ensure the potential singular species formed. Semiconductors photocatalysts, namely Fe-ZnO, Ce-ZnO and TiO2, proved to be more efficient than heterogeneous photo-Fenton processes in the presence of hydrogen peroxide and persulfate. No significant differences were observed in the degradation pathways in the presence of photocatalysis, while the SO4− mediated process promote the formation of different transformation products (TPs). Species resulting from ring-openings were observed with higher persistence in the presence of SO4−. In-silico tests on mutagenicity, developmental/reproductive toxicity, Fathead minnow LC50, D. magna LC50, fish acute LC50 were carried out to estimate the toxicity of the identified transformation products. Low toxicant properties were estimated for TPs resulting from hydroxylation onto bridge rather than onto aromatic rings, as well as those resulting from the ring-opening.

Interactions of Zinc Oxide Nanostructures with Mammalian Cells: Cytotoxicity and Photocatalytic Toxicity

This article presents a state-of-the-art review and analysis of literature studies on the morphological structure, fabrication, cytotoxicity, and photocatalytic toxicity of zinc oxide nanostructures (nZnO) of mammalian cells. nZnO with different morphologies, e.g., quantum dots, nanoparticles, nanorods, and nanotetrapods are toxic to a wide variety of mammalian cell lines due to in vitro cell-material interactions. Several mechanisms responsible for in vitro cytotoxicity have been proposed. These include the penetration of nZnO into the cytoplasm, generating reactive oxygen species (ROS) that degrade mitochondrial function, induce endoplasmic reticulum stress, and damage deoxyribonucleic acid (DNA), lipid, and protein molecules. Otherwise, nZnO dissolve extracellularly into zinc ions and the subsequent diffusion of ions into the cytoplasm can create ROS. Furthermore, internalization of nZnO and localization in acidic lysosomes result in their dissolution into zinc ions, producing ROS too in cytoplasm. These ROS-mediated responses induce caspase-dependent apoptosis via the activation of B-cell lymphoma 2 (Bcl2), Bcl2-associated X protein (Bax), CCAAT/enhancer-binding protein homologous protein (chop), and phosphoprotein p53 gene expressions. In vivo studies on a mouse model reveal the adverse impacts of nZnO on internal organs through different administration routes. The administration of ZnO nanoparticles into mice via intraperitoneal instillation and intravenous injection facilitates their accumulation in target organs, such as the liver, spleen, and lung. ZnO is a semiconductor with a large bandgap showing photocatalytic behavior under ultraviolet (UV) light irradiation. As such, photogenerated electron-hole pairs react with adsorbed oxygen and water molecules to produce ROS. So, the ROS-mediated selective killing for human tumor cells is beneficial for cancer treatment in photodynamic therapy. The photoinduced effects of noble metal doped nZnO for creating ROS under UV and visible light for killing cancer cells are also addressed.

Piezo- and Photocatalytic Activity of Ferroelectric ZnO:Sb Thin Films for the Efficient Degradation of Rhodamine-β dye Pollutant

The discovery of novel catalytic materials showing unprecedented properties and improved functionalities represents a major challenge to design advanced oxidation processes for wastewater purification. In this work, antimony (Sb) doping is proposed as a powerful approach for enhancing the photo- and piezocatalytic performances of piezoelectric zinc oxide (ZnO) thin films. To investigate the role played by the dopant, the degradation of Rhodamine-β (Rh-β), a dye pollutant widely present in natural water sources, is studied when the catalyst is irradiated by ultraviolet (UV) light or ultrasound (US) waves. Depending on the doping level, the structural, optical, and ferroelectric properties of the catalyst can be properly set to maximize the dye degradation efficiency. Independently of the irradiation source, the fastest and complete dye degradation is observed in the presence of the doped catalyst and for an optimal amount of the inserted dopant. Among ZnO:Sb samples, the most doped one (5 at. %) shows improved UV light absorption and photocatalytic properties. Conversely, the piezocatalytic efficiency is maximized using the lowest Sb amount (1 at. %). The superior ferroelectric polarization observed in this case highly favors the adsorption of electrically charged species, in particular of the dye in the protonated form (Rh-β⁺) and of OH^-, to the catalyst surface and the production of hydroxyl radicals responsible for dye degradation.

Application of Electrically Conducting Nanocomposite Material Polythiophene@NiO/Frt/GOx as Anode for Enzymatic Biofuel Cells

In this work, nano-inspired nickel oxide nanoparticles (NiO) and polythiophene (Pth) modified bioanode was prepared for biofuel cell applications. The chemically prepared nickel oxide nanoparticles and its composite with polythiophene were characterized for elemental composition and microscopic characterization while using scanning electron microscopy. The electrochemical characterizations of polythiophene@NiO composite, biocompatible mediator ferritin (Frt) and glucose oxidase (GOx) catalyst modified glassy carbon (GC) electrode were carried out using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and charge-discharge studies. The current density of Pth@NiO/Frt/GOx bioanode was found to be 5.4 mA/cm². The bioanode exhibited a good bio-electrocatalytic activity towards the oxidation of the glucose. The experimental studies of the bioanode are justifying its employment in biofuel cells. This will cater a platform for the generation of sustainable energy for low temperature devices.

Electron paramagnetic resonance and microstructural insights into the thermal behavior of simonkolleite nanoplatelets

The thermal decomposition process of simonkolleite, at 500 °C was monitored by EPR and electron microscopy. The experimental data indicate that after an 1 h at 500 °C, three morphologies can be observed from the thermal decomposition of ZHC.