Zinc oxide nanorod/rutin modified electrode for the detection of Thiourea in real samples

In this work, a novel electrochemical detection strategy was developed based on a metal-organic framework of zinc oxide nanorod nanoparticles and rutin for selective screening of Thiourea as toxic chemicals. The zinc oxide nanorod were synthesized by following direct chemical precipitation methods and characterized by X-ray diffraction and X-ray photoelectron spectroscopy analysis. The surface of modified electrodes was also characterized by field emission scanning electron microscopes, energy-dispersive X-ray spectroscopy, and attenuated total reflectance flourier transform infrared spectroscopy. Furthermore, the electrochemical activity of the developed sensor was tested by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. The modified electrode showed outstanding electro-catalytic activity towards the detection of Thiourea in phosphate buffer saline at a high pH level of 12.0. The proposed sensor showed a linear range of linearity in a concentration ranging from 5.0 × 10-6 - 900 × 10-6 molL-1 and a detection limit of 2.0 × 10-6 molL-1. Moreover, the selectivity of the developed electrochemical sensor was investigated for the detection of Thiourea in the presence of organic compounds and a group of anions. Furthermore, the proposed strategy demonstrated an excellent recovery value in the spiked farmland water and fruit juice sample.

Graphene Oxide Membranes for High Salinity, Produced Water Separation by Pervaporation

Oil and gas industries produce a huge amount of wastewater known as produced water which contains diverse contaminants including salts, dissolved organics, dispersed oils, and solids making separation and purification challenging. The chemical and thermal stability of graphene oxide (GO) membranes make them promising for use in membrane pervaporation, which may provide a more economical route to purifying this water for disposal or re-use compared to other membrane-based separation techniques. In this study, we investigate the performance and stability of GO membranes cast onto polyethersulfone (PES) supports in the separation of simulated produced water containing high salinity brackish water (30 g/L NaCl) contaminated with phenol, cresol, naphthenic acid, and an oil-in-water emulsion. The GO/PES membranes achieve water flux as high as 47.8 L m-2 h-1 for NaCl solutions for membranes operated at 60 °C, while being able to reject 99.9% of the salt and upwards of 56% of the soluble organic components. The flux for membranes tested in pure water, salt, and simulated produced water was found to decrease over 72 h of testing but only to 50-60% of the initial flux in the worst-case scenario. This drop was concurrent with an increase in contact angle and C/O ratio indicating that the GO may become partially reduced during the separation process. Additionally, a closer look at the membrane crosslinker (Zn2+) was investigated and found to hydrolyze over time to Zn(OH)2 with much of it being washed away during the long-term pervaporation.

Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities

This article reviews the recent developments in the synthesis, antibacterial activity, and visible-light photocatalytic bacterial inactivation of nano-zinc oxide. Polycrystalline wurtzite ZnO nanostructures with a hexagonal lattice having different shapes can be synthesized by means of vapor-, liquid-, and solid-phase processing techniques. Among these, ZnO hierarchical nanostructures prepared from the liquid phase route are commonly used for antimicrobial activity. In particular, plant extract-mediated biosynthesis is a single step process for preparing nano-ZnO without using surfactants and toxic chemicals. The phytochemical molecules of natural plant extracts are attractive agents for reducing and stabilizing zinc ions of zinc salt precursors to form green ZnO nanostructures. The peel extracts of certain citrus fruits like grapefruits, lemons and oranges, acting as excellent chelating agents for zinc ions. Furthermore, phytochemicals of the plant extracts capped on ZnO nanomaterials are very effective for killing various bacterial strains, leading to low minimum inhibitory concentration (MIC) values. Bioactive phytocompounds from green ZnO also inhibit hemolysis of Staphylococcus aureus infected red blood cells and inflammatory activity of mammalian immune system. In general, three mechanisms have been adopted to explain bactericidal activity of ZnO nanomaterials, including direct contact killing, reactive oxygen species (ROS) production, and released zinc ion inactivation. These toxic effects lead to the destruction of bacterial membrane, denaturation of enzyme, inhibition of cellular respiration and deoxyribonucleic acid replication, causing leakage of the cytoplasmic content and eventual cell death. Meanwhile, antimicrobial activity of doped and modified ZnO nanomaterials under visible light can be attributed to photogeneration of ROS on their surfaces. Thus particular attention is paid to the design and synthesis of visible light-activated ZnO photocatalysts with antibacterial properties.

Futuristic electron transport layer based on multifunctional interactions of ZnO/TCNE for stable inverted organic solar cells

Solution-processed inverted bulk heterojunction (BHJ) organic solar cells (OSCs) are expected to play a significant role in the future of large-area flexible devices and printed electronics. In order to catch the potential of this inverted BHJ technology for use in devices, a solar cell typically requires low-resistance ohmic contact between the photoactive layers and metal electrodes, since it not only boosts performance but also protects the unstable conducting polymer-based active layer from degradation in the working environment. Interfacial engineering delivers a powerful approach to enhance the efficiency and stability of OSCs. In this study, we demonstrated the surface passivation of the ZnO electron transport layer (ETL) by an ultrathin layer of tetracyanoethylene (TCNE). We show that the TCNE film could provide a uniform and intimate interfacial contact between the ZnO and photo-active layer, simultaneously reducing the recombination of electron and holes and series resistance at the contact interface. After successful insertion of TCNE between the ZnO film and the active layer, the parameters, such as short circuit current density (J _sc) and fill factor (FF), greatly improved, and also a high-power conversion efficiency (PCE) of ∼8.59% was achieved, which is ∼15% more than that of the reference devices without a TCNE layer. The devices fabricated were based on a poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b : 4,5-b']dithiophene-2,6-diyl]-[3-fluoro-2[(2-ethylhexyl)-carbonyl]-thieno[3,4-b]thiophenediyl]] (PTB7):(6,6)-phenyl C71 butyric acid methyl ester (PC71BM) blend system. These results suggest that this surface modification strategy could be readily extended in developing large-scale roll-to-roll fabrication of OSCs.

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.

Existence of Ligands within Sol-Gel-Derived ZnO Films and Their Effect on Perovskite Solar Cells

The sol-gel (SG) method has been well-documented as one useful way to produce ZnO films as an excellent electron transport material (ETM) for efficient perovskite solar cells (PSCs). Generally, the precursor films containing zinc acetate dihydrate and a stabilizing ligand monoethanolamine (EA) were annealed to obtain ZnO films. A noteworthy issue is the commonly reported annealing temperature (T_a) in a wide range of 150-600 °C. In this work, we investigated the effect of the annealing temperature on the film composition and first confirmed the co-existence of acetate and EA species when T_a is below 380 °C. EA still survived within the ZnO films when T_a was between 380 and 450 °C. When T_a was over 450 °C, pure ZnO films can be obtained. The presence of ligands also remarkably altered the work function of the corresponding ZnO samples, thereby resulting in the remarkably different effects on the efficiency and stability of PSCs with the ZnO samples as ETMs. This work affords a clearer understanding of ZnO films prepared by the SG method at molecular insights, promoting their application in photoelectric fields.

Nano-crater morphology in hybrid electron-collecting buffer layers for high efficiency polymer:nonfullerene solar cells with enhanced stability

Organic solar cells based on solution processes have strong advantages over conventional silicon solar cells due to the possible low-cost manufacturing of flexible large-area solar modules at low temperatures. However, the benefit of the low temperature process is diminished by a thermal annealing step at high temperatures (≥200 °C), which cannot be practically applied for typical plastic film substrates with a glass transition temperature lower than 200 °C, for inorganic charge-collecting buffer layers such as zinc oxide (ZnO) in high efficiency inverted-type organic solar cells. Here we demonstrate that novel hybrid electron-collecting buffer layers with a particular nano-crater morphology, which are prepared by a low-temperature (150 °C) thermal annealing process of ZnO precursor films containing poly(2-ethyl-2-oxazoline) (PEOz), can deliver a high efficiency (12.35%) similar to the pristine ZnO layers prepared by the conventional high-temperature process (200 °C) for inverted-type polymer:nonfullerene solar cells. The nano-crater morphology was found to greatly enhance the stability of solar cells due to improved adhesion between the active layers and ZnO:PEOz hybrid buffer layers.

Enhancing Lifetime and Efficiency of Organic Solar Cell by Applying an In Situ Synthesized Low-Crystalline ZnO Layer

By introducing an in situ synthesized low-crystalline ZnO (LC-ZnO) (amorphous) layer between the cathode and the active layer of PCPDTBT:CdSe solar cell {PCPDTBT: poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]}, the device keeps more than 80 and 40 % of its initial lifetime after 180 and 360 days without any encapsulation, respectively. In this regard, 180 days is the highest lifetime achieved for polymer-based solar cells with direct configuration. In addition, the power conversion efficiency (PCE) is improved up to 70 % in the presence of the LC-ZnO interfacial layer. The LC-ZnO layer is synthesized during polymer annealing after solution-deposition of the precursor at a low temperature (140 °C) and a short time. Highly crystalline ZnO (HC-ZnO) nanoparticles are also synthesized and applied as an interfacial layer. The results show that the LC-ZnO is superior to the HC-ZnO in acting as cathode interfacial layer and moisture scavenger because of the high coverage and surface area provided by the in situ synthesis method.