Effect of Synthesis Conditions on CuO-NiO Nanocomposites Synthesized via Saponin-Green/Microwave Assisted-Hydrothermal Method.

This work presents the synthesis of CuO-NiO nanocomposites under different synthesis conditions. Nanocomposites were synthesized by merging a green synthesis process with a microwave-assisted hydrothermal method. The synthesis conditions were as follows: concentration of the metal precursors (0.05, 0.1, and 0.2 M), pH (9, 10, and 11), synthesis temperature (150 °C, 200 °C, and 250 °C), microwave treatment time (15, 30, and 45 min), and extract concentration (20 and 40 mL of 1 g saponin/10 mL water, and 30 mL of 2 g saponin/10 mL water). The phases and crystallite sizes of the calcined nanocomposites were characterized using XRD and band gap via UV-Vis spectroscopy, and their morphologies were investigated using SEM and TEM. The XRD results confirmed the formation of a face-centered cubic phase for nickel oxide, while copper oxide has a monoclinic phase. The calculated crystallite size was in the range of 29-39 nm. The direct band gaps of the samples prepared in this work were in the range of 2.39-3.17 eV.

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries.

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Plating and Stripping Calcium Metal in Potassium Hexafluorophosphate Electrolyte toward a Stable Hybrid Solid Electrolyte Interphase.

The use of calcium (Ca) metal anodes in batteries is currently challenged by the development of a suitable solid electrolyte interface (SEI) that enables effective Ca2+ ion transport. Native calcium electrolytes produce a passivation layer on the surface of the calcium electrodes during cycling, causing a decrease in capacity during cycling and the need for large overpotentials. The use of a hybrid SEI is a strategy to mitigate the uncontrolled production of a passivation layer and reduce the overpotentials needed for the plating and stripping of calcium. Here, we report the development of a hybrid potassium (K)/Ca SEI layer investigated in symmetric Ca//Ca cell configurations. Using KPF6 salt in a ternary mixture of carbonate solvent (EC/EMC/DMC), Ca//Ca cells can be cycled up to 200 h at a capacity of 0.15 mAh/cm2 with a current density of 0.025 mA/cm2. The symmetrical cells consistently cycle at overpotentials of 1.8 V. Ex-situ X-ray diffraction (XRD) of cycled electrodes reveals plating and stripping of both calcium and potassium. Energy dispersive X-ray (EDX) maps confirm the plating of calcium and potassium during galvanostatic cycling. Scanning electron microscopy (SEM) cross-sectional views of the calcium electrodes reveal a continuous SEI layer formed over the calcium metal. XRD analysis reveals the SEI layer consists of K-based inorganics along with the identification of permanent and transient phases. FTIR outlines the parallel plating of both calcium and potassium at both regions of redox activity. Raman spectroscopy of the electrolyte reveals compositional changes over the course of cycling that promote increased plating and stripping. The results indicate that potassium electrolytes are a possible route for tuning the SEI to enable reversible calcium electrochemical cycling.

Superhydrophobic Polymer Composite Surfaces Developed via Photopolymerization.

Fabrication of superhydrophobic materials using incumbent techniques involves several processing steps and is therefore either quite complex, not scalable, or often both. Here, the development of superhydrophobic surface-patterned polymer-TiO2 composite materials using a simple, single-step photopolymerization-based approach is reported. The synergistic combination of concurrent, periodic bump-like pattern formation created using irradiation through a photomask and photopolymerization-induced nanoparticle (NP) phase separation enables the development of surface textures with dual-scale roughness (micrometer-sized bumps and NPs) that demonstrate high water contact angles, low roll-off angles, and desirable postprocessability such as flexibility, peel-and-stick capability, and self-cleaning capability. The effect of nanoparticle concentration on surface porosity and consequently nonwetting properties is discussed. Large-area fabrication over an area of 20 cm2, which is important for practical applications, is also demonstrated. This work demonstrates the capability of polymerizable systems to aid in the organization of functional polymer-nanoparticle surface structures.

A bioink blend for rotary 3D bioprinting tissue engineered small-diameter vascular constructs.

3D bioprinted vascular constructs have gained increased interest due to their significant potential for creating customizable alternatives to autologous vessel grafts. In this study, we developed a new approach for biofabricating fibrin-based vascular constructs using a novel rotary 3D bioprinter developed in our lab. We formulated a new bioink by incorporating fibrinogen with gelatin to achieve a desired shear-thinning property for rotary bioprinting. The blending of heat-treated gelatin with fibrinogen turned unprintable fibrinogen into a printable biomaterial for vessel bioprinting by leveraging the favorable rheological properties of gelatin. We discovered that the heat-treatment of gelatin remarkably affects the rheological properties of a gelatin-fibrinogen blended bioink, which in turn influences the printability of the ink. Further characterizations revealed that not only concentration of the gelatin but the heat treatment also affects cell viability during printing. Notably, the density of cells included in the bioinks also influenced printability and tissue volumetric changes of the printed vessel constructs during cultures. We observed increased collagen deposition and construct mechanical strength during two months of the cultures. The burst pressure of the vessel constructs reached 1110 mmHg, which is about 52% of the value of the human saphenous vein. An analysis of the tensile mechanical properties of the printed vessel constructs unveiled an increase in both the circumferential and axial elastic moduli during cultures. This study highlights important considerations for bioink formulation when bioprinting vessel constructs. STATEMENT OF SIGNIFICANCE: There has been an increased demand for small-diameter tissue-engineered vascular grafts. Vascular 3D bioprinting holds the potential to create equivalent vascular grafts but with the ability to tailor them to meet patient's needs. Here, we presented a new and innovative 3D rotary bioprinter and a new bioink formulation for printing vascular constructs using fibrinogen, a favorable biomaterial for vascular tissue engineering. The bioink was formulated by blending fibrinogen with a more printable biomaterial, gelatin. The systematic characterization of the effects of heat treatment and gelatin concentration as well as bioink cell concentration on the printability of the bioink offers new insight into the development of printable biomaterials for tissue biofabrication.

Charged gold nanoparticles in non-polar solvents: 10-min synthesis and 2D self-assembly.

We report a fast and highly reproducible chemical synthesis method for colloidal gold nanoparticles which are negatively charged in nonpolar solvents and coated with hydrophobic organic molecules. If a hexane droplet containing charged gold nanoparticles is mixed with a larger toluene droplet, nanoparticles immediately float to the air-toluene interface and form a close-packed monolayer film. After evaporation of the solvent molecules, the monolayer film of nanoparticles can be deposited to any substrate without any limit in size. The synthesis does not require a postsynthesis cleaning step, since the two immiscible liquid phases separate the reaction byproducts from gold nanoparticles and a minimal amount of coating molecules is used.