Jarin Joyner

Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications

Zirconia (ZrO2) based dental ceramics have been considered to be advantageous materials with adequate mechanical properties for the manufacturing of medical devices. Due to its very high compression strength of 2000 MPa, ZrO2 can resist differing mechanical environments. During the crack propagation on the application of stress on the surface of ZrO2, a crystalline modification diminishes the propagation of cracks. In addition, zirconias biocompatibility has been studied in vivo, leading to the observation of no adverse response upon the insertion of ZrO2 samples into the bone or muscle. In vitro experimentation has exhibited the absence of mutations and good viability of cells cultured on this material leading to the use of ZrO2 in the manufacturing of hip head prostheses. The mechanical properties of zirconia fixed partial dentures (FPDs) have proven to be superior to other ceramic/composite restorations and hence leading to their significant applications in implant supported rehabilitations. Recent developments were focused on the synthesis of zirconia based dental materials. More recently, zirconia has been introduced in prosthetic dentistry for the fabrication of crowns and fixed partial dentures in combination with computer aided design/computer aided manufacturing (CAD/CAM) techniques. This systematic review covers the results of past as well as recent scientific studies on the properties of zirconia based ceramics such as their specific compositions, microstructures, mechanical strength, biocompatibility and other applications in dentistry.

Enhanced supercapacitor performance of a 3D architecture tailored using atomically thin rGO–MoS2 2D sheets

A 3D architecture is fabricated using 2D nano-sheets of GO and MoS2 as the building blocks by a facile, one-pot chronoamperometry method to achieve a conductive additive free, binder free and scalable supercapacitor electrode. The superior electrochemical properties of the 3D PPy-rGO–MoS2 (PGMo) are due to its porous structure, thin wall, high surface area and high electrical conductivity that endow rapid transportation of electrolyte ions and electrons throughout the electrode matrix. The synergistic effect between the components in a proper ratio improves the supercapacitor performance and material stability of PGMo. The possible correlation of the structure and electrochemical performance of the 3D ternary composite is backed by a fully atomistic molecular dynamics (MD) simulation study. The high specific capacitance (387 F g−1) and impressive cycling stability (>1000 cycles) estimated for PGMo open up an opportunity to consider the 3D ternary nanostructures as cutting edge materials for energy storage solutions.

Characterization of tin(II) sulfide defects/vacancies and correlation with their photocurrent

The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its defects/vacancies. Herein, we report a facile solvothermal route to synthesize three-dimensional (3D) SnS nanostructures formed by {131} faceted nanosheet assembly. The 3D SnS nanostructures were calcined at temperatures of 350, 400, and 450 °C and used as counter electrodes, before their photocurrent properties were investigated. First principle computation revealed the photocurrent properties depend on the defect/vacancy concentration within the samples. It is very interesting that characterization with positron annihilation spectrometry confirmed that the density of defects/vacancies increased with the calcination temperature, and a maximum photocurrent was realized after treatment at 400 °C. Further, the defect/vacancy density decreased when the calcination temperature reached 450 °C as the higher calcination temperature enlarged the mesopores and densified the pore walls, which led to a lower photocurrent value at 450 °C than at 400 °C.

Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption

Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO2 absorption and as laser irradiation protection material.

Correlation between types of defects/vacancies of Bi2S3 nanostructures and their transient photocurrent

Crystalline nanostructures possess defects/vacancies that affect their physical and chemical properties. In this regard, the electronic structure of materials can be effectively regulated through defect engineering; therefore, the correlation between defects/vacancies and the properties of a material has attracted extensive attention. Here, we report the synthesis of Bi2S3 microspheres by nanorod assemblies with exposed {211} facets, and the investigation of the types and concentrations of defects/vacancies by means of positron annihilation spectrometry. Our studies revealed that an increase in the calcined temperature, from 350 to 400 °C, led the predominant defect/vacancy densities to change from isolated bismuth vacancies (VBi) to septuple Bi3+–sulfur vacancy associates (VBiBiBiSSSS). Furthermore, the concentration of septuple Bi3+–sulfur vacancy associates increased as the calcined temperature was increased from 400 to 450 °C. The characterized transient photocurrent spectrum demonstrates that the photocurrent values closely correlate with the types and concentrations of the predominant defects/vacancies. Our theoretical computation, through first principles, showed that VBiBiBiSSSS strongly absorbs I2(sol), easily desorbs I−(sol), and enhances the electrocatalytic activity of the nanostructures.

Eco-Friendly Polymer-Layered Silicate Nanocomposite–Preparation, Chemistry, Properties, and Applications

This chapter aims at exploring the revolutionary field of nanotechnology and some of its promising aspects in polymer nanocomposites in view of preparation, characterization, materials properties, and processing of polymer layered silicate nanocomposites. These materials are attracting considerable interest in polymer science research. Polymer layered silicate nanocomposites are an important class of hybrid, organic/inorganic materials with substantially improved mechanical, thermal, and thermomechanical properties in comparison to pristine polymers. In addition, they also show superior ultraviolet (UV) as well as chemical resistance and are widely being investigated for improving gas barrier and flame retardant properties. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of polymer–clay nanocomposites. Smectites are a valuable mineral class for industrial applications due to their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity and transparency in solution. A wide range of polymer matrices are explored for the preparation of polymer–clay nanocomposites, however, this chapter deals with special emphasis on biodegradable polymers––cellulose and natural rubber. Also, the chapter describes the common synthetic techniques in producing polymeric layered silicate nanocomposites, its properties, and applications.