Graphene Supported MoS2 Structures with High Defect Density for an Efficient HER Electrocatalysts.

The development of novel efficient and robust electrocatalysts with sufficient active sites is one of the key parameters for hydrogen evolution reactions (HER) catalysis, which plays a key role in hydrogen production for clean energy harvesting. Recently, two-dimensional (2D) materials, especially those based upon transition metal dichalcogenides such as molybdenum disulfide (MoS2), have gained attention for the catalysis of hydrogen production because of their exceptional properties. Innovative strategies have been developed to engineer these material systems for improvements in their catalytic activity. Toward this aim, the facile growth of MoS2 clusters by sulfurization of molybdenum dioxide (MoO2) particles supported on reduced graphene oxide (rGO) foams using the chemical vapor deposition (CVD) method is reported. This approach created various morphologies of MoS2 with large edges and defect densities on the basal plane of rGO supported MoS2 structures, which are considered as active sites for HER catalysis. In addition, MoS2 nanostructures on the surface of the porous rGO network show robust physical interactions, such as van der Waals and π-π interactions between MoS2 and rGO. These features result in an improved process to yield a suitable HER catalyst. In order to gain a better understanding of the improvement of this MoS2-based HER catalyst, fully atomistic molecular dynamics (MD) simulations of different defect geometries were also performed.

Interface and defect engineering of hybrid nanostructures toward an efficient HER catalyst.

The hydrogen evolution reaction (HER) plays a key role in hydrogen production for clean energy harvesting. Designing novel efficient and robust electrocatalysts with sufficient active sites and excellent conductivity is one of the key parameters for hydrogen production using water splitting devices. Recently, low-dimensional carbon materials have gained attention as metal-free catalysts for hydrogen production. Such nanostructures need to be engineered to improve their catalytic activity. Here, we designed and synthesized a B and N doped carbon nanostructure (CNS)-hBN heterostructure as an improved HER catalyst. The hBN layers on CNS could provide exposed defects and edges that act as active sites for proton adsorption and reduction. The composition, structure and chemical properties of the B and N doped CNS-hBN heterostructure were tuned to obtain excellent HER activity. Detailed morphological, structural and electrochemical characterization demonstrated that the synergistic effect rising from the interaction between B and N doped CNS and hBN structures contributes to enhance the electrocatalytic performances. To get more insight into the role of defects and doping, we performed density functional theory (DFT) calculations on the CNS-hBN heterostructure.

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.

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, zirconia's 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.