Biomass-Derived Porous Carbons Derived from Soybean Residues for High Performance Solid State Supercapacitors.

A series of heteroatom-containing porous carbons with high surface area and hierarchical porosity were successfully prepared by hydrothermal, chemical activation, and carbonization processes from soybean residues. The initial concentration of soybean residues has a significant impact on the textural and surface functional properties of the obtained biomass-derived porous carbons (BDPCs). SRAC5 sample with a BET surface area of 1945 m2 g-1 and a wide micro/mesopore size distribution, nitrogen content of 3.8 at %, and oxygen content of 15.8 at % presents the best electrochemical performance, reaching 489 F g-1 at 1 A g-1 in 6 M LiNO3 aqueous solution. A solid-state symmetric supercapacitor (SSC) device delivers a specific capacitance of 123 F g-1 at 1 A g-1 and a high energy density of 68.2 Wh kg-1 at a power density of 1 kW kg-1 with a wide voltage window of 2.0 V and maintains good cycling stability of 89.9% capacitance retention at 2A g-1 (over 5000 cycles). The outstanding electrochemical performances are ascribed to the synergistic effects of the high specific surface area, appropriate pore distribution, favorable heteroatom functional groups, and suitable electrolyte, which facilitates electrical double-layer and pseudocapacitive mechanisms for power and energy storage, respectively.

Effects of peptide concentration on remineralization of eroded enamel.

Promoting remineralization to repair eroded enamel is a promising therapy in clinics. In this study, biocompatible asparagine-serine-serine (NSS) peptide chelates free ions from artificial saliva through charged functional groups, and subsequently form nano-hydroxyapatite crystals to partially repair erosive lesions. The nanomechanical properties, cross-sectional microstructure, types of deposited minerals, and subsurface microstructure of enamel at various treatment stages were characterized by nanoindentation, scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), respectively. The results revealed that the nanohardness and elastic modulus of eroded enamel increase with peptide concentration, particularly for the 3NSS peptide system. In contrast, the structure of the 5NSS peptide is larger and longer, leading to increasing difficulty in penetrating to the deep acid-eroded regions; therefore, the remineralization effect was restricted to the top enamel surface. The 3NSS peptide with high concentration promoted the formation of smaller, finer, and staggered nanohydroxyapatite crystals. The enamel remineralized with a 100µM 3NSS exhibited the highest degree of nanohardness recovery (34%), resulting from subsurface crystalline regrowth.

Microstructure and nanomechanical properties of enamel remineralized with asparagine-serine-serine peptide.

A highly biocompatible peptide, triplet repeats of asparagine-serine-serine (3 NSS) was designed to regulate mineral deposition from aqueous ions in saliva for the reconstruction of enamel lesions. Healthy human enamel was sectioned and acid demineralized to create lesions, then exposed to the 3 NSS peptide solution, and finally immersed in artificial saliva for 24h. The surface morphology and roughness were examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. X-ray diffraction (XRD) was used to identify the phases and crystallinity of the deposited minerals observed on the enamel surface. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to quantitatively analyze the mineral variation by calculating the relative integrated-area of characteristic bands. Nanohardness and elastic modulus measured by nanoindentation at various treatment stages were utilized to evaluate the degree of recovery. Biomimetic effects were accessed according to the degree of nanohardness recovery and the amount of hydroxyapatite deposition. The charged segments in the 3 NSS peptide greatly attracted aqueous ions from artificial saliva to form hydroxyapatite crystals to fill enamel caries, in particular the interrod areas, resulting in a slight reduction in overall surface roughness. Additionally, the deposited hydroxyapatites were of a small crystalline size in the presence of the 3 NSS peptide, which effectively restrained the plastic deformations and thus resulted in greater improvements in nanohardness and elastic modulus. The degree of nanohardness recovery was 5 times greater for remineralized enamel samples treated with the 3 NSS peptide compared to samples without peptide treatment.

Characterization of the effects of 3DSS peptide on remineralized enamel in artificial saliva.

Aspartate-serine-serine (DSS) repeats are abundant in naturally occurring proteins that are critical for tooth formation. In this study, we reported a possible role of triplet repeats of aspartate-serine-serine (3DSS) peptides in promoting mineral deposition onto human enamel from free ions. Human enamel specimens were acid demineralized, exposed briefly to 3DSS peptide solution, and then immersed in artificial saliva. At various stages of treatments, nanomechanical behaviors, surface morphology, surface roughness and the sorts of deposited minerals were characterized by nanoindentation, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The results indicated that treatment with 3DSS peptide promoted the uniform deposition of apatites with small crystalline size, in terms of prohibiting deformation, which resulted in a smaller average surface roughness and higher average values of nanohardness and elastic modulus of demineralized enamel treated with 33.3 µM 3DSS peptide and immersed in artificial saliva compared to that without peptide treatment.

Influences of ionic concentration on nanomechanical behaviors for remineralized enamel.

This study evaluates the influences of 8DSS peptide and ionic concentrations of simulated body fluid on remineralization behaviors. The polished enamel specimens were acid-demineralized, exposed briefly to 8DSS peptide solution, and then immersed into simulated body fluid (SBF) that favors mineral deposition. At various stages of treatment, nanohardness and elastic modulus were determined by nanoindentation. The results show that the nanomechanical properties of the acid-demineralized enamel were greatly improved as increasing the ionic concentrations of SBF due to the acceleration of mineral deposition. Additionally, the demineralized enamel, treated with 8DSS peptide and immersed into SBF×2 solution, possesses the highest values of nanohardness and elastic modulus resulting from the combinative effects of surface roughness, morphology, microstructure and crystallinity of the newly formed nanocomposite of calcium phosphate carbonate and hydroxyapatite. The formation of pores in the subsurface induced a reduction in the nanomechanical properties for the enamel subjected into SBF×3 solution.

Effects on Hardness and Elastic Modulus for DSS-8 Peptide Treatment on Remineralization of Human Dental Tissues.

Dental remineralization may be achieved by mediating the interactions between tooth surfaces with free ions and biomimetic peptides. We recently developed octuplet repeats of aspartate-serine-serine (DSS-8) peptide, which occurs in high abundance in naturally occurring proteins that are critical for tooth remineralization. In this paper, we evaluated the possible role of DSS-8 in enamel remineralization. Human enamel specimens were demineralized, exposed briefly to DSS-8 solution, and then exposed to concentrated ionic solutions that favor remineralization. Enamel nano-mechanical behaviors, hardness and elastic modulus, at various stages of treatment were determined by nanoindentation. The phase, microstructure and morphology of the resultant surfaces were characterized using the grazing incidence X-ray diffraction (GIXD), variable pressure scanning electron microscopy (VPSEM), and atomic force microscopy (AFM), respectively. Nanoindentation results show that the DSS-8 remineralization effectively improves the mechanical and elastic properties for demineralized enamel.

Synthesis of ultra-incompressible superhard rhenium diboride at ambient pressure.

The quest to create superhard materials rarely strays from the use of high-pressure synthetic methods, which typically require gigapascals of applied pressure. We report that rhenium diboride (ReB2), synthesized in bulk quantities via arc-melting under ambient pressure, rivals materials produced with high-pressure methods. Microindentation measurements on ReB2 indicated an average hardness of 48 gigapascals under an applied load of 0.49 newton, and scratch marks left on a diamond surface confirmed its superhard nature. Its incompressibility along the c axis was equal in magnitude to the linear incompressibility of diamond. In situ high-pressure x-ray diffraction measurements yielded a bulk modulus of 360 gigapascals, and radial diffraction indicated that ReB2 is able to support a remarkably high differential stress. This combination of properties suggests that this material may find applications in cutting when the formation of carbides prevents the use of traditional materials such as diamond.