•Dispersions of graphene oxide in pore solution and cement paste was studied.•Mechanism of GO aggregation in cement paste is cross-linking of calcium cations.•Silica fume is effective to improve GO ...dispersion in cement paste.•Appropriate amount of silica fume improves GO dispersion and compressive strength.
As a 2D nanomaterial, graphene oxide (GO) has attracted considerable attentions for reinforcing cementitious materials. However, special attention must be paid to the dispersion of GO in the matrix, as the quality of nanomaterial dispersion correlates directly with its effectiveness for improving mechanical and other properties. In this study, the dispersion of graphene oxide (GO) in simulated pore solution and cement paste was investigated. It was found that severe GO aggregation occurred in presence of divalent calcium ions in both pore solution and cement paste. However, the GO aggregates were not stable under shear mixing. After vigorous mixing, the massive GO aggregates split into medium-sized particles, ranging from few to several 100μm. To improve the GO dispersion in cement paste, silica fume was used to mechanically separate individual GO nanosheets. The dispersion was then investigated using microstructure analysis and mechanical properties. The results showed that, with the addition of silica fume, the dispersion of GO nanosheets was greatly improved.
Motivated by recent experimental developments of graphitic-CN (g-CN) sheets, we investigate the suitability of hydrogen storage on Li decorated g-CN
via
first-principles calculations. We find that ...the binding energies of Li atoms are very large, ranging from 2.70 to 4.73 eV, which are significantly higher than the cohesive energy of bulk Li. Lithium atoms therefore tend to form 2D rather than 3D patterns on g-CN, promoting reversible hydrogen adsorption and desorption. Remarkably, the average adsorption energy of H
2
molecules falls in the 0.14-0.23 eV range, and the Li decorated CN shows a high theoretical gravimetric density of 10.81 wt%, which is favorable for massive hydrogen storage. Our results suggest that the Li decorated CN could be a promising hydrogen storage material under realistic conditions.
Motivated by recent experimental developments of graphitic-CN (g-CN) sheets, we investigate the suitability of hydrogen storage on Li decorated g-CN
via
first-principles calculations.
•Summarizing the latest literature on CNTs and GO reinforced cement composites.•Cement fabrication focuses on separating and avoiding re-agglomeration of nanomaterials.•Preserving the workability of ...nanocomposites is accomplished by using admixtures.•The seeding of C–S–H gel occurs on the large surface area of nanomaterials.•Reinforcement and pore refinement by 1D and 2D nanomaterials strengthen cement.
Progress in the field of nanomaterials presents an invaluable opportunity to develop cementitious composites at the nanoscale. Engineered nanomaterials exist in three principal shapes, namely 0D nanoparticle, 1D nanofiber and 2D nanosheet. The application of 0D nanoparticle and 1D nanofiber, such as nanosilica and carbon nanotubes (CNTs), respectively, has been reported in literature. The discovery of 2D nanosheet known as graphene oxide (GO) provides an extra dimension to interact with cement and concrete matrix and has yet to gain widespread attention. In this paper, recent research studies in developing cement and concrete nanocomposites are comprehensively reviewed. Also highlighted herein are the effect of incorporating nanomaterials in low dosages to the fabrication, workability, hydration, microstructure, and mechanical properties of cement-based composites.
•Surface modification methods were developed for preventing PCM leakage.•Granular PCM composites were compared with microencapsulated PCMs.•Absorption mechanisms were proposed for expanded perlite ...and paraffin.
In this study, granular phase change material (PCM) composites were developed by absorbing paraffin into the pores of expanded perlite particles with two grades of particle size. Because of the different particle sizes and pore structures, the absorption mechanisms of the expanded perlite particles were found to differ. A significant amount of paraffin leakage was found when the PCM composites were applied directly into the cement mixture. To prevent such leakage, a new method by using hydrophobic silane was investigated as surface modification for the PCM composites. The method was then compared with nanosilica deposition method. Although both methods prevented leakage effectively, cement composites incorporating silane-modified PCM composites had lower compressive strength than those incorporating nanosilica modified PCM composites. Thermal performances of expanded perlite/paraffin composites were compared with that of microencapsulated PCM and the results showed expanded perlite/paraffin composites were superior under certain conditions.
Recently, there have been intense efforts in searching for new topological insulator materials. Based on first-principles calculations, we find that all the ultrathin Bi (111) films are characterized ...by a nontrivial Z(2) number independent of the film thickness, without the odd-even oscillation of topological triviality as commonly perceived. The stable nontrivial Z(2) topology is retained by the concurrent band gap inversions at multiple time-reversal-invariant k points with the increasing film thickness and associated with the intermediate interbilayer coupling of the Bi film. Our calculations further indicate that the presence of metallic surface states in thick Bi (111) films can be effectively removed by surface adsorption.
Carbon nanotubes (CNTs) are attractive candidates as nanofillers in reinforcing ordinary Portland cement (OPC) due to their superior mechanical properties. In this study, the engineering properties ...of CNT–OPC pastes were investigated with varied ultrasonication energy (UE) and CNT concentration. It was found that UE could effectively improve the aqueous dispersion of surface functionalized CNTs with the aid of a polycarboxylate-based cement admixture (PC). A PC to CNTs mass ratio of 8 is recommended for ensuring effective dispersion of CNTs and maintaining workability of CNT–OPC pastes under sufficient ultrasonication. Furthermore, the mechanical property results of the hardened pastes obtained from pre-notched beam tests revealed the existence of an optimal UE for achieving mechanically superior CNT–OPC pastes, which was found to be 50J/mL per unit CNTs to suspensions weight ratio. The Young’s modulus E, flexural strength σf, and fracture energy GF of CNT–OPC pastes were significantly improved compared to plain OPC pastes. These results clearly demonstrate the reinforcing effect of CNTs on cement pastes because they decrease the porosity and increase crack bridging capacity of cement pastes at nanoscale level, which will be complementary to conventional microfibers in reinforcing OPC pastes.
AbstractIn this experimental study, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated. It is discovered that the introduction of 0.03% by weight GO sheets into ...the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40% due to the reduction of the pore structure of the cement paste. Moreover, the inclusion of the GO sheets enhances the degree of hydration of the cement paste. However, the workability of the GO-cement composite becomes somewhat reduced. The overall results indicate that GO could be a promising nanofillers for reinforcing the engineering properties of portland cement paste.
Many MXenes are efficient catalysts for MgH
2
hydrogen storage material. Nevertheless, the synthesis of MXenes should consume a large amount of corrosive HF to etch out the Al layers from the ...transition metal aluminum carbides or nitrides (MAX) phases, which is environmentally unfriendly. In this work, Ti
3
AlCN MAX without HF-etching was employed directly to observably enhance the kinetics and the cycling stability of MgH
2
. With addition of 10 wt% Ti
3
AlCN, the onset dehydrogenation temperature of MgH
2
was dropped from 320 to 205 °C, and the rehydrogenation of MgH
2
under 6 MPa H
2
began at as low as 50 °C. Furthermore, at 300 °C, it could provide 6.2 wt% of hydrogen in 10 min. Upon cycling, the composite underwent an activation process during the initial 40 cycles, with the reversible capacity increased from 4.7 wt% to 6.5 wt%. After that, the capacity showed almost no attenuation for up to 100 cycles. The enhancing effect of Ti
3
AlCN on MgH
2
was comparable to many MXenes. It was demonstrated that Ti
3
AlCN did not destabilize MgH
2
but acted as an efficient catalyst for MgH
2
. Ti
3
AlCN was observed to be the active sites for the nucleation and growth of MgH
2
and might also help in dissociation and recombination of hydrogen molecules. Such two factors are believed to contribute to the improvement of MgH
2
. This study not only provides a promising strategy for improving the hydrogen storage performances of MgH
2
by using noncorrosive MAX materials, but also adds evidence of nucleation and growth of MgH
2
on a catalyst.
Graphical abstract
MR (mineralocorticoid receptor) antagonists are recommended for patients with resistant hypertension even when circulating aldosterone levels are not high. Although aldosterone activates MR to ...increase epithelial sodium channel (ENaC) activity, glucocorticoids also activate MR but are metabolized by 11βHSD2 (11β-hydroxysteroid dehydrogenase type 2). 11βHSD2 is expressed at increasing levels from distal convoluted tubule (DCT) through collecting duct. Here, we hypothesized that MR maintains ENaC activity in the DCT2 and early connecting tubule in the absence of aldosterone.
We studied AS (aldosterone synthase)-deficient (AS
) mice, which were backcrossed onto the same C57BL6/J strain as kidney-specific MR knockout (KS-MR
) mice. KS-MR
mice were used to compare MR expression and ENaC localization and cleavage with AS
mice.
MR was highly expressed along DCT2 through the cortical collecting duct (CCD), whereas no 11βHSD2 expression was observed along DCT2. MR signal and apical ENaC localization were clearly reduced along both DCT2 and CCD in KS-MR
mice but were fully preserved along DCT2 and were partially reduced along CCD in AS
mice. Apical ENaC localization and ENaC currents were fully preserved along DCT2 in AS
mice and were not increased along CCD after low salt. AS
mice exhibited transient Na
wasting under low-salt diet, but administration of the MR antagonist eplerenone to AS
mice led to hyperkalemia and decreased body weight with higher Na
excretion, mimicking the phenotype of MR
mice.
Our results provide evidence that MR is activated in the absence of aldosterone along DCT2 and partially CCD, suggesting glucocorticoid binding to MR preserves sodium homeostasis along DCT2 in AS
mice.
Calcineurin, protein phosphatase 2B (PP2B) or protein phosphatase 3 (PP3), is a calcium‐dependent serine/threonine protein phosphatase. Calcineurin is widely expressed in the kidney and regulates ...renal Na+ and K+ transport. In the thick ascending limb, calcineurin plays a role in inhibiting NKCC2 function by promoting the dephosphorylation of the cotransporter and an intracellular sorting receptor, called sorting‐related‐receptor‐with‐A‐type repeats (SORLA), is involved in modulating the effect of calcineurin on NKCC2. Calcineurin also participates in regulating thiazide‐sensitive NaCl‐cotransporter (NCC) in the distal convoluted tubule. The mechanisms by which calcineurin regulates NCC include directly dephosphorylation of NCC, regulating Kelch‐like‐3/CUL3 E3 ubiquitin–ligase complex, which is responsible for WNK (with‐no‐lysin‐kinases) ubiquitination, and inhibiting Kir4.1/Kir5.1, which determines NCC expression/activity. Finally, calcineurin is also involved in regulating ROMK (Kir1.1) channels in the cortical collecting duct and Cyp11 2 expression in adrenal zona glomerulosa. In summary, calcineurin is involved in the regulation of NKCC2, NCC, and inwardly rectifying K+ channels in the kidney, and it also plays a role in modulating aldosterone synthesis in adrenal gland, which regulates epithelial‐Na+‐channel expression/activity. Thus, application of calcineurin inhibitors (CNIs) is expected to abrupt calcineurin‐mediated regulation of transepithelial Na+ and K+ transport in the kidney. Consequently, CNIs cause hypertension, compromise renal K+ excretion, and induce hyperkalemia.
PDF
