Covalent organic frameworks are a family of crystalline porous materials with promising applications. Although active research on the design and synthesis of covalent organic frameworks has been ongoing for almost a decade, the mechanisms of formation of covalent organic frameworks crystallites remain poorly understood. Here we report the synthesis of a hollow spherical covalent organic framework with mesoporous walls in a single-step template-free method. A detailed time-dependent study of hollow sphere formation reveals that an inside-out Ostwald ripening process is responsible for the hollow sphere formation. The synthesized covalent organic framework hollow spheres are highly porous (surface area B1,500 m 2 g À 1 ), crystalline and chemically stable, due to the presence of strong intramolecular hydrogen bonding. These mesoporous hollow sphere covalent organic frameworks are used for a trypsin immobilization study, which shows an uptake of 15.5 mmol g À 1 of trypsin.

This study demonstrates fast and efficient removal of dyes from the wastewater using nanostructural MoS 2 as a regenerative adsorbent. The hierarchical microspheres of MoS 2 nanosheets were prepared by one-step facile and scalable hydrothermal route using polyethylene glycol as a templating material. Chemical and morphological features of hierarchical microspheres of MoS 2 nanosheets were examined by XPS, FTIR, XRD, FESEM and HRTEM. The adsorption of a series of organic dyes using MoS 2 nanosheets was systematically investigated. The kinetic study illustrated that adsorption of methylene blue dye on to the MoS 2 nanosheets followed the pseudo second order model. The adsorption isotherm at the equilibrium was supported by Freundlich isotherm model. The hierarchical microspheres of MoS 2 nanosheets showed adsorption capacity as high as 297, 204, 216, 183, 146 mg.g -1 for methylene blue, malachite green, rhodamine 6G, fuchsin acid and congo red dyes, respectively. The high adsorption capacity was attributed to the hierarchical arrangement of MoS 2 nanosheets in the microscopic spheres, where dye molecules have very fast accessibility. Importantly, the hierarchical microspheres of MoS 2 nanosheets can be efficiently regenerated and reused for the dye adsorption of subsequent batch without compromising the adsorption capacity.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.

This study investigated the oxidative stress induced after acute oral treatment with 500, 1000 and 2000 mg kg⁻¹ doses of Al₂O₃ -30 and -40 nm and bulk Al₂O₃ in Wistar rats. Both the nanomaterials induced significant oxidative stress in a dose-dependent manner in comparison to the bulk. There was no significant difference between the two nanomaterials. However, the effect decreased with increase with time after treatment. The histopathological examination showed lesions only in liver with Al₂O₃ nanomaterials at 2000 mg kg⁻¹.

Assemblies of inorganic or glassy particles are typically brittle and cannot sustain even moderate deformations. This restricts the use of such materials to applications where they do not experience significant loading or deformation. Here, we demonstrate a general strategy to create centimeter-size macroporous monoliths, composed primarily (>90 wt %) of colloidal particles, that recover elastically after compression to about one-tenth their original size. We employ ice templating of an aqueous dispersion of particles, polymer, and crosslinker such that cross-linking happens in the frozen state. This method yields elastic composite scaffolds for starting materials ranging from nanoparticles to micron-sized dispersions of inorganics or glassy lattices. The mechanical response of the monoliths is also qualitatively independent of polymer type, molecular weight, and even cross-linking chemistry. Our results suggest that the monolith mechanical properties arise from the formation of a unique hybrid microstructure, generated by cross-linking the polymer during ice templating. Particles that comprise the scaffold walls are connected by a cross-linked polymeric mesh. This microstructure results in soft monoliths, with moduli ∼O (10 4 Pa), despite the very high particle content in their walls. A remarkable consequence of this microstructure is that the monolith mechanical response is entropic in origin: the modulus of these scaffolds increases with temperature over a range of 140 K. We show that interparticle connections formed by cross-linking during ice templating determine the monolith modulus and also allow relative motion between connected particles, resulting in entropic elasticity.

In the near future, nanotechnology is envisaged for large-scale use. Hence health and safety issues of nanoparticles (NPs) should be promptly addressed. Twenty-eight-day oral toxicity, genotoxicity, biochemical alterations, histopathological changes and tissue distribution of nano and microparticles (MPs) of manganese oxide (MnO2 ) in Wistar rats was studied. Genotoxicity was assessed using comet, micronucleus and chromosomal aberration assays. The results demonstrated a significant increase in DNA damage in leukocytes, micronuclei and chromosomal aberrations in bone marrow cells after exposure of MnO2 -NPs at 1000, 300 mg kg(-1) bw per day and MnO2 -MPs at the dose of 1000 mg kg(-1) bw per day. Our findings showed acetylcholinestrase inhibition at 1000 as well as at 300 mg kg(-1) bw per day in blood and with all the doses in the brain indicating the toxicity of MnO2 -NPs. Further, the doses significantly inhibited different ATPases in the brain P2 fraction. Significant changes were observed in aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) in the liver, kidney and serum in a dose-dependent manner. MnO2 -MPs at 1000 mg kg(-1) bw per day were found to induce significant alterations in biochemical enzymes. A significant distribution was found in all the tissues in a dose-dependent manner. MnO2 -NPs showed a much higher absorptivity and tissue distribution as compared with MnO2 -MPs. A large fraction of MnO2 -NPs and MnO2 -MPs was cleared by urine and feces. Histopathological analysis revealed that MnO2 -NPs caused alterations in liver, spleen, kidney and brain. The MnO2 -NPs induced toxicity at lower doses compared with MnO2 -MPs. Further, this study did not display gender differences after exposure to MnO2 -NPs and MnO2 -MPs. Therefore, the results suggested that prolonged exposure to MnO2 has the potential to cause genetic damage, biochemical alterations and histological changes.

Iron oxide (Fe2O3) nanoparticles are widely used in different fields of nanotechnology. However, studies on its toxicological effects in humans and the environment are scarce. Therefore in this investigation 28 days repeated dose oral toxicity studies were conducted on Fe2O3-30 nanoparticles and its counterpart Fe2O3-Bulk with special reference to target biochemical enzymes and histopathological changes in different tissues of female albino Wistar rats. The alterations observed after Fe2O3-30 treatment in various tissues of exposed rats were dose dependent. Low dose was less effective than medium and high doses with low dose demonstrating "no observed adverse effect" (NOAEL). Further, high dose treated rats showed toxic sign and symptoms but no mortality. Due to the repeated doses of Fe2O3-30 nanoparticles, significant inhibition was observed in total, Na(+)-K+, Mg2+ and Ca(2+)-ATPases in brain of exposed rats. Similarly, significant inhibition was recorded in RBC and brain acetylcholinesterase indicating that both synaptic transmission and nerve conduction were affected by this compound. Fe2O3-30 significantly increased aspartate amino transferase, alanine amino transferase and lactate dehydrogenase in serum and liver, whereas, these enzymes were significantly decreased in kidney indicating tissue necrosis and possible leakage of these enzymes into the blood stream. Increased levels of these enzymes in liver as well as in serum might be an adaptive mechanism due to the stress of iron nanoparticles. High dose treated rats of Fe2O3-30 showed dilated central vein, perivascular round cell collections in liver along with focal areas of necrosis, whereas kidney showed focal tubular damage and red pulp congestion, whereas prominent white pulp indices were observed in spleen. However, histopathological analysis of heart and brain tissues failed to show any adverse changes in their architecture exposed to repeated doses of Fe2O3-30 when compared with controls. Fe2O3-Bulk did not induce any adverse effects in either biochemical parameters or histopathology in the treated rats and the changes observed were near to controls and mostly insignificant, indicating that the counter part of nanoparticles i.e., bulk material is less potent than the nanoparticles in causing toxicity in the exposed animals. These results suggested that as particle size decreases, this iron nanoparticle showed increased toxicity, even though the same material is relatively inert in bulk form. The changes observed in these target enzyme activities could be useful as biomarkers of exposure to nanoparticles.

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