Efficient Exfoliation of Layered Double Hydroxides; Effect of Cationic Ratio,Hydration State,Anions and Their Orientations

The exfoliation ability of nitrate based Mg_1−xAl_x(OH)₂(NO₃)_x·mH₂O layered double hydroxides (Mg-Al LDH) in formamide into single or multilayer nanosheets depends strongly on nitrate anion orientation and layer charge. Our systematic studies used materials that were likely to disclose differences with respect to anion type and their concentrations in the interlayer gallery. We assured to avoid any carbonate incorporation into the galleries for nitrate, chloride, iodide, and sulfate based Mg-Al LDHs. Furthermore, the comparative exfoliation experiments were conducted for fully hydrated samples with as similar particle morphology as possible. The exfoliation of nitrate Mg-Al LDH is far superior to similar clays with carbonate, sulfate, chloride, or iodide as charge balancing anions. Quantitative analysis of exfoliation yield for pre-treated, fully hydrated samples, shows an optimum composition for exfoliation into single nanosheets of around x ≈ 0.25, while double or triple layered sheets are encountered for other x-values. We observe a clear correlation between the expansion of the interlayer gallery due to progressing tilts of nitrate anions and water molecules out of the horizontal interlayer plane, suspension turbidity, and degree of exfoliation. The established correlations extends to nitrate Ni-Al LDH materials. We finally claim that morphology is a dominating parameter, with house-of-card morphology particles exfoliation far less than platelet-like particles. Hence, hydrothermal treatment may be favorable to enhance exfoliation yields.     

聚苯乙烯共价修饰的二硫化钼钠米片宽带光限幅功能材料的合成与表征

利用原位聚合方法将聚苯乙烯（PS）共价接枝到二硫化钼纳米片表面,获得的材料MoS₂-PS能均匀地分散在常见的有机溶剂中。开孔Z-扫描实验结果表明：与MoS₂、MoS₂/PS相比,MoS₂-PS的N,N-二甲基甲酰胺（DMF）溶液及其聚甲基丙烯酸甲酯（PMMA）薄膜样品均表现出更好的非线性光学性能。相对于溶液,在532 nm和1 064 nm激光激发时,MoS₂-PS/PMMA固体薄膜表现出最大的非线性吸收系数（β_eff）,分别达到407.70 cm/GW（MoS₂-PMMA：100.69 cm/GW;MoS₂/PS/PMMA：116.55 cm/GW）和429.64 cm/GW（MoS₂-PMMA：-48.92 cm/GW;MoS₂/PS/PMMA：66.31 cm/GW）;相应的光限幅阈值分别为0.92 GW/cm²（532 nm）和1.12 GW/cm²（1 064 nm）。MoS₂-PS/PMMA固体薄膜经200℃退火处理后,β_eff和光限幅性能得到增强（β_eff分别为455.67 cm/GW和448.90 cm/GW;光限幅阈值分别为1.07 GW/cm²和0.87 GW/cm²）。     

Long-term toxicity of reduced graphene oxide nanosheets: Effects on female mouse reproductive ability and offspring development

Reduced graphene oxide (rGO) nanosheets have emerged as novel materials for cancer therapeutics. Their toxicity has attracted much attention since these nanomaterials may have great potential for clinical cancer treatment. Here we report the influence of rGO exposure on female mouse reproductive ability and offspring development. Mouse dams were injected with small or large rGO nanosheets at different doses and time points, pre- or post-fertilization. The sex hormone levels of adult female mice did not significantly change compared with the control group after intravenous injection with either small or large rGO, even at a high dose (25 mg/kg). Mouse dams could produce healthy offspring after treatment with rGO nanosheets before pregnancy and at an early gestational stage (∼6 days). Despite the successful delivery of offspring, malformed fetuses were found among rGO-injected dam litters. All mice had abortions when injected with low (6.25 mg/kg) or intermediate (12.5 mg/kg) doses at a late gestational stage (∼20 days); the majority of pregnant mice died when injected with the high dose of rGO at this stage of pregnancy. Interestingly, all surviving rGO-injected mouse mothers gave birth to another litter of healthy pups. The results presented in this work are important for a deeper understanding of the toxicity of rGO nanosheets on female reproductivity and their offspring development.     

水性聚氨酯-石墨烯纳米复合材料的等温结晶动力学

通过溶液共混法制备了水性聚氨酯-石墨烯(WPU-FGNs)纳米复合材料。采用差示扫描量热仪(DSC)研究其等温结晶过程,运用Avrami方程和Arrhenius方程对WPU-FGNs纳米复合材料的等温结晶动力学进行分析。结果表明:WPU-FGNs纳米复合材料的等温结晶过程基本符合Avrami模型;随着结晶温度的提高,复合材料半结晶时间(t_1/2)和绝对结晶度均增加。当结晶温度为287 K时,FGNs的质量分数从0.1%提高到1.0%,复合材料的结晶焓(ΔH)从-16.88 J/g增加至-35.38 J/g,WPU的结晶活化能为-0.74 kJ/mol;当FGNs的质量分数为0.1%时,复合材料的结晶活化能为-1.25 kJ/mol;当FGNs的质量分数为1.0%时,复合材料的结晶活化能为-0.83 kJ/mol。     

Flexible Supercapacitors Based on Graphene/Boron Nitride Nanosheets Electrodes and PVA/PEIGel Electrolytes

All-solid-state supercapacitors have gained increasing attention as wearable energy storage devices, partially due to their flexible, safe, and lightweight natures. However, their electrochemical performances are largely hampered by the low flexibility and durability of current polyvinyl alcohol (PVA) based electrolytes. Herein, a novel polyvinyl alcohol-polyethyleneimine (PVA-PEI) based, conductive and elastic hydrogel was devised as an all-in-one electrolyte platform for wearable supercapacitor (WSC). For proof-of-concept, we assembled all-solid-state supercapacitors based on boron nitride nanosheets (BNNS) intercalated graphene electrodes and PVA-PEI based gel electrolyte. Furthermore, by varying the electrolyte ions, we observed synergistic effects between the hydrogel and the electrode materials when KOH was used as electrolyte ions, as the Graphene/BNNS@PVA-PEI-KOH WSCs exhibited a significantly improved areal capacitance of 0.35 F/cm² and a smaller ESR of 6.02 ohm/cm². Moreover, due to the high flexibility and durability of the PVA-PEI hydrogel electrolyte, the developed WSCs behave excellent flexibility and cycling stability under different bending states and after 5000 cycles. Therefore, the conductive, yet elastic, PVA-PEI hydrogel represents an attractive electrolyte platform for WSC, and the Graphene/BNNS@PVA-PEI-KOH WSCs shows broad potentials in powering wearable electronic devices.     

Ultrasonically Processed WSe2 Nanosheets Blended Bulk Heterojunction Active Layer for High-Performance Polymer Solar Cells and X-ray Detectors

Two-dimensional (2D) tungsten diselenide (WSe₂) has attracted considerable attention in the field of photovoltaic devices owing to its excellent structure and photoelectric properties, such as ordered 2D network structure, high electrical conductivity, and high mobility. For this test, we firstly prepared different sizes (NS1–NS3) of WSe₂ nanosheets (NSs) through the ultrasonication method and characterized their structures using the field emission scanning electron microscope (FE-SEM), Raman spectroscopy, and X-ray powder diffraction. Moreover, we investigated the photovoltaic performance of polymer solar cells based on 5,7-Bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione(PBDB-T):(6,6)-phenyl-C71 butyric acid methyl ester (PCBM) with different WSe₂ NSs as the active layer. The fabricated PBDB-T:PCBM active layer with the addition of NS2 WSe₂ NSs (1.5 wt%) exhibited an improved power conversion efficiency (PCE) of 9.2%, which is higher than the pure and NS1 and NS3 WSe₂ blended active layer-encompassing devices. The improved PCE is attributed to the synergic enhancement of exciton dissociation and an improvement in the charge mobility through the modified active layer for polymer solar cells. Furthermore, the highest sensitivity of 2.97 mA/Gy·cm² was achieved for the NS2 WSe₂ NSs blended active layer detected by X-ray exposure over the pure polymer, and with the NS1 and NS2 WSe₂ blended active layer. These results led to the use of transition metal dichalcogenide materials in polymer solar cells and X-ray detectors.     

Distinct Mechanical Properties of Polymer/Polymer‐Grafting‐Graphene Nanocomposites

A nonequilibrium deformation technique based on the dissipative particle dynamics is employed to investigate the mechanical properties of polymer nanocomposites reinforced by graphene‐based nanosheets. Hierarchically packed network structure, (small‐length‐scale 2D network structure of graphene nanosheets)‐in‐(large‐length‐scale 3D network structure of homogeneously dispersed graphene nanosheets), is observed, which plays an important role in governing the mechanical properties of polymer nanocomposites. The improvements in tensional modulus over near polymer bulk (n‐P) are about 23% and 61% for polymer/pristine‐graphene blends (P/n‐Gr) and polymer/polymer‐grafting‐graphene nanocomposites (P/g‐Gr), respectively. In addition to higher tensile strength, the P/g‐Gr also exhibit higher tensile strength and yield strength. The strain hardening behaviors at larger deformation are discovered in the polymer/polymer‐grafting‐graphene nanocomposites when the polymer length is relatively larger, which does not appear in n‐P and P/n‐Gr. It is further found that the strain hardening behaviors mainly benefit from the stretching behaviors of the polymers grafting to graphene nanosheets. The results reveal the principles of diverse mechanical properties for polymer nanocomposites reinforced by graphene‐based nanosheets and may provide useful information for preparing polymer nanocomposites with excellent performance.     

Boron nitride nanosheets modified with zinc oxide nanoparticles as novel fillers of dental resin composite

ObjectiveThe purpose of this study was to synthesize boron nitride nanosheets modified with zinc oxide nanoparticles (BNNSs/ZnO) and incorporate them as a novel inorganic filler to get an antibacterial dental resin composite.MethodsThe BNNSs/ZnO nanocomposites were synthesized via the hydrothermal method and characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectrometer (EDS), X-ray Diffraction (XRD) and Fourier Transform-Infrared (FTIR) Spectroscopy. The BNNSs/ZnO or BNNSs were added into the experimental dental composite with different proportions, respectively. The mechanical and physical properties of the modified dental composite were evaluated. Their antibacterial activities were also assessed by quantitative analysis using Streptococcus mutans (S. mutans).ResultsThe BNNSs/ZnO nanocomposites were successfully synthesized, and the growth of ZnO nanoparticles (ZnO NPs) on boron nitride nanosheets was confirmed. The flexural strength (FS), flexural modulus (FM) and the compressive strength (CS) of all modified resin composites showed no change compared to the control group. The curing depth, degree of conversion, water absorption and solubility of the modified composites were still within the clinical requirement. The antibacterial rates of the modified composites were significantly increased compared to the control group, which can reach 98 % when 0.5 % BNNSs/ZnO was added.SignificanceThe modified dental resin composite with novel BNNSs or BNNSs/ZnO fillers shows significantly high antibacterial activity with suitable physicochemical and mechanical properties.     

Graphene Oxide-Induced Protein Conformational Change in Nasopharyngeal Carcinoma Cells: A Joint Research on Cytotoxicity and Photon Therapy

The objectives of this work aim to investigate the interaction and cytotoxicity between nanometric graphene oxide (GO) and nasopharyngeal carcinoma cells (NPC-BM1), and possible application in photon therapy. GO nanosheets were obtained in the size range of 100–200 nm, with a negative surface charge. This nanometric GO exhibited a limited (<10%) cytotoxicity effect and no significant dimensional change on NPC-BM1 cells in the tested GO concentration range (0.1–10 µg·mL⁻¹). However, the secondary protein structure was modified in the GO-treated NPC-BM1 cells, as determined through synchrotron radiation-based Fourier transform infrared microspectroscopy (SR-FTIRM) mapping. To further study the cellular response of GO-treated NPC-BM1 cancer cells at low GO concentration (0.1 µg·mL⁻¹), photon radiation was applied with increasing doses, ranging from 2 to 8 Gy. The low radiation energy (<5 Gy) did not cause significant cell mortality (5–7%). Increasing the radiation energy to 6–8 Gy accelerated cell apoptosis rate, especially in the GO-treated NPC-BM1 cells (27%). This necrosis may be due to GO-induced conformational changes in protein and DNA/RNA, resulting in cell vulnerability under photon radiation. The findings of the present work demonstrate the potential biological applicability of nanometric GO in different areas, such as targeted drug delivery, cellular imaging, and radiotherapy, etc.     

Balancing Strength and Ductility in Al Matrix Composites Reinforced by Few-Layered MoS2 through In-Situ Formation of Interfacial Al12Mo

In this work, few-layered MoS₂ (FLM) nanosheet-reinforced Al matrix composites are developed through powder metallurgy and hot extrusion. The microstructure, mechanical properties, and strengthening mechanisms have been systematically investigated. It is found that Al₁₂Mo and Al₂S₃ can be formed in-situ during the sintering process, resulting in the improvement of interfacial bonding between FLM and Al matrix. With 1.5 wt.% of FLM addition, an improved tensile strength of 234 MPa with a high elongation of 17% can be obtained. Moreover, the strengthening mechanisms are also demonstrated to be grain refinement, dislocation strengthening, and load transfer, and the calculation indicates that load transfer is the main contribution factor. This work will inspire more new designs of metal matrix composites with balanced strength and ductility.