Nano

Eco-friendly synthesis of metal nanoparticles has accrued utmost interest by researchers in the last decade for their distinct properties making them applicable in different fields of science and technology. With regard to its low cost, low environmental effect, zero contamination and higher reducing potential, their synthesis by green chemistry procedure is an emerging area in nanobiotechnology. Plant-based nanoparticles produced are more stable, with high rate of synthesis and are suitable for large scale biosynthesis as compared to the use of microorganisms which require stringent control on cell cultures. Plant-based nanoparticles have advantages over other methods due to presence of biomolecules acting both as capping and reducing agents by increasing the rate of reduction and stabilization of nanoparticles. Furthermore, secondary metabolites present in plants are used for reducing metal ions in single step reaction. In this review paper, we have cited 265 research articles and have outlined 106 plant extract assisted gold and silver nanoparticles. The present review highlights the achievements of metal nanoparticle synthesis, especially silver and gold nanoparticles from plant extracts, along with factors liable for the synthesis of metal nanoparticles. It also focuses on the dye degrading properties and various biological activities of metal nanoparticles, their antimicrobial mechanism of action and the physicochemical properties that influence the biological effects of metallic nanoparticles. Biological activities of metal nanoparticles were also described, including the effect of physicochemical properties of metal nanoparticles on biological activities.

Manganese-based oxides are one of the most promising high-performance supercapacitor (SC) electrode materials. In this work, a stable MnO_x nanowires@MnO_x nanosheets core–shell heterostructure electrode material consisting of MnO_x nanosheets grown uniformly on the surface of MnO_x nanowires has been prepared by a simple liquid phase method followed by thermal treatment. The electrode displays a specific capacity of 336 Fg${}^{-1}$ at 1Ag${}^{-1}$ and exhibits a good cycling life of 83% capacitance retention after 5000 cycles. This is mainly due to the synergy effect between the one-dimensional MnO_x nanowires as the backbone structure and the two-dimensional MnO_x nanosheets with large specific surface area provide more active sites and the rapid transmission of electrons.

In recent years, all inorganic bismuth lead-halide perovskite nanocrystals [CsPbX₃ (X$=$Cl, Br, I)] have received extensive attention due to their high performance in fluorescence quantum yield, narrow emission spectrum, and adjustable emission range. However, the disadvantages of high cost and poor stability have greatly limited the development prospects of the material. Here, in order to develop a perovskite quantum dot lasing cavity with high chemical stability, high quality factor and low fabrication cost, we have successfully fabricated a 3D random cavity device based on porous silicon/TiO₂ nanowires. A TiO₂ nanowire is grown on the porous silicon to form a 3D resonant cavity, and a perovskite quantum dot is spin-coated on the surface of the 3D resonant cavity to form a novel 3D complex film. The novel structure enhances the chemical stability and lasing quality factor of the resonant cavity while the fluorescence generated by the large quantum dots in the spatial interference structure constitutes the feedback loop, which will provide favorable support for the development of information optics.

In this study, CuS/SiO₂ composite modified aerogel was prepared by the incorporation of hollow spherical CuS into methyltrimethoxysilane-based SiO₂ sol and modification with hexadecafluorodecyltriethoxysilane via acid-base catalyzed sol–gel reaction and drying under ambient pressure. The CuS/SiO₂ composite modified aerogel was characterized by Fourier-transform infrared (FT-IR) spectrometry, scanning electron microscope (SEM), nitrogen gas adsorption and desorption and X-ray diffraction (XRD), respectively. The effects of CuS and fluorosilane concentration on density and porosity of aerogel, oleophobic and photocatalytic properties were evaluated. The results showed that structure and physical properties of aerogel had some effect by introducing CuS and fluorosilane, and the CuS/SiO₂ composite modified aerogel with density of 0.146g/cm³ and specific surface area of 241m²/g achieved super-oleophobicity with oil contact angle of 152.8^∘ and sliding angle of 10^∘, and good photocatalytic properties for methylene blue.

Oxygen defects of nanoflower TiO₂ photo-catalyst was fabricated at the presence of hydrogen at different temperatures (100–600^∘C) and the concentrations of oxygen defects were firstly quantitatively analyzed by hydrogen programmed temperature reduction techniques (H₂-TPR). Total oxygen defect concentration and surface oxygen defect concentration were consistent with XPS and EPR results, respectively. Even at the hydrogen thermal temperature of 600^∘C, the shape of TiO₂ was still kept as nanoflower structure as characterized by SEM. However, the rutile and anatase coexist in the composition of crystal phase when hydrogen reduction temperature of the TiO₂ catalyst reached 400^∘C to 600^∘C as proved by Raman and XRD results. TiO₂ sample with oxygen defects shows excellent photo-catalytic activity for degradation of Direct Blue 78(DB) regardless of ultraviolet light (the maximum degradation rate achieved within 100min was 93.27%) or visible light (the maximum degradation rate achieved within 100min was 88.25%). The photo-catalytic activity seems to be highly correlated with the surface oxygen defects of TiO₂ catalyst. With surface oxygen-defect concentrations increase, the degradation ability on DB was significantly enhanced, while bulk oxygen defects had negligible effect on the photo-catalytic activity. The enhanced photo-catalytic performance of TiO₂ with a fixed amount of oxygen defects was attributed to the strong capturing capability of the photo-generated electrons. In addition, the surface defects could also improve the photo-catalytic reaction efficiency.

The mesoporous CdS/TiO₂ composites were synthesized by a sol–gel method combined with solvothermal method. The material showed the gel block-like structures which were composed of heterogeneous spherical gel particles, the average size of the particles was about 14nm, with specific surface area as 300.254m²g${}^{-1}$. The mesoporous CdS/TiO₂ composites exhibited a wide absorption band to simulated sunlight whose adsorb wavelength reached to 550nm, its absorption intensity and catalytic performance of photocatalytic water-producing hydrogenation were also increased with the increase of CdS contents. When the molar ratio of TiO₂:CdS was 1:1, the photocatalytic activity reached the highest, and the average hydrogen production rate reached 2167.32$\mu$molg${}^{-1}$h${}^{-1}$.

In this work, Bi${}_{2-x}$Sm_xFe₄O₉ ($x=0.0$, 0.02, 0.06, 0.08, 0.1) nanoplates with an average thickness of 62–125nm were synthesized using a sol–gel method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The magnetic measurements show that the nanoplates have weak ferromagnetic ordering. The saturation magnetization of the nanoplates increases as the Sm content increases. The DC electric transport properties were studied by measuring the temperature dependence of the resistivity in the temperature range 300–680K. The materials show typical semiconductor features, and the conduction mechanisms are governed by electron and small polaron hopping in the low and high temperature measurement ranges, respectively. The Sm doping results in a significant enhancement in the electrical conductivity of the Bi₂Fe₄O₉ nanoplates.

In this work, the Ni–Mn layered double hydroxide (Ni–Mn LDH) nanopetals are fabricated on three-dimensional reduced graphene oxide/Ni foam (RGO/NF) by one-step hydrothermal method, in which the suspension of graphene oxide (GO) is directly reduced by nickel foam (NF) to obtain NF/RGO. The composite, which consists of interconnected Ni–Mn LDH nanopetals, forms a macroporous structure. Such an open space can promote electrolyte dispersion and ion diffusion of active substances, thus enhancing capacitance performance. Remarkable, during crystal growth, RGO can not only provide active sites for Ni–Mn LDH nanopetals, but also effectively connect Ni–Mn LDH nanopetals to NF, further promoting the electrochemical behavior of composite material. Moreover, RGO possess reasonable chemical stability which can improve the mechanical properties of the composite to obtain good stability. The experimental results show that the NF/RGO electrode material with Ni–Mn LDH nanopetals has excellent specific capacitance of 2250Fg${}^{-1}$ at 1Ag${}^{-1}$, good rate performance (the capacitance retention rate is still 64.0% at 10Ag${}^{-1})$ and excellent cycle life (45.1% at 10Ag${}^{-1}$ after 5000 cycles). NR/NM–LDH is used as the positive electrode and activated carbon is used as the negative electrode to assemble the asymmetric supercapacitor, the proper power density and energy density indicates that the NR/NM–LDH composite has great potential as an electrode material for supercapacitors.

Owing to the hazardness, the sensitive and selective detection of cyanide (CN⁻) in water or water-containing systems has still been a puzzle plaguing scientists all around the world. In this paper, a novel fluorescence probe based on covalently functionalized graphene oxide (GO) by aminocoumarin for highly selective detection of CN⁻ in deionized water was prepared under the action of EDC/NHS. This probe bears aminocoumarin group as the recognition site and fluorophore, and its fluorescence quantum yield is increased by 0.07. Simultaneously, by loading on GO, the dispersibility, selectivity and reversibility were soundly improved, which facilitated the detection process. The fluorescence spectra showed that the probe has high selectivity and sensitivity for cyanide, and has potential application in real water.

In this paper, we prepared KMnF₃:Yb${}^{3+}$, Er${}^{3+}$ nanoparticles (NPs)/polymethyl methacrylate (PMMA) composites, NaYF₄:Yb${}^{3+}$, Tm${}^{3+}$NPs/PMMA composites and NaYF₄Yb${}^{3+}$, Er${}^{3+}$NPs/PMMA composites by in situ polymerization, and these NPs/PMMA composites can emit red, blue and green up-conversion fluorescence excited by 980nm, respectively. The mixed white NPs/PMMA composites were obtained by adjusting the doping ratio of the above three NPs. These NPs/PMMA composites are transparent. We tested the up-conversion fluorescence spectra of all the NPs and NPs/PMMA composites, under 980nm excitation. The up-conversion luminescence spectra of the NPs and NPs/PMMA composites are consistent, which further indicates that the in situ polymerization has not changed the chemical structure of the NPs. Then, we prepared transparent bulk polymers by curing these NPs/PMMA composites. Under 980nm laser excitation, these NPs/PMMA bulk polymers can emit red, blue, green and white up-conversion emissions, respectively. The results indicate that the NPs/PMMA composites can be applied to three-dimensional (3D) display.

Highly efficient, cost-effective and durable electrocatalysts for water splitting are crucial for energy conversion and storage. Transition-metal phosphides have been proven to be efficient catalysts for water splitting. In this paper, surface phosphation of 3D NiCo₂O₄ nanowires grown on Ni foam (P-NiCo₂O₄/NF) have been prepared to investigate the effect of surface phosphating on catalyst activity. XRD and XPS results demonstrate that P element has been decorated on the surface of the NiCo₂O₄ nanowires. The electrochemical results prove that P-NiCo₂O₄/NF shows better electrochemical performance than pure NiCo₂O₄/NF as an electrode for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of water splitting. It achieves a current density of 10mA cm² at an overpotential of 279mV and 164mV for OER and HER in 1.0M KOH electrolyte, respectively. In addition, the P-NiCo₂O₄/NF$\parallel$P-NiCo₂O₄/NF electrode is constructed by employing P-NiCo₂O₄/NF as both the anode and cathode, it only requires a low 1.68V of cell voltage to reach the current density of 10mA cm${}^{-2}$. Notably, P-NiCo₂O₄/NF$\parallel$P-NiCo₂O₄/NF also exhibits excellent stability for over 30h-long. These results indicate that surface phosphation is an effective approach to improve the electrochemical performance of NiCo₂O₄/NF electrode materials.

A fluorescence probe has been synthesized for the detection of osthole using the nitrogen-doped carbon dots (NCDs) as shown in Fig. 1. The NCDs were fully characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, the NCDs fluorescence probe was highly selective and sensitive to osthole. The linear response range for osthole was 5.0–75$\mu$M with a detection limit of 38nM. The mechanism of the interaction of osthole and NCDs was discussed. The fluorescence probe has been applied to the analysis of biological samples. The as-synthesized NCDs with high fluorescence intensity, low toxicity and good biocompatibility were applied to cell imaging.

A hierarchical mesoporous ZSM-5 catalyst with aggregated nanocrystals structure was one-pot hydrothermally synthesized by using urea as the additive. The crystalline phase, morphology and hierarchical architectures were characterized by the XRD, SEM, TEM and N₂ adsorption/desorption analyses. The nano-aggregates showed MFI crystalline phase and were composed of connected nanoparticles. The samples had the high surface area and the pore volume from intercrystalline among the nanoparticles due to spontaneously stacking of nanocrystals. The pyridine-adsorbed FTIR and the catalytic performances in the alkylation of phenol and tert-butyl alcohol were applied to evaluate the accessibility of acid sites and the catalytic activities for the hierarchical mesoporous ZSM-5 samples. The samples possessed high accessibility of acid sites which resulted from their large amount of mesopores, and its catalytic activity was improved dramatically. The phenol conversion could reach up to 95.6%, and the corresponding selectivity of 4-TBP and 2,4-DTBP was 44% and 51.5%, respectively.

Graphene, a single layer of two-dimensional carbon material, has attracted much attention due to its excellent comprehensive properties including high mechanical strength, antibacterial property, excellent thermal and electrical conductivities, high specific surface area, impermeability, etc. In this study, 3-epoxypropyl-5,5-dimethylhydantoin (GH), as a precursor of $N$-halamine, was synthesized and attached onto graphene oxide (GO) for enhanced antibacterial activity. The synthesized GO–GH was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). After chlorination treatment by household bleach solution, the chlorinated graphene oxide-3-epoxypropyl-5,5-dimethylhydantoin (GO–GH–Cl) possessed great antibacterial efficacy. The synthesized GO–GH–Cl was added to chitosan (CS) solution to produce GO–GH–Cl/CS hybrid films via a solution casting method. The as-prepared antimicrobial hybrid films showed excellent antibacterial activity and could kill 100% of S. aureus and 100% of E. coli O157:H7 within 10min and 30min of contact time, respectively.