- [Show abstract] [Hide abstract] ABSTRACT: In this paper, a facile process was developed for anchoring of silver nanoparticles on graphitic carbon nitride sheets (Ag/g-C3N4) with high catalytic activity for reduction of 4-nitrophenol. The morphology and structure of the as-prepared Ag/g-C3N4 composite were investigated by FESEM, TEM, XRD and XPS. The reaction mechanism and the reduction kinetics of 4-nitrophenol under different light irradiation were systematically studied. The results showed that the obtained Ag/g-C3N4 composite exhibited a much higher electro/photo catalytic activity and stability for reduction of 4-nitrophenol. Significantly, due to the synergistic effect and interaction between highly dispersed Ag nanoparticles (Ag NPs, ∼7.2 nm) and lamellar g-C3N4, not only transfer of interfacial charge, but also the separation of photoinduced electrons occurred when the reaction was proceeded under light. In addition, the composite exhibited high stability and reusability during the cycling experiments. The results showed that the Ag/g-C3N4 composite is an effective and stable electro/photo catalyst for reduction of 4-nitrophenol.
- [Show abstract] [Hide abstract] ABSTRACT: Bacterial inactivation by magnetic photocatalysts has now received growing interests due to the easy separation for recycle and reuse of photocatalysts. In this study, magnetic Fe@ZnO0.6S0.4 photocatalyst was prepared by a facile two-step precipitation method. Multiple techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffused reflectance spectra (UV-vis DRS) and vibrating sample magnetometer (VSM) were employed to characterize the structure, morphology and physicochemical properties of the photocatalyst. The as-obtained Fe@ZnO0.6S0.4 possessing magnetic property was easily collected from the reaction system by a magnet. Under white light-emitting-diode (LED) lamp irradiation, Fe@ZnO0.6S0.4 nanocomposite could completely inactivate 7-log of Escherichia coli K-12 within 5 h. More importantly, almost no decrease of photocatalytic efficiency in bacterial inactivation was observed even after five consecutive cycles, demonstrating Fe@ZnO0.6S0.4 exhibited good stability for reuse. The low released rate of Fe²⁺/Fe³⁺ and Zn²⁺ from Fe@ZnO0.6S0.4 composite further indicated the photocatalyst showed low cytotoxicity to bacterium and high stability under LED lamp irradiation. Facile preparation, high photocatalytic efficiency, good stability and reusability, and magnetic recovery property endow Fe@ZnO0.6S0.4 nanocomposite to be a promising photocatalytic material for bacterial inactivation.
- [Show abstract] [Hide abstract] ABSTRACT: In this study, highly active MgO nanoparticles synthesized via sol–gel and calcination processes were used for the simultaneous bacterial disinfection and heavy metal ions removal from aqueous solution. Compared with commercial MgO, the synthesized MgO nanoparticles exhibited high efficiencies for both Escherichia coli (E. coli) inactivation and heavy metal ions (Cd²⁺ and Pb²⁺) removal. Surprisingly, the bacterial inactivation activity of MgO nanoparticles was improved in the presence of Cd²⁺ in the system. Partition experiments for bacterial inactivation, reactive oxygen species (ROS) detection and characterizations of the products adsorbed on MgO were used to further investigate the antibacterial mechanism of MgO nanoparticles in the absence and presence of Cd²⁺. It can be concluded that ROS production and the direct interaction between MgO and E. coli are mainly two factors for bacterial inactivation of MgO nanoparticles, which are prone to attack the cell membrane. When the cell membrane was damaged, heavy metal ions entered easily into bacterial cell and thus accelerated bacterial inactivation. The results in this study indicated that nanosized MgO could be a promising candidate for the treatment of wastewater contaminated by bacteria and heavy metals, due to its facile preparation, low cost, environmentally friendly characteristic and high removal efficiencies.
- [Show abstract] [Hide abstract] ABSTRACT: Herein, Ag-doped magnesium oxide (MgO) nanoparticles were prepared by a citric acid-assist sol-gel method. It is evidenced that the size of MgO particles decreases after Ag doping and a small amount of Ag is doped into MgO crystal. The bacterial inactivation of as-prepared Ag-doped MgO against Escherichia coli (E. coli) suggests that Ag doping can greatly enhance the antibacterial activity of MgO nanoparticles and 1% Ag-doped MgO inactivates effectively 7-log bacterial cells within 20 min. The releases of metal ions (Ag⁺ and Mg²⁺) from Ag-doped MgO are at a very low level, which would not play the leading role in bacterial inactivation. The mechanism for the improvement of antibacterial activity of Ag-doped MgO was concluded as three aspects. Firstly, Ag doping would inhibit the grain growth of MgO nanoparticles, resulting in smaller size of MgO particles. Secondly, when Ag⁺ is doped into MgO matrix, more oxygen vacancies will be generated to keep an overall neutral charge. Thirdly, Ag doped MgO has a relatively low electron-transfer resistance, which can accelerate the electron transfer within MgO crystal, in favour of the single-electron reduction of adsorbed oxygen. All these would substantially enhance ROS production and the contact interaction between bacterial cells and nanoparticles. Therefore, Ag doping can markedly promote the antibacterial activity of MgO nanoparticles.
- [Show abstract] [Hide abstract] ABSTRACT: Ag-MgO nanocomposite, synthesized by loading small-sized Ag nanoparticles on the surface of MgO nanoparticles, was firstly used as an effective antibacterial agent against Escherichia coli. The microstructure, morphology and composition of the nanocomposite were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray (EDX) analyzer, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and flame atomic emission spectroscopy (FAES) measurements. An interfacial interaction between Ag and MgO was confirmed by XRD and XPS analyses, which could effectively inhibit the release of silver ions (Ag+) from the nanocomposite. Antibacterial tests showed that the as-prepared Ag-MgO nanocomposite exhibited stronger antibacterial activity against E. coli, compared to pure MgO and equivalent Ag nanoparticles alone, indicating a synergistic effect between Ag and MgO. Based on the results of reactive oxygen species (ROS) detection, the enhanced antibacterial activity of Ag-MgO nanocomposite was attributed to the promotion of ROS production, because Ag particles on the surface of MgO are in favor of electron transfer, which could enhance ROS production via one-electron reduction of oxygen. Taking into consideration easy preparation, low cost, low release rate of Ag+, and high antibacterial activity of Ag-MgO nanocomposite, it is a very promising candidate material for bacterial disinfection.
- [Show abstract] [Hide abstract] ABSTRACT: A facile and environmentally friendly route was developed to synthesize silica supported silver nanoparticles (Ag NPs) through the reduction of silver ions in basic ethanol solution without adding any other reducing agents or surfactants at room temperature. The structure, morphology and composition of as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that the molar ratio of sodium hydroxide to silver nitrate was a decisive factor for the composition of final products. If the molar ratio was large than 1.1, the final product was pure silver particles; otherwise, part of the products was silver oxide. Moreover, it was also found that water had negative influence on the formation of silver particles. For the super simple experimental process, this is an efficient and facile method to synthesize silica supported Ag NPs in ethanol at room temperature. Additionally, since the as-prepared Ag NPs were not encapsulated with surface modifier, the Ag NPs with more active atoms exposed consequently exhibited excellent antibacterial activity against Escherichia coli.
- [Show abstract] [Hide abstract] ABSTRACT: Linked ZnO nanorods have been successfully prepared via a facile microwave method without any post-synthesis treatment. The X-ray diffraction (XRD) patterns indicated the precursor had completely transformed into the pure ZnO crystal. The images of field emitting scanning electron microscope (FESEM) and transmission electron microscope (TEM) showed that linked ZnO nanorods consisted predominantly of ZnO bipods. The formation process of the ZnO bipods was clearly discussed. ZnO bipods with different aspect ratios have been obtained by tuning the concentrations of reagents and microwave power. Moreover, the photocatalytic performance of ZnO bipods with different aspect ratios for degradation of methylene blue was systematically evaluated. The results of photocatalytic experiments showed that the photocatalytic activity increased with the aspect ratios of ZnO bipods increased. The reason is that ZnO bipods with larger aspect ratio have higher surface area, which can absorb more MB molecules to react with •OH radicals.
- [Show abstract] [Hide abstract] ABSTRACT: By releasing Ag+ ions and generating reactive oxygen species (ROS), silver nanoparticles (Ag NPs) not only have good anti-tumor activity but also display cytotoxicity towards normal cells which limits their further application in the medical field. Up to now, there was still no appropriate method to reduce the cytotoxicity while improving the anti-cancer activity of Ag NPs. This paper focuses on counteracting the toxic side effect of the ROS from Ag NPs while simultaneously improving their anti-cancer effect. We used α-TOS to modify Ag NPs and investigated their bioactivity in vitro for the first time. The modified Ag NPs with a high α-TOS concentration not only show much higher anti-tumor activity than Ag NPs alone but also promote the survival of normal cell lines slightly, while the modified Ag NPs with a low α-TOS concentration display a lower cytotoxicity against normal cell lines without affecting their anti-cancer activity when compared to Ag NPs alone. Therefore, this work presents a higher potential for cancer treatment than using Ag NPs alone. This journal is
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, the mesoporous silica MCM-41 supporting nano zero valent iron (MSNZVI) composite was synthesized in a facile way and characterized by XRD, FT-IR, TEM and N2 adsorption–desorption. The catalytic activity of the as-prepared MSNZVI composite as a catalyst was evaluated on the p-nitrophenol reduction in the presence of excess NaBH4. And the rate constant is 4.89 × 10−3 s−1 when the mole ratio of NaBH4 to p-nitrophenol is 500. MSNZVI composite can be reused for at least five cycles with stable catalytic activity. Moreover, a possible catalytic mechanism of MSNZVI was proposed to explain the reduction of p-nitrophenol by NaBH4.
- [Show abstract] [Hide abstract] ABSTRACT: Nano zero-valent iron (NZVI) particles were prone to forming aggregates owing to their intrinsic magnetism and van der Waals force. In this work, a composite material containing mesoporous silica MCM-41 and NZVI was prepared to avoid the problem of NZVI aggregation. The structures and morphologies of the as-prepared composite were confirmed using X-ray diffraction, Fourier transform infrared spectrometry, transmission electron microscopy, N2 adsorption-desorption, and X-ray photoelectron spectroscopy techniques. It was found that NZVI particles were well dispersed in the composite, although the size of NZVI particle was larger than that of bare NZVI. Moreover, the composite was used as adsorbent for removing Pb(II) from aqueous solution at room temperature. The effects of contact time, initial solution pH, and adsorbent dosage on the removal efficiency of Pb(II) were studied using batch adsorption experiments. The results indicated the composite exhibited enhanced adsorption properties, with the maximum adsorption capacity of 416.17 mg/g for Pb(II) removal from aqueous solution. In addition, the adsorption isotherms and adsorption kinetics were also investigated systematically, it was found that the isothermal data were well fitted to Langmuir model, and the kinetic data were well suitable to pseudo-second-order kinetics model.
- [Show abstract] [Hide abstract] ABSTRACT: Ag/ZnO/graphene (Ag/ZnO/G) nanocomposites were successfully synthesized by a facile low-temperature microwave-assisted solution method. The morphology and phase structure of the prepared samples were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The photocatalytic performance of the obtained products were evaluated by analyzing the degradation of methyl orange (MO) solution under UV irradiation. The Ag/ZnO/graphene nanocomposites showed higher photocatalytic efficiency than ZnO or Ag/ZnO. Photocatalytic activity of Ag/ZnO/graphene nanocomposites with different graphene content was studied. Firstly the photocatalytic efficiency of the Ag/ZnO/graphene nanocomposites increased with the increase of graphene oxide (GO) content from 0 to 1%, then the photocatalytic efficiency decreased while the percent of GO addition reached 2%. The photostability testing of the Ag/ZnO/graphene nanocomposites with 1% GO content showed that the catalyst has excellent photocatalytic activity and photostability for the degradation of MO. It is believed that this facile, rapid microwave-assisted strategy is scalable and can be applied to synthesize other metal/semiconductor oxide/graphene nanocomposites for different applications in different fields.
- [Show abstract] [Hide abstract] ABSTRACT: Na2O–CaO–SiO2 and Na2O–CaO–Al2O3–SiO2 glass–ceramic coatings were first prepared on commercial-purity titanium TA1 to improve its high temperature oxidation resistance. The Na2O–CaO–Al2O3–SiO2 glass–ceramic coating showed better sintering behavior than the Na2O–CaO–SiO2 glass–ceramic coating. Both glass–ceramic coatings clearly decreased the oxidation rate of TA1 at 800 °C. After high temperature oxidation, both glass–ceramic coatings showed a good adhesion to the TA1 substrate. Between the Na2O–CaO–SiO2 glass–ceramic coating and the TA1 substrate, a Ti5Si3 interface layer was observed as a result of the reaction between SiO2 in the glass and Ti. While for the Na2O–CaO–Al2O3–SiO2 glass–ceramic coating, diffusion of Al to the TA1 could also be seen under the Ti5Si3 interface layer. Cross-sectional EDS line scanning images of the glass–ceramic coatings showed that diffusion of the elements such as O, Ca and Na into TA1 was negligible, suggesting that both glass–ceramic coatings were suitable for protection of TA1 against high temperature oxidation.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, polyimide-graphite (PG) composite was prepared and used as a solid lubricant at elevated temperatures. PG composite was characterized by X-ray diffraction, and its thermal stability was evaluated based on thermogravimetric/differential thermal analysis and Fourier transform infrared spectrometry analysis. The results show that in PG composite, there was some interaction between the graphite (GR) and the polyimide (PI) matrix. Consequently, the PG composite exhibited better thermal stability than PI. The friction behavior of the PG composite sliding against steel at elevated temperatures (300–600°C at an interval of 100°C) was evaluated with a ring-on-ring tribometer. It was found that the PG composite exhibited excellent friction-reducing ability and good load-carrying capacity in the temperature range of 300–600°C and applied loads of 300–700 N. Moreover, this excellent lubricating performance of the PG composite might be attributed to its good thermal stability as a result of the interaction between the GR and the PI matrix. Therefore, PG composite could be used as an excellent solid lubricant under the high-temperature conditions.
- [Show abstract] [Hide abstract] ABSTRACT: Silver nanorods with different polydispersity were synthesized in the cetyltrimethylammonium bromide (CTAB) rod-shaped micelles by inducing the orientation growth of silver seeds and adjusting the volumes of CTAB. The reaction for the formation of silver nanorods had basically finished in 10 min. A suitable volume of CTAB (i.e., 15.0 mL of 0.1 M CTAB) is beneficial to obtain high-quality silver nanorods in the given reaction system. That is, the volume of added CTAB is a key factor to determine the polydispersity of the formed nanorods. The aging time plays a critical role in the morphology evolution of silver nanorods due to the oxidation of silver nanorods with Br-, O-2 and the Ostwald ripening of the nanoparticles. As a result, the characteristic spectral changes occurred due to the morphology evolution of silver nanorods. The ablation in the top ends of the longer nanorods is often accompanied by the growth of some shorter nanorods and nanospheres. The size distribution of silver nanorods might be more uniform in the early aging stage. All the nanorods in the colloidal solution should turn into the near-spherical nanoparticles with larger sizes and thus the characteristic absorption should change to single peak centered at about 400 nm. Based on the research results, mathematical models are proposed for explaining the formation and morphology changes of silver nanorods. The morphology evolution of silver nanorods may be important and can be used as a reference for preparing silver nanorods, nanowires and other anisotropic nanomaterials.
- [Show abstract] [Hide abstract] ABSTRACT: Li-doped MgO nanoplates were prepared by a sol-gel technique using magnesium nitrate hexahydrate and lithium nitrate as starting materials. The structures and morphologies of the as-obtained products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The influence of lithium doping on the antibacterial properties of nano-MgO was also investigated by the minimum inhibitory concentration (MIC) test and bactericidal efficacy against Escherichia coli (E. coli, ATCC 25922). It can be concluded that an appropriate amount of lithium doping can significantly enhance the antibacterial activity of nano-MgO, which can be attributed to an increase of defect concentration (oxygen vacancy) and basicity of nano-MgO, in favor of the generation and stabilization of active oxygen in MgO solution.
- [Show abstract] [Hide abstract] ABSTRACT: In this study, a series of chitosan-stabilized nano zero-valent iron (CNZVI) composites with different amounts of chitosan were prepared and characterized by Fourier transform infrared spectra, X-ray diffraction, and transmission electron microscopy. The adsorption capacity of these composites was evaluated by the removal experiment of cadmium ion (Cd2+) from aqueous solution. These results showed that the as-prepared CNZVI8 composite with loose aggregate structure has the maximum adsorption capacity for Cd2+. Furthermore, batch adsorption experiments of Cd2+ on CNZVI8 composite were performed under various conditions, such as contact time, adsorbent dosage, initial Cd2+ concentration, and the initial pH of solution. The data revealed that the maximum adsorption capacity of CNZVI8 is 124.74 mg/g. The removal efficiency of Cd2+ increased with the increase in solution pH value, and reaches 99.9% at pH 6. In addition, the adsorption isotherm and the adsorption kinetics of Cd2+ on CNZVI8 were also investigated, suggesting that the isothermal data were well fitted to the Langmuir model and the kinetic data were well suitable to the pseudo-second-order kinetic model.
- [Show abstract] [Hide abstract] ABSTRACT: Chitosan stabilised nanozero-valent iron (CNZVI) is proposed as a catalyst because of its simple preparation and high activity. The catalytic activity of CNZVI was investigated using the reduction reaction of p-nitrophenol (p-NP) by NaBH4. The result indicated that CNZVI possessed good catalytic activity, and the rate constant (k) was 2.45 × 10-3 s -1. In addition, CNZVI can be easily separated by an external magnetic field from aqueous solution, and it could also be repeatedly applied for the reduction of p-NP for at least five successive cycles with stable catalytic activity. All of these results suggest that CNZVI could be used as an excellent catalyst for the catalytic reduction of p-NP by NaBH4.
- [Show abstract] [Hide abstract] ABSTRACT: A novel glass amorphous silica composite coating was prepared by the slurry method in order to improve the oxidation resistance of Ti-6Al-4V alloy at high temperatures. The microstructure of the as-prepared composite coating was analyzed by SEM, XRD and EDS techniques. The oxidation resistance and the microstructure evolution of the composite coating at 800 degrees C for 50 h were also studied. The results show that mass gains of the specimens coated with the composite coating were far less than that of the uncoated ones after oxidation of 50 h. Thick oxide scales composed of plate-like rutile TiO2 and some granular alpha-Al2O3 formed on bare Ti-6Al-4V alloy, while quartz, cristobalite and diopside were observed in the composite coating, which are useful crystals for slowing the inward diffusion of oxygen to the substrate. The cross-sectional EDS line scanning images show that inward diffusion of oxygen and outward diffusion of Ti through the composite coating were insignificant. The microhardness profile reveals that the solid solution oxygen in Ti-6Al-4V alloy with composite coating was limited.
- [Show abstract] [Hide abstract] ABSTRACT: In this study, silver–graphene nanocomposites (SGNs) were successfully prepared by spontaneous reduction of silver ions and graphene oxide. Silver nanoparticles (about 30 nm) with narrow size distribution were distributed randomly on the surface of graphene. Different amounts of SGNs were introduced into silver flakes filled electrical conductive adhesives (ECAs) to study the effect of SGNs on the properties of the ECAs. The results showed that the volume resistivity of the ECAs decreased first and then increased with the increase of weight ratios of SGNs to silver flakes. While the weight ratio of SGNs to silver flakes was 20:80 (%), the resistivity reached the lowest value of 2.37 × 10−4 Ω cm. The lap shear strength decreased with the increase of the content ration of SGNs. And when the weight ratio of SGNs to silver flakes was 20:80 (%), the lap shear strength of ECA was about 10 MPa. According to the thermogravimetric analysis, the addition of SGNs can cause a slight decrease in the thermal stability of the ECA. In summary, SGNs are the promising candidates for the conductivity improvement of silver flakes filled electrical conductive adhesives.
Huazhong University of Science and Technology
Wu-han-shih, Hubei, China
- State Key Laboratory of Material Processing and Die & Mould Technology