Hongwei Ni

Antibacterial nano-structured titania coating incorporated with silver nanoparticles.

Titanium (Ti) implants are widely used clinically but post-operation infection remains one of the most common and serious complications. A surface boasting long-term antibacterial ability is highly desirable in order to prevent implant associated infection. In this study, titania nanotubes (TiO(2)-NTs) incorporated with silver (Ag) nanoparticles are fabricated on Ti implants to achieve this purpose. The Ag nanoparticles adhere tightly to the wall of the TiO(2)-NTs prepared by immersion in a silver nitrate solution followed by ultraviolet light radiation. The amount of Ag introduced to the NTs can be varied by changing processing parameters such as the AgNO(3) concentration and immersion time. The TiO(2)-NTs loaded with Ag nanoparticles (NT-Ag) can kill all the planktonic bacteria in the suspension during the first several days, and the ability of the NT-Ag to prevent bacterial adhesion is maintained without obvious decline for 30 days, which are normally long enough to prevent post-operation infection in the early and intermediate stages and perhaps even late infection around the implant. Although the NT-Ag structure shows some cytotoxicity, it can be reduced by controlling the Ag release rate. The NT-Ag materials are also expected to possess satisfactory osteoconductivity in addition to the good biological performance expected of TiO(2)-NTs. This controllable NT-Ag structure which provides relatively long-term antibacterial ability and good tissue integration has promising applications in orthopedics, dentistry, and other biomedical devices.

Controllable Growth of Conical and Cylindrical TiO2–Carbon Core–Shell Nanofiber Arrays and Morphologically Dependent Electrochemical Properties

Quasi-aligned cylindrical and conical core-shell nanofibers consisting of carbon shells and TiO(2) nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO(2) nanowire core 30-50 nm in diameter and a 5-10 nm-thick cylindrical carbon shell, while in the conical nanostructure the TiO(2) nanowire core has a diameter of 20-40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well-defined redox peaks of the [Fe(CN)(6)](3-/4-) redox couple and heterogeneous charge-transfer rate constants of 0.010 and 0.062 cm  s(-1) for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge-plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge-plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance.

Antibacterial properties and corrosion resistance of AISI 420 stainless steels implanted by silver and copper ions

Silver or copper ions are often chosen as antibacterial agents. But a few reports are concerned with these two antibacterial agents for preparation of antibacterial stainless steel (SS). The antibacterial properties and corrosion resistance of AISI 420 stainless steel implanted by silver and copper ions were investigated. Due to the cooperative antibacterial effect of silver and copper ions, the Ag/Cu implanted SS showed excellent antibacterial activities against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) at a total implantation dose of 2×1017 ions/cm2. Electrochemical polarization curves revealed that the corrosion resistance of Ag/Cu implanted SS was slightly enhanced as compared with that of un-implanted SS. The implanted layer was characterized by X-ray photoelectron spectroscopy (XPS). Core level XPS spectra indicate that the implanted silver and copper ions exist in metallic state in the implanted layer.

Hydrothermal synthesis of CdS nanorods anchored on α-Fe2O3 nanotube arrays with enhanced visible-light-driven photocatalytic properties

As an n-type semiconductor with an excellent physicochemical properties, iron oxide (Fe2O3) has been extensively used in the fields of environmental pollution control and solar energy conversion. However, the high recombination rate of the photoinduced electron-hole pairs and poor charge mobility for Fe2O3 nanomaterial generally result in low photocatalytic efficiency. Herein, an uniform CdS nanorods grown directly on one-dimensional α-Fe2O3 nanotube arrays (NTAs) are successfully synthesized by a facile hydrothermal method and the constructed heterojunction can be a kind of efficient and recyclable photocatalysts. Successful deposition of CdS nanorods onto the α-Fe2O3 NTAs is verified by field emission scanning electron microscopy(FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS). UV-Vis diffuse reflectance spectroscopy indicates that α-Fe2O3/CdS NTAs possess the intense visible light absorption and also display a red-shift of the band-edge compared with the pure α-Fe2O3 NTAs. The as-obtained α-Fe2O3/CdS NTAs display excellent photocatalytic activity for decomposition of methylene blue (MB), methyl orange (MO), and phenol under visible light illumination. Among all the tested photocatalysts, the film synthesized for 3h with good stability exhibits the best photocatalytic properties and produces the highest photocurrent of 1.43 mA/cm2 at 0.8 V vs. Ag/AgCl electrode, owing to its well formed heterojunction structure, effective electron-hole pair separation and direct electron transfer pathway along the CdS nanorods and α-Fe2O3 NTAs. Besides, the photogenerated holes (h+) and superoxide radicals (O2-) play dominant roles in the photocatalytic process. On the basis of the photocatalytic results and energy band diagram, the photocatalytic process mechanism is proposed. Considering the easy preparation and excellent performance, α-Fe2O3/CdS NTAs could be a promising and competitive visible-light-driven photocatalyst in the field of environment remediation.

Antibacterial properties of AISI 420 stainless steel implanted by Ag/Cu ions

AISI 420 stainless steel implanted by Ag/Cu ions was fabricated for antibacterial purpose. The implantation of Ag/Cu ions was in a total dose of 2×1017 ions/cm2 at an extracting voltage of 50 KV. The chemical composition of the implanted layer was characterized by X-ray photoelectron spectroscopy (XPS). The Ag/Cu implanted stainless steel shows good antibacterial property to both Staphylococcus aureus (S. aureus) and Aspergillus niger (A. niger).

Mechanism research on arsenic removal from arsenopyrite ore during a sintering process

The mechanism of arsenic removal during a sintering process was investigated through experiments with a sintering pot and arsenic-bearing iron ore containing arsenopyrite; the corresponding chemical properties of the sinter were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The experimental results revealed that the reaction of arsenic removal is mainly related to the oxygen atmosphere and temperature. During the sintering process, arsenic could be removed in the ignition layer, the sinter layer, and the combustion zone. A portion of FeAsS reacted with excess oxygen to generate FeAsO4, and the rest of the FeAsS reacted with oxygen to generate As2O3(g) and SO2(g). A portion of As2O3(g) mixed with Al2O3 or CaO, which resulted in the formation of arsenates such as AlAsO4 and Ca3(AsO4)2, leading to arsenic residues in sintering products. The FeAsS component in the blending ore was difficult to decompose in the preliminary heating zone, the dry zone, or the bottom layer because of the relatively low temperatures; however, As2O3(g) that originated from the high-temperature zone could react with metal oxides, resulting in the formation of arsenate residues.

Cytotoxicity effects of three-dimensional graphene in NIH-3T3 fibroblasts

The 3D configuration of graphene materials has been intensively investigated due to their novel properties in biomedical, electrical and optical applications. But few reports have been intentionally carried out to understand the biological influence of 3D graphene materials so far. Herein, we presented an evaluation of the in vitro cytotoxicity of 3D graphene sheets fabricated by carbonization of polydopamine (PDA) films on a template of aligned nanopore arrays (NPAs) on a stainless steel surface. The prepared 3D graphene sheets with a thickness of ∼20 nm displayed a nanoporous architecture that can be readily tuned by the NPA template to control the morphology of the 3D configuration. The in vitro toxicity of the nanoporous 3D graphene sheets with pore sizes of ∼50 nm and ∼240 nm was evaluated using NIH-3T3 fibroblasts as the representative mammal fibroblast cell type. The NPA structure exhibits enhanced properties in cell attachment, spreading, proliferation, and the assembly of focal adhesions and actin filament associated proteins. Morphology-dependent cytotoxicity aroused by the 3D graphene configuration should be attributed to the engulfment of the carbon nanospheres embedded in the 3D configuration and the lack of both focal adhesions and actin filament associated proteins assembling at the nanoscale.

Effect of slag composition on the cleanliness of 28MnCr5 gear steel in the refining processes

The equilibrium reaction between CaO—Al2O3—SiO2—MgO slag and 28MnCr5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The dissolved oxygen content [O] in molten steel under different top slag conditions was calculated using a thermodynamic model and was measured using an electromotive force method in slag–steel equilibrium experiments at 1873 K. The relations among [O], the total oxygen content (T.O), and the composition of the slag were investigated. The experimental results show that both [O] and T.O decrease with decreasing SiO2 content of the slag and exhibit different trends with the changes in the CaO/Al2O3 mass ratio of the slag. Increasing the CaO/Al2O3 mass ratio results in a decrease in [O] and an increase in T.O. To ensure that T.O ≤ 20 ppm and [O] ≤ 10 ppm, the SiO2 content should be controlled to <5wt%, and the CaO/Al2O3 mass ratio should be in the range from 1.2 to 1.6.

Insertion of Platinum Nanoparticles into MoS2 Nanoflakes for Enhanced Hydrogen Evolution Reaction

Pt as a chemical inert metal has been widely applied as the counter electrode in various electrochemical measurements. However, it can also be dissolved and redeposit to the working electrode under certain electrochemical circumstances. Herein we demonstrated a cyclic voltammetry (CV) cycling method to synthesize a catalyst comprising inserted Pt nanoparticles into MoS2 nanoflake stack structures on stainless steel mesh (SSM). The binder-free composite structure exhibits significantly enhanced hydrogen evolution reaction (HER) catalytic activity with an overpotentials of 87 mV at 10 mA cm−2. The deposited Pt nanoparticles significantly enhance the catalytic activity through changing the structure of MoS2 and increasing the amount of active sites. This work provides a new way forward for rational design of the nano-electrocatalysts.

In situ growth of self-supported and defect-engineered carbon nanotube networks on 316L stainless steel as binder-free supercapacitors

Self-supported and defect-engineered carbon nanotube networks directly grown on 316L stainless steel are used for binder-free supercapacitors. In situ growth of the carbon nanotube networks on 316L stainless steel is obtained through the chemical vaporization deposition and thermal treatment to generate various defects. The relationship between the microstructures of carbon nanotube networks and electrochemical characteristics is investigated. The as-prepared carbon nanotube networks are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman analysis. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy tests are also carried out to evaluate their capacitive properties, suggesting that the electrochemical characteristics are significantly affected by annealing time. The carbon nanotube networks annealed at 500 0C for 2 h display high capacitance of 11 mF cm-2 and excellent cycling lifetime with capacitance retention ration 97% at the scan rate of 0.5 mA cm-2 for 5000 periods, which is attributed to the defect engineering increasing the defects of carbon nanotube networks, enhancing hydrophilic property and facilitating the transportation of electrolyte ions.