Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed

Chemically Surface Tunable Solubility Parameter for Controllable Drug Delivery—An Example and Perspective from Hollow PAA-Coated Magnetite Nanoparticles with R6G Model Drug

Solubility parameter-dependent drug releasing property is essential in practical drug delivery systems (DDS), and how to combine magnetic nanoparticles(NPs) and suitable polymer coating towards DDS is always a crucial and valuable challenge in biomedical application. Herein, a controllable drug delivery model with a surface having a chemically tunable solubility parameter is presented using hollow magnetite/polyacrylic acid (Fe3O4/PAA) nanocomposites as nanocarrier towards DDS. This composite is prepared by simply coating the modified hollow Fe3O4 with PAA. The coating amount of PAA onto the surface of Fe3O4 (measured by TGA) is about 40% (w/w). Then, Rhodamine 6G (R6G) is selected as model drug in drug delivery experiment. The efficiency of drug loading and drug release of these Fe3O4/PAA nanocarriers are evaluated under various temperature, solvent and pH values. As a result, the best drug releasing rate was achieved as 93.0% in pH = 7.4 PBS solution after 14 h. The releasing efficiency is 86.5% in acidic condition, while a lower releasing rate (30.0%) is obtained in aqueous solution, as different forms (polyacrylic acid and polyacrylate) of PAA present different solubility parameters, causing different salt and acid effects in various solvents, swelling property of PAA, and binding force between PAA and R6G. Therefore, by changing the solubility parameter of coating polymers, the drug delivery properties could be effectively tuned. These findings prove that the DDS based on magnetic particle cores and polymer encapsulation could efficiently regulate the drug delivery properties by tuning surface solubility parameter in potential cancer targeting and therapy

Numerical Simulation of Impregnation Process of Reactive Injection Pultrusion for Glass Fiber/PA6 Composites

Pultrusion of thermoplastic composites has been the hotspot of manufacturing high-performance thermoplastic composites in recent years. The optimization of process parameters in the pultrusion usually needed repeated attempts, which wasted lots of manpower and material resources. A numerical simulation method can accelerate the optimization of process parameters. In this work, the impregnation process of reactive injection pultrusion for glass fiber reinforced nylon 6 (GF/PA6) composites was modeled and numerically simulated by a finite element/controlled volume (Fe/CV) method. Based on Darcy’s law, the impregnation process can be regarded as the two-phase flow (liquid resin and air) in porous media (undirectional glass fibers). The distribution of resin flow during the impregnation was explored. The effects of pulling rate and injection pressure on the impregnation time and resin reflux distance were analyzed, and the appropriate range of relevant process parameters was determined. The results showed that increasing the pulling rate can significantly control the reflux distance of resin in the impregnation mold and shorten the impregnation time, but too high a pulling rate would increase the impregnation time. Increasing the injection pressure can greatly shorten the resin impregnation time, but it would significantly increase the resin reflux distance. This work can effectively guide the subsequent optimization of process parameters of reactive injection pultrusion for GF/PA6 composites

Efficiently Enhancing Electrocatalytic Activity of α-MnO2 Nanorods/N-Doped Ketjenblack Carbon for Oxygen Reduction Reaction and Oxygen Evolution Reaction Using Facile Regulated Hydrothermal Treatment

Scalable, low-cost and highly efficient catalysis of oxygen electrocatalytic reactions (ORR/OER) are required for the rapid development of clean and renewable energy conversion/storage technologies. Herein, two types of α-MnO2 nanorods were prepared under hydrothermal treatment at 150 °C for 0.5 h (MnO2-150-0.5) or 120 °C for 12 h (MnO2-120-12), then supported on N-doped ketjenblack carbon (N-KB) as bi-functional ORR/OER catalysts. Their electrocatalytic activities toward ORR and OER were investigated systematically. As a result, MnO2-150-0.5/N-KB displays superior ORR catalytic activity, with much more positive half-wave potential and much larger limiting current density (0.76 V and 6.0 mA cm−2), comparable to those of 20 wt. % Pt/C (0.82 V and 5.10 mA cm−2). MnO2-150-0.5/N-KB also shows high electron transfer number (3.86~3.97) and low yield of peroxides (1–7%) during ORR process in the whole potential range of 0–1.0 V (vs. RHE). Meanwhile, the MnO2-150-0.5/N-KB also exhibits better OER activity with low overpotential, comparable to IrO2/N-KB. The excellent electrocatalytic activity of MnO2-150-0.5/N-KB can be attributed to the synergistic effect, relatively smaller size, higher amount of Mn3+, and low charge transfer resistance. This work offers a new strategy for scalable preparation of more efficient and cost-effective α-MnO2 bi-functional oxygen catalysts

Fabrication and Performance of ZnO Doped Tantalum Oxide Multilayer Composite Coatings on Ti6Al4V for Orthopedic Application

Ti6Al4V titanium alloy has been widely used as medical implant material in orthopedic surgery, and one of the obstacles preventing it from wide use is toxic metal ions release and bacterial implant infection. In this paper, in order to improve corrosion resistance and antibacterial performance of Ti6Al4V titanium alloy, ZnO doped tantalum oxide (TaxOy) multilayer composite coating ZnO-TaxOy/TaxOy/TaxOy-TiO2/TiO2/Ti (ZnO-TaxOy) was deposited by magnetron sputtering at room temperature. As a comparison, monolayer TaxOy coating was prepared on the surface of Ti6Al4V alloy. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), the elemental chemical states of coating surfaces were investigated by X-ray photoelectron spectroscope (XPS). The adhesion strength and corrosion resistance of the coatings were examined by micro-scratch tester and electrochemical workstations, respectively. The results show that the adhesion strength of multilayer ZnO-TaxOy coating is 16.37 times higher than that of single-layer TaxOy coating. The ZnO-TaxOy composite coating has higher corrosion potential and lower corrosion current density than that of TaxOy coating, showing better corrosion inhibition. Furthermore, antibacterial test revealed that multilayer ZnO-TaxOy coating has a much better antibacterial performance by contrast

Preparation of Cu2O-Reduced Graphene Nanocomposite Modified Electrodes towards Ultrasensitive Dopamine Detection

Cu2O-reduced graphene oxide nanocomposite (Cu2O-RGO) was used to modify glassy carbon electrodes (GCE), and applied for the determination of dopamine (DA). The microstructure of Cu2O-RGO nanocomposite material was characterized by scanning electron microscope. Then the electrochemical reduction condition for preparing Cu2O-RGO/GCE and experimental conditions for determining DA were further optimized. The electrochemical behaviors of DA on the bare electrode, RGO- and Cu2O-RGO-modified electrodes were also investigated using cyclic voltammetry in phosphate-buffered saline solution (PBS, pH 3.5). The results show that the oxidation peaks of ascorbic acid (AA), dopamine (DA), and uric acid (UA) could be well separated and the peak-to-peak separations are 204 mV (AA-DA) and 144 mV (DA-UA), respectively. Moreover, the linear response ranges for the determination of 1 × 10−8 mol/L~1 × 10−6 mol/L and 1 × 10−6 mol/L~8 × 10−5 mol/L with the detection limit 6.0 × 10−9 mol/L (S/N = 3). The proposed Cu2O-RGO/GCE was further applied to the determination of DA in dopamine hydrochloride injections with satisfactory results

Spherical α-MnO2 Supported on N-KB as Efficient Electrocatalyst for Oxygen Reduction in Al–Air Battery

Traditional noble metal platinum (Pt) is regarded as a bifunctional oxygen catalyst due to its highly catalytic efficiency, but its commercial availability and application is often restricted by high cost. Herein, a cheap and effective catalyst mixed with α-MnO2 and nitrogen-doped Ketjenblack (N-KB) (denoted as MnO2-SM150-0.5) is examined as a potential electrocatalyst in oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). This α-MnO2 is prepared by redox reaction between K2S2O8 and MnSO4 in acid conditions with a facile hydrothermal process (named the SM method). As a result, MnO2-SM150-0.5 exhibits a good catalytic performance for ORR in alkaline solution, and this result is comparable to a Pt/C catalyst. Moreover, this catalyst also shows superior durability and methanol tolerance compared with a Pt/C catalyst. It also displays a discharge voltage (~1.28 V) at a discharge density of 50 mA cm−2 in homemade Al–air batteries that is higher than commercial 20% Pt/C (~1.19 V). The superior electrocatalytic performance of MnO2-SM150-0.5 could be attributed to its higher Mn3+/Mn4+ ratio and the synergistic effect between MnO2 and the nitrogen-doped KB. This study provides a novel strategy for the preparation of an MnO2-based composite electrocatalyst

First Principles Study on the CO Oxidation on Mn-Embedded Divacancy Graphene

The CO oxidation mechanism on graphene with divacancy (DG) embedded with transition metal from Sc to Zn has been studied by using first principles calculations. The results indicate that O2 molecule is preferentially adsorbed on Sc, Ti, V, Cr, Mn, and Fe-DG, which can avoid the CO poisoning problem that many catalysts facing and is beneficial to the CO oxidation progress. Further study indicates that Mn-DG shows the best catalytic properties for CO oxidation with consideration of both Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) oxidation mechanisms. Along the ER mechanism, the reaction energy barrier for the first step (CO free + O2pre-adsorbed → OOCO) is 0.96 eV. Along the LH mechanism, the energy barrier for the rate limiting step (CO adsorbed + O2adsorbed → OOCO) is only 0.41 eV, indicating that the CO oxidation on Mn-DG will occur along LH mechanism. The Hirshfeld charge distributions of O2 and CO molecules is tuned by the embedded Mn atom, and the charge transfer from the embedded Mn atom to the adsorbed molecules plays an important role for the CO oxidation. The result shows that the Mn-embedded divacancy graphene is a noble-metal free and efficient catalyst for CO oxidation at low temperature