Tran Dai Lam

Magnetic nanoparticles: study of magnetic heating and adsorption/desorption for biomedical and environmental applications

This paper presents a summary of research on magnetic nanoparticles (MNPs) carried out recently at the Institute of Materials Science. Three families of oxide MNPs namely magnetite, manganite and spinel ferrite materials were prepared by several methods: co-precipitation, sol-gel and high-energy mechanical milling. Magnetite nanoparticles were encapsulated by two natural polymers, starch and chitosan. The structure of the prepared nanosystems was characterised by XRD, SEM, TEM techniques while their magnetisation was measured by VSM and PPMS. The magnetic heating (MH) of both naked and polymer-coated MNPs was studied. We also present two examples of researched applications that can be derived from this effect, namely the use of MH of magnetite NPs coated with starch to kill cancer cells, and the MH-assisted desorption of VOC from SBA/ferrite nanocomposite. Other research application examples include the use of magnetite MNPs to remove heavy toxic metals, such as arsenic, lead and nickel from contaminated water.

Highly Visible Light Activity of Nitrogen Doped TiO2 Prepared by Sol–Gel Approach

A simple approach was explored to prepare N-doped anatase TiO2 nanoparticles (N-TiO2 NPs) from titanium chloride (TiCl4) and ammonia (NH3) via sol–gel method. The effects of important process parameters such as calcination temperatures, NH3/TiCl4 molar ratio (RN) on crystallite size, structure, phase transformation, and photocatalytic activity of titanium dioxide (TiO2) were thoroughly investigated. The as-prepared samples were characterized by ultraviolet–visible spectroscopy, x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated upon the degradation of methylene blue aqueous solution under visible-light irradiation. The results demonstrated that both calcination temperatures and NH3/TiCl4 molar ratios had significant impacts on the formation of crystallite nanostructures, physicochemical, as well as catalytic properties of the obtained TiO2. Under the studied conditions, calcination temperature of 600°C and NH3/TiCl4 molar ratio of 4.2 produced N-TiO2 with the best crystallinity and photocatalytic activity. The high visible light activity of the N-TiO2 nanomaterials was ascribed to the interstitial nitrogen atoms within TiO2 lattice units. These findings could provide a practical pathway capable of large-scale production of a visible light-active N-TiO2 photocatalyst.

Fabrication of PDMS-Based Microfluidic Devices: Application for Synthesis of Magnetic Nanoparticles

In this work, we have developed a convenient approach to synthesize magnetic nanoparticles with relatively high magnetization and controllable sizes. This was realized by combining the traditional co-precipitation method and microfluidic techniques inside microfluidic devices. The device was first designed, and then fabricated using simplified soft-lithography techniques. The device was utilized to synthesize magnetite nanoparticles. The synthesized nanomaterials were thoroughly characterized using field emission scanning electron microscopy and a vibrating sample magnetometer. The results demonstrated that the as-prepared device can be utilized as a simple and effective tool to synthesize magnetic nanoparticles with the sizes less than 10xa0nm and magnetization more than 50xa0emu/g. The development of these devices opens new strategies to synthesize nanomaterials with more precise dimensions at narrow size-distribution and with controllable behaviors.

Fabrication of poly (lactic acid)/hydroxyapatite (PLA/HAp) porous nanocomposite for bone regeneration

In this study, a poly (lactic acid)/hydroxyapatite (PLA/HAp) porous nanocomposite was fabricated by melt mixing method. Polyethylene oxide (PEO) was added into the nanocomposite to improve compatibility of HAp in the PLA matrix. A porous structure of the nanocomposite was created by using a salt (NaCl) which leaches in water. The influence of HAps weight, compatibiliser content of porous agent on morphology and mechanical properties of PLA/HAp nanocomposite was investigated by SEM and tensile testing method. The obtained results indicated that the nanocomposite containing 20 wt% HAp, 5 wt% PEO, and an amount of NaCl in proportion with PLA weight (1 : 1) had good mechanical properties with a promising Youngs modulus close to the one of cancellous bone (530 MPa) as well as a high porosity. The invitro tests of nanocomposite in simulated body fluids (SBF) were carried out and then pH of SBF solution, variation of material mass (Δm), morphology and phase structure of the nanocomposite were also estimated. The results showed that pH decreased, and Δm had positive or negative values depending on composition and surface of material formed by HAp crystals and the hydrolysis of PLA during immersion time.

A Novel Route for Preparing Highly Stable Fe3O4 Fluid with Poly(Acrylic Acid) as Phase Transfer Ligand

Highly stable Fe3O4 liquid was synthesized by thermal decomposition using poly(acrylic acid) (PAA) as a phase transfer ligand. The crystalline structure, morphology, and magnetic properties of the as-prepared samples were thoroughly characterized. Results demonstrated that the magnetic Fe3O4 nanomaterial was formed in liquid phase with a spinel single-phase structure, average size of 8–13xa0nm, and high saturation magnetization (up to 75xa0emu/g). The PAA-capped Fe3O4 nanoparticles displayed high stability over a wide pH range (from 4 to 7) in 300xa0mM salt solution. More importantly, the heat-generating capacity of the nanoparticle systems was quantified at a specific absorption rate (SAR) of 70.22xa0W/g, which is 35% higher than magnetic nanoparticles coated with sodium dodecyl sulfate (SDS). These findings suggest the potential application of PAA-coated magnetic nanoparticles in magnetic hyperthermia.

Study on preparation and properties of a novel photo–catalytic material based on copper–centred metal–organic frameworks (Cu–MOF) and titanium dioxide

A Cu3BTC2 metal–organic framework (MOF) with large specific surface area of 1350 m2/g, where BTC = benzene–1,3,5–tricarboxylate, was synthesised by hydrothermal method. It was then used as a starting material for the preparation of a novel MOF based photocatalyst containing titanium dioxide. This photocatalyst, namely, TiO2@Cu3BTC2, has been prepared by hydrolysis of titanium (IV) isopropoxide under hydrothermal condition. The synthesised materials were then characterised by X–ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) techniques. The photocatalytic discolouration of methylene blue dye (MB) in aqueous solution was investigated under UV–VIS light irradiation at different illumination times using the photocatalyst TiO2@Cu3BTC2 metal–organic frameworks and a control sample of commercial TiO2 nano powder (Degussa P25). It is interesting to note that TiO2@Cu3BTC2 exhibits very strong photocatalytic activity for MB discolouration, much better than lone TiO2 nano–particles P25. Thus, this novel photocatalytic material based on copper–centred MOFs may serve as an excellent class of photocatalytic materials for different environmental applications.

Sustainable composite materials based on ethylene-vinylacetate copolymer and organo-modified silica

Abstract Silica nanoparticles (SNPs) were modified by different amounts of 3-aminopropyltriethoxysilane (APTES). Nanocomposites based on ethylene vinyl acetate copolymer (EVA) and modified SNP (m-SNP) were prepared by the melt mixing method. They were characterized by Haake torque measurement, differential scanning calorimetry (DSC), horizontal burning test, scanning electron microscopy. Accelerated weather testing of the nanocomposites was performed according to ASTM D4329 (cycle A) for 168 h. The Haake torque indicates that the relative melt viscosity of EVA/m-SNPs is slightly higher than that of EVA/SNP nanocomposites. The DSC and burning test results show that m-SNPs decrease crystallinity degree and flammability of EVA. After accelerated weather testing, the relative amount of C=O groups in EVA/m-SNP nanocomposites is lower than that in EVA/SNP nanocomposites. Micro crack of EVA/m-SNP nanocomposite is smaller than that of EVA/SNP nanocomposite. In our study, the EVA/m-SNP nanocomposites with good tensile properties, flame and weather resistance can be used as sustainable materials in some technique fields.

Electrosynthesis of a poly(1,5-diaminonaphthalene) - polypyrrole nanowire bilayer for trichlorfon insecticide biosensing

In this study, an acetylcholinesterase enzyme biosensor was developed based on a bilayer of poly(1,5-diaminonaphthalene) and polypyrrole nanowire structures modifying carbon screen-printed electrodes (SPEs). A polypyrrole nanowire inner layer was electrodeposited on the surface of SPEs to enhance conductivity and specific areas. A poly(1,5-diaminonaphthalene) outer layer was used for immobilizing acetylcholinesterase through glutaraldehyde agent. On the basis of the inhibition of organophosphate pesticides on the enzymatic activity of acetylcholinesterase enzyme, the acetylcholinesterase-immobilized bilayer of the conductive polymer electrode was designed for electrochemical determination of trichlorfon insecticide, one of the popular organophosphate pesticides. Keywords. Acetylcholinesterase, biosensors, poly(1,5-diaminonaphthalene), polypyrrole nanowire, trichlorfon.

Effects of Fe Doping on the Structural, Optical, and Magnetic Properties of TiO2 Nanoparticles

Fe-doped TiO2 nanoparticles have been prepared by the hydrolysis method. The effects of Fe doping on the structural, optical, and magnetic properties of the Ti1−xFexO2 (xxa0=xa00.00, 0.03, 0.06, 0.10, 0.13) materials were thoroughly investigated by a combination of various methods, including transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, x-ray diffraction (XRD) analysis, ultraviolet–visible (UV–Vis) reflectance spectroscopy, Raman spectroscopy, and vibrating-sample magnetometry. Analysis of the TEM and XRD measurements showed that the resulting powders had nanoscale particle size. The Fe-doped samples were found to be paramagnetic at room temperature (by magnetization measurements), with Fe acting as substitutional impurity at Ti sites in the anatase TiO2 phase. Substitution of Fe at Ti sites was also confirmed by Raman spectra. The paramagnetic nature of the Ti1−xFexO2 samples was further investigated using density functional theory calculations of their electronic band structure and density of states. Finally, the photocatalytic activity of the Fe-doped TiO2 samples was studied by investigating their photocatalytic decomposition of methylene blue.

Hydrolysis of green nanocomposites of poly(lactic acid) (PLA), chitosan (CS) and polyethylene glycol (PEG) in acid solution

Abstract Green nanocomposites based on poly(lactic acid), chitosan, and polyethylene glycol (PLA/CS/PEG) were prepared by the solution method. The content of PEG was 2–10 wt.% compared with the weight of PLA. The characterization and morphology of the nanocomposites before and after hydrolysis in acid solution were determined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry and scanning electron microscopy (SEM). The hydrolysis of PLA/CS/PEG nanocomposites in acid solution for different times was also investigated. The shift of C=O, CH3 groups in FTIR spectra of PLA/CS/PEG nanocomposites before and after hydrolysis was clearly observed. The SEM images of the nanocomposites indicate that PEG plays a role in improving the interaction between PLA and CS, resulting in limiting the permeability of acid solution into the structure of the nanocomposites in the presence of PEG. The obtained results after 28 days of testing in the acid solution show that the PLA/CS/PEG8 nanocomposite (containing 8 wt.% of PEG) had the lowest weight loss with the highest regression coefficient (R2=0.9614).