Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated g\boldsymbol\gamma–Fe₂_{\boldsymbol 2}O₃_{\boldsymbol 3} nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 10⁶ (10⁵) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperature-dependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures $\boldsymbol >$\boldsymbol >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.     

Photocatalytic activity of TiO2-capped ZnO nanoparticles

Using a combined hydrothermal and sol–gel route, TiO₂ -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ~10 nm. Formation of Zn₂TiO₄ phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO₂ shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm²) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy. Analysis of the photoactivity results according to Langmuir–Hinshelwood model revealed a two-step decolorization process with a high kinetics rate at the early stage followed by a slower step. The capped nanoparticles synthesized under specific conditions exhibited higher photodecolorization yield and faster kinetics in comparison to the uncoated ZnO and P25-Degussa TiO₂ nanoparticles.     

Effect of the preparation route,PEG and annealing on the phase stability of Fe3O4 nanoparticles and their magnetic properties

Fe₃O₄ nanoparticles are synthesised via two different methods: (1) co-precipitation of Fe²⁺ and Fe³⁺ ions and (2) oxidative alkaline hydrolysis of Fe²⁺ ions under atmospheric pressure using different protective agents (PEG 200 and PEG 3000) and urea as a base. The preparation method and the polyethylene glycol (PEG) used are concurrently affecting the phase stability of the formation of the iron oxides: the co-precipitation method using PEG 200 (E4a) or PEG 3000 (E4b) leads to the formation of different ratios of Fe₂O₃ and Fe₃O₄, whereas the oxidative hydrolysis of Fe²⁺ using PEG 200 gives Fe₃O₄ (E2) powder as a major product. The average crystallites size of E4a and E4b is almost identical, i.e. around 19?nm but the saturation magnetisation of E4b is three times larger than that of E4a. The sample E2 shows the highest saturation magnetisation value 74?emu/g, with an average crystallites size of 71?nm. Transmission electron microscopy analysis confirmed that the E2 sample shows the presence of needles crystals with typical sizes around 10 and 50?nm and its selected area diffraction (SAD) shows a typical diffraction of the spinel structure of magnetite. On the other hand, E4b sample shows elongated nanoparticles with typical sizes around 24?nm and its SAD confirmed the presence of a mixture of Fe₂O₃ and Fe₃O₄ as many dispersed spots were obtained.     

SERS property of Co complex on boron nitride nanosheets/silver nanoparticles aggregates and photophysical characterisation of interactions among Co complex ion-exchanged within zirconium phosphate

ABSTRACT

The Co(II) complex of [Co(bpy)₂(NO₃)]Cl·3H₂O, bpy = 2,2'-bipyridine, has been synthesised by the solution crystallisation method. The boron nitride nanosheets/silver nanoparticles/[Co(bpy)₂(NO₃)]Cl·3H₂O nanoaggregate was prepared in order to better analyse the adsorption orientation of the cobalt complex on the surface of silver nanoparticles. The result of the surface-enhanced Raman scattering measurement indicates that the molecular plane of the cobalt complex presents a tilted orientation with respect to the surface of silver nanoparticles. The luminescence property of [Co(bpy)₂(NO₃)]⁺ two-dimensional arrangements within the layers of zirconium phosphate (ZrP) was also investigated. Steady-state luminescence spectra of the [Co(bpy)₂(NO₃)]⁺-exchanged ZrP materials show an increase in the luminescence intensity.     

Influence of Na+ content on the structure and morphology of TiO2 nanoparticles prepared by hydrothermal transformation of alkaline titanate nanotubes

ABSTRACT

The objective of this study is to investigate the role of Na⁺ content in the morphology evolution of TiO₂ nanoparticles prepared by hydrothermal approach. Various TiO₂ morphology from 0-dimensional (0D) nanoparticles to 1-dimensional (1D) nanorods were synthesised by hydrothermally treating the alkali titanate nanotubes with different Na⁺ content. The XRD patterns show the phase transformation and crystallographic nature of alkali titanate nanotubes are strongly dependent on the Na⁺ content, the cation exchange of Na⁺ by H⁺ ion exchange affects the crystallinity of the tubes and causes disorder of the interlayers of nanotubes. The SEM and TEM images confirm that Na⁺ rich titanate nanotubes were thermally stable. Moreover, BET measurements revealed that the Na⁺ content plays an important role on the specific surface area of formed TiO₂ nanoparticles. The photocatalytic activity of the TiO₂ nanoparticles was characterised via the decomposition rate of an aqueous solution of methyl orange (MO) under UV light irradiation. The TiO₂ nanoparticles prepared by hydrothermally treating the alkali titanate nanotubes with no Na⁺ content has a surface area of 55.1 m²/g with nearly 100% photodecomposition of MO in 20 min.     

Synthesis and characterisation of Ni-doped Fe3O4/polypyrrole magnetic and conducting nanocomposites with core–shell structure

Abstract

Electrical and magnetic function materials have many potential applications. A magnetic and conducting Ni-doped Fe₃O₄/polypyrrole (PPy) nanocomposite with a core–shell structure was prepared by in situ polymerisation of a pyrrole monomer in an aqueous solution containing a dispersion of Ni-doped Fe₃O₄ nanoparticles. The structure and properties of Ni-doped Fe₃O₄/PPy nanocomposites were characterised by X-ray diffraction (XRD), TEM, infrared spectrometry (IR), vibrating sample magnetometry (VSM) and thermogravimetry (TG). The results showed that the Ni-doped Fe₃O₄ nanoparticles were completely coated by polypyrrole; the resultant Ni-doped Fe₃O₄/PPy nanocomposites exhibited a good superparamagnetic behaviour and the saturation magnetisation was as high as 25·2 emu g^?1 owing to the adoption of Ni-doped Fe₃O₄ as the magnetic source. In addition, the influences of Ni-doped Fe₃O₄ content on the electromagnetic properties of resultant nanocomposites were preliminarily investigated.     

Studying the effect of particle size on the antibacterial activity of some N-nicotinyl phosphoric triamides

Using ultrasonic top-to-down method, nanoparticles of two N-nicotinyl phosphoric triamides: C₅H₄NC(O)NHP(O)R, R?=?4-CH₃-NC₅H₁₀ (1), (CH₃)₃CNH₂ (2) were prepared for the first time and characterized by ³¹P, ¹³C, ¹H NMR, FTIR, scanning electron microscopy, energy dispersive X-ray. The average particle size of 1 and 2 were 60–70 and 40–50?nm, respectively, and the morphology was spherical for 1 and rod for 2. Solid state (powder) antibacterial effect of these compounds and two other similar reported ones, in their macro- and nanosizes, were evaluated with colony counting method on one Gram-positive (Staphylococcus aureus) and one Gram-negative (Escherichia coli) bacteria in Brain–Heart infusion culture medium. Results showed that all the macro- and nanosized compounds, except macrosized 1, were antibacterial and all nanoscaled ones had stronger antibacterial activity than their macroscaled analogues. The most effect of the particle size was observed for 1: by decreasing the particle sizes, the antibacterial activity state of 1 was changed from inactive (for macro) to potent (for nano).     

Long-term exposure of bacterial and protozoan communities to TiO2 nanoparticles in an aerobic-sequencing batch reactor

Abstract

Titanium dioxide (TiO₂) nanopowders at different concentrations (0–50 mg L^?1) were injected into an aerobic-sequencing batch reactor (SBR) to investigate the effects of long-term exposure to nanoparticles on bacterial and protozoan communities. The detection of nanoparticles in the bioflocs was analyzed by scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The SBR wastewater experiments were conducted under the influence of ultraviolet light with photocatalytic TiO₂. The intrusion of TiO₂ nanoparticles was found both on the surface and inside of the bioflocs. The change of microbial population in terms of mixed liquor-suspended solids and the sludge volume index was monitored. The TiO₂ nanoparticles tentatively exerted an adverse effect on the microbial population, causing the reduction of microorganisms (both bacteria and protozoa) in the SBR. The respiration inhibition rate of the bacteria was increased, and the viability of the microbial population was reduced at the high concentration (50 mg L^?1) of TiO₂. The decreasing number of protozoa in the presence of TiO₂ nanoparticles during 20 days of treatment with 0.5 and 1.0 mg L^?1 TiO₂ is clearly demonstrated. The measured chemical oxygen demand (COD) in the effluent tends to increase with a long-term operation. The increase of COD in the system suggests a decrease in the efficiency of the wastewater treatment plant. However, the SBR can effectively remove the TiO₂ nanoparticles (up to 50 mg L^?1) from the effluent.     

Lanthanide sorbent based on magnetite nanoparticles functionalized with organophosphorus extractants

Abstract

In this work, an adsorbent was prepared based on the attachment of organophosphorus acid extractants, namely, D2EHPA, CYANEX 272, and CYANEX 301, to the surface of superparamagnetic magnetite (Fe₃O₄) nanoparticles. The synthesized nanoparticles were coated with oleic acid, first by a chemisorption mechanism and later by the respective extractant via physical adsorption. The obtained core–shell functionalized magnetite nanoparticle composites were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, thermogravimetry, infrared absorption and vibrating sample magnetometry. All the prepared nanoparticles exhibited a high saturation magnetization capacity that varied between 72 and 46 emu g^?1 and decreased as the magnetite nanoparticle was coated with oleic acid and functionalized. The scope of this study also included adsorption tests for lanthanum, cerium, praseodymium, and neodymium and the corresponding analysis of their results. Sorption tests indicated that the functionalized nanoparticles were able to extract the four studied lanthanide metal ions, although the best extraction performance was observed when the sorbent was functionalized with CYANEX 272, which resulted in a loading capacity of approximately 12–14 mg_La/g_MNP. The magnetization of the synthesized nanoparticles was verified during the separation of the lanthanide-loaded sorbent from the raffinate by using a conventional magnet.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag composite magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles being used as seeding materials, Ag⁺ ions on the Fe₃O₄ magnetic nanoparticles reduced to the metal form by tartaric acid using heated treatment. Thus, Fe₃O₄/Ag composite core-shell magnetic nanoparticles were synthesized. The products were characterized by transmission electron microscope (TEM) and x-ray diffraction (XRD). Both TEM and XRD results showed that the Ag nanoparticles were well distributed on the surface of Fe₃O₄ magnetic nanoparticles. The size for Fe₃O₄/Ag composite magnetic nanoparticles which were spherical shape was ≃40 nm. Furthermore, the magnetic properties of samples were characterized on a vibrating sample magnetometer. Under optimal conditions, Fe₃O₄/Ag composite nanoparticles showed higher magnetism than pure Fe₃O₄ nanoparticles. The text was submitted by the authors in English.     

Luminescent impurity ion probe and low temperature phase of SrTiO3 nanoparticles

Abstract

Optical absorption and photoluminescence of Cr³⁺ impurity ion probe were studied on nanocrystalline SrTiO₃/Cr(0·1%) powders with an average particle size between 13 and 100 nm prepared by the Pechini type polymeric sol–gel method. Only O_h¹ cubic perovskite phase was revealed in the powders at room temperature. The optical absorption edge and the position of the zero-phonon emission R-line of the octahedral Cr³⁺ centres shifted to higher energies with decreasing particle size. The temperature shift of the R-line position appeared for all powders nearly the same as the 'dielectric related' one in the bulk crystals, evidencing that SrTiO₃ retains quantum paraelectric behaviour down to a particle size of about 10 nm. However, behaviour of the R-line position was unstable at low temperatures in powders with a particle size of about 13 and 20 nm. This instability was speculated as a manifestation of a possible low temperature ferroelectric phase transition in small enough SrTiO₃ nanoparticles.     

Role of the synthesis procedure on the physicochemical properties of doped magnetite

The studies presented in this paper show the results of synthesis and physicochemical characterization of modified ferrite nanoparticles, which can be described by the general formula M_xFe_3-xO₄ (where x = 0.15 or 0.45) doped with Al³⁺, Cr³⁺, Cu²⁺ and Zn²⁺ ions. The nanoparticles were obtained through procedures using either water or organic environment. The aim of this study was to determine the influence of synthetic routine and doping on the quality of the obtained structure, morphology and magnetic properties of nanoparticles. Additionally, doping concentration of selected elements is a crucial influence on the crystallinity and magnetic properties of the obtained nanoparticles. Doped nanoparticles were synthesized by two chemical methods: co-precipitation of iron chlorides in a basic solution and thermal decomposition of iron(III) acetylacetonate in an organic high-boiling solvent. Obtained nanoparticles were characterized by transmission electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry, infrared spectroscopy and Mössbauer spectroscopy.     

Synthesis and kinetics research of ZnS nanoparticles prepared by sonochemical process

Abstract

ZnS nanocrystallites have been successfully prepared by a sonochemical process. The reaction kinetics of the process was also investigated. The as prepared ZnS nanocrystallites were characterised by XRD and TEM. Results show that ZnS nanoparticles can be obtained by sonochemical process using ZnCl₂ and thiacetamide as raw materials. It is found that the as prepared ZnS nanoparticles are hexagonal phase with spherical or spherical-like morphologies. The grain size decreases with increasing ultrasonic irradiation power. Reaction kinetics shows that the weight content of ZnS nanoparticles increases linearly with reaction time at different temperatures. The synthesis activation energy of ZnS nanoparticles is calculated to be 27·80 kJ mol^–1.     

具有癌症诊疗潜力的多功能核壳纳米粒

采用乳化-溶剂挥发法制备了同时携载Mn3O4纳米粒和CuS白蛋白纳米粒的诊疗一体化多功能核壳纳米粒,可用于磁共振造影成像手段指引下的肿瘤光热消融,实现癌症的高效诊治.首先用高温热解法制备出粒径均一、分散性较好的Mn3O4纳米粒,并通过蛋白模板法制备CuS白蛋白纳米粒,之后采用可降解性聚乳酸-羟基乙酸共聚物(PLGA)作...     

Synthesis of LaF3: Yb3+ ,Ln3+ nanoparticles with improved upconversion luminescence

Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ co-doped LaF₃ nanoparticles with upconversion luminescence properties were prepared via the co-precipitation method, followed by heat treatment at different temperatures in the range of 180°C to 600°C. We investigated the influence of heat treatment temperatures on the size, morphology, and upconversion luminescence intensity of the nanoparticles. Significant increases of the particle size and upconversion luminescence intensity of the nanoparticles were observed with increasing heat treatment temperature. The upconversion mechanism of the LaF₃:Yb³⁺,Er³⁺ and LaF₃:Yb³⁺,Tm³⁺ nanoparticles was also discussed.     

Samarium-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles with improved magnetic and supercapacitive performance: a novel preparation strategy and characterization

Sm³⁺-doped magnetite (Fe₃O₄) nanoparticles were synthesized through a one-pot facile electrochemical method. In this method, products were electrodeposited on a stainless steel (316L) cathode from an additive-free 0.005 M Fe(NO₃)₃/FeCl₂/SmCl₃ aqueous electrolyte. The structural characterizations through X-ray diffraction, field-emission electron microscopy, and energy-dispersive X-ray indicated that the deposited material has Sm³⁺-doped magnetite particles with average size of 20 nm. Magnetic analysis by VSM revealed the superparamagnetic nature of the prepared nanoparticles (Ms = 41.89 emu g^?1, Mr = 0.12 emu g^?1, and H _Ci = 2.24 G). The supercapacitive capability evaluation of the prepared magnetite nanoparticles through cyclic voltammetry and galvanostat charge–discharge showed that these materials are capable to deliver specific capacitances as high as 207 F g^?1 (at 0.5 A g^?1) and 145 F g^?1 (at 2 A g^?1), and capacity retentions of 94.5 and 84.6% after 2000 cycling at 0.5 and 1 A g^?1, respectively. The results proved the suitability of the electrosynthesized nanoparticles for use in supercapacitors. Furthermore, this work provides a facile electrochemical route for the synthesis of lanthanide-doped magnetite nanoparticles.     

Synthesis process and luminescence properties of Ln doped NaY(WO4)2 nanoparticles

The hydrothermal synthesis process and luminescence properties of Ln³⁺ doped NaY(WO₄)₂ nanoparticles have been investigated. Nearly spherical Eu³⁺ doped NaY(WO₄)₂ nanoparticles can be observed. The luminescence concentration quenching of Eu³⁺ in the NaY(WO₄)₂ nanoparticles was found to be similar to that in the NaY(WO₄)₂ crystals. The upconversion luminescence intensity of the Yb³⁺-Er³⁺ codoped NaY(WO₄)₂ nanoparticles was found to be much stronger than that of the Er³⁺ doped NaY(WO₄)₂ nanoparticles.     

Surface engineered magnetic nanoparticles for removal of toxic metal ions and bacterial pathogens

Surface engineered magnetic nanoparticles (Fe₃O₄) were synthesized by facile soft-chemical approaches. XRD and TEM analyses reveal the formation of single-phase Fe₃O₄ inverse spinel nanostructures. The functionalization of Fe₃O₄ nanoparticles with carboxyl (succinic acid), amine (ethylenediamine) and thiol (2,3-dimercaptosuccinic acid) were evident from FTIR spectra, elemental analysis and zeta-potential measurements. From TEM micrographs, it has been observed that nanoparticles of average sizes about 10 and 6 nm are formed in carboxyl and thiol functionalized Fe₃O₄, respectively. However, each amine functionalized Fe₃O₄ is of size ∼40 nm comprising numerous nanoparticles of average diameter 6 nm. These nanoparticles show superparamagnetic behavior at room temperature with strong field dependent magnetic responsivity. We have explored the efficiency of these nanoparticles for removal of toxic metal ions (Cr³⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Pb²⁺ and As³⁺) and bacterial pathogens (Escherichia coli) from water. Depending upon the surface functionality (COOH, NH₂ or SH), magnetic nanoadsorbents capture metal ions either by forming chelate complexes or ion exchange process or electrostatic interaction. It has been observed that the capture efficiency of bacteria is strongly dependent on the concentration of nanoadsorbents and their inoculation time. Furthermore, these nanoadsorbents can be used as highly efficient separable and reusable materials for removal of toxic metal ions.     

Formation and stabilization of Pickering emulsions using salt-sensitive core–shell cationic nanoparticles

Pickering emulsions known for their solid emulsifiers and brilliant stability characters have attracted many researchers’ attention. The controlled stability and demulsification of emulsion are necessary in some cases such as crude oil extraction and drug release. Stimuli-responsive Pickering emulsion could provide suitable controllability and emerged in the last decade. Among various controllable factors, salt ion is known as a critical parameter, but it is rarely investigated. Here, core–shell cationic nanoparticles with a poly-(2-aminoethyl methacrylate hydrochloride) shell and a polystyrene core were used in the preparation of Pickering emulsion. The size and morphology of nanoparticles were monitored by transmission electron microscopy and dynamic light scattering. The microstructure and stability of the formed Pickering emulsion were studied via dynamic light scattering and a polarizing optical microscope under various salt ion types and concentrations. The effect of salt types (Cl^?, ClO₄^?, and PO₄^3?) and salt concentrations on the Pickering emulsion was investigated. Cl^?, ClO₄^?, and PO₄^3? are in situ generated from NaCl, NaClO₄, and (NaPO₃)₆, respectively. It showed that PO₄^3? (100–1000 mM) was unable to form stable Pickering emulsion, while Cl^? and ClO₄^? could induce stable Pickering emulsions under optimized conditions. Furthermore, after increasing the salt concentration over a critical salt concentration, the Pickering emulsion underwent rapid demulsification. This work revealed the effects of salt on size, conformation, charge, wettability, interaction, and adsorption state of nanoparticles and proposed the stability mechanisms of the Pickering emulsion. This opened up more potential applications in the field of controlled demulsification, petroleum recovery, catalyst recovery, and so on triggered by salt ions.

Graphical abstract

Salt could affect the size, conformation, and interaction of core–shell cationic nanoparticles, which then affect the formation mechanism and stability properties of Pickering emulsions from them.

     

Bio-conjugation of CaF2:Eu/chitosan nanoparticles with BSA and photoluminescent properties

CaF₂:Eu nanoparticles capped with chitosan and bio-conjugation of CaF₂:Eu/chitosan nanoparticles with bovine serum albumin (BSA) were synthesized via microemulsion method. As a surfactant, chitosan was employed to cap the nanoparticles during the synthesis process and provided functional groups, such as amino group for further bio-conjunction with BSA. CaF₂:Eu and CaF₂:Eu/chitosan–BSA nanoparticles were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), ultraviolet spectrophotometer (UV), infrared spectrophotometer (IR) and photoluminescence spectrophotometer (PL). The XRD results indicated that the CaF₂:Eu and CaF₂:Eu/chitosan-BSA nanoparticles have crystallized well and the average sizes were about 16 and 19 nm, respectively. Images of FE-SEM showed that the average grain sizes of the CaF₂:Eu and bio-conjunction of CaF₂:Eu/chitosan nanoparticles with BSA were about 19 and 20 nm. The patterns of UV spectra and IR spectra showed that BSA was linked to CaF₂:Eu/chitosan nanoparticles. In the emission spectrum of the CaF₂:Eu/chitosan–BSA nanoparticles, characteristic emission peaks of Eu³⁺ within the wavelength ranging from 500 to 700 nm were observed, corresponding to the transitions from the excited ⁵D₀ levels to ⁷F_J levels. This confirmed that the Eu³⁺dopant ion is located in a Ca²⁺ crystal site with Td symmetry.