Microwave-assisted rapid synthesis of Ag nanoparticles/graphene nanosheet composites and their application for hydrogen peroxide detection

Abstract  

Ag nanoparticles/graphene nanosheet (AgNPs/GN) composites have been rapidly prepared by a one-pot microwave-assisted reduction method, carried out by microwave irradiation of a N,N-dimethylformamide (DMF) solution of graphene oxide (GO) and AgNO₃. Several analytical techniques including UV–vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) have been used to characterize the resulting AgNPs/GN composites. It suggests that such composites exhibit good catalytic activity toward reduction of hydrogen peroxide (H₂O₂), leading to a H₂O₂ sensor with a fast amperometric response time of less than 2 s. The linear detection range is estimated to be from 0.1 to 100 mM (r = 0.999), and the detection limit is estimated to be 0.5 μM at a signal-to-noise ratio of 3.     

Chitosan loaded with silver nanoparticles,CS‐AgNPs,using thymus syriacus,wild mint,and rosemary essential oil extracts as reducing and capping agents

The present study describes the green method for the preparation of chitosan loaded with silver nanoparticles (CS‐AgNPs) in the presence of 3 different extracted essential oils. The essential oils play dual roles as reductant and capping agents. The reducing power and DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) assay for the 3 essential oils—Thymus syriacus (T), wild mint (M), and rosemary (R)—have been reported. The preparation of CS‐AgNPs was performed by 2 steps. The 3 previously extracted essential oils have been used as reducing and capping agent in the first step, while in the second step, silver nanoparticles were integrated in chitosan. The integration of AgNPs in the structure of chitosan was confirmed by ultraviolet‐visible, Fourier transform infrared spectroscopy, scanning electron microscopy techniques, and energy dispersive X‐ray. Surface plasmon resonance confirmed the formation of CS‐AgNPs with maximum absorbance at λ_max between 405 ‐ 410 and 410 ‐ 430 nm for colloidal and films of CS‐AgNPs, respectively. The intensity of bands at 3408 cm^?1 in the fourier transform infrared spectroscopy measurements was decreased substantially and shifted slightly to lower frequency (?υ = 43 cm^?1). Scanning electron microscopy shows a spherical morphology of AgNPs with size of 62 nm for both colloidal and film samples, and energy dispersive X‐ray analysis shows peaks confirming AgNPs formation.     

One-pot synthesis and characterization of rhodamine derivative-loaded magnetic core–shell nanoparticles

A new method to produce elaborate nanostructure with magnetic and fluorescent properties in one entity is reported in this article. Magnetite (Fe₃O₄) coated with fluorescent silica (SiO₂) shell was produced through the one-pot reaction, in which one reactor was utilized to realize the synthesis of superparamagnetic core of Fe₃O₄, the formation of SiO₂ coating through the condensation and polymerization of tetraethylorthosilicate (TEOS), and the encapsulation of tetramethyl rhodamine isothiocyanate-dextran (TRITC-dextran) within silica shell. Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) were carried out to investigate the core–shell structure. The magnetic core of the core–shell nanoparticles is 60 ± 10 nm in diameter. The thickness of the fluorescent SiO₂ shell is estimated at 15 ± 5 nm. In addition, the fluorescent signal of the SiO₂ shell has been detected by the laser confocal scanning microscopy (LCSM) with emission wavelength (λ_em) at 566 nm. In addition, the magnetic properties of TRITC-dextran loaded silica-coating iron oxide nanoparticles (Fe₃O₄@SiO₂ NPs) were studied. The hysteresis loop of the core–shell NPs measured at room temperature shows that the saturation magnetization (M _s) is not reached even at the field of 70 kOe (7T). Meanwhile, the very low coercivity (H _c) and remanent magnetization (M _r) are 0.375 kOe and 6.6 emu/g, respectively, at room temperature. It indicates that the core–shell particles have the superparamagnetic properties. The measured blocking temperature (T _B) of the TRITC-dextran loaded Fe₃O₄@SiO₂ NPs is about 122.5 K. It is expected that the multifunctional core–shell nanoparticles can be used in bio-imaging.     

Synthesis and magnetic properties of single-crystalline BaFe12O19 nanoparticles

Rod-like and platelet-like nanoparticles of simple-crystalline barium hexaferrite (BaFe₁₂O₁₉) have been synthesized by the molten salt method. Both particle size and morphology change with the reaction temperature and time. The easy magnetization direction (0 0 l) of the BaFe₁₂O₁₉ nanoparticles has been observed directly by performing X-ray diffraction on powders aligned at 0.5 T magnetic field. The magnetic properties of the BaFe₁₂O₁₉ magnet were investigated with various sintering temperatures. The maximum values of saturation magnetization (σ_s=65.8 emu/g), remanent magnetization (σ_r=56 emu/g) and coercivity field (H_ic=5251 Oe) of the aligned samples occurred at the sintering temperatures of 1100 °C. These results indicate that BaFe₁₂O₁₉ nanoparticles synthesized by the molten salt method should enable detailed investigation of the size-dependent evolution of magnetism, microwave absorption, and realization of a nanodevice of magnetic media.     

Sonochemical fabrication of Fe3O4 nanoparticles on reduced graphene oxide for biosensors

This study synthesized Fe₃O₄ nanoparticles of 30–40 nm by a sonochemical method, and these particles were uniformly dispersed on the reduced graphene oxide sheets (Fe₃O₄/RGO). The superparamagnetic property of Fe₃O₄/RGO was evidenced from a saturated magnetization of 30 emu/g tested by a sample-vibrating magnetometer. Based on the testing results, we proposed a mechanism of ultrasonic waves to explain the formation and dispersion of Fe₃O₄ nanoparticles on RGO. A biosensor was fabricated by modifying a glassy carbon electrode with the combination of Fe₃O₄/RGO and hemoglobin. The biosensor showed an excellent electrocatalytic reduction toward H₂O₂ at a wide, linear range from 4 × 10^?6 to 1 × 10^?3 M (R² = 0.994) as examined by amperometry, and with a detection limit of 2 × 10^?6 M. The high performance of H₂O₂ detection is attributed to the synergistic effect of the combination of Fe₃O₄ nanoparticles and RGO, promoting the electron transfer between the peroxide and electrode surface.     

A hydrogen peroxide electrochemical sensor based on Ag nanoparticles grown on ITO substrate

In this article, the Ag nanoparticles were synthesized on indium tin oxide conducting glass (ITO) substrate using the electrochemical deposition method. The morphology analysis of the deposits using scanning electron microscope (SEM) reveals that the sizes and densities of the Ag nanoparticles were tuned by varying the time of electrodeposition. The structure of the deposits was characterized by X-ray diffraction (XRD). The prepared Ag nanoparticles electrode was then applied to detect hydrogen peroxide (H₂O₂) in 0.01 M pH 7.0 phosphate buffer medium. The present electrochemical sensing platform exhibited good electrocatalytic activity towards the reduction of H₂O₂. The detection sensitivity of the sensor was 0.237 mA mM⁻¹. This method is very simple, inexpensive, and undemanding, thus it should be extensively applied in many fields for the detection of H₂O₂.     

A simple and sensitive fluorescence quenching method for the determination of H(2)O(2) using Rhodamine B and FE(3)O(4) nanocatalyst

In pH 1.99 sodium acetate-HCl buffer solutions at 60 °C, Rhodamine B exhibited a strong fluorescence peak at 584 nm using an excitation wavelength of 548 nm. The fluorescence quenching occurred when Fe₃O₄ nanoparticles catalyzed H₂O₂ oxidation of Rhodamine B. Under the chosen conditions, the fluorescence intensity at 584 nm decreased when the concentration of H₂O₂ increased. The fluorescence quenching intensity is linear with the concentration of H₂O₂ in the range of 10–200 nmol/L. Thus, a new and simple and sensitive nanocatalytic fluorescence method was proposed for the determination of H₂O₂ in synthetic sample, with satisfactory results.     

Superparamagnetic Ni:SiO<Subscript>2</Subscript>–C nanocomposites films synthesized by a polymeric precursor method

In this work, we report on the magnetic properties of nickel nanoparticles (NP) in a SiO₂–C thin film matrix, prepared by a polymeric precursor method, with Ni content x in the 0–10 wt% range. Microstructural analyses of the films showed that the Ni NP are homogenously distributed in the SiO₂–C matrix and have spherical shape with average diameter of ~10 nm. The magnetic properties reveal features of superparamagnetism with blocking temperatures T _B ~ 10 K. The average diameter of the Ni NP, estimated from magnetization measurements, was found to be ~4 nm for the x = 3 wt% Ni sample, in excellent agreement with X-ray diffraction data. M versus H hysteresis loops indicated that the Ni NP are free from a surrounding oxide layer. We have also observed that coercivity (H _C) develops appreciably below T _B, and follows the H _C ∝ [1 – (T/T _B)^0.5] relationship, a feature expected for randomly oriented and non-interacting nanoparticles. The extrapolation of H _C to 0 K indicates that coercivity decreases with increasing x, suggesting that dipolar interactions may be relevant in films with x > 3 wt% Ni.     

Synthesis and characterization of L10 FePt nanoparticles from Pt–Fe3O4 core-shell nanoparticles

Pt/Fe₃O₄ core-shell nanoparticles have been prepared by a modified polyol method. Pt nanoparticles were first prepared via the reduction of Pt(acac)₂ by polyethylene glycol-200 (PEG-200), and layers of iron oxide were subsequently deposited on the surface of Pt nanoparticles by the thermal decomposition of Fe(acac)₃. The nanoparticles were characterized by XRD and HR-TEM. The as-prepared Pt/Fe₃O₄ nanoparticles have a chemically disordered FCC structure and transformed into chemically ordered fct structure after annealing in reducing atmosphere (4% H₂, 96% Ar) at 700 °C. The ordered fct FePt phase has high magnetic anisotropy with coercivity reaching 7.5 kOe at room temperature and 9.3 kOe at 10 K.     

Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection

A simple sonochemical route was developed for the preparation of gold nanoparticles/boron nitride sheets (AuNPs/BNS) nanocomposites without using reducing or stabilizing agents. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV–vis absorption spectra were used to characterize the structure and morphology of the nanocomposites. The experimental results showed that AuNPs with approximately 20 nm were uniformly attached onto the BNS surface. It was found that the AuNPs/BNS nanocomposites exhibited good catalytic activity for the reduction of H₂O₂. The modified electrochemical sensor showed a linear range from 0.04 to 50 mM with a detection limit of 8.3 μM at a signal-to-noise ratio of 3. The findings provide a low-cost approach to the production of stable aqueous dispersions of nanoparticles/BNS nanocomposites.     

Enhanced magnetization of nanoparticles of Mg x Fe(3? x )O4 (0.5≤ x ≤1.5) synthesized by combustion reaction

For the first time nanocrystalline magnetic particles of Mg _x Fe_(3−x)O₄ with x ranging from 0.5 to 1.5 have been synthesized by a combustion reaction method using iron nitrate Fe(NO₃)₃.9H₂O, magnesium nitrate Mg(NO₃)₂.6H₂O, and urea CO(NH₂)₂ as fuel without intermediate decomposition and/or calcining steps. X-ray diffraction patterns of all systems showed broad peaks consistent with cubic inverse spinel structure of MgFe₂O₄. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures the phase purity. The mean crystallite sizes determined from the prominent (311) peak of the diffraction using Scherrer’s equation and transmission electron microscopy micrographs were c.a. 40 nm with spherical morphology. Fourier transform infrared spectra of the as-prepared material showed traces of organic and metallic salt by-products; however, these could be removed by washing with deionized water. Typical hysteresis curves were obtained for all specimens in magnetic field up to 14 T between 4 and 340 K. The saturation magnetization was 48.3 emu/g and 31.3 emu/g, 44.8 emu/g, and 28.4 emu/g for x=1.0 and 0.8 at 4 K and 340 K, respectively. The saturation magnetization, M _s , of nanoparticles of the MgFe₂O₄ specimen is about 50% higher when compared to the bulk. The enhanced magnetization measured in our nanoparticles MgFe₂O₄ specimens may be attributed to the uncompensated magnetic moment of iron ions between the A- and B-sites, i.e., changes in the inversion factor. Our magnetization results of MgFe₂O₄ specimens are comparable to the existing data for the same compound but with different particle size and prepared by different synthesis methods.     

Facile synthesis of monodispersed α-Fe2O3 microspheres through template-free hydrothermal route

Monodisperse α-Fe₂O₃ microspheres have been selectively synthesized through a facile hydrothermal method without the assistance of any surfactant, employing FeCl₃·6H₂O and NH₄NaHPO₄ as initial materials. The products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. α-Fe₂O₃ microspheres with average size about 250 nm were constructed by single crystalline nanoparticles with average diameter about 15 nm. The investigation on the evolution formation revealed that growth temperature was critical to control the assembly of the fresh formed nanocrystallites, and the microsphere formation was proved to be the Ostwald ripening process by tracking the structures of the products at different growth temperature. α-Fe₂O₃ microspheres showed a weak ferromagnetic behavior with a remanent magnetization of 0.208 emu g⁻¹ and a coercivity of 1,034.27 Oe at room temperature.     

Green synthesis of silver and gold nanoparticles using Rosa damascena and its primary application in electrochemistry

Biosynthesis and characterizations of nanoparticles have become an important branch of nanotechnology. In this paper, green synthesis of gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using the flower extract of Rosa damascena as a reducing and stabilizing agent, has been discussed. This approach is simple, cost-effective and stable for a long time, reproducible at room temperature and in an eco-friendly manner to obtain a self-assembly of AuNPs and AgNPs. The resulting nanoparticles are characterized using UV–vis, TEM, XRD and FT-IR spectroscopic techniques. A modified glassy carbon electrode using AuNPs (AuNPs/GCE) was investigated by means of cyclic voltammetry in a solution of 0.1 M KCl and 5.0×10⁻³ M [Fe(CN)₆]^3−/4−. The results show that electronic transmission rate between the modified electrode and [Fe(CN)₆]^3−/4− increased.     

ZrO<Subscript>2</Subscript>/DNA-derivated polyion hybrid complex membrane for the determination of hydrogen peroxide in milk

An efficient biosensing substrate based on ZrO₂/DNA-derivated polyion complex (PIC) membrane has been developed for the determination of hydrogen peroxide (H₂O₂) in this study. To fabricate such a PIC membrane, ZrO₂ nanoparticles were initially electrodeposited on the bare gold electrode (ZrO₂/Au), and deoxyribonucleic acid (DNA)-doped hemoglobin mixture was then assembled onto the ZrO₂/Au surface. The double-strand DNA provided a biocompatible microenvironment for the immobilization of biomolecules, greatly amplified the surface coverage of biomolecules on the electrode surface, and improved the sensitivity of the biosensor. The fabricated procedure of the proposed biosensor was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. The performance and factors influencing the performance of the biosensor were also evaluated. Under optimal conditions, the developed biosensor exhibited a well-defined electrochemical behavior toward the reduction of H₂O₂ ranging from 1.1 μM to 2.3 mM with a detection limit of 0.5 μM (S/N = 3). The biosensor was applied to the determination of H₂O₂ in milk with satisfactory results. It is important to note that the PIC membrane provided an alternative substrate for the immobilization of other proteins.     

Ultrafine α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles grown in confinement of in situ self-formed “cage” and their superior adsorption performance on arsenic(III)

Without the addition of surfactants or templates, ultrafine α-Fe₂O₃ nanoparticles were successfully synthesized by a solvent thermal process at low temperature. During the synthesis, in situ self-formed “cage” of crystallized NaCl confined the growth of α-Fe₂O₃ nanoparticles in both the precipitation and solvent thermal processes, resulting in the creation of well-crystallized α-Fe₂O₃ nanoparticles with an average particle size about 4–5 nm and a high-specific surface area of ~162 m²/g. High resolution TEM investigations provided clear evidences of the in situ self-formation of NaCl “cage” during the synthesis and its confinement effect on the growth of α-Fe₂O₃ nanoparticles. The superior performance of these α-Fe₂O₃ nanoparticles on the adsorption of arsenite(III) (As) from aqueous environment was demonstrated with both lab-prepared and natural water samples at near neutral pH environment when compared with previously reported removal effects of As(III) by Fe₂O₃. This unique approach may also be utilized in the synthesis of other ultrafine metal oxide nanoparticles for a broad range of technical applications.     

Synthesis of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids

Fe₃O₄ nanoparticles were hydrothermally synthesized under continuous microwave irradiation from FeCl₃·6H₂O and FeSO₄·7H₂O aqueous solutions, using NH₄OH as precipitating reagent and N₂H₄·H₂O as oxidation-resistant reagent. The results of X-ray powder diffraction (XRD), FT–IR spectroscopy and scanning electron microscopy (SEM) measurements showed that the synthesized magnetite (Fe₃O₄) nanoparticles had an average diameter of 10 nm. The magnetic properties of the Fe₃O₄ nanoparticles were measured using a vibrating sample magnetometer (VSM), indicating that the nanoparticles possessed high saturation magnetization at room temperature. The Fe₃O₄ nanoparticles were used to prepare magnetic fluids (MFs) based on water, and the properties of the MFs were characterized by a Gouy magnetic balance, a capillary rheometer and a rotating rheometer, respectively.     

Valency control in MoO<Subscript>3−δ</Subscript> nanoparticles generated by pulsed laser liquid solid interaction

The possibility of synthesizing binary oxides nanoparticles in a nano-scaled form by laser liquid solid interaction using a NdYAG “1.064 μm” as an irradiating laser source is reported. The case of MoO_3−δ is emphasized. Furthermore, it is demonstrated that the Mo–O electronic valence can be controlled through the coupling effects of oxygen enriched nature of the used coating liquid layer, namely pure H₂O or H₂O₂ and the laser beam fluence. Dark blue hydrated molybdic pentoxide Mo₂O₅·xH₂O and yellow molybdenum trioxide MoO₃ nano-suspensions were reproducibly synthesized with hydrogen peroxide and water, respectively, at a relatively high ablation rate. The average size of the molybdenum trioxide nanoparticles was about <ϕ>~8 nm, slightly larger than the molybdic pentoxide ones “<ϕ>~6.2 nm”.     

Electrochemical supercapacitor studies of hierarchical structured Co2+-substituted SnO2 nanoparticles by a hydrothermal method

Hierarchical structured Co-doped SnO₂ nanoparticles are prepared by a low temperature hydrothermal process. The structural and surface morphologies of the SnO₂ and Sn_1?xCo_xO₂ nanoparticles are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The Sn_1?xCo_xO₂ nanoparticles form with a tetragonal rutile structure during the hydrothermal process without further calcination. The pseudocapacitance behavior of the Sn_1?xCo_xO₂ nanoparticles is characterized by cyclic voltammetry (CV) in 1.0 M H₂SO₄ electrolyte. The specific capacitance (SC) is found to increase with an increase in cobalt content. A maximum SC of 840 F g^?1 is obtained for a Sn_0.96Co_0.04O₂ composite at a 10 mV s^?1 scan rate.     

Novel tacrine-based acetylcholinesterase inhibitors as potential agents for the treatment of Alzheimer’s disease: Quinolotacrine hybrids

A new series of quinolotacrine hybrids including cyclopenta- and cyclohexa-quinolotacrine derivatives were designed, synthesized, and assessed as anti-cholinesterase (ChE) agents. The designed derivatives indicated higher inhibitory effect on the acetylcholinesterase (AChE) with IC₅₀ values of 0.285–100 µM compared to butyrylcholinesterase (BChE) with IC₅₀ values of?>?100 µM. Of these compounds, cyclohexa-quinolotacrine hybrids displayed a little better anti-AChE activity than cyclopenta-quinolotacrine hybrids. Compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c'] diquinolin-6-one (6m) including 3-hydroxyphenyl and cyclohexane ring moieties exhibited the best AChE inhibitory activity with IC₅₀ value of 0.285 µM. The kinetic and molecular docking studies indicated that compound 6m occupied both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE as a mixed inhibitor. Using neuroprotective assay against H₂O₂-induced cell death in PC12 cells, the compound 6h illustrated significant protection among the assessed compounds. In silico ADME studies estimated good drug-likeness for the designed compounds. As a result, these quinolotacrine hybrids can be very encouraging AChE inhibitors to treat Alzheimer’s disease.

Graphic abstract

A novel series of quinolotacrine hybrids were designed, synthesized, and evaluated against AChE and BChE enzymes as potential agents for the treatment of AD. The hybrids showed good to significant inhibitory activity against AChE (0.285–100 μM) compared to butyrylcholinesterase (BChE) with IC₅₀ values of?>?100 μM. Among them, compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c′] diquinolin-6-one (6 m) bearing 3-hydroxyphenyl moiety and cyclohexane ring exhibited the highest anti-AChE activity with IC₅₀ value of 0.285 μM. The kinetic and molecular docking studies illustrated that compound 6 m is a mixed inhibitor and binds to both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE.

     

Sono-enhanced degradation of dye pollutants with the use of H2O2 activated by Fe3O4 magnetic nanoparticles as peroxidase mimetic

Sono-enhanced degradation of a dye pollutant Rhodamine B (RhB) was investigated by using H₂O₂ as a green oxidant and Fe₃O₄ magnetic nanoparticles (MNPs) as a peroxidase mimetic. It was found that Fe₃O₄ MNPs could catalyze the break of H₂O₂ to remove RhB in a wide pH range from 3.0 to 9.0 and its peroxidase-like activity was significantly enhanced by the ultrasound irradiation. At pH 5.0 and temperature 55 °C, the ultrasound-assisted H₂O₂–Fe₃O₄ catalysis removed about 95% of RhB (0.02 mmol L⁻¹) in 15 min with a apparent rate constant of 0.15 min⁻¹ for the degradation of RhB, being 6.5 and 37.6 folds of that in the simple catalytic H₂O₂–Fe₃O₄ system, and the simple ultrasonic US-H₂O₂ systems, respectively. The beneficial synergistic behavior between Fe₃O₄ catalysis and ultrasonic was demonstrated to be dependent on Fe₃O₄ dosage, H₂O₂ concentration, pH value and temperature. As a tentative explanation, the observed significant synergistic effects was attributed to the positive interaction between cavitation effect accelerating the catalytic breakdown of H₂O₂ over Fe₃O₄ nanoparticles, and the function of Fe₃O₄ MNPs providing more nucleation sites for the cavitation inception.