Preparation and characterization of nickel/zinc sulphide: Bifunctional magnetic-optical nanocomposites

Nickel nanoparticles coated with zinc sulphide can form complex spherical with a core–shell structure. This coating process was based on mercaptoacetic acid (HSCH₂COOH) as a primer to render the nickel surface vitreophilic, thus it renders nickel surface compatible with ZnS. The morphology, structure, chemical composition, optical properties and magnetic properties of the product were investigated by using various techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) spectroscope and vibrating sample magnetometer (VSM). It was found that the Ni/ZnS nanocomposites exhibited both magnetic and photoluminescent properties.     

Preparation and characterization of Bi-doped TiO2 and its solar photocatalytic activity for the degradation of isoproturon herbicide

Bi-doped TiO₂ catalyst was prepared by sol–gel method and was characterized by thermo gravimetric analysis (TGA), X-ray diffraction spectra (XRD), X-ray photo electronic spectroscopy (XPS), UV–Vis diffused reflectance spectra (DRS), photoluminescence spectra (PLS), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX) and BET surface area. The photocatalytic activity of the catalysts were evaluated for the degradation of isoproturon herbicide under solar light irradiation. The UV–Visible DRS of Bi-doped TiO₂ showed red shift in optical absorption. The presence of Bi^3+δ+ species are playing a vital role in minimizing the electron hole recombination resulting higher activity compared to bare TiO₂.     

Rapid synthesis, characterization and optical properties of TiO2 coated ZnO nanocomposite particles by a novel microwave irradiation method

A novel and rapid microwave method was used to prepare TiO₂ coated ZnO nanocomposite particles. The resulted particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Results show that ZnO nanoparticles were coated with 6-10 nm amorphous TiO₂ layers. In addition, zeta potential analysis demonstrated the presence of TiO₂ layer on the surface of ZnO nanoparticles. Photoluminescence (PL) spectroscopy and UV-visible spectroscopy were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnO nanoparticles, the TiO₂ coated ZnO nanoparticles showed enhanced UV emission. The UV-visible diffuse reflectance study revealed the significant UV shielding characteristics of the nanocomposite particles. Moreover, amorphous TiO₂ coating effectively reduced the photocatalytic activity of ZnO nanoparticles as evidenced by the photodegradation of Orange G with uncoated and TiO₂ coated ZnO nanoparticles under UV radiation.     

Enhanced luminescence of UV irradiated Zn(1−x)NixS nanoparticles

PVP-capped Zn_(1−x)Ni_xS (x = 0.001, 0.005, 0.01, 0.03, 0.05 and 0.1) nanoparticles have been synthesized using chemical precipitation route, in aqueous media, at room temperature. The synthesized nanoparticles have been irradiated by UV light for 24 h so as to study the effect on their structural and optical properties. The nanoparticles have been characterized through XRD and HRTEM to study the crystal structure and size. Characterization was also carried out through FTIR spectroscopy to reveal the presence of PVP and the effect of UV irradiation on the surface chemistry of the synthesized nanoparticles. The optical properties have been studied through UV–vis absorption spectroscopy and room temperature photoluminescence. There has been an enhancement in the intensity of the green emission centered at 547 nm, with increase in Ni concentration up to 0.5 at.% and a decrease in the intensity, observed for higher concentrations of Ni. However, the I(green)/I(blue) intensity ratio increases continuously with the increase in Ni concentration and also on prolonged UV irradiation of the samples.     

Controlled synthesis and characteristics of antireflection coatings of TiO2 produced from a organometallic colloid

Antireflection titanium dioxide (TiO₂) coatings have been developed on monocrystalline silicon by a sol–gel spin-coating process using titanium di-isopropoxidebis(acetylacetonate) colloidal precursor solution. The effect of titanium content in the precursor, spin rate, sintering duration and temperature have been studied and their effect on coating thickness and optical properties (i.e., refractive index and reflectivity) were investigated. The influence of post-deposition sintering temperature on the optical characteristics, composition and the microstructure of the coatings have been evaluated by UV–vis spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy and X-ray diffraction techniques. Solar cells made on silicon wafers with TiO₂ as antireflection layer showed enhancement of more than 20% in short circuit current density in comparison to a cell devoid of the TiO₂ coating.     

Investigation on the effect of Tb(dbm)3phen on the luminescent properties of Eu(dbm)3phen-containing mesoporous silica nanoparticles

Eu(dbm)₃phen and Tb(dbm)₃phen complexes (tris(dibenzoylmethane) mono(1,10-phenantroline) Ln(III)) were impregnated in ordered mesoporous silica nanoparticles (MSNs) with an average size of 50–70 nm and a pore diameter centred at 2.8 nm, with the aim of increasing the luminescence by avoiding concentration quenching and having mainly in mind the application as down-shifter for multi-crystalline solar cells. The morphological, structural, textural and luminescent properties of the synthesized samples were characterized by N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible spectroscopy and photoluminescence measurements. It is demonstrated that inclusion in the MSNs allows one to use much higher loadings (23 wt%) of the Eu-complex than in other matrices, and that co-doping with Tb(dbm)₃phen improves luminescence for samples with Eu(dbm)₃phen content lower than about 10 wt%. Results are interpreted by using a simple sphere of action model adapted to the case of a pore-limited system.     

Studies on morphological and optoelectronic properties of MEH-CN-PPV:TiO2 nanocomposites

Nanosized TiO₂ has been synthesized solvothermally using an autoclave. X-ray diffraction and electron microscopy studies elucidate that the synthesized nanoparticles are strongly crystalline and are dominantly in anatase phase. UV–vis and photoluminescence (PL) spectroscopy studies show a blue shift phenomenon in the synthesized nanoparticle in contrast to the bulk anatase TiO₂ which furnish evidence in support of quantum size effect. The nanocomposites of TiO₂ and MEH-CN-PPV have been prepared and characterized structurally (AFM, TEM) and optically (absorbance and photoluminescence). The nanocomposites have been used in light emitting diodes and electroluminescence (EL) and current density (J–V) of the device has been evaluated. The enhanced EL at elevated voltages for MEH-CN-PPV:5% TiO₂ hybrid device suggests influence of the reduced particle size and modified surface morphology.     

Oxidant-assisted preparation of CaMoO4 thin film using an irreversible galvanic cell method

CaMoO₄ thin films were prepared by an irreversible galvanic cell method at room temperature; the crystalline phase structure, surface morphology, chemical composition and room temperature photoluminescence property were characterized by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy as well as photoluminescence spectroscopy. Our results reveal that it is very difficult to directly deposit dense and uniform CaMoO₄ thin films in saturated Ca(OH)₂ solution at room temperature by the irreversible galvanic cell method. After adding some oxidant (NaClO solution or H₂O₂ solution), the growth of CaMoO₄ grains has been promoted, and well-crystallized, dense, and uniform CaMoO₄ films were obtained. The as-prepared CaMoO₄ films exhibit a good green photoluminescence, with the excitation of various wavelengths (220 nm, 230 nm, 240 nm, 250 nm and 270 nm) of ultraviolet irradiation.     

Surface functionalization for subsequent receptor coupling on inorganic nanoparticles

A two-stages process for an effective coupling of inorganic nanoparticles with biological receptor molecules is reported. Initial particle surface functionalization applies an ethylene glycol-based phosphonic acid or a corresponding ester analog with an azide functional group for subsequent receptor coupling under mild click chemistry conditions. A simple carbohydrate was applied as model receptor, while a luminescent LaPO₄:Ce,Tb with dimensions of 5–7 nm was chosen for the nanoparticle. Analysis of the particle surface applied IR and TGA, while effects of the surface modification on the particle core were investigated by XRD, TEM, SAXS, and fluorescence spectroscopy. The receptor content was determined using a photometric assay, leading to a surface loading of ~40 receptors per particle. This translates to a surface area of ~6.5 nm² per receptor based on the inorganic particle core.     

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO₂–TiO₂) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO₂–TiO₂ hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.     

Carbon-nanotube-supported Ag and Cu2O nanoparticles: Dendrimer-mediated synthesis and their broadband optical limiting properties

Multiwalled carbon nanotubes (MWCNTs) were covalently functionalized with fourth-generation poly(amido amine) (PAMAM) dendrimers with a trimesyl core (DT4), and the as-synthesized MWCNT-DT4 was used as the template for in situ growth of Ag and Cu₂O nanoparticles on MWCNTs. Extensive characterizations of the resultant hybrids have been performed using X-ray diffraction, transmission electron microscopy (TEM), high resolution TEM, energy dispersive X-ray spectroscopy, selected area electron diffraction, thermal gravimetric analysis, and X-ray photoelectron spectroscopy. The side-wall of the nanotubes was uniformly coated with the nanoparticles with mean sizes of 7–8 nm. The optical limiting property measurements of the nanoparticle-modified MWCNTs were carried out by the open-aperture z-scan technique. The results demonstrate that the samples suspended in water show broadband OL performance, and their OL behavior is better than that of MWCNT-DT4 in water due to the presence of Ag and Cu₂O nanoparticles.     

Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe₃O₄–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe₃O₄ (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe₃O₄ NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe₃O₄ NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe₃O₄ NPs with inverse spinel phase were formed. The results of VSM imply that the Fe₃O₄–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe₃O₄ NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.     

ZnO micro and nanocrystals with enhanced visible light absorption

In this paper, we investigate the effect of the particle size and morphology on the optical properties of ZnO. A series of ZnO micro and nanocrystals were synthesized by the hydrothermal processing of zinc acetate dihydrate and sodium hydroxide as the starting materials, and polyvinylpyrrolidone (PVP) as the polymer surfactant. The particle size and morphology were tailored by adjusting the reactant molar ratios [Zn²⁺]/[OH⁻], while the reaction temperature and the time remained unchanged. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) have shown that the micro and nanocrystals have a high crystalline pure wurtzite-type hexagonal structure with nanosized crystallites. The size and morphology of the ZnO micro and nanocrystals were investigated by field emission scanning electron microscopy (FE-SEM), which showed a modification from micro-rods via hexagonal-faceted prismatic morphology to nanospheres, caused by simple adjustment of the reactant molar ratio [Zn²⁺]/[OH⁻] from 1:1 to 1:5. The optical properties of the ZnO micro and nanocrystals, as well as their dependence on the particle size and morphology were investigated by Raman and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The UV–vis spectra showed that the modification of the particle size and morphology from nanospheres to micro-rods resulted in increased absorption, and a slight red-shift of the absorption edge (0.06 eV). Besides, the band gap energy of the synthesized ZnO micro and nanocrystals showed the red shift (∼0.20 eV) compared to bulk ZnO. According to the results of a Raman spectroscopy, the enhanced visible light absorption of the ZnO micro and nanocrystals is related to two phenomena: (1) the existence of lattice defects (oxygen vacancies and zinc interstitials), and (2) the particle surface sensitization by PVP.     

Solvothermal synthesis of LiFePO4 nanoplates with (010) plane and the uniform carbon coated on their surface by esterification reaction

A facile solvothermal synthesis and esterification reaction combined with a high temperature calcination technique has been developed to prepare the uniform carbon coating LiFePO₄ nanoplates. The carbon coating LiFePO₄ nanoplates are investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatic intermittent titration technique (GITT) and galvanostatic charge–discharge test. A reasonable growth mechanism of LiFePO₄ nanoplates is proposed on the basis of time dependent experimental results. The results show that each nanoplate is a LiFePO₄ single crystal with the large (010) plane. According to Raman spectroscopy analysis, carbon is uniformly coated on the surface of LiFePO₄ nanoplates. Electrochemical test results also indicate that the carbon coating LiFePO₄ nanoplates exhibit a high reversible specific capacity of 144.8 mAh g⁻¹ at 0.5 C and 116.9 mAh g⁻¹ under lower discharging rate at −20 °C.     

Architecture of Cu2O@TiO2 core–shell heterojunction and photodegradation for 4-nitrophenol under simulated sunlight irradiation

A Cu₂O@TiO₂ core–shell heterojunction photocatalyst was prepared by an in situ hydrolysis and crystallization method. The as-prepared catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. Under simulated sunlight irradiation, it exhibited high photocatalytic activity and stability for 4-nitrophenol (4-NP) degradation. Compared with neat Cu₂O and Cu₂O/TiO_2(PM) prepared by physical mixing, the heightened photocatalytic activity of Cu₂O@TiO₂ was attributed to the improvement of charge separation since large close interface was formed between the two semiconductors. The in situ method may generally be applied to develop other core–shell heterojunction photocatalysts.     

Facile synthesis and optical band gap calculation of Mn3O4 nanoparticles

Mn₃O₄ nanoparticles were prepared by a simple solid state decomposition method. Four manganese benzoic acid complexes were synthesized through semi-solid phase reaction method as precursors for the preparation of Mn₃O₄ nanoparticles. The calcination temperature of the precursors was determined from thermal gravimetrical analyses (TGA). The resulting nanoparticles were characterized by XRD, SEM, STM and HRTEM. The obtained particle size is in the range 39–90 nm. HRTEM indicated the formation of spherical nanoparticles. The optical absorption measurements for the obtained nanoparticles showed that the fundamental absorption edge obeys Tauc's relation for the allowed direct transition. It was found that, the optical band gap (E_g) increases with the decrease of the particle size of the Mn₃O₄ nanoparticles.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Characterization and corrosion behavior of electroless Ni–P/nano-SiC coating inside the CO2 containing media in the presence of acetic acid

In this research, Ni–P and Ni–P/nano-SiC coatings were applied on the X70 steel substrate successfully without any surfactant. Then, CO₂ corrosion in the presence of acetic acid (HAc) was investigated using electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used for surface analyses of the coatings. The electrochemical behavior of corrosion was investigated using polarization test and electrochemical impedance spectroscopy (EIS). XRD pattern of Ni–P/nano-SiC coating was very similar to that of Ni–P coating. EDS results demonstrated the presence of SiC particles in the coating. SEM images confirmed the presence of SiC nano-particles with almost uniform distribution in the coating. The corrosion current density was less in the Ni–P and Ni–P/nano-SiC coated samples than uncoated X70 steel. Ni–P/nano-SiC coated sample had the most corrosion resistance because of less effective metallic area available for corrosive media. The overall protection mechanism of Ni–P and Ni–P/nano-SiC coatings was achieved by formation of a layer of adsorbed hypophosphite anions (H₂PO₂⁻).     

Bifunctional Fe3O4@C/YVO4:Sm composites with the core–shell structure

A novel Fe₃O₄@C/YVO₄:Sm³⁺ composites with magnetic and luminescent properties were reported. Firstly, the as-synthesized Fe₃O₄ nanoparticles were coated by carbon as a shell via a simple hydrothermal method. Furthermore, the Fe₃O₄@C nanoparticles were modified by YVO₄:Sm³⁺ phosphors through a simple sol–gel process to prepared the Fe₃O₄@C/YVO₄:Sm³⁺ microspheres. The characterization of as-prepared products were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and vibrating sample magnetometer (VSM). It is shown that Fe₃O₄@C/YVO₄:Sm³⁺ composites with well-crystallized and core–shell structure were prepared. Additionally, the Fe₃O₄@C/YVO₄:Sm³⁺ composites show excellent magnetic properties (13 emu/g) and luminescent properties, which made the composites useful for applications in biomedical devices such as magnetic bio-separation and drug/gene delivery.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.