Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300 ± 70 nm to 90 ± 20 nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80 ± 10 nm to 13 ± 5 nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO₃) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.     

Thickness dependence of optical parameters for Ge–Se–Te thin films

The present work deals with thickness dependent study of the thin films of Ge₁₀Se_90 − xTe_x (x = 0, 10) chalcogenide glasses. Bulk samples of Ge₁₀Se₉₀ and Ge₁₀Se₈₀Te₁₀ have been prepared by melt quenching technique. Thin films (thickness d = 800 nm and 1100 nm) of the prepared samples have been deposited on glass substrate using vacuum evaporation technique. The optical parameters i.e. optical band gap (E_g^opt), absorption coefficient (α), refractive index (n) and extinction coefficient (k) are calculated from the transmission spectrum in the range 400–1500 nm. The optical band gap decreases with the increase of thickness from 1.87 ± 0.01 eV (d = 800 nm) to 1.80 ± 0.01 eV (d = 1100 nm) for Ge₁₀Se₉₀ and from 1.62 ± 0.01 eV (d = 800 nm) to 1.48 ± 0.01 eV (d = 1100 nm) for Ge₁₀Se₈₀Te₁₀ thin films.     

Hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer

We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V_OC = 1.041 V, J_SC = 2.97 mA/cm², FF = 32.3%) to 2.6% (V_OC = 1.336 V, J_SC = 4.65 mA/cm², FF = 41.98%) due to the eliminated interfacial series resistance.     

Study on the ITO work function and hole injection barrier at the interface of ITO/a-Si:H(p) in amorphous/crystalline silicon heterojunction solar cells

For this study we focused on the front contact barrier height of HIT (ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)) solar cell. The ITO films with low resistivity of 1.425 × 10^?4 Ω cm were deposited by pulsed DC magnetron sputtering as a function of substrate temperature (T_s). There were improvement in Φ_ITO from 4.15 to 4.30 eV and delta hole injection barrier from 0 to 0.129 eV for the HIT solar cell. The results show that the high values of Φ_ITO and the delta hole injection barrier at the front interface of ITO/p-layer lead to an increase of open circuit voltage (V_oc), fill factor (FF) and efficiency (η). The performance of HIT device was improved with the increase of T_s and the best photo voltage parameters of the device were found to be V_oc = 635 mV, FF = 0.737 and η = 14.33% for T_s = 200 °C.     

Stoichiometric and non-stoichiometric films in the Si–O–N system: mechanical,electrical, and dielectric properties

A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H₃Si–O–SiH₃) and ammonia (NH₃), is described to deposit stoichiometric, Si₂N₂O, and non-stoichiometric, SiO_xN_y, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si₂N₂O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min⁻¹ with complete hydrogen elimination. The deposition rate of SiO_xN_y on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10⁻⁶ Torr was ∼1.5 nm min⁻¹, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si₂N₂O, and the capacitance–voltage (C–V) as a function of frequency and leakage current density–voltage (J_L–V) characteristics were determined on MOS (Al/Si₂N₂O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and J_L at 6 V for a 20 nm Si₂N₂O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm⁻², respectively.     

Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R_air/R_alcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R² of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.     

Effects of aluminum substitution on photocatalytic property of BiVO4 under visible light irradiation

Novel visible-light-driven Al/BiVO₄ photocatalysts were synthesized via a facile hydrothermal method for the first time. The samples were characterized by X-ray diffraction, N₂-sorption, UV–vis diffuse reflectance spectra, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transformed infrared spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of methylene blue under visible light irradiation (400 nm < λ <580 nm) and was compared with that of single-phase BiVO₄. The results revealed that the introduction of Al can improve photocatalytic performance greatly and different concentration of Al resulted in different photocatalytic activity. The highest activity is obtained by the sample with a doping concentration of 12 at%. The reason for the enhanced photocatalytic activities of Al/BiVO₄ samples was also discussed in this paper.     

Synthesis and magnetic properties of Pr0.57Ca0.43MnO3 nanoparticles

Pr_0.57Ca_0.43MnO₃ nanoparticles with an average particle size of ∼20 nm have been synthesized using hydrothermal method in combination with post-annealing, and characterized using X-ray diffraction, X-ray photoelectron spectrometer, high-resolution transmission electron microscopy and superconducting quantum interference device magnetometery. The results show that the hydrothermal synthesis of Pr_1−xCa_xMnO₃ compound below 240 °C is difficult. The Pr_0.57Ca_0.43MnO₃ nanoparticles obtained by annealing the hydrothermal products at 900 °C for 2 h present an orthorhombic perovskite structure with the same lattice as bulk Pr_0.6Sr_0.4MnO₃. Magnetic characterization reveals that the low-temperature antiferromagnetic and charge ordering transitions identified in bulk Pr_0.57Ca_0.43MnO₃ are completely suppressed in the nanoparticles, while a ferromagnetic transition occurs at ∼110 K. The spin-freezing behavior at low temperature for the Pr_0.57Ca_0.43MnO₃ nanoparticles is demonstrated.     

Silver nanoparticle-loaded chitosan–starch based films: Fabrication and evaluation of tensile,barrier and antimicrobial properties

The fabrication of silver nanoparticles was accomplished by γ-ray irradiation reduction of silver nitrate in a chitosan solution. The obtained nanoparticles were stable in the solution for more than six months, and showed the characteristic surface plasmon band at 411 nm as well as a positively charged surface with 40.4 ± 2.0 mV. The silver nanoparticles presented a spherical shape with an average size of 20–25 nm, as observed by TEM. Minimum inhibitory concentration (MIC) against E. coli, S. aureus and B. cereus of the silver nanoparticles dispersed in the γ-ray irradiated chitosan solution was 5.64 µg/mL. The silver nanoparticle-loaded chitosan–starch based films were prepared by a solution casting method. The incorporation of silver nanoparticles led to a slight improvement of the tensile and oxygen gas barrier properties of the polysaccharide-based films, with diminished water vapor/moisture barrier properties. In addition, silver nanoparticle-loaded films exhibited enhanced antimicrobial activity against E. coli, S. aureus and B. cereus. The results suggest that silver nanoparticle-loaded chitosan–starch based films can be feasibly used as antimicrobial materials for food packaging and/or biomedical applications.     

Low-temperature synthesis,structural and magnetic properties of self-dopant LaMnO3+δ nanoparticles from a metal-organic polymeric precursor

Self-dopant LaMnO_3+δ nanoparticles have been successfully synthesized by metal citrate complex method based on Pechini-type reaction route, at low temperature (773 K). Powder X-ray diffraction and transmission electron microscope revealed pure and nanostructured phase of LaMnO_3+δ (δ = 0.125) with an average grain size of ∼72 nm (773 K) and ∼80 nm (1173 K). DC-magnetization measurements under an applied magnetic field of H = ±60 kOe showed an increase in the magnetization with the increase of calcination temperature. Ferromagnetic nature shown by non-stoichiometric LaMnO_3+δ was verified by well-defined hysteresis loop with large remanent magnetization (M_r) and coercive field (H_c). Surface areas of LaMnO_3+δ nanoparticles were found to be 157.4 and 153 m² g⁻¹ for the samples annealed at 773 K and 1173 K, respectively.     

Synthesis of nanocrystalline GaN from Ga2O3 nanoparticles derived from salt-assisted spray pyrolysis

Gallium nitride (GaN) nanoparticles were successfully produced from nano-sized gallium oxide (Ga₂O₃) particles under a flow of ammonia gas. The gallium oxide nanoparticles were prepared by salt-assisted spray pyrolysis (SASP). Highly crystalline Ga₂O₃ nanoparticles with an average diameter of approximately 10 nm were obtained at various temperatures when a flux salt (LiCl, 5 mol/l) was added to the precursor solution. The effects of the crystallinity of the Ga₂O₃ particles and nitridation time on transformation to GaN were characterized using X-ray diffraction and scanning/transmission electron microscopy. Highly crystalline GaN nanoparticles with a mean size of 23.4 nm and a geometric standard deviation of 1.68 nm were obtained when Ga₂O₃ nanoparticles with relatively low crystallinity were used as the starting material. The resulting GaN nanoparticles showed a photoluminescence peak at 364 nm under UV excitation at 254 nm.     

Microwave-assisted hydrothermal synthesis of zinc oxide particles starting from chloride precursor

Zinc oxide (ZnO) was synthesized using a microwave assisted hydrothermal (MAH) process based on chloride/urea/water solution and under 800 W irradiation for 5 min. In the bath, Zn²⁺ ions reacted with the complex carbonate and hydroxide ions to form zinc carbonate hydroxide hydrate (Zn₄CO₃(OH)₆·H₂O), and the conversion from Zn₄CO₃(OH)₆·H₂O to ZnO was synchronously achieved by a MAH process. The as-prepared ZnO has a sponge-like morphology. However, the initial sponge-like morphology of ZnO could change to a net-like structure after thermal treatment, and compact nano-scale ZnO particles were finally obtained when the period of thermal treatment increased to 30 min. Pure ZnO nanoparticles was obtained from calcination of loose sponge-like ZnO particles at 500 °C. The analysis of optical properties of these ZnO nanoparticles showed that the intensity of 393 nm emission increased with the calcination temperature because the defects were reduced and the crystallinity was improved.     

Template-free hydrothermal derived cobalt oxide nanopowders: Synthesis,characterization, and removal of organic dyes

Pure spinel cobalt oxide nanoparticles were prepared through hydrothermal approach using different counter ions. First, the pure and uniform cobalt carbonate (with particle size of 21.8–29.8 nm) were prepared in high yield (94%) in an autoclave in absence unfriendly organic surfactants or solvents by adjusting different experimental parameters such as: pH, reaction time, temperature, counter ions, and (Co²⁺:CO₃^2?) molar ratios. Thence, the spinel Co₃O₄ (with mean particle size of 30.5–47.35 nm) was produced by thermal decomposition of cobalt carbonate in air at 500 °C for 3 h. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and thermal analysis (TA). Also, the optical characteristics of the as-prepared Co₃O₄ nanoparticles revealed the presence of two band gaps (1.45–1.47, and 1.83–1.93 eV). Additionally, adsorption of methylene blue dye on Co₃O₄ nanoparticles was investigated and the uptake% was found to be >99% in 24 h.     

Synthesis of carboxyl-capped and bright YVO4:Eu,Bi nanoparticles and their applications in immunochromatographic test strip assay

Carboxyl-capped YVO₄:Eu,Bi nanoparticles with average diameter of ∼10 nm were synthesized via a copolymer of phosphono and carboxylic acid mediated hydrothermal method. Under a 350 nm ultraviolet light excitation, the YVO₄:Eu,Bi NPs exhibit sharp and bright red emission peaked at 615 nm and with highest quantum yield of ∼43%. Furthermore, the nanoparticles show good water/buffer stability and feasible bioconjugation benefiting from the carboxylic groups on their surface. Based on these kind optical and surface properties of the YVO₄:Eu,Bi nanoparticles, an immunochromatographic test strip assay for quantitative determination of human IgG was achieved. This protocol can be extended to other rare-earth nanoparticles with the purpose of developing bioprobes for desired applications.     

Synthesis of tellurium nanowires and their transport property

By using Na₂TeO₃ and Na₂S₂O₃ as starting materials, tellurium nanowires with diameter around 25 nm were synthesized via a hydrothermal reaction at 160 °C, X-ray diffraction (XRD) showed that the product was a pure trigonal phase and TEM image indicated the widths of nanowires were in the range of 10–40 nm. Through further high-resolution TEM (HRTEM) analysis, a preferential growth direction along the [0 0 1] zone axis was observed. The intrinsic structure of tellurium, as well as the directing role of PVP leading to the formation of the 1D nanostructure was briefly discussed. Field effect transistor from individual nanowire was constructed, the nanowire device revealed a pronounced gating effect, and yield a threshold voltage of 40 V, an on–off ratio as high as 10³_, and a mobility of 163 cm² V^?1 S^?1 at V_ds = ?0.1 V.     

Effect of processing methods on physicochemical properties of titania nanoparticles produced from natural rutile sand

Titania (TiO₂) nanoparticles were produced from natural rutile sand using different approaches such as sol–gel, sonication and spray pyrolysis. The inexpensive titanium sulphate precursor was extracted from rutile sand by employing simple chemical method and used for the production of TiO₂ nanoparticles. Particle size, crystalline structure, surface area, morphology and band gap of the produced nanoparticles are discussed and compared with the different production methods such as sol–gel, sonication and spray pyrolysis. Mean size distribution (d₅₀) of obtained particles is 76 ± 3, 68 ± 3 and 38 ± 3 nm, respectively, for sol–gel, sonication and spray pyrolysis techniques. The band gap (3.168 < 3.215 < 3.240 eV) and surface area (36 < 60 < 103 m² g^?1) of particles are increased with decreasing particle size (76 > 68 > 38 nm), when the process methodology is changed from sol–gel to sonication and sonication to the spray pyrolysis. Among the three methods, spray pyrolysis yields high-surface particles with active semiconductor bandgap energy. The effects of concentration of the precursor, pressure and working temperature are less significant for large-scale production of TiO₂ nanoparticles from natural minerals.     

Activated hydride-mediated solution phase synthesis of crystallized antimony(0) nanoparticles

This work presents a simple method to produce large quantities of crystallized antimony(0) nanoparticles through SbCl₃ chemical reduction using t-BuONa-activated sodium hydride. t-BuONa acts as a superficial stabilizer of Sb(0) nanoparticles inhibiting their growth and avoiding aggregation. The Sb(0) nanoparticles were characterized using transmission electron microscopy, XPS analysis and X-ray powder diffraction. Results obtained show that rhombohedral Sb(0) with diameters of ca. 4.7 ± 1.9 nm were produced. The influence of purification conditions on the aggregation state of Sb(0) particles is also described.     

Statistical optimization of experimental parameters for synthesis of manganese carbonate and manganese oxide nanoparticles

Taguchi robust design was used for optimization of direct precipitation reaction conditions in order to simple and fast synthesis of manganese carbonate nanoparticles. Manganese carbonate nanoparticles were synthesized in this study by addition of manganese ion solution to the aqueous carbonate reagent. Effects of several reaction variables, such as manganese and carbonate concentrations, flow rate of reagent addition and temperature on particle size of prepared manganese carbonate were investigated. The significance of these parameters in tuning the size of manganese carbonate particles was quantitatively evaluated by analysis of variance. The results showed that manganese concentration and carbonate concentration in the solutions and also flow rate have significant effects in preparation of manganese carbonate nanoparticles. Also, optimum conditions for synthesis of manganese carbonate nanoparticles via precipitation reaction were proposed. Analysis of variance showed that under the optimum condition, the size of manganese carbonate nanoparticles will be about 54 ± 12 nm. In another part of this study, solid state thermal decomposition reaction of precursor was used for preparation of Mn₂O₃ nanoparticles. The results showed that Mn₂O₃ nanoparticles synthesized via thermal decomposition of manganese carbonate nanoparticles have average size of 90 nm.     

Vanadium oxide nanodisks: Synthesis,characterization, and electrochemical properties

Highly crystallined VO_1.6·H₂O nanodisks assembled from nanoparticles have been successfully fabricated under hydrothermal conditions by using bulk V₂O₅ and Na₂S₂O₃ as the starting materials in the presence of surfactant polyethylene glycol 4000 (PEG-4000). The nanodisks have a diameter of 200 nm and thickness of 40 nm. Hollow nanodisks are occasionally observed, which is similar to Chinese ancient copper coins. The formation of nanodisks can be ascribed to a novel solid-solution-solid growth mechanism. Compared with other methods, the solid state transformation method is simple and economic. In addition, the nanodisks exhibit good electrochemical behavior and promising to be used in lithium-ion battery.     

Preparation and characterization of LTA-type zeolite framework dispersed ruthenium nanoparticles and their catalytic application in the hydrolytic dehydrogenation of ammonia–borane for efficient hydrogen generation

The safe and efficient hydrogen storage and production are major obstacles to use hydrogen as an energy carrier. Therefore, significant efforts have been focused on the development of new materials for the chemical hydrogen storage and production. Of particular importance, ammonia–borane (NH₃BH₃) is emerging as one of the most promising solid hydrogen carrier due to its high gravimetric hydrogen storage capacity (19.6 wt.%) and low molecular weight (30.8 g/mol). ammonia–borane can release hydrogen gas upon catalytic hydrolysis under mild conditions. Herein, the discovery of a new catalytic material, ruthenium nanoparticles stabilized by ZK-4 zeolite framework, for this important reaction has been reported. This new catalyst system was prepared by borohydride reduction of ruthenium(III)-exchanged ZK-4 zeolite in water at room temperature. The characterization of the resulting material by advanced analytical tools shows the formation of ZK-4 zeolite dispersed ruthenium nanoparticles (2.9 ± 0.9 nm). The catalytic performance of the resulting supported ruthenium nanoparticles depending on activity, lifetime and reusability was demonstrated in the hydrolytic dehydrogenation of ammonia–borane. They were found to be highly active (initial TOF = 5410 h^?1), long-lived (TTO = 36,700) and reusable catalyst (retaining of >85% of initial activity in the 5th reuse) in this important catalytic reaction at room temperature under air.