Simple one-pot sonochemical synthesis of copper sulphide nanoparticles for solar cell applications

Copper sulphide nanoparticles for solar cell applications were synthesized by a single step sonochemical method using copper acetate and thiourea as precursors. The effects of sonication time, ultrasonic bath temperature and annealing temperature on particle properties were studied. Synthesized particles were characterized using scanning electron microscope, transmission electron microscope, X-ray diffraction spectrophotometer and UV–visible spectrophotometer. The particles were found to be a mixture of chalcocite, covellite and djurleite. The optical band gap of the particles was found to be in the range of 1.6–2.1 eV. Heat treatment of the particles was found to give rise to needle shaped particles while a bath temperature of 55 °C yielded few nanoplates.     

Synthesis of fluorine doped tin oxide nanoparticles by sol–gel technique and their characterization

This article presents novel attempt to synthesis of fluorine doped tin oxide (FTO) nanoparticles by sol–gel technique. The synthesized FTO nanoparticles were obtained after calcination. Temperatures of calcination were 600 and 700 °C due to identify changes in the particles size growth. A DG/DTA and FTIR study identifies the oxide and formation of the nanopowders. The XRD studies confirm the tetragonal crystallite structure of fluorine doped tin oxide. The TEM image confirms the size of FTO particles in nanoscale. The electrical studies on FTO nanopowders results the decrease in resistivity profile with increasing calcinations. The optical band gap studies for sol–gel synthesis FTO nanoparticles is found to be in the range of 4.11–3.84 eV conforming decreasing optical band gap with increasing calcinating temperatures.     

Sol–gel derived nanostructured nickel oxide films: Effect of solvent on crystallographic orientations

Nickel oxide films were deposited onto glass substrates by sol–gel dip coating method using solvents of different polarities without any catalysts, templates or surfactants. Methanol, 1,4-butanediol, ethanol, and 2-propanol were used as solvents. The structural, optical and electrical properties of NiO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and Hall effect measurements, respectively. Nickel oxide thin films with cubic phase crystal structure of various preferred orientations were obtained in the different solvents. The XRD results showed that films deposited from solution using higher polar solvents develop a (1 1 1) preferred orientation, while the (2 0 0)-orientated films were obtained using lower polar solvents. The average particle size increases with viscosity of solvents. Surface morphology of the nickel oxide film consisted of nanoparticles with uniform coverage of the substrate surface. The solvent of higher viscosity induced larger particle size. Band gap narrowing from 4.42 to 3.87 eV was observed using different solvents. The lower resistivity and Hall coefficient was obtained for prepared NiO films using higher polar solvents. The relationships between solvent physicochemical properties, preferred orientation, structural, optical and electrical properties of NiO films were investigated.     

Investigation of structural,optical and photoluminescence properties of non-essential amino acid capped zinc sulfide nanoparticles for optoelectronic applications

The objective of the study is to synthesize Zinc Sulphide nanoparticles (ZnS) with different amino acid capping agents in aqueous solution by a simple and cost effective facile chemical co precipitation method and analyze their optoelectronic features. Bio compatibility with less toxic amino acids such as l-Glutamic acid, l-Alanine and l-Asparagine were used as capping agents. These amino acids are from Non-essential amino acid group and its capping behavior suitable for semiconducting nanoparticles like ZnS. The role of non essential amino acids were to stabilize the nanoparticle against agglomeration and also to provide chemical passivation that leads to a significant influence on the improved structural, optical and photoluminescence properties of ZnS nanoparticles. The detailed structural analysis of Zinc Sulphide nano particles revealed by X-ray diffraction method (XRD). From this analysis observed the formation of Cubic ZnS nanoparticles with an average crystallite size in the range of 2.08–2.22 nm.The morphology of the nano particles studied by Field emission scanning electron microscope (FESEM). Particle size examined by Dynamic Light scattering studies (DLS) and which revealed that particle size ranges are below 50 nm. The functional groups of nanoparticles were identified by Fourier transform Infrared spectroscopy (FT-IR) studies. Photoluminescence studies attributed that the considerable emission bands. The UV–Vis analysis disclosed the optical band gap range from 3.77 eV to 3.95 eV.     

Low-temperature synthesis and microstructural control of titania nano-particles

Nanocrystalline titania powders were synthesized at low temperature (⩽100°C) by a sol–gel method that achieved fine control of particle size and polymorph fraction. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis spectroscopy were used to characterize the phase assemblages, crystal size and band gap of the powders. It was demonstrated that larger, well-ordered titania crystals can be obtained by increasing aging temperature and time. These processing parameters can be adjusted to select specific polymorphs from the gel precursors with particular size and shape. The quantum size effect was observed in the size-controlled nanocrystalline titania particles, leading to a blue shift in UV absorption with decreasing in particle size. The anatase to rutile transformation, which may proceed with brookite as a transition phase, is dependent on both particle size and surface structure of the nascent crystals.     

Simple and low-temperature synthesis of NiO nanoparticles through solid-state thermal decomposition of the hexa(ammine)Ni(II) nitrate, [Ni(NH3)6](NO3)2, complex

NiO nanoparticles with an average size of about 12 nm were easily prepared via the thermal decomposition of hexa(ammine)Ni(II) nitrate complex, [Ni(NH₃)₆](NO₃)₂, at low temperature of 250 °C. The product was characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), UV-Vis spectroscopy, BET specific surface area measurement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and magnetic measurement. The magnetic measurement revealed a small hysteresis loop at room temperature, confirming a superparamagnetic (weak ferromagnetic) nature of the synthesized NiO nanoparticles. Indeed, the NiO nanoparticles prepared by this method could be an appropriate semiconductor material due to the optical band gap of 3.35 eV which shows a red shift in comparison with the previous reports. This method is simple, fast, safe, low-cost and also suitable for industrial production of high purity NiO nanoparticles for applied purposes.     

Preparing undoped and Mn-doped ZnO nanoparticles: a comparison between sol–gel and gel-combustion methods

Undoped and Mn doped ZnO nanoparticles were synthesized by two wet chemical techniques: sol–gel and gel-combustion. We were able to prepare Mn-doped ZnO nanoparticles free from the second phases at calcining temperatures 400 and 500 °C using sol–gel and gel combustion, respectively. Complete crystallization occurs in both methods, but it is found that the crystallization is better performed in the ZnO based solid solution prepared by the sol–gel method. TEM images show that the average size of the nanoparticles synthesized by gel-combustion is smaller than that of prepared by sol–gel method. Optical characterizations such as vibrational properties, lattice dynamical parameters, absorption edges and optical band gap energies were also carried out by FTIR and UV–Vis spectroscopies. The quantitative estimations led to the conclusion that the effects of the method on the particle size and the optical band gap energy of the prepared samples are very significant.     

Double-Layer TiO2 Electrodes with Controlled Phase Composition and Morphology for Efficient Light Management in Dye-Sensitized Solar Cells

The light-scattering effect in the dye-sensitized solar cells (DSCs) was studied by controlling TiO₂ phase composition and morphology by fabrication of double-layer cells with different arrangement modes. The starting material for preparation of TiO₂ cells was synthesized by an aqueous sol–gel process. X-ray diffraction and field emission scanning electron microscopic analyses revealed that TiO₂ nanoparticles had particle size ranging between 18 and 44 nm. The optical property and band gap energy of TiO₂ nanoparticles were studied through UV–Vis absorption. The indirect optical band gap energy of anatase and rutile nanoparticles was found to be 3.47 and 3.41 eV, respectively. The double-layer DSC made of nanostructured TiO₂ film with phase composition of 78 % anatase and 22 % rutile as the under-layer and mixtures of anatase-nanoparticles and anatase-microparticles as the over-layer (i.e., NM solar cell) was shown the highest power conversion efficiency (PCE) of 6.04 % and open circuit voltage of 795 mV. This was achieved due to the optimal balance between the light scattering effect and dye sensitization parameters. Optimum light scattering of photoanode led to improve the PCE of NM double-layer solar cell which was demonstrated by diffuse reflectance spectroscopy.     

Preparation of CuCrO2 nanoparticles with narrow size distribution by sol–gel method

Copper chromium oxide (CuCrO₂) nanoparticles were synthesized by sol–gel method. The effect of annealing temperature, duration of heat treatment and metallic ion concentration in precursor solution on the structural properties of the nanoparticles was investigated. The delafossite structure of CuCrO₂ powder was confirmed by X-ray diffractometer. It was found that the crystallite sizes as well as the size of the nanoparticles increased with annealing temperature and duration of heat treatment but decreased with metallic ion concentration. Nanoparticles’ size was obtained using particle size analyzer. The synthesized CuCrO₂ nanoparticles with 0.7 M metallic ion concentration have the lowest crystallite and particle sizes with a narrow size distribution in the range of 13.5–15.6 nm. In the presence of this metallic ion concentration, we could also produce single crystal CuCrO₂ nanoparticles. Moreover, the CuCrO₂ nanoparticles exhibit a large optical band gap that increases with metallic ion concentration. The optical band gap of the nanoparticles fabricated with 0.7 M metallic ion concentration in precursor solution is about 3.99 eV.     

Effect of the annealing temperature on crystalline phase of copper oxide nanoparticle by copper acetate precursor and sol–gel method

A sol–gel route to synthesize copper oxide nanoparticles with an average size of ca. 63 nm from copper acetate precursor and monoethanolamine as the capping agent is reported. Structural characterization showed the formation of a cubic phase for CuO. The effect of annealing temperature on formation of crystalline phases was investigated. Characterization of the products was performed using thermo-gravimetric analysis, X-ray diffraction, field emission scanning electron microscopy, and diffuse reflectance. The results showed that there are significant differences in the morphological, crystallographic, structural, and optical properties of the nanostructures prepared at different annealing temperatures. The optical properties and band gap of CuO nanoparticles were studied by UV–Vis spectroscopy. According to the results of the optical measurements, the band gap is estimated to be 1.41 eV. These results showed that the band gap energy changed with increase of annealing temperature, which can be attributed to the change in grain size of the samples.     

Characterization and surface reactivity of ferrihydrite nanoparticles assembled in ferritin

Ferrihydrite nanoparticles with nominal sizes of 3 and 6 nm were assembled within ferritin, an iron storage protein. The crystallinity and structure of the nanoparticles (after removal of the protein shell) were evaluated by high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). HRTEM showed that amorphous and crystalline nanoparticles were copresent, and the degree of crystallinity improved with increasing size of the particles. The dominant phase of the crystalline nanoparticles was ferrihydrite. Morphology and electronic structure of the nanoparticles were characterized by AFM and STM. Scanning tunneling spectroscopy (STS) measurements suggested that the band gap associated with the 6 nm particles was larger than the band gap associated with the 3 nm particles. Interaction of SO2(g) with the nanoparticles was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and results were interpreted with the aid of molecular orbital/density functional theory (MO/DFT) frequency calculations. Reaction of SO2(g) with the nanoparticles resulted primarily in SO(3)2- surface species. The concentration of SO3(2-) appeared to be dependent on the ferrihydrite particle size (or differences in structural properties).     

Nanoparticle Size and Concentration Dependence of the Electroactive Phase Content and Electrical and Optical Properties of Ag/Poly(vinylidene fluoride) Composites

This paper describes the processing of silver‐nanoparticle‐doped poly(vinylidene fluoride). The effects of the concentration and size of the filler on the electroactive phase of the polymer and the optical and electrical properties are discussed. Spherical silver nanoparticles incorporated into the poly(vinylidene fluoride) polymeric matrix induce nucleation of the electroactive γ phase. The electroactive phase content strongly depends on the content and size of the nanoparticles. In particular, there is a critical nanoparticle size, below which the filler losses its nucleation efficiency due to its small size relative to that of the polymer macromolecules. Furthermore, the presence of surface plasmon resonance absorption in the composites is observed, which once again shows a strong dependence on the concentration and size of the particles. The absorption is larger for higher concentrations, and for a given concentration increases with particle size. This behavior is correlated to the electrical response and is related to the extra bands and electrons provided by the nanoparticles in the large energy band gap of the polymer.     

反应物的变化对吸附相反应技术制备NiO/SiO2的影响

以SiO2为载体,研究反应物种类和浓度对吸附相反应技术制备NiO粒子的影响。首先采用滴定法测定了各个反应物在载体表面的吸附过程,利用TEM、XRD分析,对比了不同反应物制备得到的NiO粒子的形貌。在确定了反应物的基础上,进一步设计了2种水量下制备实验,研究反应物浓度对粒子形貌的影响。XRD结果表明,1.0mL水量下NiO粒子的晶粒粒径随着反应物浓度增加先缓慢减少后增大。而随反应物浓度增加,5.0mL水量得到的粒子晶粒粒径则一直变大。2种吸附层中不同的反应速率使得相同条件下,高水量(5.0mL)得到的NiO粒子粒径要小于1.0mL水量下得到的粒子。物理吸附层中形成的粒子与载体结合力较弱,使得焙烧后5.0mL水量下得到的粒子在SiO2上分布不均匀。     

TiO2纳米粒子制备方法对其光催化活性的影响

分别用胶溶法、金属醇盐水解法和低温水解法制备了TiO2纳米粒子;采用XRD和BET技术,测试了TiO2粒子的粒径、晶型及表面积。以庚烷的气相光催化氧化为探针反应,考察了不同方法、不同温度处理的TiO2粒子的光催化活性。结果表明,以胶溶法和金属醇盐水解法制备的TiO2粒子,随焙烧温度的增加TiO2粒子长大,晶型由锐钛矿向金红石型转变,光催化活性降低。用低温水解法,可在低温下制得金红石型TiO2粒子,但其催化活性很低。说明由原料和制备方法所决定的TiO2粒子的物理化学性质,影响其光催化行为。锐钛矿型TiO2粒子催化活性较金红石型TiO2好。这是由于前者的表面羟基含量较高且带隙能较大的缘故。     

Size control synthesis of sulfur doped titanium dioxide （anatase） nanoparticles, its optical property and its photo catalytic reactivity for CO2 ＋ H2O conversion and phenol degradation

Sulfur doped anatase TiO2 nanoparticles (3 nm−12 nm) were synthesized by the reaction of titanium tetrachloride, water and sulfuric acid with addition of 3M NaOH at room temperature. The electro-optical and photocatalytic properties of the synthesized sulfur doped TiO2 nanoparticles were studied along with Degussa commercial TiO2 particles (24 nm). The results show that band gap of TiO2 particles decreases from 3.31 to 3.25 eV and for that of commercial TiO2 to 3.2 eV when the particle sizes increased from 3 nm to 12 nm with increase in sulfur doping. The results of the photocatalytic activity under UV and sun radiation show maximum phenol conversion at the particle size of 4 nm at 4.80% S-doping. Similar results are obtained using UV energy for both phenol conversion and conversion of CO2+H2O in which formation of methanol, ethanol and proponal is observed. Production of methanol is also achieved on samples with a particle size of 8 and 12 nm and sulfur doping of 4.80% and 5.26%. For TiO2 particle of 4 nm without S doping, the production of methanol, ethanol and proponal was lower as compared to the S-doped particles. This is attributed to the combined electronic effect and band gap change, S dopant, specific surface area and the light source used.     

花状铜锌锡硫纳米颗粒的溶剂热法制备和结构表征

以金属氯化物为金属源,硫脲为硫源,聚乙二醇和乙二醇为混合溶剂,采用溶剂热法一步合成了花状的铜锌锡硫纳米颗粒.利用X射线衍射仪,扫描电子显微镜、能谱仪、透射电子显微镜、紫外-可见分光光度计分析了铜锌锡硫纳米颗粒的物相、结构、形貌及光学性能,并初步探讨了铜锌锡硫的生长机理.结果表明,所得到的铜锌锡硫纳米颗粒具有锌黄锡矿结构,直径在500～2 000nm范围内可调,其中花状的铜锌锡硫纳米颗粒由大量厚度约25nm的纳米片构成.所制备的铜锌锡硫纳米颗粒对可见光具有明显的吸收;利用外延法推算得到其禁带宽度约为1.5eV,与太阳能电池所需的最佳禁带宽度相近,显示其有望在新一代太阳能电池中得到应用和推广.     

Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition

Using Fourier Transform InfraRed (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM), we characterize the structure and/or morphology of hematite (alpha-Fe(2)O(3)) particles with sizes of 7, 18, 39 and 120 nm. It is found that these nanoparticles possess maghemite (gamma-Fe(2)O(3))-like defects in the near surface regions, to which a vibrational mode at 690 cm(-1), active both in FTIR and Raman spectra, is assigned. The fraction of the maghemite-like defects and the net lattice disorder are inversely related to the particle size. However, the effect is opposite for nanoparticles grown by sintering of smaller hematite precursors under conditions when the formation of a uniform hematite-like structure throughout the aggregate is restricted by kinetic issues. This means that not only particle size but also the growth kinetics determines the structure of the nanoparticles. The observed structural changes are interpreted as size-induced alpha-Fe(2)O(3)<-->gamma-Fe(2)O(3) phase transitions. We develop a general model that considers spinel defects and absorbed/adsorbed species (in our case, hydroxyls) as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions. These changes are represented by trajectories in a phase diagram built in three phase coordinates-concentrations of spinel defects, absorbed impurities, and adsorbed species. The critical size for the onset of the alpha-->gamma phase transition depends on the particle environment, and for the dry particles used in this study is about 40 nm. The model supports the existence of intermediate phases (protohematite and hydrohematite) during dehydration of goethite. We also demonstrate that the hematite structure is significantly less defective when the nanoparticles are immersed in water or KBr matrix, which is explained by the effects of the electrochemical double layer and increased rigidity of the particle environment. Finally, we revise the problem of applicability of IR spectroscopy to the lattice vibrations of hematite nanoparticles, demonstrating that structural comparison of different samples is much more reliable if it is based on the E(u) band at about 460 cm(-1) and the spinel band at 690 cm(-1), instead of the A(2u)/E(u) band at about 550 cm(-1) used in previous work. The new methodology is applied to analysis of the reported IR spectra of Martian hematite.     

Absorption and fluorescence spectroscopy of growing ZnO quantum dots: size and band gap correlation and evidence of mobile trap states

ZnO nanoparticles constitute a convenient model system for fundamental studies with many possible technical applications in, for example, sensors and the field of catalysis and optoelectronics. A large set of ZnO quantum dots in the size range 2.5-7 nm have been synthesized and analyzed in detail. Time resolved in situ UV-vis absorption measurements were used to monitor the growth of these particles in solution by correlating the optical band gap to particle size given from X-ray diffraction (XRD) measurements. The particles formed were isotropic in shape, but small initial deviations gave indications of a transition from thermodynamic to kinetically controlled growth for particles around 4 nm in diameter. On the basis of this, the behavior and mechanisms for the particle growth are discussed. The fluorescence dependence on particle size was investigated by combining fluorescence and UV-vis measurements on growing particles. This revealed that the positions of the fluorescence trap states are mobile toward the conduction- and valence band. A broadening of the trap states was also found, and a surface dependent mechanism of the trap state shift and broadening is proposed.     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Optical transmittance of indium tin oxide nanoparticles prepared by laser-induced fragmentation in water

Laser-induced fragmentation of indium tin oxide nanoparticles was performed in water by laser irradiation with various laser energies. Fragmentation of the nanoparticles proceeded with increased laser energy. The fragmented nanoparticles showed high transmittance in the visible region and lower transmittance in the ultraviolet and infrared regions. The optical band gap of the fragmented nanoparticles increased with decreasing average particle size. The increase of the band gap was possibly caused by the Burstein-Moss effect due to the increasing concentration of carriers generated by the surface defects of the oxygen vacancies on smaller nanoparticles.