Variation Of Precursor Concentration Research Articles

Tweaking and collating the structural, optical and magnetic properties of auto combusted lanthanum ferrites - study on effect of precursor concentration

A novel sol-gel auto-combustion technique is utilized to prepare nano-sized, perovskite-structured LaFeO3 powders. The nanoparticles were synthesized for three distinct precursor concentrations (0.5, 1 and 1.5 M) maintaining pH, annealing temperature and time. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray absorption spectroscopy (EDAX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) study and vibrating sample magnetometer (VSM). XRD revealed that all the prepared samples have shown an orthorhombic phase with space group Pnma. DRS suggested a marginal increase in bandgap and the average band gap was found to be 2.2 eV VSM analysis has shown that all the prepared samples exhibit weak ferromagnetic behaviour due to uncompensated canted spins. All the studies performed revealed a significant modification of structural, optical and magnetic properties with the variation of precursor concentration.

Tuneable structural and optical properties of inorganic mixed halide perovskite nanocrystals

AbstractHighly fluorescent cesium lead‐based (CsPbX3, X═Br, Cl, I) inorganic metal halide perovskites semiconductors have gained immense popularity in the last decade due to the economic and straightforward fabrication techniques involved in these materials along with their excellent electrical and optoelectronic properties. Cesium lead halide nanocrystals are well known for their fluorescence in the visible region with extremely high internal quantum efficiencies; thus making them highly suitable for the fabrication of efficient light‐emitting diodes, transistors and photodetectors. Although perovskite nanocrystals (NCs) are more fluorescent compared to their bulk counterpart, there have been very few reports on the synthesis and characterization of CsPbX3 perovskite NCs. In this work, we have synthesized and investigated the CsPbBr3 and CsPbBr2I NCs to understand the fundamental optoelectronic properties and structural integrity in mixed halide perovskite NCs. We have estimated ~10 nm average particle size of CsPbBr3 nanocrystals from the high‐resolution transmission electron microscopy (HRTEM) while CsPbBr2I has ~16 nm average particle size with slightly higher polydispersity. Most interestingly, we do not observe any phase segregation of bromide and iodide ions in mixed halide perovskite quantum dots due to finite size effect. This is also confirmed by the energy dispersive X‐ray spectroscopy (EDS) mapping data. However, CsPbBr3 nanocrystals are relatively more stable than the mixed halide perovskite nanocrystals due to fewer defects. Anomalous behavior is observed in the photoluminescence intensity with the variation of precursor concentration indicating a complex nature nanoparticle synthesis.

Oxygen Vacancy and Adsorbed Superoxides Dependent Photocatalytic Activity of TiO2 Quantum Dot Thin Films for Degradation of Methylene Blue with Variation of Precursor Concentration

Growth of TiO2 quantum dot thin films on ITO glass substrate by hydrothermal method at 180 °C with variations of titanium precursor concentration (0.3, 0.5, 0.7, and 1 ml) is reported. UV–vis absorption spectrum shows a strong absorbance peak in the UV region. The bandgap of samples ranged from 3.2 to 3.6 eV. FESEM analysis shows a layered sieve-like porous morphological structure. The particle size is less than 10 nm. The FTIR analysis reveals the presence of isolated adsorbed Ti–OH and –OH groups which take part in photocatalysis reactions to oxidize dye molecules. The superoxides and hydroxyl radicals were yielded by the protonation process. The oxygen vacancies, confirmed from XPS analysis, play an important role in the formation of impurity level states below the conduction band with the accumulation of a large number of electrons. These electrons further take part in the hydrogen production process. This investigation demonstrates that thin film with 0.5 ml precursor volume shows enhanced MB dye degradation activity under UV light. The PL emission is quenched in the UV region for a sample having 0.5 ml precursor volume, enhancing the probability of charge carrier separation. Thus significant results in photocatalytic MB dye degradation activity are obtained.

Synthesis of a nanocomposite composed of reduced graphene oxide and gold nanoparticles

We report a seeded-growth process that results in the adhesion of size-controlled gold (Au) nanoparticles (NPs) to the surface of reduced graphene oxide (rGO), leading to the formation of rGO-Au nanocomposites. The synthesis approach involves the utilization of Au molecular precursors (i.e., the seeds) bonded to oxygen functionalities which intrinsically exist on GO. Upon reduction of the Au precursors, surface deposition of Au NPs is ensured. It is found that the size of Au NPs is controlled via the variation of precursor concentration in the growth solution. The redox chemistry between GO and Au precursors causes the reduction of GO to rGO and the generation of Au NPs on the surface of rGO. Microscopic and spectroscopic measurements have been performed to provide evidence for the suggested redox chemistry.

Micro-structural investigations of spray hydrolyzed TiO2

Hydrolysis across tiny spray droplet allows a facile one step synthesis of interesting sub-micrometric structures owing to the large available surface area unlike bulk hydrolysis. In the present work, it has been demonstrated that titania precursor concentration plays a significant role in effecting morphological transformation during spray hydrolysis. While hollow microspheres are formed primarily at low precursor concentration, fractal like grains, having two levels of hierarchy, result at high precursor concentration. Mesoscopic structure of these spray hydrolyzed grains has been investigated by ultra small-angle neutron scattering, small-angle X-ray scattering and scanning electron microscopy. Thermal evolution of initial amorphous phase of titania into crystalline rutile phase, through intermediate anatase and brookite phases, is followed by high temperature X-ray diffraction. A plausible mechanism has been elucidated for the observed morphological transition with variation of precursor concentration.

수열합성에 의한 c축 배향 ZnO 나노로드 배열의 성장과 구조, 광학적 특성

ZnO nanorods array have been grown on the seed crystal coated Si(100) substrate by hydrothermal method. The growth, structural and optical properties of ZnO nanorods array were investigated with a variation of precursor concentration from 0.01 M to 0.04 M. The array density of grown ZnO nanorods per same area was increased with increasing the concentration of precursor solution. Vertically aligned ZnO nanorods with hexagonal wurtzite structure have highly preferred c-axis orientation along (002) lattice plane. Especially, ZnO nanorods array developed from 0.04 M precursor solution showed a diameter of about 85 nm and length of 1.2 <TEX>{\mu}m$</TEX> without any crystallographic defects. The photoluminescence spectra of ZnO nanorods from heavier precursor concentration exhibited stronger UV emission around 380 nm corresponding with near-band-edge emission.

High-Temperature Synthesis of CdSe Nanocrystals in a Serpentine Microchannel: Wide Size Tunability Achieved under a Short Residence Time

A three-dimensional serpentine microchannel was applied in the reaction part of a microreactor for the synthesis of CdSe nanocrystals (NCs). The local fluctuation of velocity in the turns created by the continuous variation of channel geometry was demonstrated to be effective to maintain a uniform residence time and monomer concentration for the constrained fluid under fast flow rates. Therefore, an enhanced growth rate for NCs within a narrow size distribution was accomplished with a short residence time. The triple-ligand system (trioctylphosphine oxide−oleic acid−oleylamine) was demonstrated to be powerful to achieve high-quality CdSe NCs with a short reaction time. The superior kinetic control achieved via the variation of precursor concentration and Se/Cd ratio provided effective control of the size of CdSe NCs, which allowed the rapid synthesis (8−10 s) of CdSe NCs in a wide size range with diameters ranging from 2.1 to 4.0 nm, while maintaining excellent color purity and a high photoluminescence (P...