Morphology Evolution Of Nanoparticles Research Articles

Temperature controlled morphology transformation during aging of colloidal copper nanoparticles produced by laser ablation in water

The colloidal nanoparticles produced from bulk metal by laser ablation in water usually oxidize during aging. Such transformation could be used as a tool for nanoarchitecture if the control parameters are known. Here we studied in detail the transformation of copper-based nanoparticles in water during the colloid aging and the evolution of nanoparticle morphology at various temperatures. The spherical Cu@Cu2O core-shell nanoparticles were produced by laser ablation of Cu target in water. The aging of prepared colloid was investigated in situ by UV–visible absorption spectroscopy. The nanoparticle morphology and composition were characterized by scanning and transmitting electron microscopies, X-ray photoelectron and Raman spectroscopies. The aging of colloidal nanoparticles resulted in morphology changes and composition transformation to CuO. The nanoparticle sizes enlarged due to Ostwald ripening and aggregative growth either isotropically at room temperature (25 ℃) or by forming elongated nano-spindles at temperature above 35 ℃. The occurred transformation was characterized by Kolmogorov-Johnson-Mehl-Avrami approach which allowed to extract the activation energy of the process. The obtained results are useful for both nanoarchitecture and gaining colloid stability.

Designed Synthesis of Fe x Co100−x Alloy Nanoparticles by Polyol Reduction: An Evolution of Structural, Morphological and Magnetic Properties

Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100−<i>x</i></sub> nanoparticles with different stoichiometry ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x = 0$ </tex-math></inline-formula> –100) have been prepared by a facile synthesis process and compositions confirmed using X-ray fluorescence spectroscopy. X-ray diffraction measurements suggest alloy formation in the body-centered cubic (BCC) phase, with a progressive shift of peak positions to account for the stoichiometric changes. The evolution of nanoparticle morphology is from cubic for iron to hexagonal for cobalt, and the entire composition range has been examined. Magnetic behavior has been accessed by Mössbauer spectroscopy and vibrating sample magnetometric measurements, which suggests an increase of magnetization values of iron upon alloying with cobalt. A detailed account of the synthesis scheme has been presented, to achieve uniform alloy nanoparticles in the pristine state with minimum aggregation and surface oxidation, by carefully adjusting the reaction timescales.

Electron microscopy observation of electric field-assisted sintering of stainless steel nanoparticles

The intrinsic role of electrical current on the electric field-assisted sintering (EFAS) process of stainless steel 316L nanoparticles has been revealed by both ex situ and in situ experiments. A novel device on the Si chip has been designed and fabricated to fit into the sample holder of a transmission electron microscope for these experiments. The evolution of nanoparticle morphology and microstructures during the EFAS process has been studied using scanning electron microscopy and transmission electron microscopy, which has been combined with the simultaneous measurement of the electric voltage and current changes. A preliminary four-stage mechanism for the EFAS process of stainless steel 316L nanoparticles has been proposed based on these experimental investigations.

Morphologies and magnetic properties of La-doped CeO2 nanoparticles by the solvothermal method in a low magnetic field

La-doped CeO2 nanoparticles were prepared successfully by the solvothermal method. The effects of La dopant concentration and an external magnetic field of 0.8T on the morphologies and magnetic properties of La-doped nanoparticles were researched. The results showed that La-doped CeO2 nanoparticles had a face centered cubic lattice structure and La rare earth ions had been substituted into the CeO2 crystal lattice. At 5 wt% La dopant, the nanoparticles showed the flake shape. When the La dopant concentration was 30 wt%, a small number of nanorods appeared in the morphology. When the La dopant concentration reached 40 wt%, the nanoparticles basically consisted of nanorods. Interestingly, when an external magnetic field of 0.8T was applied during the reaction process, it was found that the nanoparticles consisted of nanorods at the 30 wt% La dopant concentration. The introduction of external magnetic field promoted the formation of nanorods. There existed the weak ferromagnetic behavior in the La-doped CeO2 nanoparticles. The morphology evolution of nanoparticles had an important effect on their magnetic properties.

Highly efficient photocatalysis by BiFeO3/α(γ)-Fe2O3 ferromagnetic nano p/n junctions formed by dopant-induced phase separation

A series of Bi1−x Ca x FeO3 (BCFO) nanoparticles (with x = 0.0, 0.03, 0.07, 0.10, 0.15, and 0.20) have been synthesized by sol–gel reaction. X-ray diffraction patterns establish the formation of hexagonal bismuth ferrite as the prominent phase, with a small contribution of the Bi2Fe4O9 phase (as reported by others as well) which diminishes rapidly with the increase in Ca concentration. Interestingly, above a calcium dopant concentration of about 10 % peaks of Fe2O3 (both α and γ components) are observed with a concomitant enhancement of ferromagnetism. Small contribution of the Bi6Ca4O13 phase is also noted in these samples. This phase evolution is driven by dopant-induced strain energy and increasing oxygen vacancy concentration for local charge balance. Transmission electron microscopy (with elemental scanning) and Mossbauer spectroscopy techniques bring out the evolution of nanoparticle morphology (and elemental distribution) and phase configuration, respectively. Measurements of photocatalytic activity (and photo-Fenton activity with H2O2) reveal that Ca doping at the Bi site in BFO enhances the activity significantly in the concentration regime where BFO/α(γ)-Fe2O3 phases coexist in the form of a nanocomposite. The enhancement can thus be attributed to the carrier transfer between BFO and α(γ)-Fe2O3 across nano p/n junctions leading to enhanced carrier lifetime. Importantly, the magnetization of the nanocomposite (about 16 emu gm−1 at x = 0.20) provides a convenient way to collect the photocatalyst with the help of an external magnet for reuse.