Several microreactors combined with an online detector were used as a combinatorial synthesis system to optimize nanoparticle synthesis for rapid and flexible development of nanoparticles to meet various needs and applications. Three reaction parametersstemperature, reaction time, and reaction additive (dodecylamine) concentrationswere combined systematically to produce synthesis condition sets (five points each, total of 125 points). The photoluminescence (PL) wavelength, PL quantum yield (PLQY), PL full width at halfmaximum (PL fwhm), particle size, and product yield (PY) of the products were determined for each condition to obtain property data sets. The average time to complete all procedures to obtain one reaction condition per particle property data set was approximately 20 min. The reaction conditions were varied to provide a series of data sets meeting three specific objectives: (1) to seek condition sets producing superior properties, (2) to assess reaction condition effects on property data sets and elucidate their underlying mechanisms, and (3) to find reaction conditions meeting practical requirements for applications and achieve a balance of criteria. These objectives were met. High reproducibility verified the system reliability. Data set maps were used to determine the reaction conditions to produce high-QY particles (56%). These maps supported systematic assessment of the reaction condition effects on product properties. The data sets show agreement with formally reported findings related to QY dependence on particle size and CdSe deposition rate enhancement with amine concentration, thereby confirming the system reliability. Results also showed that high amine concentration suppressed the deposition rate. The maximum deposition rate of 5-10% indicated that these systems can be assessed quantitatively to achieve balanced conditions. Finally, by applying a weighting function to the data sets, a point of balance among properties was determined easily. This approach is effective for determination and selection of optimum conditions for practical applications.
Citrate-stabilized gold nanoparticles (Au-NPs) of a nearly spherical shape with four different diameters (3.7, 11.0, 21.7, and 40.8 nm) were immobilized on a 4-aminobutylsiloxane monolayer-modified indium-tin oxide (ITO) electrode. From the results of coulometric measurements using potential step sequences, the number of electrons per particle to be transferred to attain a new equilibrium state after applying a potential step was found to increase in proportion to the square of the diameter. The double layer integral capacitance of the Au-NP surface per unit area in the potential range from −0.4 V to 0.6 V (Ag/AgCl/sat'd KCl) is ca. 70 μF cm -2 , being independent of the particle size. The differential capacitance of the Au-NP surface is a function of the potential with a maximum at 0.32 V, while the function is again independent of the particle size. The kinetics of the charging was discussed using the analysis of the potential step transient current. The potential dependent shift of the plasmon absorption band obtained by constant-potential and potential-modulated transmission-absorption spectroscopic measurements revealed that a smaller Au-NP exhibits a greater blue-shift of the plasmon band when applying more negative potentials, being in line with the Mie-Drude theory.
A density functional theory (DFT) based method is proposed for efficient screening of metal precursors for nanomaterial syntheses. For this study, we examined the effectiveness of our DFT approach for predicting bulk properties of precursor metal complexes, which is a key of our method. The DFT calculations were applied for a series of copper(II) β-diketonate complexes to estimate values related to complex stabilities such as complex formation energies ΔE
total
complex, total energy changes for two-electron reduction ΔE
total
reduction, and so on. The value of ΔE
total
complex was compared to the stability constant β2 collected from the relevant literature; ΔE
total
reduction was compared with reduction potentials measured using cyclic voltammetry. Results obtained from these comparisons revealed that simple DFT calculations predicted the trend of the complex stabilities that were determined experimentally as a bulk property. Our method can predict precursor properties and can greatly contribute to efficient precursor selection for nanomaterial synthesis.
Time dependent spectral change of Au nanoparticles immobilized on an ITO electrode upon the change of electrode potential was investigated. Au nanoparticles of a diameter of 11 nm were immobilized on a monolayer of alkylsiloxane with an amine or thiol end group on an ITO electrode.In addition to the previously clarified charging-discharging process of the particles in response to the sine-wave potential modulation at frequencies higher than 8 Hz, very slow relaxation of visible light absorption after a potential step was found in the present work
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