Operando electrochemical SERS monitors nanoparticle reactions by capping agent fingerprints

Nanomaterials are frequently employed in daily life goods,including health,textile,and food industry.A comprehensive picture is lacking on the role of the capping agents,added ligand molecules,in case of nanoparticle reactions and degradation in aqueous solutions,like surface waters or biofluids.Here,we aim to elucidate the capping agent influence on nanoparticle reactivity probing two commonly employed capping agents citrate and polyvinylpyrrolidone(PVP).Their influence on silver nanoparticle(AgNP)transformation is studied,which is particularly important due to its application as an antimicrobial agent.We induce oxidation and reduction processes of AgNPs in halide solutions and we monitor the associated transformations of particles and capping agents by spectro-electrochemical surface-enhanced Raman spectroscopy(SERS).Raman bands of the capping agents are used here to track chemical changes of the nanoparticles under operando conditions.The sparingly soluble and non-plasmon active silver salts(AgBr and AgCl)are formed under potential bias.In addition,we spectroscopically observe plasmon-mediated structural changes of citrate to cis-or trans-aconitate,while PVP is unaltered.The different behavior of the capping agents implies a change in the physical properties on the surface of AgNPs,in particular with respect to the surface accessibility.Moreover,we showcase that reactions of the capping agents induced by different external stimuli,such as applied bias or laser irradiation,can be assessed.Our results demonstrate how SERS of capping agents can be exploited to operando track nanoparticle conversions in liquid media.This approach is envisaged to provide a more comprehensive understanding of nanoparticle fates in complex liquid environments and varied redox conditions.

Ionic liquid-assisted synthesis of silver nanorods by polyol reduction

Silver nanorods have been successfully synthesized in large scale by the ethylene glycol（EG） reduction in the presence of ionic liquid（IL） 1-butyl-3-methylimidazolium tetrafluoroborate（bmimBF_4） and polyvinyl-pyrrolidone（PVP）.The silver nanorods were characterized by scanning electron microscopy（SEM）,high-resolution transmission electron microscopy（HRTEM）,transmission electron microscopy（TEM）,electron energy disperse spectroscopy（EDS） and UV-vis spectroscopy.The results showed that the uniform silver nanorods have an average diameter of about 100 nm and the aspect ratio from 15 to 20.IL,bmimBF_4 may play a role of capping agent together with PVP in the formation of silver nanorods.On the other band,bmimBF_4 may accelerate nucleation and improve the stability of the resulting Ag nanorods due to the low interface tension of IL.

Synthesis of CaWO_4:Eu^(3+) phosphor powders via ethylene glycol route and its optical properties

Eu3＋ doped CaWO4 with tetragonal system were prepared at comparatively low temperature （125 ℃） in ethylene glycol medium. The phosphor was further investigated by X-ray difffactometer （XRD）, photoluminescence spectrophotometer （PL）, Fourier transform infra red （FT-IR） spectroscopy and transmission electron microscopy （TEM）. XRD analysis indicated a decrease in the unit cell volume of CaWO4 with increasing Eu3＋ ion concentration. It indicated the homogeneous substitution of Ca2＋ ions in CaWO4 by the Eu3＋ ions. TEM images showed that the particle size ranged from 20 to 200 nm and it could extend the application of the nanoparticles. The photoluminescence study showed that the intensity of electric dipole transition （SD0→TF2） at 614 nm dominated over the magnetic dipole transition （SD0→TFx） at 592 nm. The optimum concentration of Eu3＋ for the highest luminescence was found to be 20 at.%. The as prepared samples were found to be dispersible in water and methanol.

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe3＋ in polyethylene glycol and the concentration of C1- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe3＋ modulated the hydrolysis kinetics of Fe3＋and prevented the aggregation of β-FeOOH nanorods; while C1- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.