Detection of single metal nanoparticle collision events in non-aqueous media.

In this work, the detection of metal nanoparticle collision events in a non-aqueous solvent-here, toluene and acetonitrile-using gold nanoparticles and a platinum ultramicroelectrode (UME) is reported. The collisions were monitored by the oxidation of tri-n-propylamine (TPrA) under diffusion-dominated conditions. Based on the current response, it was observed that the current steps were indicative of a mediated Faradaic reaction. Current steps as small as 1-2 pA could be clearly observed. Larger current steps were caused by agglomeration of the nanoparticles attributed to the polarity of the mixed solvent. The experimentally observed collisions per second ranged from 0.07 to 0.51, indicating that particle agglomeration in solution occurs rapidly, reversibly and can subsequently cause rapid and, often, repeated collisions.

Photoactive porous silicon nanopowder.

Bulk processing of porous silicon nanoparticles (nSi) of 50-300 nm size and surface area of 25-230 m(2)/g has been developed using a combustion synthesis method. nSi exhibits consistent photoresponse to AM 1.5 simulated solar excitation. In confirmation of photoactivity, the films of nSi exhibit prompt bleaching following femtosecond laser pulse excitation resulting from the photoinduced charge separation. Photocurrent generation observed upon AM 1.5 excitation of these films in a photoelectrochemical cell shows strong dependence on the thickness of the intrinsic silica shell that encompasses the nanoparticles and hinders interparticle electron transfer.

Got TiO2 nanotubes? Lithium ion intercalation can boost their photoelectrochemical performance.

Cations such as H(+) and Li(+) are intercalated into TiO(2) nanotube arrays by subjecting them to short-term electrochemical pulses at controlled potentials (<-1.0 V vs Ag/AgCl). The intercalation of these small cations has a profound effect toward enhancing photocurrent generation under UV light irradiation. A nearly three-fold increase in the photoconversion efficiency (IPCE) was observed upon intercalation of Li(+) ions into TiO(2) nanotube arrays. The intercalation process is visualized by the color change from gray to blue. Spectroelectrochemical measurements were carried out to monitor the absorption changes at different applied potentials. The analysis of the V(oc) decay following termination of UV light shows a significant decrease in the rate of recombination of accumulated electrons upon Li(+) ion intercalation.