Effect of Bias Potential on the Interface of a Solid Electrolyte and Electrode during XPS Depth Profiling Analysis.

Depth profiling is an essential method to investigate the physical and chemical properties of a solid electrolyte and electrolyte/electrode interface. In conventional depth profiling, various spectroscopic tools such as X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are utilized to monitor the chemical states along with ion bombardment to etch a sample. Nevertheless, the ion bombardment during depth profiling results in an inevitable systematic error, i.e., the accumulation of mobile ions at the electrolyte/electrode interface, known as the ion pile-up phenomenon. Here, we propose a novel method using bias potential, the substrate-bias method, to prevent the ion pile-up phenomena during depth profiling of a solid electrolyte. When the positive bias potential is applied on the substrate (electrode), the number of accumulating ions at the electrolyte/electrode interface is significantly reduced. The in-depth XPS analysis with the biased electrode reveals not only the suppression of the ion pile-up phenomena but also the altered chemical states at the interfacial region between the electrolyte and electrode depending on the bias. The proposed substrate-bias method can be a good alternative scheme for an efficient yet precise depth profiling technique for a solid electrolyte.

Simultaneous detection of enrofloxacin and ciprofloxacin in milk using a bias potentials controlling-based photoelectrochemical aptasensor.

It is important to develop highly-active photoelectrochemical (PEC) materials and use novel sensing strategy for constructing high-PEC-performance sensors with multiplex detection abilities, owing to the simultaneous presence of multiple antibiotic residues in food. Herein, a bias-potential-based PEC aptasensor was prepared for the trace detection of dual antibiotic analytes, enrofloxacin (ENR) and ciprofloxacin (CIP), which often coexist in milk samples. Here, two materials were developed with excellent PEC performance: three-dimensional nitrogen-doped graphene-loaded copper indium disulfide (CuInS2/3DNG) and Bi3+-doped black anatase titania nanoparticles decorated with reduced graphene oxide (Bi3+/B-TiO2/rGO). By applying different bias potentials to the two materials near one ITO electrode, the cathodic current generated by CuInS2/3DNH and the anodic current generated by Bi3+/B-TiO2/rGO could be clearly distinguished without interfering with each other. Then, ENR and CIP aptamers were respectively modified onto the surface of CuInS2/3DNH and Bi3+/B-TiO2/rGO to construct a PEC aptasensor for the sensitive detection of ENR and CIP. Under optimal conditions, the proposed aptasensor exhibited wide linear ranges of ENR (0.01-10000 ng/mL) and CIP (0.01-1000 ng/mL), and relatively low detection limits of 3.3 pg/mL to ENR and CIP (S/N = 3). The aptasensor was successfully applied to the detection of ENR and CIP in milk samples.

Highly efficient photoelectrochemical removal of atrazine and the mechanism investigation: Bias potential effect and reactive species.

In this work, efficient photoelectrochemical (PEC) removal of atrazine, one of the most widely used chemical herbicides in the world, was obtained by adjusting the bias potential applied on the photo-anode, and the optimal atrazine removal efficiency reached 96.8% at the potential of 0.2 V vs. SCE in 2 h with the reaction rate constant of 1.72 h-1. The results indicated at the optimal potential, the separation efficiency of photo-generated holes and electrons was the highest with the lowest electron transfer resistance. Mechanism investigation revealed that superoxide radicals, hydroxyl radicals and holes all contributed to atrazine degradation, and the bias potential on the photo-anode could influence atrazine removal efficiency by changing the generation amount and distribution of the reactive oxygen species (ROS). It was presumed the nucleophilicity of superoxide radical played an important role in atrazine dechlorination, leading to the enhanced removal efficiency. However, the bias potential did not show obvious influence on the degradation intermediates of atrazine in the PEC system compared with that in photocatalytic oxidation, since it was actually an electro-assisted photocatalytic process in the potential range investigated. The work will provide fundamental basis for establishing efficient PEC system for pollutant remediation experimentally and theoretically.

Influence of ruthenium doping on UV- and visible-light photoelectrocatalytic color removal from dye solutions using a TiO2 nanotube array photoanode.

The photocatalytic activity of TiO2 anodes was enhanced by synthesizing Ru-doped Ti|TiO2 nanotube arrays. Such photoanodes were fabricated via Ti anodization followed by Ru impregnation and annealing. The X-ray diffractograms revealed that anatase was the main TiO2 phase, while rutile was slightly present in all samples. Scanning electron microscopy evidenced a uniform morphology in all samples, with nanotube diameter ranging from 60 to 120 nm. The bias potential for the photoelectrochemical (PEC) treatment was selected from the electrochemical characterization of each electrode, made via linear sweep voltammetry. All the Ru-doped TiO2 nanotube array photoanodes showed a peak photocurrent (PP) and a saturation photocurrent (SP) upon their illumination with UV or visible light. In contrast, the undoped TiO2 nanotubes only showed the SP, which was higher than that reached with the Ru-doped photoanodes using UV light. An exception was the Ru(0.15 wt%)-doped TiO2, whose SP was comparable under visible light. Using that anode, the activity enhancement during the PEC treatment of a Terasil Blue dye solution at Ebias(PP) was much higher than that attained at Ebias(SP). The percentage of color removal at 120 min with the Ru(0.15 wt%)-doped TiO2 was 98% and 55% in PEC with UV and visible light, respectively, being much greater than 82% and 28% achieved in photocatalysis. The moderate visible-light photoactivity of the Ru-doped TiO2 nanotube arrays suggests their convenience to work under solar PEC conditions, aiming at using a large portion of the solar spectrum.

Nanohardness and Residual Stress in TiN Coatings.

TiN films were prepared by the Cathodic arc evaporation deposition method under different negative substrate bias. AFM image analyses show that the growth mode of biased coatings changes from 3D island to lateral when the negative bias potential is increased. Nanohardness of the thin films was measured by nanoindentation, and residual stress was determined using Grazing incidence X ray diffraction. The maximum value of residual stress is reached at -100 V substrate bias coinciding with the biggest values of adhesion and nanohardness. Nanoindentation measurement proves that the force-depth curve shifts due to residual stress. The experimental results demonstrate that nanohardness is seriously affected by the residual stress.