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ACS Appl Mater Interfaces ; 6(14): 11424-38, 2014 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-24960114


A novel microsensor, consisting of crossed Cu micropillars coated with ZnO nanorods, was fabricated by electrochemical methods for detecting gas in a small space. The Cu micropillars (80 µm diameter, 10 mm long) were prepared by microanode-guided electroplating (MAGE) on the periphery of a square copper pad (dimensions 5.0 mm × 5.0 mm × 1.0 mm). The micropillars were electrochemically coated with a 500 nm thick layer of ZnO nanorods deposited from a bath containing 2.0 mM zinc chloride and H2O2 varying in 5, 10, 15, and 20 mM. Two ZnO-coated pillars were crossed to form a microsensor by approaching the Cu pads below, which was adhered to an alumina substrate with silver paste and connected to conducting wires for measurement. The morphology of the coating of ZnO nanorods, which was found to be determined by the concentration of H2O2 in the bath, influenced the gas sensing. The morphology of the coating was characterized by scanning electron microscopy; the structural analysis was carried out by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM); the surface analysis was carried out by X-ray photoelectron spectroscopy; and the defects were determined with photoluminescence (PL) spectra. We thus investigated the effect of the morphology of the coating on the sensing properties by introducing a stream of gases varying in CO/air ratios to understand the sensing mechanism of the microsensor.

ACS Appl Mater Interfaces ; 5(16): 7937-49, 2013 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-23865744


It has been suggested that a high concentration of Fe(3+) in solution, a low pH, and noncomplexing ions of high ionic strength are all essential for developing a high-quality hematite array. Our curiosity was piqued regarding the role of the electrolyte ions in the hydrothermal synthesis of hematite photoanodes. In this study, we prepared hematite photoanodes hydrothermally from precursor solutions of 0.1 M FeCl3 at pH 1.55 with a background electrolyte of 1.0 M sodium halide (NaF, NaCl, NaBr, or NaI). We compared the structures and properties of the as-obtained hematite photoanodes with those of the material prepared in 1.0 M NaNO3, the most widely adopted electrolyte in previous studies. Among our studied systems, we found that the hematite photoanode prepared in NaCl solution was the only one possessing properties similar to those of the sample obtained from the NaNO3 solution-most importantly in terms of photoelectrochemical performance (ca. 0.2 mA/cm(2) with +0.4 V vs SCE). The hematites obtained from the NaF, NaBr, and NaI solutions exhibited much lower (by approximately 2 orders of magnitude) photocurrent densities under the same conditions, possibly because of their relatively less ordered crystallinity and the absence of rodlike morphologies. Because the synthetic protocol was identical in each case, we believe that these two distinct features reflect the environments in which these hematite photoanodes were formed. Consistent with the latest studies reported in the literature of the X-ray photoelectron spectra of fast-frozen hematite colloids in aqueous solutions, it appears that the degree of surface ion loading at the electrolyte-hematite interface (Stern layer) is critical during the development of hematite photoanodes. We suspect that a lower ion surface loading benefits the hematite developing relatively higher-order and a rodlike texture, thereby improving the photoelectrochemical activity.

Eletrodos , Compostos Férricos/química , Brometos/química , Catálise , Compostos Férricos/síntese química , Cloreto de Sódio/química , Compostos de Sódio/química , Fluoreto de Sódio/química , Iodeto de Sódio/química
Artigo em Inglês | MEDLINE | ID: mdl-15717789


Wafer grinding extraction solution was passed through a supported liquid membrane (SLM) that contained PC88A (2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester) as a carrier, to separate gallium from arsenic by selective permeation. The SLM separation process was conducted under various conditions. The kind of membrane supporter, the pH of the feed, the feed concentration, and the HCl content in the strip governed the concentration of gallium and arsenic in the strip phase. The conditions determined as optimal in the laboratory test were used to perform the pilot test. Well separation between gallium and arsenic was performed in both laboratory and pilot tests. Hydrophobic membrane polytetrafluoroethylene (PTFE) with 0.2 microm pores was the best of three membrane supporters. The most efficient separation was obtained using an acidic feed (pH at 1.8) with 1000 ppm gallium. Over a 12-h period of stripping, the striped Ga concentration increased with the HCl concentration from 0.5 to 2.0 M and then leveled off. The recovery rate in the pilot test exceeded that on the laboratory scale because the membrane area was greater. The pilot test yielded a high recovery percentage of gallium (at 91%) and a low recovery of arsenic (merely 1.3 ppm) in the strip over 72 h.

Arsênico/isolamento & purificação , Gálio/isolamento & purificação , Poluentes da Água/isolamento & purificação , Purificação da Água/métodos , Substâncias Perigosas , Indústrias , Membranas Artificiais , Politetrafluoretileno