No abstract

An electrochemical method was developed to analyze the quantity and oxidation state of exposed Cu impregnated in porous carbon. Carbons of different Cu contents were prepared from Cu͑NO 3 ) 2 impregnation followed by heat-treatment at different temperatures. X-ray diffraction has shown the transformation of the deposited Cu from high to low oxidation states upon increasing the treatment temperature. The crystalline size was also found to increase with temperature. A linear potential sweep from the open-circuit potential of the carbons to Ϫ1.4 V vs. SCE in KOH was able to directly estimate the amounts of CuO and Cu in the carbon from the charge consumed in associated reduction peaks. All the Cu species can be oxidized to CuO at 0.2 V vs. SCE, and this was employed to estimate the amounts of total Cu and Cu 2 O. The present work has demonstrated that because of the conductive feature of carbon, electrochemical measurement becomes an important option to quantitatively analyze metals of different oxidation states present in carbon.Qualitative and quantitative characterizations of oxides formed on metals, such as copper, are considered an issue in application of the metals as electric or magnetic wires. 1 The characterizations have been achieved through electrochemical routes 1 because of the conductive feature of the metal substrate. As for carbon materials, carbon surface oxides on carbon substrates have been extensively explored for several decades. 2-7 Characterization of metal oxides on carbon is rather difficult because of the complicated interactions between metal and carbon. Porous carbons deposited with copper have been widely used as catalysts for wastewater or flue gas treatments. [8][9][10][11][12] In our recent studies, 10-12 activated carbons impregnated with copper have proved to be active in catalyzing NO reduction with NH 3 . The activity of the Cu-loaded carbon is a strong function of the treatment temperature. The influence from heattreatment can be attributed to the change of oxidation state and aggregate size of Cu upon heating. 12 Based on this description the chemical and physical states of metal impregnated in carbon are important factors determining the activity of the metal-loaded carbon. Thus, the development of a metal characterization technique is sought in the present work, and copper is used as an example of the metal loaded. To estimate the amounts of copper oxides, some spectroscopic techniques are useful for qualitative analysis but are not necessarily adequate for quantitative measurement, especially for dispersed metals on porous materials. These techniques include X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron spin resonance spectroscopy, etc. 13-16 As mentioned previously, an electrochemical route becomes an option for quantitative analysis under the condition that the substrate for the oxides is electrically conductive. Potential sweep voltammetry, which is a widely used technique, is able to identify electrochemical reactions of some deposited metal ...