2.4. Catalytic reduction of p-nitrophenol
To measure the catalytic reactivity of supported and unsupported nanoalloys, 1 mL aqueous solution was mixed with 32 mM sodium borohydride (NaBH4) at a 1:1 volumetric ratio. To start the reduction reaction, 10 μL of 20 mM PNP was added into a 2 mL catalyst-NaBH4 mixture in a standard UV/vis quartz cuvette. The progress of the reduction was monitored using a UV/vis spectrophotometer (Agilent Cary 300). The reactive solution was stirred the whole time using a glass rod. The absorption of light from 220 to 520 nm by the reactive solution was recorded once every minute. Before each experiment, the baseline was measured using a solution consisting of 1 mL of the corresponding material solution and 1 mL of 32 mM NaBH4 without PNP. The baseline was subtracted from the absorption spectra of the reactive solution for the quantification of PNP. The PNP concentration was converted from absorbance using a calibration curve obtained with PNP solutions of known concentrations. To test the reactivity of the catalysts in repeated use, the reaction solution was centrifuged at 17,000 × g for 5 min to recover the catalysts. The catalysts were re-dispersed in 1 mL water by 5 min sonication and the catalytic activity was tested as described above.