Facile Aqueous Phase Synthesis of (200) Faceted Au-AgCl Cubes Using Bael Gum and Its Activity Toward Oxidation and Detection of o-PDA

A new, facile, one step, single-pot, green synthesis of (200) faceted Au-AgCl cubes, at room temperature, is reported. The simultaneous addition of aqueous solutions of HAuCl4 and AgNO3, at room temperature, to an aqueous solution of bael gum results in the formation of nanocubes consisting of Au and AgCl, as evidenced by a combination of characterization techniques such as UV-visible spectroscopy, powder X-ray diffraction, XPS, SEM, and STEM. The formation of silver chloride with (200) as the preferred surface facet might arise from the controlled release of chloride ions, which in turn could arise from the slow reduction rate of HAuCl4 by bael gum. This claim is supported by the preparation of Au-AgCl cubes having no specific orientation synthesized by the successive addition of HAuCl4 followed by AgNO3, where the release of the chloride ion is not controlled. The Au-AgCl cubes exhibit selective activity toward the oxidative dimerization of ortho-phenylenediamine (o-PDA), in the absence of H2O2. The time required for this conversion is less than 30 min. This in turn enables the detection of o-PDA in a trace amount with the minimum being 2 ppm via fluorescence and 15 ppm via UV-visible spectroscopy. Control experiments suggest the specific and rapid activity shown by the (200) facet-oriented Au-AgCl cubes might arise from its smaller size and morphology.