The Developments And Applications Of Non-aggregation Based Colorimetric Sensors Based On Surface Plasmon Resonance Of Gold Nanorods And AgBr@Au&Ag Plasmonic Nanophotocatalyst

Gold nanorods （GNRs） exhibit strong transverse and longitudinal surface plasmon resonance absorption, and longitudinal surface plasmon resonance absorption （LPA） is highly dependent on their aspect ratio （length / width, R）. The strong oxidization of Cr （VI） enables it to etch GNRs selectively at tips. The redox etching causes R to decrease, resulting in the LPA blue shifts and the color of GNRs distinctly changes. But, S^2– causes GNRs to strip with a faster stripping rate along longitudinal axis, which makes R increase and LPA red shift with vivid color changes. Besides, both LPA wavelength changes （△λ） are linearly to the concentration of Cr （VI） and S^2–, respectively. And two sensitive, selective and responsive non-aggregation colorimetric sensors have been developed for the on-line analysis of Cr （VI） and S^2– in the waters, and the results agree well with ICP–MS and methylene blue method respectively. Meanwhile, the mechanism of sensors detection has also been discussed. Moreover, GNRs of negative charge were synthesized using HAuCl₄ as precursor, CTAB as stabilizer and NaBH₄ as reducing agent. When slightly excessive Ag⁺ was added to CTAB stabilized AuGR solution, Ag⁺ could react with Br^– of CTAB to form [AgBr]+ of positive charge. The formed [AgBr]+ could react with GNRs of negative charge via electrostatic self-assembly to produce AgBr@Au. Then, AgBr@Au&Ag core-shell plasmonic nanophotocatalyst was synthesized via one pot ultrasonic cavitation based on the catalytic effect of GNRs and it was characterized by electron microscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The deposited gold and silver nanoparticles on AgBr surface can strongly absorb visible light because of their plasmon resonance and effectively protect the photogenerated electron away from combining the Ag⁺ of AgBr to form Ag0 atom, which increases the number of effective electron-hole pairs. AgBr@Au&Ag can efficiently utilize sunlight and shows excellent sunlight driven photocatalytic degradation of coomassie brilliant blue in 25 min with the degradation of 98.6%. The mechanism of AgBr@Au&Ag synthesis and its catalytic degradation was discussed.