Nanowires of metal (Cd,Cu) halide complexes with 8-hydroxyquinoline for photoelectrochemical and electrochemiluminescence sensing

Metal-hydroxyquinoline-halogen (MqX, M?=?Cd, Cu; q?=?8-hydroxyquinoline; X?=?Cl, Br, I) nanowires are synthesized via a sonochemical-assisted method. The elemental analysis (EA), inductively coupled plasma-optical emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS) support an M/q/X ratio of 1:1:1. The electron microscope images reveal a typical CdqX and CuqX nanowire diameter of 30–50 nm and a nanowire length of 400–600 nm. In addition, the synthesis of the MqX nanowires is only observed when there is an excess of halide ions (X/q molar ratio of 3 or greater). This halide deficiency results in the formation of micrometer-sized Mq₂ sheets. We demonstrated the conversion of the MqX nanowires to Mq₂ micro-sheets in an ultrasonic bath of 1 M 8-Hq ethanol solutions (50%, w/w) at 50 °C for 2 h, but not vice versa. The MqX nanowires exhibited excellent properties for photoluminescence, electrochemiluminescence (ECL), and photoelectrochemistry (PEC). The CdqBr and CdqI nanowires were coated onto a glass carbon and a fluorine-doped tin oxide glass electrode to develop the above ECL and PEC methods for the detection of H₂O₂ and Cu²⁺, respectively. In the range of 2 to 14 μM, the ECL intensity of the CdqBr nanowires was inversely proportional to the concentration of H₂O₂ with a detection limit of 0.26 μM. For Cu²⁺ sensing, the photocurrent of the CdqI nanowires exhibited a linear response to Cu²⁺ over the range of 2 to 16 μM of which a detection limit of 0.2 μM was observed.