All electrochemical experiments were performed with a
CHI660A electrochemical workstation (Shanghai Chenhua Apparatus
Co., China) in conjunction with a standard three-electrode
system: a hydroxyapatite-modified carbon ionic liquid electrode
(1.8mm in diameter) was used as working electrode; a platinum
wirewas applied as the counter electrode and an Ag/AgCl (3MKCl)
reference electrode (all from CH Instruments, USA). All potentials
were reported with respect to the reference electrode. A magnetic
stirrer (Model 79-1)was used to stir the testing solution during the
pre-conditioning and pre-concentration steps. The scanning electron
microscopy (SEM) images and energy dispersive analysis of
X-ray measurements (EDAX) were performed on a FEI-Quanta 200
microscope (Holland FEI company).