Effect of CNTs concentration on the microstructure and the sensing behavior of UIO-66-NH2/CNTs towards Pb2+ detection

Developing electroactive materials with superior sensitivity, selectivity, and so on is an important issue for target ions detection. Hierarchically heterostructured nanomaterials represent a kind of promising active materials for electrochemical sensors due to the synthetic effect between different components and the high surface area. Herein, heterostructured UIO-66-NH2/CNTs nanocomposites have been successfully synthesized via the solvothermal method and investigated for the detection of Pb2+ ions. The SEM, TEM, XRD and FTIR collectively confirmed that the UIO-66-NH2 was successfully loaded on the surface of the CNTs. The specific surface areas of the UIO-66-NH2/CNTs are 4-7 times higher than that of activated CNTs and more mesoporous structures appear in composite materials. The electrochemical impedance spectroscopy measurements showed that the concentration of CNTs could influence the electron mobility and the UIO-66-NH2/CNTs-15 exhibits the lowest charge transfer resistance and the highest capacitive property. The cyclic voltammetry study towards K3[Fe(CN)6] further demonstrated that the CNTs can improve the conductivity of the composites especially for the UIO-66-NH2/CNTs-15, which was conducive to the sensing behavior confirmed by follow-up performance experiments. Under the optimized condition, UIO-66-NH2/CNTs-15 exhibits the best sensing performance towards Pb2+. Correspondingly, a high sensitivity of 1.64 μA (μmol L-1)-1 and a low detection limitation of 0.206 μmol L-1 (S/N=3) are achieved. Meanwhile, a wide detection range, excellent selectivity, repeatability, and stability are also obtained. The recovery experiment by standard addition method is also carried out and a satisfactory result has been attained indicating a promising sensor for practical application.