Controllable preferential-etching synthesis of ZnO nanotube arrays on SiO2 substrate for solid-phase microextraction

An improved route to obtain ZnO nanotube arrays and its first application to headspace solid-phase microextraction (HSSPME) as an adsorptive coating were described. The ZnO nanotube arrays were synthesized by a two-step chemical process including the hydrothermal synthesis of ZnO nanorod arrays on the surface of silica fiber (SiO2) in the first step, and the formation of ZnO nanotubes by selectively etching in NH3 center dot H2O solution in the second step. The influence of NH3 center dot H2O concentration, etching time, reaction temperature, and aging time in the ZnO nanotubes formation process was investigated, and arrays of ZnO nanotube with tailored dimensions (250 nm external diameters, 70 nm wall thicknesses and 2 mu m lengths) could be obtained by varying the conditions. In addition, the feasibility of ZnO nanotube arrays adopted for HSSPME was evaluated by extracting volatile organic compounds (VOCs) by use of benzene, toluene, ethylbenzene, o-, m-and p-xylene (BTEX) as model compounds and the results showed that the coating has good extraction capability. The analytes were linear in the range of 10-600 mu g L-1 (r > 0.9960) and the detection limits were about 0.005-0.01 mu g L-1, lower than that obtained with ZnO nanorod arrays. The relative standard derivations (RSD) for the repeatability of single fiber and fiber-to-fiber were lower than 9.5% and 13.8%, respectively. The prepared coating showed good recoveries in the range of 87%-108% and long lifetime (more than 50 times), implying to be a potential absorbent for the VOCs in water samples.