Porous Diamond Membrane Fabricated By Templated Growth for Electrochemical Separation Processes
In this paper, we report our recent progress with respect to the templated diamond growth using quartz fiber paper as the growth template. With optimized microwave CVD growth, nanocrystalline diamond film is fully coated onto the quartz fiber as has been confirmed via SEM. The growth conditions in terms of temperature, methane concentration and boron/carbon ratio are investigated in detail. The diamond quality is evaluated via Raman spectroscopy, and the boron concentration is determined via SIMS. The potential window of the diamond membrane is determined via cyclic voltammetry in an aqueous NaClO4 solution to be ~2.5 V. By applying potential to the membrane, ions will accumulate inside the membrane and change its porosity. As a result, the ion flux through the membrane can be well tuned. This ion selectivity can be used to separate charged molecules. As an example, 5-Carboxyfluorescein and substance P are separated by the diamond membrane under different biases. In a neutral solution, for example, negatively charged 5-caboxyfluorescein can penetrate a positively charged membrane, while the positively charged substance P cannot. Therefore, this membrane can potentially be used for separation processes in biochemical and biomedical applications. Finally, due to the robustness of diamond, the membrane can be cleaned via a high potential (+3 V vs Ag/AgCl) oxidation process in 2 M H2SO4. Metal deposits and organic contaminants are proved to be removable by this method. Therefore, this membrane is also suitable for applications like undersea activities where only simple in-situ maintenances are possible.
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