Development of boron-doped diamond (BDD) deposited on carbon nanotubes (CNT) to form BDD/CNT structures relevant for electrochemical degradation

This work presents a new class of Boron-Doped Diamond (BDD) anode for electrochemical degradation. BDD deposition on carbon nanotubes (CNT) is the base for the electrode, because the nanodiamond seeding of oxidized CNT makes diamond nucleation and onset growth very efficient. For the tests presented in this work, the CNT was grown on a carbon fiber (CF) cloth. The BDD electrodes developed with only 10 min of diamond growth (named BDD-10) were tested for brilliant green (BG) dye degradation and showed excellent electrochemical characteristics as large surface area, large potential window, low charge transfer resistance and high degradation rates (kapp). For precise kapp determination in a setup using 360 mL of solution with 100 mg/L of the BG dye, the degradation experiments operated at low current density (5 and 10 mA/cm2). Dye degradation characterization used both UV/Vis color removal and HPLC. Few experiments at higher current densities and at a fixed time of 10 min showed an increase of color removal compatible with a linear dependence of kinetics on current. The kapp found are relatively high (≈0.033 min−1 at 10 mA/cm2), and an important result is the low value of energy consumption to decrease BG dye concentration by one order-of-magnitude (EEO < 0.4 Wh/L). The low energy consumption correlated with the low average voltage during degradation and with the electrode low charge transfer resistance. FEG-SEM and Raman spectroscopy surface characterization show that BDD-10 electrode preserves their morphological and structural characteristics after BG dye degradation, showing that the short time BDD growth is enough to preserve electrode from surface deterioration. The BDD-10 outperformed all anodes of intermediary phases of electrode production: the CF, the oxidized CNT deposited on CF with and without purification to remove surface iron particles. Lifetime tests showed the electrode fails soon, after 8–9 h under a current of 25 mA/cm2. However, the analysis and characterization of the lifetime test shows that erosion of CF/CNT interfaces caused the failure. The BDD/CNT structure remains completely preserved. These findings may suggest this as an excellent and economical method to produce BDD degradation anodes.