Synthesis and Stabilization of Blue-Black TiO₂ Nanotube Arrays for Electrochemical Oxidant Generation and Wastewater Treatment

Abstract

Efficient, inexpensive, and stable electrode materials are key components of commercially viable electrochemical wastewater treatment system. In this study, blue-black TiO2 nanotube array (BNTA) electrodes are prepared by electrochemical self-doping. The 1-D structure, donor state density, and Fermi energy level position are critical for maintaining the semimetallic functionality of the BNTA. The structural strength of the BNTA is enhanced by surface crack minimization, reinforcement of the BNTA-Ti metal interface, and stabilized by a protective overcoating with nanoparticulate TiO2 (Ti/EBNTA). Ti/EBNTA electrodes are employed as both anodes and cathodes with polarity switching at a set frequency. Oxidants are generated at the anode, while the doping levels are regenerated along with byproduct reduction at the cathode. The estimated maximum electrode lifetime is 16 895 h. Ti/EBNTA has comparable hydroxyl radical production activity (6.6 × 10–14 M) with boron-doped diamond (BDD, 7.4 × 10–14 M) electrodes. The chlorine production rate follows a trend with respective to electrode type of Ti/EBNTA > BDD > IrO2. Ti/EBNTA electrodes operated in a bipolar mode have a minimum energy consumption of 62 kWh/kg COD, reduced foam formation due to less gas bubble production, minimum scale formation, and lower chlorate production levels (6 mM vs 18 mM for BDD) during electrolytic wastewater treatment.

Enhancing the activity of oxygen-evolution and chlorine-evolution electrocatalysts by atomic layer deposition of TiO2

“…The idea that TiO 2 may be able to play a role in the active site is consistent with both experimental and computational literature which indicates that TiO 2 may hydrate and evolve both chlorine and oxygen. 3,[29][30][31] The Tafel slopes for all active IrO 2 and RuO 2 based catalysts agree well with previously reported Tafel slopes (B60 mV dec À1 and B30 mV dec À1 for the OER and CER respectively; Tables S5, S6 and Fig. S11, ESI †), 32 consistent with expectations that addition of TiO 2 does not fundamentally change the mechanism or the potential determining step for either reaction.…”

Release of Ag/ZnO Nanomaterials and Associated Risks of a Novel Water Sterilization Technology

“…Poor water quality and unsustainable supply limits national economic development and can lead to adverse health and economic impacts. Nanotechnology is a key emerging technology with significant potential for innovation in water treatment [1] (e.g., using advanced materials like nanostructured photocatalysts with surface chemistries, band-edge energies and bandgaps that enable selective binding and degradation of targeted contaminants using sunlight [2,3]); using nanostructured carbon-based materials with high electronic conductivity and hierarchical porous structure as electrodes for electrosorption/capacitive deionization to enhance desalination performance [4,5]; engineering the morphology and surface area of electrodes through the use of nanotube arrays or three-dimensional macroporous structures to improve kinetics and mass transfer in electrochemical oxidation [6][7][8][9]; functionalizing the surface of nanomaterials by organic ligands for the efficient detection and adsorption of organic or inorganic materials from contaminated water [10][11][12][13][14][15][16][17][18][19][20], and controlling the size of magnetic nanoparticles to enhance superparamagnetism for low-energy separation and recovery with magnets [21]. The introduction of such advanced materials in water treatment requires an assessment of the potential environmental and human health risks of these materials.…”

Self-doped TiO2 nanotube electrodes: A powerful tool as a sensor platform for electroanalytical applications

“…A new class of TiO 2 NT with improved electrochemical properties has been recently developed by simple cathodic polarization (electrochemically self-doped TiO 2 NT). These works showed that self-doped TiO 2 NT can be applied as supercapacitors [11][12][13][14][15], anodes for lithium ion batteries [16], anodes for the generation of oxidants [12,14,17,18], photoanodes in photoelectrochemical water splitting [19] and the degradation of contaminants [20,21]. These possibilities can be engendered by activating the TiO 2 semiconductor via self-doping once Ti 3+ dopant states are created, leading to an almost metallic behavior of the material [15,22].…”