Shift of the Reactive Species in the Sb–SnO₂-Electrocatalyzed Inactivation of E. coli and Degradation of Phenol: Effects of Nickel Doping and Electrolytes

Abstract

The electrocatalytic behavior and anodic performance of Sb-SnO2 and nickel-doped Sb-SnO2 (Ni-Sb-SnO2) in sodium sulfate and sodium chloride electrolytes were compared. Nickel-doping increased the service lifetime by a factor of 9 and decreased the charge transfer resistance of the Sb-SnO2 electrodes by 65%. More importantly, Ni doping improved the electrocatalytic performance of Sb-SnO2 for the remediation of aqueous phenol and the inactivation of E. coli by a factor of more than 600% and ∼20%, respectively. In the sulfate electrolyte, the primary reactive oxygen species (ROS) identified were OH radicals (Faradaic efficiency η = 2.4%) with trace levels of ozone and hydrogen peroxide (η < 0.01%) at Sb-SnO2. In contrast, the primary ROS at Ni-Sb-SnO2 was ozone (η = 9.3%) followed by OH radicals (η = 3.7%). In the chloride electrolyte, the production of hypochlorite (OCl(-)) was higher (η = 0.73%) than that of ozone (η = 0.13%) at Sb-SnO2, whereas the level of ozone (η = 13.6%) was much higher than that of hypochlorite (η = 0.24%) at Ni-Sb-SnO2. Based on the shift of the reactive species, the primary effect of Ni doping is to catalyze the six-electron oxidation of water to ozone and inhibit the competing one or two-electron oxidation of water (generation of OH radicals, hydrogen peroxides, and hypochlorites). A range of electrochemical and surface analyses were performed, and a detailed mechanism was proposed.

Deposition efficiency in the preparation of ozone-producing nickel and antimony doped tin oxide anodes

“…Indeed, higher dopant levels in the precursor solution (1000:53:11 molar ratios of Sn:Sb:Ni) were used by Yang et al [17] with water as solvent, however no reason for this change is given in the paper. In a later publication [26] they used ethanol as solvent but kept the high dopant levels in the precursor solution.…”

“…The metal salts SnCl45H2O, SbCl3 and NiCl26H2O were dissolved in alcohol to the molar ratios of 1000: (16)(17)(18)(19)(20):(2-6) (Sn:Sb:Ni) [7,[9][10][11][12][13]15]. This precursor solution is then coated on a pre-treated titanium substrate (foil or mesh) by brush, dip or spray coating.…”

“…The variation in current efficiencies in the above-mentioned studies can depend on a number of parameters such as number of applied layers [11,14], electrolyte type [9,11,17] and concentration [9,11], current densities and potentials [9,14], cell design [12], or calcination temperatures [14,18]. In the present study, we have focused on the importance of the Sn, Sb, and Ni precursor salts.…”

Ultra-high oxidation potential of Ti/Cu SnO2 anodes fabricated by spray pyrolysis for wastewater treatment

“…For the low oxidation power anode such as IrO 2 -based electrodes [2,3], the interaction between electrode and hydroxyl radical is strong, which results in a low current efficiency for organics oxidation. Compared to the low oxidation power anodes, the high oxidation power anodes including SnO 2 -based electrodes [4][5][6][7][8] and boron-doped diamond (BDD) [9,10] have weaker interaction with the hydroxyl radical leading to high current efficiency for organics oxidation. The oxidation power of the anodes is determined by oxidation potential corresponding to the onset potential of oxygen evolution.…”

TiO2 Nanotube Array Photoelectrocatalyst and Ni–Sb–SnO2 Electrocatalyst Bifacial Electrodes: A New Type of Bifunctional Hybrid Platform for Water Treatment

“…1,4−11 Despite this low-potential requirement, the faradaic efficiency for the generation of ROS (R2 and R3) is not sufficiently high because of competing oxygen evolution reaction R1. 12 Therefore, increasing the applied potential does not necessarily enhance the water treatment kinetics. 13 In contrast, the faradaic efficiencies and energy consumptions of high-oxygen evolution potential anodes for the decomposition of organic species are ∼7 times higher 1,11,14 and ∼5 times lower, 11,14 respectively, than those of low-oxygen evolution potential anodes, presumably because of the efficient generation of OH radicals (R2).…”