Enhanced Photocatalytic Performance of Nitrogen-Doped TiO2 Nanotube Arrays Using a Simple Annealing Process

Abstract

Nitrogen-doped TiO2 nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N2 gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH4F/ethylene glycol solution. The N-doping concentration (0–9.47 at %) can be varied by controlling N2 gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm−2. N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h−1, which was a 125% improvement over that of TNAs (0.115 h−1). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.

TiO2 and Au-TiO2 Nanomaterials for Rapid Photocatalytic Degradation of Antibiotic Residues in Aquaculture Wastewater

“…Also, there were no rutile peaks, indicating that the TiO 2 nanomaterials in this study possessed a pure anatase phase. This result agreed with those reported in [4,5,13,19,48,49]. A closer inspection of the (004) peaks revealed that Au (111) component was found in the (004) peaks of Au-TNAs and Au-TNWs/TNAs, as demonstrated in Figure 1c, confirming the presence of crystalline Au NPs in these samples.…”

“…During the anodization process, TNA growth is driven by the anodic-oxidation reaction (to form TiO 2 from Ti) and the chemical dissolution of the TiO 2 layer under the presence of electric field [19,51,52,53]. The reactions are given below:…”

“…However, the large band gap of TiO 2 (3.2 eV) limits it light absorption to only 5% of the solar spectrum [14,15,16]. Considerable effort has been made to improve the light absorption of TiO 2 by doping with non-metals (N, F, S) [17,18,19] or chemical modification to narrow the band gap [20]. In addition, visible-light absorption can also be achieved by coupling TiO 2 to small-band-gap quantum dots [21].…”

Development and Validation of a LC-MS/MS Method for Determination of Multi-Class Antibiotic Residues in Aquaculture and River Waters, and Photocatalytic Degradation of Antibiotics by TiO2 Nanomaterials

“…We selected the aquaculture wastewater samples with high antibiotic concentrations, including OTC (CM-DD 5 , 112.6 ng•mL −1 ), DXC (AG-CT 8 , 55.6 ng•mL −1 ), SMX (CM-DD 9 , 83.5 ng•mL −1 ), SMZ (AG-CT 2 , 48.4 ng•mL −1 ), and LCM (BL-HB 4 , 60.7 ng•mL −1 ) to study photocatalytic degradation of the antibiotics by TNAs and TNWs/TNAs under UV-VIS exposure at various reaction times of 0, 5, 9, 14, and 20 min. The pseudo-first-order rate constants were determined by fitting the data with the Langmuir-Hinshelwood kinetics rate model [63,79]. Figure 4a,b show the photocatalytic degradation kinetic of LCM, DXC, OTC, SMZ, and SMX using TNAs and TNWs/TNAs under UV-VIS irradiation.…”

“…Antibiotics are widely used for treatment and prevention of infectious diseases in humans and in domestic and food-producing animals, including fish [1,2]. The use and overuse of antibiotics in aquaculture is of great concern because it may cause antibiotic residues in aquatic environments and and non-toxicity [46,47,[60][61][62][63][64]. In this study, TiO 2 nanotube arrays (TNAs) and TiO 2 nanowires on nanotube arrays (TNWs/TNAs) are of interest because they can provide a large surface-to-volume ratio and unidirectional electrical channel [65,66].…”