Effects of pH and Catalyst Concentration on Photocatalytic Oxidation of Aqueous Ammonia and Nitrite in Titanium Dioxide Suspensions

Abstract

Batch experiments were conducted to study the effects of titanium dioxide (TiO2) concentration and pH on the initial rates of photocatalytic oxidation of aqueous ammonium/ ammonia (NH4+/NH3) and nitrite (NO2-) in UV-illuminated TiO2 suspensions. While no simple kinetic model could fit the data at lower TiO2 concentrations, at TiO2 concentrations > or = 1 g/L, the experimental data were consistent with a model assuming consecutive first-order transformation of NH4+/NH3 to NO2- and NO2- to nitrate (NO3-). For TiO2 concentrations > or = 1 g/L, the rate constants for NO2 photocatalytic oxidation to NO3 were far more dependent on TiO2 concentration than were those for NH4+/NH3 oxidation to NO2-, suggesting that, without sufficient TiO2, complete oxidation of NH4+/NH3 to NO3- will not occur. Initial NH4+/NH3 photocatalytic oxidation rates were proportional to the initial concentrations of neutral NH3 and not total NH3(i.e., [NH4+] + [NH3]). Thus, the pH-dependent equilibrium between NH4+ and NH3, and not the pH-dependent electrostatic attraction between NH4+ and the TiO2 surface, is responsible for the increase in rates of NH4+/NH3 photocatalytic oxidation with increasing pH. Electrostatic adsorption, however, can partly explain the pH dependence of the initial rates of NO2- photocatalytic oxidation. Initial rates of NO2- photocatalytic oxidation were 1 order of magnitude higher for NO2- versus NH4+/NH3, indicating thatthe rate of NH4+/NH3 photocatalytic oxidation to NO3- was limited by NH4+/NH3 oxidation to NO2- under our experimental conditions.

Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2

“…Several studies have investigated wastewater purification by the photocatalytic oxidation of aqueous ammonia using TiO 2 and/or PtTiO 2 [9][10][11][12][13][14]. Some of these studies reported the effect of pH [9,10], whereas others focused on the effects of Pt loading on the TiO 2 [13] or the presence of inorganic anions [14].…”

“…Some of these studies reported the effect of pH [9,10], whereas others focused on the effects of Pt loading on the TiO 2 [13] or the presence of inorganic anions [14]. In these studies, the initial concentrations of ammonia in the reaction solution were on the order of ppm (∼10 −4 M), and relatively long reaction times were required for oxidation.…”

Electrochemical process combined with UV light irradiation for synergistic degradation of ammonia in chloride-containing solutions

“…High concentrations of ammonia in wastewater effluents deplete dissolved oxygen, reduce chlorine disinfection efficiency, and exhibit acute toxicity to aquatic life. There are several methods for ammonia removal from water and wastewater, including biological process (Kalyuzhnyi et al, 2006), ammonia stripping (Bonmati and Flotats, 2003), ion exchange (Lin and Wu, 1996), breakpoint chlorination (Thomas et al, 1972), photocatalysis (Zhu et al, 2005) and electrochemical process (Chiang et al, 1995;Kim et al, 2006;Wang et al, 2006). Electrochemical method for the advanced treatment of ammonia in the wastewater has attracted a great deal of attention because of its advantages such as a minimal generation of secondary waste, easy operation, remote control, etc.…”

Pemanfaatan Limbah Fly Ash Untuk Penanganan Limbah Cair Amonia

“…Merujuk pada penelitian yang dilakukan oleh Putra (2015), Mohammadi, Sharifnia, dan Shavisi (2016), (Zendehzaban, Sharifnia, dan Hosseini 2013), dan (Zhu et al 2004), degradasi amonia mengikuti model kinetika Langmuir-Hinshelwood, sehingga Model Langmuir-Hinshelwood digunakan untuk mengetahui kinetika reaksi dari degradasi amonia menggunakan fotokatalisis pada penelitian ini.…”