Surface Interactions between Imazapyr and the TiO₂ Surface: An in Situ ATR-FTIR Study

Abstract

Herein we present a detailed report concerning the mode of surface interactions between imazapyr, 2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl)­pyridine-3-carboxylic acid, and the TiO2 surface. Adsorption of imazapyr onto a TiO2 film has been investigated in situ using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The adsorption of imazapyr is pH dependent and occurs through electrostatic interactions and chemical bonding between the probe molecule and the charged TiO2 surface involving different functional groups of imazapyr species present in solution. Based upon the ATR-FTIR spectra of imazapyr recorded at different pH values, it is concluded that the adsorption of imazapyr onto the TiO2 surface is favored at pH values below the TiO2’s point of zero charge. Upon adsorption, the carboxylic acid group of imazapyr binds at surface Ti­(IV) centers mainly as a bridging ligand at pH < pHzpc. With increasing pH values, the binding of imazapyr to the surface becomes less favorable. Furthermore, evidence is presented for additional contributions of other binding modes. Attempting to understand the influence of these interactions on the initial photocatalytic degradation rate of imazapyr, the results of this study confirm experimentally the aspects of the photocatalytic oxidation mechanism of imazapyr discussed previously on the basis of semiempirical calculations [Osajima et al. Monatshefte für Chemie - Chem. Mon. 2007, 139, 7–11, and Carrier et al. Appl. Catal. B Environ. 2006, 65, 11–20].

Factors Influencing Imazapyr Herbicide Removal from Wastewater Using Photocatalytic Ozonation

“…The optimal amount of Hombikat UV 100 agrees well with reported results by other authors. [14][15][16][17][18][19][20][21][22][23][24][25][26] This improvement can be attributed to the increasing of active sites by providing more TiO 2 particles, which plays the semiconductor role in the photocatalysis process. Consequently, the formation of electron-hole pairs and reactive hydroxyl radicals on the surface of semiconductor increased, which improved the oxidation of imazapyr into other intermediates.…”

“…Consequently, the formation of electron-hole pairs and reactive hydroxyl radicals on the surface of semiconductor increased, which improved the oxidation of imazapyr into other intermediates. [15][16][17][18][19][20][21][22][23][24][25][26][27] …”

“…Among the various pesticides, imazapyr is one of the most widespread types of contaminants of waters and soils, often found in the municipal sewage effluents and soil with varying trace concentrations in different parts of the world. 1- 2 Imazapyr, 2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid, being a hetero aromatic molecule, 3 is a non-selective herbicide which belongs to the imadazolinone family. Imazapyr is a persistent herbicide, with a half-life varying from 21 days to 49 months, and a high mobility in soils.…”

“…Imazapyr is a persistent herbicide, with a half-life varying from 21 days to 49 months, and a high mobility in soils. [3][4] Therefore, it is likely suspected to contaminate groundwater. 5 Elimination of imazapyr present in drinking water by treatment with ozone has been demonstrated to be unsuccessful since half of the initial compound remains in water after the process.…”

“…[10][11][12] However, The degradation of Imazapyr has also been investigated by other authors using photocatalysis and ozone and results showed lower concentration compared to photocatalytic ozonation. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The photocatalytic ozonation degradation of pesticides is largely dependent on operating parameters such as TiO 2 dosage, initial herbicide concentration and solution pH. [31][32] Understanding the effects of these factors on the photocatalytic degradation efficiency have an importance when designing a sustainable and efficient technique for wastewater treatment.…”