Influence of electron acceptors on the kinetics of metoprolol photocatalytic degradation in TiO₂ suspension. A combined experimental and theoretical study

Abstract

ARTICLE This journal isMetoprolol (MET) belongs to a group of frequently used β 1 -blockers, which often occur in waste waters. The objective of this work was to employ liquid chromatography (LC) and total organic carbon methods to study the photocatalytic degradation of MET in UV irradiated aqueous suspensions of TiO 2 (Wackherr's "Oxyde de titane standard" and Degussa P25), in the presence of different electron acceptors such as molecular oxygen, hydrogen peroxide, potassium bromate, and ammonium persulfate. The degradation rates were found to be strongly influenced by the kind of electron acceptor and the type of catalyst. The optimal amount of hydrogen peroxide and potassium bromate was investigated as well. MET photocatalytic degradation was fastest in the presence of O 2 and potassium bromate with TiO 2 Degussa P25, while mineralization was most efficient in the presence of molecular oxygen alone. In all investigated cases, degradation followed a pseudo-first order kinetics. Reaction intermediates of MET degradation in the presence of different electron acceptors with both catalysts were studied in detail and a number of them were indentified using LC-ESI-MS/MS. The interactions with MET of reactive radical species relevant to this study ( − • 2 O , • OH, • 2 BrO , and − • 4 SO ) were theoretically investigated by means of density functional theory (DFT) computations. § Electronic supplementary information (ESI) available: Influence of electron acceptors on the kinetics of metoprolol photocatalytic degradation in TiO2 suspension. A combined experimental and theoretical study.− 2 8 2 O S , and − 3BrO , can act as electron acceptors to enhance the photodegradation efficiency. These electron acceptors can have several effects including: (I) avoidance of e − −h + recombination because of scavenging of conduction-band electrons; (II) increase of the concentration of • OH and (III) production of other oxidizing species that can enhance the oxidation rate of the substrate and of its intermediate compounds. 10

Factors Influencing Imazapyr Herbicide Removal from Wastewater Using Photocatalytic Ozonation

“…Similar finding have been reported by Usharani et al, 14 and by Gar Alalma et al 15 These authors have reported first order reaction kinetics for the degradation and mineralization of chlorinated pesticides and insecticides and other various water pollutants by photocatalytic ozonation. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The results, shown in figure 5, demonstrates that the optimal conditions for imazapyr degradation with photocatalytic ozonation is neutral pH. On the other hand, the combination of two oxidation systems, ozonation and photocatalysis, for water treatment under optimal conditions are reported to have increased oxidation efficiencies (synergy) compared to the sum oxidation efficiencies of these two oxidation systems separately.…”

“…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] …”

“…A possible explanation resides in the fact that as imazapyr concentration rises, it is possible that more organic substances are deposed on the surface of TiO 2 , whereas less number of photons are available to reach the catalyst surface and the probability of reaction between imazapyr molecules and oxidizing species also decreases, thus resulting in less degradation percentage. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] …”

“…[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.…”