Light intensity dependence of the kinetics of the photocatalytic oxidation of nitrogen(ii) oxide at the surface of TiO2

Abstract

Air pollution by nitrogen oxides represents a serious environmental problem in urban areas where numerous sources of these pollutants are concentrated. One approach to reduce the concentration of these air pollutants is their light-induced oxidation in the presence of molecular oxygen and a photocatalytically active building material which uses titanium dioxide as the photocatalyst. Herein, results of an investigation concerning the influence of the photon flux and the pollutant concentration on the rate of the photocatalytic oxidation of nitrogen(II) oxide in the presence of molecular oxygen and UV(A) irradiated titanium dioxide powder are presented. A Langmuir-Hinshelwood-type rate law for the photocatalytic NO oxidation inside the photoreactor comprising four kinetic parameters is derived being suitable to describe the influence of the pollutant concentration and the photon flux on the rate of the photocatalytic oxidation of nitrogen(II) oxide.

Different Roles of Water in Photocatalytic DeNOx Mechanisms on TiO2: Basis for Engineering Nitrate Selectivity?

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 14 In principle, the photocatalysis process can be divided into three mechanistic steps: (1) the adsorption of target molecules, (2) degradation of adsorbed molecules under light illumination, and (3) desorption of degraded substances. Adsorption is a competitive process and NO and NO 2 molecules compete for adsorption sites, which include sites provided by chemisorbed water [40][41][42] . Molecular (physisorbed) water also participates in the photocatalytic process [43][44] , so the distribution of physi-and chemi-sorbed water is likely to be an important controlling variable in defining photocatalytic efficiency.…”

“…NO ads can be oxidised on the illuminated TiO 2 following several well-established photocatalytic pathways 38,41,[45][46] , (see equations (3)- (8)). In these, adsorbed water plays important but different indirect roles:…”

Revised Disrupted Langmuir–Adsorption Model of Photocatalysis

“…TiO 2 , as a function of both ρ and [P], for example by Dillert et al 6 , as illustrated in figure 2. However, it can also be used to fit with equal success, the kinetic results arising from other, similar, probing photocatalytic studies, such as that of oxidation of phenol (PhOH) 15 , see 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 …”

“…Alternatively, others 6 have assumed the key oxidation process is direct hole oxidation of P, i.e. ] ss to be used in the rate expression for reaction (18), it follows that the quantum yield/quantum efficiency for the process must be necessarily low, unless a radical chain reaction mechanism pertains 16 ; since in the latter case quantum yields/efficiencies > 1 can be achieved.…”

“…To date, this revised model has been used primarily to fit the observed variation in initial rate for the photocatalysed oxidation of NO 6,7 , sensitised by P25…”