hexylic

Hexylic acid (hexanoic acid) and hexylamine from Sigma-Aldrich have been used as short-chain amphiphilic molecules.

Meanwhile, a solution containing short-chain amphiphilic molecules (0.3 g hexylic acid in water, the ratio of Ti[O.sub.2] to amphiphilic molecules was adapted from [24]), was prepared.

The pH was adjusted to pH 3.5 with 0.1 M NaOH if necessary (in case of using hexylic acid as amphiphilic agent).

For example, Ti[O.sub.2]-foam-1 (with hexylic acid) has an average pore size of approx.

P25 shows a surface area of 58.9 [+ or -] 1.8 [m.sup.2] x [g.sup.-1] whereas Ti[O.sub.2]-foam-1 (with hexylic acid) has a surface area of 51.7 [+ or -] 1.6 [m.sup.2] x [g.sup.-1] and Ti[O.sub.2]-foam-2 (with hexylamine) has a surface area of 58.1 [+ or -] 2.5 [m.sup.2] x [g.sup.-1].

From the results presented in Table 1, the following conclusions can be drawn: the Ti[O.sub.2]-foam-1 (using hexylic acid as amphiphilic molecule) adsorbs more NO than P25 powder and produces more N[O.sub.2] and N[O.sub.x] (HN[O.sub.3]).

Figure 6 presents the change of the NO concentration at the reactor outlet during irradiation of AEROXIDE P25, Ti[O.sub.2]-foam-1(with hexylic acid), and Ti[O.sub.2]-foam-2 (with hexylamine) with varying NO inlet concentrations.

(b) SEM photographs of Ti[O.sub.2]-foam-1 (hexylic acid as amphiphilic molecule) with different magnifications.

Caption: Figure 5: Concentration changes of NO, N[O.sub.2], and N[O.sub.x] as a function of UV illumination time in a typical experimental run for a AEROXIDE P25 (a) and Ti[O.sub.2]-foam-1 (with hexylic acid) sample (b).

Caption: Figure 6: (a) Concentration changes of NO at the reactor outlet observed during three typical experimental run for a AEROXIDE P25, Ti[O.sub.2]-foam-1 (with hexylic acid), and Ti[O.sub.2]-foam-2 (with hexylamine) as a function of UV illumination.