Photochemical Behavior of Ammonia in Aqueous Suspension of TiO₂

Abstract

Ammonia is produced in huge quantities worldwide not only by commercial chemical factories but by decaying vegetation, garbage, even decomposition of the other protein materials. Ammonia with foul odor causes a serious environmental pollution in the atmosphere. Therefore, the decomposition of ammonia has attracted considerable attention in respect to environmental pollution of the atmosphere.Earlier investigation on the decomposition of ammonia using a light was performed by means of radiolysis 1,2 and photolysis 3-8 in the gaseous state. Ammonia molecules are incorporated into water droplets and form liquid aerosols which can range in diameter with nanoscale particle.9 Recently, we have reported on the photochemical decomposition of aqueous ammonia in the absence and presence of oxygen using 184.9 nm UV light. 10 It was found that hydrazine was mainly produced by the dimerization of NH 2 radicals and oxygen affected the formation of hydrazine. In order for a photochemical reaction to occur, reactant chemical species must absorb the light illuminated. NH 3(aq) , NH 4 + (aq) , OH aq and H 2 O species exist in the aqueous ammonia solution. Since such chemical species have relatively strong intramolecular chemical force, a high enough energy is necessary to begin the photochemical reaction. It corresponds to vacuum UV light to break the chemical bond of such chemical species. The photochemical reaction of aqueous ammonia can not be carried out by a natural ultraviolet solar radiation on the earth's surface, because the solar energy reached on the earth's surface is the wavelength above λ = 314 nm UV light. It is necessary to use a photocatalyst to begin the photochemical decomposition of aqueous ammonia. Metal oxide such as titanium oxide and zinc oxide may be used for the purpose as a photocatalyst. It is well known that titanium oxide absorbs photons with energy higher than its bandgap (~3.2 eV) and electronhole pairs, so called geminated form, are produced.11 To our knowledge, there has been no report to date on the quantitative results for photochemical reaction of aqueous ammonia in the presence of TiO 2 particles. Since the photochemical reactions are very fast, products analysis is generally used to determine the photochemical behavior in a system. The aim of this study is to present the quantitative results for the photochemical reaction of the aqueous ammonia containing TiO 2 particles using 253.7 nm UV light, and to elucidate the behavior of TiO 2 during the photochemical reaction of aqueous ammonia based on the product analysis. Experimental SectionLightsource and Actinometry. Irradiations were carried out at 25 o C usinglow pressure Hg lamp (Osram HNS 10W/ U OFR). Low pressure Hg lamp is classified into two types depending on the method of its emitting wavelength; ozone generating lamp and ozonefree lamp. 12 The ozonefree lamp used in this study emits only 253.7 nm UV light, but on the other hand ozone generating lamp emits two monochromatic lights of 184.9 and 253.7 nm. The lamp was mounted in a quart...