The effect of Pt oxidation state and concentration on the photocatalytic removal of aqueous ammonia with Pt-modified titania

Platinum-modified titanium (IV) oxide (Pt-TiO2) was used to photocatalytically oxidize aqueous ammonia selectively to nitrogen gas. The photocatalyst was solvent deposited on acrylic (PMMA) supports for use in simple distributive reactors. Pt was photodeposited on the titania surface within each reactor with concentrations ranging from 0.4% (w/w) to 5.1% (w/w) Pt. The oxidation state of the deposited Pt was subsequently modified using reduced phosphotungstic acid. Time-dependent kinetic studies were used to demonstrate the effect of oxidation state on the photocatalytic activity of the Pt-TiO2. It was determined that treatment with reduced phosphotungstic acid enhanced the reaction rate and selectivity to nitrogen gas of the Pt-TiO2 photocatalysts. Most significantly, treatment of Pt-TiO2 with reduced phosphotungstic acid shifts the optimum Pt concentration to higher Pt loadings. The reactor containing 3.2% (w/w) post-treated Pt demonstrated the most favorable combination of NH3 degradation rate and selectivity to N2, resulting in the removal of 28.34% total nitrogen from 1.7 L of a 45.5 ppm NH3-N solution within 72 h.