(425a) Photocatalytic Concrete Slab for Passive NOx /O3 Pollution Control

NOx emissions have become a constraint for sustainable economic development due to ozone non-attainment. Under light illumination over a photocatalyst free radicals are generated to oxidize or decompose pollutants. While volatile organic compounds (VOCs) are oxidized to water, CO2, and chloride, NOx are oxidized to nitric acid, neutralized by the alkaline materials in concrete, and washed away by rain. Ozone can be decomposed to oxygen over photocatalysts. Recent developments in Europe Japan, Hong Kong, and US have demonstrated the interest in deploying photocatalytic technologies for environmental remediation. The photocatalytic coating has potential to economically reduce nitrogen oxides (NOx) emissions at

ambient conditions nearly maintenance-free.

We report here the application of photocatalytic coatings on a concrete slab to simulate road pavements for passive NOx pollution control. Catalysts tested include Degussa P-25 TiO2 and TiO2 - boosted with BaTiO3, Nd2O3, and Fe2O3. Both NO and NO2 oxidation including the effects of inlet NO concentration, residence time, and humidity are investigated. The removal efficiencies are in the range of 86-93% from 200 ppb-2000 ppb NO. Relative Humidity (RH) is seen to have some beneficial effect at <35% RH while lowering NO conversion by ~10% at > 35% RH. The additives Nd2O3, Fe2O3, and BaTiO3 are observed to depress the NO2 generation while improving NO conversion when using fiber-optic as a support. When tested on catalytic concrete slabs, however, Degussa P-25 offers the best NO removal, even though Fe2O3 and Nd2O3 offer better NO2 suppression. The optimal TiO2 to cement ratio is of interest because TiO2:SiO2 photocatalyst shows twin peaks in their activity in atrazine oxidation and the fact that cement also contains Fe2O3. A CFD simulation of NOx plumes from a tail pipe shows the likely distribution of concentration and residence time due to dispersion; that, in turn, can provide a useful guide for future lab investigations.

Catalyst-coated concrete photoreactors with small dimensions of 8? X 4? X 2?were fabricated according to the ACI mix design with a 3-mm catalytic layer with Type 1 Portland cement: Degussa P-25 TiO2 = 2:1 (weight ratio) and TiO2 : SiO2 : CaO : Fe2O3 = 1 : 0.58 : 1.77 : 0.09 (mole % ratio). Two 4 watt UVA (Black Light) gives a total radiation exposure is 380 watt/m2. Catalyst loading is 13 mg/m2 in 3 mm(~1/8?) uniform layer. Experiments are conducted to find out the NO oxidation different inlet NO concentrations (200 ppb, 500 ppb, 1500 ppb & 2000 ppb) and different RT (5sec, 10 sec, 15 sec & 20 sec). Ozone is generated using Ozone generating UV lamps and oxygen. Ozone oxidation on the catalyst coated photoreactor boosted with MnO2 at different inlet Ozone concentration and different Residence Time will be tested. Ozone is analyzed using the ozone analyzer (model: 49C O3 analyzer, Thermoscientific Instruments Inc.). HONO measurement to find out whether there is any formation during photocatalysis reaction for both NO and NO2 oxidation leaving the photocatalytic reactor using the HPLC analysis.