No abstract

We describe a screening methodology that can be used to quickly determine the effectiveness of newly synthesized photocatalysts. We were particularly interested in measuring the destruction of organic molecules painted onto a photocatalytic surface by spraying, with destruction proceeding in ambient air (as a model for airborne toxin destruction). Our method can utilize photocatalysts that are synthesized as powders (such as doped and undoped titanium oxide) and which are then calcined onto a glass substrate disk at 600°C. Herein, we used UV illumination of Aeroxide P-25 TiO(2), but the method is general and can accommodate any region of the light spectrum.

Sterilization using titanium dioxide-mediated photocatalysis has been shown to be a powerful biocidal process due to the production of reactive redox species (RRS). More specifically, these RRS generated from TiO 2 photocatalysis are able to completely oxidize organic material, including microorganisms. Photocatalysis is a potentially useful application for the production of u.v.-illuminated self-sterilizing surfaces such as in surgical suites or water purification. Some organisms are able to protect themselves from radicals and oxidants by producing carotenoid pigments which scavenge free radicals and oxidants. In this work we have created a micellar model with a target dye and used the model to demonstrate that when b-carotene is incorporated into the system it will protect the target dye from photocatalytic destruction. Our model will help to predict how difficult it will be to destroy microbes when exposed to photocatalysis. Our data showed that 50% of the target dye was protected after 5 min of photocatalytic oxidation when b-carotene was present in the micellar system. However, when the micellar system lacked b-carotene protection, 82% of the dye was destroyed via photocatalysis. As a frame of reference, we subjected our model system to standard oxidative Fenton conditions namely, Fe(NO 3 ) 3 / H 2 O 2 . We demonstrated that after 90 min exposure to the above reagents 80% of the target dye remained when bcarotene was present in the micellar system. However, when no b-carotene was present 62% of the dye was destroyed under Fenton conditions.

Volatile low-weight polycyclic aromatic hydrocarbons (PAHs) are known to be potentially toxic to humans and animals. Their detection in ambient air has been of great interest in recent years and various detection methods have been implemented. In this study, we used naphthalene as a basic model of such compounds and constructed our own version of a titanium oxide-based sensor system for its detection. The main goal of the study was to clearly demonstrate the effectiveness of this type of sensor, record its response under well-controlled conditions, and compare that response to concentration measurements made by the widely accepted spectrophotometric method. With that goal in mind, we recorded the sensor response while monitoring naphthalene vapor concentrations down to 95 nM as measured by spectrophotometry. Air flow over the sensor was passed continuously and sample measurements were made every 3 min for a period of up to 2 h. Over that period, several cycles of naphthalene contamination and cleaning were implemented and measurements were recorded. The relative humidity and temperature of the air being sampled were also monitored to assure no major variations occurred that could affect the measurements. The sensor showed high sensitivity and a reproducible response pattern to changes in naphthalene concentration. It could be easily “cleaned” of the compound in ten minutes by means of the application of UV light and the passing of fresh air. Pending testing with other volatile PAH, this type of sensor proves to be an effective and inexpensive way to detect naphthalene in air.