THE Quality of Indoor Air has become increasingly important given that the amount of time spent indoors is more than ever before. Indoor Air has been found to be contaminated with microbials (including viruses, microscopic bacteria, fungi, etc.), harmful gases (like VOCs, radon, formaldehyde, H2S, etc.) and particulates (PMx , dust, etc.) that are responsible for “building related diseases”( US EPA, 1990; WHO 1989). Building Related Diseases also known as Sick Building Syndrome is the collective name of illnesses such as asthma, bronchitis, allergic reactions, headache, nose or throat irritation, dry cough, hypersensitivity pneumonitis, allergic rhinitis, etc. that are caused by Polluted Indoor Air (BOULAY and BOULET, 2003). Indoor Air Pollution is a significant problem that needs an efficient solution.
The traditional methods of purifying air like filtration, adsorption and disinfection have a limited ability to effectively achieve suitable IAQ Standards. Recently, promising technologies such as PHI (Photo Hydro Ionization), bipolar ionization and UVGI have displayed greater efficiencies in cleaning selected aspects of the Indoor Air. Research shows that on combining these powerful technologies, an even more efficient system with unforeseen triple benefits can be formed, PHIO+.
PHIO+ also called as Photo Hydro Ionized Oxidation + is a technology in which an existing PHI product is combined with a bipolar ionization cell to neutralize all the aspects of Indoor Air contaminants and even provide energy saving and health improvement benefits to the user.
The Indoor Air is made up of various gaseous substances that have the ability to pose a threat to the health of human occupants. VOCs have been found at higher concentrations than those allowed by the existing standards due to the extensive use of synthetic building materials and furnishings (Zhang & Yang, 2005). High VOC concentrations are responsible for allergic reactions; headache; eye, nose or throat irritation; dry cough; dizziness and nausea; difficulty in concentrating and tiredness (Kim et al., 2001). A honeycomb structured advanced PHI cell has been shown to be the most effective in reducing VOCs at a significant rate (Zhang & Yang, 2005).
The air purification technique of PHIO+ commonly uses nano semiconductor catalysts and ultraviolet (UV) light to convert organic compounds in indoor air into harmless and odourless constituents like water vapor (H2O) and carbon dioxide (CO2) (Tompkins, 2001). The PHI cell uses nano-titania (TiO2) as the catalyst that is activated by UV light. Fig. 1 shows a diagram of the PHI process of VOCs using TiO2 as the catalyst. An electron in an electron-filled valence band (VB) is excited by photoirradiation and jumps to a vacant conduction band (CB), leaving a positive hole in the VB. These electrons and positive holes are responsible for reduction and oxidation reactions, respectively, of compounds adsorbed on the surface of Titanium...