Development of Room-temperature Thin-film Volatile Organic Compound Gas Sensors for Environmental Health Monitoring (Innovation and Technology Fund (ITF) project number ITS/558/09)
Formaldehyde is a volatile organic compound (VOC) broadly used in many aspects, like being a disinfectant in hospital; a building block in synthesizing complex compounds for making building boards, plywood and paints etc. It is also contained in furniture and could be released to contaminate indoor atmosphere. At a concentration of 0.08 parts per million by volume (ppm) in air, it can cause throat and nasal irritation; at 0.1 ppm, it irritates human eyes and mucous membranes, inducing watery eyes and headache; at 2 – 3 ppm, it causes serious tingling of the nose and throat; at 4 - 5 ppm, discomfort further increases; and at 10 - 20 ppm or higher, breathing difficulty occurs and more serious damages are caused.
The maximum permitted level of exposure to formaldehyde is 0.1 ppm in American and European countries; 0.08 ppm according to the World Health Organization (WHO) standard; and 1 ppm according to that of the National Institute for Occupational Safety and Health.
Results of a survey conducted by the Department of Civil and Structural Engineering of PolyU (Guo et al. 2009) for 100 homes in Hong Kong showed that their 24-h average formaldehyde concentrations fell in a range of 0.0345 – 0.349 ppm (TVB Jade channel news on 28-5-2009, Ming Pao Daily on 20-2-2009 and Wenweipo on 26-5-2008), with a mean of 0.0837 ppm. 37 homes in the sample pool have formaldehyde concentrations exceeding the WHO standard. The worst one is 3.5 times of the permitted value of the American/European standard. The mean is 1.7 and 3 times of those of Taiwan and Japan, respectively.
Referring to the deficiencies of many existing sensor products for detection of formaldehyde, Dr. C.W. Ong of the Department of Applied Physics of PolyU was successful in getting a grant from the Innovation and Technology (ITF) Commission to carry out a project (from 16 Dec, 2010 – 15 June 2012), entitled “Development of Room-temperature Thin-film Volatile Organic Compound Gas Sensors for Environmental Health Monitoring (ITS/558/09)” to develop the technology of making metal oxide thin films for detection of formaldehyde. The sensors were made by using Supersonic Cluster Beam Deposition. The gas sensing material has a highly porous structure formed by assembling metal oxide nanoclusters. The nano size of the clusters ensures the sensor to have a large surface-to-volume ratio for achieving a high sensitivity of gas detection; and the high porosity allows the target gas to diffuse very quickly in the structure to achieve a fast response rate. Under ultraviolet illumination, most of the expected targets, such as high enough sensitivity and fast enough response rate, have been achieved after a number of technical problems has been solved.
This article is posted on the CoWIN Website because the research team promised the ITF Commission to present the project and the results to the public through CoWIN in order to encourage new generations to note the influence of VOCs to human health. Upon approval of the final report of the project (submitted in 15 August, 2012), more information will be published on the ITF website at www.itf.gov.hk for access by the public and the public will be allowed to copy, distribute copies, or otherwise make use of this information for non-commercial use.