Polymeric Sorbents for Air Purification

摘要

Adequate indoor air quality is a crucial factor determining the occupants' well-being and productivity. Exposure to indoor air pollutants at certain levels is known to contribute to adverse health effects. Indoor air purifiers are a major solution to the problem of indoor air pollution. Yet, extensive research is ongoing to improve the existing and develop new technologies for use in air purifiers to increase the removal efficiency of the different types of air pollutants commonly found indoors. Activated carbon and its various preparations is the most common material used in air purifiers to remove air contaminants. Activated-carbon-based sorbents are highly effective against most indoor air pollutants, but certain volatile organic compounds (VOCs) present a challenge for them. Therefore, improved sorbents and technologies are needed to improve removal of the VOCs, for which activated carbon is less effective. Due to the physics of the adsorption process, within most classes of VOCs, the efficiency of adsorption drops with the decreasing molecufar weight. The compounds, for which most research to improve adsorption efficiency is carried out include aldehydes. Formaldehyde, the lowest-molecular-weight member in the group of aldehydes, is the focus of this study. We investigated effectiveness of three different activated carbon preparations used in indoor air purifiers and compared them to the effectiveness of four hypercrossiinked polystyrenic sorbents. We applied a digitally controlled formaldehyde-sptked-air generation system. The system employed a three-step process; formaldehyde solution atomization, vaporization, and dilution, with a tunable humidification system. A stable stream of air with a variety of formaldehyde concentrations and at different relative humidity (26 - 34 ± 2 %) was obtained. The formaldehyde-spiked air with a set relative humidity was passed through stainless-steel capsules filled with a known mass of a sbrbent. The concentration of formaldehyde was monitored using an electrochemical sensor. We found that the polymeric sorbents are efficient at formaldehyde removal from the air. The most effective of the four polymeric sorbents with 10 - 200 nm pores reduced formaldehyde concentration from 0.463 ± 0.037 mg/m~3 to 0.020 ± 0.002 mg/m~3, a reduction of over 95 %. We also carried out Brunauer-Emmett-Teller (BET) sorption analysis for the seven investigated sorbents and found that the measured polymeric sorbents' nitrogen sorption capacity was comparable to that of the activated carbon mixes. For one of the four polymeric sorbents, the BET-anafysis-based calculated surface area was considerably higher (1370.4924 ± 19.1847 m~2/g) than that of the best-performing activated carbon type (941.7570 ± 18.0973 m~2/g). This high BET surface area is indicative of a potential for these polymeric sorbents to be highly effective adsorbents for a wide range of other VOCs that need to be investigated in the future. The newly introduced adsorbent system is currently commercially available at a considerably higher cost than activated-carbon-based sorbents. However, the synthesis of these sorbents is very economical, and they may be recyclable, increasing the potential competitiveness.