Removal of VOCs and H₂CO from air by nanoparticulate silica adsorbents or TiO₂ photocatalysts

• Main Author: Ewlad-Ahmed, Abdunaser Mabruk S.
• Published: University of Strathclyde 2013
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.588985

Constant concentrations of selected VOCs (toluene, ethylbenzene, cumene and dichlorobenzene) and formaldehyde (H₂CO) were successfully generated in separated sampling chambers. A commercially available sorbent (Tenax TA) and silica C18 cartridges impregnated with trapping solution were used to determine experimental masses "references masses" of VOCs and H₂CO, respectively, using selected sampling conditions. Mesoporous silica samples (MCM-41, MWD-MCM-41 and SBA-15) were synthesised under harsh conditions by traditional sol-gel methods. Extraction efficiencies of these adsorbents were compared to Tenax TA, and showed similar performances (64 to 69 %) for VOCs extraction. However, SBA-15 had slightly higher dynamic capacity due to its bimodal pore structure which includes microporores. Novel silica green nanomaterials (GNs) were synthesised using a bioinspired route; under mild conditions of natural pH and ambient temperature, rapid synthesis (15 min) and in all aqueous solutions. However produced GN materials have significantly lower surface areas (58 - 355 m² g⁻¹) compared to MCM-41 (1014 m² g⁻¹), they had similar or better extraction efficiencies (60-80 %) of MCM-41 due to their unique porosity including micropores. In addition they had comparable capacities per unit surface area with MCM-41. A novel synthesis route "green" was applied to produce mesoporous silica (USG) with high surface area (up to 1100 m² g⁻¹), pore size of 2.6 nm and large pore volume (1.00 cm³ g⁻¹) which are similar to MCM-41 properties. The new produced USG demonstrated a similar performance (60%) and adsorption capacity for VOCs extraction compared with MCM-41. Furthermore all silica adsorbents were successfully functionalised with organic amine groups in order to examine their performance for H₂CO extraction. Results demonstrated that H₂CO was removed from air permanently by chemisorption on functionalized adsorbents. Finally, porous TiO₂ coated onto glass beads were used for VOCs degradation as the first time. The results indicated that the best performance of VOCs degradation (up to 80%) was achieved by using smaller glass beads, at lower flow rate or an increase of coating number (thickness of films).