SUNSPACE, A Porous Material to Reduce Air Particulate Matter (PM)

Abstract

The World Health Organization reports that every year several million people die prematurely due to air pollution. Poor air quality is a by-product of unsustainable policies in transportation, energy, industry, and waste management in the world's most crowded cities. Particulate matter (PM) is one of the major element of polluted air. PM can be composed by organic and inorganic species. In particular, heavy metals present in PM include, lead (Pb), mercury (Hg), cadmium, (Cd), zinc (Zn), nickel (Ni), arsenic (As), and molybdenum (Mo). Currently, vegetation is the only existing sustainable method to reduce anthropogenic PM concentrations in urban environments. In particular, the PM-retention ability of vegetation depends on the surface properties, related to the plant species, leaf and branch density, and leaf micromorphology. In this work, a new hybrid material called SUNSPACE (SUstaiNable materials Synthesized from by-Products and Alginates for Clean air and better Environment) is proposed for air PM entrapment. Candle burning tests are performed to compare SUNSPACE with Hedera Helix L. leafs with respect to their efficacy of reducing coarse and fine PM. The temporal variation of PM₁₀ and PM_2.5 in presence of the trapping materials, shows that Hedera Helix L. surface saturates more rapidly. In addition, the capability of SUNSPACE in ultrafine PM trapping is also demonstrated by using titanium dioxide nanoparticles with 25 nm diameter. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) images of SUNSPACE after entrapment tests highlight the presence of collected nanoparticles until to about 0.04 mm in depth from the sample surface. N₂ physisorption measurements allow to demonstrate the possibility to SUNSPACE regeneration by washing.

Keywords: SUNSPACE; air particulate matter (PM) capture; azure chemistry; leaf; nanoparticles; porous material.

Figure 1

Possible SUNSPACE applications, based on the selected synthesis form (massive, coating, thin layer).

Figure 2

TEM images (120 kV) of silica fume sample (A,B) SUNSPACE prepared by sonication (C,D) SUNSPACE ultrathin slices (E,F), and EDX spectra of Silica Fume and SUNSPACE (G). Silica fume shows particles of diameter of 20–500 nm. Once embedded in epoxy resin and cut in ultrathin slices, SUNSPACE sample shows pores of 200–600 nm diameter (arrows). Elemental analysis of SUNSPACE shows presence of Iodium and Calcium not measured in silica fume sample.

Figure 3

(A,B) SEM images of SUNSPACE, reported at different magnifications and 3 (C) SEM image of the Hedera Helix L. leaf surface.

Figure 4

PM₁₀ (A) and PM_2.5 (B) concentrations emitted by the candle burning source in the experimental box and detected when a trapping material (Hedera Helix L. leaf or SUNSPACE) is used (test 1). The trapping test was repeated for both trapping materials (test 2).

Figure 5

TEM (120 kV) images of SUNSPACE sample exposed to JRCNM1005a titanium dioxide nanoparticles (arrows) (A,B). Elemental analysis in STEM mode at 120 kV (C–E). Titanium dioxide nanoparticles (green) interact and are co-localized (circle) with SUNSPACE material (silicium, red) only.

Figure 6

(A,B) SEM images of SUNSPACE sample after titania nanoparticles capture, at different magnification. The circle (B) highlights the iodine salts presence.

Figure 7

(A) SEM image of the cross-section of the sample, at a depth of 0.28 mm (B) corresponding elemental composition map with color code. Titanium signal is represented by magenta (C) corresponding EDS spectra at 0.02 mm from surface, 0.04 mm from surface and 0.1 mm from surface.

Figure 8

(A) 30000X SEM image of the cross-section of the SUNSPACE sample, at a depth of 0.045 mm from the surface (B) corresponding elemental composition map with color code. Titanium signal is represented by magenta (C) EDS spectrum of the volume with high Titanium content.

Figure 9

Result from N₂ physisorption at the liquid temperature: physisorption isotherms (A) and BJH pore size distributions calculated from the desorption branches (B).