Carbon Dioxide Adsorption onto Polyethylenimine-Functionalized Porous Chitosan Beads

Polyethylenimine-functionalized porous chitosan (PEI–CS) beads were prepared and their CO₂ adsorption performance was evaluated. The CO₂ adsorption capacity of PEI–CS was dependent upon both the amine content and surface area of the functionalized beads. PEI–CS showed a CO₂ adsorption capacity of 2.3 mmol/g at 313 K and 15 kPa of CO₂ in the absence of water vapor that considerably increased to 3.6 mmol/g in the presence of water vapor. To rationalize this phenomenon, the CO₂ adsorption mechanisms in the absence and presence of water vapor were investigated by diffuse reflectance infrared Fourier transform spectroscopy. The results indicated that the mechanism of CO₂ adsorption onto PEI–CS, in both the absence and presence of water vapor, involved the formation of carbamate. Therefore, the higher CO₂ adsorption capacity in the presence of water vapor was attributed to the increased accessibility to amino groups of PEI–CS, owing to swelling of the polyethylenimine chain and/or chitosan framework upon adsorption of water. The herein reported chitosan-based material displays high CO₂ adsorption capacity as well as excellent regenerability and, thereby, shows potential as an adsorbent for CO₂ capture

Experimental design.

<p>(<b>A</b>) Schematic diagrams showing the experimental procedure where the floating ends of the two DNAs were manipulated with optical tweezers while their root positions were controlled by stage movement. Numbers correspond to those in <b>B</b>–<b>D</b>. (<b>B</b>) Snapshots of bright-field (1–3; sequential frames) and fluorescence images (4–12; averaged over 30 frames = 1 s). Arrows in 1–3 show the direction of stage movement. Rectangles in 9 show the regions where the DNA images were fitted with a line to estimate the braid length. The scale bar in 12 shows 5 µm (57.5 pixels). (<b>C, D</b>) Time courses of the braid length (<b>C</b>) and the DNA tension sensed by the lower-left bead in <b>B</b> (<b>D</b>). Time 0 is the end of stage movement. After the processive unbraiding at ∼60 s, we slightly increased the tension at ∼70 s. Gray dots in <b>C</b> were calculated on images averaged over 30 frames, and further averaging over 120 frames (4 s) shown in blue. Red broken lines show the way the burst time was estimated. Green horizontal bars in <b>C</b> indicate portions shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034920#pone.0034920.s005" target="_blank">Viedo S1</a>. The total tension in <b>D</b> represents (<i>T</i>_x²+<i>T</i>_y²)^1/2, and thus noise, converted to positive values, dominates over the actual tension when the latter is below the noise level. The tension is essentially zero at stages 4 and 12.</p

Distribution of unbraiding burst sizes.

<p>(<b>A</b>) The expected length of unbraiding. If a topo IIα molecule binds at <i>i</i>-th turn (circle) from an end of a braid of <i>n</i> turns, and if the topo IIα stays and remains active for a sufficient period, then the braid length will become <i>n</i> – 2<i>i</i>, or the unbraiding length will be 2<i>i</i>, because the two DNA segments forming the braid can freely slide against each other to keep the braid center at the same position. For random binding, <i>i</i> is anywhere between 0 and <i>n</i>/2, and thus the unbraiding length 2<i>i</i> will distribute equally between 0 and <i>n</i>, averaging <i>n</i>/2. Thermal motion of DNA will increase the unbraiding length by several turns (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034920#pone.0034920.s006" target="_blank">Text S1</a>). (<b>B</b>) Observed distribution. The unbraiding lengths in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034920#pone-0034920-g002" target="_blank">Figure 2A</a> are normalized by the length before unbraiding (corresponding to <i>n</i> in <b>A</b>). Data with an initial length greater than 1 µm have been selected and analyzed. The leftmost bars with stripes represent cases where unbraiding was undetected in the length assay; the normalized unbraiding lengths for these data should be less than 0.25 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034920#pone.0034920.s004" target="_blank">Figure S4</a>).</p

Unbraiding burst sizes.

<p>(<b>A</b>) Burst sizes estimated from the braid length in fluorescence images. (<b>B</b>) Burst sizes in terms of braid turns; the braid length was converted to braid turns using the calibration equation described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034920#pone.0034920.s003" target="_blank">Figure S3</a>. For both panels, dots show individual observations, plotted in two or three lines for clarity. Large circles show averages for the first (blue or purple), second (green), and third (cyan) bursts, counterclockwise (CCW) and clockwise (CW) braids not distinguished. The averages are for the data in which unbraiding was confirmed as a change in braid length (dots in the central white zone). Dots in the top shaded zone indicate cases where a braid completely disappeared by the time the tension was set up (time 0). The shaded zone below vertical zero shows cases where a length change was undetected but mechanical unwinding at the end (300 s) revealed remaining braid turns of less than 30. The bottom shaded zone is for no reaction cases where the braid number remained 30 until 300 s as confirmed by mechanical unwinding. Insets at top right show histograms of unbraided length/turns at 3.7 pM topo IIα; <i>ud</i>, undetected; <i>nr</i>, no reaction.</p