Integrated CO2 capture-fixation chemistry via interfacial ionic liquid catalyst in laminar gas/liquid flow

Simultaneous capture of carbon dioxide (CO2) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO2-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO2 in gas–liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas–liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO2 in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81–97% yields under mild conditions. The platform would enable direct CO2 utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps.


Supplementary Tables
Supplementary Table 1

Fabrication of DBU-IL catalyst embedded SiNws microreactor:
The DBU-IL catalyst imbedded on thimble of SiNWs microreactor for interfacial organic synthesis was fabricated by following way:

Selective -SH functionalization on thimble of superamphiphobic SiNWs:
Mercaptosilane was selectively modified the thimble of superamphiphobic SiNWs by reported method. 1 A simple flow diagram is shown in Supplementary Fig. 1.
Step 1. Patterning of protective AZ photoresist layer on Si wafer: Si nanowire chip were made by soft photolithographic patterning method as reported. 1,2 In this method, boron doped p-type silicon (100) wafer was cleaned by acetone, isopropyl alcohol followed by deionized water to remove oxidized layer and dried by N 2 flow. Then, the wafer was spin coated by AZ 1512 positive photoresist consecutively at 500 rpm and 2500 rpm for 5 sec and 30 sec, respectively, to get homogeneous thickness of AZ1512 photoresist. Subsequently, the photoresist coated silicon wafer was soft baked on a preheated hot plate at 125 o C for 10 min.
Then the baked silicon wafer was covered by photo-mask (Supplementary Fig. 1 and irradiated under UV light (λ = 250-400 nm, 4.5 mW cm -2 ) for 10 min, followed by post baking at 95 o C for 1 min. The pattern was developed by using AZ developer, and washed 5 min with water and dried by nitrogen flow (Supplementary Fig. 1, Patterned silicon wafer).

Fabrication of the modified PDMS channel and DBU-IL catalyst immobilization:
Whole fabrication process was followed by reported method 1,4 . A simple flow diagram is shown in Supplementary Fig. 9.  Fig. 1(b), right) and irradiated with UV light. After 10 min exposure of UV light, the wafer was immediately post baked at 75 o C for 1 min and 105 o C for 3 min.
The post baked silicon wafer was developed by SU-8 developer for 5 min to get a SU-8 pattern, and washed with isopropyl alcohol, followed by water and dried with nitrogen flow.  Fig. 9, indicating a thin AHPCS coating on channel surface as a dark layer.

Fabrication of PDMS channel
The Si-H groups of the cured AHPCS surface was then converted to Si-OH by hydrolysis with 0.5N NaOH solution for 2 h at 30 o C, and rinsed thoroughly with deionized water, as confirmed by a time dependent hydrolyzed FTIR spectra in Supplementary Fig. 10. The peak at 3500 cm -1 , correspond to -O-H stretching, becomes prominent as the hydrolysis time increases. Note that the hydrolysis step in alkali condition converted the AHPCS polymer to the silicate glass layer with thin layer 5 .  Fig. 10).

Two types of ILs catalyst immobilization over SiNWs microreactor:
As seen at above of immobilization chemistry over SiNWs surface, thiol-ene chemistry has been exploited to immobilize the DBU by reaction of A-DBU with the -SH functionalized thimble part of SiNWs and the surface of AHPCS coated PDMS channel ( Supplementary   Fig. 11). Two types of DBU-ILs catalytic microreactors were made by immobilizing; (type 1) only on thimble of SiNWs Supplementary Fig. 11(a), (type 2) on thimble of SiNWs and AHPCS coated PDMS inner surface (Supplementary Fig. 11(b)). For type 1 of SiNWs/PDMS microreactor, the A-DBU solution in THF was filled into the channel through tubing using a syringe , then UV light (365 nm, 4.6 mW cm -2 ) was exposed for 15 min and  Fig. 2 & 12).

Selection of a suitable solvent for DBU-ILS catalytic microreaction:
A number of solvents were tested, and DMSO was found to facilitate complete solubility of the reactant and product, and provide desired contact angle over SiNWs due to its high surface tension (Supplementary Table 1).

Chemical reactions in the DBU
The molar ratio calculations of reagent and CO 2 gas: ( Table 1( The molar ratio calculations in reaction for mass balance check (Table 1(

Gravimetrically analysis of absorbed CO 2 by liquid phase:
Some part of CO 2 could be absorbed by DMSO solvent (γ 1 ) and reactant/product (γ 2 ). 8 The qualitative analysis of absorbed CO 2 peak was confirmed by FTIR spectrum which one shown in Supplementary Fig. 28(d).  Fig. 27). This phenomena confirmed the stable gas-liquid laminar flow in the SiNWs microreactor. of CO 2 , and the product was collected at da ily base. In the beginning of 1st to 2nd days, yield of product fall gradually from 98 to 92% then after became constant at ~90%. The graph between the yields of product and time has been shown in Supplementary Fig. 29.

Typical procedure to solvent switching in an integrated continuous -flow manner:
To switch the solvent containing the product from DMSO to DCM, the additional PTFE membrane embedded phase separator was connected to outlet of the SiNWs/PDMS microreactor as similarly as reported 9,10 (Supplementary Fig. 31). The phase separator was fabricated as following: polyethylene films (PE, 60 mm × 60 mm × 240 μm thickness) were manually punched to form a single groove with rectangular shape (8.2 mm × 35.5 mm) ( Supplementary Fig. 32) Note that low flow rate of water resulted in incomplete extraction of product into DCM.