Roll-to-Roll Transfer of Electrospun Nanofiber Film for High-Efficiency Transparent Air Filter

Transcription

1 Supporting Information Roll-to-Roll Transfer of Electrospun Nanofiber Film for High-Efficiency Transparent Air Filter Jinwei Xu 1,, Chong Liu 1,, Po-Chun Hsu 1, Kai Liu 1, Rufan Zhang 1, Yayuan Liu 1, Yi Cui 1,2, * 1 Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States 2 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States These authors contribute equally to this work. *Correspondence should be addressed to Y.C. ( yicui@stanford.edu)

2 Methods: Electrospinning. The solution system for the polymers used in this work is 20 wt% Nylon-6 (Sigma-Aldrich) in formic acid (Baler Analyzed), 6 wt% PAN (MW = g mol -1, Sigma-Aldrich) in dimethylformamide (EMD Millipore). The polymer solution was loaded in a 1-ml syringe with 22-gauge needle tip, which is connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). The solution was pumped out of the needle tip using a syringe pump (KD Scientific). In direct-spinning method, the fiberglass wire mesh (New York Wire) was sputter-coated (AJA International) with ~150 nm of copper on both sides and was grounded to collect the electrospun nanofibers. The wire diameter was inch. In transfer method, the electrodeposited copper foil (Pred Materials) was grounded to collect electrospun nanofibers. The applied potential, the pump rate and the needle-collector distance were 15 kv, 0.06 ml/h, 15 cm for Nylon- 6 electrospinning and 10 kv, 0.1 ml/h, 15 cm for PAN electrospinning. Optical transmittance measurement. The transmittance measurement used a xenon lamp (69911, Newport) as the light source, coupled with a monochromator (74125, Newport) to control the wavelength. An iris was used to trim the beam size to ~5 mm 5 mm before entering an integrating sphere (Newport) for transmittance measurement. A photodetector (70356, Newport) was inserted into one of the ports of integrating sphere. The photodiode is connected to lock-in radiometry system (70100 Merlin, Newport) for photocurrent measurement. The samples were placed in front of the integrating

3 sphere; therefore, both specular transmittance and diffuse transmittance were included. For air filters composed of nanofiber film and mesh, a clean mesh with the same geometry was used as a reference. The transmittance spectrum was then weighted by AM1.5 solar spectrum from 400 to 800 nm to obtain the average transmittance. PM generation and efficiency measurement. The PM particles were generated from incense smoke by burning. The smoke PM particles have a wide size distribution from <300 nm to >10 μm, with the majority of particles being <1 μm. The inflow concentration was controlled by diluting the smoke PM by air to a hazardous pollution level equivalent to the PM2.5 index >300. PM particle number concentration was detected with and without filters by a particle counter (CEM) and the removal efficiency was calculated by comparing the number concentration before and after filtration. The pressure drop was measured by a differential pressure gauge (EM201B, UEi test instrument). Unless mentioned, the wind velocity used in the efficiency test was 0.21 m/s and the humidity was 60%. Characterization and tensile tests. The SEM images were taken by FEI XL30 Sirion SEM with an acceleration voltage of 5 kv. The Tensile tests were performed by using Instron 5500 Series. There were two specimens used each nanofiber film sample where the samples were prepared in 1 cm in width and 2 cm in length. The thickness was measured by a micrometer screw gauge. The tensile speed was 5 mm/min.

4 Supplementary Figures and Movies: Figure S1. Snapshot images from Movie S1 showing the superior mechanical properties of the Nylon-6 transparent air filter with transmittance of ~75%. Image from left to right showing poking, twisting and stretching of the Nylon-6 transparent air filter.

5 Figure S2. SEM image of electrospun nanofibers showing the diameter of the fibers is about 100 nm. Scale bar is 200 nm.

6 Figure S3. Pressure drops and quality factors of air filters at different PM2.5 removal efficiencies.

7 Figure S4. Humidity dependence of the PM2.5 removal efficiencies of air filters at different transmittances.

8 Figure S5. Tensile test of a Nylon-6 transparent air filter with transmittance of ~75%. Sample dimension is 2 cm in length, 1 cm in width and 1.5 µm in thickness.

9 Movie S1. Demonstration of the strong, flexible and free-standing Nylon-6 transparent air filter. Movie S2. Roll-to-roll production of transparent air filter.