Graphene Oxide-Modified Polyacrylonitrile Nanofibrous Membranes

Subscriber access provided by Bibliothèque de l'Université Paris-Sud

Article

Graphene Oxide-Modified Polyacrylonitrile Nanofibrous Membranes for Efficient Air Filtration Chaoran Zhang, Lu Yao, Zhi Yang, Eric Siu-Wai Kong, Xiaofeng Zhu, and Yafei Zhang ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.9b00806 • Publication Date (Web): 10 May 2019 Downloaded from http://pubs.acs.org on May 10, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Nano Materials

Graphene

Oxide-Modified

Polyacrylonitrile

Nanofibrous Membranes for Efficient Air Filtration Chaoran Zhang,a Lu Yao,a Zhi Yang,a Eric Siu-Wai Kong,a Xiaofeng Zhub and Yafei Zhang*a a Key Laboratory for Thin Film and Microfabrication Technology of the Ministry of Education, School of Electronics, Information and Electrical Engineering, Shanghai Jiao Tong University, Dong Chuan Road No.800, Shanghai, 200240, P. R. China b Beijing Municipal Institute of Labor Protection, Beijing,100054, P.R. China

ACS Paragon Plus Environment

ACS Applied Nano Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Particulate matter (PM) pollution has brought about severe threats to public health nowadays. PM2.5, referring to particles with an aerodynamic diameter smaller than 2.5 micrometers, is the most common form of pollutants triggering disease. To cease these detrimental effects of PM2.5 on our physical fitness, air filters with high efficiency, high stability, and low cost are urgently called for. Herein, we introduce a new kind of nanofibers (PAN/GO) composed of polyacrylonitrile (PAN) and graphene oxide (GO) to capture PM pollutants. The nanofibers are synthesized by a simple and versatile electrospinning method. Nanofibrous membranes possess large adsorption capacity, high adsorption efficiency and excellent long-term removal efficiency for PM2.5. When PAN/GO nanofibers are exposed in an environment where the concentration of PM2.5 reaches ~460 μg m-3, the PM2.5 removal efficiency can turn out to be 99.6%. After 100hour adsorption, PAN/GO nanofibers can still maintain a PM2.5 removal efficiency of 99.1%, showing an excellent and stable long-term adsorption ability. As-synthesized PAN/GO nanofibers can act as a prominent contender for practical applications as air filtration masks, showing competitive potential in large-scale production and becoming an up-and-coming alternative for air purification media.

Keywords: air filtration; nanofibers; graphene oxide; polyacrylonitrile; long-term adsorption ability


Page 2 of 27

Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION With high-speed urbanization and industrialization, severe air pollution shows threatening influences on individuals’ health, especially in developing countries.1-5 Particular matter (PM), a kind of airborne pollutants generated from various manufacturing processes, is commonly considered as solid and liquid aerosols accompanying with air or gases such as nitrogen oxides (NOx), carbon monoxide (CO), sulfur dioxide (SO2), ozone (O3).6-8 PM pollutants can be mainly classified into two kinds according to their aerodynamic diameters: PM2.5 and PM10. PM2.5 refers to pollutants whose diameter is less than or equal to 2.5 μm; while PM10 refers to pollutants with diameter less than or equal to 10 μm.9 Compared with PM10, PM2.5 is much more hazardous to individual health, causing disease and increasing mortality rate since our respiratory and cardiovascular systems can be attacked immediately after exposure.10-12 PM2.5 pollutants also possess large surface area and are loaded with pathogenic substances which also improve morbidity of disease and imperil global public health.13-18 To minimize the negative effects of air pollution on our health, not only should rigorous regulations be enforced, but high-efficiency air filters are also expected to be prepared. Researches have been conducted that the PM2.5 pollutants can reach and be mixed with the indoor environment, resulting in the damage of people’s health.19-21 However, currently large-scale air purification devices are generally expensive, energyintensive and low-efficiency. Commercial masks also suffer drawbacks of high costs and low-efficiency, which can be attributed to the deficiency at the filtering membrane



embedded in purification systems and masks. The existing air filters and membranes generally sustain low removal efficiency, low quality factor, safety hazards from electret failure, and ineffective capture for ultrafine particles.8 Therefore, an airfiltration membrane featuring both high-efficiency and cost-effectiveness is urgently needed for large-scale production. Electrospinning is a newly emerging technology which can be exploited to fabricate ultrathin fibers made of polymers and polymer composites. Electrospinning provides a novel and versatile method preparing fibers composed of spider-net-like nanowebs, which can be used in a variety of applications.22-24 The electrospun fibers characteristically have high mechanical strength and large surface area, allowing the fibers to capture high-mass droplets and ultrafine particles. Besides, ascribed to merits of the reticular support structure and winding pore channels, electrospun fibers have the desirable capability to tackle PM and air flow can be synchronously implemented.25 There are many materials used in electrospinning process for air filtration for now, such as polyacrylonitrile (PAN),26-28 poly(lactic acid) (PLA),29-30 polyvinylpyrrolidone (PVP),26 polyvinylidene fluoride (PVDF)31 and so on. Nevertheless, the adsorption capacity as well as the adsorption stability of these electrospun fibers can still be further improved with enhanced performance. In this investigation, we introduced graphene oxide (GO) powders into PAN solution of dimethylformamide (DMF) to electrospin nanofibers, resulting in a conspicuous enhancement in the fiber adsorption capability. The as-prepared nanofibers were light-weighted, air-permeable and long-term stable, showing great potential for


Page 4 of 27

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


practical filtration devices such as masks and window screens as well as other air purification systems. The diameters of nanofibers were mainly distributed at ~250 nm, ensuring higher efficiency in air filtration and higher stability in particulate adsorption. Compared with filtering materials in commercial masks and pure PAN nanofibers, the removal efficiency of PAN/GO nanofibers surpasses them by 99.1% and 15.1% respectively after 100 hours of usage. In summary, electrospinning, a facile and environmentally friendly technique, complemented by PAN/GO nanofibers, present a highly efficient air filtration system.

EXPERIMENTAL SECTION Materials Graphite powder (500 meshes) was purchased from Shandong Jinrilai Co. Ltd (China). Polyacrylonitrile (PAN) (Mw = 90,000) was purchased from Macklin. N, N’dimethylformamide (DMF) was purchased from Shanghai Boer Chemical Reagents Co. Ltd (China). Other chemicals were purchased from Shanghai Chemical Reagents Co. Ltd (China). All the chemicals were used without further purification.

Synthesis of Graphene Oxide The graphene oxide (GO) was synthesized by modified Hummers’ method as reported in former work.32 Typically, 1 g graphite powder was added into a flask followed by addition of 25 mL concentrated sulfuric acid. After vigorous stirring, 1.25 g NaNO3 was added and another 1-hour stirring was followed. Then, 3.7 g KMnO4 was added continuously within 2 hours under an ice bath. After the solution was heated to



35 ℃, the reaction was allowed to proceed for 2 hours. Afterwards, 100 mL ice water and 3.5 mL H2O2 (30%) were added. As-prepared GO was then filtered and washed with hydrochloric acid and deionized water for several times. Finally, GO was dialyzed to obtain a neutral aqueous solution.

Fabrication of PAN/GO Nanofibers Graphene oxide (GO) was added into DMF solvent. Subsequently, the mixed solution was ultrasonicated for 1 h and then a 12-hour magnetic stirring was performed, resulting in a homogeneous GO solution in DMF. PAN powder was then added into the GO/DMF solution. To form a uniform PAN/GO/DMF solution, the mixture was stirred for another 12 hours. The PAN/GO nanofibers were prepared by electrospinning, during which the voltage was controlled at 20 kV. The solution injection rate was kept at 3 mL h-1 and the distance between the capillary port and the collector was 15 cm. For comparison, pure PAN nanofibers were electrospun using the same parameters as those for the PAN/GO nanofibers.

Characterization The morphology of materials has been observed by field effect scanning electron microscopy (FE-SEM, Carl Zeiss Ultra 55) and transmission electron microscopy (TEM, JEM-2100, JEOL). Raman spectra have been measured using an inVia/Reflex Lasser Micro-Raman spectroscope (Renishaw) using an excitation laser beam with a wavelength of 514 nm. The atomic force microscopy was carried out on Multimode Nanoscope IIIa AFM. The mechanical strength of materials has been evaluated by DMA (TA-Q850, TA Instruments-Waters LLC). Contact angles measurements have


Page 6 of 27

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


been performed on a drop shape analyzer (Kruss, DSA100). Fourier transform infrared spectra were obtained using a VERTEX 70 spectrometer (KBr pellets) ranging from 400 to 4000 cm-1. A home-made PM2.5 adsorption system was assembled, including a PM2.5 generating subsystem, a micro-injection pump and PM2.5 detectors (Nova Fitness Co. Ltd), to simulate a PM2.5-filled environment. When the detecting adsorption ability of different nanofibers, the rate of air flow crossing the nanofibers was controlled by adjusting the power of the pump. The air flow rate has been controlled at 0.2 m s-1. The unfiltered and filtered air were detected by PM2.5 detectors respectively. Then the different concentrations of PM2.5 in two cabinets of the adsorption system would be recorded.

RESULTS AND DISCUSSION The process of electrospinning nanofibers is depicted in Figure 1a. During the fabrication procedure, different mass ratios of GO (0, 0.015, 0.03, 0.05 and 2wt%) have

Figure 1 (a) A fabrication scheme of electrospun nanofibers. (b) Constituents of solutions for further electrospinning.



been introduced to enhance the adsorption ability of PAN nanofibers; and they are denoted as PAN, PAN/GO-1, PAN/GO-2, PAN/GO-3 and PAN/GO-4, respectively. The GO powders we synthesized were characterized as shown in Figure S1. A layered structure can be clearly observed in the microscopic images (Figure S1a and b). The atomic force microscopy image is also shown to demonstrate a layered structure of assynthesized GO sheets, as observed in Figure S1c. We can see clearly that the typical GO sheet possesses a thickness of 0.6 nm, indicating that GO sheet owns few-layered structure. As for Raman spectra (Figure S1d), the typical D-band at 1354 cm-1 and Gband at 1584 cm-1 can be observed as well, which is consistent with the characteristic peaks of GO. All the characterizations above demonstrate that GO powders we synthesized comply with standards for use. The chemical structures, three-dimensional molecular models of PAN and GO, are drafted in Figure 1b. Solution 1 with transparent light yellow color contains PAN and DMF while solution 2 contains GO, PAN and DMF showing transparent dark brown. Both solution 1 and solution 2 would be further used for electrospinning. Then the electrospun nanofibers were fabricated on an aluminum foil and collected afterwards. As the fabrication time increased, the thickness and optical transmittance of nanofibers increased and decreased respectively. So, we set the proper electrospinning time to get nanofibers with optimal thickness and an appropriate


Page 8 of 27

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2 The diameter distributions of (a) commercial fibers, (b) PAN nanofibers and (c) PAN/GO-3 nanofibers. SEM images before adsorption of (d) commercial fibers, (e) PAN nanofibers and (f) PAN/GO-3 nanofibers. SEM images after adsorption of (g) commercial fibers, (h) PAN nanofibers and (i) PAN/GO-3 nanofibers. transparency for further adsorption tests. Scanning electron microscopy (SEM) has been used to examine the morphology and microscopic features of the as-prepared nanofibers. In Figure 2, both the diameter distributions and the SEM images of nanofibers with different constituents are exhibited. The diameter distributions were estimated on the basis of SEM, as shown in Figure 2ac. We have observed diameters of ca. 100 nanofibers in order to establish these distributions of nanofibers and create the distribution curves. It can be seen clearly that the diameters of commercial fibers are almost one order of magnitude larger than that of electrospun nanofibers. The diameter distributions of commercial fibers, PAN



nanofibers and PAN/GO nanofibers are all against Gaussian Distribution. According to the fitting results, the most centered diameters of commercial fiber, PAN nanofiber and PAN/GO-3 nanofibers are 4.5 μm, 202 nm and 270 nm, respectively. The diameter of PAN/GO nanofibers is apparently larger than that of pure PAN nanofibers, as can be observed in the SEM images. From the observation of Figure 2d-i, a manifest diversity of adsorption capacity can be concluded. Compared with commercial fibers, the labfabricated nanofibers were more uniform and thinner. There was merely a small amount of PM2.5 adsorbed onto thinner commercial fibers while nothing was caught onto the thicker fibers in commerical filter. As a comparison, PM2.5 was mostly adsorbed at the nodes of PAN nanofibers while a little PM2.5 was adsorbed on the nanofibers in an ellipse-like shape. There was also an evident phenomenon that PM2.5 was adsorbed more evenly on every string of PAN/GO nanofibers under the same duration time of adsorption. Additionally, PM2.5 adsorbed onto PAN/GO nanofibers was larger than that on either PAN nanofibers or commercial fibers in volume. The adsorbed PM2.5 on PAN/GO nanofibers tend to form a bead-like shape rather than ellipse-like shape, and the PM2.5-absorbed nanofibers tend to a moniliform-like structure. The overall adsorption behaviors of the nanofibers are shown in Figure S2, indicating that the results above are not local coincidences. Simply speaking, the crisscrossed nanofibers function as nanomesh to separate fresh air from the pollution of PM2.5, which means that nanofibers adsorb the particles and block them outside the atmosphere we breathe


Page 10 of 27

Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3 (a-c) SEM images of PAN nanofibers and (d-f) SEM images of PAN/GO-3 nanofibers after PM2.5 adsorption. in. In addition, the constituents of PM2.5 particles have been analyzed by EDS mapping (Figure S3), which showed that the elements such as C, O and Cl exist in the adsorbed particles. C, O, and Cl elements may form various kinds of compounds, whose surface functional groups will form interaction with the functional groups on the nanofibers. Since there are extra functional groups on GO sheets, PAN/GO nanofibers can form synergistic interactions with each other in terms of the adsorption effects towards PM2.5. In detail, the patterns of adsorbed PM2.5 on PAN nanofibers and PAN/GO-3 nanofibers were as follows. When the duration time of adsorption controlled the same, different sizes of PM particles adsorbed on nanofibers appeared. As shown in Figure 3, we are able to observe that the particulates were caught onto PAN nanofibers but mostly aggregated at nodes (Figure 3a-c); while the PM2.5 particles on PAN/GO-3 nanofibers were more uniform on every string (Figure 3d-f). After adsorption, the volume of asabsorbed PM2.5 could be estimated within permission, and this would also correspond with the adsorption properties demonstrated later. Indeed, the adsorption process can be elucidated as shown in Figure 4. The drafted



Figure 4 Illustration of fibers before and after adsorption of (a)(d) Commercial fibers, (b)(e) PAN nanofibers and (c)(f) PAN/GO-3 nanofibers. fibers with different colors are in line with fibers composed of different constituents. There are many forms of PM2.5 movements like inertial impaction, gravitational settling, Brownian motion and so on.33-34 When unpurified air flows through filters, the PM2.5 is adhered with moisture and the air gets purified. However, there remains differences among three kinds of nanofibers. When unpurified air flows through commercial fibers, only a few particles can strike and be adsorbed on thin fibers while almost nothing can be attached onto thick fibers. It can be proposed that there are so many void spacings existing among fibers and there are not enough effective contacts between thick fibers and PM2.5 particles, especially chemical interactions. In other words, most fibers in commercial filter just acted as a physical barrier against PM2.5-contained air flow and very few of them could adsorb those tiny particles passively,35 leading to a poor removal efficiency consequently (Figure 4a and d). As for PAN nanofibers, PM2.5 particles were adsorbed unevenly on those strings, but an apparent enhancement in removal efficiency can be obtained compared with commercial fibers. PM2.5 particles are generally


Page 12 of 27

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


aggregated at the nodes of nanofibers while a small number of ellipse-like droplets are on the middle of strings (Figure 4b and e). The reason why PM2.5 particles can gather onto PAN nanofibers may be ascribed to the dipole moment interaction between nitrile groups of PAN nanofibers and polar surface functional groups of PM2.5 particles.26 However, the local aggregation at nodes may be due to interactions among as-adsorbed PM2.5 particles. And the densely local distribution of nanofibers at the nodes should also be one of the reasons why PM2.5 particles tend to gather here. Stronger chemical forces existing at the nodes interact with more PM2.5 particles, and PM2.5 particles will be physically tangled at the node more easily. When more and more PM2.5 particles are blocked at the place where as-adsorbed PM2.5 particles exist, closed area of PM2.5 droplets at nodes can get gradually enlarged as well, leading to further adsorption process of PM2.5 particles. Regarding PAN/GO nanofibers, the PM2.5 is adsorbed evenly on every string of nanofibers (Figure 4c and f). After the addition of GO powders, there are more hydrophilic functional groups in newly electrospun nanofibers, facilitating the uniform combination of PM2.5 particles and nanofibers. In addition to nitrile groups in PAN, many oxygen-containing groups in GO exhibit excellent hydrophilicity, making an impetus to uniform adsorption of PAN/GO nanofibers. The hydrophilicity of oxygen-containing groups aids to adsorb more moisture in air flow so that easier adsorption obtains since PM2.5 is generally solid or liquid aerosols. As a result, PAN/GO nanofibers gain an additional improvement in removal efficiency in comparison of pure PAN nanofibers. This hypothesis would also correspond with experimental data, as



Figure 5 (a)Stress-strain curves of various nanofibers. (b) FTIR of GO, PAN and PAN/GO3. Contact angles of nanofibrous membranes comprised of (c) PAN, (d) PAN/GO-1, (e) PAN/GO-2, (f) PAN/GO-3 and (g) PAN/GO-4. discussed later. The mechanical properties have been measured. In Figure 5a, the stress-strain


Page 14 of 27

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


curves of pure PAN, PANGO-1, PAN/GO-2, PAN/GO-3 and PAN/GO-4 are depicted. The nanofibrous membranes are mechanically tested and measured in the same size, which is 25 mm in length, 8 mm in width and 0.1 mm in thickness. It turns out that only moderate concentrations contribute to mechanical strength positively (the samples with GO concentration of 0.03wt% and 0.05wt%). No linear relationship between GO concentration and mechanical strength can be concluded. To further investigate the functional groups, Fourier transform infrared spectroscopy was detected. In Figure 5b, different spectra of GO, PAN nanofibers and PAN/GO nanofibers are shown. Obviously, at ~3410 cm-1 and 1389 cm-1, a broad absorption band and a sharp absorption band emerged in the FTIR spectrum of GO, referring to the stretching vibration and bending vibration of hydroxyl groups respectively.36 A sharp peak located at 1610 cm-1 can be attributed to the stretching vibration of aromatic C=C bond.37 In addition, a couple of absorption peaks at 1726 cm-1 and 1079 cm-1 have been assigned to the stretching vibrations of C=O and alkoxy C-O groups, respectively.38 In terms of pure PAN, there were typical peaks located at 2933 cm-1, 2244 cm-1, 1625 cm-1 and 1454 cm-1, which were assigned to the stretching vibration of CH2, stretching vibration of C≡N, stretching vibration of C=C and bending vibration of CH2. After adding GO, the spectrum of PAN/GO nanofibers exhibited an evident combination of that of PAN and GO. The peak emerging at 1739cm-1 would be related to stretching vibration of remnant C=O formed from hydrolyzed PAN and unevaporated DMF.39 Copious functional groups on the PAN/GO nanofibers show great advantages towards PM2.5 adsorption, during which mutual interactions among functional groups of both PAN/GO nanofibers and PM2.5



Figure 6 (a) A schematic illustration of apparatus in purification process and photographs of front and back side of the PAN/GO-3 filter. (b) Concentration difference curves of commercial fiber, PAN nanofibers and PAN/GO-3 nanofibers within 1600 s. (c) Comparison of final efficiencies of 1000-second adsorption of various fibers. (d) Short-term removal efficiencies of various nanofibers during initial 1000 s. (e) Longterm removal efficiency of various nanofibers within 100 hours. (f) Comparison of final efficiencies of 100-hour adsorption of various fibers. would exhibit.31 To detect the difference of hydrophilicity before and after the addition of GO powders, contact angles have been examined as shown in Figure 5c-g. The contact angle of pure PAN nanofibrous membrane is 47°; while those of PAN/GO-1, PAN/GO-2, PAN/GO-3 and PAN/GO-4 are 45°, 43°, 39° and 32°, respectively. Not


Page 16 of 27

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


only the contact angle get decreased after introduction of GO, but also the higher concentration of GO in PAN/GO nanofibers makes the hydrophilicity gradually increased, which can be attributed to the hydrophilic groups of GO sheets. The PM2.5 capture test was undertaken in a home-made apparatus mentioned above. The adsorption process is shown in Figure 6a. The air filtration membrane was composed of either commercial fibers or electrospun nanofibers. To guarantee a controlled PM2.5 concentration, incense was burned to generate an atmosphere full of PM2.5. The concentration difference of PM2.5 was measured and controlled at 460 μg m3

at room temperature. As we can see in Figure 6b, with adsorption time going, the

concentration difference of PM2.5 changes and membranes composed of different materials perform distinctly. When the concentration difference of PM2.5 reached peak value, incense was stopped burning and the adsorption totally started. The adsorption rate of PAN/GO-3 nanofibers excelled in comparison to the other two fibers. As a matter of fact, the commercial fibers showed the worst adsorption rate. After 1200 seconds, the apparatus embedded with PAN/GO-3 nanofibers removed the surplus PM2.5 and the concentration difference of PM2.5 was maintained at 3.9 μg m-3. However, the commercial fibers and PAN nanofibers reached the adsorption balance with PM2.5 concentration difference of 58.7 μg m-3 at 1635 s and 23.4 μg m-3 at 1470 s, respectively. Figure 6c shows the histograms of balanced removal efficiencies of various nanofibers, where the performance of PAN/GO-3 nanofibers stands out among them. The removal efficiency of commercial fibers, PAN, PAN/GO-1, PAN/GO-2, PAN/GO-3 and PAN/GO-4 were 88.3%, 95.1%, 98.5%, 99.2%, 99.6% and 99.4%, respectively. To



study the removal efficiency in detail, dynamic removal efficiency curves of different fibers are shown in Figure 6d. The curves illustrated the detail process before reaching an equilibrium. As we can see, the removal efficiency of PAN/GO nanofibers was higher than that of PAN nanofibers and commercial fibers at any same time. The whole adsorption process would be illustrated in detail afterwards. Apparently, commercial fibers had a low adsorption rate while PAN nanofibers and PAN/GO nanofibers exhibited higher adsorption rates in the first 100 s. In the period of 100~500 s, the adsorption rates of three materials were all gradually improved, during which PAN nanofibers and nanofibers still owned higher adsorption rates. After 500 s, PAN nanofibers and PAN/GO nanofibers achieved their adsorption equilibrium. The commercial fibers did not tend to adsorption equilibrium until 900 s. It has been observed that PAN/GO nanofibers firstly reached the adsorption balance with a removal efficiency of 99.6%, followed by PAN nanofibers with 95.1% and commercial fibers with 88.3%. All measurements were under a 460 μg m-3-concentration-difference of PM2.5. Further experiments were carried out to find out the long-term adsorption performances, whose results were depicted in Figure 6e. The concentration difference of PM2.5 was also simulated at 460 μg m-3 using the same methods mentioned above, during which the concentration difference was maintained unless the test was terminated. From the figure, we can observe that PAN-contained nanofibers are endowed with stable adsorption properties while the removal efficiency of commercial fibers decreased drastically from 88.3% to 0 within 20 hours. As for PAN/GO nanofibers, the presence of GO made removal efficiency more and more stable during


Page 18 of 27

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 The quality factor of various nanofibers. Pressure drop (Pa) Efficiency (E%) Quality factor (Pa-1) 462 88.3 0.0046 183 95.1 0.0165 118 98.5 0.0356 124 99.2 0.0389 117 99.6 0.0472 156 99.4 0.0328 QF=-ln(1-E/100)/ Δp QF, quality factor; E, removal efficiency; Δp, pressure drop

Sample name Commercial PAN PAN/GO-1 PAN/GO-2 PAN/GO-3 PAN/GO-4

Table 2 The quality factor of various nanofibers after 100-hour adsorption. Sample name Pressure drop (Pa) Efficiency (E%) Quality factor (Pa-1) Commercial 0 0 PAN 536 84.0 0.0034 PAN/GO-1 497 94.2 0.0057 PAN/GO-2 451 96.7 0.0076 PAN/GO-3 387 99.1 0.0122 PAN/GO-4 473 98.2 0.0085 QF=-ln(1-E/100)/ Δp QF, quality factor; E, removal efficiency; Δp, pressure drop the testing period. As we could observe, the removal efficiency of pure PAN nanofibers decreased by 10% within 100 hours while that of PAN/GO-1, PAN/GO-2, PAN/GO-3, and PAN/GO-4 dropped by 4.3%, 2.5%, 0.5% and 1.2%, respectively. After 100-hour adsorption, the removal efficiencies of PAN, PAN/GO-1, PAN/GO-2, PAN/GO-3 and PAN/GO-4 could be maintained at 84%, 94.2%, 96.7%, 99.1% and 98.2%, respectively (Figure 6f). What we can conclude from the data above is that the addition of GO makes the removal efficiency stabilized. In other words, the GO has enhanced the long-term adsorption ability of the PAN nanofibers. Detail adsorption parameters of various nanofibers are provided in Table 1 and Table 2. Apart from the removal efficiencies, pressure drops of different nanofibers are exhibited above. The pressure drop of commercial fibers is several times bigger than



that of lab-fabricated nanofibers, and with a relatively low removal efficiency. The quality factor of commercial fibers only turns out to be 0.0046 Pa-1. In contrast, the GOcontained nanofibers obviously outperform pure PAN nanofibers by tens of Pa in pressure drop. In accordance to the formula in Table 1, we are aware that PAN/GO-3 nanofibers possess the best quality factor, which is consistent with the adsorption properties. And we may know that the addition of GO powders into the configuration shows great benefits towards the PM2.5 adsorption not only in adsorption capacity but also in long-term stable adsorption ability (as shown in Table 2). The commercial filters are encountering with adsorption failure after 100-hour adsorption. Though the pressure drops and quality factors of nanofibrous membranes are increased and decreased respectively, nanofibers made of PAN/GO-3 still stand out among other nanofibers in many ways. The boosted adsorption ability should give priority to interactions between functional groups of PAN/GO nanofibers and that of PM particles. It is known that there are numerous functional groups grafted on GO sheets like -COOH, -OH and so on, which may induce interactions between PM2.5 particles and the as-prepared nanofibers. The oxygen-containing groups of GO increase the number of active sites for PM2.5 adsorption. In addition, the surface-bound water on nanofibers provides shortcuts for


Page 20 of 27

Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7 A comparison between our work and others’ works. PM2.5 as well. The relationship between mechanical strength and adsorption ability is not clearly demonstrated. However, we surmise that there is an optimum concentration of GO for its modification of adsorption ability, which is nearly 0.05wt%. Above this concentration, the more mechanically stable the nanofibers are, the better adsorption ability will be achieved (comparison from PAN/GO-3 and PAN/GO-4). If the mechanical strength is about the same, the nanofibers with optimum concentration of GO stand out (comparison from PAN, PAN/GO-1, PAN/GO-2 and PAN/GO-4). For practical utility, photographs of non-woven fabrics further used in masks are shown in Figure S4a and b. Besides, the sandwiched structure is also illustrated in Figure S4c. We can easily observe that between the two layers of non-woven fabric, there is a PAN/GO-nanofibers layer to remove PM2.5 particles efficiently. As shown in Figure S4d, a photograph of wearing masks made in this sandwiched structure is demonstrated.



In Figure 7, comparative data points are shown to demonstrate the difference of adsorption ability between our work and others’ works.43-44 à 40-41 The complementary data are also listed in Table S1. We can conclude from the data above that our work reaches an optimal balance among removal efficiency, long-term adsorption stability and outside PM2.5 concentration. Compared with former works, the as-prepared PAN/GO nanofibers exhibit ultralong adsorption stability and 99.1% removal efficiency can be still maintained after 100 hours. The costs will be substantially lowered due to outstanding removal efficiency and excellent long-term stability, which show a pathway for daily air filtration and provide a low-cost choice to better individual health condition. Additionally, the simple and facile synthetic method of nanofibers offers an advantage of straight-forward fabrication and processing, which is of great significance vis-a-vis high-rate mass production.

CONCLUSIONS In this work, novel PAN/GO nanofibers for efficient air filtration have been prepared using the electrospinning method. The as-prepared PAN/GO nanofibers have outperformed pure PAN nanofibers as well as commercial fibers in capturing PM2.5 pollutants. The GO-containing samples have been demonstrated to possess enhanced PM2.5 adsorption rate, increased adsorption capacity and enhanced adsorption stability. As a result, the PAN/GO nanofibers can be applied as window screens to ameliorate the hazards due to outdoor PM2.5, as well as to remove PM2.5 pollutants existing indoor. In addition, the novel nanofibers can also be applied as air filtration masks for individuals


Page 22 of 27

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


to remove PM2.5 pollutants from the environment. In a nutshell, the PAN/GO nanofibers offer wide application in the air filtration industry, providing people with a much cleaner air and more healthy living environment.

ACKNOWLEDGEMENTS We gratefully acknowledge the financial supports from the National Natural Science Foundation of China (no. 61574091 and no. 61874012), Natural Science Foundation of Shanghai (17ZR1414100), and Research Center of DC Science & Technology Co. Ltd. We also acknowledge the analysis supports from the Instrumental Analysis Center of Shanghai Jiao Tong University and the Center for Advanced Electronic Materials and Devices of Shanghai Jiao Tong University.

ASSOCIATED CONTENT Supporting Information SEM image,TEM image, Raman spectra and AFM image of GO sheet; overall SEM image after adsorption;EDS mapping of adsorbed PM2.5 particles; photographs of nonwoven fabrics before and after electrospinning; demonstration of sandwiched structure; photograph of practical masks; complementary data of others’ work.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: (+86) 21-3420 5665 ORCID Chaoran Zhang: 0000-0002-4707-3333



Zhi Yang: 0000-0002-0871-5882 Notes The authors declare no competing financial interest.

REFERENCES (1) Mahowald, N. Aerosol Indirect Effect on Biogeochemical Cycles and Climate. Science 2011, 334, 794-796. (2) Andreae, M. O.; Rosenfeld, D. Aerosol–Cloud–Precipitation Interactions. Part 1. The Nature and Sources of Cloud-Active Aerosols. Earth-Sci. Rev. 2008, 89, 13-41. (3) Nel, A. Air Pollution-Related Illness: Effects of Particles. Science 2005, 308, 804-806. (4) Fang, M.; Chan, C. K.; Yao, X. Managing Air Quality in A Rapidly Developing Nation: China. Atmos. Environ. 2009, 43, 79-86. (5) Gurjar, B. R.; Butler, T. M.; Lawrence, M. G.; Lelieveld, J. Evaluation of Emissions and Air Quality in Megacities. Atmos. Environ. 2008, 42, 1593-1606. (6) Brook, R. D.; Rajagopalan, S.; Pope, C. A.; Brook, J. R.; Bhatnagar, A.; Diez-Roux, A. V.; Holguin, F.; Hong, Y.; Luepker, R. V.; Mittleman, M. A.; Peters, A.; Siscovick, D.; Smith, S. C.; Whitsel, L.; Kaufman, J. D. Particulate Matter Air Pollution and Cardiovascular Disease. Circulation 2010, 121, 2331-2378. (7) Harrison, R. M.; Yin, J. Particulate Matter in The Atmosphere: Which Particle Properties Are Important for Its Effects on Health? Sci. Total Environ. 2000, 249, 85-101. (8) Zuo, F.; Zhang, S.; Liu, H.; Fong, H.; Yin, X.; Yu, J.; Ding, B. Free‐Standing Polyurethane Nanofiber/Nets Air Filters for Effective PM Capture. Small 2017, 13, 1702139. (9) Xing, Y.-F.; Xu, Y.-H.; Shi, M.-H.; Lian, Y.-X. The Impact of PM2.5 on The Human Respiratory System. J. Thorac. Dis. 2016, 8, E69-E74. (10) Janssen, N. A. H.; Fischer, P.; Marra, M.; Ameling, C.; Cassee, F. R. Short-Term Effects of PM2.5, PM10 and PM2.5–10 on Daily Mortality in The Netherlands. Sci. Total Environ. 2013, 463-464, 20-26. (11) Polichetti, G.; Cocco, S.; Spinali, A.; Trimarco, V.; Nunziata, A. Effects of Particulate Matter (PM10, PM2.5 and PM1) on The Cardiovascular System. Toxicology 2009, 261, 1-8. (12) Dominici, F.; Peng, R. D.; Bell, M. L.; Pham, L.; McDermott, A.; Zeger, S. L.; Samet, J. M. Fine Particulate Air Pollution and Hospital Admission for Cardiovascular and Respiratory Diseases. J. Am. Med. Assoc. 2006, 295, 1127-1134. (13) Li, N.; Xia, T.; Nel, A. E. The Role of Oxidative Stress in Ambient Particulate Matter-Induced Lung Diseases and Its Implications in The Toxicity of Engineered Nanoparticles. Free Radical Biol. Med. 2008, 44, 1689-1699. (14) Shi, Y.; Ji, Y.; Sun, H.; Hui, F.; Hu, J.; Wu, Y.; Fang, J.; Lin, H.; Wang, J.; Duan, H.; Lanza, M. Nanoscale Characterization of PM2.5 Airborne Pollutants Reveals High Adhesiveness and Aggregation Capability of Soot Particles. Sci. Rep. 2015, 5, 11232. (15) Zhang, L.; Jin, X.; Johnson, A. C.; Giesy, J. P. Hazard Posed by Metals and As in PM2.5 in Air of Five Megacities in the Beijing-Tianjin-Hebei Region of China During APEC. Environ. Sci. Pollut. Res. 2016, 23, 17603. (16) Li, Q.; Li, X.; Jiang, J.; Duan, L.; Ge, S.; Zhang, Q.; Deng, J.; Wang, S.; Hao, J. Semi-coke Briquettes: Towards Reducing Emissions of Primary PM2.5, Particulate Carbon, and Carbon Monoxide from Household Coal Combustion in China. Sci. Rep. 2016, 6, 19306.


Page 24 of 27

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17) Taner, S.; Pekey, B.; Pekey, H. Fine Particulate Matter in The Indoor Air of Barbeque Restaurants: Elemental Compositions, Sources and Health Risks. Sci. Total Environ. 2013, 454–455, 79-87. (18) Fisk, W. J.; Faulkner, D.; Palonen, J.; Seppanen, O. Performance and Costs of Particle Air Filtration Technologies. Indoor Air 2002, 12, 223-224. (19) Agrawal, S. Effect of Indoor Air Pollution From Biomass and Solid Fuel Combustion on Prevalence of Self-Reported Asthma Among Adult Men And Women in India: Findings From A Nationwide LargeScale Cross-Sectional Survey. J. Asthma 2012, 49, 355-365. (20) Wu, L.-L.; Yang, X. Research Progress on Indoor Air Pollution and Human Health. J. Environ. Health 2008, 25, 551-553. (21) Peck, R. L.; Grinshpun, S. A.; Yermakov, M.; Rao, M. B.; Kim, J.; Reponen, T. Efficiency of Portable HEPA Air Purifiers Against Traffic Related Combustion Particles. Build. Environ. 2016, 98, 21-29. (22) Li, D.; Xia, Y. Electrospinning of Nanofibers: Reinventing the Wheel? Adv. Mater. 2004, 16, 11511170. (23) Wang, X.; Ding, B.; Sun, G.; Wang, M.; Yu, J. Electro-Spinning/Netting: A Strategy for The Fabrication of Three-Dimensional Polymer Nano-Fiber/Nets. Prog. Mater. Sci. 2013, 58, 1173-1243. (24) Liang, J.; Yuan, C.; Li, H.; Fan, K.; Wei, Z.; Sun, H.; Ma, J. Growth of SnO2 Nanoflowers on NDoped Carbon Nanofibers as Anode for Li- and Na-ion Batteries. Nano-Micro Lett. 2018, 10, 21. (25) Zhang, S.; Liu, H.; Zuo, F.; Yin, X.; Yu, J.; Ding, B. A Controlled Design of Ripple-Like Polyamide6 Nanofiber/Nets Membrane for High-Efficiency Air Filter. Small 2017, 13, 1603151. (26) Liu, C.; Hsu, P.-C.; Lee, H.-W.; Ye, M.; Zheng, G.; Liu, N.; Li, W.; Cui, Y. Transparent Air Filter for High-Efficiency PM2.5 Capture. Nat. Commun. 2015, 6, 6205. (27) Yang, Y.; Zhang, S.; Zhao, X.; Yu, J.; Ding, B. Sandwich Structured Polyamide-6/Polyacrylonitrile Nanonets/Bead-on-String Composite Membrane for Effective Air Filtration. Sep. Purif. Technol. 2015, 152, 14-22. (28) Wang, N.; Si, Y.; Wang, N.; Sun, G.; El-Newehy, M.; Al-Deyab, S. S.; Ding, B. Multilevel Structured Polyacrylonitrile/Silica Nanofibrous Membranes for High-Performance Air Filtration. Sep. Purif. Technol. 2014, 126, 44-51. (29) Wang, Z.; Zhao, C.; Pan, Z. Porous Bead-on-String Poly(lactic acid) Fibrous Membranes for Air Filtration. J. Colloid and Interface Sci. 2015, 441, 121-129. (30) Liu, Y.; Park, M.; Ding, B.; Kim, J.; El-Newehy, M.; Al-Deyab, S. S.; Kim, H.-Y. Facile Electrospun Polyacrylonitrile/Poly(acrylic acid) Nanofibrous Membranes for High Efficiency Particulate Air Filtration. Fibers and Polym. 2015, 16, 629-633. (31) Zhao, X.; Li, Y.; Hua, T.; Jiang, P.; Yin, X.; Yu, J.; Ding, B. Cleanable Air Filter Transferring Moisture and Effectively Capturing PM2.5. Small 2017, 13, 1603306. (32) Hu, N.; Wang, Y.; Chai, J.; Gao, R.; Yang, Z.; Kong, E. S.-W.; Zhang, Y. Gas Sensor Based on Pphenylenediamine Reduced Graphene Oxide. Sens. Actuator, B 2012, 163, 107-114. (33) Wang, C.-S.; Otani, Y. Removal of Nanoparticles from Gas Streams by Fibrous Filters: A Review. Ind. Eng. Chem. Res. 2013, 52, 5-17. (34) Li, P.; Wang, C.; Zhang, Y.; Wei, F. Air Filtration in the Free Molecular Flow Regime: A Review of High‐Efficiency Particulate Air Filters Based on Carbon Nanotubes. Small 2014, 10, 4543-4561. (35) Xiao, J.; Liang, J.; Zhang, C.; Tao, Y.; Ling, G.-W.; Yang, Q.-H. Advanced Materials for Capturing Particulate Matter: Progress and Perspectives. Small Methods 2018, 1800012. (36) Wu, N.; She, X.; Yang, D.; Wu, X.; Su, F.; Chen, Y. Synthesis of Network Reduced Graphene Oxide in Polystyrene Matrix by A Two-Step Reduction Method for Superior Conductivity of The Composite. J.



Mater. Chem. 2012, 22, 17254-17261. (37) Rana, U.; Malik, S. Graphene Oxide/Polyaniline Nanostructures: Transformation of 2D Sheet to 1D Nanotube and In Situ Reduction. Chem. Commun. 2012, 48, 10862-10864. (38) Zhang, H.; Hines, D.; Akins, D. L. Synthesis of A Nanocomposite Composed of Reduced Graphene Oxide and Gold Nanoparticles. Dalton Trans. 2014, 43, 2670-2675. (39) Ji, L.; Zhang, X. Ultrafine Polyacrylonitrile/Silica Composite Fibers via Electrospinning. Mater. Lett. 2008, 62, 2161-2164. (40) Li, J.; Zhang, D.; Yang, T.; Yang, S.; Yang, X.; Zhu, H. Nanofibrous Membrane of Graphene Oxidein-Polyacrylonitrile Composite with Low Filtration Resistance for The Effective Capture of PM2.5. J. Membr. Sci. 2018, 551, 85-92. (41) Zhao, X.; Wang, S.; Yin, X.; Yu, J.; Ding, B. Slip-Effect Functional Air Filter for Efficient Purification of PM2.5. Sci. Rep. 2016, 6, 35472.


Page 26 of 27

Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents Graphic and Synopsis


Graphene Oxide-Modified Polyacrylonitrile Nanofibrous Membranes

Recommend Documents