key: cord-0798006-h6wd8kf9 authors: Goswami, Manoj; Yadav, Ashvini Kumar; Chauhan, Viplov; Singh, Netrapal; Kumar, Satendra; Das, Abhradeep; Yadav, Vishal; Mandal, Ajay; Tiwari, Jitendar Kumar; Siddiqui, Hafsa; Ashiq, Mohammad; Sathish, N.; Kumar, Surender; Biswas, Debasis; Srivastava, A. K. title: Facile Development of Graphene-Based Air Filters Mounted on 3D Printed Mask for COVID-19 date: 2021-05-20 journal: nan DOI: 10.1016/j.jsamd.2021.05.003 sha: 132cbb8b33200f54bfc0c9cc75ff4d0fbd2a1c2b doc_id: 798006 cord_uid: h6wd8kf9 COVID-19 belongs to a typical class of viruses that predominantly affects the human respiratory system, thereby proving to be fatal to many. The virus, along with other air pollutant particulates poses a severe threat to the human respiratory organs. Since the most common transmission mode is respiratory fomites and aerosol particulates, it is necessary to prevent their ingression through a mask. The primary use of masks is to prevent aerial particulates. This paper reveals the development of masks with air filters coated with functionalized graphene (fG) mounted on a 3D-printed facial mask replica. The fused deposition modeling (FDM) process is used for fabricating the facial mask replica. fG associated with nanosheets has an additional adsorbing capacity with a high surface area to volume ratio. fG coat is used over a polypropylene (PP) cloth through a dip coating method to enhance the antiviral and antimicrobial properties. The quality of fG is investigated through Raman spectroscopy and other characterization techniques such as SEM, XRD, and FTIR were used for visual interpretation of distributions of fG on a polypropylene (PP) fabric. Fabricated fG coated MB filters show 98.2 % of bacterial filtration efficiency with 1.10 mbar of breathing resistance. The efficacy of the fG coated filter is tested against SARS-CoV-2 viral particles, which shows a complete arrest of viral transmission at the fG coated layer. Coronavirus is typically an airborne virus that has manifested itself as a severe acute respiratory syndrome (SARS) causing fatal respiratory infections and has been declared as a global health emergency by World Health Organization (WHO). The SARS CoV-2 is suspected of having its epicenter in the Hunan seafood market in the Wuhan region of China and spread globally. Infected person ejects the virions as respiratory fomites (cough & sneezes), and since viruses can sustain themselves over any surface for a significant period, people could be infected either by physical contact with an infected one or surface. The process of virus-host cell interaction proceeds in four steps, viz. (i) attachment of virus spike protein with host cell receptors; (ii) endocytosis; (iii) replication; (iv) exocytosis [1] . The J o u r n a l P r e -p r o o f coronavirus pathogenesis can be described briefly as the ingression of the virus, the propagation of viral genetic material into a host cell, the cellular immune response of host cell, and the external transmission of virions as aerosol dispersed particulates. To avert the spreading of the coronavirus and other airborne particulates culpable for respiratory diseases, N95 masks are used extensively by medical practitioners and commoners as personal protective equipment (PPE). The estimated size of the SARS causing coronavirus is about 0.08-0.14 µm in diameter [2] . The N95 mask has the lowest protection factor value for these micro-organisms [3] , albeit that N95 masks usually exhibit up to 95 % bacterial filtration efficiency (BFE). However, it depends on various factors such as the relative humidity (RH), the surrounding temperature, active material for air filters, facial fitting, methods of decontamination, and reusability frequency. N95 masks consist of multi-layered fabrics that ensure an effective shielding from the pollutant particles using an electrostatic force field induced in the fiber. Since COVID-19 virions are positively charged species, hence electrets material fibers are irreplaceable. Variable-sized aerosol dispersed particles adhere to the fabrics by electrostatic action as well as Van der Waals interaction. Particles with a diameter >1 µm are considerably large particulates, ∽0.3 µm are medium-sized, and <0.1 µm are classified as small-sized particulates. The corona virions are characterized as small-sized particulates exhibiting Brownian motion, as shown by the yellow path in Schematic 1, as its ingression trajectory. Extensive research is going on regarding the enhancement of efficacy in the field of PPEs, most specifically on protective facial equipment. N95 masks are accepted widely for electretfibers necessary to avoid viral ingression. Cellulosic fiber filters with the addition of poly J o u r n a l P r e -p r o o f (ethylenimine) (PEI) gives them an antiviral property [4] , polypropylene microfibres with diameters in the range of ∽1−10 µm [5] , and nanoparticles of silver and copper are also introduced for an enhancement in anti-microbial properties. Activated carbon-based masks are also a potent material for air filters. Similarly, functionalized graphene (fG) has been a competitive material for air filters and can be used to modify N95 masks. fG & its derivatives have gained popularity for their antimicrobial and antiviral properties, high surface-to-volume ratios, unique physicochemical properties and biocompatibility [6] [7] [8] [9] [10] . It is a two-dimensional (2D) monolayer sheet of sp 2hybridized carbon atoms arranged in a hexagonal honeycomb-like lattice structure with a thickness of 1.84 nm [11] . The negative charge and unique nanosheet structure of fG play a crucial role in the antiviral activity for virus destruction and inactivation [12] . Negatively charged fG interacts with the positive-sensed viruses via hydrogen bonding, electrostatic interactions, and redox reaction [13, 14] . The surface-bound virus gets adsorbed on the fG and can then be washed off. Structural integrity loss (exterminated envelope and crown) is an outcome of physicochemical interaction of virus and functionally tailored graphene nanosheets leading to inhibition in viral functions. Long exposure time and concentration contribute to enhanced antiviral action of graphene [15] . Furthermore, the efficacy of a mask depends on the perfectness of placement of the facepiece in the proper position (facial fit) so that the chances of ingressing virions and releasing fomites are significantly minimized. Facial masks can be fabricated as a customized items using 3D printing technology. 3D printing of polymeric materials, such as PLA, is an efficient approach to fabricating customizable mass products for a better facial fit and enhancing protection. Herein, we report a facile development of a graphene-based air filter mounted on a 3D printed mask for COVID-19. fG is obtained using Hummer's method by oxidizing purchased graphene platelets, as shown in Schematic 2. Firstly, sodium nitrate (1.5 gm) was added to a concentrated sulphuric acid (70 ml). To this solution, graphene platelets (3 gm) were added with vigorous stirring, and a black color colloidal mixture was obtained. After this, using an ice bath, the mixture was cooled to 5 °C. Once the mixture is cooled, potassium permanganate (9 gm) was introduced in J o u r n a l P r e -p r o o f the mixture with proper care and patience. After this, 140 ml of deionized (DI) water was slowly added, which further results in an exothermic reaction raising the temperature to 98 °C and maintained at this temperature for 15 minutes. Subsequently, the external heating was removed, and the colloid is allowed to cool down to room temperature. Additional DI water (420 ml) was introduced into the mixture, followed by hydrogen peroxide (3 ml) to stop the reaction. This reaction was left untouched for one day so that the fG settles down, which was then washed using ethanol and DI water several times. The washing process is further discussed in the supporting information (SI). A customized design of the fG mask has been generated using a 3D-CAD model platform (Rhinoceros software). The design was then converted into a meshed model (.stl format). This file was then transferred to Cura (open-source software provided by Ultimaker) for slicing. The slicing was configured for the Ultimaker 2 + 3D printer. Polylactic acid (PLA) in the form of filament was used as the base material for the mask prototype with a printing speed of 60 mm s -1 . No support structure was required while a brim was provided for build plate adhesion. The sliced design was converted into g-code format and transferred to the printer. The build platform was preheated to 70 °C, while the nozzle (diameter 0.4 mm) was heated to 200 °C. All the printed parts were then assembled to make the mask prototype. Schematic 3 is a graphical representation of the steps involved in this process. printer setup, and d) 3D printed mask prototype. The dip-coating method was used to coat fG over the polypropylene (PP) fabric cloth. A mixture of 9:1 ratio of fG and polyvinyl alcohol (PVA) was mixed in N-methyl-2-pyrrolidone (NMP). The mixture was stirred for a few hours to prepare a homogenous dispersion. After this, the fabric cloth was dipped into the solution for 30 seconds. The dipped cloth was taken out and dried at 50 -60 °C for 24 hours. This process was repeated two times. The developed air filter is a stack of four layers, as depicted in figure 1. Outer layers are fixed with 20 µm pore-sized PP fabric for each configuration (schematic S1). The middle one is changed with 20 and10 µm pore-sized PP fabric, and 3 µm melt-blown (MB) and are referred to as fG coated 20 µm filter, fG coated 10 µm filter, and fG coated melt-blown filter for further designation, respectively. The use of multilayer stacking helps in stopping the penetration of droplets. In this configuration, the first layer is used to absorb micro-aerosol droplets, and the middle layer is used to prevent micro-organism and small particulates. On the other side, the third layer is specially used to absorb fluids (during sneezing) from the mask wearer. J o u r n a l P r e -p r o o f Figure 2b . This mask can now be used to stop the spreading of droplets coming out from the mouth during sneezing or coughing. A 3D printed mask can be easily customized using simple software and thus gives a perfect fit. When a typical surgical mask or N95 masks are used multiple times, they might suffer from the masks' wear and tear, but no such problems occur with a 3D printed mask. Another advantage of the printed mask over the surgical masks is that it can be sanitized easily using spray sanitizers while the fabric masks require extensive washing before reusing. On the other hand, the printed mask requires a comparatively far less amount of fG coated cloth and it provides a perfect fit to cover the leak from the nasal bridge and can be configured according to an individual. Masks have been the most problematic for people using spectacles. As the usual face masks are not air-tight near the nasal bridge region, the face fogs of the spectacles' glasses, but no such problem is observed when a 3D printed mask is used. The washability and reusability of the printed mask are also a significant advantage over the other masks as only the filter needs to be changed instead of the complete mask, which reduces the waste and disposing of the used mask may contain a virus. J o u r n a l P r e -p r o o f In order to investigate the presence of planes and functional groups of fG, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) was used. The XRD pattern was recorded in the 2-thetha range of 20° to 60° with 0.02° per second step size. In Figure 3a , the broad diffraction peak (002) can be seen at 26.10° with an interlayer distance of 3.39 Å. Hence, it is confirmed that the synthesized material is composed of well-ordered graphene platelets. The FT-IR data, Figure 3b , was recorded between 500 -4000 cm -1 wavenumbers. Raman spectroscopy can provide qualitative and quantitative information on carbon-based materials to investigate various physical properties (defects, crystallite size, vacancies, and several layers, etc.) [18] . Figure 4a , represents the de-convoluted Raman spectra of fG prepared by Hummer's method. It was recorded using a 532 nm green DPSS laser source at room temperature. Correspondingly, Figure 4b displays the higher wavenumber Raman spectra with the same source. An intense band at 1602 cm -1 shows the spectrum of a single graphite crystal. It is assigned to the E 2g degenerative vibrational mode, called as the G band. The shifting of G band to the higher wavenumber is due to the occurrence of two additional bands: D' band (1621 cm -1 ) and D** band (1577 cm -1 ). They are observed due to the highly defective structure of synthesized graphene. Another small band is observed at 1346 cm -1 , termed as D band which corresponds to the A 1g mode. It is the result of either small crystallites or defects from boundaries in polycrystalline samples. The D band is attributed to two small bands due to the rich sp 3 phase of the disordered nature of amorphous carbon. It has been observed that side peaks in both bands increase by the disorder, leading to the broadening of bands. As the broadness of the D band (31 cm -1 ) is inversely related to the crystallite size (L a ), it represents the amorphousness in the prepared sample. In disordered carbon-based materials, the integrated intensity ratio of D and G peaks (1.15) has a noticeable relation for obtaining the sp 2 crystallite size (in-plane). The high intensity of the D band indicates that the sp 2 bonds are broken, which turn into sp 3 bonds in the sample. Apart from that, this intensity ratio also depends upon the excitation laser energy wavelength (λ). From Equation (1), the crystallite size of the sample was obtained: 16.71 nm. The second spectra consist of four less intense characteristic peaks, namely G*, 2D, D+G, and 2D'. FDA-recognized ASTM F2100-11 is the primarily known standard for the performance of materials used in the filters. ASTM F2100-11 standard was also defined for the testing of N95, As observed from the previous studies, the trapping of aerosol particles through any fiber mask can be attributed to different mechanisms, such as gravity sedimentation, inertial impaction, diffusion, and electrostatic attraction [16] . All of the mechanisms mentioned above (Schematic 4) are depending on the size of particles. It has been stated that gravity sedimentation plays an essential role for aerosols with sizes 1-10 µm as gravity forces provide an initial impact on the wide exhaled droplets. While in the case of inertial impaction, particles with enough inertia (to avoid flowing across the fibres in the filtration layers) are stuck into the mask layer and filtered. The diffusion mechanism occurs when the particles of sizes less than 0.1 µm size are diffused and trapped in the fiber layers because of the Brownian motion carried by the porous matrix of the fiber mask. However, the electrostatic attraction mechanism differs from described mechanisms. In this mechanism, the electrocharge polymer filter or cloth is applied as a filter that attracts oppositely charged particles and traps them. The mechanism as mentioned above may be responsible for the high BFE of our fabricated bare MB filter. The filtration mechanism of bare MB cloth is shown in schematic 4. In the bare MB filter case, the first layer with 20 µm ±2 µm of pore size absorbs or prevents the penetration of large aerosol generated particulates while it allows micro-organism and smallsized particulates towards the second layer. The second layer made of MB with 3 µm ±1 of pore size can filter small sizes of particulates and micro-organisms except for the nanosized bacteria or viruses. To overcome this issue, the middle layer (second layer) was coated with fG for the inactivation of micro-organism during the inhale/exhale process. The antimicrobial surfaces can be designed with graphene-based nanomaterials. The exact mechanism of bacterial inactivation is still a major topic to investigate. However, several efforts have been taken to identify the role of graphene in the inactivity of bacterial species. Schematic 5, shows the sharp-edge insertion, cell entrapment, and oxidative stress mechanism of graphene with bacteria. Graphene has very sharp edges that can cause physical damages to the cell membrane upon direct contact with bacterial cells. Hu. et al., [18] confirmed the sharp-edge insertion of graphene into the E.coli bacteria via transmission electron microscopy. In oxidative stress, the graphene sheets interfere with bacterial metabolism due to the imbalance between oxidation and anti-oxidation. Besides, cell entrapment is also a possible mechanism for the inactivity of bacterial species. In this mechanism, the bacterial cells are captured by graphene sheets which isolate bacterial cells from the outer environment and sufficient nutrition. To simulate the real-life scenario wherein the mask wearer is likely to be exposed to dropletborne aerosols emanating from an infected person in talking, coughing or sneezing, we used an atomizing nozzle spray (EXAIR, SR102055) to generate aerosols of 16-25 µm of diameter. The spray of aerosols was allowed to be incident first on a Petri plate of 90 mm diameter for a period of 5 minutes. The petri plate was then flooded immediately with 1 ml of VTM, and the same was used for RNA extraction and RT-PCR to capture the viral load in the initial incident To demonstrate the efficacy of the masks in arresting the passage of SARS-CoV-2 viral particles, we compared viral RNA titers in different layers of the mask when an incident spray charged with varying viral loads was projected on them. Table 4 COVID-19 infection: Origin, transmission, and characteristics of human coronaviruses A narrative literature review on traditional medicine options for treatment of corona virus disease 2019 (COVID-19) Respiratory performance offered by N95 respirators and surgical masks: Human subject evaluation with NaCl aerosol representing bacterial and viral particle size range A new material for airborne virus filtration Can N95 Respirators Be Reused after Disinfection? How Many Times? Determination of lisinopril using β-cyclodextrin/graphene oxide-SO3H modified glassy carbon electrode Polystyrene-graphene oxide modified glassy carbon electrode as a new class of polymeric nanosensors for electrochemical determination of histamine In situ observation of graphene sublimation and multi-layer edge reconstructions Surface activation of graphene oxide nanosheets by ultraviolet irradiation for highly efficient anti-bacterials Graphene oxide-silver nanocomposite as a highly effective antibacterial agent with species-specific mechanisms Honeycomb carbon : A Review of Graphene Nanomeshstructured ultrathin membranes harnessing the unidirectional alignment of viruses on a graphene-oxide film Herpes simplex virus type-1 attachment inhibition by functionalized graphene oxide Processable aqueous dispersions of graphene nanosheets A Raman spectroscopic investigation of graphite oxide derived graphene An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks Graphene-based antibacterial paper The author acknowledges the SYST scheme of DST, New Delhi (File no SP/YO/2019/1554) for their financial support. Author(s) declare no Conflict of Interest involved in this manuscript titled "Facile Development of Graphene-Based Air Filters Mounted on a 3D Printed Mask for COVID-19". This manuscript is checked and approved by the all authors.