Graphene oxide/silver nanoparticle (GO/AgNP) impregnated polyacrylonitrile nanofibers for potential application in air filtration

Highlights

• Developed a multi-layered composite nanofibrous membrane filter.

• It acts as a potent air filter for the removal of particulate matter.

• Nanofibrous membrane with synergistic antibacterial effect due to GO and AgNPs.

• This membrane could be used as an additional layer in the commercial masks.

Abstract

There is an immediate necessity for the development of air filtration personal protective equipment (PPE) in order to eliminate the deterioration of air quality. In specific, the airborne pollutants such as aerosols, particulate matter (PM${}_{\mathrm{2.5}}$, PM₁₀) and microbes etc. causes serious health hazards. Herein, PAN templated composite nanofibrous membrane using GO/AgNP as filler materials was fabricated by electrospinning. It was developed for their dual application as a potential point of use (POU) filter for airborne pollutants and microbes. The properties of the developed PAN-GO/AgNP composite nanofibrous membrane was studied by various analytical techniques such as field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and Atomic force microscopy (AFM). The disc diffusion assay exhibited effective bactericidal efficacy having zone of inhibition (ZOI) of $\sim$19 and $\sim$18 mm against the bacterial strains such as S.aureus and GFP E. coli, respectively. Henceforth, the developed composite nanofibrous membrane can be used as potential nanofibrous filter for airborne pollutants and microbes.

Introduction

Particulate matter (PM) is an intricate mixture of both solid and liquid particles present in the air which is composed of both organic (e.g. elemental carbon) and inorganic matter (e.g. SiO₂) such as liquid droplets, smoke, vehicular emission, road dust, microbes etc. [1]. It also constitutes sulfate, ammonia compounds, silicates and organic components. Upon inhalation, these compounds enter the bronchi and impede airway passages causing serious health issues including respiratory disorders such as aggravate asthma and bronchitis, cardiovascular morbidity and mortality, etc [2]. Ultrafine particles are potentially harmful as it contains hydrocarbons which are toxic to human organ systems. Short-term exposure decreases the quality of life and the long term inhalement is highly deleterious as reported in cohort studies conducted to this effect. Particulate matter is divided into two types based on the hydrodynamic size of the particle with PM${}_{\mathrm{2.5}}$ and PM₁₀, respectively. These toxic particles cause serious health hazards especially in developing countries such as China, India etc. Henceforth there is immediate solution through cutting edge technology is required for the remediation of toxic air pollutants.

Currently, conventional filters are extensively used in commercial air filtration applications. These are generally made of porous films such as non-woven fibrous mats with uneven orientation of micron sized fibers and have various disadvantages. First of all, they are either synthesized chemically or by using petroleum based materials such as fiberglass or polypropylene possessing very limited functional properties resulting in insufficient pollutant interactions. Secondly, limited surface area causing deterioration of filtration capacity of filters. Also the percentage reusability is low which has to be disposed resulting in increase in the pollution load to the environment [3].

To overcome these discrepancies in the conventional filters, Electrospun nanofibers based filters is of great interest in recent decades [4]. Four primary mechanisms in the filtration process are sieving, inertial impaction, interception and diffusion. However, sieving is suitable for the pollutants which are larger than the pore size of the filter and hence the other three are the dominant mechanisms for the filtration process. The interception occurs when the particles flow through the air and the critical role of this process is the interaction between the fibers and the small particles. Whereas, the diffusion process is effective for even the particles having aerodynamic size less than 100 nm in which there is predominant Brownian motion and filtered by random collision process. Therefore the developed electrospun nanofibrous based filter follows these mechanisms and can be a better filter compared to the traditional air-filters in current use. The advantages of nanofibers include high interaction between the pollutants and the fiber network due to the adsorption. Further these nanofibers provide more active sites for rejecting the pollutants smaller in size which is essential for the practical considerations [5], [6].

Furthermore, these nanofibers with functional modifications acquire requisite properties from which the interception of PM becomes easier with a much tenuous air filter [7]. The efficiency can be improved by modifying the surface properties of the nanofibrous filters by studying the chemistry of the particulate matter moieties [8]. Other techniques for the synthesis of nanoscale fibers are melt-blown multicomponent process and mechanical fiber spinning [9]. Electrospinning has been used to produce diverse kinds of carbon and metal oxide based nanofibers [10], [11], [12], metal oxides [13], metallic, ceramics and composites etc. [14]. Among these, polymeric nanofibers are extensively used as air filters which is non-bulky and easier to synthesize in the form of membranes for filtration purpose.

Herein, we fabricated and developed polyacrylonitrile (PAN) templated GO/AgNP composite nanofibrous membrane. Also the filtration capability was demonstrated using an assembled filtration set up using incense stick and cigarette smoke. Further we also investigated the synergistic antibacterial properties of the nanofibrous membrane using two different bacterial models such as Gram positive S.aureus and Gram negative GFP E. coli, respectively. The inclusion of graphene oxide (GO) as the filler material further enhances the adsorptive and mechanical stability to the membrane [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27] and the AgNP with its bactericidal properties are reported in the earlier work  [28], [29]. Therefore the developed nanofibrous membrane could be a potential filter for the effective remediation of airborne pollutants.