There has been a growing urgency for the replacement of synthetic materials given their significant ecological footprint (Rinaudo 2007; Rostami et al. 2019). Cellulose, an organically derived biopolymer, has been increasingly investigated over the past few decades as a desirable alternative due to its biodegradability, biocompatibility, and renewability. In addition, it also possesses great mechanical properties, a low mass density, and inexpensive production costs (van de Ven et al. 2016). Furthermore, cellulose is very resistant to acids, extreme temperatures, and proteolytic enzymes (Pandey et al. 2012; Peng et al. 2011). Among many cellulose papers available, Korean traditional cellulose paper, Hanji, is an especially intriguing alternative to synthetic polymer, as one of the most stable and durable papers with a life span exceeding 1000 years (Choi et al. 2012). It is made of bast fibers of paper mulberry trees and comprises long cellulose fibers and pores, showing a 7000 ~ 9000 range of high degree of polymerization (Jeong et al. 2014). In the current industry, it is mainly used as wrappers or packaging material. It has low inherent antibacterial activity, but its antimicrobial performance can be improved by surface treatment (Jung et al. 2016). As such, Korean paper has already been used for antibacterial activity in combination with different types of metallic NPs (zinc, titanium, gold, silver, etc.) (Du et al. 2013; Kamal et al. 2022; Yang et al. 2023; Anwar et al. 2023; Maslana et al. 2021; Onyszko et al. 2020). However, synthesizing metallic NPs is challenging, costly, and environmentally harmful (Exbrayat et al. 2015; Jamkhande et al. 2019). Nowadays, carbon-based nanomaterials are attracting attention in combating microbial contamination. Especially, carbon nanotubes (CNTs) show antibacterial activity (Deokar et al. 2013) due to their ability to rupture the bacterial cell walls. Therefore, a composite of CNTs and cellulose paper would result in a highly efficient product that has the ability to deal with antimicrobial resistance.
Recently, the increasing concern over air pollution has led to a growing demand for filters. The development of filters has become crucial, not only for their primary function of filtering out particulate matter, fine dust, and volatile organic compounds from the atmosphere but also for their antimicrobial ability against bioaerosols such as bacteria. Poor air quality has been linked to around four million premature deaths annually (Asefa et al. 2022). Globally, air pollution contributes to 1 out of 10 deaths and caused approximately 5.5 million deaths in 2013 (Gonzalez-Martin et al. 2021). Additionally, poor air quality can reduce employee productivity by 10–15% in workplaces (Cincinelli et al. 2016). On the other hand, over the past 60 years, we have been losing the battle against bacteria as they are continuously developing resistance to antibiotics. Consequently, these disease-causing agents are now becoming antibiotic-resistant. The European Center for Disease Prevention and Control (ECDC) and the European Medicines Agency (EMEA) estimated annual losses of over €1.5 billion due to antimicrobial resistance (Serwecińska 2020). In 2013, the USA reported over 23,000 deaths caused by resistant infections (Dhingra et al. 2020). The European Commission also reported approximately 33,000 deaths per year due to antimicrobial resistance (AMR). A World Health Organization (WHO) report confirmed a global shortage of effective antibiotics due to AMR problems (Aljeldah 2022). Therefore, it is essential to find efficient and cost-effective substitutes for conventional antibiotics.
In this study, we synthesized multi-walled carbon nanotubes (MWCNTs) coated Hanji paper using a simple dipping method and investigated their antibacterial activity against E. coli. We coated MWCNTs onto Hanji paper solely through the dipping method without acid modification of the MWCNTs, and it is more cost-effective and easily synthesized than SWCNTs. Furthermore, the MWCNT-coated Hanji paper showed improved mechanical strength, enhanced electrical conductivity, increased hydrophobicity, and exceptionally stable adhesion to the Hanji surface. We suggest that MWCNT-coated Hanji paper could be used as a mask, air pollution filter, and wallpaper in hospitals and residential complexes, reducing the risk of infections.