Activated carbon (AC) has been widely used in indoor air quality (IAQ) control for removal of hazardous volatile organic compounds (VOCs). A detrimental effect of this adsorption technology is that bacteria multiplied on AC may deteriorate IAQ. In this paper, antibacterial AC nanocomposites with well-dispersed silver nanoparticles (Ag/ACs) were prepared by the attachment of Ag+ on the functionalized AC surface via ion–dipole interactions and the subsequent in-situ reduction of Ag+. The surfaces and microporous structures of the obtained Ag/ACs were analyzed by means of scan electron microscope (SEM) and pore size surface area analysis. Antibacterial tests were performed using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as model bacteria. Antibacterial activity against airborne bacteria and toluene adsorption capacity of AC nanocomposites were further evaluated. It was found that the introduction of Ag nanoparticles significantly improves antibacterial effect of AC but slightly reduces toluene adsorption ability. Ag/ACs can efficiently kill bacteria within 100 min without decreasing adsorption ability toward toluene.
Indoor air quality (IAQ) remains a very important issue today due to the fact that most people spend an average of 90% of their time in enclosed buildings. Volatile organic compounds (VOCs) released from building materials and furniture are regarded as major source of indoor air contaminants, which significantly impact indoor air quality and pose a health threat. A long-term exposure to VOCs will be detrimental to human health causing sick building syndrome (SBS) such as headaches, dizziness, nausea, or allergic reaction [1] and [2]. There are a number of technologies available for VOCs abatement, among which, the adsorption-based air cleaning technology has been employed in various applications [3], [4], [5] and [6].
Activated carbon (AC) is the most widespread adsorbent to eliminate VOCs because of its large surface area and outstanding adsorption capacity [7], [8] and [9]. Although AC cannot effectively collect airborne microorganisms, some fraction of airborne bacteria can deposit on the AC. The deposited bacteria are easy to multiply on the AC surface because carbon materials have high biocompatibility [10]. As a result, indoor airborne bacteria accumulate in large quantities on its surface and consequently deteriorating IAQ because AC itself can become a source of bacterial contamination. On the other hand, VOCs produced by bacterial metabolism can be emitted from the contaminated AC. This inevitably brings the secondary indoor air pollution. Therefore, antibacterial AC, which can remove VOCs but also kill bacteria, is required for good IAQ.
Silver is well known as a potential antimicrobial agent because of its broad-spectrum antibacterial activity [11], [12] and [13]. Many silver-containing carbon composites have been developed in antibacterial application using sol–gel method and Ag-coated method [14], [15], [16], [17], [18], [19] and [20]. For Ag-coated method, Ag nanoparticles are loaded on AC by directly mixing Ag nanoparticles solution with AC or depositing gas-phase Ag nanoparticles. Differently, Ag ions are loaded on AC, and subsequently in-situ reduced to Ag nanoparticles for sol–gel method. Although these materials cannot collect airborne microorganisms, they can still exhibit good antibacterial effect for deposited bacteria. Major limitations for preparation of these composites are aggregation of Ag particles and tedious reaction process. The aggregation of Ag particles may reduce antibacterial activity since homogeneous dispersion is a prerequisite for sufficient contact and interaction between Ag and microbial species [11]. Besides, the large-size Ag particles generated from aggregation can block micropores and reduce the adsorption capacity. Currently, challenging issues for silver-containing carbon composites are the uniform and well-adherent coating of Ag particles on carbon surface to achieve highly efficient antibacterial effect and good adsorption capacity.
In this paper, Ag-coated AC nanocomposites (Ag/ACs) with well-dispersed silver nanoparticles were prepared by the attachment of Ag+ on the functionalized AC via ion–dipole interactions and the subsequent in-situ reduction of Ag+. In this approach, oxygen-containing groups on the functionalized AC surface serve as the dispersing and stabilizing effect of Ag+, thus suppressing the coagulation and overgrowth of Ag particles in the next reduction step. Hence, Ag nanoparticles can be well distributed on AC surface. The investigation of antibacterial activity and adsorption capacity for toluene as model VOCs show that the introduction of uniform Ag nanoparticles on AC not only can provide highly efficient antibacterial activity, but also can maintain high adsorption capacity.
We have successfully developed a methodology to prepare Ag-coated activated carbon nanocomposites with homogeneous distribution. Ag particles were stably coated on AC surface via the attachment of Ag+ on the functionalized AC with oxygen-containing groups and the subsequent in-situ reduction of Ag+. Ag-coated AC nanocomposites (Ag/ACs) with well distributed Ag nanoparticles and various contents can be obtained by tuning AgNO3 concentration. Antibacterial test showed that Ag/ACs can efficiently kill bacteria in air and in aqueous environment because of homogeneous distribution of Ag particles on AC surface. More importantly, the presence of moderate Ag nanoparticles does not change significantly toluene adsorption ability and morphology of AC. Ag/AC-2 with optimized Ag content (0.98%) can efficiently kill airborne bacteria but also maintain almost same toluene adsorption ability to AC. Ag-coated activated carbon nanocomposites exhibit a promising future in IAQ control for elimination of airborne bacteria and VOCs.
