Silver Functionalized Cellulose /CNT Composites for Phthalates Detection—A Sensitivity Enhancement

Phthalates are widely known plasticizer types used in the production of flexible plastic products. However, these do not form chemical bonds with the matrix material, such that they can easily leach into the environment over time. Exposure to certain phthalates causes adverse health and environmental impacts. Therefore, some countries have already banned the use of some phthalates in consumer products. Despite these adverse effects, many countries are still using phthalates in plastic processing. Therefore, rapid and easy monitoring of the presence of phthalates in different environments is crucial. Recently our research team has introduced a novel phthalate adsorbing cellulose/carbon nanotube (CNT) composite material that can be coupled with Electrochemical Impedance Spectroscopy or Four-Probe conductivity measurement techniques to identify the phthalates in solutions, which shows potential for overcoming the limitations of already existing phthalate detecting methods. Adsorption of dielectric phthalate molecules with bulky side groups onto the highly electrically conductive CNTs present inside the cellulose matrix would increase the electron tunneling distances between the CNTs, resulting in a conductivity decrease. This conductivity decrease of the composite after phthalate adsorption was detected by performing three-electrode Electrochemical Impedance Spectroscopy (EIS) using a potentiostat. However, the developed composite was only sensitive down to 1000 (v/v) ppm concentrated phthalates in methanol solution at room temperature. Therefore, in this study, we introduced a method of enhancing the sensitivity of this developed composite material by following the approach of using heterogeneous integration of mixed dimensional fillers that has high affinity to phthalates. Specifically, the cellulose matrix was functionalized with Ag nanoparticles.. The impregnation of Ag nanoparticles was primarily confirmed by Raman Spectroscopy. Further experiments are in progress to confirm the presence and the distribution of Ag nanoparticles in the cellulose matrix. This impregnation would modify the hydroxyl groups of cellulose molecules by forming O^- ⁺Ag ionic bonds. These Ag⁺O^- groups show the potential to create intermolecular interactions, including hydrogen bonds, ion-dipolar interactions, and van der Waals interactions with the phthalates. Since the incorporation of Ag onto cellulose promotes phthalate absorption along with the CNTs, which adsorb phthalates via the formation of π-π electron donor-acceptor interactions, seems to be the reason behind the enhanced sensitivity limit of the newly developed material compared to CNT/cellulose composite. The Ag nanoparticle functionalized cellulose/CNT composite paper successfully detected DNOP and DPHP with concentrations down to 1 ppm (v/v) in methanol solution at room temperature. Moreover, all these conductivity reductions after phthalate absorption were able to detect using a four-probe conductivity meter, which is much less sensitive than the potentiostat. Here, the current change variation of the composite paper before and after the absorption of phthalates was observed. High sensitivity, easy tunability of sensitivity based on the composition of integrated mixed dimensional materials, and the ability to directly test the phthalates without any other materials unlike with the potentiostat are some of the advantages observed with the use of mixed dimensional fillers (0D Ag nanoparticles and 1D CNTs) incorporated to the matrix (cellulose) of the phthalate sensing paper. This newly developed material shows more potential for developing into a portable, real-time, and in-situ phthalate-detecting sensor.