Silver, Zinc and Iron Nanoparticles Impregnated Cellulose Nanocomposites: Synthesis, Characterization and their Biomedical and Environmental Applications

Abstract

Nanotechnology has revolutionized the world due to its applications in industries to daily life. Biomedical and other health related properties have added a new element in medicines, food, additives and preservatives etc. Likewise, environmental applications e.g. water purification, remediation and degradation are thought for betterment of human kind. This piece of research work emphases on the impregnation of zinc, iron and silver nanoparticles (NPs) on cellulose that has been used for i) biomedical application due to antibacterial properties, free radical quenching property, and other biological applications. Alongside these nanoparticles were also impregnated on cotton that was used for abolition of some aqueous and airborne pollutants like heavy metals, dyes and microbes. Initially, cellulose extracted from citrus peel waste was used as substrate for doping metallic NPs. Synthesis of cellulose based silver and zinc nanocomposites (abridged as AgC and ZnC respectively) were separately doped with their respective silver and zinc NPs by the Co-precipitation method. Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and x-ray diffraction (XRD) were used for the characterization of composite materials. The obtained XRD patterns proved the presence of nanoparticles separately doped onto the cellulosic material by displaying their respective characteristic peaks. SEM micrographs further illustrated the morphology of cellulose surface before and after deposition of these nanoparticles. Silver-cellulose (AgC) and zinc oxide impregnated cellulose (ZnC) showed significant antibacterial activity potential against both S. aureus and E. coli strains as investigated through disc diffusion assay and colony forming method (more than 90% reduction of S. aureus culture within 150 min). The nanocomposites also presented enhanced antioxidant potentials when compared with the respective bare NPs and merely extracted cellulose. These antioxidant potentials were determined by their defending aptitude with biological system against reactive oxygen species with electron donating capacity, prevention of chain initiation reactions and decomposition of peroxides etc. Additionally, both AgC and ZnC exhibited effective time dependant photocatalytic activity against methylene blue under sunlight irradiation. Silver, zinc and iron nanoparticles were later impregnated on cotton and the nanocomposite materials (abbreviated as AgCt, ZnCt and FeCt respectively) were used for wastewater treatment and air filtration. These nanocomposites were characterized by FTIR, XRD and SEM, which showed successful impregnation of the nanoparticles onto the cellulosic matrix within the size range of 10–30 nm size. Further, the metals removal from synthetic wastewater by adsorption onto the fabricated nanocomposites were studied. AgCt and ZnCt significantly adsorbed most of the selected metals better than FeCt during the batch reaction of synthetic wastewater. The Hg2+ exhibited maximum adsorption capacity on both AgCt and ZnCt while Ni2+ showed highest sorption capacity for FeCt adsorbent. The inter-metallic competitive adsorption follows the sequence as Hg2+ > Ni2+ > Cr3+ > Co2+ > Pb2+. However, as compared to the control treatment; the FeCt composite displayed enhanced metal adsorption capacity. The adsorption values of Hg2+ and Cr3+ follow Langmuir Isotherm while Co2+, Pb2+ and Ni2+ are matched with the Freundlich model for AgCt and ZnCt adsorbents. Whereas, for FeCt, the Langmuir isotherm values show more perfection for Hg2+, Cr3+, Pb2+ and Ni2+ when compared with Freundlich isotherm except for Co2+ among all the five metals tested. The sorption processes for AgCt, ZnCt and FeCt altogether are best fitted by pseudo second order kinetics as compared to the pseudo-first-order rate. The adsorption kinetics and competitive behaviour of metals were further justified by Hotelling t2 and t-statistics. Based on removal of heavy metal efficiency and bacterial reduction property, the nanocomposites were also used to treat the water of Rawal lake Islamabad. The nanocomposites demonstrated 100% of adsorption efficiency for Ag+, Co2+, Fe3+, Zn2+ and Cu2+ whereas lesser adsorption aptitude for Cd2+ and Cr3+. The efficiency ranking of adsorbents for metal ions sorption was generally found as AgCt>ZnCt>FeCt while among all the seven metals was observed as Fe3+>Co2+>Zn2+>Cu2+>Ag+>>Cr3+>Cd2+. Majority of the data (except for Cd2+ and Cr3+) for all the three adsorbents was found well fitted to the Langmuir model. However, the values of Cd2+ for all adsorbents and Cr3+ for ZnCt only were fitted well into the Freundlich isotherm model. The sorption process follows pseudo-second-order rate kinetics comparatively to the pseudo-first-order reaction kinetics. The maximum microbial reduction was exhibited by AgCt followed by ZnCt and FeCt, respectively. A number of direct-dyes (that are frequently used in textile industries) were used as the model organic pollutants to analyse their degradability by the photocatalytic action of our prepared nanocomposites. These cotton based nanocomposites degraded the dyes up to a certain limit under direct sunlight irradiation within the time span of 90 min. The AgCt catalyst was found significantly more active based on the rate and maximum number of dyes degradation followed by ZnCt and FeCt catalysts. In air filtration testing with the same nanocomposites, the maximum physical removal efficiency (PRE) determined by an optical particle counter (OPC) was 99.9±0.7% for ZnCt, followed by AgCt and FeCt filters respectively for the aerosolized E. coli particles (>500 nm). All the three filters showed 100% viable removal efficiency (VRE), whereas the control filter exhibited only 80.09±3.13% (VRE). Moreover, even after the four cycles treatment for bacterial deactivation; the VRE remained consistent on approximately 99% relatively to control filter. Overall, the current study presented potential employment of the cellulose based nanocomposites as alternative remedial low-cost material in the field of biomedical and ecological safety due to the enhanced antimicrobial and antioxidant potentials for curbing pathogens and speeding-up the process of wound closure through protection of various kinds of biomolecules from oxidation; functional adsorbents for treating wastewater i.e. contaminated with heavy metals and organics; and effective filters to treat waterborne and airborne contaminants. This hybrid treatment scheme illustrated a synergistic progression for the pollutants elimination efficiency and might be able to be employed as a reasonable alternative purification processes for contaminated air and wastewater retrieval.