Nanocellulose-based materials for sustainable soil remediation and water purification

Abstract

Soil and water pollution are intricately linked environmental issues that have gained significant global attention due to their adverse effects on ecosystems, public health, and overall sustainability. In this dissertation, the pressing need for sustainable pollutant treatment using ecofriendly and biodegradable nanocellulose (CNC) biopolymers is addressed. This research focuses on the development of CNC-based materials, characterization of their adsorption behaviors, evaluation of CNC-mediated algal toxicity, and exploration of the application of the these materials in sustainable soil remediation and water purification. In the first part, the utilization of CNC nanofluid as an eco-friendly agent for the remediation of phenanthrene (PHE) contaminated soil is proposed. This marks the first exploration of CNC nanofluid’s effectiveness in mobilizing PHE in soil, with a focus on the influence of environmental factors. The findings demonstrate the critical role of temperature and ionic strength in PHE removal. This study also reveals the interactions between CNC and soil components, elucidating the primary PHE removal mechanism. Additionally, our research highlights the detoxification effect of CNC nanofluid on PHE-contaminated soil, providing a promising alternative for site remediation. In the second part, inspired by the hierarchical fibrous structure and antibacterial properties of natural silkworm cocoons, a guanidine-functionalized sericin/nanocellulose aerogel (GSNA) is designed for application in the rapid removal of both bacteria and heavy metals from water. The grafted polyhexamethylene biguanide (PHMB) endows the biomimetic aerogel with exceptional bactericidal activity. The incorporated sericin protein brings abundant surface functional groups for heavy metal complexation. Moreover, this study provides in-depth insights into the bonding mechanism between metal ions and GSNA through density functional theory (DFT)-assisted X- ray absorption near edge structure (XANES) analysis, representing a pioneering effort in elucidating the adsorption mechanism of heavy metals within nanocellulose-based aerogels. In the third part, a recyclable sericin/nanocellulose composite aerogel (SNCA) is introduced for efficient tetrabromobisphenol A (TBBPA) removal from water. The developed SNCA exhibits exceptional compressibility, hydrophilicity, and adsorption capacity. In addition, the SNCA can be easily recycled through a simple compression method, demonstrating remarkable reusability even after 10 regeneration cycles. Furthermore, toxicity evaluations reveal that SNCA effectively mitigates the adverse effects of TBBPA on freshwater algae, emphasizing its environmental friendliness. DFT calculations provide insights into the TBBPA adsorption mechanism, indicating the involvement of hydrogen bonding and electron donor-acceptor interactions. In the fourth part, the investigation reveals that the presence of CNC significantly reduce ZnO NP aggregation, enhancing bioavailability and toxicity to freshwater algae. The interaction of ZnO NPs with CNCs leads to envelopment of algal cells and induces oxidative stress, affecting membrane lipids and antioxidant enzyme activity. The introduction of CNCs enhances intracellular transportation of Zn ions, influencing substance flow between algae cells and the environment. This study advances our understanding of the combined effects of multiple nanomaterials on aquatic organisms, allowing for the identification of composite risks. In summary, this research explores novel and sustainable approaches for pollutant treatment and environmental remediation, utilizing biodegradable nanocellulose materials. These efforts contribute to reducing environmental impact and promoting eco-friendly solutions for soil and water purification.