Two dimensional nanochannels for efficient ion transport inspired by hearing organ

Nanostructured Ion Selective Membranes (ISMs) have emerged as attractive materials among researchers for their comprehensive sensing and ion separation applications in water purification, energy harvest, and biomedical treatments, with the basis of all standing on mineral recovery. This technology has constantly been developing mostly over the last 50 years, where the recently developed ISMs have proven to have a high potential to recover precious minerals such as Lithium (Li+). 

Inspired by the human auditory system, the ISMs can also be introduced as the potential candidate to mimic the inner ear in which the ion extraction process is followed by stimulation of a biological complex called the Organ of Corti (OoC). This essential organ lies on top of the basilar membrane (BM) and embraces the mechanosensory hair cells, which bring frequency and ion transport selectivity, respectively. 

Based on this concept, this thesis aims to achieve two overarching goals, including developing bio-inspired ISMs for lithium recovery for mainly energy harvesting applications and an advanced artificial hearing organ using the conceptualisation proved for membranebased ion recovery. 

The research framework of this thesis and its objectives are discussed in the introductory chapter focusing on the growing concern about hearing loss among Australians and the new multidisciplinary technologies that are beneficial in developing efficient treatment methods. The second chapter carefully reviews the literature to investigate the recent advances in developing ISMs and their potential to be used as the artificial inner ear. 

In the third chapter published in Advanced Materials Technologies (IF = 8.856), the basis of ion separation has been fundamentally investigated using a 2D nanostructured membrane. This study uses a tannic acid-functionalised graphene oxide membrane to separate singlecharged cations from divalent ions selectively. 

Chapter four, published in the journal of Desalination (IF = 11.211), focuses on developing a new 2D asymmetrical architecture for highly efficient metal-ion sieving of monovalent ions. The proposed design leads to a new ion transport mechanism named “Energy Surge Baffle” (ESB) that substantially recovers Li+. 

To develop the artificial inner ear and OoC, the first step is to evaluate using 2D materials in hair cell fabrication and investigate their response after exposure to sound stimuli. In chapter five, published in ACS Applied Materials & Interfaces (IF = 10.383), a design of a susceptible artificial hair cell sensor is presented, consisting of polyvinyl alcohol (PVA) hydrogel coated with 2D vertical graphene nanosheets (VGNs). 

Since 2D materials are the perfect candidates for developing sound-activated hair cell sensors, chapter six focuses on using them for developing a membrane-based sensor capable of mimicking the OoC to provide a bigger picture for developing the inner ear. The membrane design presented in this chapter benefits from a highly stable and flexible GObased membrane with tuneable ionic conductivity. The delivered manuscript continues our previous publication and is ready to submit to the same journal as chapter five. Finally, in chapter seven, I have added a conclusion and a summary of the results, along with a look at future perspectives. 

In conclusion, the novel approach introduced in this PhD thesis can pave the way for designing and developing the next generation of ion-selective membranes (ISM) using advanced 2D nanomaterials applicable in various applications from energy harvesting to biomedical engineering.