Rational synthesis of nanostructured silver composites for multifunctional applications
Student thesis: Doctoral Thesis
Related Research Unit(s)
Developing robust antibacterial materials that prevent the attachment of bacteria to solid surface is of importance for a wide range of applications such as in biomedical engineering, environment, and water treatment. Although artificial surface that can kill bacteria by the physical effect alone has been recently proposed to be a promising alternative to combat biofilm formation, the majority of the approaches still involve the use of chemical antibiotics or inorganic coating. In particular, due to their broad-spectrum antibacterial performances and relatively lower toxicity to human cells, silver based nanomaterials (inorganic) have been extensively developed. The objective of this thesis is to develop silver based nanocomposites with various morphology and composition for enhanced antibacterial activity. In the first part of this dissertation, a facile approach is developed to synthesize a novel nanoparticle with a three dimensional (3D) architecture. The nanoparticle has a Fe3O4/polydopamine (PD) core and this core is covered by silver pedals. Moreover, by simple surface modification with 1H,1H,2H,2H-perfluorodecanethiol, this nanoparticle exhibits a superhydrophobic and oleophilic property. Interestingly, we find that the hydrophobic coating can be easily dissolved in the wet solution and therefore the silver ions can be released, leading to pronounced antibacterial and antifouling activity against both Escherichia coli (E. coil) and Thalassiosira pseudonana (T. P.). Moreover, by harnessing the different affinity towards oil and water as well as the magnetic property, the as-prepared nanoparticles can be used for oil/water separation with high selectively and purity. To allow for sustainably release of silver ions even in presence of ligands (for example, Cl-, PO43-, S2-, and SO42-) which can easily react with released silver ions and induce unwanted precipitation, a bimetallic composite with hierarchical architecture are designed in the second part of the thesis. This bimetallic composite is composed of microstructured copper foam and nanoscale silver dendrites by using a facile galvanic replacement reaction. After a simple thermal oxidation process, this composite displays an excellent superhydrophobicity which inhibits the adhesion of bacteria in the dry environment. Interestingly, this composite can also kill the bacteria by continuously releasing the silver and copper ions upon the collapse of its superhydrophobicity. Previous studies have shown that the antibacterial effect rendered by the silver ion is associated with the generation of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). Moreover, the level of H2O2 concentration is an important indicator of chemistry, food industry, pharmaceutical, and environmental protection. Thus, the ability to detect the H2O2 concentration in a sensitive manner is important for many applications. In the third part of the thesis, a facile, one-step strategy is developed to prepare nanostructured silver nanowires (Ag NWs)-reduced graphene oxide (rGO) hybrids for enhanced electrochemical detection of H2O2. The simple one-step process allows for simultaneous formation of interconnected Ag NWs and rGO networks, avoiding the interface problems encountered in the multiple-step process. The electrochemical experiments reveal the Ag NWs-rGO based biosensor exhibits fast amperometric sensing, low detection limitation, wide linear responding range, and perfect selectivity for non-enzyme H2O2 detection. Finally, to further improve the sensitivity of the hydrogen peroxide sensor, bimetallic Pt/Ag nanoraspberries modified rGO nanosheets are synthesized by a two-step wet-chemical reduction method. The encapsulation of bimetallic nanoraspberries between rGO not only significantly increases the electro-conductibility of the rGO layers, but also inhibits the aggregation and restacking of rGO layers. Meanwhile, the hydrophilicity and large surface area of the rGO avoids the common interface problem caused by incomplete wetting of modified electrodes in the solution. Owing to these synergistic effects, the nanostructured Pt/Ag/rGO hybrids exhibit enhanced electrochemical catalytic performance toward hydrogen peroxide compared with Ag/rGO hybrids.
- Silver compounds, Nanocomposites (Materials)