Bio-inspired metal-organic hybrid structures for photochemical applications

Abstract

Metal recovery from industrial wastewater has recently received much attention, particularly regarding the recycling of precious metals and the prevention of hazardous heavy metals emission. For example, precious metal recovery from electronic waste (E-waste) has been termed ‘urban mining’, and aims to recover precious metals that have accumulated in industrial wastes. In this dissertation, I introduced the photochemical approach for metal ion recovery from E-waste using inorganic-organic hybrid materials through various biomimetic surface modification including polyphenol mediated surface modification and mussel-inspired polydopamine. First, the mussel-inspired catechol oxidative chemistry for the synthesis of colloidal metal nanoparticles is further investigated using a catechol-grafted polymer. The catechol-grafted polymer acts as a polymer template, which leads to the formation of dendritic gold nanostructures the spontaneous reduction of metal ions complexed with the catechol-grafted polymer. Second, colloidal porous hybrid microspheres were synthesized via polydopamine (PDA) coating to enhance the adsorption of gold ions when irradiated with light. The polymer microspheres coated with polydopamine were irradiated with light to greatly increase the adsorption of gold ions. The Langmuir adsorption theory was used to investigate the adsorption of gold ions, and it was shown that only gold ions were adsorbed selectively even when various metals were included. Finally, tannins and titanium dioxides were used to synthesize direct Z-scheme heterostructures that can further amplify gold ion adsorption when exposed to light. Titanium dioxide can excite electrons in both the support and the coating layer, and also recombine the electrons of the titanium dioxide and the holes of tannin through energy band differences, thereby further promoting gold ion adsorption and reduction. These findings suggest that the direct Z-scheme heterostructure of polyphenol and semiconductor provides a promising photochemical pathway for efficient and selective metal ion recovery from electronic waste.