Applications Of Biomimetic Dopamine In Photocatalysis And Photo-initiated Polymerization

Dopamine, as a biomolecule, its most common format is dopamine hydrochloride. It owns catechol and amine groups and can undergo oxidative self-polymerization in alkaline solution producing polydopamine (PDA). PDA containing a lot of hydroxyl and amine groups, possesses a freestanding reduction and adhesion properties. Because of its nontoxicity, biocompatibility and biodegradation, PDA has been widely used in the many fields such as surface modification, drug delivery, and catalysis and so on. In addition, under oxygen-free and UV irradiation conditions, the hydrogen from the hydroxyl and amino functional groups in PDA can be abstracted to generate radicals which can induce the polymerization of a series of monomers including methacrylates, acrylates and styrene. Besides, PDA capsules with pH responsive properties and controllable shell thickness, have received much attention. Now, there are generally two methods to prepare PDA capsules (soft templates and hard templates). However, these methods suffer from tedious steps and difficulty to remove the templates, which limit the wide applications of PDA capusles. In addition, polymerization induced self-assembly (PISA) is a new technology in which polymerization and self-assembly carry on at the same time. PISA can also tailor the structures of the polymers. PISA has attracted great interests due to its high production, various morphologies and simple operation. Based on the outstanding properties of dopamine chemistry, the aim of the thesis is to explore a green, mild and facile method to prepare micro/nanomaterials via dopamine chemistry, co-precipitation method, photo-induced polymerization and PISA technology. The structures, properties and functions of different PDA-based micro/nanomaterials are studied in detail. The specific contents of this thesis is as follows:Chapter 1 is a brief introduction of different polymerization methods of dopamine and different morphologies of polydopamine and their applications are reviewed. The researches on photocatalysis of Ag/AgCl and carbon nitride and photo-induced polymerization are underdrawn. In addition, the development of PISA is outlined. At last, the topic basis and the content of this thesis are demonstrated.In Chapter 2, a PDA-supported Ag@AgCl (P-Ag@AgCl) photocatalyst has been fabricated employing dopamine hydrochloride as the chloride source and reductant at room temperature. The obtained photocatalysts exhibited tunable morphology, composition and improved performace by alteration of the initial pH value and the concentration of the surfactant. Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectra (UV-Vis) are used to characterize the samples. The results revealed that the photocatalysts had different compositions because of different initial pH values. The photocatalytic degradation of model dyes proved that the photocatalysts showed high efficiency, high stability and recyclability which could reused for at least 15 times.In Chapter 3, by virtue of the strong adhesion properties and high electron transition properties of PDA, we present a simple and versatile approach for the construction of plasmonic Ag/AgCl-polydopamine-CN (SPCN) composites for enhanced photocatalytic properties by mussel chemistry. SEM, XRD, XPS, UV-vis DRS, Fourier transform infrared (FTIR) spectroscopy, Thermo gravimetric analysis (TGA) Photoluminescence (PL) Spectroscopy, photoelectron responses and the experiment of free radicals capture are conducted. Dopamine hydrochloride acts as both the reactant and the reducing agent and the product polydopamine (PDA) serves as the adhesive layer and the electron transfer bridge. The photocatalytic degradation of rhodamine B (RhB) exhibited that the SPCN50 owned excellent photocatalytic activity. The radical trapping experiment indicated that holes were the main oxidative species in the photocatalytic process. And a possible photocatalytic mechanism was also proposed. All the results proved that PDA indeed improved the separation efficiency of photogenerated carriers, the photocatalytic activity and enhanced the interaction between Ag/AgCl and CN without disrupting the structure of CN.In Chapter 4, based on the method of PISA, DA as the photoinitiator took place of the macromolecular intiator (macroinitiator) or macromolecular-chain transfer agent (macro-CTA). Polydopamine capsules are prepared under oxygen-free and UV irradiation conditions via photo-triggered polymerization-induced self-assembly (photo-PISA) and the oxidative self-polymerization of DA. TEM, SEM and TGA are conducted to characterize the capsules. The results indicated that the morphologies and sizes of PDA capsules could be tailored via the concentration of DA and styrene. After carbonization, the capsules exhibited hollow structure and owned good ORR properties.