Application Of Polydopamine And Its Functional Micro-or Nano-materials In Degradation Of Dyes

Due to the redox conversion between quinones and phenols,quinones can be used as redox mediators?RMs?to transfer electrons.In the past few decades,the role of electron transfer quinone as a catalyst in the fields of dye degradation,energy and biomedicine has been paid more and more attention.Dopamine?DA?is ubiquitous in nature as an important neurotransmitter in the brain,and identified as a small molecule mimic of mussel foot proteins containing both catechol and amine functional groups.It can self-polymerize under alkaline conditions to generate polydopamine?PDA?material,which possess excellent adhesive property,and can firmly stick to a variety of organic or inorganic materials surface.PDA is also reported to be an environmentally friendly,non-toxic,and hydrophilic material with excellent biocompatibility.And PDA also has a phenol/quinone coexistence of functional groups,so that it can be used as RMs,mediated a variety of redox reaction.In addition,PDA-coated noble metal nanoparticles can be prepared easily and conveniently with DA as a reducing agent.Based on these,this work has carried out the following aspects:?1?PDA microparticles?MPs?as redox mediators for catalytic reduction of dyesPDA MPs were synthesized by DA autoxidation under mild NaOH solution,and have narrow size distribution with good dispersion in water.And then PDA MPs were used as RMs for the catalytic reduction of methylene blue?MB?and rhodamine B by NaBH₄ at room temperature.The morphology,structure and composition of the samples prepared were characterized by transmission electron microscope?TEM?,Fourier-transform infrared?FTIR?spectra and X-ray photoelectron spectroscopy?XPS?.Moreover,the catalytic activity and stability of the PDA MPs were investigated and the possible catalytic mechanism was also discussed.The result indicated that PDA MPs with a phenol/quinone coexistence structure receive electrons from the electron donor BH₄-,the reduced phenols then transfer the electrons to the final electron acceptor dyes,inducing the reductive degradation of the dyes.In addition,PDA MPs exhibit good stability,and can achieve eight times recycling.?2?PDA-coated Fe₃O₄ nanoparticles as synergistic RMs for catalytic reduction of dyes.The PDA-coated Fe₃O₄ nanoparticles?Fe₃O₄@PDA NPs?were synthesized by in-situ polymerization of DA on Fe₃O₄ NPs surface,and then utilized as synergistic redox mediators for the catalytic reduction,by NaBH₄,of azo dyes such as methyl orange?MO?and methyl red?MR?.The morphology,structure and composition of the samples prepared were characterized by TEM,X-ray diffraction?XRD?,vibrating sample magnetometer?VSM?,FTIR spectra and XPS.Moreover,the catalytic activity and stability of the Fe₃O₄@PDA NPs were investigated and the possible catalytic mechanism was also discussed.The results indicated that the existence of synergy between phenol/quinone units and Fe?III?/Fe?II?in Fe₃O₄@PDA NPs induced the higher catalytic activity compared with PDA MPs.Moreover,Fe₃O₄@PDA NPs,with an excellent stability,could be reused five times.?3?Fe₃O₄@PDA NPs as Fenton reagent for catalytic oxidation of dyesIn this part,Fe₃O₄@PDA NPs were used as the Fenton catalyst to catalyze the oxidative degradation of MB.The catalytic activity and stability of the catalyst were evaluated and the mechanism of the catalytic reaction was discussed.The results show that PDA with phenol/quinone units can promote the cycling between Fe?III?and Fe?II?,which makes Fe₃O₄@PDA NPs have stronger catalytic oxidation activity than Fe₃O₄ NPs.In addition,Fe₃O₄@PDA NPs can be recycled.?4?Preparation of PDA-coated gold nanoparticles and their application for catalytic reduction of 4-nitrophenolPDA-coated gold nanoparticles?Au@PDA NPs?were synthesized by one-step method using DA as the reductants.In addition,Au@PDA NPs were characterized by UV-Vis spectra and TEM.The effect of the pH,oxygen content in synthesized system,mercaptoethanol and free radical scavenger,on the synthesis of Au@PDA NPs were investigated to speculate the feasible synthesis mechanism.The results show that the reductive center in the preparation of Au@PDA NPs with DA as reducing agent is not the phenol or phenoxy anion proposed by other researchers,but the semiquinone free radicals.In addition,Au@PDA NPs can be used as a catalyst to catalyze the reduction of 4-nitrophenol by Na BH₄.