Cu₂O Nanocrystals And Their Composites:Shape-controlled Synthesis And Applications In Catalytic And Antibacterial Fields

As an important P-type semiconductor material with a direct band gap of about 2.17eV,cuprous oxide?Cu₂O?is always paid much attention in chemistry and materials science,owing to extensively potential applications in many fields including antibiosis,photo/electrocatalysis,and sensing.A great deal of studies have uncovered that the properties of nanomaterials are related to their morphology,size and crystallinity.Therefore,it is still significance of designing and synthesizing Cu₂O nanocrystals with specific morphology,size and crystallinity,as well composite materials,and exploring their applications in catalysis and antibiosis in therory and practice.In this dissertation,cuprous oxide nanomaterials with various morphologies and their composites with Fe₃O₄ and carbon were successfully synthesized or constructed by various synthetic strategies.Their applications were investigated in some fields,including catalytic reduction for small organic molecules,electrochemical detection,electrochemical hydrogen evolution and antibiosis.The main contents are listed as follows:1.A simple vapor-solid reaction was designed for preparation of porous Cu₂O nanorods with good HER catalytic performance,employing Cu?OH?₂ nanorods as the precursor and ethylene glycol?EG?as the reductant.The reaction was carried out in Ar atmosphere at the temperature of 200-280?C for 2 h.It was found that pure Cu₂O was always obtained in the temperature region of 200-280?C and well retained the outline of the precursor.Nevertheless,electrochemical experiments showed that porous Cu₂O nanorods prepared at 200?C?labeled as Cu₂O-200?exhibited much stronger HER catalytic activity than those obtained at higher temperatures,which were named as Cu₂O-220,Cu₂O-240,Cu₂O-260 and Cu₂O-280,respectively.In an alkaline solution of1.0 M KOH,Cu₂O-200 presented a low overpotential of?184 mV and a high durability over 20 h at a current density of 10 mA cm^-2.The above good performances were attributed to high surface area and high-speed electronic transmission networks of Cu₂O-200,which provided fast transportation and short diffusion path for the electrolyte and evolved H₂ bubbles.2.Porous Cu₂O/C octahedral composite nanostructures were successfully prepared by the abovementioned gas-solid reaction route,employing HKUST-1 as the precursor and ethylene glycol as the reducing agent.The reaction was carried out in Ar atmosphere at 300?C for 2 h.The BET measurement showed that the as-obtained porous Cu₂O/C octahedral composite nanostructures owned a larger specific surface area of 58.5 m² g^-1.The electrochemical experiments displayed that the as-obtained porous Cu₂O/C octahedral composite nanostructures had a good response to glucose in aqueous systems,which could be prepared into a simple enzyme-free glucose electrochemical sensor with a limit of detection of 0.33?M and a linear range of 1.0×10^-61.1×10^-3 mol L^-1 in 0.1mol L^-1 NaOH solution containing 0.1 mmol L^-1 glucose.Also,the as-obtained glucose sensor exhibited excellent selectivity.Some interfering substances with the same concentration,such as Uric acid?UA?,Ascorbic acid?AA?,and Dopamine?DA?,as well as NaCl with 100 times concentration,hardly affected the detection of glucose.The present work provides a new catalyst selection for electrochemical detection of glucose in aqueous systems.3.Multifunctional Fe₃O₄@resorcinol-formaldehyde resins/Cu₂O?denoted as Fe₃O₄@RF/Cu₂O?composite microstructures were successfully constructed via a simple two-step wet chemical route.First,Fe₃O₄@RF nanospheres were modified by silane coupling agent KH550 and maleic anhydride;then,Cu²⁺ions were adsorbed on the surface of Fe₃O₄@RF nanospheres modified and reduced by NH₂OH?HCl at room temperature.The investigations showed that the as-obtained microstructures presented not only excellent antibacterial activity to S.aureus?gram-positive bacteria?and E.coli?gram-negative bacteria?,but also highly-efficient catalytic ability for the reduction of4-nitrophenol?4-NP?in excess NaBH₄ solution.Owing to the presence of Fe₃O₄,the antibacterial reagent and the catalyst could be readily collected from the mixed systems under the assistance of an external magnetic field.It was found that the as-obtained microstructures displayed good cycling stability in antibacterial and catalytic applications.Fe₃O₄@RF/Cu₂O microstructures still retained more than 87%of antibacterial efficiency after 5 cycles,and 89%of catalytic efficiency after 10 cycles.4.Combining the abovementioned two-step wet chemical route with gas-solid reaction technology,Fe₃O₄@RF@Cu₂O/C composite microstructures were successfully constructed.Firstly,Fe₃O₄@RF nanospheres modified by silane coupling agent KH550and maleic anhydride were obtained according to the above two-step wet chemical route.After Cu²⁺ions were adsorbed on the surface of Fe₃O₄@RF nanospheres modified,a mixed solution of NaOH,N,N-diethylethanamine and 1,3,5-benzenetricarboxylic acid?BTC?was introduced.The mixed system was heated at 85?C for 24 h to prepare Cu-BTC-coated Fe₃O₄@RF core-shell structures?Finally,Fe₃O₄@RF@Cu₂O/C composite structures were obtained in Ar atmosphere at 300?C for 24 h,using Cu-BTC-coated Fe₃O₄@RF core-shell structures as the Cu²⁺ion source and EG as the reductant.Experiments showed that as-obtained Fe₃O₄@RF@Cu₂O/C microstructures presented outstanding catalytic activity to reduce 4-nitrophenol?4-NP?and Rhodamine B?RhB?in excess NaBH₄.In the precence of 6 mg L^-1 catalyst,it took only 3 min and 6min to completely reduce 4-NP and RhB with the concentration of 1.0×10^-44 mol L^-1,respectively.Moreover,the present catalyst could be easily recovered and re-used.After5 cycles,⁹4%of the catalytic efficiency for 4-NP was still retained,implying the excellent cycle stability of the present catalyst.5.Cu₂O microcrystals with cube,octahedron and hollow sphere were prepared through employing AA,glucose and a mixture of diglycol?DG?and EG as the reductants,respectively.Subsequently,Cu₂O microcrystals with various shapes were used as the antibacterial reagent to restrain the propagation of Escherichia coli?E.coli?.It was found that all Cu₂O microcrystals with various shapes presented strong abilities to restrain the propagation of E.coli.Nevertheless,FESEM observations showed that the morphology of Cu₂O microcrystals regularly changed in the antibacterial process.During the devitalization,the shape change always started from?100?planes.Cu₂O microcrystals with various shapes presented similar change trend and finally was converted into flowerlike microstructures constructed by abundant nanosheets.Also,XRD analyses uncovered that the flowerlike products were still cubic Cu₂O.However,the crystallinities markedly decreased.Further investigation by the tetrazolium blue?NBT?method exhibited that many active oxygen radicals?·O₂^-?appeared in the antibacterial process of Cu₂O.Based on this finding,a new antibacterial mechanism was suggested:it was believed that the high antibacterial efficiency should be attributed to the synergistic action between Cu²⁺ions and?O₂^-radicals?The present work is significant of exploring the antibacterial mechanism of Cu₂O and the shape evolution of the antibacterial reagent.