Studies On Controllable Synthesis,Formation Mechanism And Performance Of Micro/Nano Rings

Nanorings with closed and one-dimensional(1D)nanostructures have gained considerable attention because of their distinct geometry,novel properties,and specific applications.Nanorings,as a simple plasmonic structure,exhibit multiresonant behavior in the visible range to the NIR regions.They are also thought to be plasmonic nanoantennas which can generate strong electromagnetic field enhancement effects.Multiple scattering,oscillation resonance absorption,microantenna radiation,and interference confer nanorings with various potential applications in microwave absorption,magnetic random access memory,catalysts,sensors,and solar cell upconverters.Based on the novel properties of nanorings,β-Co(OH)2 microrings,ZnO nanorings and ZnO/graphene oxide sheets composites were synthesized in this paper and their formation mechanism,electrochemical detection performance,and photocatalytic activity were systematically investigated.The main contents can be summarized as follows:1.Controllable synthesis and formation mechanism of single-crystal β-Co(OH)2 microrings as sensors for detection of nitrite ionsAn easy and low-temperature mixed-solvent method was developed for one-step fabrication of single-crystal β-Co(OH)2 hexagonal microrings(MRs)by aging in situ generated β-Co(OH)2 microsheets(MSs)at room temperature for 24～60 h.Dynamic factors(i.e.,concentration,water-to-ethanol volume ratio(δ),amount of water added(V),aging temperature,and aging time(ta))were used to control the size and structure of the resulting MRs.β-Co(OH)2 MRs were easily formed under conditions of low aging temperatures,appropriate δ,additional H2O,or extended aging.The morphological evolution from micro sheets to microrings could be ascribed to the dissolution-diffusion-recrystallization behavior on the(0001)facets.The proposed method is simple and environmentally benign.The unique as-obtained β-Co(OH)2 MRs function as the modified electrode and exhibit excellent sensitivity to NO2-.The controllable synthesis of β-Co(OH)2 MRs with exposed(0001)plane offers an effective means for developing layered electrode materials with high sensitivity for detecting nitrite ions.2.Zn polar surface-guided chemical etching synthesis of ZnO nanostructures for enhanced photocatalytic activityThis study proposes a simple,low-temperature chemical etching method for selective preparation of monodispersed,hexagonal,single-crystal ZnO nanostructures.The morphological evolution from nanoplates(NPs)to nanoseals(NSs),nanobowls(NBs),and nanorings(NRs)is initiated by positively charged(0001)-Zn polar surface and driven by the principle of minimum energy.The relationship among morphology,dimension,and function of ZnO was determined by investigating polar planes,surface area,energy band,optical properties,and catalytic activity for rhodamine B.The ZnO NBs and ZnO NRs exhibit the improved optical and photocatalytic performance because of enhanced light harvesting and plasmonic resonance-enhanced absorption.Surface recombination plays a key role in apparent rate constant k for ZnO NBs with small size and those formed at low reaction temperatures.The photocatalytic activity of ZnO NBs formed at high reaction temperatures decreases with increasing size because of decreased surface area.3.Synthesis and plasmonic enhanced photocatalytic properties of ZnO/reduced graphene oxide sheets(ZnO/rGO)composites with controllable morphology and compositionZnO with various morphologies and contents was used to decorate reduced graphene oxide sheets(rGO)via an easy one-step low-temperature chemical etching route to improve photocatalytic properties.The ZnO shape and content in ZnO/rGO composites were adjusted by changing aging time,heating mode,and rGO mass added.Shape andcontent-dependent optical and photocatalytic properties are observed in ZnO/rGO composites.A moderate amount of ZnO nanorings(NRs)decorated with rGO can significantly improve the light absorption and photo-luminescence emission because of plasmonic resonant absorption and plasmonic nanoantenna radiation,respectively.ZnO NR/rGO composites with a moderate ZnO content of 29.54 wt.%exhibit the optimum photocatalytic activity with a 0.025 min-1 apparent rate constant,which is significantly higher than those of pure rGO(0.0085 min"1)and ZnO NRs(0.018 min-1).The improved performance is ascribed to the synergistic effect of enhanced adsorption capacity,plasmonic light absorption,plasmonic nanoantenna radiation,and the prolonged lifetime of photogenerated electron-hole pairs.Our findings not only offer insights into the plasmon enhanced optical and photocatalytic properties of ZnO NR/rGO composites but also suggest the possibility of fabricating ZnO NR/rGO photocatalyst with enhanced performance.