Functional nanomaterials of zinc oxide and compounds of vanadium

Nanomaterials and, among them, elongated morphologies such as nanowires, nanotubes and nanorods attract a dramatic deal of attention in the current materials research. They are capable of extending functionalities of modern devices and are considered to have exciting applications in a variety of fields including sensors, lightand electron emitting devices, energy conversion and storage, intelligent switches and self-cleaning materials. The ability to produce large quantities of nanomaterials is needed for testing their properties for a broad scope of applications and for the commercialization of emerging technologies. The development of efficient synthesis methods capable of mass production of nanomaterials is becoming crucial. In this thesis the applicability of ball milling to the efficient production of nanomaterials is assessed. Two key technological materials, ZnO and V2O5, are chosen as model systems. ZnO is well known for its semiconducting and piezoelectric properties; it is used in electronics, sensors, light sources and other applications. And V2O5 is a widely used material in the field of catalysis and electrochemistry, with applications in electrochromic devices and batteries. Ball milling of ZnO is found to increase the evaporation ability of the milled material. The effect is not related to the changes in the surface area but attributed to the structural changes in the material. ZnO nanowires are grown by evaporation of the milled powder. Their luminescent spectrum is dominated by a green emission band (at 510 nm) while the near-band-edge emission (at 390 nm) is suppressed. The unusual morphology of corrugated ZnO nanowires produced by evaporation of the ball milled powder is studied in detail. The nanowires have a hexagonal cross section while their side surfaces are converted into the sequences of predominant {101̄1} and {101̄1̄} facets. The formation of this unusual morphology is attributed to the presence of stacking faults in nanowires and a high vapor supersaturation. Ball milling of V2O5 powder with a subsequent annealing in a fluidized bed leads to a mass production of nanorods. 1 g of V2O5 nanorods is produced in a proof-ofconcept test. The formation of nanorods is related to the minimization of surface energy, and surface diffusion plays an important role in the growth mechanism. The beneficial crystal orientation of V2O5 nanorods provides an improved cycling stability for lithium intercalation The large quantities of V2O5 nanorods produced by ball milling and subsequent annealing in a fluidized bed can be converted to nanorods of other vanadium compounds by simple reduction techniques which preserve the primary morphology. The formation of VO2(B), V2O3 and VN phases is achieved by pseudomorphic reduction in vacuum and NH3 atmospheres. Finally, the electrochemical properties of vanadium nitride for potential applications of this material in supercapacitors are studied. VN possesses capacitive properties in acidic (1M H2SO4), alkaline (1M KOH) and neutral (3M NaCl) electrolytes. The material synthesized by NH3 reduction of V2O5 can retain about 80 % of its capacitance at a high current load of 1 A g−1. The cycling stability of VN in 1M H2SO4 and 3M NaCl electrolytes is tested. Five peer-reviewed journal articles based on the results of the thesis have been published, and one more is currently under preparation. Journal publications related to this thesis A. Glushenkov, Y. Chen, ’Synthesis of ZnO nanowires using ball-milling and annealing method’, Mater. Forum 30: 1-6 (2006). A.M. Glushenkov, H.Z. Zhang, J. Zou, G.Q. Lu, Y. Chen, ’Efficient production of ZnO nanowires by a ball milling and annealing method’, Nanotechnology 18: 175604 (2007). A.M. Glushenkov, H.Z. Zhang, Y. Chen, ’Anomalous evaporation behavior of ZnO powder milled mechanically under high-energy conditions’, Mater. Lett. 62: 715-718 (2008). A.M. Glushenkov, H.Z. Zhang, J. Zou, G.Q. Lu, Y. Chen, ’Unusual corrugated nanowires of zinc oxide’, J. Cryst. Growth 310: 3139-3143 (2008). A.M. Glushenkov, V.I. Stukachev, M.F. Hassan, G.G. Kuvshinov, H.K. Liu, Y. Chen, ’A novel approach for real mass transformation from V2O5 particles to nanorods’, Crystal Growth & Design 8: 3661-3665 (2008).