Novel Semiconductor Composites Based On Protonated Titanate Nanotubes And Their Photocatalytic Study

Recent years, the synthesis and application of low dimensional inorganicnanomaterials are hot topics in the field of nanomaterials sciences. In this paper, thechemical component, structure, growth mechanism, phase transformation, exfoliation,and morphology control of the protonated titanate nanotubes are systematicallystudied. The X-ray photoelectron spectroscopy(XPS) study is carried to clear thechemical states of Ti?O atoms in the protonated titanate nanotubes. The splitting ofO-1s peak revealed the O atoms in protonated titanate nanotubes are of three differentchemical states such as lattice oxygen, hydroxyl oxygen and oxygen from bound H2O.The XPS sensitivity factor method is employed to calculate the element ratio Ti/O(about1/3), and the component of as-prepared nanotubes is close to H2Ti2O4(OH)2.The key effect of NaOH solvent concentration on the scroll and fabrication of titanatenanotubes is reported, while1-D nanotubes and2-D n anosheets are respectivelyobtained by varying the NaOH concentration. A low temperature crystallizationmethod is exploited to yield protonated titanate nanotubes to transform tophotocatalytic active anatase crystals under100?. The correlation betweenphotocatalytic activity and heat treatment parameters are studied with as well thefitting of first order kinetics.In order to modify the protonated titanate nanotubes, the transition metal ammoniacomplexes are coordinated to the surface of protonated titanate nanotubes in alkali pHenvironment. The absorption capacities of protonated titanate nanotubes toward metalions are improved. The absorption phenomena of Co2+, Zn2+, Cd2+, Cu2+and Ag+byprotonated titanate nanotube are studied. XPS studies are employed to systematicallyinvestigate the chemical state of absorbed metal ions on protonated titanate nanotubesand the influence of absorption reaction to the Ti-2p binding energy shift on thenanotube surface. It is shown the Ti-2p peaks of protonated titanate nanotubes all shiftto the higher energy by absorption of transition metal ions. In addition, the chemicalstates of oxygen atoms on these nanotubes before and after absorption reaction arestudied by fitting of the O-1s spectra.The technology to fabricate semiconductor composites is one of the main methodsto improve the activity of photocatalytic materials. By the growth of heterogeneoussemiconductor particles on semiconductor nanotube surface, it is promising to produce high active composited semiconductor photocatalysts with enhanced lightabsorption and improved migration efficiency of photogenerated charge carriers. Howto efficiently grow heterogeneous semiconductor nanoparticles to modify thenanotubes is becoming a research hot topic. By using the protonated titanatenanotubes to absorb and distribute cadmium ions on nanotube surface, and then by thefollowed chemical reaction on nanotube surface, CdS nanoclusters(<5nm) aregrown on the multilayered tubewalls of1-D protonated titanate nanotubes with welldistribution of tens of nanoclusters along the axis of the nanotubes(about100nm).The structure of nanoclusters@nanotube composite nanosystem, their phasetransformation and photocatalytic activities are studied. In addition, the influence ofdifferent heat treatments conditions to their photocatalytic activity is investigated,including the fitting of first order kinetics. The modification of protonated titanatenanotubes by CdS nanoclusters highly improved the photocatalytic performance oftheir crystallized products by3times.By using the protonated titanate nanotubes to complex and release silver ions,AgBr nanoclusters are fabricated on different locations including directly on thenanotube surface or surrounding the nanotubes. The AgBr nanocrystals formedsurrounding the protonated titanate nanotubes are in radical and gradient distribution,with gradually decreases of sizes (mini~5nm) relating to the distance from thenanotube surface. The high photocatalytic activity is shown by the as prepared AgBrnanocrystals. Moreover, by the inducing effect of the AgBr nanoparticle seeds toreduce free Ag+in the solution, silver metal unit are attached on the exclusive one sideof the AgBr seeds forming dumbbell-like hybrid structures, unlike the reportedirregular and uncontrolled deposit of metal nanoparticles on semiconductor surface.Each as prepared hybrid particle contains a metal unit on one end of the particle withopposition to the semiconductor unit on the other end. The two units are intimatedconnected with solid interfacial contact between them. This novel structure not onlycontrolled the site-selective growth of component in particle-level, but also enrichedthe nano-science and nano-technology which would inspire the development of moreadvanced materials or potential applications in nano devices.