Qianqian Shen

Crystallization behavior and formation mechanism of dendrite Cu2O crystals

The crystal growth behavior of dendrite-like Cu2O crystals during galvanostatic electrodeposition was investigated. The deposited Cu2O particles are single-phase cuprites and their morphologies change from octahedral in a static electrolyte to dendrites in a stirred electrolyte. The morphology evolution is attributed to the enhancement of the transfer of Cu2+ and the break in the Cu2+ depletion zone around the nuclei, which promotes the deposition of Cu2+ ions along the directions to form a face-centered cubic (FCC) Cu lattice under a cathodic potential. Meanwhile, O atoms diffuse into the Cu lattice to form a cuprite Cu2O lattice with a corresponding lattice expansion. Consequently, the morphology of the Cu2O crystals develops into dendrites and the growth direction of the dendritic branches are all along the directions. Furthermore, the conduction type of Cu2O was also changed from p-type to n-type when the morphology of the Cu2O crystals varied from octahedral to dendrites. The mechanism of the morphology evolution in the present reaction system is helpful for controlling the morphology of the Cu2O crystals.

The study on properties of CdS photocatalyst with different ratios of zinc-blende and wurtzite structure

The mixtures of zinc blende and wurtzite CdS nanoparticles were prepared via a solvothermal method by controlling the precursor ratio (Cd/S molar ratio). The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and ultraviolet-visible (UV-vis) spectroscopy. These results demonstrate that not only the morphology but also the phase composition of CdS nanostructures was sensitively altered by the precursor ratio (Cd/S molar ratio). Photocatalysis test results show that the photocatalytic activity was mainly dependent on the ratio between zinc blende and wurtzite phases in CdS samples. The product prepared with 1:2 Cd/S molar ratio exhibited higher photocatalytic activities in comparison with products prepared with other Cd/S molar ratios, which can be attributed to the improved charge separation at the zinc blende/wurtzite junction interface.

Shape-controlled synthesis of three-dimensional branched CdS nanostructure arrays: structural characteristics and formation mechanism

Through a combination of electrodeposition and subsequent solvothermal reaction, three-dimensional (3D) branched CdS nanostructure arrays were fabricated by nanowires self-assembly in ethanediamine solution containing thiourea and hexamethylenetetramine (HMTA) for the first time, where HMTA acted as a capping agent. In the absence of HMTA, only disordered CdS nanowires were obtained. The reaction conditions influencing the synthesis of 3D branched CdS nanostructure arrays, such as the concentration of HMTA and thiourea, reaction temperature and reaction time, were studied and optimized. The 3D branched CdS nanostructure arrays were characterized by X-ray diffraction, field emitting scanning electron microscopy and transmission electron microscopy. The results show that HMTA played an important role in the formation of 3D branched CdS nanostructure arrays. A growth process of HMTA-assisted gradual crystallization and subsequent oriented attachment was proposed as a plausible mechanistic interpretation for the formation of the 3D branched nanostructure arrays. In addition, the photoluminescence property of the novel 3D branched CdS nanostructure arrays was investigated.

Facile and time-saving synthesis of octahedral Cu2O crystals by an ethanol-assisted solution method at low temperatures

Size-uniform octahedral Cu2O crystals were synthesized by a facile and time-saving ethanol-assisted solution method at low temperatures. The synthesized products were systematically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that the amount of ethanol has strong effects on the phase purity and morphology development of the products. By adjusting the amount of ethanol, the morphology of Cu2O gradually changed from sphere to octahedron. The possible crystal growth processes are proposed. The presence of more oxygen in ethanol is helpful to the formation of octahedral Cu2O seeds with truncated low index {111} planes. It is suggested that the oriented attachment mechanism plays an important role in the transition from tiny Cu2O crystals to large octahedral Cu2O single crystals. The preferential adsorption of ethanol molecules on the Cu2O {111} facets makes the octahedral Cu2O more stable.

The surface wettability of TiO2 nanotube arrays: which is more important—morphology or chemical composition?

The wettability of TiO2 nanotube arrays (TiO2-NTAs) synthesized by electrochemical anodization was intensively investigated. It was found that annealing temperature of TiO2-NTAs has significant effect on the hydrophilicity of TiO2-NTAs. With the increase of annealing temperature, the fluorine element content on TiO2-NTAs surface decreases, which results in decrease in water contact angle and increase in hydrophilicity for TiO2-NTAs. The reason is that F− ions escape from the lattice and oxygen vacancies are created at the two coordinated oxygen bridging sites at TiO2-NTAs surface after annealing in argon atmosphere. And these defects can in turn increase the affinity for hydroxyl ions formed by dissociation of chemisorbed water molecules and thereby form hydrophilic domains. In addition, TiO2 crystal becomes well organized gradually with the increase of annealing temperature, F− ions are not favored to exist in the lattice and thus escape from the lattice. Less F element content results in better hydrophilicity of TiO2-NTAs.

The influence of Au nuclei layer on formation and photoelectrochemical properties of Cu2O thin films

The smooth and uniform Cu2O thin films were prepared by electrodeposition with the introduction of Au nuclei layer. The influence of Au nuclei layer on the formation of these thin films was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the optical absorption (UV–vis/DR) methods. Smooth and uniform Cu2O thin films without any islands and pinholes are formed when the electrodeposition is conducted after sputtering Au nuclei layer on ITO. Au nuclei layer provides much larger surface area, enhances the Cu2+ ion migration, and consequently prompts the deposition of Cu2O nuclei on Au nuclei layer to form smooth and uniform Cu2O thin films. Further, the Au nuclei layer plays an important role in improving photoelectrochemical performance of Cu2O thin films. The samples with Au nuclei layer exhibits increased absorption and red shift of absorption edge. The observed steady-state photocurrent of samples with Au nuclei layer is much higher than that of samples without Au nuclei layer as a result of the formation of space charge region in Cu2O thin films when the Au and Cu2O are in contact, which greatly improves the production and separation of photo-induced electrons and holes.