Spectroscopic Properties of Phase-Pure and Polytypic Colloidal Semiconductor Quantum Wires

Room-Temperature Interconversion Between Ultrathin CdTe Magic-Size Nanowires Induced by Ligand Shell Dynamics

The formation mechanisms of colloidal magic-size semiconductor nanostructures have remained obscure. Herein, we report the room temperature synthesis of three species of ultrathin CdTe magic-size nanowires (MSNWs) with diameters of 0.7 ± 0.1 nm, 0.9 ± 0.2 nm, and 1.1 ± 0.2 nm, and lowest energy exciton transitions at 373, 418, and 450 nm, respectively. The MSNWs are obtained from Cd(oleate)₂ and TOP-Te, provided diphenylphosphine and a primary alkylamine (RNH₂) are present at sufficiently high concentrations, and exhibit sequential, discontinuous growth. The population of each MSNW species is entirely determined by the RNH₂ concentration [RNH₂] so that single species are only obtained at specific concentrations, while mixtures are obtained at concentrations intermediate between the specific ones. Moreover, the MSNWs remain responsive to [RNH₂], interconverting from thinner to thicker upon [RNH₂] decrease and from thicker to thinner upon [RNH₂] increase. Our results allow us to propose a mechanism for the formation and interconversion of CdTe MSNWs and demonstrate that primary alkylamines play crucial roles in all four elementary kinetic steps (viz., monomer formation, nucleation, growth in length, and interconversion between species), thus being the decisive element in the creation of a reaction pathway that leads exclusively to CdTe MSNWs. The insights provided by our work thus contribute toward unravelling the mechanisms behind the formation of shape-controlled and atomically precise magic-size semiconductor nanostructures.

Molecularly imprinted polymer-based photocatalyst for highly selective degradation of methylene blue

ZnO quantum dots were synthesized by chemical precipitation, CuFe₂O₄ nanoparticles were prepared by in situ synthesis of cellulose, and then ZnO/CuFe₂O₄ (ZCF) composites were fabricated. A photocatalyst (ZCF@MB-MIP) with specific molecule recognition and photocatalytic degradation characteristics was then produced by a surface imprinting method using methylene blue (MB) as the template molecule. The structure of ZCF@MB-MIP was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and X-ray diffraction. The photocatalytic efficiency of ZCF@MB-MIP and its specific recognition performance in MB degradation was analyzed. The adsorption kinetics of MB by ZCF@MB-MIP conformed to the quasi-secondary adsorption kinetics model. ZCF@MB-MIP displayed effective photocatalytic degradation of MB under natural light. The degradation rate reached 95.8%, which was much higher than those of ZCF, CuFe₂O₄ nanoparticles, and a non-imprinted reference sample under the same conditions. This work is a useful reference for the construction of photocatalysts that show highly selective recognition of dye molecules.

Growth of MSe semiconductor nanowires on metal substrates through an Ag2Se-catalyzed solution–solid–solid mechanism (M = Zn, Cd and Mn)

Solution-phase growth of MSe nanowires on their respective metal foil or flakes (M = Zn, Cd and Mn) has been realized by a recently developed solution–solid–solid mechanism initiated by preexisting Ag2Se seeds.

A Molecularly Imprinted Fluorescence Sensor Based on the ZnO Quantum Dot Core-Shell Structure for High Selectivity and Photolysis Function of Methylene Blue

ZnO quantum dots and CuFe2O4 nanoparticles were synthesized by chemical precipitation. The ZCF composite was created by the solvothermal method. A new molecularly imprinted fluorescence sensor (ZCF@MB-MIP) with unique optical properties and specific MB recognition was successfully generated. ZCF@MB-MIPs were characterized by Fourier-transform infrared spectroscopy, transmission electron microscopy, and X-ray diffraction and were applied for the selective detection of methylene blue (MB). The optimal working time of ZCF@MB-MIPs was 15 min, and the optimal working concentration was 37 mg·L-1. The fluorescence intensity was linearly quenched within the 0-100 μmol·L-1 MB range, and the detection limit was 1.27 μmol·L-1. The imprinting factor of the sensor (IF, K MB-MIPs/N-MIPs) was 5.30. At the same time, a real-time monitoring system was established for the photodegradation process of MB, which had the effect of reflecting the degradation degree of MB at any given time. Hence, ZCF@MB-MIPs are a promising candidate for use in MB monitoring, and they also provides a new strategy for constructing a multifunctional fluorescence sensor with a high selectivity and photolysis function.

Unique Growth Pathway in Solution-Solid-Solid Nanowires: Cubic to Hexagonal Phase Transformation

Solution-solid-solid (SSS) nanowires can be catalyzed by superionic Ag₂S via ion diffusion. Here, we synthesize ZnS nanowires of the wurtzite crystal structure and heterostructures via a low-temperature growth pathway. Single-crystalline ZnS nanowires were produced by varying reaction time and temperature (120-200 °C) via thermal decomposition of a single-source precursor, Zn(DDTC)₂. A phase transformation (zinc blende → wurtzite) was observed during the synthesis with a three-step growth pathway proposed. Temperature-controlled phase transformation facilitates oriented attachment into a 1D nanowire, followed by helical epitaxial and lateral growths during ripening. Additionally, the CdS-ZnS heterostructured nanowires can be obtained after introducing the Cd(DDTC)₂ precursor. ZnS nanowires of defined diameters (5-10 nm) are served as backbones to grow heterostructures of ternary semiconductors with multicolor photoluminescence (450-800 nm). Structural and optical characterizations (PL, 2D PLE, and TCSPC) are investigated to confirm origins of broadband emission from multiple lifetimes (0.5-12 ns) for exciton recombination in heterostructures. Our study demonstrates this unique growth pathway for SSS nanowire synthesis under mild, facile, and atmospheric conditions.

Tellurium Precursor for Nanocrystal Synthesis: Tris(dimethylamino)phosphine Telluride

Preparations of CdTe quantum platelets, magic-size (CdTe)₁₃ nanoclusters, and CdTe quantum wires are described using (Me₂N)₃PTe (with (Me₂N)₃P) as a Te precursor. The (Me₂N)₃PTe/(Me₂N)₃P precursor mixture is shown to be more reactive than mixtures of trialkylphosphine tellurides and the corresponding trialkylphosphines, R₃PTe/R₃P, which are commonly employed in nanocrystal syntheses. For syntheses conducted in primary amine solvents, (Me₂N)₃PTe and (Me₂N)₃P undergo a transamination reaction, affording (Me₂N) _x(RHN)_{3- x}PTe and (Me₂N) _x(RHN)_{3- x}P (R = n-octyl or oleyl). The transaminated (Me₂N) _x(RHN)_{3- x}PTe derivatives are shown to be the likely Te precursors under those conditions. The enhanced reactivities of the tris(amino)phosphine tellurides are ascribed to increased nucleophilicity due to the amino-N lone pairs.

Synthesis of alloyed Zn1–xMnxS nanowires with completely controlled compositions and tunable bandgaps

This study reported the successful synthesis of Zn_1–xMn_xS nanowires with completely controlled compositions (0 ≤ x ≤ 1); the x values could be well controlled by tuning the feeding ratio of [(C₄H₉)₂NCS₂]₂Zn to [(C₄H₉)₂NCS₂]₂Mn precursors.

Role of Precursor-Conversion Chemistry in the Crystal-Phase Control of Catalytically Grown Colloidal Semiconductor Quantum Wires

Crystal-phase control is one of the most challenging problems in nanowire growth. We demonstrate that, in the solution-phase catalyzed growth of colloidal cadmium telluride (CdTe) quantum wires (QWs), the crystal phase can be controlled by manipulating the reaction chemistry of the Cd precursors and tri-n-octylphosphine telluride (TOPTe) to favor the production of either a CdTe solute or Te, which consequently determines the composition and (liquid or solid) state of the Bi_xCd_yTe_z catalyst nanoparticles. Growth of single-phase (e.g., wurtzite) QWs is achieved only from solid catalysts (y ≪ z) that enable the solution-solid-solid growth of the QWs, whereas the liquid catalysts (y ≈ z) fulfill the solution-liquid-solid growth of the polytypic QWs. Factors that affect the precursor-conversion chemistry are systematically accounted for, which are correlated with a kinetic study of the composition and state of the catalyst nanoparticles to understand the mechanism. This work reveals the role of the precursor-reaction chemistry in the crystal-phase control of catalytically grown colloidal QWs, opening the possibility of growing phase-pure QWs of other compositions.