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Oriented attachment growth of monocrystalline cuprous oxide nanowires in pure water.

ABSTRACT: As a crucial mechanism of non-classical crystallization, the oriented attachment (OA) growth of nanocrystals is of great interest in nanoscience and materials science. The OA process occurring in aqueous solution with chemical reagents has been reported many times, but there are limited studies reporting the OA growth in pure water. In this work, we report the temperature-dependent OA growth of cuprous oxide (Cu₂O) nanowires in pure water through a reagent-free electrophoretic method. Our experiments demonstrate that Cu₂O quantum dots randomly coalesced to form polycrystalline nanowires at room temperature, while they form monocrystalline nanowires at higher temperatures by the OA mechanism. DFT modeling and computations indicate that the water coverage on the Cu₂O nanoparticles could affect the particle attachment mechanisms. This study sheds light on the understanding of the effects of water molecules on the OA mechanism and shows new approaches for better controllable non-classical crystallization in pure water.

SUBMITTER: Meng J

PROVIDER: S-EPMC9417747 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Oriented attachment growth of monocrystalline cuprous oxide nanowires in pure water.

Meng Jun J Hou Chengyi C Wang Hongzhi H Chi Qijin Q Gao Yi Y Zhu Beien B

Nanoscale advances 20190325 6

As a crucial mechanism of non-classical crystallization, the oriented attachment (OA) growth of nanocrystals is of great interest in nanoscience and materials science. The OA process occurring in aqueous solution with chemical reagents has been reported many times, but there are limited studies reporting the OA growth in pure water. In this work, we report the temperature-dependent OA growth of cuprous oxide (Cu<sub>2</sub>O) nanowires in pure water through a reagent-free electrophoretic method. ...[more]

PMID: 36131967

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Project description:Augmenting the oriented attachment (OA) crystal growth phenomena, herein, we demonstrate fabrication of ultrathin CuO nanowires from self-assembled one-dimensional (1D) nanowires of Cu(OH)2 nanocrystals. A facile environmentally benign sol-gel approach, which utilizes base-catalyzed hydrolysis followed by directed self-assembly and crystal growth of nanocrystals, is developed to prepare Cu(OH)2 nanowires. The sol of Cu(OH)2 nanocrystals shows aggregative self-assembly guided by the OA crystal growth process to form ultrathin Cu(OH)2 nanowires, with an average length of 675 ± 4 nm and diameter of 6 ± 2 nm. The time-dependent UV-visible spectral traces, along with real-time imaging of nanocrystals self-assembly and growth under the transmission electron microscope, are evidenced the concept of the OA crystal growth directed self-assembly, yielding 1D colloidal nanoarrays of Cu(OH)2. The powder XRD traces collected during the self-assembly and crystal growth process reveal the directional aggregative crystal growth along the facet of [001], confirming the OA directed crystal growth and fusion of nanocrystals to yield 1D nanostructures. The gradual blue-shift in optical absorption maxima from 770 nm in initial precursor solution, to 670 nm for Cu(OH)2 nanocrystals sol, and finally to 647 nm for self-assembled 1D Cu(OH)2 nanowires have further evidenced the formation of Cu(OH)2 nanowires. Upon subjecting self-assembled Cu(OH)2 nanowires for post-annealing treatment, ultrathin CuO nanowires with average length of 7 ± 0.50 μm and diameter of 27 ± 2 nm is obtained in high purity. The experimental powder XRD patterns of Cu(OH)2 and CuO nanowires match the simulated XRD patterns, indexing the crystal unit cell structures to orthorhombic and monoclinic, respectively. The tailored narrow optical band gaps for Cu(OH)2 and CuO nanowires are found to be 1.51 eV and 1.10 eV. The theoretical band gap predicted for Cu(OH)2 nanowires is 1.52 eV and is in good agreement with its optical band gap, whereas theoretical band computed for CuO nanowires is 0.13 eV lower than from its optical band gap.

Project description:ConspectusIntuitively, chemists see crystals grow atom-by-atom or molecule-by-molecule, very much like a mason builds a wall, brick by brick. It is much more difficult to grasp that small crystals can meet each other in a liquid or at an interface, start to align their crystal lattices and then grow together to form one single crystal. In analogy, that looks more like prefab building. Yet, this is what happens in many occasions and can, with reason, be considered as an alternative mechanism of crystal growth. Oriented attachment is the process in which crystalline colloidal particles align their atomic lattices and grow together into a single crystal. Hence, two aligned crystals become one larger crystal by epitaxy of two specific facets, one of each crystal. If we simply consider the system of two crystals, the unifying attachment reduces the surface energy and results in an overall lower (free) energy of the system. Oriented attachment often occurs with massive numbers of crystals dispersed in a liquid phase, a sol or crystal suspension. In that case, oriented attachment lowers the total free energy of the crystal suspension, predominantly by removal of the nanocrystal/liquid interface area. Accordingly, we should start by considering colloidal suspensions with crystals as the dispersed phase, i.e., "sols", and discuss the reasons for their thermodynamic (meta)stability and how this stability can be lowered such that oriented attachment can occur as a spontaneous thermodynamic process. Oriented attachment is a process observed both for charge-stabilized crystals in polar solvents and for ligand capped nanocrystal suspensions in nonpolar solvents. In this last system different facets can develop a very different reactivity for oriented attachment. Due to this facet selectivity, crystalline structures with very specific geometries can be grown in one, two, or three dimensions; controlled oriented attachment suddenly becomes a tool for material scientists to grow architectures that cannot be reached by any other means. We will review the work performed with PbSe and CdSe nanocrystals. The entire process, i.e., the assembly of nanocrystals, atomic alignment, and unification by attachment, is a very complex and intriguing process. Researchers have succeeded in monitoring these different steps with in situ wave scattering methods and real-space (S)TEM studies. At the same time coarse-grained molecular dynamics simulations have been used to further study the forces involved in self-assembly and attachment at an interface. We will briefly come back to some of these results in the last sections of this review.

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Oriented attachment growth of monocrystalline cuprous oxide nanowires in pure water.

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Oriented attachment growth of monocrystalline cuprous oxide nanowires in pure water.

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