Crystal growth during hydrothermal coarsening of mercaptoethanol-capped nanocrystalline ZnS occurs via a two-stage process. In the first stage, the primary particle quickly doubles in volume. The initial growth rate can be fitted by an asymptotic curve that cannot be explained by any existing power-law dependence kinetic model developed for more coarsely crystalline material. High-resolution transmission electron microscope (HRTEM) data indicate that crystal growth within spherical nanoparticle aggregates occurs via crystallographically specific oriented attachment, despite the presence of surface-bound organic ligands. The size stabilizes for a period of time that depends on the coarsening temperature. In the second stage, following the dispersal of nanoparticles, an abrupt transition from asymptotic to cubic parabola growth kinetics occurs. The crystal growth data can be fitted by a standard Ostwald ripening volume diffusion model consistent with growth controlled by the volume diffusion of ions in solution. However, HRTEM data indicate that oriented attachment-based growth occurs in the early part of the second stage, followed by a significant reduction in aggregate surface topography, probably via surface diffusion as well as volume diffusion. We propose a new kinetic model based on oriented attachment-based growth to explain the asymptotic growth in the first stage of coarsening. The presence of surface-bound organic ligands may control the aggregation state of the nanoparticles and may permit an almost exclusive crystallographically specific oriented attachment-based growth to dominate in the first stage.

The crystal growth mechanism, kinetics, and microstructure development play a fundamental role in tailoring the materials with controllable sizes and morphologies. The classical crystal growth kinetics-Ostwald ripening (OR) theory is usually used to explain the diffusion-controlled crystal growth process, in which larger particles grow at the expense of smaller particles. In nanoscale systems, another significant mechanism named "oriented attachment (OA)" was found, where nanoparticles with common crystallographic orientations directly combine together to form larger ones. Comparing with the classical atom/molecular-mediated crystallization pathway, the OA mechanism shows its specific characteristics and roles in the process of nanocrystal growth. In recent years, the OA mechanism has been widely reported in preparing low-dimension nanostructural materials and reveals remarkable effects on directing and mediating the self-assembly of nanocrystals. Currently, the interests are more focused on the investigation of its role rather than the comprehensive insight of the mechanism and kinetics. The inner complicacy of crystal growth and the occurrence of coexisting mechanisms lead to the difficulty and lack of understanding this growth process by the OA mechanism.In this context, we review the progress of the OA mechanism and its impact on materials science, and especially highlight the OA-based growth kinetics aiming to achieve a further understanding of this crystal growth route. To explore the OA-limited growth, the influence of the OR mechanism needs to be eliminated. The introduction of strong surface adsorption was reported as the effective solution to hinder OR from occurring and facilitate the exclusive OA growth stage. A detailed survey of the nanocrystal growth kinetics under the effect of surface adsorption was presented and summarized. Moreover, the development of OA kinetic models was systematically generalized, in which the "molecular-like" kinetic models were built to take the OA nanocrystal growth behavior as the collision and reaction between molecules. The development of OA growth kinetics can provide a sufficient understanding of crystal growth, and the awareness of underlying factors in the growth will offer promising guidance on how to control the size distribution and shape development of nanostructural materials.

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The thermodynamic behaviour of small particles differs from that of the bulk material by the free energy term gammaA--the product of the surface (or interfacial) free energy and the surface (or interfacial) area. When the surfaces of polymorphs of the same material possess different interfacial free energies, a change in phase stability can occur with decreasing particle size. Here we describe a nanoparticle system that undergoes structural changes in response to changes in the surface environment rather than particle size. ZnS nanoparticles (average diameter 3 nm) were synthesized in methanol and found to exhibit a reversible structural transformation accompanying methanol desorption, indicating that the particles readily adopt minimum energy structural configurations. The binding of water to the as-formed particles at room temperature leads to a dramatic structural modification, significantly reducing distortions of the surface and interior to generate a structure close to that of sphalerite (tetrahedrally coordinated cubic ZnS). These findings suggest a route for post-synthesis control of nanoparticle structure and the potential use of the nanoparticle structural state as an environmental sensor. Furthermore, the results imply that the structure and reactivity of nanoparticles at planetary surfaces, in interplanetary dust and in the biosphere, will depend on both particle size and the nature of the surrounding molecules.

Nanoparticles may contain unusual forms of structural disorder that can substantially modify materials properties and thus cannot solely be considered as small pieces of bulk material. We have developed a method to quantify intermediate-range order in 3.4-nanometer-diameter zinc sulfide nanoparticles and show that structural coherence is lost over distances beyond 2nanometers. The zinc-sulfur Einstein vibration frequency in the nanoparticles is substantially higher than that in the bulk zinc sulfide, implying structural stiffening. This cannot be explained by the observed 1% radial compression and must be primarily due to inhomogeneous internal strain caused by competing relaxations from an irregular surface. The methods developed here are generally applicable to the characterization of nanoscale solids, many of which may exhibit complex disorder and strain.

CdS/g-C3N4 core/shell nanowires with different g-C3N4 contents were fabricated by a combined solvothermal and chemisorption method and characterized by X-ray powder diffraction, scanning electronic microscopy, transmission electron microscopy, and UV-vis diffuse reflection spectroscopy. The photocatalytic hydrogen-production activities of these samples were evaluated using Na2S and Na2SO3 as sacrificial reagents in water under visible-light illumination (λ≥420 nm). The results show that after a spontaneous adsorption process g-C3N4 is successfully coated on CdS nanowires with intimate contact and can significantly improve the photocatalytic hydrogen-production rate of CdS nanowires, which reaches an optimal value of up to 4152 μmol h(-1) g(-1) at the g-C3N4 content of 2 wt %. More importantly, g-C3N4 coating can substantially reinforce the photostability of CdS nanowires even in a nonsacrificial system. The synergic effect between g-C3N4 and CdS, which can effectively accelerate the charge separation and transfer corrosive holes from CdS to robust C3N4, was proposed to be responsible for the enhancement of the photocatalytic activity and photostability. The possible conditions necessary for the synergic effect to work in a CdS/g-C3N4 core/shell configuration is also discussed.

In order to achieve a high quantum efficiency, doping crystals with appropriate elements such as sodium cations (ref. [8]) to reduce electronic dimension is a useful method. [5,8] However, doping also tends to cause nonradiation recombination loss. [13] Therefore, a reliable and promising way is to synthesize high-quality inorganic metal halide single crystal (SC) with natural lowdimensional structure to realize stable and high quantum efficiency white-light illumination application.In this work, we successfully synthesized 1D CsCu 2 I 3 SC by replacing toxic Pb with eco-friendly and abundant Cu, and organic molecules with large-radius Cs. [12,13] The "one dimension" we noted here is localized dimension of electron. [14] Through density functional theory (DFT) calculation, in 1D CsCu 2 I 3 SC, [Cu 2 I 3 ] − octahedra contributes most electronic states, and Cs + only forms a 1D electronic structure with isolated [Cu 2 I 3 ] − in 2D direction. Therefore, CsCu 2 I 3 SC obtains a high photoluminescence quantum yield (PLQY ≈15.7%) of the IWE at room temperature. [2] We also calculated that the crystal has a high radiation recombination rate which is owning to the 1D localized electronic structure, and this rate is the key to its high PLQY. [15,16] Under a strong injection and atmospheric environment, the PL intensity of all-inorganic CsCu 2 I 3 SC only decays about 5% after 750 min ( Figure S5, Supporting Information). This excellent stability demonstrates that the all-inorganic CsCu 2 I 3 SC possesses a great prospect in high-efficiency lighting applications.High-quality CsCu 2 I 3 SCs were synthesized by antisolvent infiltration method. [17,18] Cesium iodide and cuprous (I) iodide in certain ratio were dissolved in dimethyl formamide (DMF)dimethyl sulfoxide (DMSO) (4:1) to obtain a saturated solution. Then, methanol (antisolvent) was slowly dropped into the saturated solution to form a white precipitate (the white precipitate quickly dissolved again) until it no longer dissolved. The solution was filtered and then placed in a beaker with methanol atmosphere to grow crystals. Several days later, centimeter-scale high-quality CsCu 2 I 3 SCs were obtained (refer to the Supporting information and the Experimental Section for more details). Figure 1a shows an optical image of a rod-shaped CsCu 2 I 3 SCs excited by ultraviolet light. The SC has a size of about 10 mm × 1.5 mm, being colorless and transparent at room temperature but having strong white-light emission under ultraviolet light. Crystal structure of the CsCu 2 I 3 SC was obtained through single-crystal X-ray diffraction (SCXRD) test (Figure 1b,c), which belongs to orthorhombic system. The 1D Energy-saving white lighting from the efficient intrinsic emission of semiconductors is considered as a next-generation lighting source. Currently, white-light emission can be composited with a blue light-emitting diode and yellow phosphor. However, this solution has an inevitable light loss, which makes the improvement of the energy utilization efficiency more difficult. T...

Branched SnO(2)/alpha-Fe(2)O(3) semiconductor nanoheterostructures (SNHs) of high purity were synthesized by a low-cost and environmentally friendly hydrothermal strategy, through crystallographic-oriented epitaxial growth of the SnO(2) nanorods onto the alpha-Fe(2)O(3) nanospindles and nanocubes, respectively. It was demonstrated that the SnO(2) nanorods would change their preferential growth direction on the varied alpha-Fe(2)O(3) precursors with distinct crystallographic surface, driven by decrease in the distortion energy induced by lattice mismatch at the interfaces. All of the prepared SNHs were of high purity, ascribing to the successful preinhibition of the SnO(2) homonucleation in the reaction system. Significantly, some of the SnO(2)/alpha-Fe(2)O(3) SNHs exhibited excellent visible light or UV photocatalytic abilities, remarkably superior to their alpha-Fe(2)O(3) precursors, mainly owing to the effective electron-hole separation at the SnO(2)/alpha-Fe(2)O(3) interfaces.