Continuous Production of Cu₂ZnSnS₄ Nanocrystals in a Flow Reactor

A procedure for the continuous production of Cu₂ZnSnS₄ (CZTS) nanoparticles with controlled composition is presented. CZTS nanoparticles were prepared through the reaction of the metals' amino complexes with elemental sulfur in a continuous-flow reactor at moderate temperatures (300–330 °C). High-resolution transmission electron microscopy and X-ray diffraction analysis showed the nanocrystals to have a crystallographic structure compatible with that of the kesterite. Chemical characterization of the materials showed the presence of the four elements in each individual nanocrystal. Composition control was achieved by adjusting the solution flow rate through the reactor and the proper choice of the nominal precursor concentration within the flowing solution. Single-particle analysis revealed a composition distribution within each sample, which was optimized at the highest synthesis temperatures used

Triphenyl Phosphite as the Phosphorus Source for the Scalable and Cost-Effective Production of Transition Metal Phosphides

Transition metal phosphides have great potential to optimize a number of functionalities in several energy conversion and storage applications, particularly when nanostructured or in nanoparticle form. However, the synthesis of transition metal phosphide nanoparticles and its scalability is often limited by the toxicity, air sensitivity, and high cost of the reagents used. We present here a simple, scalable, and cost-effective “heating up” procedure to produce metal phosphides using inexpensive, low-toxicity, and air-stable triphenyl phosphite as source of phosphorus and chlorides as metal precursors. This procedure allows the synthesis of a variety of phosphide nanoparticles, including phosphides of Ni, Co, and Cu. The use of carbonyl metal precursors further allowed the synthesis of Fe₂P and MoP nanoparticles. The fact that minor modifications in the experimental parameters allowed producing nanoparticles with different compositions and even to tune their size and shape shows the high potential and versatility of the triphenyl phosphite precursor and the presented method. We also detail here a methodology to displace organic ligands from the surface of phosphide nanoparticles, which is a key step toward their application in energy conversion and storage systems

Cu₂ZnSnS₄‑Pt and Cu₂ZnSnS₄‑Au Heterostructured Nanoparticles for Photocatalytic Water Splitting and Pollutant Degradation

Cu₂ZnSnS₄, based on abundant and environmental friendly elements and with a direct band gap of 1.5 eV, is a main candidate material for solar energy conversion through both photo­voltaics and photo­catalysis. We detail here the synthesis of quasi-spherical Cu₂ZnSnS₄ nano­particles with unprecedented narrow size distributions. We further detail their use as seeds to produce CZTS-Au and CZTS-Pt hetero­structured nano­particles. Such hetero­structured nano­particles are shown to have excellent photo­catalytic properties toward degradation of Rhodamine B and hydrogen generation by water splitting

Extending the Nanocrystal Synthesis Control to Quaternary Compositions

The ample chemical and structural freedom of quaternary compounds permits engineering materials that fulfill the requirements of a wide variety of applications. In this work, the mechanisms to achieve unprecedented size, shape, and composition control in quaternary nanocrystals are detailed. The described procedure allows obtaining tetrahedral and penta-tetrahedral quaternary nanocrystals with tuned size distributions and controlled compositions from a plethora of I₂–II–IV–VI₄ semiconductors

Metal Ions To Control the Morphology of Semiconductor Nanoparticles: Copper Selenide Nanocubes

Morphology is a key parameter in the design of novel nanocrystals and nanomaterials with controlled functional properties. Here, we demonstrate the potential of foreign metal ions to tune the morphology of colloidal semiconductor nanoparticles. We illustrate the underlying mechanism by preparing copper selenide nanocubes in the presence of Al ions. We further characterize the plasmonic properties of the obtained nanocrystals and demonstrate their potential as a platform to produce cubic nanoparticles with different composition by cation exchange

Size and Aspect Ratio Control of Pd₂Sn Nanorods and Their Water Denitration Properties

Monodisperse Pd₂Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd₂Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd₂Sn nanorods to have improved catalytic performance. In view of these results, Pd₂Sn nanorods were also evaluated for water denitration

Cu₂ZnGeSe₄ Nanocrystals: Synthesis and Thermoelectric Properties

A synthetic route for producing Cu₂ZnGeSe₄ nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu₂ZnGeSe₄ is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C

Crystallographic Control at the Nanoscale To Enhance Functionality: Polytypic Cu₂GeSe₃ Nanoparticles as Thermoelectric Materials

The potential to control the composition and crystal phase at the nanometer scale enable the production of nanocrystalline materials with enhanced functionalities and new applications. In the present work, we detail a novel colloidal synthesis route to prepare nanoparticles of the ternary semiconductor Cu₂GeSe₃ (CGSe) with nanometer-scale control over their crystal phases. We also demonstrate the structural effect on the thermoelectric properties of bottom-up-prepared CGSe nanomaterials. By careful adjustment of the nucleation and growth temperatures, pure orthorhombic CGSe nanoparticles with cationic order or polytypic CGSe nanoparticles with disordered cation positions can be produced. In this second type of nanoparticle, a high density of twins can be created to periodically change the atomic plane stacking, forming a hexagonal wurtzite CGSe phase. The high yield of the synthetic routes reported here allows the production of single-phase and multiphase CGSe nanoparticles in the gram scale, which permits characterization of the thermoelectric properties of these materials. Reduced thermal conductivities and a related 2.5-fold increase of the thermoelectric figure of merit for multiphase nanomaterials compared to pure-phase CGSe are systematically obtained. These results are discussed in terms of the density and efficiency of phonon scattering centers in both types of materials

Scalable Heating-Up Synthesis of Monodisperse Cu₂ZnSnS₄ Nanocrystals

Monodisperse Cu₂ZnSnS₄ (CZTS) nanocrystals (NCs), with quasi-spherical shape, were prepared by a facile, high-yield, scalable, and high-concentration heat-up procedure. The key parameters to minimize the NC size distribution were efficient mixing and heat transfer in the reaction mixture through intensive argon bubbling and improved control of the heating ramp stability. Optimized synthetic conditions allowed the production of several grams of highly monodisperse CZTS NCs per batch, with up to 5 wt % concentration in a crude solution and a yield above 90%