Cu 2 ZnSnS 4 , 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 Cu 2 ZnSnS 4 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. C urrent functional nanomaterials must meet numerous very demanding properties that cannot be realized with a unique compound. Thus, the use heterostructured nanomaterials or nanocomposites is generally required in a wide range of applications. In such multiphase materials, not only the properties of the compounds but also those of their interface have a determinant influence over their performance. In particular, an efficient photocatalytic system requires an intimate interface between two phases, a light-absorbing semiconductor and a co-catalyst. Such hybrid materials can be produced with composition control at the nanometer scale through the direct growth in solution of one of the compounds from the surface of the other, which acts as a seed.1 Such direct growth of the heterostructured nanomaterial ensures a fast and efficient charge transfer between the two phases.Solar energy conversion to electricity or its storage in renewable fuels is a particularly interesting application requiring the development of high-performance, environmental friendly, and cost-effective heterostructured materials. While several semiconductors have been proposed to harvest sunlight, 2 Cu 2 ZnSnS 4 (CZTS) uniquely combines both outstanding optoelectronic properties, with a direct band gap energy of 1.5 eV, and a composition based on elements that abound in the Earth's crust. Such an environmental friendly and low-cost material has been demonstrated to be an excellent light absorber in photovoltaic devices and to have a large potential for photodegradation of pollutants and for photocatalytic generation of hydrogen and other value-added chemicals.3 CZTS and related quaternary nanocrystals can currently be produced by different procedures. 4 However, due to the difficulties in tuning the composition, phase, size, and shape of such complex materials, the preparation of CZTS-based heterostructures and particularly CZTS-metal hybrid nanoparticles has not yet been achieved.In the present work, we detail a procedure to produce colloidal CZTS-metal heterostructured nanoparticles with strongly electrically coupled interfaces. Au and Pt were the metals chosen due to their potential for plasmonic enhancement (Au) and a proper over-potential for hydrogen generation (Pt) (Scheme 1). Heterostructures were tested for photodegration of pollutants in solution using Rhodamine B as the model system, and for photocatalytic hydrogen generation from wate...

This review provides an overview of the recent achievements in self-assembly of colloidal nanoparticles with anisotropic shapes into functional superstructures.

expected to exhibit intriguing optical properties. [22,23] This is because the coordinated metal octahedra are spatially isolated by surrounding inorganic or organic cations, resulting in strong exciton confinement and self-trapped exciton (STE) emission effects. The STE emission in 0D lead-free metal halides originates from the lattice deformation of metal halide structures and possesses some typical features, such as broadband PL emission and large Stokes shift. [24][25][26] Recently, a series of 0D lead-free metal halides have been reported to exhibit intriguing STE emissions. [27][28][29][30][31][32][33][34] 0D all-inorganic copper halides are one kind of enthralling materials due to their low toxicity and earth-abundant elements. In particular, Cu atoms are fourfold coordinated with halide ions to form tetrahedral structure, [35] which favors the Jahn-Teller distortion to produce strong STE emission. [36,37] Although the synthesis and optical properties of 0D Cs 3 Cu 2 I 5 NCs have been reported, [38] it is still challenging to prepare high-quality colloidal NCs of 0D all-inorganic copper(I) halides materials with isostructural series (such as Cs 3 Cu 2 X 5, X = I, Br, and Cl), and systematically investigate their halogen-dependent optical properties. Herein, we present the colloidal syntheses and optical characterizations of Cs 3 Cu 2 X 5 (X = I, Br, and Cl) NCs. These colloidal cesium cuprous halide NCs possess well-defined shapes, narrow size distributions, and tunable emissions. Intriguingly, with halogen ions changing from I − to Br − , and Cl − , Cs 3 Cu 2 X 5 NCs exhibit gradually redshifted emission peaks. Meanwhile, the high PL quantum yield (PLQY) of 48.7% is achieved on Cs 3 Cu 2 Cl 5 NCs, while Cs 3 Cu 2 I 5 NCs exhibit considerable air stability over 45 days.In our work, Cs 3 Cu 2 X 5 NCs were obtained via a hot injection method. [39,40] In particular, Cs 3 Cu 2 I 5 NCs were prepared based on a hot plate route in air. Typically, oleylammonium iodide (OLA-I) precursor was injected into 1-octadecene (ODE) solution containing cupric acetate, cesium carbonate and oleic acid (OA) (see details in supporting information, SI) to initiate the reaction. The OLA-I precursor not only offers iodine ion, but also reduces Cu(II) to Cu(I) cations. Subsequently, Cu + combines with Cs + and I − to form Cs 3 Cu 2 I 5 NCs stabilized by OA and OLA ligands. The feeding ratio of inorganic salt precursors and the amount of OA are revealed to play key roles in producing Cs 3 Cu 2 I 5 NCs with pure orthorhombic phase ( Figures S1 and S2, Supporting Information). Figure 1a presents a representative transmission electron microscopy (TEM) image of as-prepared Cs 3 Cu 2 I 5 NCs, 0D lead-free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs 3 Cu 2 X 5 (X = I, Br, and Cl) NCs with orthorhombic structure and well-defined morphologies. All these Cs 3 Cu 2 X 5 NCs exhibit broadband blue-green photolum...

Graphical abstract Scheme 1. NiSn nanoparticles towards methanol oxidation reactions Highlights A new colloidal synthesis route for 3-5 nm NiSn bimetallic nanoparticles with tuned Ni/Sn ratio was developed. The first study of the performance of NiSn as electrocatalysis of methanol oxidation reaction (MOR) is presented. NiSn electrodes showed excellent performance towards MOR, with the most Ni-rich alloy exhibiting mass current densities of 820 mA mg -1 at 0.70 V vs. Hg/HgO, comparable to state of the art Ni electrocatalysts. Stability of NiSn electrodes was clearly superior to that of Ni-based electrodes. NiNi 2+ CH 3 OH Ni 3+Products e e e e e e e e e e e e e e e e e e e e e e e e e e AbstractNickel is an excellent alternative catalyst to high cost Pt and Pt-group metals as anode material in direct methanol fuel cells. However, nickel presents a relatively low stability under operation conditions, even in alkaline media. In this work, a synthetic route to produce bimetallic NiSn nanoparticles (NPs) with tuned composition is presented. Through co-reduction of the two metals in the presence of appropriate surfactants, 3-5 nm NiSn NPs with tuned Ni/Sn ratios were produced. Such NPs were subsequently supported on carbon black and tested for methanol electro-oxidation in alkaline media. Among the different stoichiometries tested, the most Ni-rich alloy exhibited the highest electrocatalytic activity, with mass current density of 820 mA mg -1 at 0.70 V (vs. Hg/HgO). While this activity was comparable to that of pure nickel NPs, NiSn alloys showed highly improved stabilities over periods of 10000 s at 0.70 V. We hypothesize this experimental fact to be associated to the collaborative oxidation of the byproducts of methanol which poison the Ni surface or to the prevention of the tight adsorption of these species on the Ni surface by modifying its surface chemistry or electronic density of states.

The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom–up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS–Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS–Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K.

Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystal (NC) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu3SbSe4 (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopies, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with the Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes and which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times.Peer ReviewedPostprint (author's final draft

The development of highly active, low cost and stable electrocatalysts for direct alcohol fuel cells remains a critical challenge. While Pd2Sn has been reported as an excellent catalyst for the ethanol oxidation reaction (EOR), here we present DFT analysis results showing the (100) and (001) facets of orthorhombic Pd2Sn to be more favourable for the EOR than (010). Accordingly, using tri-n-octylphosphine, oleylamine (OLA) and methylamine hydrochloride as size and shape directing agents, we produced colloidal Pd2Sn nanorods (NRs) grown in the [010] direction. Such Pd2Sn NRs, supported on graphitic carbon, showed excellent performance and stability as an anode electrocatalyst for the EOR in alkaline media, exhibiting 3 times and 10 times higher EOR current densities than that of Pd2Sn and Pd nanospheres, respectively. We associate this improved performance with the favourable faceting of the NRs.Peer ReviewedPostprint (published version

Highlights  A new procedure was developed to produce single-phase PdP2 crystals in the nanometer size region.  PdP2 nanocrystals were applied as electrocatalysts for ethanol oxidation reaction for the first time.  PdP2 nanocrystals supported on reduced graphene oxide showed excellent performances, comparable to the best Pt-and Pd-based catalysts.  PdP2 and PdP2/rGO nanocrystal-based catalysts demonstrated improved stability when compared with Pd and Pd/rGO.