Coinage Metal Complexes with Di-tertiary-butyl Sulfide as Precursors with Ultra-Low Decomposition Temperature.

We report here the synthesis of [Cu2 (TFA)4 (t Bu2 S)2 ] (1), [Ag4 (TFA)4 (t Bu2 S)4 ] (2) and [AuCl(t Bu2 S)] (3) (TFA=trifluoroacetate), which decompose in solution medium at ultra-low temperature (e. g., in boiling toluene) to afford phase-pure and highly crystalline Cu9 S5 , Ag2 S and metallic Au nanoparticles, respectively. The low decomposition temperature of these precursors is attributed to the facile decomposition mechanism in the di-tertiary-butyl sulfide ligand. These results are a significant step in the direction of establishing a general low-temperature strategy spanning a range of systems including thermodynamically metastable materials and incorporate them in technologies that are sensitive to the harsh conditions.

Molecules versus Nanoparticles: Identifying a Reactive Molecular Intermediate in the Synthesis of Ternary Coinage Metal Chalcogenides.

The identification of reactive intermediates during molecule-to-nanoparticle (NP) transformation has great significance in comprehending the mechanism of NP formation and, therefore, optimizing the synthetic conditions and properties of the formed products. We report here the room temperature (RT) synthesis of AgCuSe NPs from the reaction of di-tert-butyl selenide with trifluoroacetates (TFA) of silver(I) and copper(II). The isolation and characterization of a molecular species during the course of this reaction, [Ag2Cu(TFA)4(tBu2Se)4] (1), which shows extraordinary reactivity and interesting thermochromic behavior (blue at 0 °C and green at RT), confirmed that ternary metal selenide NPs are formed via this intermediate species. Similar reactions with related dialkyl chalcogenide R2E resulted in the isolation of molecular species of similar composition, [Ag2Cu(TFA)4(R2E)4] [R = tBu, E = S (2); R = Me, E = Se (3); R = Me, E = S (4)], which are stable at RT but can be converted to ternary metal chalcogenides at elevated temperature. Density functional theory calculations confirm the kinetic instability of 1 and throw light on its thermochromic properties.

Single source precursor route to nanometric tin chalcogenides.

Low-temperature solution phase synthesis of nanomaterials using designed molecular precursors enjoys tremendous advantages over traditional high-temperature solid-state synthesis. These include atomic-level control over stoichiometry, homogeneous elemental dispersion and uniformly distributed nanoparticles. For exploiting these advantages, however, rationally designed molecular complexes having certain properties are usually required. We report here the synthesis and complete characterization of new molecular precursors containing direct Sn-E bonds (E = S or Se), which undergo facile decomposition under different conditions (solid/solution phase, thermal/microwave heating, single/mixed solvents, varying temperatures, etc.) to afford phase-pure or mixed-phase tin chalcogenide nanoflakes with defined ratios.

Room-temperature conversion of Cu2-xSe to CuAgSe nanoparticles to enhance the photocatalytic performance of their composites with TiO2.

Rational design and precise engineering are needed to optimize the structural and chemical parameters of functional materials. In this work, we demonstrate how pre-formed binary metal selenides can be an excellent synthetic choice for the synthesis of ternary coinage metal selenide nanoparticles (NPs) with controlled composition. The mild conditions required to obtain these ternary coinage metal selenide NPs offered an easy synthesis of n% CuAgSe-TiO2 (n = 0.01, 0.1, 0.3 and 1.0 mol%) nanocomposites for photocatalytic applications without compromising the structural and morphological characteristics of TiO2 and without having any organic ligands around the NPs. The use of ternary metal selenide nanocomposites CuAgSe-TiO2 results in a clear improvement in their photocatalytic activity for the photodegradation of formic acid as compared to the well-known benchmark for photocatalysis, TiO2 (P25), and its binary metal selenide nanocomposites Cu2-xSe-TiO2. DFT calculations establish semi-metallic behavior of CuAgSe NPs and show that CuAgSe-TiO2 forms a semimetallic-semiconductor heterojunction allowing a better charge separation to enhance its photocatalytic activity.

Precursor-mediated synthesis of Cu2-xSe nanoparticles and their composites with TiO2 for improved photocatalysis.

The direct synthesis of copper selenide nanoparticles from the reaction of ditertiarybutyl selenide tBu2Se with copper(ii) trifluoroacetate Cu(TFA)2 under mild conditions is reported. The isolation of a molecular species during the course of this reaction, established as [Cu2(TFA)2(tBu2Se)3], by spectroscopic studies and single crystal X-ray structure analysis, confirmed that metal selenide NPs are formed via this intermediate species containing a reduced copper center. Extending this reaction in the presence of commercial TiO2 (P25) offered an easy synthesis of copper selenide-titania nanocomposites with different Cu/Ti ratios. These nanocomposites, well-characterized by powder XRD, STEM, TEM, BET, XPS, EDX and UV-Vis studies, were examined as photocatalysts for the degradation of formic acid (FA). The nCu2-xSe-TiO2 nanocomposites with low mol% of copper selenide, i.e. n = 0.1 and 0.3 mol%, displayed a superior catalytic activity over P25, which is an established benchmark for photocatalysis under UV light.

Cubic mesoporous Ag@CN: a high performance humidity sensor.

The fabrication of highly responsive, rapid response/recovery and durable relative humidity (%RH) sensors that can precisely monitor humidity levels still remains a considerable challenge for realizing the next generation humidity sensing applications. Herein, we report a remarkably sensitive and rapid %RH sensor having a reversible response using a nanocasting route for synthesizing mesoporous g-CN (commonly known as g-C3N4). The 3D replicated cubic mesostructure provides a high surface area thereby increasing the adsorption, transmission of charge carriers and desorption of water molecules across the sensor surfaces. Owing to its unique structure, the mesoporous g-CN functionalized with well dispersed catalytic Ag nanoparticles exhibits excellent sensitivity in the 11-98% RH range while retaining high stability, negligible hysteresis and superior real time %RH detection performances. Compared to conventional resistive sensors based on metal oxides, a rapid response time (3 s) and recovery time (1.4 s) were observed in the 11-98% RH range. Such impressive features originate from the planar morphology of g-CN as well as unique physical affinity and favourable electronic band positions of this material that facilitate water adsorption and charge transportation. Mesoporous g-CN with Ag nanoparticles is demonstrated to provide an effective strategy in designing high performance %RH sensors and show great promise for utilization of mesoporous 2D layered materials in the Internet of Things and next generation humidity sensing applications.