Precursor-mediated synthesis of Cu_2−xSe nanoparticles and their composites with TiO₂ for improved photocatalysis

Abstract

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.

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

“…Unfortunately, our efforts to corroborate further above theory by measuring the single crystal X-ray structure of 1 at room temperature were not successful due to instability of this compound which decomposed after few frames of data collections. previously reported by us, 27 can be explained by the fact that only half of the Cu(TFA)2 is consumed during the formation of the heterometallic 1 which has 2:1 ratio of the Ag and Cu atoms. The blue crystals of 1 were isolated and washed with cold n-pentane.…”

“…The tendency of the TFA to act as an assembling ligand to afford heterometallics has previously been highlighted. 31 27,28 The four oxygen atoms around Cu1 are essentially in the same plane and at almost same distance from the copper (Cu-O = 1.941(6)-1.944(6) Å]. 32 These trinuclear Ag2Cu species are discrete in nature with shortest intermolecular Ag…Ag interaction being 8.5 Å (Fig.…”

“…We then attempted to mimic the above reaction with the Me2E (E = Se, S) ligands, for which there is no possibility of decomposition via β-hydrogen elimination pathway. 27,28,35,36 As expected, these reactions yielded molecular complexes of similar composition and angles (°): Ag1-S1 2.458(2), Ag1-S2 2.476(2), Ag1-O1 2.511(6), Ag1-O3 2.528(6), Ag2-S4 2.486(2), Ag2-S3 2.461(2), Ag2-O8 2.501 7, Ag2-O6 2.438 7, Cu1-O2…”

“…1.933(5), Cu1-O4 1.946(5), Cu1-O7 1.932(6), Cu1-O5 1.934(6), S1-Ag1-S2 153.63 7 formed via these intermediates. 27,28 The synthesis of ternary metal chalcogenide materials is even more challenging and there are very few single source precursors (SSPs) reported so far for them. The heterometallics [Ag2Cu(TFA)4(R2E)4] (R = Me, t Bu; E = S, Se) described here not only fill this clear void of SSPs for such ternary chalcogenide materials, but more importantly, some of them were isolated as highly reactive intermediates, which can provide tailored reactivity for investigating the fundamentals of nucleation and growth of these ternary materials.…”

“…[17][18][19][20][21][22] The use of non-silylated R2E ligands, which have high coordinating ability as compared to R2E2, [23][24][25][26] may potentially lead to isolation of intermediate molecular species which could throw light on the possible mechanism of molecule-to-nanoparticle transformation. 27,28 Starting with a well-defined precursors may also overcome the problem of controlling the stoichiometry of the constituent elements, which often hinders the reproducibility in the synthesis of ternary metal chalcogenides. In this work, we sought to explore divergent reactivity of R2E (E = Se, S: R = Me, t Bu) with Cu(TFA)2 and Ag(TFA) as a means to establish a well-defined chemical route for the mild synthesis of the ternary copper silver chalcogenide nanoparticles by attempting to isolate and characterize molecular intermediates on the way to materials in the solution phase.…”