Spectroscopic Identification of Tri-n-octylphosphine Oxide (TOPO) Impurities and Elucidation of Their Roles in Cadmium Selenide Quantum-Wire Growth

Abstract

Tri-n-octylphosphine oxide (TOPO) is the most commonly used solvent for the synthesis of colloidal nanocrystals. Here we show that the use of different batches of commercially obtained TOPO solvent introduces significant variability into the outcomes of CdSe quantum-wire syntheses. This irreproducibility is attributed to varying amounts of phosphorus-containing impurities in the different TOPO batches. We employ 31P NMR to identify 10 of the common TOPO impurities. Their beneficial, harmful, or negligible effects on quantum-wire growth are determined. The impurity di-n-octylphosphinic acid (DOPA) is found to be the important beneficial TOPO impurity for the reproducible growth of high-quality CdSe quantum wires. DOPA is shown to beneficially modify precursor reactivity through ligand substitution. The other significant TOPO impurities are ranked according to their abilities to similarly influence precursor reactivity. The results are likely of general relevance to most nanocrystal syntheses conducted in TOPO.

Facile Synthesis of Straight and Branched CdTe Nanowires Using CdO as Precursor

“…In order to further optimize the synthesis of straight CdTe NWs, DPA was tentatively replaced by DOPA, which was shown to assist CdSe NWs growth. 18 A similar phenomenon occurred in the synthesis of CdTe NWs. While adding 0.32 mmol of DOPA, the NWs synthesized at both 275 C (Fig.…”

“…Akin to the recent report, [18][19] it was also found that the synthesis of good-quality NWs often gave irreproducible results if using different batches of commercial TOPO and TOP. In order to further optimize the synthesis of straight CdTe NWs, DPA was tentatively replaced by DOPA, which was shown to assist CdSe NWs growth.…”

Effect of the phosphorous-containing ligands on synthesis and properties of GaSe nanoparticles

“…Also, ODPA anhydride perfects crystallinity (sharpness of XRD peaks), ageing resistance and optical features of GaSe particles. On the contrary, OPA is the most stable compound among all the TOPO impurities (including TOPO itself) [14]. Shorter carbon chain phosphonic acids (methyl-or hexyl-) are more stable and have lower boiling points.…”

Surface Chemistry of Colloidal Semiconductor Nanocrystals: Organic, Inorganic, and Hybrid

“…Wang et al identified up to 10 impurities present in the commonly used 90%-purity (technical) grade of TOPO using 31 P NMR spectroscopy ( Fig. 7.2) [17]. These include phosphonic and phosphinic acids, H 3 PO 4 , and H 3 PO 3 .…”