Long chain alkyl phosphines providing excellent colloidal media for high-temperature experimentation
Since the first “bottom-up” syntheses of CdE type (E=S, Se, Te) Quantum Dots (QD) , trioctylphosphine oxide (TOPO:15-6660 CAS 78-50-2 , and 15-6661 CAS 78-50-2 became a nearly irreplaceable solvent (mp 51-52°C) for high-temperature preparation of various type of nanocomposites. TOPO has a very high boiling point (411°C) which is an important prerequisite for the homogeneous nucleation and good crystallinity of the nanoparticles. In addition, long alkyl chains stabilize the nanoparticles in solution, control aggregation and mitigate uncontrolled growth. However, at times, TOPO is not enough and additional surfactants are needed for better stabilization of the particles and to adjust optical properties. These surfactants with different functional groups are adsorbed on the metallic surface and have a substantial effect on the physical properties of the colloidal particles.[2-5]
One of the most popular capping surfactants used in combination with TOPO is trioctylphosphine (TOP: 15-6655 CAS 4731-53-7). In conjunction with elemental selenium, trioctylphosphine selenide (TOPSe) is an important reagent for selenation of QDs. Alternatively, CdSe QDs can be prepared in TOPO by injection of a Me2Cd:Se powder (93-3416 CAS 7782-49-2 or 34-0090) CAS7782-49-2solution into tributylphosphine or using CdO (93-4835, CAS 7782-49-2 93-4817 CAS 1306-19-0 48-0800) CAS 1306-19-0 as a precursor.
Some research groups prefer to work with technical grade TOPO (15-6660) CAS 78-50-2given its low price. However, it has been reported that the impurities present in technical grade TOPO (min. 90% purity) may have deleterious effects on the QD synthesis.[ 1, 9] Prior to use, technical grade TOPO is usually melted at temperatures between 120°C and 200°C and kept under vacuum for a period of time in order to reduce the water content. Alternatively, QDs prepared in a high purity TOPO (15-6661, CAS 78-50-2 99%) seem to possess excellent physical properties. Moreover, high purity TOPO can be used as purchased and does not require further purification.[ 10-12]
For other long-chained alkylphosphonic acids used as reagents in the chemical synthesis of nanoparticles (including QDs), please review product numbers 96-1525 CAS 96-1525(Kit); 15-0958; CAS 6874-60-8 15-1835; CAS 5137-70-2 15-2400 CAS4721-17-9 15-2410; CAS 4721-24-8 15-3510 CAS 4724-47-4 15-3520; CAS 4724-48-5 15-5145.CAS 4724-48-5