The symmetric and asymmetric stretching vibration from the amine ( ν s(NH 2) and ν as(NH 2) at 32 cm −1) instead disappear 47, 50. 2a), which is attributed to the ion NH 3+…SH − 47, and of a weak peak at 2564 cm −1 attributed to S–H stretching vibration 48, 49. The reaction is exothermic (∆ H 298 0 = −93.05 kJ mol −1 for NH 3 + H 2S = NH 4HS 46) and forms a stable, highly viscous fluid (it flows readily above 35–40 ☌ mesitylene or other organic solvents can also be added to decrease its viscosity and facilitate handling at room temperature).Ĭharge separation causes the appearance of a broad and weak FTIR absorption shoulder at ~2520 cm −1 (Fig. OLAHS can be produced by bubbling H 2S (either from a cylinder or produced in situ, e.g., by a reaction between bulk metal sulfide ores with an acid) into OLA. Characterization and versatility of OLAHS Therefore, making OLAHS releases energy with high atom economy and using it yields a cleaner product whose excess reagents can be easily recycled (Fig. The former reacts or leaves the system as a gas to be scrubbed back into OLA forming new precursor. Using OLAHS as a precursor releases H 2S and OLA in situ. By scrubbing H 2S with OLA-one of the most commonly used ligands in nanoparticle synthesis 45, and a biorenewable chemical-we discovered that the resulting salt, OLAHS, is a stable, highly viscous ionic liquid that forms exothermically and quantitatively. H 2S is commonly trapped and stabilized in industrial processes by scrubbing it with amines to form ammonium hydrosulfide salts 44. In summary, a lot of energy and chemicals are used to store H 2S into a dirtier (but safer) precursor of itself, and to convert it back to H 2S to initiate the synthesis.Īchieving a sustainable synthetic process using oleylammonium hydrosulfide (OLAHS) 27, 28, 29, 30 It has been shown that H 2S is the active sulfur source in several syntheses 2, 31.
Usually through the application of heat, these precursors release H 2S during the synthesis (and, if unreacted completely, during the purification process), often together with a number of by-products. Traditional precursors for the synthesis of sulfide nanocrystals (e.g., elemental sulfur (S 8), Bis(trimethylsilyl) sulfide ((TMS) 2S), thiols, xanthates, dithiocarbamates, thiourea, substituted thioureas) are obtained from H 2S through multiple energy/material intensive steps 26 (Fig. Hydrogen sulfide is the most abundant (and in part renewable) sulfur feedstock 24, 25. Other green chemistry principles, such as reducing waste, recycling, improving yield and atom economy, and minimizing auxiliaries and reaction steps have rarely been addressed 13, 22, 23. Therefore, less sustainable synthetic approaches 5, 10, 11 (e.g., high-temperature reactions 12, reactions carried out at low concentration (mM), non-stoichiometric reaction mixtures 13, size-selective precipitation 14, terminating reactions well before their completion 15 due to ripening at low supersaturation 2) are usually used to obtain the desired particle quality.Įfforts to find sustainable approaches to nanoparticle synthesis (mostly oxides and metals, rarely other compositions 11, 16, 17) have focused on finding renewable feedstocks 2, 16, 17, 18, 19, 20, 21. Finding such a precursor for the synthesis of nanoparticles is very challenging 8, 9 because their size and shape have to be tightly controlled to yield the desired physical properties. According to the principles of green chemistry 4, a renewable feedstock that leads to a product with high yield and atom economy, with little to no waste, the smallest number of steps, minimal processing and solvents, high-energy efficiency and safety is always preferable 5, 6, 7. For example, the translation of colloidal nanoparticles to technologies is limited by the poor sustainability of their synthesis 1, 2, 3.
SILICON ZINC SULFIDE CORE SHELL NANOCRYSTALS DRIVER
Sustainability is an important and necessary driver for new chemistry.
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