Phase-Programmed Nanofabrication: Effect of Organophosphite Precursor Reactivity on the Evolution of Nickel and Nickel Phosphide Nanocrystals

Abstract

A better understanding of the chemistry of molecular precursors is useful in achieving more predictable and reproducible nanocrystal preparations. Recently, an efficient approach was introduced that consists of finetuning the chemical reactivity of the synthetic molecular precursors used, while keeping all other reaction conditions constant. Using nickel phosphides as a research platform, we have studied how the chemical structure and reactivity of a family of commercially available organophosphite precursors (P(OR)3, R = alkyl or aryl) alter the preparation of metallic and metal phosphide nanocrystals. Organophosphites are a versatile addition to the pnictide synthetic toolbox, nicely complementing other available precursors such as elemental phosphorus or trioctylphosphine (TOP). Experimental and computational data show that different organophosphite precursors selectively yield Ni, Ni12P5, and Ni2P and that these phases evolve over time through separate mechanistic pathways. Based on our observations, we propose that nickel phosphide formation requires organophosphite coordination to a nickel precursor, followed by intramolecular rearrangement. We also propose that metallic nickel formation involves outer sphere reduction by uncoordinated organophosphite. These two independent pathways are supported by the fact that preformed Ni nanocrystals do not react with some of the most reactive phosphide-forming organophosphites, failing to evolve into nickel phosphide nanocrystals. Overall, the rate at which organophosphites react with nickel(II) chloride or acetate to form nickel phosphides increases in the order P(OMe)3 < P(OEt)3 < P(OnBu)3 < P(OCH2tBu)3 < P(OiPr)3 < P(OPh)3. Some organophosphites, such as P(OMe)3 or P(OiPr)3, transiently form zerovalent, metallic nickel, while this is the only persistent product observed with the bulky organophosphite P(O-2,4-tBu2C6H4)3. We expect that these results will alleviate the need for timeconsuming testing and random optimization of several different reaction conditions, thus enabling a faster development of these and similar pnictide nanomaterials for practical applications. Disciplines Chemistry CommentsReprinted (adapted) with permission from Chemistry of Materials 27 (2015) ABSTRACT: A better understanding of the chemistry of molecular precursors is useful in achieving more predictable and reproducible nanocrystal preparations. Recently, an efficient approach was introduced that consists of fine-tuning the chemical reactivity of the synthetic molecular precursors used, while keeping all other reaction conditions constant. Using nickel phosphides as a research platform, we have studied how the chemical structure and reactivity of a family of commercially available organophosphite precursors (P(OR) 3 , R = alkyl or aryl) alter the preparation of metallic and metal phosphide nanocrystals. Organophosphites are a versatile addition to the pnictide synthetic toolbox, nicely complementing other available precursors such as elemental phosphorus or trioctylphosphine (TO...

Triphenyl Phosphite as the Phosphorus Source for the Scalable and Cost-Effective Production of Transition Metal Phosphides

“…To the best of our knowledge, in only one previous report the reactivity of TPOP was studied among that of several other candidates as a source of phosphorous for the synthesis of nickel phosphide. 63 Surprisingly, in spite of the promising results obtained in this previous work, no follow up report has considered TPOP as phosphorous precursor. Apart from this, TPOP has been rarely used as a stabilizer in the synthesis of Au 64 and CuInS 2 65, 66 NPs.…”

Soft Chemistry, Coloring and Polytypism in Filled Tetrahedral Semiconductors: Toward Enhanced Thermoelectric and Battery Materials

“…Solution phase LiZnP was originally prepared by injecting diethyl zinc into a solution containing lithium hydride in trioctylphosphine at 250 °C (nucleation temperature), followed by subsequent heating to 330 °C (growth temperature). The reaction proceeds through a mechanism similar to some binary metal phosphides . Specifically, metallic Zn seeds are formed upon injection of the zinc precursor, followed by intercalation of Li and P. This synthesis is also extremely flexible, with multiple Li, Zn, and P precursors able to be used successfully.…”

“…[12] Solution phase LiZnP was originally prepared by injecting diethyl zinc into as olution containing lithium hydride in trioctylphosphine at 250 8C( nucleation temperature), followed by subsequenth eatingt o3 30 8C( growth temperature).T he reaction proceeds through am echanism similart os omeb inary metal phosphides. [25][26][27][28][29][30][31][32][33] Specifically,m etallicZ ns eeds are formed upon injection of the zinc precursor,f ollowed by intercalationo fL ia nd P. This synthesis is also extremelyf lexible, with multiple Li, Zn, and Pp recursors able to be used successfully.F or instance, the homogeneity and overall controlo ft he reactionc an be increased with organolithium reagents such as n-butyllithium or lithium diisopropylamide. These reagents undergo b-hydride elimination to yield LiH in situ when heated past % 125 8C.…”

Mild and Selective Hydrogenation of Nitrate to Ammonia in the Absence of Noble Metals

“…35 Initially thought to be a semiconductor, electronic structure calculations revealed that bulk Ni 2 P is actually metallic. 36,37,38 Interestingly, their resemblance to noble metals goes well beyond HER, as first row transition metal phosphides are also active catalysts in hydrotreating (HDX, X = S or hydrodesulfurization, 39,40,41,42 O or hydrodeoxygenation 43,44,45 , and N or hydrodenitrogenation 46,47 ), alkyne hydrogenation, 48,49,50,51 and hydrodearomatization reactions. 52 The ability of Ni 2 P and other Earth-abundant, binary metal phosphides to readily and reversibly adsorb hydrogen (H 2 ), perform a wide range of hydrogenation-like reactions, and achieve high product selectivities strongly suggest that they could also catalyze the hydrogenation of other, typically more challenging reactants, such as nitrate (NO 3 -).…”