Shults Andrey A, Lu Guanyu, Caldwell Joshua D, Macdonald Janet E
Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA.
Vanderbilt Institute for Nanoscale Science and Engineering, Nashville, TN 37235, USA.
Nanoscale Horiz. 2023 Sep 26;8(10):1386-1394. doi: 10.1039/d3nh00227f.
Techniques are well established for the control of nanoparticle shape and size in colloidal synthesis, but very little is understood about precursor interactions and their effects on the resultant crystalline phase. Here we show that oleate, a surface stabilizing ligand that is ubiquitous in nanocrystal synthesis, plays a large role in the mechanism of phase selection of various metal sulfide nanoparticles when thiourea is used as the sulfur source. Gas and solid-phase FTIR, C, and H NMR studies revealed that oleate and thiourea interact to produce oleamide which promotes the isomeric shift of thiourea into ammonium thiocyanate, a less reactive sulfur reagent. Because of these sulfur sequestering reactions, sulfur deficient and metastable nanoparticles are produced, a trend seen across four different metals: copper, iron, nickel, and cobalt. At low carboxylate concentrations, powder XRD indicated that the following phases formed: covellite (CuS); vaesite (NiS); smythite (FeS), greigite (FeS), marcasite (FeS) and pyrite (FeS); and cattierite (CoS). At high sodium oleate concentration, these phases formed: digenite (CuS), nickel sulfide (NiS), pyrrhotite (FeS), and jaipurite (CoS).
在胶体合成中，控制纳米颗粒形状和尺寸的技术已经相当成熟，但对于前驱体相互作用及其对最终晶相的影响却知之甚少。在此，我们表明油酸酯（一种在纳米晶体合成中普遍存在的表面稳定配体）在以硫脲作为硫源时，对各种金属硫化物纳米颗粒的相选择机制起着重要作用。气相和固相傅里叶变换红外光谱、碳谱和氢谱研究表明，油酸酯与硫脲相互作用生成油酰胺，油酰胺促使硫脲异构化为硫氰酸铵，一种反应活性较低的硫试剂。由于这些硫螯合反应，生成了硫含量不足且亚稳的纳米颗粒，这种趋势在四种不同金属（铜、铁、镍和钴）中均有体现。在低羧酸盐浓度下，粉末X射线衍射表明形成了以下物相：铜蓝（CuS）；紫硫镍矿（NiS）；硫铁矿（FeS）、硫复铁矿（FeS）、白铁矿（FeS）和黄铁矿（FeS）；以及硫钴矿（CoS）。在高油酸钠浓度下，形成了以下物相：辉铜矿（CuS）、硫化镍（NiS）、磁黄铁矿（FeS）和贾普尔矿（CoS）。
