Marzun Galina, Bönnemann Helmut, Lehmann Christian, Spliethoff Bernd, Weidenthaler Claudia, Barcikowski Stephan
Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 45141, Essen, Germany.
NanoEnergieTechnikZentrum (NETZ), University of Duisburg-Essen, 47057, Duisburg, Germany.
Chemphyschem. 2017 May 5;18(9):1175-1184. doi: 10.1002/cphc.201601315. Epub 2017 Mar 20.
The role of molecular oxygen dissolved in the solvent is often discussed as being an influential factor on particle oxidation during pulsed laser ablation in liquids. However, the formation of the particles during laser synthesis takes place under extreme conditions that enable the decomposition of the liquid medium. Reactive species of the solvent may then affect particle formation due to a chemical reaction in the reactive plasma. Experimental results show a difference between the role of dissolved molecular oxygen and the contribution from the oxygen in water molecules. Using a metallic Cu target in air-saturated water, laser ablation led to 20.5 wt % Cu, 11.5 wt % Cu O, and 68 wt % CuO nanoparticles, according to X-ray diffraction results. In contrast to particles obtained in air-saturated water, no CuO was observed in the colloid synthesized in a Schlenk ablation chamber in completely oxygen-free water. Under these conditions, less-oxidized nanoparticles (25 wt % Cu and 75 wt % Cu O) were synthesized. The results show that nanoparticle oxidation during laser synthesis is mainly caused by reactive oxygen species from the decomposition of water molecules. However, the addition of molecular oxygen promotes particle oxidation. Storage of the Cu colloid in the presence of dissolved oxygen leads, due to aging, to nanostructures with a higher oxidation state than the freshly prepared colloid. The XRD pattern of the sample prepared in air-saturated acetone showed no crystalline phases, which is possibly due to small crystallites or low particle concentration. Concentration of the particles by centrifugation showed that in the large fraction (>20 nm), even less oxidized nanoparticles (46 wt % Cu and 54 wt % Cu O) were present, although the solubility of molecular oxygen is higher in acetone than in water. The nanoparticles in acetone were stable due to a Cu-catalyzed graphite layer formed on their surfaces. The influence of the solvent on alloy synthesis is also crucial. Laser ablation of PtCu in air-saturated water led to separated large CuO and Pt-rich spherical nanoparticles, whereas homogeneous PtCu alloy nanoparticles were formed in acetone.
溶解在溶剂中的分子氧的作用常被认为是液体中脉冲激光烧蚀过程中影响颗粒氧化的一个因素。然而，激光合成过程中颗粒的形成发生在能使液体介质分解的极端条件下。由于反应性等离子体中的化学反应，溶剂的活性物种可能会影响颗粒的形成。实验结果表明，溶解分子氧的作用与水分子中氧的贡献存在差异。根据X射线衍射结果，在空气饱和的水中使用金属铜靶进行激光烧蚀，得到了20.5 wt%的铜、11.5 wt%的氧化亚铜和68 wt%的氧化铜纳米颗粒。与在空气饱和水中获得的颗粒相比，在完全无氧的水中的Schlenk烧蚀室中合成的胶体中未观察到氧化铜。在这些条件下，合成了氧化程度较低的纳米颗粒（25 wt%的铜和75 wt%的氧化亚铜）。结果表明，激光合成过程中纳米颗粒的氧化主要是由水分子分解产生的活性氧物种引起的。然而，分子氧的添加会促进颗粒氧化。由于老化，在溶解氧存在下储存铜胶体导致纳米结构的氧化态高于新制备的胶体。在空气饱和丙酮中制备的样品的XRD图谱未显示结晶相，这可能是由于微晶尺寸小或颗粒浓度低。通过离心浓缩颗粒表明，在大部分（>20 nm）中，即使分子氧在丙酮中的溶解度高于在水中，也存在氧化程度更低的纳米颗粒（46 wt%的铜和54 wt%的氧化亚铜）。丙酮中的纳米颗粒由于其表面形成了铜催化的石墨层而稳定。溶剂对合金合成的影响也至关重要。在空气饱和水中对铂铜进行激光烧蚀会导致分离出大的氧化铜和富铂球形纳米颗粒，而在丙酮中则形成均匀的铂铜合金纳米颗粒。
