Thyr Jakob, Montero José, Österlund Lars, Edvinsson Tomas
Department of Materials Science and Engineering, Division of Solid State Physics, Uppsala University, P.O. box 35, SE 75103 Uppsala, Sweden.
ACS Nanosci Au. 2021 Dec 21;2(2):128-139. doi: 10.1021/acsnanoscienceau.1c00040. eCollection 2022 Apr 20.
The ability to control electronic states by utilizing quantum confinement of one of the material components in heterojunctions is a promising approach to perform energy-level matching. In this work, we report the possibility to achieve optimum energy alignment in heterojunctions made from size-controlled quantum dots (Q-dots) of ZnO in combination with three copper oxides: CuO, CuO, and CuO. Quantum confinement effects on the ZnO nanoparticles in the diameter range 2.6-7.4 nm showed that the direct optical band gap decreased from 3.99 to 3.41 eV, with a dominating shift occurring in the conduction band (CB) edge, and thus the possibility to obtain close to 0.6 eV CB edge shift by controlling the size of ZnO. The effect was utilized to align the electronic bands in the ZnO Q-dot/copper oxide heterojunctions to allow for charge transfer between the materials and to test the ability to improve the photocatalytic performance for the system, evaluated by the transformation of a dye molecule in water. The catalyst materials were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet-visible (UV-vis), photoluminescence, and Raman spectroscopy. The most promising material combination was found to be the CuO copper oxide in combination with an energy aligned ZnO Q-dot system with approximately 7 nm diameter, showing strong synergy effects in good agreement with the energy-level analysis, outperforming the added effect of its individual components, ZnO-Q-dots and CuO, by about 140%. The results show that utilization of a heterojunction with controllable energy alignment can provide a drastically improved photocatalytic performance. Apart from increased photocatalytic activity, specific surface states of ZnO are quenched when the heterojunction is created. It is anticipated that the same approach can be utilized in several material combinations with the added benefit of a system with controllable overpotential and thus added specificity for the targeted reduction reaction.
通过利用异质结中一种材料组分的量子限域来控制电子态，是实现能级匹配的一种很有前景的方法。在这项工作中，我们报道了在由尺寸可控的ZnO量子点（Q点）与三种氧化铜（CuO、Cu₂O和CuO）组合而成的异质结中实现最佳能量对准的可能性。对直径范围在2.6 - 7.4 nm的ZnO纳米颗粒的量子限域效应表明，直接光学带隙从3.99 eV降至3.41 eV，主要的位移发生在导带（CB）边缘，因此通过控制ZnO的尺寸有可能获得接近0.6 eV的CB边缘位移。该效应被用于使ZnO Q点/氧化铜异质结中的电子能带对准，以允许材料之间的电荷转移，并测试改善该系统光催化性能的能力，通过水中染料分子的转化来评估。通过X射线衍射、扫描电子显微镜、紫外可见（UV-vis）、光致发光和拉曼光谱对催化剂材料进行了研究。发现最有前景的材料组合是CuO氧化铜与直径约为7 nm的能量对准的ZnO Q点系统，显示出很强的协同效应，与能级分析结果高度一致，其性能比其单个组分ZnO-Q点和CuO的相加效应高出约140%。结果表明，利用具有可控能量对准的异质结可以显著提高光催化性能。除了提高光催化活性外，形成异质结时ZnO的特定表面态会被猝灭。预计相同的方法可用于多种材料组合，该系统还具有可控过电位的额外优势，从而对目标还原反应具有更高的特异性。
