Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States.
Langmuir. 2011 Apr 5;27(7):3672-7. doi: 10.1021/la105147u. Epub 2011 Feb 28.
Chemical bath deposition (CBD) is an inexpensive and reproducible method for depositing ZnO nanowire arrays over large areas. The aqueous Zn(NO(3))(2)-hexamethylenetetramine (HMTA) chemistry is one of the most common CBD chemistries for ZnO nanowire synthesis, but some details of the reaction mechanism are still not well-understood. Here, we report the use of in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to study HMTA adsorption from aqueous solutions onto ZnO nanoparticle films and show that HMTA does not adsorb on ZnO. This result refutes earlier claims that the anisotropic morphology arises from HMTA adsorbing onto and capping the ZnO {10 1 0} faces. We conclude that the role of HMTA in the CBD of ZnO nanowires is only to control the saturation index of ZnO. Furthermore, we demonstrate the first deposition of ZnO nanowire arrays at 90 °C and near-neutral pH conditions without HMTA. Nanowires were grown using the pH buffer 2-(N-morpholino)ethanesulfonic acid (MES) and continuous titratation with KOH to maintain the same pH conditions where growth with HMTA occurs. This semi-batch synthetic method opens many new opportunities to tailor the ZnO morphology and properties by independently controlling temperature and pH.
化学浴沉积（CBD）是一种在大面积上沉积 ZnO 纳米线阵列的廉价且可重复的方法。水相 Zn(NO(3))(2)-六亚甲基四胺（HMTA）化学是 ZnO 纳米线合成中最常用的 CBD 化学之一，但反应机制的一些细节仍未得到很好的理解。在这里，我们报告了使用原位衰减全反射傅里叶变换红外（ATR-FTIR）光谱研究 HMTA 从水溶液吸附到 ZnO 纳米颗粒膜上的情况，并表明 HMTA 不会吸附在 ZnO 上。这一结果反驳了早先关于各向异性形貌是由于 HMTA 吸附在 ZnO{1010}面上并对其进行封端的说法。我们得出结论，HMTA 在 CBD 合成 ZnO 纳米线中的作用仅在于控制 ZnO 的过饱和度指数。此外，我们还展示了在没有 HMTA 的情况下，于 90°C 和近中性 pH 条件下首次沉积 ZnO 纳米线阵列。使用 pH 缓冲剂 2-（N-吗啉基）乙磺酸（MES）进行纳米线生长，并通过连续滴加 KOH 来维持与 HMTA 生长相同的 pH 条件。这种半分批合成方法通过独立控制温度和 pH 值，为调整 ZnO 的形貌和性能提供了许多新的机会。
