Jeong Chanyoung, Jung Jeki, Sheppard Keith, Choi Chang-Hwan
Department of Advanced Materials Engineering, Dong-eui University, Busan 47340, Republic of Korea.
Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
Nanomaterials (Basel). 2023 Jan 13;13(2):342. doi: 10.3390/nano13020342.
Control of the morphology and hierarchy of the nanopore structures of anodic alumina is investigated by employing stepwise anodizing processes, alternating the two different anodizing modes, including mild anodization (MA) and hard anodization (HA), which are further mediated by a pore-widening (PW) step in between. For the experiment, the MA and HA are applied at the anodizing voltages of 40 and 100 V, respectively, in 0.3 M oxalic acid, at 1 °C, for fixed durations (30 min for MA and 0.5 min for HA), while the intermediate PW is applied in 0.1 M phosphoric acid at 30 °C for different durations. In particular, to examine the effects of the anodizing sequence and the PW time on the morphology and hierarchy of the nanopore structures formed, the stepwise anodization is conducted in two different ways: one with no PW step, such as MA→HA and HA→MA, and the other with the timed PW in between, such as MA→PW→MA, MA→PW→HA, HA→PW→HA, and HA→PW→MA. The results show that both the sequence of the voltage-modulated anodizing modes and the application of the intermediate PW step led to unique three-dimensional morphology and hierarchy of the nanopore structures of the anodic alumina beyond the conventional two-dimensional cylindrical pore geometry. It suggests that the stepwise anodizing process regulated by the sequence of the anodizing modes and the intermediate PW step can allow the design and fabrication of various types of nanopore structures, which can broaden the applications of the nanoporous anodic alumina with greater efficacy and versatility.
通过采用逐步阳极氧化工艺来研究阳极氧化铝纳米孔结构的形态和层级控制，交替使用两种不同的阳极氧化模式，即温和阳极氧化（MA）和硬质阳极氧化（HA），并在两者之间插入一个扩孔（PW）步骤。在实验中，MA和HA分别在40 V和100 V的阳极氧化电压下，于0.3 M草酸溶液中，在1℃下进行固定时长的阳极氧化（MA为30分钟，HA为0.5分钟），而中间的PW步骤则在0.1 M磷酸溶液中，于30℃下进行不同时长的处理。特别地，为了研究阳极氧化顺序和PW时间对所形成的纳米孔结构的形态和层级的影响，逐步阳极氧化以两种不同方式进行：一种是没有PW步骤，如MA→HA和HA→MA；另一种是在两者之间插入定时的PW步骤，如MA→PW→MA、MA→PW→HA、HA→PW→HA和HA→PW→MA。结果表明，电压调制阳极氧化模式的顺序以及中间PW步骤的应用导致阳极氧化铝纳米孔结构呈现出超越传统二维圆柱形孔几何形状的独特三维形态和层级。这表明由阳极氧化模式顺序和中间PW步骤调控的逐步阳极氧化工艺能够实现各种类型纳米孔结构的设计与制造，从而可以更高效、更具通用性地拓宽纳米多孔阳极氧化铝的应用范围。
