Electrochemical Synthesis of TiO₂ Photocatalyst with Anodic Porous Alumina

Hattori, Takanori,Fujino, Takayoshi,Ito, Seishiro Materials Research Society of Korea 2007 한국재료학회지 Vol.17 No.11

Aluminum was anodized in a $H_2SO_4$ solution, and titanium (IV) oxide ($TiO_2$) was electrodeposited into nanopores of anodic porous alumina in a mixed solution of $TiOSO_4$ and $(COOH)_2$. The photocatalytic activity of the prepared film was analyzed for photodegradation of methylene blue aqueous solution. Consequently, we found it was possible to electrodeposit $TiO_2$ onto anodic porous alumina, and synthesized it into the nanopores by hydrolysis of a titanium complex ion under AC 8-9 V when film thickness was about $15-20{\mu}m$. The photocatalytic activity of $TiO_2$-loaded anodic porous alumina ($TiO_2/Al_2O_3$) at an impressed voltage of 9 V was the highest in every condition, being about 12 times as high as sol-gel $TiO_2$ on anodic porous alumina. The results revealed that anodic porous alumina is effective as a substrate for photocatalytic film and that high-activity $TiO_2$ film can be prepared at low cost.

Effect of Aluminum Purity on the Pore Formation of Porous Anodic Alumina

Kim, Byeol,Lee, Jin Seok Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.2

Anodic alumina oxide (AAO), a self-ordered hexagonal array, has various applications in nanofabrication such as the fabrication of nanotemplates and other nanostructures. In order to obtain highly ordered porous alumina membranes, a two-step anodization or prepatterning of aluminum are mainly conducted with straight electric field. Electric field is the main driving force for pore growth during anodization. However, impurities in aluminum can disturb the direction of the electric field. To confirm this, we anodized two different aluminum foil samples with high purity (99.999%) and relatively low purity (99.8%), and compared the differences in the surface morphologies of the respective aluminum oxide membranes produced in different electric fields. Branched pores observed in porous alumina surface which was anodized in low-purity aluminum and the size; dimensions of the pores were found to be usually smaller than those obtained from high-purity aluminum. Moreover, anodization at high voltage proceeds to a significant level of conversion because of the high speed of the directional electric field. Consequently, anodic alumina membrane of a specific morphology, i.e., meshed pore, was produced.

나노 기공성 알루미나의 생성과 화학적 용해 거동

오한준(Han-Jun Oh),정용수(Yongsoo Jeong),지충수(Choong-Soo Chi) 한국표면공학회 2010 한국표면공학회지 Vol.43 No.5

For an application as templates of high performance with proper pore size and shape, porous anodic alumina films were prepared by anodization in oxalic acid, and formation behaviors of anodic alumina layer as well as dissolution process in acid solution have been investigated. The surface characteristics on anodic alumina layer were shown to be dependent on the fabrication parameters for anodization. For the dissolution behaviors of anodic alumina, the thickness of the barrier-type alumina layer decreased linearly with the rate of 0.98 ㎚/min in H3PO4 solution at 30℃. The changes of the anodic alumina layers were analyzed by SEM and TEM.

Correlation between Self-Organized Pore Formation Behaviors and the Current-Time Characteristics in Porous Anodic Alumina: A Quantitative Analysis of the Voltage Dependence of Pore Morphological Changes

최용찬,J. Y. Hyeon,부상돈 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1

We report the self-organized pore formation behaviors of porous anodic alumina (PAA) by investigating the correlation between morphological changes at the metal/oxide interface and the current-time I-t characteristics during anodization. PAA is fabricated by anodizing aluminum at voltages of 20-60 V in 0.3 M oxalic acid. In comparing the I-t curves of PAA anodized at various voltages, we found that all curves showed similar shapes, regardless of voltage, but that the values and times at the maximum and the minimum points of the curves were different depending on the voltages. In order to explain the correlation between the morphological changes and the I-t curves, we categorized the curves into four regions based on their common features: Regions I, II,III, and IV correspond to barrier layer formation, pore initiation, steady-state pore formation, and self-arrangement of pores, respectively. Then, we proposed an equation consisting of four formulas,one corresponding to each region. We found that the pore size increased and its density decreased during the anodization process of regions I-III, whereas they remained constant after the anodization of region III. The size, density, and arrangement of pores were also governed by the anodizing voltage. These changes could be explained using variations of coefficients in the formulas.

Effect of Aluminum Purity on the Pore Formation of Porous Anodic Alumina

Byeol Kim,이진석 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.2

Anodic alumina oxide (AAO), a self-ordered hexagonal array, has various applications in nanofabrication such as the fabrication of nanotemplates and other nanostructures. In order to obtain highly ordered porous alumina membranes, a two-step anodization or prepatterning of aluminum are mainly conducted with straight electric field. Electric field is the main driving force for pore growth during anodization. However, impurities in aluminum can disturb the direction of the electric field. To confirm this, we anodized two different aluminum foil samples with high purity (99.999%) and relatively low purity (99.8%), and compared the differences in the surface morphologies of the respective aluminum oxide membranes produced in different electric fields. Branched pores observed in porous alumina surface which was anodized in low-purity aluminum and the size; dimensions of the pores were found to be usually smaller than those obtained from high-purity aluminum. Moreover, anodization at high voltage proceeds to a significant level of conversion because of the high speed of the directional electric field. Consequently, anodic alumina membrane of a specific morphology, i.e., meshed pore, was produced.

Highly ordered anodic alumina nanotemplate with about 14 nm diameter

정수환,Tae-Yong Kim 한국화학공학회 2008 Korean Journal of Chemical Engineering Vol.25 No.3

A novel method for the fabrication of highly ordered nanopore arrays with very small diameter of 14 nm was demonstrated by using low-temperature anodization. Two-step anodization was carried out at 25 V, sulfuric acid concentration of 0.3M, and electrolyte temperature of −15 oC. After anodization, a regular pore array with mean diameter of 14 nm and interpore distance of 65 nm was formed. The pore diameter and regular arrangement were confirmed by scanning electron microscopy (SEM) and fast Fourier transformation (FFT), respectively. The present results strongly suggest that the diameter of pores in a highly ordered alumina template can be reduced by lowering the anodization temperature

FERROELECTRIC NANOTUBE (FNT) CAPACITORS FOR HIGH-DENSITY SEMICONDUCTOR MEMORIES

SHAISLAMOV, U.,SEO, B.,LEE, S.,PARK, B.,KIM, I.,HONG, S.,YANG, B. Taylor Francis 2006 Integrated ferroelectrics Vol.81 No.1

<P>Ferroelectric high-density memories (> 64 Mb) using the integrated cells of size less than 0.l um 2 will be more increased in upcoming ubiquitous era. Thus in this report we suggest fabrication of 3D nanotube capacitors for high-density semiconductor memories. Herein we discuss preparation of Pt and BLT nanotubes as an initial step toward 3D nanotube capacitors. We have used simple and convenient method, wetting of pore walls of porous templates. Templates could be either macroporous Si or nanoporous alumina. In future, characteristics of Pt and BLT nanotubes by PFM and TEM will be performed in order to make next steps toward 3D nanotube capacitors.</P>

양극산화법에 의한 나노와이어 제조I. 알루미나 나노 템플레이트의 특성

조수행,오한준,박치선,장재명,지충수,Jo, Su-Haeng,O, Han-Jun,Park, Chi-Seon,Jang, Jae-Myeong,Ji, Chung-Su 한국재료학회 2002 한국재료학회지 Vol.12 No.2

Anodic alumina layer can be used as templates for preparation of nano-structured materials, because porous oxide layer on aluminum shows a uniform pore size and a high pore density. In order to find out possibility for template material to prepare nano wire, the effects of the anodic applied potential, anodic time and the temperature of electrolyte on pore diameter of anodic alumina layer were studied using SEM and AFM. The pore diameter of anodic alumina layer increased with applied anodic potential and electrolytic temperature. Especially, the pore diameter of anodic oxide layers formed in chromic acid can be well replicated by widening process in $H_3$$PO_4$solution.

양극산화 용액 및 화학적 식각이 다공성 양극산화 알루미나 형태에 미치는 영향

김진우,최기쁨,조삼연,부상돈 한국물리학회 2016 새물리 Vol.66 No.9

We report here the effects of an anodizing solution and chemical etching on the shape of porous anodic alumina (PAA). PAA was synthesized by using a conventional anodization method for aluminum in two mixed solutions: (1) an oxalic acid and phosphoric acid mixture and (2) an oxalic acid and ethanol mixture. We prepared various samples of PAA anodized at various voltages from 40 to 120 V, various mixing ratios, and various etching times; then, we examined their pore morphologies. We found that the inter-pore distance of PAA grown in the oxalic acid and phosphoric acid solution could be controlled over a wide range from 192 nm to 282 nm. The fastest PAA growth rate of about 153.15 nm/min was found for the mixed anodizing solution of 95% oxalic acid and 5% ethanol. Also, the pore arrangement of PAA grown in the mixed solution of 90% oxalic acid and 10% ethanol was the best. The pore size, inter-pore distance, and pore arrangement of PAA can be controlled in various metal-oxide nanostructures. 본 연구에서는 옥살산 그리고 인산 혼합 용액, 옥살산 그리고 에탄올 혼합 용액의 두 가지 혼합 용액에서 2차 양극산화 방법으로 다공성 양극산화 알루미나 (porous anodic alumina, PAA)를 성공적으로 성장시켰다. 이 과정에서 양극산화 전압과 용액 혼합 비율이 PAA에서의 기공 크기, 기공 사이의 거리, 기공 정렬도 그리고 기공 성장 속도에 미치는 영향을 조사하였다. 옥살산 그리고 인산 혼합 용액에서 성장된 PAA의 경우 기공 사이의 거리를 192 nm 에서부터 282 nm까지의 넓은 범위에서 조절하면서 성장시킬 수 있었다. 또한 5%의 에탄올이 들어 있는 옥살산 그리고 에탄올 혼합 용액에서 성장된 PAA가 가장 큰 성장속도, 약 153.15 nm/min을 가지는 것을 알 수 있었다. 그리고 10%의 에탄올이 들어 있는 옥살산 그리고 에탄올 혼합 용액에서 성장된 PAA가 가장 좋은 기공 정렬도를 가지는 것을 알 수 있었다. 아울러 기공 크기 조절의 경우, 화학적 식각을 통해서 기공의 크기를 32 nm에서 64 nm까지 넓힐 수 있었다. 이러한 기공 크기, 기공 사이의 거리, 기공 정렬도 조절은 다양한 기능성 나노 구조물 제작에 있어서 주형틀로 사용되는 PAA 조절 기술로 사용될 수 있다.

Effects of Impurities on Phase Transition Changes According to Heat Treatment of Porous Anodic Alumina Fabricated in Oxalic Acid and Phosphoric Acid Electrolytes

Sam Yeon Cho,Jin Woo Kim,Sang Don Bu 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.9

In this study, porous anodic alumina (PAA) was fabricated using oxalic acid and phosphoric acid as electrolytes, and the effects of impurities on the phase transition of PAA according to changes in the heat-treatment temperature were investigated. The average pore diameter of PAA fabricated using oxalic acid and phosphoric acid increased from 43 nm to 64 nm and from 145 nm to 183 nm, respectively, in proportion to the increase in the heat-treatment temperature. An X-ray diffraction (XRD) structure analysis revealed the structure of PAA fabricated in oxalic acid to be amorphous at or below 800 ◦ C and it changed to γ-alumina at 850 ◦ C. At higher temperatures, as the heattreatment temperature was increased, a coexistence of γ- and δ-alumina phases was observed in the 900 − 1000 ◦ C range, and the existence of δ-alumina was observed only at 1050 ◦ C. Finally, at 1100 ◦ C, a coexistence of δ- and α-alumina phases was observed. On the other hand, for PAA fabricated in phosphoric acid, while an amorphous structure appeared at or below 800 ◦ C, as was the case with PAA fabricated in oxalic acid, only δ-alumina existed in the 850 − 1100 ◦ C range. On the basis of 27Al magic-angle-spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectrometry (FT-IR) results, we concluded that such a discrepancy in the phase transition was attributable to interactions between impurities originating from the electrolytes.