SYNTHESIS AND ENVIRONMENTAL APPLICATION OF METAL OXIDE THIN FILMS AND MAGNETIC-CORED DENDRIMER

Abstract

Advances in nanoscale science and engineering suggest that many of the current problems involving water quality could be resolved or greatly ameliorated using nanotechnology. This dissertation not only presents practical methods to synthesize novel nanomaterials for water purification, but also tries to understand the underlying scientific principles related with the proposed nanomaterials and the contaminants in this dissertation. A combination of oxygen plasma and rapid thermal annealing was suggested in order to oxidize the surface of titanium into TiO2 in Chapter 2. A plasma was formed by employing pure oxygen at 150 W, 300 W, and 400 W under a pressure of 7.5 to 8.5 Pa for 5 to 10 min. The TiO2 was then subjected to rapid thermal annealing (RTA) at a temperature of 400 to 500 ℃ for 1 min. An RF power of 300 W for 5 min was observed to be sufficient to produce an optimal photocatalytic TiO2 film. Optimal conditions were confirmed by additional experiments involving humic acid (HA) degradation of the TiO2 films. When compared to a traditional TiO2 film, a TiO2 film prepared with an oxygen-plasma treatment and RTA system exhibited improved photocatalytic capability for HA photodegradation in an aqueous solution. Therefore, this process proposed in this work can be an excellent alternative to the traditional method for fabricating photocatalytic TiO2 films. In Chapter 3, titanium dioxide nanotubes (ntTiO2) were fabricated by self-organized electrochemical potentiostatic anodization of titanium thin film. Then anodic condition was maintained at 20 ℃ for 20 min. Field Emmision Scanning Electron Microscopy (FE-SEM) and X-ray Diffractometer (XRD) were used to characterize the micromorphology and crystalline structure of the titanium dioxide nanotube thin film. A diameter of the nanotube was 100 nm and the length was approximately 1 µ m. Then ntTiO2 underwent annealing process at 450 ℃ and observed an anatase phase. To evaluate photocatalytic capacity of ntTiO2 thin film, degradation of humic acid (HA) was carried out. The photocatalytic capacity of ntTiO2 is six times higher than powder-based photocatalysis. Iron oxide nanoleaf (INL) were fabricated with potentiostatic anodization of iron foil in 1M Na2SO4 containing 0.5 wt% NH4F electrolyte, holding the potential at 20, 40 and 60 V for 20 min, respectively, in Chapter 4. The potential of 40 V for 20 min was observed to be sufficient to produce an optimal catalytic film. Cyanide dissolved in water was degraded through the Fenton-like reaction using INT film with hydrogen peroxide. In case of INL-40V in the presence of H2O2 3%, the first-order rate constant was found to be 1.7 × 10-2 min-1, and indicated to be 1.2 × 10-2 min-1 on commercial magnetite powder. Therefore, the process proposed in this chapter can be an excellent alternative to the traditional catalyst for Fenton-like reaction. In Chapter 5, we reported the synthesis of self-organized nanoporous zero valent iron film treated with anodization and electro-reduction of iron foil. The iron nanotubes were fabricated in 1M Na2SO4 + 0.5 wt% NaF electrolyte by supplying constant electric currents of 50 mV/s, and holding the potential at 20 V for 20 min. A nanoporous shape was produced by anodic oxidation of Iron film. After anodizing process, electro-reduction of nanoporous iron film converted crystallization iron oxide to zero valent iron. Electro-reduction process was carried out by electro-reducing with power supply and holding the potential at 20 V for 20 min. The surface of iron nanotube film was examined by BET and the thickness of the oxidized films was evaluated by Scanning Electron Microscope (SEM). The crystalline structures of the fabricated films were evaluated using X-ray diffraction (XRD). Magnetic-cored dendrimer (MCD) was synthesized on the surface of magnetite nanoparticles (MNP) for heavy metal binding in Chapter 6. The synthesized MNP and MCD were characterized using FT-IR, FE-TEM, XRD, and SQUID. Transmission electron microscopy (TEM) revealed clear dispersion of the MCD in methanol solution. Cd ion was bound from 10 mg/L solutions in the batch-type procedure and the binding efficiency was 99 % at a pH of 7. Moreover the binding/unbinding of Cd was evaluated in six cycles, and demonstrated high regeneration rates of about 97 %. Consequently, the novel engineering nanomaterials are certainly considered to be a highly effective and green technology for environmental purification. |나노과학과 공학의 발전은 수자원의 질을 포함한 현재의 많은 문제들의 해결법을 제시할 수 있으며, 나노기술의 발전을 통해 개발되는 나노흡착제, 나노촉매, 대생물작용성 나노파티클, 나노구조의 멤브레인이나 필터를 사용하여 크게 개선이 가능하다. 더불어 나노기술이 적용된 물질들은 수질기준과 건강기준을 만족시킬 수 있도록 독성물질의 농도를 ppb 단위까지 저감이 가능하도록 도와줄 수 있다. 이 논문에서는 합성된 나노물질들을 이용하여 수질정화에 적용한 묶음이다. 첫 번째 연구는 산소플라즈마와 급속열처리를 이용하여 titanium 표면을 TiO2로 산화하는 방법을 제안하였다. 플라즈마는 순수한 산소를 7.5-8.5 Pa하에서 각각 5분과 10분간 150 W, 300 W, 400 W의 전압으로 수행하였다. 또한 이 박막의 경우 급속열처리법에 의해 400에서 500 ℃에서 1 분간 수행하였다. 이 결과 RF-power가 300 W에서 5분간 산화하여 급속열처리 하였을 때 최적의 광촉매 효율을 나타내었다. 따라서 이 공정은 기존의 광촉매 박막제작방법의 대체가 가능한 우수한 효율을 갖는다. 두 번째 연구는 전기화학적 양극산화에 의한 titanium dioxide nanotube를 제작하였다. 전해질은 1 M의 황산나트륨과 0.5 wt% 플루오르화나트륨으로 제조되었으며, 양극산화의 조건은 20 ℃에서 20 분간 수행하였다. 또한 FE-SEM과 XRD를 이용하여 형태와 결정형을 분석하였다. 이렇게 제작된 nanotube의 직경은 100 nm이고, 길이는 대략 1 µ m 정도이다. 이 후 450 ℃에서 어낼링을 수행하였고, 아나타제 결정형을 관찰하였다. 이 연구에서 titanium dioxide nanotube의 효율을 평가하기 위해 휴믹산 광분해 실험을 수행하였고, 그 결과는 Langmuir-Hinshelwood kinetic 패턴을 따르는 것으로 나타났다. 또한 패러데이법칙을 이용하여 반응을 정량적으로 평가하였는데, titanium dioxide nanotube의 경우 기존의 광촉매 파우더에 비해 약 6배정도 더 높은 효율을 나타내는 것으로 나타났다. 세 번째 연구는 전기화학적 양극산화에 의해 산화철 나노잎구조를 제작하였다. 전해질은 1 M의 황산나트륨과 0.5 wt% 플루오르화 암모늄으로 제조되었으며, 양극산화의 조건은 20 V, 40 V, 60 V에서 20 분간 수행하였다. 유사펜톤반응을 통한 시안을 분해하는 실험으로 박막이 40 V에서 20 분간 수행하였을 경우 촉매로서의 최적의 효율을 나타내었다. 이 경우 40 V에서 제작된 나노잎 행태의 산화철 박막이 과수 3 %로 유사펜톤반응을 진행하였을 경우 1.7 × 10-2 min-1의 일차반응상수를 나타내었고, 상용 마그네타이트 촉매의 경우 1.2 × 10-2 min-1 의 값을 나타내었다. 네 번째 연구는 전기화학적 양극산화방법과 전기적 음극환원법을 이용하여 영가철 나노튜브를 제작하는 연구를 수행하였다. 전해질은 1 M의 황산나트륨과 0.5 wt% 플루오르화 나트륨으로 제조되었으며, 전류는 50 mV/s로 공급되었다. 양극산화 시에는 20 V로 20 분간 수행하였고, 이 후 서로의 극을 바꾸어 20 V에서 20 분간 음극환원을 진행하였다. 이 논문의 마지막 연구로는 마그네타이트 나노파티클 표면에 중금속인 카드뮴의 흡착이 강화된 자성중심 덴드리머를 합성하였다. 이 후 합성된 마그네타이트 나노파티클과 자성중심 덴드리머는 FT-IR, FE-TEM, XRD, SQUID로 분석하였으며, TEM을 이용하여 크기를 측정하였다. 카드뮴 이온은 10 mg/L로 제작하여 pH 7에서 배치타입으로 흡착실험을 수행하였다. Langmuir와 Freundlich 등온흡착식은 둘 다 잘 맞았으며, 6회의 흡/탈착 실험을 수행하여 97 %의 높은 재생률을 나타내었다. 결론적으로 이러한 새로운 공학나노물질들은 높은 효율과 녹색기술로서 환경정화기술로 사용하기에 충분히 고려가능하며, 이것은 또한 다른 산업분야에서도 적용가능할 것으로 확신한다.; m. Then ntTiO2 underwent annealing process at 450 ℃ and observed an anatase phase. To evaluate photocatalytic capacity of ntTiO2 thin film, degradation of humic acid (HA) was carried out. The photocatalytic capacity of ntTiO2 is six times higher than powder-based photocatalysis. Iron oxide nanoleaf (INL) were fabricated with potentiostatic anodization of iron foil in 1M Na2SO4 containing 0.5 wt% NH4F electrolyte, holding the potential at 20, 40 and 60 V for 20 min, respectively, in Chapter 4. The potential of 40 V for 20 min was observed to be sufficient to produce an optimal catalytic film. Cyanide dissolved in water was degraded through the Fenton-like reaction using INT film with hydrogen peroxide. In case of INL-40V in the presence of H2O2 3%, the first-order rate constant was found to be 1.7 × 10-2 min-1, and indicated to be 1.2 × 10-2 min-1 on commercial magnetite powder. Therefore, the process proposed in this chapter can be an excellent alternative to the traditional catalyst for Fenton-like reaction. In Chapter 5, we reported the synthesis of self-organized nanoporous zero valent iron film treated with anodization and electro-reduction of iron foil. The iron nanotubes were fabricated in 1M Na2SO4 + 0.5 wt% NaF electrolyte by supplying constant electric currents of 50 mV/s, and holding the potential at 20 V for 20 min. A nanoporous shape was produced by anodic oxidation of Iron film. After anodizing process, electro-reduction of nanoporous iron film converted crystallization iron oxide to zero valent iron. Electro-reduction process was carried out by electro-reducing with power supply and holding the potential at 20 V for 20 min. The surface of iron nanotube film was examined by BET and the thickness of the oxidized films was evaluated by Scanning Electron Microscope (SEM). The crystalline structures of the fabricated films were evaluated using X-ray diffraction (XRD). Magnetic-cored dendrimer (MCD) was synthesized on the surface of magnetite nanoparticles (MNP) for heavy metal binding in Chapter 6. The synthesized MNP and MCD were characterized using FT-IR, FE-TEM, XRD, and SQUID. Transmission electron microscopy (TEM) revealed clear dispersion of the MCD in methanol solution. Cd ion was bound from 10 mg/L solutions in the batch-type procedure and the binding efficiency was 99 % at a pH of 7. Moreover the binding/unbinding of Cd was evaluated in six cycles, and demonstrated high regeneration rates of about 97 %. Consequently, the novel engineering nanomaterials are certainly considered to be a highly effective and green technology for environmental purification.