본 실험에서는 광촉매의 빛의 흡수파장을 가시광선 영역으로 이동시키고, 효율을 향상시키기 위하여 Fe³⁺ 2.5-99.5 mol%의 농도범위로 Ti0₂에 첨가한 혼합광촉매인 Fe/Ti를 제조하였다. 제조한 Fe/Ti 혼합광촉의 특성을 UV/VIS, TEM-EDP, XRD,EDAX,그리고 XPS를 사용하여 관찰하였으며, dichloroacetic acid(DCA)의 공분해 반응속도와 actinometry를 통한 빛의 세기(2.68μE/sec)측정을 통하여 농도별 혼합광촉매의 photonic efficiency를 조사하였다. TEM-EDP와 XRD pattern의 관찰결과, 입자의 지름이 약 4nm인 anatase TiO₂임을 확인하였으며,Fe/Ti의 빛의 흡수 파장 onset이 순수 TiO₂와 비교하여 red-shift되는 것이 밝혀졌다(10% Fe/Ti의 경우 순수 TiO₂보다 약 0.5eV감소). EDAX결과 로부터 제조된 혼합광촉매가 이론적인 Fe의 농도과 근사함을 확인하였으며, XPS로 Fe(Ⅲ)의 존재를 관찰할 수 있었다. Potonic efficiency는 본 실험조건하에서 10 mol% Fe/Ti의 경우 0.22로 최대이었는데. 이는 다양한 혼합광촉매에서 공통적으로 나타나는 경향으로 dopant의 함유량이 증가할수록 점진적으로 전자트랩 효과에 의하여 광촉매 효율이 상승하다가, 적정농도 이상이 첨가되는 경우에는 오히려 전자/정공 트랩장소간의 거리 감소와 띠에너지 감소로 인하여 전자-정공의 재결합이 촉진되기 때문이다. 또한 가시광선의 DCA 광화학반응에의 활용정도를 cut-off filter를 사용하여 조사하였다. 385 nm cut-off필터를 사용하였을 경우 순수 TiO₂는 분해반응을 유발하지 않았으나, 10 mol% Fe/Ti의 경우에는 320 nm cut-off 필터를 사용한 순수 TiO₂ 정도의 분해 속도를 보여주었다. 이 결과로부터, 제조된 Fe/Ti 혼합광촉매의 400 nm부근 흡수가 광활성을 진 띠에너지 전이흡수이며, 이를 이용하여 유기물질을 분해할 수 있다는 결론을 얻었다.

In this study, iron-doped TiO₂(Fe/Ti)mixed oxide nanoparticles were prepared with the Fe content varying from 2.5up to 99.5 mol% to shift the absorption onset into the visible part, and to enhance the efficiency by retarding the e-_h⁺recombination. While they were characterized by UV/VIS, TEM-EDP, XRD, EDAX, and XPS, potonic effciency was also investigated with the degradation rate of dichloroacetate (DCA) and light intensity measured by actinometry (2.68μE/sec). TEM-EDP and XRD showed that particles were in the form of anatase with diameter of ca. 4nm. Appreciabel red-shift in UV/VIS absorption spectra with the addition of Fe, starting UV/VIS absorption in the case if 10% Fe/Ti at around 0.5 eV less than in nano-sized pure TiO₂(around 3,42eV) EDAX verified that the amount of Fe in the prepared mixed oxides was obtained as wished, and XPS revealed that Fe(Ⅲ) existed in TiO₂lattice. Measured photonic efficiency turned out to be increased up to 0.22 at 10 mol% Mo, and then decreased as Fe content kept increasing higher than that. This was explained by the changing prevailing phenomena-electron trapping and recombination-as the amount of dopant increased. Whil photocatalytic decompostion of DCA was not taken place with pure TiO₂using a 385 nm cut-off filter, DCA degradation rate with 10% Fe/Ti was the same as that with pure TiO₂with a 320nm cut-off filter under the same experimental conditions. From this result, it was concluded that the absorption of light around 400 nm was for the bandgap transition and could be used to degrade the contaminated organics.

Mixed Photocatalyst Nano-Sized Partcle Photonic Efficiency.

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