Direct Solar Conversion of CO2 into Longer Hydrocarbons using Nafion Coated Pd-TiO2

2

염료감응형 광촉매: 환경정화 및 에너지 응용

2

An Effect of Hot Isostatic Pressing on Translucency of Zirconia

학위논문 (석사)-- 서울대학교 치의학대학원 : 치의학과, 2015. 2. 한중석.연구 배경 및 목적 지르코니아는 도재 중에서 가장 우수한 기계적 성질을 지니고 있으며 치과분야에서는 상온에서 상전이 현상 때문에 TZP(Tetragonal Zirconia Polycrystalline)형태로 이용되고 있다. 열간 등방 가압(hot isostatic pressing, HIP)처리는 도재 소결과정에서 발생하는 defect, porosity 등을 줄이기 위해 도입되었고 이를 통해 지르코니아의 기계적 성질을 향상 시킬 수 있었다. 하지만 지르코니아는 도재 중에서 가장 낮은 투광도를 지니고 있기 때문에 심미적인 면에서 한계를 가지고 있으며 아직까지 지르코니아의 투광도를 증가시키기 위한 연구는 미비한 편이다. 본 연구에서는 지르코니아의 투광도를 증가시킬 수 있는 방안을 모색하기 위해서 열간 등방 가압 처리가 지르코니아의 투광도에 미치는 영향을 평가해보고 소결 온도 및 yttrium oxide 조성의 차이가 지르코니아의 투광도에 어떤 영향을 미치는지 분석해 보고자 한다. 실험재료 및 방법 0.3mm 두께의 ZirPremium NP+, HT, UT (Acucera, INC.) 지르코니아 시편을 제작하여 투광도를 비교하였으며 UPCERA Zirconia blank-A2 (UPCERA Co.) 시편을 대조군으로 사용하였다. ZirPremium NP+ 의 경우, 2시간동안 각각 1450, 1500, 1550, 1600℃의 온도조건에서 소결을 하였다. 1500℃에서 소결한 ZirPremium NP+ 시편에 대해서 소결 후 각각1300, 1350, 1400, 1450, 1500, 1550℃의 온도 조건에서 열간 등방 가압 처리를 하여 처리 하지 않은 시편과 투광도를 비교하였다. 투광도는 입사한 빛의 intensity에 대한 투광한 빛의 intensity에 대한 비로 측정하였다. 실험결과 및 토의 ZirPremium-NP+를 1300, 1350, 1400, 1450℃의 온도에서 열간 등방 가압 처리 한 경우, 열간 등방 가압 처리를 하지 않은 시편보다 높은 투광도를 보였다. 이는 열간 등방 가압처리에 의해서 지르코니아 내부에 빛의 산란을 일으키는 주된 원인인 porosity가 감소한 결과로 보인다. 소결처리 온도가 가장 낮았던 ZirPremium UT가 NP+, HT 보다 높은 투광도를 보였는데 ZirPremium UT의 경우 5.5 mol % Yttrium oxide가 첨가되었고 지르코니아의 결정 내에 cubic phase의 증가로 인하여 투광도가 증가한 것으로 보인다. 본 연구를 통해 열간 등방 가압 처리는 지르코니아의 투광도를 향상시킬 수 있는 열처리 방법이 될 수 있다는 점을 확인했고 지르코니아의 yttrium oxide의 조성변화를 통한 투광도 향상을 위해서는 지르코니아의 기계적, 광학적 성질을 동시에 고려한 열처리과정이 필요함을 알 수 있었다.제 1 장 서 론.................. ............................... 6 제 1 절 연구 배경 및 목적....................... 6 제 2 장 본 론................ ................................ 13 제 1 절 실험재료 및 방법........................ 13 제 3 장 결 론................................................. 15 제 1 절 실험결과................................... 15 제 2 절 토 의........................................ 19 제 3 절 결 론........................................ 27 참고문헌...................................................... 28 Abstract...................................................... 33Maste

Visible-induced Photocatalysts for Solar Fuel Production

2

Oxygen vacancy control of tungsten oxide for water oxidation and oxygen reduction reaction

2

Photosynthetic and Photocatalytic Conversion using Dye-sensitization and Surface Modified TiO2

DoctorThis study investigated solar conversion systems with hybrids catalysts based on titanium oxide. In particular, the photocatalytic reduction of CO2 is a promising method to reduce excess CO2 present in the atmosphere, and simultaneously produce solar fuels (e.g. CO, CH4 and CH3OH) by means of an environmental friendly approach (i.e. artificial photosynthesis). However, the efficiency of the process is still very low (<1%) because CO2 one electron reduction to form CO2•- is highly undesirable. An alternative and more favorable pathway is to reduce CO2 though proton-assisted multiple-electron transfer (PMET). Although its detailed mechanism remains unclear, it is proposed to involve intermediates and different side reaction pathways. Thus, Nafion was introduced on Pd-TiO2 surface for enhancing PMET via keeping high proton concentration in the first work. However, it still demends further studies to improve the photocatalytic efficiency and to utilize the visible light which is abundant in the solar light. Therefore, in the 2nd - 4th work, sensitizers were used for visible light activity. In the second work, introducing thin Al2O3 overlayer on dye-sensitized TiO2 markedly enhances the visible photocatalytic activity for hydrogen production and dechlorination of chlorinated organic compound, CCl4. By measuring TDR spectra of bare TiO2 and Al2O3/TiO2 in slurry, the main role of the alumina barrier layer is proven to retard the charge recombination between the electron injected from the excited dye and the oxidized dye. In the third work, water-soluble [SnIV(OH2)2-TPyHP]6+ (s-SnP) and water-insoluble SnIV(OH)2TPP (ins-SnP) were synthesized and immobilized on SiO2 (hetero-SnP) for enrironmental remediation. In the fourth, s-SnP have been also applied for H2 production. This study reports a porphyrin-sensitized TiO2 system for hydrogen production under visible light in which the adsorption of sensitizer on TiO2 is not needed. Although SnP hardly adsorbs on TiO2, hydrogen was successfully produced under visible light. This non-adsorbing sensitizer is liberated from the breaking of anchoring group and dye desorption caused by an extreme conditions during photolysis in aqueous solution. SnP can also improve the price competitiveness comparing with Ru-complexes. 1. Nafion (perfluorinated polymer with sulfonate groups) overlayer on TiO2 was employed for the photoreduction of CO2 in the absence of a sacrificial electron donor. Introducing a thin Nafion overlayer on Pd-TiO2 significantly increased the photosynthetic activity for CO2 reduction under UV and solar light. The main role of the Nafion overlayer is to provide high proton concentration within the layer to facilitate the proton-coupled multielectron transfer reactions and to retard the oxidative degradation of intermediates and products of CO2 reduction. The production of hydrocarbons such as methane, ethane, and propane was clearly higher with Nf/Pd-TiO2 than Pd-TiO2. The photosynthetic activity of Nf/Pd-TiO2 catalyst was maintained through repeated cycles of photoreaction, which confirms the stability of Nafion layer. 2. Dye-sensitized TiO2 nanoparticles that were loaded simultaneously with Pt and Al2O3 overlayer (Al2O3/TiO2/Pt) were synthesized and investigated for the photocatalytic activity under visible light. Introducing thin Al2O3 overlayer (~1 nm thick) on dye-sensitized TiO2 markedly enhanced the visible light activities for the production of hydrogen (in the presence of EDTA as an electron donor) and the dechlorination of CCl4. The Al2O3/TiO2/Pt powder was characterized by HRTEM, EDX, and XPS. In agreement with the photocatalytic activity data, the photocurrent collected via electron shuttles on a Pt electrode immersed in an aqueous photocatalyst suspension under visible light was also enhanced in the presence of Al2O3 overlayer, which indicates an enhanced interfacial electron transfer despite the presence of an insulating surface layer. The initial H2 and chloride generation rate increased from 0.4 and 5 μM min-1 on TiO2/Pt to 0.9 and 7.5 μM min-1 on Al2O3/TiO2/Pt, respectively. The visible light activity of the sensitized photocatalytic reactions highly depended on the thickness of the alumina layer and was optimized at a low level of Al loading (Al/Ti atom ratio ~0.01) above which the activity was markedly reduced with thickening the layer. It is suggested that the alumina layer retards the charge recombination between the electron injected from the excited dye and the oxidized dye. The slower charge recombination in the presence of alumina overlayer was confirmed by time-resolve diffuse reflectance (TDR) spectroscopy.3. Visible light photocatalysis using water-soluble tin porphyrin (s-SnP, [Sn(OH2)2(TPyHP)](NO3)6) and water-insoluble tin porphyrin Sn(OH)2(TPP) (ins-SnP) immobilized on SiO2 (hetero-SnP) was investigated. The visible light photocatalytic activities of s-SnP and hetero-SnP were successfully demonstrated for the degradation of 4-chlorophenol (4-CP) and acid orange 7 (AO7) in water. The visible light activity of hetero-SnP increased with the ins-SnP loading and was saturated above 77 mg/g-SiO2, which corresponded to the homogeneous concentration of [ins-SnP] = 50 μM. It is Q-band of SnP (500-650 nm) that is photocatalytically active under visible light, not Soret band (420-430 nm) whose absorption intensity is much higher. When applied to the degradation of 4-CP and AO7, hetero-SnP was particularly stable and could be used repeatedly without losing the activity whereas the activity of s-SnP was gradually reduced with repeated uses. The photocatalytic degradation reactions of 4-CP, AO7, and other organic substrates were systematically studied to show that the operating mechanisms are very different depending on the kind of substrates. The properties and activities of s-SnP and hetero-SnP as a visible light photocatalyst were investigated in various ways and discussed in detail.4. Hydrogen was successfully produced under visible light irradiation in a tin porphyrin (SnP)-sensitized TiO2 system in the wide pH range (pH 3-11) although SnP hardly adsorbs on TiO2. The number of H2 produced in the SnP/TiO2 system after 9 h irradiation corresponds to the turnover number of 410. The apparent photonic efficiency for H2 evolution was estimated to be 35% with the monochromatic radiation of 550±10 nm. The photochemical production of hydrogen is mediated through the formation of the π-radical anion (SnP•-) that subsequently transfers electron to TiO2. The photogenerated SnP•- was monitored by transient absorption spectroscopy and its lifetime is long enough to survive the slow diffusion from the solution bulk to the TiO2 surface, which makes the adsorption of SnP on TiO2 not required for hydrogen production. This is clearly contrasted with the common ruthenium complex-sensitized TiO2 system where the adsorption of the sensitizer complex is essentially required and the hydrogen production is limited to the acidic condition where the adsorption of the sensitizers on TiO2 is allowed. The photocatalytic activity of SnP was mainly attributed to the Q-band (500-650 nm), not the Soret band (420-430 nm) of which absorption intensity is much higher

The photocatalytic CO2 reduction using Nafion coated Pd-TiO2

2

Phototosynthetic and photocatalytic conversion using dye-sensitized and surface modified TiO2

2

Visible light sensitized production of hydrogen using Tin-porphyrin/TiO2: A case of non-adsorbing sensitizer

2

Tungsten oxide defect engineering for solar-induced water treatment and oxygen reduction reaction

2