To improve photocatalytic performance, a PbS/ZnO/TiO2 nanotube catalyst was synthesized, and its surface characteristics and photocatalytic efficiency were investigated. The hybrid photocatalysts were produced by anodic oxidation and successive ionic layer adsorption and reaction(SILAR). The photocatalytic efficiency was evaluated using the dye degradation rate. The PbS/ZnO/TiO2 photocatalyst significantly enhanced the photocatalytic activity for dye degradation, which was ascribed to the synergistic effect of their better absorption of solar light and a decrease in the rate of excited electron-hole recombination.

ZnS powder was synthesized using a relatively facile and convenient glycothermal method at various reaction temperatures. ZnS was successfully synthesized at temperatures as low as 125 oC using zinc acetate and thiourea as raw materials, and diethylene glycol as the solvent. No mineralizers or precipitation processes were used in the fabrication, which suggests that the spherical ZnS powders were directly prepared in the glycothermal method. The phase composition, morphology, and optical properties of the prepared ZnS powders were characterized using XRD, FE-SEM, and UV-vis measurements. The prepared ZnS powders had a zinc blende structure and showed average primary particles with diameters of approximately 20~30 nm, calculated from the XRD peak width. All of the powders consisted of aggregated secondary powders with spherical morphology and a size of approximately 0.1~0.5 μm; these powders contained many small primary nanopowders. The as-prepared ZnS exhibited strong photo absorption in the UV region, and a red-shift in the optical absorption spectra due to the improvement in powder size and crystallinity with increasing reaction temperature. The effects of the reaction temperature on the photocatalytic properties of the ZnS powders were investigated. The photocatalytic properties of the assynthesized ZnS powders were evaluated according to the removal degree of methyl orange (MO) under UV irradiation (λ = 365 nm). It was found that the ZnS powder prepared at above 175 oC exhibited the highest photocatalytic degradation, with nearly 95 % of MO decomposed through the mediation of photo-generated hydroxyl radicals after irradiation for 60 min. These results suggest that the ZnS powders could potentially be applicable as photocatalysts for the efficient degradation of organic pollutants.

The formation mechanism and photocatalytic properties of a multiwalled carbon nanotube (MWCNT)/TiO2- based nanotube (TNTs) composite are investigated. The CNT/TNT composite is synthesized via a solution chemical route. It is confirmed that this 1-D nanotube composite has a core-shell nanotubular structure, where the TNT surrounds the CNT core. The photocatalytic activity investigated based on the methylene blue degradation test is superior to that of with pure TNT. The CNTs play two important roles in enhancing the photocatalytic activity. One is to act as a template to form the core-shell structure while titanate nanosheets are converted into nanotubes. The other is to act as an electron reservoir that facilitates charge separation and electron transfer from the TNT, thus decreasing the electronhole recombination efficiency.

메조포러스 공극구조를 갖는 광촉매 멤브레인은 다양한 환경기술에 적용될 수 있다. 본 연구에서는 TiO2 층을 형 성시킨 광촉매 반응기용 세라믹 멤브레인을 개발하고 이를 염색용액 처리에 적용하였다. 높은 공극률과 균질성을 지닌 TiO2 광촉매층을 그라프트 공중합체를 사용하여 제조하였다. 멤브레인은 광촉매 반응기와 멤브레인 여과를 결합시킨 하이브리드 광촉매 반응기에 성공적으로 적용하였다. 실험결과 정렬된 구조의 TiO2 층이 Al2O3 지지체에 형성되었다. TiO2 층 형성 후 제조된 세라믹 분리막의 순수 투과도는 형성된 광촉매 층 저항으로 감소하였다. 정렬된 구조의 TiO2 층은 UV 결합 시 5시간 안에 완벽한 염색용액 분해를 달성시킬 수 있었다. 광촉매 멤브레인의 염색용액 분해는 Langmuir-Hinshelwood 흡착 모델로 잘 설명할 수 있었다. 또한 TiO2 층이 고정화된 세라믹 멤브레인의 model Congo Red에 대한 1차 속도상수는 Al2O3 지지체 단독인 경우에 비해 약 6배 정도 큰 값을 나타내었다(0.0081 vs. 0.0013 min-1).

본 연구에서는 TiO2 nanotube 광촉매의 고도산화처리능을 비교하기 위해서 OH 라디칼 생성 력을 평가하고자 하였다. 자외선 조사에 따른 Probe compound인 4-Chlorobenzoic acid (pCBA)의 농 도 감소에 따라 OH radical 생성량을 산정하는 방법으로 광촉매 효율을 평가하였는데, TiO2 nanotube 표면에서의 전자의 흐름을 원활하게 하기 위하여 전기적 에너지를 주었을 시 광촉매 효율의 증가 가능 성 또한 확인하고자 자외선 조사 시 전류밀도를 인가하는 방법으로 실험을 진행하였다. 실험에 사용된 TiO2 nanotube는 전극효과를 부여하기 위해 양극산화법으로 티타늄판을 이용하여 제조하였으며, pCBA 용액에는 전도도를 부여하기 위하여 NaCl을 첨가하여 전해질로 사용하였다. 정전류 정전압 조건하에서 자외선조사 실험을 진행하였으며, 전류가 흐르는 광촉매에 자외선 조사 시 OH 라디칼 생성량은 광촉매 없이 자외선만 조사하였을 때에 비해 약 5.6배, TiO2 광촉매와 함께 자외선을 조사하였을 보다 약 2.2 배 증가하였다. 결과적으로 광촉매반응에 전기적 에너지를 부여하였을 시 시너지효과를 가져올 수 있는 가능성을 확인할 수 있었다.

Reactive oxygen species (ROS) can be produced by interactions between sunlight and light-absorbing substances in natural water environments and can completely destroy various organic pollutants in waste water. In this study, we used graphene oxide modified Ag2Se nanoparticles to enhance photochemically generated oxygen (PGO) species activity. Surface area and pore volumes of the Ag2Se-graphene (Ag2Se-G) samples showed catastrophic decrease due to deposition of Ag2Se. The generation of reactive oxygen species was detected through the oxidation reaction of DPCI to DPCO. The photocurrent density and the PGO effect increase in the case of the use of modified graphene. The PGO effect of the graphene modified with Ag2Se composites increased significantly due to a synergetic effect between graphene and the Ag2Se nanoparticles. The photocatalytic activity of sample was evaluated by measuring the degradation of organic pollutants such as methylene blue (MB) and industrial dyes such as Texbrite BA-L (TBA) under visible light.

금속산화물 반도체 중 하나인 산화아연은 인체에 무해하고 친환경적이며, 우수한 화학적, 열 적 안정성의 특성을 지니며 3.37 eV의 넓은 밴드갭 에너지와 60 meV의 높은 엑시톤 바인딩 에너지로 인해 태양전지, 염료페기물의 분해, 가스센서 등 다양한 분야에 응용이 가능한 물질이다. 산화아연은 입 자 형상 및 결정성의 변화에 따라 광촉매 활성이 변하게 된다. 따라서, 다양한 실험변수와 첨가제를 사 용하여 입자를 합성하는 것이 매우 중요하다. 본 논문에서는 마이크로파 수열합성법을 사용하여 산화아연을 합성하였다. 전구체로는 질산아연을 사 용하였고, 수산화나트륨을 사용하여 용액의 pH를 11로 조정하였다. 첨가제로는 계면활성제인 에탄올아 민, 세틸트리메틸암모늄브로마이드, 소듐도데실설페이트, 솔비탄모노올레이트를 첨가하였다. 합성된 입자 는 별모양, 원추형, 씨드형태, 박막형태의 구형의 형상을 보였다. 합성된 산화아연의 물리・화학적 특성 은 XRD, SEM, TGA을 통하여 확인하였고, 광학적 특성은 UV-vis spectroscopy, PL spectroscopy, Raman spectroscopy으로 확인하였다.

A TiO2/CNT nanohybrid photocatalyst is synthesized via sol-gel route, with titanium (IV) isopropoxide and multi-walled carbon nanotubes (MWCNTs) as the starting materials. The microstructures and phase constitution of the nanohybrid TiO2/CNT (0.005wt%) samples after calcination at 450oC, 550oC and 650oC in air are compared with those of pure TiO2 using field-emission scanning electron microscopy and X-ray diffraction, respectively. In addition, the photocatalytic activity of the nanohybrid is compared with that of pure TiO2 with regard to the degradation of methyl orange under visible light irradiation. The TiO2/CNT composite exhibits a fast grain growth and phase transformation during calcination. The nanocomposite shows enhanced photocatalytic activity under visible light irradiation in comparison to pure TiO2 owing to not only better adsorption capability of CNT but also effective electron transfer between TiO2 and CNTs. However, the high calcination temperature of 650oC, regardless of addition of CNT, causes a decrease in photocatalytic activity because of grain growth and phase transformation to rutile. These results such as fast phase transformation to rutile and effective electron transfer are related to carbon doping into TiO2.

In this study, a flat-type photocatalytic reactor is applied under solar irradiation for simultaneous treatment of target pollutants: reduction of Cr(VI) to Cr(III) and oxidation of EDCs (BPA, EE2, E2). An immobilized type of photocatalyst was fabricated to have self-grown nanotubes on its surface in order to overcome limitations of powdery photocatalyst. Moreover, Ti mesh form was chosen as substrate and modified to have both larger surface area and photocatalyst content. Ti mesh was anodized at 50V and 25°C for 30min in the mixed electrolytes (NH4F-H2O-C2H6O2) and annealed at 450°C for 2 hours in ambient oxygen to have anatase structure. Surface characterization was done with SEM and XRD methodologies. Fabricated NTT was applied to water treatment, and coexisting Cr(VI) and organics (EDCs) enhanced each other's reactions by scavenging holes and electrons and thus impeding recombination. Also, several experiments were conducted outdoor under direct sunlight and it was observed that both solar-tracking and applying modified photocatalyst were proven to enhance reaction efficiency.

Well-dispersed Ag3VO4 nanoparticles @polyacrylonitrile (PAN) nanofibers were synthesized by an easily controlled, template-free method as a photo-catalyst for the degradation of methylene blue. Their structural, optical, and photocatalytic properties have been studied by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy equipped with rapid energy dispersive analysis of X-ray, photoluminescence, and ultraviolet–visible spectroscopy. The characterization procedures revealed that the obtained material is PAN nanofibers decorated by Ag3VO4 nanoparticles. Photocatalytic degradation of methylene blue investigated in an aqueous solution under irradiation showed 99% degradation of the dye within 75 min. Finally, the antibacterial performance of Ag3VO4 nanoparticles @PAN composite nanofibers was experimentally verified by the destruction of Escherichia coli. These results suggest that the developed inexpensive and functional nanomaterials can serve as a non-precious catalyst for environmental applications.

TiO2 nanoparticles were synthesized by a sol-gel process using titanium tetra isopropoxide as a precursor at room temperature. Ag-doped TiO2 nanoparticles were prepared by photoreduction of AgNO3 on TiO2 under UV light irradiation and calcinated at 400 oC. Ag-doped TiO2 nanoparticles were characterized for their structural and morphological properties by Xray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The photocatalytic properties of the TiO2 and Ag-doped TiO2 nanoparticles were evaluated according to the degree of photocatalytic degradation of gaseous benzene under UV and visible light irradiation. To estimate the rate of photolysis under UV (λ = 365 nm) and visible (λ ≥ 410 nm) light, the residual concentration of benzene was monitored by gas chromatography (GC). Both undoped/doped nanoparticles showed about 80 % of photolysis of benzene under UV light. However, under visible light irradiation Ag-doped TiO2 nanoparticles exhibited a photocatalytic reaction toward the photodegradation of benzene more efficient than that of bare TiO2. The enhanced photocatalytic reaction of Ag-doped TiO2 nanoparticles is attributed to the decrease in the activation energy and to the existence of Ag in the TiO2 host lattice, which increases the absorption capacity in the visible region by acting as an electron trapper and promotes charge separation of the photoinduced electrons (e−) and holes (h+). The use of Ag-doped TiO2 nanoparticles preserved the option of an environmentally benign photocatalytic reaction using visible light; These particles can be applicable to environmental cleaning applications.

To improve photocatalytic efficiency, graphene/Ag/TiO2 nanotube catalyst was synthesized, and its surface characteristics and photocatalytic activity investigated. For deposition of Ag nanoparticles on the TiO2 nanotubes, a polymer compound containing CH3COOAg/poly(Llactide) was utilized, and the silver particles were precipitated by reducing the silver ions during the annealing process. Graphene deposition on the Ag/TiO2 nanotubes was achieved using an electrophoretic deposition process. Based on the dye degradation results, it was determined that the photocatalytic efficiency was significantly affected by deposition of silver particles and graphene on the TiO2 catalyst. Highly efficient destruction of the dye was obtained with the new graphene/Ag/TiO2 nanotube photocatalyst. This may be attributed to a synergistic effect of the graphene and Ag nanoparticles on the TiO2 nanotubes.

The potential use of UV-TiO2 photocatalytic oxidation absorbent reactor in the removal of gaseous formaldehyde was studied. This study was conducted inside a bench-type circulation reactor chamber at ambient air conditions. PCO (Photocatalytic Oxidaion) degradation test for formaldehyde was done repeatedly and the average was reported. It was evident that photocatalytic oxidation was proven to be an effective method to control indoor air pollutants, like formaldehyde in indoor air. However, by-products are produced in the case of formaldehyde degradation also CO2, CO, H2O and formic acid are produced. These by-products can inhibit the active site of the photocatalyst. Thus, addition of adsorbent succeeding the PCO-TiO2, acts as a secondary treatment wherein produced by-products from the degradation and unreacted HCHO will adhere to the surface of the adsorbent. In this study, synthetic zeolite and activated carbon pellets were used to control of by-products of formaldehyde. PCOTiO2 degradation alone achieves 86% for a period of 60 minutes. Addition of adsorbent improves the removal efficiency achieving 90% and 96% using activated carbon pellet and zeolite, respectively.

Cubic mesocrystal CeO2 was synthesized via a hydrothermal method with glutamic acid (C5H9NO4) as a template. The XRD pattern of a calcined sample shows the face-centered cubic fluorite structure of ceria. Transmission electron microscopy (TEM) and the selected-area electron diffraction (SAED) pattern revealed that the submicron cubic mesocrystals were composed of many small crystals attached to each other with the same orientation. The UV-visible adsorption spectrum exhibited the red-shift phenomenon of mesocrystal CeO2 compared to commercial CeO2 particles; thus, the prepared materials show tremendous potential to degrade organic dyes under visible light illumination . With a concentration of a rhodamine B solution of 20 mg/L and a catalyst amount of 0.1 g/L, the reaction showed higher photocatalytic performance following irradiation with a xenon lamp (≥ 380 nm). The decoloring rate can exceed 100% after 300 min.

In this study, flat-type photocatalytic reaction system is applied to reduce toxic hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) in aqueous solution under UV irradiation. To overcome the limitation of conventional photocatalysis, a novel approach toward photocatalytic system for reduction of hexavalent chromium including nanotubular TiO2 (NTT) on two kinds of titanium substrates (foil and mesh) were established. In addition, modified Ti substrates were prepared by bending treatment to increase reaction efficiency of Cr(VI) in the flat-type photocatalytic reactor. For the fabrication of NTT on Ti substrates, Ti foil and mesh was anodized with mixed electrolytes (NH4F-H2O-C2H6O2) and then annealed in ambient oxygen. The prepared NTT arrays were uniformly grown on two Ti substrates and surface property measurements were performed through SEM and XRD. Hydraulic retention time(HRT) and substrate type were significantly affected the Cr(VI) reduction. Hence, the photocatalytic Cr(VI) reduction was observed to be highest up to 95% at bended(modified) Ti mesh and lowest HRT. Especially, Ti mesh was more effective as NTT substrate in this research.

To synthesize a high-performance photocatalyst, N doped TiO2 nanotubes deposited with Ag nanoparticles were synthesized, and surface characteristics, electrochemical behaviors, and photocatalytic activity were investigated. The TiO2 nanotubular photocatalyst was fabricated by anodization; the Ag nanoparticles on the TiO2 nanotubes were synthesized by a reduction reaction in AgNO3 solution under UV irradiation. The XPS results of the N doped TiO2 nanotubes showed that the incorporated nitrogen ions were located in interstitial sites of the TiO2 crystal structure. The N doped titania nanotubes exhibited a high dye degradation rate, which is effectively attributable to the increase of visible light absorption due to interstitial nitrogen ions in the crystalline TiO2 structure. Moreover, the precipitated Ag particles on the titania nanotubes led to a decrease in the rate of electron-hole recombination; the photocurrent of this electrode was higher than that of the pure titania electrode. From electrochemical and dye degradation results, the photocurrent and photocatalytic efficiency were found to have been significantly affected by N doping and the deposition of Ag particles.

PURPOSES: In areas of high traffic volume, such as expressway across large cities, the amount of nitrogen oxides (NOx) emitted into the atmosphere as air pollution can be significant since NOx gases are the major cause of smog and acid rain. Recently, the importance of NOx removal has arisen in the world. Titanium dioxide (TiO2), that is one of photocatalytic reaction material, is very efficient for removing NOx. The NOx removing mechanism of TiO2 is the reaction of solar photocatalysis. Therefore, TiO2 in road structure concrete need to be contacted with ultraviolet rays (UV) to be activated. In general, TiO2 concretes are produced by replacement of TiO2 as a part of concrete binder. However, considerable portion of TiO2 in concrete cannot contact with the pollutant in the air and UV. Therefore, TiO2 penetration method using the surface penetration agents is attempted as an alternative in order to locate TiO2 to the surface of concrete structure. METHODS: This study aimed to evaluate the NOx removal efficiency of photocatalytic concrete due to various TiO2 application method such as mix with TiO2, surface spray(TiO2 penetration method) on hardened concrete and fresh concrete using surface penetration agents. The NOx removal efficiency of TiO2 concrete was confirmed by NOx Analyzing System based on the specification of ISO 22197-1. RESULTS: The NOx removal efficiency of mix with TiO2 increased from 11 to 25% with increasing of replacement ratio from 3 to 7%. In case of surface spray on hardened concrete, the NOx removal efficiency was about 50% due to application amount of TiO2 with surface penetration agents as 300, 500 and 700g/m2. The NOx removal efficiency of surface spray on fresh concrete due to all experimental conditions, on the other hand, which was very low within 10%. CONCLUSIONS: It was known that the TiO2 penetration method as surface spray on hardened concrete was a good alternative in order to remove the NOx gases for concrete road structures.

PURPOSES : About 35% of air pollutant is occurred from road transport. NOx is the primary pollutant. Recently, the importance of NOx removal has arisen in the world. TiO2 is very efficient for removing NOx by photocatalytic reaction. The mechanism of removing NOx is the reaction of photocatalysis and solar energy. Therefore, TiO2 in concrete need to be contacted with solar radiation to be activated. In general, TiO2 concrete are produced by substitute TiO2 as a part of concrete binder. However, 90% of TiO2 in the photocatalysis can not contacted with the pollutant in the air and solar radiation. Coating and penetration method are attempted as the alternative of mixing method in order to locate TiO2 to the surface of structure. METHODS : The goal of this study was to attempt to locate TiO2 to the surface of concrete, so we can use the concrete in pavement construction. The distribution of TiO2 along the depth were confirmed by basing on the comparison of TiO2 compare by using the EDAX(Energy Dispersive X-ray Spectroscopy). RESULTS : TiO2 were distributed within 3mm from concrete surface. This distribution of TiO2 is desirable, since the TiO2 induce photocatalysis are located to where they can be contacted with the air pollutant and solar radiation. CONCLUSIONS : Nano size TiO2 is easily penetration in the top 3mm of concrete surface. By the penetration TiO2 concrete can be produced with the use of only 10% of TiO2, by comparing the mixing types.

The objective of this study is to maintain the same frequency as the electrode material, concentration, duration of decomposition efficiency, power consumption and voltage measurements using a composite catalyst according to the change of process parameters to obtain the optimum state of the process and the maximum decomposition efficiency. In this paper, known as a major cause of air pollution, such as NO, NO2, SO2, frequency, flow rate, concentration, the material of the electrodes, and using TiO2 catalyst reactor with surface discharge caused by discharging the reactor plasma NOx, SOx decompose the harmful gas want to remove.