Publications by authors named "Wan In Lee"

35 Publications

Controllable synthesis and self-template phase transition of hydrous TiO colloidal spheres for photo/electrochemical applications.

Adv Colloid Interface Sci 2021 Sep 21;295:102493. Epub 2021 Jul 21.

MOE Key Laboratory of Resources and Environmental Systems Optimization, College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China. Electronic address:

Hydrous TiO colloidal spheres (HTCS) derived from the direct precipitation of titanium alkoxides have attracted continuous interests since 1982. Entering the 21st century, rapid progress in the development of structure-directing agents (SDAs) have enabled reproducible and size-controllable synthesis of highly uniform HTCS with diameters in the nano- to micro-meter range. The availability of various HTCS provides versatile self-templating platforms for the targeted synthesis of nanoporous TiO and titanate spheres with tunable composition, crystallographic phases, and internal structures for a variety of advanced photo/electrochemical applications. This review provides a historical overview for the evolution of HTCS, along with an insightful discussion for the formation mechanism of self-assembly of HTCS during the sol-gel process. Key synthetic parameters including SDA, solvent, reaction temperature and water dosage are discussed for the size and morphology control of HTCS with predictable textural properties. Then, we describe the synthetic strategies of nanoporous TiO and titanate spheres using various HTCS as self-templates. Here, the focus lies on the interactions between TiO nanobuilding blocks with precursors or media at the solid/liquid and solid/solid interfaces, the concurrent phase transitions, and the microstructural and morphological evolutions. Selective formation of crystal phase and internal structures (e.g., solid, hollow, core-shell, yolk-shell) are discussed by manipulating the crystallization kinetics. To further elucidate the composition-structure-property-performance relationship for the resulting nanoporous TiO and titanate spheres, their applications in photo(electro)catalysis, mesoscopic solar cells, and lithium-ion batteries are scrutinized. Finally, we share opinions on key challenges and perspectives for the future controllable preparation, formation mechanisms, and applications of HTCS and their crystalline derivatives.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cis.2021.102493DOI Listing
September 2021

Remarkable variation of visible light photocatalytic activities of M/SnSbO/TiO (M=Au, Ag, Pt) heterostructures depending on the loaded metals.

Chemosphere 2021 Feb 1;265:129160. Epub 2020 Dec 1.

Department of Chemistry and Chemical Engineering, Inha University, Incheon, 22212, Republic of Korea. Electronic address:

SnSbO/TiO (ATO/TiO) heterostructure is a potential visible light photocatalysts that function via an inter-semiconductor hole-transport mechanism. Herein we selectively deposited Au, Ag, or Pt onto the ATO surface of ATO/TiO to investigate charge-trapping behaviors of the noble metals and their effects on photocatalytic performance. We observed that Pt deposition greatly enhanced the photocatalytic activity whereas effects of Au or Ag depositions were not significant. The result of spectroscopic analysis also indicates that Pt is the most effective in scavenging the electrons from the ATO CB. Particularly, Pt/ATO/TiO (ATO:TiO = 15:85 in weight) produced CO of 42 ppmv in 2 h, which is 16 times and 4.8 times that of bare ATO/TiO and nitrogen-doped TiO, respectively. Pt deposition on the ATO seems to suppress two independent charge recombination pathways, that is, recombination of electron-hole pairs in ATO and electron transport from the ATO CB to TiO VB.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chemosphere.2020.129160DOI Listing
February 2021

Mesoporous WO/TiO spheres with tailored surface properties for concurrent solar photocatalysis and membrane filtration.

Chemosphere 2021 Jan 14;263:128344. Epub 2020 Sep 14.

MOE Key Laboratory of Regional Energy and Environmental Systems Optimization, College of Environmental Science and Engineering, North China Electric Power University, Beijing, 102206, China; Beijing Key Laboratory of Novel Thin Film Solar Cells, North China Electric Power University, Beijing, 102206, China. Electronic address:

The strategical integration of membrane water filtration with semiconductor photocatalysis presents a frontier in deep purification with a self-cleaning capability. However, the membrane fouling caused by the cake layer of the reclaimed TiO nanoparticles is a key obstacle. Herein, mesoporous WO/TiO spheres (∼450 nm in diameter) consisting of numerous self-assembled WO-decoated anatase TiO nanocrystallites are successfully prepared via a facile wet-chemistry route. The decoration of monolayered WO significantly affects the surface, photocatalytic, and optical properties of original mesoporous TiO spheres. XRD and Raman analyses show the presence of monolayered WO suppresses the crystal growth of TiO during the calcination process, significantly improves the surface acidity, and causes an obvious red shift in absorption edge. These favorable textural properties, coupling the enhanced interfacial charge carrier separation, render mesoporous WO/TiO spheres with a superior photocatalytic activity in degradation of methylene blue under UV, visible, and solar light irradiations. The optimal molar ratio of W/Ti is examined to 6%. The synthesized mesoporous WO/TiO spheres also show much higher flux during membrane filtration in both dead-end and cross-flow modes, suggesting a promising photocatalyst for concurrent membrane filtration and solar photocatalysis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chemosphere.2020.128344DOI Listing
January 2021

Controllable Synthesis and Crystallization of Nanoporous TiO Deep-Submicrospheres and Nanospheres via an Organic Acid-Mediated Sol-Gel Process.

Langmuir 2020 Jul 18;36(26):7447-7455. Epub 2020 Jun 18.

MOE Key Laboratory of Resources and Environmental Systems Optimization, College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China.

Although considerable progress has been achieved in the preparation of uniform hydrous TiO spheres (HTS) through the sol-gel process, there is plenty of room left in tailoring the size and morphology of HTS on the deep-submicron scale or even nanoscale since the diameters of the so far reported HTS are mostly on the (sub)micron scale (0.3-1.2 μm). Here, we develop a novel titanium tetraisopropoxide (TTIP)-organic acid (OA)-acetonitrile (ACN)-methanol (MeOH)-HO system, which facilitates the control of nanoporous HTS to the range of 50-300 nm. The synthetic parameters including OA, (co-)solvent, concentration of precursor, and reaction temperature are comprehensively optimized, aiming at reproducible preparation and precise size control. Among the various OAs, -valeric acid presents the best capability in controlling the spherical morphology and size uniformity. The synthesized amorphous HTS containing numerous micropores and mesopores show excellent hydrothermal stability and offer suitable self-template for the subsequent synthesis of mesoporous anatase TiO spheres (MAT) with a large surface area of 99.1 m/g. The obtained TiO deep-submicrospheres and nanospheres with tunable sizes show great potential in various research fields.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.0c01008DOI Listing
July 2020

Highly efficient adsorptive removal of sulfamethoxazole from aqueous solutions by porphyrinic MOF-525 and MOF-545.

Chemosphere 2020 Jul 5;250:126133. Epub 2020 Feb 5.

Department of Chemical Engineering, Inha University, Incheon, 22201, Republic of Korea. Electronic address:

The metal-organic frameworks MOF-525 and MOF-545 comprised of Zr-oxide clusters and porphyrin moieties in different geometries were synthesized solvothermally and applied for the adsorptive removal of the broadly used organic contaminant sulfamethoxazole (SMX) from water. Both MOFs were found highly efficient for the adsorption of SMX with the maximum adsorption capacities of 585 and 690 mg/g for MOF-525 and MOF-545, respectively. The latter value is the highest adsorption capacity reported so far for the adsorption of SMX molecules on any adsorbent. The adsorption equilibrium could be modeled successfully by the Langmuir model, which showed close to matching with the experimental data. Their adsorption equilibriums were attained within 120 and 30 min for MOF-525 and MOF-545, respectively. MOF-545 with mesopores demonstrated superior adsorption kinetics to MOF-525 with micropores, and the simulation by the pseudo-second-order kinetic model indicated ca. 20 times faster adsorption by MOF-545 than MOF-525. Both showed pH-dependent adsorption of SMX with a gradual reduction at high pH due to the repulsion between negatively charged adsorbent and SMX. The adsorption of SMX conducted over a group of representative MOFs with different physicochemical properties and detailed characterization confirmed that the high adsorption capacity of the porphyrin MOFs is achieved by H-bonding between the SMX molecule and the N-sites of the porphyrin units in the MOFs, π-π interaction, and the high surface area. The adsorbents were easily regenerated by simple washing with acetone and reusable with >95% efficiency during 4 repeated adsorption-desorption cycles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chemosphere.2020.126133DOI Listing
July 2020

Dual-Function [email protected]:Eu Smart Film for Enhanced Power Conversion Efficiency and Long-Term Stability of Perovskite Solar Cells.

Sci Rep 2017 07 28;7(1):6849. Epub 2017 Jul 28.

Korea Center for Artificial Photosynthesis and Department of Chemistry, Sogang University, #1 Shinsu-dong, Mapo-gu, Seoul, 121-742, Republic of Korea.

In the present study, a dual-functional smart film combining the effects of wavelength conversion and amplification of the converted wave by the localized surface plasmon resonance has been investigated for a perovskite solar cell. This dual-functional film, composed of Au nanoparticles coated on the surface of YO:Eu phosphor ([email protected]:Eu) nanoparticle monolayer, enhances the solar energy conversion efficiency to electrical energy and long-term stability of photovoltaic cells. Coupling between the YO:Eu phosphor monolayer and ultraviolet solar light induces the latter to be converted into visible light with a quantum yield above 80%. Concurrently, the Au nanoparticle monolayer on the phosphor nanoparticle monolayer amplifies the converted visible light by up to 170%. This synergy leads to an increased solar light energy conversion efficiency of perovskite solar cells. Simultaneously, the dual-function film suppresses the photodegradation of perovskite by UV light, resulting in long-term stability. Introducing the hybrid smart [email protected]:Eu film in perovskite solar cells increases their overall solar-to-electrical energy conversion efficiency to 16.1% and enhances long-term stability, as compared to the value of 15.2% for standard perovskite solar cells. The synergism between the wavelength conversion effect of the phosphor nanoparticle monolayer and the wave amplification by the localized surface plasmon resonance of the Au nanoparticle monolayer in a perovskite solar cell is comparatively investigated, providing a viable strategy of broadening the solar spectrum utilization.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-017-07218-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5533740PMC
July 2017

Silicotungstate, a Potential Electron Transporting Layer for Low-Temperature Perovskite Solar Cells.

ACS Appl Mater Interfaces 2017 Aug 20;9(30):25257-25264. Epub 2017 Jul 20.

Department of Chemistry and Chemical Engineering, Inha University , Incheon 22212, Korea.

Thin films of a heteropolytungstate, lithium silicotungstate (LiSiWO, termed Li-ST), prepared by a solution process at low temperature, were successfully applied as electron transporting layer (ETL) of planar-type perovskite solar cells (PSCs). Dense and uniform Li-ST films were prepared on FTO glass by depositing a thin Li-ST buffer layer, followed by coating of a main Li-ST layer. The film thickness was controlled by varying the number of coating cycles, consisting of spin-coating and thermal treatment at 150 °C. In particular, by employing 60 nm-thick Li-ST layer obtained by two cycles of coating, the fabricated CHNHPbI PSC device demonstrates the photovoltaic conversion efficiency (PCE) of 14.26% with J of 22.16 mA cm, V of 0.993 mV and FF of 64.81%. The obtained PCE is significantly higher than that of the PSC employing a TiO layer processed at the same temperature (PCE = 12.27%). Spectroscopic analyses by time-resolved photoluminescence and pulsed light-induced transient measurement of photocurrent indicate that the Li-ST layer collects electrons from CHNHPbI more efficiently and also exhibits longer electron lifetime than the TiO layer thermally treated at 150 °C. Thus, Li-ST is considered to be a promising ETL material that can be applied for the fabrication of flexible PSC devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.7b05146DOI Listing
August 2017

Selective Oxidizing Gas Sensing and Dominant Sensing Mechanism of n-CaO-Decorated n-ZnO Nanorod Sensors.

ACS Appl Mater Interfaces 2017 Mar 8;9(11):9975-9985. Epub 2017 Mar 8.

Department of Materials Science and Engineering, Inha University , 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea.

In this work, we investigated the NO and CO sensing properties of n-CaO-decorated n-ZnO nanorods and the dominant sensing mechanism in n-n heterostructured one-dimensional (1D) nanostructured multinetworked chemiresistive gas sensors utilizing the nanorods. The CaO-decorated n-ZnO nanorods showed stronger response to NO than most other ZnO-based nanostructures, including the pristine ZnO nanorods. Many researchers have attributed the enhanced sensing performance of heterostructured sensors to the modulation of the conduction channel width or surface depletion layer width. However, the modulation of the conduction channel width is not the true cause of the enhanced sensing performance of n-n heterostructured 1D gas sensors, because the radial modulation of the conduction channel width is not intensified in these sensors. In this work, we demonstrate that the enhanced performance of the n-CaO-decorated n-ZnO nanorod sensor is mainly due to a combination of the enhanced modulation of the potential barrier height at the n-n heterojunctions, the larger surface-area-to-volume ratio and the increased surface defect density of the decorated ZnO nanorods, not the enhanced modulation of the conduction channel width.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.6b15995DOI Listing
March 2017

Morphology and Optical Properties of Bare and Silica Coated Hybrid Silver Nanoparticles.

J Nanosci Nanotechnol 2016 May;16(5):5200-6

Owing to their wide applications in the field of optoelectronics, photonics, catalysis, and medicine; plasmonic metal nanoparticles are attaining considerable interest nowadays. The optical properties of these metal nanoparticles depend upon their size, shape, and surrounding medium. The present work studies the morphology and optical properties of bare silver nanoparticles and silica coated hybrid silver nanoparticles. Aqueous phase mediated synthesis and water-in-oil microemulsion mediated synthesis are two different wet chemical routes employed for nanosynthesis. Direct coating of silica is performed in water-in-oil microemulsion on pre-synthesized silver nanoparticles using tetraethyl orthosilicate as silica precursor. This study shows that using different wet chemical routes the size of the synthesized nanoparticles could be tuned. In addition, using reverse micelles as nanoreactors, the thickness of the silica shell around the core silver nanoparticles could be significantly controlled. Further, the optical properties of silver nanoparticles could be adjusted through the size and the surface coating.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1166/jnn.2016.12155DOI Listing
May 2016

Vertically aligned nanostructured TiO2 photoelectrodes for high efficiency perovskite solar cells via a block copolymer template approach.

Nanoscale 2016 Jun;8(22):11472-9

Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea. and KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea.

We fabricated perovskite solar cells with enhanced device efficiency based on vertically oriented TiO2 nanostructures using a nanoporous template of block copolymers (BCPs). The dimension and shape controllability of the nanopores of the BCP template allowed for the construction of one-dimensional (1-D) TiO2 nanorods and two-dimensional (2-D) TiO2 nanowalls. The TiO2 nanorod-based perovskite solar cells showed a more efficient charge separation and a lower charge recombination, leading to better performance compared to TiO2 nanowall-based solar cells. The best solar cells employing 1-D TiO2 nanorods showed an efficiency of 15.5% with VOC = 1.02 V, JSC = 20.0 mA cm(-2) and fill factor = 76.1%. Thus, TiO2 nanostructures fabricated from BCP nanotemplates could be applied to the preparation of electron transport layers for improving the efficiency of perovskite solar cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6nr01010eDOI Listing
June 2016

Novel Carbazole-Based Hole-Transporting Materials with Star-Shaped Chemical Structures for Perovskite-Sensitized Solar Cells.

ACS Appl Mater Interfaces 2015 Oct 30;7(40):22213-7. Epub 2015 Sep 30.

Department of Chemistry and Chemical Engineering, Inha University , Incheon 402-751, Korea.

Novel carbazole-based hole-transporting materials (HTMs), including extended π-conjugated central core units such as 1,4-phenyl, 4,4'-biphenyl, or 1,3,5-trisphenylbenzene for promoting effective π-π stacking as well as the hexyloxy flexible group for enhancing solubility in organic solvent, have been synthesized as HTM of perovskite-sensitized solar cells. A HTM with 1,3,5-trisphenylbenzene core, coded as SGT-411, exhibited the highest charge conductivity caused by its intrinsic property to form crystallized structure. The perovskite-sensitized solar cells with SGT-411 exhibited the highest PCE of 13.00%, which is 94% of that of the device derived from spiro-OMeTAD (13.76%). Time-resolved photoluminescence spectra indicate that SGT-411 shows the shortest decay time constant, which is in agreement with the trends of conductivity data, indicating it having fastest charge regeneration. In this regard, a carbazole-based HTM with star-shaped chemical structure is considered to be a promising candidate HTM.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.5b04662DOI Listing
October 2015

50 nm sized spherical TiO2 nanocrystals for highly efficient mesoscopic perovskite solar cells.

Nanoscale 2015 May;7(19):8898-906

Department of Chemistry and Chemical Engineering, Inha University, Incheon 402-751, Korea.

Single crystalline TiO2 nanoparticles (NPs) with spherical morphology are successfully synthesized by a hydrothermal reaction under basic conditions. TiO2 NPs, selectively controlled to the sizes of 30, 40, 50, and 65 nm, are then applied to a mesoporous photoelectrode of CH3NH3PbI3 perovskite solar cells. In particular, a spherical TiO2 NP of 50 nm size (NP50) offers the highest photovoltaic conversion efficiency (PCE) of 17.19%, with JSC of 21.58 mA cm(-2), VOC of 1049 mV, and FF of 0.759 while the enhancement of PCE mainly arises from the increase of VOC and FF. Furthermore, the fabricated photovoltaic devices exhibit reproducible PCE values and very little hysteresis in their J-V curves. Time-resolved photoluminescence measurement and pulsed light-induced transient measurement of the photocurrent indicate that the device employing NP50 exhibits the longest electron lifetime although the electron injection from perovskite to TiO2 is less efficient than the devices with smaller TiO2 NPs. The extended electron lifetime is attributed to the suppression of electron recombination due to optimized mesopores generated by the spherical NP50.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5nr01364jDOI Listing
May 2015

Fabrication and NO2 gas sensing performance of TeO2-core/CuO-shell heterostructure nanorod sensors.

Nanoscale Res Lett 2014 27;9(1):638. Epub 2014 Nov 27.

Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea.

Unlabelled: TeO2-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In2O3, TiO2, Ga2O3, etc. TeO2/CuO core-shell nanorods were fabricated by thermal evaporation of Te powder followed by sputter deposition of CuO. Scanning electron microscopy and X-ray diffraction showed that each nanorod consisted of a single crystal TeO2 core and a polycrystalline CuO shell with a thickness of approximately 7 nm. The TeO2/CuO core-shell one-dimensional (1D) nanostructures exhibited a bamboo leaf-like morphology. The core-shell nanorods were 100 to 300 nm in diameter and up to 30 μm in length. The multiple networked TeO2/CuO core-shell nanorod sensor showed responses of 142% to 425% to 0.5- to 10-ppm NO2 at 150°C. These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO2 is also a promising sensor material. The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO2 nanorods over the same NO2 concentration range. The underlying mechanism for the enhanced NO2 sensing properties of the core-shell nanorod sensor can be explained by the potential barrier-controlled carrier transport mechanism.

Pacs: 61.46. + w; 07.07.Df; 73.22.-f.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/1556-276X-9-638DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4256961PMC
December 2014

Room temperature, ppb-level NO2 gas sensing of multiple-networked ZnSe nanowire sensors under UV illumination.

Beilstein J Nanotechnol 2014 22;5:1836-41. Epub 2014 Oct 22.

Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea.

Reports of the gas sensing properties of ZnSe are few, presumably because of the decomposition and oxidation of ZnSe at high temperatures. In this study, ZnSe nanowires were synthesized by the thermal evaporation of ZnSe powders and the sensing performance of multiple-networked ZnSe nanowire sensors toward NO2 gas was examined. The results showed that ZnSe might be a promising gas sensor material if it is used at room temperature. The response of the ZnSe nanowires to 50 ppb-5 ppm NO2 at room temperature under dark and UV illumination conditions were 101-102% and 113-234%, respectively. The responses of the ZnSe nanowires to 5 ppm NO2 increased from 102 to 234% with increasing UV illumination intensity from 0 to 1.2 mW/cm(2). The response of the ZnSe nanowires was stronger than or comparable to that of typical metal oxide semiconductors reported in the literature, which require higher NO2 concentrations and operate at higher temperatures. The origin of the enhanced response of the ZnSe nanowires towards NO2 under UV illumination is also discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3762/bjnano.5.194DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4222409PMC
November 2014

14.8% perovskite solar cells employing carbazole derivatives as hole transporting materials.

Chem Commun (Camb) 2014 Nov;50(91):14161-3

Department of Chemistry and Chemical Engineering, Inha University, Incheon 402-751, Korea.

Three novel carbazole-based molecules have been synthesized and successfully applied as hole-transporting materials (HTMs) of CH3NH3PbI3-based perovskite solar cells. In particular, the perovskite cell with SGT-405, having a three-arm-type structure, exhibited a remarkable photovoltaic conversion efficiency (PCE) of 14.79%.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4cc06716aDOI Listing
November 2014

Effects of functionalization of TiO2 nanotube array sensors with Pd nanoparticles on their selectivity.

Sensors (Basel) 2014 Aug 27;14(9):15849-60. Epub 2014 Aug 27.

Department of Materials Science and Engineering, Inha University, 253 Yonghyun-Dong, Incheon 402-751, Korea.

This study compared the responses of Pd-functionalized and pristine titanate (TiO2) nanotube arrays to ethanol with those to acetone to determine the effects of functionalization of TiO2 nanotubes with Pd nanoparticles on the sensitivity and selectivity. The responses of pristine and Pd-functionalized TiO2 nanotube arrays to ethanol gas at 200 °C were ~2877% and ~21,253%, respectively. On the other hand, the responses of pristine and Pd-functionalized TiO2 nanotube arrays to acetone gas at 250 °C were ~1636% and 8746% respectively. In the case of ethanol sensing, the response and recovery times of Pd-functionalized TiO2 nanotubes (10.2 and 7.1 s) were obviously shorter than those of pristine TiO2 nanotubes (14.3 and 8.8 s), respectively. In contrast, in the case of acetone sensing the response and recovery times of Pd-functionalized TiO2 nanotubes (42.5 and 19.7 s) were almost the same as those of pristine TiO2 nanotubes (47.2 and 17.9 s). TiO2 nanotube arrays showed the strongest response to ethanol and Pd functionalization was the most effective in improving the response of TiO2 nanotubes to ethanol among six different types of gases: ethanol, acetone, CO, H2, NH3 and NO2. The origin of the superior sensing properties of Pd-functionalized TiO2 nanotubes toward ethanol to acetone is also discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/s140915849DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4208149PMC
August 2014

Novel coupled structures of FeWO4/TiO2 and FeWO4/TiO2/CdS designed for highly efficient visible-light photocatalysis.

ACS Appl Mater Interfaces 2014 Jun 3;6(12):9654-63. Epub 2014 Jun 3.

Department of Chemistry and Chemical Engineering, Inha University , Incheon 402-751, Korea.

A quadrilateral disk-shaped FeWO4 nanocrystal (NC) with an average size of ∼35 nm was prepared via hydrothermal reaction. The obtained dark brown FeWO4 NC with a bandgap (Eg) of 1.98 eV was then coupled with TiO2 to form FeWO4/TiO2 composites. The valence band (VB) of FeWO4 (+2.8 eV vs NHE) was more positive than that of TiO2 (+2.7 eV); thus this system could be classified as a Type-B heterojunction. Under visible-light irradiation, 5/95 FeWO4/TiO2 (by wt %) exhibited remarkable photocatalytic activity: the amount of CO2 evolved from gaseous 2-propanol (IP) and the decomposition rate of aqueous salicylic acid (SA) were, respectively, 1.7 and 2.5 times greater than those of typical nitrogen-doped TiO2 (N-TiO2). This unique catalytic property was deduced to arise from the intersemiconductor hole transfer between the VBs of FeWO4 and TiO2. Herein, several experimental evidence were also provided to confirm the hole-transfer mechanism. To further enhance the catalytic efficiency, double-heterojunctioned FeWO4/TiO2/CdS composites were prepared by loading CdS quantum dots (QDs) onto the FeWO4/TiO2 surface. Surprisingly, the catalytic activity for evolving CO2 from IP was 2.6 times greater than that of bare FeWO4/TiO2 and 4.4 times greater than that of N-TiO2, suggesting that both holes and electrons were essential species in decomposing organic compounds.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am502079xDOI Listing
June 2014

Enhanced near-band edge emission from ZnO nanorods by V2Os coating and subsequent thermal annealing.

J Nanosci Nanotechnol 2014 Jul;14(7):5181-6

V2O5-coated ZnO 1D nanostructures were prepared by using a two step process: thermal evaporation of a mixture of ZnO and graphite powders (ZnO:C = 1:1) in an oxidative atmosphere and sputter-deposition of V2O5. Scanning electron microscopy revealed that the nanostructures had a rod-like morphology with the thickness diminishing gradually from an end to the other. The thicknesses and lengths of the nanorods range from a few tens to a few hundreds of nanometers and from a few to a few tens of micrometers, respectively. Transmission electron microscopy and X-ray diffraction analyses revealed that the ZnO cores and V2O5 shells of the core-shell nanorods were wurtzite-type hexagonal close-packed structured single crystal and amorphous, respectively. The intensity ratio of the near-band edge (NBE) emission to the deep-level emission was increased about three times by coating the ZnO nanorods with a V2o5 thin film about 10 nm thick. The NBE emission enhancement may be mainly attributed to two sources: the effects of suppression of capturing of carriers by surface states and suppression of visible emission and nonradiative recombination by depletion regions formed in the ZnO cores. In addition, it was found that postannealing of V2O5-coated ZnO nanorods is not desirable, whereas post annealing makes a positive effect on the NBE emission enhancement in uncoated ZnO nanorods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1166/jnn.2014.8415DOI Listing
July 2014

Design and development of highly efficient PbS quantum dot-sensitized solar cells working in an aqueous polysulfide electrolyte.

Chem Commun (Camb) 2013 Jul;49(54):6054-6

Department of Chemistry, Inha University, Incheon 402-751, Korea.

PbS quantum dot-sensitized solar cells (QDSCs) with a photovoltaic conversion efficiency (η) of 5.73% have been fabricated by applying Au/CuS/FTO as a counter electrode (CE), post-annealing the deposited PbS QDs, and introducing the bilayered TiO2 nanostructure as a photoanode.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c3cc40754cDOI Listing
July 2013

Highly sensitive ratiometric fluorescent chemosensor for silver ion and silver nanoparticles in aqueous solution.

Org Lett 2012 Sep 5;14(18):4746-9. Epub 2012 Sep 5.

Bioorganic Chemistry Laboratory, Department of Chemistry, Inha University, Yunghyun-dong, Nam-gu, Incheon, 402-751, Republic of Korea.

A pyrene derivative chemosensor (Pyr-WH) based on a dipeptide shows a highly sensitive ratiometric response to Ag(I) as well as silver nanoparticles in aqueous solution at physiological pH. Pyr-WH penetrated live HeLa cells and exhibits a ratiometric response to intracellular Ag(I). The binding mode of Pyr-WH with Ag(I) was characterized based on fluorescence changes in different pH, NMR, and ESI mass spectrometer experiments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ol301991hDOI Listing
September 2012

Effect of layer-by-layer assembled SnO2 interfacial layers in photovoltaic properties of dye-sensitized solar cells.

Langmuir 2012 Jul 3;28(28):10620-6. Epub 2012 Jul 3.

Department of Chemistry, Inha University, Incheon 402-751, Korea.

Ultrathin SnO(2) layers were deposited on FTO substrate by the layer-by-layer (LbL) self-assembly technique utilizing negatively charged 2.5 nm sized SnO(2) nanoparticles (NPs) and cationic poly(allylamine hydrochloride) (PAH). For the construction of dye-sensitized solar cells (DSC), the bulk TiO(2) layer was deposited over the (PAH/SnO(2))(n) (n = 1-10) and subsequently calcined at 500 °C to remove organic components. With introducing four layers of self-assembled SnO(2) interfacial layer (IL), the short circuit current density (J(sc)) of DSCs was increased from 8.96 to 10.97 mA/cm(2), whereas the open circuit voltage (V(oc)) and fill factor (FF) were not appreciably changed. Consequently, photovoltaic conversion efficiency (η) was enhanced from 5.43 to 6.57%. Transient photoelectron spectroscopic analyses revealed that the ultrathin SnO(2) layer considerably increased the electron diffusion coefficient (D(e)) in TiO(2) layer, but the electron lifetime (τ(e)) was decreased unexpectedly. The observed unusual photovoltaic properties would be caused by the unique conduction band (CB) location of the SnO(2), inducing the cascadal energy band matching among the CBs of TiO(2), SnO(2), and FTO.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la3015699DOI Listing
July 2012

Effect of five-membered heteroaromatic linkers to the performance of phenothiazine-based dye-sensitized solar cells.

Org Lett 2011 Nov 4;13(21):5784-7. Epub 2011 Oct 4.

Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea.

Phenothiazine derivatives with various conjugated linkers (furan, thiophene, and 3,4-ethylenedioxythiophene) were synthesized and used in dye-sensitized solar cells to study the effect of conjugated linkers on device performance. Among them, one with furan as a conjugated linker showed a solar energy-to-electricity conversion efficiency (η) of 6.58%, an improvement of over 24% compared with the T2-1 reference cells' 5.29% under AM 1.5 G irradiation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ol2023517DOI Listing
November 2011

Ultraintense luminescence in semiconducting-material-sheathed MgO nanorods.

Adv Mater 2011 May 28;23(17):1982-7. Epub 2011 Mar 28.

Department of Materials Science and Engineering, Inha University, 253 Yonghyeon-dong, Incheon 402-751, Republic of Korea.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201004266DOI Listing
May 2011

Effect of calcination temperature on the textural properties and photocatalytic activities of highly ordered cubic mesoporous WO3/TiO2 films.

J Nanosci Nanotechnol 2010 Jul;10(7):4747-51

School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore.

Highly organized cubic mesoporous WO3/TiO2 films were successfully prepared by evaporation-induced self-assembly (EISA) process, employing triblock copolymer as template. The characterization results by XRD, SEM, TEM, UV-Vis. spectrophotometry, and nitrogen adsorption-desorption isotherms reveal that the mesoporous films are made up of well-defined 3-D cubic (lm3m space group) mesoporous structure and nanocrystalline anatase frameworks with high surface area, uniform pore sizes and excellent optical transparency. Photocatalytic properties of the mesoporous WO3/TiO2 films in decomposing gaseous 2-propanol to CO2 were analyzed as a function of calcinations temperature. The highest photocatalytic activity was obtained for the films calcined at 450 degrees C, which possess an appropriate crystallinity and relevant ordering of mesoporous structure. It was found that that long-range ordering of mesopores is one of the important factors in determining the photocatalytic degradation of gaseous organics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1166/jnn.2010.1672DOI Listing
July 2010

Unsymmetric Ru(II) complexes with N-heterocyclic carbene and/or terpyridine ligands: synthesis, characterization, ground- and excited-state electronic structures and their application for DSSC sensitizers.

Inorg Chem 2010 Aug;49(16):7340-52

Intelligent Textile System Research Center, Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.

Three ruthenium(II) complexes with N-heterocyclic carbene (NHC) or NHC/2,2':6',2''-terpyridine (tpy) hybrid ligands, bis[2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine-4-carboxylic acid]ruthenium(II) (BCN), [2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acid](2,2';6'2''-terpyridine)ruthenium(II) (TCN), and [2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine](2,2';6'2''-terpyridine-4'-carboxylic acid)ruthenium(II) (CTN), have been synthesized and characterized by (1)H and (13)C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular geometry of the TCN complex was determined by X-ray crystallography. Electronic absorption spectra of these complexes exhibit typical pi-pi* and metal-to-ligand charge transfer bands in the UV and visible regions, respectively. The lowest energy absorption maxima were 430, 448, and 463 nm with molar extinction coefficients of 28,100, 15,400, and 7400 M(-1)cm(-1) for BCN, TCN, and CTN, respectively. Voltammetric data suggest that energy levels of the highest occupied molecular orbitals (HOMOs) of the three complexes reside within a 10 meV window despite the varying degrees of electronic effect of the constituent ligands. The electronic structures of these complexes calculated via density functional theory (DFT) indicate that the three HOMOs and the three lowest unoccupied MOs (LUMOs) are metal and ligand centered in character, for the former and the latter, respectively. Time-dependent DFT (TD-DFT) calculation predicts that the lowest energy absorption bands of each complex are comprised of multiple one-electron excitations. TD-DFT calculation also suggests that the background of spectral red shift stems most likely from the stabilization of unoccupied MOs rather than the destabilization of occupied MOs. The overall efficiencies of the dye-sensitized solar cell systems of these complexes were found to be 0.48, 0.14, and 0.10% for BCN, TCN, and CTN, respectively, while that of a commercial bis(4,4'-dicarboxylato-2,2'-bipyridine)-bis(isothiocyanoto)ruthenium(II) (N719) system was 6.34%.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ic100325cDOI Listing
August 2010

Improvement of photovoltaic efficiency of dye-sensitized solar cell by introducing highly transparent nanoporous TiO2 buffer layer.

J Nanosci Nanotechnol 2010 Jan;10(1):340-4

Department of Chemistry, Inha University, Incheon, 402-751, Korea.

13 nm-sized highly-dispersible TiO2 nanoparticle was synthesized by solvothermal reaction of titanium isopropoxide in a basic condition with tetrabutylammonium hydroxide (TBAH). The prepared TiO2 nanoparticle was applied to fabrication of the transparent nanoporous TiO2 layer with 1.2 microm-thickness. By introducing this buffer layer between FTO and main TiO2 layer in the dye-sensitized solar cell (DSSC), the photovoltaic conversion efficiency was improved from 5.92% to 7.13%. Due to the excellent antireflective role of nanoporous TiO2 buffer layer, the transmittance of FTO glass was increased by 9.2%, and this seemed to be one of the major factors in enhancing photovoltaic conversion efficiency. Moreover, the presence of nanoporous TiO2 buffer layer induces excellent adhesion between FTO and main TiO2 layer, as well as it suppresses the back reaction by blocking direct contact between I3- and FTO electrode.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1166/jnn.2010.1528DOI Listing
January 2010

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor.

Talanta 2009 May 20;78(3):903-9. Epub 2009 Jan 20.

Bioorganic Chemistry Laboratory, Department of Chemistry, Inha University, 253 Younghyun-Dong, Nam-Gu, Inchon-City, 402-751, South Korea.

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg(2+), Cd(2+), Pb(2+), Zn(2+), and Ag(+) in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd(2+), Pb(2+), Zn(2+), and Ag(+) were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.talanta.2008.12.062DOI Listing
May 2009

Formation of efficient dye-sensitized solar cells by introducing an interfacial layer of long-range ordered mesoporous TiO2 thin film.

Langmuir 2008 Nov 16;24(22):13225-30. Epub 2008 Oct 16.

Nano Materials and Devices Laboratory, Department of Chemistry, Inha University, Incheon 402-751, Korea.

Long-range ordered cubic mesoporous TiO 2 films with 300 nm thickness were fabricated on fluorine-doped tin oxide (FTO) substrate by evaporation-induced self-assembly (EISA) process using F127 as a structure-directing agent. The prepared mesoporous TiO 2 film (Meso-TiO 2) was applied as an interfacial layer between the nanocrystalline TiO 2 film (NC-TiO 2) and the FTO electrode in the dye-sensitized solar cell (DSSC). The introduction of Meso-TiO 2 increased J sc from 12.3 to 14.5 mA/cm (2), and V oc by 55 mV, whereas there was no appreciable change in the fill factor (FF). As a result, the photovoltaic conversion efficiency ( eta) was improved by 30.0% from 5.77% to 7.48%. Notably, introduction of Meso-TiO 2 increased the transmittance of visible light through the FTO glass by 23% as a result of its excellent antireflective role. Thus the increased transmittance was a key factor in enhancing the photovoltaic conversion efficiency. In addition, the presence of interfacial Meso-TiO 2 provided excellent adhesion between the FTO and main TiO 2 layer, and suppressed the back-transport reaction by blocking direct contact between the electrolyte and FTO electrode.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la802340gDOI Listing
November 2008

Shape transformation and relaxation dynamics of photoexcited TiO2/Ag nanocomposites.

J Nanosci Nanotechnol 2008 Jun;8(6):3197-202

School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.

The laser-induced sintering of TiO2 nanoparticles into larger nanospheres is accelerated by adsorbed silver particles. For the same weight fraction of silver, silver nanoparticles of 5 nm in diameter modify TiO2 nanoparticles more effectively than those of 1.5 nm do, suggesting that the photocatalysis of TiO2 nanoparticles as well as their stability is highly dependent on the sizes, the shapes, and the distribution of adsorbed metal nanoparticles. The photoexcited electrons of TiO2 nanoparticles are quenched at trap sites and surface states by transfer to the conduction band of silver, implying that the presence of adsorbed silver nanoparticles enhances the photocatalytic effect of TiO2.
View Article and Find Full Text PDF

Download full-text PDF

Source
June 2008

Effect of TiO2 particle size on the performance of viologen-anchored TiO2 electrochromic device.

J Nanosci Nanotechnol 2007 Nov;7(11):4106-10

Department of Chemistry, Inha University, Incheon 402-751, Korea.

The effect of TiO2 particle size on the performance of the electrochromic device (ECD) has been investigated in this work by applying the TiO2 nanoparticles in 7, 15, and 30 nm sizes. The phosphonated viologen, bis(2-phosphonoethyl)-4,4'-bipyridinium dibromide, was anchored on the TiO2 surfaces for the construction of ECD. The ECD derived from 7 nm-sized TiO2 demonstrated the highest contrast ratio with high optical transparency, whereas it showed the slowest switching response. The enhancement of coloration efficiency with decrease of TiO2 particle size is due to the increased amount of the anchored viologen on TiO2 electrode. On the other hand, the relatively slower switching response would be caused by the difficulty of diffusion for the electrolytes and counter-ions through the small pores of the nanocrystalline TiO2 electrode derived from 7 nm-sized nanoparticles.
View Article and Find Full Text PDF

Download full-text PDF

Source
November 2007
-->