Investigation of the Physico-chemical Properties of Sr2FeNb1−xWxO6 (0.0 ≤ x ≤ 0.1) for Visible-light Photocatalytic Water-splitting Applications

P. H. Borse,K. T. Lim,J.H. Yoon,배종성,M. G. Ha,E. H. Chung,정의덕,김현규 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.2

Incorporation of the pentavalent W-ion has been investigated in Sr2FeNb1−xWxO6 for 0.0 ≤ x< 0.15. The synthesized double perovskite system was used to study its structural and opticalproperties. The optical, as well as structural, properties were found to change with the varyingNb:W stoichiometric ratio. The Sr2FeNb1−xWxO6 samples with 0.0 ≤ x < 0.1 were furtherinvestigated for visible-light photocatalytic water splitting. At an optimized value of x ∼0.01,i.e., Sr2FeNb0.99W0.01O6, the perovskite lattice yielded an efficient photocatalyst, it displayed amoderately-altered direct band-gap of 2.17 eV, and gave twice the higher quantum yield for photosplittingin a H2O-CH3OH mixture compared to that for x ∼0 under visible light (λ ≥ 420 nm). For x > 0.1, the Sr2FeNb1−xWxO6 showed no change in the optical properties but crystal structurewas drastically affected , exhibiting impurity phases and a disordered structure, thus yielding a degradedphotocatalytic behavior. The higher absorption coefficient in the Sr2FeNb0.99W0.01O6 anda higher electron-density acquired by n-type lattice doping seems to be responsible for the betterefficient charge separation in Sr2FeNb1−xWxO6 (0.01 ≤ x ≤ 0.20) and consequently the higherphotocatalytic activity in co-catalyst loaded photocatalysts.

Improved Photolysis of Water from Ti Incorporated Double Perovskite Sr2FeNbO6 Lattice

P. H. Borse,조채용,S. M. Yu,J.H. Yoon,홍태은,배종성,정의덕,김현규 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

The Ti incorporation at Fe-site in the double perovskite lattice of Sr2FeNbO6 (SFNO) system is studied. The Ti concentration optimization yielded an efficient photocatalyst. At an optimum composition of Ti as x = 0.07 in Sr2Fe1-xTixNbO6, the photocatalyst exhibited 2 times the quantum yield for photolysis of H2O in presence of CH3OH, than its undoped counterpart under visible light (λ ≥ 420 nm). Heavily Ti-doped Sr2Fe1-xTixNbO6 lattice exhibited poor photochemical properties due to the existence of constituent impurity phases as observed in the structural characterization, as well as deteriorated optical absorption. The higher electron-density acquired by n-type doping seem to be responsible for the more efficient charge separation in Sr2Fe1-xTixNbO6 (0.05 < x < 0.4) and thus consequently displays higher photocatalytic activity. The Ti incorporated structure also found to yield stable photocatalyst.

Simultaneous hydrogen production and decomposition of H₂S dissolved in alkaline water over CdS-TiO₂ composite photocatalysts under visible light irradiation

Jang, J.S.,Gyu Kim, H.,Borse, P.H.,Lee, J.S. Pergamon Press ; Elsevier Science Ltd 2007 International journal of hydrogen energy Vol.32 No.18

A process of simultaneous hydrogen production and H<SUB>2</SUB>S removal has been investigated over a highly active composite photocatalyst made of bulk CdS decorated with nanoparticles of TiO<SUB>2</SUB>, i.e. CdS(bulk)/TiO<SUB>2</SUB>. The photocatalytic activity was evaluated for hydrogen production from aqueous electrolyte solution containing H<SUB>2</SUB>S dissolved in water or alkaline solution under visible light irradiation. The rate of hydrogen production from the H<SUB>2</SUB>S-containing alkaline solution was similar to the rate obtained from photocatalytic hydrogen production from water containing sacrificial reagents (Na<SUB>2</SUB>S+Na<SUB>2</SUB>SO<SUB>3</SUB>) in the similar concentration. The isotope experiment was carried out with D<SUB>2</SUB>O instead of H<SUB>2</SUB>O to investigate the source of hydrogen from photocatalytic decomposition of H<SUB>2</SUB>S dissolved in H<SUB>2</SUB>O or alkali solution under visible light. Hydrogen originated from both H<SUB>2</SUB>S and H<SUB>2</SUB>O when the reaction solution contained H<SUB>2</SUB>S absorbed in alkaline water.

Photophysical Properties of Nanosized Metal-Doped TiO2 Photocatalyst Working under Visible Light

S. W. Bae,P. H. Borse,S. J. Hong,장점석,이재성,J. S. Jin,E.D. Jeong,T. E. Hong,J.H. Yoon,H. G. Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I

Metal-doped TiO$_2$ nanoparticles were prepared by the sol-gel and hydrothermal synthesis methods. The estimated quantum yields (QYs) of Pt/Cr-doped TiO$_2$ nanoparticles was ca. 0.3 \%. Cr-, Co- and N-doped TiO$_2$ showed the photocatalytic activity for IPA degradation to CO$_2$, but only Cr-doped TiO$_2$ produced H$_2$ photocatalytically in the presence of methanol-water aqueous solution under visible light ($\lambda$ $>$ 420 nm). Thus, in the case of Pt/Co-doped TiO$_2$, the electron excited to the conduction band has a sufficient reduction potential to reduce H$^+$ ion, but hole in the valence band has lower oxidation potential than required for CH$_3$OH degradation to CO$_2$. Therefore, Cr- , Co- and N-doped TiO$_2$ show the different activity for the photocactalytic reaction of gases and solution phases. The results of the calculated electronic structure and experimental optical properties are correlated to schematically to describe the possible mechanism of the photocatalytic behavior of the system under study.

Structural, Optical and Visible-light Photocatalytic Properties of Sr3FeNb2O9 Oxide

Y. J. Cha,배종성,홍태은,J.H. Yoon,E. H. Chung,정의덕,김현규,P. H. Borse,K. T. Lim 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.4

A simple solid-state route has been utilized to prepare Sr3FeNb2O9 particles with the tetragonal(SG P4/mmm), double-perovskite structure. The structural investigation and a calcination temperatureoptimization in the range of 700 − 1300 C revealed that a pure phase Sr3FeNb2O9 couldbe achieved at a temperature of 1200 C. The crystallites with the sizes in the range of 5 − 10μm, exhibited a bandgap of 2.25 eV as deduced from diffuse reflectance studies. The structural andthe optical properties demonstrated its suitability for visible-light active photocatalyst applications. The electrochemical characterization indicated a comparatively negative flat-band potential valuefor Sr3FeNb2O9 particles with respect to the reduction potential of water, indicating its capabilityto reduce water molecule. A very low Pt loading (< 0.2 wt%) over Sr3FeNb2O9 yielded a highphotocatalytic hydrogen evolution efficiency under visible light ( 420 nm). Its photoreductionactivity for water was found to be 1.4 times higher than that of the reference Sr2FeNbO6 photocatalystprepared separately. The overall physico-chemical analysis in this study revealed thatthe suitable band-edge position of Sr3FeNb2O9 could be attributed to its superior performance ascompared to Sr2FeNbO6. A mechanism is proposed to explain the photocatalytic behavior of theSr3FeNb2O9 photocatalyst.

Optical Properties and Glass-forming Region of the K2O-Sm2O3-TeO2 Glass System

K. S. Hong,Y. J. Cha,M. G. Ha,최세용,J. P. Kim,B. S. Lee,정의덕,김현규,P. H. Borse 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9

The optical properties and the glass-forming region of the K2O-Sm2O3-TeO2 glass system arestudied. In the K2O-Sm2O3-TeO2 system, only the 5K2O-5Sm2O3-90TeO2 composition gives atransparent glass. The refractive index, n, and the optical band-gap energy, Eg, of the 5K2O-5Sm2O3-90TeO2 glass are n = 2.04 ± 0.003 and Eg = 3.2 eV, respectively. A single Sm2Te6O15phase is found to be formed by a two-step thermal treatment process at 370 C for 5 h and 390 Cfor 5 h. This is the first report on the crystallization and the preparation of the K2O-Sm2O3-TeO2glass system.

Improved Photolysis of Water from Ti Incorporated Double Perovskite Sr₂FeNbO₆ Lattice

Borse, P.H.,Cho, C.R.,Yu, S.M.,Yoon, J.H.,Hong, T.E.,Bae, J.S.,Jeong, E.D.,Kim, H.G. Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

The Ti incorporation at Fe-site in the double perovskite lattice of $Sr_2FeNbO_6$ (SFNO) system is studied. The Ti concentration optimization yielded an efficient photocatalyst. At an optimum composition of Ti as x = 0.07 in $Sr_2Fe_{1-x}Ti_xNbO_6$, the photocatalyst exhibited 2 times the quantum yield for photolysis of $H_2O$ in presence of $CH_3OH$, than its undoped counterpart under visible light (${\lambda}{\geq}420nm$). Heavily Ti-doped $Sr_2Fe_{1-x}Ti_xNbO_6$ lattice exhibited poor photochemical properties due to the existence of constituent impurity phases as observed in the structural characterization, as well as deteriorated optical absorption. The higher electron-density acquired by n-type doping seem to be responsible for the more efficient charge separation in $Sr_2Fe_{1-x}Ti_xNbO_6$ (0.05 < x < 0.4) and thus consequently displays higher photocatalytic activity. The Ti incorporated structure also found to yield stable photocatalyst.

Synthesis of Barium Ferrite for Visible Light Photocatalysis Applications

P. H. Borse,조채룡,K. T. Lim,Y. J. Lee,T. E. Hong,J. S. Bae,정의덕,김해진,H. G. Kim,조채용 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.6

Orthorhombic phase BaFe_2O_4 powder was synthesized by using a solid state reaction method and investigated for its visible light photocatalytic properties. The crystallization of the structural phase was found to occur at a temperature above 1000 ℃ yielding a pure orthorhombic phase BaFe_2O_4 (SG- B b21m) at 1100 ℃. The estimated band gap, as determined by UV-Vis diffuse reflectance studies, was ∼1.9 eV (652 nm). A new material was designed and fabricated as Pt/RuO_2/BaFe_2O_4 to enhance its photocatalytic activity. A very low (<1 wt% RuO_2) co-catalyst doping over BaFe_2O_4 was important for achieving high photocatalytic efficiency. The newly designed system was investigated for photo-decomposition of isopropyl alcohol (IPA) and of water under visible light (≥420 nm). Its photocatalytic activity was significantly higher than that of platinized TiO_(2−x)N_x. A mechanism has been proposed to explain the photocatalytic behavior of the designed BaFe_2O_4 photocatalyst.

Photocatalytic Hydrogen Generation from Water-methanol Mixtures Using Nanocrystalline ZnFe2O4 under Visible Light Irradiation

P. H. Borse,장점석,S. J. Hong,이재성,정종현,T. E. Hong,안창원,정의덕,K. S. Hong,J. H. Yoon,김현규 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.4

A spinel crystal structure of ferrite containing zinc (ZnFe2O4) was synthesized by using the polymer complex method. A pure phase ZnFe2O4 was obtained at a relatively lower temperature of 900˚C. The as-synthesized nanoparticles are agglomerates of crystals with an average size of ∼50 nm, as estimated from the X-ray diffraction analysis. The band gap of the n-type semiconducting metal oxide, as determined by using an ultraviolet-visible diffuse reflectance spectrometer was found to be 1.90 eV (653 nm). The photocatalytic activity of ZnFe2O4 was investigated by using the photoreduction of water under visible light (≥420 nm), which was found to be much higher than that of the well-known TiO2−xNx photocatalyst. This superior performance is attributed to the larger surface area, the uniform and well-dispersed deposition of the Pt co-catalyst over the surface, and the small band gap of the chemically-prepared ferrite photocatalyst.

Ultrathin MoS2-MoO3 nanosheets functionalized CdS photoanodes for effective charge transfer in photoelectrochemical (PEC) cells

Pareek, A.,Kim, H.,Paik, P.,Borse, P. Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.4

<P>The present study focuses on the synthesis of MoS2-MoO3 nanostructures via a hydrothermal method and their application in the modification of CdS photoanodes. Structural characterization reveals that with an increase in the hydrothermal reaction time the fraction of the MoS2 phase increases in the MoS2-MoO3 nanostructures, with MoS2 being dominant in the sample obtained at the maximum reaction time. TEM characterization reveals the formation of ultra thin nanosheets in the MoS2-MoO3 system. Correspondingly, the bandgaps estimated from the Tauc plot analysis indicate a bandgap tuning from 2.40 eV to 1.73 eV for these Mo-nanostructures. The surfaces of spray deposited nanostructured CdS thin films were further modified with these Mo-nanostructures via a very simple and economic chemical impregnation method. The CdS photoanodes modified with the MoS2-MoO3 nanosheets exhibit the highest PEC performance which is 4 times the photocurrent of bare CdS photoanodes. In addition, the stability of the modified photoanodes is enhanced to more than 8 hours compared to a few minutes for bare and photocorrosive CdS. The improved PEC performance is attributed to the formation of the n-CdS/p-MoS2 junction that suppresses the undesirable electron-hole recombination process and thus improves the charge transfer process. A solar-to-hydrogen conversion efficiency of 1.9% is reported for the MoS2-MoO3 nanosheets modified CdS photoanode.</P>