Ratio Dependence of the Visible Light Photocatalytic Efficiency for Zn_2Ti_(0.9)Cr_yFe_([0.1]-y)O_4: Cr/Fe (0.02 < y < 0.08) Photocatalyst Synthesized by Using a Solid State Reaction Method

Pramod H. Borse,조채용,K. T. Lim,Y. J. Lee,배종성,정의덕,H. G. Kim 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.1

We synthesized four different photocatalyst systems viz. Zn_2TiO_4, Zn_2Ti_(1-x)Fe_xO_4, Zn_2Ti_(1-x)Cr_xO_4 (0 ≤ x < 0.8) and Zn_2Ti_(0.9)Cr_yFe_([0.1]-y)O_4 (0.022TiO<SUB>4</SUB> was converted to visible light active material by controlled doping/co-doping of Cr and Fe metal-ions at Ti substitutional site. We investigated their structural, optical and photocatalytic water decomposition property. The co-doping induces strong absorption bands in visible region (at λ~ 480 nm and λ~ 620 nm) in the host band gap. The optimum system of Zn_2Ti_(0.9)Cr_(0.05)Fe_(0.05)O_4 yielded maximum H<SUB>2</SUB> generation. In contrast to the visible light inactivity of Fe and Cr doped Zn_2TiO_4, the H_2 production under visible light irradiation from co-doped samples, increased till the optimum ‘y’ value. Consequently, there exists an optimized co-dopant concentration for efficient photocatalytic hydrogen production under visible light (λ ≥ 420 nm).

Ti-dopant-enhanced Photocatalytic Activity of a CaFe₂O₄/MgFe₂O₄ Bulk Heterojunction under Visible-light Irradiation

Pramod H. Borse,김재영,이재성,임권택,정의덕,배종성,윤장희,Seong Mi Yu,김현규 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.1

The effect substitution of Ti⁴⁺ at the Fe³⁺ site in a CaFe₂O₄/MgFe₂O₄ bulk hetero-junction (BH) lattice photocatalyst was explored and the Ti ion concentration was optimized to fabricate an efficient photocatalyst. A BH consisting of an optimum dopant concentration (Ti⁺⁴) level of <i>x</i> = 0.03 exhibited an increased band gap and generated a 1.5 times higher photocurrent. The newly fabricated Ti ion doped photocatalyst showed an enhanced quantum yield (upto ∼13.3%) for photodecomposition of a H₂O-CH₃OH mixture, as compared to its undoped BH counterpart under visible light (λ ≥ 420 nm). In contrast, the material doped with a very high Ti-dopant concentration displayed deteriorated photochemical properties. An efficient charge-separation induced by Ti-ion doping seems to be responsible for the higher photocatalytic activity in a doped bulk BH.

Enhanced Photocatalytic Properties due to Electron-rich Ti-ion Doping in ZnFe_2O_4 under Visible Light Irradiation

Pramod H. Borse,김현규,장점석,이재성,F. Nawaz Khan,하명규,김종필,배종성,정의덕 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.4

The substitution effect of Ti^(4+) at Fe^(3+) site in ZnFe_2O_4, a spinel-phase system, has been studied and further optimized to fabricate an efficient photocatalyst. The material doped with electron donor (Ti^(+4)), ZnFe_(2−x)Ti_xO_4 with an optimum composition of x=0.06 exhibited a unchanged band gap, but generated two times higher photocurrent, and showed enhanced quantum yield (upto 0.77%) for photodecomposition of H_2O-CH_3OH mixture, than undoped material under visible light ((λ≥420 nm). In contrast, the material doped with very high concentration of Ti revealed deteriorated photochemical properties due to constituent impurity phases. The higher electron density by n-type doping seems to be responsible for the more efficient charge separation in ZnFe_(2−x)Ti_xO_4 (0.01 < x < 0.09), and hence, the high photocatalytic activity.

Comparision of Zn₂TiO₄and rutile TiO₂photocatalysts for H₂production under UV and near-visible light irradiation

Pramod H. Borse,김현규,조채용,K. T. Lim,홍태은,정의덕,J.H. Yoon,S.M. Yu 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.1

Zn2TiO4 a spinel-type structure photocatalyst, was synthesized by a solid-state reaction method, and obtained as a single phase in the temperature range of 900-1200 oC. The average particle size for case of the as-synthesized Zn2TiO4 sample, sintered at 1200 oC was found to be 5 μm, whereas it lay in the range of 0.5-2 μm for the case of TiO2 calcined at 650 oC. The band gap of Zn2TiO4 and TiO2 (rutile) samples determined by UV-Vis diffuse reflectance spectra (DRS) was 3.10 eV (400 nm). The Zn2TiO4 sample calcined at 1200 oC exhibited a higher hydrogen production rate than that of rutile TiO2 from a watermethanol mixture under UV (λ ≥ 210 nm) and near-visible (μ ≥ 400 nm) light irradiation. In spite of having the same bandgap energy, the photocatalytic activity of Zn2TiO4 was found to be higher than that of rutile TiO2, manily because of its more negative conduction band edge than rutile TiO2.

Nanocrystalline Magnesium Ferrite Prepared for Photocatalytic Applications by Using the Polymerized Complex Method

Rekha Dom,Pramod H. Borse,Kyong-Soo Hong,Seyong Choi,Byeong Seob Lee,Myoung Gyu Ha,Jong Pil Kim,Euh Duck Jeong,Hyun Gyu Kim 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.9

Magnesium ferrite (MgFe2O4) exhibiting a spinel phase was synthesized by using the polymerized complex and the solid-state reaction methods, and its physico-chemical properties were studied to explore the water-splitting under visible light photons. The study revealed the potential for using MgFe2O4 particles for photo-catalytic application. The structural study provided information on ferrite nano-crystallites fabricated by using the polymer complex method. The morphological studies demonstrated that, in contrast to the solid-state reaction method, a homogenous, monodispersed ferrite photocatalyst could be formed by using the polymerized complex method. The optical study revealed a larger visible-light absorption capability for the nanosized MgFe2O4 photocatalysts prepared by using the polymer complex methods, and indicated a red-shift of the bandgap by 0.06 eV as compared to the bandgap of the bulk. These nanocrystallites were highly photoactive with respect to the photodegradation and photocatalytic hydrogen evolution applications. The electrochemical analysis showed that they exhibited favorable bandedge positions suitable for photocatalytic H2 evolution. Thus, nanocrystalline MgFe2O4 is an active visible-light photocatalyst, that might be useful for the decomposition of water.

Effective charge separation in site-isolated Pt-nanodot deposited PbTiO₃ nanotube arrays for enhanced photoelectrochemical water splitting

Ahn, Chang Won,Borse, Pramod H.,Kim, Ju Hun,Kim, Jae Young,Jang, Jum Suk,Cho, Chae-Ryong,Yoon, Jang-Hee,Lee, Byoung-seob,Bae, Jong-Seong,Kim, Hyun Gyu,Lee, Jae Sung Elsevier 2018 Applied Catalysis B Vol.224 No.-

<P><B>Abstract</B></P> <P>Highly uniform, self-supported PbTiO<SUB>3</SUB> nanotube arrays are fabricated on a transparent conducting glass by an all solution-based, hard-templating procedure. A new concept of site-isolation has been realized by Pt-sol infiltration only in the internal core of deposited nanotube arrays and thus physically separating electron and hole reaction sites on inside and external surface of the nanotubes, respectively. The effective charge separation by the site-isolated Pt-nanodot deposited PbTiO<SUB>3</SUB> nanotube photoanode leads to greatly enhanced photocurrent generation and H<SUB>2</SUB> evolution efficiencies relative to those of the particulate-type photoanode or PbTiO<SUB>3</SUB> nanotube without Pt infiltration in photoelectrochemical water splitting under visible light. The physical site isolation through nano-engineering of the material fabrication is expected to offer an effective strategy for preparation of high-efficiency photoelectrochemical devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Site-isolated Pt-dot@PbTiO<SUB>3</SUB> nanotube array is fabricated on FTO glass by an AAO templating method. </LI> <LI> It separates e<SUP>−</SUP> and h<SUP>+</SUP> reaction sites on inside and external surface of the nanotubes, respectively. </LI> <LI> The effective charge separation leads to greatly enhanced PEC water splitting activity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Size effects of WO₃ nanocrystals for photooxidation of water in particulate suspension and photoelectrochemical film systems

Hong, Suk Joon,Jun, Hwichan,Borse, Pramod H.,Lee, Jae Sung Elsevier 2009 International journal of hydrogen energy Vol.34 No.8

<P><B>Abstract</B></P><P>Monoclinic WO<SUB>3</SUB> nanocrystals were synthesized by a hydrothermal reaction and post calcination. Their particle sizes were varied from 30nm to 500nm by changing calcination temperature from 500°C to 800°C. Photooxidation of water was studied in particulate suspension (PS) system and photoelectrochemical (PEC) film system. For PS system, WO<SUB>3</SUB> nanocrystals were suspended in 50mM AgNO<SUB>3</SUB> solution to measure O<SUB>2</SUB> evolution rate. For PEC system, WO<SUB>3</SUB> films were fabricated by doctor blade method using synthesized nanocrystals. Photocurrent density was measured at AM 1.5G (1 sun) solar condition in 0.5M H<SUB>2</SUB>SO<SUB>4</SUB>. In PS system, the sample calcined at the highest temperature generated the largest amount of oxygen, whereas in PEC system the sample calcined at 600°C showed the maximum photocurrent. The two systems also showed opposite response to deposition of the Pt co-catalyst. These different behaviors were attributed to different mechanisms of charge separation in the two systems.</P>

Nanostructure Zn–Cu <i>co</i>-doped CdS chalcogenide electrodes for opto-electric-power and H₂ generation

Pareek, Alka,Thotakuri, Rambabu,Dom, Rekha,Kim, Hyun Gyu,Borse, Pramod H. Elsevier 2017 International journal of hydrogen energy Vol.42 No.1

<P><B>Abstract</B></P> <P>An efficient photoanode of Zn–Cu: doped nanostructure CdS film has been fabricated by a very simple and commercially usable <I>chemical bath deposition</I> methodology. The electrodes of various sizes were deposited, those ranged from 10 × 10 mm to 100 × 100 mm. Physico-chemical property of the film is investigated <I>in-depth</I> for the photo-electrochemical (PEC) hydrogen production and electric-power generation application. Especially, we studied the effect of Zn and Cu <I>co</I>-doping in the hexagonal CdS-lattice <I>w.r.t.</I> the structural, optical and PEC properties of the nanostructure film. Zn-doping induces an increase in the absorption of visible light photons. The doping enhances the photocurrent by twice as to the undoped, and generates a net photocurrent of ∼817 μA/cm<SUP>2</SUP>, at a very low applied potential of 0.1 V/SCE, in contrast to 366 μA/cm<SUP>2</SUP> of its undoped counterpart. Electrochemical impedance spectroscopy demonstrated that the reduced <I>e–h</I> recombination is responsible for the superior performance of the electrodes. PEC cell fabricated by these electrodes showed a <I>maximum hydrogen generation</I> rate of ∼6.74 μmol/h as compared to 0.58 μmol/h from undoped counterpart; Further a <I>photo to electric-power</I> conversion efficiency of ∼0.16% has been achieved even at <I>low biasing</I> potential of <I>0.1 V</I>/SCE under AM 1.5 solar simulated illumination. Undoped, Zn doped and Cu <I>co</I>-doped films are highly useful for <I>dual applications</I> of “<I>solar power-generation</I>” and “<I>solar hydrogen-generation</I>”, revealing that the Zn doped PEC solar cell is most efficient system for the hydrogen generation even at a very low voltage bias of 0.1 V/SCE.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Deposition of Zn and Cu <I>co</I>-doped nanostructure films by chemical bath deposition. </LI> <LI> Structural and optical properties are revealed. </LI> <LI> Doping and <I>Co</I>-doping enhances the photocurrent by more than twice in CdS. </LI> <LI> Zn doped CdS shows improved power conversion and STH efficiency of 0.50% and 0.16% respectively. </LI> <LI> Low cost method for fabrication of dual purpose PEC cell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fe controlled charge-dynamics in ZnO for solar hydrogen generation

Dom, Rekha,Baby, Lijin Rose,Kim, Hyun Gyu,Borse, Pramod H. Elsevier 2017 International journal of hydrogen energy Vol.42 No.9

<P><B>Abstract</B></P> <P>An efficient photoanode of Fe doped ZnO was fabricated using an economic and simple <I>spray pyrolysis technique</I>. It exhibited <I>5</I>-fold photocurrent enhancement as compared to an un-doped photoelectrode irradiated under simulated solar radiation (AM 1.5G). The photo-conversion efficiencies of the electrodes fabricated by variation in the dopant concentration in the range 10<SUP>−4</SUP>–10<SUP>−1</SUP>% of Fe have been estimated and compared. The doping enabled to control the charge dynamics in ZnO photoanode to yield enhanced photocurrent. The photo electrochemical hydrogen evolution under solar-photons from the doped photoanode was <I>17-times</I> larger in magnitude <I>i.e. ∼</I>307 μmol/h, than un-doped film electrodes (18 μmol/h). The film exhibited <I>wurtzite</I> structure (Space Group – <I>P 63mc</I>) which did not show any structural lattice deformation after Fe doping of ≤10<SUP>−1</SUP>%. Optical studies revealed a <I>red-shift</I> in the band-gap, while a decrease in the <I>absorption-coefficient</I>, with the increase in Fe concentration. These photoanodes also displayed higher Incident-Photon-Current-Conversion efficiency (IPCE) in the 400–430 nm wavelength range. Electrochemical studies revealed <I>n</I>-type conductivity of these photoanodes. An anodic shift in the flat-band potential was observed with an increase in the Fe dopant concentration in the ZnO lattice. The result of the experimental study is illustrated in the form of schematic diagram which demonstrates the suitability of the doped system for solar hydrogen generation. Dopant induced improved optical absorption is mainly attributed to the enhancement in photo-response of these Fe doped ZnO films. The study indicates high potential of these ZnO films for solar energy applications especially <I>with respect to</I> their ability to work under solar radiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanostructured ZnO-film as large as 10 × 10 cm<SUP>2</SUP> deposited by simple spray pyrolysis deposition. </LI> <LI> Stable photocurrent generation yielded 307 micro mol/hr hydrogen. </LI> <LI> The films showed excellent IPCE of >5% in visible light range of 385–425 nm. </LI> <LI> Film showed 0.15% STH efficiency <I>viz</I>. 17 times more H<SUB>2</SUB> evolution than undoped ZnO. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Formation of Layered Bi₅Ti₃FeO₁₅ Perovskite in Bi₂O₃-TiO₂-Fe₂O₃ Containing System

Borse, Pramod H.,Yoon, Sang-Su,Jang, Jum-Suk,Lee, Jae-Sung,Hong, Tae-Eun,Jeong, Euh-Duck,Won, Mi-Sook,Jung, Ok-Sang,Shim, Yoon-Bo,Kim, Hyun-Gyu Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.12

Structural and thermo-analytical studies were carried out to understand the phase formation kinetics of the single phase $Bi_5Ti_3FeO_{15}$ (BTFO) nanocrystals in $Bi_2O_3-Fe_2O_3-TiO_2$, during the polymerized complex (PC) synthesis method. The crystallization of Aurivillius phase $Bi_5Ti_3FeO_{15}$ layered perovskite was found to be initiated and achieved under the temperature conditions in the range of ${\sim}$800 to 1050$^{\circ}C$. The activation energy for grain growth of $Bi_5Ti_3FeO_{15}$ nanocrystals (NCs) was very low in case of NCs formed by PC (2.61 kJ/mol) than that formed by the solid state reaction (SSR) method (10.9 kJ/mol). The energy involved in the phase transformation of Aurivillius phase $Bi_5Ti_3FeO_{15}$ from $Bi_2O_3-Fe_2O_3-TiO_2$ system was ${\sim}$ 69.8 kJ/mol. The formation kinetics study of $Bi_5Ti_3FeO_{15}$ synthesized by SSR and PC methods would not only render a large impact in the nanocrystalline material development but also in achieving highly efficient visible photocatalysts.