Monolithic and shrinkage-free hydrophobic silica aerogels via new rapid supercritical extraction process

Mahadik, D.B.,Lee, Y.K.,Chavan, N.K.,Mahadik, S.A.,Park, H.H. PRA Press ; Elsevier Science Ltd 2016 The Journal of supercritical fluids Vol.107 No.-

Aerogels have unusual mechanical and thermal properties and are useful in thermal insulation applications. However, aerogel production can be a tedious process if aerogels are made using supercritical extraction of a solvent from a sol-gel matrix. We employ a new rapid and simple supercritical extraction process that is better than conventional methods. This technique relies on rapid heating of the sol in a confined mold under a 50bar initial pressure supplied by dry N<SUB>2</SUB> gas in an autoclave. The initial pre-pressure of N<SUB>2</SUB> gas and base catalyst concentration dictate whether aerogels or xerogels are formed. A model is presented based on the various experimental results that predicts that gelation occurred after the solvent reached a supercritical state. Aerogels produced using this new rapid supercritical extraction process are monolithic, shrinkage-free, have a prescribed shape and size, and possess high surface area (~800m<SUP>2</SUP>/g) and low thermal conductivity (~0.035-0.041W/(mK)). The hydrophobicity as measured by water contact angle was enhanced from 119<SUP>o</SUP> to 158<SUP>o</SUP> using a hydrophobic co-precursor in the sol.

Fabrication of A/R-TiO₂ composite for enhanced photoelectrochemical performance: Solar hydrogen generation and dye degradation

Mahadik, Mahadeo A.,An, Gil Woo,David, Selvaraj,Choi, Sun Hee,Cho, Min,Jang, Jum Suk Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.426 No.-

<P><B>Abstract</B></P> <P>Anatase/rutile TiO<SUB>2</SUB> nanorods composites were prepared by a facile hydrothermal method followed by dip coating method using titanium isopropoxide in acetic acid and ethanol solvent. The effects of the titanium isopropoxide precursor concentration, on the formation of dip coated anatase/rutile TiO<SUB>2</SUB> nanorods composite were systematically explored. The growth of anatase on rutile TiO<SUB>2</SUB> nanorods can be controlled by varying the titanium isopropoxide concentration. The morphological study reveals that anatase TiO<SUB>2</SUB> nanograins formed on the surface of rutile TiO<SUB>2</SUB> nanorod arrays through dip coating method. Photoelectrochemical analyses showed that the enhancement of the photocatalytic activities of the samples is affected by the anatase nanograins present on the rutile TiO<SUB>2</SUB> nanorods, which can induce the separation of electrons and holes. To interpret the photoelectrochemical behaviors, the prepared photoelectrodes were applied in photoelectrochemical solar hydrogen generation and orange II dye degradation. The optimized photocurrent density of 1.8mAcm<SUP>−2</SUP> and the 625μmolhydrogen generation was observed for 10mM anatase/rutile TiO<SUB>2</SUB> NRs composites. Additionally, 96% removal of the orange II dye was achieved within 5h during oxidative degradation under solar light irradiation. One of the benefits of high specific surface area and the efficient photogenerated charge transport in the anatase/rutile TiO<SUB>2</SUB> nanorod composite improves the photoelectrochemical hydrogen generation and orange dye degradation compared to the rutile TiO<SUB>2</SUB>. Thus, our strategy provides a promising, stable, and low cost alternative to existing photocatalysts and is expected to attract considerable attention for industrial applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dip coated A/R-TiO<SUB>2</SUB> composite strategy using titanium isopropoxide is proposed. </LI> <LI> Effective light scattering and improved charge transport improves the PEC performance. </LI> <LI> Composite enhances the photocurrent density of A/R-TiO<SUB>2</SUB> electrods. </LI> <LI> A/R-TiO<SUB>2</SUB> composite achieves hydrogen generation activity of 156.25μmol/h. </LI> <LI> A/R-TiO<SUB>2</SUB> composite exhibits excellent performance to remove orange (II) dye. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of improved TiO2/FTO interface and surface modification via cocatalyst for a highly efficient and stable 3D Ni(OH)2/CdS/ZnIn2S4/TiO2 heterojunction

( Mahadik Mahadeo Abasaheb ),( Pravin S. Shinde ),이현휘,조민,장점석 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.0

A simple and effective strategy was used to fundamentally improve the performance of a heterostructuredNi(OH)2/CdS/ZnIn2S4/TiO2 photoanode. TiO2 nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) were annealed at 500°C. The annealing effect minimized the defects in TiO2 grain boundaries and also aids to enhance the interface between the FTO and TiO2 nanorods for efficient electron transport. The stepwise introduction of ZnIn2S4 and CdS on annealed TiO2 improved both the absorption in the visible spectrum range and electron/hole separation in CdS/ZnIn2S4/TiO2. Additionally, the Ni(OH)2 co-catalyst can acts as effective hole trapping sites and improved the stability of the photoelectrode through the timely consumption of the photogenerated charges, particularly the holes.

Structural and electrochemical properties of SnO₂-carbon composite aerogels for Li-ion battery anode material

Mahadik, D.B.,Lee, Yoon Kwang,Kim, Taehee,Han, Wooje,Park, Hyung-Ho Elsevier 2018 Solid state ionics Vol.327 No.-

<P><B>Abstract</B></P> <P>Nanostructured tin oxide-carbon composite aerogel material (SnO<SUB>2</SUB>/C) is synthesized using a sol-gel process, followed by annealing treatment under N<SUB>2</SUB> atmosphere. Varying the temperature of annealing leads to different textural properties and phases of the carbon/tin oxide material. The performance of this composite aerogel as an anode material for Li-ion battery is studied, and favorable retention properties are observed SnO<SUB>2</SUB>/C annealed at 500 °C. This study provides insight into the role of moderately inactive carbon-based porous materials in composites with SnO<SUB>2</SUB> for improving the cyclability of tin oxide, an anode material that shows rapid fading. Incorporation into composite networks of inactive porous carbon enhances the mechanical properties of the tin oxide, which in turn strongly improves the cycling stability in Li-ion battery applications. The material exhibits an initial charge capacity of 1012 mAh g<SUP>−1</SUP> and retains 63% of its initial capacity after 50 cycles at a current density of 637 mAh g<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SnO<SUB>2</SUB>/RF composite aerogels were prepared by sol-gel process. </LI> <LI> Annealing treatment leads to a formation of inactive porous carbon and SnO<SUB>2</SUB> composite. </LI> <LI> SnO<SUB>2</SUB>/C_500°C aerogel composite exhibits an initial charge capacity of 1012 mAh g<SUP>−1</SUP>. </LI> <LI> The composite aerogel retains 63% of its initial capacity after 50 cycles at a current density of 637 mAh g<SUP>−1</SUP>. </LI> <LI> The microstructure of inactive carbon material provides additional space and support for SnO<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Elastic and Superhydrophobic Monolithic Methyltrimethoxysilane-based Silica Aerogels by Two-step Sol-gel Process

Mahadik, D.B.,Jung, Hae-Noo-Ree,Lee, Yoon Kwang,Lee, Kyu-Yeon,Park, Hyung-Ho The Korean Microelectronics and Packaging Society 2016 마이크로전자 및 패키징학회지 Vol.23 No.1

The flexible and superhydrophobic properties of silica aerogels are extremely important material for thermal insulation and oil spill cleanup applications for their long-term use. Flexible silica aerogels were synthesized by using a two-step sol-gel process with precursors, methyltrimethoxysilane (MTMS) followed by supercritical drying. Silica aerogels were prepared at different molar ratio of methanol to MTMS (M). It was observed that the silica aerogels prepared at M=28 were monolithic but inelastic in nature, however, for M=35, the obtained aerogels were monolithic, elastic in nature with less shrinkage. The microstructural studies were carried out using scanning electron microscopy and surface area measurements. The hydrophobicity was confirmed by Fourier transform Infrared spectroscopy and water contact angle measurements. The detailed insight mechanism for flexible nature of silica aerogels and hydrophobic behavior were studied.

Fabrication of a ternary CdS/ZnIn₂S₄/TiO₂ heterojunction for enhancing photoelectrochemical performance: effect of cascading electron–hole transfer

Mahadik, Mahadeo A.,Shinde, Pravin S.,Cho, Min,Jang, Jum Suk The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.46

<▼1><P>A novel, three-dimensional, ternary CdS/ZnIn2S4/TiO2 heterojunction has been fabricated <I>via</I> a three-step facile hydrothermal method.</P></▼1><▼2><P>A novel, three-dimensional, ternary CdS/ZnIn2S4/TiO2 heterojunction has been fabricated <I>via</I> a three-step facile hydrothermal method. In this structure, one-dimensional TiO2 nanorods were directly grown on conductive fluorine-doped tin oxide (FTO) substrates. Next, to form a ternary heterojunction of CdS/ZnIn2S4/TiO2, ZnIn2S4 nanosheets were designed on the TiO2 nanorods and sensitized by CdS nanograins. A systematic photoelectrochemical study shows that the photocurrent density of the ternary heterojunction architecture is as high as 1.4 mA cm<SUP>−2</SUP> at a potential of 0.1 V <I>versus</I> Ag/AgCl (under optimized conditions). A more detailed study shows that the photocurrent density is more than two times higher than that of a single CdS/TiO2 heterojunction (0.615 mA cm<SUP>−2</SUP>) and three times higher than that of ZnIn2S4/TiO2 (at 0.1 V <I>vs.</I> Ag/AgCl). This excellent photoelectrochemical performance is ascribed to the way that the band structure of TiO2 nanorods synergistically cascades with ZnIn2S4 and CdS, which allows for the absorption of a wider portion of the solar spectrum and improves the effective separation of the generated electron–hole pairs. Electrochemical impedance spectroscopy (EIS) studies also reveal the significant changes in both the interface resistance and the charge transfer resistance of the CdS/ZnIn2S4/TiO2 heterostructure. This can be attributed to the efficient hierarchical cascading that occurs during the electron–hole transfer from the excited CdS to TiO2 through the enlarged interface of ZnIn2S4 upon visible light illumination.</P></▼2>

Highly efficient and stable 3D Ni(OH)₂/CdS/ZnIn₂S₄/TiO₂ heterojunction under solar light: Effect of an improved TiO₂/FTO interface and cocatalyst

Mahadik, M.A.,Shinde, P.S.,Lee, H.H.,Cho, M.,Jang, J.S. North-Holland ; Elsevier Science Ltd 2017 Solar energy materials and solar cells Vol.159 No.-

A simple and effective strategy was used to fundamentally improve the performance of a heterostructured Ni(OH)<SUB>2</SUB>/CdS/ZnIn<SUB>2</SUB>S<SUB>4</SUB>/TiO<SUB>2</SUB> photoanode. TiO<SUB>2</SUB> nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) and annealed at 500<SUP>o</SUP>C yielded an optimal photocurrent density of ~988μAcm<SUP>-2</SUP> at 0.1V vs. Ag/AgCl under simulated illumination conditions. The annealing process minimized the defects in TiO<SUB>2</SUB> and assisted in the formation of close contacts between the FTO and TiO<SUB>2</SUB> nanorods, which allowed for efficient electron transport. The stepwise introduction of ZnIn<SUB>2</SUB>S<SUB>4</SUB> and CdS on annealed TiO<SUB>2</SUB> enhanced absorption in the visible range and electron/hole separation in CdS/ZnIn<SUB>2</SUB>S<SUB>4</SUB>/TiO<SUB>2</SUB>. Additionally, the Ni(OH)<SUB>2</SUB> cocatalyst functioned in hole trapping and improved the stability of the photoelectrode through timely consumption of the photogenerated charges, particularly the holes.

CdS/Zr:Fe2O3 Nanorod Arrays with Al2O3 Passivation Layer for Photoelectrochemical Solar Hydrogen Generation

Mahadik, M. A.,Subramanian, A.,Chung, H. S.,Cho, M.,Jang, J. S. WILEY-VCH 2017 ChemSusChem Vol.10 No.9

<P>CdS-sensitized 1D Zr:Fe2O3 nanorod arrays were synthesized on fluorine-doped tin oxide substrates by a two-step hydrothermal method. The photoelectrochemical results demonstrate that the current density (4.2mAcm(-2) at 0V vs. Ag/AgCl) recorded under illumination for the CdS/1D Zr:Fe2O3 photoanodes is 2.8time higher than the bare 1D Zr:Fe2O3. The extended absorbance spectrum, the reduced recombination, and the effective transport of photogenerated holes in CdS to the electrolyte facilitate enhancement in the photoelectrochemical performance. From X-ray photoelectron spectroscopy and TEM observations of the bare and aluminum oxide-treated CdS/1D Zr:Fe2O3 photoanodes, we could confirm that the 1D Zr:Fe2O3 nanorods were covered by the CdS layer and Al2O3 layer present on surface of CdS. Furthermore, the photocurrent and stability of the CdS/1D Zr:Fe2O3 nanorods was significantly enhanced by Al2O3 compared to bare CdS/1D Zr:Fe2O3 heterojunction owing to its ability to act as an effective holetransport- as well as photocorrosion-protecting layer. These remarkable enhancements in light-energy harvesting, improvement in charge transport, and stability directly suggest the usefulness of photoanodes for solar hydrogen generation.</P>

A hydrothermally grown CdS nanograin-sensitized 1D Zr:α-Fe₂O₃/FTO photoanode for efficient solar-light-driven photoelectrochemical performance

Mahadik, Mahadeo A.,Subramanian, Arunprabaharan,Ryu, Jungho,Cho, Min,Jang, Jum Suk The Royal Society of Chemistry 2017 Dalton Transactions Vol.46 No.7

<▼1><P>A CdS nanograin sensitized 1D Zr:Fe2O3 nanorod arrays nanostructure was hydrothermally synthesized and showed an excellent photoelectrochemical performance due to the combined effect of light absorption in CdS and effective charge transport in one dimensional Zr:Fe2O3 nanorod arrays.</P></▼1><▼2><P>Well-defined CdS nanograin-sensitized one-dimensional (1D) Zr:α-Fe2O3 nanostructured arrays with enhanced photoelectrochemical performance are synthesized directly on F-doped SnO2 (FTO) using the hydrothermal method. Owing predominantly to the appropriate photogenerated electron–hole separation and charge collection in 1D Zr:α-Fe2O3 nanorods, hydrothermally deposited CdS/1D Zr:α-Fe2O3 samples exhibit improved photocurrent density over CdS/Fe2O3 nanosheets prepared by other methods. In our work, compared with 1D Zr:α-Fe2O3, the CdS-sensitized 1D Zr:α-Fe2O3 nanorod arrays show 1.9 times improved photoelectrochemical performance. Unfortunately, CdS nanograin-sensitized 1D Zr:α-Fe2O3 nanorod arrays suffer from instability problem. Nickel hydroxide loading, however, can boost the photoelectrochemical performance of the heterojunction and also act as a protective layer that improves the stability of the Ni(OH)2/CdS/1D Zr:α-Fe2O3 electrode compared to CdS/1D Zr:α-Fe2O3. This enhanced PEC activity may be ascribed to the strong heterojunctions between CdS nanograins and 1D Zr:α-Fe2O3 nanorod arrays as well as effective charge separation. This work will provide a new insight into the fabrication and protection of many new photosensitive electrode materials to engineer photoelectrochemical and photocatalytic devices in the near future.</P></▼2>

Facile synthesis of Bi₂S₃ nanosheet/Zr:Fe₂O₃ nanorod heterojunction: Effect of Ag interlayer on the change transport and photoelectrochemical stability

Mahadik, Mahadeo A.,Park, Jin Woo,Chae, Weon-Sik,Choi, Sun Hee,Chung, Hee-Suk,Cho, Min,Jang, Jum Suk Elsevier 2019 Journal of industrial and engineering chemistry Vol.70 No.-

<P><B>Abstract</B></P> <P>In this work, the hydrothermal approach has been used to prepare and control the morphology of Bi<SUB>2</SUB>S<SUB>3</SUB> nanosheet (NS)/Zr doped Fe<SUB>2</SUB>O<SUB>3</SUB> nanorod (NR) heterojunction grown on fluorine doped tin oxide (FTO) phoptoelectrodes. The effect of morphology of Bi<SUB>2</SUB>S<SUB>3</SUB> NS was examined by comparing the photocatalytic activity of Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> nanorod with synthesized heterojunctions. This novel heterojunction photoanode exhibits the light harvesting, the photoinduced electron–hole separation and yielding a maximum photocurrent density of ∼1.27mAcm<SUP>−2</SUP> at −0.4V vs. Ag/AgCl under one sun illumination. Bi<SUB>2</SUB>S<SUB>3</SUB> NS on surface of the Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> NR will act as the active material which shows the dramatic improvement in photocurrent generation. Further, effect of silver interlayer on the interface properties of Bi<SUB>2</SUB>S<SUB>3</SUB> NS/Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> NR heterojunction was also studied. The results indicated that the silver interlayer reduces charge recombination at interface of Bi<SUB>2</SUB>S<SUB>3</SUB> and Zr:Fe<SUB>2</SUB>O<SUB>3</SUB>. Also, the surface plasmon resonance of Ag and controlled morphology enhances the performance (1.5mAcm<SUP>−2</SUP> at −0.4V) as well as improves the stability of Bi<SUB>2</SUB>S<SUB>3</SUB>/Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> heterojunction photoelectrode. This unique design of the nanoarchitecture provides an attractive pathway for the photogenerated electrons and the silver interlayers has great impact on enhancing charge separation and improving stability of photoanode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bi<SUB>2</SUB>S<SUB>3</SUB> nanosheet/Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> nanorod photoanodes were prepared first time via hydrothermal process. </LI> <LI> Morphology control of Bi<SUB>2</SUB>S<SUB>3</SUB> sensitizer network led to enhanced light harvesting. </LI> <LI> Ag interlayer reduces the energy barrier at the interface of heterojunction and charge recombination’s. </LI> <LI> Unique design of heterostructure exhibits an attractive pathway for enhancing photoelectrochemical performance and stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Morphology controlled Ag nanoparticles bridged Bi<SUB>2</SUB>S<SUB>3</SUB> anosheet/Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> heterojunction photoanode was successfully prepared through hydrothermal approach. Improved stability of the structure is due to the combination of SPR and synergistic effects of Bi<SUB>2</SUB>S<SUB>3</SUB> anosheet and Zr:Fe<SUB>2</SUB>O<SUB>3</SUB> nanorods.</P> <P>[DISPLAY OMISSION]</P>