Mesoporous Layer-by-Layer Ordered Nanohybrids of Layered Double Hydroxide and Layered Metal Oxide: Highly Active Visible Light Photocatalysts with Improved Chemical Stability

Gunjakar, Jayavant L.,Kim, Tae Woo,Kim, Hyo Na,Kim, In Young,Hwang, Seong-Ju American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.38

<P>Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O<SUB>2</SUB> generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn–Cr-layered double hydroxide (Zn–Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn–Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O<SUB>2</SUB> generation with a rate of ∼1.18 mmol h<SUP>–1</SUP> g<SUP>–1</SUP>, which is higher than the O<SUB>2</SUB> production rate (∼0.67 mmol h<SUP>–1</SUP> g<SUP>–1</SUP>) by the pristine Zn–Cr-LDH material, that is, one of the most effective visible light photocatalysts for O<SUB>2</SUB> production, under the same experimental condition. This result highlights an excellent functionality of the Zn–Cr-LDH–layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn–Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-38/ja203388r/production/images/medium/ja-2011-03388r_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja203388r'>ACS Electronic Supporting Info</A></P>

A chemical bath deposition route to facet-controlled Ag₃PO₄ thin films with improved visible light photocatalytic activity

Gunjakar, J.L.,Jo, Y.K.,Kim, I.Y.,Lee, J.M.,Patil, S.B.,Pyun, Jae.Chul.,Hwang, S.J. Academic Press 2016 Journal of solid state chemistry Vol.240 No.-

<P>A facile, economic, and reproducible chemical bath deposition (CBD) method is developed for the fabrication of facet-controlled Ag3PO4 thin films with enhanced visible light photocatalytic activity. The fine control of bath temperature, precursor, complexing agent, substrate, and solution pH is fairly crucial in preparing the facet-selective thin film of Ag3PO4 nanocrystal. The change of precursor from silver nitrate to silver acetate makes possible the tailoring of the crystal shape of Ag3PO4 from cube to rhombic dodecahedron and also the bandgap tuning of the deposited films. The control of [Ag+]/[phosphate] ratio enables to maximize the loading amount of Ag3PO4 crystals per the unit area of the deposited film. All the fabricated Ag3PO4 thin films show high photocatalytic activity for visible light-induced degradation of organic molecules, which can be optimized by tailoring the crystal shape of the deposited crystals. This CBD method is also useful in preparing the facet-controlled hybrid film of Ag3PO4-ZnO photocatalyst. The present study clearly demonstrates the usefulness of the present CBD method for fabricating facet controlled thin films of metal oxosalt and its nanohybrid. (C) 2016 Published by Elsevier Inc.</P>

Efficient Hybrid‐Type CO₂ Adsorbents of Reassembled Layered Double Hydroxide 2D Nanosheets with Polyoxometalate 0D Nanoclusters

Gunjakar, Jayavant L.,Kim, In Young,Hwang, Seong‐,Ju Wiley-VCH 2015 European journal of inorganic chemistry Vol. No.

<P><B>Abstract</B></P><P>Porous nanohybrids of cationic Mg‐Al‐LDH 2D nanosheets and anionic polyoxometalate (POM, V<SUB>10</SUB>O<SUB>28</SUB><SUP>6–</SUP> and W<SUB>7</SUB>O<SUB>24</SUB><SUP>6–</SUP>) 0D nanoclusters are synthesized by an exfoliation–reassembling process. The electrostatically derived reassembling between two kinds of nanostructures yields a layer‐by‐layer‐ordered intercalation structure with porous structures composed of mesopores and micropores. The hybridization with POM leads to the remarkable enhancement of CO<SUB>2</SUB> adsorption capacity (adsorptivity) of Mg‐Al‐LDH by about 10‐fold. Of prime importance is that the CO<SUB>2</SUB> adsorptivity of the nanohybrid is strongly dependent on the type of guest POM species, strongly suggesting that the CO<SUB>2</SUB> adsorptivity of the LDH‐based nanohybrid materials can be optimized by ones selection of guest species. The present study clearly demonstrates that the exfoliation–reassembling method is quite effective at enabling synthesis of new LDH nanosheet‐based hybrid materials with improved CO<SUB>2</SUB> adsorption capabilities.</P>

Direct growth of 2D nickel hydroxide nanosheets intercalated with polyoxovanadate anions as a binder-free supercapacitor electrode

Gunjakar, Jayavant L.,Inamdar, Akbar I.,Hou, Bo,Cha, SeungNam,Pawar, S. M.,Abu Talha, A. A.,Chavan, Harish S.,Kim, Jongmin,Cho, Sangeun,Lee, Seongwoo,Jo, Yongcheol,Kim, Hyungsang,Im, Hyunsik The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.19

<P>A mesoporous nanoplate network of two-dimensional (2D) layered nickel hydroxide Ni(OH)2 intercalated with polyoxovanadate anions (Ni(OH)2-POV) was built using a chemical solution deposition method. This approach will provide high flexibility for controlling the chemical composition and the pore structure of the resulting Ni(OH)2-POV nanohybrids. The layer-by-layer ordered growth of the Ni(OH)2-POV is demonstrated by powder X-ray diffraction and cross-sectional high-resolution transmission electron microscopy. The random growth of the intercalated Ni(OH)2-POV nanohybrids leads to the formation of an interconnected network morphology with a highly porous stacking structure whose porosity is controlled by changing the ratio of Ni(OH)2 and POV. The lateral size and thickness of the Ni(OH)2-POV nanoplates are ∼400 nm and from ∼5 nm to 7 nm, respectively. The obtained thin films are highly active electrochemical capacitor electrodes with a maximum specific capacity of 1440 F g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP>, and they withstand up to 2000 cycles with a capacity retention of 85%. The superior electrochemical performance of the Ni(OH)2-POV nanohybrids is attributed to the expanded mesoporous surface area and the intercalation of the POV anions. The experimental findings highlight the outstanding electrochemical functionality of the 2D Ni(OH)2-POV nanoplate network that will provide a facile route for the synthesis of low-dimensional hybrid nanomaterials for a highly active supercapacitor electrode.</P>

Self-assembly of layered double hydroxide 2D nanoplates with graphene nanosheets: an effective way to improve the photocatalytic activity of 2D nanostructured materials for visible light-induced O₂ generation

Gunjakar, Jayavant L.,Kim, In Young,Lee, Jang Mee,Lee, Nam-Suk,Hwang, Seong-Ju The Royal Society of Chemistry 2013 Energy & environmental science Vol.6 No.3

<P>Highly efficient photocatalysts for visible light-induced O<SUB>2</SUB> generation are synthesized <I>via</I> an electrostatically derived self-assembly of Zn–Cr-LDH 2D nanoplates with graphene 2D nanosheets. In the obtained nanohybrids, the positively charged Zn–Cr-LDH nanoplates are immobilized on the surface of negatively charged graphene nanosheets with the formation of a highly porous stacked structure. A strong electronic coupling of the subnanometer-thick Zn–Cr-LDH nanoplates with reduced graphene oxide (RGO)/graphene oxide (GO) nanosheets gives rise not only to the prominent increase of visible light absorption but also to a remarkable depression of the photoluminescence signal. The self-assembled Zn–Cr-LDH–RGO nanohybrids display an unusually high photocatalytic activity for visible light-induced O<SUB>2</SUB> generation with a rate of ∼1.20 mmol h<SUP>−1</SUP> g<SUP>−1</SUP>, which is far superior to that of the pristine Zn–Cr-LDH material (∼0.67 mmol h<SUP>−1</SUP> g<SUP>−1</SUP>). The fact that pristine Zn–Cr-LDH is one of the most effective visible light photocatalysts for O<SUB>2</SUB> production with unusually high quantum efficiency of 61% at <I>λ</I> = 410 nm highlights the excellent functionality of the Zn–Cr-LDH–RGO nanohybrids as visible light active photocatalysts. The Zn–Cr-LDH–RGO nanohybrid shows a higher photocatalytic activity than the Zn–Cr-LDH–GO nanohybrid, providing strong evidence for the superior advantage of the hybridization with RGO. The present findings clearly demonstrate that graphene nanosheets can be used as an effective platform for improving the photocatalytic activity of 2D nanostructured inorganic solids.</P> <P>Graphic Abstract</P><P>Highly efficient photocatalysts for visible light-induced O<SUB>2</SUB> generation are synthesized by a self-assembly of layered double hydroxide nanoplates with graphene nanosheets. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3ee23989f'> </P>

Exploration of Nanostructured Functional Materials Based on Hybridization of Inorganic 2D Nanosheets

Gunjakar, Jayavant L.,Kim, In Young,Lee, Jang Mee,Jo, Yun Kyung,Hwang, Seong-Ju American Chemical Society 2014 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.118 No.8

<P>The 2D nanosheets of layered inorganic solids prepared by soft-chemical exfoliation reaction can be used as effective building blocks for hybridization with inorganic, organic, bio-, and polymer molecules/nanostructures. In comparison with graphene nanosheets, the 2D inorganic nanosheets boast much higher tunability in their chemical composition and physicochemical properties, leading to the creation of unexpected novel functionalities upon hybridization. Despite such unique and intriguing advantages of inorganic nanosheets, there are still only limited numbers of studies regarding the inorganic nanosheet-based hybrid materials. This Feature Article focuses on fundamental aspects of diverse synthetic strategies of the 2D nanosheet-based nanohybrids such as electrostatically derived reassembling, layer-by-layer deposition, crystal growth on the surface sites of nanosheets, and so on. Also, diverse functionalities of these 2D nanohybrid materials are discussed with an emphasis on the energy and environmental applications such as Li-ion batteries, supercapacitors, photocatalysts, fuel cells, and greenhouse gas capture. A prospect for the exploration of novel inorganic 2D nanosheet-based functional materials is provided along with new strategies to optimize the functionality of 2D inorganic nanosheets and their nanohybrids.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-8/jp410626y/production/images/medium/jp-2013-10626y_0014.gif'></P>

Phase Tuning of Nanostructured Gallium Oxide via Hybridization with Reduced Graphene Oxide for Superior Anode Performance in Li-Ion Battery: An Experimental and Theoretical Study

Patil, Sharad B.,Kim, In Young,Gunjakar, Jayavant L.,Oh, Seung Mi,Eom, Taedaehyeong,Kim, Hyungjun,Hwang, Seong-Ju American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.33

<P>The crystal phase of nanostructured metal oxide can be effectively controlled by the hybridization of gallium oxide with reduced graphene oxide (rGO) at variable concentrations. The change of the ratio of Ga<SUB>2</SUB>O<SUB>3</SUB>/rGO is quite effective in tailoring the crystal structure and morphology of nanostructured gallium oxide hybridized with rGO. This is the first example of the phase control of metal oxide through a change of the content of rGO hybridized. The calculations based on density functional theory (DFT) clearly demonstrate that the different surface formation energy and Ga local symmetry of Ga<SUB>2</SUB>O<SUB>3</SUB> phases are responsible for the phase transition induced by the change of rGO content. The resulting Ga<SUB>2</SUB>O<SUB>3</SUB>–rGO nanocomposites show promising electrode performance for lithium ion batteries. The intermediate Li–Ga alloy phases formed during the electrochemical cycling are identified with the DFT calculations. Among the present Ga<SUB>2</SUB>O<SUB>3</SUB>–rGO nanocomposites, the material with mixed α-Ga<SUB>2</SUB>O<SUB>3</SUB>/β-Ga<SUB>2</SUB>O<SUB>3</SUB>/γ-Ga<SUB>2</SUB>O<SUB>3</SUB> phase can deliver the largest discharge capacity with the best cyclability and rate characteristics, highlighting the importance of the control of Ga<SUB>2</SUB>O<SUB>3</SUB>/rGO ratio in optimizing the electrode activity of the composite materials. The present study underscores the usefulness of the phase-control of nanostructured metal oxides achieved by the change of rGO content in exploring novel functional nanocomposite materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-33/acsami.5b05154/production/images/medium/am-2015-051549_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b05154'>ACS Electronic Supporting Info</A></P>

Solvothermal synthesis of high-performance Ni-Co layered double hydroxide nanofoam electrode for electrochemical energy storage

Patel, R.,Inamdar, A.I.,Hou, B.,Cha, S.,Ansari, A.T.,Gunjakar, J.L.,Im, H.,Kim, H. ELSEVIER 2017 CURRENT APPLIED PHYSICS Vol.17 No.4

<P>A nanofoam nickel cobalt layered double hydroxide (NiCo(OH)(2)) electrode film is fabricated on a stainless-steel substrate with the use of a simple one-step solvothermal process. The nanofoam NiCo(OH)(2) electrode exhibits a high specific capacitance of 2710.2 Fig at a current density.of 9.1 A/g, and a good capacity retention of similar to 70% after 2000 charge-discharge cycles at a high current density of 31.8 A/g. An energy density of 60.23 Wh/kg is obtained at a power density of 1.8 kW/kg. The excellent electrochemical energy storage performance of the NiCo(OH)(2) electrode is due to the synergetic effect of a significantly improved ionic diffusion and an effective charge transfer, which is linked to a well-dispersed interconnected nanofoam morphology and binder-free direct contact with the current collector. (C) 2017 Elsevier B.V. All rights reserved.</P>

Solvothermal synthesis of high-performance Ni-Co layered double hydroxide nanofoam electrode for electrochemical energy storage

라즈쿠마파텔,Akbar I. Inamdar,Bo Hou,차승남,Abu Talha Ansari,Jayavant L. Gunjakar,임현식,김형상 한국물리학회 2017 Current Applied Physics Vol.17 No.4

A nanofoam nickel cobalt layered double hydroxide (NiCo(OH)2) electrode film is fabricated on a stainless-steel substrate with the use of a simple one-step solvothermal process. The nanofoam NiCo( OH)2 electrode exhibits a high specific capacitance of 2710.2 F/g at a current density of 9.1 A/g, and a good capacity retention of ~70% after 2000 charge-discharge cycles at a high current density of 31.8 A/g. An energy density of 60.23 Wh/kg is obtained at a power density of 1.8 kW/kg. The excellent electrochemical energy storage performance of the NiCo(OH)2 electrode is due to the synergetic effect of a significantly improved ionic diffusion and an effective charge transfer, which is linked to a well-dispersed interconnected nanofoam morphology and binder-free direct contact with the current collector.

One-step facile route to copper cobalt sulfide electrodes for supercapacitors with high-rate long-cycle life performance

Ahmed, Abu Talha Aqueel,Chavan, Harish S.,Jo, Yongcheol,Cho, Sangeun,Kim, Jongmin,Pawar, S.M.,Gunjakar, Jayavant L.,Inamdar, Akbar I.,Kim, Hyungsang,Im, Hyunsik Elsevier 2017 Journal of alloys and compounds Vol.724 No.-

<P><B>Abstract</B></P> <P>The impressive electrochemical energy storage performance of Earth-abundant ternary copper cobalt sulfide (CCS) thin film electrodes that are prepared on stainless steel substrates via a simple and cost-effective hydrothermal process is demonstrated. The optimized CCS electrode shows a high specific capacitance of ∼516 F/g at a current density of 10 A/g, a good rate capability of ∼72% at a high current density of 50 A/g, and a good cycling retention of ∼66% with a coulombic efficiency of ∼99% after 10,000 charge-discharge cycles. The CCS electrode exhibits a high energy density of ∼35.2 Wh/kg at a power density of ∼6.6 kW/kg. The excellent electrochemical supercapacitor properties of the CCS electrode are a result of a synergetic effect between the uniform full coverage, robust adhesion, and desired chemical composition. A low charge transfer resistance, resulting from the large electrochemically active surface area (ECSA) and good diffusion, significantly contributes to the enhanced electrochemical supercapacitor performance. This excellent CCS electrode material has the potential to become a low-cost and long-cycle life electrode for the next-generation high-power-capacity supercapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A binder-free CuCo<SUB>2</SUB>S<SUB>4</SUB> electrode is synthesized using one-pot hydrothermal deposition. </LI> <LI> Superior electrochemical energy storage-deliver performance is demonstrated. </LI> <LI> High specific capacitance, excellent rate performance, and high rate long-term cyclic stability are obtained. </LI> </UL> </P>