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Efficient CO Oxidation by 50-Facet Cu<sub>2</sub>O Nanocrystals Coated with CuO Nanoparticles
Harzandi, Ahmad M.,Tiwari, Jitendra N.,Lee, Ho Sik,Jeon, Himchan,Cho, Woo Jong,Lee, Geunsik,Baik, Jaeyoon,Kwak, Ja Hun,Kim, Kwang S. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.3
<P>As carbon monoxide oxidation is widely used for various chemical processes (such as methanol synthesis and water-gas shift reactions H2O + CO reversible arrow CO2 + H-2) as well as in industry, it is essential to develop highly energy efficient, inexpensive; and eco-friendly catalysts for CO oxidation. Here we report green synthesis of similar to 10 nm sized CuO nanoparticles (NPs) aggregated on similar to 400 nm sized 50-facet Cu2O polyhedral nanocrystals. This CuO-NPs/50-facet Cu2O shows remarkable CO oxidation reactivity with very high specific CO oxidation activity (4.5 mu mol(CO) m(-2) s(-1) at 130 degrees C) and near-complete 99.5% CO conversion efficiency at similar to 175 degrees C. This outstanding catalytic performance by CuO NPs over the pristine multifaceted Cu2O nanocrystals is attributed to the surface oxygen defects present in CuO NPs which facilitate binding of CO and O-2 on their surfaces. This new material opens up new possibilities of replacing the usage of expensive CO oxidation materials.</P>
Pourjavadi A.,Harzandi A. M.,Hosseinzadeh H. The Polymer Society of Korea 2005 Macromolecular Research Vol.13 No.6
A novel, polysaccharide-based, superabsorbent hydrogel was synthesized through crosslinking graft copolymerization of methacrylic acid (MAA) onto kappa-carrageenan ($_{k}C$), using ammonium persulfate (APS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. A proposed mechanism for $_{k}C$g-polymethacrylic acid ($_{k}C$-g-PMAA) formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The effect of grafting variables, including MBA, MAA, and APS concentration, was systematically optimized to achieve a hydrogel with the maximum possible swelling capacity. The swelling kinetics in distilled water and various salt solutions were preliminarily investigated. Absorbency in aqueous salt solutions of lithium chloride, sodium chloride, potassium chloride, calcium chloride, and aluminum chloride indicated that the swelling capacity decreased with increased ionic strength of the swelling medium. This behavior can be attributed to the charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. The swelling of super absorbing hydrogels was measured in solutions with pH ranging from 1 to 13. In addition, the pH reversibility and on-off switching behavior, at pH levels of 3.0 and 8.0, give the synthesized hydrogels great potential as an excellent candidate for the controlled delivery of bioactive agents.
Yoon, Taeseung,Song, Gyujin,Harzandi, Ahmad M.,Ha, Miran,Choi, Sungho,Shadman, Sahar,Ryu, Jaegeon,Bok, Taesoo,Park, Soojin,Kim, Kwang S. The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.33
<P>We demonstrate a new class of synthetic process for three-dimensional porous Ge materials (3D-pGe). Starting from zeotype-borogermanate microcubes, the 3D-pGe sample was synthesized through a thermal deformation of artificial Ge-rich zeolite, etching, and subsequent hydrogen reduction. After the synthesis, the resultant byproducts were simply removed by warm water instead of a harmful etchant such as hydrofluoric acid. Benefiting from the structural advantages with meso/macro porosity in the overall framework, the as-prepared 3D-pGe exhibits good electrochemical properties as anode materials for lithium-ion batteries with a high capacity (770 mA h g<SUP>−1</SUP>), cycling stability (capacity retention over 83%) after 250 cycles at 1C, and excellent rate capability (32% for 10C with respect to C/5) as well as pseudocapacitive contribution by surface-controlled reaction. This study paves the way to a new synthesis strategy of 3D porous Ge anode materials from zeolite for large-scale energy storage applications.</P>
Tiwari, Jitendra N.,Lee, Wang Geun,Sultan, Siraj,Yousuf, Muhammad,Harzandi, Ahmad M.,Vij, Varun,Kim, Kwang S. American Chemical Society 2017 ACS NANO Vol.11 No.8
<P>A key challenge in developing fuel cells is the fabrication of low-cost electrocatalysts with high activity and long durability for the two half-reactions, i.e., the methanol/ethanol oxidation reaction (MOR/EOR) and the oxygen reduction reaction (ORR). Herein, we report a conductivity-enhanced bifunctional electrocatalyst of nanoscale-coated Pt-Pd alloys on both tin-doped indium (TDI) and reduced graphene oxide (rGO), denoted as Pt-Pd@TDI/rGO. The mass activities of Pt in the Pt-Pd@TDI/rGO hybrid toward MOR, EOR, and ORR are 2590, 1500, and 2690 mA/mg, respectively. The ORR Pt specific activity and mass activity of the electrocatalyst are 17 and 28 times larger, respectively, than commercial Pt/C catalysts. All these remarkable catalytic performances are attributed to the role of TDI in enhancing the catalytic activity,by protecting Pt from oxidation as well as rapid mass/charge transfer due to the synergistic effect between surface Pt-Pd alloys and TDI/rGO.</P>
Pt-like hydrogen evolution on a V2O5/Ni(OH)2 electrocatalyst
Meena, Abhishek,Ha, Miran,Chandrasekaran, S. Selva,Sultan, Siraj,Thangavel, Pandiarajan,Harzandi, Ahmad M.,Singh, Bhupendra,Tiwari, Jitendra N.,Kim, Kwang S. The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.26
<P>We report a highly efficient and cost-effective binder-free catalyst for the hydrogen evolution reaction (HER) using V2O5 particles on nickel foam (NF) (V2O5/Ni(OH)2@NF). This low-cost catalyst exhibits Pt-like activity with a low overpotential of 39 mV at 10 mA cm<SUP>−2</SUP> (lowest among V-based materials which are known to be generally non-explosive and safe) and long-term stability in a 1 M KOH solution. The overall performance is highly comparable to that of a commercial 20% Pt/C catalyst on NF. Furthermore, the V2O5/Ni(OH)2@NF outperforms the Pt/C catalyst at a higher current density (100 mA cm<SUP>−2</SUP>) which is more preferable for industrial applications. First principles calculations show that the remarkable HER activity is ascribed to the near-zero adsorption free energy (Δ<I>G</I>H*) on the Ni-site of Ni(OH)2@NF and the Ni- and O-sites of <I>in situ</I> generated V2O5@NF, due to the charge transfer arising from adsorbed O atoms on Ni(111), along with high conductivity of NF. O-adsorption on the Ni transition metal surface downshifts the d-band center of the transition metal, which helps in quick hydrogen desorption by weakening the hydrogen binding strength. As a result, most Ni fcc sites of V2O5/Ni(OH)2@NF are more active than pristine Ni fcc sites. The V2O5/Ni(OH)2@NF catalyst initiates overall water splitting at 1.53 V in a 6 M KOH solution for solar-to-hydrogen generation in a two-electrode set-up using a solar panel.</P>
Accelerated Bone Regeneration by Two-Photon Photoactivated Carbon Nitride Nanosheets
Tiwari, Jitendra N.,Seo, Young-Kyo,Yoon, Taeseung,Lee, Wang Geun,Cho, Woo Jong,Yousuf, Muhammad,Harzandi, Ahmad M.,Kang, Du-Seok,Kim, Kwang-Youn,Suh, Pann-Ghill,Kim, Kwang S. American Chemical Society 2017 ACS NANO Vol.11 No.1
<P>Human bone marrow-derived mesenchymal stem cells (hBMSCs) present promising opportunities for therapeutic medicine. Carbon derivatives showed only marginal enhancement in stem cell differentiation toward bone formation. Here we report that red-light absorbing carbon nitride (C3N4) sheets lead to remarkable proliferation and osteogenic differentiation by runt-related transcription factor 2 (Runx2) activation, a key transcription factor associated with osteoblast differentiation. Accordingly, highly effective hBMSCs-driven mice bone regeneration under red light is achieved (91% recovery after 4 weeks compared to 36% recovery in the standard control group in phosphate-buffered saline without red light). This fast bone regeneration is attributed to the deep penetration strength of red light into cellular membranes via tissue and the resulting efficient cell stimulation by enhanced photocurrent upon two-photon excitation of C3N4 sheets near cells. Given that the photoinduced charge transfer can increase cytosolic Ca2+ accumulation, this increase would promote nucleotide synthesis and cellular proliferation/differentiation. The cell stimulation enhances hBMSC differentiation toward bone formation, demonstrating the therapeutic potential of near-infrared two-photon absorption of C3N4 sheets in bone regeneration and fracture healing.</P>