Gubbala V. Ramesh

Photocatalytic Water Splitting under Visible Light by Mixed-Valence Sn3O4

A mixed-valence tin oxide, (Sn(2+))2(Sn(4+))O4, was synthesized via a hydrothermal route. The Sn3O4 material consisted of highly crystalline {110} flexes. The Sn3O4 material, when pure platinum (Pt) was used as a co-catalyst, significantly catalyzed water-splitting in aqueous solution under illumination of visible light (λ > 400 nm), whereas neither Sn(2+)O nor Sn(4+)O2 was active toward the reaction. Theoretical calculations have demonstrated that the co-existence of Sn(2+) and Sn(4+) in Sn3O4 leads to a desirable band structure for photocatalytic hydrogen evolution from water solution. Sn3O4 has great potential as an abundant, cheap, and environmentally benign solar-energy conversion catalyst.

Low‐Temperature Remediation of NO Catalyzed by Interleaved CuO Nanoplates

A copper(II)-oxide-based exhaust catalyst exhibits better activity than Pt- and Rh-nanoparticle catalysts in NO remediation at 175 °C. Following theoretical design, the CuO catalyst is rationally prepared; CuO nanoplates bearing a maximized amount of the active {001} facet are arranged in interleaved layers. A field test using a commercial gasoline engine demonstrates the ability of the catalyst to remove NO from the exhaust of small vehicles.

Gold photosensitized SrTiO3 for visible-light water oxidation induced by Au interband transitions

Gold nanoparticle (NP) photosensitization over semiconductors with a large band gap has emerged as a promising strategy for developing visible-light responsive photocatalytic materials. However, its application in harsh photocatalytic oxidation still remains a significant challenge. Furthermore, energetic charge carriers created in Au interband transitions under visible light are frequently ignored in this field. In the current work, for the first time, a remarkable visible-light photocatalytic water oxidation activity (14.9 μmol h−1: 0.2 g catalyst, 5 mmol AgNO3), even slightly higher than that of commercial WO3, was achieved over Au photosensitized SrTiO3 (1.1 wt%). In an elaborate study, electron transfer from gold to SrTiO3 was confirmed by STEM-EDS characterization on selective Ag deposition over SrTiO3. A combined investigation of apparent quantum efficiency results, theoretical simulation study on Au NPs optical excitation and relative band position analysis in Au/SrTiO3 reveals that these hot electrons transferred from gold to SrTiO3 mainly come from Au interband transitions other than plasmon resonance, while leaving holes on Au with enough oxidative potentials are responsible for water oxidation. The capability of involving Au interband transition in photosensitization for visible light water oxidation opens up new opportunities in designing and preparing visible-light responsive photocatalysts.

Activated interiors of clay nanotubes for agglomeration-tolerant automotive exhaust remediation†

Naturally occurring clay nanotubes, halloysite (Al2Si2O5(OH)4·2H2O), with exterior and interior surfaces, respectively, composed of SiOx and AlOx layers, act as an agglomeration-tolerant exhaust catalyst when copper–nickel alloy nanoparticles (Cu–Ni NPs, 2–3 nm) are immobilized at the AlOx interior. Co-reduction of Cu2+ and Ni2+ (respectively derived from CuCl2 and NiCl2) in the presence of sodium citrate (Na3C6H5O7·2H2O) and halloysite yielded the required nanocomposite, Cu–Ni@halloysite. Cu–Ni@halloysite efficiently catalyzes the purification of simulated motor vehicle exhaust comprising nitrogen monoxide (NO) and carbon monoxide (CO) near the activation temperature of Pt-based exhaust catalysts, ≤400 °C, showing its potential as an alternative to Pt-based catalysts. In contrast, a different halloysite nanocomposite with the SiOx exterior decorated with Cu–Ni NPs, Cu–Ni/halloysite, is poorly active even at >400 °C because of particle agglomeration. The enhanced exhaust-purification activity of Cu–Ni@halloysite can ultimately be attributed to the topology of the material, where the alloy NPs are immobilized at the tubular AlOx interior and protected from particle agglomeration by the tubular form and SiOx exterior.

Promoted C–C bond cleavage over intermetallic TaPt3 catalyst toward low-temperature energy extraction from ethanol

Novel intermetallic TaPt3 nanoparticles (NPs) are materialized, which exhibit much higher catalytic performance than state-of-the-art Pt3Sn NPs for electrooxidation of ethanol. In situ infrared-reflection-absorption spectroscopy (IRRAS) elucidates that the TaPt3 NPs cleave the C–C bond in ethanol at lower potentials than Pt NPs, efficiently promoting complete conversion of ethanol to CO2. Single-cell tests demonstrate the feasibility of the TaPt3 NPs as a practical energy-extraction catalyst for ethanol fuels, with more than two times higher output currents than Pt-based cells at high discharge currents.

Synthesis and electrocatalytic performance of atomically ordered nickel carbide (Ni3C) nanoparticles

Atomically ordered nickel carbide, Ni3C, was synthesized by reduction of nickel cyclopentadienyl (NiCp2) with sodium naphthalide to form Ni clusters coordinated by Cp (Ni-Cp clusters). Ni-Cp clusters were thermally decomposed to Ni3C nanoparticles smaller than 10 nm. The Ni3C nanoparticles showed better performance than Ni nanoparticles and Au nanoparticles in the electrooxidation of sodium borohydride.

Stimulation of Electro-oxidation Catalysis by Bulk-Structural Transformation in Intermetallic ZrPt3 Nanoparticles

Although compositional tuning of metal nanoparticles (NPs) has been extensively investigated, possible control of the catalytic performance through bulk-structure tuning is surprisingly overlooked. Here we report that the bulk structure of intermetallic ZrPt3 NPs can be engineered by controlled annealing and their catalytic performance is significantly enhanced as the result of bulk-structural transformation. Chemical reduction of organometallic precursors yielded the desired ZrPt3 NPs with a cubic FCC-type structure (c-ZrPt3 NPs). The c-ZrPt3 NPs were then transformed to a different phase of ZrPt3 with a hexagonal structure (h-ZrPt3 NPs) by annealing at temperatures between 900 and 1000 °C. The h-ZrPt3 NPs exhibited higher catalytic activity and long-term stability than either the c-ZrPt3 NPs or commercial Pt/C NPs toward the electro-oxidation of ethanol. Theoretical calculations have elucidated that the enhanced activity of the h-ZrPt3 NPs is attributed to the increased surface energy, whereas the stability of the catalyst is retained by the lowered bulk-free-energy.

Mixed-valence NaSb3O7 support toward improved electrocatalytic performance in the oxygen-reduction reaction

Nanocrystals of sodium antimony oxide, NaSb3O7 (pyrochlore structure, a = 1.030 nm), act as an efficient catalyst support for the electrocatalytic oxygen-reduction reaction (ORR) in acidic media. The NaSb3O7 nanocrystals (edge length ∼ 150 nm) were synthesized by hydrothermal decomposition of SbCl5 in aqueous solution of NaOH. The NaSb3O7 nanocrystals were then decorated with Pt nanoparticles by chemical reduction of H2PtCl6 in water to yield an ORR catalyst, Pt/NaSb3O7. The Pt/NaSb3O7 exhibited higher ORR performance than the state-of-the-art Pt/TiO2- or Pt/C catalysts in terms of the +40 mV higher half-wave reduction potential and the retained electrochemical surface area than the Pt/TiO2 after 10 000-times repeated ORR in an acidic electrolyte. Unlike NaSb3O7, Pt-decorated Sb2O5 (Pt/Sb2O5) was much less active than the Pt/TiO2 or Pt/C. The enhanced ORR activity of the Pt/NaSb3O7 may be attributed to the promoted electron hopping between the Sb3+ and Sb5+ ions in mixed-valence Na1+(Sb3+Sb25+)O7, which is inhibited in single-valence Sb25+O5.

Interleaved mesoporous copper for the anode catalysis in direct ammonium borane fuel cells.

Mesoporous materials with tailored microstructures are of increasing importance in practical applications particularly for energy generation and/or storage. Here we report a mesoporous copper material (MS-Cu) can be prepared in a hierarchical microstructure and exhibit high catalytic performance for the half-cell reaction of direct ammonium borane (NH3BH3) fuel cells (DABFs). Hierarchical copper oxide (CuO) nanoplates (CuO Npls) were first synthesized in a hydrothermal condition. CuO Npls were then reduced at room temperature using water solution of sodium borohydride (NaBH4) to yield the desired mesoporous copper material, MS-Cu, consisting of interleaved nanoplates with a high density of mesopores. The surface of MS-Cu comprised high-index facets, whereas a macroporous copper material (MC-Cu), which was prepared from CuO Npls at elevated temperatures in a hydrogen stream, was surrounded by low-index facets with a low density of active sites. MS-Cu exhibited a lower onset potential and improved durability for the electro-oxidation of NH3BH3 than MC-Cu or copper particles because of the catalytically active mesopores on the interleaved nanoplates.