Srinivas Gadipelli

Graphene Oxide Framework Materials: Theoretical Predictions and Experimental Results†

A series of idealized model systemswith various diboronic acid linker concentrations (and con-sequently different pore size, pore volume, and surface areas)were examined (see Supporting Information for details).Structural optimization yielded a circa 1.1 nm interlayerseparation for these ideal structures. The simulated absolute

Switching effective oxygen reduction and evolution performance by controlled graphitization of a cobalt–nitrogen–carbon framework system

We report a purposely designed route for the synthesis of a promising carbon-based electrocatalyst for both ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) from zeolitic imidazolate frameworks (ZIFs). Firstly, precursor ZIFs are rationally designed with a blend of volatile zinc to induce porosity and stable cobalt to induce graphitic domains. Secondly, the self-modulated cobalt–nitrogen–carbon system (SCNCS) is shown to be an effective ORR catalyst after graphitization at mild temperatures. Finally, the best OER catalyst is developed by enhancing graphitization of the SCNCS. For the first time, solely by switching the graphitization conditions of SCNCS, excellent ORR or OER performance is realized. This approach not only opens up a simple protocol for simultaneous optimization of nitrogen doping and graphitization at controlled cobalt concentrations, but also provide a facile method of developing such active catalysts without the use of extensive synthesis procedures.

Nanoconfinement and Catalytic Dehydrogenation of Ammonia Borane by Magnesium‐Metal–Organic‐Framework‐74

Ammonia borane (NH3BH3, AB) has recently received much attention as a promising hydrogen-storage medium among a very large number of candidate materials because of its satisfactory air stability, relatively low molecular mass (30.7 gmol ), and remarkably high energy-storage densities (gravimetric and volumetric hydrogen capacities are 19.6wt% and 140 gL , respectively). However, the direct use of pristine AB as a hydrogen energy carrier in onboard/fuel-cell applications is prevented by its very slow dehydrogenation kinetics below 100 8C and the concurrent release of detrimental volatile by-products such as ammonia, borazine, and diborane. Many different methods have been adopted to promote efficient H2 generation from AB, including catalytic hydrolysis in aqueous solution, ionic liquids, organic solvents, and thermodynamic modifications by formation of hybrid structures with transition metals, alkali-, or alkaline-earth metal/hydrides, 12] or nanoconfined phases using porous scaffolds. However, many of these methods rely on the usage of heavy metal catalysts, aqueous or nonaqueous solutions, and ionic liquids, all of which make the hydrogen density of the systems unacceptably low for practical applications. Furthermore, the vigorous reactions, hygroscopic properties, and water solubility of borohydrides have negative impacts on the dehydrogenation performance and make it difficult to control the release of hydrogen. The other approach is made, in particular, nanocomposition of AB within porous scaffoldings. However, systems still suffers one or more of the followings: either the nanocomposite is heavier or cannot prevent the generation of all the volatile by-products. Hence, more work needs to be done to explore the potential role that catalysts can play to further improve the controllable H2-release kinetics under moderate conditions while at the same time preventing the generation of detrimental byproducts. Over the past few years, porous metal–organic frameworks (MOFs) have emerged as promising multifaceted materials, combining such functions as catalytic activity, 24] shape-selectivity, templating, and purification. Crystalline MOF structures are composed of metal sites linked to organic ligands, yielding three-dimensional extended frameworks that often possess considerable porosity. In principle, the combination of nanoporosity and active metal sites in MOFs makes them potentially useful materials for promoting the decomposition of AB. However, until now, such a use of MOFs has been rare and any future success would depend crucially on the particular choices of a suitable metal center, pore structure, and thermal stability. For instance, Li et al. were the first to show that Y-based MOF as a solid state decomposition agent for AB. The main drawback of AB-Y-MOF is largely added weight due to the heavy Y metal. In addition, for the given very narrow pore structure of Y-MOF, as low as approximately 8 wt% of AB loading is achieved for the reported 1:1 mole ratio. Thus, it is highly desirable to have a light weight MOF with stable and suitable nanopore channels that can hold more than one AB molecule. Herein, we show that the porous MgMOF-74 (Mg2ACHTUNGTRENNUNG(DOBDC), DOBDC=2, 5-dioxido-1, 4-benzenedicarboxylate) is a promising candidate for nanoconfinement and catalytic decomposition of AB for clean and efficient H2 generation. Mg-MOF-74 has a rigid framework, composed of one-dimensional (1D) hexagonal channels (Figure 1a) with a nominal diameter of approximately 12 running parallel to the DOBDC ligands. In as-synthesized material, the Mg cations are coordinated with five oxygen atoms from the DOBDC ligands and one oxygen atom from a terminal water molecule. However, upon heating under vacuum, the terminal water molecules can be easily removed, leading to unsaturated (open) Mg metal sites (decorated on the edges of the hexagonal pore channels) with an open pore structure of high surface area (>1000 mg ). The open Mg metal sites play a vital role in enhanced binding of various gas molecules (H2, CH4, C2H2, NO, etc. ) and successfully used to promote molecular separation. Figure 1b represents AB confinement within the MOF pores as obtained [a] Dr. S. Gadipelli, Dr. J. Ford, Dr. W. Zhou, Dr. H. Wu, Dr. T. J. Udovic, Dr. T. Yildirim NIST Center for Neutron Research Gaithersburg MD 20899-6102 (USA) Fax: (+1)301-921-9847 E-mail : taner@seas.upenn.edu gsrini@seas.upenn.edu [b] Dr. S. Gadipelli, Dr. J. Ford, Dr. T. Yildirim Department of Materials Science and Engineering University of Pennsylvania, Philadelphia PA, 19104 (USA) [c] Dr. W. Zhou, Dr. H. Wu Department of Materials Science and Engineering University of Maryland, College Park MD, 20742 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100090.

Sodium magnesium amidoborane: the first mixed-metal amidoborane

The first example of a mixed-metal amidoborane Na(2)Mg(NH(2)BH(3))(4) has been successfully synthesized. It forms an ordered arrangement in cation coordinations, i.e., Mg(2+) bonds solely to N(-) and Na(+) coordinates only with BH(3). Compared to ammonia borane and monometallic amidoboranes, Na(2)Mg(NH(2)BH(3))(4) can release 8.4 wt% pure hydrogen with significantly less toxic gases.

Tuning of ZIF‐Derived Carbon with High Activity, Nitrogen Functionality, and Yield – A Case for Superior CO2 Capture

A highly effective and facile synthesis route is developed to create and tailor metal-decorated and nitrogen-functionalized active microporous carbon materials from ZIF-8. Clear metal- and pyrrolic-N-induced enhancements of the cyclic CO2 uptake capacities and binding energies are achieved, particularly at a much lower carbonization temperature of 700 °C than those often reported (1000 °C). The high-temperature carbonization can enhance the porosity but only at the expense of considerable losses of sample yield and metal and N functional sites. The findings are comparatively discussed with carbons derived from metal–organic frameworks (MOFs) reported previously. Furthermore, the porosity of the MOF-derived carbon is critically dependent on the structure of the precursor MOF and the crystal growth. The current strategy offers a new and effective route for the creation and tuning of highly active and functionalized carbon structures in high yields and with low energy consumption.

A thermally derived and optimized structure from ZIF-8 with giant enhancement in CO2 uptake

We report a new, simple and versatile method to obtain highly active MOF structures by carefully controlled post-synthesis thermal annealing. The active ZIF-8 structure shows highly enhanced CO2/N2 selectivity and a stable cyclic CO2 uptake of ≥1.5 mmol g−1 at 1 bar and 25 °C with a heat of adsorption of ≥30 kJ mol−1, which is over 100% greater than ≈0.7 mmol g−1 and ≈17 kJ mol−1, respectively of ZIF-8.

An Ultrahigh Pore Volume Drives Up the Amine Stability and Cyclic CO2 Capacity of a Solid‐Amine@Carbon Sorbent

Carbon monoliths of ultrahigh pore volume (5.35 cm(3) g(-1) ) and high surface area (2700 m(2) g(-1) ) accommodate a record high level of amine(tetraethylenepentamine), up to 5 g g(-1) within its hierarchically networked micro-/mesopores over a wide range. Thus, this solid-amine@carbon shows exceptional CO2 sorption and stable cyclic capacities at simulated flue-gas conditions.

A highly practical route for large-area, single layer graphene from liquid carbon sources such as benzene and methanol†

Through a detailed systematic study, we determined the parameters critical for high-quality, single-layer graphene formation and developed a straightforward synthesis that requires no explosive hydrogen or methane gas flow. The synthesis is further simplified by using only a liquid carbon source such as methanol. Of over a dozen liquid carbon sources studied, methanol is found to be unique in that it acts as both a carbon/hydrogen source and an inhibitor to amorphous carbon growth. No deposition of amorphous carbon was observed, regardless of vapor pressure, unlike methane and other hydrocarbons. Finally, we describe a protocol to control graphene growth to a single side or selected location on the copper substrate, which is required for most device applications. Using our novel methods, we have prepared high-quality, single-layer graphene samples at the inch scale that have been thoroughly characterized with Raman spectroscopy, optical transmittance, scanning electron microscopy and sheet resistance measurements. Our method is safe, simple, and economical and will be of value to both fundamental researchers and nanodevice engineers.

Superior CO2 adsorption from waste coffee ground derived carbons

Utilising the hugely abundant waste from spent coffee grounds (CGs), KOH activated highly microporous carbons with surface areas of 2785 m2 g−1 and micropore volumes of 0.793 cm3 g−1 were synthesised that are capable of uptake capacities near 3 mmol g−1 at 50 °C and 1 bar. Importantly such uptake capacities are achieved though the materials superior microporous character and without doping within the carbon matrix, thereby ensuring facile regeneration with a binding enthalpy of only 26 kJ mol−1 and therefore being capable of energy unintensive cycleable adsorption processes. Furthermore, excellent tunability of pore-size is demonstrated from narrow micropores through to narrow mesopores, enabling optimised adsorption over a range of pressures.

Salt Templating with Pore Padding: Hierarchical Pore Tailoring towards Functionalised Porous Carbons

We propose a new synthetic route towards nanoporous functional carbon materials based on salt templating with pore-padding approach (STPP). STPP relies on the use of a pore-padding agent that undergoes an initial polymerisation/ condensation process prior to the formation of a solid carbon framework. The pore-padding agent allows tailoring hierarchically the pore-size distribution and controlling the amount of heteroatom (nitrogen in this case) functionalities as well as the type of nitrogen (graphitic, pyridinic, oxides of nitrogen) incorporated within the carbon framework in a single-step-process. Our newly developed STPP method offers a unique pathway and new design principle to create simultaneously high surface area, microporosity, functionality and pore hierarchy. The functional carbon materials produced by STPP showed a remarkable CO2 /N2 selectivity. At 273 K, a carbon with only micropores offered an exceptionally high CO2 adsorption capacity whereas a carbon with only mesopores showed promising CO2 -philicity with high CO2 /N2 selectivity in the range of 46-60 %, making them excellent candidates for CO2 capture from flue gas or for CO2 storage.