Solar Energy Harvesting on S- and N-doped nanoporous Carbons

Nowadays heteroatom-containing carbonaceous materials such as graphene or CNT have gained more and more attention of the scientists searching for inexpensive substitutes of the catalysts for energy related applications such an oxygen reduction reactions. Discovery of graphene and an extensive characterization of its electronic properties caused that the surface of traditional activated carbon has been viewed from other, unexplored before, angles. The main advantage of activated or nanoporous carbons, within the family of carbonaceous materials, is their porosity where the confined pore space effect can be utilized. Recently we have shown that specific nanoporous carbons obtained from commodity polymers can catalyze oxygen evolution reactions1, oxygen reduction reaction2 and exhibit photoluminescence properties3. This behavior was attributed to the specificity of surface microstructure, texture, and chemistry. It was found that the carbons obtained at relatively low temperature (800 oC) contain 10 nm graphic units enhancing their DC conductivity. They have also rich surface chemistry based on sulfur, nitrogen and oxygen containing groups. Even though small sp2 clusters should be important to affect the width of the band gap, the sulfur and nitrogen containing groups are hypothesized to act as chromophores/antenna accepting visible light energy. Electron deficiency on them promotes water splitting in small pores. These groups also change the electronic structure of the carbons surface and bring some level hydrophobicity to it. These features were found as important for oxygen reduction reactions4. These reactions enhance the performance of carbons as supercapcitors when the process takes place in the visible light5. References 1. Ania, C.O.; Seredych, M.; Rodriguez-Castellon, E.; Bandosz, T.J. Visible light driven photoelectrochemical water splitting on metal free nanoporous carbon promoted by chromophoric functional groups. Carbon 79 (2014) 432–441. 2. Seredych, M.; Idrobo, J-C.; Bandosz, T.J. Effect of confined space reduction of graphite oxide followed by sulfur doping on oxygen reduction reaction in neutral electrolyte. J. Mater. Chem. A. 1 (2013) 7059-7067. 3. Bandosz, T.J.; Rodriguez-Castellon, E.; Montenegro J.M.; Seredych, M. Photoluminescence of nanoporous carbons: Opening a new application route for old materials.. Carbon 77 (2014) 651–659. 4. Confined space reduced graphite oxide doped with sulfur as metal-free oxygen reduction catalyst. Seredych, M.; Rodriguez-Castellon, E.; Bandosz, T.J. Carbon 66 (2014) 227-233. 5. Seredych, M.; Rodriguez-Castellon, E.; Biggs, MJ. Skinner, W.l Bandosz, T.J. Effect of visible light and electrode wetting on the capacitive performance of S- and N-doped nanoporous carbons: Importance of surface chemistry. Carbon 78 (2014) 540–558.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Building MOF Nanocomposites with Oxidized Graphitic Carbon Nitride Nanospheres: The Effect of Framework Geometry on the Structural Heterogeneity

Composite of two MOFs, copper-based Cu-BTC (HKUST-1) and zirconium-based Zr-BDC (UiO-66), with oxidized graphitic carbon nitride nanospheres were synthesized. For comparison, pure MOFs were also obtained. The surface features were analyzed using x-ray diffraction (XRD), sorption of nitrogen, thermal analysis, and scanning electron microscopy (SEM). The incorporation of oxidized g-C3N4 to the Cu-BTC framework caused the formation of a heterogeneous material of a hierarchical pores structure, but a decreased surface area when compared to that of the parent MOF. In the case of UiO-66, functionalized nanospheres were acting as seeds around which the crystals grew. Even though the MOF phases were detected in both materials, the porosity analysis indicated that in the case of Cu-BTC, a collapsed MOF/nonporous and amorphous matter was also present and the MOF phase was more defectous than that in the case of UiO-66. The results suggested different roles of oxidized g-C3N4 during the composite synthesis, depending on the MOF geometry. While spherical units of UiO-66 grew undisturbed around oxidized and spherical g-C3N4, octahedral Cu-BTC units experienced geometrical constraints, leading to more defects, a disturbed growth of the MOF phase, and to the formation of mesopores at the contacts between the spheres and MOF units. The differences in the amounts of CO2 adsorbed between the MOFs and the composites confirm the proposed role of oxidized g-C3N4 in the composite formation

Exploring the Silent Aspect of Carbon Nanopores

Recently, owing to the discovery of graphene, porous carbons experienced a revitalization in their explorations. However, nowadays, the focus is more on search for suitable energy advancing catalysts sensing, energy storage or thermal/light absorbing features than on separations. In many of these processes, adsorption, although not emphasized sufficiently, can be a significant step. It can just provide a surface accumulation of molecules used in other application-driving chemical or physical phenomena or can be even an additional mechanism adding to the efficiency of the overall performance. However, that aspect of confined molecules in pores and their involvement in the overall performance is often underrated. In many applications, nanopores might silently advance the target processes or might very directly affect or change the outcomes. Therefore, the objective of this communication is to bring awareness to the role of nanopores in carbon materials, and also in other solids, to scientists working on cutting-edge application of nonporous carbons, not necessary involving the adsorption process directly. It is not our intention to provide a clear explanation of the small pore effects, but we rather tend to indicate that such effects exist and that their full explanation is complex, as complex is the surface of nanoporous carbons

Highly mesoporous carbons obtained using a dynamic template method

New nanoporous carbons with extremely high mesopore volumes and surface areas were obtained using mesoporous silica with a 3-D wormhole porous framework as templates. Mesoporous silica was synthesized following the literature described methods. Polystyrene sulfonic acid-based organic salts were used as carbon precursors. To evaluate the effect of sodium on porosity development silica matrices with various thicknesses of pore walls were synthesized. Prior to carbonization, in order to increase surface heterogeneity, the precursor chemistry was modified by cation exchange with catalytically active metals (i.e., copper, nickel, cobalt). Carbonization followed by HF etching of silica templates generated mesoporous carbons with large surface areas and high pore volumes, which is accompanied by high dispersion of catalytically active metals on the carbon surface. Sodium present in the carbonaceous precursor causes in the dynamic template effect via its reactions with a silica matrix during carbonization. This, along with reactive gases evolved during heating lead to the expansion of the carbonaceous structure, and thus to the unique wide mesopore size distributions of the templated carbons with pore sizes between 10 and 50 nm and their volume exceeding 2.5 cm3 g−1.The financial support for this research, provided by FICYT and PSC CUNY (PSC CUNY 66382-0035) is gratefully acknowledged. We thank Dr. Pis and Dr. Beguin for kindly providing SEM and XRD, and TEM, respectively. Thomas Cacciaguerra is also acknowledged for assistance in TEM analysis.Peer reviewe

Sodium on the Surface of Activated Carbons as a Factor Enhancing Reactive Adsorption of Dibenzothiophene

On the basis of the results described in the literature on the reactivity of sodium toward DBT and its derivates, the effect of sodium dispersed on the surface of a carbonaceous support on the removal of DBT from hexane solution at ambient conditions has been investigated. Since the main objective of this paper is to demonstrate the effect of sodium on the reactive adsorption of DBT from an organic solvent, hexane was chosen as a model solvent. As adsorbents, two carbons with and without sodium on the surface were investigated. The carbons are obtained by carbonization of polystyrene−sulfonic acid−co-maleic acid in sodium salt at 800 °C in nitrogen. The results show that sodium present on the surface of carbon takes part in the reaction with DBT in which sodium metalates and sodium sulfides are formed.This work was supported by FICYT and PSC CUNY (PSC CUNY 66382-0035). The authors thank Dr. Martin Gorbaty of ExxonMobil for inspiration and fruitful discussion. Dr. Alvarez is kindly acknowledged for his help in SEM.Peer reviewe

CO2 interactions with porous carbons: Is the surface stable at ambient conditions?

Interactions of CO2 with polymer derived carbon/rGO composites at ambient conditions were studied. Both, dynamic adsorption tests and equilibrium adsorption measurements were analyzed. The samples differed in the porosity, oxidation level and speciation of sulfur on the surface. Even though more CO2 was adsorbed on the oxidized sample than in the unmodified one, the surface chemistry of the latter was found as having more pronounced effect on attracting CO2 to the pore system. The results showed the marked changes in S-doped nanoporous carbon composite surface chemistry upon CO2 adsorption at ambient conditions. The changes were more pronounced for carbon with higher density of sulfur in thiophenic configurations on the surface emphasizing the role of these species in CO2 reduction. Even though CO could not be the target of our detection, identification of water, SO and SO2 as products of surface reactions supports our hypothesis that CO2 adsorption was accompanied by some extent of its reduction to CO. CO is formed in the process of electron transfer from thiophenes to CO2 in which the former are oxidized forming sulfones and sulfonic acids. Those species are likely thermodynamically unstable and decompose forming SO/SO2 and water providing additional electrons for CO2 reduction. Conductivity of carbon matrix and the local increase in this feature owing to the presence of the graphene-based phase facilitate this process. Based on the results collected, it is recommended that the stability of carbons towards carbon dioxide should be evaluated before it is used as CO2 sequestration medium

Robust graphene-based monoliths of homogeneous ultramicroporosity

Graphite oxide (GO) and graphene monoliths were prepared using the unidirectional freezing of GO water suspension. These materials were saturated with a poly(ammonium-4-styrene sulfonate) water soluble polymer and then carbonized at 1123 K. This process increases significantly the materials strength and density. A uniform deposition of the polymer-derived carbon on the external layers of the graphene sheets of the monolith was found. The carbon from polymer not only provided more contact between the graphene sheets but also apparently increased the overall graphitization level (based on Raman spectra). The modification decreased the electrical resistance by one order of magnitude compared to that of the graphene monolith. N-2 adsorption at 77 K showed that the thus-treated graphene monoliths have quite homogenous pores with the pore width of 0.7 nm. These pores, combined with large transport pores, and conductive properties make the monoliths tested the promising materials for separation, energy storage, and/or gas sensing. The tunability of the properties and pore structure of the robust graphene ultramicroporous monolith through the control of chemistry of the initial GO monolith was shown. (C) 2015 Elsevier Ltd. All rights reserved.ArticleCARBON. 87:87-97 (2015)journal articl

The effects of activated carbon surface features on the reactive adsorption of carbamazepine and sulfamethoxazole

© 2014 Elsevier Ltd. All rights reserved.Two commercial carbons, coconut shell- and wood-based were chosen to evaluate the mechanisms of carbamazepine (CBZ) and sulfamethoxazole (SMX) adsorption from a low (ppm level) concentration of these pharmaceuticals. The initial sample and those after adsorption were extensively characterized using potentiometric titration, thermal analysis combined with mass spectroscopy, FTIR, and XPS. It was found that not only porosity but also surface chemistry plays an important role in the adsorption process. The results show that extensive surface reactions take place during adsorption and adsorbates undergo significant transformations in the pore system. The ability of carbon surfaces to form superoxide ions results in the oxidation of CBZ and SMX, and their partial decomposition. Surface chemistry also promotes dimerization of the latter species. Moreover, functional groups of CBZ and SMX, mainly amines, react with oxygen groups of the carbon surface. Thus not only microporous carbons with sizes of pores similar to those of adsorbate molecules, but the carbons with large pores, rich in oxygen groups, can efficiently remove these pharmaceuticals following the reactive adsorption mechanism

Utilization of Third-Stage Waste from a Rice Production for Removal of H2S, NO2 and SO2 from Air:

Materials derived from rice husk fly ash were tested as adsorbents of hydrogen sulphide, sulphur dioxide and nitrogen dioxide. Breakthrough experiments were carried out at ambient temperature either in dry or moist air. The second-stage waste obtained in the extraction of silica from fly ash using sodium hydroxide exhibits the better adsorption capacity compared with that of caustic-modified activated carbons. The high performance is related to the presence of residual sodium hydroxide and other metals such as calcium, which react with acidic gases forming corresponding salts. Moreover, a high dispersion of the alkali and alkaline earth metal sites in the mesopores renders the pH of the solution basic, aiding in the dissociation of hydrogen sulphide, thereby facilitating its oxidation. The oxidation of species is also catalyzed by the carbonaceous surface. While in the case of hydrogen sulphide and sulphur dioxide, water helps in acid-base reactions, the opposite effect is found for NO2. Because its react..

Sulfur-mediated photochemical energy harvesting in nanoporous carbons

This work provides new insights in the field of applied photochemistry based on semiconductor-free nanoporous carbons and its application to sunlight energy harvesting. Using carbon materials of increasing average pore size, chemical functionalization to introduce a variety of O- and S-containing functional groups and monochromatic light, we have shown the dependence of the photochemical conversion of phenol in the confinement of the carbons nanopore space with the wavelength of the irradiation source, the dimensions of the pore voids and their surface chemistry. The photochemical conversion of phenol inside the carbons pore space was found to be very sensitive to the nature of the S-containing groups and the confinement state of the adsorbed pollutant.COA thanks the financial support of the European Research Council through a Consolidator Grant (ERC-CoG-648161-PHOROSOL) and the Spanish MINECO (CTM2014/56770-R). AGB thanks her PhD fellowship (BES-2012-060410). TJB acknowledges the NSF support (CBET 1133112)