Effect of confinement of horse heart cytochrome c and formate dehydrogenase from Candida boidinii on mesoporous carbons on their catalytic activity.

This study reports the immobilization of two biocatalysts (e.g., cytochrome c-Cyt c-and the non-metalloenzyme formate dehydrogenase from Candida boidinii-cbFDH) on a series of mesoporous carbons with controlled pore sizes. The catalytic activity of the nanoconfined proteins was correlated with the pore size distribution of the carbon materials used as supports. The electrochemical behaviour of nanoconfined Cyt c showed direct electron transfer electroactivity in pore sizes matching tightly the protein dimension. The pseudo-peroxidase activity towards H2O2 reduction was enhanced at pH 4.0, due to the protein conformational changes. For cbFDH, the reduction of CO2 towards formic acid was evaluated for the nanoconfined protein, in the presence of nicotinamide adenine dinucleotide (NADH). The carbons displayed different cbFDH uptake capacity, governed by the dimensions of the main mesopore cavities and their accessibility through narrow pore necks. The catalytic activity of nanoconfined cbFDH was largely improved, compared to its performance in free solution. Regardless of the carbon support used, the production of formic acid was higher upon immobilization with lower nominal cbFDH:NADH ratios.

Photochemical and electrochemical reduction of graphene oxide thin films: tuning the nature of surface defects.

Individual and combined photo(electro)chemical reduction treatments of graphene oxide thin films have been performed to modulate the type of defects introduced into the graphene sheets during the reduction. These were characterized by X-ray photoelectron and Raman spectroscopies, nuclear reaction analysis and electrochemical methods. Illumination of the graphene oxide thin film electrodes with low irradiance simulated solar light provoked the photoassisted reduction of the material with negligible photothermal effects. The photoreduced graphene oxide displayed a fragmented sp2 network due to the formation of a high density of defects (carbon vacancies) and the selective removal of epoxides and hydroxyl groups. In contrast, the electrochemical reduction under mild polarization conditions favored the formation of sp3 defects over vacancies, with a preferential removal of carbonyl and carboxyl groups over hydroxyl/epoxides. Used in conjunction, mild photochemical and electrochemical treatments allowed the obtainment of reduced graphene oxides with varied reduction degrees (ca. C/O ratio ranging from 4.9 to 2.2), and surface defects. Furthermore, the electrochemical reduction prevented the formation of vacancies during the subsequent illumination step. In contrast, both types of defects were accumulated when the GO electrode was first exposed to illumination and then polarized.

Photochemical Degradation of Cyanides and Thiocyanates from an Industrial Wastewater.

We have explored the simultaneous degradation of cyanides and thiocyanate present in wastewaters from a cokemaking factory using photoassisted methods under varied illumination conditions (from simulated solar light to UV light). Overall, the photochemical degradation of cyanides was more efficient than that of thiocyanates, regardless of the illumination conditions, the effect being more pronounced in the absence of a photocatalyst. This is due to their different degradation mechanism that in the case of thiocyanates is dominated by fast recombination reactions and/or charge transfer reactions to electron scavengers. In all cases, cyanate, ammonia, nitrates, and nitrites were formed at different amounts depending on the illumination conditions. The conversion yield under simulated solar light was almost complete for cyanides and quite high for thiocyanates after 6 h of illumination. Regarding toxicity, photochemical oxidation at 254 nm and under simulated solar light decreased significantly the toxicity of the pristine wastewater, showing a correlation with the intensity of the irradiation source. This indicate that simulated light can be effectively used to reduce the toxicity of industrial effluents, opening an interesting perspective for optimizing cyanide detoxification systems based on natural light.

Surface Modification of a Nanoporous Carbon Photoanode upon Irradiation.

The photocorrosion of a nanoporous carbon photoanode, with low surface functionalization and high performance towards the photoelectrochemical oxidation of water using simulated solar light, was investigated. Two different light configurations were used to isolate the effect of the irradiation wavelength (UV and visible light) on the textural and chemical features of the carbon photoanode, and its long-term photocatalytic performance for the oxygen evolution reaction. A complete characterization of the carbon showed that the photocorrosion of carbon anodes of low functionalization follows a different pathway than highly functionalized carbons. The carbon matrix gets slightly oxidized, with the formation of carboxylic and carbonyl-like moieties in the surface of the carbon anode after light exposure. The oxidation of the carbon occurred due to the photogeneration of oxygen reactive species upon the decomposition of water during the irradiation of the photoanodes. Furthermore, the photoinduced surface reactions depend on the nature of the carbon anode and its ability to photogenerate reactive species in solution, rather than on the wavelength of the irradiation source. This surface modification is responsible for the decreased efficiency of the carbon photoanode throughout long illumination periods, due to the effect of the oxidation of the carbon matrix on the charge transfer. In this work, we have corroborated that, in the case of a low functionalization carbon material, the photocorrosion also occurs although it proceeds through a different pathway. The carbon anode gets gradually slightly oxidized due to the photogeneration of O-reactive species, being the incorporation of the O-groups responsible for the decreased performance of the anode upon long-term irradiation due to the effect of the oxidation of the carbon matrix on the electron transfer.

Design and development of a controlled pressure/temperature set-up for in situ studies of solid-gas processes and reactions in a synchrotron X-ray powder diffraction station.

A novel set-up has been designed and used for synchrotron radiation X-ray high-resolution powder diffraction (SR-HRPD) in transmission geometry (spinning capillary) for in situ solid-gas reactions and processes in an isobaric and isothermal environment. The pressure and temperature of the sample are controlled from 10(-3) to 1000 mbar and from 80 to 1000 K, respectively. To test the capacities of this novel experimental set-up, structure deformation in the porous material zeolitic imidazole framework (ZIF-8) by gas adsorption at cryogenic temperature has been studied under isothermal and isobaric conditions. Direct structure deformations by the adsorption of Ar and N2 gases have been observed in situ, demonstrating that this set-up is perfectly suitable for direct structural analysis under in operando conditions. The presented results prove the feasibility of this novel experimental station for the characterization in real time of solid-gas reactions and other solid-gas processes by SR-HRPD.

Visible-light photochemical activity of nanoporous carbons under monochromatic light.

By using monochromatic light the ability of semiconductor-free nanoporous carbons to convert the low-energy photons from the visible spectrum into chemical reactions (i.e. phenol photooxidation) is demonstrated. Data shows that the onset wavelength of the photochemical activity can be tuned by surface functionalization, with enhanced visible-light conversion upon introducing N-containing groups.

Linz-Donawitz steel slag for the removal of hydrogen sulfide at room temperature.

Slags collected from the basic oxygen furnaces of two Linz-Donawitz steel making plants were tested as adsorbents for H(2)S removal at room temperature (298 K). Two different particle size fractions, namely <212 and 212-500 µm, were selected from the original slag samples. Dynamic adsorption tests were carried out using a column-bed configuration and retention capacities were calculated after bed exhaustion. Retention capacities as high as 180 mg of H(2)S g(-1) of slag were attained, in spite of the very low specific surface area of the steel slags. As expected, humidity played a crucial role in the removal of H(2)S. Particle size had also an important effect on the capacity of the adsorption beds. Analysis of the exhausted slags revealed considerable amounts of elemental sulfur on the surface of the particles. Sulfates were also found on the exhausted slags, especially on the 212-500 µm size fractions. The characterization of the slags prior and after the H(2)S adsorption experiments allowed us to postulate plausible mechanisms to understand the outstanding capacity of these steel byproduct for H(2)S adsorption.

Performance of a C-containing Cu-based photocatalyst for the degradation of tartrazine: Comparison of performance in a slurry and CPC photoreactor under artificial and natural solar light.

A carbon-containing Cu-based material (Cu@C) was used as photocatalyst for the degradation of a commonly food-industry azo-dye (tartrazine, also called Y5), under solar light at laboratory and pilot scale photoreactors. Important performance parameters such as dark adsorption capacity, catalyst́s loading and initial concentration of the dye were first optimized in a slurry photoreactor at laboratory scale under artificial solar light following the kinetics of degradation of the dye. Afterwards, the photocatalytic activity was investigated at pilot scale in a compound parabolic collector (CPC) photoreactor operating for 10 h of irradiation. The degradation of tartrazine is among the highest values reported for alternative metal oxide semiconductors, in both photoreactor configurations. Catalytic data revealed a 3 times faster degradation kinetics of tartrazine in the CPC photoreactor under natural solar light than in the slurry reactor under artificial solar light. This behavior indicates that a moderate photon flux in the CPC is more adequate to operate with the prepared photocatalyst, as it minimizes the recombination of charge carriers in the catalyst. This is important, since most of the photocatalytic tests designed to evaluate the activity of novel materials are frequently carried out under simulated solar light and disregard the impact of photon flux in outdoor conditions.

Fabrication of a biocathode for formic acid production upon the immobilization of formate dehydrogenase from Candida boidinii on a nanoporous carbon.

The immobilization of the non-metallic enzyme formate dehydrogenase from Candida boidinii (CbFDH) into a nanoporous carbon with appropriate pore structure was explored for the bioelectrochemical conversion of CO2 to formic acid (FA). Higher FA production rates were obtained upon immobilization of CbFDH compared to the performance of the enzyme in solution, despite the lower nominal CbFDH to NADH (ß-nicotinamide adenine dinucleotide reduced) cofactor ratio and the lower amount of enzyme immobilized. The co-immobilization of the enzyme and a rhodium complex as mediator in the nanoporous carbon allowed the electrochemical regeneration of the cofactor. Preparative electrosynthesis of FA carried out on biocathodes of relatively large dimensions (ca. 3 cm × 2 cm) confirmed the higher production rate of FA for the immobilized enzyme. Furthermore, the incorporation of a Nafion binder in the biocathodes did not modify the immobilization extent of the CbFDH in the carbon support. Coulombic efficiencies close to 46% were obtained for the electrosynthesis carried out at -0.8 V for the biocathodes prepared using the lowest Nafion binder content and the co-immobilized enzyme and rhodium redox mediator. Although these values may yet be improved, they confirm the feasibility of these biocathodes in larger scales (6 cm2) beyond most common electrode dimensions reported in the literature (ca. a few mm2).

How Reproducible are Surface Areas Calculated from the BET Equation?

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Carbon Black as Conductive Additive and Structural Director of Porous Carbon Gels.

This work investigates the impact of carbon black (CB) as a porogenic agent and conductive additive in the preparation of electrically conductive nanoporous carbon gels. For this, a series of materials were prepared by the polycondensation of resorcinol/formaldehyde mixtures in the presence of increasing amounts of carbon black. The conductivity of the carbon gel/CB composites increased considerably with the amount of CB, indicating a good dispersion of the additive within the carbon matrix. A percolation threshold of ca. 8 wt.% of conductive additive was found to achieve an adequate "point to point" conductive network. This value is higher than that reported for other additives, owing to the synthetic route chosen, as the additive was incorporated in the reactant's mixture (pre-synthesis) rather than in the formulation of the electrodes ink (post-synthesis). The CB strongly influenced the development of the porous architecture of the gels that exhibited a multimodal mesopore structure comprised of two distinct pore networks. The microporosity and the primary mesopore structure remained rather unchanged. On the contrary, a secondary network of mesopores was formed in the presence of the additive. Furthermore, the average mesopore size and the volume of the secondary network increased with the amount of CB.

Carbon-Based Sorbent Coatings for the Determination of Pharmaceutical Compounds by Bar Adsorptive Microextraction.

Thirteen carbon materials comprising commercial activated carbons and lab-made materials (activated carbons, hydrochars, and low-T and high-T activated hydrochars) were assayed as sorbent coatings in bar adsorptive microextration (BAµE) to monitor trace levels of ten common pharmaceutical compounds (PhCs) in environmental water matrices including surface water, seawater, tap water, and wastewater. Polar and nonpolar pharmaceuticals were selected, sulfamethoxazole, triclosan, carbamazepine, diclofenac, mefenamic acid, 17-α-ethinylestradiol, 17-ß-estradiol, estrone, gemfibrozil, and clofibric acid, as model compounds to cover distinct therapeutic classes. Despite having a less-developed porosity, data showed that "in-house" prepared low-T activated hydrochars, obtained from carbohydrates and an eutectic salt mixture at low temperature (i.e., 180 °C) and autogenerated pressure, compete with the best commercial activated carbons for this particular application. The combination of a micro and mesopore network with a rich oxygen-based surface chemistry yielding an acidic nature allowed these low-T activated hydrochars to present the best overall recoveries (between 20.9 and 82.4%) for the simultaneous determination of the ten target PhCs with very distinct chemical properties using high performance liquid chromatography-diode array detection (HPLC-DAD).

Porous Organic Polymers Containing Active Metal Centers for Suzuki-Miyaura Heterocoupling Reactions.

A new generation of confined palladium(II) catalysts covalently attached inside of porous organic polymers (POPs) has been attained. The synthetic approach employed was straightforward, and there was no prerequisite for making any modification of the precursor polymer. First, POP-based catalytic supports were obtained by reacting one symmetric trifunctional aromatic monomer (1,3,5-triphenylbenzene) with two ketones having electron-withdrawing groups (4,5-diazafluoren-9-one, DAFO, and isatin) in superacidic media. The homopolymers and copolymers were made using stoichiometric ratios between the functional groups, and they were obtained with quantitative yields after the optimization of reaction conditions. Moreover, the number of chelating groups (bipyridine moieties) available to bind Pd(II) ions to the catalyst supports was modified using different DAFO/isatin ratios. The resulting amorphous polymers and copolymers showed high thermal stability, above 500 °C, and moderate-high specific surface areas (from 760 to 935 m2 g-1), with high microporosity contribution (from 64 to 77%). Next, POP-supported Pd(II) catalysts were obtained by simple immersion of the catalyst supports in a palladium(II) acetate solution, observing that the metal content was similar to that theoretically expected according to the amount of bipyridine groups present. The catalytic activity of these heterogeneous catalysts was explored for the synthesis of biphenyl and terphenyl compounds, via the Suzuki-Miyaura cross-coupling reaction using a green solvent (ethanol/water), low palladium loads, and aerobic conditions. The findings showed excellent catalytic activity with quantitative product yields. Additionally, the recyclability of the catalysts, by simply washing it with ethanol, was excellent, with a sp2-sp2 coupling yield higher than 95% after five cycles of use. Finally, the feasibility of these catalysts to be employed in tangible organic reactions was assessed. Thus, the synthesis of a bulky compound, 4,4'-dimethoxy-5'-tert-butyl-m-terphenylene, which is a precursor of a thermal rearrangement monomer, was scaled-up to 2 g, with high conversion and 96% yield of the pure product.

Adsorption of naphthalene from aqueous solution on activated carbons obtained from bean pods.

The preparation of activated carbons from bean pods waste by chemical (K(2)CO(3)) and physical (water vapor) activation was investigated. The carbon prepared by chemical activation presented a more developed porous structure (surface area 1580 m(2) g(-1) and pore volume 0.809 cm(3) g(-1)) than the one obtained by water vapor activation (258 m(2) g(-1) and 0.206 cm(3) g(-1)). These carbons were explored as adsorbents for the adsorption of naphthalene from water solutions at low concentration and room temperature and their properties are compared with those of commercial activated carbons. Naphthalene adsorption on the carbons obtained from agricultural waste was stronger than that of carbon adsorbents reported in the literature. This seems to be due to the presence of large amounts of basic groups on the bean-pod-based carbons. The adsorption capacity evaluated from Freundlich equation was found to depend on both the textural and chemical properties of the carbons. Naphthalene uptake on biomass-derived carbons was 300 and 85 mg g(-1) for the carbon prepared by chemical and physical activation, respectively. Moreover, when the uptake is normalized per unit area of adsorbent, the least porous carbon displays enhanced naphthalene removal. The results suggest an important role of the carbon composition including mineral matter in naphthalene retention. This issue remains under investigation.

Molecular Sieves for the Separation of Hydrogen Isotopes.

Stable molecular hydrogen isotopes, D2 and T2, are both scarce and essential in several energy, industrial, and large-scale fundamental research applications. Due to the chemical similarity of these isotopes, their extraction and purification from hydrogen has relied for decades on expensive and energy-demanding processes. However, factoring in the phenomenon of quantum sieving could provide a new route for these separations. In this work, we have explored how to separate hydrogen isotopes by adsorption taking these quantum effects into account. To this end, we have conducted adsorption measurements to test our deuterium model and performed a widespread computational screening over 210 pure-silica zeolites for D2/H2 and T2/H2 separations. Based on low-coverage adsorption properties, a reduced set of zeolites have been singled out and their performance in terms of adsorption capacity, selectivity, and dynamic behavior have been assessed. Overall, the BCT-type zeolite clearly stands out for highly selective separations of both D2 and T2 over H2, achieving the highest reported selectivities at cryogenic temperatures. We also identified other interesting zeolites for the separation of hydrogen isotopes that offer an alternative way to tackle similar isotopic separations by an aimed selection or design of porous materials.

Chemically activated high grade nanoporous carbons from low density renewable biomass (Agave sisalana) for the removal of pharmaceuticals.

HYPOTHESIS: Enlarging the range of viable nanoporous carbon precursors, namely by the acid treatment of low density biomass residues, can overcome issues related with the availability and quality of raw materials that have potential impact on cost and quality grade of the final product. EXPERIMENTS: Nanoporous carbons were prepared following a two-step process: H2SO4 digestion/polycondensation of biomass waste (Agave sisalana, sisal) at temperature below 100 °C and atmospheric pressure to obtain acid-chars that were further chemically activated with KOH or K2CO3. Selected synthesized nanoporous carbons were tested for the removal of pharmaceutical compounds - ibuprofen and iopamidol - in aqueous solutions. FINDINGS: The structure and density of the acid-chars are highly dependent on the concentration of H2SO4 used in the digestion and polycondensation steps. An adequate choice of the acid-char synthesis conditions, activating agent and contact method allowed to feature nanoporous carbons with specific surface areas ranging from 600 to 2300 m2 g-1 and apparent densities reaching 600 kg m-3. The adsorption capacity of a sample obtained by KOH-activation for the removal of micropollutants from water was twice higher than the value attained by a golden activated carbon (Cabot-Norit) commercialized for this specific purpose.

Insights on the Use of Carbon Additives as Promoters of the Visible-Light Photocatalytic Activity of Bi2WO6.

We have explored the impact of the incorporation of various amounts of carbons from varied physicochemical features as additives to Bi2WO6 for the photocatalytic degradation of a dye using simulated solar light. Data has revealed that the composition and acidic character of the carbon additive are important parameters in the performance of the Bi2WO6/carbon catalysts. The presence of a carbon additive improved the conversion of the dye, evidencing the occurrence of charge transfer reactions that involve radical mediated reactions. The catalysts prepared with 2 and 5 wt.% of carbon additive outperformed the bare semiconductor, despite the shielding effect of the carbon matrix. The acidic nature of the Bi2WO6/carbon catalysts governs the degradation pathway (due to the preferential adsorption of the dye), that proceeds via the deethylation of the auxochrome groups of the dye at short irradiation times, followed by the cleavage of the chromophore at long irradiation times. Regarding the characteristics of the carbons, the photocatalytic degradation rate is accelerated by carbons of acidic character and high oxygen content, whereas the porosity seems to play a minor role. The presence of the carbon additives also affects the toxicity of the treated solutions, rendering lower values after shorter irradiation periods.

Tailoring the textural properties of an activated carbon for enhancing its adsorption capacity towards diclofenac from aqueous solution.

A series of activated carbons (ACs) were prepared by modifying a commercial AC by physical activation using CO2 during different activation times. The ACs were designated as F, F12, F24, and F40 corresponding to the activation times of 0, 12, 24, and 40 h, respectively. The surface area, total pore volume, micropore volume, and mean micropore width were determined for all the ACs. The textural properties of the modified ACs increased substantially with the activation time, and the capacity of the ACs for adsorbing diclofenac (DCF) was almost linearly dependent upon the surface area of the ACS. The maximum adsorption capacities of F, F12, F24, and F40 carbons towards diclofenac (DCF) from aqueous solution were 271, 522, 821, and 1033 mg/g, respectively. Hence, the adsorption capacities of ACs were considerably enhanced with the activation time, and F12, F24, and F40 carbons presented the highest adsorption capacities towards DCF reported in the technical literature. The F40 adsorption capacity was at least twice those of other carbon materials. The adsorption capacities decreased by raising the pH from 7 to 11 due to electrostatic repulsion between the ACs surface and anionic DCF in solution. The removal of DCF from a wastewater treatment plant (WWTP) effluent was effectively carried out by adsorption on F40. Hence, the capacity of ACs for adsorbing DCF can be optimized by tailoring the porous structure of ACs.

Guest-induced modification of a magnetically active ultramicroporous, gismondine-like, copper(II) coordination network.

A novel ultramicroporous coordination polymer, namely [Cu(F-pymo)2(H2O)1.25]n (1, F-pymo = 5-fluoropyrimidin-2-olate), has been prepared and structurally characterized. 1 displays a zeolitic gismondine (GIS) topology, with ca. 2.9 A wide helical channels which, in the thermally activated counterpart (1'), account for a 13% void volume and are responsible for the observed selective solid-gas adsorption properties toward H2, N2, and CO2. At 77 K 1' behaves as a molecular sieve, selectively adsorbing H2 over N2, possibly due to size-exclusion reasons. At variance, although CO2 molecules are slightly larger than the pore size, they are readily incorporated by 1' at temperatures as high as 433 K. Variable-temperature X-ray powder diffraction (TXRPD) studies, in the temperature range 303-473 K, show that dehydration is reversible and has almost negligible effects on the network. At variance, the uptake of CO2 occurs through a transient phase and channels expansion. While the gas storage capacity of 1' is not very high-H2, 0.56 wt % and 0.010 kg H2/L at 90 K and 900 Torr, and CO2, 7.6 wt % at 273 K and 900 Torr-the guest molecules achieve very high densities, comparable to that of the liquid for H2 (0.023 vs 0.021 molecules A-3) and to that of the solid for CO2 (0.014 vs 0.022 molecules A-3). In addition, we have also studied the effect of the perturbation exerted by the guest molecules on its magnetic properties. The results show that while dehydration of 1 has negligible effect on its spin-canted antiferromagnetic behavior, CO2 incorporation in the pores is responsible for an increment of the transition temperature at which the weak ferromagnetic ordering takes place from 22 to 29 K.

Role of surface adsorption and porosity features in the molecular recognition ability of imprinted sol-gels.

Organically modified molecularly imprinted silicas (MIS) for nafcillin recognition were prepared using a simple sol-gel procedure. Molecular recognition of the template was observed by tuning the chemical and structural properties of the MIS. The relative amounts of organically modified alkoxysilane precursors were found to be key in the textural and morphological characteristics of the MIS as well as for developing an imprinting effect in the materials. The recognition properties of the imprinted materials were found to be strongly influenced by the hydrolytic stability of the alkoxysilanes and their inductive effects during sol-gel hydrolysis/condensation stages. The concept was to combine properties of organic groups with those of glass-like materials in order to develop synergetic properties through variations in the composition. Results from batch rebinding experiments as well as from the thorough study of the N(2) adsorption properties and the textural and structural characteristics of the MIS revealed that an imprint effect could be attributed to the presence of the template during the synthesis of MIS.