RESUMO
In this paper, we present the results of the gamma irradiation method to obtain N-doped mesoporous activated carbons. Nitrogen-enriched mesoporous carbons were prepared from three chosen commercial activated carbons such as Carbon Black OMCARB C-140, KETJENBLACK EC-600JD and PK 1-3 Norit. HRTEM, SEM, Raman spectra, elemental analysis, XPS studies and widely approved N2 adsorption-desorption measurements allowed us to evaluate the effectiveness of N atom insertion and its influence on the BET surface area and the pore structure of modified carbons. The obtained materials have an exceptionally high N content of up to 3.2 wt.%. Additionally, selected N-doped activated carbons were fully characterized to evaluate their applicability as carbon electrode materials with particular emphasis on Oxygen Reduction Reaction (ORR). The proposed method is a relatively facile, efficient and universal option that can be added to the already known methods of introducing heteroatoms to different carbons.
RESUMO
A strategy for the bioconjugation of the enzyme Candida antarctica lipase B onto titania ceramic membranes with varied pore sizes (15, 50, 150, and 300 kDa) was successfully performed. The relationship between the membrane morphology, i.e.,the pore size of the ceramic support, and bioconjugation performance was considered. Owing to the dimension of the enzyme (~33 kDa), the morphology of the ceramics allowed (50, 150, and 300 kDa) or did not allow (15 kDa) the entrance of the enzyme molecules into the porous structure. Such a strategy made it possible to better understand the changes in the material (morphology) and physicochemical features (wettability, adhesiveness, and surface charge) of the samples, which were systematically examined. The silane functionalization and enzyme immobilization were accomplished via the covalent route. The samples were characterized after each stage of the modification, which was very informative from the material point of view. As a consequence of the modification, significant changes in the contact angle, roughness, adhesion, and zeta potential were observed. For instance, for the 50 kDa membrane, the contact angle increased from 29.1 ± 1.5° for the pristine sample to 72.3 ± 1.5° after silane attachment; subsequently, it was reduced to 57.2 ± 1.5° after the enzyme immobilization. Finally, the contact angle of the bioconjugated membrane used in the enzymatic process rose to 92.9 ± 1.5°. By roughness (Sq) controlling, the following amendments were noticed: for the pristine 50 kDa membrane, Sq = 1.87 ± 0.21 µm; after silanization, Sq = 2.33 ± 0.30 µm; after enzyme immobilization, Sq = 2.74 ± 0.26 µm; and eventually, after the enzymatic process, Sq = 2.37 ± 0.27 µm. The adhesion work of the 50 kDa samples was equal to 136.41 ± 2.20 mN m-1 (pristine membrane), 94.93 ± 2.00 mN m-1 (with silane), 112.24 ± 1.90 mN m-1 (with silane and enzyme), and finally, 69.12 ± 1.40 mN m-1 (after the enzymatic process). The materials and physicochemical features changed substantially, particularly after the application of the membrane in the enzymatic process. Moreover, the impact of ceramic material morphology on the zeta potential value is here presented for the first time. With an increase in the ceramic support cut-off, the amount of immobilized lipase rose, but the specific productivity was higher for membranes possessing smaller pores, owing to the higher grafting density. For the enzymatic process, two modes of accomplishment were selected, i.e., stirred-tank and cross-flow. The latter method was characterized by a much higher effectiveness, with a resulting productivity equal to 99.7 and 60.3 µmol h-1 for the 300 and 15 kD membranes, respectively.
RESUMO
A highly effective method was developed to functionalize ceramic supports (Al2O3 powders and membranes) using newly synthesized spacer molecules. The functionalized materials were subsequently utilized for Candida antarctica lipase B enzyme immobilization. The objective is to systematically evaluate the impact of various spacer molecules grafted onto the alumina materials will affect both the immobilization of the enzymes and specific material surface properties, critical to enzymatic reactors performance. The enzyme loading was significantly improved for the supports modified with shorter spacer molecules, which possessed higher grafting effectiveness on the order of 90%. The specific enzyme activity was found to be much higher for samples functionalized with longer modifiers yielding excellent enantioselectivity >97%. However, the enantiomeric ratio of the immobilized lipase was slightly lower in the case of shorter spacer molecules.
RESUMO
Reverse electrodialysis (RED) is an electro-membrane process for the conversion of mixing energy into electricity. One important problem researchers' face when modeling the RED process is the choice of the proper membrane transport equations. In this study, using experimental data that describe the membrane Nafion 120 in contact with NaCl aqueous solutions, the linear transport equation of irreversible thermodynamics was applied to calculate the power density of the RED system. Various simplifying assumptions about transport equation (i.e., four-, three-, and two-coefficients approaches) are proposed and discussed. We found that the two-coefficients approach, using the membrane conductivity and the apparent transport number of ions, describes the power density with good accuracy. In addition, the influence of the membrane thickness and the concentration polarization on the power density is also demonstrated.
