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Chemically functionalized multi-walled carbon nanotubes (CNTs) are used as carriers for laccase immobilization. In this work, CNTs were modified using different approaches with a combination of methods involving hydrothermal oxidation with nitric acid, treatment with 3-aminopropyltriethoxysilane, glutaraldehyde, N-ethyl-N-(3-(dimethylamino)-propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. The enzyme immobilization efficiency and recovered activity were evaluated towards-azino-bis(3-ethylbenzathiazoline-6-sulfonic acid) biocatalytic oxidation. The best compromise between immobilization efficiency and recovered activity was obtained using the CNTs functionalized with 0.3 M HNO 3 , treated with N-ethyl-N-(3-(dimethylamino)propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. This catalyst also showed the best thermal stability (at 50 and 60 ºC). The bioconjugate based on this material was characterized by vibrational spectroscopies (FTIR and Raman) and by N 2 adsorption. The results from reutilization tests showed that laccase activity was kept above 65% of its initial value after five consecutive cycles of reuse. The biocatalytic performance of the immobilized enzyme was evaluated for the degradation of a mixture of phenolic compounds in water containing phenol, resorcinol, 4-methoxyphenol and 4-chlorophenol. As means of cost efficient to enzyme reutilization, laccase was immobilized over polysulfone membranes blended with the functionalized CNTs and studied in the degradation of 4-methoxyphenol.

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a b s t r a c tCarbon nanotube-titanium dioxide composite materials were produced by two routes: hydration-dehydration and one-pot oxidation. Au, Pt, Ir and Pd were loaded on TiO 2 -based materials by an incipient wetness method. The resulting materials were calcined and afterwards reduced at two distinct temperatures, 473 and 673 K. Characterization was carried out by temperature programmed desorption, infrared and UV-Vis spectroscopy, N 2 adsorption, SEM and TEM. Compared with reference TiO 2 , composite catalysts presented increased activity for photocatalytic production of H 2 from methanol solutions. The highest activity was obtained for the Pt-loaded composite produced by the one-pot synthesis method, with 485 mol of H 2 being generated after two hours of irradiation, contrasting with 205 mol of H 2 obtained using Pt/TiO 2 . This synergic effect was discussed in terms of the action of carbon nanotubes as dispersing media for TiO 2 particles as well as their action as photosensitizers. The relative efficiency of the catalysts was related to the work function of each metal and the sizes of the metal nanoparticles. H 2 generation from photocatalytic reforming of saccharides, namely arabinose, glucose, fructose and cellobiose was performed using TiO 2 and CNT-TiO 2 based catalysts. The relative efficiency of H 2 production from these biomass-derived compounds has been discussed based on their structural arrangement, H:C ratio and availability of ␣-hydrogens.

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Diatomic catalysts, particularly those with heteronuclear active sites, have recently attracted considerable attention for their advantages over single-atom catalysts in reactions involving multielectron transfers. Herein, we report bimetallic iridium–iron diatomic catalysts (IrFe–N–C) derived from metal–organic frameworks in a facile wet chemical synthesis followed by postpyrolysis. We use various advanced characterization techniques to comprehensively confirm the atomic dispersion of Ir and Fe on the nitrogen-doped carbon support and the presence of atomic pairs. The as-obtained IrFe–N–C shows substantially higher electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) when compared to the single-atom counterparts (i.e., Ir–N–C and Fe–N–C), revealing favorable bifunctionality. Consequently, IrFe–N–C is used as an air cathode in zinc–air batteries, which display much better performance than the batteries containing commercial Pt/C + RuO2 benchmark catalysts. Our synchrotron-based X-ray absorption spectroscopy experiments and density functional theory (DFT) calculations suggest that the IrFe dual atoms presumably exist in an IrFeN6 configuration where both Ir and Fe coordinates with four N atoms and two N atoms are shared by the IrN4 and FeN4 moieties. Furthermore, the Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the OER. The dual-atom sites work synergistically, reducing the energy barrier of the rate-determining step and eventually boosting the reversible oxygen electrocatalysis. The IrFe–N–C catalysts hold great potential for use in various electrochemical energy storage and conversion devices.