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In this work, the effect of controlled thermal treatment to tune biochar surface properties such as area/porosity, functionalities and reactivity was investigated. TG-MS, CHN, Raman, IR, BET, Zeta and SEM analyses suggested that thermal treatment led to the decomposition of an organic complex/amorphous phase to produce micropores based on graphene nanostructures and a strong increase on surface area from 3mg for biochar to 30, 408 and 590mg, at 400, 600 and 800°C, respectively. The treatment also led to a gradual decrease on oxygen content from 27 to 14wt% at 800°C due to decomposition of surface functionalities changing surface properties such as zeta potential, adsorption of anionic and cationic species and an increase on the activity for sulfide oxidation which is discussed in terms of increase in surface area and the presence of surface redox quinone groups.

The development of heterogeneous catalysts capable of selectively converting lignin model compounds into products of added value offers an exciting avenue to explore in the production of renewable chemical feedstocks. The use of metal–organic frameworks (MOFs) in such chemical transformations relies largely on the presence of accessible open metal sites found within highly porous networks that simultaneously allow for fast transport and strong interactions with desired substrates. Here, we present the first systematic study on the modulation of catalytic performance of a cationic framework, [Cu2(L)­(H2O)2]­(NO3)2·5.5H2O (L = 1,1′-bis­(3,5-dicarboxylatophenyl)-4,4′-bipyridinium), achieved through the exchange of anionic guests. Remarkably, the catalytic activity proves to be highly anion-dependent, with a nearly 10-fold increase toward the aerobic C–C bond cleavage of a lignin model compound when different anionic species are incorporated within the MOF. Moreover, we demonstrate that the cationic nature of the MOF, imparted by the incorporation of viologen moieties within the linker, tunes the electrophilicity of the active copper­(II) sites, resulting in stronger interactions with the substrate. As such, the copper-based framework exhibits enhanced catalytic performance when compared to its neutral counterpart, emphasizing the appeal of charged frameworks for use as green heterogeneous catalysts.

In this work, reactive iron nanoparticles dispersed in a carbon matrix were produced by the controlled thermal decomposition of Fe(3+) ions in sucrose. During the sucrose decomposition, the Fe(3+) ions are reduced to form iron nanometric cores dispersed in a porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4, and 8 wt.% and heated at 400, 600, and 800 °C. Analyses by X-ray diffraction, Mössbauer spectroscopy, magnetization measurements, Raman spectroscopy, termogravimetric analyses, BET surface area, scanning, and transmission electron microscopy showed that at 400 °C, the materials are composed essentially of Fe3O4 particles, while treatments at higher temperatures, i.e., 600 and 800 °C, produced phases such as Fe(0) and Fe3C. The composites were tested for the oxidation of methylene blue with H2O2 by a Fenton-type reaction and also H2O2 decomposition, showing better performance for the material containing 8 % of iron heated at 400 and 600 °C. These results are discussed in terms of Fe(2+) surface species in the Fe3O4 nanoparticles active for the Fenton reaction.

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