Several motivations have prompted the scientific community towards the application of hybrid magnetic carbon nanocomposites in catalytic wet peroxide oxidation (CWPO) processes. The most relevant literature on this topic is reviewed, with a special focus on the synergies that can arise from the combination of highly active and magnetically separable iron species with the easily tuned properties of carbon-based materials. These are mainly ascribed to increased adsorptive interactions, to good structural stability and low leaching levels of the metal species, and to increased regeneration and dispersion of the active sites, which are promoted by the presence of the carbon-based materials in the composites.The most significant features of carbon materials that may be further explored in the design of improved hybrid magnetic catalysts are also addressed, taking into consideration the experimental knowledge gathered by the authors in their studies and development of carbonbased catalysts for CWPO. The presence of stable metal impurities, basic active sites and sulphur-containing functionalities, as well as high specific surface area, adequate porous texture, adsorptive interactions and structural defects, are shown to increase the activity of carbon materials when applied in CWPO, while the presence of acidic oxygen-containing functionalities has the opposite effect.

Carbon materials with different structural and chemical properties, namely activated carbons, carbon xerogels, carbon nanotubes, graphene oxide, graphite and glycerol-based carbon materials, were tested under different operating conditions for their ability to catalyse hydrogen peroxide (H 2 O 2 ) decomposition in aqueous solutions. Activated carbons treated with concentrated sulphuric acid (ACS) are the most active catalytic materials for H 2 O 2 decomposition in most of the conditions studied, due to the presence of sulphur containing functional groups at their surface. In addition, ACS proved to be a stable catalyst in reutilization tests for H 2 O 2 decomposition. Methanol was used as selective scavenger of hydroxyl radicals (HO • ), to show that activated carbons with a markedly basic character lead to the highest yield of HO • formed during the H 2 O 2 decomposition process (14%, after 150 min of reaction). Overall, from the mechanistic interpretation of H 2 O 2 decomposition, it is concluded that the presence of sulphur containing functional groups at the surface of the activated carbons improves the removal of H 2 O 2 in aqueous solutions, but, on the other hand, the selective decomposition of H 2 O 2 via HO • formation is enhanced by the presence of basic active sites on the carbon surface.

This work involves the application of carbon xerogels in the removal of two emerging contaminants, caffeine and diclofenac, from aqueous solutions. Textural characterization of the carbon xerogels prepared by polycondensation of resorcinol with formaldehyde (with a molar ratio of 1:2) has been investigated using N 2 adsorption-desorption at-196 o C. Chemical surface groups were analyzed by FTIR spectroscopy, elemental microanalysis and determination of isoelectric point. The equilibrium tests were carried out using different weights of adsorbent and the experimental data were best correlated by Sips isotherm equation. The kinetic experimental data were described using pseudo-first and pseudo-second order kinetic models, being well described by a pseudo-second order model. The maximum adsorption capacity was observed for adsorption of caffeine onto a xerogel treated with urea solution (182.5 mg.g-1), due to the presence of Lewis bases on its surface, which increase the adsorption affinity for organic compounds. On the other hand, the higher extent of diclofenac adsorption was obtained with a carbon xerogel treated with sulphuric acid (80.0 mg.g-1), mainly due to electronic interactions. Comparing these results with other data reported in the literature, the carbon xerogels employed in our study were found to exhibit comparable adsorption capacities and higher kinetic properties.

a b s t r a c tNovel magnetic carbon xerogels consisting of interconnected carbon microspheres with iron and/or cobalt microparticles embedded in their structure were developed by a simple route. As inferred from the characterization data, materials with distinctive properties may be directly obtained upon inclusion of iron and/or cobalt precursors during the sol-gel polymerization of resorcinol and formaldehyde, followed by thermal annealing. The unique properties of these magnetic carbon xerogels were explored in the catalytic wet peroxide oxidation (CWPO) of an antimicrobial agent typically found throughout the urban water cycle -sulfamethoxazole (SMX).A clear synergistic effect arises from the inclusion of cobalt and iron in carbon xerogels (CX/CoFe), the resulting magnetic material revealing a better performance in the CWPO of SMX at the ppb level (500 g L −1 ) when compared to that of monometallic carbon xerogels containing only iron or cobalt. This effect was ascribed to the increased accessibility of highly active iron species promoted by the simultaneous incorporation of cobalt.The performance of the CWPO process in the presence of CX/CoFe was also evaluated in environmentally relevant water matrices, namely in drinking water and secondary treated wastewater, considered in addition to ultrapure water. It was found that the performance decreases when applied to more complex water and wastewater samples. Nevertheless, the ability of the CWPO technology for the elimination of SMX in secondary treated wastewater was unequivocally shown, with 96.8% of its initial content being removed after 6 h of reaction in the presence of CX/CoFe, at atmospheric pressure, room temperature (T = 25 • C), pH = 3, [H 2 O 2 ] 0 = 500 mg L −1 and catalyst load = 80 mg L −1 . A similar performance (97.8% SMX removal) is obtained in 30 min when the reaction temperature is slightly increased up to 60 • C in an ultrapure water matrix. Synthetic water containing humic acid, bicarbonate, sulphate or chloride, was also tested. The results suggest the scavenging effect of the different anions considered, as well as the negative impact of dissolved organic matter typically found in secondary treated wastewater, as simulated by the presence of humic acid.An in-situ magnetic separation procedure was applied for catalyst recovery and re-use during reusability cycles performed to mimic real-scale applications. CWPO runs performed with increased SMX 171 concentration (10 mg L −1 ), under a water treatment process intensification approach, allowed to evaluate the mineralization levels obtained, the antimicrobial activity of the treated water, and to propose a degradation mechanism for the CWPO of SMX.

Reduced graphene oxide (rGO) samples were prepared from graphene oxide (GO) using different reducing agents (i.e., glucose, hydrazine and vitamin C, resulting in rGOG, rGOH and rGOV, respectively). These samples were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol (4-NP) solutions (5 g L-1) at mild operating conditions (i.e., atmospheric pressure, T = 323 K, pH = 3, [catalyst] = 2.5 g L-1 and [H 2 O 2 ] 0 = 17.8 g L-1). The highest catalytic activity was found for the rGOV sample, reaching a 4-NP removal of 1294 mg g-1 and a TOC removal of 241 mg g-1 after 24 h runs