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- Carbon-Coated Magnetic Catalysts for Enhanced Degradation of Nitrophenols: Stability and Efficiency in Catalytic Wet Peroxide OxidationPublication . Baldo, Arthur P.; Bezerra, Ana J.B.; Silva, Adriano S.; Silva, Ana P. F.; Roman, Fernanda; Çaha, Ihsan; Bañobre-López, Manuel; Deepak, Francis Leonard; Gomes, HelderNitrophenols are persistent organic pollutants that pose serious environmental and health risks due to their toxic and lipophilic nature. Their persistence arises from strong aromatic stability and resistance to biodegradation, while their lipophilicity facilitates bioaccumulation, exacerbating ecological and human health concerns. To address this challenge, this study focuses on the synthesis and characterization of two different types of hybrid multi-core magnetic catalysts: (i) cobalt ferrite (Co-Fe2O4), which exhibits ferrimagnetic properties, and (ii) magnetite (Fe3O4), which demonstrates close superparamagnetic behavior and is coated with a novel and less hazardous phloroglucinol–glyoxal-derived resin. This approach aims to enhance catalytic efficiency while reducing the environmental impact, offering a sustainable solution for the degradation of nitrophenols in aqueous matrices. Transmission electron microscopy (TEM) images revealed the formation of a multi-core shell structure, with carbon layer sizes of 6.6 ± 0.7 nm for cobalt ferrite and 4.2 ± 0.2 nm for magnetite. The catalysts were designed to enhance the stability and performance in catalytic wet peroxide oxidation (CWPO) processes using sol–gel and solution combustion synthesis methods, respectively. In experiments of single-component degradation, the carbon-coated cobalt ferrite (CoFe@C) catalyst achieved 90% removal of 2-nitrophenol (2-NP) and 96% of 4-nitrophenol (4-NP), while carbon-coated magnetite (Fe3O4@C) demonstrated similar efficiency, with 86% removal of 2-NP and 94% of 4-NP. In the multi-component system, CoFe@C exhibited the highest catalytic activity, reaching 96% removal of 2-NP, 99% of 4-NP, and 91% decomposition of H2O2. No leaching of iron was detected in the coated catalysts, whereas the uncoated materials exhibited similar and significant leaching (CoFe: 5.66 mg/L, Fe3O4: 12 mg/L) in the single- and multi-component system. This study underscores the potential of hybrid magnetic catalysts for sustainable environmental remediation, demonstrating a dual-function mechanism that enhances catalytic activity and structural stability.
- Synthesis of coated nanoparticles for the oxidative denitrogenation of fuelsPublication . Bezerra, Ana J.B.; Gomes, Hélder; Giona, Renata MelloThe presence of nitrogen compounds in fossil fuels leads to the formation of NOx during combustion, harmful pollutants that represent a significant challenge for the environment and health, making its removal very important. Hydrotreatment, currently the most common strategy for denitrogenation, requires severe operating conditions, which motivates the search for more sustainable alternatives. This study investigates oxidative denitrogenation (ODN) as a promising strategy, analyzing the oxidation of quinoline, a nitrogen-containing compound common in fossil fuels, using catalysts based cobalt ferrite and its variants coated with silica (CoFe2O4@SiO2) and carbon (CoFe2O4@C), applied in a biphasic system containing isooctane as the organic phase and hydrogen peroxide as the oxidant. Cobalt ferrite was synthesized using the sol-gel method, followed by silica and carbon coatings. Characterization techniques such as XRD, FTIR and contact angle measurements confirmed the successful synthesis of core-shell structures, with crystallite sizes in the 19-20 nm range. The coatings significantly modified the surface properties, reducing the hydrophobicity of the ferrite, with the contact angle reduced from 130° to 40° with silica. Quinoline adsorption tests revealed a low adsorption capacity of the materials, in line with the low surface area and low pore volume determined by N2 adsorption isotherms at 77 K (SBET = 9-10 m2/g). In the oxidation reactions, CoFe2O4@SiO2 showed the best catalytic performance removing 74% of quinoline in 8 hours, likely due to its hydrophilic surface, favorable to the generation of reactive oxygen species through the decomposition of H2O2 and consequent greater quinoline removal. GC-MS identified intermediate degradation products, including species suggesting the opening of pyridine rings, while TOC analysis confirmed significant quinoline mineralization. The study highlights the potential of oxidative denitrogenation systems, combined with coated catalysts, to effectively remove nitrogen impurities from liquid fuels, offering a promising alternative to conventional hydrotreatment.
- Polyolefin and Polystyrene‐Derived Carbon Nanotubes: Catalysts for Oxidative Desulfurization Under a Biphasic SystemPublication . Roman, Fernanda; Batista, Maria C.; Silva, Adriano S.; Bezerra, Ana J.B.; Tuesta, Jose L. de Diaz de; Mambrini, Raquel V.; Silva, Adrián; Faria, Joaquim L.; Gomes, HelderThe conversion of plastic solid waste into carbon nanotubes (CNTs) via chemical vapor deposition (CVD) and the effectiveness of these CNTs as catalysts for oxidative desulfurization (ODS) of a simulated fuel were investigated. The primary focus is on the use of CNTs synthesized from various polymer sources, including polyolefins and polystyrene (PS), to remove sulfur compounds using hydrogen peroxide (H 2 O2 ) as an oxidant. The surface modification of CNTs by using acids (H2 SO4 or HNO3 ), the influence of the carbon feedstock (polyolefins vs PS), the use of co-catalysts, and the effect of the extractant phase were all evaluated on the oxidative removal of dibenzothiophene from a simulated fuel. Results revealed that CNTs derived from polyolefins displayed higher desulfurization efficiency (up to 77% in 8 h), with nitric acid-treated CNTs showing the best performance under oil-water biphasic systems. Replacing water with acetonitrile and adding a co-catalyst (formic acid) resulted in a desulfurization of 91% in 2 h of reaction. Under certain conditions, C─S bond cleav-age was observed. This research contributes to the valorization of plastic solid waste and the reduction of atmospheric pollution, promoting circular economy practices and environmental sustainability.