Percorrer por autor "Guari, Nathalia Maria Costa"
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- Hybrid cobalt ferrite/carbon catalysts: synthesis, characterization and applications in water treatmentPublication . Guari, Nathalia Maria Costa; Gomes, Helder; Cordeiro, Patricia Hissae Yassue; Díaz de Tuesta, Jose LuisThis work deals with the development of carbon-coated magnetic cobalt ferrite nanoparticles as catalysts for the treatment of water containing Contaminants of Emerging Concern (CEC) by Catalytic Wet Peroxide Oxidation (CWPO), using paracetamol (PCM) as model pollutant. For this purpose, a magnetic core (CoFe2O4) is developed by the sol-gel method, the core is subsequently coated with a resin prepared from formaldehyde, resorcinol and tetraethyl orthosilicate (TEOS), and later carbonized by pyrolysis at 600 °C under a N2 atmosphere. Afterwards, the silica generated from TEOS is removed by etching with NaOH to create a void inside the particle, creating a yolk-shell shape denoted as CoFe2O4@void@C. XRD, TEM and FTIR analysis revealed that the uncoated core is composed by a CoFe2O4 cubic spinel structure with space group Fd-3m and a crystallite size of 53 nm, calculated using the W-H method, that matches very well with the average size observed by TEM equals to 53.51 4.2 nm. The average size of the nanoparticles for the hybrid coated ferrite increases to 58.7 8.1 nm. After the preparation of the catalysts, reaction runs were performed to assess its suitability for the degradation of PCM by CWPO. The concentration of paracetamol, hydrogen peroxide and Total Organic Carbon (TOC) were recorded against the reaction time. The performance of the CoFe2O4@void@C catalyst was compared to that of the uncoated ferrite, the CoFe2O4 and CoFe2O4@void@C materials allowing TOC values of 46 and 58% respectively at 24h. The hybrid coated ferrite succeeds in avoid iron leaching and to be a stable catalyst. The amount of leached iron at the end of the treatment was equal to 1.59 mg·L-1, which is within the limit concentration of 2 mg·L-1 of iron allowed in waters, as established EU regulations. A kinetic model was proposed describing the decomposition of hydrogen peroxide and the removals of the pollutant PCM and TOC with the CoFe2O4@void@C as catalyst, applying an empirical kinetic model composed of a second-order and an autocatalytic expression to describe the decomposition of H2O2 and PCM, respectively. The kinetic model for TOC can be well-described as a sum of the initial pollutant plus the oxidation intermediates from the PCM and the organic components that are refractory to the process.
- Magnetic CoFe2O4@carbon yolk-shell nanoparticles as catalysts for the catalytic wet peroxide oxidation of paracetamol: kinetic insightsPublication . Guari, Nathalia Maria Costa; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Pöttker, Walmir Eno; Cordeiro P.Y.; Gomes, HelderThis work focuses on the use of carbon-coated magnetic cobalt ferrite nanoparticles as catalysts for catalytic wet peroxide oxidation (CWPO) of the emerging concern pollutant paracetamol (PCM). The magnetic core of the catalyst is composed of CoFe2O4 developed by a sol-gel method. The core is subsequently coated with a formaldehyde-resorcinol resin and TEOS, further carbonized at 600 degrees C, and etched with NaOH to create a yolk-shell structure denoted as CoFe2O4@void@C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformed infra-red (FTIR) analysis revealed that the uncoated core is composed of a CoFe2O4 cubic spinel structure with a crystallite size of 53 nm calculated using the Williamson-Hall (W-H) method, matching very well the average size observed by TEM (53.51 +/- 4.2 nm). Comparing the performances of CoFe2O4@void@C and the bare CoFe2O4 in the CWPO of paracetamol, total organic carbon (TOC) removals of 58% and 46% are obtained respectively after 24 h of reaction. An empirical kinetic model based on second-order and autocatalytic expressions was developed to suitably describe the decomposition of H2O2 and the removal of paracetamol using CoFe2O4@void@C as catalyst. The disappearance of TOC was well-described (r(2) = 0.98) by a lumped kinetic model as the sum of TOCA, TOCB and TOCC, where TOCA is the TOC of the PCM, TOCB refers the intermediate products and TOCC is the TOC of the final products obtained during the CWPO of PCM.