New insights into modified carbon-based catalysts shaped as gas diffusion electrodes for efficient H2O2 production under wastewater treatment processes: a material engineering approach

Author(s)

Matheus Schiavon Kronka

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2023-08-25

Examining board members

Marcos Roberto de Vasconcelos Lanza; Christiane de Arruda Rodrigues; Ignacio Sirés Sadornil; Lucia Helena Mascaro Sales; Mauro Coelho dos Santos

• Advisor: Marcos Roberto de Vasconcelos Lanza

Abstract

The design of highly efficient catalysts to produce hydrogen peroxide (H2O2) through oxygen reduction reaction (ORR) is crucial to make electro-Fenton (EF) and photoelectro-Fenton (FEF) processes feasible for real wastewater treatment. The aim of this thesis was to develop and optimize low metal catalysts supported on Printex L6 carbon (PL6C) to achieve high selectivity for the production of H2O2 (SH2O2). The feasibility of a novel design of gas diffusion electrodes (GDE) operating at flow-by reactor for treating real effluents contaminated with pesticides was also aimed studied in this thesis. In Chapter I, a catalyst containing a <1 wt.% Pd loading modifying PL6C matrix (Pd1%/PL6C) was developed, which achieved high SH2O2 (~90%) and an overpotential gain at the onset reaction of 320 mV compared to the matrix unmodified. This effect was explained thanks to the low metal content and the large interparticle spacing of Pd nanoparticles that avoided the readsorption mechanism of H2O2. The Pd1%/PL6C was efficiently applied for the removal of 0.5 mmol L-1 of methylparaben in 8 minutes by the PEF process at j = 33.3 mAcm2. However, it was noted that the functional groups of the carbon matrix had an effect on the partial positive charge of the metal nanoparticles. Then, an alternative support based on ZrO2 dispersed in PL6C was developed in Chapter II through microwave assisted hydrothermal synthesis (MAH). The material consisting of 5.1wt.% ZrO2 was obtained in the optimum condition of the MAH synthesis, exhibiting 88.8% of SH2O2. Apart from being stable in acidic media, the ZrO2/PL6C support material exhibited a 140 mV gain on the overpotential of ORR onset. Thus, the use of ZrO2/PL6C as a hybrid substrate suitable for noble metal nanoparticles was evaluated in Chapter III as a catalyst for H2O2 production. Instead of Pd, Au nanoparticles were used in order to study the interaction between the noble metal nanoparticle and the hybrid support. The electrochemical results revealed that the Au_ZrO2/PL6C showed excellent catalytic performance by showing a SH2O2=97% with an early reaction onset of 350 mV compared to bare PL6C. For H2O2 production assays, the Au_ZrO2/PL6C-modified GDE produced 600 mg L-1 compared to 374 mg L-1 for the Au/PL6C catalyst at j = 50 mA cm-2, confirming its higher catalytic effectiveness. The Au_ZrO2 GDE was also effectively applied in a continuous flow-by reactor for the complete removal of 10 mg L-1 of Carbaryl contained in the real effluent after 6 minutes using the PEF process. Although the presence of H2O2 scavenger species on real wastewater, the high performance of the catalyst provided sufficient H2O2 concentration to achieve homogeneous &bull;OH for the complete removal of the pollutant. Therefore, it is expected that the contributions present in this thesis can contribute to further advances in the development of materials and systems for producing high-efficiency H2O2 that enables wastewater treatment by using electrochemical technology. (AU)

• FAPESP's process: 17/23464-3 - Study of agrochemical degradation paraquat, sodium-metham and carbaryl by Electrochemical Advanced Oxidation Process (EAOP) using gas diffusion electrode modified with bimetallic oxides
• Grantee: Matheus Schiavon Kronka
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)