Heterogeneous Fenton process based on layered double hydroxides for urban wastewater treatment

Author(s)

Nayara de Melo Costa Serge

• Document type: Doctoral Thesis
• Press: Araraquara. 2023-03-30.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2023-03-17
• Advisor: Raquel Fernandes Pupo Nogueira

Abstract

The interest in the application of Layered Double Hydroxides (LDHs) as catalysts in heterogeneous Fenton has become frequent due to their interesting structural properties, low production cost, ease of synthesis, the possibility of incorporation of different types of elements in the same structure and application under neutral conditions. The improvement and use of these materials as catalysts in secondary treated urban wastewater (STWW), would bring benefits to human health and the environment. These perspectives motivated this study, where LDHs based on CuMgFe were synthesized for the activation of different oxidizing agents, hydrogen peroxide (H2O2), persulfate (PDS = S2O8 2-), and peroxymonosulfate (PMS = HSO5 -) in the generation of reactive species for the degradation of pharmaceuticals and inactivation of pathogens in STWW. Initially, two pyroaurite-type LDHs (MgFe-CO3 and CuMgFe-CO3) were synthesized by the coprecipitation method at constant pH to evaluate the influence of the insertion of Cu in the LDH on the degradation of the sulfathiazole antibiotic (STZ) in the dark and under LED-Vis irradiation. XPS analyzes confirmed the insertion of Cu(II) in the LDH structure and the presence of Cu(I), which increased the degradation efficiency of 150 μg L-1 of STZ, and achieving non detectable concentration was after 90 min using 4 mmol L-1 of H2O2 and 0.5 g L-1 of CuMgFe-CO3 at pH 7.5, under LED-Vis irradiation. In view of the potential of the LDH with copper to remove the antibiotic at a pH close to neutral and the high stability of the catalyst even after 4 cycles of reuse, it was decided to study the influence of the interlamellar anion on the activity. Four LDHs of CuMgFe were synthesized, with a variation of the interlamellar anion: B(OH)4 -, CO3 2-, NO3 - and SO4 2-, for the removal of the anticancer 5- fluorouracil (5-FU) in the dark and under solar radiation. XRD and XPS results showed the phase purity of the catalysts synthesized and the intercalation of the respective anions. The degradation process in the dark showed that the interlamellar anion has a strong effect on the catalytic properties of the LDH, showing the following pseudo-first order (k) rate constant sequence: CuMgFe-B(OH)4 > CuMgFe-NO3 > CuMgFe-SO4 > CuMgFe-CO3. The highest efficiency of LDH with boron was explained based on FTIR and XPS results, which showed the interactions B-O and B-OH, which were responsible for inducing modifications on the electronic density of CuMgFe-B(OH)4, accelerating the reduction of Cu(II) and Fe(III) and thus favoring the generation of reactive oxygen species in the Fenton process. This catalyst allowed the complete degradation of 200 μg L-1 of 5-FU under solar radiation after 20 min and after 40 min in the dark, with degradation efficiency maintained above 90% until the fourth cycle of use in the presence of 10 mmol L -1 H2O2 and 0.5 g L-1 LDH. The excellent performance of CuMgFe-B(OH)4 in the degradation of 5-FU, motivated the studies on the application of this catalyst in the simultaneous degradation of the antibiotics sulfamethoxazole (SMX), ciprofloxacin (CIP), cephalexin (CFX) and amoxicillin (AMX) and inactivation of Escherichia coli and Enterococcus faecalis pathogens with different oxidizing agents, H2O2, PDS, and PMS. In each system with different oxidants, CuMgFe-B(OH)4 behaved differently. LDH-activated PMS was the most efficient process and provided more than 90% removal of all antibiotics after 120 min and complete inactivation of pathogens using 0.5 g L-1 LDH and 4 mmol L-1 PMS. However, the LDH system with H2O2 was efficient for disinfection, but not for the degradation of antibiotics due to the formation of complexes between the cations present in the catalyst structure and H2O2. The PDS activated system occurred by a non-radical pathway involving mainly singlet oxygen (1O2) and Cu(III) with the removal of antibiotics, but limited disinfection capacity for Escherichia coli. In the experiments performed in this thesis, high stability of the synthesized LDHs and excellent performance under neutral conditions were observed, which is important for the application of these materials as catalysts. (AU)

• FAPESP's process: 18/17517-0 - Layered double hydroxide as catalysts in heterogeneous photo Fenton process for degradation of drugs present in hospital effluent
• Grantee: Nayara de Melo Costa Serge
• Support Opportunities: Scholarships in Brazil - Doctorate