LaCoO3/Graphene Catalysts As a Novel Catalyst for Peroxymonosulfate Activation to Degrade Aquatic Organic Pollutants: A Singlet Oxygen-Dominated Nonradical Pathway
Authors: Hammad Mohaned , Angel Steven , Asghar Anam , Wiggers Hartmut , Segets Doris 
Published: August 2024

Trace organic pollutants including pharmaceuticals, industrial chemicals, pesticides, and personal care items pose considerable risks to the environment and human health due to their enduring nature, toxicity, and tendency to accumulate in biological systems [1,2]. In addressing this, sulfate radical-based advanced oxidation processes have emerged as highly promising advanced oxidation process methods for water and wastewater treatment in the past decade. Recently, transition metal-based perovskites like LaCoO3 nanoparticles have gained attention in sulfate radical-based advanced oxidation processes due to their structural and compositional flexibility, strong electronic conductivity, and ability to create oxygen vacancies [3]. However, their practical application is hindered by metal leaching during wastewater treatment. Additionally, the robust and scalable synthesis of stable perovskite-based catalysts with large surface areas is crucial for their practical implementation in wastewater treatment but has been rarely achieved so far.
In this study, we developed a cost-effective and scalable approach to produce novel LaCoO3/graphene nanocomposites for eliminating organic pollutants from wastewater. These newly developed catalysts demonstrated outstanding catalytic degradation (> 99%) of diclofenac, metoprolol, carbamazepine, and bisphenol A at a high concentration (40 mg/l) in less than 10 minutes in the peroxymonosulfate activation system, with a respective mineralization of 57%, 55%, 61%, and 62%. This improved performance compared to LaCoO3 nanoparticles is attributed to the nanocomposite's abundant oxygen vacancies, synergistic effects between LaCoO3 and graphene, and its larger surface area. More importantly, the LaCoO3/graphene nanocomposites showed good catalytic performance over a broad range of pH (from 3 to 11) and exhibited excellent reusability with consistent catalytic activity. Moreover, their catalytic efficacy remained largely unaffected in samples of drinking water and tap water, presenting high resistance to co-existing ions and NOM, proving the potential of LaCoO3/graphene materials for practical application in real wastewater treatment systems.
The fabrication of LaCoO3/graphene composites effectively prevents cobalt leaching and increases the content of Co2+ in the structure, resulting in significantly higher catalytic activity than that of pure LaCoO3. Experiments involving radical quenching and electron paramagnetic resonance revealed the involvement of both radical (SO4
•–, •OH and O2
•–) and non-radical pathways (1O2) in pollutant degradation, with the 1O2 radical playing a predominant role in the oxidation of the pollutant. The relative contributions of •OH, SO4
•–, and 1O2/O2
•– were determined to be 13.4%, 32.6%, and 54% for bisphenol A removal, respectively. Overall, our findings demonstrate the potential utilization of the LaCoO3/graphene system for peroxymonosulfate activation in environmental remediation.

REFERENCES:

[1] A. Asghar, M. Hammad, K. Kerpen, F. Niemann, A.K. Al-Kamal, D. Segets, H. Wiggers, T.C. Schmidt, Ozonation of carbamazepine in the presence of sulfur-dopped graphene: Effect of process parameters and formation of main transformation products, Sci. Total Environ. 864 (2023) 161079. https://doi.org/https://doi.org/10.1016/j.scitotenv.2022.161079.
[2] M. Hammad, P. Fortugno, S. Hardt, C. Kim, S. Salamon, T.C. Schmidt, H. Wende, C. Schulz, H. Wiggers, Large-scale synthesis of iron oxide/graphene hybrid materials as highly efficient photo-Fenton catalyst for water remediation, Environ. Technol. Innov. 21 (2021) 101239. https://doi.org/https://doi.org/10.1016/j.eti.2020.101239.
[3] M. Hammad, B. Alkan, A.K. Al-kamal, C. Kim, M.Y. Ali, S. Angel, H.T.A. Wiedemann, D. Klippert, T.C. Schmidt, C.W.M. Kay, H. Wiggers, Enhanced heterogeneous activation of peroxymonosulfate by Ruddlesden-Popper-type La2CoO4+δ nanoparticles for bisphenol A degradation, Chem. Eng. J. 429 (2022) 131447. https://doi.org/https://doi.org/10.1016/j.cej.2021.131447.