Biopolymer-Derived Structured Graphitic Carbons as Metal-Free Heterogeneous Ozonation Catalysts in Water

The development of metal-free heterogeneous catalysts for advanced oxidation processes is an important area of research, advancing in sustainability, with potential practical applications in water treatment. In this work, we report the development of defective structured graphitic carbons synthesized from biomass including alginate or chitosan polysaccharides and used as metal-free ozonation catalysts in water. These solids were characterized by several techniques, including powder X-ray diffraction, several spectroscopies (i.e. X-ray photoelectron, Raman or Fourier Transform infrared), elemental combustion analyses, thermogravimetric measurements, and electron microscopic techniques. The catalytic performance of graphitic carbon was examined in the ozonation reaction and the graphitic carbon derived from alginate (G) was found to be the most active catalyst by showing complete degradation in less than 4 h under the operational conditions as oxalic acid (50 mg/L), catalyst (100 mg/L), 20 ◦C, O3 dosage (140 mg·h-1) at pH 3. Importantly, this solid retains its activity mostly upon reuse for more than 20 h, an observation that compares favorably with previous reports using graphene-based materials. In addition, activity of partially deactivated catalyst can be recovered by a pyrolysis process associated to the reconstitution of graphitic active sites of the catalyst. Experimental evidence by electron spin resonance together with specific (photo)catalytic experiments is provided to support the role of 1O2 as key intermediate during the oxalic acid degradation in water in the presence of the graphitic carbon. This study exemplifies the activity of active graphitic-based solids from biomass precursors as ozonation heterogeneous catalysts in water in the absence of any metal.