Waste-derived catalytic hydrochars from coffee grounds doped with BiOCl, CeO2, and α-Fe2O3: Structural insights and enhanced photocatalytic performance
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In this study, hydrochars were synthesized from coffee grounds via a solvothermal process and doped with metallic oxides, resulting in hydrochars being denoted as H, H-Bi (BiOCl), H-Bi/Ce (BiOCl-CeO2), and H-Bi/Fe (BiOCl-Fe2O3). The photocatalytic degradation of indigo blue dye was evaluated under UV light, with varying parameters such as pH (3, 7, and 11), initial hydrochar mass (0.1, 0.2, and 0.3 »g/L), and dye concentration (25-75 »mg/L). H is directly degraded by electron transfer and UV light, with limited reactive oxygen species (ROS) generation. H-Bi generates abundant •OH and O₂•⁻, with h⁺ predominating under alkaline conditions. H-Bi/Ce combines h⁺ and •OH due to oxygen defects in CeO₂. H-Bi/Fe utilizes Fenton and photo-Fenton reactions at acidic pH, with •OH being the primary mechanism. The highest degradation efficiency (100 »%) was achieved with H, H-Bi, and H-Bi/Fe, using 0.1 »g/L of hydrochar at pH 3. Under the same conditions, the hydrochars maintained their carbon-oxygen spherical structure and uniform dopant dispersion after four use cycles. Meanwhile, DRS, XPS, and TEM confirmed the presence of heterojunctions, which supported their photocatalytic activity. XPS and energy-EDS indicated the presence of BiOCl, CeO₂, and Fe₂O₃ after four cycles. The higher photocurrent density at 1.23 »V vs. RHE was obtained for H-Bi/Fe, demonstrating excellent electrochemical stability under light and a higher electron transfer resistance in basic electrolytes compared to an acid medium. These results demonstrate the effectiveness of these doped hydrochars, offering insights into the transformative potential of biomass-based composites for sustainable industrial applications. © 2025 Elsevier Ltd.
Palabras clave
BiOCl, Coffee grounds, Hydrochar, Indigo blue, Photodegradation, Waste-derived, Alkalinity, Binary alloys, Bismuth alloys, Bismuth compounds, Carbon, Cerium oxide, Chlorine compounds, Doping (additives), Dyes, Electron transitions, Heterojunctions, Iron oxides, Oxidation, Oxygen, Photocatalytic activity, Sustainable development, CeO 2, Coffee grounds, Hydrochar, Indigo blue, Photo degradation, Photocatalytic performance, Structural insights, UV-light, Waste-derived, α-Fe, Photodegradation