ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Synergistic valorization of eggshell and coffee grounds for the design of an efficient photocatalyst under real solar irradiation

Sadjia Benhabiles, Farid Ait Merzeg, Atmane Djermoune, Farida Bounaas, and Asma Laouici

Laboratory for the Study of Material–Environment Interactions (LIME), University of Jijel, Jijel, Algeria

E-mail: sadjia.benhabiles@univ-jijel.dz

Received: 26 April 2025  Accepted: 3 March 2026

Abstract:

This study explores photocatalysis as an environmentally friendly and effective solution for the degradation of organic pollutants, focusing on the development of a novel, low-cost, and sustainable photocatalyst derived from waste materials, specifically coffee grounds and eggshells. Three materials were synthesized by calcination at 900 °C for one hour: PHO1 (from eggshells), PHO2 (from coffee grounds), and PHOM (a mixture of both). The photocatalysts were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, UV-Visible spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results show that PHOM exhibits enhanced crystallinity, good structural stability, and the lowest band gap (2.86 eV), allowing for more efficient absorption of solar light. Photocatalytic performance was evaluated using methylene blue under solar irradiation. PHOM achieved 95% degradation within 5 min at an initial concentration of 10 mg/L, with a kinetic rate constant of 0.042 min^{− 1} (R² = 0.993). At higher concentrations, the rate constants remained significant: 0.0386 min^{− 1} (R² = 0.988) at 20 mg/L and 0.0350 min^{− 1} (R² = 0.967) at 30 mg/L. In contrast, PHO1 and PHO2 showed much lower efficiencies across all conditions. These findings highlight the effectiveness of the synergy between coffee grounds and eggshells in designing an innovative photocatalytic material. PHOM emerges as a promising, sustainable, and economical solution for water depollution under natural sunlight.

Keywords: Photocatalysis; Waste valorization; Coffee grounds; Eggshells; Solar irradiation; Methylene blue degradation

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04781-x

Chemical Papers 80 (6) 6501–6516 (2026)