Ultrasound-assisted removal of Acid Red 17 using nanosized Fe₃O₄-loaded coffee waste hydrochar

The Fe₃O₄-loaded coffee waste hydrochar (Fe₃O₄-CHC) was synthesized using a simple precipitation method. The as-prepared adsorbent was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FT-IR). The EDX analysis indicated the presence of Fe in the structure of Fe₃O₄-CHC. The specific surface area of hydrochar increased from 17.2 to 34.7 m²/g after loading of Fe₃O₄ nanoparticles onto it. The prepared Fe₃O₄-CHC was used for removal of Acid Red 17 (AR17) through ultrasound-assisted process. The decolorization efficiency decreased from 100 to 74% with the increase in initial dye concentration and from 100 to 91 and 85% in the presence of NaCl and Na₂SO₄, respectively. The synthesized Fe₃O₄-CHC exhibited good stability in the repeated adsorption-desorption cycles. The high correlation coefficient (R² = 0.997) obtained from Langmuir model indicated that physical and monolayer adsorption of dye molecules occurred on the Fe₃O₄-CHC surface. Furthermore, the by-products generated through the degradation of AR17 was identified by gas chromatography–mass spectrometry analysis.