Synthesis and Characterization of MWCNT-COOH/Fe₃O₄ and CNT-COOH/Fe₃O₄/NiO Nanocomposites: Assessment of Adsorption and Photocatalytic Performance

In this study the adsorption and photodegradation capabilities of modified multi-walled carbon nanotubes (MWCNTs), using tartrazine as a model pollutant, is demonstrated. MWCNT-COOH/Fe₃O₄ and MWCNT-COOH/Fe₃O₄/NiO nanocomposites were prepared by precipitation of metal oxides in the presence of MWCNTs. Their properties were examined by X-ray diffraction in powder (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based Scanning PhotoElectron Microscopy (SPEM), and Brunauer-Emmett-Teller (BET) analysis. It was found that the optimal adsorption conditions were pH 4 for MWCNT-COOH/Fe₃O₄ and pH 3 for MWCNT-COOH/Fe₃O₄/NiO, temperature 25 °C, adsorbent dose 1 g L^-1, initial concentration of tartrazine 5 mg L^-1 for MWCNT-COOH/Fe₃O₄ and 10 mg L^-1 for MWCNT-COOH/Fe₃O₄/NiO and contact time 5 min for MWCNT-COOH/Fe₃O₄/NiO and 15 min for MWCNT-COOH/Fe₃O₄. Moreover, the predominant degradation process was elucidated simultaneously, with and without simulated sunlight irradiation, using thermal lens spectrometry (TLS) and UV-Vis absorption spectrophotometry. The results indicated the prevalence of the photodegradation mechanism over adsorption from the beginning of the degradation process.