Green Synthesis Nanokomposit Mnfe2o4/Cdots Untuk Fotodegradasi Rhodamine B Di Bawah Sinar Ultraviolet, Visible Light Dan Sunlight

Naqwa Mumtazah Purba, Prof. Dr. Eng. Edi Suharyadi, S.Si., M.Eng.

2025 | Tesis | S2 Ilmu Fisika

Nanokomposit MnFe2O4/Cdots (MFC) berhasil difabrikasi melalui metode green synthesis menggunakan larutan Moringa oleifera sebagai agen pereduksi ion Mn2+/Fe3+ dan kulit semangka sebagai sumber karbon. Proses penggabungan dilakukan dengan bantuan sonikasi dan diperoleh MFC1, MFC2, MFC3, MFC4, dan MFC5 berdasarkan variasi volume Cdots sebesar 10, 15, 20, 25, dan 30 mL. Hasil uji X-ray diffraction menunjukkan bahwa seluruh sampel memiliki struktur kristal spinel kubik dengan penurunan ukuran kristalit MnFe2O4 akibat penambahan Cdots yaitu (8,0 ± 0,2), (7,8 ± 0,1) dan (7,6 ± 0,1) nm untuk MnFe2O4, MFC1 dan MFC4. Citra transmission electron microscopy memperlihatkan morfologi spherical dengan ukuran rata-rata 12,7 ± 2,2 nm dan dispersi yang baik, sedangkan hasil scanning electron microscopy-energy dispersive X-ray dan mapping unsur mengonfirmasi distribusi homogen Mn, Fe, O, dan C tanpa impuritas. Analisis Fourier transform infra-red menunjukkan pita serapan khas Fe–O serta gugus C=O dan C–O–C dari Cdots. Hasil pengujian vibrating sample magnetometer memperlihatkan karakteristik superparamagnetik dengan nilai magnetisasi saturasi menurun dari 20,4 menjadi 14,0 emu/g seiring peningkatan Cdots. Sifat magnetik tersebut mendukung proses pemisahan katalis secara eksternal serta menunjukkan kemampuan reusability tanpa penurunan efisiensi yang signifikan. Spektrum UV–Vis diffuse reflectance menunjukkan pergeseran serapan ke daerah tampak dengan energi celah pita 2,40–2,20 eV yang menandakan peningkatan penyerapan foton visible. Uji fotokatalitik terhadap larutan rhodamine B menunjukkan efisiensi degradasi meningkat dari 79,7% (MFC1) menjadi maksimum 98,5 % pada MFC4, kemudian menurun menjadi 82,1% (MFC5) akibat efek shielding. Aktivitas optimum MFC4 juga diamati pada penyinaran UV, visible light, dan sunlight dengan efisiensi berturut-turut 98,5%, 76,8%, dan 85,7%, serta mempertahankan efisiensi di atas 90 % setelah tiga siklus penggunaan ulang. Dengan stabilitas tinggi, sifat magnetik menengah, dan kinerja fotokatalitik yang konsisten, nanokomposit MFC hasil green synthesis ini berpotensi digunakan sebagai fotokatalis ramah lingkungan untuk degradasi pewarna organik dan pengolahan air berkelanjutan sesuai prinsip SDGs 6.

MnFe2O4/Cdots (MFC) nanocomposites were successfully fabricated through a green synthesis approach using Moringa oleifera extract as a reducing agent for Mn²?/Fe³? ions and watermelon peel as a carbon source. The composite formation was assisted by sonication, producing MFC1, MFC2, MFC3, MFC4, and MFC5 based on Cdots volume variations of 10, 15, 20, 25, and 30 mL, respectively. X-ray diffraction results confirmed that all samples exhibited a cubic spinel crystal structure, with the crystallite size of MnFe2O4 decreasing due to Cdots addition, namely (8.0 ± 0.2), (7.8 ± 0.1) dan (7.6 ± 0.1) nm for MnFe2O4, MFC1, and MFC4, respectively. Transmission electron microscopy images revealed spherical morphology with an average particle size of 12.7 ± 2.2 nm and good dispersion, while scanning electron microscopy–energy dispersive X-ray and elemental mapping confirmed homogeneous distributions of Mn, Fe, O, and C without impurities. Fourier transform infrared spectroscopy analysis showed characteristic absorption bands of Fe–O and functional groups of C=O and C–O–C from Cdots. Vibrating sample magnetometer measurements indicated superparamagnetic behavior, with saturation magnetization values decreasing from 20.4 to 14.0 emu/g as Cdots content increased. This magnetic property supports external catalyst separation and demonstrates reusability without a significant reduction in efficiency. The UV–Vis diffuse reflectance spectra exhibited a red shift toward the visible region, with Eg energies ranging from 2.40 to 2.20 eV, indicating enhanced visible-light photon absorption. Photocatalytic tests against Rhodamine B solution revealed that the degradation efficiency increased from 79.7% (MFC1) to a maximum of 98.5% for MFC4, then slightly decreased to 82.1% (MFC5) due to the shielding effect. The optimal activity of MFC4 was also observed under UV, visible, and sunlight irradiation, with efficiencies of 98.5%, 76.8%, dan 85.7% respectively, while maintaining above 90?ter three reuse cycles. With high structural stability, moderate magnetic properties, and consistent photocatalytic performance, the green-synthesized MFC nanocomposite shows strong potential as an environmentally friendly photocatalyst for organic dye degradation and sustainable water treatment in accordance with SDG 6 principles.

Kata Kunci : Nanokomposit MnFe2O4/Cdots, Moringa oleifera, green synthesis, Fotokatalisis, Rhodamine B