Institutional Repository UIN Sunan Kalijaga YogyakartaSINTESIS DAN KARAKTERISASI CARBON NANODOTS (C-DOTs) BERBASIS KULIT BUAH NAGA (HYLOCEREUS POLYRHIZUS) UNTUK DEGRADASI ZAT WARNA RHODAMIN BNIM.: 19106020032Ummi Alifa AlfiyantiauthorEnvironmental pollution caused by synthetic dyes has become an issue of increasing concern. Rhodamine B is one of the synthetic dyes that may contribute to environmental pollution. On the other hand, red dragon fruit peel (Hylocereus polyrhizus) is a biomass waste containing organic carbon, which makes it a potential precursor for carbon-based materials. One promising carbon-based material is Carbon Nanodots (C-Dots), which possess distinctive optical properties and potential applications in dye treatment. Therefore, this study aimed to synthesize C-Dots from red dragon fruit peel waste, investigate their optical characteristics, and evaluate their ability to reduce the concentration of Rhodamine B. The utilization of red dragon fruit peel is also expected to enhance the value of biomass waste while providing an alternative material for reducing environmental pollution.This experimental study consisted of several stages, including material preparation, C-Dots synthesis, optical characterization, and Rhodamine B degradation testing. The red dragon fruit peels were cleaned, dried, and carbonized in a furnace at 300°C for 30 minutes. The carbonized product was subsequently subjected to sonication, centrifugation at 3000 rpm for 40 minutes, and filtration to obtain the C-Dots filtrate. The optical characteristics of the C-Dots were examined using a 365 nm UV lamp and UV-Vis spectrophotometry. The degradation test was conducted using a 5 ppm Rhodamine B solution with treatment times of 60 and 120 minutes. Changes in Rhodamine B concentration were analyzed using UV-Vis spectrophotometry based on a calibration curve at a maximum wavelength of 553.5 nm.The C-Dots filtrate exhibited bluish-gray luminescence under 365 nm UV irradiation. UV-Vis characterization showed strong absorption in the ultraviolet region, with an absorbance of 0.718 at a wavelength of 283 nm. The Rhodamine B calibration curve at a maximum wavelength of 553.5 nm yielded a linear regression equation of y = 0.103365x + 0.00529292, with an R² value of 0.99980. After 60 minutes of treatment, the final Rhodamine B concentration was 2.164 ppm, corresponding to a degradation efficiency of 56.72%. After 120 minutes, the final concentration was 2.213 ppm, with a degradation efficiency of 55.75%. Based on the treatment times investigated, the red dragon fruit peel-derived C-Dots were capable of reducing the concentration of Rhodamine B, with the highest degradation efficiency obtained at 60 minutes.530 Fisika2026-08-18UIN SUNAN KALIJAGA YOGYAKARTA;FAKULTAS SAINS DAN TEKNOLOGIThesis

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