Electronic Theses and Dissertation

Rayhana fajrin. (2026). sintesis sulfur doped carbon quantum dots (cqds) dari limbah kopi arabika pada matriks polivinil alcohol (pva) sebagai sensor ion besi dan kalsium. [skripsi. universitas syiah kuala]. dibawah bimbingan kana puspita, s.pd., m.si.p., dan dr. muhammad nazar, s.pd., mscst. lingkungan perairan dan tanah mengandung ion mineral yang berperan penting bagi kestabilan ekosistem, namun aktivitas antropogenik dapat menyebabkan ketidakseimbangan konsentrasi ion logam esensial seperti fe³⁺ dan ca²⁺. kondisi ini mendorong perlunya pengembangan sensor yang cepat, selektif, sensitif, ramah lingkungan, dan mudah diaplikasikan. penelitian ini bertujuan mensintesis sulfur-doped carbon quantum dots (s-cqds) dari limbah kopi arabika dalam matriks polyvinyl alcohol (pva) serta mengevaluasi potensinya sebagai sensor fluoresensi ion fe³⁺ dan ca²⁺. s-cqds disintesis melalui metode hidrotermal menggunakan arang aktif ampas kopi arabika dan serbuk sulfur sebagai sumber doping. selanjutnya, film pva/s-cqds diformulasikan dan dioptimasi menggunakan response surface methodology dengan rancangan box-behnken design pada tiga variabel, yaitu ph, konsentrasi s-cqds, dan massa pva. karakterisasi dilakukan melalui spektrofotometri uv-vis, photoluminescence (pl), dan uji ketebalan film. hasil penelitian menunjukkan formulasi optimum diperoleh pada ph 5, konsentrasi s-cqds 1 wt%, dan massa pva 3 gram. film optimum menunjukkan puncak absorbansi pada 256 nm dan puncak emisi pl pada 445 nm dengan intensitas 1832,97 a.u. uji sensor menunjukkan respons yang lebih kuat terhadap fe³⁺ dibandingkan ca²⁺, ditunjukkan oleh penurunan fluoresensi yang lebih nyata seiring peningkatan konsentrasi fe³⁺. nilai limit of detection (lod) sebesar 30,45 µm untuk fe³⁺ dan 48,67 µm untuk ca²⁺. hasil ini menunjukkan bahwa film pva/s-cqds berbasis limbah kopi arabika berpotensi dikembangkan sebagai sensor fluoresensi yang selektif dan sensitif terhadap ion fe³⁺. kata kunci: cqds terdoping sulfur, limbah kopi arabika, polivinil alkohol, sensor fluoresensi, ion fe³⁺ dan ca²⁺.

Rayhana Fajrin. (2026). Synthesis of Sulfur Doped Carbon Quantum Dots (S-CQDs) from Arabica Coffee Waste in a Polyvinyl Alcohol (PVA) Matrix as Sensors for Iron and Calcium Ions. [Undergraduate thesis, Universitas Syiah Kuala]. Supervised by Kana Puspita, S.Pd., M.Si.P., and Dr. Muhammad Nazar, S.Pd., M.Sc. Environmental water and soil contain mineral ions that play an important role in maintaining ecosystem stability; however, anthropogenic activities can cause an imbalance in the concentration of essential metal ions such as Fe3+ and Ca2+. This condition highlights the need for sensors that are fast, selective, sensitive, environmentally friendly, and easy to apply. This study aimed to synthesize sulfur-doped carbon quantum dots (S-CQDs) from Arabica coffee waste in a polyvinyl alcohol (PVA) matrix and to evaluate their potential as fluorescent sensors for Fe3+ and Ca2+ ions. The S-CQDs were synthesized via a hydrothermal method using activated charcoal derived from Arabica coffee grounds and sulfur powder as the doping source. Subsequently, PVA/S-CQDs films were formulated and optimized using Response Surface Methodology with a Box-Behnken Design on three variables, namely pH, S-CQDs concentration, and PVA mass. Characterization was carried out using UV-Vis spectrophotometry, photoluminescence (PL), and film thickness testing. The results showed that the optimum formulation was obtained at pH 5, 1 wt% S-CQDs concentration, and 3 g PVA. The optimum film exhibited an absorbance peak at 256 nm and a PL emission peak at 445 nm with an intensity of 1832.97 a.u. Sensor testing showed a stronger response to Fe3+ than to Ca2+, indicated by a more pronounced fluorescence quenching as the Fe3+ concentration increased. The limit of detection (LoD) values were 30.45 µM for Fe3+ and 48.67 µM for Ca2+. These results indicate that the Arabica coffee waste-based PVA/S-CQDs film has the potential to be developed as a selective and sensitive fluorescent sensor for Fe3+ ions. Keywords: Sulfur-doped CQDs, Arabica coffee waste, polyvinyl alcohol, fluorescent sensor, Fe3+ and Ca2+ ions.