Abstrak. Asid amino merupakan bahan asas dalam tisu tumbuhan dan haiwan. Tirosina (Tr) salah satu jenis asid amino yang mengandungi gelang aromatik, telah dipilih sebagai sampel untuk proses degradasi dalam medium akueus. Ini bertujuan melihat kesan penggunaan mangkinfoto dalam sinaran ultralembayung (λ < 400 nm) atau cahaya matahari ke atas molekul tirosina. Kajian telah dijalankan menggunakan sistem cahaya, mangkin serbuk TiO 2 , hidrogen peroksida, H 2 O 2 dan ion logam. Penambahan ion logam

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... seperti Ni 2+ , Cu 2+ , Ag + , Mn 2+ , Co 2+ , Fe 2+ dan Cd 2+ dan agen pengoksidaan, iaitu hidrogen peroksida adalah untuk mendapatkan kaedah yang paling cekap. Keputusan menunjukkan penambahan H 2 O 2 dan ion Fe 2+ dan Ni 2+ berjaya meningkatkan kecekapan proses degradasifoto tirosina. Ion Ni 2+ memberikan keputusan terbaik berbanding ion-ion lain. Ion Cu 2+ , Ag + , Mn 2+ dan Cd 2+ merencat proses degradasi. Keputusan juga menunjukkan cahaya matahari adalah setanding dengan cahaya ultralembayung. Kepekatan H 2 O 2 terbaik adalah 5.0 × 10 -2 M dan semakin banyak TiO 2 digunakan semakin baik peratus degradasi tirosina. Oleh itu kaedah optimum untuk proses degradasifoto ialah Tr 2.5 × 10 -4 M + TiO 2 + H 2 O 2 5.0 × 10 -3 M + M n+ 1.0 × 10 -2 M. Proses degradasifoto dikaji menggunakan spektroskopi ultralembayung-nampak pada julat panjang gelombang 400-200 nm. Abstract. Amino acid is a basic component in plant or animal tissue. Tyrosine (Tr), an amino acid which contains aromatic ring, was chosen as a sample for a photodegradation process in an aqueous system. The purpose of the experiment is to study the effect of photocatalysis under UV (λ < 400 nm) or sunlight on tyrosine. The experiment was carried out by using UV light, catalyst powder (TiO 2 ), hydrogen peroxide H 2 O 2 and metal ions system. The addition of oxidising agent H 2 O 2 and metal ions such as Ni 2+ , Cu 2+ , Ag + , Mn 2+ , Co 2+ , Fe 2+ and Cd 2+ were used in order to achieve the most efficient system. Results showed that the system with added H 2 O 2 and metal ions such as Ni 2+ and Fe 2+ had successfully enhanced the process of the tyrosine photodegradation. Other metal ions system such as Cu 2+ , Ag + , Mn 2+ and Cd 2+ were found to inhibit the degradation process. The results also showed that sunlight was comparable to ultraviolet light. The best H 2 O 2 concentration was 5.0 ×10 -2 M and the percentage of tyrosine degradation increased with the addition of more TiO 2 by mass. Therefore, the optimum condition for tyrosine photodegradation process was in Tr 2.5 × 10 -4 M + TiO 2 + H 2 O 2 5.0 × 10 -3 M + H 2 O 2 1.0 × 10 -2 M. The disappearance of tyrosine in the photo degradation process was monitored by UV-visible spectroscopy between 400-200 nm.