Judul: Sintesis, Karakterisasi, dan Aktivitas Antioksidan Grafena Oksida (GO) dari Biji Pinang (Areca catechu)
Abstrak: Grafena oksida (GO) merupakan lembaran grafit oksida yang terdiri atas satu lapisan atau beberapa lapisan atom karbon seperti grafena yang mengandung gugus-gugus fungsional oksigen. GO adalah salah satu turunan dari grafena dan banyak memiliki potensi aplikasi. Biji pinang merupakan biomassa yang dapat digunakan untuk sintesis GO karena dapat menjadi sumber grafit. GO disintesis menggunakan modifikasi metode Hummers. Penelitian ini bertujuan menyintesis, mengkarakterisasi, serta menguji aktivitas antioksidan dari GO. Spektrum UV menunjukkan puncak tajam pada 228,3 nm yang merupakan daerah serapan GO. Spektrum FTIR menunjukkan gugus fungsi O-H, C-O, C-C, dan C-H. Spektrum Raman menunjukkan pita D, G, dan 2D yang merupakan ciri khas dari GO, serta rasio (ID/IG) dihasilkan sebesar 0,86 yang menandakan struktur GO memiliki kualitas baik. Nilai IC50 GO dengan metode FRAP sebesar 81,80 μg/mL yang menunjukkan aktivitas antioksidan yang kuat., Graphene oxide (GO) is a graphite oxide sheet consisting of one layer or several layers of carbon atoms, such as graphene, which contains oxygen functional groups. GO is a derivative of graphene and has many potential applications. Areca nut is a biomass that can be used for GO synthesis because it can be a source of graphite. GO was synthesized using a modification of the Hummers method. This study aims to synthesize, characterize, and test the antioxidant activity of GO. The UV spectrum shows a sharp peak at 228.3 nm indicating the GO absorption region. The FTIR spectrum shows the functional groups O-H, C-O, C-C, and C-H. The Raman spectrum shows D, G, and 2D bands which are characteristic of GO, and the resulting ratio (ID/IG) is 0,86, indicating that the GO structure has good quality. The IC50 GO value using the FRAP method was 81,80 μg/mL which indicated high antioxidant activity.
Keyword: antioksidan, biji pinang, grafena oksida, metode Hummers

Judul: Sintesis Oksida Grafena dari Gambir (Uncaria gambir Roxb.) sebagai Antibakteri dan Antioksidan
Abstrak: Oksida grafena merupakan produk nanoteknologi yang memiliki banyak keunggulan dan saat ini masih terus dikembangkan dalam berbagai penelitian. Penelitian ini bertujuan menghasilkan senyawa oksida grafena berbahan dasar gambir sebagai antibakteri dan antioksidan. Oksida grafena dari arang tersebut berhasil disintesis menggunakan modifikasi metode Hummers. Hasil spektrum ultraviolet terdapat puncak serapan pada 224,8 nm. Gugus fungsi beroksigen yang muncul pada spektrum inframerah menandakan oksida grafena berhasil terbentuk. Hasil analisis difraksi sinar X menggunakan puncak 2θ pada sudut 25,04°. Hasil uji Raman menunjukkan adanya tiga puncak yaitu puncak D, puncak G, dan puncak 2D pada bilangan ~1373 cm-1, ~1592 cm-1, dan ~2866 cm-1. Diameter zona hambat pertumbuhan bakteri Escherichia coli sebesar 8,82 mm lebih kecil dari bakteri Staphylococcus aureus sebesar 9,21 mm. Nilai IC50 oksida grafena metode DPPH (2,2-difenil-1-pikrilhidrazil) adalah 220,77 μg/mL, termasuk tingkat antioksidan sedang dan IC50 oksida grafena metode FRAP (Ferric Reducing Antioxidant Power) adalah 64,24 μg/mL, termasuk tingkat antioksidan kuat., Graphene oxide is a nanotechnology product with many advantages and is currently still being developed in various studies. This study aims to produce graphene oxide compounds based on gambier as antibacterial and antioxidant. Graphene oxide from charcoal was successfully synthesized using a modification of the Hummers method. The ultraviolet spectrum result showed an absorption peak of 224,8 nm. Oxygen functional groups that appear in the infrared spectrum indicate that graphene oxide has been successfully formed. The results of X-ray diffraction analysis used a 2θ peak at an angle of 25,04°. Raman test results showed three peaks, namely D peak, G peak, and 2D peak at ~1373 cm-1, ~1592 cm-1, and ~2866 cm-1. The diameter of the inhibition zone for Escherichia coli bacteria was 8,82 mm. It was 9,21 mm smaller than that of Staphylococcus aureus. The IC50 value of graphene oxide by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method was 220,77 μg/mL, including moderate antioxidant levels and the IC50 value of graphene oxide by the FRAP (Ferric Reducing Antioxidant Power) method was 64,24 μg/mL, including intense antioxidant levels.
Keyword: antibacterial, antioxidant, gambier, graphene oxide, Hummers method

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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