Judul: Characterization and Modification of Natural Zeolites as Media Material Detection, Case Studies: Hexavalent Chromium
Abstrak: Zeolites are widely used for various agricultural applications and industrial catalysts. An abundant amount of natural zeolite has not been widely utilized. So this study aims to characterize and to modify surface of natural zeolite samples from Indonesia. The zeolite samples contain some impurities, chraracterized by X-ray diffraction (XRD) pattern. Acid and alkaline modification do not alter the structure of the the zeolite significantly, for samples from Bayah and Cikalong. Modification both samples using barium cation do not increase the adsorption capacity of Cr(VI), although adsorption of barium cation occurs on to zeolite surface. Surface modification using iron ion yield significant adsorption of anion Cr (VI) on to the zeolite. This is characterized by the change of XRD peak patterns
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Judul: Elektrode Pasta Karbon Zeolit Alam Termodifikasi Heksadesiltrimetilamonium Bromida untuk Deteksi Kromium(VI)
Abstrak: The extensive use of chromium in metallurgic, leather tanning, electroplating, lumber, electricity generating and other industries have promoted enormous ecological impact in numerous sites that are being contaminated by chromium. Chromium has two dominant species, namely Cr(III) and Cr(VI). Among them, attention concerning the possible hazards arising from the use of Cr(VI) than Cr(III) because hexavalent chromium is around 1000 times more toxic than trivalent one. Therefore, methods for differentiation and quantification of these species are very important in water analysis. Research on chemical modified carbon paste electrode have been carried out starting from 1990 especially in electroanalysis field caused by better improvement than conventional electrode. Continuous research on chemical modified carbon paste electrode has been increasing use of inorganic materials as a modifiers of electrode material. Among inorganic materials, zeolites have been widely used as an ion exchanger due to size, shape, and unique charge selectivity, high capacity ion exchangers, high thermal stability, low cost resistance to extreme conditions. Zeolites have a permanent negative charge on its crystal structure making it suitable as a cation exchanger. This negative charge is also possible to do modifications on the zeolite surface using cationic surfactant of hexadecyltrimethylammonium (HDTMA) ions. Cation exchange capacity value of zeolite origin from Cikembar (23.7 meq/100 g), Cikalong (47.6 meq/100 g), Bayah (39.7 meq/100 g), and Lampung (42.4 meq/100 g). After activation with NaOH, all cation exchange capacity values showed increasing were Cikembar (60.4 meq/100 g), Cikalong (60.4 meq/100 g), Bayah (42.5 meq/100 g), and Lampung (107.5 meq/100 g). Therefore, Lampung zeolite was selected to do modification with surfactant and was obtained highest adsorption amount of 200 mM HDTMABr as 3.9923 mmol/g zeolit. Cr(VI) adsorption test using diphenylcarbazide (DPC) method toward Lampung zeolite, 100 mM and 200 mM HDTMABr modified NaOH activated Lampung zeolite showed increasing adsorption capacity (Q). Cr(VI) adsorption capacity (Q) at steady state were obtained toward Lampung zeolite, 100 mM and 200 mM zeolite-NaOH-HDTMABr as 58.0457, 134.0522, 148.5602 mg Cr(VI)/g zeolite, respectively. This showed an increase of Cr(VI) amount bound on the zeolite surface. XRD characterization showed 3 significant peaks were obtained on Lampung zeolite, Lampung zeolite activated NaOH, and HDTMABr modified zeolite-NaOH. This showed no structural change on natural and modified zeolite. The degree of crystallinity decreased with the order of natural zeolite, zeolite-NaOH, and HDTMABr modified zeolite-NaOH showed partial loss of impurities contained in natural zeolite and adsorption of HDTMABr molecules on zeolite surface. Zeolite-NaOH-HDTMABr showed incorporation of absorption peaks originating from bending δH-O-H (1637.65 cm-1), vibration vT-O (T= Si,Al) symmetric (1055.56 cm-1), vT-O asymmetric (793.17 cm-1), δSi-O-Al (608.86 cm-1 and 525.67 cm-1), and δO-T-O (468.41 cm-1) also peak absorption originating from HDTMABr were stretching vC-H methylene asymmetric (2920.05 cm-1) and bending δC-H methylene (2851.01 cm-1, 1489.21 cm-1). Characterization by thermal analysis (TG-DTA) showed percentage of loss mass was quite large aat 15.1% in temperature range of 200-300 oC. This result indicates surfactant double layer formed by hydrophobic-hydrophobic interaction of nonpolar groups on the surface of HDTMABr modified Lampung zeolite. The existence of electrostatic interactions between HDTMABr molecules on zeolite surface forming s single layer
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Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf