Judul: Pengembangan pengekstrak fase padat berbasis zeolit untuk adsorpsi kromium heksavalen
Abstrak: Kromium terutama valensi VI, dapat membahayakan kesehatan karena bersifat karsinogenik. Oleh karena itu harus diminimumkan keberadaannya, hingga tidak lebih dari 50 μg/L dalam air minum. Salah satu metode untuk menurunkan kandungan Cr adalah dengan ekstraksi fase padat, salah satunya dengan zeolit. Guna meningkatkan daya jerapnya, zeolit harus dimodifikasi oleh surfaktan kationik heksadesiltrimetilamonium bromida (HDTMABr). Kapasitas adsorpsi Cr(VI) oleh zeolit sebesar 1.90 mg/g yang diperoleh pada kondisi terbaiknya ialah larutan Cr(VI) pH 3 dengan waktu kontak selama 18 jam. Adsorpsi zeolit terhadap Cr(VI) mengikuti pola isoterm Freundlich. Kapasitas adsorpsi zeolit terhadap Cr(VI) terbaik (40.99 mg/g) diperoleh pada konsentrasi HDTMABr 1000 ppm dengan waktu kontak 30 jam. Adsorpsi HDTMABr mengikuti pola isoterm Langmuir. Campuran larutan NaOH 0.5 M dan Na2CO3 0.28 M (1:1 v/v) dapat mendesorpsi Cr(VI) sebesar 65.67% (tumpak) dan 3.93% (lapik tetap). Pencirian zeolit setelah modifikasi ditunjukkan oleh pita pada 2856.33 dan 2927.65 cm-1 yang berasal dari CH3 pada HDTMABr.
Keyword: Zeolites, Hexavalent chromium, Bogor Agricultural University, Institut Pertanian Bogor, IPB

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: Analisis jaringan komunikasi dalam masyarakat tradisional kampung naga: Kasus dalam usahatani padi
Abstrak: Masyarakat Kampung Naga merupakan satu-satunya tipe masyarakat tradisional yang masih ada di Kabupaten Tasikmalaya. Usahatani padi yang merupakan mata pencaharian pokok masyarakat Kampung naga memperlihatkan suatu model usahatani yang masih tradisional. Norma masyarakat setempat memegang peranan yang cukup kuat di dalam mengatur perilaku dan kehidupan masyarakat Kampung.
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