SINTESIS Mg/Al-NO3 HIDROTALSIT TERINTERKALASI DAN TERIMOBILISASI ASAM SITRAT UNTUK ADSORPSI [AuCl4]�

NUR RAISAH M, Prof. Dr. Sri Juari Santosa, M.Eng

2017 | Tesis | S2 Ilmu Kimia

Adsorben Mg/Al-NO3 hidrotalsit terinterkalasi asam sitrat (Mg/Al-Sit HT) dan terimobilisasi asam sitrat (Mg/Al-NO3 HT-Sit) telah berhasil disintesis untuk adsorpsi [AuCl4]-. Mg/Al-Sit HT disintesis secara kopresipitasi melalui pendekatan bottom-up menggunakan mikroreaktor-T dan Mg/Al-NO3 HT-Sit disintesis melalui pendekatan top-down. Kondisi optimum sintesis kedua adsorben dikaji dengan menentukan pH dan konsentrasi optimum prekursor. Sebelum digunakan sebagai adsorben, stabilitas kedua adsorben telah dikaji dengan mengukur % stabilitas asam sitrat dari adsorben pada berbagai pH media menggunakan spektrofotometer UV-Visibel. Aplikasi kedua adsorben untuk adsorpsi [AuCl4]- dipelajari dengan menentukan model kinetika dan isoterm adsorpsi. Padatan hasil sintesis dikarakterisasi dengan difraktometer sinar-X dan spektrofotometer infra-merah. Hasil penelitian menunjukkan bahwa sintesis adsorben Mg/Al-Sit HT optimum pada pH 10 dengan perbandingan konsentrasi Mg2+:Al3+:Sitrat adalah 2:1:1,5 mmol. Pada adsorben Mg/Al-NO3 HT-Sit, pH optimum dicapai pada pH 7 dengan kapasitas adsorpsi asam sitrat adalah 121,95 mg g-1. Karakterisasi XRD menunjukkan bahwa dengan pendekatan sintesis bottom-up maka asam sitrat berhasil terinterkalasi pada daerah antarlapis hidrotalsit dengan peningkatan basal spacing d(003) mencapai 13,17 Ã, dan dengan menggunakan pendekatan top-down, asam sitrat berhasil terimobilisasi di permukaan adsorben dengan basal spacing d(003) adalah 7,99 Ã. Uji stabilitas menunjukkan bahwa kedua adsorben stabil pada rentang pH 3-7 dengan % stabilitas asam sitrat untuk adsorben Mg/Al-Sit HT dan Mg/Al-NO3 HT-Sit masing-masing sebesar 84-87 dan 43-52%. Adsorpsi [AuCl4]- oleh kedua adsorben berlangsung optimum pada pH 3 dan mengikuti model kinetika pseudo orde dua Ho dan model isoterm adsorpsi Langmuir. Kapasitas adsorpsi Mg/Al-Sit HT dan Mg/Al-NO3 HT-Sit untuk [AuCl4]- masing-masing adalah 208,33 dan 126,58 mg g-1.

Synthesis of Mg/Al-NO3 hydrotalcite intercalated by citric acid (Mg/Al-Sit HT) and immobilized by citric acid (Mg/Al-NO3 HT-Sit) have been conducted for [AuCl4]- adsorption. The Mg/Al-Sit HT was prepared by co-precipitation method through bottom-up approach using T-microreactor while Mg/Al-NO3 HT-Sit was synthesized by conventional co-precipitation method through top-down approach. Optimum condition for the synthesis of both adsorbents were studied by determining the optimum acidity and concentration of precursors. Before being used as adsorbent, stability of adsorbents was tested by examination of % stability of citric acid from hidrotalcite matrix at various pH media with UV-Visible sprectrofotometer. Application of adsorbents for [AuCl4]- adsorption was studied by determining their kinetics and isoterm adsorption model. Both adsorbents were characterized with X-ray difractometer and infra-red spectrophotometer. The results showed that optimum acidity for the synthesis of Mg/Al-Sit HT was obtained at pH 10 with mole ratio of Mg2+:Al3+:Citric respectively 2:1:1,5 mmole, while the optimum acidity for the synthesis of Mg/Al-NO3 HT-Sit was at pH 7 with adsorption capacity of citric acid was 121.95 mg g-1. The XRD difractogram showed that synthesis of Mg/Al-Sit HT through the bottom-up approach, citric acid was successfully intercalated into interlayer of hydrotalcite which basal spacing d(003) enlarged to 13.17 Ã; while synthesis of Mg/Al-NO3 HT-sit through the top-down approach, citric acids only immobilized onto the surface of citric acid with basal spacing d(003) was 7.99 Ã. The stability test showed that both Mg/Al-Sit HT and Mg/Al-NO3 HT-Sit were stable at pH range 3-7 with % stability of citric acid was 84-87 and 43-52%, respectively. Adsorption of [AuCl4]- by both adsorbents was optimum at pH 3 and fitted well to pseudo second-order and Langmuir isoterm model. The adsorption capacity of Mg/Al-Sit HT and Mg/Al-NO3 HT-Sit for [AuCl4]- adsorption was 208.33 and 126.58 mg g-1, respectively.

Kata Kunci : Mg/Al-NO3 hidrotalsit, interkalasi, imobilisasi, asam sitrat, adsorpsi, [AuCl4]�.