Sintesis Zeolit Magnetik Terimobilisasi Ditizon dan Kajian Adsorpsinya terhadap ion Pb(II)

Carissa Ayu Susiana, Prof. Drs. Mudasir, M.Eng., Ph.D; Prof. Dr. Bambang Rusdiarso, DEA.

2023 | Tesis | S2 Ilmu Kimia

Penelitian tentang sintesis zeolit magnetik terimobilisasi ditizon dan kajian adsorpsinya terhadap ion Pb(II) telah dilakukan. Tujuan dari penelitian ini adalah melakukan sintesis dan karakterisasi zeolit magnetik (ZTM) dan zeolit magnetik terimobilisasi ditizon (ZTM-Dtz), mengkaji parameter yang mempengaruhi adsorpsi ion Pb(II), serta menentukan mekanisme interaksi antara ion Pb(II) dengan adsorben secara desorpsi sekuensial menggunakan berbagai jenis pelarut yaitu aquabidest, KNO3, NH2OH·HCl, dan Na2·EDTA. 

Zeolit alam diaktivasi menggunakan HCl 6 M dengan proses refluks selama 4 jam. Adsorben zeolit magnetik (ZTM) dipreparasi dengan metode kopresipitasi menggunakan prekusor campuran ion Fe(II) dan Fe(III) dalam suasana basa. Imobilisasi ditizon pada zeolit magnetik (ZTM-Dtz) dilakukan dalam medium air/basa menggunakan NaOH 1,5 M selama 8 jam. Adsorben yang diperoleh kemudian dikarakterisasi menggunakan FTIR, XRD, dan VSM. Uji kemampuan adsorpsi ion Pb(II) menggunakan sistem batch meliputi pengaruh pH, massa adsorben, waktu kontak, konsentrasi adsorbat, dan temperatur untuk penentuan kinetika, energi aktivasi, isoterm, dan parameter termodinamika adsorpsi. 

Hasil penelitian menunjukkan bahwa adsorben ZTM dan ZTM-Dtz telah dapat disintesis dan ditizon berhasil diimobilisasikan pada permukaan zeolit magnetik. Kajian adsorpsi ion Pb(II) menunjukkan bahwa kondisi optimum adsorpsi oleh ZTM dan ZTM-Dtz berturut-turut dicapai pada pH 6 dan 5, massa adsorben 20 mg, waktu kontak 60 menit, dan konsentrasi awal adsorbat 80 mg L-1. Kinetika adsorpsi dari kedua adsorben mengikuti model pseudo orde dua dengan tetapan laju adsorpsi (k2) meningkat seiring kenaikan temperatur. Energi aktivasi (Ea) ZTM dan ZTM-Dtz berturut-turut sebesar 31,51 kJ mol-1 dan 23,84 kJ mol-1. Isoterm adsorpsi mengikuti isoterm Langmuir dengan kapasitas adsorpsi maksimal 8,23 mg/g untuk ZTM dan 39,53 mg/g untuk ZTM-Dtz. Parameter termodinamika menunjukkan adsorpsi berlangsung spontan, terjadi secara endotermik dan dipicu oleh faktor entropi. Berdasarkan hasil desorpsi sekuensial interaksi antara adsorben ZTM dan ion Pb(II) didominasi pertukaran ion sedangkan pada ZTM-Dtz terbentuk ikatan hidrogen dan kompleksasi. 

Research on the synthesis of dithizone-immobilized magnetic zeolite and its adsorption study towards Pb(II) ions have been conducted. The study aims to synthesize and characterize magnetic zeolite (ZTM) and dithizone-immobilized magnetic zeolite (ZTM-Dtz), to study parameters affecting adsorption and determine the mechanism of interaction between Pb(II) ions and the adsorbents with sequential desorption approach using various types of solvents, namely double-distilled water, KNO3, NH2OH·HCl, and Na2·EDTA. 

Natural zeolite was first activated using 6 M HCl under a reflux process for 4 hours. Magnetic zeolite adsorbent was prepared by the coprecipitation method utilizing a mixture of Fe(II) and Fe(III) ions as precursors in alkaline conditions. Dithizone immobilization on the magnetic zeolite was carried out in an aqueous/alkaline medium using 1.5 M NaOH for 8 hours. The obtained adsorbent was then characterized using FTIR, XRD, and VSM. The adsorption ability of Pb(II) ions was tested in a batch system by examining the effect of the pH, adsorbent mass, contact time, adsorbate concentration, and temperature to determine the kinetics, activation energy, isotherms, and thermodynamic parameters of the adsorption.

The results show that ZTM and ZTM-Dtz adsorbents has been formed and dithizone has been successfully immobilized on the magnetic zeolite surface. The adsorption study show that the optimum conditions of adsorption on ZTM and ZTM-Dtz are achieved at pH 6 and 5, the mass of the adsorbent is 20 mg, for contact time is 60 minutes, and the initial concentration of the adsorbate is 80 mg L-1. The adsorption kinetics of both adsorbents comply the pseudo-second-order model with the adsorption rate constant (k2) increases along with the increasing temperatures. The activation energies (Ea) of ZTM and ZTM-Dtz are 31.51 kJ mol-1 and 23.84 kJ mol-1 respectively. The adsorption isotherm follows the Langmuir isotherm model with a maximum adsorption capacity of 8.23 mg/g for ZTM and 39.53 mg/g for ZTM-Dtz. The thermodynamic parameters reveals that the adsorption takes place spontaneously with the value of the change in Gibbs free energy becomes more negative as the temperature increases, occurs endothermically, and is driven by the entropy factor. Based on the results of the sequential desorption, the interaction between the ZTM adsorbent and Pb(II) metal ions is dominated by ion exchange while in ZTM-Dtz are predicted by hydrogen bonds and complexation. 

Kata Kunci : magnetized zeolite, dithizone, Pb(II) ions, adsorption, desorption