OPTIMIZATION OF THE SYNTHESIS OF ?-CARRAGEENAN ADSORBENT MODIFIED WITH POLYETHYLENEIMINE AND GLYOXAL USING CENTRAL COMPOSITE DESIGN FOR CR(VI) ION ADSORPTION

• Main Author: Rhea Amalia, Khalisha
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/83613
• Institution: Institut Teknologi Bandung

Heavy metal pollution in aquatic environments is a significant issue of global concern. One significant source of heavy metal pollution is chromium, frequently used in industries such as textiles, aerospace, wood preservation, dye production, and drilling mud. Cr(VI) ions are classified as Group 1 carcinogens by the World Health Organization (WHO). Long-term exposure to Cr(VI) levels exceeding 0.05 mg L-1 can cause respiratory issues, liver and kidney damage, and cancer. Various techniques exist for removing Cr(VI) ions from wastewater, including precipitation, electrocoagulation, membrane filtration, ion exchange resins, photocatalysis, and others. Among these methods, adsorption is considered a promising technology for removing toxic metals from industrial wastewater and natural water. Adsorption offers several advantages, such as simplicity of use, high removal efficiency, reusability, and cost-effectiveness. Carrageenan is an anionic biopolymer with sulfate ester groups attached to one of its carbon atoms. ? carrageenan, a major type of carrageenan, is known for its strong gel-forming properties. In this study, an adsorbent based on ?-carrageenan modified with polyethyleneimine (PEI) and glyoxal was developed to reduce Cr(VI) ion contamination in wastewater. PEI is a polymer containing primary, secondary, and tertiary amine groups. It is water-soluble, aliphatic, and positively charged, available in both linear and branched forms. Glyoxal, a cross-linking agent with two aldehyde groups, is widely used for nucleophiles such as hydroxyl, sulfide, mercaptan, sulfite, and amide groups. In this study, glyoxal acted as a cross-linking agent between PEI and ?-carrageenan, with the mixture composition optimized using central composite design. The optimal composition, resulting in maximum adsorption capacity and minimum swelling degree, was found to be 2.11 %w/v ?-carrageenan, 1.75 %v/v PEI, and 0.92 %v/v glyoxal. Characterization of the adsorbent cubes using Fourier Transform Infrared (FTIR) spectroscopy revealed absorption peaks for imine (C=N) and hemiacetal (C?O?C) bonds at 1648 cm-1 and 1076 cm-1, respectively, indicating successful cross-linking between glyoxal, PEI, and ?-carrageenan. Scanning Electron Microscopy (SEM) showed that the surface morphology of the ?-carrageenan adsorbent cubes changed from rough blocks to smooth surfaces after modification with PEI and glyoxal, confirming the cross-linking reaction. Energy Dispersive Spectroscopy (EDS) after Cr(VI) ion adsorption showed an increase in the Cr atom percentage from 0.02% to 1.48%, demonstrating successful adsorption on the adsorbent surface. The optimal adsorption conditions were determined to be at pH 3, a contact time of 45 minutes, and an adsorbent mass of 0.10 g for 25 mL of the analyte solution. The adsorption of Cr(VI) ions by the adsorbent cubes followed a pseudo-second-order kinetic model with an R2 value of 0.9973 and a rate constant of 0.0255 mg g-1 min-1. The adsorption process adhered to the Langmuir isotherm model with an R2 value of 0.9846 and a maximum adsorption capacity of 190.16 mg g-1. The Langmuir isotherm indicates that the adsorption process involves monolayer formation on a homogeneous adsorbent surface with identical and fully saturated active sites. Thermodynamic studies revealed that the adsorption process is exothermic, spontaneous, and results in increased order. Testing the reusability of the adsorbent using 0.1 M HNO3 as a desorbing agent showed that the synthesized adsorbent maintained good reusability up to the 4th cycle.