Ammonium Ions Removal Using Carrageenan Activated Carbon from Aqueous Solution

This study focuses on developing and utilising activated carbon (AC) derived from carrageenan, a polysaccharide found in red seaweeds, for efficient ammonium ions removal from wastewater. This study entails a two-step activation procedure, involving the partial carbonisation of carrageenan followed by chemical activation. Initially, carrageenan powder was partially carbonised in a muffle furnace at 300oC for one hour. Subsequently, it was treated with phosphoric acid (H3PO4) before undergoing activation at 500oC for two hours in a self-generated atmosphere. Throughout the chemical activation process, a balanced 1:1 ratio was maintained between the chemical activator, H3PO4, and the partially carbonised carbon produced from the partial carbonisation step. Physical and chemical analysis of the produced carrageenan AC (CAC) included assessing yield, moisture and ash content, pH, bulk density, iodine determination, identification of functional groups, crystallinity structure, and evaluation of thermal stability. The Fourier transform infrared spectroscopy (FTIR) analysis of CAC before and after adsorption reveals key functional groups involved in adsorption. Initially, peaks at 3365 cm-1 (hydroxyl groups), 2326 cm-1 (C≡C stretching or adsorbed CO2), and 1630 cm-1 (carbonyl groups) were identified. Post-adsorption shifts in these peaks, particularly at 3339 cm-1 (O-H stretching), 1638 cm-1 (carbonyl groups), and 1169 cm-1 (ether groups); indicate effective interaction with ammonium ions. X-ray Diffraction (XRD) analysis showed a predominantly amorphous structure with some crystalline phases, enhancing surface area and adsorption capacity. Thermogravimetric (TGA) analysis suggested that CAC exhibits good thermal stability, with significant decomposition occurring between 200oC and 600oC. Adsorption experiments varied contact time, adsorbent dosage, and initial ammonium concentration, with Ultraviolet-visible (UV-Vis) spectroscopy measuring ammonium ions concentration. Besides, response surface methodology (RSM) was utilised to optimise critical factors such as contact time (min), adsorbent dosage (mg), and initial ammonium concentration (mg/L). The experimental design employed central composite design (CCD) to delve into the intricate relationship among these variables and their impact on adsorption capacity. Optimal conditions were found to be a contact time of 35 min and an adsorbent dosage of 2 mg, achieving an ammonium ions removal efficiency of 91.4% at an initial concentration of 50 mg/L. This is very close to the predicted value of 92.6%, with a minimal error of 1.3%, indicating the model’s accuracy and reliability.