Sequestration of Congo Red from aqueous solution using raw and citric acid-modified Dicerocaryum eriocarpum biomass: isotherm, kinetics and thermodynamics

Abstract

In recent times, dyes such as Congo Red have proven to be resilient environmental pollutants affecting freshwater portability among other media. Its toxicity to humans, animals and plant life is both a cause of concern and a motivation to prioritize decontamination. Many materials have been explored for the removal of this pollutant via adsorption; however, there are notable areas of improvement. Dicerocaryum eriocarpum (DE) seed is a non-toxic, cost-effective plant material which is possible as a sorbent and has not been reported in Congo Red sequestration. This research is therefore based on the removal of Congo Red dye from aqueous solution using raw (RDE) and citric acid-modified DE (CDE). The sorbents were characterized before and after sorption using various characterization techniques such as FTIR, EDS, SEM and BET. The effects of contact time, adsorbent dosage, concentration, pH and temperature were optimized during the experiment. According to experimental findings, modification with citric acid resulted in a reduction of the equilibration interval from 90 to 60 min. Sorption effectiveness increased with an increase in temperature for CDE but a decrease in temperature for RDE. The equilibrium data were best described by the Langmuir isotherm with maximum sorption capacity (qmax) of 51.02 mg/g and 53.19 mg/g for RDE and CDE, respectively. Pseudo-second-order model better suited the kinetic data, while thermodynamic analysis revealed a spontaneous sorption process. Five cycles of desorption experiments using 0.1 M NaOH revealed that the regenerated sorbent effectively removed CR dye for the first three cycles at comparable efficiency to the virgin samples. This study therefore supports the use of DE seed as an easily accessible and efficient sorbent for remediation of harmful dyes from water.