Biosorption Mechanism of Cadmium by Acid-treated Non-living Rhodopseudomonas sp. strain SBL

This research aimed to evaluate the effects of initial cadmium concentration and contact time on the biosorption capacity of cadmium by acid-treated non-living Rhodopseudomonas sp. strain SBL, to analyse the mechanism of the biosorption by kinetic models, and to characterise the morphological and functional group changes of Rhodopseudomonas sp. strain SBL in the biosorption process. The biosorption capacity of cadmium was quantitatively evaluated using an Atomic Absorption Spectrophotometer (AAS). The data was then subjected to pseudo-first-order and pseudo-second-order models to analyse the mechanism of the biosorption process. The changes in the morphological and functional group of Rhodopseudomonas sp. strain SBL in the biosorption process were observed using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The effect of initial cadmium concentration showed that the percentage biosorption decreased with increasing initial cadmium concentration, where an initial cadmium concentration of 0.5 mg/L gave the highest biosorption capacity of 77.5%. The effect of contact time revealed that the percentage biosorption increased with contact time and reached equilibrium after 30 minutes. The optimal contact time is at minute 30, with a biosorption capacity of 68.5%. In the biosorption kinetic study, the data obtained fit the pseudo-second-order model, indicating that the biosorption process occurs via chemisorption. The observation under SEM showed morphological changes of Rhodopseudomonas sp. strain SBL from smooth to rough surfaces, with the formation of pores following the biosorption process. The FTIR analysis showed hydroxyl, carbonyl, and carboxyl groups as the main functional groups involved in the biosorption process. The findings in this study suggested that the acid-treated non-living Rhodopseudomonas sp. strain SBL has a promising potential as a biosorbent for the removal of cadmium via biosorption.