The Application of Adsorption Modeling and Fourier Transform Infrared Spectroscopy to the Comparison of Two Species of Plant Growth–Promoting Rhizobacteria as Biosorbents of Cadmium in Different pH Solutions

Batch experiments were performed to determine the cadmium absorption capacity of two plant growth–promoting rhizobacteria at different pH levels and in different cadmium concentrations. Comparison of the mean metal removal from two species of bacteria studied showed that Pseudomonas florescence is the superior species for removing cadmium at all cadmium concentrations. The maximum cadmium absorption by P. florescence and P. putida were at 5 mg/L of cadmium concentration in pH 6 and 7, respectively. The applicability of the Langmuir and Freundlich isotherm models was surveyed. Comparison of two isotherm parameters (Q _m and a) further confirmed that P. fluorescence was better at binding cadmium ions (52.6 and 7.7 mg/g, respectively). Adsorption reaction also was considered by Fourier transform infrared (FTIR) spectroscopy. The FTIR analysis implied that the principal functional sites in the bacterial cell walls were phosphoryl and hydroxyl, carboxyl, amide I, amide II, and amine groups.