Study of orthophosphate uptake by diffusive gradient in thin film (DGT) system with Co-loaded chitosan bentonite biocomposite binding gel and the effect of its anion interferences on the phosphate response

The binding gel in DGT has been modified with Co-loaded chitosan-bentonite (Co-CSBent) biocomposite in order to enhance the phosphate binding capacity. The comparison was also performed by Chitosan-bentonite (CSBent). The binding and diffusive gel for this method were made from acrylamide, ammonium persulfate, and N, N-methylenebisacrylamide. The synthesized binding gel and biocomposite were characterized using Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Characterization results showed that biocomposites had been synthesized successfully. For control, DGT Co-CSBent and CSBent were tested with 2 ppm phosphate and without anions, C_DGT of orthophosphate value of 1.9127 μg/mL and 1.6643 μg/mL were obtained respectively. Both binding gels in DGT were examined with various anions including Cl^-, SO₄ ^2-, HCO₃ ^-, and NO₃ ^- in the concentration ranging from 0.5 mg/L to 2.5 mg/L. At higher SO₄ ^2- inhibitor concentration, C_DGT value of 1.0153 μg/mL (CSBent) and 1.2736 μg/mL (Co-CSBent) were obtained. Whereas, at higher Cl^- inhibitor, C_DGT value of 1.2934 μg/mL (CSBent) and 1.9584 μg/mL (Co-CSBent) were obtained. At higher HCO₃ ^- inhibitor concentration, C_DGT value of 0.7371 μg/mL (CSBent) and 0.8628 μg/mL (CoCSBent) were obtained. And, at higher NO₃ ^- inhibitor concentration, C_DGT value of 0.459 μg/mL (CSBent) and 0.5889 μg/mL (Co-CSBent) were obtained. Based on the obtained data, Cl^- and SO₄ ^2- do not affect the C_DGT of orthophosphate value. However, NO₃ ^- and HCO₃ ^- anions gradually reduced the C_DOT of orthophosphate value compared with C_DOT of the control value. Phosphate binding by biocomposite is controlled by ion exchange, electrostatic force, and Lewis metal ion complexation.