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

Abstract

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, CDGT 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, CDGT value of 1.0153 μg/mL (CSBent) and 1.2736 μg/mL (Co-CSBent) were obtained. Whereas, at higher Cl− inhibitor, CDGT value of 1.2934 μg/mL (CSBent) and 1.9584 μg/mL (Co-CSBent) were obtained. At higher HCO3 − inhibitor concentration, CDGT value of 0.7371 μg/mL (CSBent) and 0.8628 μg/mL (CoCSBent) were obtained. And, at higher NO3 − inhibitor concentration, CDGT 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 CDGT of orthophosphate value. However, NO3 − and HCO3 − anions gradually reduced the CDOT of orthophosphate value compared with CDOT of the control value. Phosphate binding by biocomposite is controlled by ion exchange, electrostatic force, and Lewis metal ion complexation.