The application of green tea extract to prepare bentonite-supported nanoscale zero-valent iron and its performance on removal of Cr(VI): Effect of relative parameters and soil experiments

Abstract

Bentonite-supported “green” nanoscale zero-valent iron (B-nZVI) were prepared using green tea extracts characterized and employed for Cr(VI) adsorption. FE-SEM-EDS, TEM confirmed that nZVI (40–80 nm) has been successfully loaded and efficiently dispersed on bentonite. According FTIR and EDS analysis the synthesized B-nZVI were composed of polyphenols and other C-containing molecules from green tea extracts acting as both reducing and capping agents. Batch experiments were conducted to measure the effects on adsorption of Cr(VI) of different parameters such as initial concentrations, ionic strength, adsorbent dosage, pH of the medium and contact times. The results showed that synthesized B-nZVI has much higher adsorption capacity for Cr(VI) compared to bentonite. The adsorption was highly dependent on pH providing maximum adsorption at pH range of 2–6. The adsorption isotherm and kinetic data for B-nZVI was fitted well with the Langmuir and pseudo-second order model, respectively, which implied that the adsorption process was chemisorptions. The results of soil experiment showed that the addition of adsorbents including bentonite and B-nZVI decreased the release of Cr as compared with Cr-control treatment. However, application of B-nZVI (2 and 4%) significantly reduced the exchange fraction (EX) and subsequently increased the FeMn oxide-bound (ox), and residual (RS) fractions. These results indicated the adsorption property of B-nZVI gives the compound with great potential for applications in environmental remediation.