Plant extract as environmental-friendly green catalyst for the reduction of hexavalent chromium in tannery effluent

The aqueous extract of various plants like Coriandrum sativum (AECS), Alternanthera tenella colla (AEAT), Spermacoce hispida (AESH) and Mollugo verticillata (AEMV) was studied for its hexavalent chromium (Cr^VI) reduction property. Even though antioxidant activity was present, AEAT, AESH and AEMV did not reduce Cr^VI. AECS showed rapid and dose-dependent Cr^VI reduction. The efficient reduction of 50 mg/L of Cr^VI using AECS was attained in the presence of 250 µg/mL of starting plant material, incubating the reaction mixture at pH 2, 30°C and agitation at 190 rpm. Under such conditions, about 40 mg/L of Cr^VI was reduced at 3 h of incubation. FT-IR analysis revealed the involvement of phenols, alcohols, alpha-hydroxy acid and flavonoids present in the AECS for the Cr^VI reduction. These results indicate that not all the plant extracts with rich antioxidants are capable of reducing Cr^VI. Using the conditions standardized in the present study, AECS reduced about 80% of Cr^VI present in the tannery effluent. These results signify the application of AECS as an eco-friendly method in the wastewater treatment.