Adsorption of anionic dyes on spent tea leaves modified with polyethyleneimine (PEI-STL)

This paper investigates the adsorption performance of spent tea leaves (STL) modified with polyethylenimine (PEI) on two anionic dyes, namely Reactive Black 5 (RB5) and Methyl Orange (MO), from simulated wastewater. Modification of STL surface with PEI reduced the STL surface area. Abundant basic groups and high point of zero charge were found for PEI-STL. Adsorption capacities of 71.9 mg/g (RB5) and 62.11 mg/g (MO) on PEI-STL were recorded. The adsorption performance of PEI-STL increased with contact time until 100 min, when it became nearly constant. Increasing pH resulted in lower adsorption performance of PEI-STL on RB5 and MO. A positive correlation between adsorbent dosage and adsorption performance of PEI-STL was also observed. Higher temperature promoted the adsorption performance of RB5 dyes, but reduced the adsorption performance of MO. It is proposed that the dyes adsorption proceeds via electrostatic attraction and hydrogen bonding between dyes molecules and adsorbent, while the role of pore filling is minimal. This study demonstrates the superior property of PEI-STL in adsorption of RB5 and MO dyes without carbonization and activation.