Thermal and chemical pretreatment of Terminalia mantaly seed husk biosorbent to enhance the adsorption capacity for Pb2+

Abstract

A novel biosorbent, modified Terminalia mantaly seed (TM) husk was explored for its potential in removing Pb2+ from aqueous solutions. The biosorbent was prepared by pulverizing the husk oven-dried for 1 h at 110 °C. The ground husk was modified at 550 °C and then activated with NaOH and H3PO4 to get four different adsorbents. The adsorbents were characterized by Fourier ransform Infra-red Spectroscope (FTIR), Thermogravimetric analyser (TGA), and scanning electron microscope (SEM). The FTIR result showed that there were new functional groups as a result of the activation/modification with heat, NaOH and, H3PO4. The TGA revealed that the modified TM biosorbents were thermally stable up to 400 °C, while the unmodified TM is only thermally stable up to 40–45 °C indicating the differences in the degree of thermal stability. The TGA also revealed that the thermal decomposition of the adsorbents assumed three or less well-pronounced stages, with appreciable mass losses. The SEM image showed that TM possessed the right percentage of carbon content to be used in adsorbent synthesis (> 74%). It also showed that the outer surfaces of the adsorbents were rough and discontinuous in their formation; they cannot be considered as pores but connecting channels to the interior of the adsorbent. Observation revealed that the TM, NaOH and, H3PO4 modified TM activated carbon were well described by the Freundlich isotherm model which suggests multilayer Pb2+ binding mechanism onto the adsorbents. Thermally modified Terminalia mantaly (TMTM) was experimentally the best adsorbent having the highest adsorption capacity (99.95 mg/g) as predicted by the experimental design result. Performance evaluation of the adsorbents revealed that they are capable of removing Pb2+ ions from aqueous solutions efficiently.