Low temperature synthesis of nitrogen-rich biomass for high-performance removal of phosphate

Abstract

Eutrophication in water bodies provokes the exploit of efficient tactics for phosphate removal from wastewaters. Herein, biowaste oil-tea shell (OTS) was adopted as a precursor. Through a facile two-step dipping method of nitric acid (HNO3) and polyethyleneimine (PEI), the functionalized OTS (denoted as NP-OTS) was prepared and applied for the efficient removal of phosphate in wastewater. Characterization using XRD, FTIR, SEM and XPS showed that the as-obtained NP-OTS were mainly cellulose with abundant N-containing groups. The effect of solution pH, adsorption dosage, contact time, initial concentration, and co-existing ions were systemically investigated. As a result, the adsorption behavior of phosphate on NP-OTS was in best pertinence with pseudo-second-order kinetic model and Langmuir model, and the thermodynamics results suggested that the adsorption of the phosphate is spontaneous. The maximum uptake capacity of NP-OTS was 125.24 mg/g estimated by Langmuir model, which was about 4.4-fold higher than the pristine oil-tea shell (28.32 mg/g), and over 1.4-fold higher than either the HNO3 modified OTS (65.19 mg/g) or the PEI decorated OTS (83.94 mg/g) at 25 °C. The phosphate adsorbed NP-OTS was also easy to regenerate within five stable cycles. Furthermore, electrostatic adsorption and hydrogen bonding were revealed as the underlying adsorption mechanism. This work paves a new way for the high-value utilization of biowaste and the removal of phosphate in acid wastewater.