Biosorbents prepared from pomelo peel by hydrothermal technique and its adsorption properties for congo red

A new kind of biosorbent was prepared from pomelo peel by using potassium hydroxide as activating agent and hydrothermal treatment method. The characteristics of materials were analyzed by SEM, BET and FTIR. Increasing the adsorbent dosage (from 2.5 to 17.5 g l−1) and contents of congo red in solution (from 20 to 50 mg l−1) cause the increment of removal rate of congo red. On the other side, the removal rate is decrement with rising of temperature and pH. The maximum adsorption quantity of biosorbent was 144.93 mg g−1 at 303 K, which calculated by Langmuir model. The pseudo-first-order kinetic model, pseudo-second-order kinetic model and intra-particle diffusion model were used to explain adsorption process. The value of Gibbs free energy (∆G) is −7.63 (kJ/mol) at 303 K and the enthalpy change (∆H) is −31.43 (kJ/mol), meaning that adsorption behavior for congo red is spontaneous.