Preparation of biochar orange peel for the adsorption of 4-chlorophenol from aqueous solutions

Phenolic derivatives discharged into the water systems from the textile, petroleum, rubber, cosmetic, and plastics industries are one of the main organic pollutants that must be removed or degraded [1]. This study investigates the 4-chlorophenol removal from aqueous solutions through the adsorption process onto biochar obtained orange peel (OP). OP waste as zero value byproduct generated from fruit juice production industries [2]. OP waste is obtained from the local fruit juice shop in Ardabil, Iran. The adsorbent is first washed with water and air dried in oven at 65 ºC for 72 h. After drying, they are grinded and further treated with dilute nitric acid to remove further adsorbent pollutants. After washing with distilled water until the decanted water became colorless and pH reached at neutral, the color-abated OP is then dried in oven at 70 ºC and further sieved to obtain the particles of 354–420 µm mesh size. After then, they were activated at 700 ºC in a Muffle furnace for 2 h in a constant flow of N2 gas. After cooling in a desiccator the activated OP was ready for use. Results indicate that a small amount of proposed adsorbent (20 mg) is responsible for successful removal of 5-40 mg L−1 of 4-chlorophenol in a short time (60 min) and optimum pH of 3. Adsorption kinetic data are fitted well with pseudo-second-order model with correlation coefficient greater than 0.99 and rate constant of 0.011 g mg-1 min-1. Equilibrium data followed Freundlich isotherm model with maximum adsorption capacity of 9.65 mg g−1 for 40 ppm initial adsorbate concentration. RL value obtain for 40 mg L-1 4-chlorophenol concentration are 0.72. RL values between 0 and 1 confirming that the adsorption isotherm is favorable. Our results demonstrate OP waste is a good source for the produce of low-cost adsorbent and able to effectively remove 4-chlorophenol from aqueous solutions. The adsorption of 4-chlorophenol onto OP is endothermic. Biochar prepared from orange peel is very cheap, easily available and renewable. This study revealed that this adsorbent could be used as a tool for the development of low-cost adsorbents for the treatment of other pollutants such as colored dyes.