The removal of 2,4-dinitrophenol from aqueous solutions by orange peel ash as an eco-friendly adsorbent

This study investigates the adsorption potential of natural materials waste. The fine powder of orange peel (OP) was used for the removal of 2,4-dinitrophenol from aqueous solutions. Several biomasses such as fungi, algae, fern, and moss have been used for the removal of heavy metal ions, dyes, pigments and other toxic organic compounds, but no study has been done on the removal of 2,4-dinitrophenol by orange peel [1]. Orange is a fruit that grows widely in the fruit gardens of Mazandaran and Bam in the north and south of Iran, respectively. It is important to find new treatment technologies for removing pollutants from water. Adsorption is one of the simplest and most effective treatment technologies for treating water containing toxic organic compounds such as 2,4-dinitrophenol rather than other expensive techniques [2]. The OP are first washed with preheated double distilled water for several times and air dried in oven at 65 ºC for 72 h. Then, it was crushed manually with a ceramic mortar and sieved to the desired particle size of 354–420 µm. 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. Studied parameters are: the initial 2,4-dinitrophenol concentration, the pH of the solution, the temperature, the speed of shaking, the amount of adsorbent, and contact time. The highest 2,4-dinitrophenol adsorption capacity is obtained at pH 4, for a speed shaking of 250 rpm, a temperature of 283 K, a contact time of 60 min, adsorbent dose of 50 mg, and initial concentration of 20 ppm. The kinetic studies showed that the adsorption rate constants could be calculated better by pseudo-second-order expression with rate constant of 0.019 g mg-1 min-1. The adsorption data could be fitted well to Freundlich adsorption isotherm with coefficient of determination values greater than 0.99. The obtained results are shown that OP is a good biosource for the produce of low-cost adsorbent and able to effectively remove of 2,4-dinitrophenol from aqueous solutions. The adsorption of 2,4-dinitrophenol onto activated OP is spontaneous and exothermic.