Abstract
Five different activated carbons (ACs) have been prepared from dried date pits using air and phosphoric acid as activating agents. The used phosphoric acid:date pit ratio dictated the characteristics of the prepared ACs; the equivalent BET-nitrogen surface area varied from 794 m2/g for a ratio of 5:1, to 1707 m2/g for a ratio of 2:1, whereas the micropore volume changed in value from 0.24 cm3/g for the 5:1 ratio to 0.59 cm3/g for the 2:1 ratio. The prepared ACs were tested to remove 4-chlorophenol (4-CP) from aqueous solutions by means of batch adsorption process. The prepared 2:1 AC exhibited the highest uptake with a maximum of 525 mg/g. Equilibrium pH studies showed that 4-CP removal was pH dependent; the maximum uptake occurred at an equilibrium pH value of 5.5. Dynamic studies showed that 4-CP uptake on 2:1 AC is rapid, with 80% of the maximum uptake achieved during the first 40 min. Both surface adsorption and intraparticle diffusion were identified to be effective adsorption mechanisms. Kinetic studies indicated a pseudo second-order reaction. Results of equilibrium adsorption experiments showed that the adsorption of the 4-CP on 2:1 AC is best described by the Langmuir model. The thermodynamics parameters of the adsorption (ΔG0, ΔH0, and ΔS0) were determined by studying the adsorption equilibrium at different temperatures. The values of these parameters indicated the spontaneous and endothermic nature of the adsorption phenomenon of 4-CP on the prepared ACs.
Highlights
Chlorophenols and other phenol-based compounds have come to represent some of the most dangerous and persistent organic pollutants because of their various industrial applications [1].Many of these compounds are byproducts of industrial processes including pharmaceutical, pesticide, paint and solvent production, and wood, paper, and pulp processing
Studies have shown that date pit-derived activated carbon is effective as an adsorbent for phenol and heavy metal contaminants [38,39]; here, we investigate its use in the sorption of 4-chlorophenol (4-CP) from aqueous solutions
These results can be explained on the basis of different activation mechanisms, namely the pyrolysis of the raw materials enhanced the cross-linkage and, created highly porous materials, while activation with phosphoric acid led to the elimination of water and, destruction of the cellulosic structure [20,41]
Summary
Chlorophenols and other phenol-based compounds have come to represent some of the most dangerous and persistent organic pollutants because of their various industrial applications [1]. Many of these compounds are byproducts of industrial processes including pharmaceutical, pesticide, paint and solvent production, and wood, paper, and pulp processing. The removal of chlorophenols, and the precursor phenols, from polluted areas and water sources is of utmost importance. Many methods for their removal have been investigated, Materials 2016, 9, 251; doi:10.3390/ma9040251 www.mdpi.com/journal/materials
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