A study on the preparation of pitch-based high-strength columnar activated carbon and mechanism of phenol adsorption from aqueous solution

Abstract

Coal tar pitch was ground into powder and hydroformed with high pressure. After pre-oxidation, the pitch was activated by CO₂ at high temperature. The effects of different preparation conditions on the yield, pore structure and phenol adsorption capacity of activated carbon were investigated, and activated carbon prepared under suitable conditions had good adsorption performance. A pore volume of 1–10 nm is the main absorption structure according to the analysis of pore size distribution and phenol adsorption capacity. The activated carbon showed high mechanical strength through compressive strength tests. Graphite nanocrystals around 5 nm were observed in the TEM images, and it illustrates that grain refinement results in the high strength. These nanocrystal stacked structures are easier to make and enlarge pores by activation than graphite layer stacked structures. Surface functional groups are considered not to be the active sites of phenol adsorption as suggested by the results of FTIR and Boehm's titration, and acidic oxygen-containing functional groups are harmful to phenol adsorption, which happen to be removed in the reductive preparation atmosphere. The donor–acceptor complex mechanism can be ruled out, and the π–π interactions are considered the most likely mechanism. The Langmuir and Redlich–Peterson models are better fitted to the adsorption isotherms. Adsorption kinetics fit the intraparticle diffusion model best. Comparison of different activated carbons shows that suitable pore size is important for phenol adsorption. Thermodynamic parameters demonstrate that the adsorption process is spontaneous and exothermic, and the entropy increases. Pitch-based high-strength columnar activated carbon is an effective and low cost adsorbent for phenol wastewater treatment. This carbon nanocrystal material also provides a new direction for catalyst carriers.