Cross-polymerization between bio-oil and polyaniline: synergistic effects on pore development in subsequent activation and adsorption of phenol

Bio-oil is a major product from pyrolysis of biomass, which serves as a carbon source to produce carbon material, due to its high reactivity to polymerization itself or cross-polymerization with other organic feedstocks. Using this property, it can react with nitrogen-containing basic polyaniline to prepare nitrogen doped porous activated carbon under the activation of potassium oxalate. Their work was published in the journal Industrial Chemistry & Materials on March 2024.

“Polyaniline (PANI) was used for preparation of N-doped porous carbon material from bio-oil. PANI was selected as a nitrogen source, which was based on the consideration that it is an alkaline and contain benzene ring for the occurrence of polymerization via electrophilic substitution reactions. The generated product will unavoidably be impacted by a cross-reaction between the PANI and the bio-oil.” explains Xun Hu, a professor at the University of Jinan. 

The research found that the cross-reactions of the two feedstocks of varied origin did have a clear impact on the evolution of pore structures of activated carbon (AC). “The direct activation of the mixture of PANI and bio-oil enhanced the yield of AC by 15% (with calculated average as a base), due to cross-polymerization occurring between PANI and organics in the bio-oil. Such cross-polymerization also showed synergistic effects in enhancing the specific surface area of the resultant AC as 1677.9 m² g^-1 (calculated average) into 1771.3 m² g^-1 with also more micropores generated.” said Hu.

The researchers found that the pre-polymerization pretreatment of PANI and the bio-oil at 200 °C generated thermally more stable organics, enhancing their resistivity towards cracking/gasification in the activation. This enhanced the yield of AC from heating directly the mixture of PANI and bio-oil from 15.0% to 23.3% via the pre-polymerization plus activation, which, however, diminished the pore development and also generated more micropores. The pre-polymerization formed the carbon crystal structure in resulting AC with less lattice distortion and retained more oxygen species. “In addition, the mixing of PANI with bio-oil and the pre-polymerization pretreatment formed the AC of smooth surface, due to coverage of surface of AC with heavy components of bio-oil. This enhanced yield of AC at expense of pore development but increased the hydrophilicity for adsorption of polar organics.” said Hu.

The pore structure was not a determining factor for phenol adsorption and the lower efficiency of AC (derived from the single activation of PANI with the highest specific surface area) for adsorption of phenol from aqueous solution was related to its high hydrophobicity. The AC obtained by direct activation of PANI mixed with bio-oil with the high abundance of micropores and also high hydrophilicity showed the superior performance for adsorption. While the AC from activation of the bio-oil also showed high capability for adsorption of phenol, although the specific surface area was not high. That was because the abundance of oxygen-containing functional groups on the surface of AC resulted from the bio-oil provided the adsorption sites for the phenol adsorption.

The researchers also found that the developed pore structures of AC provided abundant anchoring points for Ni, which effectively catalyzed the hydrogenation of o-chloronitrobenzene and vanillin (conversion rate reached to 100%).

This study confirmed the cross-interactions of bio-oil with PANI during the activation and demonstrated the influence of which on property of AC. But looking ahead, the unresolved issue herein is how do these organics formed from the cross-polymerization reactions between the PANI and bio-oil affect the pore development. The reason underneath the higher resistivity towards cracking reactions during the activation needs to be further explored.

The research team includes Baihong Li, Chao Li, Dianqiang Li, Lijun Zhang and Xun Hu* from the University of Jinan

This research is funded by the National Natural Science Foundation of China (No. 52276195), program for supporting innovative research from Jinan (202228072); Program of agricultural development from Shandong (SD2019NJ015).

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. Icm publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials.