Effectiveness and potential of straw- and wood-based biochars for adsorption of imidazolium-type ionic liquids

• Biochar is superior to commercial activated carbon for removal of ionic liquids (ILs).
• High adsorption capacity of ILs on straw- and wood-based biochar is observed.
• Straw- and wood-based biochar show different adsorption mechanism.
• Adsorption of ILs is pH-dependent and can be greatly enhanced by PO43− anions.
• Both biochars can be reused for 10 times without loss of high adsorption capacity.

The growing industrial application of imidazolium-type ionic liquids (ITILs) is likely to result in their release to the environment. Water-soluble ITILs are difficult to remove from wastewaters using traditional adsorbents. In this work, we developed different biochars derived from straw and wood (named as SBB and WBB, respectively) to improve the adsorption effectiveness for removal of ITILs from wastewaters. SBB had high O/C element ratio (0.143), while WBB had high ratio of Vmicro/Vtotal (61.5%) compared with commercial activated carbon (AC). Both of them showed greater adsorption of ITILs than AC with different adsorption mechanisms. FTIR spectra revealed that electrostatic interactions were the dominant driving force in SBB adsorption, while high micropore volume promoted adsorption in WBB. The adsorption of [C2mim][BF4] on SBB and WBB was strongly enhanced by trivalent PO43− anions, suggesting that PO43− anions could be used as promoter to increase the removal efficiency of ITILs from wastewater. Using HCl solution (pH=0.5) as regenerant, SBB and WBB were regenerated with nearly 100% recovery of adsorption capacity over ten consecutive adsorption-desorption cycles. Straw-based biochar and wood-based biochar are efficient sorbents for removal of water-soluble ionic liquids from aqueous solutions.

Figure optionsDownload as PowerPoint slide