From liquid hot water pretreatment solution to lignin-based hydrophobic deep eutectic solvent for highly efficient extraction of Cr (VI).

Liquid hot water (LHW) pretreatment has been widely investigated attributed to its advantages, such as environmental friendliness, the potential application of dissolved hemicellulose, and no chemical addition. Expanding the portfolio of products that can be made from LHW pretreatment solutions will be critical to enabling a viable LHW-based economy. We provide a one-step method to separate and functionalize lignin from the LHW pretreatment solution. A hydrophobic deep eutectic solvent (hDES) was prepared by using methyltrioctylammonium chloride (MTAC) and the LHW pretreatment solution and directly applied to the extraction of Cr (VI) in an aqueous solution. In the process of forming hDES, the removal rate of liquid hot water lignin (LHWL) was reached 99%. The new LHW-hDES exhibited excellent extraction performance for Cr (VI), the extraction capacity was as high as 198.402 mg g, optimum extraction conditions at the mass of hDES 0.10 g, vortex time 90 s, room temperature, and natural pH. Notably, we have shown that the method of combining the separation and functionalization of lignin in the LHW pretreatment solution, which can provide a way of thinking for the application of the LHW pretreatment solution.