A novel aminated lignin/geopolymer supported with Fe nanoparticles for removing Cr(VI) and naphthalene: Intermediates promoting the reduction of Cr(VI)

A novel, inexpensive and eco-friendly aminated lignin/geopolymer supported with Fe nanoparticles (Fe@N-L-GM) composite was successfully synthesized using kaolin and lignin as the major precursors. The prepared Fe@N-L-GM had larger specific surface area, rich oxygen-containing and nitrogen-containing functional groups, greater electron transfer ability and interconnective porous structure. The Fe@N-L-GM could be employed as the adsorbent of Cr(VI) and the activator of potassium peroxymonosulfate (PMS) for treatment of Cr(VI) and naphthalene (NAP) in wastewa-ter. The adsorption and degradation results indicated that the maximum adsorption capacity of Cr(VI) could reach 65.83 mg g-1, whereas the maximum NAP degradation efficiency could reach 97.81 %. The adsorbed Cr(VI) was mostly converted to the low toxic Cr(III) through the reduction of electron donors such as Fe(II), amino and hydroxyl groups. The quenching experiment results confirmed that center dot OH might be the crucial ROSs in mediating NAP degrada-tion. In the simultaneous removal experiment of Cr(VI) and NAP, the Cr(VI) removal rate was significantly improved in the presence of NAP, while phenol as the degradation intermediate of NAP might be the main substance for promot-ing the reduction of Cr(VI). This work provided the theoretical foundation and a new type of material for the simulta-neous removal of heavy metal and persistent organic pollutants (POPs).

Automated summary

A novel, inexpensive and eco-friendly composite material (Fe@N-L-GM) consisting of aminated lignin, geopolymer, and Fe nanoparticles was synthesized and used for the simultaneous removal of Cr(VI) and NAP in wastewater. The material showed excellent adsorption capacity for Cr(VI) and high degradation efficiency for NAP. The adsorbed Cr(VI) was transformed into less toxic Cr(III) through reduction by electron donors, while ·OH radicals played a crucial role in mediating NAP degradation. The presence of NAP enhanced the removal rate of Cr(VI), with phenol as the main substance promoting Cr(VI) reduction. This work provides a new material and theoretical foundation for the simultaneous removal of heavy metals and persistent organic pollutants.