Mechanistic insights into sequestration of U(VI) toward magnetic biochar: Batch, XPS and EXAFS techniques

The magnetic iron oxide（Fe3O4） nanoparticles stabilized on the biochar were synthesized by fast pyrolysis of Fe（II）-loaded hydrophyte biomass under N2 conditions. The batch experiments showed that magnetic biochar presented a large removal capacity（54.35 mg/g）at pH 3.0 and 293 K. The reductive co-precipitation of U（VI） to U（IV） by magnetic biochar was demonstrated according to X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis. According to extended X-ray absorption fine structure analysis, the occurrence of U-Fe and U-U shells indicated that high effective removal of uranium was primarily inner-sphere coordination and then reductive co-precipitation at low pH. These observations provided the further understanding of uranium removal by magnetic materials in environmental remediation.

Adsorption and mechanistic study of the invasive plant-derived biochar functionalized with CaAl-LDH for Eu(Ⅲ) in water

Herein,we developed the invasive plant-derived biochar (IPB) functionalized with CaAl-LDH at five mass ratios using a physical mixture method,assessed their adsorption perform for Eu(Ⅲ),and explored the relative mechanisms.Results show that the IPB successfully loaded CaAl-LDH in five composites and their Eu(Ⅲ) sorption affinities were strongly affected by solution p H,contact time,temperature,and the mass ratio of LDH and IPB.All the sorpiton process for Eu(Ⅲ) occurred on the heterogeneous surface of five composites and the boundary layer diffusion limited the chemical sorption rate.Interestingly,the CaAl-LDH/IPB composite with high ratio of IPB had higher sorption capacity than the one with high ratio of LDH due to larger porosity of the former.Three mechanisms containing ion exchange between Al and Eu ions,surface complexation with carboxyl-and oxygen-containing functional groups,and precipitation were involved in the Eu(Ⅲ) sorption,but the dominant sorption mechanism for each CaAl-LDH/IPB composite differed with different mass ratio of CaAl-LDH and IPB.In composite with more IPB (e.g.,CaAl-LDH/IPB-13),both ion exchange and surface complexes dominated the sorption process and the intensity of Eu^3+ was identified with the one of Eu2O3.Whereas in composites with high LDH,ion exchange dominated the sorption and the intensity of Eu^3+ was obviously higher than the one of Eu_2O_3.This research will provide a new perspective for the application of the LDH/biochar materials.

Interaction of radionuclides with natural and manmade materials using XAFS technique

The X-ray absorption fine structure(XAFS)technology has exhibited a very unique application in the study of sorption mechanism,chemical species and microstructures of radionuclides at the natural solid-water interfaces.In this review,the interaction mechanism of radionuclides with clay minerals and nanomaterials under different environmental conditions are summarized from the XAFS spectroscopy analysis.The coordination number and the bond distances of radionuclides,the oxidation-reduction reactions,the influence of humic substances and microorganisms on the species and structures of radionuclides at molecule level are reviewed and compared.This review is helpful to understand the interactions of radionuclides with oxides,natural clay minerals and nanomaterials,which is also crucial to evaluate the physicochemical behaviors of radionuclides in the natural environment.