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Copper(Cu)is an essential element to plant,but excessive Cu(concentrations)in soil systems canadversely affect biological systems.Biochar,a carbon-rich by-product from bioenergy production,has recently been used as an adsorbent for heavy metals in soil.Having a strong affinity for Cuand being recalcitrant,biochar can be used for long-term stabilization of excessive Cu in soilenvironment.Here we have probed the nanometer-scale chemical heterogeneities of biochar andits molecular-level complexation characteristics with Cu.The Jerusalem artichoke stem waschosen as a precursory biomass material because it is a common agricultural waste without acost-effective method to recycle.Synchrotron scanning transmission X-ray microscopy(STXM)and near-edge X-ray absorption fine structure(NEXAFS)spectroscopy,X-ray diffraction(XRD),and Fourier transform infrared spectroscopy(FTIR)were used to show how the plant materialunderwent chemical transitions as charring temperature increased from 300 to 700 ℃,and theresultant impact on the complexation of the produced biochar particles with Cu.Various carbonspecies,including aromatic,ketonic/phenolic and carboxylic functional groups,were found in allthe biochars produced at different temperatures.STXM micrographs exhibited that the functionalgroups of the biochars varied on nanometer-scale,and so did the Cu species.Both thecomplexation of Cu with hydroxyl and carboxyl groups and the surface coprecipitation of Cu(asCu3(CO3)2(OH2)and CuO)contributed to its adsorption on biochars.The results showed thatbiochar from Jerusalem artichoke stem could be used for adsorbing Cu,and molecular-levelcharacterization of Cu adsorption on biochar will improve the understanding of biochar adsorptionproperties for the remediation of Cu-excessive soils.