Efficient removal of Cr(VI) by polydopamine-modified lignin from aqueous solution: Batch and XAFS studies

Lignocellulose has the potential to become a bio-based adsorbent due to its biodegradability and renewability.In this study,a novel polydopamine functionalized-lignin(lignin@PDA),prepared via self-polymerization of dopamine(PDA)on lignin,was used as a bio-based adsorbent for rapid scavenging of hexavalent chromium(Cr(VI)).The morphology,functional groups,crystalline structure,and chemical composition of lignin@PDA were characterized with a scanning electron microscope-energy dispersive spectrometer,Fourier transform infrared spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The Cr(VI)adsorption process of lignin@PDA was studied using batch experiments as a function of pH,ionic strength,adsorbent dose,and contact time at room temperature.The adsorption rate of lignin@PDA was five times greater than that of the unmodified lignin,with a maximum adsorption capacity of 102.6 mg/g in an acidic medium.The adsorption of Cr(VI)on lignin@PDA fit the pseudo-secondorder equation and the Freundlich model,indicating that the adsorption process was mainly dominated by chemisorption and surface complexation.The thermodynamic parameters showed that adsorption of Cr(VI)on lignin@PDA was an endothermic and spontaneous process.The X-ray absorption fine structure results showed that sorption and reduction of Cr(VI)into Cr(II)occurred simultaneously on lignin.Moreover,PDA coating not only improved the reactivity of lignin but also promoted the complete reduction of Cr(VI)by lignin.According to these results,polydopamine functionalized-lignin is a promising bio-based adsorbent for immobilization of Cr(VI)from wastewater.

Reduced He ion irradiation damage in ZrC-based high-entropy ceramics

Excellent irradiation resistance is the basic property of nuclear materials to keep nuclear safety.The high-entropy design has great potential to improve the irradiation resistance of the nuclear materials,which has been proven in alloys.However,whether or not high entropy can also improve the irradiation resistance of ceramics,especially the mechanism therein still needs to be uncovered.In this work,the irradiation and helium(He)behaviors of zirconium carbide(ZrC)-based high-entropy ceramics(HECs),i.e.,(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C,were investigated and compared with those of ZrC under 540 keV He ion irradiation with a dose of 1×10^(17) cm^(−2) at room temperature and subsequent annealing.Both ZrC and(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C maintain lattice integrity after irradiation,while the irradiation-induced lattice expansion is smaller in(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C(0.78%)with highly thermodynamic stability than that in ZrC(0.91%).After annealing at 800℃,ZrC exhibits the residual _(0.2)0%lattice expansion,while(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C shows only 0.10%.Full recovery of the lattice parameter(a)is achieved for both ceramics after annealing at 1500℃.In addition,the high entropy in the meantime brings about the favorable structural evolution phenomena including smaller He bubbles that are evenly distributed without abnormal coarsening or aggregation,segregation,and shorter and sparser dislocation.The excellent irradiation resistance is related to the high-entropy-induced phase stability,sluggish diffusion of defects,and stress dispersion along with the production of vacancies by valence compensation.The present study indicates a high potential of high-entropy carbides in irradiation resistance applications.