Carboxylated graphene oxide-chitosan spheres immobilize Cu<sup>2+</sup> in soil and reduce its bioaccumulation in wheat plants: Fid-Bau Portal

Carboxylated graphene oxide-chitosan spheres immobilize Cu²⁺ in soil and reduce its bioaccumulation in wheat plants

Zhao, Lianqin / Guan, Xin / Yu, Baowei / Ding, Na / Liu, Xinmei / Ma, Qiang / Yang, Shengnan / Yilihamu, Ailimire / Yang, Sheng-Tao

Abstract

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Highlights • Carboxylated graphene oxide was incorporated into chitosan to prepare composite spheres (GO-COOH/CS). • GO-COOH/CS spheres showed high adsorption capability in adsorbing Cu²⁺ from both water and soil. • GO-COOH/CS spheres largely reduced the bioaccumulation of Cu²⁺ in wheat from soil.

Abstract Due to the strong interaction with pollutants and the huge adsorption capacity, graphene adsorbents are widely applied in water decontamination. However, graphene adsorbents are seldom used in soil remediation, because the adsorptive sites on graphene would be occupied by soil components. In this study, we prepared carboxylated graphene oxide-chitosan (GO-COOH/CS) spheres for the immobilization of Cu²⁺ from water and soil. The pores in GO-COOH/CS allowed the internal diffusion of Cu²⁺ solution, while they blocked the direct contact between the solid soil and the adsorptive sites on graphene sheets. Therefore, the high adsorption capacity of GO-COOH/CS spheres (78 mg/g) was largely retained for the soil Cu²⁺ fixation. The partition coefficient (PC) for Cu²⁺ adsorption onto GO-COOH/CS spheres was 4.2 mg/g/μM at C e of 0.48 mg/L and q e of 31 mg/g, while the PC value decreased to 0.096 mg/g/μM at C e of 91.4 mg/L and q e of 78 mg/g. At initial Cu²⁺ concentrations of 120 mg/L and lower, the fixation efficiencies were all higher than 99% and the corresponding free Cu²⁺ concentrations in leachates were lower than 1.0 mg/L. The Cu²⁺ fixation on GO-COOH/CS spheres largely reduced its bioaccumulation in wheat roots from 127.8 μg/g to 51.2 μg/g. The toxicity evaluations suggested that GO-COOH/CS spheres were of low toxicity to wheat seedlings and did not amplify the toxicity of Cu²⁺. The implications to the design of graphene adsorbents for soil remediation are discussed. Overall, our results collectively indicated that porous GO-COOH/CS spheres were high-performance adsorbents for the immobilization of Cu²⁺ to reduce Cu²⁺ bioaccumulation in plants.