A wood sponge sensor for heavy metal ion detection and adsorption

As a kind of absorbent material, the porous properties of wood sponge as the heavy metal ion detection and adsorption materials have been widely studied in the field of water pollution treatment. In this study, sodium chlorite and sodium hydroxide were used to remove lignin and hemicellulose from the poplar wood, so that it could become a porous three-dimensional cellulose skeleton structure. Subsequently, β-cyclodextrin was cross-linked with cellulose skeleton through hydroxyl bond which can enhance the heavy metal adsorption capacity of wood sponge. By vacuum impregnation, the wood sponge which was attached to carbon quantum dots was a kind of stable fluorescent solution that can be quenched by heavy metal ions. In this way, the wood sponge became a heavy metal ion detecting sensor and absorber, which can sense and absorb heavy metal ions. The microstructure of the obtained wood sponge was investigated by scanning electron microscopy. The results showed that the wood cell wall became thinner after lignin and hemicellulose were removed, but the cellulose skeleton was retained. The carbon quantum dots and β-cyclodextrin successfully cross-linked on the cellulose skeleton by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The selectivity and sensitivity of a wood sponge capable of detecting and adsorbing heavy metal ions were explored. Among the ions, the wood sponge had a quenching reaction to Cu²⁺. Moreover, the wood sponge showed lower intensity of brightness with increasing Cu²⁺ concentrations. The wood sponge with cross-linking β-cyclodextrin showed excellent heavy metal ions adsorption performance and the adsorption capacity reached 60 mg/g at the adsorption equilibrium time of 3 h. At a pH value of 5, adsorption temperature of 60 °C, and adsorbent dosage of 3 g, the wood sponge had the best adsorption effect.