To improve the adsorption capacity of wheat straw (WS) for Cd(Ⅱ) in water sample, a novel adsorbent, named mercaptopropionyl wheat straw (MPWS), was prepared by chemically modifying WS by sodium hydroxide (NaOH), L-cysteine (L-Cys), carbondiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS). The optimal preparation condition of MPWS was determined by using Plackett-Burman experiment, steepest ascent experiment, and central composite design (CCD) of response surface method. The synthesis mechanism of MPWS was characterized, and the adsorption performances of WS, CWS (chemically pretreated wheat straw) and MPWS for Cd(Ⅱ) were also investigated. The results showed that: (1) the P
value of the quadratic regression equation established by response surface method was 0.0002, indicating that the model was highly significant; (2) When the particle size of WS was 30 mesh (0.60 mm), the concentration of NaOH solution was 0.07 mol/L, the molar ratio between EDC·HCl and L-Cys was 0.099:1, the mass ratio between NHS and EDC·HCl was 0.5:1, the mass ratio between L-Cys and CWS was 4:1, the pH value in reaction medium was at
11, the reaction temperature was at
40 ℃, and the reaction time was 2.39 h, MPWS prepared under these conditions had the best removal performance of Cd(Ⅱ) in water sample. Furthermore, at 10 g/L of MPWS dosage, the experimental value of the Cd(Ⅱ) removal rate was 84.55%. It was close to 84.80% of predicted value, and the relative deviation was -0.29%; (3) The mercaptopropionyl groups was introduced into the structure of WS, and the chelation and adsorption for Cd(Ⅱ) by MPWS were well performed; (4) The order of adsorption capacity for Cd(Ⅱ) was MPWS>CWS>WS, suggesting that the adsorption capacity for Cd(Ⅱ) was enhanced by modifying WS with chemical pretreatment and graft modification. When the dosage of MPWS was 20 g/L, the removal rate of Cd(Ⅱ) by MPWS could reach 95.56%. These results show that response surface method can be used to optimize the preparation condition of MPWS, and the adsorption performance for Cd(Ⅱ) can be effectively improved by modifying WS with the mercaptopropionyl groups.