Preparation Of Cellulose/bentonite Grafted Polyacrylic Acid Hydrogels And Adsorption Of Cadmium In Aqueous And Soil Environments

Cd,a toxic heavy metal,poses risks to the ecological environment and human health when found in water bodies and soils.Urgent measures are needed to address Cd pollution effectively.Hydrogels,with their intricate three-dimensional network structure,demonstrate remarkable adsorption capacity,making them a promising candidate for addressing the remediation of Cd-contaminated soil and water bodies.However,single copolymer hydrogels have limited adsorption performance and effectiveness in Cd remediation and wastewater purification.To enhance adsorption,researchers are exploring organic-inorganic composite hydrogels formed by combining monomeric copolymer hydrogels with other materials.This research provides valuable insights and methods for environmental remediation and wastewater treatment.The aim of this study was to prepare a high-performance cellulose/bentonite grafted polyacrylic acid hydrogel（MCC/Ben-g-PAA）using microcrystalline cellulose（MCC）and bentonite（Ben）as raw materials.The prepared hydrogel was evaluated for its ability to remove Cd（Ⅱ）from soil and water environments.The adsorption potential and adsorption mechanism were investigated by adsorption kinetics,intra-granular diffusion,isotherm and thermodynamic model,combined with adsorption characterization methods（SEM,XPS,FT-IR,TG）.The passivation effect of MCC/Ben-g-PAA on Cd（Ⅱ）in soil and its impact on the growth of pakchoi were examined through a pot experiment conducted in Cd-contaminated soil.The main results are as follows:（1）The SEM results revealed that the MCC/Ben-g-PAA had a rough and uneven network framework structure with evenly distributed C and O groups throughout the adsorbent.Additionally,the adsorption sites were found to be widely distributed.The FTIR results indicated that MCC/Ben-g-PAA contained various functional groups such as-OH,-COOH,C-O,C=O,making it an ideal adsorbent.By comparing the FTIR analysis results before and after adsorption,it was observed that various functional groups were involved in the adsorption of Cd（Ⅱ）through different mechanisms,such as hydrogen bonding,electrostatic attraction,and ion complexation.XPS further confirmed the results of FTIR analysis.TG results showed that MCC/Ben-g-PAA had good thermal stability before and after adsorption,and MCC/Ben-g-PAA made the main chain structure of the polymer more stable due to the stronger hydrogen bond of the adsorbent after adsorption of Cd（Ⅱ）.（2）Batch adsorption tests showed that the maximum adsorption capacity of Cd（Ⅱ）by MCC/Ben-g-PAA was 242.53 mg/g,which was much higher than that of other similar hydrogel adsorbents.The adsorption process of Cd（Ⅱ）by MCC/Ben-g-PAA is endothermic and spontaneous.In addition,the removal rate of Cd（Ⅱ）by MCC/Ben-g-PAA was still as high as 95.37%in the presence of multiple competing ions,indicating that MCC/Ben-g-Pa A has high adsorption selectivity for Cd（Ⅱ）.After 10 cycles of adsorption and desorption,the removal rate of MCC/Ben-g-PAA can be maintained at 88.37%,showing a reusable performance.Combined with the performance characterization and batch test of MCC/Ben-g-PAA,we conclude that the adsorption mechanisms of Cd（Ⅱ）by MCC/Ben-g-PAA are mainly electrostatic,ionic recombination,physical adsorption and hydrogen bonding.（3）In the pot experiment,treating Cd-contaminated soil with MCC/Ben-g-PAA and PAA effectively reduced the soil’s Cd content.The passivation effect of MCC/Ben-g-PAA on soil Cd was higher than that of PAA at the same addition level.Among the treatments,the M1treatment(MCC/Ben-g-PAA with 1 g kg^-1)showed the most significant reduction,with an8.41%decrease in the effective soil Cd content.Under Cd stress,the addition of M1(MCC/Ben-g-PAA with 1 g kg^-1),M2(MCC/Ben-g-PAA with 3 g kg^-1),P1(PAA with 1 g kg^-1),and P2(PAA with 1 g kg^-1)of MCC/Ben-g-PAA resulted in increased pakchoi yield,with M1 treatment having the best effect.The addition of MCC/Ben-g-PAA and PAA inhibited the migration and enrichment of Cd to cabbage leaves,and the M1 treatment was optimal,reducing the Cd content in cabbage by 27.35%.The moderate addition of MCC/Ben-g-PAA increased the content of soluble sugar and vitamin C,reduced the nitrate content of chard,and effectively improved the growth quality of chard.Overall,compared with PAA,the addition of MCC/Ben-g-PAA not only performed better in soil passivation,but also effectively inhibited the migration of Cd to the leaves.This study involved the preparation of MCC/Ben-g-PAA through grafting copolymerization and intercalation,using cellulose and bentonite as raw materials.The adsorption properties and action mechanism of MCC/Ben-g-PAA for Cd（Ⅱ）were elucidated,along with its passivation effect on soil Cd and its impact on pakchoi growth.