| In recent years, endocrine disruptors in water (EDCs) and heavy metals are threatening the safety of water environment ecological and drinking water. Adsorption is a simple and efficient technique for the removal of EDCs and heavy metal. As one kind of bio-adsorbent, the agricultural and forestry residue has many advantages, like extensive sources, abundant functional groups, easy to be modified and low price, and so on. As a result, the bio-adsorbent is better than the conventional adsorption materials such as activated carbon in some respects. In this paper, citric acid and β-cyclodextrin (β-CD) were used for the modification of pine sawdust, and the modified pine sawdust were used in the adsorption of heavy metal ions, dye and organic pollutants. What’s more, the catalytic effect of cyclodextrin and the enhanced removal of bisphenol A (BPA) in the presence of P-CD modified pine sawdust were studied. This paper is focused on the adsorption and photocatalytic performance of the modified low-cost bio-sorbents. The main works are as followed:Firstly, different bio-materials and pretreatment methods were compared with each other, consequently, pine sawdust pretreated with NaOH (B-PS) presented the best performance, which was used for the following adsorption and modification. B-PS was chemically modified with polybasic carboxylic acid through the esterification reaction. The citric acid modified pine sawdust (CA-PS) were made through the optimized method, followed by the physical and chemical characterization, including SEM, EDS, FT-IR, and so on. Comparising with B-PS, CA-PS had more carboxyl group amount, which is better for the adsorption of copper ion and methylene blue (MB).Then the removal of copper ion from aqueous solutions by B-PS and CA-PS in the single system was investigated in detail, and the competitive adsorption of certain divalent heavy metal ions by CA-PS was studied. The adsorption isotherm of B-PS and CA-PS could be well elucidated with the Langmuir model, the maximum adsorption capacity of CA-PS (0.216 mmol/g) was almost three times higher than that of B-PS (0.079 mmol/g) under the conditions that:pH=5.0, adsorbent=4.0 g/L, T=25 ℃. The adsorption ability of CA-PS was significantly increased with the help of citric acid modification. The pH value had a significant effect on copper adsorption. Competitive adsorption occured in the binary-systems. The adsorption preference of copper ion, cadmiun ion and lead ion in the binary systems onto CA-PS could be ordered as lead> copper> cadmium. According to the above results, the main adsorption force was ion-exchange effect in the adsorption of copper by CA-PS. In addition, CA-PS was used as an adsorbent for the removal of MB, and the competitive adsorption of copper and MB was studied in detail. The isotherm studies indicated that the Langmuir model provided the best correlation of the experimental data in the single systems as well as in the binary systems. Under the conditions that:pH=5.0, adsorbent=4.0 g/L, T=25 ℃, the adsorption capacity of CA-PS for MB (0.239 mmol/g) from Langmuir isotherm model was higher than that of B-PS (0.085 mmol/g). The initial pH value had a relatively little effect on MB adsorption, which is due to the combined effect of hydrogen effect and ion-exchange effect.For the adsorption of organic pollutant, B-PS was modified with citric acid and β-CD. What’s more, β-CD modified pine sawdust (P-CD-PS) was characterized using different technologies. The characterization results confirmed the successful introduction of carboxyl group and hydroxyl group with the help of the modification. What’s more, the adsorption properties of B-PS, CA-PS and β-CD-PS towards to aniline, BPA, copper and MB were investigated. The results came out that all of the adsotption results fitted the Langmuir model well. On the basis of the Langmuir analysis, the maximum adsorption capacities of P-CD-PS towards to aniline, BPA, copper and MB were 99.7%,8.10%,47.7% and 19.7% higher than that of CA-PS, respectively. β-CD-PS showed the strongest adsorption ability for aniline, BPA, copper and MB. The reason for the better adsorption ability is the introduction of carboxyl and cyclodextrin cavity, which ensures the adsorption by different effects.On the basis of the above analysis, the UV (254 nm) photo-degradation technology was introduced for the regeneration of the modified adsorbent. Firstly, the photo-degradation of MB, aniline, and phenol with a-CD and β-CD in the homogeneous systems have been conducted in this work. After comparing with the blank experiment, a-CD had no catalytic effect for the photo-degradation of BPA. While the photo-degradation of BPA was considerably improved in the presence of β-CD. And 99.0% of BPA were photo-degraded in the presence of P-CD within 120 min of UV irradiation, which was 32.5% higher than the BPA removal efficiency in the blank experiment (66.5%). P-CD could include BPA, which influenced the bond energy of the BPA molecule, consequently, the photo-degradation of BPA was promoted. In addition, the experimental results confirmed that the immobilized β-CD still retains the catalytic effect for the photo-degradation of BPA. In the heterogeneous systems with UV irradiation, the removal efficiency of BPA in the presence of P-CD-PS (94.0%) was higher than that in the blank experiment (66.5%) after 120 min of UV irradiation. β-CD-PS is one kind of adsorbent with photo-catalytic function. β-CD-PS could enhance not only adsorption but also photo-degradation of BPA significantly, and the immobilized (β-CD could act as catalyst for the photo-degradation of the included BPA, as a result, in-situ regeneration was achieved and additional vacant adsorption sites were generated for further BPA adsorption in the solution.The low-cost pine sawdust presented excellent adsorption and catalytic performance with the coupling of citric acid/cyclodextrin modification and photo-catalytic degradation. This study provides a new idea for the renewable catalyist, and a new practical way for the preparation of efficient adsorbent with photo-catalytic effect. |
