| Adsorption is recognized as one of the most common and important processes in the field of water treatment because of its simple operation,low cost and high efficiency.Adsorbents are the decisive factor in the adsorption process.Therefore,the search for efficient,environmentally friendly and economical adsorbents has become the key to the treatment of water pollution by adsorption.Sodium alginate,which contains carboxyl and hydroxyl groups,can be complexed with bivalent metal ions to form hydrogels to remove heavy metal ions.Structurally,chitosan has a large amount of free amino groups,which can be protonated in an acidic solution and electrostatically react with negatively charged groups such as anions in the wastewater to remove contaminants.Based on the research status at home and abroad,this paper uses sodium alginate to adsorb heavy metal ions and combines sodium alginate with chitosan to obtain a novel porous scaffold material with simple preparation process,high adsorption efficiency and recyclability.And try to use for heavy metal ions and acid dye wastewater treatment.The porous scaffold adsorbent was prepared by using freeze-drying technology using sodium alginate as raw material.Scanning electron microscope(SEM)and mercury injection apparatus(MIP)were used to observe the morphology of the porous scaffolds prepared at different concentrations and to test their pore structure.It was found that the average pore size of the porous scaffold with a concentration of 5wt%was 41.57 μm and the porosity was 92.2%,it has a pore structure which is suitable for adsorption.The sodium alginate scaffold was pre-crosslinked with calcium chloride solution,and the pre-crosslinked scaffold was used to adsorb heavy metal ions Cd2+,Pb2+and Cu2+,and the pH value,ambient temperature,adsorption time and initial ion concentration were investigated.The adsorption conditions of sodium alginate scaffolds were optimized for the adsorption of Cd2+,Pb2+and Cu2+.Under these conditions,the adsorption rates of Cd2+,Pb2+and Cu2+were 73.67%,99.43%and 59.25%,respectively.The adsorption processes of three kinds of heavy metal ions were simulated by quasi-first-order kinetics,quasi-second-order kinetics and intra-particle diffusion model.Scanning electron microscope,X-ray energy spectrum analyzer,Fourier transform infrared analyzer and TG-DSC were used to characterize the porous alginate scaffolds before and after adsorption of heavy metal ions,which all showed that the scaffolds had an ideal adsorption effect on Cd2+,Pb2+and Cu2+.After five cycles,the percentage of removal of Cd2+,Pb2+and Cu2+decreased by 24.65%,24.58%and 16.17%,respectively.The prepared sodium alginate/chitosan composite porous scaffold was used as adsorbent to study its adsorption behavior and adsorption performance for anionic dye acid red B14.The composite porous scaffolds with different concentration ratios were prepared by using a molar ratio of sodium alginate carboxyl group to chitosan amino group of 2:1,1.5:1,1:1,1:1.5,1:2.The morphology and pore structure of the composite scaffolds were observed and tested by SEM and MIP,and the adsorption performance of the composite scaffold prepared at each molar ratio was investigated.The adsorption capacity of the scaffolds on the dyes was investigated under the conditions of pH=2 and pH=7,respectively.The decolorization rate showed that the acid red B14 was adsorbed in a large amount under the condition of pH=2,the decolorization effect was significantly better than pH=7,and the equilibrium adsorption capacity of the stent was about 1400 mg·g-1.It was found that the composite scaffold adsorbent showed the adsorption performance of the control group under various conditions.After adsorption of acid red B14,a large number of particles remained on the surface of the composite scaffold and the pores were blocked by dye molecules.FTIR and Zeta potentiometers were used to analyze the adsorption mechanism between the scaffold and the dye,and it was found that the main driving force of adsorption was the electrostatic force generated between the amino group of chitosan in the scaffold and the carboxyl group of acidic red B14.In addition,quasi-first-order kinetics,quasi-second-order kinetics and intraparticle diffusion model were used to simulate the adsorption process of acid red B14 adsorbed by composite porous scaffolds.The results showed that the fitting effect of quasi-secondary kinetics was better,indicating acid red.The adsorption process of B14 on the composite scaffold is dominated by chemical adsorption.The decolorization effect of the composite scaffold was investigated.The results showed that the acid red B14 was basically clarified after one-time adsorption,the removal rate was 99.4%,and the removal rate reached 99.99%after the secondary adsorption.The regeneration performance of the scaffold was analyzed.It was found that the adsorption capacity of the composite scaffold after adsorption-desorption was 1176.9±21.7 mg·g-1,which was maintained at 80.13%. |
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