Synthesis And Capture Efficiency Of Starch Based Heavy Metal Trapping Materials

In this paper,natural starch was used as raw material to synthesize starch based heavy metal trapping materials by stepwise molecular modification,and the trapping ability of copper and nickel ions was evaluated.The starch molecules first introduce cationic quaternary ammonium groups through etherification.On this basis,continue to introduce the phosphorylation of anionic groups.The addition of urea in the synthesis process could promote the cross-linked structure of various types of groups and introduced nonionic groups.Finally,modified starch products with multiple charge distribution were obtained.The microstructure and characteristics of starch based catcher were studied by infrared spectroscopy,solid state nuclear magnetic resonance,thermogravimetric analysis and scanning electron microscopy.Finally,the starch based heavy metal trapping materials were put into the metal ion solutions containing different types and different concentrations,and their capture efficiency was studied.The optimum capture conditions were determined by changing the amount and time,and the trap mechanism was explored according to the capture process.The results of the study are as follows:Natural starch is modified by wet method.The influence of the amount of modifier,the ratio of material to liquid,the reaction temperature and the reaction time on the content of the anion group in the modified product was studied.On the basis of the preparation of starch based heavy metal trapping materials,the products with the best capture effect are found.The results showed that the dosage of CHPTAC was 4%?mL/g?of starch quality,reaction temperature was 50?for 4h,the degree of cation substitution was 0.0161.The mass concentration of sodium tripolyphosphate was 4%,pH value as 6-7,reaction temperature was120?for 2h,the degree of substitution of negative charged could reach 0.026.Low concentration of urea can improve the reaction efficiency of phosphorylated starch.When the mass percentage concentration is higher than 3%,it can enhance the cross-linking of starch with the molecular carbamate.The products with different degree of substitution have a certain trapping effect on the copper and nickel ions.When the cationic and anionic phosphate esterification degree of substitution were 0.014%and 0.018,the removal rate of 30 mg/L copper and nickel ions solution could reach 98%.The microstructure and properties of the starch based catcher were studied by infrared spectroscopy,solid state nuclear magnetic resonance,X-ray diffraction,thermogravimetry and scanning electron microscopy.The results showed that the characteristic absorption peak of quaternary ammonium group appeared at 1480cm^-11 in the infrared spectrogram of starch based heavy metal trapping material,and the absorption peak of P=O stretching vibration and absorption peak appeared at 1100cm^-1,and the absorption peak of amide group appeared at1681cm^-1.This shows that the cationic quaternary ammonium group,the anion phosphate group and the nonionic group are successfully introduced.The spectral peak integral values of C₂,C₃ and C₅ have been decreased in NMR spectra,which indicate that some active hydroxyl groups in starch are involved in the reaction,and starch is successfully modified.After thermogravimetric analysis of heavy metal trapping materials,there is a higher weight loss rate at 350⁵50?,and the thermal stability is higher than that of intermediate products and natural starches.The results of X-ray diffraction showed that starch base still maintained the structural characteristics of A crystal,and the crystallinity decreased,but the thermal stability was higher than that of the original starch.The specific surface area increased and the molecular weight increased.Compared with the intermediate products,final products and the original starch scanning electron microscopy,the starch molecules tend to be denser,the gap increases and the surface area increases,which is more beneficial to the adsorption.The aforementioned starch based heavy metal trapping materials were put into a single or mixed metal solution of 50mL 30mg/L for adsorption.In a single metal solution,starch based heavy metal trapping material can adsorb 80%nickel ions in 10min,while copper ion capture is slower.However,after stirring and adsorbing 2h,it can remove more than 98%metal ions,which can meet the national emission standard.According to the influence of various factors,the best adsorption conditions were determined as follows:0.6g starch based trapping material stirred 2h in 50mL30mg/L single metal ion solution,and pH value of solution was 5,the removal effect of metal ions was the best.In mixed metal solution,the influence of other impurities in the wastewater on the adsorption of heavy metal ions is mainly studied.Among them,the higher concentration of inorganic salt K⁺,the complexing agent EDTA and tartaric acid will have a certain effect on the capture of metal ions,while the inorganic salt Ca²⁺has no significant effect on the capture of metal ions.After capture,the heavy metal chelate of starch based catcher can be degraded when the concentration of nitric acid is 2mol/L and H₂O₂ is over 6%,and the degradation effect of higher temperature on chelate is relatively small,which can only reach 23%.After the elution,the starch based trapping material was reused.After 5 cycles,the adsorption efficiency was gradually reduced and the national emission standard was still reached within 3 times.Taking copper and nickel ions as an example,the adsorption kinetics of the starch based trapping materials were studied by changing the time and the equilibrium concentration.The results showed that the adsorption process consisted of two ways,namely,the electrostatic attraction process and the diffusion adsorption in the particles.The adsorption thermodynamics curve simulation showed that the adsorption of copper and nickel ions and other heavy metal ions by starch based heavy metal trapping materials accorded with Langmuir adsorption and was a monolayer adsorption.After the adsorption,the Zeta potential and the changes in the surface of the starch granules confirmed the existence of the two pathways.Comparing the adsorption process of copper and nickel ions were found:starch based heavy metal trapping materials on the adsorption of nickel ions rapidly,electrostatic adsorption constant,electrostatic adsorption plays a major role in the adsorption process of nickel ion;copper ion adsorption process is slow,but the adsorption constant,adsorption value is higher than the nickel ion,particle in the play the role of large adsorption diffusion.