Preparation And Application Of PH-responsive Hydrogels

For a long time,dye wastewater is difficult to be biodegraded due to the characteristics of high salinity,high color and high chemical oxygen demand.Adsorption method has attracted much attention because of its advantages of high adsorption capacity and easy separation from water.The molecular structure of pH responsive hydrogel contains a large number of weak acid(or base)groups.By adjusting the pH value of dye solution,the adsorption or desorption of ionic dyes can be achieved.However,such hydrogels still have problems such as the single type of adsorbent dyes,the obvious decrease of adsorption efficiency under high salinity,and the difficulty in recycling.Therefore,two kinds of pH responsive hydrogels were designed and constructed,and their adsorption properties for different ionic dyes were discussed.The main results are as follows:1)Two kinds of pH responsive hydrogel were synthesized:binary dual network anionic pH responsive hydrogel and ternary dual network amphoteric pH responsive hydrogel.Using maleic acid(MA),acrylamide(AM)and two methylamino ethyl methacrylate(DM)as the main monomers,the first network P(MA-co-AM)or P(MA-co-AM-co-DM)macromolecules were synthesized by free radical polymerization under thermal initiation.At the same time,polyvinyl alcohol(PVA)was introduced as the second enhancement network,and PVA/MA/AM and PVA/MA/AM/DM hydrogels were finally synthesized under the action of hydrogen bonding.2)FTIR characterization showed that two kinds of hydrogel macromolecules were successfully polymerized.SEM showed that two kinds of hydrogels were dense porous structure,and mesoporous pore size of BET was 0.015 cm~3/g and 0.003 cm~3/g,respectively.The specific surface area was 10.434 m~2/g and 0.791 m~2/g respectively.3)To study the pH sensitivity of the two hydrogels:adjusting the pH=2 of the solution to pH=10,the swelling degree of the PVA/MA/AM hydrogel can be increased by 2.74 times,the swelling degree in the environment of pH=10 is 17.46 g/g,and the swelling degree of the PVA/MA/AM/DM hydrogel in the range of pH=2?12 is between 3.69 g/g and 10.86 g/g.4)To study the adsorption properties and mechanism of two kinds of hydrogels on ionic dyes:the results showed that the removal rate of methylene blue by PVA/MA/AM hydrogel could reach 95.69%under pH=8,but the removal rate was only 7.01%under pH=1.In addition,the removal rate was 2.50%under Na Cl concentration of=10 g/L,the first desorption rate of PVA/MA/AM hydrogel for MB was 86.79%,and the adsorption rate after 7 cycles of adsorption and desorption was>75%.PVA/MA/AM/DM hydrogels respectively adsorbed methylene blue or reactive red 195in a single dye solution at pH=12 and 2 respectively.The removal rates were 91.71%and 89.48%respectively,and the removal rates were 44.96%and 76.67%respectively under high salt concentration(C(NaCl)=20 g/L).In addition,quasi two stage kinetics and Langmuir adsorption isotherm can better simulate the adsorption mechanism of two kinds of hydrogels.In this experiment,two kinds of pH responsive hydrogels were successfully prepared,which could achieve"smart"adsorption or desorption of negative(cationic)dyes by adjusting the pH value,and PVA/MA/AM/DM hydrogel could still maintain good adsorption under high salinity.It has positive significance for the treatment of dye wastewater.