Study On The Removal Behavior Of Reactive Dyes By Polyacrylamide Composite

Dyes are stubborn compounds in various industrial wastewater,which are relatively difficult to remove.So far,adsorption is still the most common way to physically remove dyes.Adsorption is to concentrate dyes on solid matrix and remove stubborn organic compounds including reactive dyes from wastewater.However,the adsorption capacity of many adsorbents is low and inefficient,which cannot meet the treatment requirements.Polyacrylamide(PAM)is a kind of polymer.When it is controlled in the low concentration range,the internal of polyacrylamide solution is basically a network structure.The mechanical entanglement between chains and the interaction of hydrogen bonds make the network structure form;when the concentration is controlled in a high range,more chain link contacts in the solution will cause the PAM solution to become a gel,which can be crosslinked with other materials.Graphene has many derivatives,and graphene oxide(GO)is one of them.There are various oxygen-containing groups in GO,such as-OH,-COOH,C=O and-CH(O)CH-.When they are dispersed in aqueous solution,they can become a suspension with colloidal properties,which can improve the adsorption capacity when combined with polyacrylamide.Casein(CN)is a common polymer protein,which is non-toxic and degradable.It has many hydrophilic functional groups,has good surface activity and stability,and is very suitable for the preparation of hydrogels.Nicandra physalodes(Linn.)Gaertn.seed gum(NPG)is a colorless,odorless,nontoxic and edible colloid,which can be crosslinked with polyacrylamide and other materials to form a gel with spatial network structure.NPG aerogel gel has the advantages of no pollution,easy recovery,biodegradation and good economy.Based on the above research background,this paper mainly completes the following:Polyacrylamide/ Nicandra physalodes(Linn.)Gaertn.seed gum(PAM/NPG)composite gel material was prepared by freeze-drying method using PAM as substrate and NPG as green biomass material.The surface morphology and physicochemical properties of the obtained composites were characterized by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),thermogravimetric analyzer(TGA)and specific surface area analyzer(BET).The results of static adsorption experiments show that PAM/NPG composite has the highest removal rate of CR under neutral conditions,and the adsorption effect is not ideal when p H is too high or too low.When the temperature was298 K and the p H was 6,the maximum adsorption capacity was 684.931 mg/g when the initial concentration of CR was 80 mg/L and the adsorbent dosage was 10 mg.The obtained experimental data were simulated and analyzed by origin,and the isotherm model and kinetic model were selected for fitting.The Freundlich isotherm model and pseudo-firstorder kinetic model can more effectively reflect the whole adsorption process.The two models can explain that the adsorption process is multilayer adsorption,and the adsorption is mainly carried out on the heterogeneous surface of the gel.Thermodynamic analysis of the experiment showed that the whole adsorption experiment was a spontaneous exothermic process.According to the experimental results,it is speculated that the adsorption of CR by PAM/NPG is mainly driven by hydrogen bonds,electrostatic adsorption and polar group interaction.PAM was modified by GO based on its good gelation and adsorption properties,and the PAM/GO/CN composites were successfully prepared by using the stability of CN.PAM/GO/CN composites were prepared by vacuum freeze drying and vacuum heating drying.By comparing the two production methods,a better vacuum freeze-drying method was finally selected.The surface morphology and physicochemical properties of the new biomass adsorbent were characterized by SEM,FTIR and BET.The effects of temperature,initial solution p H,contact time and adsorbent dosage on the adsorption of MB by PAM/GO/CN were investigated.The experimental results show that the adsorption capacity of the prepared material can reach 326.35 mg/g at 298 K,p H=10,and adsorbent dosage of10 mg.Finally,the adsorption equilibrium can be achieved at about 700 min.The adsorption isotherm analysis showed that the adsorption of MB by PAM/GO/CN was more in line with the Langmuir model,and the adsorption kinetics study showed that it conformed to the pseudo-first-order kinetic model.The whole adsorption experiment was composed of three stages.Thermodynamic studies show that the adsorption of MB by PAM/GO/CN is a feasible spontaneous exothermic process,and the disorder of adsorption at the solid-liquid interface is reduced.After five times of solution-adsorption experiments,the removal rate of MB by PAM/GO/CN remained above 81 % of the first adsorption effect,indicating that PAM/GO/CN had good reproducibility.