Preparation And Adsorption Properties Of Modified Wheat Spent Grains And Their Functionalized PLA Nonwovens

In order to meet the demand of green and environmental treatment of dye wastewater,natural polymer adsorption materials have become a hot research topic.Spent grain is the main byproduct in the brewery industry.Because of its loose and porous surface and abundant cellulose and hemicellulose,these macromolecules contain many functional groups such as hydroxyl and carboxyl,so it is considered as an environmentally friendly adsorption material.NaOH modified spent grain and etherified modified spent grain for adsorbing methylene blue（MB）were prepared from spent grain by NaOH modification and etherification modification.The effects of modification process parameters on the modification effect were discussed separately.The materials were characterized by SEM,N₂ adsorption and desorption,FTIR,XPS and pH_pzc.The effects of pH value of MB solution,adsorption time and dosage on the adsorption performance were investigated.The adsorption mechanism was analyzed by establishing adsorption isothermal model and adsorption kinetic model.Polylactic acid（PLA）nonwoven is a new type of biodegradable material,with good physical and mechanical properties,and has a wide range of applications in agriculture,medical treatment,construction and other fields.In order to solve the shortcomings such as difficult recovery and poor recyclability of spent grain,functionalized PLA nonwoven was prepared by using PLA nonwoven as carrier,after hydrophilic modification with dopamine,and then attached spent grain to the surface of nonwoven by suction filtering uniform aqueous etherification modified spent grain dispersion.The morphology,water contact angle,pore size,binding fastness and adsorption-desorption recycling of the functionalized PLA nonwoven was characterized and analyzed.The results are as follows:When the concentration of NaOH was 0.2 mol/L,the modification temperature was 50℃,and the modification time was 30 min,NaOH modified spent grain with better modification effect were obtained.When the pH of MB solution was 8,the adsorption time was 2 h,and the dosage was 1.5 g/L,the removal rate of 30 mL 100mg/L MB was increased from 79.05%to 97.32%.The isothermal adsorption of MB followed the Langmuir model,and the adsorption kinetics followed the pseudo second order kinetic model,indicating that chemical adsorption was the main adsorption mode.Under the conditions of NaOH to ClCH₂COOH was 2.5:2.0,reaction temperature of 75℃and reaction time of 2.5 h,the adsorption effect of etherified modified spent grain was better.When the pH of MB solution was 8,the adsorption time was 60 min,and the dosage was 1.5 g/L,the utilization rate was higher,and the removal rate of 30mL 200 mg/L MB increased from 80.71%to 98.83%.The isothermal adsorption of MB conforms to the Langmuir model,and the adsorption kinetics conforms to the pseudo-second-order kinetic model,which proved that the adsorption mechanism of MB is mainly monolayer chemical adsorption caused by ion exchange.The water contact angle of PLA nonwoven after hydrophilic modification is almost0°.When the loading of etherified modified spent grain is 0.04 g,the functionalized PLA nonwoven has the best removal effect on 20 mL 100 mg/L MB,and the removal rate reaches 99.75%.Its mass loss rate is 2.46%,showing high binding fastness.And its removal rate is still above 89%after 4 cycles,showing good recyclable performance.