| Moringa is a tropical and subtropical plant.Moringa seed has high nutritional value and edible value.However,the utilization rate of moringa seed shell was low.It used to be discarded or burned directly as agricultural and forestry waste,which caused environment pollution and waste of resources.How to recycle moringa seed shell effectively and improve its added value had become an urgent problem.This paper took moringa seed shell as the research object.First,the adsorbability of moringa seed shell was studied.Methylene blue was selected as the adsorbed object to investigate the influence of adsorption time,particle size,temperature,initial solution concentration and pH on the adsorption performance.In order to study its adsorption characteristics,data was fitted by adsorption isotherm model and kinetic model.Also,the samples were characterized by scanning electron microscopy and infrared spectroscopy.In addition,the lignin in moringa seed shell was extracted by alkaline method,formic acid method and p-toluenesulfonic acid method under normal temperature and pressure.The lignin was purified with 90%1,4-dioxane solution to remove impurities for characterization.The properties and structure differences of the lignin extracted by the three methods were compared.Finally,the lignin extracted by the p-toluenesulfonic acid method was used to prepare lignin Pickering emulsion.The effects of lignin addition,oil addition,ultrasonic time and ultrasonic power on the particle size and dispersion of the emulsion were investigated.The storage stability of emulsion under optimal conditions was studied by response surface optimization test with emulsion particle size as index,lignin dosage,oil dosage and ultrasonic time as factors.The main conclusions are as follows:(1)Moringa seed shell could effectively remove methylene blue from water.The results showed that under the condition of adding 10 g/L of moringa seed shell,the optimum adsorption conditions were adsorption time 1.5 h,particle size>80 mesh,temperature 25?,methylene blue solution concentration 200 mg/L and pH>5.The adsorption process followed the Langmuir model and the pseudo-second-order kinetic model.The maximum theoretical saturated adsorption capacity was 94.25 mg/g.The adsorption process was a common result of physical adsorption and chemisorption,and mainly by physical adsorption.(2)The yields of lignin extracted by alkali method,formic acid method,and p-toluenesulfonic acid method were 6.27%,9.02%,and 19.07%,respectively.The results showed that p-toluenesulfonic acid method could effectively separate lignin from moringa seed shell under normal temperature and pressure.It was found that the three kinds of lignin had similar chemical structures and properties through characterization.All the three kinds of lignin were GSH-type.The lignin extracted by p-toluenesulfonic acid method had the best thermal stability,followed by the formic acid method and the alkaline method.The three kinds of lignin also showed strong antioxidant properties,and the removal efficiency for DPPH was significantly higher than that of commercial antioxidant BHT.Scanning electron microscopy showed that there were a large number of pores on the surface of the lignin,which might cause good adsorption performance.(3)The optimal process parameters of lignin emulsion preparation were:oil phase volume fraction 1%,lignin addition 125 mg,and ultrasonic time 12.60 min.A verification test was performed on the optimized conditions.The particle size of the measured nanoemulsion was 233.64 nm,which was close to the predicted value of233.74 nm.The measured value had a good fit with the model fitting value.The prepared emulsions had good stability at pH 7?11,heat treatment temperature50?90?,Na~+concentration<0.4 mol/L and long term storage at room temperature. |
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