Experimental design for the preparation of low-cost carboxymethylcellulose hydrogel and its adsorption performance
[Objective]Carboxymethylcellulose hydrogels,rich in carboxyl and hydroxyl functional groups,are effective in adsorbing organic pollutants in water and wastewater.Their wide application in the treatment of printing and dyeing wastewater in China is attributed to their high biocompatibility and ease of recovery.However,the traditional process for preparing these hydrogels has shortcomings,such as being time-consuming,costly,and causing secondary pollution.[Methods]In line with the government's commitment to resource development and environmental protection,we propose a room-temperature,rapid green synthesis process for carboxymethylcellulose hydrogel.This method uses cellulose hydrogel instead of cellulose powder as the raw material and partially replaces the organic solvent with water.This novel green method allows for a high degree of substitution on the hydrogel surface owing to the insolubility of raw cellulose hydrogels.Additionally,the COO-functional groups can be retained on the hydrogels because there was no need for acidification.This process is also more time-efficient owing to its simplicity compared to traditional one-pot synthesis methods.Typically,our preparation procedure consists of three steps:alkaline activation,crosslinking,and carboxymethyl conversion.This simplifies the process significantly compared to traditional methods.We began by optimizing various parameters that affect the synthesis of carboxymethylcellulose hydrogels,such as reaction solvent,activation time,crosslinker amount,crosslinking time,conversion time,and final drying method.[Results]Based on characterizations reflecting the morphologies and surface functional groups of the as-prepared carboxymethylcellulose hydrogels,we established an optimized synthesis process.In this process,the reaction medium was set as isopropyl alcohol/water at 1∶1(v/v),the NaOH activation time was 40 min,the crosslinking time was 20 min with a crosslinker amount of 1.0 mL,the conversion time was 3 h,and the final drying method was freeze-drying.The cost analysis results showed a dramatic decrease in synthesis time from 44 to around 4 h,resulting in a significant cost reduction of 95％.We further evaluated the adsorption performance of the as-prepared carboxymethylcellulose hydrogels by targeting methylene blue(MB),a typical dye pollutant found in water.The results showed that the adsorption capacity of the as-prepared carboxymethylcellulose hydrogel for MB was as high as 722 mg g-1,and the adsorption equilibrium could be achieved quickly in 60 min.We also assessed the adsorption performance under different initial pH values.The results demonstrated that our carboxymethylcellulose hydrogels exhibited high adaptability,with a considerable adsorption capacity of around 800 mg g-1 across a wide pH range from 3 to 10.Scanning electron microscope images confirmed the successful adsorption of MB on the hydrogel surface.[Conclusions]Overall,this study proposed a novel,green,and cost-effective method for preparing carboxymethylcellulose hydrogels,which shows a high application potential for dye adsorption.The entire experimental design involved adsorption kinetics,adsorption isotherms,and other related experimental knowledge of materials chemistry and environmental engineering,in which the characterization techniques and data analysis were covered.The aim of this study is not only to cultivate scientific knowledge but also to cultivate undergraduates'comprehensive abilities and rigorous scientific attitudes.Through literature review,problem analysis,experimental design,data collection and analysis,and thesis writing,we aim to build a strong foundation for students'future endeavors in related research areas.
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