Development And Application Of Natural Wood-Based Adsorbents For Water Treatment

Tetracycline,as an antibiotic drug,is widely used in the treatment and prevention of bacterial diseases of humans and animals.However,tetracycline cannot be completely absorbed by humans and animals,and it will be discharged into the environment in its original form,which has adverse effects on ecosystems and human health.Adsorption is considered an effective method to remove antibiotics.However,powder and particle adsorbents have the disadvantages of poor selectivity,low absorption efficiency and dust pollution,so it is necessary to develop environmentally friendly adsorption materials with high adsorption efficiency.Natural wood is an environmentally friendly material with sustainable,renewable and biodegradable properties.Using natural wood as adsorption membrane to treat pollutants in surface water has the advantages of easy access,low production cost and small energy consumption.Moreover,the nature of wood in water is stable,and no toxicity will not cause secondary pollution to water.In addition,the natural three-dimensional and irregular pore structure of wood is conducive to improving the water flux and increasing the opportunities for pollutant ions to contact with the adsorption sites of wood on the channel.The alkali-innocuous citric acid modified wood membranes(WMs)is a facile,economical,and effective adsorption membranes to remove tetracycline(TC)from water.,which hold promise for application in water purification.In spite of this,it remains challenging to make-COOHs located deep inside wood cell walls due to the recalcitrant structure of the lignocellulosic materials.Therefore,it is necessary to pre-treat the raw wood to destroy the lignin structure of wood and make it easier to introduce-COOH structure into the inner wall of wood,so as to improve the removal efficiency of TC.In the modification method,alkali pretreatment method not only has the characteristics of simple operation,but also has the advantages of economic and environmental protection because alkali can be recycled and reused.In this study,pinewood(PW)and basswood(BW)membranes were pretreated with different concentrations of sodium hydroxide,and then esterified with citric acid(CA)to adsorb tetracycline in water.Alkali pretreatment was beneficial to the esterification of citric acid and lignocellulose,which greatly increased the-COOH content of the wood membrane.The pine membrane and basswood membrane before and after modification were characterized by SEM,EDX,XRD,ATR-FTIR,TGA.contact angle and zeta potential.The influence of alkali concentration on wood membrane was investigated by alkali treatment with different concentrations of NaOH,so as to determine the optimal alkali concentration.When the NaOH concentration increased from 2%to 6%,lignin began to decompose,and finally the cellulose structure began to dissolve.The hydroxyl hydrogen bonds on C3 and C6 were transformed into C2 and C6,and cellulose Ⅰ was transformed into cellulose Ⅱ,which was conducive to the esterification of cellulose and CA,and the content of-COOH was increased.The adsorption breakthrough curve of TC showed that the effective filtration volume of 4PW-80 was 1205 BV(bed volume)when the alkali concentration was 4%and the effluent concentration of TC was 2 mg·L-1,and the effective filtration volume of TC was the largest.Compared with the raw pine,the effective treatment volume of xPW-80 was increased by 8～12 times,and the adsorption capacity was also larger.When the alkali concentration was 6%and the effluent concentration of TC was 0.5 mg·L-1,the effective filtration volume of 6BW-80 was 1968 BV,which was about 48 times higher than that of unmodified wood membrane.After four cycles,the adsorption rates of TC on modified pinewood and basswood membrane were 93%and 97%,respectively When the effluent concentration of TC was 0-0.5 mg·L-1,the cost of modified linden and pine water treatment was 0.0054～0.0126 US$·m-3 and 0.01-0.024 US$·m-3.Therefore,the modified wood membrane has great application prospect in removing TC in water.The cost analysis and comparison with other adsorbents show that the preparation cost of modified basswood membrane is lower than that of modified pine membrane,and the effective filtration volume is also higher than that of modified pine membrane.Therefore,it is considered that modified WMS is an environmentally friendly,economical and effective adsorbent for TC removal in water.At low pH,TC forms a complex with the surface of wood membrane through Lewis acid-base interaction.When the pH was about 5,the hydrogen bonding between the Ocarboxyl-H group on the surface of the wood film and the O=Camide group of the zwitterionic TC was beneficial to the adsorption of the wood film and the increase of the adsorption amount of TC.With the further increase of pH value,adsorption efficiency of TC decreased due to electrostatic repulsion between wood membrane and TC.This study provides an effective strategy to overcome the key limitations related to WM application,and designs a competitive membrane material for environmental remediation,which provides a new idea for the development of economic and effective adsorption of wood membrane to remove pollutants in water.