Investigation On Preparation Of Lanthanum-based Aerogel And Its Adsorption Performance And Capture Mechanism Of Phosphate

Eutrophication is caused by the amounts of phosphate in water exceeding its nutrient load which has adverse effects on water ecology and human environment.Therefore,removal of excess phosphate has become an urgent task to improve the eutrophication of water bodies.Among diverse strategies of phosphate removal,Adsorption method with simple operation,satisfactory removal efficiency,cost-effective and,in most cases,recyclable adsorption has shown great superiority.In many developed materials for phosphate adsorption,the low-toxicity metal lanthanum（La）has a strong affinity for phosphate and becomes a candidate material for effective removal of phosphate.Unfortunately,due to the aggregation and leaching of La compound particles in water,it is not only inefficient in the actual adsorption of phosphate,but also difficult to separate from water.For solving the above problems,it is necessary to find porous adsorption substrates that are easy to recover and to distribute La compounds uniformly on the surface of pores or porous materials.In this study,common silica aerogels,carbon aerogels and cellulose aerogels were used as the substrate for fixing La,and La-modified aerogel adsorbents were prepared to obtain adsorbents that were easy to be separated and collected from aqueous solutions.The aerogel adsorbent prepared was characterized by physical and chemical properties.Moreover,the adsorption performance,selective adsorption capacity,regeneration performance and adsorption mechanisms were investigated by adsorption experiments.Most importantly,the aerogel with the best phosphate adsorption performance among the three aerogel adsorbents prepared was used in the actual eutrophication water environment in order to investigate its practical application potential.The main work of this paper includes:（1）Lanthanum modified silica aerogels（SA-La-X）were synthesized by La-modified calcination using cellulose nanocrystals（CNCs）as bio-oriented template.The presence of La on the surface of silica aerogel（SA）was determined by some characterization techniques.The results showed that the specific surface areas of the aerogels obtained were 262.69,251.23 and 197.18 m² g^-1,respectively,for SA-La-5（Si/La ratio:5:1）,SA-La-10（Si/La mole ratio:10:1）and SA-La-25（Si/La mole ratio:25:1）.Among them,SA-La-5 had the strongest phosphate adsorption capacity,and the maximum adsorption capacity was 42.08 mg g^-1.In addition,the reusability of SA-La-5 was studied and the results showed that SA-La-5 had bright regeneration ability,and the adsorption capacity of 82.73%could still be maintained after 5 cycles.According to the study of the adsorption mechanism,it was found that the binding mechanism of SA-LA-5 with phosphate includes electrostatic adsorption and precipitation.（2）Waste paper,as a recyclable resource,has the potential to be reused.Therefore,in order to promote the recycling of resources and the preparation of environmentally friendly adsorbents,a low-cost lanthanum doped porous carbon aerogels（La-CCA-X）were prepared using waste paper as carbon source by one-step method for phosphate adsorption.The results indicated that La-CCA-X presented abundant macroporous structure,which was beneficial to reduce the adsorption resistance.Through a series of adsorption experiments,it was found that the maximum phosphate adsorption capacity of La-CCA-30（added lanthanum nitrate hexahydrate accounting for 30%of the mass of waste paper）was 44.32 mg g^-1 at p H 3.0.Moreover,La leaching experiment demonstrated that La was firmly existed in La-CCA-30 over a wide p H range of 3.0-11,and would not pose threat to aquatic organisms,which proved that La-CCA-30could be used as an effective and stable adsorbnet tu remove phosphate.At the same time,.The main effects of La-CCA-30 on phosphate were included electrostatic interaction,ligand exchange and complexation.（3）Cellulose aerogels（CA）with staggered porous network were synthesized using filter paper as cellulose source.Lanthanum-functionalized cellulose aerogels（La-CA-X）with selective phosphate adsorption ability were prepared by water bath method.It was confirmed by characterization that La existed mainly in the form of La（OH）₃ on La-CA-X.Batch adsorption experiments showed that the maximum adsorption capacity of La-CA-30（adding 30%lanthanum nitrate hexahydrate to filter paper）for phosphate was up to 54.38 mg g^-1（p H=3.0）,and the leaching of La was negligible.Moreover,the mechanism analysis proved that La-CA-30 had a specific adsorption effect on phosphate,which was mainly manifested as electrostatic adsorption of phosphate and formation of complexes through ligand exchange.Among them,ligand exchange was the main mechanism.More importantly,La-CA-30 could remove 97.61%of phosphates from actual eutrophic water.Furthermore,the overall cylindrical shape of La-CA-X made it easier to separate from water than powdered adsorbents,which provided new possibilities for the practical application of adsorbents in phosphate adsorption.