| Phosphorus(P)is an indispensable nutrient for all crops to carry out vital life processes,However,excessive loss of phosphorus from agricultural soil into water bodies may result in potential adverse impacts such as water eutrophication.Although ceasing the application of phosphorus fertilizer can prevent further escalation of soil dissolved phosphorus loss,the current discharge of soil phosphorus into surface water remains significant and persistent.Controlling the use of phosphorus fertilizer alone cannot achieve satisfactory results;additional measures are required to address this environmental issue.Therefore,in this study,artificial humus-ferrihydrite composite materials were synthesized via adsorption and co-precipitation techniques.Surface morphology,particle size distribution,crystal structure,and surface functional groups of various materials were analyzed using a range of characterization techniques.Equilibrium adsorption capacity for different materials was determined by fitting adsorption isotherms and kinetics models.FT-IR and XPS analyses were conducted to characterize the samples before and after phosphate adsorption,followed by an exploration of the mechanism underlying phosphate adsorption.Subsequently,an optimal artificial humus-hydropyrite composite material was selected for a soil phosphorus fixation experiment.The main research findings are as follows:(1)Hydrothermal humification(HIT)was employed to synthesize artificial humus(A-HS)materials,including artificial humic acid(A-HA)and artificial fulvic acid(A-FA).Subsequently,A-HS was combined with ferrihydrite(Fh)through adsorption and co-precipitation.The resulting composite materials of artificial fulvic acid-ferrihydrite(FA/Fh)and artificial humic acid-ferrihydrite(HA/Fh)were prepared and characterized.The analysis mainly comprises of scanning electron microscopy,transmission electron microscopy,particle size analysis,zero point of charge determination,X-ray Diffraction(XRD)and Fourier Transform Infrared Spectroscopy(FT-IR).The results indicate that the zero potential point of the adsorbed artificial humus-ferrihydrite composite increases in comparison with Fh,while that of the co-precipitated artificial humus-ferrihydrite composite decreases.Additionally,the particle size of HA/Fh material is observed to increase.FT-IR analysis reveals that A-HS binds with ferrihydrite primarily through ligand exchange reaction between carboxyl groups on A-HS surface and hydroxyl groups on ferrihydrite.(2)The phosphate adsorption properties of the aforementioned materials were investigated using adsorption kinetics and isotherm.The pseudo-first-order kinetics,pseudo-second-order kinetics,Elovich model,and in-particle diffusion model were employed to fit the adsorption kinetics data,while Langmuir and Freundlich models were used to fit the adsorption isotherm data.Compared to ferrihydrite,the phosphate adsorption capacity of adsorbed artificial humus-ferrihydrite composite increases,while that of co-precipitated artificial humus-ferrihydrite composite decreases.The mechanism behind phosphate adsorption by the artificial humus-ferrihydrite composite was investigated through FT-IR analysis and Xray photoelectron spectroscopy(XPS).Results indicate that ligand exchange,electrostatic attraction,and hydrogen bond are the primary mechanisms involved.(3)Through the above adsorption performance measurement,we selected the artificial humic acid-ferrihydrite composite material(A-HA/Fh-20)with the best phosphate adsorption performance,and applied the material to the study of soil phosphorus fixation.The results showed that,adding 2% AHA/Fh-20 can improve the soil phosphorus adsorption capacity from 0.15 to 0.7 mg/kg,and A-HA/Fh-20 can convert more phosphate into soil available phosphorus,so as to increase the soil available phosphorus content.In addition,we quantitatively analyzed the soil organic matter content in different treatment groups,and found that adding A-HA/Fh-20 could increase the soil organic matter content. |
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