Characteristics and influencing factors of phosphorus release from hydroxyapatite nanomaterials
The excellent ability of hydroxyapatite nanoparticles(nHAP)to resist heavy metal contamination and its impacts on plant nutrition have drawn much attention.The characteristics of phosphorus release kinetics and the factors that influence it remain obscure,despite the fact that this process is crucial in determining phosphorus interception efficiency and fertilizer supply performance.Here,two types of nHAPs(nHAP2 h and nHAP12h)with short rod-like structures were synthesized using wet chemical co-precipitation method to regulate the aging time(2 and 12 h).The effects of temperature,pH of the solution,coexisting humic acid,and soil solution environment on the phosphorus release kinetics from nHAPs were systematically investigated.The results revealed that the nHAP crystal grew larger with longer age times and that the nHAP12 h crystal length was 17％longer than the nHAP2h crystal length.Under experimental conditions,phosphate release from nHAP12h of larger crystal size was 61％～232％lower than that from nHAP2h.The phosphorus release gap caused by the ageing time of the material was widened by elevated temperature,increased pH,or soil solutions,however,the gap was narrowed by coexisting humic acid.With the exception of the soil solution system,nHAPs phosphate release typically occurring in two phases:an early rapid release phase and a later slow buildup phase until equilibrium was attained,with the apparent phosphate release rate constant K varying from 0.09～4.36 min-1 to 0.01～0.78 min-1.Raising the temperature from 5 ℃ to 25 ℃ increased nHAPs phosphate release(2％～19％),while 10 and 50 mg C·L-1 of co-existing humic acids with carboxyl and phenolic groups interacting with nHAPs similarly promoted nHAPs phosphate release(10％～195％)and raising the pH from 5 to 8.5 decreased nHAPs phosphate release(3％～15％).In the soil solution system,the phosphorus effectiveness of nHAPs was drastically decreased(18％～76％).This work paves a new theoretical reference for the application of nHAP as soil aids and novel agricultural nano aids.
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