Sorption Behavior And Mechanisms Of Organic Contaminants By Humic Acid Coatedhematite Nanoparticles

Nanoparticles that have a tiny size and large surface area are widely used in many areas.Engineered nanoparticles(NPs)have been broadly used in the remediation of soil and water pollution,but exhibit toxicity potential to microbes,plants,animals and even our human beings when entering into the environment.Hence,recent researches shift their focus to natural NPs when considering the environmental risk of these engineered NPs.These NPs are naturally derived and have been in the environment with the evolution of the earth and human beings,their environmental risk has been lessened and showed good compatibility with the environment.The main objectives of this study were to investigate the capabilities of humic acid(HA)coated hematite NPs for the sorption of typical hydrophobic organic contaminates in aqueous solution.Ionizable pentachlorophenol(PCP)and non-ionizable phenanthrene(PHE)were chosen as representative hydrophobic organic contaminates.The effects of HA coating amount,type,and the pH value on sorption capacities were investigated to understand the mechanisms behind the sorption phenomenon.The main results were as follows:Sorption capacities of hematite NPs for PCP and PHE were enhanced about 1-2 order of magnitudes after coated with HAs.The sorption capacities for PCP and PHE were different due to their different polarity,HA coated hematite NPs had a higher sorption capacity for PHE which has relative lower polarity.By using the methods of Fourier Transform Infrared Spectroscopy analysis,13C Nuclear Magnetic Resonance analysis and elemental analysis,we speculated that the coating of HAs would increase the surface hydrophobicity of hematite NPs,and introduce a number of organic function groups which would induce various interactions between organic contaminants and hematite NPs.The sorption capacities for PCP and PHE increased with the amount of HAs.However,under the same coating amount,peat humic acid(HApeat)coated hematite NPs had higher partition coefficient(Kd)than soil humic acid(HAsoil)coated hematie NPs for both PCP and PHE,which indicated the properties of HAs had an effect on the sorption of hydrophobic organic contaminants.Comparing the organic carbon-normalized sorption coefficients(KOC),the HAs adsorbed by hemaitie NPs had high value of KOC than their original ones,which indicated the fraction of HAs by hematite NPs.The KOC value of 1:5 HA-hematite is smaller than others,indicated the conformation change of HAs was involved.As pH value of the background solution changing from 2 to 12,the sorption capacities of HA coated hematie NPs for PCP and PHE decreased substantially.Combined effect of hydrophobic interaction,H-bond interaction,electrostatic interaction,conformation change,dissociation of organic contaminants caused higher sorption capacities of PHE and PHE at low pH condition than those in high pH condition.The decrease of sorption sites would be offseted by the enhancement of hydrophobic interaction and H-bonding interaction at low pH values.We concluded,the property change of HAs at different pH values dominated the whole sorption process.