Effect Of Humic Acid And Cation On Suspension Behavior Of Titanate Nano-particles

In this study,TiO₂ NPs,which is widely used,was selected as the research object to analyze the adsorption behavior of two different sources of humic acid on TiO₂ NPs surface,and the suspension/sedimentation behavior of TiO₂ NPs.The suspension/sedimentation behavior of TiO₂ NPs was analyzed under the combined action of physical and chemical elements of water including pH value,ionic strength and humic acid?HA?.The research results mainly include the following contents:?1?The adsorption behavior of humic acid from different sources on TiO₂ NPs was different.The adsorption of humic acid on TiO₂ NPs is mainly through electrostatic interaction,hydrophobic effect and chemical reaction between functional groups.At pH=2.0,the adsorption reached the maximum value,which was mainly due to the fact that TiO₂ NPs had a positive charge under acidic conditions,while humic acid had a negative charge,and electrostatic interaction played a major role on the adsorption.Under the same condition of solution pH value,the adsorption amount of HA1?from lignite?on TiO₂ NPs surface is greater than that HA2?from water?,its mainly because HA1 has more hydrophobic function groups than HA2,and more easily to adsorbed on the surface of TiO₂ NPs.Comparing the adsorption time of the two humic acids,HA1 reached the adsorption equilibrium at 12 hours,while HA2reached the adsorption equilibrium at 8 hours.This may be due to the effect of electrostatic adsorption on HA2 adsorption,while the two kinds of humic acids have a good fit for secondary kinetics.For HA1,the fitting property of Langmuir isotherm and Freundlich isotherm is similar,while for HA2,the fitting property of Langmuir isotherm is better,which indicates that the adsorption of HA2 on TiO₂ NPs surface is single-layer adsorption.?2?pH values and source of HA have a significant impact on the suspension/sedimentation behavior of TiO₂ NPs.When the solution pH valu is 3.0 or10.0,TiO₂ NPs is not easy to aggregation and sedimentation;when the pH value is7.0,TiO₂ NPs is most easy to aggregation and sedimentation.This is mainly because when the solution pH value neart the isoelectric point of TiO₂ NPs,the density of surface charges on TiO₂ NPs surface is mininum,electrostatic repulsion between particles decreases.when the solution pH deviated from the isoelectric point,there are more surface charge on TiO₂ NPs surface,and electrostatic repulsion between particles increases.The adsorption of HA on the TiO₂ NPs surface would improve the suspension of TiO₂ NPs,especially under the condition of soulution pH=3.0.This is mainly because the more adsorption of humic acid on TiO₂ NPs surface.The adsorption of HA on the surface of TiO₂ NPs will increase the energy barrier between nanoparticles,and the effect of steric hinders of HA would improve the suspension of TiO₂ NPs.?3?The effects of cation and HA on the suspension/sedimentation behavior of TiO₂ NPs are different.The effects of HA,Na⁺,Mg²⁺,and Ca²⁺on the suspension/settlement behavior of TiO₂ NPs were studied,the results indicat that the order of influence of the three kinds of cations on the suspension/sedimentation behavior of TiO₂ NPs is Na⁺<Mg²⁺<Ca²⁺in the presence of HA.This is mainly because Ca²⁺has a strong bridging effect,which will cause the particle size of nanoparticles to increase sharply at first and then decrease slightly.However,at high Ca²⁺ionic strength,the aggregation degree of nanoparticles will decrease.Moreover,the Ca²⁺would strongly induced electrical double layer?EDL?compression than Na⁺and Mg²⁺.For the same ions,with the increase of ionic strength,the TiO₂ NPs would hardly aggregation and suspension in the solution.