Preparation Of Titanate Nanomaterials And Their Removal Of Heavy Metal Ions From Aqueous Solution

The continuous acceleration of urbanization in China and the rapid development of industry and agriculture have exacerbated the problems of environmental problems,such as the heavy metal pollution caused by the accumulation of heavy metals.The untreated or incompletely treated heavy metal contaminants migrate,retain and accumulate after entering the environment or ecosystem,resulting in great harm to human health.Such as Cd(?)and Cr(?)have been confirmed to give rise to the damage of human liver,kidney and even cause cancer.So it is imminent to solve the problem of heavy metal pollution.Titanate nanomaterials(TNs),as a new type of nanomaterials,have the advantages of large specific surface area,high porosity,stable structure,good self-settling performance in water,and strong ion exchange,which are gradually used as adsorbents in the field of heavy metal pollution.The property of TNs depends on the preparation process,but the effect of hydrothermal reaction temperature on the morphology and adsorption properties of TNs has not been studied systematically.In this work,a series of titanate nanomaterials were synthesized hydrothermally using TiO2 nano powder and NaOH.The morphology of TNs was tuned by regulating the reaction temperature.The physico-chemical properties of TNs,such as morphology,structure,surface area,and chemical composition were characterized.The Cd(?)adsorption properties of TNs in aqueous solutions were measured in the static system to reveal its ability to remove Cd(?).The results showed that the morphology of TNs evolved from nanosheets into nanotubes with increasing temperature.Furthermore,the nanotube becomes nanorod as it keeps growing in length.Its crystallinity was enhanced as the temperature increased.Upon reaching 190?,the phase transformation from anatase to rutile was emerged though.TNs-150 that was prepared at 150 ? showed the highest adsorption capacity of Cd(?)as 254.66 mg/g while the optimum pH was at 5.0.The removal rate and desorption rate of Cd(II)by TNs-150 were more than 93%in 6 cycles.The adsorption mechanism was mainly ion exchange between Cd(?)and Na+/H+ in the layers of TNs.Combined with the experimental results above,the amino-modified titanate nanotubes(TNTS-NH2)was synthesised by covalently grafting 3-aminopropyltrimethoxysilane(APTMS)onto protonated titanate nanotubes(HTNTs)with considerable surface hydroxyl groups.The Cr(?)adsorption properties of HTNTs and TNTS-NH2 in aqueous solutions were measured in the static system to reveal its ability to remove Cr(?).Batch adsorption experiments showed that pseudo-second-order kinetics model and Langmuir isotherm model fitted the adsorption data very well for both materials,and the Cr(?)adsorption capacity of TNTS-NH2 calculated by Langmuir model was up to 113.64 mg/g at pH 3.0 and 30?,much larger than that of HTNTs(23.29 mg/g).The more anions were introduced into the solution,the stronger competition with Cr(?),and the lower adsorption capacity of Cr(?).When the amount of nitrate was 5 times of the Cr(?)concentration,the adsorption capacity decreased by 12.86%,which showed that TNTS-NH2 had good selectivity to Cr(?),Cr(?)can be adsorbed by electrostatic attraction in a wide pH range because of the large zero potential(8.59)of TNTS-NH2;The desorption rate of[TNTS-NH2-Cr(VI)]was above 95%at pH 10.The adsorption capacity was decreased by 13.14%compared with the virgin TNTS-NH2 after 4 cycles.In conclusion,TNTS-NH2 are promising materials for efficient and economical remover of Cr(?)from various aqueous waste streams.