This　paper　investigates　the　applicable　pH　value　ranges　for　TiO2　to　remove　F-　from　water.　First,　TiO2-Ca　and　TiO2-Mg　nanoparticles　modified　by　Ca2+　and　Mg2+　are　successfully　gained　by　in-situ　hydrolysis　and　doping.　Then　field　emission　scanning　electron　microscopy(FESEM),　X-ray　diffraction(XRD),　Fourier　transform　infrared　spectroscopy(FT-IR),　N2　adsorption-desorption　analysis　and　Zeta　potential　analysis　are　carried　out　for　characterization.　The　results　show　that　the　modified　anatase　phase　TiO2　was　successfully　synthesized,　and　that　the　isoelectric　points　of　TiO2-Ca　and　TiO2-Mg　were　increased　to　4.51　and　5.08　respectively.　The　modified　TiO2　samples　were　applied　to　remove　the　low-concentration　fluoride　ions　from　water.　The　results　show　that　the　adsorption　of　fluoride　ions　by　TiO2-Ca　and　TiO2-Mg　can　reach　equilibrium　within　20　min,　with　the　adsorption　capacity　reaching　22.51　mg·g-1　and　20.87　mg·g-1　respectively.　Compared　with　the　raw　TiO2,　the　applicable　pH　value　ranges　of　TiO2-Ca　and　TiO2-Mg　are　expanded　to　5　and　6　respectively,　and　their　sedimentation　performance　is　greatly　improved.　Among　the　common　coexisting　ions,　only　high-concentrations　PO3-4　and　CO2-3　can　significantly　affect　their　adsorption　performance.　After　the　desorption　and　regeneration　cycle　was　repeated　20　times,　the　adsorption　of　F-　in　water　by　TiO2-Ca　and　TiO2-Mg　did　not　decrease　significantly.　This　shows　that　modification　by　Ca2+　and　Mg2+　has　obvious　effects　on　the　physicochemical　properties　and　fluorine　ion　adsorption　of　TiO2　samples.　In　addition,　the　adsorption　is　a　spontaneous　exothermic　process　and　the　removal　of　F-　by　TiO2-Ca　and　TiO2-Mg　mainly　involves　ion　exchange.　The　research　results　will　provide　theoretical　and　technical　support　for　the　application　of　the　environmental-friendly　TiO2　in　the　removal　of　low-concentration　fluoride　ions　from　water.　©　2022　Xi＇an　Jiaotong　University.　All　rights　reserved.