This　study　aimed　to　provide　new　insights　into　the　mechanism　of　Cs+　sorption　on　titanium　hexacyanoferrate　(Ti–Fe　PBA)　focusing　on　the　influence　of　the　structure　and　vacancies.　Ti–Fe　PBA　was　synthesized　with　specific　vacancies　using　a　coprecipitation　synthesis　method.　The　study　successfully　demonstrated　the　unique　structure　of　Ti–Fe　PBA　and　determined　the　ratio　of　vacancies　within　its　framework　through　various　characterization　techniques,　including　X-ray　diffraction,　Fourier　transform-infrared　spectrometry,　thermogravimetry,　scanning　electron　microscopy,　X-ray　photoelectron　spectroscopy　and　sodium　hydroxide　titration.　The　synthesized　Ti–Fe　PBA　exhibited　an　impressive　Cs+　sorption　capacity　of　3.53　mmol　g−1　and　demonstrated　high　selectivity,　with　a　Kd　value　1.5　×　106　for　Cs+　sorption.　In　addition,　Ti–Fe　PBA　displayed　excellent　stability,　rapid　uptake　kinetics　and　maintained　high　selectivity,　even　in　the　presence　of　high　concentrations　of　coexisting　ions.　Moreover,　our　new　findings　revealed　that　K–Cs　ion　exchange　specifically　occurring　at　the　interstitial　sites　within　the　framework　structure　accounted　for　∼35　%　of　the　total　Cs+　sorption.　A　sorption-surface　complexation　model　utilizing　a　coupling　technique　that　integrated　PHREEQC　with　Python　enabled　in-depth　analysis　of　titration,　pH　effects　and　sorption　isotherms.　The　modelling　results　revealed　that　the　strong　ion　exchange　sites　≡SsOH　and　≡SsONa　on　surfaces　and　vacancies　contributed　∼65　%　of　the　total　Cs+　sorption.　©　2023　The　Author(s)