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Abstract Novel smart polystyrene-poly(N -isopropylmethacrylamide-acrylic acid) [PSt@p(NIPMAM-Aac] core/shell gel particles were prepared by two step precipitation polymerization method and used as adsorbent for removal of heavy metal ions such as Pb(II), Cu(II), Cd(II) and Cr(III) from aqueous medium. The adsorption capacity of gel particles for Pb(II), Cu(II), Cd(II) and Cr(III) ions was found as 555.6, 526.3, 476.2 and 434.8 mg/g, respectively. Adsorption process was also studied under different adsorption conditions such as adsorbent dose, metal ions concentration, agitation time, pH and temperature. Adsorption isotherms study was performed for heavy metal ions removal under optimum adsorption conditions. Langmuir and Freundlich adsorption isotherms were employed to evaluate the mechanism of adsorption process. Kinetic study showed the adsorption process followed pseudo second order kinetics. Thermodynamic study enlightens the nature of adsorption process on the basis of thermodynamic parameters such as standard Gibbs energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°). Fourier transform infrared (FTIR) spectroscopy was used to elucidate the characteristics of gel and metal ions loaded gel particles. pH sensitivity and size of gel particles were evaluated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. Recoverability and reusability of gel particles for Pb(II) ions removal were also studied to investigate the repeated usage of our reported adsorbent for removal of pollutants from aqueous medium. Graphical abstract Unlabelled Image Highlights • Core/shell polymer particles with narrow size distribution were successfully synthesized. • Core/shell microgel particles have excellent ability to extract heavy metals from aqueous medium. • Langmuir adsorption isotherm model best interprets the metal ions adsorption process. • The adsorbent system has high stability and recoverability and can be re-used. [ABSTRACT FROM AUTHOR]