The amino functionalisation of the surface of dendritic mesoporous silica nanoparticles (DMSN) was carried out via post-coupling using 3-Aminopropyltriethoxysilane (APTES) in an aqueous-alcohol medium. The physicochemical characteristics of the synthesised material were studied using Fourier-transform infrared spectroscopy (FTIR), low-temperature nitrogen adsorption/desorption, differential thermal analysis (DTA), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The quantity of specific functional groups presents on the DMSN surface before (-OH group) and after (-NH2 group) functionalisation was determined by means of titration. he adsorption capacity of the materials for copper ions was investigated in the concentration range of 10 to 100 mg/L. Additionally, the effects of the pH of the aqueous medium and the contact time between the potential adsorbent and the contaminated solution on Cu(II) removal efficiency were examined. The equilibrium copper concentration was determined using inductively coupled plasma atomic emission spectroscopy (ICP-OES). It was found that surface modification of DMSN led to a more than tenfold increase in the number of functional groups and corresponding adsorption centres. As a result, the efficiency of copper ion removal within the pH range of 3–6 increased to over 87%. The adsorption equilibrium time decreased from 60 to 15 minutes. The maximum adsorption capacity for the amine-functionalised sample reached 35 mg/g, compared to just 0.62 mg/g for the unmodified DMSN. Pseudo-first-order and pseudo-second-order kinetic models, along with Langmuir and Freundlich isotherm models, were applied to analyse the adsorption mechanism. XPS analysis of the spent adsorbent further supported assumptions regarding the copper ion adsorption process.