The aim of this work was to develop a superadsorbent for the removal of Hg2+ ions from aqueous solutions. In this regard, a porous covalent triazine ring-based nanoneedle was synthesized through a facile hydrothermal method. The structure and morphology of the synthesized covalent triazine ring-based adsorbent were characterized by different techniques. The structural stability of the synthesized superadsorbent was examined under different temperatures and pH conditions. The maximum adsorption capacity of the prepared organic framework is 1826 mg g(-1) for removing Hg2+ ions at ambient temperature and an optimum pH of 5. Different linear and nonlinear models were applied for the fitting of the obtained adsorption data. It was found that the adsorption data can be well fitted to the linear Langmuir model (R-2 = 0.998). The adsorption kinetics can also be well described by the linear pseudo-second-order model. To make a portable, highly sensitive, and low-cost device for in situ sensing of trace amounts of Hg2+ ions, the smartphone colorimeter platform was developed using accessible equipment. The response of the developed system for the determination of Hg2+ ions was linear in the concentration range of 0.25-15 mg L-1, and the detection limit of the system is 0.063 mg L-1 Hg2+. The total cost of the developed system is lower than 400 US dollars, and the cost of each analysis is lower than 0.05 US dollars. Ultrahigh adsorption capacity, chemical stability, and fast adsorption kinetics make the synthesized triazine-based covalent organic framework a suitable candidate for the removal of Hg2+ ions from industrial effluents.