Engineering a Positively Charged Surface on g‑C₃N₄ via CTAB Modification for Ultrahigh Capacity and pH-Robust...

Congo red (CR) poses significant environmental and health risks, making its effective removal a critical objective in wastewater treatment. To address this challenge, this research modified bulk g-C₃N₄ (BCN) with the surfactant cetyltrimethylammonium bromide (CTAB) via a hydrothermal method. The resulting adsorbent, 0.2CTAB/CN, demonstrated an optimal performance in CR removal. 0.2CTAB/CN exhibited a zeta potential of +25.1 mV, in contrast to -17.7 mV for BCN. This positive surface charge promotes effective adsorption of the anionic dye CR, achieving a removal efficiency exceeding 98% over a broad pH range (pH of 1-12). The maximum adsorption capacity of 0.2CTAB/CN for CR, as fitted by the Langmuir model (R ² = 0.981), reached 1945 mg/g at 313 K, surpassing most reported CN-based adsorbents. Importantly, the modified adsorbent maintained excellent CR removal performance not only in ultrapure water (98.6%) but also exhibited comparable efficiency in complex water matrices, including tap water (98.5%) and natural river water (98.8%), demonstrating its potential for practical wastewater treatment applications. This research provides valuable insights into the design of high-performance adsorbents and offers fundamental support for the advanced treatment of wastewater containing anionic dyes.