Bi-functional carbon doped and decorated ZnO nanorods for enhanced pH monitoring of dairy milk and adsorption of hazardous dyes

This study demonstrates a simple and low-cost process for the in-situ doping and decoration of ZnO nanorods with carbon (CC–ZnO). In CC–ZnO, C-doping decreased the charge density (1.75 × 10¹⁸ cm⁻³) at the non-active sites of ZnO and decreased the charge transfer resistance (101 Ω) at the C-doped-ZnO/electrolyte interface by suppressing native defects and reducing the Schottky barrier height (–0.20 eV), respectively. Moreover, C-decoration enhanced the amphoteric performances of ZnO to react efficiently with H⁺ and OH⁻ ions in an aqueous electrolyte, demonstrating a high pH sensitivity (48 mV/pH) and fast response time (7 s). Moreover, C-decoration enhanced the dispersion stability (92 h for 7.5 mg/mL concentration) and surface area (43.08 m^2·g⁻¹) of CC–ZnO in liquid phase, improving the monolayer adsorption capacity (119.40 mg/g) for the removal of rhodamine B (RhB) from aqueous solution. The optimum concentration and pH value of CC–ZnO and aqueous solution were determined to be 25 mg and 6.5, respectively, for maximum (84 %) removal of RhB in the initial five hours of reaction. Adsorption rate analysis revealed that CC–ZnO removed RhB through pseudo-second-order kinetics.