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Nature of synergistic effect of N and S co-doped graphene for enhanced simultaneous determination of toxic pollutants.

N-doped graphene (NG), S-doped graphene (SG) and N and S co-doped graphene nanocatalysts with different doping sequences (N-SG and S-NG) are successfully synthesized by a facile low-temperature hydrothermal method. By changing the synthetic sequence, S-NG significantly increases the electron transport rate of the sensor and the electrocatalytic ability compared to NG, SG and N-SG due to the optimal proportion of doping element content and suitable N- and S-bonding configurations. The origin of the synergistic effect of N and S co-doped graphene is confirmed. Traces of S doping greatly enhance the electrochemical performance. The large volume of S-Ox groups may prevent the analytes approaching the catalytic sites of the sensing materials due to a steric hindrance effect. S-NG, which possesses less S-Ox groups, exhibits better performance than that of N-SG. Pyridinic N plays an important role in enhancing the electrochemical activity and conductivity. The simultaneous determination of aniline (AN), p-phenylenediamine (PPD) and nitrobenzene (NB) as typical toxic pollutants is performed by employing the S-NG nanoarchitecture. The detection limits (S/N = 3) for AN, PPD and NB are 0.023, 0.051, 0.216 μM, respectively. In addition, the S-NG sensors also have excellent anti-interference, stability and reproducibility. The precise control and synthesis of multi-heteroatoms into graphene represent a promising strategy to enhance the electrocatalytic performance in energy and environmental fields.