Zero-valent iron/peroxymonosulfate (Fe⁰/PMS) has been considered as a promising approach for wastewater treatment. Anions and cations are widely present in wastewater and have significant effects on the performance of the Fe⁰/PMS system for wastewater treatment. Thus, in the present study, tartrazine was selected as the target model; SO₄²⁻, NO₃⁻, HCO₃⁻, and Cl⁻ were selected as representative anions and Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ were chosen as representative cations. The effect of these anions and cations on tartrazine removal and major radicals in the Fe⁰/PMS were systematically investigated. The presence of a certain concentration of SO₄²⁻ and Cl⁻ had positive, NO₃⁻ had negative, and HCO₃⁻ had negligible effects on tartrazine removal in the Fe⁰/PMS system. SO₄²⁻ and HCO₃⁻ had a small effect on the contribution proportion of reduction, SO₄^•− and ^•OH; a certain concentration of Cl⁻ could enhance the contribution proportion of ^•OH; and NO₃⁻ would decrease the contribution proportion of SO₄^•− and ^•OH. A certain concentration of each of Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ could enhance the tartrazine removal in the Fe⁰/PMS system. Ca²⁺, Cu²⁺, and Mg²⁺ had no effect of the contribution of reduction, SO₄^•− and ^•OH, while a certain concentration of Mn²⁺ could enhance the contribution proportion of SO₄^•−. These results can provide some references for the Fe⁰/PMS system to treat actual wastewater containing anions and cations.

In this experiment, C₃N₅ was synthesized by pyrolysis of 3-amino-1,2,4 triazole material, and then 1% Co-C₃N₅, 3% Co-C₃N₅, 5% Co-C₃N₅, 7% Co-C₃N₅, and 9% Co-C₃N₅ were synthesized by varying the mass ratio of cobalt chloride to C₃N₅ by stirring and ultrasonic shaking. SEM, XPS, and XRD tests were performed on the synthesized materials. The experimental results showed that Co atoms were successfully doped into C₃N₅. The electrocatalytic reduction experiments were performed to evaluate their NH₃ yields and electrochemical properties. The results showed that the ammonia yield obtained by the electrolysis of the 9% Co-C₃N₅ catalyst as the working electrode in a mixed electrolytic solution of 0.1 mol/L KNO₃ and 0.1 mol/L KOH for 1 h at a potential of −1.0 V vs. RHE was 0.633 ± 0.02 mmol∙h⁻¹∙mg_cat⁻¹, and the Faraday efficiency was 65.98 ± 2.14%; under the same experimental conditions, the ammonia production rate and Faraday efficiency of the C₃N₅ catalyst were 0.049 mmol∙h⁻¹∙mg_cat⁻¹ and 16.41%, respectively, and the ammonia production rate of the C₃N₅ catalyst was nearly 13-fold worse than the 9% Co-C₃N₅, which suggests that Co can improve the Faraday efficiency and ammonia yield of the electrocatalytic reduction of NO₃⁻. This is due to the strong synergistic effect between the cobalt and C₃N₅ components, with C₃N₅ providing abundant and homogeneous sites for nitrogen coordination and the Co-N species present in the material being highly efficient active sites. The slight change in current density after five trials of 9% Co-C₃N₅ and the decrease in ammonia yield by about 12% in five repetitions of the experiment indicate that 9% Co-C₃N₅ can be recycled and work stably in electrocatalytic reactions and has good application prospects.