Abstract: Capacitive Fe-doped Ni₂P(Fe_2xNi_2(1-x)P) is synthesized via the modified solvothermal method to form Ohmic Schottky heterojunctions with monolayer Ti₃C₂ (MLTC). The composite (10 % 0.1FNP/CdS-2 % MLTC) achieved a high hydrogen evolution rate (HER) of 19.18 mmol h^-1 with a 50 mg sample. In a mere span of 3 h, an impressive NO₃^- reduction of 0.42 mg/L was achieved, accompanied by an exceptional 92 % N₂ selectivity. Quantum efficiency (QE) can reach 56.22 % (λ = 475 nm) by adding 0.1FNP and MLTC. In contrast to previous catalysts, the QE of visible light after 500 nm has been improved to 45.2 % (λ = 500 nm) or 36.4 % (λ = 550 nm). The significant enhancement of HER and NO₃^- reduction is attributed to the enhanced adsorption of oxygen-containing reactants, the lowering of the reduction overpotential, further enhanced separation efficiency of photogenerated carriers through the ohmic Schottky heterojunction after iron doping. Additionally, the observed capacitor-like nature of 0.1FNP is also an essential factor for the enhanced reduction ability of the composites.

Key words: Fe-doping, Multiphase heterojunctions, Nitrate reduction, Denitrification, Photocatalysis