Single Atom Embedding Enhanced Macroscopic Polarization in Carbon Nitride Nanosheets for pH-Universal Piezo-Photocatalytic Nitrate Reduction over a Wide Concentration Range

Piezo-photocatalytic nitrate reduction reaction (NO 3 – RR) is an ammonia synthesis approach as a promising alternative to the conventional energy-intensive Haber–Bosch process. Herein, we designed carbon nitride nanosheet supported Cu single atom (C 3 N 4 /Cu) catalysts with tunable electronic structures via coordination environment engineering. The embedding of single atoms into carbon nitride leads to enhanced piezoelectricity, which originates from the induced non-centrosymmetric cavities in nanosheets. The resulting macroscopic polarization facilitates the transport of photogenerated charge carriers together with suppressed charge recombination endowed by rich nitrogen vacancies in C 3 N 4 /Cu. Furthermore, it favors the dissociation of water to provide sufficient active hydrogen for the hydrogenation of NO 3 – with reduced energy barriers during the NO 3 – RR. Consequently, C 3 N 4 /Cu attains an ammonia yield rate of up to 25.2 mg h –1 g cat –1 without a sacrificial reagent. Moreover impressively, it maintains yield rates above 5 mg h –1 g cat –1 at pH values of 1–14 and over a wide range of NO 3 – concentrations from 0.01 to 2 mol L –1, indicative of its catalytic versatility for actual wastewater treatment.