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 (NO3–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 (C3N4/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 C3N4/Cu. Furthermore, it favors the dissociation of water to provide sufficient active hydrogen for the hydrogenation of NO3– with reduced energy barriers during the NO3–RR. Consequently, C3N4/Cu attains an ammonia yield rate of up to 25.2 mg h–1 gcat–1 without a sacrificial reagent. Moreover impressively, it maintains yield rates above 5 mg h–1 gcat–1 at pH values of 1–14 and over a wide range of NO3– concentrations from 0.01 to 2 mol L–1, indicative of its catalytic versatility for actual wastewater treatment.