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• A simple and mild method was used for the synthesis of Fe-doped Ni 2 P nanosheets. • Designed ohmic Schottky heterojunctions to improve photogenerated carrier separation efficiency. • Composites showed excellent activity and stability in photocatalytic hydrogen production and NO 3 − reduction tests. • The optimization of the surface adsorption energy of the NO 3 − reduction reaction by doping a small amount of Fe was investigated using DFT calculations. • Ohmic Schottky heterojunction enables higher utilization of visible light in semiconductor composites. Capacitive Fe-doped Ni 2 P(Fe 2 x Ni 2(1- x) P) is synthesized via the modified solvothermal method to form Ohmic Schottky heterojunctions with monolayer Ti 3 C 2 (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 NO 3 − reduction of 0.42 mg/L was achieved, accompanied by an exceptional 92 % N 2 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 NO 3 − 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. The optimised method synthesises 0.1FNP and MLTC together to form an Ohmic contact Schottky heterojunction to achieve efficient photogenerated electron-hole separation and obtain high performance photocatalytic HER and NO 3 − reduction catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Copper oxide nanosheets grown on nickel foam realizes rapid, selective and efficient conversion of nitrate in water. [Display omitted] • Porous copper oxide nanosheets grow in situ on nickel foam surface (NF). • Removes low-concentration nitrate rapidly with almost no production. • CuO/NF exhibits excellent stability and N 2 selectivity in nitrate reduction. Electrochemical techniques have shown advantages for the removal of low-concentration nitrate. Here, copper oxide nanosheets were grown on self-supporting nickel foam (NF) to prepare electrodes (CuO/NF), which realized the rapid and highly selective conversion of nitrate pollutants in sewage into nontoxic and harmless N 2. The CuO/NF afforded 100% NO 3 – removal within 100 min and 99.53% selectivity for N 2 at –50 mA without producing a lot of by-products (NO 2 –, NH 4 +, and N 2 H 4). Furthermore, 81.8% of NO 3 – was removed under the given conditions after six experimental repetitions. These results suggest that the catalyst has excellent electrochemical stability. The performance of CuO/NF for the electrocatalytic removal of NO 3 – in simulated wastewater (which contained Cl– and SO 4 2–) was almost unaffected. Because of the high efficiency, high stability, and low cost of CuO/NF, this catalyst is practical for the removal of nitrate for wastewater purification. [ABSTRACT FROM AUTHOR]

Nitrate is having a much higher potential than N 2 for catalytic NH 3 synthesis under ambient conditions. [Display omitted] • The differences between N 2 and NO 3 − for NH 3 synthesis are systematically analyzed. • Recent advances in photo/electrochemical NO 3 − reduction to NH 3 are summarized. • Possible strategies to improve the selectivity and catalytic activity are proposed. Artificial catalytic synthesis of ammonia has become a hot research frontier in recent years. It is regarded as a promising approach that may replace the Haber-Bosch process and reduce global carbon dioxide emission. However, it is extremely difficult for the cleavage of nitrogen molecules under ambient conditions. Thus the ammonia yield rate is still low and the study is still limited in lab scale. If nitrites or nitrates are used as nitrogen sources, rather than nitrogen gas, the catalytic efficiency can be significantly improved, and the residual nitrate and nitrite contaminations in water systems can be efficiently eliminated and converted to energy sources at the same time. It is an emerging alternative for artificial ammonia synthesis, while there is not enough focus on the reduction of nitrate and nitrite. Herein, we systematically compared the differences between the reduction of nitrogen and nitrates, as well as listed the challenges in this area. The total conversion rate and energy efficiency of catalytic nitrate reduction are much higher than nitrogen gas reduction due to the much higher solubility and better converting pathway, which might be further enhanced by employing catalysts improvement strategies. Further, we also proposed suitable materials as well as a few future researches needs that may help boost the development of artificial ammonia synthesis using nitrate. [ABSTRACT FROM AUTHOR]