The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low‐cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g‐C₃N₄) from a low‐cost precursor, urea, is reported. The g‐C₃N₄ exhibits an extraordinary hydrogen‐evolution rate (ca. 20 000 μmol h⁻¹ g⁻¹ under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g‐C₃N₄ photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen‐evolution rate is significantly enhanced.

Bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are highly desirable for rechargeable metal–air batteries and regenerative fuel cells. However, the commercial oxygen electrocatalysts (mainly noble metal based) can only exhibit either ORR or OER activity and also suffer from inherent cost and stability issues. It remains challenging to achieve efficient ORR and OER bifunctionality on a single catalyst. Metal-free structures offer relatively large scope for this bifunctionality to be engineered within one catalyst, together with improved cost-effectiveness and durability. Herein, by closely coupled computational design and experimental development, highly effective bifunctionality was achieved in a phosphorus and nitrogen co-doped graphene framework (PNGF) – with both ORR and OER activities reaching the theoretical limits of metal-free catalysts, superior to their noble metal counterparts in both (bi)functionality and durability. In particular, with the identification of active P–N sites for OER and N-doped sites for ORR, we successfully intensified these sites by one-pot synthesis to tailor the PNGF. The resulting catalyst achieved an ORR potential of 0.845 V vs. RHE at 3 mA cm⁻² and an OER potential of 1.55 V vs. RHE at 10 mA cm⁻². Its combined ORR and OER overpotential of 705 mV is much lower than those previously reported for metal-free bifunctional catalysts.

It is a key challenge to explore an efficient, stable and low-cost catalyst for the oxygen evolution reaction (OER). Herein, we show a facile strategy to significantly enhance the electrocatalytic activity and stability of crystalline α-FeOOH by rapid heat treatment. We identify that crystalline α-FeOOH shows not only electrocatalytic activity as high as the benchmark FeOOH catalyst (amorphous γ-FeOOH), but also the highest stability among all FeOOH electrocatalysts for the OER in alkaline solutions. Our findings not only deepen the fundamental understanding of the OER process on these materials but also guide further development of new low-cost electrocatalysts for energy storage via water splitting.

The exploration of simultaneous removal of co-existing or multiple pollutants from water by the means of nanomaterials paves a new avenue that is free from secondary pollution and inexpensive. In the aquatic environment, river water contains a mixture of ions, which can influence the adsorption process. In this respect, removing heavy metal ions becomes a true challenge. Here, four heavy metal ions, namely, Pb²⁺, Cd²⁺, Cu²⁺, and Ni²⁺, have been successfully removed simultaneously from river water using ultrafine mesoporous magnetite (Fe₃O₄) nanoparticles (UFMNPs) based on the affinity of these metal ions toward the UFMNP surfaces as well as their unique mesoporous structure, promoting the easy adsorption. The individual removal efficiencies of Pb²⁺, Cd²⁺, Cu²⁺, and Ni²⁺ ions from river water were 98, 87, 90, and 78%, respectively, whereas the removal efficiencies of the mixed Pb²⁺, Cd²⁺, Cu²⁺, and Ni²⁺ ions were 86, 80, 84, and 54%, respectively, in the same river water. Thus, the data clearly indicate the complex removal of heavy metal ions in multi-ion systems. This study has demonstrated the huge potential of UFMNPs to be effective for their use in wastewater treatment, especially to simultaneously remove multiple heavy metal ions from aqueous media.

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low‐cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g‐C₃N₄) from a low‐cost precursor, urea, is reported. The g‐C₃N₄ exhibits an extraordinary hydrogen‐evolution rate (ca. 20 000 μmol h⁻¹ g⁻¹ under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g‐C₃N₄ photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen‐evolution rate is significantly enhanced.

The oxygen reduction reaction (ORR) plays a critical role in sustainable energy systems. Among the most promising metal free ORR electrocatalysts, nitrogen-doped carbon materials have generated significant research interest. Nitrogen doping within a graphitic/turbostratic network of carbon atoms generates active sites for the ORR via C–N bond polarisation that induces a reduced energy barrier towards the ORR on the adjacent carbon atom. At the same time, nitrogen doping leads to an increased electrical conductivity due to electron excess in the delocalised π-system. Thus, the electrical conductivity and the number and the nature of the active sites are two important factors determining the performance of nitrogen-doped carbons in the ORR. Herein, N-doped nanocarbon/graphene composites were carefully designed, synthesized, characterized and tested as electrocatalysts in the ORR in order to decouple these two factors and investigate the underlying relationships between them. Chitosan was used as a nitrogen precursor for nanocarbon, while reduced graphene oxide was introduced to tune the electrical conductivity. Our results show that a low conductivity limits the exertion of active sites and results in a conductivity-dependent ORR activity. However, when the conductivity reaches a critical value, the active sites can be fully utilized and contribute to a positively correlated ORR activity.