As a metal-free semiconductor, graphitic carbon nitride (g-C₃N₄) has received extensive attention due to its high stability, nontoxicity, facile and low-cost synthesis, appropriate band gap in the visible spectral range and wide availability of resources. The dimensions of g-C₃N₄ can influence the regime of the confinement of electrons, and consequently, g-C₃N₄ with various dimensionalities shows different properties, making them available for many stimulating applications. Although there are some reviews focusing on the synthesis strategy and applications of g-C₃N₄, there is still a lack of comprehensive review that systemically summarises the synthesis and application of different dimensions of g-C₃N₄, which can provide an important theoretical and practical basis for the development of g-C₃N₄ with different dimensionalities and maximises their potential in diverse applications. By reviewing the latest progress of g-C₃N₄ studies, we aim to summarise the preparation of g-C₃N₄ with different dimensionalities using various structural engineering strategies, discuss the fundamental bottlenecks of currently existing methods and their solution strategies, and explore their applications in energy and environmental applications. Furthermore, it also puts forward the views on the future research direction of these unique materials.

Ammonia is a key industrial raw material for fertilisers, chemicals and energy. The annual artificial ammonia synthesis via the Haber–Bosch process results in about 2% of global energy consumption and can lead to 1.6% CO₂ emission. Hence, it is urgent to develop low-cost and environmentally friendly approaches for artificial ammonia synthesis under ambient conditions. Recently, bismuth (Bi)-based catalysts have attracted great interest due to their excellent nitrogen fixation performance in electrochemical and photocatalytic fields. However, there is still a lack of a comprehensive review on Bi-based nitrogen-fixation materials focusing on their crystal structure, surface engineering and modification methods, which is highly desirable for facilitating their further development towards applications. Herein, we provide an up-to-date review on Bi-based nitrogen-fixation materials and classify them as metallic Bi, bismuth oxide, bismuth oxyhalide, and Bi-based polyoxometalates. Starting from the underlying crystal structure, we analyse the internal electric field, surface engineering and modification methods of Bi-based nitrogen fixation materials. Then, we highlight the latest achievements of Bi-based materials and reveal the challenges and obstacles in the development and application of Bi-based nitrogen-fixation materials. More importantly, this review presents the surface and structure engineering strategies, and future directions for the development of new Bi-based nitrogen-fixation materials under ambient conditions.

A red-emitting phosphor, Eu²⁺-activated Ca₄(PO₄)₂O phosphor was synthesized by conventional solid-state reaction. X-ray powder diffraction confirmed the phase formation. The band gap of Ca₄(PO₄)₂O was estimated to be about 4.75 eV from the diffuse reflection spectrum. The excitation and emission spectra, and the concentration dependence of emission intensity were investigated. The results showed that under excitation at 460 nm, the Ca₄(PO₄)₂O:Eu²⁺ phosphors exhibit strong red emission centered at 665 nm, and the optimum concentration of Eu²⁺ in Ca₄(PO₄)₂O:Eu²⁺ is about 0.07 mol per mol Ca²⁺ ions. The nature of the Eu²⁺ ion emission in Ca₄(PO₄)₂O, i.e. the main mechanism for concentration quenching was discussed. A white LED was fabricated using a blue 460 nm chip pumped by a phosphor blend of green-emitting Sr₂SiO₄:Eu²⁺ and red-emitting Ca_3.93(PO₄)₂O:0.07Eu²⁺. When the applied current was 20 mA, the white LED has Commission International de I'Eclairage color coordinates of (0.3135, 0.3316) for white light (correlated color temperature = 6446 K) and an excellent color rendering index of 90.5.