Enhancing the selectivity of hydrocarbon in CO₂ is a great challenge. Herein, taking widely-used and highly-stable TiO₂ as an example, we found that the protonation step, the key step for CH₄ production, can change from endoergic to exoergic by using red phosphorus quantum dots. Consequently, the main product in CO₂ reduction can be shifted from CO into CH₄. The preparation method is very simple, which just ultrasonically treating the red P in the presence of TiO₂. With an initial rate of CH₄ production of 4.69 μmol·g⁻¹·h⁻¹, under simulated solar light, it manifests a significant 49.4-fold enhancement of CH₄ yield over TiO₂. Density functional calculation indicates that the red P optimizes the surface electronic structure. The Gibbs free energy for CHO* formation (−1.12 eV) becomes lower than the desorption energy of the CO (−0.01 eV) when red P is introduced. This indicates that the CO intermediates on the surface are rapidly protonated to produce CHO*. Subsequently, the CHO* will be converted into CH₄ instead of being desorbed from the surface to produce CO. This study demonstrates that red P quantum dot is a promising candidate for the development of efficient photocatalyst for CO₂ photoreduction to CH₄ under solar light irradiation.

Coupling two-dimention carbon materials like graphene on photodelectrode can achieve high-efficiency photoelectrochemical cells. Bottom-up synthesis of carbon-based two-dimensional materials in green media from simple molecules is very attractive but remains a challenge. Carbohydrate is an ideal precursor for the synthesis but previous report requires pyrolysis at high temperature (> 700 ℃). Herein, starting with glucose, we develop a low temperature (210 ℃) synthesis of carbonaceous nanosheets in aqueous solution of glucose. With the aid of ethylenediamine and Fe³⁺/Fe²⁺/Co²⁺/Ni²⁺ ions, the nanosheets can grow on hematite nanorod array with very close contact. Importantly, a metallic region is formed at the interface due to atom distribution distortion, which can promote the charge transfer. The activity can be greatly enhanced by about 500% due to fast charge transfer. This is much better than that prepared by physically or chemically mixing graphene and hematite (< 200%). The enhancement is mainly due to the deformation area between the nanosheets and the hematite. The effective hole diffusion length increases from 2 to 8 nm and lifetime of charge carrier also increases, as confirmed by ultrafast transient absorption spectra. This method provides more opportunity for simple, mild and cost-effective fabrication of carbon-based two-dimensional by bottom-up method.