In this work, for the first time, carbon self-repairing porous g-C3N4 nanosheets (CPCN-NSs) with high surface area (220.7 m2 g−1) are prepared by a solvothermal process coupled with post multistep thermal treatment in air. Then a facile hydrothermal method is developed to synthesize carbon self-repairing porous g-C3N4 nanosheets/NiCo2S4 nanoparticles (CPCN-NSs/NCS-NPs) hybrid composite for supercapacitor electrode. With large surface area as well as ultrathin thickness and porous structure, the as-prepared CPCN-NSs could be served as an excellent scaffold to combine with NiCo2S4 nanoparticles (NCS-NPs), while the NCS-NPs with high conductivity could function as conductive linkers between CPCN-NSs and improve the electrical conductivity of the hybrid composite. Electrochemical characterizations indicate that the as-prepared hybrid composite delivers excellent electrochemical properties, exhibiting a high capacitance (1557 F g−1 at current density of 1 A g−1) and excellent cycling stability (only 7.4% loss after 10000 cycles). These results clearly demonstrate that the combination of CPCN-NSs with NCS-NPs can substantially improve the capacitive performance of materials and ultimately increase the cycling stability of supercapacitor electrode.

As a promising photocatalyst, the large bandgap (3.2 eV) of anatase TiO2 seriously limits its light absorption of the UV portion of the solar spectrum, making it less applicable in industrial fields. A popular approach for enhancing visible light activity by narrowing the bandgap is doping, however, the dopant-induced defect states in the TiO2 lattice may act as recombination centers for the photogenerated charge carriers. Here we report a facile soft-chemical route to engineer the surface properties of TiO2 crystals using ethanol as the sole organic solvent. The individual TiO2 nanocrystals synthesized in the first step, possessing high affinity with ethanol molecules, tend to assemble together by interfacial Ti–Ti bonding during the following ethanol evaporation induced self-assembly process. Formation of Ti–Ti bonds at the interface simultaneously brings about the decrease of surface oxygen atoms in the TiO2 structural unit, which dramatically alters the electronic structure and extends the light absorption to ∼550 nm. Such a dopant-/additive-free TiO2 assembly exhibits considerable photocatalytic activity under visible light due to its narrower bandgap than individual nanocrystals. Further, an electron paramagnetic resonance measurement is used to confirm the capability of generating reactive ˙OH radicals on the surface of assembled TiO2 under visible-light irradiation.