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A highly efficient photoenergy conversion is strongly dependent on the cumulative cascade efficiency of the photogenerated carriers. Spatial heterojunctions are critical to directed charge transfer and, thus, attractive but still a challenge. Here, a spatially ternary titanium-defected TiO2@carbon quantum dots@reduced graphene oxide (denoted as VTi@CQDs@rGO) in one system is shown to demonstrate a cascade effect of charges and significant performances regarding the photocurrent, the apparent quantum yield, and photocatalysis such as H2 production from water splitting and CO2 reduction. A key aspect in the construction is the technologically irrational junction of Ti-vacancies and nanocarbons for the spatially inside-out heterojunction. The new "spatial heterojunctions" concept, characteristics, mechanism, and extension are proposed at an atomic-/nanoscale to clarify the generation of rational heterojunctions as well as the cascade electron transfer.

Hierarchical MoS2@TiO2 heterojunctions were synthesized through a one-step hydrothermal method by using protonic titanate nanosheets as the precursor. The TiO2 nanosheets prevent the aggregation of MoS2 and promote the carrier transfer efficiency, and thus enhance the photocatalytic and electrocatalytic activity of the nanostructured MoS2. The obtained MoS2@TiO2 has significantly enhanced photocatalytic activity in the degradation of rhodamine B (over 5.2 times compared with pure MoS2) and acetone (over 2.8 times compared with pure MoS2). MoS2@TiO2 is also beneficial for electrocatalytic hydrogen evolution (26 times compared with pure MoS2, based on the cathodic current density). This work offers a promising way to prevent the self-aggregation of MoS2 and provides a new insight for the design of heterojunctions for materials with lattice mismatches.

Hierarchical semiconductors are the most important photocatalysts, especially for visible light-induced hydrogen production from water splitting. We demonstrate herein a hierarchical electrostatic assembly approach to hierarchical CdS/m-TiO2/G ternary photocatalyst, which exhibits high photoactivity and excellent photostability (more than twice the activity of pure CdS while 82% of initial photoactivity remained after 15 recycles during 80 h irradiation). The ternary nanojunction effect of the photocatalyst has been investigated from orbitals hybrid, bonding energy to atom-stress distortion and nano-interface fusion. And a coherent separation mechanism of charge carriers in the ternary system has been proposed at an atomic/nanoscale. This work offers a promising way to inhibit the photocorrosion of CdS and, more importantly, provide new insights for the design of ternary nanostructured photocatalysts with an ideal heterojunction.

The homojunction of oxygen/metal vacancies and its interfacial n–p effect on the physiochemical properties are rarely reported. Interfacial n–p homojunctions of TiO2 are fabricated by directly decorating interfacial p-type titanium-defected TiO2 around n-type oxygen-defected TiO2 nanocrystals in amorphous–anatase homogeneous nanostructures. Experimental measurements and theoretical calculations on the cell lattice parameters show that the homojunction of oxygen and titanium vacancies changes the charge density of TiO2; a strong EPR signal caused by oxygen vacancies and an unreported strong titanium vacancies signal of 2D 1H TQ-SQ MAS NMR are present. Amorphous–anatase TiO2 shows significant performance regarding the photogeneration current, photocatalysis, and energy storage, owing to interfacial n-type to p-type conductivity with high charge mobility and less structural confinement of amorphous clusters. A new “homojunction of oxygen and titanium vacancies” concept, characteristics, and mechanism are proposed at an atomic-/nanoscale to clarify the generation of oxygen vacancies and titanium vacancies as well as the interface electron transfer.

Hierarchically dual-mesoporous TiO2 microspheres have been synthesized by a solvothermal process in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and diethylenetriamine (DETA) as co-templates. Secondary mesostructured defects in the hierarchical TiO2 microspheres produce oxygen vacancies, which not only significantly enhance photocatalytic activity in the degradation of methylene blue (1.7 times that with P25) and acetone (2.9 times that with P25), but are also beneficial for lithium storage. Moreover, we propose a mechanism to rationalize the role of this dual mesoporosity of the TiO2 microspheres in enhancing molecular diffusion, ion transportation, and electronic transitions.