Bimetal-organic-framework (Bi-MOF) NH2-MIL-125(Ti/Cu)-derived nanocomposites are systematically investigated to elucidate the role of individual species TiO2, CuxO and the porous carbon matrix in photocatalytic activity. Among the studied samples, the TiO2/CuxO/C nanocomposite derived from heat processing NH2-MIL-125(Ti/Cu) under Ar/H2O vapor demonstrates the highest photocatalytic H2 evolution performance due to the formation of a phasejunction between the well-crystallized anatase/rutile TiO2 polymorph, the optimized and codoped nitrogen/carbon in the composites, the formation of p-n heterojunctions between the TiO2 and CuxO nanoparticles, as well as their uniform distribution in a hydrophilic porous carbon matrix decorated with N and carboxylic functional groups. These parameters enable the in situ-formed multi-heterostructures in these nanocomposites to not only possess relatively narrower energy band gaps and improved spatial charge separation due to the formed type-II staggered p-n heterojunctions but also offer multiple pathways for charge diffusion, resulting in lower charge-transfer resistance, suppressed bulk charge recombination, and consequently, much improved visible-light absorption. Therefore, the Bi-MOF NH2-MIL-125(Ti/Cu)-derived TiO2/CuxO/C nanocomposite provides easily accessible active sites with an excellent photocatalytic H2 evolution activity of 3147 μmol gcat-1 h-1, 99 times higher than that of bare TiO2. This work provides a simple one-step approach to producing tunable novel nanocomposites for efficient photocatalytic H2 evolution without using expensive noble metals as cocatalysts.

Surface-functionalized nitrogen/carbon co-doped polymorphic TiO₂ phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal–organic framework (MOF), NH₂-MIL-125(Ti) at 700 °C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH₂-MIL-125(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO₂ along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO₂ nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO₂/C_ArW demonstrates H₂ evolution activity of 426 µmol g_cat^-1 h⁻¹, which remarkably outperforms commercial TiO₂ (P-25) and N-C-TiO₂/C_Ar with a 5-fold and 3-fold H₂ generation, respectively. This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups, as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states. This work also demonstrates that by optimizing the anatase–rutile phase composition of the TiO₂ polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO₂/C nanocomposites, the photocatalytic H₂ generation activity can be further enhanced.

In situformation of p-n heterojunctions between TiO₂and Cu_xO in heteroatom-doped carbon nanocomposites and their applications in photocatalytic H₂evolution were demonstrated. One-step pyrolysis of bimetal-organic-frameworks NH₂-MIL-125(Ti/Cu) in steam at 700 °C forms a p-n heterojunction between TiO₂and Cu_xO nanoparticles. Concurrently, a phasejunction between nitrogen/carbon co-doped anatase and rutile TiO₂is formed, accompanied by the formation of Cu_xO heterostructures. These multi-heterostructures are embedded in N-containing and hydrophilic carboxyl functionalized carbon matrix. The optimized TiO₂/Cu_xO/C composite multi-heterostructures offer multiple pathways for photoinduced electrons and holes migration, absorb more visible light, and provide an increased number of active sites for photocatalytic reactions. Without loading expensive noble metals, the TiO₂/Cu_xO/C nanocomposite derived at 700 °C in steam exhibited a superior photocatalytic H₂generation activity of 3298 μmol g_cat⁻¹h⁻¹under UV-Visible light, 40 times higher than that of commercial TiO₂. This work offers a simple approach to fabricate novel photocatalytic nanocomposites for efficient H₂generation.