Hierarchical TiO₂ nanohorns/nanocrystalline diamond heterostructures for efficient methylene blue photodegradation

Achieving efficient photocatalytic degradation of organic pollutants requires precise control over semiconductor-substrate interfaces. In this work, we report a hierarchical TiO₂ nanohorn (TNH) architecture grown hydrothermally over nanocrystalline diamond (NCD) films. The NCD films induce the growth of ultra-nano TNH over primary nanohorns, facilitated by sp³-sp² hybridized carbon framework and high-density grain boundaries. These grain boundaries provide high-energy nucleation sites that facilitate localized charge accumulation and promote strain-relief-driven secondary nanohorn growth during hydrothermal processing. This distinct TNH/NCD heterostructure exhibits enhanced interfacial charge transfer and efficient photocarrier separation, as evidenced by advanced spectroscopic and microscopic characterization. Under low-power UV irradiation, the TNH/NCD heterostructure exhibits significantly enhanced photocatalytic activity toward methylene blue (MB 5 ppm), achieving 89.7% degradation within 210 min with a pseudo-first-order rate constant (k = 0.0108 min^-1), along with excellent structural stability and recyclability over five successive cycles. The TNH/NCD heterostructure attained enhanced photocatalytic activity in MB degradation, which is attributed to the synergistic effects of interfacial chemistry, high surface area, enhanced light-matter interaction, reduced recombination rates, and improved charge carrier dynamics facilitated by the sp³-sp² hybridized NCD framework. Our findings highlight the crucial influence of substrate selection on photocatalyst performance and establish NCD as a highly effective platform for constructing advanced TiO₂-based photocatalytic systems for environmental remediation.