Graphene-Based Modulation on the Growth of Urchin-like Na₂Ti₃O₇ Microspheres for Photothermally Enhanced H₂ Generation from Ammonia Borane

Structural optimization and surface engineering of photocatalysts are considered as promising approaches to improve their performances effectively. The precise control of morphology and compositions during synthesis of photocatalysts is important but yet challenging. In this work, without any aid of surfactant, urchin-like reduced graphene oxide/sodium titanate (RGO/Na2Ti3O7) microspheres were fabricated by a facile, one-pot hydrothermal reaction with good reproducibility. Both microsized and nanosized graphene oxide sheets can serve as catalysts of manipulating the growth kinetics of urchin-like Na2Ti3O7 microspheres by accelerating nucleation while inhibiting Ostwald ripening. The coupling of hierarchical Na2Ti3O7 with RGO significantly enhanced photoelectrochemical and photocatalytic performances under visible-light irradiation. The steady-state photocurrent density of RGO/Na2Ti3O7-based photoanode was 13.6 times higher than those based on pristine Na2Ti3O7, thanks to the narrowed bandgap, enhanced light harvesting, and effective electron transfer. The surfactant-free RGO/Na2Ti3O7 microspheres were further demonstrated as photocatalysts endowed with photothermal effect enhanced photocatalytic activity. Toward H2 generation by hydrolysis of ammonia borane, the maximum hydrogen production rate of RGO/Na2Ti3O7 reached 2.73 times higher than that of Na2Ti3O7, mainly due to the excellent photothermal efficiency up to 67.2% (higher than that of noble metal, e.g., Au dumbbell-like structure). It is believed that our understanding and reliable strategy could be extendable to construct new photocatalysts and systems toward effective solar energy harvesting and utilizations.