Graphitic carbon nitride-based upconversion photocatalyst for hydrogen production and water purification

Upconversion luminescence (UCL) is mainly a nonlinear optical method that some engineered nanomaterials can attain and helps in the transformation of low energy phonons (near-infrared photons) into higher energy phonons (ultraviolet (UV)  and visible light photons). Upconversion (UC) nanomaterials are a suitable candidate for preparing near-infrared (NIR) light-responsive photocatalytic systems by mixing with other photocatalysts. Many reports have been published on lanthanide-based UC materials (Ln3+ ions as dopants) and carbon quantum dots (CQDs) carrying UC property with their use in photocatalytic removal of pollutants and energy production. Besides these UC nanomaterials, graphitic carbon nitride (g-C3N4) as a potential photocatalyst (metal-free and ecofriendly) has gained attention owing to its unique and amazing possessions. But some limitations and inadequate utilization of visible light restrict its photocatalytic applicability. Therefore, to enhance or widen its light-harvesting property towards the NIR region, the integration of upconversion nanocrystals (UC NCs) into g-C3N4 is considered an effective approach. Thus, the present review is focused on the amalgamation of g-C3N4 with UC nanomaterials for full solar spectrum absorption in H2 production and pollutant degradation via NIR light absorption.