High-efficiency Photocatalyst Design Based on Up-converted Carbon Nanoparticles

High-efficiency photocatalysis systems, especially those operative in the visible region, may offer promising remedy to tackle today's environmental and energy problems.[1-3] Semiconductors are usually selected as photocatalysts because of their narrow gap and strong light absorption in the visible range. [1-5] To perform as photocatalysis, a semiconductor needs to absorb energy equal to or greater than its energy gap to generate exitons or electron-hole (e-/h+) pairs. TiO2 is the perhaps most studied semiconductor and potentially a facile and low-cost catalyst for removing environmental wastes and tainted water due to its physical and chemical stability, low cost, non-toxicity, and superior electronic and optical properties. However, one obstacle hindering its effective utilization lies in the fact that only less than 5% of the sunlight (in UV zone) is absorbed by the undoped TiO2 because of its wide band gap. While other semiconductors with a narrower band gap (such as TiS2, CdS, and ZnS etc.) can capture visible light but they always suffer from photocorrosion. Numerous promising visible-light-activated TiO2 nano-powders have been produced via doping and modification, however those photocatalysts usually suffer from instability problem, and their catalytic abilities are dependent on morphology, size, crystal phase, and/or doping concentration.[1-5] Consequently, design of catalysts with controlled properties, especially the energy gap, composition, and surface modification, remain the urgent and important challenges.To improve catalyst efficiency, an ideal photocatalyst system should be able to utilize the full spectrum of sunlight, photo-stable (i.e. not prone to photocorrosion), inexpensive, and non-toxic. We have recently produced carbon nanoparticles (CNPs) with excellent up-conversion luminescence properties. Significantly, our preliminary results have shown that the up-converted CNPs are potentially a powerful energy transfer component in photocatalyst design. Based on the up-conversion properties of CNPs, wehave revealed that the photocatalyst TiO2/CNPs and SiO2/CNPs composite systems are capable of harnessing the use of the full spectrum of sun light. Consequently, we seek in this proposal to further develop the potential of the up-converted CNPs in the design of efficient photocatalysts. Towards this aim, we plan to control the synthetic route for CNPs, understand the mechanisms of the up-converted luminescence properties of CNPs, and exploit CNPs as an energy transfer component in the design of high-efficiency photocatalysts. Ultimately we plan to develop a new general approach to high-efficiency photocatalyst design based on the combination of the up-converted CNPs and semiconductors nanoparticles for environment and energy applications.