Abstract
The use of photocatalysts to purify wastewater and simultaneously convert solar energy into clean hydrogen energy is of considerable significance in environmental science. However, it is still a challenge due to their relatively high costs, low efficiencies, and poor stabilities. In this study, a metal-free carbon quantum dots (CQDs) modified graphitic carbon nitride photocatalyst (CCN) was synthesized by a facile method. The characterization and theoretical calculation results reveal that the incorporation of CQDs into the g-C3N4 matrix significantly improves the charge transfer and separation efficiency, exhibits a redshift of absorption edge, narrows the bandgap, and prevents the recombination of photoexcited carriers. The hydrogen production and simultaneous degradation of methylene blue (MB) or rhodamine B (RhB) in simulated wastewaters were further tested. In the simulated wastewater, the CCN catalyst showed enhanced photodegradation efficiency, accompanied with the increased hydrogen evolution rate (1291 µmol·h−1·g−1). The internal electrical field between the g-C3N4 and the CQDs is the main reason for the spatial separation of photoexcited electron-hole pairs. Overall, this work could offer a new protocol for the design of highly efficient photocatalysts for dye wastewater purification with simultaneous hydrogen production.
Highlights
The application of photocatalysts to purify wastewater with simultaneous hydrogen production has received persistent interest [1]
Since the report of Wang and Domen documented that a polymer semiconductor based on defective graphitic carbon nitride (g-C3N4) owns the performance of hydrogen evolution from water [7], the research towards this promising nontoxic metal-free photocatalyst has attracted considerable attention, due to its facile synthesis, visible-light responding energy gap (Eg = 2.68 eV), high physicochemical stability, and “earth-abundant” nature [8,9]
The TG and DTG analytical results (Figure S1 in Supporting Materials) indicated that the synthesized carbon quantum dots (CQDs) were stable under nitrogen
Summary
The application of photocatalysts to purify wastewater with simultaneous hydrogen production has received persistent interest [1]. Current photocatalysts still have several fundamental problems that need to be solved, such as low photoabsorption efficiency (which leads to the low quantum efficiency), high electron-hole recombination rate, high cost, and poor stability [6] It still needs a follow-up study to solve these defects and develop an efficient photocatalyst. G-C3N4 is fabricated by thermal polymerization of abundant nitrogen-rich precursors such as melamine [9], dicyandiamide [10], cyanamide [11], urea [12], thiourea, and ammonium thiocyanate [13] This material has enormous application potential, such as organic pollutant degradation [14]. To the best of our knowledge, only a few reports have studied both the theoretical basis and the possible applications in dye wastewater purification with simultaneous hydrogen production [22,23,24]
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