摘要:

The widely spilled diclofenac (DCF) in water has attracted broad attention because of its potential environmental risk. In this work, palladium quantum dots (PQDs) deposited g-C3N4 photocatalysts (PCNs) were fabricated through a two-step process, i.e., initial thermal polymerization followed by an in-situ reduction for PQDs deposition. In addition, the synthesized g-C3N4 (43.09 m2/g) composing of ultrathin sheets had 4 times larger specific surface area than bulk g-C3N4 (8.73 m2/g), thus offered abundant sites for reaction. The optimized material (PCN2) with 1 wt% PQDs loading content achieved the highest cost-efficiency for DCF degradation, and exhibited a kinetic rate constant (k1) of 0.072 min−1, which was  8 times higher than bulk g-C3N4. The mechanisms on enhanced photocatalytic activity of PCN are interpreted as: (1) decoration of PQDs can alter the optical band structure of g-C3N4, leading to a narrowed bandgap; (2) PQDs can act as electron transfer mediator to retard the recombination of photogenerated charge carriers; and (3) a photosensitization-like electron transfer pathway occurs from highest occupied molecular orbital (HOMO) of DCF to conduction band (CB) of g-C3N4 by means of PQDs. Radical quenching experiments and electron spin resonance (ESR) analysis indicated •O2- was the primary radical for DCF degradation. Density functional theory (DFT) calculation combined intermediates identification further revealed that the Cl11 and N12 atoms with high Fukui index (f 0) were more venerable to attack. PCN2 also remained good stability after five continuous cycles for DCF degradation, showing the great potential for practical application in water treatment area.

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