Controllable Approach to Carbon‐Deficient and Oxygen‐Doped Graphitic Carbon Nitride: Robust Photocatalyst Against Recalcitrant Organic Pollutants and the Mechanism Insight

Abstract

Polymeric g‐C3N4 is a promising visible‐light‐responsive photocatalyst; however, the fast recombination of charge carriers and moderate oxidation ability remarkably restrict its photocatalytic oxidation efficiency towards organic pollutants. To overcome these drawbacks, a self‐modification strategy of one‐step formaldehyde‐assisted thermal polycondensation of molten urea to prepare carbon‐deficient and oxygen‐doped g‐C3N4 (VC‐OCN) is developed, and the carbon vacancy concentration is well‐controlled by changing formaldehyde dosage. The VC‐OCN catalysts exhibit interesting carbon vacancy concentration‐dependent photocatalytic removal efficiency to p‐nitrophenol (PNP) and atrazine (ATN), in which VC‐OCN15 with appropriate carbon vacancy concentration displays significantly higher pollutant removal efficiency than bulk g‐C3N4. The apparent first‐order rate constant of VC‐OCN15 for PNP and ATN removal is 4.4 and 5.2 times higher than that of bulk g‐C3N4. A combination of the experimental results and theoretic calculations confirm that the synergetic effect of carbon vacancies and oxygen doping sites can not only delay the recombination of charge carriers but also facilitate adsorption of oxygen molecules on the carbon vacancies, which leads to the generation of plentiful active oxygen species including not only superoxide anion radicals but also indirectly formed hydroxyl radicals and singlet oxygen. These active oxygen species play a dominant role in the removal of target pollutants.

Molybdenum (VI)‐oxo Clusters Incorporation Activates g‐C3N4 with Simultaneously Regulating Charge Transfer and Reaction Centers for Boosting Photocatalytic Performance

“…This finding indicated that few • OH radicals were generated in CN suspensions during photodegradation, which was probably resulted from the direct O 2 reduction through multi-electron reaction processes. [8,24] Unexpectedly, the [Mo 7 O 24 ] 6− -pCN sample exhibited an obviously enhanced characteristic signal with the intensity of 1:2:2:1, affirming that more • OH radicals were produced after intercalation, which could adsorb on catalyst surface for oxidation reactions. As presented in Figure 4c, only a weak characteristic signal from BMPO-• O 2 − adducts was detected over CN under Xe lamp irradiation (λ > 420 nm), whereas the signal was markedly enhanced in the [Mo 7 O 24 ] 6− -pCN system, and the peak intensities become stronger with the extension of the illumination time (Figure S14a O 24 ] 6− -pCN@BPA2, respectively), which were displayed in Figure 4e(i,ii).…”

“…After being excited, CN showed two decay times ≈1.81 and 9.40 ns, which originated from the spontaneous radiation decay and nonradiative transition of charge carriers, respectively. [24] After intercalation, the average PL lifetime (Ave. τ) was prolonged from 7.53 ns (CN) to 8.82 ns ([Mo 7 O 24 ] 6− -pCN), stating that the sandwiched Mo-POMs could gather photoelectrons from planar aromatic rings and thus severely hindered the recombination of e − -h + pairs. [29] Electron paramagnetic resonance (EPR) examination was also conducted to verify the unique electronic structure and unpaired electrons of different catalysts (Figure S10, Supporting Information).…”

“…A few • OH radicals on catalyst surface were generated from direct O 2 reduction by high-density electrons gathered around O atoms of [Mo 7 O 24 ] 6− polyanions. [24] During photodegradation, the O atoms in Mo−O clusters not only served as primary active sites to accumulate e − for producing ROSs, but also adsorbed phenols pollutants by binding to their OH groups, thus reducing the migration distance of ROSs. Under the attack of •O 2 − , surface-adsorbed • OH, and h + , phenols pollutants (e.g., BPA and 4-CP) could be decomposed completely.…”

Plasmonic Nanozyme of Graphdiyne Nanowalls Wrapped Hollow Copper Sulfide Nanocubes for Rapid Bacteria‐Killing

“…Simultaneously, some additional e − and h + are generated in the VB and CB of GDY. Since carbon vacancies at the CuS@GDY interfaces are active centers for adsorption and decomposition of H 2 O 2 , [28] plentifully localized e − and h + can react with H 2 O 2 molecules to produce a large amount of O 2 (Equation 1) and •OH radicals (Equation 2), and further convert to •O 2 − anion radicals via oneelectron oxygen reduction (Equation 3). Meanwhile, •O 2 − anion radicals combine with h + to yield 1 O 2 (Equation 4).…”

Effective H2O2 Production via Favorable Intermediate Desorption in Fluctuating Electrical Fields from Matrix‐Filler Mutually Enhanced P‐C3N4/PVDF‐HFP Porous Composite**

“…The interaction of PVDF-HFP and PCN causes the valence band to further move towards the fermi level. [46] The narrowed energy gap make the electrons more easily activated by external electrical field, beneficial to the piezoelectric catalysis. Correspondingly, the differential charge density diagram in Figure 6d shows that the presence of PVDF will lead to electron accumulation on the surface of PCN, which is conducive to the piezocatalytic reaction process.…”