Decoupled active centers on crystalline carbon nitride nanoarrays for synergistic photocatalytic hydrogen peroxide synthesis

Nitrogen gas was introduced into the sample for 10 minutes to remove impurities. The sample was placed in a dark environment and oxygen and water were introduced, and spectral data were collected every 5 minutes. After dark adsorption was completed, the background value of the sample was subtracted and recorded once, and then the sample was irradiated with a 300 watt xenon lamp (with an AM1.5G filter) and spectral data were collected every 5 minutes.Photocatalytic H2O2 productionThe photocatalytic system consisted of 10 mg catalyst in 50 mL aqueous suspension, which was ultrasonicated for 15 min to ensure complete dispersion.

Before irradiation, the suspension was purged with oxygen and magnetically stirred in the dark for 15 min to achieve adsorption-desorption equilibrium. The reaction was then initiated under continuous irradiation provided by a 300 W xenon lamp, with oxygen bubbled through the solution at a constant rate of 100 mL min-1. During the reaction, samples were taken at predetermined intervals.

The light source (PLS-SXE300, Beijing Perfect Light) was equipped with an AM 1.5G cutoff filter.Determination of H2O2 concentrationThe concentration of hydrogen peroxide was quantified using the DPD-POD (N,N-diethyl-p-phenylenediamine peroxidase) method. At predetermined time intervals, reaction aliquots were collected and immediately filtered through a 0.22 μm nylon membrane. For analysis, 3 mL of phosphate buffer solution, 50 μL of DPD reagent, and 50 μL of POD enzyme solution were added to the filtered sample, and the total volume was adjusted to 10 mL.

After a development period of 45 seconds, the absorbance at 551 nm was measured with a UV-1800PC spectrophotometer (Shanghai Mapada Instrument Co., Ltd.). A calibration curve was prepared using dilutions of a standard 30% hydrogen peroxide solution to determine the sample concentrations.Isotopic experimentsIsotopic experiments using H218O were conducted by charging a reactor containing In-CCN with 5 mL of H218O. The solution was purged with Ar to remove O2, then subjected to 2 h of irradiation (Xe lamp, AM 1.5G filter).

The composition of the headspace gas was subsequently analyzed by GC-MS.Density functional theory calculationsSpin-polarized density functional theory (DFT) calculations were employed using the Vienna Ab-initio Simulation Package (VASP). The electron exchange correlation was described by the generalized gradient approximation (GGA) with the function of revised Perdew‐Burke‐Ernzerhof. The Brillouin zone was sampled by 3 × 3 × 1 k-points using the Monkhorst–Pack scheme in structural optimizations.

For all geometry relaxation herein, the energy cutoff was set to 420 eV. To avoid interactions between repeated images, a vacuum gap of 20 Å was adopted. The energy and force convergence thresholds for the iterations in the self-consistent field (SCF) were set to 10-5 eV and 0.02 eV Å-1, respectively.

The long-range van der Waals interactions were considered through the DFT‐D3 scheme.DFT calculations were carried out with the B3LYP functional with the combination of the Grimme’s D3BJ version of dispersion correction[3]. The basis set of 6-31G (d, p) for C, H, N, K and Lanl2dz for In were adopt for the geometry optimization and frequency calculation with the solvent of water. The geometries were fully optimized without any structural constraints.

Single-point energy calculations were conducted at the B3LYP-D3(BJ)/6-311++G(d,p)&SDD level of theory with the solvent of water, employing a more accurate basis set to achieve enhanced precision. The HOMO-LUMO visualized by Multiwfn software packages[4] and VMD[5].