Preparation of Structure Vacancy Defect Modified Diatomic‐Layered g‐C3N4 Nanosheet with Enhanced Photocatalytic Performance

Abstract Structure self‐modification of graphitic carbon nitride (g‐C3N4) without the assistance of other species has attracted considerable attention. In this study, the structure vacancy defect modified diatomic‐layered g‐C3N4 nanosheet (VCN) is synthesized by thermal treatment of bulk g‐C3N4 in a quartz tube with vacuum atmosphere that will generate a pressure‐thermal dual driving force to boost the exfoliation and formation of structure vacancy for g‐C3N4. The as‐prepared VCN possesses a large specific surface area with a rich pore structure to provide more active centers for catalytic reactions. Furthermore, the as‐formed special defect level in VCN sample can generate a higher exciton density at photoexcitation stage. Meanwhile, the photogenerated charges will rapidly transfer to VCN surface due to the greatly shortened transfer path resulting from the ultrathin structure (≈1.5 nm), which corresponds to two graphite carbon nitride atomic layers. In addition, the defect level alleviates the drawback of enlarged bandgap caused by the quantum size effect of nano‐scaled g‐C3N4, resulting in a well visible‐light utilization. As a result, the VCN sample exhibits an excellent photocatalytic performance both in hydrogen production and photodegradation of typical antibiotics.


Photocatalytic test
The photocatalytic H 2 evolution was carried out in a closed online system (Beijing Merry Change Technology Co.,Ltd) at ambient temperature.In a typical photocatalytic procedure, 30 mg of as-prepared sample was placed into a 50 mL aqueous solution using 5 mL of triethanolamine (TEOA) as sacrificial agent and H 2 PtCl 6 as cocatalyst.The obtained catalyst suspension was ultrasonically treated and fully degassed before light irradiation.The amount of H 2 product was detection by a gas chromatography (TCD detector) with argon as carrier gas.
To evaluate the photocatalytic degradation efficiency of as-prepared samples, 30 mg of photocatalyst for degradation of typical antibiotic ciprofloxacin (CIP, 10 mg L -1 , 80 mL) and tetracycline hydrochloride (TC, 30 mg L -1 , 80 mL) were studied by using a 300 W Xe lamp as light source (λ > 420 nm, Merry Change, MCPF300B).To ensure the adsorption-desorption equilibrium between the target contaminant and photocatalyst, the suspension was treated by ultrasonic and stirred in the dark for 30 min.During the irradiation process, 3 mL suspension was extracted at given time intervals, then separated by centrifugation at 10000 rpm to remove the solid photocatalysts.The residual concentration of antibiotic CIP and TC was analyzed by spectrophotometer (UV-vis NIR, TU-1900).

Figure S1 .
Figure S1.The amplified region for high-resolution C-NHx XPS peak of GCN, NCN and VCN samples.

Figure S2 .
Figure S2.(A) SEM image and (B) TEM image of as-prepared NCN sample.

Figure S3 .
Figure S3.The Mott-Schottky plots with various frequencies of NCN sample.

Figure S4 .
Figure S4.The apparent quantum efficiency of NCN and GCN under the light irradiation wavelengths of 420, 450 and 475 nm.

Figure S6 .
Figure S6.(A) Photocatalytic degradation and (B) corresponding degradation kinetics of TC for GCN, NCN and VCN photocatalysts; (C) Comparison of degradation rate of TC for as-prepared samples; (D) The trapping experiment of TC by using VCN photocatalyst.

Table S1 .
Pore size, Pore volume and BET surface area of synthesized photocatalysts.

Table S4 .
∆G(H*) for the adsorption of H* on g-C 3 N 4 and supported platinum as a cocatalyst.

Table S5 .
∆G(H*) for the adsorption of H* on structure vacancy defect modified g-C 3 N 4 and 9supported platinum as a cocatalyst.ele 