Sulfur-doped Graphitic Carbon Nitride Research Articles

Adsorption of Lead on Sulfur-Doped Graphitic Carbon Nitride Nanosheets: Experimental and Theoretical Calculation Study

Two-dimensional (2D) layered materials for environmental remediation require abundant functional groups and high affinity for target pollutions. In this work, a heteroatom sulfur-doped graphitic carbon nitride (S3.9%-g-C3N4) material had been fabricated by pyrolysis for S- and N-rich supramolecular polymer precursor. A hierarchically porous structure with multimodal pore size distribution can facilitate Pb(II) ions’ diffusion from wastewater to the S3.9%-g-C3N4 surface. Batch adsorption experiments revealed that the resulting S-doped conjugated system of g-C3N4 exhibited enhanced adsorption capacity (52.63 mg g–1) as compared with that of individual g-C3N4 (31.25 mg g–1) at pH = 4.5. Accordingly, the higher adsorption ability for S3.9%-g-C3N4 was on account of its binding sites (i.e., soft S ligand) for coordination with Pb(II) than g-C3N4. Significantly, thermodynamic parameters demonstrated that the adsorption of Pb(II) on S3.9%-g-C3N4 was a spontaneous and endothermic process, and the kinetic experiments suggested that the chemisorption governed the adsorption process. Additionally, all geometries of (S-g-C3N4)–Pb(II) systems were thoughtfully constructed to explore the optimized structure, and these results were combined with the results of Density Functional Theory calculations to show that the enrichment of Pb(II) on S3.9%-g-C3N4 was energetically favored in C3N4–S–N3—the monosubstituted system with high Ead value (4.75 eV), in which the chemical binding sites of S–Pb and N–Pb were further evidenced by XPS analysis. The presented results not only demonstrated a facile and environmentally friendly strategy to synthesize porous S3.9%-g-C3N4 nanosheets with preferable Pb(II) adsorption ability, but also revealed the underlying adsorption mechanism for Pb(II) by experiments and theory simulation.

Sulfur-doped carbon nitride as a non-metal heterogeneous catalyst for sulfate radical-based advanced oxidation processes in the absence of light irradiation

As graphene-like materials are demonstrated as non-metal catalysts to activate persulfate (PSF)/peroxymonosulfate (PMS), co-doping sulfur and nitrogen with graphene is a promising approach to improve catalytic activities. In this study, a convenient one-step approach is adopted to prepare sulfur-doped graphitic carbon nitride (SCN), which shows crumpled morphology and porosity on its surface, making SCN exhibit a much higher surface area than the common CN. Chemical analyses also confirm that a part of N atoms in CN skeleton are substituted by S. To evaluate PSF/PMS activation by SCN, decolorization of Rhodamine B (RhB) is selected as a model test. SCN showed a much higher catalytic activity than carbon nitride (CN) to activate PSF/PMS for RhB decolorization. Behaviors of PSF/PMS activation by SCN are explored by evaluating various effects on RhB decolorization, including temperature, pH, and salt. SCN-activated PSF/PMS for RhB decolorization is much favorable at elevated temperatures and neutral conditions. The presence of NaCl does not significantly inhibit the PSF/PMS activation by SCN. Several radical inhibitors on SCN-activated PMS are also evaluated and the RhB mechanism is shown to involve both sulfate and hydroxyl radicals. Potential mechanisms of PSF/PMS activation by SCN are proposed and ascribed to the more active carbon sites of SCN induced by the co-dopants of sulfur and nitrogen. SCN can be also re-used to activate PSF/PMS without catalytic activity loss. These features demonstrate that SCN is a conveniently-prepared but effective and sustainable non-metal heterogeneous catalyst for activating PSF/PMS.

In situ fabrication of SnO2/S-doped g-C3N4 nanocomposites and improved visible light driven photodegradation of methylene blue

Herein, several Sn/CNS composite photocatalysts consisted of SnO2 and sulfur-doped graphitic carbon nitride (CNS) were in situ fabricated through thermal condensation of thiourea and tin(IV) chloride as starting materials. The synthesized Sn/CNS photocatalysts with different SnO2 contents (1.6, 7.7 and 8.5wt%) were characterized by several techniques. The phase structures and morphology results of composite indicated that the perfect crystalline structure and the stacking degree of CNS phase were disrupted during the formation of SnO2 particles, so that specific surface area of composite was enhanced about 2.8 times compared with that of pure CNS photocatalyst. The optimized photocatalyst, i.e. SnO2(7.7)/CNS composite, showed the highest photocatalytic efficiency for degrading methylene blue (MB) under visible light irradiation among the individual CNS and SnO2 photocatalysts. The improved photoactivity could be related to introducing S dopant in CNS backbone which led to increasing the visible light absorption. Besides, due to loading the SnO2 nanoparticles, heterojunctions were formed between SnO2 and CNS which facilitated the effective charge transfer through interfacial interactions between both components. The heterojunction prepared by the in situ strategy illustrated excellent stability for the photocatalytic activity under optimized conditions obtained by response surface methodology (RSM) method. It may be attributed to the strong surface interaction between individual components during evolution of CNS structure. It was also found that •O2− was the main reactive species in the degradation reaction and a possible mechanism for the enhanced photocatalytic activity of the SnO2(7.7)/CNS composite was discussed in detail.

Controllable Synthesis of Mesoporous Sulfur-Doped Carbon Nitride Materials for Enhanced Visible Light Photocatalytic Degradation.

Mesoporous sulfur-doped graphitic carbon nitride (MCNS) materials were successfully synthesized using thiourea as a low-cost precursor and SiO2 gel solution as a template through a simple thermal condensation method. The effects of three synthesis key factors, namely, the reaction temperature, the reaction time, and the weight ratio of SiO2/thiourea, and also their interactions on the removal rate of methyl orange (MO) were investigated using response surface methodology, and the samples were subjected to several characterization techniques. Results showed that the optimized physicochemical properties could be achieved for the MCNS samples by controlling the synthesis key factors, and it was found that the reaction temperature and the reaction time had significant influences on the MO photocatalytic removal. Among bulk graphitic carbon nitride (g-C3N4), CN (undoped g-C3N4), CNS (sulfur-doped g-C3N4 without template), and TiO2 (Degussa P25) samples, the optimized MCNS-4 illustrated the highest photocatalytic activity toward the removal of MO under visible light irradiation. The enhanced performance originated from the synergistic effects of high surface area, mesoporous texture, sulfur doping, and high visible light absorption, which were helpful for the separation and transportation of the photogenerated electron-hole pairs. Furthermore, MCNS-4 revealed high reusability and stability without any significant decrease in its efficiency. Our findings not only confirm the importance of simultaneous sulfur doping and mesoporous structure to synthesize highly active photocatalysts but also might provide a new insight into textural engineering of carbon nitride materials only by the optimization of the synthesis key variables, considering their interactions without relying on extra metal oxides.

Phthaloyanine-sensitized CNS nanocomposites with efficient photocatalytic activity under visible-light irradiation

Phthalocyanine sensitized sulfur-doped graphitic carbon nitride (CNS) nanocomposite photocatalysts were fabricated via a facile impregnation method. The as-prepared phthalocyanine/CNS nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TG), UV–vis diffuse reflectance spectroscopy (DRS), fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD). The samples showed well-defined hierarchical nanostructures, and their absorption was extended to the near-infrared region. The photocatalytic activities of the phthalocyanine/CNS composites were evaluated by the decomposition of methylene blue (MB) under visible-light irradiation. It was found that the phthalocyanine/CNS composites showed enhanced visible-light photocatalytic performances compared to pure dyes and CNS.

Synthesis and characterization of dye/CNS nanocomposites with enhanced visible light photocatalytic activity

In this paper, sulfur-doped graphitic carbon nitride (CNS) was synthesized by a facile and efficient heating method, phthalocyanine sensitized CNS via an ultrasound-assisted impregnation method to construct dye/CNS composite materials. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), UV–vis diffused reflectance spectra (DRS), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric Analysis Meter (TGA) and Fourier transform infrared spectra (FT-IR). Under visible-light irradiation, the products exhibited enhanced photocatalytic performances for degrading methylene blue (MB). The dramatically improved performance of the composites can be attributed to the increase of specific surface area, the enhancement of the visible-light absorption, and the efficient separation of the photogenerated electron-hole pairs.

A simple fabrication for sulfur doped graphitic carbon nitride porous rods with excellent photocatalytic activity degrading RhB dye

Constructing special nanostructures with large surface areas and tuning the band gap by element doping are efficient strategies to enhance the photocatalytic activity of semiconductor materials. Here we combined both strategies in one material to form sulfur-doped graphitic carbon nitride porous rods (S-pg-C3N4) in one pot by simply pyrolysis of the melamine-trithiocyanuric acid complex with different temperatures. The samples were characterized by XRD, FT-IR, and elemental analysis; nitrogen adsorption isotherms, SEM and TEM images; and UV–vis DRS and photoluminescence spectra. Characterizations showed that S-pg-C3N4 possessed porous rod structure with a larger surface area (20–52m2/g) than that of bulk g-C3N4, and the surface area of the S-pg-C3N4 samples increased with the increase of heating temperature. Meanwhile, the trace sulfur remained in the framework of g-C3N4 formed sulfur doped g-C3N4, and the visible light absorption edge of the S-pg-C3N4 was extended, corresponding to a narrowed band gap. As a result, the S-pg-C3N4 samples exhibited an enhanced physical adsorption and photocatalytic activity in the degradation of Rhodamine B dye under visible light.

Sulfur-doped graphitic carbon nitride decorated with zinc phthalocyanines towards highly stable and efficient photocatalysis

A series of sulfur-doped graphitic carbon nitride (g-CNS) materials were prepared by thermal condensation of a high-quality thiourea and melamine under air atmosphere. When zinc phthalocyanine (ZnTNPc) was combined with g-CNS, the photocatalytic performance of ZnTNPc/g-CNS was 4.4 times higher than that of pure ZnTNPc under visible irradiation. More importantly, the ZnTNPc/g-CNS composites exhibited higher photocatalytic activity for the degradation of methylene blue than ZnTNPc/g-C3N4 under the same conditions. Some typical scavengers were added to identify the active species in the photocatalytic oxidation process. Mott-Schottky curve reveals that the introduction of sulfur atoms in the graphitic carbon nitride not only narrows the band gap but also results in a downshift of the conduction band. The mechanism of the enhanced photocatalytic activity of ZnTNPc/g-CNS is based on the synergetic effect between ZnTNPc and g-CNS, which causes a rapid photo induced charge separation and suppresses the possibility of recombination of electron-hole pairs. Our effects will provide a novel system to increase the number of active species participated in the photocatalytic process, and thus enhance the photocatalytic activity of carbon-based catalysts.

Sulfur-Doped g-C3N4/BiVO4 Composite Photocatalyst for Water Oxidation under Visible Light

To achieve sustainable utilization of solar energy, development of an efficient photocatalyst for water oxidation, the driving force of reductive solar fuel formation, is strongly needed. Herein, composite photocatalysts with bismuth vanadate (BiVO4) and sulfur-doped graphitic carbon nitride (SCN) are developed by using a one-pot impregnated precipitation method. Fourier transform infrared and X-ray photoelectron spectroscopy analyses demonstrate that the surface of SCN is oxidized during impregnation and the oxidized surface becomes the synthetic site for BiVO4 composition. Among the composites with various ratios, the B7S catalyst, which is our best achievement, shows an oxygen evolution rate of 750 μmol h–1 g–1 that is >2-fold higher than that of pristine BiVO4 (i.e., 328 μmol h–1 g–1) under identical reaction conditions [0.05 M AgNO3 aqueous solution under visible light irradiation (λ > 420 nm)]. The photonic efficiency of B7S is also measured as 19%. The mechanism behind this is the enhanced charge c...

Sulfur-doped graphitic carbon nitride decorated with graphene quantum dots for an efficient metal-free electrocatalyst

A rational assembly of graphene quantum dots in situ decorated onto sulfur-doped graphitic carbon nitride nanosheets for an efficient electrocatalyst.

Nanoporous sulfur-doped graphitic carbon nitride microrods: A durable catalyst for visible-light-driven H2 evolution

Nanoporous sulfur-doped graphitic carbon nitride microrods are prepared by direct thermal condensation of a high-quality melamine-trithiocyanuric acid supramolecular cocrystal under N2 atmosphere. The as-obtained carbon nitride material serves as a highly active photocatalyst for H2 evolution under visible-light irradiation, affording an activity about 9.3 times higher than that of the reference carbon nitride material that is prepared using melamine as the precursor. In addition, this material also exhibits satisfactory stability because there is no loss of catalytic activity after the catalytic H2 evolution for 60 h. The simultaneous achievement of the porosity, sulfur-doping and 1D morphology in the carbon nitride material as well as its superior photocatalytic activity, in turn, highlights the importance of the synthetic strategy reported herein.

Biomolecule-assisted synthesis of carbon nitride and sulfur-doped carbon nitride heterojunction nanosheets: An efficient heterojunction photocatalyst for photoelectrochemical applications.

A biomolecule-assisted pyrolysis method has been developed to synthesize sulfur-doped graphitic carbon nitride (CNS) nanosheets. During the synthesis, sulfur could be introduced as a dopant into the lattice of carbon nitride (CN). Sulfur doping changed the texture as well as relative band positions of CN. By growing CN on preformed sulfur-doped CN nanosheets, composite CN/CNS heterojunction nanosheets were constructed, which significantly enhanced the photoelectrochemical performance as compared with various control counterparts including CN, CNS and physically mixed CN and CNS (CN+CNS). The enhanced photoelectrochemical performance of CN/CNS heterojunction nanosheets could be ascribed to the efficient separation of photoexcited charge carriers across the heterojunction interface. The strategy of designing and preparing CN/CNS heterojunction photocatalysts in this work can open up new directions for the construction of all CN-based heterojunction photocatalysts.