P-doped g-C3N4 Research Articles

Phosphorus vapor assisted preparation of P-doped ultrathin hollow g-C3N4 sphere for efficient solar-to-hydrogen conversion

The design and synthesis of g-C3N4 with favourable physical-chemical architecture are important factors in influencing its photoactivity. Herein, a phosphorus (P) vapor assisted synthetic strategy was employed to fabricate the P-doped hollow g-C3N4 photocatalysts with ultrathin shell structure (< 25 nm in thickness). The doping of P and the compression of shell thickness of the hollow g-C3N4 were induced simultaneously by the P vapor during the heating process. The as-prepared P-doped ultrathin hollow g-C3N4 sphere (P/UH-CNS) photocatalysts exhibited enlarged surface area and light responsive range, and improved charge transportation efficiency by suppressing the charge recombination and self-trapping within g-C3N4. These resulted in a high photocatalytic hydrogen evolution rate of 9653 μmol h−1 g−1. The charge dynamics in this P/UH-CNS system was revealed in detail by using the ultrafast time-resolved spectroscopy.

Highly photocatalytic hydrogen generation over P-doped g-C3N4 with aromatic ring structure

Phosphorus doped g-C3N4 with aromatic ring structure (AS/P-CN) was successfully synthesized by a simple calcination method. Experimental results showed that the incorporated dopants promote the visible light absorption and the separation of charge carriers. AS/P-CN with optimal loading amounts of aromatic and phosphorus showed the highest hydrogen production rate of 550 μmol h−1 g−1, which is remarkably higher than that of pristine CN (120 μmol h−1 g−1). This work demonstrates that AS/P-CN are potential photocatalysts with effective solar energy conversion.

The synergistic effect of P doping and Ni(II) electron cocatalyst boosting photocatalytic H2-evolution activity of g-C3N4

Doping heteroatoms and coupling cocatalysts are an effective way toward enhancing photocatalytic activity of semiconductor-based photocatalysts. Herein, Ni(II) modified P-doped g-C3N4 (NiPCN) was successfully prepared by an ion impregnation and phosphidation method. The Ni(II) as the electron cocatalyst and P-doping lead to 10 times of H2 evolution activity (1213 μmol h−1 g−1) compared with pristine g-C3N4 photocatalyst (117 μmol h−1 g−1). Detailed experimental results together with theoretical study revealed that the P-doping and Ni(II) as an electron cocatalyst can speed up electron transfer, leading to an enhancement of photocatalytic activity. The ultrafast transient absorption spectroscopy results disclosed that the synergistic effect of Ni(II) as an electron cocatalyst and P doping helps to increase the carrier's lifetime, resulting in the efficient electron transfer and long-lived charge separation. It is believed that this work opens up a possible way for optimizing the separation of photoexcited carriers for photocatalytic H2-evolution. (~1761 ps) is much slower than that (τ2) of the CN (576 ps)

Embedding 1D WO3 Nanotubes into 2D Ultrathin Porous g-C3N4 to Improve the Stability and Efficiency of Photocatalytic Hydrogen Production

Recently, two-dimensional (2D) g-C3N4 has attracted great interest for visible-light-driven H2 production. Thinning, doping, and reticulation have been demonstrated as effective strategies to improve the efficiency of photocatalysis, but are a challenge for structural stability. Herein, a targeted method was implemented by embedding the one-dimensional (1D) WO3 nanotubes matrix into the frameworks of 2D porous g-C3N4 to form a porous P-doped g-C3N4 nanosheets/WO3 nanotubes (PCNS/WNT) by a flexible electrostatic self-assembly process. As a visible-light-sensitive photocatalyst, the as-prepared hybrids exhibited impressive performance for hydrogen generation, which was attributed to the advantages of synergetic mechanism owing to a higher specific surface area, more reaction active sites, enhanced light absorption, and a better photogenerated carrier separation. Interestingly, the insertion of 1D WO3 nanotubes not only accelerates electrons transfer along the 1D channel but also provides robust support for 2D porous g-C3N4 architecture. As a result, the maximum photocatalytic H2 evolution rate of PCNW-50 is 547 μmol g–1 h–1, which is about four times higher than that of pure PCNS, and there is no significant reduction of H2 production after five cycles. Moreover, this 2D/1D PCNS/WNT hybrid was first reported in the area of photocatalytic hydrogen evolution and provides ideas for designing novel stable architecture of photocatalyst.

First-principle calculations study of pristine, S-, O-, and P-doped g-C3N4 as ORR catalysts for Li-O2 batteries

In this work, we investigated the ORR process on the surface of graphitic carbon nitride (g-C3N4), S-, O-, and P-doped g-C3N4 by the DFT method. According to the results, the reaction begins with Li adsorption and the first adsorbed Li atom is probably trapped on the considered substrates so the ORR process was also investigated on the surface with one trapped Li atom. The overpotential of the discharge process was obtained as 0.41 V for g-C3N4.S and 0.84 V for g-C3N4.S/Li which indicates that g-C3N4.S could be a promising candidate for application in Li-O2 battery.

Solvent-free coupling of aldehyde, alkyne, and amine over a versatile catalyst: Ag-functionalized mesoporous S, P-doped g-C3N4

In the present study, we introduce mesoporous g-C3N4/Ag co-doped with P and S which was designed and acquired by using mesoporous silica (SBA-15) as a hard templating agent and thiourea and chitosan phosphate as the dopants. The prepared catalyst was completely identified by FT-IR (Fourier-transform infrared spectroscopy), XRD (X-ray powder diffraction), FE-SEM (field-emission scanning electron microscopy), EDX (energy-dispersive spectroscopy), TEM (transmission electron microscopy), and Raman spectroscopy. The efficiency of the synthesized catalyst was evaluated toward the three-component coupling reaction, frequently named as A3 coupling. The higher activity of the prepared catalyst is because of the synergistic effects of phosphorus and sulfur co-doped together with Ag deposition. The desired products were achieved by an environmentally safe catalyst under the optimized conditions in high yields and short reaction time ranges.

Self-assembly synthesis of phosphorus-doped tubular g-C3N4/Ti3C2 MXene Schottky junction for boosting photocatalytic hydrogen evolution

Establishing highly effective charge transfer channels in carbon nitride (g-C3N4) to enhance its photocatalytic activity is still a challenging issue. Herein, the delaminated 2D Ti3C2 MXene nanosheets were employed to decorate the P-doped tubular g-C3N4 (PTCN) for engineering 1D/2D Schottky heterojunction (PTCN/TC) through electrostatic self-assembly. The optimized PTCN/TC exhibited the highest hydrogen evolution rate (565 μmol h−1 g−1), which was 4.3 and 2.0 -fold higher than pristine bulk g-C3N4 and PTCN, respectively. Such enhancement may be primarily attributed to the phosphorus heteroatom doped and unique structure of 1D/2D g-C3N4/Ti3C2 Schottky heterojunction, enhancing the light-harvesting and charges’ separation. One-dimensional pathway of g-C3N4 tube and built-in electric field of interfacial Schottky effect can significantly facilitate the spatial separation of photogenerated charge carriers, and simultaneously inhibit their recombination via Schottky barrier. In this composite, metallic Ti3C2 was served as electrons sink and photons collector. Moreover, ultrathin Ti3C2 flake with exposed terminal metal sites as a co-catalyst exhibited higher photocatalytic reactivity in H2 evolution compared to carbon materials (such as reduced graphene oxide). This work not only proposed the mechanism of tubular g-C3N4/Ti3C2 Schottky junction in photocatalysis, but also provided a feasible way to load ultrathin Ti3C2 as a co-catalyst for designing highly efficient photocatalysts.

Tuning the strength of built-in electric field in 2D/2D g-C3N4/SnS2 and g-C3N4/ZrS2 S-scheme heterojunctions by nonmetal doping

Single photocatalysts usually exhibit unsatisfactory performance due to the serious recombination of photogenerated electron‒hole pairs. Combining two photocatalysts to construct S-scheme heterojunction could solve this problem. In S-scheme mechanism, the interfacial built-in electric field (IEF) provides a vital driving force for efficient charge separation. Modifying the IEF is a feasible strategy to further improve the photocatalytic activity. Herein, a novel idea of tuning the strength of IEF in 2D/2D graphitic carbon nitride (g-C3N4)/MS2 (M = Sn, Zr) S-scheme heterojunctions by nonmetal doping was developed by employing density functional theory calculation. Three nonmetal elements (O, P, and S) were severally introduced into g-C3N4/MS2 composites. Charge density difference suggested that O and S doping led to increased interfacial electron transfer, while P doping had minimal influence. As expected, the calculated field strength of O- and S-doped g-C3N4/MS2 composites was significantly larger than that of pristine and P-doped g-C3N4/MS2 composites. Therefore, O and S doping endowed g-C3N4/MS2 S-scheme heterojunctions with enhanced IEF and more thorough charge transfer. Correspondingly, the experimentally synthesized O-C3N4/SnS2 composite exhibited better photocatalytic H2-production activity than g-C3N4/SnS2 composite. This work proposed an original idea of employing proper nonmetal doping to magnify the advantage of S-scheme heterojunction in accelerating charge separation.

Computational and experimental evidence of Pd supported P-doped porous graphitic carbon nitride as a highly efficient and exceptionally durable photocatalyst for boosted visible-light-driven benzyl alcohol oxidation

Here, we present the low cost and environmentally friendly photocatalyst, P-doped porous g-C3N4/Pd (P-pCN/Pd) for the first time. The designed photocatalyst was fabricated successfully via thermal copolymerization of melamine in the presence of H3PO4 as a phosphorous source. In pursuance of comparison, a series of photocatalysts including bulk g-C3N4, g-C3N4 nanosheets, porous g-C3N4, N-doped porous g-C3N4, S-doped porous g-C3N4, P-doped porous g-C3N4, P-doped porous g-C3N4/Ag, P-doped porous g-C3N4/Cu, and P-doped porous g-C3N4/Pd were synthesized. Also, as a result of the calculation, it has appeared that the presence of Pd nanoparticles significantly makes the band gap narrower, facilitates the electron transfer, and increases the catalyst efficiency. Developing photocatalysts for the oxidation of organic materials hold considerable promise for the generation of high-value-added products such as benzaldehyde under visible light irradiation. All materials were characterized physico-chemically and the efficiency of the synthesized photocatalysts was evaluated toward catalyzing benzyl alcohol oxidation to benzaldehyde derivatives. The experiments uncovered that P-doped porous g-C3N4/Pd exhibits significant visible light activity at room temperature.

Photo-generated charges escape from P+ center through the chemical bridges between P-doped g-C3N4 and RuxP nanoparticles to enhance the photocatalytic hydrogen evolution

Many researches have shown that phosphorus doping can affect the photocatalytic activity, mainly because the incorporation of P atoms significantly alters the electronic, surface chemical, and properties of different semiconductors. However, excessive phosphorous doping will form the accumulation and recombination center of photo-generated charge carrier, thereby limiting the activity of photocatalytic reactions. In this work, we successfully prepared excessive P-doping g-C3N4 with ruthenium phosphide nanoparticles (RuxP/PCN), which had excellent performance of hydrogen evolution (1.94 mmol g−1 h−1). Specifically, C was replaced by P in the melon units of PCN and positive charge center (P+) was introduced, reinforcing the chemical connection between PCN and RuxP. In fact, excessive P+ centers became the traps and stacking centers of photo-generated carriers. However, due to the introduction of RuxP NPs, the accumulated charges in the P+ centers through the chemical bridges between PCN and RuxP NPs migrated to surface and then separated on RuxP NPs. Our research illustrates the mechanism of the accumulated charges caused by excessive phosphorus doping migrate to the surface and separate on phosphides, which can prolong the lifetime of photo-generated carriers. This result promoted the significant increase of photocatalytic hydrogen production activity. Our research clarifies the mechanism of excessive phosphorus doping and phosphides act on this photocatalytic system, which will provide a new way to design a photocatalytic system with higher HER performance.

Hydrothermally exfoliated P-doped g-C3N4 decorated with gold nanorods for highly efficient reduction of 4-nitrophenol

Au nanorods (AuNRs) decorated phosphorus doped graphitic carbon nitride AuNRs/g-C3N(4-x)Px-NS catalyst have been designed and prepared by a facile hydrothermal approach, which is useful for the efficient reduction of nitroaromatics in aqueous solution using NaBH4− as reductant. A series of conventional characterizations like X-ray diffraction, scanning/transmission electron microscopy, Electron dispersive scanning, elemental mapping, Fourier transform infrared FT-IR, photoluminescence, and X-ray photoelectron spectroscopy were used to identify the physicochemical properties of AuNRs/g-C3N(4-x)Px-NS. The catalytic activities of AuNRs/g-C3N(4-x)Px-NS nanohybrid were studied under different conditions, including the amount of catalyst, NaBH4 dosage, and various temperatures for reduction of 4-nitrophenol (40 mL, 3 mM). Results showed that AuNRs/g-C3N(4-x)Px-NS nanohybrid exhibited superior catalytic performance with turning over (TOF) of 967 for 4-nitrophenol reduction, which is impressively high. In addition, the catalyst exhibited the best performance in reducing the 4-nitrophenol in the shortest possible time. The recyclability and stability of AuNRs/g-C3N(4-x)Px-NS catalyst was also examined.

Activating Co nanoparticles on graphitic carbon nitride by tuning the Schottky barrier via P doping for the efficient dehydrogenation of ammonia-borane

A highly active Mott–Schottky nanocatalyst for the efficient dehydrogenation of ammonia-borane was constructed by rationally tuning the Schottky barrier of Co/PxCN (P-doped g-C3N4) via simply varying the doping amount of P atoms.

High surface area Nanoflakes of P-gC3N4 photocatalyst loaded with Ag nanoparticle with intraplanar and interplanar charge separation for environmental remediation

The photocatalytic performance of gC3N4 is majorly restricted by insufficient collection of photogenerated charges on the surface during reaction due to highly dense stacking of lamellar structures with lateral size ranging in microns. This deficiency can be overcome by forming thin nanoflakes by systematically breaking the weak bonds that hold the gC3N4 framework without destroying the basic heptazine unit. With this aim, herein, a combination of three different strategies was implemented to design and develop, Ag-loaded and P-doped gC3N4 nanoflakes (Ag3-P1-NF-gC3N4). Using a systematic synthesis method, bulk gC3N4 was first converted into thin nanosheets, followed by fragmentation into nanoflakes, with a planar size up to 100 nm. P doping to replace the corner C atoms in the gC3N4 matrix (forming PN bonds) and intercalation of plasmonic Ag nanoparticles within the interlayers also assists in the bifurcation of the stacked layers and formation of nanoflake morphology. These strategies result in a significant increase in BET surface area to ∼196 m2/g from 12 m2/g of bulk gC3N4. Improved inter-planar and intra-planar charge mobility was recorded as a result of the reduced sizes. Doping with P also causes higher absorption of the visible spectrum in gC3N4 while the formation of heterojunction with Ag nanoparticles induces efficient separation of photo-generated charges. All these promoting photo-physical properties lead to an outstanding photocatalytic activity towards degradation of aqueous pollutants with reaction rates ∼20 times higher than bulk gC3N4. Complete mineralization of the pollutant and formation of non-toxic byproducts was also confirmed with suitable chromatography techniques.

The synergy of thermal exfoliation and phosphorus doping in g-C3N4 for improved photocatalytic H2 generation

Photocatalytic H2 generation has been believed to be a hopeful technology to deal with the current energy shortage issue. Among multifarious photocatalysts, graphitic carbon nitride (g-C3N4) has acquired enormous interests in virtue of its numerous advantages, such as peculiar physicochemical stability, favorable energy band structure and easy preparation. However, the insufficient light response range, low specific surface area, and inferior charge separation efficiency make its photocatalytic activity still unsatisfactory. In this work, the thermal exfoliation method was taken to prepare the thin g-C3N4 nanosheets with significantly improved specific surface area, which can afford more reaction sites and shorten the charge migration distance. Moreover, phosphorus (P) doping in g-C3N4 nanosheets can greatly expand its light absorption, improve the conductivity and charge-transfer capability. Due to the synergistic effect of these two strategies, the optimal H2 generation performance of P-doped g-C3N4 nanosheets came up to 1146.8 μmol g−1 h−1, which improved 15, 2.94 and 2.62 times compared to those of original bulk g-C3N4, thermally exfoliated g-C3N4 and P-doped bulk g-C3N4, respectively. The synergistic effect will inspire the design of other photocatalytic systems to achieve the efficient photocatalytic H2 generation activity.

Enhanced Photocatalytic H2 Evolution over P-Doped g-C3N4 with Aromatic Rings Composites

Introduction Photocatalytic water splitting is a promising strategy to convert solar energy into chemical energy [1]. In recent years, graphitic carbon nitride (g-CN) has attracted attention due to its desirable properties, including nontoxicity, low cost, thermal stability and visible-light activity [2]. However, the photocatalytic activity of g-CN is limited by the high recombination rate of photoinduced electron-hole pairs [3,4]. In this study, phosphorus doped g-CN with aromatic rings (A/P-CN) composites were prepared. Those composites were evaluated by the photocatalytic hydrogen production under visible light (λ ≥ 420 nm) and characterized by some instrumental analysis. Results and Discussion In summary, A/P-CN composite photocatalysts with enhanced photocatalytic H2 evolution performance were successfully synthesized by the calcination of the mixture of urea, 1,3,5-hydroxy benzene and Cl6N3P3. The sample with optimal loading amounts of aromatic rings and phosphorus showed the highest H2 production rate of 550 μmol h-1 g-1, which was about 4.5 times higher than that of pristine g-CN (120 μmol h-1 g-1) (Figure 1). Thus, aromatic rings and phosphorus doped composites push the g-C3N4-based materials forward as the promising visible-light-active photocatalysts with high efficiency in the energy applications.

Highly effective degradation of imidacloprid by H2O2/ fullerene decorated P-doped g-C3N4 photocatalyst

In this work, P-doped g-C3N4 (PCN) was coupled with another conducting material, fullerene (C60). P doping led to an expansion in solar-light-responsive range, prolongation in charge carrier lifetime, facilitation in charge separation, and transportation, while on the other hand, C60 captured electrons from PCN and reduced the recombination of charge carrier. C60/PCN nanocomposites (with different C60 ratios) were successfully synthesized via a simple ultrasonic method for imidacloprid (IMI) pesticide degradation. Raman and N2-adsorption-desorption measurement techniques were implemented to scrutinize structural properties and the successful formation of the nanocomposite. The photocatalytic degradation of IMI signified a loading of 0.04 wt.% amount of C60 as its optimal concentration. Through Brunauer–Emmett–Teller (BET) isotherm, two times larger specific surface area was observed in 0.04 wt.% C60/PCN than PCN. 60 mg/mL and 1 × 10−4 M were witnessed as an optimal catalyst dose and pesticide concentration at pH 4. Addition of H2O2 enhanced photodegradation processes since it also served as a good electron acceptor, which boosted charge carrier separation. Photodegradation results confirmed that 0.04 wt.% C60/PCN/H2O2 and 0.04 wt.% C60/PCN nanocomposites exhibited 95 % and 91 % removal efficiency, respectively, which were higher than the percentages exhibited by other tested photocatalysts. A promising mechanism of C60/PCN nanocomposite against IMI degradation was also proposed, validating the role of h+, O2− and OH radicals in the photocatalytic process.

Constructing Internal Electric Field in g-C3N4 Significantly Promotes the Photocatalytic Performance for H2O2 Generation

Solar-to-H2O2 photocatalytic conversion has attracted increasing attention since H2O2 is a vital oxidizing reagent and the solar energy is inexhaustible and sustainable. Though it has been widely recognized that the photocatalytic performance for H2O2 generation could be enhanced through P incorporating into g-C3N4 framework, its intrinsic reason is still ambiguous. In the present work, internal electronic field (IEF) was ascertained to be constructed in the framework of P doped g-C3N4 (PDCN), and its intensity could be feasibly adjusted through changing the P doping amount. Particularly, PDCN-10, as the optimum photocatalyst synthesized when the P doping amount was 10%, possessed an IEF intensity of 3.1 times than the pristine g-C3N4, leading to 10.0-folds higher of H2O2 yield. The present research for the first time discloses the intrinsic reason for the promoted photocatalytic performance for H2O2 generation over P doped g-C3N4, thereby providing a new insight for the design of photocatalyst with satisfactory performance via constructing IEF.

Three-dimensional P-doped porous g-C3N4 nanosheets as an efficient metal-free photocatalyst for visible-light photocatalytic degradation of Rhodamine B model pollutant

As a typical metal-free photocatalyst, graphitic carbon nitride (g-C3N4) has attracted great attention for photocatalytic degradation of various organic pollutants. In this study, three-dimensional (3-D) phosphorus (P)-doped porous g-C3N4 nanosheets were prepared successfully via the thermal oxidation and element doping associated method. Abundant in-plane mesopores (from 2 nm to 50 nm), high specific surface area (202.9 cm2 g−1) and desirable P content (0.87%) were obtained for this 3-D P-doped porous g-C3N4 nanosheets. Taking Rhodamine B as a model pollutant, the photocatalytic properties of this 3-D P-doped porous g-C3N4 nanosheets photocatalyst were investigated, and the mechanism of photocatalytic degradation was also proposed. The 3-D P-doped porous g-C3N4 nanosheets showed the much enhanced visible-light photocatalytic activity, with Rhodamine B degradation ratio of 99.5% and a kinetic reaction rate constant of 0.120 min−1, compared to porous g-C3N4 nanosheets (58.2% and 0.031 min−1). The catalytic mechanism analysis shows that the active radicals of •OH and •O2− have strong oxidizing property, which can quickly decompose target organic dyes. The mesoporous structure and high P content of doping endowed photocatalyst with abundant active sites, high conductivity, and efficient separation of photoproduced electron-hole pairs.

P‐doped g‐C3N4 as an efficient photocatalyst for CO2 conversion into value‐added materials: a joint experimental and theoretical study

AbstractThe photocatalytic yield of g‐C3N4 for CO2 reduction was modified by phosphorus doping. Possible reaction pathways for CO2 reduction on the P‐doped g‐C3N4 (PCN) surface were investigated by density function theory calculations for the first time. The experimental results showed that P doping increases the carriers' lifetime, which improves the production of CH4 through the increase in the driving force of the electrons. The partial density of states of the PCN showed that the valence band maximum and conduction band minimum are composed of px, py, and, s orbitals of the N atoms and pz states of carbon, nitrogen, and phosphorus, respectively. Mechanism studies confirm that formic acid, formaldehyde, methanol, and methane are the most probable products. Methane, having positive adsorption energy, can be easily desorbed from the PCN surface, and the Gibbs activation energy of the final step is 1.98 eV. The formation of H2COOH is the rate‐determining step.

Controlled preparation of P-doped g-C3N4 nanosheets for efficient photocatalytic hydrogen production

Hydrogen production by photolysis of water by sunlight is an environmentally-friendly preparation technology for renewable energy. Graphitic carbon nitride (g-C3N4), despite with obvious catalytic effect, is still unsatisfactory for hydrogen production. In this work, phosphorus element is incorporated to tune g-C3N4's property through calcinating the mixture of g-C3N4 and NaH2PO2, sacrificial agent and co-catalyst also been supplied to help efficient photocatalytic hydrogen production. Phosphorus (P) doped g-C3N4 samples (PCN-S) were prepared, and their catalytic properties were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet diffuse reflection (UV-DRS) were used to study their structures and morphologies. The results show that the reaction rate of PCN-S is 318 μmol h−1 g−1, which is 2.98 times as high as pure carbon nitride nanosheets (CN) can do. Our study paves a new avenue, which is simple, environment-friendly and sustainable, to synthesize highly efficient P doping g-C3N4 nanosheets for solar energy conversion.