g-C3N4 Composites Research Articles

Visible-light-driven photocatalytic disinfection by S-scheme α-Fe2O3/g-C3N4 heterojunction: Bactericidal performance and mechanism insight

High-performance photocatalytic applications require to develop heterostructures between two semiconductors with matched band energy levels to facilitate charge-carrier separation. The S-scheme photocatalytic system has great potential to be explored, in terms of the improvement of charge separation, however, small efforts have been made in photocatalytic disinfection application. In this study, a non-toxic and low-cost S-scheme photocatalytic system composed of α-Fe2O3 and g-C3N4 was fabricated by in-suit production of g-C3N4 and firstly applied into water disinfection. The α-Fe2O3/g-C3N4 junction demonstrated an enhanced activity for photocatalytic bacterial inactivation, with the complete inactivation of 7 log10 cfu·mL-1 of Escherichia coli K-12 cells within 120 min under visible light irradiation. Its logarithmic bacterial inactivation efficiency was nearly 7 times better than that of single g-C3N4. The experimental results suggested that the effective prevention of charge-carrier recombination led to an improved generation of reactive oxygen species (ROSs), resulting in impressive disinfection performance. Moreover, the DNA gel electrophoresis experiments validated the reason for the irreversible death of bacteria, which was the leakage and destruction of chromosomal DNA. In addition, this S-scheme heterojunction also showed excellent photocatalytic disinfection performance in authentic water matrices (including tap water, secondary treated sewage effluent, and surface water) under visible light irradiation. Hence, the α-Fe2O3/g-C3N4 composite has great potential for sustainable and efficient photocatalytic disinfection applications.

Effect of thermal program on structure–activity relationship of g-C3N4 prepared by urea pyrolysis and its application for controllable production of g-C3N4

Graphitic carbon nitride (g-C3N4) can be easily prepared by urea pyrolysis; however, its properties are greatly affected by the thermal program used in the pyrolysis process, especially the heating rate, owing to the complexity of the pyrolysis reaction. In this work, the effects of three main parameters—pyrolysis temperature, heating time, and heating rate—on the structure and performance of g-C3N4 are systematically investigated, and the results are used to guide the controllable production of g-C3N4 to obtain suitable properties for application as a photocatalyst, adsorbent, or lubricant. The results show that urea pyrolysis follows the same reaction path regardless of the parameters. However, the polymerization reaction rate significantly affects the structure, morphology, and surface composition of g-C3N4, indicating a clear structure–activity relationship. Rapid heating produces g-C3N4 with loose thin layers, a larger surface area, more amino defects, and more conjugated structure; these characteristics promote adsorption and photocatalysis. Slow heating produces g-C3N4 with a higher polymerization degree, more complete layer structure, and tighter layer spacing, which is suitable for lubrication. A high pyrolysis temperature and long heating period further enhance the performance of g-C3N4. This study provides a reference for large-scale controllable production of g-C3N4 by urea pyrolysis.

Enhanced photodegradation ability and mechanism study of g-C3N4 by dual modified with sulfur-containing quantum dots doping after oxidization

A series of dual modified g-C3N4 (CN) composites were synthesized by integrating oxidation and doping quantum dots. Oxidation made the valance band and conduction band of the modified CN shifted to the opposite direction, resulting in higher redox activity. Meanwhile, the oxidized CN (O-CN) is more conducive to the deposition of SCNQDs due to electrostatic interaction. The introduction of sulfur-containing carbon nitride quantum dots (SCNQDs) can improve the light trapping ability and the separation efficiency of photogenerated charge-carriers. Moreover, quantum confinement effect of SCNQDs contributes to the upshift of valance band to enhance the reduction ability of composite (CN/SCNQDs), even though the band gap was not changed. The synergistic effect of dual modification made the composite (10:1-O-CN/SCNQDs) own the highest photodegradation rate of 1.43 mg/ (h·100 mg catalyst), which was 4.5, 2.0 and 1.9 times of CN, CN/SCNQDs and O-CN, respectively. Photodegradation mechanism of the composite was inferred that holes and superoxide radical played primary roles, whereas hydroxyl radical showed neglect effect. This work may provide some beneficial ideas for constructing high-performance co-modified organic photocatalysts.

Porous g-C3N4 and α-FeOOH bridged by carbon dots as synergetic visible-light-driven photo-fenton catalysts for contaminated water remediation

Merging photocatalysis with Fenton-like reaction provides a promising synergetic advanced oxidation technology for water treatment, whereas the rational design of efficient cooperative photo-Fenton system still remains a great challenge. In this study, a ternary α-FeOOH/carbon dots/porous g-C3N4 (α-FeOOH/CDs/p-GCN) composite is developed as visible-light-driven heterogeneous photo-Fenton catalyst for contaminated water remediation. α-FeOOH nanorods are in-situ grown on porous g-C3N4 substrates, among which CDs are intercalated as high-speed electron transmission bridges, simultaneously preventing the photogenerated electron-hole recombination and accelerating the Fe3+/Fe2+ redox cycle. The distinctive heterostructure and synergetic catalytic effect endow α-FeOOH/CDs/p-GCN with superior efficiency, reusability, and universality for recalcitrant pollutant elimination, the reaction rate of which is nearly 13.6, 7.3, 3.4, 1.4, and 5.1 times higher than that of α-FeOOH, bulk g-C3N4 (b-GCN), p-GCN, α-FeOOH/p-GCN, and α-FeOOH/CDs/b-GCN, respectively. The FeOOH/CDs/p-GCN also demonstrates excellent tolerance to realistic environmental matrices including deionized water, sea water, river water, wastewater, and underground water. HO• and •O2− radicals are proved to be the predominant contributors in the photo-Fenton system. This work provides an efficient synergetic visible-light-driven photo-Fenton catalyst possessing great potential for practical contaminated water remediation.

Insights into enhancement of photocatalytic properties of g-C3N4 by local electric field induced by polarization of MgO(111)

Photocatalysis has attracted worldwide attention in the fields of energy storage and environmental remediation. However, the solar-to-energy conversion efficiency is still low due to fast charge carrier recombination in the bulk phase of conventional photocatalysts. Herein, a series of photocatalysts including g-C3N4 (GCN), non-polar MgO(110)/GCN composite, MgO(110)+GCN mixture, polar MgO(111)/GCN composite, and MgO(111)+GCN mixture are prepared and their photocatalytic activities are investigated systematically. The polar and non-polar MgO improve the photocatalytic properties of GCN in the following order: MgO(111)+GCN>MgO(110)/GCN>MgO(111)/GCN>MgO(110)+GCN>GCN. Benefiting from charge carrier separation rendered by the local electric field (LEF) induced by MgO(111) polarization, MgO(111) improves the performance of GCN significantly when it is mixed with GCN. However, the enhancement effects are reduced when it is combined with or integrated into GCN as in the MgO(111)/GCN composite, where the traditional heterojunction effect constitutes the main enhancement mechanism. Our study reveals that the photocatalytic enhancement by the LEF effect is superior to that by the traditional heterojunction effect based on polar supporting materials. Our results offer insights into the enhancement mechanism of photocatalysts with polar supporting materials and reveal a simple strategy to optimize photocatalytic processes to exploit solar energy efficiently.

Efficient solar-light induced photocatalytic capacity of Mg-Al LDO coupled with N-defected g-C3N4

To enhance the photocatalytic activity of Mg-Al layered double oxide (LDO) for solar-light excited RhB removal, Mg-Al LDO coupling with N-defected g-C3N4 (Mg-Al@CN) composites were prepared using Mg-Al layered double hydroxide (LDH) and melamine as raw materials. Compared with Mg-Al LDO, Mg-Al@CN exhibited the better adsorption and photocatalytic capacity of RhB due to the combined effect between Mg-Al LDO and g-C3N4. The removal efficiency of RhB over optimal Mg-Al@CN-3 was 91.12% of 60 mg L-1 RhB solution within 120 min, and decreased to 86.11% after five cycles. The enhanced photocatalytic performance of Mg-Al@CN for RhB removal was due to the narrow band-gap structure, extending visible-light capture, and efficient transfer and separation of photo-generated carriers. •O2− radical was vital for the Mg-Al@CN assisted photocatalytic reaction.

Efficient peroxymonosulfate nonradical activity of Zn-Mn-Al2O3@g-C3N4 via synergism of Zn, Mn doping and g-C3N4 composite

Electronic structural engineering is critical to high-performance catalysis. However, it is difficult to achieve the best state with a single method to control the electronic structure. In this, Zn, Mn orbital hybridization, and polarization built-in electric field (heterostructure of g-C3N4 composite ZnMn-Al2O3) was used to control the electronic structure of Al2O3 to catalyze peroxymonosulfate to deal with environmental pollution. The obtained Zn-Mn-Al2O3@g-C3N4 (ZnMnAlO-CN) exhibits an intrinsic activity 71.1 times higher than that of Al2O3. Experiments and theoretical calculations have determined that the hybridization of Zn and Mn orbitals generates new orbitals that cross the Fermi level, and the polarization built-in electric field (polarization electric field) promotes the charge polarity on ZnMnAlO-CN. Orbital hybridization regulation and polarized electric field can coordinately adjust the electronic structure, thereby synergizing the non-radical reaction of surface reactive complexes and 1O2. The optimized catalytic mechanism shows good adaptability to pH, anions, and actual water bodies (tap water, surface water, and groundwater). It can stably remove environmental pollutants in continuous flow reaction. The coordinated use of multiple control methods is expected to provide ideas for releasing the inherent activity of the catalyst.

Ni-doped SnO2/g-C3N4 nanocomposite with enhanced gas sensing performance for the eff ;ective detection of acetone in diabetes diagnosis

Abstract The development of metal oxides semiconductor-based gas sensors for the accuracy detection of acetone in human exhaled breath is highly desirable for diabetes diagnosis. Herein, we use calcining and hydrothermal method to grow highly ordered Ni-doped SnO2 nanosheets onto g-C3N4 lamina. The prepared Ni-SnO2/g-C3N4 composite presents high gas response of 142.5 (Resistance ratio, defined as S = Rair/Rgas) toward 10 ppm acetone at the optimized operating temperature of 125 °C, under the environment temperature of 25 °C, 80 %RH. Moreover, the Ni-SnO2/g-C3N4 based senor also maintains fast response–recovery time, good stability and extraordinary humidity resistance for detecting acetone, including the theoretical detection limit (LOD) as low as 1.38 ppb. The greatly improved gas sensing properties of the Ni-SnO2/g-C3N4 composite can be due to the highly ordered hierarchical structure, Ni dopant and SnO2/g-C3N4 heterojunctions. We believe this novel Ni-SnO2/g-C3N4 nanocomposite promises to be a potential gas sensing material for diabetes diagnosis.

Facile preparation of metallic 1T phase molybdenum selenide as cocatalyst coupled with graphitic carbon nitride for enhanced photocatalytic H2 production

Low-cost, highly active and efficient alternative co-catalysts that can replace precious metals such as Au and Pt are urgently needed for photocatalytic hydrogen evolution reaction (HER). Herein, we show that 1T phase MoSe2 can act as the co-catalyst in the 1T-MoSe2/g-C3N4 composites and we synthesize this composite by a one-step hydrothermal method to promote photocatalytic H2 generation. Our prepared 1T-MoSe2/g-C3N4 composite exhibits highly enhanced photocatalytic H2 production compared to that of g-C3N4 nanosheets (NSs) only. The 7 wt%-1T-MoSe2/g-C3N4 composite presents a considerably improved photocatalytic HER rate (6.95 mmol·h−1·g−1), approximately 90 times greater than that of pure g-C3N4 (0.07 mmol·h−1 g−1). Moreover, under illumination at λ = 370 nm, the apparent quantum efficiency (AQE) of the 7 wt%-1T-MoSe2/g-C3N4 composite reaches 14.0%. Furthermore, the 1T-MoSe2/g-C3N4 composites still maintain outstanding photocatalytic HER stability.

Enhanced photocatalytic degradation of cationic and anionic dyes by Ag-modified g-C3N4 composite: Insights on different mechanisms under visible light

Ag/g-C3N4 was synthesized by thermopolymerization and photo-deposition methods, and the performance of Ag/g-C3N4 was evaluated by degrading cationic dye methylene blue (MB) and anionic dye tartrazine (TZ) under visible light. Results showed that the photocatalytic efficiency of Ag/g-C3N4 for MB and TZ was significantly improved compared with pristine g-C3N4. 80% of MB was removed in 120 min and TZ could be completely degraded in 90 min by Ag/g-C3N4. The improvement of photocatalytic efficiency can be ascribed to the better light absorption and lower recombination rate of e−/h+ after loading of Ag nanoparticles. The degradation efficiency of Ag/g-C3N4 for MB was improved as pH increased, while the efficiency for TZ was decreased at the same condition. This study also revealed the different photocatalytic mechanisms of MB and TZ. It showed that hole played a dominant role in degrading MB, while the degradation of TZ mainly relied on superoxide radical.

Efficient light-free activation of peroxymonosulfate by carbon ring conjugated carbon nitride for elimination of organic pollutants

Realizing graphitic carbon nitride (g-C3N4) being active in light-free heterogeneous catalysis remains a big challenge as a result of its inertness if not irradiated. Herein, we demonstrate the successful construction of g-C3N4-based in-plane heterostructure by intimately connecting g-C3N4 framework with carbon ring via strong π-conjugated bonds, which regulates the electron density distribution of the g-C3N4 composite. The optimized carbon ring conjugated carbon nitride (CCN0.1) with porous architecture and modulated electronic structure delivers admirable catalytic performance in peroxymonosulfate (PMS) activation without the need of light, with its specific activity being significantly superior to nonmetal-doped g-C3N4 and comparable to part of active nitrogen-doped carbon materials. Experimental data and theoretical results revealed the two domains of g-C3N4 with higher electron density and the conjugated carbon ring with lower electron density in CCN0.1 involve in PMS conversion accounting for PMS reduction and oxidation, respectively, which simultaneously facilitates dissolved oxygen reduction over the g-C3N4 field. Moreover, CCN0.1 shows robust stability in PMS activation, and meanwhile, the CCN0.1/PMS system exhibits potential effectiveness in actual industrial wastewater remediation. This work expands the range of nonmetallic g-C3N4-based materials for light-free activation of persulfate and deepens the mechanistic understanding of persulfate conversion process for wider environmental applications.

Facile fabrication of sulfur-doped Cu2O and g-C3N4 with Z-scheme structure for enhanced photocatalytic water splitting performance

Sulfur-doped copper oxide (S–Cu2O) and graphic carbon nitride (g-C3N4) composites are prepared with a facile in-situ generation method. The photophysical and physical properties of the S–Cu2O modified g-C3N4 hybrids are characterized to investigate how the S–Cu2O nanoparticles work with the g-C3N4 substrate. The sulfur doping strategy not only inhibits the photogenerated electrons and holes recombination but also stabilizes the photocatalysts compared to the precursor without sulfur doping treatment. The visible light photocatalytic hydrogen production is enhanced by 89% and the stability can still maintain 88.7% after 5 cycles. In addition, the Z-scheme configuration makes the composites capable of splitting water into H2 and O2 without using sacrificial reagent. With better performance in hydrogen production, the overall water splitting activity is improved as well.

ZIF-67 derived Co@NC/g-C3N4 as a photocatalyst for enhanced water splitting H2 evolution

Graphitic carbon nitride (g-C3N4), as the one of the most promising photocatalysts, usually relies on noble metal co-catalysts in the photocatalytic water splitting H2 evolution process, which greatly increases the use cost. Here, a zeolite imidazole framework (ZIF-67) derived Co@NC/g-C3N4 composite was constructed through facile thermal condensation of ZIF-67 and melamine. The obtained Co@NC/g-C3N4 composites can drive water splitting H2 evolution without any noble metal co-catalyst under simulated sunlight. The optimal sample exhibits the highest H2 evolution rate of 161 μmol g−1·h−1, which is 6 times of pure g-C3N4. The N doped carbon in carbonized ZIF-67 can not only quickly capture separated electrons from g-C3N4, but also serve as the co-catalyst. The well dispersed cobalt intermediate on carbonized ZIF-67 also play a role in promoting electron conversion. The formation of junction between carbonized ZIF-67 and g-C3N4 could promote quick charge carrier separation and transfer. This work provides a new idea for photocatalytic H2 evolution without noble metal co-catalysis.

Anthracene‐based g‐C 3 N 4 photocatalyst for regeneration of NAD (P)H and sulfide oxidation based on Z‐scheme nature

Direct conversion of sunlight into value-added chemicals through artificial photosynthesis has been recognized as one of the most promising ways to address the global energy needs and to utilize the sustainable energy source. Even though the various semiconducting materials have been used for the solar-driven production of chemicals, many experimental efforts have been still focusing on developing clean and reusable photocatalysts. In this study, we report the new metal-free graphitic carbon nitride (g-C3N4) composite including anthracene moieties as a primary photosensitizer. The morphological and electronic structure of anthracene-based g-C3N4 (An-g-C3N4) composite were characterized by optical spectroscopies, electrochemical measurements, and theoretical calculations based on density-functional theory. The An-g-C3N4 composite exhibited outstanding photocatalytic efficiency for the regenerations of NAD(P)H cofactors owing to the prominent charge-transferred character and the superb light absorption. This study demonstrates that the catalytic reaction employing the combination of An-g-C3N4 photocatalyst and Z-scheme nature would be a suitable option for artificial photosynthesis.

Graphitic carbon nitride embedded with graphene materials towards photocatalysis of bisphenol A: The role of graphene and mediation of superoxide and singlet oxygen

Composite photocatalysts comprising graphitic carbon nitride (g-C3N4) and graphene materials were synthesized and evaluated in the photocatalysis of bisphenol A (BPA) with a focus on elucidating the reaction mechanism. Embedding reduced graphene oxide (rGO) to g-C3N4 significantly accelerated the photocatalysis rate of BPA by three folds under visible light irradiation at neutral pH. We showed that rGO synthesized in intimate contact with g-C3N4 increased the surface areas and electrical conductivity of the g-C3N4 composites and promoted the electron-hole pair separation. The BPA photodegradation mechanism involved selective oxidants as superoxide (O2•−) and singlet oxygen (1O2) that were formed through one-electron reduction of O2 and the unique oxidation of O2•− by photogenerated hole (h+), respectively. The synthesized photocatalyst exhibited superior visible light photoreactivity to that of N-doped P25 TiO2, good photo-stability and reuse potential, and was operative in complex wastewater. rGO embedded g-C3N4 achieved good photomineralization of BPA at 80% in 4 h compared to 40% of bare g-C3N4. This study sheds light on the photocatalysis mechanism of BPA with a metal-free, promising rGO/g-C3N4 photocatalyst.

In-situ synthesis of ZnO modified g-C3N4 composite: a potential photocatalyst and adsorbent for waste water remediation

ABSTRACT In-situ synthesis of zinc oxide modified graphitic carbon nitride composite (in-situ ZnO-g-C3N4) was carried out via a one-step thermal condensation method where [ZnCl2.2{HONC(CH3)2}] was used as a precursor for zinc oxide while urea was taken as a source of g-C3N4. In another synthesis process, urea was also decomposed with ZnO nanoparticles to yield ZnO-g-C3N4 composite and urea alone decomposed to g-C3N4. The in-situ ZnO-g-C3N4 has a higher surface area, 128.68 m2/g as compared to ZnO-g-C3N4 (88.99 m2/g) and g-C3N4 (87.22 m2 /g). The enhanced photocatalytic activity performance of materials against MB i.e. in-situ ZnO-g-C3N4, 99.37%; ZnO-g-C3N4, 97.02% and g-C3N4, 92.12% degradation within 90 minutes in sunlight. The adsorption capacities towards Pb2+, Cd2+ and Cr3+ heavy metal ions on in-situ ZnO-g-C3N4 is 48.144 mg.g-1, 48.883 mg.g-1 and 40.108 mg.g-1; on ZnO-g-C3N4 is 43.043 mg.g-1, 45.005 mg.g-1 and 37.766 mg g-1;and ong-C3N4 is 39.057 mg.g-1, 41.495 mg.g-1 and33.855 mg.g-1.

Efficient photocatalytic degradation of doxycycline by coupling α-Bi2O3/g-C3N4 composite and H2O2 under visible light

Antibiotic pollutants have posed a huge threat to the ecological environment and human health. In this work, α-Bi2O3/g-C3N4 composite was prepared and coupled with H2O2 for the rapid and efficient degradation of doxycycline (DOX) in water under visible light irradiation. The composite exhibited enhanced photocatalytic activity and 80.5% of DOX could be degraded in 120 min. The addition of H2O2 significantly improved the degradation efficiency of DOX under visible light, resulting in 79.0% of it degraded within 30 min, and the degradation rate constant of DOX was 3.6 times than that without H2O2. On the one hand, the Z-scheme heterojunction of α-Bi2O3/g-C3N4 promoted the separation rate of photogenerated electron-hole pairs, thereby enhancing the photocatalytic activity of the composite. On the other hand, the improvement of photocatalytic efficiency also benefited from the extra hydroxyl radicals generated by the reaction of photogenerated electrons with H2O2 in the photocatalytic system. Free radicals trapping experiments and electron spin resonance tests proved that ▪ played prominent role in the degradation process. After adding H2O2, OH also became important active species. Cyclic degradation experiments demonstrated the recyclability of the composite photocatalyst in DOX elimination applications. This work provides an efficient, clean, and recyclable purification strategy for removing antibiotic contaminants from water.

CaAl2O4:Eu2+,Nd3+-coupled g-C3N4 composites as novel light-free photocatalyst for organic methyl orange (MO) degradation

CaAl2O4:Eu2+,Nd3+-coupled g-C3N4 composites as novel light-free photocatalyst for organic methyl orange (MO) degradation

Sensitive sandwich-type voltammetric immunosensor for breast cancer biomarker HER2 detection based on gold nanoparticles decorated Cu-MOF and Cu2ZnSnS4 NPs/Pt/g-C3N4 composite.

A sandwich-type sensitive voltammetric immunosensor for breast cancer biomarker human epidermal growth factor receptor 2 (HER2) detection was prepared. The electrochemical immunosensor was developed based on gold nanoparticles decorated copper-organic framework (AuNPs/Cu-MOF) and quaternary chalcogenide with platinum-doped graphitic carbon nitride (g-C3N4). Cu2ZnSnS4 nanoparticle (CZTS NP) quaternary chalcogenide with platinum (Pt)-doped g-C3N4 composite (Pt/g-C3N4) was tagged as CZTS NPs/Pt/g-C3N4. AuNPs/Cu-MOF composite was successfully synthesized by amidation reaction between AuNPs functionalized with amino group and Cu-MOFs containing carboxylic acid. After the conjugations of primer HER2 antibody and antigen HER2 protein to AuNPs/Cu-MOF as sensor platform, CZTS NPs/Pt/g-C3N4 composite was prepared by one-pot hydrothermal method. After immune reaction of 30min, the prepared HER2 immunosensor was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The developed immunosensor showed high sensitivity with a detection limit of 3.00fgmL-1. Additional properties of the voltammetric immunosensor are high selectivity, stability, reproducibility, and reusability.

Neodymium oxide (Nd2O3) coupled tubular g-C3N4, an efficient dual-function catalyst for photocatalytic hydrogen production and NO removal

Graphitic carbon nitride (g-C3N4) has emerged as a most promising photocatalyst, non-toxicity and low density, but it is plagued by low activity due to the small specific surface area and poor quantum efficiency. Morphological engineering and coupling with other materials to form hybrids have proven to be effective strategies for enabling high photocatalytic performances. Here, neodymium oxide (Nd2O3) coupled tubular g-C3N4 composites had been facilely synthesized by a solvent evaporation and high-temperature calcination method to realize efficient photocatalytic activity of hydrogen production and NO removal. A series of characterizations, such as XRD, ESR, in-situ DRIFTS, etc., were used to analyze the physical and chemical properties of the bifunctional photocatalyst, which demonstrated that the composite material had more active sites and a faster electron transfer rate. The optimal sample (1 wt% Nd2O3/CN-T) had a H2 generation rate of 4355.34 μmol·g−1·h−1, which was 9.46 times than that of original g-C3N4 obtained through heating melamine (CN-M). In addition, the NO removal rate was also 32.32% higher than that of original CN-M. On the basis of the above photocatalytic experimental results and characterizations, a possible mechanism or pathway was proposed and illustrated. This work could provide a feasible strategy to fabricate tubular g-C3N4-based composites with rare earth metal oxides (dual-factor regulation) to simultaneously enhance photocatalytic hydrogen production and NO removal efficiently (double application).