An amorphous MoSx modified g-C3N4 composite for efficient photocatalytic hydrogen evolution under visible light

In this work, an MoS_x/g-C₃N₄ composite photocatalyst was successfully fabricated by a sonochemical approach, where amorphous MoS_x was synthesized using a hydrothermal method with Na₂MoO₄·H₂O, H₄SiO₄(W₃O₉)₄ and CH₃CSNH₂ as precursors, and g-C₃N₄ nanosheets were produced using a two-step thermal polycondensation method. The hydrogen-evolution performance of the MoS_x/g-C₃N₄ composite was tested under visible light. The results show that the H₂-evolution rate of the MoS_x/g-C₃N₄ (7 wt%) photocatalyst reaches a maximum value of 1586 μmol g⁻¹ h⁻¹, which is about 70 times that of pure g-C₃N₄ nanosheets. The main reason is that amorphous MoS_x forms intimate heterojunctions with g-C₃N₄ nanosheets, and the introduction of MoS_x into g-C₃N₄ nanosheets not only enhances the ability to convert H⁺ into H₂, but also promotes the separation of photoinduced electron–hole pairs for the photocatalyst. BET analysis shows that the specific surface area and pore volume of g-C₃N₄ are decreased in the presence of MoS_x. XPS analysis manifests that MoS_x provides a number of active sites. Mott–Schottky plots show that the conduction band of MoS_x (−0.18 V vs. E_Ag/AgCl, pH = 7) is more negative than that of g-C₃N₄ nanosheets.

An MoS_x/g-C₃N₄ composite photocatalyst was successfully fabricated by a sonochemical approach, where amorphous MoS_x was synthesized using a hydrothermal method, and g-C₃N₄ nanosheets were produced using a two-step thermal polycondensation method.     

Design of a p–n heterojunction in 0D/3D MoS2/g-C3N4 composite for boosting the efficient separation of photogenerated carriers with enhanced visible-light-driven H2 evolution

Constructing a 0D/3D p–n heterojunction is a feasible strategy for accelerating photo-induced charge separation and promoting photocatalytic H₂ production. In this study, a 0D/3D MoS₂/g-C₃N₄ (0D/3D-MCN) photocatalyst with a p–n heterojunction was prepared via a facile light-assisted deposition procedure, and the 3D spongy-like g-C₃N₄ (3D-CN) was synthesized through simple thermolysis of NH₄Cl and melamine mixture. For comparison, 2D-MoS₂ nanosheets were also embedded in 3D-CN by a solution impregnation method to synthesize a 2D/3D-MCN photocatalyst. As a result, the as-prepared 0D/3D-MCN-3.5% composite containing 3.5 wt% 0D-MoS₂ QDs exhibited the highest photocatalytic H₂ evolution rate of 817.1 μmol h⁻¹ g⁻¹, which was 1.9 and 19.4 times higher than that of 2D/3D-MCN-5% (containing 5 wt% 2D-MoS₂ nanosheets) and 3D-CN, respectively. The results of XPS and electrochemical tests confirmed that a p–n heterojunction was formed in the 0D/3D-MCN-3.5% composite, which could accelerate the electron and hole movement in the opposite direction and retard their recombination; however, it was not found in 2D/3D-MCN-5%. This study revealed the relationship among the morphologies of MoS₂ using g-C₃N₄ as a substrate, the formation of a p–n heterojunction, and the H₂ evolution activity; and provided further insights into fabricating a 3D g-C₃N₄-based photocatalyst with a p–n heterojunction for photocatalytic H₂ evolution.

A 0D/3D p–n heterojunction was formed in the MoS₂/g-C₃N₄ composite, which could promote the separation of electrons and holes efficiently.     

WS2/g-C3N4 composite as an efficient heterojunction photocatalyst for biocatalyzed artificial photosynthesis

A heterogeneous WS₂/g-C₃N₄ composite photocatalyst was prepared by a facile ultrasound-assisted hydrothermal method. The WS₂/g-C₃N₄ composite was used for photocatalytic regeneration of NAD⁺ to NADH, which were coupled with dehydrogenases for sustainable bioconversion of CO₂ to methanol under visible light irradiation. Compared with pristine g-C₃N₄ and the physical mixture of WS₂ and g-C₃N₄, the fabricated WS₂/g-C₃N₄ composite catalyst with 5 wt% of WS₂ showed the highest activity for methanol synthesis. The methanol productivity reached 372.1 μmol h⁻¹ g_cat⁻¹, which is approximately 7.5 times higher than that obtained using pure g-C₃N₄. For further application demonstration, the activity of the WS₂/g-C₃N₄ composite catalyst toward photodegradation of Rhodamine B (RhB) was evaluated. RhB removal ratio approaching 100% was achieved in 1 hour by using the WS₂/g-C₃N₄ composite catalyst with 5 wt% of WS₂, at an apparent degradation rate approximately 2.6 times higher than that of pure g-C₃N₄. Based on detailed investigations on physiochemical properties of the photocatalysts, the significantly enhanced reaction efficiency of the WS₂/g-C₃N₄ composite was considered to be mainly benefiting from the formation of a heterojunction interface between WS₂ and g-C₃N₄. Upon visible-light irradiation, the photo-induced electrons can transfer from the conduction band of g-C₃N₄ to WS₂, thus recombination of electrons and holes was decreased and the photo-harvesting efficiency was enhanced.

A heterogeneous WS₂/g-C₃N₄ composite photocatalyst was prepared by a facile ultrasound-assisted hydrothermal method.     

Novel magnetic g-C3N4/α-Fe2O3/Fe3O4 composite for the very effective visible-light-Fenton degradation of Orange II

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was successfully synthesized through a simple hydrothermal method. The structure, morphology, and optical properties of the catalyst were characterized. The photocatalytic activity of the heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst for the photo-Fenton degradation of Orange II in the presence of H₂O₂ irradiated with visible light (λ > 420 nm) at neutral pH was evaluated. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ photocatalyst was found to be an excellent catalyst for the degradation of Orange II and offers great advantages over the traditional Fenton system (Fe(ii/iii)/H₂O₂). The results indicated that successfully combining monodispersed Fe₃O₄ nanoparticles and g-C₃N₄/α-Fe₂O₃ enhanced light harvesting, retarded photogenerated electron–hole recombination, and significantly enhanced the photocatalytic activity of the system. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ (30%) sample gave the highest degradation rate constant, 0.091 min⁻¹, which was almost 4.01 times higher than the degradation rate constant for α-Fe₂O₃ and 2.65 times higher than the degradation rate constant for g-C₃N₄/α-Fe₂O₃ under the same conditions. A reasonable mechanism for catalysis by the g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was developed. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was found to be stable and recyclable, meaning it has great potential for use as a photo-Fenton catalyst for effectively degrading organic pollutants in wastewater.

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was firstly synthesized and exhibited very effective visible-light-Fenton degradation of Orange II at neutral pH.     

Effect of calcination temperature,pH and catalyst loading on photodegradation efficiency of urea derived graphitic carbon nitride towards methylene blue dye solution

In this study, the photodegradation of methylene blue (MB) dye was performed using urea based graphitic carbon nitride (g-C₃N₄). Interestingly, it has been observed that the calcination temperature for the synthesis of g-C₃N₄ along with factors (pH and catalyst loading) influencing the photodegradation process, can make an impactful improvement in its photodegradation activity towards MB dye solution. The concept behind the comparatively improved photoactivity of g-C₃N₄ prepared at 550 °C was explored using various characterisation techniques like XRD, FTIR, SEM, BET and DRS. The FTIR and XRD patterns demonstrated that synthesis of g-C₃N₄ took place properly only when the calcination temperature was above 450 °C. The evolution of morphological and optical properties based on calcination temperature led to dramatically increased BET surface area and a decreased optical band gap value of g-C₃N₄ prepared at 550 °C. The effects of pH conditions and catalyst concentration on the MB dye degradation rate using optimally synthesised g-C₃N₄ are discussed. The value of the apparent rate constant was found to be 12 times more in the case of photodegradation of the MB dye using g-C₃N₄ prepared at 550 °C at optimum pH and catalyst loading conditions when compared with g-C₃N₄ prepared at 450 °C showing the lowest photoactivity potential. Further, high stability of the photocatalyst was observed for four cyclic runs of the photocatalytic reaction. Hence, g-C₃N₄ can be considered as a potential candidate for methylene blue photodegradation.

The appropriate synthesis temperature and optimized photodegradation reaction conditions result in an appreciable enhancement of the photocatalytic activity of urea derived innate g-C₃N₄ towards MB dye degradation.     

A type II heterojunction α-Fe2O3/g-C3N4 for the heterogeneous photo-Fenton degradation of phenol

The heterogeneous photo-Fenton reaction is an effective method of chemical oxidation to remove phenol in wastewater with environmental friendliness and sustainability. Herein, the composite α-Fe₂O₃/g-C₃N₄, as a catalyst of the heterogeneous photo-Fenton reaction, has been synthesized by hydrothermal-calcination method using the abundant and low-cost FeCl₃·6H₂O and g-C₃N₄ as raw materials. The influence of the annealing temperature during calcination was also investigated. The UV-Vis diffuse reflectance spectra of samples show that the composite α-Fe₂O₃/g-C₃N₄ possesses the widest light response range. Furthermore, the transient photocurrent response curves demonstrated the strongest intensity of α-Fe₂O₃/g-C₃N₄. The annealed α-Fe₂O₃/g-C₃N₄ is indicative of the highest degradation efficiency in all samples due to the improvement of the charge transfer ability caused by the tight heterojunction structure. The results of the scavenger trapping experiments show that the hydroxyl radical was the main active species in degradation. Based on experimental results, a type II heterojunction should be built in the composite α-Fe₂O₃/g-C₃N₄, driving the photoelectrons transfer and migration by internal electronic field. This work provides a facile and new method to synthesize α-Fe₂O₃/g-C₃N₄ as an effective heterogeneous photo-Fenton catalyst for environmental remediation.

Composite α-Fe₂O₃/g-C₃N₄ with type II heterojunction to degrade phenol by heterogeneous photo-Fenton reaction.     

Enhanced photocatalytic hydrogen evolution and ammonia sensitivity of double-heterojunction g-C3N4/TiO2/CuO

The performance of semiconductor photocatalysts has been limited by rapid electron–hole recombination. One strategy to overcome this problem is to construct a heterojunction structure to improve the survival rate of electrons. In this context, a novel g-C₃N₄/TiO₂/CuO double-heterojunction photocatalyst was developed and characterized. Its photocatalytic activity for hydrogen production from water–methanol photocatalytic reforming was explored. Methanol is always used to eliminate semiconductor holes. The g-C₃N₄/TiO₂/CuO double-heterojunction photocatalyst with a narrow bandgap of ∼1.38 eV presented excellent photocatalytic activity for hydrogen evolution (97.48 μmol (g h)⁻¹) under visible light irradiation. Compared with g-C₃N₄/TiO₂ and CuO/TiO₂, the photocatalytic activity of g-C₃N₄/TiO₂/CuO for hydrogen production was increased approximately 7.6 times and 1.8 times, respectively. Below 240 °C, the sensitivity of g-C₃N₄/TiO₂/CuO to ammonia was approximately 90% and 46% higher than that of g-C₃N₄/TiO₂ and CuO/TiO₂, respectively. The enhancement of the photocatalytic activity and gas sensing properties of the g-C₃N₄/TiO₂/CuO composite resulted from the close interface contact established by the double heterostructure. The trajectory of electrons in the double heterojunction conformed to the S-scheme. UV-vis, PL, and transient photocurrent characterization showed that the double heterostructure effectively inhibited the recombination of e⁻/h⁺ pairs and enhanced the migration of photogenerated electrons.

The trajectory of electrons in the g-C3N4/TiO2/CuO double-heterojunction conforms to the S-scheme.     

2D–2D ZnO/N doped g-C3N4 composite photocatalyst for antibiotics degradation under visible light

ZnO and g-C₃N₄ provide excellent photocatalytic properties for degradation of antibiotics in pharmaceutical wastewater. In this work, 2D–2D ZnO/N doped g-C₃N₄ (NCN) composite photocatalysts were prepared for degradation of tetracycline (TC), ciprofloxacin (CIP) and ofloxacin (OFLX). The addition of ZnO resulted in higher separation efficiency and lower recombination rate of photogenerated charge under visible light. The composite photocatalyst showed better degradation performance compared to ZnO or NCN alone. The TC degradation reached 81.3% in 15 minutes by applying the prepared 20% ZnO/NCN composite photocatalyst, showing great competitiveness among literature reported g-C₃N₄ based photocatalysts. After 30 minutes, the degradation rate of TC, CIP and OFLX reached 82.4%, 64.4% and 78.2%, respectively. The TC degradation constant of the composite photocatalyst was 2.7 times and 6.4 times higher than NCN and CN, respectively. Radical trapping experiments indicated that ·O₂⁻ was the dominant active substance. The transference of excited electrons from the conduction band (CB) of NCN to ZnO enhanced the separation of photogenerated electron–hole pairs and simultaneously suppressed their recombination. This study provides a possibility for the design of high-performance photocatalysts for antibiotics degradation in wastewater.

2D–2D ZnO/N doped g-C₃N₄ (NCN) composite photocatalysts were prepared for degradation of antibiotics with high efficiency.     

Facile one-step hydrothermal synthesis of α-Fe2O3/g-C3N4 composites for the synergistic adsorption and photodegradation of dyes

With the expansion of industrialization, dye pollution has become a significant hazard to humans and aquatic ecosystems. In this study, α-Fe₂O₃/g-C₃N₄-R (where R is the relative percentage of α-Fe₂O₃) composites were fabricated by a one-step method. The as-prepared α-Fe₂O₃/g-C₃N₄-0.5 composites showed excellent adsorption capacities for methyl orange (MO, 69.91 mg g⁻¹) and methylene blue (MB, 29.46 mg g⁻¹), surpassing those of g-C₃N₄ and many other materials. Moreover, the ionic strength and initial pH influenced the adsorption process. Relatively, the adsorption isotherms best fitted the Freundlich model, and the pseudo-second-order kinetic model could accurately describe the kinetics for the adsorption of MO and MB by α-Fe₂O₃/g-C₃N₄-0.5. Electrostatic interaction and π–π electron donor–acceptor interaction were the major mechanisms for MO/MB adsorption. In addition, the photocatalytic experiment results showed that more than 79% of the added MO/MB was removed within 150 min. The experimental results of free-radical capture revealed that holes (h⁺) were the major reaction species for the photodegradation of MO, whereas MB was reduced by the synergistic effect of hydroxyl radicals (·OH) and holes (h⁺). This study suggests that the α-Fe₂O₃/g-C₃N₄ composites have an application potential for the removal of dyes from wastewater.

Simple one-step hydrothermal synthesis of α-Fe₂O₃/g-C₃N₄ composites for the synergistic adsorption and photodegradation of dyes     

Construction of a double heterojunction between graphite carbon nitride and anatase TiO2 with co-exposed (101) and (001) faces for enhanced photocatalytic degradation

This study aimed to promote the separation of photogenerated carriers and improve the redox performance of graphite carbon nitride (g-C₃N₄) by synthesizing a double-heterojunction-structure photocatalyst, g-C₃N₄/(101)-(001)-TiO₂, through the solvothermal method. The photocatalyst comprised a Z-system formed from g-C₃N₄ and the (101) plane of TiO₂, as well as a surface heterojunction formed from the (101) and (001) planes of TiO₂. The results showed that g-C₃N₄/(101)-(001)-TiO₂ had strong photocatalytic activity and stable performance in the photodegradation of paracetamol. The active species ·O₂⁻ and ·OH were found to play important roles in the photocatalytic degradation of paracetamol through a radical-quenching experiment. The charge-transfer mechanism was also described in detail. Overall, this work provided a new strategy for the Z-system heterojunction and opened up the application of this structure in the degradation of organic pollutants.

A double-heterojunction-structure photocatalyst g-C₃N₄/(101)-(001)-TiO₂ with Z-system and surface heterojunction, was synthesized, which can effectively promote the separation of photogenerated e⁻–h⁺ pairs and the degradation of organic pollutants.     

A dual polymer composite of poly(3-hexylthiophene) and poly(3,4-ethylenedioxythiophene) hybrid surface heterojunction with g-C3N4 for enhanced photocatalytic hydrogen evolution

A surface heterojunction catalyst of g-C₃N₄–PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as constructed g-C₃N₄–PEDOT/P3HT composite exhibits a photocatalyst H₂ evolution rate up to 427703.3 μmol h⁻¹ g⁻¹ which is 1059 times higher than that of g-C₃N₄, 118 times higher than that of g-C₃N₄–PEDOT with ascorbic acid as sacrificial reagents. What''s more, the g-C₃N₄–PEDOT/P3HT can even show an obviously enhanced photocatalytic H₂ evolution rate which is 6.1 times higher than that of pure g-C₃N₄ in pure water without any sacrificial reagent. Combining the experimental results and molecular dynamic (MD) simulation results, a possible mechanism can be drawn that the existed PEDOT possesses relatively higher hole mobility and can be used as a hole conductor between g-C₃N₄ and P3HT. Then, the photogenerated holes migration can be accelerated by PEDOT from the VB of g-C₃N₄ to the VB of P3HT. All those factors may benefit the synergy among g-C₃N₄, PEDOT and P3HT, which finally facilitates the rapid migration of photoinduced electron–hole pairs and eventually improves the photocatalytic H₂ activity process of g-C₃N₄–PEDOT/P3HT with visible light. The present work may provide useful insights for designing a surface heterojunction composite photocatalyst with high photocatalytic activity for H₂ production.

A surface heterojunction catalyst of g-C₃N₄-PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as prepared photocatalyst with much improved photocatalytic activity for H₂ production.     

Bimetallic zeolite-imidazole framework-based heterostructure with enhanced photocatalytic hydrogen production activity

Bimetallic zeolite-imidazole frameworks with controllable flat band position, band gap and hydrogen evolution reaction characteristics were adopted as a photocatalytic hydrogen production catalyst. Furthermore, the g-C₃N₄–MoS₂ 2D–2D surface heterostructure was introduced to the ZnM-ZIF to facilitate the separation as well as utilization efficiency of the photo-exited charge carriers in the ZnM-ZIFs. On the other hand, the ZnM-ZIFs not only inhibited the aggregation of the g-C₃N₄–MoS₂ heterostructure, but also improved the separation and transport efficiency of charge carriers in g-C₃N₄–MoS₂. Consequently, the optimal g-C₃N₄–MoS₂–ZnNi-ZIF exhibited an extraordinary photocatalytic hydrogen evolution activity 214.4, 37.5, and 3.7 times larger than that of the pristine g-C₃N₄, g-C₃N₄–ZnNi-ZIF and g-C₃N₄–MoS₂, respectively, and exhibited a H₂-evolution performance of 77.8 μmol h⁻¹ g⁻¹ under UV-Vis light irradiation coupled with oxidation of H₂O into H₂O₂. This work will furnish a new MOF candidate for photocatalysis and provide insight into better utilization of porous MOF-based heterostructures for hydrogen production from pure water.

The g-C₃N₄-MoS₂ could facilitate the separation as well as utilization efficiency of the photo-generated charge carriers in the ZnM-ZIFs, and hence improved the photocatalytic H₂ production with and without sacrificial agent.     

A visible light active,carbon–nitrogen–sulfur co-doped TiO2/g-C3N4 Z-scheme heterojunction as an effective photocatalyst to remove dye pollutants

Heterojunction formation and heteroatom doping could be viewed as promising strategies for constructing composite photocatalysts with high visible light catalytic activity. In this work, we fabricated a carbon, nitrogen and sulfur co-doped TiO₂/g-C₃N₄ (CNS-TiO₂/g-C₃N₄) Z-scheme heterojunction photocatalyst composite via one-step hydrothermal and calcination methods. Compared with pure TiO₂ and g-C₃N₄, the CNS-TiO₂/g-C₃N₄ Z-scheme heterojunction photocatalyst possessed excellent degradation performance under visible light irradiation. Due to the formation of the Z-scheme heterostructure, the utilization rate of the photogenerated electrons–holes generated by the catalyst was increased, which enhanced the catalytic activity. Moreover, the heteroatom doping (C, N and S) could efficiently tailor the band gap of TiO₂ and facilitate electron transition, contributing to enhancing the degradation ability under visible light. The CNS-TiO₂/g-C₃N₄-2 exhibited a superior photocatalytic degradation efficiency (k = 0.069 min⁻¹) for methyl orange dye (MO), which is higher than those of pure TiO₂ (k = 0.001 min⁻¹) and g-C₃N₄ (k = 0.012 min⁻¹), showing excellent photocatalytic activity against organic pollutants.

The CNS-TiO₂/g-C₃N₄ photocatalyst with excellent visible light catalytic activity was successfully manufactured, benefiting from the construction of the Z-scheme heterojunction and the co-doping of heteroatoms (C, N and S).     

Synthesis of a well-dispersed CaFe2O4/g-C3N4/CNT composite towards the degradation of toxic water pollutants under visible light

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route. CaFe₂O₄ acted as a photosensitizer medium and the CNT acted as a co-catalyst, which remarkably enhanced the photocatalytic performances of g-C₃N₄ towards the degradation of hexavalent chromium (Cr(vi)) and the antibiotic tetracycline (TC) under visible light irradiation. To investigate the morphological and topological features of the photocatalyst, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses were performed. The surface properties and oxidation state of the CaFe₂O₄/g-C₃N₄/CNT composite were determined by X-ray photoelectron spectroscopy (XPS). The recombination rate of the charge carriers and the band gap values of the as-synthesized catalysts were analyzed by photoluminescence spectroscopy (PL) and diffused reflectance spectroscopy (UV/Vis DRS) studies, respectively. Besides the degradation reactions, the high hydrogen production rate of 1050 μmol h⁻¹ under visible light using the CaFe₂O₄/g-C₃N₄/CNT composite loaded with 5 wt% CNT was observed. The superior photocatalytic performances of the CaFe₂O₄/g-C₃N₄/CNT composite can be ascribed to the effective heterojunction formed between g-C₃N₄ and the CaFe₂O₄ matrix, in which the CNT act as a conducting bridge in the system, promoting the production of photoinduced charge carriers in the semiconductor system. Finally, the plausible photocatalytic mechanism towards the degradation of pollutants and hydrogen production was discussed carefully.

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route.     

Evaluation of dual layered photoanode for enhancement of visible-light-driven applications

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C₃N₄ film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron–hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 × 10⁻³ min⁻¹, which is about four times faster than that of bare TCN film. Furthermore, we estimated the H₂ evolution of the dual layered film to be 44.9 μmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (∼50 ohm cm²) compared to the TCN film, the ternary structures and bulk g-C₃N₄ film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron–hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method.     

Construction of Z-scheme NiO/NiC/g-C3N4 composites using NiC as novel cocatalysts for the efficient photocatalytic degradation

A novel composite consisting of NiO/NiC/g-C₃N₄ with excellent photocatalytic properties was successfully synthesized by the simple calcination of layered double metal hydroxide (LDH) and melamine. The color and chemical composition of the as-prepared composites could be tailored by changing the mass ratio of NiAl-LDH and g-C₃N₄. For the L4C composite at the ratio of 1 : 1, it showed the desired dark color due to the generated NiC. It also showed high photodegradation efficiency under visible light irradiation, reaching 97.5% toward Rhodamine B and 92.6% toward tetracycline. The high photodegradation efficiency could be mainly attributed to the unique formation of NiC cocatalysts coupled with g-C₃N₄ and NiO semiconductors, which constructed a Z-scheme system and facilitated the efficient separation of the photogenerated electron–hole pairs. The present findings provide a promising approach for fabricating the new types of composite photocatalysts for pollutant degradation.

A novel composite consisting of NiO/NiC/g-C₃N₄ with excellent photocatalytic properties was successfully synthesized by the simple calcination of layered double metal hydroxide (LDH) and melamine.     

Tubular g-C3N4/carbon framework for high-efficiency photocatalytic degradation of methylene blue

The preparation of high-efficiency, pollution-free photocatalysts for water treatment has always been one of the research hotspots. In this paper, a carbon framework formed from waste grapefruit peel is used as the carrier. A simple one-step chemical vapor deposition (CVD) method allows tubular g-C₃N₄ to grow on the carbon framework. Tubular g-C₃N₄ increases the specific surface area of bulk g-C₃N₄ and enhances the absorption of visible light. At the same time, the carbon framework can effectively promote the separation and transfer of charges. The dual effects of static adsorption and photodegradation enable the g-C₃N₄/carbon (CNC) framework to quickly remove about 98% of methylene blue within 180 min. The recyclability indicates that the tubular g-C₃N₄ can stably exist on the carbon framework during the photodegradation process. In the dynamic photocatalytic test driven by gravity, roughly 77.65% of the methylene blue was degraded by the CNC framework. Our work provides an attractive strategy for constructing a composite carbon framework photocatalyst based on the tubular g-C₃N₄ structure and improving the photocatalytic performance.

Tubular g-C₃N₄ grown on a carbon framework increased the surface area of bulk g-C₃N₄, enhanced the absorption of visible light and promoted the photocatalytic performance.     

Synthesis and photocatalytic properties of visible-light-responsive,three-dimensional,flower-like La–TiO2/g-C3N4 heterojunction composites

We prepared a new three-dimensional, flower-like La–TiO₂/g-C₃N₄ (LaTiCN) heterojunction photocatalyst using a solvothermal method. Analysis and characterization were performed by conducting scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform-infrared spectroscopy, ultraviolet-visible spectrophotometry, and nitrogen adsorption and desorption. The prepared g-C₃N₄ nanosheets could reach 100 nm in size and covered the TiO₂ surface. A tightly bound interface formed between the g-C₃N₄ and TiO₂, speeding up the effective transfer of photo-induced electrons. In addition, the incorporation of La³⁺ reduced the electron–hole recombination efficiency. Consequently, the prepared La–TiO₂/g-C₃N₄ composite material exhibited better visible-light catalytic activity than pure TiO₂.

A new visible-light-responsive, three-dimensional, flower-like La–TiO₂/g-C₃N₄ heterojunction photocatalyst was prepared by a solvothermal method.     

Construction of g-C3N4 and FeWO4 Z-scheme photocatalyst: effect of contact ways on the photocatalytic performance

Photocatalysis has been regarded as an attractive strategy for the elimination of contaminants, but its performance is usually limited by the fast recombination of photogenerated electron–holes. A heterojunction photocatalyst could achieve the effective separation of electron–holes. However, the electrons migrate to the less negative band while holes move to the less positive band, leading to a weakened redox ability. Z-scheme photocatalysis is a feasible way to realize the efficient separation of photogenerated electron–holes without sacrificing the reductive ability of electrons and oxidative ability of holes. In this work, a new Z-scheme photocatalyst, composed of g-C₃N₄ (photocatalyst I), FeWO₄ (photocatalyst II) and RGO (electron mediator), was fabricated through a facile hydrothermal and mixing method. The effect of contact ways (the electron mediator firstly combined with photocatalyst I or with photocatalyst II) on the Z-scheme photocatalytic performance was investigated. The photocatalytic removal rate of rhodamine B (RhB) was largely enhanced by the construction of a Z-scheme photocatalyst, compared with the g-C₃N₄/FeWO₄ composite without RGO. The contact ways could affect the photocatalytic ability of a Z-scheme photocatalyst. The enhanced photocatalytic performance was attributed to the Z-scheme induced efficient separation of photogenerated charge carriers. Furthermore, remaining holes (on the VB of FeWO₄) or remaining electrons (on the CB of g-C₃N₄) with powerful oxidation or reduction ability would promote the photocatalytic degradation of RhB.

g-C₃N₄ (photocatalyst I), FeWO₄ (photocatalyst II) and RGO (electron media) constitutes a novel Z-scheme photocatalyst for effective RhB removal.     

MoS2 nanosheet mediated ZnO–g-C3N4 nanocomposite as a peroxidase mimic: catalytic activity and application in the colorimetric determination of Hg(ii)

A novel colorimetric sensing platform using the peroxidase mimicking activity of ternary MoS₂-loaded ZnO–g-C₃N₄ nanocomposites (ZnO–g-C₃N₄/MoS₂) has been developed for the determination of Hg(ii) ions over co-existing metal ions. The nanocomposite was prepared using an exfoliation process, and the product was further characterized using SEM, TEM, XRD and FTIR analysis. The ZnO–g-C₃N₄/MoS₂ possesses excellent intrinsic catalytic activity to induce the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in aqueous solution in the presence of H₂O₂ to generate deep blue coloured cation radicals (TMB⁺) which can be viewed with the naked eye and produce absorbance at a wavelength of 652 nm. The addition of a well known bioradical scavenger, glutathione (GSH), to the solution hinders the generation of cation radicals and turns the solution colourless. The introduction of Hg(ii) to this solution brings the blue colour back into it, due to the strong affinity of the thiol in the GSH. Based on this mechanism, we have developed a simple and rapid colorimetric sensor for the highly sensitive and selective detection of Hg(ii) ions in aqueous solution with a low detection limit of 1.9 nM. Furthermore, the prepared colorimetric sensor was effectively applied for the quantification analysis of real water samples.

A novel colorimetric sensing platform using the peroxidase mimicking activity of ternary MoS₂-loaded ZnO–g-C₃N₄ nanocomposites (ZnO–g-C₃N₄/MoS₂) has been developed for the determination of Hg(ii) ions over co-existing metal ions.