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.     

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 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.     

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).     

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.     

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.     

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst

Selective photocatalytic reduction of CO₂ has been regarded as one of the most amazing ways for re-using CO₂. However, its application is still limited by the low CO₂ conversion efficiency. This work developed a novel Pt/In₂O₃/g-C₃N₄ multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO₂ reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In₂O₃ and g-C₃N₄ acted as visible photocatalysts, in which porous g-C₃N₄ facilitated H₂ production from water splitting while the In₂O₃ nanosheets embedded in g-C₃N₄ pores favored CO₂ fixation and H adsorption onto the Lewis acid sites. Besides, the In₂O₃/g-C₃N₄ heterojunctions could efficiently inhibit the photoelectron–hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H₂ production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron–hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO₂ molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO₂ conversion was 63.1 μmol g⁻¹ h⁻¹ and could reach up to 736.3 μmol g⁻¹ h⁻¹ at 40 atm.

A multifunctional Pt/In₂O₃/g-C₃N₄ catalyst exhibited high activity and selectivity to HCOOH during CO₂ reduction owing to the synergy between visible-light harvesting, CO₂ activation, HER, and photoelectron–hole separation via heterojunctions.     

Regenerable g-C3N4–chitosan beads with enhanced photocatalytic activity and stability

In this study, a series of regenerable graphitic carbon nitride–chitosan (g-C₃N₄–CS) beads were successfully synthesized via the blend crosslinking method. The prepared beads were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The structural characterization results indicate that the g-C₃N₄ granules were uniformly distributed on the surface of the chitosan matrix, and the structures of g-C₃N₄ and CS are maintained. In addition, the prepared g-C₃N₄–CS beads exhibited efficient MB degradation and stability. The optimum photocatalytic activity of our synthesized g-C₃N₄–CS beads was higher than that of the bulk g-C₃N₄ by a factor of 1.78 for MB. The improved photocatalytic activity was predominantly attributed to the synergistic effect between in situ adsorption and photocatalytic degradation. In addition, the reacted g-C₃N₄–CS beads can be regenerated by merely adding sodium hydroxide and hydrogen peroxide. Additionally, the regenerated g-C₃N₄–CS beads exhibit excellent stability after four runs, while the mass loss is less than 10%. This work might provide guidance for the design and fabrication of easily regenerated g-C₃N₄-based photocatalysts for environmental purification.

In this study, a series of regenerable graphitic carbon nitride–chitosan (g-C₃N₄–CS) beads were successfully synthesized via the blend crosslinking method.     

Enhanced photocatalytic degradation of organic contaminants over a CuO/g-C3N4 p–n heterojunction under visible light irradiation

As a kind of metal-free organic semiconductor photocatalyst, g-C₃N₄ has been widely explored for use in photocatalysis. However, the low quantum yield, small absorption range, and poor conductivity limit its large-scale application. Introducing another kind of semiconductor, particularly an oxide semiconductor, can result in some unexpected properties, such as an improved change transfer, enhanced light absorption, and better conductivity. In this work, CuO/g-C₃N₄ is successfully prepared through an impregnation and post-calcination method. A series of measurements support the formation of an organic-inorganic hybrid p–n heterojunction at the CuO (p-type) and g-C₃N₄ (n-type) interface. Furthermore, the photoactivity of the composite is evaluated via photocatalytic NO removal and the visible degradation of rhodamine B (RhB). Results show that the photocatalytic properties of CuO/g-C₃N₄ are almost twice as high as those of g-C₃N₄. In comparative tests, the photocatalytic degradation performance of Mix-CuO/g-C₃N₄ (the mixture of CuO and g-C₃N₄ nanosheets prepared by mechanically mixing) is even lower than that of pure g-C₃N₄. The degradation of RhB is only 19.7% under visible light after 30 min of irradiation. The improvement in the photoactivity of CuO/g-C₃N₄ results from the built-in electric field close to the formed p–n heterojunction, which switches the electron transfer mechanism from a double-charge transfer mechanism to a Z-scheme mechanism. In addition, the formed p–n heterojunction favors charge transfer, and thus the photocatalytic performance is significantly improved.

The p–n heterojunction could enhance the photocatalytic RhB degradation performance of Cu/g-C₃N₄.     

Synthesis of Bi2O3/g-C3N4 for enhanced photocatalytic CO2 reduction with a Z-scheme mechanism

Bi₂O₃/g-C₃N₄ nanoscale composites with a Z-scheme mechanism were successfully synthesized by high temperature calcination combined with a hydrothermal method. These synthesized composites exhibited excellent photocatalytic performance, especially the 40 wt% Bi₂O₃/g-C₃N₄ composite, which produced about 1.8 times the CO yield of pure g-C₃N₄. The obtained products were characterized by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and so on. Characterization results revealed that Bi ions had well covered the surface of g-C₃N₄, thus restraining the recombination of electron–hole pairs and resulting in a stronger visible-light response and higher CO yield. In addition, the electron transfer process through the Z-scheme mechanism also promoted the photocatalytic activity.

Bi₂O₃/g-C₃N₄ composites were synthesized and used in photocatalytic reduction of CO₂ with a Z-scheme mechanism.     

Atomic layer deposition with rotary reactor for uniform hetero-junction photocatalyst,g-C3N4@TiO2 core–shell structures

A heterojunction of TiO₂ grown on g-C₃N₄ particles is demonstrated using atomic layer deposition (ALD), equipped with a specifically designed rotary reactor for maintaining stable mechanical dispersion of g-C₃N₄ particles during ALD. The photocatalytic activity of the g-C₃N₄@ALD-TiO₂ core–shell composites was examined using the degradation of rhodamine B dye under visible light irradiation. The optimal composite with 5 ALD cycles of TiO₂ exhibited the highest photocatalytic reaction rate constant among the composites with a range of ALD cycles from 2 to 200 cycles, which was observed to be 3 times higher than that of pristine g-C₃N₄ and 2 times higher than that of g-C₃N₄@TiO₂ composite prepared using a simple impregnation method. The ALD-TiO₂ were well-dispersed on the g-C₃N₄ surface, while TiO₂ nanoparticles were agglomerated onto the g-C₃N₄ in the g-C₃N₄@TiO₂ composite prepared by the impregnation method. This created uniform and stable heterojunctions between the g-C₃N₄ and TiO₂, thus, enhancing the photocatalytic activity.

A heterojunction of TiO₂ grown on g-C₃N₄ particles is demonstrated using atomic layer deposition (ALD), equipped with a specifically designed rotary reactor for maintaining stable mechanical dispersion of g-C₃N₄ particles during ALD.     

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.     

Continuous g-C3N4 layer-coated porous TiO2 fibers with enhanced photocatalytic activity toward H2 evolution and dye degradation

TiO₂/g-C₃N₄ composite photocatalysts with various merits, including low-cost, non-toxic, and environment friendliness, have potential application for producing clean energy and removing organic pollutants to deal with the global energy shortage and environmental contamination. Coating a continuous g-C₃N₄ layer on TiO₂ fibers to form a core/shell structure that could improve the separation and transit efficiency of photo-induced carriers in photocatalytic reactions is still a challenge. In this work, porous TiO₂ (P-TiO₂)@g-C₃N₄ fibers were prepared by a hard template-assisted electrospinning method together with the g-C₃N₄ precursor in an immersing and calcination process. The continuous g-C₃N₄ layer was fully packed around the P-TiO₂ fibers tightly to form a TiO₂@g-C₃N₄ core/shell composite with a strong TiO₂/g-C₃N₄ heterojunction, which greatly enhanced the separation efficiency of photo-induced electrons and holes. Moreover, the great length–diameter ratio configuration of the fiber catalyst was favorable for the recycling of the catalyst. The P-TiO₂@g-C₃N₄ core/shell composite exhibited a significantly enhanced photocatalytic performance both in H₂ generation and dye degradation reactions under visible light irradiation, owing to the specific P-TiO₂@g-C₃N₄ core/shell structure and the high-quality TiO₂/g-C₃N₄ heterojunction in the photocatalyst. This work offers a promising strategy to produce photocatalysts with high efficiency in visible light through a rational structure design.

TiO₂@g-C₃N₄ core/shell fibers with a continuous g-C₃N₄ layer packing around exhibit high photocatalytic efficiency toward H₂ production and RhB degradation due to the intimate core/shell structure with a high-quality TiO₂/g-C₃N₄ heterojunction.     

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.     

In situ growth of CuS nanoparticles on g-C3N4 nanosheets for H2 production and the degradation of organic pollutant under visible-light irradiation

The solar-to-fuel conversion using a photocatalyst is an ideal method to solve the energy crisis and global warming. In this contribution, photocatalytic H₂ production and organic pollutant removal using g-C₃N₄/CuS composite was demonstrated. Well dispersed CuS nanoparticles (NPs) with a size of about 10 nm were successfully grown on the surface of g-C₃N₄ nanosheet via a facile hydrothermal method. The as-prepared g-C₃N₄/CuS nanocomposite at an optimized loading exhibited a much higher visible light photoactivity, giving up to 2.7 times and 1.5 times enhancements in comparison to pure g-C₃N₄ for photocatalytic H₂ production and methylene orange (MO) degradation, respectively. These enhanced photocatalytic activities are attributed to the interfacial transfer of photogenerated electrons and holes between g-C₃N₄ and CuS, which leads to effective charge separation on both parts. That is, under the visible light irradiation, electrons in the valence band (VB) of g-C₃N₄ can directly transfer to the CuS NPs, which can act as an electron sink and co-catalyst to promote the separation and transfer of photo-generated electrons, thus significantly improving the photocatalytic efficiency.

A novel ternary g-C₃N₄/CuS photocatalyst shows a good photocatalytic H₂ production and methylene orange degradation under visible light.     

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.     

Enhanced catalytic degradation of amoxicillin with TiO2–Fe3O4 composites via a submerged magnetic separation membrane photocatalytic reactor (SMSMPR)

A novel photo-Fenton catalytic system for the removal of organic pollutants was presented, including the use of photo-Fenton process and a submerged magnetic separation membrane photocatalytic reactor (SMSMPR). We synthesized TiO₂–Fe₃O₄ composites as the photocatalyst and made full use of the magnetism of the photocatalyst to realize the recollection of the catalyst from the medium, which is critical to the commercialization of photocatalytic technology for wastewater treatment. The photo-Fenton performance of TiO₂–Fe₃O₄ is evaluated with amoxicillin trihydrate (AMX) as a target pollutant. The results indicate that the TiO₂–Fe₃O₄/H₂O₂ oxidation system shows efficient degradation of AMX. Fe₃O₄ could not only enhance the heterogeneous Fenton degradation of organic compounds but also allow the photocatalyst to be magnetically separated from treated water. After four reaction cycles, the TiO₂–Fe₃O₄ composites still exhibit 85.2% removal efficiency of AMX and show excellent recovery properties. Accordingly, the SMSMPR with the TiO₂–Fe₃O₄ composite is a promising way for removing organic pollutants.

With a TiO₂–Fe₃O₄ composite as the catalyst, amoxicillin was degraded via a photo-Fenton process using a submerged magnetic separation membrane photocatalytic reactor.     

Bi2O3 and g-C3N4 quantum dot modified anatase TiO2 heterojunction system for degradation of dyes under sunlight irradiation

A facile and feasible method was successfully utilized to incorporate Bi₂O₃ and g-C₃N₄ quantum dots on TiO₂ surface to synthesize a novel composite g-C₃N₄/TiO₂/Bi₂O₃. The photocatalytic activity of the composite g-C₃N₄/TiO₂/Bi₂O₃ for degradation of dyes under sunlight and UV light irradiation was evaluated. It possessed the higher photocatalytic performance than that of pristine TiO₂ or g-C₃N₄ under the same conditions. Under sunlight irradiation, the reaction rate constants of the g-C₃N₄/TiO₂/Bi₂O₃ was about 4.2 times and 3.3 times higher than that of TiO₂ and g-C₃N₄, respectively. The promising photocatalytic performance was attributed to the broader light absorption range and efficient separation of photoinduced carriers. Moreover, based on the TEM, XPS, XRD, UV-vis spectrum, radicals scavenging test and Mott–Schottky analysis systematic mechanism for photodegradation process was proposed. This work provides a promising strategy for the modification of TiO₂-based semiconductors by incorporating different quantum dots and promoting the efficiency of the photocatalysts in practical application.

A facile and feasible method was successfully utilized to incorporate Bi₂O₃ and g-C₃N₄ quantum dots on TiO₂ surface to synthesize a novel composite g-C₃N₄/TiO₂/Bi₂O₃.     

Fabrication of TiO2 on porous g-C3N4 by ALD for improved solar-driven hydrogen evolution

Porous graphitic carbon nitride (P-g-C₃N₄) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C₃N₄ showed 48% higher photocatalytic H₂ production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C₃N₄) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO₂ was uniformly deposited on P-g-C₃N₄ by 60–300 cycles of atomic layer deposition (ALD) to form the TiO₂@P-g-C₃N₄ composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO₂ and P-g-C₃N₄. Among all composites, the sample deposited with 180 ALD cycles of TiO₂ showed the highest H₂ production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C₃N₄ deposited with 180 cycles of TiO₂.

Schematic of Pt-loaded TiO₂@P-g-C₃N₄ 2D/2D heterojunction structure and the proposed mechanism of charge transfer for photocatalytic H₂ evolution.     

Graphitic carbon nitride with thermally-induced nitrogen defects: an efficient process to enhance photocatalytic H2 production performance

Graphitic carbon nitride (g-C₃N₄, CN) with nitrogen vacancies was synthesized by a controlled thermal etching method in a semi-closed air-conditioning system. The defect-modified g-C₃N₄ shows an excellent photocatalytic performance demonstrated by water splitting under visible light irradiation. With proper heat-treatment durations such as 2 h (CN2) and 4 h (CN4) at 550 °C, the hydrogen production rates significantly increase to 100 μmol h⁻¹ and 72 μmol h⁻¹, which are 11 times and 8 times the rate of the pristine CN (8.8 μmol h⁻¹) respectively. The excellent hydrogen production performance of nitrogen defect modified CN2 is due to the synergy effect of the decreased band gap, enlarged specific surface area and increased separation/migration efficiency of photoinduced charge carriers. This simple defect engineering method provides a good paradigm to improve the photocatalytic performance by tailoring the electronic and physical structures of g-C₃N₄.

An efficient thermal-treatment method was developed for the preparation of defect modified g-C₃N₄ with excellent photocatalytic H₂ production performance.