ZnO-embedded S-doped g-C3N4 heterojunction: mediator-free Z-scheme mechanism for enhanced charge separation and photocatalytic degradation

The design of UV-visible light active photocatalysts for organic pollutant removal is a challenging task. Herein, we have developed an LED light active ZnO-embedded S-doped g-C₃N₄ (SCN) heterojunction by a facile sol–gel assisted calcination method. The heterojunction between ZnO and SCN nanoparticles generates a Z-scheme photocatalyst, which helps to separate the photo-induced charge carriers in the opposite direction, and is beneficial for more visible light absorption for photocatalytic dye degradation. The composite heterojunction shows better photocatalytic redox in comparison with pristine nanomaterials. The enhanced degradation efficiency is attributed to the high production rate of ˙OH (hydroxyl) radicals during the photocatalysis process, which is analyzed by the TA test and elemental trapping experiment. Hence, we hope that this Z-scheme heterojunction provides a new way to develop UV-visible light active photocatalysts for environmental remediation applications.

We have developed the LED light active ZnO-embedded S-doped g-C₃N₄ (SCN) mediator free Z-scheme heterojunction photocatalyst for effective organic pollutant degradation.     

Facile assembly of novel g-C3N4@expanded graphite and surface loading of nano zero-valent iron for enhanced synergistic degradation of tetracycline

The two-stage removal process of tetracycline (TC) in aqueous solutions using a novel photocatalyst based on nano-zero-valent iron (NZVI), g-C₃N₄ and expanded graphite by carbon layer (EGC) is reported for the first time. The composite (NZVI/g-C₃N₄@EGC) exhibits remarkable adsorption, reduction ability and visible light activity over the reaction course. Compared with pristine g-C₃N₄ (25.9%) and pure NZVI (45.9%), NZVI/g-C₃N₄@EGC achieves high degradation efficiency of TC (98.5%) due to the formation of a heterogeneous photo-Fenton system. This study shows that synergistic effects are achieved in the reaction system, including maintaining the reduction ability of NZVI and enhancing the photocatalytic activity of g-C₃N₄ by facilitating the separation of photogenerated electrons (e⁻) and holes (h⁺). TC removal involved a two-stage process of adsorption–reduction and photo-degradation. The quencher experiments determined that holes (h⁺) and superoxide radicals (˙O₂⁻) are the major reactive species in the degradation of TC. The degradation pathways of TC were proposed based on the analysis of the intermediates. In addition, NZVI/g-C₃N₄@EGC revealed a high stability in a five-cycle test and good magnetic properties for facile separation from aqueous solutions. From an application viewpoint, NZVI/g-C₃N₄@EGC has favorable prospects in the direction of the photocatalytic degradation of antibiotic wastewater.

The two-stage removal process of tetracycline (TC) in aqueous solutions using a novel photocatalyst based on nano-zero-valent iron (NZVI), g-C₃N₄ and expanded graphite by carbon layer (EGC) is reported for the first time.     

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.     

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.     

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).     

Biomass porous carbon as the active site to enhance photodegradation of oxytetracycline on mesoporous g-C3N4

Graphitic carbon nitride (g-C₃N₄) is widely used in photocatalytic adsorption and degradation of pollutants, but there are still some problems such as low adsorption performance and high electron–hole recombination efficiency. Herein, we propose a new molten salt assisted thermal polycondensation strategy to synthesize biomass porous carbon (BPC) loaded on g-C₃N₄ composites (designated as BPC/g-C₃N₄) with a hollow tubular structure, which had a high surface area and low electron–hole recombination rate. The study shows that the morphology of g-C₃N₄ changes dramatically from massive to hollow tubular by molten salt assisted thermal polycondensation, which provides a base for the loading of BPC, to construct a highly effective composite photocatalyst. BPC loaded on g-C₃N₄ could be used as the active site to enhance Oxytetracycline (OTC) removal efficiency by adsorption and with higher electron–hole separation efficiency. As a result, the BPC(5%)/g-C₃N₄ sample presented the highest photocatalytic degradation efficiency (84%) for OTC degradation under visible light irradiation. The adsorption capacity and photocatalytic reaction rate were 3.67 and 5.63 times higher than that of the g-C₃N₄, respectively. This work provided a new insight for the design of novel composite photocatalysts with high adsorption and photocatalytic performance for the removal of antibiotic pollutants from wastewater.

A novel mesoporous g-C₃N₄ loaded with biomass porous carbon was synthesized by molten salt assisted thermal polycondensation, and the formation of hollow tubular structure increased the specific surface area.     

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.     

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.     

Highly dispersed NiS2 quantum dots as a promising cocatalyst bridged by acetylene black significantly improved the photocatalytic H2 evolution performance of g-C3N4 nanosheets

In this work, ternary nanocomposite (CNs–AB/NiS₂) as a novel efficient H₂ evolution photocatalyst without the use of noble metals was successfully synthesized by depositing acetylene black (AB) and ultra-fine NiS₂ nanoparticles on the surface of CNs (g-C₃N₄) through ultrasonic dispersion and chemical vapor deposition methods, respectively. It was revealed that the loaded AB and NiS₂ nanoparticles have significantly improved the photocatalytic H₂ evolution efficiency of the CNs by improving the photogenerated electron–hole pair separation, visible light absorption and hydrogen evolution kinetics. Besides acting as a cocatalyst, AB served as a conductive electron bridge between CNs and NiS₂, which accelerated the effective transfer of electrons from CNs to NiS₂ and improved the H₂ evolution kinetics of the NiS₂ cocatalyst. The H₂ evolution experiments revealed that the ternary photocatalyst CNs–AB/NiS₂10 displayed a H₂ evolution rate of up to 2434.85 μmoL g⁻¹ h⁻¹, which was a 1.41 times enhancement compared to that of the binary composite CNs–NiS₂10 and was 12.43 times higher than that of the pure CNs. Moreover, the ternary photocatalyst CNs–AB/NiS₂10 not only exhibited excellent photocatalytic activity and stability in the tests, but provided a novel idea for the development of high-efficiency catalysts free of noble metals as well.

We have successfully designed and synthesised a series of binary and ternary photocatalysts without noble metal cocatalysts for H₂ generation by dispersing NiS₂ and acetylene black nanoparticles on ultra-thin g-C₃N₄ nanosheets.     

Rational design direct Z-scheme BiOBr/g-C3N4 heterojunction with enhanced visible photocatalytic activity for organic pollutants elimination

A rapid recombination of photo-generated electrons and holes, as well as a narrow visible light adsorption range are two intrinsic defects in graphitic carbon nitride (g-C₃N₄)-based photocatalysts. Inspired by natural photosynthesis, an artificially synthesized Z-scheme photocatalyst can efficaciously restrain the recombination of photogenerated electron–hole pairs and enhance the photoabsorption ability. Hence, to figure out the above problems, BiOBr/g-C₃N₄ composite photocatalysts with different mass ratios of BiOBr were successfully synthesized via a facile template-assisted hydrothermal method which enabled the BiOBr microspheres to in situ grow on the surface of g-C₃N₄ flakes. Furthermore, to explore the origin of the enhanced photocatalytic activity of BiOBr/g-C₃N₄ composites, the microstructure, photoabsorption ability and electrochemical property of BiOBr/g-C₃N₄ composites were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS) and photocurrent (PC) response measurements. As a result, the introduction of BiOBr on g-C₃N₄ to constitute a direct Z-scheme heterojunction system can effectively broaden the light absorption range and promote the separation of photo-generated electron–hole pairs. Hence, compared with pure g-C₃N₄ and BiOBr, the resultant BiOBr/g-C₃N₄ composites exhibit the remarkable activity of photodegradated rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) under visible light irradiation. Simultaneously, the optimal BiOBr content of the BiOBr/g-C₃N₄ composites was obtained. The BiOBr/g-C₃N₄ composites exhibit an excellent photostability and reusability after four recycling runs for degradation RhB. Moreover, the active-group-trapping experiment confirmed that ·OH, ·O₂⁻ and h⁺ were the primary active groups in the degradation process. Based on the above research results, a rational direct Z-scheme heterojunction system is contrastively analyzed and proposed to account for the photocatalytic degradation process of BiOBr/g-C₃N₄ composites.

The morphology, electrochemical property, photoabsorption ability and photocatalytic activity of BiOBr/g-C₃N₄ composites are discussed. A rational photocatalytic mechanism is proposed.     

Highly efficient visible light active Cu–ZnO/S-g-C3N4 nanocomposites for efficient photocatalytic degradation of organic pollutants

The photocatalytic activity of photocatalysts is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺. In the current study, the photocatalytic efficiency of Cu–ZnO/S-g-C₃N₄ (CZS) nanocomposites was investigated against MB dye. The composite materials were designed via chemical co-precipitation method and characterised by important analytical techniques. Distinctive heterojunctions developed between S-g-C₃N₄ and Cu–ZnO in the CZS composite were revealed by TEM. The synthesized composites exhibit a huge number of active sites, a large surface area, a smaller size and better visible light absorption. The considerable enhancement in the photocatalytic activity of CZS nanocomposites might be accredited to the decay in the e–h pair recombination rate and a red shift in the visible region, as observed by PL and optical analysis, respectively. Furthermore, the metal (Cu) doping into the S-g-C₃N₄/ZnO matrix created exemplary interfaces between ZnO and S-g-C₃N₄, and maximized the photocatalytic activity of CZS nanocomposites. In particular, CZS nanocomposites synthesized by integrating 25% S-g-C₃N₄ with 4% Cu–ZnO (CZS-25 NCs) exhibited the 100% photocatalytic degradation of MB in 60 minutes under sunlight irradiation. After six cycles, the photocatalytic stability of CZS-25 NCs was excellent. Likewise, a plausible MB degradation mechanism is proposed over CZS-25 NCs based on photoluminescence and reactive species scavenger test observation. The current research supports the design of novel composites for the photocatalytic disintegration of organic contaminants.

The photocatalytic activity of photocatalyst is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺.     

The controlled synthesis of g-C3N4/Cd-doped ZnO nanocomposites as potential photocatalysts for the disinfection and degradation of organic pollutants under visible light irradiation

The in situ growth of well-dispersed Cd-doped ZnO nanoparticles (Cd-ZnO NPs) on graphitic carbon nitride (g-C₃N₄) nanosheets was successfully achieved through the co-precipitation method for the formation of Cd-doped ZnO nanocomposites with g-C₃N₄ (Cd-ZnO/g-C₃N₄ NCs). The effect of different compositions of ternary nanocomposites (Cd-ZnO/g-C₃N₄ NCs) on photocatalytic properties was investigated. Ternary NCs, in which 60% g-C₃N₄ hybridized with 7% Cd-doped ZnO (g-C₃N₄/Cd-ZnO) NCs were proven to be optimum visible-light-driven (VLD) photocatalysts for the degradation of methylene blue (MB) dye. The enhanced photodegradation of MB is mainly due to the increase in the generation of photogenerated charge carriers (reactive oxygen species (ROS), O²⁻, and ˙OH radicals). The electron spin resonance (ESR) experiment revealed that the superoxide and hydroxyl radicals were the leading species responsible for the degradation of MB. Moreover, the NC exhibited tremendous stability with a consistently high MB degradation rate for 10 successive catalytic cycles. The structural and optical properties of CdO, ZnO NPs, Cd-ZnO NPs, g-C₃N₄ NSs, and g-C₃N₄/Cd-ZnO NCs were investigated via XRD, SEM, EDX, TEM, FTIR spectroscopy, UV-Vis spectroscopy, ESR spectroscopy, and PL spectroscopy techniques. The synthesized photocatalysts were also applied against Gram-positive and Gram-negative bacterial strains to evaluate their antibacterial activities.

The controlled design of novel Z-scheme g-C₃N₄/Cd-ZnO heterojunction via chemical co-precipitation technique. 60% g-C₃N₄ hybridized with 7% Cd-doped ZnO (g-C₃N₄/Cd-ZnO) NCs have been proved to be optimum visible-light-driven (VLD) photocatalysts.     

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.     

Y2O3:Yb3+, Tm3+/ZnO composite with a heterojunction structure and upconversion function for the photocatalytic degradation of organic dyes

Endowing photocatalytic materials with a broader range of light responses is important for improving their performance and solar energy utilization. In this study, a simple sol–gel method was used to prepare Yb³⁺/Tm³⁺-co-doped Y₂O₃ upconversion materials and Y₂O₃:Yb³⁺, Tm³⁺/ZnO (Y/Z) composite photocatalysts for the photocatalytic degradation of dyes. The Y/Z composite photocatalyst achieved degradation rates of 38%, 95%, and 89% for methyl orange, methylene blue (MB), and acid chrome blue K dye solutions, respectively, within 30 minutes. The degradation efficiency for MB after three cycles of degradation was 86%. The spherical Y₂O₃:Yb³⁺, Tm³⁺ particles had diameters of 20–50 nm and attached to the ZnO nanosheets, forming a heterojunction structure with ZnO. Fluorescence spectroscopy showed that Y₂O₃:Yb³⁺, Tm³⁺ could convert near-infrared (NIR) light into three sets of ultraviolet light (290, 320, and 360 nm) under NIR excitation. Photoluminescence spectroscopy demonstrated that the photogenerated electron–hole pair recombination probability of the composite photocatalyst was significantly lower than that of ZnO nanosheets, thereby reducing the energy loss during the migration process. Furthermore, the addition of Y₂O₃:Yb³⁺, Tm³⁺ to ZnO substantially improved the absorption capacity for ultraviolet light, which enhanced the photocatalytic activity. A possible mechanism for the enhanced photocatalytic performance of the Y/Z composites was proposed based on the synergistic effect of heterojunction formation and the photoconversion process. The composite photocatalyst with upconversion characteristics and heterogeneous structure provides a new strategy for removing organic pollutants from water.

Upconversion heterojunction synergistic effect for photocatalytic degradation of organic pollutants.     

ZnO nanorod arrays grown on g-C3N4 micro-sheets for enhanced visible light photocatalytic H2 evolution

The designed synthesis of noble-metal-free photocatalysts with hierarchical heteroassemblies in a facile, mild and eco-friendly way becomes more and more important, because we can explore the novel properties and applications of novel heterostructures via this method. Herein we report a two-step aqueous strategy for novel hierarchical heterostructures of ZnO nanorod (NR) arrays grown on graphitic carbon nitride (g-C₃N₄). The novel g-C₃N₄/ZnO NR heterostructures that integrate g-C₃N₄ and ZnO NR via high-quality g-C₃N₄–ZnO heterojunctions have beneficial properties such as high specific surface area (SSA), open spatial architecture, good electronic conductivity, and effective charge transfer interfaces, and are promising in many related areas such as water splitting, solar cells, etc. As a noble-metal-free and visible-light-responsive photocatalytic material, a typical g-C₃N₄/ZnO NR photocatalytic system exhibits enhanced photocatalytic activity toward H₂ evolution, almost 3.5 times higher than that of pure g-C₃N₄. The superior photocatalytic property can be ascribed to the synergistic effect of the unique g-C₃N₄/ZnO NR heterostructures.

The designed synthesis of photocatalysts with hierarchical heteroassemblies in a facile, mild and eco-friendly way becomes more and more important, since we can explore the novel properties and applications of novel heterostructures via this method.     

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.     

One step synthesis of high-efficiency AgBr–Br–g-C3N4 composite catalysts for photocatalytic H2O2 production via two channel pathway

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized. XRD, UV-Vis, N₂ adsorption, TEM, XPS, EPR and PL were used to characterize the obtained catalysts. The as-prepared AgBr–Br–g-C₃N₄ composite catalyst shows the highest H₂O₂ equilibrium concentration of 3.9 mmol L⁻¹, which is 7.8 and 19.5 times higher than that of GCN and AgBr. A “two channel pathway” is proposed for this reaction system which causes the remarkably promoted H₂O₂ production ability. In addition, compared with another two-component modified catalyst, Ag–AgBr–g-C₃N₄, AgBr–Br–g-C₃N₄ composite catalyst displays the higher photocatalytic H₂O₂ production ability and stability.

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized.     

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.     

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.