Effective Photocatalytic Activity of Sulfate-Modified BiVO4 for the Decomposition of Methylene Blue Under LED Visible Light

In this study, we investigated sulfate-modified BiVO4 with the high photocatalytic activity synthesized by a sol-gel method in the presence of thiourea, followed by the annealing process at different temperatures. Its structure was characterized by thermal gravimetric analysis (TGA), powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The BiVO4 synthesized in the presence of thiourea and calcined at 600 °C (T-BVO-600) exhibited the highest photocatalytic degradation efficiency of methylene blue (MB) in water; 98.53% MB removal was achieved within 240 min. The reaction mechanisms that affect MB photocatalytic degradation on the T-BVO-600 were investigated via an indirect chemical probe method, using chemical agents to capture the active species produced during the early stages of photocatalysis, including 1,4-benzoquinone (scavenger for O2-), ethylenediaminetetraacetic acid disodium salt (scavenger for h+), and tert-butanol (scavenger for HO•). The results show that holes (h+) and hydroxyl radicals (HO•) are the dominant species of MB decomposition. Photoluminescence (PL) measurement results of terephthalic acid solutions in the presence of BiVO4 samples and BiVO4 powders confirm the involvement of hydroxyl radicals and the separation efficiency of electron-hole pairs in MB photocatalytic degradation. Besides, the T-BVO-600 exhibits good recyclability for MB removal, achieving a removal rate of above 83% after five cycles. The T-BVO-600 has the features of high efficiency and good recyclability for MB photocatalytic degradation. These results provide new insight into the purpose of improving the photocatalytic activity of BiVO4 catalyst.

Urea and Melamine Formaldehyde Resin-Derived Tubular g-C3N4 with Highly Efficient Photocatalytic Performance

Construction of various nanostructure g-C₃N₄, especially those with a tubular structure, is gaining considerable research interest because of their large specific surface area, high carrier transport efficiency, and excellent mass transfer. In this study, a novel multistage tubular g-C₃N₄ (TCN) has been prepared by the copolymerization of melamine formaldehyde (MF) resin with urea. With the introduction of MF resin, the electrostructure of TCN and its hydrophilicity property have been obviously ameliorated, thereby enhancing its visible-light absorption and improving the interface contact between TCN and water. Moreover, photocurrent response and electrochemical impedance spectra indicate that the special multistage tubular structure facilitates the spatial charge transfer and photogenerated carrier separation. Thus, the as-prepared TCN exhibits excellent photoactivities under visible-light irradiation. Among the samples, TCN-0.1 shows the best performance. Its hydrogen evolution rate is approximately 7505 μmol·g^-1·h^-1, which is 6.05 times greater than that of g-C₃N₄ (prepared by urea at 600 °C), and its apparent quantum efficiency is nearly 19.2% at 400 nm. In addition, TCN is also endowed with outstanding visible-light performance and durability for the degradation of tetracycline and methyl orange. This work might provide a significant inspiration for the design of new, highly efficient g-C₃N₄-based materials and further deepen our understanding of the preparation of tubular photocatalysts.

A Unique Interactive Nanostructure Knitting based Passive Sampler Adsorbent for Monitoring of Hg2+ in Water

This work reports the development of ultralight interwoven ultrathin graphitic carbon nitride (g-CN) nanosheets for use as a potential adsorbent in a passive sampler (PAS) designed to bind Hg²⁺ ions. The g-CN nanosheets were prepared from bulk g-CN synthesised via a modified high-temperature short-time (HTST) polycondensation process. The crystal structure, surface functional groups, and morphology of the g-CN nanosheets were characterised using a battery of instruments. The results confirmed that the as-synthesized product is composed of few-layered nanosheets. The adsorption efficiency of g-CN for binding Hg²⁺ (100 ng mL⁻¹) in sea, river, rain, and Milli-Q quality water was 89%, 93%, 97%, and 100%, respectively, at natural pH. Interference studies found that the cations tested (Co²⁺, Ca²⁺, Zn²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Bi³⁺, Na⁺, and K⁺) had no significant effect on the adsorption efficiency of Hg²⁺. Different parameters were optimised to improve the performance of g-CN such as pH, contact time, and amount of adsorbent. Optimum conditions were pH 7, 120 min incubation time and 10 mg of nanosheets. The yield of nanosheets was 72.5%, which is higher compared to other polycondensation processes using different monomers. The g-CN sheets could also be regenerated up to eight times with only a 20% loss in binding efficiency. Overall, nano-knitted g-CN is a promising low-cost green adsorbent for use in passive samplers or as a transducing material in sensor applications.

Constructing a novel family of halogen-doped covalent triazine-based frameworks as efficient metal-free photocatalysts for hydrogen production

Halogens, as typical non-metal dopants, have attracted intensive interests for developing highly active photocatalysts. However, the essential factors and underlying mechanism of halogen modification are still unclear. Herein, we systematically report the development of halogen (F, Cl and Br)-doped covalent triazine-based frameworks (CTFs) via a facile thermal treatment of CTFs and an excess of ammonium halide. The introduction of halogen atoms endowed CTFs with multiple superior effects such as improved optical absorption, promoted charge migration, narrowed band gaps and tuned band positions. The newly developed halogen-doped CTFs showed remarkable photocatalytic activities for H₂ evolution under visible-light irradiation. Notably, the most enhanced photocatalytic performance was obtained with Cl-doped CTFs, which exhibited 7.1- and 2.4-fold enhancements compared to un-doped CTFs and Cl-doped g-C₃N₄, respectively. The electronegativity and atomic radius of the halogen atoms affected the modification of the optical and electronic properties, leading to different photocatalytic performances of F-, Cl- and Br-doped CTFs. The conclusions presented in this work will provide some new insights into the understanding of the doping effect for the improvement of the photocatalytic activity of halogen-doped CTF photocatalysts.

Highly sensitive detection of microcystin-LR under visible light using a self-powered photoelectrochemical aptasensor based on a CoO/Au/g-C3N4 Z-scheme heterojunction

Based on the unique photoelectrochemical properties of a CoO/Au/g-C₃N₄ Z-scheme heterojunction, a self-powered photoelectrochemical (PEC) aptasensor was constructed for the detection of microcystin-leucine arginine (MC-LR). Z-scheme heterojunctions can promote the separation of a photo-induced electron-hole pair, and the surface plasmonic resonance (SPR) of Au nanoparticles can significantly enhance the adsorption of visible light. Importantly, MC-LR molecules were captured by aptamers initially immobilized on the modified electrode due to their high affinity, and then oxidized by the photogenerated holes, which caused an amplified photocurrent signal, allowing the quantitative analysis of MC-LR by measuring the photocurrent intensity change. This PEC MC-LR aptasensor showed high sensitivity and selectivity within a wide linear response range from 0.1 pM to 10 nM and a detection limit of 0.01 pM. The application of this sensor in the analysis of lake water samples provided accurate results with a relative standard deviation (RSD) of 2.6%-4.2%.

Plasmon-assisted demolition of antibiotic using sono-photoreduction decoration of Ag on 2D C3N4 nanophotocatalyst enhanced with acid-treated clinoptilolite

In this study, the plasmon silver/bulk graphitic carbon nitride-clinoptilolite (denoted as: Ag/BCN-CLT) nanophotocatalysts synthesized using sono-photoreduction dispersion of Ag over C₃N₄ nanophotocatalyst with various contents of acid-treated clinoptilolite (10, 20, 40 wt%) that was employed in the tetracycline degradation, as the model antibiotic pollutant, using simulated solar-light radiation. X-ray diffraction, field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy-Dot mapping, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda, particle size distribution, and Ultraviolet-Visible diffuse reflectance spectroscopy analyses results showed a high quality of synthesis of nanophotocatalysts and good dispersion of particles on the surface of nanophotocatalyst. Using photodegradation results, the Ag/BCN-CLT(10) sample with 10 wt% of clinoptilolite showed a better tetracycline degradation efficiency (87.23%), which is a result of a high surface area of nanophotocatalyst due to the exerting sonication in synthesis procedure. Also, using Ag nanoparticles as a noble metal and creation of surface plasmon resonance effect, the edge of light absorption was shifted to the visible light region, which was proven by UV-Vis DRS results. Furthermore, the using of both Ag and acid-treated clinoptilolite had an efficient influence on decreasing band gap energy position. At last, the effect of different operational parameters and the reusable property of the photocatalyst have experimented. Finally, the suggested mechanisms of the tetracycline degradation reactions were drawn and were analyzed accurately.

Doping-Induced Hydrogen-Bond Engineering in Polymeric Carbon Nitride To Significantly Boost the Photocatalytic H2 Evolution Performance

Unlike graphene, graphitic carbon nitride (CN) polymer contains a weak hydrogen bond and van der Waals (vdWs) interactions besides a strong covalent bond, which controls its final morphology and functionality. Herein, we propose a novel strategy, hydrogen-bond engineering, to tune hydrogen bonds in polymeric CN through nonmetal codoping. Incorporation of B and P dopants breaks partial hydrogen bonds within the layers and simultaneously weakens the vdWs interaction between neighboring layers, resulting in ultrathin codoped CN nanosheets. The two-dimensional structure of the ultrathin sheet, broken hydrogen bonds, and incorporated dopants endow them with efficient visible light harvesting, improved charge separation, and increased active edge sites that synergistically enhance the photocatalytic activity of doped CN. Specifically, the B/P-codoped CN exhibits an extremely high hydrogen-evolution rate of 10877.40 μmol h^-1 g^-1, much higher than most reported values of CN. This work demonstrates that hydrogen bond engineering is an effective strategy to modify the structure and properties of polymers for various applications.

β-FeSe nanorods composited g-C3N4 with enhanced photocatalytic efficiency

A series of β-FeSe nanorods composited g-C3N4 were prepared. The structure, morphology, chemical state, photocatalytic activity, electrochemical impedance and photoluminescence of β-FeSe/g-C3N4 composites were well characterized. It is found that the decolourization rate of 3 wt% β-FeSe/g-C3N4 composites reaches 4.4 times than that of g-C3N4. The improved photocatalytic properties could be ascribed to the reduced recombination of photogenerated electrons and holes, which is derived from the excellent ability of β-FeSe to capture and transfer electrons. This work provides an alternative co-catalyst for decolourizing organic matter.

Effect of calcination on structure and photocatalytic property of N-TiO2/g-C3N4@diatomite hybrid photocatalyst for improving reduction of Cr(Ⅵ)

The N-TiO₂/g-C₃N₄@diatomite (NTCD) composite has been prepared through a simple impregnation method, using titanium tetrachloride as precursor and urea as nitrogen-carbon source. Then the effects of calcination temperature on structure, surface property and photocatalytic activity of the catalysts were investigated. And XRD, TEM, XPS, FTIR and UV-vis diffuse adsorption spectroscopy were used to characterize the obtained powders. The photocatalytic activity of the NTCD was evaluated through the reduction of aqueous Cr (VI) under visible light irradiation (λ > 400 nm). The results demonstrated that the nano-TiO₂ particles ranging from 15 to 30 nm in the crystal of anatase are well deposited on the surface of diatomite in the NTCD-500 which calcined at 500 °C for 2 h. Furthermore, the g-C₃N₄ with the lay thickness of 0.92 nm was attached to the surface of nano-TiO₂. The N-doped TiO₂ and g-C₃N₄ doped catalysts could co-enhance response in the visible light region and reduce band gap of NTCD-500 (Eg = 3.07 eV). And the NTCD-500 sample exhibited nearly 100% removal rate within 5 h for photocatalytic reduction of Cr (VI) which was higher activity than P25, crude TiO₂@diatomite and g-C₃N₄@diatomite.

Hollowsphere Nanoheterojunction of g-C3N4@TiO2 with High Visible Light Photocatalytic Property

In this work, g-C₃N₄@TiO₂ nanostructures with hollow sphere morphology, small grain size, high crystalline quality, and high surface area are successfully synthesized by the annealing method using melamine and hollowsphere precursor, which could be a universal method to synthesis hollow sphere nanoheterojunction. Excellent photocatalytic property was observed from the as-prepared g-C₃N₄@TiO₂ nanostructure with 466.43 μmol·g^-1·h^-1 hydrogen generation rate under visible light irradiation (>420 nm), which was 5.5 times as much as the control couple, nanoparticle nanoheterojunction g-C₃N₄@TiO₂. No apparent deactivation was found during the follow-up cycle performance test. The special morphology and the heterojunction construction contribute to both visible light absorption and photogenerated electron-hole pair separation efficiency and finally to the photocatalytic property. The content of g-C₃N₄ was proved to be an important parameter for the promotion of the photocatalytic property. Overlarge content may lead to lower photogenerated electron-hole pair separation efficiency.

Single-stranded DNA modified protonated graphitic carbon nitride nanosheets: A versatile ratiometric fluorescence platform for multiplex detection of various targets

Facile and cost-effective detection of multiple targets is essential for a variety of applications ranging from life sciences to environmental monitoring. Here, we report a versatile ratiometric fluorescence platform for multiple detection of various targets based on the conjugation of single-stranded DNA (ssDNA) with protonated graphitic carbon nitride nanosheets (Pg-C₃N₄ NSs). We demonstrate that intrinsic peroxidase-like activity of Pg-C₃N₄ NSs is enhanced by conjugating with ssDNA, and thus the oxidation of substrate o-phenylenediamine (OPD) is promoted in the presence of H₂O₂. The oxidation product 2,3-diaminophenazine (DAP) can deliver a new fluorescence signal at 564 nm, and concurrently quench the intrinsic fluorescence of conjugates ssDNA/Pg-C₃N₄ NSs at 443 nm upon excitation at 370 nm. The transformation of fluorescence provides us a novel strategy for ratiometric fluorescence-based analytical sensing. Taking ssDNA as the target-recognition element of the conjugates ssDNA/Pg-C₃N₄ NSs, we favorably present ratiometric fluorescence detection of various targets including heavy metal ions (Hg²⁺) and biomolecules (Aflatoxin B1 (AFB1) and adenosine triphosphate (ATP)) in real samples by varying the ssDNA sequences. The present work provides a new strategy to develop facile methods for quantitative determination of various analytes and uncovers an innovative horizon for Pg-C₃N₄ NSs-based sensing platform fabrication.

Mechanistic investigation in degradation mechanism of 5-Fluorouracil using graphitic carbon nitride

The present study reports the synthesis of metal-free polymeric catalyst, graphitic carbon nitride (g-C₃N₄), through sonochemical method followed by thermal treatment. The synthesized g-C₃N₄ was characterized using XRD, DRS, FESEM, TGA, EDX, etc. and the characterization results revealed that it possesses medium band-gap energy, high thermal and chemical stability. The photo-activity of the catalyst was also evaluated using degradation of 5-Fluorouracil under different experimental conditions. The results revealed that the addition of H₂O₂ during sonolysis process did not show any significant synergy. This is attributed to the low vapor pressure of H₂O₂ that does not allow it to diffuse into the cavitation bubble to produce OH radicals through sonolysis process. Using sono-hybrid process, more than 90% degradation was seen within 5 min of treatment with a rate constant of 3.95 × 10^-2 s^-1. In alkaline medium, 5-Fluorouracil degradation occurred through defluorination and subsequently substitution of -OH group to the aromatic ring leading to formation of intermediates such as 2-fluoro-3-oxopropanoic acid and urea. While sono-hybrid advanced oxidation processes (AOPs) helped towards complete mineralization through formation of smaller molecular compounds such as maleic acids, lactic acids, propanol, etc. On the other hand, the maximum synergy effect of ∼2.4 was seen for sonocatalysis process followed by hybrid-AOPs of (US + g-C₃N₄ + H₂O₂ + UVC) with a synergy factor of ∼2.2. Also, the synthesized catalyst exhibited the same catalytic activity even after 5 runs of sono-photocatalysis process for degradation of 5-Fluorouracil.

Graphitic carbon nitride (g-C3N4)-based photocatalysts for water disinfection and microbial control: A review

Microbial contamination in drinking water is of great concern around the world because of high pathogenic risks to humans. Semiconductor photocatalysis has aroused an increasing interest as a promising environmental remediation technology for water disinfection and microbial control. Among various photocatalysts, graphitic carbon nitride (g-C₃N₄), as a fascinating two-dimensional conjugated polymer consisting of low-cost, earth-abundant elements, has drawn broad attention as a robust, metal-free, and visible-light-active material in the fields of both environmental remediation and solar energy conversion. Photocatalytic applications of g-C₃N₄-based nanomaterials for water splitting, hydrogen production, carbon dioxide reduction, and pollutant degradation have been extensively investigated and systematically reviewed. In contrast, their antimicrobial properties have been explored more recently due to the complex structure and unique metabolism of living microorganisms compared with chemicals. The corresponding rapidly increasing research efforts in the last five years have inspired us to conduct the review. This review is the first to comprehensively summarize the progress in design and antimicrobial performance of g-C₃N₄-based photocatalysts for water disinfection and microbial control, involving not only bacteria but also viruses and microalgae. Moreover, the underlying inactivation mechanisms of photocatalysts for microorganisms are evaluated to provide further understanding of g-C₃N₄-based advanced disinfection processes. In addition, some exciting future opportunities and challenges at the forefront of this research platform are pointed out. It is expected that this review can pave a new avenue for the development of a facile, cost-effective, environmental-friendly, and sustainable disinfection alternative.

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

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.

Novel design of hollow g-C3N4 nanofibers decorated with MoS2 and S, N-doped graphene for ternary heterostructures

Herein, we newly design 1-dimensional ternary structure of HGCNF/MoS₂/SNG via a one-pot hydrothermal treatment at relatively low temperature and showed a higher double layer capacitance with HER activity.

Physicochemical exfoliation of graphene sheets using graphitic carbon nitride

The development of methods for the synthesis of graphene on a large scale at an affordable cost using less toxic materials has attracted significant interest in recent years.

Physical vapor deposition (PVD): a method to fabricate modified g-C3N4 sheets

We develop a method of physical vapor deposition (PVD) to fabricate modified g-C₃N₄ sheets with abundant defects.

Graphitic carbon nitride synthesized by simple pyrolysis: role of precursor in photocatalytic hydrogen production

g-C₃N₄ with structural defects and low polymerization synthesized by urea as the precursor for photocatalytic H₂ production under visible light.

Graphite-like carbon nitride quantum dot (CNQD)-modified Bi2MoO6 heterostructure with high visible-light photocatalytic activity

Here, g-C₃N₄ quantum dot (CNQDs)/Bi₂MoO₆ nanoheterostructures were successfully synthesized. The CNQDs/Bi₂MoO₆ nanocomposite exhibited enhanced photocatalytic activity.

Visible light-driven enhanced CO2 reduction by water over Cu modified S-doped g-C3N4

We synthesized Cu modified S-doped g-C₃N₄ thin sheets using calcination followed by a wet-impregnation method. The photocatalytic activity was studied for reduction of CO₂ to CO and CH₄ in the presence of water and a plausible mechanism is explained.

Heterostructured d-Ti3 C2 /TiO2/ g-C3 N4 Nanocomposites with Enhanced Visible-Light Photocatalytic Hydrogen Production Activity

The construction of a 2D-2D heterostructured composite is an efficient method to improve the photocatalytic hydrogen generation capability under visible light. In this work, simple heat treatment of a mixture of g-C₃ N₄ and delaminated Ti₃ C₂ was used to prepare a series of d-Ti₃ C₂ /TiO₂ /g-C₃ N₄ nanocomposites. The d-Ti₃ C₂ not only acted as the support layer and resource to glue the anatase TiO₂ particles and g-C₃ N₄ layers together but also served as the fast electron transfer channel to improve the photogenerated charge carriers' separation efficiency. By tuning the g-C₃ N₄ /d-Ti₃ C₂ mass ratio, heating temperature and soaking time, the d-Ti₃ C₂ /TiO₂ /g-C₃ N₄ nanocomposite 4-1-350-1 achieved an excellent H₂ evolution rate of 1.62 mmol h^-1  g^-1 driven by a 300 W Xe lamp with a 420 nm cutoff filter. The heterostructured composite photocatalyst was stable even after 3 cycles, representing excellent potential for the practical application in solar energy conversion.

Recent Progress in Constructing Plasmonic Metal/Semiconductor Hetero-Nanostructures for Improved Photocatalysis

Hetero-nanomaterials constructed by plasmonic metals and functional semiconductors show enormous potential in photocatalytic applications, such as in hydrogen production, CO2 reduction, and treatment of pollutants. Their photocatalytic performances can be better regulated through adjusting structure, composition, and components’ arrangement. Therefore, the reasonable design and synthesis of metal/semiconductor hetero-nanostructures is of vital significance. In this mini-review, we laconically summarize the recent progress in efficiently establishing metal/semiconductor nanomaterials for improved photocatalysis. The defined photocatalysts mainly include traditional binary hybrids, ternary multi-metals/semiconductor, and metal/multi-semiconductors heterojunctions. The underlying physical mechanism for the enhanced photocatalysis of the established photocatalysts is highlighted. In the end, a brief summary and possible future perspectives for further development in this field are demonstrated.

Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on Phosphorus-Doped Covalent Triazine-Based Frameworks

Seeking efficient visible-light-driven photocatalysts for water splitting to produce H₂ has attracted much attention. Chemical doping is an effective strategy to enhance photocatalytic performance. Herein, we reported phosphorus-doped covalent triazine-based frameworks (CTFs) for photocatalytic H₂ evolution. Phosphorus-doped CTFs were fabricated by a facile thermal treatment using easily available red phosphorus as the external phosphorus species. The introduction of phosphorus atoms into the frameworks modified the optical and electronic property of CTFs, thus promoting the generation, separation, and migration of photoinduced electron-hole pairs. Consequently, the photocatalytic H₂-production efficiency of phosphorus-doped CTFs was greatly improved, which was 4.5, 3.9, and 1.8 times as high as that of undoped CTFs and phosphorus-doped g-C₃N₄ calcined from melamine and urea, respectively.

Influence of g-C3N4 Precursors in g-C3N4/NiTiO3 Composites on Photocatalytic Behavior and the Interconnection between g-C3N4 and NiTiO3

In this study, composite photocatalysts were produced from NiTiO₃ and N₂-rich precursors (dicyandiamide, melamine, urea, and thiourea) under N₂ flow conditions. The goal of the study was to investigate the interaction between NiTiO₃ and the synthesized g-C₃N₄. The properties of the g-C₃N₄/NiTiO₃ (CNT) composites were different depending on the starting materials. Dicyandiamide and thiourea created strong connections with NiTiO₃ and resulted in the generation of Ti-N and Ti-O-S bonds. Urea and melamine, however, had difficulty forming g-C₃N₄ structures or interconnections with NiTiO₃. The Ti-N and Ti-O-S bridges in the composite photocatalysts led to increased photocatalytic activity as well as inhibition of the recombination rate. Additionally, the band diagrams of g-C₃N₄ prepared from dicyandiamide and thiourea exhibited positions suitable for the Z-scheme charge-transfer model with NiTiO₃, implying that the composite photocatalysts were applicable for photocatalytic degradation of organic contaminants under the visible-light irradiation. Higher reaction rate constants for the composites prepared with dicyandiamide and thiourea confirmed the significant role of the Ti-N/Ti-O-S bridge between g-C₃N₄ and NiTiO₃.