Unmodified g-C3N4 Research Articles

(Ag–NiO)/g-C3N4 with enhanced photocatalytic activity for hydrogen evolution under simulated sunlight

g-C3N4 is a promising metal-free photocatalyst for hydrogen production, whose application is difficult due to the low mobility of charge carriers and rapid electron-hole recombination. Here we propose a new route to improve its response to simulated sunlight and prevent electron-hole recombination by grafting mixed Ag–NiO (1:1 nominal Ag/NiO weight ratio) materials, as an alternative to platinum group metal co-catalysts. g-C3N4 was prepared by urea pyrolysis, whereas Ag–NiO was prepared by a co-precipitation method, and then the composites were prepared by physical mixing using sonication-grinding. The presence of Ag–NiO on the surface plays a key role in accepting excited electrons and enhancing their lifetime for a subsequent reduction of protons to hydrogen. Hydrogen production was carried out from the photoreforming of ethanol under simulated sunlight. The results revealed that 2% (Ag–NiO)/g-C3N4 is effective among others with 5.2 times higher H2 production than unmodified g-C3N4. The percentage of ethanol in the ethanol/water ratio is very important as we have found that with increasing its quantity, the evolution of hydrogen becomes significant.

Composite photocatalysts g-C<SUB>3</SUB>N<SUB>4</SUB>/TiO<SUB>2</SUB> for hydrogen production and dye decomposition

The photocatalytic activity of the g-C3N4 /TiO2 composite samples in the processes of dye (methylene blue) decomposition and hydrogen evolution from an aqueous ethanol solution under the action of visible radiation (400 nm) has been studied. A new original method for the synthesis of the g-C3N4 /TiO2 composite by depositing g-C3N4 /TiO2 to TiO2 nanoparticles during sol-gel synthesis is proposed. The synthesized photocatalysts were characterized by X-ray diffraction, low-temperature gas adsorption, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, and diffuse reflectance spectroscopy in the UV and visible regions. The maximum activity in the hydrogen evolution reaction was 1.3 mmol h–1, which exceeds the rate of hydrogen evolution on the unmodified g-C3N4 and TiO2 samples.

Synthesis of carbon nitride nanosheets with N vacancies boosted by S doping for photocatalytic efficient killing of E. coli under visible light

To address the problem of bacterial contamination in drinking water, we synthesized non-metallic photocatalysts for the inactivation of Escherichia coli in drinking water. In this paper, S-g-C3N4 (S-g-CN) composite nanomaterials were synthesized via a one-step calcination method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) analyses confirmed the successful synthesis of S-g-CN with N vacancies. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analyzed the layered morphology and chemical structure of g-C3N4 before and after modification. Optical characterization revealed significantly enhanced light absorption, electron-hole separation efficiency, and carrier mobility in the modified samples. Bactericidal assays demonstrated that under visible light, 0.3 % S-g-CN nanomaterials exhibited superior bactericidal effects against E. coli compared to unmodified g-C3N4. Furthermore, 0.3 % S-g-CN demonstrated excellent degradation of Rhodamine B (RhB) under various conditions (pollutant concentration, pH, and catalyst dosage). Recyclability studies over three cycles confirmed the catalyst's stability and reusability.

Conductive Co1.5MoS3.2 promoted photocatalytic H2 production over g-C3N4.

In this work, Co1.5MoS3.2 (CMS) nanoparticles were synthesized using a one-step hydrothermal approach, series CMS/g-C3N4 photocatalysts with various CMS amount were obtained using a physical solvent evaporation method. The investigation indicates that introducing CMS as cocatalysts can greatly enhance the H2 production activity of g-C3N4 by two orders of magnitude. The H2 production rate reaches up to 17607 μmol·g−1·h−1 over 40 wt% CMS/g-C3N4, resulting in a 185-fold increase when compared to the unmodified g-C3N4 (94.8 μmol·g−1·h−1), far better than 40 wt% MoS2/g-C3N4 (125.2 μmol·g−1·h−1), 40 wt% Co3S4/g-C3N4 (7948.6 μmol·g−1·h−1), even widely 3 wt% Pt/g-C3N4 (12803 μmol·g−1·h−1). The improvement can be ascribed to the Schottky junction effect between CMS and g-C3N4, the highly conductive CMS can receive electrons from the conduction band of g-C3N4, preventing charge recombination. Meanwhile, CMS can obviously lower the H2 evolution potential and provide more active site for the H2 evolution reaction, those all lead to a faster H2 evolution kinetics. Additionally, CMS as a cocatalyst offers advantages such as simple preparation, low cost, and remarkable effectiveness, making it highly promising for further development.

Au/Ti3C2/g-C3N4 Ternary Composites Boost H2 Evolution Efficiently with Remarkable Long-Term Stability by Synergistic Strategies.

The use of novel two-dimensional MXene materials and conventional g-C3N4 photocatalysts to fabricate the composites for hydrogen evolution reaction (HER) has attracted much attention, for which there is plenty of room for the enhancement of hydrogen evolution rates particularly under visible light and photostability. Herein, g-C3N4 was modified by copolymerization of malonamide and melamine and used to fabricate the ternary composites of Au particles and Ti3C2 MXene, and based on the synergistic effect, the composites enhanced the hydrogen evolution rates by 2.1, 99.8, and ∞ times compared with the unmodified g-C3N4 under UV, simulated sunlight, and visible light illumination, respectively. Moreover, the composite exhibited a sustained hydrogen evolution capacity in the cycle test for up to 120 h. Theoretical calculations and experimental results indicated that the hot electrons of Au are injected into the modified g-C3N4 and transferred to Ti3C2 simultaneously along with the photogenerated electrons of the modified g-C3N4 and then further transferred to Au, forming a photogenerated electron transfer channel of Au and modified g-C3N4 → Ti3C2 → Au within the composite. Ti3C2 acts as a bridge for fast separation of photogenerated electrons and holes on Au and modified g-C3N4, playing a key role in the enhanced photocatalytic performance. In addition, the visible light absorption ability of Au also positively contributed to the enhancement of visible light photocatalytic performance by providing hot electrons. Therefore, the selection of suitable cocatalysts for the design of composites is a crucial research direction to improve the photocatalytic performance and photostability of photocatalysts.

Carbon dots prepared from waste wood and residual adhesive and their use as catalysts for hydrogen production

Large quantities of waste wood with residual resin adhesives are not recycled efficiently. To address this issue, waste wood with residual resin adhesives was synthesized into carbon dots (CDs) via a facile hydrothermal self-assembly method to enhance the H2 evolution performance of graphite C3N4 (g-C3N4), a metal-free photocatalyst. Among all samples, the most significant enhanced sample was MCN-UF-3.5, which has an H2 evolution of 22.1 mmol·g-1·h-1, which is 3.91 times that of unmodified g-C3N4. The band gap and recombination of photogenerated charges were both improved by the doping of CDs. Meanwhile, the DFT calculation showed that adding CDs, especially with the -NH2 group, can significantly deform the structure and destroy the symmetry. This consequence implies an enhancement in the activity of the hydrogen evolution reaction, confirming the feasibility of the modification.

Ionic liquids assisted synthesis of graphite carbon nitride for one-pot aerobic oxidation of cyclohexane to adipic acid

Adipic acid (AA) is a crucial intermediate in the production of nylon monomers, which is generally obtained by the oxidation of cyclohexane. However, difficult C-H activation and easy overoxidation make it extremely challenging to obtain highly selective AA. Herein, ionic liquid (IL) assisted synthesis of graphitic carbon nitride (g-C3N4) was designed for one-pot oxidation of cyclohexane to AA. The incorporation of C and S elements and the formation of N vacancies were brought with the presence of IL. 26.1% conversion and 51.2% AA selectivity were achieved over [Bmim][HSO4] (1-Butyl-3-methylimidazolium hydrogen sulfate) modified g-C3N4, which significantly increased AA selectivity by 18% compared to unmodified g-C3N4. The changes in electronic structure of g-C3N4 were assumed resposible for the improvement of AA selectivity by increasing the adsorption of cyclohexanone. Besides, the reduction of alkaline sites caused by the introduction of S atoms and N vacancies was benefit to remove AA avoiding excessive oxidation.

Pt nanoclusters modified porous g-C3N4 nanosheets to significantly enhance hydrogen production by photocatalytic water reforming of methanol

For the use of green hydrogen energy, it is crucial to have efficient photocatalytic activity for hydrogen generation by water reforming of methanol under mild conditions. Much attention has been paid to g-C3N4 as a promising photocatalyst for the generation of hydrogen. To improve the separation of photogenerated charge, porous nanosheet g-C3N4 was modified with Pt nanoclusters (Pt/g-C3N4) through impregnation and following photo-induced reduction. This catalyst showed excellent photocatalytic activity of water reforming of methanol for hydrogen production with a 17.12 mmol·g−1·h−1 rate at room temperature, which was 311 times higher than that of the unmodified g-C3N4. The strong interactions of Pt–N in Pt/g-C3N4 constructed effective electron transfer channels to promote the separation of photo-generated electrons and holes effectively. In addition, in-situ infrared spectroscopy was used to investigate the intermediates of the hydrogen production reaction, which proved that methanol and water eventually turn into H2 and CO2via formaldehyde and formate. This study provides insights for understanding the photocatalytic hydrogen production in the water reforming of methanol.

Convenient fabrication of ultrafine VOx decorated on porous g-C3N4 for boosting photocatalytic degradation of pharmaceuticals with peroxymonosulfate

While VOx-based catalysts attracted extensive attention as Fenton-like catalysts for organic transformations, they remain underutilized in the area of the wastewater treatment by coupling photocatalysis with peroxymonosulfate (PMS) oxidation. Herein, we report VOx sites anchored on porous g-C3N4 that functions as a reusable heterogeneous photocatalyst for the efficient activation of PMS to decompose and mineralize pharmaceuticals in water. The VOx hybrid nanomaterials were synthesized by a facile and cheap route via a thermal polymerization and mild ammonium metavanadate decomposition process, which successfully immobilized ultrafine VOx on the porous carbon nitride. Systematic characterizations displayed that the interaction of VOx clusters and porous g-C3N4 could effectively speed up the charge carriers separation and restrain the recombination of photoexcitons. The ultrafine VOx species offered abundant active sites for PMS activation to produce active radicals under light, which had strong oxidating ability to degrade pharmaceutical pollutions. The V(V)/V(IV) recycle also ensured the continuous production of reactive oxygen species (ROS). Owing to these merits, VOx-based catalysts presented outstanding catalytic activity and stability in the pharmaceuticals decomposition with PMS and simulated sunlight. The removal rate of carbamazepine (CBZ) can reach >99% within 15 min in the PMS system with 8%VOx@CN catalyst under optimized conditions, nearly 12.8 times as much as unmodified g-C3N4. This study offers a promising candidate to efficiently eliminate organic pharmaceuticals in wastewater, which is suitable for practical application.

One-Pot Preparation of Imidazole-Ring-Modified Graphitic Carbon Nitride Nanozymes for Colorimetric Glucose Detection

Nanozymes are highly desired to overcome the shortcomings of natural enzymes, such as low stability, high cost and difficult storage during biosensing applications. Herein, by imitating the structure of natural enzymes, we propose a one-pot annealing process to synthesis imidazole-ring-modified graphitic carbon nitride (g-C3N4-Im) with enhanced peroxidase-like activity. g-C3N4-Im shows enhanced peroxidase-like activity by 46.5 times compared to unmodified g-C3N4. Furthermore, imidazole rings of g-C3N4-Im make it possible to anchor Cu(II) active sites on it to produce g-C3N4-Im-Cu, which shows a further increase in peroxidase-like activity by three times. It should be noted that the as-prepared g-C3N4-Im-Cu could show obvious peroxidase-like activity over a broad range of pH values and at a low temperature (5 °C). The ultrahigh peroxidase-like activity is attributed to the electronic effect of imidazole rings and the active sites of Cu(II) for ·OH production. Based on the enhanced peroxidase-like activity, a H2O2 and glucose biosensor was developed with a high sensitivity (limit of detection, 10 nM) and selectivity. Therefore, the biosensor shows potential for applications in diabetic diagnoses in clinical practice.

Constructing benzene ring modified graphitic carbon nitride with narrowed bandgap and enhanced molecular oxygen activation for efficient photocatalytic degradation of oxytetracycline

Popular graphitic carbon nitride (g-C3N4) photocatalyst always faces the problems of weak visible light absorption and fast recombination of photogenerated electron-hole pairs. Herein, a novel benzene ring modified g-C3N4 nanosheet (BCNNS) was synthesized by a simple calcination method. The degradation rate of oxytetracycline by BCNNS under visible light can reach 72% (within 60 min), significantly higher than that of the unmodified g-C3N4 nanosheet (50%). And the degradation rate constant of BCNNS is 0.025 min−1, which is 2.1 times higher than that of g-C3N4 (0.012 min−1). The improvement in the photocatalytic degradation performance can be attributed to the introduction of benzene ring, which can significantly broaden the light absorption range and intensify. In addition, the introduction of benzene ring can adjust the original electronic structure, thereby effectively suppressing the recombination of electron-hole pairs. Furthermore, density functional theory (DFT) calculations demonstrate that the introduction of benzene ring can significantly promote the surface adsorption of molecular oxygen and promote the transfer of electrons to molecular oxygen. This demonstrates that the embedded benzene ring can effectually advance the activation of molecular oxygen, which also well confirms that O2− and 1O2 are the main active species in the system of BCNNS photocatalytic degradation of oxytetracycline. This study reveals that benzene ring modified g-C3N4 has great potential in environmental purification, and provides a promising strategy for the removal of stubborn water contaminants.

Ortho-Terphenylene Viologens with Through-Space Conjugation for Enhanced Photocatalytic Oxidative Coupling and Hydrogen Evolution.

A series of novel ortho-terphenylene viologen derivatives (o-TPV2+) with through-space conjugation (TSC) via the combination of ortho-terphenylene skeletons with viologen structure is reported. Their optoelectronic properties can be adjusted by N-arylation or N-alkylation reactions. Compared with other viologen derivatives, o-TPV2+ not only exhibits strong photoluminescence but also retards the charge recombination process and stabilizes the diradical state without forming a quinoid structure due to the special TSC effect. Based on their special redox characteristics, o-TPV2+ was applied to the photocatalytic oxidative coupling of benzylamine with 96% yield. In addition, pTA-o-TPV2+ (tethered with p-toluic acid)-modified g-C3N4 was used for visible-light-driven hydrogen production for the first time, exceeding 15 times the rate over unmodified g-C3N4.

Preparation and application of defective graphite phase carbon nitride photocatalysts

With the development of industry and agriculture, the problems of environmental pollution and energy shortage have become increasingly severe. Semiconductor photocatalysis technology is one of the effective ways to solve environmental pollution and energy crisis. The principle of photocatalysis is based on the oxidation-reduction ability of photocatalysts under light conditions, which can achieve the purposes of purification of pollutants, material synthesis and transformation. Graphite phase carbon nitride (g-C3N4), as a new high-efficiency catalyst, has good stability and shows great engineering application potential in photocatalytic technology. However, the unmodified g-C3N4 has a limited visible light response range, and the photo-excited charge carrier recombination rate is high, resulting in low photocatalytic activity. Nitrogen defects are introduced into the g-C3N4 framework. These defects can manipulate the electronic structure, and the interstitial state produced can be used as a band-tail state, which can overlap with the valence band or the conduction band. The mid-gap state of semiconductors can extend the light response and act as an active center for electron-hole excitation. Introducing defects into g-C3N4 can improve the photocatalytic activity of g-C3N4. This paper systematically reviews the physical, chemical and electrochemical properties of g-C3N4 on the basis of experimental and theoretical research progress. The synthesis methods of defect g-C3N4 are summarized, including adjustment before polymerization, adjustment during polymerization, and adjustment after polymerization. The adjustment before polymerization is to introduce defects by changing the precursor, such as adding hydroxide, sodium borohydride and other substances to the precursor. The adjustment during polymerization is to provide a reducing atmosphere during polymerization can prepare g-C3N4 with different nitrogen-vacancy densities, such as hydrogen, ammonia and so on. The adjustment after polymerization is to modify the synthesized defect-free g-C3N4, such as recalcining or acid treatment to achieve the purpose of synthesizing nitrogen vacancies. The effect of defect sites on g-C3N4 is also discussed. The intermediate state induced by nitrogen defects can be transformed into active centers excited by electron holes, and the optical response of defect g-C3N4 is broadened due to the narrowing of the band gap. In the range, nitrogen defects can trap photo-generated carriers and prevent their recombination, thereby increasing the overall quantum efficiency. However, excessive introduction of nitrogen defects will produce deeper interstitial states. These deeper interstitial states can not only capture photo-generated electrons, but also photo-generated h+, which then become the recombination sites of photo-generated carriers. In addition, we separately summarized the application of the defect g-C3N4 in water treatment, such as the degradation of antibiotics and organic pesticides and the reduction of the toxicity of heavy metals, as well as water decomposition, carbon dioxide conversion and photocatalytic denitrification. Defect g-C3N4 has achieved good results in these applications. Although considerable progress has been made in the research of g-C3N4 in recent years, there are still many challenges in preparing g-C3N4 with high-efficiency catalytic performance. Finally, in view of the challenges faced by the application of defective g-C3N4, key discussions and future prospects are proposed from the aspects of mechanism exploration and material development.

Construction of novel in-situ photo-Fenton system based on modified g-C3N4 composite photocatalyst

In this study, a reduced g-C3N4/PDI/Fe (R-gCPF) photocatalyst was synthesized by loading Fe ion onto a reduced g-C3N4/PDI (R-gCP), which was obtained by reducing g-C3N4/PDI with NaBH4. The synthesized R-gCPF photocatalyst was used to construct a novel in-situ photo-Fenton system under visible light for pollutants removal. The R-gCPF2 (0.7% mass ratio of Fe/R-gCP) exhibited the optimal degradation efficiency toward benzoic acid (BA) and the photocatalytic degradation was much better than that of the unmodified g-C3N4/PDI (gCP). The X-ray photoelectron spectroscopy (XPS) characterization indicated that Fe was successfully loaded and bounded to the R-gCP material in the form of Fe2O3. The quenching experiments and the electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the photo-Fenton system was built up, and water was oxidized to OH in the system. Further, the Mott-Schottky and UV–vis diffuse reflectance spectrometry (UV–vis DRS) measurements confirmed the ability of valence band on R-gCPF to oxidize water. Photoluminescence spectral (PL) analysis indicated that loaded Fe could promote the separation of photogenerated electrons and holes, and consequently improved the photocatalytic efficiency of materials. The effect of initial pH, different ions and dissolved organic matter (DOM) on BA degradation was also studied. The stability of the photocatalyst was confirmed by recycle and the leaching experiments.

ZIF-8-derived carbon-modified g-C3N4 heterostructure with enhanced photocatalytic activity for dye degradation and hydrogen production.

In this study, a metal-organic framework (ZIF-8)-derived nitrogen-doped carbon (C-ZIF)-modified g-C3N4 composite was directly prepared by pyrolysis. C-ZIF@g-C3N4 composites with different loadings were prepared by changing the precursor content. The charge transfer process that occurs at the interface of the ZIF-8-derived nitrogen-doped carbon/g-C3N4 heterostructures strongly hinders the recombination of photoinduced electron-hole pairs, thereby effectively enhancing the photocatalytic activity of C-ZIF@g-C3N4. Meanwhile, the unique hierarchical inorganic/organic heterostructure provides an abundance of active sites for photocatalytic reactions. Upon visible-light irradiation, C-ZIF@g-C3N4 with an optimal ratio of g-C3N4 to C-ZIF components exhibits both enhanced photocatalytic activity and excellent separability during the degradation of dye and hydrogen evolution compared to unmodified g-C3N4.

Improved H2O2 photogeneration by KOH-doped g-C3N4 under visible light irradiation due to synergistic effect of N defects and K modification

KOH-doped graphitic carbon nitride (g-C3N4) prepared by thermal copolymerization in the presence of KOH was used for photogeneration of H2O2 under visible light irradiation. The H2O2 yield of the KOH-doped g-C3N4 photocatalyst with isopropanol (IPA) as a scavenger was 704 μM·g−1g-C3N4·h−1, twelve times that of unmodified g-C3N4. The total H2O2 output with IPA as a scavenger increased to 86.08 mM after 60 h. The photogeneration of H2O2 with g-C3N4 occurred as two single-electron reactions in which oxygen was reduced to the superoxide radical by one photogenerated electron and further reduced to H2O2 by reacting with another electron and two protons released by oxidization of IPA by holes. KOH doping had a synergistic effect owing to the strong electron-withdrawing ability of N defects caused by N vacancies and cyano groups, and enhanced electron transport due to K bridges between the C3N4 layers. These effects significantly enhanced the H2O2 photogeneration performance of g-C3N4 by improving the quantum efficiency, narrowing the band gap, strengthening IPA adsorption on g-C3N4, and lowering the energy barrier of the oxygen reduction reaction. This work provides an attractive and promising strategy for green H2O2 production.

Maleic hydrazide-based molecule doping in three-dimensional lettuce-like graphite carbon nitride towards highly efficient photocatalytic hydrogen evolution

A three-dimensional (3D) lettuce-like g-C3N4 with maleic hydrazide-based molecule doping was successfully developed. Based on systematic physicochemical characterizations and density functional theory (DFT) calculation, it was found that the diazine organic groups of maleic hydrazide, which occupied the positions of partial tris-triazine units, participated in the construction of valence band maximum (VBM) and promoted the formation of effective charge transfer channel from the diazine organic group in maleic hydrazide to the adjacent tris-triazine unit to promote the generation and separation of photo-generated carriers. Meanwhile, the 3D lettuce-like microstructure constituted by thin g-C3N4 nanosheets could shorten the migration distance of carriers to further inhibit the recombination of photo-generated carriers, and also bring the ultrahigh surface area to provide more active sites for photocatalytic reaction. The superior visible-light-driven photocatalytic H2-evolution activity was obtained (7689.6 μmol h−1 g−1), which was 31.5 times that of unmodified g-C3N4, and the apparent quantum efficiency was up to 8.53 % at 425 nm.

Enhanced n→π* electron transition of porous P-doped g-C3N4 nanosheets for improved photocatalytic H2 evolution performance

Graphitic carbon nitride (g-C3N4) has been demonstrated to be a rising star among semiconductor materials for photocatalytic hydrogen (H2) production. However, pristine g-C3N4 usually suffers from inferior activity due to the inadequate visible light harvesting capacity and quick charge recombination. Herein, porous P doped g-C3N4 nanosheets (PCNNSs) were fabricated via a simple thermal condensation of adenosine phosphate and urea followed by thermal exfoliation method. The synergetic effect of the porous structure and P dopant can provide abundant active sites for the photocatalytic reaction, which can enhance light absorption range extending from 450 nm to 700 nm attributed to the n→π* electronic transition, and improve hydrophilicity for easier water molecules adsorption via introducing hydroxyl groups. Furthermore, impurity level caused by the P dopant would change the excitation process and accelerate the charge separation efficiency. Therefore, the PCNNSs exhibited significantly elevated photocatalytic H2 generation performance (9523.7 μmolg-1h-1) under visible-light (λ > 420 nm) irradiation, which was about 20 times that of unmodified g-C3N4 (458 μmol-1h-1).

Metal ion adsorption from wastewater by g-C3N4 modified with hydroxyapatite: a case study from Sarcheshmeh Acid Mine Drainage

Hydroxyapatite (Hap) modified graphitic carbon nitride (g-C3N4) powders (Hap/g-C3N4) were prepared and characterized. The sorption activities of g-C3N4 and Hap/g-C3N4 were evaluated for the removal of Cu2+, Mn2+, Zn2+, Pb2+, Fe3+ and Cd2+ metal ions from simulated wastewater (synthetic solutions containing metal ions) and acid mine drainage from the sSarcheshmeh Copper Mine. The results indicated that the sorption capacities (SC) of g-C3N4 remarkably increased after the modification by Hap. Hap/g-C3N4 possessed higher SC than unmodified g-C3N4. So, the sorption mechanisms appear mainly attributable to the chemical interactions between the metal ions and functional groups on the Hap/g-C3N4 surface. More adsorption sites were formed on Hap/g-C3N4, which possessed abundant surface hydroxyl, phosphate and –NH2/–NH–/=N groups causing the higher efficiency of metal ion uptakes. Divalent metal cations are first adsorbed on the Hap/g-C3N4 surface and then substitution with Ca2+ ion can occur. Effect of pH evaluations confirmed that SC increased steeply with the pH increasing on both g-C3N4 and Hap/g-C3N4 adsorbents. The kinetic study demonstrated that the adsorption data were correlated well with the Langmuir isotherm model, and the adsorption process successfully followed the pseudo-second-order model.

Insight into the enhanced CO2 photocatalytic reduction performance over hollow-structured Bi-decorated g-C3N4 nanohybrid under visible-light irradiation

In this study, hollow-structured Bi decorated g-C3N4 hybrids were successfully fabricated by a simple solvothermal method and applied for the first time to the photocatalytic reduction of CO2. Remarkably, the composites exhibited excellent CO2 conversion efficiencies in the presence of H2O under visible light irradiation compared to unmodified g-C3N4, especially for the production of CH4. The optimum photocatalyst 30-Bi/g-C3N4 presented the best production of CO and CH4, approximately 3 times and 9 times as high as those of unmodified g-C3N4, respectively. A series of characterizations were conducted to explore the essence behind such an enhancement; we found that enhanced light harvesting, quick separation of photoinduced carriers and more negative conduction band, due to the formation of a Schottky junction between g-C3N4 and Bi metal and the solvothermal process, co-contributed for the enhanced CO2 conversion; A more important finding was that the surprising improvement of CH4 yield stem primarily from the introduction of the hollow-structured Bi, which enabled the accumulation of electrons on its surface exhibiting the metal-like property. The CO2 photocatalytic conversion process was also investigated by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) spectroscopy and we found that HCO3− and CO2− were active intermediates over 30-Bi/g-C3N4 and Bi doping could promote the activation of CO2. In summary, this work presented hollow-structured Bi decorated g-C3N4 composites as new materials for energy applications, proving once more the meta-like nature of bismuth, and laying the groundwork for the utilization of Bi in CO2 photocatalytic reduction processes.