Attaining an extremely efficient photocatalyst has drawn a great deal of attention in the worldwide pursuit of using solar power as an abundant and cheap energy source. Layered compounds have ...demonstrated a wide range of physicochemical properties that support their potential practical applications. Because dimensionality plays a crucial role in determining fundamental properties of lamellar structure, when they go under exfoliation down to few-layer or monolayer nanosheets, their characteristics will differ from those of their stacked bulks. The photocatalytic properties of these few-layer or mono-layer materials can be improved through in-plane and inter-plane structural modification by doping with metal or non-metal elements. Among the various layered materials, graphitic carbon nitride (g-C3N4) has emerged as one of the most promising photocatalysts due to its metal-free nature, abundance in raw material, thermal and physicochemical stability and suitable bandgap. Although its bulk structure shows a weak photocatalytic activity, its thermally or chemically exfoliated nanosheets demonstrate greatly improved activity. Further, the electronic structure of the nanostructures can be modified by elemental doping with triazine units to activate the π-conjugated system in the photocatalytic reaction. In this review paper, we analyze the latest developments, particularly in the area of phosphorous-doped graphitic carbon nitride (P-doped g–C3N4) photocatalysts and their molecular and structural modifications for improving H2 generation and CO2 conversion to solar fuels.
•A brief historical background for g–C3N4 has been presented.•Challenges and perspectives regarding g–C3N4 photocatalysts were discussed.•The latest developments on P-doped g–C3N4 photocatalysts were reviewed.•The modifications for improving H2 generation and CO2 conversion were analyzed.•Prospects regarding P-doped g-C3N4 for photocatalytic applications was mentioned.
Herein, the fabrication of S-scheme CdS/ZMO photocatalysts through EDTA bridges for hydrogen production was reported. In this system, the role of EDTA molecules as a linker for binding CdS and ZMO ...(ZnMn
2
O
4
/Mn
3
O
4
spinel oxides composite) was investigated in detail. The optimized sample showed superior photocatalytic hydrogen evolution rate of 26.34 mmol.g
−1
.h
−1
, nearly two times higher than the system without EDTA. The outstanding photocatalytic activity could be due to the efficient charge transfers caused by the interaction between EDTA molecules and two semiconductors. This study provides a clear insight into the critical role of inexpensive organic electron mediators in enhancing the photocatalytic performance of heterojunction photocatalysts.
Graphical Abstract
Herein, the transparent omniphobic coating on glass slides was fabricated by using three different colloidal dispersions as sacrificial templates for a silica sol to make nano-scale surface ...roughness. These surface structures were further functionalized with a long chain fluorinated silane. These coatings showed a stable repellency to both water and low-surface tension liquids with the maximum contact angle of 156° to water and of about 130° to corn and paraffin oils. The prepared glass slides presented very high transparency with a light transmittance of about 92–98%. The coated surfaces were stable up to 400 °C and represented a good resistance under corrosive conditions by immersing 24 h in aqueous solutions of H
2
SO
4
(pH 2) and KOH (pH 14).
The poor selectivity and activity of the photocatalysts developed has hindered the photocatalytic production of hydrogen peroxide (H2O2). Therefore, modification techniques need to be pursued to ...improve the selectivity and activity of photocatalysts toward the two-electron oxygen reduction reaction. In this study, homogeneous self-modification by nitrogen vacancies is adopted as an efficient technique to narrow the band gap and induce the mid-gap states in the nanostructures of g-C3N4 synthesized by cyanuric acid–melamine supramolecular adducts. The presence of the vacancies in the structure and their respective effects on the optoelectronic features of the catalysts were thoroughly investigated by different characterizations. The optimized photocatalyst showed greatly improved H2O2 production of 200 μM under 1 h visible light irradiation, as compared with that of the bulk (35 μM) and the pristine nanostructured sample (85 μM), with acceptable reusability. This study also provides a new perspective on devising synergistic approaches to modify the performance of supramolecular-based carbon nitride photocatalysts.
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•Stable cyanuric acid-melamine supramolecular adducts were prepared in water.•g-C3N4 nanosheets were obtained by calcination of the adducts under the air.•The nanosheets showed ...efficient degradation of TC and RhB under visible light.••O2-, h+ were the main active species involved in both TC and RhB degradation.•The TC degradation pathway was presented by identifying the intermediates.
Highly condensed g-C3N4 nanosheets with an exceptional surface area and porous structure were simply prepared by thermal condensation of stable preorganized supramolecular structures of cyanuric acid and melamine formed in water as the solvent. Different techniques were employed for the characterization of the structural, morphological, electrical, and optical features of the as-synthesized catalyst. All the characterizations confirmed the successful formation of nanosheets with magnificent properties compared to the pristine sample which was prepared by melamine polycondensation. Not only did these nanosheets exhibit a superb photocatalytic activity over the degradation of tetracycline (over 60%) and rhodamine B (100%) under visible light irradiation just for 15 min, but they also could maintain their stability during the reaction keeping over 98% of their original degradation even in 5 cycles. Superoxide anion radicals and holes were determined to be the main active species by trapping experiments. LC-Mass analysis was also performed to identify the intermediates and propose the possible pathway for photodegradation of tetracycline. The promising performance of this catalyst can be a notable step forward for prosperous industrial applications in the field of photodegradation of hazardous and not-easily degradable organic compounds in wastewater treatment plants.
Graphitic carbon nitride (g-C3N4) has attracted considerable attention since its discovery for its catalysis of water splitting to hydrogen and oxygen under visible light irradiation. However, ...pristine g-C3N4 confers only low photocatalytic efficiency and requires surface cocatalysts to reach moderate activity due to a lack of accessible surface active sites. Inspired by the high specific surface area and superior electron transfer of graphene, we developed a strongly coupled binary structure of graphene and g-C3N4 aerogel with 3D porous skeleton. The as-prepared 3D structure photocatalysts achieve a high surface area that favors efficient photogenerated charge separation and transfer, enhances the light-harvesting efficiency, and significantly improves the photocatalytic hydrogen evolution rate as well.
The photocatalyst performance is observed to be optimized at the ratio 3:7 (g-C3N4:GO), leading to photocatalytic H2 evolution of 16125.1 mmol. g-1. h-1 under visible light irradiation, more than 161 times higher than the rate achieved by bulk g-C3N4. KCI Citation Count: 0
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•Ba-doped g-C3N4 was fabricated via a thermal condensation method.•A lower recombination rate of photo-induced e− and h+ pairs in Ba-doped g-C3N4.•91.94% of tetracycline (TC) was ...degraded within 120 min irradiation at an optimal pH of 10.•Ba-doped g-C3N4 retained high stability even after five cycles of use.•h+ is the predominant oxidative species for TC photodegradation.
A novel photocatalyst, Ba-doped graphitic carbon nitride (g-C3N4), was synthesized via a facial thermal condensation method. Ba at a loading of 2% revealed the highest photocatalytic degradation efficiency of tetracycline (TC) (91.94%) after 120 min of visible light irradiation at an optimal pH of 10. An overall synergy of 69.26% was observed in the case of Ba (2%)-doped g-C3N4 over pure g-C3N4. The remarkable improvement in the TC degradation performance is due to the narrower band-gap energy, the larger surface areas and the lower recombination rate of charge carriers detected through photoluminescence (PL) quenching, suggesting the multiple roles of the Ba doping. The synthesized novel photocatalyst displayed extremely high stability after 5 cycles as confirmed through various characterization techniques. The intermediates generated during the photocatalytic reaction were also detected through liquid chromatography–mass spectrometry (LC-MS) analysis and used to predict the degradation pathway of TC. Photoelectrochemical (PEC) measurements combined with photocatalytic performance obviously demonstrated that Ba doping effectively enhanced the separation of charge carriers and decreased the electron/hole recombination in the g-C3N4 structure.
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•Mesoporous g-C3N4 nano-clusters with nitrogen defects were synthesized.•Reverse replica of silica clusters as hard template confined g-C3N4 planes’ growth.•Complete photodegradation ...of TC and RhB was achieved in a short time.•O2−, h+ were the main active species involved in the degradation process.•The toxicity of produced intermediates of TC was lower in compared to TC.
Constructing high-performance visible-light responsive photocatalyst to remediate organic pollutants from wastewater is of great challenge in recent years. In this study, by using SiO2 clusters as a template, mesoporous graphitic carbon nitride nano-clusters (NC MCN) were fabricated as a high-activity photocatalyst. The confined growth of carbon nitride in the presence of SiO2 clusters introduced extra structural defects to the carbon nitride framework including nitrogen vacancies and cyano groups, which was confirmed by employing different characterization analyses. These structural defects created midgap states below the conduction band, which improved light-harvesting efficiency and suppressed electron-hole recombination. Thus, NC MCN showed high photocatalytic activity toward degradation of both tetracycline and rhodamine B under visible light irradiation. Complete degradation of 15 mL solution of 15 ppm tetracycline was achieved in 30 min compared to the bulk catalyst (taking more than 3 h). Furthermore, NC MCN demonstrated high stability after reusing for 8 consecutive photodegradation cycles. The total organic carbon concentration at different reaction time showed a rising and falling trend, which illustrate photodegradation process, i.e. adsorption, photodegradation, and mineralization. By liquid chromatography-mass spectroscopy analysis, the produced intermediates during the tetracycline degradation were proposed, which showed the formation of smaller molecules in just 15 min. The toxicity of the intermediates was analyzed using quantitative structure–activity relationship estimation and the outcomes exhibited that the toxicity of the solution reduced as the reaction time increased. This comprehensive study from photodegradation process to mineralization of TC demonstrated NC MCN as a promising photocatalyst for sustainable treatment of wastewater.
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•Hexagonal rosettes of CM adduct were fabricated as a precursor for g-C3N4.•The confined polymerization of the CM rosettes was performed at 500 °C.•Condensation of CM adduct leads to ...the formation of hexagonal rosettes of g-C3N4.•A thorough mechanism pathway for the polymerization process was elaborated.•The rosette g-C3N4 showed superb photocatalytic activity for H2 and H2O2 production.
Photocatalytic sustainable fuel production attracted extensive attention because of the urgent need of the society to shift from fossil fuels to solar fuels. Herein, the synthesis of hexagonal rosettes of g-C3N4 with an efficient performance toward hydrogen evolution and hydrogen peroxide production as the two kinds of solar fuels were reported. The hexagonal rosettes of g-C3N4 were simply fabricated via controlled solid-state polymerization of three-dimensional hexagonal rosettes of cyanuric acid-melamine adduct at 500 °C. The hexagonal rosettes of g-C3N4 showed an amorphous nature with an extremely high surface area of 400 m2 g−1. Also, the as-obtained catalyst demonstrated remarkable photocatalytic activity in hydrogen production of 1285 μmol g−1 h−1 and hydrogen peroxide production of 150 μmol g−1 h−1. The mechanism for the polymerization process of the cyanuric acid-melamine (CM) complex to hexagonal rosettes of g-C3N4 was thoroughly described employing electron microscopy tools. This study identified that the CM complex condensation is accomplished via a dehydration process by producing a highly condensed and active structure of g-C3N4, which is different from the previously reported condensation mechanism of the melamine and its derivatives performed through a deamination process.
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•A novel hierarchical 3D TiO2 nanotree/Ag /g-C3N4 photoanode was fabricated.•3D TiO2 NT arrays as ETL were synthesized via a hydrothermal growth treatment.•Ag /g-C3N4 was deposited on ...3D TiO2 NT with different coating methods.•Ultrasonic assisted spin coating deposition method exhibited the best PEC performance.•The optimized photoanode showed a photocurrent density of 1.4 mAcm−2 at 1.23 V/RHE.
Graphitic carbon nitride (g-C3N4) has been extensively studied as a model of polymeric semiconductor material in photoelectrochemical (PEC) water oxidation reaction; however, its low PEC performance is still a concern of significant importance among researchers. Herein, we did a novel host-guest design of a photoanode device comprising three dimensional (3D) TiO2 nanotree (NT) arrays as an electron transfer layer (ESL) and Ag/g-C3N4 heterojunction as a photo absorber layer. In this design, 3D TiO2 NT arrays synthesized via a hydrothermal growth treatment were deposited with an alcoholic suspension of Ag/g-C3N4 using different coating methods such as drop casting, spin coating, and ultrasonic assisted-spin (U-spin) coating methods. The optimized photoanode prepared via U-spin coating exhibited a remarkable photocurrent density of 1.4 mA cm−2 at 1.23 V vs. RHE and a negatively shifted onset potential of 0.2 V in 1.0 M KOH when it was illuminated from the backside using a Xenon lamp (150 W) equipped with a 400 nm cut off filter. This hierarchical 3D design photoanode demonstrated constant stability during the water oxidation reaction for at least 8 h.
