Thermal Polycondensation Research Articles

In situ formation of oxygen-deficient WO3-x nanosheets for enhanced photocatalytic activity in water splitting and plastic reforming

Photocatalytic pathways are essential for the sustainable production of chemicals and fuels, pivotal for achieving a pollution-free planet. Electron-hole recombination is a critical problem that has, so far, limited the efficiency of the photocatalytic materials. Here, oxygen-deficient WO3-x nanosheets were in situ grown in a polymeric carbon nitride (PCN) support during the thermal polycondensation of melamine. The introduction of defect in WO3-x, accompanied by spin polarization and the formed WO3-x/PCN heterostructure, greatly accelerated the charge separation and transfer. The synthesized WO3-x/PCN composite exhibited a tenfold increase in hydrogen generation activity than pure PCN under visible-light (420 ≤ λ ≤ 780 nm). The WO3-x/PCN also demonstrated consecutive 24 h and stable photocatalytic H2 production in the aqueous plastic-containing [poly(vinyl alcohol) (PVA), poly(ethylene terephthalate) (PET) and the PET bottle] solutions under visible light. The hydrogen production rates were determined to be 111.2, 50.5, and 7.8 μmol·h−1·g−1 in PVA, PET and PET bottle, respectively. In addition, the oxygen vacancies WO3 with their localized surface plasmon resonance effect, facilitated efficient utilization of NIR photon and the hydrogen evolution rate over WO3-x/PCN reached to 120 μmol h−1·g−1 under NIR light (700 ≤ λ ≤ 780 nm). This research not only advances the potential applications of WO3-x/PCN in sustainable energy production but also provides insights into environmental remediation through the conversion of plastic wastes.

Enhanced photocatalytic performance of magnetically reclaimable N-doped g-C3N4/Fe3O4 nanocomposites for efficient tetracycline degradation

The growing environmental challenge posed by the persistence of tetracycline (TC) antibiotics in natural waters is of increasing concern. To address this, there is an imperative need for advanced methods to mitigate TC residues. Herein, we demonstrate the preparation of nitrogen-doped graphitic carbon nitride integrated with magnetic Fe3O4 (N-g-CN/Fe3O4) composites, showcasing narrow band gaps optimized for TC degradation. These advanced materials, conceived through a thermal poly-condensation approach, utilize citric acid and melamine as precursors for nitrogen and g-CN, respectively. These composites exhibit a face-centered cubic architecture, with particle dimensions between 8 to 12 nm and encompassing both meso and microporous structure. The results of the Brunauer–Emmett–Teller analysis indicated specific surface areas of 6.73 m²/g for g-CN, 69.80 m²/g for N-g-CN, 62.55 m²/g for Fe3O4, and 148.32 m²/g for N-g-CN/Fe3O4. These values demonstrate an increase in surface area upon the incorporation of heteroatom of nitrogen and Fe3O4, into the g-CN matrix, thus influence the photocatalytic performance. Under solar light exposure, the synthesized photocatalysts demonstrated photocatalytic activity with a degradation efficiency of 94.16 % within 120 min. Specifically, the N-g-CN/Fe3O4 (22.5 %) composites exhibited remarkable photocatalytic efficiency due to the narrow band gap energy between N-g-CN and Fe3O4, enhanced light absorption in the visible range, and effective charge carrier separation and transportation to the pollutants. N-g-CN/Fe3O4 (22.5 %) composites demonstrated good recyclability (five cycles), magnetic sustainability, and stability for the degradation of TC and emerging pollutants from wastewater using photocatalysts. Similarly, FGCN composites exhibited good recyclability (five cycles), magnetic retrievability, and stability for degrading organic and emerging pollutants from wastewater through photocatalysis. This efficiency can be attributed to the harmonious combination of nitrogen doping, refined surface area, and the natural heterojunction between N-g-CN and Fe3O4.

Inflated electronic and optical assessment of gC3N4/ZnO nanocomposite as a potential emissive layer material for OLED application

Organo-inorganic nanocomposite materials have been proven to be novel hybrid materials with inflated electronic and optical performance that can be tailored with the judicious selection of the building units or their combinations. Here, hydrothermal, thermal polycondensation, and ultrasonication techniques were used to synthesize pure ZnO, gC3N4, and gC3N4/ZnO with varying weights % such as 10 %, 15 %, 20 %, and 25 % of ZnO inorganic filler elements in gC3N4 matrix. The crystalline phase (hexagonal wurtzite) and crystallite size (10.0 nm, 17.6 nm, and 15.90 nm) of the synthesized materials were examined by X-ray diffractometer. The FESEM and HRTEM characterizations revealed the sheet-like gC3N4 and spherical-type ZnO nanoparticle-like microstructures of the samples. The present functional groups, corresponding vibrational frequency, chemical states, and binding energy were investigated using FTIR and XPS spectroscopic methods. Optical parameters such as optical band gap energy (Eg = 3.24 eV), Urbach energy (Eu = 0.41 eV), refractive index (n = 1.99), emission quantum yield (∼ 69.03 %), and color purity of the nanocomposites were examined using UV visible and photoluminescence spectroscopic techniques. IV and Hall measurements techniques were used to determine the semiconducting parameters of the optimized sample, such as conductivity (∼62.90×10−5 S/cm), carrier mobility (∼ 44.1 cm2/Volt. Sce), carrier concentrations (∼1.825×1014 cm−3), and sheet resistance (∼1.062×103 Ω/cm2). Due to their excellent optical and electrical behavior, the nanocomposite materials were found to be fairly suitable as a potential emissive layer material for OLED applications.

Synthesis and Characterization of Poly (Erythritol Sebacate)

AbstractErythritol is a sweetener polyol widely distributed in nature. Its industrial production is based on biotechnological fermentative processes using yeasts. It is used essentially in nutrition and pharmaceutical fields. However, due to its still high price, the use of erythritol is not widespread and is lower than that of other polyols. The use of erythritol for polymer synthesis remains largely unexplored by the scientific community. This work describes the synthesis and characterization of polyester, poly (erythritol sebacate) (PES), obtained by thermal polycondensation of erythritol and sebacic acid in a two steps approach. A prepolymerization step was realized at different temperatures (150 °C, 160 °C and 170 °C, respectively) followed by a cure step at 150 °C. It was found that using a higher temperature allows the same degree of polymerization (50%) to be achieved in a shorter period, but this leads to prepolymers with a more heterogeneous oligomeric composition. This is reflected in the final properties of the polymers after curing. Synthesis at 150 °C produced a polymer with superior mechanical performance (ultimate tensile strength: 0.5 MPa; Young’s modulus: 0.44 MPa: elongation at break: 123%) and higher chemical resistance to solvents than polymers synthesized at 160 °C and 170 °C. The glass transition temperature (Tg) is between − 20 and 0 °C for all polymers and density is 1.08 g/cm3. Based on these results, we believe that PES is a good elastomer with tunable properties and potential for selective absorption of molecules, such as ethanol, that could be useful for beverage industry and biotechnological applications. Graphical Abstract

Synergistic photocatalytic activity of Bi2O3/g-C3N4/ZnO ternary heterojunction with dual Z-scheme charge transfer towards textile dye degradation

It is clear that a wide range of organic substances, including synthetic textile dyes, have the potential to negatively impact the environment. It is crucial to rationally develop highly effective photocatalysts for the degradation of such type of pollutants. In this regard, a heterostructured photocatalyst comes with enhanced charge separation and extended light absorption ability that improves photocatalytic performance. Therefore, In this study, a Bi2O3/g-C3N4/ZnO (BCNZ) ternary heterojunction photocatalyst was synthesized for the degradation of methylene blue (MB) textile dye.. Thermal polycondensation method was opted to synthesize g-C3N4, while ZnO and Bi2O3 photocatalysts were fabricated using co-precipitation method. Similarly, ternary heterojunction of BCNZ was constructed through co-precipitation method. The ternary heterojunction photocatalyst demonstrated better photodegradation ability due to dual Z-scheme charge transfer route. The dual Z-scheme heterojunction enabled the ternary heterojunction to exhibit enhanced light absorption capabilities with reduced recombination rates as well as enhanced charge separation and migration efficiency (confirmed via transient photocurrent response) that resulted in improved photocatalytic performance. The BCNZ dual Z-scheme photocatalyst displayed 92 % of degradation efficiency which was much higher than that of other (binary and pristine) photocatalysts. Scavenging tests and electron spin resonance spectroscopy revealed the significant role of the •O2−, and •OH radicals in the photodegradation of MB. Furthermore, the reusability test presented good stability and recyclability of the ternary photocatalyst with 80 % degradation efficiency after five catalytic cycles.

Thermal insulating, flame retardant, and superhydrophobic polybenzoxazine/silica aerogels fabricated in water-ethanol solvent using eco-friendly method

Polybenzoxazine (PBz) aerogels have garnered considerable attention as an innovative and excellent thermal insulation material, celebrated for its lightweight, low thermal conductivity, and outstanding mechanical properties. However, the use of high boiling point toxic solvents in the preparation process requires a cumbersome solvent exchange procedure coupled with insufficient flame-retardant properties, which hinder the potential application of PBz aerogels. Herein, we employed tetraethyl orthosilicate (TEOS) into PBz using an easy, eco-friendly, and cost-less process to achieve hybrid structure polybenzoxazine/silica (PBz/SiO2) aerogels, by thermal catalysis (72 °C) ring-opening polymerization and polycondensation in water-ethanol solvent without any catalysts. The resulting PBz/SiO2 aerogels were characterized with low density (0.181 g/cm3), low thermal conductivity (0.0315 W/(m·K)), excellent flame-retardancy (PHRR value of 32.3 W/g and THR value of 6.3 kJ/g), and superhydrophobicity (the water contact angle up to 155°). Environment-friendly preparation strategy for the PBz/SiO2 aerogels with excellent comprehensive performance, poised to play a pivotal role in energy-saving buildings and fire-resistant applications.

Photocatalytic activity of self-heterojunctioned intermediate phases in HCl protonated and HNO3 deconjugated g-C3N4 nanostructures

This research involved the different acid-treatment conditions of graphitic carbon nitride and its modified nanostructures through thermal polycondensation of urea at various temperatures. X-ray diffraction patterns revealed that processing at a lower temperature than 500 °C resulted in melem and its derivatives, indicating incomplete transformation of urea to g-C3N4. However, treatment at higher temperatures and the HCl acid treatment led to the formation and expansion of g-C3N4 networks, as evidenced by notable differences in peak intensities observed in their Fourier-transform infrared and Raman spectra. Scanning electron microscopy analysis illustrated a transition from the granular morphology of melamine to the layered structure characteristic of g-C3N4. The nanoparticle morphology observed in the HNO3 acid treatment sample was attributed to the deconjugation of nanosheets through the highly oxidative acid medium. The most suitable photocatalytic activity for Methylene Blue (MB) degradation under UV and visible light illumination was observed for the samples prepared at 550 °C and HCl post-processed nanostructures. It is proposed that the enhanced photocatalytic activity observed in these samples is most likely attributed to the reduced recombination of photogenerated charge carriers facilitated by heterojunctions formed between different intermediate phases. These findings highlight the potential of modified g-C3N4 and its derivatives as promising photocatalytic materials for water purification applications.

Reliable determination of polymeric carbon nitride wettability: A standardized sessile drop method for pressed-tablet samples

The wettability of polymeric carbon nitride (PCN) is an important surface chemical factor affecting its catalytic and separation performance. However, due to the amphipathic characteristics of hydrophilic/lipophilic and porous powder properties, the contact angle (CA) of PCN measured by the common sessile drop method will be interfered by the substrate, resulting in randomness of the results. Herein, the pristine PCNs obtained by thermal polycondensation of different precursors in air or nitrogen atmosphere were used as the wettability research object. The CA of the PCNs was measured by a modified sessile drop method after the traditional powders were replaced by pressed-tablet samples. The influence of sample mass and applied pressure on specific surface area, pore volume, surface morphology and CA of the pressed-tablet samples was investigated carefully, and the optimal experimental conditions were determined. When the sample mass was 0.15 g and the applied pressure was 10 MPa, the measured water CA of PCNs was between 27 ∼ 34°, and the diiodomethane CA is between 24 ∼ 29°. The measurement results showed considerable stability and reproducibility. This improved CA measurement method provides a simple and standardized way to accurately explore the surface chemistry of PCN, and has the potential to be applied to other hydrophilic and/or oleophilic porous powder materials.

In Situ Synthesis and Characterization of Graphitic Carbon Nitride/Metakaolin Composite Photocatalysts Using a Commercial Kaolin

Kaolin-based graphitic carbon nitride (g-CNx) composite photocatalysts were synthesized from a urea precursor using a commercial kaolin. Structural characterization by X-ray diffraction and infrared spectroscopy (FTIR) verified the successful thermal polycondensation of g-CNx along the thermal dehydroxylation of kaolinite to metakaolin at 550 °C. The g-CNx content of the composites were estimated by thermogravimetry and CHN analysis, ranging from ca. 87 m/m% to ca. 2 m/m% of dry mass. The addition of kaolin during the composite synthesis was found to have a significant effect: the yield of in situ formed g-CNx drastically decreased (from ca. 4.9 m/m% to 3.8–0.1 m/m%) with increasing kaolin content. CHN and FTIR indicated the presence of nitrogen-rich g-CNx, having a specific surface area of 50 m2/g, which synergistically increased after composite synthesis to 67–82 m2/g. Estimated optical band gaps indicated the affinity to absorb in the visible light spectrum (λ < 413 nm). Photocatalytic activity upon both UV and artificial sunlight irradiation was observed by hydroxyl radical evolution, however, without the synergistic effect expected from the favorable porosity.

Boosting visible-light photocatalytic performance of graphitic carbon nitride by regulating its donor-acceptor structure via maleamide

Graphitic carbon nitride (GCN) has attracted much attention due to its many advantages as a kind of photocatalyst, including low cost, easy to prepare, eco-friendly and so on. However, GCN suffers from limited light-absorption capacity and rapid recombination of photogenerated charge carriers. Herein, a new kind of photocatalyst based on GCN has been synthesized by introducing a small molecule compound (maleamide) through a facile thermal polycondensation method (550 ℃ for 180 min) and applied it to photocatalytic removal of bisphenol A (BPA). The optimized GCN-20 (20 mg maleamide in 10 g urea) exhibits the best BPA degradation performance and good stability. The UV–vis test shows that the introduction of maleamide broadens the optical response threshold of GCN from 435 nm to 460 nm. The promoted photocatalytic performance is mainly attributed to enhanced donor-acceptor structure by electron-withdrawing group, which accelerates charge separation and inhibits recombination of free holes and electrons. The active species including superoxide radicals (⋅O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (⋅OH), play dominant roles in the photocatalytic degradation process.

Stage development characteristics of oxygen-lean combustion of coal in fire zone: Leap-migration mechanism, kinetic transition mechanism, and critical oxygen concentration

Effectively preventing the re-ignition of fire zones and safely unsealing enclosed fire zones are challenging. To address these issues, a thermogravimetric analysis technique was used to explore the leap-migration mechanism of the characteristic parameters (burnout index (H), comprehensive combustion performance parameters (Cb, S, and HF), and maximum combustion mass loss rate (dWmax))/temperatures (maximum pyrolysis mass loss rate point temperature (TVmax), pyrolysis endpoint temperature (Td), thermal polycondensation endpoint temperature (Tp), maximum combustion mass loss rate point temperature (TWmax), burnout temperature (Th), and combustion half-peak width (ΔT1/2)) of low-rank coal oxygen-lean combustion under different time-scale effects (TSEs). The sensitivity of characteristic parameters/temperatures to changes in oxygen concentration under coal rank transition was analyzed. Simultaneously, the kinetic real-time transformation mechanism during the oxygen-lean combustion stage progression was investigated. The results revealed that because of the competition between oxidation and pyrolysis, the leap-migration interval of characteristic parameters/temperatures for oxygen-lean combustion of low-rank coals is in the range of 5 %–3% oxygen concentration. This feature was less affected by the coal rank but is not affected by the TSE. In the low oxygen-lean range (5 %-1%), a change of oxygen concentration was more sensitive to the coal rank, and the high sensitivity of the oxygen concentration change reduced the influence of the coal rank on coal combustion performance. In addition, the apparent activation energy (Eα) curves during the early stage of combustion were relatively concentrated with the change of oxygen concentration, but relatively dispersed during the late stage of combustion. At 3 % oxygen concentration, the Eα values of different coals began to continuously decrease with increasing conversion rate, approaching the spontaneous reaction activation energy value of 40 kJ/mol. At oxygen concentration of 1 % reflected the complete limitation of the oxidation consumption reaction. Therefore, the critical oxygen concentration of typical low-rank coal oxygen-lean combustion was determined below 3 % oxygen concentration. The results of this study can provide scientific guidance for the unsealing of fire zones, and the effective prevention and control of the formation of new fire zone disasters.

Iron-cobalt loading carbon nitride bimetallic catalyst activates peroxymonosulfate for bisphenol A degradation

In order to reduce metal leaching loss and carbon emissions, an active Peroxymonosulfate (PMS) catalyst (Fe/Co–CN) was prepared using a one-step thermal polycondensation method for the efficient treatment of wastewater containing bisphenol A (BPA). Fe/Co–CN has a low metal leaching (＜1 mg/L) and has good catalytic degradation performance for BPA. The degradation efficiency was 90.7% in 5 min and ∼100% in 10 min, which is much higher than single metal-loaded Fe–CN (77.2%) and Co–CN (73.2%). Nonradical species dominated by 1O2 and high-valent species were the main reactive oxygen species that degraded BPA in the Fe/Co–CN/PMS system. By strictly controlling the energy consumption during the synthesis and application of Fe/Co–CN, lower carbon emissions have been achieved than most catalysts reported. This achievement is of great significance for applying advanced oxidation methods to treat organic micro-pollutants and provides reference for the calculation of PMS catalysts carbon emissions.

Carbonaceous structures as electronic bridges to enhance charge migration and radical reactions in composite photocatalysts: An effective way to achieve efficient mineralization of pollutants

The intrinsic correlation between photo-induced extraction of hole and free radical reactions can facilitate the mineralization of contaminants via promoting the transfer of electrons from the semiconductor to the solution. TiO2/C/g-C3N4 composite photocatalysts are prepared using thermal polycondensation and sol-gel methods in this paper. The introduction of carbon at the interface between the two phases creates charge migration channels that facilitate electron transfer at the interface of semiconductor catalyst as well as collisions of dissolved oxygen to the catalytic sites, which are able to promote catalytic oxidation reactions. Considering Rh-B as target, the removal rate is 97.2±0.2 % within 90 min. The involvement of hydroxyl radicals and superoxide radicals is confirmed by carrying out radical quenching experiments and ESR characterization, suggesting that effective electron transfer synergistically promotes the production of hydroxyl radicals. Therefore, it emphasizes the importance of the indeterminate carbon bridged 2D/3D interface for constructing charge migration channels as well as promoting the efficiency of carrier separation in the process of photocatalytic efficient degradation of dyes.

Synthesis of spinnable isotropic pitch from low-softening-point coal tar pitch via Blanc bromomethylation-dehydrobromination towards carbon fibers with enhanced mechanical properties

Blanc bromomethylation-dehydrobromination is proposed to synthesize isotropic pitches with superior spinnability, utilizing refined coal tar pitch as the feedstock. This strategy involves introducing bromomethyl functional groups into pitch molecules through the Blanc bromomethylation reaction. In the subsequent process of dehydrobromination, methylene bridges generate between neighboring aromatic molecules. The pitch precursor prepared by this method not only displays an increased level of oligomerization and pitch yield, but also exhibits a more linear molecular structure compared with that produced through purely thermal polycondensation. The enhanced linear molecular configuration contributes to the improved spinnability of the pitch precursor and the oxidation reactivity of its derived fiber. Furthermore, the tensile strength of the resulting carbon fibers rises with an elevation in the amount of polyoxymethylene, and it exhibits the trend of an initial growth followed by a subsequent decrease as the stabilization temperature escalates. The carbon fibers obtained from the pitch prepared through thermal polycondensation present a low Young’s modulus of 24 GPa and a low tensile strength measuring of 456 MPa. In contrast, carbon fibers derived from the pitch synthesized via Blanc bromomethylation-dehydrobromination exhibit superior mechanical performance, offering Young’s modulus and tensile strength of 58 GPa and 1210 MPa, separately.

Enhanced detection of 4-nitrophenol in drinking water: ECL sensor utilizing velvet-like graphitic carbon nitride and molecular imprinting

In this work, a molecularly imprinted electrochemiluminescence (ECL) sensor was developed for selective detection of 4-nitrophenol (4-NP) in drinking water for the first time. By synthesizing velvet-like graphitic carbon nitride (V-g-C3N4) via one-step thermal polycondensation and integrating it with a molecularly imprinted polymer (MIP), the ECL sensor was fabricated. The MIP-modified V-g-C3N4 composites (MIP/V-g-C3N4) were synthesized using a sol-gel method with 4-NP as the template molecule. Under optimal conditions, the ECL sensor exhibited a wide detection range (5 × 10−10-1 × 10−5 mol/L) and a low detection limit (1.8 × 10−10 mol/L). In testing with actual drinking water samples, it displayed high accuracy (recoveries for intraday and inter-day: 93.50–106.2% and 97.00–107.3%, separately) and precision (RSDs for intraday and inter-day: 1.54–4.59% and 1.53–4.28%, respectively). The developed MIP-based ECL sensor demonstrated excellent selectivity, stability, and reproducibility, offering a promising and reliable approach for highly sensitive and selective determination of 4-NP in drinking water.

Z-scheme based photoactive ZnO:TiO2:CdO:g-C3N4 nanocomposites for advance oxidation process

Z-scheme-based hybrid [(ZnO0.40:0.60TiO2):CdO1.00]:g-C3N4] nanocomposites (NCs) were synthesized by sol-gel precipitation and thermal polycondensation methods. Microscopic FE-SEM images varied from a compact crystal-like structure to a mesoporous sheet-type structure. XRD patterns confirmed the polycrystallinity for all samples. Meanwhile, the g-C3N4 interacts extensively with Zn+2 and Cd+2. The optical bandgap increased from 2.12 eV to 2.25 eV with the addition of g-C3N4 concentration. Z-scheme [(ZnO0.40:0.60TiO2):CdO1.00]:[g-C3N4] NCs of the particular composition named ZTCG4 showed the highest photocatalytic activity and degraded the methylene blue (MB), methyl green (MG), and methyl orange (MO) to be 99.7 %, 99.8 %, and 99.9 %, respectively, under the illumination of the visible light. Mineralized factors: chemical oxygen demand (COD) and biochemical oxygen demand (BOD) achieved the maximum removal efficiencies of 89.4 % and 88.9 % for the sample g-C3N4. Prepared photocatalysts can be utilized to remove the organic pollutants from the drainage systems under visible light exposure.

Synthesis and structural evolution of coal-based mesophase pitch by hydrogenation-vacuum thermal polycondensation process

As high-performance carbon materials precursor, the controlled synthesis of mesophase pitches has received widespread attention. Coal tar pitch and Tetrahydronaphthalene (THN) were selected as raw material and hydrogen supply solvent to synthesize mesophase pitches through hydrogenation and vacuum polycondensation. The compositions and structure of resultant hydrogenated and mesophase pitches were characterized and analyzed by various methods. The results revealed that the introduction of THN could effectively increase the H content in hydrogenated pitches, and the transformation of HN to Har was observed with the extension of the reaction time. The softening point of the resultant mesophase pitches was 230–245 °C, the Mn ranged from 1400 to 2000 Da, the anisotropic content was up to 96 %, and the contents of the four subfractions were THFI > HI-TS > HS > TI-THFS in descending order. This work provided an efficient and convenient approach for the synthesis of mesophase pitches, with a view to providing a theoretical and practical foundation for spinning-grade mesophase pitch preparation.

Carbon doping and bridging oxygen benefit for g-C3N4 to photocatalytic H2 production from methanol/water splitting: Experiments and theoretical calculations

Water-based homogeneous pre-assembly and thermal polycondensation were used to prepare carbon-doped oxygen-bridged layer-twisted graphite carbon nitride (g-C3N4) heterojunction for highly efficient photocatalytic hydrogen evolution (PHE). Despite the narrow band gap of around 0.91 eV, g-C3N4 heterojunction exhibited an excellent hydrogen evolution rate (563.87 μmolg−1h−1) in 30 % methanol/water solution without precious metal assisting catalysts, 36.85 times higher than g-C3N4. C doping in heptazine ring and bridging O caused the adjacent layer of g-C3N4 to twist by 11° in three-dimensional space. Noticeably, carbon doping in triazine ring was favorable to the establishment of build-in electric field between adjacent layers owing to the delocalized large π bonds. Bridging oxygen acted as a conversion switch for electron storage and transport of photogenerated charge from innerlayer (unmodified layer) with high Fermi level to outlayer (modified layer) with low Fermi level. This work provided an insightful guidance to novel layer-twisted g–C3N4–based photocatalysts for efficient H2 production.

The interference mechanism of Na+ and Cl- on photocatalytic properties of phosphate-oxygen co-doped graphite carbon nitride for hydrogen production from water splitting: Experimental and theoretical calculations

Phosphorus-oxygen co-doped graphite carbon nitride (POx-CN) are successfully fabricated by in situ impregnation and two-stage thermal polycondensation to investigate the effect of Na+ and Cl- on the photocatalytic hydrogen evolution from artificial seawater splitting. The as-prepared POx-CN exhibits a hydrogen evolution rate of 1054.29 μmolg−1h−1 in artificial seawater, lower than fresh water, indicating that Na+ and Cl- play an inhibitory effect on hydrogen evolution reaction. The theoretical calculation indicates that the phosphorus-oxygen binary doping changed the electrostatic potential of the modified layer in carbon nitride molecule, accelerating the electron transfer rate from the structural O in triazine ring to P-N bond. In artificial seawater, the competition between Na+ and Pt2+ at active sites in the modified layer and electron capture by Cl- in the mutual conversion of Cl- and chlorine radicals result in the reduction of hydrogen evolution efficiency.

High-Efficiency Photo-Fenton-like Catalyst of FeOOH/g-C3N4 for the Degradation of PNP: Characterization, Catalytic Performance and Mechanism Exploration.

The composite photocatalyst FeOOH/g-C3N4 was prepared through thermal polycondensation and co-precipitation methods, followed by XRD, SEM and UV-vis characterization. The stability of FeOOH/g-C3N4 was explored by the recycling test. The active species in the reaction system were investigated by the capture experiment. The results indicated that the optimal preparation condition for g-C3N4 involved calcination at 600 °C for 4 h. XRD analysis revealed that g-C3N4 exhibits a high-purity phase, and Fe in FeOOH/g-C3N4 exists in a highly dispersed amorphous state. SEM analysis showed that FeOOH/g-C3N4 has a rough surface with an irregular layered structure. Element composition analysis confirmed that the content of elements in the prepared catalyst is consistent with the theoretical calculation. FeOOH/g-C3N4 possesses the largest specific surface area of 143.2 m2/g and a suitable pore distribution. UV-vis DRS analysis showed that the absorption intensity of FeOOH/g-C3N4 is stronger than that of g-C3N4. When the catalyst dosage was 1.0 g/L, the H2O2 dosage was 4 mmol/L, the PNP initial concentration was 10 mg/L and the initial pH value was 5, the PNP removal could reach 92% in 120 min. Even after 5 cycles, the efficiency of PNP removal by FeOOH/g-C3N4 remains nearly 80%. The capture experiment indicated that both •OH and •O2- play roles in the photocatalytic degradation of PNP, with •OH being more significant. These findings affirm that FeOOH has been successfully incorporated into g-C3N4, resulting in a conspicuous catalytic effect on the degradation of PNP in the visible light-assisted Fenton-like reaction.