Oxygen-doped Graphitic Carbon Nitride Research Articles

A robust floating oxygen-doped graphitic carbon nitride sheet for efficient photocatalytic CO2 conversion

Photocatalytic CO2 reduction offers a promising approach for converting CO2 into valuable chemicals. However, typical conversion systems suffer from inefficient CO2 mass transfer and complex recycling processes. In this study, we developed a floating sheet as a robust photocatalytic CO2 conversion system by integrating graphitic carbon nitride (CN) nanosheets onto polytetrafluoroethylene (PTFE) fiber membrane, followed by oxygen (O) doping into the CN (CN-O) via oxygen-plasma treatment. The floatable CN-O/PTFE sheet exhibits slight wettability in water under 0.25 MPa of CO2 pressure in our reactor system, facilitating the delivery of dissolved CO2 to the CN-O photocatalyst surface. O-doping enhances the visible light absorption and improves the separation and transport efficiency of photogenerated electrons and holes due to O-doping-induced states in CN. Consequently, the floating CN-O/PTFE system achieves an exceptional photocatalytic CO2 conversion rate of 102.3 μmol g-1h-1, approximately 4.8 times higher than a conventional CN-powder dispersion system in water. Moreover, the sheet demonstrates excellent cycling durability, with no significant exfoliation of the catalytic layer or reduction in CO2 photoreduction activity after 20 consecutive cycles. This study presents a novel approach to designing photocatalytic systems for efficient CO2 conversion.

Oxygen‐Doped Graphitic Carbon Nitride for Electrochemical Uric Acid Sensing: Method Without Metals

AbstractThe present study examined potential benefits of heteroatom doping to manipulate the electrical structure and to enhance the efficiency of the sensor, with an emphasis on developing inexpensive, metal‐free electrochemical sensors. Melamine and ammonium oxalate were used as precursors in a one‐step thermal polymerization technique yielding oxygen‐doped graphitic carbon nitride (O‐gCN). Following synthesis, the material's structural and morphological properties were thoroughly examined using a multitude of analytical techniques, including EIS. A notable decrease in impedance was observed, suggesting improved conductivity. Additionally, the doping approach exhibited a noticeable improvement in reduction current receptivity and surface area as compared to unmodified graphitic carbon nitride (g‐CN). Utilizing both differential pulse voltammetry (DPV) and the classical cyclic voltammetry (CV) methods, we investigated the electro oxidation of uric acid (UA) as well as concentration dependence and selectivity studies using oxygen‐doped graphitic carbon nitride modified glassy carbon electrode (O‐gCN@GCE). O‐gCN@GCE demonstrated remarkable performance, allowing the detection of UA concentrations as low as 7.784 µAµM−1cm−2. Its low detection limit of 0.57 µM and wider linear range (5–120 µM) further highlighted its potential for extremely sensitive assays and its remarkable capacity to operate over a broad UA concentration range.

Degradation of Oxytetracycline in Saturated Porous Media by In Situ Chemical Oxidation Using Oxygen-Doped Graphitic Carbon Nitride and Peroxymonosulfate: Laboratory-Scale Column Experiments

Degradation of Oxytetracycline in Saturated Porous Media by In Situ Chemical Oxidation Using Oxygen-Doped Graphitic Carbon Nitride and Peroxymonosulfate: Laboratory-Scale Column Experiments

Oxygen doped g-C3N4/LDH composite as highly efficient photocatalyst for wastewater treatment

Abstract Herein, we fabricated a highly efficient oxygen-doped graphitic carbon nitride (O–CN) and layered double hydroxide (LDH) nanocomposite photocatalyst and utilized it in the degradation of organic dyes in wastewater. The composite’s structure, morphology, and different optical features were examined using different techniques such as FT-IR spectroscopy, UV-visible spectroscopy, scanning electron microscopy (SEM), SEM-EDX, energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The composite has shown a crystalline structure, in contrast to the amorphous nature of oxygen-doped g-C3N4. Using a wide range of experimental parameters, including dye concentration, visible light, irradiation time, catalyst dose, contact time, and pH, the increase in the reaction performance of the catalyst was observed. The results reveal that 98.5 % adsorption degradation efficiency increased with the increase in catalyst dosage, contact time, and pH. The as-fabricated photocatalyst generated reactive species that were involved in the degradation of methylene blue (MB) dye upon exposure to visible light irradiation.

Microbial lipid synthesis based on visible light-driven oxygen doped-graphitic carbon nitride /oleaginous yeast hybrid system

The use of solar energy and heterotrophic microbes to synthesize microbial lipids is a promising strategy to solve energy crisis and reduce CO2 emissions. In this study, a photocatalyst, oxygen-doped graphitic carbon nitride (O-g-C3N4), was synthesized and combined with an oleaginous yeast strain, Cutaneotrichosporon dermatis ZZ-46, to construct a photocatalyst-microbe hybrid (PMH) system. Under illumination, the lipid yield of the PMH system reached 1.61 g/L after 96 h (87 % higher than that of control). NADPH/NADP+ ratio of ZZ-46 cells in the PMH system increased. Metabolomics results revealed that glutathione generation was increased, and the fatty acid decomposition pathway in ZZ-46 cells was inhibited in the PMH system. This study provides a new approach for the synthesis of microbial lipids based on solar energy and heterotrophic microbes.

Robust interaction of ZnO and TiO2 nanoparticles with layered graphitic carbon nitride for enhanced photocatalytic oxidative desulfurization of fuel oil: mechanism, performance and stability.

Sulfur compounds in fuel such as thiophene, benzothiophene and dibenzothiophene are the primary source of SO x emissions, leading to environmental pollution and acid rain. In this study, we synthesized a layered oxygen-doped graphitic carbon nitride (OCN) structure and integrated ZnO and TiO2 nanoparticles onto the OCN surface through a microwave-assisted sol-gel method. The X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) results confirmed a robust interaction between the ZnO and TiO2 nanoparticles and the oxygen-doped g-C3N4 (OCN) surface, as indicated by the formation of C-N-Ti and C-O-Ti bonds. This interaction notably improved the optoelectronic properties of the ZnO-TiO2/OCN composite, yielding increased visible light absorption, reduced charge recombination rate, and enhanced separation and transfer of photogenerated electron-hole pairs. The oxygen doping into the CN network could alter the band structure and expand the absorption range of visible light. The ZnO-TiO2/OCN photocatalyst demonstrated remarkable desulfurization capabilities, converting 99.19% of dibenzothiophene (DBT) to dibenzothiophene sulfone (DBT-O2) at 25 °C, and eliminating 92.13% of DBT from real-world fuel oil samples. We conducted in-depth analysis of the factors impacting the redox process of DBT, including the ZnO ratio, initial DBT concentration, catalyst dosage, stability, and O/S molar ratio. Radical trapping experiments established that ˙O2 -, ˙OH and h+ radicals significantly influence the reaction rate. The obtained results indicated that the ZnO-TiO2/OCN photocatalyst represents a promising tool for future fuel oil desulfurization applications.

Bandgap-Engineered In2S3 Quantum Dots Anchored on Oxygen-Doped g-C3N4: Forging a Dynamic n-n Heterojunction for Enhanced Persulfate Activation and Degradation of Metronidazole

Herein, an ultrasonication approach was used to anchor In2S3 quantum dots (QDs) onto oxygen-doped graphitic carbon nitride (O@g-C3N4), resulting in a novel heterojunction catalyst. Characterization techniques validated the successful incorporation...

Transport of Oxygen-Doped Graphitic Carbon Nitride in Saturated Sand: Effects of Concentration, Grain Size, and Ionic Strength

In this study, the characteristics and transport of oxygen-doped graphitic carbon nitride (OgCN) were investigated in comparison with multi-walled carbon nanotube (MWCNT), and the transport of OgCN was evaluated under various conditions. OgCN was superior to MWCNT in transport within a quartz sand layer with less attachment and more detachment than MWCNT, which is attributable to more diverse and abundant functional groups, charges, defects, and amorphous graphitic structures. OgCN transport was well described by a one-dimensional advection–dispersion–retention model. The coefficients of retention (Smax), attachment (ka), and detachment (kd) calculated by the model were not always well-correlated with OgCN concentration and the grain size of the medium, suggesting that the OgCN transport was affected by various factors such as attachment, detachment, and pore size. However, it was clearly and significantly inhibited by ionic strength, via improved aggregation of OgCN. It is believed that the results of this study contribute to establish proper sub-surface injection strategies of carbonaceous materials for in situ chemical oxidation.

Degradation of toxic textile effluent rhodamine-B dyes using oxygen doped graphitic carbon nitride nanosheets

A metal-free oxygen-doped graphitic carbon nitride (O-gCN) is prepared by thermal decomposition techniques using urea and oxalic acid (OA). The O-gCN physio-chemical properties are obtained by using different analytical analyses. The O-gCN is utilized as a photocatalyst and applied to degrade rhodamine-B toxic environmental dye. The higher photocatalytic ability of O-gCN is ascribed to the nanostructure with a porous nature. In addition, the porous nature of prepared O-gCN initiated more reactive sites for the degradation of target pollutants. The dopant oxygen atoms in the gCN tri-s-triazine units have extended enormous light absorption capability in the visible range. Radical scavenging experiments exhibited that the reactive radicals played a key role in the photocatalytic degradation of rhodamine B (RhB). The treated waters' toxic and non-toxic nature is observed using mung bean seed germination. Hence, this present study portrayed a simple, eco-friendly, and cost-effective technique to prepare O-gCN nanosheets for environmental remediation applications.

Synergistic enhancement of photocatalytic hydrogen evolution by ultrathin oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide

Graphitic carbon nitride (g-C3N4, CN) is widely utilized in the field of photocatalytic hydrogen production owing to its exceptional visible light absorption, addressing the challenge of energy scarcity. However, its development has been hindered by the issue of low charge separation efficiency. In this study, an ultrathin (∼1.65 nm) oxygen-doped graphitic carbon nitride nanosheets loaded amorphous mesoporous nickel hydroxide (a-Ni(OH)2/OCN) photocatalyst was developed through a straightforward calcination and stirring approach. Under visible light irradiation, a-Ni(OH)2/OCN exhibited a remarkably high photocatalytic hydrogen evolution rate of 4764.9 μmol·h−1 g−1, which is 4.7 times greater than that of the original CN. The synergistic effect between O-doping and heterojunction was proved by experimental data analysis combined with DFT calculations. Totally, the introduction of oxygen into CN led to a reduction in its band gap, while a-Ni(OH)2/OCN heterojunction achieved a broaden light absorption range and an effective charge separation due to a type-Ⅱ internal electric fields.

A novel method to synthesis of oxygen doped graphitic carbon nitride with outstanding photocatalytic efficiency for the degradation organic pollutants

Contamination of water sources with organic pollutants seriously threatens the environment and living organisms, so it is necessary to remove them from these sources with a proper method. Photocatalytic degradation of such pollutants can be an effective, low-cost and eco-friendly method. In this study, a new method, porous oxygen-doped Graphitic carbon nitride (POCN) photocatalyst was synthesized by pre-exfoliation of bulk graphitic carbon nitride in hydrogen peroxide followed by calcination of the resulting exfoliated and oxygenated sample at 550 °C. In fact, in this method, a combination of three strategies, nanostructure preparation, band gap engineering and defect introduction into the g-C3N4 were used to improve the efficiency of photocatalyst. The synthesized sample was characterized using XRD, FESEM, TEM, FTIR, DRS, PL, EDX, XPS, and BET-EJH. The efficiency of the prepared photocatalyst was evaluated with its ability to degrade Congo Red (CR) in aqueous solution under visible light using two light sources, LED lamp and daylight. POCN removed the CR in a short time. The degradation rate was higher under sunlight. The free radical trapping tests showed that superoxide radical anions (O2−) are the active species and are mainly responsible for color degradation.

Solar-light-driven photocatalytic conversion of monosaccharide by oxygen-doped graphitic carbon nitride/artificial steel converter slag composite

The development of high performance, low-cost and resource-efficient photocatalysts with improved solar light harvesting capabilities can significantly enhance the practicability and viability of photocatalytic conversion of biomass-based substances to value-added chemicals. This work reports the construction of heterojunction between oxygen-doped graphitic carbon nitride and artificial steel converter slag (OCN/artCS) as efficient photocatalysts for conversion of biomass-derived monosaccharide to lactic acid under the simulated solar light. The OCN/artCS composites were facilely fabricated by the thermal polymerization of the mixtures of dicyanamide (DA) and oxalic acid (OA), which are precursors of OCN. The artCS acts as photocatalyst support for OCN to grow on its surface and can provide Ca2Fe2O5 semiconductor to possibly form the OCN/Ca2Fe2O5-containing artCS heterojunction. Compared with pristine OCN, the OCN/artCS composites exhibited higher photocatalytic performance for selective production of lactic acid, possibly due to the effective separation of photogenerated charge carriers after creation of OCN/artCS heterojunction. At the optimal content of artCS in the composites, the OCN/5%artCS delivered 99% glucose conversion and 90% lactic acid yield within 60 min at 50 °C under the simulated sunlight irradiation. This work can be a platform for the efficient utilization of industrial solid wastes for production of high-performance photocatalysts, enabling their promising applications in photobiorefinery and other photocatalytic processes.

Oxygen doped graphite carbon nitride as efficient metal-free catalyst for peroxymonosulfate activation: Performance, mechanism and theoretical calculation

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5−) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L−1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of −0.855 kcal/mol than that of the pristine g-C3N4 (Eads: −0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•−) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

Synthesis of 3‐Arylquinoxalin‐2(1H)‐ones under Visible‐Light Irradiation with Oxygen‐Doped Carbon Nitride as Heterogenous Photocatalyst

AbstractA novel oxygen‐doped graphitic carbon nitride (OCN) material was designed and synthesized via the hydrothermal‐calcination method with melamine and hydroperoxide as starting materials. The OCN material was utilized as a highly efficient solid metal‐free photocatalyst for the synthesis of 3‐arylquinoxalin‐2(1H)‐ones via the catalytic decomposition of aryl diazonium salts under blue light irradiation. Following this approach, various 3‐arylquinoxalin‐2(1H)‐one derivatives could be obtained in moderate to excellent yields with broad substrate scope under mild conditions. Also, the OCN solid photocatalyst shows good recyclability in the reaction, there was no appreciable loss in yields observed even after 5 cycles. This methodology offers a practical, mild, and metal‐free alternative to the preparation of 3‐arylquinoxalin‐2(1H)‐ones.

Metal-free hybrid composite particles with phosphorus and oxygen-doped graphitic carbon nitride dispersed on kaolin for catalytic activity toward efficient hydrogen release

Here, hybrid kaolin-g-C3N4 heterostructure particles were fabricated by calcination in the first step, followed by hydrothermal phosphoric acid activation in the second step, and phosphorus (P) and oxygen (O) doped kaolin-g-C3N4 metal-free catalyst was synthesized. This hybrid metal-free catalyst was used for the first time for the production of effective hydrogen (H2) from sodium borohydride (NaBH4) methanolysis. The hydrogen generation rate (HGR) value of 5500 ml min−1g−1 was obtained with the P and O doped kaolin-g-C3N4 catalyst. The activation energy (Ea) of 31.90 kJ mol−1 by P and O doped kaolin-g-C3N4 for the production of H2 was obtained. The kaolin-g-C3N4 and P and O doped kaolin-g-C3N4 metal-free catalysts were systematically characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). Based on the results obtained, the mechanism of P and O-doped kaolin-g-C3N4 catalyst on H2 production from NaBH4 methanolysis was also proposed.

Trap engineering using oxygen-doped graphitic carbon nitride for high-performance perovskite solar cells

We demonstrated an effective trap passivation strategy of using oxygen-doped g-C3N4 to simultaneously heal the Sn dangling bonds and –OH traps in SnO2 ETLs for efficient and stable perovskite solar cells.

Oxygen doping facilitated N-vacancies in g-C3N4 regulates electronic band gap structure for trimethoprim and Cr (VI) mitigation: Simulation studies and photocatalytic degradation pathways

The strategic designing of graphitic carbon nitride (CN)by elemental doping is likely to generate nitrogen vacancies which benefit by serving as electron trapping sites or by introducing additional energy levels (mid-gap states). In this work, uracil-assisted oxygen doped graphitic carbon nitride (OCNv-Ux) was synthesized by the hydrothermal method. The OCNv-U40 exhibited vigorous photocatalytic efficiency for 98% trimethoprim (TMP) antibiotic degradation and 90.8% Cr (VI) reduction under visible light irradiations. A combined inference from experimental results and simulation studies indicates band gap reduction from 2.7 to 2.34 eV for extended visible light absorption up to 620 nm. In particular, the density of states comprehends band structure regulation by the electron redistribution resulting in valence band up shifting and downshift of the conduction band, as validated by Mott-Schottky spectra. The synergistic outcomes of nitrogen vacancies and oxygen doping sites restrain the recombination of electron-hole pairs by mid-gap state formation and also promote high oxygen molecule adsorption on the nitrogen vacancies. The pioneering advantage of highly adsorbed oxygen molecule leads to the generation of plentiful superoxide anion radicals along with indirect production of hydroxyl radicals via in-situ produced H2O2, evident by radical scavenging and electron paramagnetic resonance experiments. The effect of chloride and nitrate anions showed inhibitory effect on the TMP degradation efficiency. The identification of formed intermediates and TMP degradation mechanism involving oxidation, hydroxylation, and cleavage was proposed, as investigated by TMP DFT studies. This research accomplishes significant enhancement in pristine CN photocatalytic activity by the virtue of increased specific surface area, fully exposed N-vacancies active sites, optimized electronic, structure and visible light active band gap.

Organosilica-assisted superhydrophilic oxygen doped graphitic carbon nitride for improved photocatalytic H2 evolution

The regulation of surface wettability and heteroelement doping have been proved to be effective strategies to enhance photocatalytic H2 evolution activity of graphitic carbon nitride (CN) based photocatalysts. Herein, we report, for the first time, an organosilica assisted method was adopted to synthesize the superhydrophilic oxygen doped graphitic carbon nitride (O–CN). The presence of organosilica induced simultaneous oxygen-containing groups grafting and oxygen doping within carbon nitride substrate. The grafted oxygen-containing groups improved the surface hydrophilicity and water adsorption. Oxygen doping tailored electronic structure and localized electron distribution, contributing to extended visible light harvesting and elevated photoelectric conversion efficiency. As a result, the H2 generation rate of O–CN photocatalyst was 5.4 times higher than that of pristine CN photocatalyst attributed to the formation of hydrophilic groups and the oxygen doping.

Changes in the catalytic activity of oxygen-doped graphitic carbon nitride for the repeated degradation of oxytetracycline

Metal-free carbonaceous catalysts have gained growing interest because of their excellence in organic pollutant degradation. However, most of them suffer from deactivation after use, and the origins have not been investigated or understood. In this study, the changes in the characteristics after multiple uses of a carbonaceous catalyst, i.e., oxygen-doped graphitic carbon nitride (O-gCN), were investigated to identify the key factors affecting its reactivity. The O-gCN was repeatedly used to remove an antibiotic (oxytetracycline, OTC) in the presence of peroxymonosulfate (PMS). OTC removal was significantly reduced as the O-gCN was repeatedly used. The reactivity of O-gCN used five times (O-gCN5) corresponded well with the decreased signals of DMPO-X, DMPO-O2•−, and TEMP-1O2 in electron paramagnetic resonance spectra. These signal changes were accompanied by a shift of the involved reactive species from 1O2 and OH• for O-gCN to 1O2 and SO4•− for O-gCN5. The changes in activity and involved reactive species were attributed to the changes in the properties of O-gCN, considering the negligible OTC adsorption and slight PMS consumption. The results of X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in the degree of defects, graphene-like layers, and crystallinity in graphitic structures, but an increase in the fractions of N and O, for O-gCN5. However, the OTC degradation pathways and intermediates were not significantly different for O-gCN and O-gCN5. These results provide valuable information for developing strategies for the design, practical use, and regeneration of carbonaceous catalysts.

Visible light-driven photocatalytic reduction of monovalent silver using a composite of Ni3Bi2S2 and O-doped gC3N4

In this study, nickel bismuth sulphide (Ni2Bi2S3) was synthesized through solvothermal method and was used to functionalize oxygen-doped graphitic carbon nitride to form a nanocomposite (Ni2Bi2S3/O-gC3N4). Characterizations of the nanocomposite were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and UV–vis spectrophotometer. The nanocomposite was used to photocatalytically reduce monovalent silver to useful metallic silver. The effects of process parameters including Ag+ concentration, pH of the solution, the dosage of the photocatalyst, light intensities, addition of persulfate and mixed organic pollutants were studied, and the data obtained were fitted into pseudo-first order kinetics. About 93.08% (pseudo first order rate constant of 0.0460 min−1) of Ag+ was photocatalytically removed within 1 h using 25 mg of the photocatalyst. Mixed organic pollutants and persulfate were found to have inhibitory effects on the rate of photocatalytic reduction. Finally, the Ni2Bi2S3/O-gC3N4 photocatalyst was found to retain over 80% of its efficiency even after three cycles, and the scavenging experiment revealed that electrons, holes and superoxide played prominent roles in the photocatalytic process.