g-C3N4 Samples Research Articles

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.

Sodium thiosulfate modified graphitic carbon nitride for enhancing the photocatalytic production of aldehydes

The oxidation of alcohols to aldehydes is one of the most relevant reactions in organic chemistry. The currently implemented methods based on expensive noble metallic catalysts, toxic solvents, and high temperature and pressure conditions have released the seek for softer and cheaper alternatives such as photocatalysis. In this sense, graphitic carbon nitride has been modified with sodium thiosulfate as a source of S and Na+ incorporation in the structure, aimed at enhancing the photocatalytic performance on the oxidation of alcohols to aldehydes, i.e. cinnamaldehyde, benzaldehyde, and vanillin in aqueous solution. Three g-C3N4 samples synthesized from different precursors, i.e. melamine, thiourea, and urea, were treated with sodium thiosulfate. Urea led to the g-C3N4 with the highest mesoporosity (surface area, 69 m2 g−1) and photocatalytic activity. The modification with 5 % (wt.) of Na2S2O3 enhanced the pseudo-first order rate constant of cinnamyl alcohol oxidation from 0.265 h−1 (bare sample) to 0.792 h−1 (Na2S2O3-modified). The characterization of the material suggests a better charge separation of the photogenerated charges after S and Na+ incorporation in the structure, minimizing the recombination rate of photogenerated charges. The optimum photocatalyst, tested in aqueous solution, was most selective in the production of benzaldehyde (selectivity, >100 %) > cinnamaldehyde (>23 %) > vanillin (∼5 %). The selectivity was considerably boosted under acetonitrile as the solvent medium, raising in the case of cinnamaldehyde the 23 % recorded in water to 51 % in pure acetonitrile. The degradation mechanism suggests a strong influence of the photogenerated holes and the superoxide radical, the latter being more selective in the oxidation of the alcohol.

Enhanced PMMA Denture Bases Using Functionalized MWCNT Fused g-C3N4 Nanocomposites

This study presents the development and analysis of a new metal-free nanocomposite that incorporates functionalized multi-walled carbon nanotubes (f-MWCNTs) with graphitic carbon nitride (g-C3N4) for reinforcing polymethyl methacrylate (PMMA) denture bases. The f-MWCNTs were integrated with g-C3N4 nanoparticles, and their structural and morphological features were examined using various techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy. A mechanical blending process was employed to synthesize the nanocomposite by mixing 2 wt% of the f-MWCNT/g-C3N4 with PMMA polymer powder, followed by heat curing to form the composite material. Specimens for mechanical testing were crafted to measure flexural strength, impact resistance, compressive performance, and hardness. The findings revealed that the f-MWCNT/g-C3N4-reinforced PMMA composites outperformed standard PMMA in mechanical robustness. Surface examination of the tested samples through SEM showed distinctive dimpling and roughness, indicating a toughened fracture surface in comparison to pure PMMA and g-C3N4 samples. The study concludes that this innovative f-MWCNT/g-C3N4 composite is a promising reinforcement for PMMA denture bases, enhancing both their mechanical and physical attributes.Keywords: PMMA, functionalization, MWCNTs, Graphitic Carbide Nitride, Mechanical Properties and Denture Base

Synergistic effect of NiO-loaded gold NPs modified exfoliated graphitic carbon nitride (E-gC3N4) with the role of hot electrons and hole scavengers for boosting solar hydrogen production

The photocatalytic hydrogen production capabilities of a well-designed NiO–Au loaded exfoliated graphitic carbon nitride (E-gC3N4) were evaluated after it was synthesized in a straightforward, template-free, single-step process. This study delves into the synergistic impact of utilizing exfoliated g-C3N4 (E-gC3N4) loaded with NiO to trap electrons and plasmonic Au to elevate solar-driven H2 evolution through the surface plasmon resonance effect. Using 2 % NiO/E-gC3N4 and 0.3 % Au/E-gC3N4 samples, the H2 yield of 2620 and 2725 μmol g−1, were obtained, which were 25 and 26 folds higher than using bulk g-C3N4, respectively. The highest photocatalytic H2 production of 4750 μmol g−1 was obtained with 1 % NiO-0.3 % Au/E-gC3N4, which was 1.74, 1.81 and 45.24-fold more than it was produced with 0.3 % Au/E-gC3N4, 2 % NiO/E-gC3N4 and bulk g-C3N4 samples, respectively. Increased visible light absorption and charge production due to the SPR effect of Au and efficient charge separation due to NiO co-catalyst led to an increase in H2 generation. The composite was also stable for the consecutive four cycles, in which continuous H2 evolution was obtained. This novel strategy offers promise for synthesizing effective composites for visible-light-driven H2 evolution.

Effect of precursors on Cu particle distribution in g-C3N4 nanosheets towards efficient photocatalytic degradation and H2 generation

N-rich precursors govern the thermal polymerization formation of graphitic carbon nitride (g-C3N4) based catalysts towards enhanced photocatalytic performance. In this paper, Cu components were introduced in superior thin g-C3N4 nanosheets using the thermal polymerization copper acetate and bulk g-C3N4 created by different precursors including melamine, dicyandiamide, and thiourea, such as melamine-g-C3N4 (MCN), dicyandiamide-g-C3N4 (DCN), and thiourea-g-C3N4 (TCN). The performance of Cu-g-C3N4 nanosheets depended strongly on the precursors of bulk g-C3N4 samples. The well-developed Cu nanoparticles with clear lattice fringes were observed in the sample prepared using MCN (sample Cu-MCN) while the crystallinity of Cu nanoparticles became worse in the sample prepared using DCN (sample Cu-DCN). Interestingly, Cu clusters were homogeneously distributed in superior thin g-C3N4 nanosheets in the case of using TCN (sample Cu-TCN) because of S components in thiourea affected the thermal polymerization. The photocatalytic activity of Cu-TCN was drastically improved compared with other Cu-g-C3N4 samples. The photocatalytic hydrogen production rate of Cu-TCN with 1% of Cu components was 4035.6 μmol g-1 h-1. Cycle stability test indicated that sample Cu-TCN revealed high stability, in which the H2 generation rate was retained 95% of their initial value after 5 cycles. These results supply efficient approaches for the study and application of g-C3N4 based photocatalysts.

3D-printed Al2O3 framework supported carbon-bridged tri-s-triazine of g-C3N4 for photocatalytic tetracycline oxidation

Powder-like g-C3N4 has been widely used as a photocatalyst but exhibits several drawbacks, including unrecyclable, high charge recombination, and limited light absorption. In this study, carbon-bridged g-C3N4 was successfully prepared and coated on a 3D-printed Al2O3 substrate for the photocatalytic oxidation of tetracycline. Oxamide (OD), malonamide (MD), and succinamide (SD) were used as carbon-containing linkers to react with precursors (melamine and urea) and produce carbon-bridged g-C3N4. Carbon substitution at the bridged N atoms of g-C3N4 improved light absorption, reduced charge recombination, and resulted in high photocatalytic tetracycline removal efficiency. Computational calculations were also employed, and Bader charge analysis supported the charge redistribution and charge transfer of the carbon-bridged g-C3N4 samples. Our results indicated that the degradation of tetracycline followed step-by-step oxidation, deamination, and mineralization to form CO2 and H2O. The 3D-printed Al2O3-supported carbon-bridged g-C3N4 exhibited a high removal rate of 85–90 % and stability for photocatalytic reactions and can be reused for at least 10 cycles. This study demonstrates that the 3D-printed Al2O3-supported carbon-bridged g-C3N4 catalyst is an efficient and effective catalyst support system for photocatalytic reactions.

Synthesis of heterostructure composite (g-C3N4/phosphomolybdic acid) for synergistic piezo/photo-catalytic degradation of CR dye and S. aureus bacteria

In photocatalysis systems, piezocatalytic effect is widely utilized to achieve efficient separation of photo-produced carriers for powerfully decomposing organic contaminants and bacteria under both mechanical vibrations and visible illumination. Herein, an efficient heterogeneous composite of phosphomolybdic acid (PMA)-immobilized onto g-C3N4 has been constructed via ionothermal and impregnation methods. After characterization, the g-C3N4/PMA hybrid has been applied for piezophotocatalytic degradation of Congo red dye (CR) and bacterial inactivation of staphylococcus aureus (S. aureus) under visible-light illumination and ultrasonication. Compared with the photocatalysis, the g-C3N4/PMA hybrid exhibited improved piezophotocatalytic degradation of CR, reaching 99 % within only 60 min, indicating the piezoelectric polarization promotes considerably photocatalytic activity. Also, high bacterial inactivation performance (>94.0 %) has been obtained compared with pristine g-C3N4 and PMA samples after 180 min of visible-illumination/ultrasonication. These improved outcomes were due to the synergistic impact between high reversible redox capabilities of PMA with the controllable electronic structured of g-C3N4, and piezoelectric polarization, which acts as a driving force to prevent the recombination of generated charges, leading to an efficient separation rate and transfer of the photogenerated electrons-holes, and thus boosting degradation and bacterial inactivation efficiencies. The recommended mechanisms for piezophotocatalytic degradation of both CR dye and S. aureus bacteria have been clarified and supported by trapping experiments, which confirmed the significant roles of •O2– and electrons. The reusability investigations demonstrated the high stability performance of g-C3N4/PMA hybrid during five sequential piezophotocatalytic cycles.

Facile synthesis of Fe single-atom porous photocatalysts via direct metal atomization achieving efficient photocatalytic nitrogen fixation

Photocatalytic nitrogen fixation has been explored as a feasible pathway for ammonia synthesis. However, the convenient and efficient preparation of photocatalysts for nitrogen fixation remains a challenge. Meanwhile, the reaction pathway and mechanism of photocatalytic nitrogen fixation are unclear. Herein, single-atom Fe-porous g-C3N4 (FPx) samples were manufactured using a one-step anneal technique via bubble template and direct metal atomization. Characterization results indicate that FPx has a porous structure and single-atom Fe. The porous structure exposed more active centers. Simultaneously, single-atom Fe changes the adsorption mode of N2 from physical to chemical and turns the photocatalytic nitrogen fixation from the associative distal pathway to the associative alternating pathway. Consequently, without any sacrificial agent or cocatalysts, FPx presents a prominent increase in photocatalytic activity, reaching 62.42 µmol h−1 g−1, over fivefold larger than that of bulk g-C3N4. This work provides new insights into photocatalytic nitrogen fixation and achieves efficient N2 photoreduction by constructing single-atom photocatalysts.

Rational Design of Monolithic g-C3N4 with Floating Network Porous-like Sponge Monolithic Structure for Boosting Photocatalytic Degradation of Tetracycline under Simulated and Natural Sunlight Illumination.

In order to solve the problems of powder g-C3N4 catalysts being difficult to recycle and prone to secondary pollution, floating network porous-like sponge monolithic structure g-C3N4 (FSCN) was prepared with a one-step thermal condensation method using melamine sponge, urea, and melamine as raw materials. The phase composition, morphology, size, and chemical elements of the FSCN were studied using XRD, SEM, XPS, and UV-visible spectrophotometry. Under simulated sunlight, the removal rate for 40 mg·L-1 tetracycline (TC) by FSCN reached 76%, which was 1.2 times that of powder g-C3N4. Under natural sunlight illumination, the TC removal rate of FSCN was 70.4%, which was only 5.6% lower than that of a xenon lamp. In addition, after three repeated uses, the removal rates of the FSCN and powder g-C3N4 samples decreased by 1.7% and 2.9%, respectively, indicating that FSCN had better stability and reusability. The excellent photocatalytic activity of FSCN benefits from its three-dimensional-network sponge-like structure and outstanding light absorption properties. Finally, a possible degradation mechanism for the FSCN photocatalyst was proposed. This photocatalyst can be used as a floating catalyst for the treatment of antibiotics and other types of water pollution, providing ideas for the photocatalytic degradation of pollutants in practical applications.

Enhancing fluorescence sensing of metal species by g-C3N4 prepared by co-polymerization of melamine and urea precursors

In this work, several g-C3N4 samples have been synthesized by thermal co-polymerization of melamine and urea precursors, analyzing the impact and advantages of the combination of both precursors, and finally choosing the sample with the highest fluorescent emission to study the detection of Ag+, Fe3+, and Cr(VI) species. The g-C3N4 samples were characterized by several techniques such as XRD, FTIR, DRS, SEM, and PL where the excitation wavelength (λexc) was set at 250 nm for monitoring the quenching of the emission band centered at 371 nm. In this sense, the 10U-g-C3N4 sample was examined for the detection of metal species in aqueous media, showing excellent correlation coefficients (R2 > 0.988) and limits of detection (LOD) of 7.2, 8.4, and 1.9 μmol/L for Fe3+, Ag+, and Cr(VI), respectively. The sensing of Ag+ and Fe3+ ions can be related to a photoinduced electron transfer (PET) mechanism, while the detection of Cr(VI) species is associated with an inner filter effect (IFE). The results show that the graphitic carbon nitride obtained by a co-polymerization route yields better results than g-C3N4 obtained by the calcination of single precursors. This approach enhances the fluorescence sensing of different metal species with a simple synthetic procedure and avoids complex, harmful, or expensive processes.

Ultrathin graphitic carbon nitride (g-C3N4) nanosheets: Synthesis, properties, and photocatalytic application

In recent years graphitic carbon nitride (g-C3N4) has been considered the most popular candidate for replacing graphene and other similar materials in various applications. The g-C3N4 has unique electronic and mechanical properties, huge photoluminescence in the wide optical region, and promising properties in energy conversion and storage, water splitting, etc. Here we show a simple method of bulk g-C3N4 (BCN) synthesis using thermal polymerization of melamine and ultrathin 2D g-C3N4 nanosheets (NCN) prepared by ultrasonic exfoliation of BCN in water. The g-C3N4 samples were tested with XRD, FTIR, Raman, luminescence spectroscopy, and N2 adsorption at 77 K. We characterize its photocatalytic properties in H2 evolution by direct water splitting. We utilize the low-cost 10 W white LEDs photoreactor with visible light and flow conditions. In the water-splitting reaction, we found that the NCN were about 5 times more reactive than the primary BCN sample.

Single-Step Synthesis of Graphitic Carbon Nitride Nanomaterials by Directly Calcining the Mixture of Urea and Thiourea: Application for Rhodamine B (RhB) Dye Degradation

Recently, polymeric graphitic carbon nitride (g-C3N4) has been explored as a potential catalytic material for the removal of organic pollutants in wastewater. In this work, graphitic carbon nitride (g-C3N4) photocatalysts were synthesized using mixtures of low-cost, environment-friendly urea and thiourea as precursors by varying calcination temperatures ranging from 500 to 650 °C for 3 h in an air medium. Different analytical methods were used to characterize prepared g-C3N4 samples. The effects of different calcination temperatures on the structural, morphological, optical, and physiochemical properties of g-C3N4 photocatalysts were investigated. The results showed that rhodamine B (RhB) dye removal efficiency of g-C3N4 prepared at a calcination temperature of 600 °C exhibited 94.83% within 180 min visible LED light irradiation. Photocatalytic activity of g-C3N4 was enhanced by calcination at higher temperatures, possibly by increasing crystallinity that ameliorated the separation of photoinduced charge carriers. Thus, controlling the type of precursors and calcination temperatures has a great impact on the photocatalytic performance of g-C3N4 towards the photodegradation of RhB dye. This investigation provides useful information about the synthesis of novel polymeric g-C3N4 photocatalysts using a mixture of two different environmentally benign precursors at high calcination temperatures for the photodegradation of organic pollutants.

Gamma irradiation-induced elemental O/N co-doping and structural reinforcement in g-C3N4 photo-electrocatalyst

Herein, we reported a new modification of Urea-derived g-C3N4 through gamma radiation treatment (10 kGy up to 100 kGy) for enhancing the photoelectrochemical (PEC) water splitting performance. Undoubtedly, the gamma irradiation altered the morphology, crystallinity, optical absorption, chemical bonding and electronic properties of g-C3N4. The forceful ionizing radiation (gamma radiation) modified the elemental composition via co-doping of oxygen and nitrogen atoms in g-C3N4 structure. Gamma rays exposure modified the chemical bonding and electronic properties as elucidated via X-ray photoelectron spectroscopy (XPS) analysis, enhancing the photostability of the photoanode. The morphology transformed from seaweed structure to “compact” and “agglomerate” as the irradiation increased from 10 kGy up to 100 kGy, indicating improved catalytic sites, surface area as well as light absorption. However, as probed in by Raman spectroscopy, enhanced crystallinity with reinforced structure emerged significantly as observed in the (I707/I725) position. X-ray diffraction (XRD) also showed a larger crystallite sizes as the g-C3N4 samples were gamma irradiated. Moreover, post-irradiation shows a reduction in the band gap from 2.84 eV (pure g-C3N4) to 2.74 eV (radiated), respectively. All in all, the photocurrent density increased by >200 %, reaching ∼ 4.35 μA cm−2 and 8.26 μA cm−2 for the pristine and irradiated g-C3N4, respectively. Our findings express the significance of gamma irradiation for developing impressive photostable photoanodes via ionizing radiation (γ radiation).

Preparation and photocatalytic degradation of Sulfamethoxazole by g-C3N4 nano composite samples

Abstract Graphite-carbon nitride (g-C3N4) was prepared by thermocondensation, and g-C3N4/BiVO4 material (GCB) and g-C3N4/CNTs composite material (GCC) were prepared by doping different contents of BiVO4 and carbon nanotubes (CNTs) with g-C3N4 samples, respectively. Then, BiVO4, CNTs, and g-C3N4 samples with different contents were doped to prepare ternary composite material (GCBC). In the performance experiment, Sulfamethoxazole (SMZ) was used as degradation material to evaluate the photocatalytic performance of the prepared samples, and the degradation reaction kinetics equation, quadric cycle stability experiment, free radical capture, and intermediates identification were studied. The intermediates of photocatalytic degradation of SMZ were analyzed by high-performance liquid chromatography-mass spectrometry. From the experimental data, it can be seen that for SMZ solution, when the reaction time T = 0 min and retention time rt = 7.53 min, there is a peak corresponding to the substance with m/z [M + H]+ of 254, which is judged as SMZ. At 20, 40, and 60 min, rt was 2.00, 7.06, and 9.57 min, indicating the presence of intermediates in the photocatalytic process. Experimental analysis shows that there are three intermediates of SMZ degradation by composite sample GCBC. In this work, three kinds of composite materials were successfully prepared, and a variety of characterization, SMZ as pollutants, test the photocatalytic performance of composite materials (GCB, GCC, and GCBC) samples, and elucidated the cyclic stability of the material, active species capture, and photocatalytic degradation mechanism.

Synergistic effect of gold NPs modified graphitic carbon nitride nanotubes (g-CNT) with the role of hot electrons and hole scavengers for boosting solar hydrogen production

The efficient and selective photocatalysts for the evolution of hydrogen are highly demanding, however, many semiconductors are complex in nature and have lower photocatalytic efficiency. This is because of their small exposed surface area, poor light penetration, and unregulated charge recombination rate. Herein, well-designed graphitic carbon nitride with hierarchical nanotextures loaded with plasmonic gold (Au) nanoparticles has been investigated for stimulating photocatalytic H2 evolution. Hole scavengers, diffusion effects, duration, and mass transfer were used to evaluate the photoactivity activity in a slurry type continuous flow photoreactor system. Due to better charge carrier separation and enhanced light permeability, H2 evolution was boosted by two times when bulk g-C3N4 structure was alternated with graphitic carbon nitride nanotubes (g-CNT). The maximum H2 generation rate was 455 μmol g−1 h−1 with 0.3% Au/g-CNT nanotexture, which was 17.8 and 8.9 times greater than utilizing g-C3N4 and g-CNT samples, respectively. The key factors influencing this improvement in photoactivity were the unique interlayer opening, higher light penetration, more light utilization due to plasmonic effect, enhanced surface reactive active sites, and decreased charge carrier recombination. The hot electrons due to plasmonic gold was another important feature to promote H2 evolution rate under solar energy. It is possible to employ these freshly developed nanotextures, which have a gold plasmonic effect, for solar energy conversion and other energy-related applications.

Determination of the key role to affect the piezocatalytic activity of graphitic carbon nitride for tetracycline hydrochloride degradation in water

Graphitic carbon nitride (g-C3N4) has been proved to possess intrinsic piezoelectricity and its two-dimensional (2D) nanosheets present piezocatalytic activity to produce hydrogen from water splitting and eliminate organic pollutants in wastewater. Specific surface area and piezoelectric polarization are of great significance to achieve high piezocatalytic activity, but it is difficult to simultaneously improve both of them. Herein, to reveal the dominant role in the piezocatalysis of g-C3N4, we investigated the effect of exfoliation level on the piezocatalytic activity for degrading tetracycline hydrochloride (TC). Characterization results indicated that the specific surface area of the bulk g-C3N4 was much lower than those of exfoliated g-C3N4 samples due to the decrease of size and thickness. However, piezoresponse force microscopy (PFM) and kelvin probe force microscopy (KPFM) examinations suggested the bulk g-C3N4 possessed the biggest piezoelectric polarization that gradually declined as increasing the exfoliation temperature. Through testing the piezocatalytic abatement of TC, the activity decline following the order of decrease in polarization was confirmed, which demonstrated the piezoelectric polarization was the dominant factor in the piezocatalysis of g-C3N4. This conclusion was also verified by the step-by-step performance decrease of the bulk g-C3N4 during the successive four piezocatalytic runs, where the ultrasound treatment promoted the delamination of g-C3N4. In addition, superoxide (·O2−) radical, hydroxyl (·OH) radical and polarized positive charge were determined to be main active species, and accordingly the bulk g-C3N4 had the highest ·OH and ·O2− concentrations, as well as the highest piezocurrent response. This work reveals the main role to affect the piezocatalytic performance of g-C3N4, and also provides a possible strategy to design piezocatalysts with optimized piezocatalytic activity.

Plasmonic Ag-nanoparticles decorated phosphorus and boron co-doped g-C3N4 for enhanced photocatalytic H2 production

Solar water splitting by semiconductor photocatalysts has emerged as a favorable approach for green hydrogen production. Graphitic carbon nitride (g-C3N4) has gained substantial recognition amongst numerous semiconductor photocatalysts as a metal-free semiconductor with suitable band gap, appropriate band edge positions, and satisfactory photocatalytic activity for hydrogen production. However, its practical application is severely affected by high charge carrier recombination rate and inefficient visible light absorption. Introducing non-metal dopants into the g-C3N4 structure could suppress charge carrier recombination and tune the electronic property. Also, metal nanoparticles exhibit surface plasmon resonance (SPR) upon light interaction increasing the visible light absorption by the transport of hot electrons into the g-C3N4 framework. In this work, we report hybrid photocatalytic materials containing Ag-plasmonic metal and non-metal (B/P) dual heteroatom-doped g-C3N4 prepared via in-situ thermal polycondensation and succeeded by the photodeposition of Ag NPs. The structure of the prepared materials was studied through PXRD and FTIR spectroscopy; XPS was used for chemical analysis; SEM was used to study the morphology; and optical characteristics were studied through UV–Vis and PL spectroscopic techniques. The synergistic effects of SPR and heteroatom co-doping exhibit superior photocatalytic hydrogen production compared to pristine, B or P individual-doped, and B/P co-doped g-C3N4 samples. The optimized 1Ag/PBCN photocatalyst has demonstrated the highest photocatalytic hydrogen production rate of 1825 μmolh-1g−1, 18.3 times greater than g-C3N4. The modified hybrid material shows better activity due to the efficient charge carriers separation and extended visible light absorption. This work indicates that elemental co-doping and loading plasmonic nanoparticles on g-C3N4 to form hybrid nanocomposites may be a potential strategy to achieve better photocatalytic hydrogen evolution. The proposed methodology and outcomes will be helpful in the design and development of plasmon-enhanced hybrid photocatalysts for solar-driven green hydrogen production from water splitting.

Understanding the intermediates and carbon dioxide adsorption of potassium chloride-incorporated graphitic carbon nitride with tailoring melamine and urea as precursors

In this study, we demonstrated the synthesis of potassium chloride (KCl)-incorporated graphitic carbon nitride, (g-C3N4, CN) with varying amounts of N-vacancies and pyridinic-N as well as enhanced Lewis basicity, via a single-step thermal polymerization by tailoring the precursors of melamine and urea for carbon oxide (CO2) capture. Melamine, as a precursor, undergoes a phase transformation into melam and triazine-rich g-C3N4, whereas the addition of urea polymerizes the mixture to form melem and heptazine-rich g-C3N4 (CN11). Owing to the abundance of pyridinic-N and the high surface area, CN11 adsorbed higher amounts of CO2 (44.52 μmol m−2 at 25 °C and 1 bar of CO2) than those reported for other template-free carbon materials. Spectroscopic analysis revealed that the enhanced CO2 adsorption is due to the presence of pyridinic-N and Lewis basic sites on the surface. The intermediates of CO2adsorption, including carbonate and bicarbonate species, attached to the CN samples were identified using in-situ Fourier-transform infrared spectroscopy (FTIR). This work provides insights into the mechanism of CO2 adsorption by comparing the structural features of the synthesized KCl-incorporated g-C3N4 samples. CN11, with an excellent CO2 uptake capacity, is viewed as a promising candidate for CO2 capture and storage.

2D/2D V2C mediated porous g-C3N4 heterojunction with the role of monolayer/multilayer MAX/MXene structures for stimulating photocatalytic CO2 reduction to fuels

2D vanadium carbide (V2C) MXene nanosheets coupled 2D porous g-C3N4 (PCN) was designed and tested for photocatalytic CO2 reduction under visible light. Controlled coupling g-C3N4 with V2C MXene resulted in higher visible light absorption and efficient charge separation. Comparatively, V2C MXene found more favorable than V2AlC MAX due to more proficient charge separation. Highest performance was achieved with optimized 15%-V2C/g-C3N4, in which CO and CH4 generation rates of 151 and 205 µmol g−1, respectively, were attained. This enhancement was significantly higher than using V2AlC/g-C3N4 and pure g-C3N4 samples due to higher conductivity and large CO2 adsorption capacity. The performance of V2C/g-C3N4 composite was further examined under a variety of conditions such as pressure, catalyst loading, and reducing agents. With increasing pressure, higher yield of CO and CH4 was attained due to increased reactant adhesion to the catalyst surface, whereas increasing catalyst loading has adverse effects. Water was the best reducing agent for CO evolution, while the methanol–water system enhanced CH4 generation. Furthermore, the stability of composite lasted for several cycles without showing any obvious deterioration. The potential outcomes are assigned to a porous structure with intimate contact, effective charge carrier separation and porous 2D g-C3N4 transporting electrons towards MXene surface. This study shows that 2D V2C MXene could be a potential carrier for constructing 2D/2D heterojunctions in photocatalytic CO2 reduction to produce useful solar fuel.

Synergistic effect of Cu and Ru decoration on g-C3N4 for electrocatalytic CO2 reduction

Electrocatalytic CO2 reduction is an emerging approach for the reduction of CO2 in a feasible, green, and effective manner. In this study, bimetallic compounds of Cu and Ru were both decorated onto a π-conjugated g-C3N4 surface (CuxRuyCN), which functioned as an electrode for electrochemical CO2 reduction. From the X-ray photoelectron and X-ray absorption spectra, Cu and Ru on CuxRuyCN were identified as the oxidative states of CuO/Cu2O and RuO2, respectively. The mixed states of CuO and Cu2O served as active sites to both adsorb and activate CO2 for effective reduction, while RuO2 synergistically served as the hole-enrichment center and transferred H protons to promote CO2 reduction. Consequently, the electrochemical current density of CuxRuyCN was significantly enhanced compared with the corresponding densities of CN or Cu-doped CN. The current density of CuxRuyCN reduced to less than −0.05 mA cm−2 at an applied voltage of −1.5 V in an air or Ar atmosphere, indicating that the high current density of CuxRuyCN was associated with the flow of CO2 and its reduction. Moreover, the current density of CuxRuyCN was maintained at approximately −0.3 mA cm−2 for at least 2000 s at an applied voltage of −1.4 V (vs Ag/AgCl), indicating its high stability during CO2 reduction. In summary, both Cu and Ru-modified g-C3N4 samples used to produce CuO/Cu2O- and RuO2-decorated g-C3N4 acted as effective catalysts for electrocatalytic CO2 reduction and demonstrated several potential electrochemical applications.