Mesoporous Carbon Nitride Research Articles

Defect engineered mesoporous graphitic carbon nitride modified with AgPd nanoparticles for enhanced photocatalytic hydrogen evolution from formic acid

Hydrogen energy, as an ideal renewable resource and green energy replacement, has attracted growing attention. However, constructing highly active and stable catalysts for hydrogen evolution from Formic acid (FA) is still a challenging issue for development of renewable hydrogen energy. Herein, we develop a facile defect engineering strategy to construct N-deficient ordered mesoporous graphitic carbon nitride coupled with AgPd nanoparticles (denoted as AgPd/N-ompg-C3N4). Impressively, the as-prepared Ag0.1Pd0.9/N-ompg-C3N4 catalyst exhibits remarkable activity with the Turnover frequency (TOF) value of 1588.2 h−1 and robust stability with only a slight decrease in activity after ten cycles. Such markedly enhanced catalytic performance of Ag0.1Pd0.9/N-ompg-C3N4 is mainly attributed to the unique structure of N-ompg-C3N4 with higher surface area and abundant surface defects, the strong metal − support interaction between AgPd and N-ompg-C3N4, and charge transfer from Pd to Ag. This study provides a novel and efficient strategy for designing efficient catalysts to drive the hydrogen evolution from FA.

Organic terpyridine molecule as an efficient cocatalyst for metal–free CO2 photoreduction mediated by mesoporous graphitic carbon nitride

Metal-free catalytic conversion of CO2 with high selectivity and efficiency is promising for achieving carbon neutrality. However, nonmetallic catalytic sites for highly selective and efficient CO2 photoconversion are still challenging. In this work, organic terpyridine molecules are developed as highly active cocatalysts for visible-light-driven CO2 reduction with a CO evolution rate of 1.92 × 104 μmol g−1h−1 and 99.8% selectivity in aqueous solution, which is among the highest CO evolution rates for metal-free CO2 photoreduction. Mechanistic studies revealed that efficient electron transfer from organic light-absorbing photosensitizer to terpyridine molecules was mediated by mesoporous g-C3N4 (mpg-C3N4), with no need of much efforts to optimize inherent fast charge recombination of pristine mpg-C3N4. The synergistic effect of mpg-C3N4 and terpyridine molecule suppressed H2 evolution process from CB of mpg-C3N4 and promoted CO2 reduction at terpyridine sites. These results pave a feasible way to achieve robust metal-free CO2 photoreduction by employing organic molecular hybrid photocatalysis.

The heterojunction diode application of mesoporous graphitic carbon nitride (mpg-C3N4)

In this study, morphological properties and Schottky diode application of mpg-C3N4 material were investigated. XRD, SEM and TEM analyzes of this material were performed. When the SEM image is examined, it is seen that mpg-C3N4 particles are coated on the surface homogeneously. The p-Si crystal was used as the base material and mesoporous graphitic carbon nitride material mpg-C3N4 was coated on the crystal with spin coating. Thus, reference and mpg-C3N4/p-Si heterojunctions were fabricated. Using the current-voltage (I–V) measurements of the diode, the ideality factory (n) and barrier height (Φb) values were calculated at the room temperature. These values of Ni/mpg-C3N4/p-Si/Al heterojunction diode were determined as n = 1.25 and Φb = 0.83 eV by the Thermionic Emission (TE) method. Furthermore diode parameters (n, Φb and series resistance (Rs) were determined with Cheung and Norde functions. Also capacity-voltage (C–V) measurements of this device were taken for different frequency values. Using this measurements carrier concentration (Na), barrier heights (Φb), Fermi energy level (Ef) and diffusion potential (Vd) values were determined.

Highly Mesoporous g-C3N4 with Uniform Pore Size Distribution via the Template-Free Method to Enhanced Solar-Driven Tetracycline Degradation.

A highly mesoporous graphitic carbon nitride g-C3N4 (GCN) has been produced by a template-free method and effectively photodegrade tetracycline (TC) antibiotic under solar light irradiation. The mesoporous GCN (GCN-500) greatly improves the photoactivity (0.0247 min−1) by 2.13 times, as compared to that of bulk GCN (0.0116 min−1). The efficiently strengthened photoactivity is ascribed to the high porosity (117.05 m2/g), and improves the optical absorption under visible light (Eg = 2.65 eV) and good charge carrier separation efficiency. The synthesized mesoporous GCN shows a uniform pore size (~3 nm) distribution. GCN-500 shows large pore volume (0.210 cm3/g) compared to GCN-B (0.083 cm3/g). Besides, the GCN-500 also exhibits good recyclability and photostability for TC photodegradation. In conclusion, GCN-500 is a recyclable photocatalyst for the removal of TC under visible light irradiation.

Effect of carbon nitride synthesized by different modification strategies on the performance of carbon nitride/PVDF photocatalytic composite membranes

Carbon nitride (CN)/polyvinylidene fluoride (PVDF) photocatalytic composite membrane (PCM) is considered as a promising candidate to improve the anti-fouling characteristic of conventional PVDF membrane and overcome the difficulty encountered during recovery of powder catalyst simultaneously. However, the effects of differently-modified CN on PCM and its mechanism are still unclear. In this study, bulk-CN (BCN), carbon defects CN (CCN), nitrogen defect CN (DCN), mesoporous CN (MCN), and nitrogen-rich CN (NCN) were incorporated into PVDF by phase inversion method. The influence of changes in the physical and chemical properties of CN, including hydrophilic groups, photocatalytic activity, and particle size, on the permeability, anti-fouling characteristic, and photocatalytic self-cleaning activity of CN/PVDF was systematically analyzed. The mechanism of excellent performance of PCM was revealed by experimental test and theoretical calculation. The flux of PCM was significantly improved by increasing the hydrophilic group on modified CN. However, the differences in particle size and interaction between different types of modified CN and PVDF chains endowed the CN/PVDF with different porosity. DCN/PVDF showed high porosity and hydrophilicity, leading to high water flux and rejection rate of 293.6 L (m2 h)−1 and 90.1%, respectively. Compared to pure PVDF, the flux recovery rate of DCN30/PVDF increased by 27.6%, and the irreversible fouling decreased from 36.9% to 9.2%. The modified CN/PVDF showed excellent photocatalytic activity for the removal of cefotaxime (CFX) and E. coli. Owing to the narrow band gap of DCN, large specific surface area, and low photogenerated carrier recombination rate, the CFX removal rate reached 99% in 2 h, and E. coli inactivation achieved 3.7 log within 4 h via DCN30/PVDF.

3D mesoporous ultra-thin g-C3N4 coupled with monoclinic β-AgVO3 as p-n heterojunction for photocatalytic hydrogen evolution

In this study, 3D mesoporous ultra-thin graphite carbon nitride (UCN) was successfully prepared using a simple hydrothermal pretreatment route and annealing step. The β-AgVO3 nanorods prepared by the hydrothermal method were uniformly anchored into the UCN network, and a novel type of UCN/β-AgVO3 p-n heterojunction photocatalyst was synthesized. The porous structure not only provides more surface active sites for hydrogen production, but also facilitates mass transfer at the contact interface between UCN and β-AgVO3. UV–Vis diffuse reflectance spectroscopy and fluorescence tests showed that UCN/β-AgVO3 exhibits excellent visible light trapping ability and broadened spectral absorption range, extending the life of photoinduced carriers. The results of photoelectric chemistry tests revealed that the composite material has more effective charge separation efficiency and greatly reduces the hydrogen evolution overpotential. The overall structure effectively promotes the utilization of photosensitizer and sacrificial agents, and achieves excellent hydrogen evolution efficiency. This work provides a feasible strategy for the rational design of binary synergistic photocatalytic systems with porous nanomaterials as the core.

Excellent stability of Pd/mpg-C3N4 in catalytic hydrodebenzylation of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12- hexaazaisowurtzitane (HBIW)

The low stability and poisoning of the palladium-based catalysts in the debenzylation of HBIW elevated the cost of the hydrogenolysis, and thus restricted the application of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW). To address this problem, Pd/mpg-C3N4 was prepared by depositing palladium nanoparticles on mesoporous graphite carbon nitride (mpg-C3N4), and used for the catalytic hydrogenolysis in the conversion of HBIW to TADBIW under the atmospheric pressure. After optimizing the reaction condition and the usage amount, the highest yield of 81.7 % was obtained at 45℃ after reaction for 8 h when the ratio of palladium to HBIW was 1%. A yield of 74 % was obtained when the ratio of palladium to HBIW was 0.4 %. More importantly, Pd/mpg-C3N4 can be recycled unprecedently for three times in the conversion of HBIW to TADBIW while preserving the reasonable activity. Such results should benefit for promoting the application of HNIW and also the design of the heterogeneous catalysts for hydrodebenzylation.

Enhanced photocatalytic degradation of dimethyl phthalate by magnetic dual Z-scheme iron oxide/mpg-C3N4/BiOBr/polythiophene heterostructure photocatalyst under visible light

A new magnetic dual Z-scheme heterostructure photocatalyst, consisting of mesoporous graphitic carbon nitride (mpg-C3N4), BiOBr, polythiophene (PTh), and magnetic iron oxide, was developed, and its structural, optical, and electrochemical properties were analyzed. The photocatalyst was employed for the degradation of dimethyl phthalate (DMP) in water under visible light to evaluate its photocatalytic activity. The results revealed that the photocatalytic activity of the new heterostructure photocatalyst was superior to that of its single-component counterparts. The reaction kinetics of photocatalytic DMP degradation followed pseudo first-order kinetics and the reaction rate constant was 3.7- and 4.5-fold higher than those of pristine g-C3N4 and BiOBr, respectively. The enhanced photocatalytic performance was chiefly attributed to the dual Z-scheme heterostructure generated between mpg-C3N4, PTh, and BiOBr, which effectively hindered the recombination of photogenerated electron and hole pairs in mpg-C3N4 and BiOBr, improving the photogenerated carrier transfer efficiency. Radical trapping test results indicated that the active species, h+, ·O2–, and ·OH, coexisted during the photocatalytic reaction process, and that h+ played a major role in the destruction of DMP molecules. DMP was degraded into intermediate small-molecule products, such as acids and alcohols, which were ultimately mineralized to CO2 and H2O. The magnetic property of the new heterostructure photocatalyst enabled its straightforward separation from water using magnetic separation technology for further reuse. This study provides a new material and method for the effective removal of DMP from aqueous solution.

Perylenetetracarboxylic diimide covalently bonded with mesoporous g-C3N4 to construct direct Z-scheme heterojunctions for efficient photocatalytic oxidative coupling of amines

Photocatalytic oxidative coupling of amines is a promising method for imine synthesis. In this paper, a robust covalently-bonded direct Z-scheme heterostructure (PDI/mpgCN) for photocatalytic oxidative coupling of amine was reported for the first time. Perylenetetracarboxylic diimide (PDI) molecules were covalently connected to the surface of mesoporous carbon nitride (mpgCN) via an in-situ condensation strategy. Compared with the poor conversion efficiency upon pristine g-C3N4, PDI/mpgCN heterostructure exhibits a remarkable enhancement on amine oxidation rate (AOR), with the optimal AOR reaches to as high as 20.63 mmol g−1 h−1 upon 20 % PDI/mpgCN. As far as we know, it is the highest AOR achieved so far for amine photooxidation coupling with heterojunction materials. Transient absorption studies proved the formation of Z-scheme junction, and efficient interfacial charge transfer. Our study not only makes an insight into the heterojunction design with chemical bond precision, but highlights the great prospects of Z-scheme photocatalyst in photo-chemical synthesis.

Acid-assisted synthesis of nitrogen-deficient mesoporous graphitic carbon nitride for hydrogen storage

Defect engineering is an important strategy to tune the surface physical and chemical properties of carbon nitride materials. Herein, a nitrogen-deficient mesoporous graphitic carbon nitride (ND-MCN) with a high specific surface area of 62.6 m2 g−1 was synthesized via hydrochloric acid-assisted thermal polycondensation of melamine and its potential application in hydrogen storage was investigated. Hydrochloric acid acting as activation agent can increase the specific surface area of carbon nitride, and introduce nitrogen-vacancy defects into the framework, leading to a stronger interaction between ND-MCN and hydrogen molecules. As a result, the ND-MCN shows a high hydrogen storage density of 6.39 × 10−3 wt%·g m−2 at 298 K under 20 bar.

Synthesis of novel Ag-modified Pd-supported mesoporous carbon nitride for selective hydrogenation of acetylene with an excellence ethylene selectivity

Novel nanocatalysts were developed for selective hydrogenation of acetylene to ethylene. The mesoporous carbon nitride (MCN) was synthesized and employed as catalyst support that was loaded by Pd active sites. Moreover, for the first time, the Pd loaded MCN nanocatalysts were modified by different Ag/Pd ratios (in the range of 0.5:1, 1:1, and 3:1) which could bring about great results in terms of the acetylene conversion and ethylene selectivity. The prepared Ag–Pd/MCN nanocatalysts were thoroughly characterized by FESEM, TEM, BET, FTIR, and XRD methods. The catalytic performance of the nanocatalysts was evaluated in temperature range of 40–200 °C. It was found that loading Pd over the MCN results in better performances compared to the commercial Pd/α−Alumina catalyst. Furthermore, modifying the Pd/MCN nanocatalysts by adding Ag led to significant performances with about 99.8% acetylene conversion. In addition, the ethylene selectivity of the sample prepared by using the optimum Ag/Pd ratio (1:1), reached 98.1% at 200 °C which is an excellent performance. The significant performance of the Ag–Pd/MCN (1:1) nanocatalyst in selective acetylene hydrogenation is attributed to the simultaneous roles of MCN catalyst support (with the surface area of 152 m2/g) and also the Ag modifiers which could modify the adsorption strength of the Pd active sites toward ethylene and accordingly enhance the ethylene selectivity.

Strontium oxide modified mesoporous graphitic carbon nitride/titanium dioxide nanocomposites (SrO-mpg-CN/TiO2) as efficient heterojunction photocatalysts for the degradation of tetracycline in water

We report herein a facile synthesis of a ternary nanocomposite of strontium oxide modified mesoporous graphitic carbon nitride supported titanium dioxide (SrO-mpg-CN/TiO2) as an efficient heterojunction photocatalyst for the degradation of tetracycline (TC) in water. The morphology, optical and textural properties of as-prepared nanocomposites are systematically investigated by various advanced analytical techniques, and the structure-photocatalytic efficiency was related by proposing a plausible mechanism. The photocatalytic performance of SrO-mpg-CN/TiO2 nanocomposites was evaluated in the TC degradation in water by studying several reaction parameters including the catalyst dosage, initial TC concentration, pH and irradiation time. The photocatalytic experiments exhibited that the activity of SrO-mpg-CN/TiO2 nanocomposites for TC degradation was higher than binary SrO-mpg-CNnanocomposites and pristine TiO2. The enhanced photocatalytic activity of SrO-mpg-CN/TiO2 nanocomposites is attributed to the moderator role of SrO for electron transportation in the photocatalysis mechanism, which ensures a high charge mobility, suppresses electron/hole recombination, and improves the redox capacity under UVA irradiation. The detailed optimization studies revealed that the highest TC degradation efficiency of 91.73% was obtained by using 0.1 g/L catalyst dosage and 10 mg/L TC concentration at natural pH of 5.06 for 180 min reaction time under UVA irradiation. Moreover, the scavenging experiments showed that OHads· andO2·-radicals are the dominant species for the TC degradation in water. Moreover, SrO-mpg-CN/TiO2 nanocomposites were reusable up to the five successive runs without a significant drop in their initial activity.

Dual-atom Pt heterogeneous catalyst with excellent catalytic performances for the selective hydrogenation and epoxidation

Atomically monodispersed heterogeneous catalysts with uniform active sites and high atom utilization efficiency are ideal heterogeneous catalytic materials. Designing such type of catalysts, however, remains a formidable challenge. Herein, using a wet-chemical method, we successfully achieved a mesoporous graphitic carbon nitride (mpg-C3N4) supported dual-atom Pt2 catalyst, which exhibited excellent catalytic performance for the highly selective hydrogenation of nitrobenzene to aniline. The conversion of ˃99% is significantly superior to the corresponding values of mpg-C3N4-supported single Pt atoms and ultra-small Pt nanoparticles (~2 nm). First-principles calculations revealed that the excellent and unique catalytic performance of the Pt2 species originates from the facile H2 dissociation induced by the diatomic characteristics of Pt and the easy desorption of the aniline product. The produced Pt2/mpg-C3N4 samples are versatile and can be applied in catalyzing other important reactions, such as the selective hydrogenation of benzaldehyde and the epoxidation of styrene.

Precursor Nuclearity and Ligand Effects in Atomically‐Dispersed Heterogeneous Iron Catalysts for Alkyne Semi‐Hydrogenation

AbstractNanostructuring earth‐abundant metals as single atoms or clusters of controlled size on suitable carriers opens new routes to develop high‐performing heterogeneous catalysts, but resolving speciation trends remains challenging. Here, we investigate the potential of low‐nuclearity iron catalysts in the continuous liquid‐phase semi‐hydrogenation of various alkynes. The activity depends on multiple factors, including the nuclearity and ligand sphere of the metal precursor and their evolution upon interaction with the mesoporous graphitic carbon nitride scaffold. Density functional theory predicts the favorable adsorption of the metal precursors on the scaffold without altering the nuclearity and preserving some ligands. Contrary to previous observations for palladium catalysts, single atoms of iron exhibit higher activity than larger clusters. Atomistic simulations suggest a central role of residual carbonyl species in permitting low‐energy paths over these isolated metal centers.

A molecular approach to the synthesis of platinum-decorated mesoporous graphitic carbon nitride as selective CO2 reduction photocatalyst

Platinum nanoparticles (Pt-NPs) have been directly synthesized through the organometallic approach onto the surface of mesoporous graphitic carbon nitride (mpg-CN) semiconductor with two different metal loadings. Thorough multi-technique characterization reveals a very good dispersion of nanoparticles with a narrow size distribution centered at ca. 2.5 nm, regardless of the metal loading, and composed primarily of platinum metal with a minor contribution of oxidic surface species. Compared to bare mpg-CN, the Pt-NPs decorated materials show improved charge separation properties upon band gap excitation, ascribed to electron extraction by Pt-NPs from the conduction band of mpg-CN, as demonstrated by time-resolved fluorescence measurements. The so-obtained materials show photocatalytic activity for CO2 reduction under both UV and visible light irradiation, with improved selectivity towards highly reduced products such as methanol and methane with respect to the bare semiconductor, which leads to the formation of carbon monoxide as the main product. The obtained results shed light on the pathways that determine selectivity in photocatalytic CO2 conversion, contributing to the development of selective photocatalysts, which is one of the cornerstones in this promising technology for direct solar-to-chemical energy conversion.

Peroxydisulfate activation by photo-generated charges on mesoporous carbon nitride for removal of chlorophenols

Photogenerated charges were found to involve in activation of peroxydisulfate (PDS) on mesoporous carbon nitride (MCN) with Lewis basic sites under visible light irradiation. Photogenerated hole (h+), superoxide radical (O2·−) and singlet oxygen (1O2) were verified as the most important active species for 2,4,6-trichlorophenol (TCP) removal. Lewis basic sites of MCN induced the interface hydrolysis of PDS to produce hydroperoxyl anions (HOO−) and peroxide ions (O22−), which was further reacted with h+ to generate O2·− and 1O2 predominantly. The efficiently separated electron (e−) was responsible for the nucleophilic attack toward the CCl bond of TCP. Moreover, the electrical energy per order (EEO) of vis/MCN/PDS (3.75 × 106 kW h m−3 order−1) was an order of magnitude lower than that of UV/PDS (3.14 × 107 kW h m−3 order−1). This work highlighted the metal-free MCN with Lewis basic sites as a photocatalyst to activate PDS and elucidated a new strategy of PDS activation for chlorophenol pollutants removal.

Construction of mesoporous C3N4/rGO composite with enhanced visible light photocatalytic activity

A feasible template-free calcination method was carried out to synthesize the hybrid of mesoporous graphitic carbon nitride (mpg-C3N4) and reduced graphene oxide (rGO) with highly efficient photocatalytic ability. The morphology and microstructure of the heterojunction photocatalysts (mpg-C3N4/rGO) were characterized and discussed. The results revealed that the mpg-C3N4/rGO exhibited high surface area 84.974 m2/g and mesoporous morphology, which provides tremendous contact area for rGO sheets. The introduction of rGO led to red-shift of the absorption spectrum and improved the conductive property of the mpg-C3N4/rGO, facilitating the transfer of photo-generated electrons. The formation of heterojunction provided an efficient transfer pathway to separate the photoinduced carriers. The mpg-C3N4/rGO heterojunction exhibited an enhanced visible light-activated degradation of rhodamine B (RhB). The RhB dye was almost removed within 40 min, exhibiting higher photocatalytic efficiency about 5.7 times that of pristine g-C3N4. The synergetic effect of mesporous framework and interface heterojunction contributes to the prominent performance of the photocatalyst.

Photocatalytic integrated production of hydrogen and imines from aromatic amines via Ni-mesoporous carbon nitride: An acceptorless dehydrogenative pathway

Photocatalysis manifests an invariably quite sustainable process for various chemical transformations. Utilization of electrons and holes for H2 production and organic transformation boost up the chemical economics for the simultaneous production of H2 and value-added organic chemicals. This work demonstrated a photocatalytic acceptorless dehydrogenation (PAD) of aromatic amines to imines coupled with H2 evolution over mesoporous carbon nitride (SGCN) photocatalyst by using non-noble metal (Ni). As synthesized 2 wt% Ni@SGCN catalyst showed superior photocatalytic activity (visible light) for furfuryl amine valorization with H2 generation rate of 5.03 μmol/h/g along with 12.5% conversion to imine in 6 h. Among all, 4-methoxybenzylamine depicted a high H2 production rate of 23.58 μmol/h/g along with a maximum 36% conversion in 6 h. Eventually, an experiment under natural sunlight showed an H2 generation rate of 4.6 μmol/h/g along with 12% conversion of furfuryl amine in 6 h. Moreover, the AQE (%) of the H2 production was estimated to be 1.1% (400 nm, 20 mg catalyst).

Metal-free in situ carbon-nanotube-modified mesoporous graphitic carbon nitride nanocomposite with enhanced visible light photocatalytic performance

We synthesized a metal-free photocatalyst comprising mesoporous carbon nitride (mpg-C3N4) and carbon nanotubes (CNT), via a facile method involving polymerization of melamine as the precursor in the presence of CNT in refluxing methanol. Under visible light, the CNT/mpg-C3N4 composite resulted in a greater than 8.6 × faster rhodamine B photodecomposition rate compared with bulk graphitic C3N4, and 1.6 × faster compared with pure mpg-C3N4. We attribute the promoted photocatalytic performance of the composite to the synergistic effects of open-ended CNT and mpg-C3N4. The highly interconnected CNT in mpg-C3N4 effectively enhances the transfer of photo-generated electrons, harvests more incident visible light, and provides specific channels for oxygen adsorption and photoreactions. We propose a possible reaction mechanism and report a scavenger experiment that found that superoxide radical (·O2−) is mainly responsible for dye photodegradation. The CNT/mpg-C3N4 retained good stability after several cycles. This work supplies a promising method of exploiting a stable, metal-free, efficient, and visible light-driven semiconductor to enhance solar energy use for environmental remediation.

Continuous Gas–Liquid–Solid Slug Flow for Sustainable Heterogeneously Catalyzed PET-RAFT Polymerization

Gas-liquid-solid (G-L-S) three-phase slug flow provides an efficient pathway to utilize solid catalysts in continuous flow and was adopted in the mesoporous graphite carbon nitride (mpg-C3N4)-catalyzed photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of methyl methacrylate (MMA) in this work. Kinetic studies and chain extension experiments illustrated the realization of reversible deactivation radical polymerization (RDRP) and the to scale upadvantage of a continuous-flow reactor as compared to its batch counterpart. The light intensity played an important role on the PET-RAFT polymerization. An increasing amount of photocatalyst favored the monomer conversion within a limited range due to higher light blockage, and the monomer conversion reached a stable level at a lower catalyst concentration when higher light power was applied. When compared with fully continuous flow, the G-L-S slug flow was beneficial to the PET-RAFT polymerization due to the intensified swirling strength and narrower velocity field. Decreasing the gas-To-slurry ratio also led to narrower velocity distribution, which favored the polymerization as well. Moreover, the polymerization rates remained stable in multiple recycles, demonstrating that the present G-L-S slug flow was a reliable and easy processing approach for utilizing the solid catalyst.