Fabrication of a Nanosized g-C3N4-Loaded Cellulose Microfiber Bundle to Induce Highly Efficient Water Treatment via Photodegradation

Graphite carbon nitride (g-C3N4) with a suitable structure and strong amine activity is designed and prepared to serve as a hydrogen bond donor for the microfibrilization of corncob cellulose to form a cellulose microfiber (CMF) bundle. Simultaneously, well-dispersed nanosized g-C3N4 is loaded into the bundle to form a photocatalyst for efficient photodegradation of rhodamine B (Rh B) in water. Under the optimal preparation conditions at 165 °C, 10 min, and 0.08 mol/L H2SO4, the yield of g-C3N4-functionalized cellulose microfibers (CMF-g-C3N4) reaches to the highest over 70%. The catalytic rate of CMF-g-C3N4 is 3.3 times larger than that of pure g-C3N4. The degradation rate of Rh B is maintained at over 90% in 10 cycles of photocatalytic degradation. The obtained CMF-g-C3N4 also has good thermal stability and mechanical properties. This research suggests a particularly simple way to transform cellulose into a highly efficient photocatalyst for water treatment.

Electrostatic Self-Assembled Synthesis of Amorphous/Crystalline g-C3N4 Homo-Junction for Efficient Photocatalytic H2 Production with Simultaneous Antibiotic Degradation

g-C3N4 has been regarded as a promising photocatalyst for photo-reforming antibiotics for H2 production but still suffers from its high charge recombination, which has been proven to be solvable by constructing a g-C3N4 homo-junction. However, those reported methods based on uncontrollable calcination for preparing a g-C3N4 homo-junction are difficult to reproduce. Herein, an amorphous/crystalline g-C3N4 homo-junction (ACN/CCN) was successfully synthesized via the electrostatic self-assembly attachment of negatively charged crystalline g-C3N4 nanorods (CCN) on positively charged amorphous g-C3N4 sheets (ACN). All the ACN/CCN samples displayed much higher photo-reforming of antibiotics for H2 production ability than that of pristine ACN and CCN. In particular, ACN/CCN-2 with the optimal ratio exhibited the best photocatalytic performance, with a H2 evolution rate of 162.5 μmol·g-1·h-1 and simultaneous consecutive ciprofloxacin (CIP) degradation under light irradiation for 4 h. The UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and electrochemical results revealed that a homo-junction is formed in ACN/CCN due to the difference in the band arrangement of ACN and CCN, which effectively suppressed the charge recombination and then led to those above significantly enhanced photocatalytic activity. Moreover, H2 was generated from the water reduction reaction with a photogenerated electron (e-), and CIP was degraded via a photogenerated hole (h+). ACN/CCN exhibited adequate photostability and reusability for photocatalytic H2 production with simultaneous CIP degradation. This work provides a new idea for rationally designing and preparing homo-junction photocatalysts to achieve the dual purpose of chemical energy production and environmental treatment.

NOx degradation ability of S-g-C3N4/MgAl-CLDH nanocomposite and its potential application in cement-based materials

In this study a new photocatalytic nanocomposite, S-g-C₃N₄/MgAl-CLDH, was synthesized and implemented into cement mortar by internal mixing or coating. The photocatalytic NO_x degradation efficiency of the S-g-C₃N₄/MgAl-CLDH and photocatalytic mortar was investigated. The NO_x degradation efficiency and photoluminescence spectra of S-g-C₃N₄/MgAl-CLDH after being immersed in the simulated concrete pore solution were evaluated to assess its chemical stability. The results show that compared with S-g-C₃N₄, the S-g-C₃N₄/MgAl-CLDH exhibits a narrower bandgap (2.45 eV), a lower photogenerated electron-hole pair recombination rate and a higher specific surface area (36.86 m² g^-1). After 21 min of visible light irradiation, the NO_x degradation rate of S-g-C₃N₄/MgAl-CLDH achieves 100% as compared to merely 81.5% of S-g-C₃N₄. After being submerged in simulated concrete pore solution, the S-g-C₃N₄/MgAl-CLDH exhibits only a slight decrease of 5% in degradation rate after 12 min of irradiation, confirming a good compatibility and stability in cement-based materials. The NO_x degradation ability of the internally mixed mortar is enhanced with an increase in the dosage of S-g-C₃N₄/MgAl-CLDH. For coated mortar, in contrast, a decline in NO_x degradation rate is observed after 5 layers of coating owing to the lower porosity of mortar after excessive coating.

A review on dimensionally controlled synthesis of g-C3N4 and formation of an isotype heterojunction for photocatalytic hydrogen evolution

g-C3N4-based isotype heterojunction towards visible light induced photocatalytic H2 generation.

Linear piezoresistive strain sensor based on graphene/g-C3N4/PDMS heterostructure

Here we report a novel hybrid material consists of 2D graphitic carbon nitride (g-C₃N₄) and graphene heterostructure that exhibits piezoresistivity superior to graphene and potentially being used as a strain sensor. The g-C₃N₄ that contains periodically spaced triangular nanopores is used for improving the piezoresistivity of the sensor imparting change in the polarization upon application of strain. In this work, we have investigated graphene/g-C₃N₄ interfaced materials and quantified its piezoresistive effects through experimental analysis and density functional theory (DFT) based computational studies provide insights into the electronic structures of the hybrid interfaces. We have observed a linear response in electrical resistance for a wide range of uniaxial strains up to ∼25%. The observed increase in resistance upon application of strain corroborates with our computational finding of strain-dependent band gap opening. Further, it has been realized that band-gap opening occurs exclusively in the graphitic layer of the composite materials under strain. However, the g-C₃N₄ bands remain intact at the interface. The linearity and a considerably small gauge factor (1.89) make graphene/g-C₃N₄ a promising heterostructure material unlike conventional metal gauge sensor in wide strain pressure sensor devices.

Self-cleaning isotype g-C3N4 heterojunction for efficient photocatalytic reduction of hexavalent uranium under visible light

Photocatalysis is a promising method to eliminate hexavalent uranium (U(Ⅵ)) and recycle it from wastewater. However, most of researched photocatalysts are metal-contained, inactive in visible light, and inconvenient to recycle, which unfortunately impedes the further utilization of photocatalytic technology in U(Ⅵ) pollution treatment. Herein, g-C₃N₄ isotype heterojunction with interpenetrated tri-s-triazine structure (ipCN) was prepared by inserting urea into the interlayer of tri-s-triazine planes of thiourea-derived g-C₃N₄ and in-site thermal treating. The synthesized nanocomposites were used to convert soluble U(Ⅵ) ions into U(Ⅳ) sediment under visible light. Experimental and characterization results reveal that ipCN possess larger BET surface area, more negative-charged surface, higher U(Ⅵ) adsorption capability, and more efficient mass diffusion and charges transfer properties. With these excellent characteristics, nearly 98% U(Ⅵ) could be removed within 20 min over ipCN_5:1 and 92% photoreduction efficiency could also be kept after 7 cycle uses, which were equal to or even superior than most reported metal-based photocatalysts. It is also proven that the configuration of U(Ⅵ) and photogenerated ·O₂^- play a significant role in the photocatalytic U(Ⅵ) reduction process, with (UO₂)_x(OH)_y^2x-y are more prone to be adsorbed and the photoinduced process of ·O₂^- will steal electrons from photocatalysts. Furthermore, with the self-generated ·O₂^- and H₂O₂, a green and facile regeneration process of photocatalysts was proposed This work provides a promising scheme to extract U(Ⅵ) from the perspectives of photocatalysts exploitation, photocatalytic reduction, and photocatalysts regeneration, which is meaningful for the sustainable U(Ⅵ) resource recovery and U(Ⅵ) pollution purification.

Manipulatable Interface Electric Field and Charge Transfer in a 2D/2D Heterojunction Photocatalyst via Oxygen Intercalation

Charge separation is the most important factor in determining the photocatalytic activity of a 2D/2D heterostructure. Despite the exclusive advantages of 2D/2D heterostructure semiconductor systems such as large surface/volume ratios, their use in photocatalysis is limited due to the low efficiency of charge separation and high recombination rates. As a remedy for the weak interlayer binding and low carrier transport efficiency in 2D/2D heterojunctioned semiconductors, we suggested an impurity intercalation method for the 2D/2D interface. PtS2/C3N4, as a prototype heterojunction material, was employed to investigate the effect of anion intercalation on the charge separation efficiency in a 2D/2D system using density functional theory. With oxygen intercalation at the PtS2/C3N4 interface, a reversed and stronger localized dipole moment and a built-in electric field were induced in the vertical direction of the PtS2/C3N4 interface. This theoretical work suggests that the anion intercalation method can be a way to control built-in electric fields and charge separation in designs of 2D/2D heterostructures that have high photocatalytic activity.

Construction of phosphorus-doped carbon nitride/phosphorus and sulfur co-doped carbon nitride isotype heterojunction and their enhanced photoactivity

Photocatalysis was one of the most promising techniques for environmental remediation. Exploring photocatalysts with high efficiency, low cost and easy preparation was still an ongoing issue. In this work, phosphorus-doped carbon nitride/phosphorus and sulfur co-doped carbon nitride (P-C₃N₄/PS-C₃N₄) isotype heterojunction was prepared by a two-step calcination method. The composite displayed a sheet-like structure with a surface area of 23 m²/g. Compared with pure C₃N₄, band gaps of P-C₃N₄ and PS-C₃N₄ were only slightly modified during the heteroatom-doping process. Therefore, a well-matched band alignment was constructed, which not only improved the separation efficiency of photogenerated electron-hole pairs, but also well preserved the high oxidizability of holes on valance band and good reducibility of electrons on conduction band. Because of the similarity in physicochemical properties, the interface resistance between P-C₃N₄ and PS-C₃N₄ was low, which accelerated the electron transfer and prolonged the lifetime of charge carriers. Although the visible-light utilization was somewhat low in comparison with P-C₃N₄ and PS-C₃N₄, by taking advantage of above merits, P-C₃N₄/PS-C₃N₄ displayed the high photocatalytic activity in rhodamine B degradation, and the reaction rate constant was 0.183 min^-1, about 8.7 and 4.0 times higher than those of P-C₃N₄ and PS-C₃N₄. Besides high catalytic activity, isotype heterojunction displayed good recyclability, since 95.3% of catalytic activity was maintained after the 5^th cycle. The method presented here was facile, economic and environmentally benign, thus it was highly attractive for the application in environmental remediation.

Photocatalytic degradation of trihalomethanes and haloacetonitriles on graphitic carbon nitride under visible light irradiation

Trihalomethanes (THMs) and haloacetonitriles (HANs), most common disinfection by-products in drinking water, pose adverse environmental impacts and potential risks to human health. There is a pressing need to develop innovative, economically feasible, and environmentally benign processes to control these persistent contaminants. In this paper, visible-light-responsive graphitic carbon nitride (g-C₃N₄) samples were synthesized to degrade the THMs and HANs and the photocatalytic degradation mechanism was explored. The results indicated that a carbon-doped g-C₃N₄ with an optimum dopant content (MCB_0.07) displayed the best photocatalytic activity for the total trihalomethanes (TTHM) and total haloacetonitriles (THAN), with the reaction rate constant of 11.6 and 10.4 (10^-3 min^-1), respectively. MCB_0.07 demonstrated a high THMs and HANs removal efficiency under visible light irradiation and could be reused. According to scavenger tests of the selected reactive species and X-ray photoelectron spectroscopy, holes play a dominant role for both THMs and HANs degradation on the MCB_0.07. The degradation of HANs by holes proceeded mainly through breakage of the CC bond in the CCN group. The THMs degradation was achieved through hydrogen abstraction or/and dehalogenation. The brominated-THMs/HANs were more photosensitive than their chlorinated analogous and were less stable than bromo-chloro-THMs/HANs. This study sheds light on the mechanism of the photocatalytic degradation of THMs and HANs under visible light irradiation by carbon-doped g-C₃N₄. Furthermore, it could provide insights for engineering applications and contaminant control in drinking water purification.

Fabrication of a full-spectrum-response Cu2(OH)2CO3/g-C3N4 heterojunction catalyst with outstanding photocatalytic H2O2 production performance via a self-sacrificial method

Over the past few decades, near infrared light (NIR), as an important part of sunlight, has seldom been utilized in photocatalytic reactions.

Construction of a wide-spectrum-driven VN-g-C3N4/Cu2(OH)2CO3 heterojunction catalyst from VIS to NIR light via the in situ self-sacrificial method: the effect of oxygen on the N2 photofixation ability

In this work, an N vacancy-doped g-C₃N₄/Cu₂(OH)₂CO₃ (V_N-GCN/CuCOH) heterojunction catalyst with superior wide-spectrum-driven (from VIS to NIR) N₂ photofixation ability was synthesized via the in situ self-sacrificial method.

Chemical Simultaneous Synthesis Strategy of Two Nitrogen-Rich Carbon Nanomaterials for All-Solid-State Symmetric Supercapacitor

Present work demonstrates a single step process for simultaneous synthesis of metal-nanoparticle-encapsulated nitrogen-doped bamboo-shaped carbon nanotubes (M/N-BCNTs) and graphitic carbon nitride (G-C₃N₃). The synthesis of two different carbon nanostructures in a single step is recognized for the first time. This process involves the use of inexpensive and nontoxic precursors such as melamine as carbon and nitrogen sources for the growth of G-C₃N₃ and M/N-BCNTs. In this technique, the utilization of unwanted gases such as ammonia and hydrocarbons released during the decomposition of melamine is the key to grow M/N-BCNTs over the catalyst along with the formation of G-C₃N₄. The implementation of M/N-BCNTs as the electrode material for all-solid-state symmetric supercapacitor results in a maximum specific capacitance of ∼368 F g^-1 with excellent electrochemical stability with 97% capacity retention after 10 000 cycles. Furthermore, fabricated symmetric supercapacitor shows maximum high energy and power density up to 10.88 W h kg^-1 and 2.06 kW kg^-1, respectively. The superior electrochemical activity of M/N-BCNTs can be attributed to its high surface to area volume ratio, unique structural characteristics, ultrahigh electrical conductivity, and carrier mobility.

A Composite Polymeric Carbon Nitride with In Situ Formed Isotype Heterojunctions for Highly Improved Photocatalysis under Visible Light

Introducing heterojunction is an effective way for improving the intrinsic photocatalytic activity of a graphitic carbon nitride (GCN) semiconductor. These heterostructures are mostly introduced by interfacing GCN with foreign materials that normally have entirely different physicochemical properties and show unfavorable compatibility, thus resulting in a limited improvement of the photocatalytic performance of the resultant materials. Herein, a composite polymeric carbon nitride (CPCN) that contains both melon-based GCN and triazine-based crystalline carbon nitride (CCN) is prepared by a simple thermal reaction between lithium chloride and GCN. Thanks to the intimate contact and good compatibility between GCN and CCN, an in situ formed heterojunction acts as a driving force for separating the photogenerated charge carriers in CPCN. As a result, CPCN exhibits a significantly improved photocatalytic performance under visible light irradiation, which is, respectively, 10.6 and 5.3 times as high as those of the GCN and CCN alone. This well designed isotype heterojunction by a coupling of CCN presents an effective avenue for developing efficient GCN photocatalysts.

In situ construction of Z-scheme g-C3N4/Mg1.1Al0.3Fe0.2O1.7 nanorod heterostructures with high N2 photofixation ability under visible light

By tuning the metal ratio, a Z-scheme g-C₃N₄/MgAlFeO nanorod composite was prepared in situ.

Facile synthesis of a g-C3N4 isotype composite with enhanced visible-light photocatalytic activity

A novel metal-free g-C₃N₄ isotype composite was successfully prepared and presents significant enhancement in the photocatalytic activity.