Facile and Scale Up Synthesis of Red Phosphorus-Graphitic Carbon Nitride Heterostructures for Energy and Environment Applications

Efficient photoelectrochemical real textile wastewater detoxification using photoanodes of C3N4-BiVO4

Photoelectrochemical systems utilizing solar energy have garnered significant attention for their sustainability in remediating contaminated water. This study focuses on advancing photoanode development through the utilization of carbon nitrides (C3N4) and bismuth vanadate (BiVO4), two promising semiconductor materials renowned for their efficient electron-hole pair separation leading to enhanced photocatalytic activity. Four distinct materials were synthesized and compared: BiVO4 over C3N4, C3N4 over BiVO4, and pristine BiVO4 and C3N4. Upon electrochemical analysis, the C3N4-BiVO4 heterostructure exhibited the highest photoelectrocatalytic charge transfer constant, mobility, and lifetime of charge carriers. Capitalizing on these exceptional properties, the composite was applied to remove organic matter real effluent from the textile industry. The photoelectrodegradation of the effluent demonstrated substantial removal of Total Organic Carbon (TOC) and the generation of low toxicity degradation products, accompanied by low energy consumption. The compelling results underscore the high potential of the synthesized C3N4-BiVO4 heterostructure for industrial applications, particularly in addressing environmental challenges associated with textile industry effluents.

Graphitic Carbon Nitride as Reinforcement of Photopolymer Resin for 3D Printing

Digital light processing (DLP) has the advantages of higher printing speed and product precision than other 3D printing technologies. However, DLP products have low mechanical strength owing to the inherent properties of photocurable materials. Graphitic carbon nitride (GCN), which is an abundant hydrogen bonding motif (-NH2, -NH), has low solubility in most solvents; thus, to use GCN as a reinforcement of the polymer matrix, optimal dispersion processes must be applied. In this study, GCN was proposed as a novel reinforcing material to improve the mechanical properties of photocurable epoxy acrylate (EA) resins for DLP. Herein, two-step (planetary mixing and ultrasonication) processes were applied to disperse GCN within EA, and the dispersion performance was identified by checking the degree of precipitation over time. To test the printability of the dispersed GCN/EA composites subjected to DLP 3D printing, cube specimens of GCN/EA composites were prepared, and the dispersed GCN/EA output had a low dimensional error of 0.3-1.3%, while the undispersed composite output showed larger dimensional errors of 27.7-36.2%. Additionally, in the mechanical test of the DLP-3D-printed sample (dispersed GCN/EA composite), the tensile strength and elastic modulus of the dispersed GCN/EA composite specimen were measured to be 75.56 MPa and 3396 MPa, respectively, which were improved by 22% (tensile strength) and 34% (modulus of elasticity) in relation to those of the neat EA specimen. This study is the first to use GCN as a reinforcement and manufacture a composite product for DLP with excellent performance (22% increased tensile strength) through the optimal dispersion of GCN. Considering the high mechanical performance, DLP products using the GCN/EA composites can be used in industries such as automobiles, shipbuilding, and aviation.

Exploring the Enhanced Catalytic Activity of Pt Nanoparticles Generated on the Red Phosphorus/Graphitic Carbon Nitride Binary Heterojunctions in the Photo-assisted Hydrolysis of Ammonia Borane

Ammonia borane (AB) holds great promise for chemical hydrogen storage, but its slow dehydrogenation kinetics under ambient conditions requires a suitable catalyst to facilitate hydrogen production from AB. Here, we fabricated binary red phosphorus/graphitic carbon nitride (RP/g-CN) heterojunctions decorated with Pt nanoparticles (NPs, denoted Pt/RP/g-CN) with a facile ultrasound-assisted two-step protocol as a photo-assisted catalyst for the hydrolysis of AB (HAB). The heterojunction established through intimate P-O-N bonds was proven to have improved photophysical properties such as a lower electron-hole recombination and enhanced visible light utilization compared to the pristine components. With the incorporation of Pt NPs, the optical properties of RP/g-CN heterojunctions were further improved through Schottky junction formation between semiconductors and Pt NPs, enabling a superb hydrogen gas (H2) generation rate of 142 mol H2·mol Pt-1·min-1 under visible light irradiation. Even though g-CN is a well-known host material for many metal NPs, here we discovered that the interaction of Pt NPs with RP in the ternary heterojunction structure is more favorable than that of g-CN, stressing the key role of RP as a support material in the designed ternary heterostructure. The band alignment of the ternary heterojunction catalyst along with the flow of charge carriers was also studied and shown to be a type-II heterojunction structure without hole migration, namely, a complex type-II heterojunction. Several scavenger experiments were also conducted to explain the mechanism of the photo-assisted HAB. To the best of our knowledge, this is the first example of a dual mechanism proposed for the visible light-assisted HAB. While the majority of the H2 was believed to be produced on the Pt NPs surface with the traditional B-N bond dissociation mechanism, the strong oxidizing action of OH• radicals formed by the heterojunction photocatalyst was also speculated to account for the 33% increase in the activity upon visible light irradiation through another mechanism.

Biomimetic Synthesis of PANI/Graphitic Oxidized Carbon Nitride for Supercapacitor Applications

Polyaniline (PANI) composites have gained momentum as supercapacitive materials due to their high energy density and power density. However, some drawbacks in their performance remain, such as the low stability after hundreds of charge-discharge cycles and limitations in the synthesis scalability. Herein, we report for the first time PANI-Graphitic oxidized carbon nitride composites as potential supercapacitor material. The biomimetic polymerization of aniline assisted by hematin, supported by phosphorous and oxygen-modified carbon nitrides (g-POCN and g-OCN, respectively), achieved up to 89% yield. The obtained PAI/g-POCN and PANI/g-OCN show enhanced electrochemical properties, such as conductivity of up to 0.0375 S/cm, specific capacitances (C_s) of up to 294 F/g (at high current densities, 5 A/g) and a stable operation after 500 charge-discharge cycles (at 3 A/g). In contrast, the biomimetic synthesis of Free PANI, assisted by stabilized hematin in cosolvents, exhibited lower performance properties (65%). Due to their structural differences, the electrochemical properties of Free PANI (conductivity of 0.0045 S/cm and C_s of up to 82 F/g at 5 A/g) were lower than those of nanostructured PANI/g-POCN and g-OCN supports, which provide stability and improve the properties of biomimetically synthesized PANI. This work reveals the biomimetic synthesis of PANI, assisted by hematin supported by modified carbon nitrides, as a promising strategy to produce nanostructured supercapacitors with high performance.

Flexible Nano-TiO2 Sheets Exhibiting Excellent Photocatalytic and Photovoltaic Properties by Controlled Silane Functionalization-Exploring the New Prospects of Wastewater Treatment and Flexible DSSCs

TiO₂ nanoparticles surface-modified with silane moieties, which can be directly coated on a flexible substrate without the requirement of any binder materials and postsintering processes, are synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, time-correlated single-photon counting, and transmission electron microscopy. The viability of the prepared surface-modified TiO₂ (M-TiO₂) sheets as a catalyst for the photo-induced degradation of a model dye, methylene blue, was checked using UV-visible absorption spectroscopy. The data suggest that, compared to unmodified TiO₂, M-TiO₂ sheets facilitate better dye-degradation, which leads to a remarkable photocatalytic activity that results in more than 95% degradation of the dye in the first 10 min and more than 99% of the degradation in the first 50 min of the photocatalytic experiments. We also demonstrate that M-TiO₂ can be recycled with negligible reduction in photocatalytic activity. Further, the photovoltaic properties of the developed M-TiO₂ sheets were assessed using UV-visible absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and photochronoamperometry. Dye-sensitized solar cells (DSSC) fabricated using M-TiO₂ as the photoanode exhibited a photoconversion efficiency of 4.1% under direct sunlight. These experiments suggested that M-TiO₂ sheets show enhanced photovoltaic properties compared to unmodified TiO₂ sheets, and that, when N-719 dye is incorporated, the dye-TiO₂ interaction is more favorable for M-TiO₂ than bare TiO₂. The simple solution processing method demonstrated in this paper rendered a highly flexible photoanode made of M-TiO₂ with superior charge-separation efficiency to an electrode made of bare TiO₂. We propose that our findings on the photovoltaic properties of M-TiO₂ open up arenas of further improvement and a wide scope for the large-scale production of flexible DSSCs on plastic substrates at room temperature in a cost-effective way.

Red Phosphorus: An Up-and-Coming Photocatalyst on the Horizon for Sustainable Energy Development and Environmental Remediation

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

One-pot synthesis of S-scheme MoS2/g-C3N4 heterojunction as effective visible light photocatalyst

Despite pioneering as the holy grail in photocatalysts, abundant reports have demonstrated that g-C₃N₄ performs poor photocatalytic activity due to its high recombination rate of photo-induced charge carriers. Many efforts have been conducted to overcome this limitation in which the semiconductor-semiconductor coupling strategies toward heterojunction formation were considered as the easiest but the most effective method. Herein, a one-pot solid-state reaction of thiourea and sodium molybdate as precursors at different temperatures under N₂ gas was applied for preparing composites of MoS₂/g-C₃N₄. The physicochemical characterization of the final products determines the variation in contents of components (MoS₂ and g-C₃N₄) via the increase of synthesis temperature. The enhanced photocatalytic activity of the MoS₂/g-C₃N₄ composites was evaluated by the degradation of Rhodamine B in an aqueous solution under visible light. Therein, composites synthesized at 500 °C showed the best photocatalytic performance with a degradation efficiency of 90%, much higher than that of single g-C₃N₄. The significant improvement in photocatalytic performance is attributed to the enhancement in light-harvesting and extension in photo-induced charge carriers' lifetime of composites which are originated from the synergic effect between the components. Besides, the photocatalytic mechanism is demonstrated to well-fit into the S-scheme pathway with apparent evidences.

Hydrothermally Assisted Synthesis of Porous Polyaniline@Carbon Nanotubes-Manganese Dioxide Ternary Composite for Potential Application in Supercapattery

In this study, ternary composites of polyaniline (PANI) with manganese dioxide (MnO₂) nanorods and carbon nanotubes (CNTs) were prepared by employing a hydrothermal methodology and in-situ oxidative polymerization of aniline. The morphological analysis by scanning electron microscopy showed that the MnO₂ possessed nanorod like structures in its pristine form, while in the ternary PANI@CNT/MnO₂ composite, coating of PANI over CNT/MnO₂, rods/tubes were evidently seen. The structural analysis by X-ray diffraction and X-ray photoelectron spectroscopy showed peaks corresponding to MnO₂, PANI and CNT, which suggested efficacy of the synthesis methodology. The electrochemical performance in contrast to individual components revealed the enhanced performance of PANI@CNT/MnO₂ composite due to the synergistic/additional effect of PANI, CNT and MnO₂ compared to pure MnO₂, PANI and PANI@CNT. The PANI@CNT/MnO₂ ternary composite exhibited an excellent specific capacity of 143.26 C g^-1 at a scan rate of 3 mV s^-1. The cyclic stability of the supercapattery (PANI@CNT/MnO₂/activated carbon)-consisting of a battery type electrode-demonstrated a gradual increase in specific capacity with continuous charge-discharge over ~1000 cycles and showed a cyclic stability of 119% compared to its initial value after 3500 cycles.

Fabrication, characterization, and application of ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite for photodegradation of tetracycline in aqueous solutions

We aim at fabricating a ternary magnetic recyclable Bi₂WO₆/BiOI@Fe₃O₄ composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe₃O₄ loading ratio on the Bi₂WO₆/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi₂WO₆/BiOI@5%Fe₃O₄ composite has the highest TC removal (97%), as compared to the Bi₂WO₆ (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.

Elemental red phosphorus-based materials for photocatalytic water purification and hydrogen production

Semiconductor-based photocatalysis is a renewable and sustainable technology to solve global environmental pollution and energy shortage problems. It is essential to exploit highly efficient photocatalyst materials. Recently, Earth-abundant elemental red phosphorus (RP) with broader light-harvesting and appropriate band structure characteristics has been widely studied in photocatalysis. In this review, the crystal and electronic structures of RP (e.g., amorphous, Hittorf's and fibrous phosphorus) materials are firstly summarized along with the current advancement in the synthesis strategies of RP and RP-based materials in photocatalysis accompanied by a thorough discussion of the applications of RP-based materials in photocatalytic pollutant degradation, bacterial inactivation, and water splitting. Finally, this review also offers some guidance and perspectives for the future design of efficient visible-light-driven photocatalysts.

The highly efficient photocatalytic and light harvesting property of Ag-TiO2 with negative nano-holes structure inspired from cicada wings

The negative replica of biomorphic TiO₂ with nano-holes structure has been effectively fabricated directly from nano-nipple arrays structure of cicada wings by using a simple, low-cost and highly effective sol-gel ultrasonic method. The nano-holes array structure was well maintained after calcination in air at 500 °C. The Ag nanoparticles (10 nm–25 nm) were homogeneously decorated on the surface and to the side wall of nano-holes structure. It was observed that the biomorphic Ag-TiO₂ showed remarkable photocatalytic activity by degradation of methyl blue (MB) under UV-vis light irradiation. The biomorphic Ag-TiO₂ with nano-holes structure showed superior photocatalytic activity compared to the biomorphic TiO₂ and commercial Degussa P25. This high-performance photocatalytic activity of the biomorphic Ag-TiO₂ may be attributed to the nano-holes structure, localized surface plasmon resonance (LSPR) property of the Ag nanoparticles, and enhanced electron-hole separation. Moreover, the biomorphic Ag-TiO₂ showed more absorption capability in the visible wavelength range. This work provides a new insight to design such a structure which may lead to a range of novel applications.

Alloy-Based Anode Materials toward Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered as promising alternatives to lithium-ion batteries owing to the abundant sodium resources. However, the limited energy density, moderate cycling life, and immature manufacture technology of SIBs are the major challenges hindering their practical application. Recently, numerous efforts are devoted to developing novel electrode materials with high specific capacities and long durability. In comparison with carbonaceous materials (e.g., hard carbon), partial Group IVA and VA elements, such as Sn, Sb, and P, possess high theoretical specific capacities for sodium storage based on the alloying reaction mechanism, demonstrating great potential for high-energy SIBs. In this review, the recent research progress of alloy-type anodes and their compounds for sodium storage is summarized. Specific efforts to enhance the electrochemical performance of the alloy-based anode materials are discussed, and the challenges and perspectives regarding these anode materials are proposed.

Amorphous red phosphorus nanosheets anchored on graphene layers as high performance anodes for lithium ion batteries

A facile solution-based method was developed to combine the advantage of amorphous nanoscale red P sheets and highly conductive graphene, forming a high-performance P/graphene composite anode for advanced lithium ion batteries. Graphene can be easily expanded into a 3D framework in solution with rich interior porosity and abundant adsorption points, which enables a large percentage of red P to be loaded and form a uniform P/graphene hybrid structure. The nanoscale and amorphous features of red P effectively reduce the volume expansion and mechanical stress within individual P sheets, thereby alleviating P pulverization during cycling. The well dispersed graphene serves as a buffer layer to accommodate the volume expansion and adsorb the stress during electrochemical reactions, thereby maintaining a robust electrode structure. Besides, the highly conductive graphene greatly enhances the ionic/electronic conductivity of the electrode, which favors efficient redox reactions and high P utilization. Based on the superior composite structure, the potentials of both components can be fully exerted, resulting in excellent electrochemical performance. The P/graphene electrode delivered a high reversible capacity of 1286 mA h g^-1 based on the weight of the composite after 100 cycles at 200 mA g^-1. Even at a high current density of 1000 mA g^-1, the composite electrode exhibits a high capacity of 1125 mA h g^-1, revealing its potential as a high-performance P-carbon composite anode for advanced lithium ion batteries.

Simple and Large Scale Construction of MoS2-g-C3N4 Heterostructures Using Mechanochemistry for High Performance Electrochemical Supercapacitor and Visible Light Photocatalytic Applications

The design of heterojunctions for efficient electrochemical energy storage and environmental remediation are promising for future energy and environment applications. In this study, a molybdenum disulfide-graphitic carbon nitride (MoS₂-g-C₃N₄) heterojunction was designed by applying simple mechanochemistry, which can be scaled up for mass production. The physical-chemical and photophysical properties of the as-prepared MoS₂-g-C₃N₄ heterojunction were analyzed using a range of characterization techniques. The supercapacitance performance was determined by electrochemical half-cell measurements, and visible light-induced photoelectrochemical and photocatalytic performance was studied using photocurrent and model organic pollutant degradation experiments. The resulting MoS₂-g-C₃N₄ under the optimized experimental conditions showed significantly higher photocatalytic activity and photoelectrochemical performance under similar visible photoirradiation conditions compared to the bare materials. The resulting heterostructure electrode delivered a higher capacitance of 240.85 F/g than the bare material (48.77 F/g) with good capacitance retention. The superior performance was attributed mainly to the robust light harvesting ability, improved charge separation, high surface area, increased mass transfer, and capacitive and conductive behavior. The convenient and mass production of heterojunctions using a simple and cost-effective method will provide a good example for the efficient design of visible light active photocatalysts and capacitor electrode materials for environmental remediation and energy storage device applications.

Facile and sustainable synthesis of carbon-doped ZnO nanostructures towards the superior visible light photocatalytic performance

Design of carbon doped ZnO nanostructures towards enhanced visible light driven photocatalytic and photoelectrochemical performance.

Recent advances in non-metal modification of graphitic carbon nitride for photocatalysis: a historic review

This review provides a comprehensive survey and critical comments on the development of photocatalysts with a focus on the metal-free materials.