Graphitic carbon nitride based Z scheme photocatalysts: Design considerations, synthesis, characterization and applications

Dual Z-scheme TCN/ZnS/ ZnIn2S4 with efficient separation for photocatalytic nitrogen fixation

The development of an efficient catalyst that can use solar energy for NH3 production is of great significance in solving the environmental and energy crisis caused by the traditional ammonia synthesis process. In this work, a dual Z-scheme tubular carbon nitride/zinc sulfide/zinc indium sulfide ternary composited photocatalyst (TCN/ZnS/ZnIn2S4) with excellent nitrogen photofixation performance under visible light was prepared by self-assembly and hydrothermal methods. The crystal structure studies confirmed that tubular carbon nitride (TCN) had more active sites that could promote N2 adsorption. The photochemical studies proved that the double charge transfer channel provided by the dual Z-scheme heterojunction could improve the efficiency of electron-hole separation and achieve excellent photocatalytic nitrogen fixation. The ammonia production rate of the TCN/ZnS/ZnIn2S4 catalyst was up to 136.56 μmol/L, and it also has good stability and reusability. This work provides new insight into the development of Z-scheme heterojunction photocatalysts with green and efficient nitrogen fixation.

Advances in photocatalytic NO oxidation by Z-scheme heterojunctions

The fast development of urbanisation and industrialisation has led to a rise in nitrogen oxide (NOx) emissions, specifically nitric oxide (NO). One effective method for reducing the harmful effects of this dangerous air pollutant on both human health and the environment is the photocatalytic oxidation of NO. Z-scheme heterojunctions enhance incident light utilisation and increase photocatalytic activity, eventually leading to better NO oxidation performance by encouraging the effective separation of charges and migration. A comprehensive discussion of Z-scheme-based heterojunctions is provided in this review paper, with a focus on their applications in the photocatalytic oxidation of NO. Significant progress has been made in the fabrication of efficient photocatalytic devices in recent years, with Z-scheme-based heterojunctions proving to be particularly successful. The review looks into the various methodologies used to create Z-scheme-based heterojunctions as well as photocatalytic NO oxidation mechanisms. Recent studies on photocatalysts employing Z-scheme heterojunctions for the photocatalytic oxidation of NO are also discussed. The possibilities for new opportunities as well as the present challenges, barriers, advances, and solutions have been emphasized.

A Targeted Review of Current Progress, Challenges and Future Perspective of g-C3 N4 based Hybrid Photocatalyst Toward Multidimensional Applications

The increasing demand for searching highly efficient and robust technologies in the context of sustainable energy production totally rely onto the cost-effective energy efficient production technologies. Solar power technology in this regard will perceived to be extensively employed in a variety of ways in the future ahead, in terms of the combustion of petroleum-based pollutants, CO₂ reduction, heterogeneous photocatalysis, as well as the formation of unlimited and sustainable hydrogen gas production. Semiconductor-based photocatalysis is regarded as potentially sustainable solution in this context. g-C₃ N₄ is classified as non-metallic semiconductor to overcome this energy demand and enviromental challenges, because of its superior electronic configuration, which has a median band energy of around 2.7 eV, strong photocatalytic stability, and higher light performance. The photocatalytic performance of g-C₃ N₄ is perceived to be inadequate, owing to its small surface area along with high rate of charge recombination. However, various synthetic strategies were applied in order to incorporate g-C₃ N₄ with different guest materials to increase photocatalytic performance. After these fabrication approaches, the photocatalytic activity was enhanced owing to generation of photoinduced electrons and holes, by improving light absorption ability, and boosting surface area, which provides more space for photocatalytic reaction. In this review, various metals, non-metals, metals oxide, sulfides, and ferrites have been integrated with g-C₃ N₄ to form mono, bimetallic, heterojunction, Z-scheme, and S-scheme-based materials for boosting performance. Also, different varieties of g-C₃ N₄ were utilized for different aspects of photocatalytic application i. e., water reduction, water oxidation, CO₂ reduction, and photodegradation of dye pollutants, etc. As a consequence, we have assembled a summary of the latest g-C₃ N₄ based materials, their uses in solar energy adaption, and proper management of the environment. This research will further well explain the detail of the mechanism of all these photocatalytic processes for the next steps, as well as the age number of new insights in order to overcome the current challenges.

g-C3N4-Based Direct Z-Scheme Photocatalysts for Environmental Applications

Photocatalysis represents a promising technology that might alleviate the current environmental crisis. One of the most representative photocatalysts is graphitic carbon nitride (g-C3N4) due to its stability, cost-effectiveness, facile synthesis procedure, and absorption properties in visible light. Nevertheless, pristine g-C3N4 still exhibits low photoactivity due to the rapid recombination of photo-induced electron-hole (e−-h+) pairs. To solve this drawback, Z-scheme photocatalysts based on g-C3N4 are superior alternatives since these systems present the same band configuration but follow a different charge carrier recombination mechanism. To contextualize the topic, the main drawbacks of using g-C3N4 as a photocatalyst in environmental applications are mentioned in this review. Then, the basic concepts of the Z-scheme and the synthesis and characterization of the Z-scheme based on g-C3N4 are addressed to obtain novel systems with suitable photocatalytic activity in environmental applications (pollutant abatement, H2 production, and CO2 reduction). Focusing on the applications of the Z-scheme based on g-C3N4, the most representative examples of these systems are referred to, analyzed, and commented on in the main text. To conclude this review, an outlook of the future challenges and prospects of g-C3N4-based Z-scheme photocatalysts is addressed.

Photoreduction of CO2 to CH4 over Efficient Z-Scheme γ-Fe2O3/g-C3N4 Composites

A series of composite γ-Fe₂O₃/g-C₃N₄ (denoted as xFeCN with x equal 5, 10, 15, and 20 of γ-Fe₂O₃ percentage in weight) was prepared by calcination and precipitation-impregnation methods. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectrometry (XPS) characterizations indicated the successful synthesis of Z-scheme FeCN composites. A red shift of the light absorption region was revealed by UV-vis diffuse reflectance spectroscopy (UV-DRS). In addition, photoluminescence spectroscopy (PL) spectra showed an interface interaction of two phases Fe₂O₃ and g-C₃N₄ in the synthesized composites that improved the charge transfer capacity. The photocatalytic activity of these materials was studied in the photoreduction of CO₂ with H₂O as the reductant in the gaseous phase. The composites exhibited excellent photoactivity compared to undoped g-C₃N₄. The CH₄ production rate over 10FeCN and 15FeCN composites (2.8 × 10^-2 and 2.9 × 10^-2 μmol h^-1 g^-1, respectively) was ca. 7 times higher than that over pristine g-C₃N₄ (0.4 × 10^-2 μmol h^-1 g^-1). This outstanding photocatalytic property of these composites was explained by the light absorption expansion and the prevention of photogenerated electron-hole pairs recombination due to its Z-scheme structure.

High concentration of methyl orange elimination by targeted construction of an α-Bi2O3/Ph–CC–Cu Z-scheme

We anchored Ph–CC–Cu onto the surface of α-Bi2O3 nanoparticles to directionally construct Z-scheme heterojunctions, which are significantly efficient for the elimination of methyl orange with high concentration (98 mg L−1) in waste water.

Heterojunction photocatalysts for artificial nitrogen fixation: fundamentals, latest advances and future perspectives

As an indispensable energy source, ammonia plays an essential role in agriculture and various industries. Given that the current ammonia production is still dominated by the energy-intensive and high carbon footprint Haber-Bosch process, photocatalytic nitrogen fixation represents a low-energy consuming and sustainable approach to generate ammonia. Heterostructured photocatalysts are hybrid materials composed of semiconductor materials containing interfaces that make full use of the unique superiorities of the constituents and synergistic effects between them. These promising photocatalysts have superior performances and substantial potential in photocatalytic reduction of nitrogen. In this review, a wide spectrum of recently developed heterostructured photocatalysts for nitrogen fixation to ammonia are evaluated. The fundamentals of solar-to-ammonia conversion, basic principles of various heterojunction photocatalysts and modification strategies are systematically reviewed. Finally, a brief summary and perspectives on the ongoing challenges and directions for future development of nitrogen photofixation catalysts are also provided.

Recent progress and advances in the environmental applications of MXene related materials

MXenes are a new type of two-dimensional (2D) transition metal carbide or carbonitride material with a 2D structure similar to graphene. The general formula of MXenes is M_n+1X_nT_x, in which M is an early transition metal element, X represents carbon, nitrogen and boron, and T is a surface oxygen-containing or fluorine-containing group. These novel 2D materials possess a unique 2D layered structure, large specific surface area, good conductivity, stability, and mechanical properties. Benefitting from these properties, MXenes have received increasing attention and emerged as new substrate materials for exploration of various applications including, energy storage and conversion, photothermal treatment, drug delivery, environmental adsorption and catalytic degradation. The progress on various applications of MXene-based materials has been reviewed; while only a few of them covered environmental remediation, surface modification of MXenes has never been highlighted. In this review, we highlight recent advances and achievements in surface modification and environmental applications (such as environmental adsorption and catalytic degradation) of MXene-based materials. The current studies on the biocompatibility and toxicity of MXenes and related materials are summarized in the following sections. The challenges and future directions of the environmental applications of MXene-based materials are also discussed and highlighted.