Graphitic carbon nitride-based photocatalysts: Toward efficient organic transformation for value-added chemicals production

Fabrication of Bi4O5Br2 photocatalyst for carbamazepine degradation under visible-light irradiation

Bi₄O₅Br₂ with irregular flake shape was synthesized by a facile and energy-saving hydrolysis method. Its band gap energy (E_g) was 2.1 eV. The formation mechanism was proposed. The Bi₄O₅Br₂ exhibited superb visible-light-induced photocatalytic activity (>90%) toward the oxidation of carbamazepine. The kinetics rate constant (k) attained 0.0196 min^-1. The effect of Bi₄O₅Br₂ dosage, initial solution pH value, and inorganic anions on carbamazepine degradation was investigated. During the oxidation process, photogenerated holes (h⁺) and superoxide radical anions (•O₂^-) were the main active species. Based on the reaction intermediates results determined through a combined system of liquid chromatography and mass spectrometry, a possible reaction mechanism was speculated. The degree of contamination of carbamazepine solution after treatment was evaluated through the teratogenic effect experiment. After 120 min of visible light exposure, the carbamazepine solution is free of pollution. Also, the as-synthesized Bi₄O₅Br₂ maintains good chemical stability and could be reused in the photodegradation process, indicating its potential in practical applications.

Modulating oxygen vacancies on bismuth-molybdate hierarchical hollow microspheres for photocatalytic selective alcohol oxidation with hydrogen peroxide production

Photocatalytic selective oxidation of alcohols into high value-added carbonyl compounds accompanied by producing hydrogen peroxide (H₂O₂) is undoubtedly a more efficient solar energy conversion strategy with high atom economy. Herein, we have developed an efficient photocatalyst of bismuth-molybdate (Bi₂MoO₆) hierarchical hollow microspheres with tunable surface oxygen vacancies (OVs) for promoting the photocatalytic selective alcohol oxidation with H₂O₂ production. The effect of surface OVs on the photocatalytic efficiency is studied systematically by comparing the performance of different photocatalysts. The benzaldehyde and H₂O₂ production rates over the OV-rich Bi₂MoO₆ photocatalyst reach up to 1310 and 67.2 μmol g^-1 h^-1, respectively, which are 2.3 and 4.0 times those generated from the OV-poor Bi₂MoO₆ hollow microspheres. The roles of various active radicals in the photocatalytic reaction are probed by a series of controlled experiments and in situ ESR measurements, revealing that both superoxide radical (•O₂^-) and carbon-centered radical are the key active intermediates. The introduction of surface OVs on Bi₂MoO₆ hollow microspheres accelerates the separation and transfer of photo-generated charge carriers as well as enhances the adsorption and activation of reactant molecules, thereby greatly promoting the photocatalytic selective oxidation of alcohols along with H₂O₂ production. This work not only demonstrates a facile strategy for the preparation of high-efficiency photocatalysts by simultaneous modulations of morphology and surface defects, but also offers insight into developing the dual-functional photocatalytic reactions for the full utilizations of photoinduced electrons and holes.

Intense Visible-Light Absorption in SrRuO3/C3N4 Heterostructures for the Highly Efficient Reduction of Hg(II)

Strontium ruthenium oxide (SrRuO₃) is recognized as a metallic itinerant ferromagnet and utilized as a conducting electrode in heterostructure oxides with unforeseen optical characteristics, including remarkably low-reflection and high-absorption visible-light spectrum compared to classical metals. By coupling mesoporous SrRuO₃ nanoparticles (NPs) with porous g-C₃N₄ nanosheets for the first time, we evidence remarkably promoted visible light absorption and superior photocatalytic performances for Hg(II) reduction under illumination with visible light. The photocatalytic performance of g-C₃N₄ increased upon boosting the SrRuO₃ percentage to 1.5%, and this (1.5% SrRuO₃/g-C₃N₄ heterostructure) is considered the optimum condition to obtain a high photocatalytic efficiency of about 100% within 50 min. It was promoted 3.68 and 5.75 times compared to SrRuO₃ and g-C₃N₄, respectively. Also, a Hg(II) reduction rate of 1.5% SrRuO₃/g-C₃N₄ was enhanced3.84- and 6.28-fold than those of pure SrRuO₃ NPs and g-C₃N₄, respectively. Such a high photocatalytic performance over SrRuO₃/g-C₃N₄ photocatalysts was explained by the characteristics of SrRuO₃ NPs incorporated on porous g-C₃N₄ layers, which demonstrate strong absorption of visible light with a narrow band gap, a large photocurrent density of ∼9.07 mA/cm², well-dispersed and small particle sizes, and cause facile diffusion of HCOOH and Hg(II) ions and electrons. The present work provides a dramatic novel approach to the challenge of constructing visible-light photosensitive photocatalysts for wastewater remediation.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

Nanoarchitectonics: what's coming next after nanotechnology?

In science and technology today, the crucial importance of the regulation of nanoscale objects and structures is well recognized. The production of functional material systems using nanoscale units can be achieved via the fusion of nanotechnology with the other research disciplines. This task is a part of the emerging concept of nanoarchitectonics, which is a concept moving beyond the area of nanotechnology. The concept of nanoarchitectonics is supposed to involve the architecting of functional materials using nanoscale units based on the principles of nanotechnology. In this focus article, the essences of nanotechnology and nanoarchitectonics are first explained, together with their historical backgrounds. Then, several examples of material production based on the concept of nanoarchitectonics are introduced via several approaches: (i) from atomic switches to neuromorphic networks; (ii) from atomic nanostructure control to environmental and energy applications; (iii) from interfacial processes to devices; and (iv) from biomolecular assemblies to life science. Finally, perspectives relating to the final goals of the nanoarchitectonics approach are discussed.

Novel broad-spectrum-driven g-C3N4 with oxygen-linked band and porous defect for photodegradation of bisphenol A, 2-mercaptophenthiazole and ciprofloxacin

Abundant active oxygen free radicals could efficiently remove refractory organic pollutants. In previous research, the original carbon nitride can form more hydrogen peroxide, however, owing to the limitation of its band structure, the original carbon nitride cannot decompose the hydrogen peroxide to generate more active oxygen free radicals. Herein, this work reports a simple bottom-up synthesis method, which synthesize a broad-spectrum-response carbon nitride (CN-CA) with oxygen-linked band and porous defect structure, while adjusting the band structure, and the introduction of the oxygen-linked band structure can also decompose the hydrogen peroxide produced by the original carbon nitride to form more active oxygen free radicals. Instrumental characterization and analysis of experimental results revealed the important role of oxygen-linked band and porous defects in adjusting the CN-CA energy band structure and improving its visible light absorption. The optimal CN-CA displays an outstanding photocatalytic degradation ability, that degradation rate of bisphenol A (BPA) reaches 99.8% within 150 min, the reaction rate constant of which is 6.77 times higher than that of pure g-C₃N₄, as also demonstrated with 2-mercaptophenthiazole (MBT) and ciprofloxacin (CIP). Meanwhile, the excellent degradation performance under blue LED (450-462 nm) and green LED (510-520 nm) exhibits the broad-spectrum characteristics of CN-CA. The degradation pathways of BPA and MBT were analyzed via HPLC-MS. Moreover, the primary active species were detected as O₂^-, OH and h⁺ based on the trapping experiments and ESR. This research provides a new strategy for g-C₃N₄ modified by porous defects and oxygen-linked band structure for environmental remediation.

Promoting Visible Light Generation of Hydrogen Using a Sol-Gel-Prepared MnCo2O4@g-C3N4 p-n Heterojunction Photocatalyst

The production of hydrogen using a new type of heterogeneous photocatalyst under visible light is considered a remarkable essential pathway for sustainable, pure energy not only on the laboratory scale but also on a bigger scale. Hence, a new nanocomposite of mesoporous MnCo₂O₄, g-C₃N₄, and MnCo₂O₄@g-C₃N₄ was produced utilizing a sol-gel method with variable MnCo₂O₄ contents. The crystal structure of MnCo₂O₄ was effectively confirmed by the X-ray diffraction pattern and integrated onto the g-C₃N₄ structure. The MnCo₂O₄ nanoparticles were displayed as spherical particles by TEM images and dispersed in a uniform way inside the g-C₃N₄ nanosheet. The synthesized nanocomposites in the form of MnCo₂O₄@g-C₃N₄ were examined as a new effective photocatalyst against glycerol as a source for H₂ production with visible light. The MnCo₂O₄ contents indicated a corroborative impact for the photocatalytic action related to the H₂ production process. A maximum H₂ production molecular value was observed (21,870 μmol·g^-1·h^-1) for a 1.5 wt % MnCo₂O₄@g-C₃N₄ nanocomposite as a considerable increase in its photocatalytic activity. The yields of H₂ are ∼55 and 23 times higher than those of g-C₃N₄ and MnCo₂O₄, respectively. Up to five times cycles of visible lighting were the maximum number of repeated cycles by which the 1.5 wt % MnCo₂O₄@g-C₃N₄ product showed higher stability and durability.

Visible-light harvesting innovative W6+/Yb3+/TiO2 materials as a green methodology photocatalyst for the photodegradation of pharmaceutical pollutants

In this work, we report on the synthesis of a new-age reusable visible-light photocatalyst using a heterojunction nanocomposite of W⁶⁺/Yb³⁺ on a mixed-phase mesoporous network of monolithic TiO₂. The structural properties of the monolithic photocatalysts are characterized using p-XRD, SEM-EDAX, TEM-SAED, XPS, PLS, UV-Vis-DRS, FT-IR, micro-Raman, TG-DTA, and N₂ isotherm analysis. The electron microscopic analysis reveals a mesoporous network of ordered worm-like monolithic design, with a polycrystalline mixed-phase (anatase/rutile) TiO₂ composite, as indicated by diffraction studies. The UV-Vis-DRS analysis reveals a redshift in the light absorption characteristics of the mixed-phase TiO₂ monolith as a function of W⁶⁺/Yb³⁺ co-doping. It is observed that the use of (8.0 mol%)W⁶⁺/0.4 (mole%)Yb³⁺ co-doped monolithic TiO₂ photocatalyst, with an energy bandgap of 2.77 eV demonstrates superior visible-light photocatalysis, which corroborates with the PLS studies in terms of voluminous e^-/h⁺ pair formation. The practical application of the photocatalyst has been investigated through a time-dependent dissipation of enrofloxacin, a widely employed antimicrobial drug, and its degradation pathway has been monitored by LC-MS-ESI and TOC analysis. The impact of physio-chemical parameters such as solution pH, sensitizers, drug concentration, dopant/codopant stoichiometry, catalyst quantity, and light intensity has been comprehensively studied to monitor the process efficiency.

Impact of Unadorned Carbon Nitride on Photodegradation and Bioavailability of Multifungicides in the Environment

Unadorned carbon nitride was synthesized via different nitrogen-rich precursors by thermal polymerization and applied to multifungicides for simultaneous photodegradation in the present study. Urea-derived carbon nitride (UCN) was verified to be most efficient in fungicide removal. The influences of catalyst dosage and pH were studied during the photodegradation process. Hydroxyl radical (^•OH) and holes (h⁺) are the active species during photodegradation of each of the eight fungicides within an aqueous environment. The primary photodegradation products and pathways of all eight fungicides were systematically identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In addition, the UCN catalyst was also applied to potted plants. The experimental results revealed that UCN could reduce fungicide residues in plants grown within a contaminated matrix. This study shows promising applications of the UCN catalyst in alleviating the hazards of pesticide residue.

The ZnFe2O4@mZnO–N/RGO nano-composite as a carrier and an intelligent releaser drug with dual pH- and ultrasound-triggered control

Graphical design of the synergistic of nano-carriers for targeted controlled anti-cancer Cur drug delivery and their interactions with site-specific cancer cells and tumor tissues in order to enhance the selectivity of cancer therapy.

Sub 10 nm CoO nanoparticle-decorated graphitic carbon nitride for solar hydrogen generation via efficient charge separation

Solar hydrogen generation is one of the most compelling concepts in modern research to address both the energy and environmental issues simultaneously for the survival of the human race. A Type II heterojunction (CoO-GCN) was fabricated by decorating sub 10 nm CoO nanoparticles (NPs) on the graphitic carbon nitride (GCN) surface. It exhibited improved absorption of UV-VIS light and efficiently separate the photogenerated electrons and holes in opposite directions. A maximum hydrogen generation rate of 9.8 mmol g-1 h-1 was recorded using CoO-GCN from 10% aqueous triethanolamine under simulated sunlight in the presence of 1 wt% Pt. The rate is 3.8 times higher than that of bare GCN. Furthermore, it showed excellent stability for up to five repeated uses. Interestingly, the study also revealed that untreated seawater could replace the deionized water. The cooperative participation of the uniform shape and size of CoO NPs firmly grafted on GCN resulted in remarkable performance for solar hydrogen generation.

Dramatic enhancement of photocatalytic H2 evolution over hydrolyzed MOF-5 coupled Zn0.2Cd0.8S heterojunction

MOF-5 has been criticized for its poor water stability, which results in complete damage of its traditional functionality. Therefore, there are very few researches about the further application of hydrolyzed MOF-5 (h-M). However, in this work, the h-M can function as both superior support and semiconductor for photocatalytic reaction after a water-based process. Herein, a rational design of Zn_0.2Cd_0.8S@h-MOF-5 (ZCS@h-M) heterojunction photocatalyst has been synthesized via a hydrothermal method with different mass ratio of ZCS. As demonstrated in the results of SEM and TEM, during the hydrothermal process, MOF-5 exfoliated into two-dimensional small sheets and ZCS nanoparticles embedded into h-M frameworks, which is in favor for the dispersion of ZCS and better interface connection, thus further boosts the migration of photogenerated charge carriers and protect the photocorrosion of ZCS, ultimately improves the photocatalytic hydrogen production. Optimal ZCS content of 10 wt% exhibited a significantly enhanced visible light photocatalytic hydrogen production efficiency of 15.08 mmol h^-1 g^-1, which far surpassed bare ZCS at 7.62 times. Furthermore, the ZCS@h-M showed outstanding stability during photocatalytic hydrogen production over a number of cycles.

Facile synthesis of a novel nitrogen-doped carbon dot adorned zinc oxide composite for photodegradation of methylene blue

Nitrogen-doped carbon dot decorated zinc oxide nanoparticles were successfully fabricated by an economical wet-impregnation method and used as a photocatalyst for the degradation of aqueous methylene blue dye under UV-light at room temperature.