Novel magnetically separable g-C 3 N 4 /Fe 3 O 4 /Ag 3 PO 4 /Co 3 O 4 nanocomposites: Visible-light-driven photocatalysts with highly enhanced activity

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Recent advances in g-C3N4-based photocatalysis for water treatment: Magnetic and floating photocatalysts, and applications of machine-learning techniques

Over the past decade, there has been a substantial increase in research investigating the potential of graphitic carbon nitride (g-C3N4) for various environmental remediations. Renowned for its photocatalytic activity under visible light, g-C3N4 offers a promising solution for treating water pollutants. However, traditional g-C3N4-based photocatalysts have inherent drawbacks, creating a disparity between laboratory efficacy and real-world applications. A primary practical challenge is their fine-powdered form, which hinders separation and recycling processes. A promising approach to address these challenges involves integrating magnetic or floating materials into conventional photocatalysts, a strategy gaining traction within the g-C3N4-based photocatalyst arena. Another emerging solution to enhance practical applications entails merging experimental results with contemporary computational methods. This synergy seeks to optimize the synthesis of more efficient photocatalysts and pinpoint optimal conditions for pollutant removal. While numerous review articles discuss the laboratory-based photocatalytic applications of g-C3N4-based materials, there is a conspicuous absence of comprehensive coverage regarding state-of-the-art research on improved g-C3N4-based photocatalysts for practical applications. This review fills this void, spotlighting three pivotal domains: magnetic g-C3N4 photocatalysts, floating g-C3N4 photocatalysts, and the application of machine learning to g-C3N4 photocatalysis. Accompanied by a thorough analysis, this review also provides perspectives on future directions to enhance the efficacy of g-C3N4-based photocatalysts in water purification.

Fabrication of Co3O4/Co3S4/CNTs for photocatalytic treatment of wastewater under xenon lamp

The current study is about the synthesis of nanoparticles (NPs) of cobalt oxide (CO) and cobalt sulfide (CS) followed by their nanocomposites as CO/CS and CO/CS/CNT by ultrasonication approach. The addition of carbon-based materials in the oxides and sulfides enhances their performance by developing physico-chemical interactions. Prepared NPs were utilized for the photodegradation of organic contaminants. The characteristics, as well as the efficiency of the prepared samples, have been systematically examined by X-ray diffraction (XRD) technique, Fourier transform infrared spectroscopy (FTIR), and UV-vis spectroscopy. Photocatalytic activities of bare samples and synthesized nanocomposites were tested for the degradation of methyl orange (MO) using a xenon lamp. The percentage degradation of dye was 24.14%, 57.94%, 71.66%, and 85.04% in the presence of CO, CS, CO/CS, and CO/CS/CNT, respectively. Crystal violet (CV), Rhodamine B (rho-B), and industrial wastewater were also degraded by the ternary composite. The comparative studies showed the best performance of CO/CS/CNT, which enhanced the generation of electron-hole pairs by absorption of photons of incoming radiations, increased charge separation, and maximum surface area for adsorption.

Rational optimization of g-C3N4/Co3O4 nanocomposite for enhanced photodegradation of Rhodamine B dye under visible light

Heterogeneous catalysis is widely known as an efficient, clean, and low-cost technology to mitigate the environmental pollution of industrial effluents. This research aimed at optimizing the preparation and characterization of efficient g-C₃N₄/Co₃O₄ nanocomposite for catalytic removal of Rhodamine B (Rh B) dye. The detected XRD peaks for the prepared nano-Co₃O₄ are matched with the cubic crystal structure. In contrast, the broad peak at 27.3° corresponding to the graphite reflection of hkl (002) was noticeably weakened in the XRD pattern of the g-C₃N₄/Co₃O₄ composite. FTIR spectra of g-C₃N₄/Co₃O₄ nanocomposites revealed the active vibrational modes of each Co₃O₄ and g-C₃N₄ component. The microstructure study of g-C₃N₄ showed the strong interlayer stacking of carbon nitride nanosheets, while the surface morphology of g-C₃N₄/Co₃O₄ nanocomposite revealed a hybrid particulate system. EDS analysis indicated that the spot area of g-C₃N₄/Co₃O₄ confirmed the chemical ratios of carbon, nitrogen, cobalt, and oxygen. BET measurements of g-C₃N₄/Co₃O₄ showed a significant increase in the surface area and pore volume of single components due to the lamination of stacked g-C₃N₄ nanosheets by the intercalated Co₃O₄ nanoparticles. The prepared 30% g-C₃N₄/Co₃O₄ revealed the lowest value of E_g ~1.2 eV and the highest light absorptivity suggesting strong promotion for the photocatalytic performance under visible light. The maximum photocatalytic activity of about 87% was achieved by 30% g-C₃N₄/Co₃O₄ due to the photonic enhancement, which reduces the recombination of excited electrons. The developed nanocomposite with a g-C₃N₄/Co₃O₄ ratio of 0.3 exhibited high stability in its photocatalytic performance after four recycling times, and a slight decrease of about 7% was estimated after the 5th reuse test.

Construction of Aptamer-Based Nanobiosensor for Breast Cancer Biomarkers Detection Utilizing g-C3N4/Magnetic Nano-Structure

An electrochemical aptasensor has been developed to determine breast cancer biomarkers (CA 15-3). Aptamer chains were immobilized on the surface of the electrode by g-C₃N₄/Fe₃O₄ nanoparticles, which increased the conductivity and active surface area of the electrode. X-ray diffraction analysis (XRD), Fourier-transformed infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) measurements have been carried out to characterize the nanomaterials. Cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy have been used to characterize the developed electrode. The results demonstrate that the modified electrode has better selectivity for CA 15-3 compared to other biological molecules. It has a good electrochemical response to CA 15-3 with a detection limit of 0.2 UmL^-1 and a linear response between 1 and 9 UmL^-1. It has been used as a label-free sensor in potassium ferrocyanide medium and as methylene blue-labeled in phosphate buffer medium. This electrode was successfully applied to analyze the serum of diseased and healthy individuals, which corroborates its high potential for biosensing applications, especially for the diagnosis of breast cancer.

Solar light induced photocatalytic degradation of tetracycline in the presence of ZnO/NiFe2O4/Co3O4 as a new and highly efficient magnetically separable photocatalyst

In this study, a new solar light-driven magnetic heterogeneous photocatalyst, denoted as ZnO/NiFe₂O₄/Co₃O₄, is successfully prepared. FT-IR, XPS, XRD, VSM, DRS, FESEM, TEM, EDS, elemental mapping, and ICP analysis are accomplished for full characterization of this catalyst. FESEM and TEM analyses of the photocatalyt clearly affirm the formation of a hexagonal structure of ZnO (25–40 nm) and the cubic structure of NiFe₂O₄ and Co₃O₄ (10–25 nm). Furthermore, the HRTEM images of the photocatalyst verify some key lattice fringes related to the photocatalyt structure. These data are in very good agreement with XRD analysis results. According to the ICP analysis, the molar ratio of ZnO/NiFe₂O₄/Co₃O₄ composite is obtained to be 1:0.75:0.5. Moreover, magnetization measurements reveals that the ZnO/NiFe₂O₄/Co₃O₄ has a superparamagnetic behavior with saturation magnetization of 32.38 emu/g. UV-vis DRS analysis indicates that the photocatalyst has a boosted and strong light response. ZnO/NiFe₂O₄/Co₃O₄, with band gap energy of about 2.65 eV [estimated according to the Tauc plot of (αhν)²vs. hν], exhibits strong potential towards the efficacious degradation of tetracycline (TC) by natural solar light. It is supposed that the synergistic optical effects between ZnO, NiFe₂O₄, and Co₃O₄ species is responsible for the increased photocatalytic performance of this photocatalyst under the optimal conditions (photocatalyst dosage = 0.02 g L⁻¹, TC concentration = 30 mg L⁻¹, pH = 9, irradiation time = 20 min, and TC degradation efficiency = 98%). The kinetic study of this degradation process is evaluated and it is well-matched with the pseudo-first-order kinetics. Based on the radical quenching tests, it can be perceived that ^•O₂⁻ species and holes are the major contributors in such a process, whereas the ^•OH radicals identify to have no major participation. The application of this methodology is implemented in a facile and low-cost photocatalytic approach to easily degrade TC by using a very low amount of the photocatalyst under natural sunlight source in an air atmosphere. The convenient magnetic isolation and reuse of the photocatalyst, and almost complete mineralization of TC (based on TOC analysis), are surveyed too, which further highlights the operational application of the current method. Notably, this method has the preferred performance among the very few methods reported for the photocatalytic degradation of TC under natural sunlight. It is assumed that the achievements of this photocatalytic method have opened an avenue for sustainable environmental remediation of a broad range of contaminants.

Synthesis and application of g-C3N4/Fe3O4/Ag nanocomposite for the efficient photocatalytic inactivation of Escherichia coli and Bacillus subtilis bacteria in aqueous solutions

Contamination of water with bacteria is one of the main causes of waterborne diseases. The photocatalytic method on the basis of bacterial inactivation seems to be a suitable disinfectant due to the lack of by-products formation. Herein, g-C3N4/Fe3O4/Ag nanocomposite combined with UV-light irradiation was applied for the inactivation two well-known bacteria namely, E. coli and B. subtilis. The nanocomposite was prepared by a hydrothermal method, and subsequently it was characterized by XRD, FT-IR, SEM, EDX and PL analyses. The optimum conditions established for the inactivation of both bacteria were as follows: nanocomposite dosage 3 g/L and bacterial density of 103 CFU/mL. In the meantime, the efficient inactivation of E. coli and B. subtilis took 30 and 150 min, respectively. The results also revealed that inactivation rate dropped with an increase in the bacterial density. It is also pointed out that OH˚ was found out to be the main radical species involved in the inactivation process. Finally, the kinetic results indicated that the inactivation of E. coli and B. subtilis followed the Weibull model. It is concluded that C3N4/Fe3O4/Ag nanocomposite along with UV-light irradiation is highly effective in inactivating E. coli and B. subtilis bacteria in the aqueous solutions.

Recent advancements of g-C3N4-based magnetic photocatalysts towards the degradation of organic pollutants: a review

Heterogeneous photocatalysis premised on advanced oxidation processes has witnessed a broad application perspective, including water purification and environmental remediation. In particular, the graphitic carbon nitride (g-C₃N₄), an earth-abundant metal-free conjugated polymer, has acquired extensive application scope and interdisciplinary consideration owing to its outstanding structural and physicochemical properties. However, several issues such as the high recombination rate of the photo-generated electron-hole pairs, smaller specific surface area, and lower electrical conductivity curtail the catalytic efficacy of bulk g-C₃N₄. Another challenging task is separating the catalyst from the reaction medium, limiting their reusability and practical applications. Therefore, several methodologies are adopted strategically to tackle these issues. Attention is being paid, especially to the magnetic nanocomposites (NCs) based catalysts to enhance efficiency and proficient reusability property. This review summarizes the latest progress related to the design and development of magnetic g-C₃N₄-based NCs and their utilization in photocatalytic systems. The usefulness of the semiconductor heterojunctions on the catalytic activity, working mechanism, and degradation of pollutants are discussed in detail. The major challenges and prospects of using magnetic g-C₃N₄-based NCs for photocatalytic applications are highlighted in this report.

Novel magnetically retrievable In2O3/MoS2/Fe3O4 nanocomposite materials for enhanced photocatalytic performance

The current work involves synthesis of hybrid nanomaterial of In2O3/MoS2/Fe3O4 and their applications as photocatalysts for disintegration of esomeprazole under visible light illumination. The data emerged from various analyses testified to the successful construction of the desired nano-scaled hybrid photocatalyst. Tauc plot gave the band gap of In2O3/MoS2/Fe3O4 to be ~ 2.15 eV. Synergistic effects of the integrant components enabled efficacious photocatalytic performances of the nanocomposite. The nanohybrid photocatalyst In2O3/MoS2/Fe3O4 showed photodecomposition up to ~ 92.92% within 50 min. The current work realizes its objective of constructing metal oxide based hybrid nano-photocatalyst supported on MoS2 sheets for activity in the visible spectrum, which displayed remarkable capacity of disintegrating emerging persistent organic contaminants and are magnetically recoverable.

Microwave-Assisted Synthesis of Cobalt Oxide/Reduced Graphene Oxide (Co3O4–rGo) Composite and its Sulfite Enhanced Photocatalytic Degradation of Organic Dyes

One-pot synthesis of Co3O4 nanocrystals on reduced graphene oxide (rGO) was carried out by reacting cobalt nitrate, L-arginine, extract of Laportae aestuans as oxidant, fuel and reducing agent, respectively, in a domestic microwave. Morphologies of Co3O4–rGo (RGCO) composite was elucidated using UV-Vis, FT-IR, TEM, SEM, EDX, XRD and photoluminescence spectroscopies. The synthesized RGCO composite was applied as heterogeneous photocatalyst in the activation of Na2SO3 (sulfite) as sacrificial agent to degrade cationic dyes: rhodamine B (RhB) and methylene blue (MB), under visible light, at neutral pH 7.0. Photocatalytic performance of as-prepared RGCO was significantly enhanced in the presence of Na2SO3. Enhanced photocatalytic activity of RGCO was attributed to the synergistic effects between sulfite radicals generated in situ, and reduced graphene oxide, in which rGO served as electron sink to suppress recombination of photogenerated charge carriers. Plausible mechanistic pathways responsible for the activation of sulfite anions in situ are presented in this paper.

Accelerated photodeterioration of class I toxic monocrotophos in the presence of one-pot constructed Ag3PO4/polyaniline@g-C3N4 nanocomposite: efficacy in light harvesting

Water and soil contamination has become unavoidable due to the enormous usage of pesticides in agriculture. Among the pesticides, monocrotophos (MCP), a popular and largely used pesticide, is extremely toxic to birds and humans, which is easily leached into the environment. Therefore, establishment of a green tactic to clean the environment from such hazard is very essential. Herein, we have developed a novel ternary nanocomposite, Ag₃PO₄/polyaniline@g-C₃N₄ with enhanced electron-hole separation efficiency, a condition which is very much required for any photocatalyst. The nanocomposite was one-pot synthesized by a simple and economical hydrothermal method. The strategically modulated band gaps of the nanocomposite help harvest the sunlight efficaciously for the robust degradation of MCP (99.6%). It has been found that the active species involved in the photo-cleaning process are OH^· and O₂^·-. A suitable reaction mechanism has been proposed and discussed. Analytical techniques, which include energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), elemental mapping analysis, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and X-ray diffraction (XRD), were used to characterize the synthesized nanocomposite. This nano-photocatalyst, which is simple, stable, and reusable, certainly has potential applications in soil contamination remediation, sewage treatments, and other environment decontaminations. Also, a study of this kind offers more strategic plans for the production of clean energy (hydrogen) by solar-driven water splitting.

Nickel sulfide/graphitic carbon nitride/strontium titanate (NiS/g-C3N4/SrTiO3) composites with significantly enhanced photocatalytic hydrogen production activity

NiS/g-C₃N₄/SrTiO₃ (NS/CN/STO) composites were prepared using a facile hydrothermal method. The synergistic effect of g-C₃N₄/SrTiO₃ (CN/STO) heterojunction and NiS cocatalyst enhanced the photocatalytic hydrogen evolution activity of NS/CN/STO. A hydrogen production rate of 1722.7 μmol h^-1 g^-1 was obtained when the 2%NiS/20%g-C₃N₄/SrTiO₃ (2NS/20CN/STO) was used for the photocatalytic hydrogen evolution in the presence of methanol used as a sacrificial agent under UV-vis light irradiation; the photocatalytic hydrogen production rate of 2NS/20CN/STO is 32.8, 8.9 and 4.2 times the value of that obtained with pure g-C₃N₄, SrTiO₃ and 20%g-C₃N₄/SrTiO₃ (20CN/STO), respectively. Moreover, in photoelectrochemical investigations when compared with 20CN/STO, SrTiO₃ and g-C₃N₄, 2NS/20CN/STO exhibited significant photocurrent enhancement. The heterojunction and cocatalyst in NS/CN/STO improved the charge separation efficiency and the lifetime of the charge carriers, leading to the enhanced generation of electrons for photocatalytic hydrogen production.