A novel photocatalytic system coupling metal-free Carbon/g-C3N4 catalyst with persulfate for highly efficient degradation of organic pollutants

A variety of photocatalytic systems have emerged as the effective methods for the degradation of organic pollutants. In this research, a novel photocatalytic system, named CNC-PDS has been proposed, which couples a metal-free carbon/g-C₃N₄ (CNC) photocatalyst with persulfate (PDS), and applied for efficient degradation of paracetamol (PCM) under simulated sunlight. The CNC-PDS system exhibited excellent photocatalytic capability, where the PCM was completely degraded in 40 min under simulated sunlight. The degradation rate of CNC-PDS system was 9.5 times compared with the g-C₃N₄ and PDS coupled systems. The CNC-PDS system can efficiently degrade other representative pollutants in neutral solutions, such as pharmaceuticals, endocrine disrupting compounds (EDCs), azo dyes. The excellent catalytic activity of CNC-PDS system should be ascribed to the two aspects: a) the increased light absorption range led to more photo-induced electron-hole pairs generation compared with the original g-C₃N₄. Meanwhile, the charge separation efficiency of the CNC photocatalyst was drastically enhanced which was proved by the results of PL and EIS analysis. These results represented the carbon/g-C₃N₄ might offer more e^- to promote PDS activation. b) The introduction of CO and the improved specific surface area provided more active sites for PDS activation. In addition, the EPR analysis and quenching experiments indicated that O₂^.-, h⁺ and ¹O₂ were the main active species for PCM in the CNC-PDS system under simulated sunlight, and the contribution order was O₂^.->¹O₂>h⁺. The degradation pathways of PCM in the CNC-PDS system are proposed based on the results of HPLC-MS. The novel CNC-PDS photocatalytic system has provided a viable option for treatment of contaminated water by organic pollutants.

Research Progress on Graphitic Carbon Nitride/Metal Oxide Composites: Synthesis and Photocatalytic Applications

Although graphitic carbon nitride (g-C3N4) has been reported for several decades, it is still an active material at the present time owing to its amazing properties exhibited in many applications, including photocatalysis. With the rapid development of characterization techniques, in-depth exploration has been conducted to reveal and utilize the natural properties of g-C3N4 through modifications. Among these, the assembly of g-C3N4 with metal oxides is an effective strategy which can not only improve electron-hole separation efficiency by forming a polymer-inorganic heterojunction, but also compensate for the redox capabilities of g-C3N4 owing to the varied oxidation states of metal ions, enhancing its photocatalytic performance. Herein, we summarized the research progress on the synthesis of g-C3N4 and its coupling with single- or multiple-metal oxides, and its photocatalytic applications in energy production and environmental protection, including the splitting of water to hydrogen, the reduction of CO2 to valuable fuels, the degradation of organic pollutants and the disinfection of bacteria. At the end, challenges and prospects in the synthesis and photocatalytic application of g-C3N4-based composites are proposed and an outlook is given.

Site-Specific Electron-Driving Observations of CO2 -to-CH4 Photoreduction on Co-Doped CeO2 /Crystalline Carbon Nitride S-Scheme Heterojunctions

Photoexcited dynamic modulation, maximizing the effective utilization of photoinduced electron-hole pairs, dominates the multiple electrons-involving reduction pathways for terminal CH₄ evolution during CO₂ photoreduction. Yet, the site-specific regulation of directional charge transfer by modification of an S-scheme heterojunction has seldom been discussed. Herein, an atomic-level tailoring strategy by anchoring single-atomic Co into CeO₂ co-catalyst rather than carbon nitride supports, which can selectively favor CO₂ -to-CH₄ photoreduction, is reported. Through in situ dynamic tracking investigations, this study identifies that surface Co-embedded bimetallic CeCo conjunction is the key feature driving a strong interconnection of dynamical charge states through S-scheme heterojunctions. The Co-embedded modification into CeO₂ co-catalysts is demonstrated to have a critical effect on directional charge control, accelerating the driving of electrons from the carbon nitride donations to site-specific Co hubs, which thereby promotes electronic transferability for electrons-involving CH₄ formation. As a result, an unprecedented CH₄ yield (181.7 µmol g^-1 ) is obtained with a high turnover number (411.4) through a fully gas-solid reaction, demonstrating its potential toward targeted CH₄ formation without adding any sacrificial agent.

Facile Synthesis of Magnetic Biochar Derived from Burley Tobacco Stems towards Enhanced Cr (VI) Removal: Performance and Mechanism

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr(VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr(VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-step mechanism of Cr(VI) removal by MBTS was further put forward, i.e., (1) Cr(VI) exchanged with hydroxyl groups on MBTS, (2) the reduction in Cr(VI) to Cr(III) mediated by oxygen-containing groups, and (3) the chelation of produced Cr(III) with the amino groups on MBTS. FTIR spectra further revealed that C-N, C-H, and C=C groups played an important role in Cr(VI) removal. Furthermore, the adsorption equilibrium and kinetics of Cr(VI) on MBTS could better be described by the Langmuir equation and pseudo-second-order rate equation. This study clearly demonstrated that ferric-loaded biochar derived from burley tobacco stems could serve as a cost-effective magnetic adsorbent for the high-efficiency removal of soluble Cr(VI) from wastewater. Tobacco stem-adsorbed Cr(VI) realized a green path for treating waste by waste.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

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.

Separable Magnetic Fe3O4@MoS2 Composite for Adsorption and Piezo-Catalytic Degradation of Dye

Well-designed composite catalysts are of increasing concern due to their improved performance compared to individual components. Herein, we designed and synthesized an Fe3O4@MoS2 composite via a simple hydrothermal method. As for the resultant composite, the MoS2 nanolayers presented a novel piezo-catalytic effect, while the Fe3O4 core provided a magnetic separation property. The structure and properties of Fe3O4@MoS2 were determined by relevant experiments. It was found that Fe3O4@MoS2 exhibited enhanced piezo-catalytic degradation of rhodamine B and good magnetic recovery/recycling features. The kobs for rhodamine B degradation over Fe3O4@MoS2 was 0.019 min−1—a little longer than that over MoS2 (0.013 min−1). Moreover, Fe3O4@MoS2 also showed a favorable ability to adsorb rhodamine B in solution, with a saturation adsorption of 26.8 mg/g. Further studies revealed that piezo-electrons, holes, and superoxide anions were key species in the piezo-catalytic degradation of rhodamine B. Notably, the step where oxygen trapped electrons to produce superoxide anions had a significant impact on the degradation of the dye. This work, not limited to the development of a high-performance MoS2-based piezo-catalyst, is expected to provide new insights into the working mechanisms and process profiles of composite piezo-catalysts.

Kinetics control over the Schiff base formation reaction for fabrication of hierarchical porous carbon materials with tunable morphology for high-performance supercapacitors

Schiff base formation reaction is highly dynamic, and the microstructure of Schiff base polymers is greatly affected by reaction kinetics. Herein, a series of Schiff base cross-linked polymers (SPs) with different morphologies are synthesized through adjusting the species and amount of catalysts. Nitrogen/oxygen co-doped hierarchical porous carbon nanoparticles (HPCNs), with tunable morphology, specific surface area (SSA) and porosity, are obtained after one-step carbonization. The optimal sample (HPCN-3) possesses a coral reef-like microstructure, high SSA up to 1003 m²g^-1, and a hierarchical porous structure, exhibiting a remarkable specific capacitance of 359.5 F g^-1(at 0.5 A g^-1), outstanding rate capability and cycle stability in a 1 M H₂SO₄electrolyte. Additionally, the normalized electric double layer capacitance (EDLC) and faradaic capacitance of HPCN-3 are 0.239 F m^-2and 10.24 F g^-1respectively, certifying its superior electrochemical performance deriving from coral reef-like structure, high external surface area and efficient utilization of heteroatoms. The semi-solid-state symmetrical supercapacitor based on HPCN-3 delivers a capacitance of 55 F g^-1at 0.5 A g^-1, good cycle stability of 86.7% after 5000 GCD cycles at 10 A g^-1, and the energy density ranges from 7.64 to 4.86 Wh kg^-1.

Ag nanoparticle-decorated 2D/2D S-scheme g-C3N4/Bi2WO6 heterostructures for an efficient photocatalytic degradation of tetracycline

The 2D/2D S-scheme Ag–g-C₃N₄–Bi₂WO₆ composite with efficient charge transfer, displayed a remarkable degradation activity of tetracycline under visible light irradiation.

A novel ternary magnetic Fe3O4/g-C3N4/Carbon layer composite for efficient removal of Cr (VI): A combined approach using both batch experiments and theoretical calculation

Heavy metal pollution has posed a potential hazard to the ecological environment and human health. Herein, a novel ternary magnetic adsorbent (Fe₃O₄/g-C₃N₄/Carbon layer, Carbon layer: hydrothermal products from sucrose) was synthesized through a simple hydrothermal carbonization (HTC) method for removal of hexavalent chromium (Cr (VI)) removal. The Carbon layer (CL) formed during the HTC of carbon precursors (sucrose) acted as a reducing agent. Also, it has abundant oxygen-containing groups on its surface. The Fe₃O₄/g-C₃N₄/CL had a high removal capacity for Cr (VI) (50.09 mg/g), and excellent regeneration and magnetic separation performance. Importantly, the Fe₃O₄/g-C₃N₄/CL could not only improve the adsorption ability for Cr (VI), but also strengthen the immobilization of Cr (III). Based on the comprehensive experiments and characterization, combined with DFT calculations, we proposed that, the first time, the removal of Cr (VI) was controlled by three consecutive processes: (1) ion exchange of Cr (VI) by hydroxyl groups, (2) reduction of Cr (VI) to Cr (III) by electron-donor (oxygen-containing) groups (EDGs), and (3) complexation of Cr (III) by amine groups. This study provides a new avenue for the removal of toxic oxygen anions and reveals an original removal mechanism of Fe₃O₄/g-C₃N₄/CLx (x = hydrothermal products from carbon precursors (glucose, ascorbic acid, cellulose)).

Versatile Functional Porous Cobalt-Nickel Phosphide-Carbon Cocatalyst Derived from a Metal-Organic Framework for Boosting the Photocatalytic Activity of Graphitic Carbon Nitride

Metal-organic framework-templated g-C₃N₄-NiCoP₂-porous carbon (PC) ternary hybrid nanomaterials were designed by taking full advantage of the metal-organic framework (MOF) derivative in the photocatalytic reaction for the first time. The MOF-templated porous structure could prevent the stacking of the carbon nitride nanosheet, and the carefully designed NiCoP₂, possessing low electrocatalytic hydrogen evolution reaction (HER) overpotential and flat-band potential, could improve the separation as well as the utilization efficiency of photogenerated electron-hole pairs. Moreover, the ligand-templated porous carbon, acting as an interface mediator between g-C₃N₄ and the NiCoP₂ cocatalyst, could boost the charge carrier transport. Consequently, the optimal ternary g-C₃N₄-NiCoP₂-PC heterostructure exhibited enhanced photocatalytic HER performance and considerable H₂ evolution performance of 5.8 μmol/h/g under UV-visible light with stoichiometric H₂O₂ production even in pure water. This work took full advantage of the MOF derivative for improving the photocatalytic reaction activity and provided a method that can hopefully help in designing a novel high-performance catalyst for solar conversion.

Facile one-step hydrothermal synthesis of α-Fe2O3/g-C3N4 composites for the synergistic adsorption and photodegradation of dyes

With the expansion of industrialization, dye pollution has become a significant hazard to humans and aquatic ecosystems. In this study, α-Fe₂O₃/g-C₃N₄-R (where R is the relative percentage of α-Fe₂O₃) composites were fabricated by a one-step method. The as-prepared α-Fe₂O₃/g-C₃N₄-0.5 composites showed excellent adsorption capacities for methyl orange (MO, 69.91 mg g⁻¹) and methylene blue (MB, 29.46 mg g⁻¹), surpassing those of g-C₃N₄ and many other materials. Moreover, the ionic strength and initial pH influenced the adsorption process. Relatively, the adsorption isotherms best fitted the Freundlich model, and the pseudo-second-order kinetic model could accurately describe the kinetics for the adsorption of MO and MB by α-Fe₂O₃/g-C₃N₄-0.5. Electrostatic interaction and π–π electron donor–acceptor interaction were the major mechanisms for MO/MB adsorption. In addition, the photocatalytic experiment results showed that more than 79% of the added MO/MB was removed within 150 min. The experimental results of free-radical capture revealed that holes (h⁺) were the major reaction species for the photodegradation of MO, whereas MB was reduced by the synergistic effect of hydroxyl radicals (·OH) and holes (h⁺). This study suggests that the α-Fe₂O₃/g-C₃N₄ composites have an application potential for the removal of dyes from wastewater.

Simple one-step hydrothermal synthesis of α-Fe₂O₃/g-C₃N₄ composites for the synergistic adsorption and photodegradation of dyes

Boosting the photocatalytic hydrogen evolution activity of g-C3N4 nanosheets by Cu2(OH)2CO3-modification and dye-sensitization

The positive synergetic effects among g-C₃N₄, Cu₂(OH)₂CO₃ and fluorescein dramatically boost the H₂-evolution activity over a fluorescein-sensitized Cu₂(OH)₂CO₃/g-C₃N₄ photocatalyst.