Search Results (51)

The excessive discharge of antibiotics into aquatic systems is a major issue in many countries worldwide and poses a threat to human health and the sustainable development of society. Hence, developing efficient treatment methods and purification technologies to degrade antibiotics is essential. Herein, we present the synthesis of low-cost, self-propelled tubular Fe³⁺-incorporated graphitic carbon nitride (g-C₃N₄-Fe@KF) micromotors using kapok fibers (KFs) as templates and their application as photo-catalysts for the photo-Fenton degradation of tetracycline (TC) under visible-light irradiation. The g-C₃N₄-Fe@KF micromotors moved rapidly when being propelled by oxygen bubbles generated in a hydrogen peroxide (H₂O₂) solution as a result of a photo-assisted Fenton reaction. The motion behavior of the g-C₃N₄-Fe@KF micromotors was dependent on the concentration of H₂O₂ and the length of the micromotors. The propulsion mechanism was discussed in detail. The micromotors efficiently degraded antibiotics via the photo-Fenton process. Photo-Fenton degradation efficiency was attributed to the synergistic effects of the doped Fe³⁺ and g-C₃N₄ under visible-light irradiation and self-propulsion of the micromotors. In addition, the micromotors possessed good reusability, thereby efficiently realizing multiple cycles of degradation. The current work offers an avenue for the design of micromotors, using inexpensive approaches, for various potential environmental applications. Full article

Peroxymonosulfate (PMS, SO₅²⁻)-based oxidation is an efficient pathway for degrading organic pollutants, but it still suffers from slow degradation efficiency and low PMS utilization. In this work, we report the preparation of porous Fe-doped g-C₃N₄ catalysts by one-step thermal polymerization using urea and transition metal salts as precursors and investigate the effect of atmosphere conditions (air and nitrogen) on the catalytic performance. Systematic characterizations show that Fe-doped g-C₃N₄ prepared in air (FeN_x-CNO) has a larger specific surface area (136.2 m² g⁻¹) and more oxygen vacancies than that prepared in N₂ (FeN_x-CNN, 74.2 m² g⁻¹), giving it more active sites to participate in the reaction. Meanwhile, FeN_x-CNO inhibits the recombination of photogenerated carriers and improves the light utilization. The redox cycling of Fe(III) and Fe(II) species in the photocatalytic system ensures the continuous generation of SO₅•⁻ and SO₄•⁻. Therefore, FeN_x-CNO can remove CBZ up to 96% within 20 min, which is 3.4 times higher than that of CNO and 3.1 times higher than that of FeN_x-CNN, and the degradation efficiency can still retain 93% after 10 cycles of reaction. This study provides an economical and efficient method for photocatalysis in the degradation of medicines in contaminated water. Full article

Nutrient pollution poses a significant global environmental threat, and addressing this issue remains an ongoing challenge. Biochar has been identified as a potential adsorbent for environmental remediation. However, raw biochar has a low nitrate adsorption capacity; thus, biochar modification is necessary for targeted environmental applications. This work explored and compared the performance of Fe-doped, N-doped, and N-Fe-co-doped biochars from Douglas fir toward nitrate removal from an aqueous solution. A central composite experimental design was used to optimize processing variables, maximizing the surface area and nitrate adsorption capacity. Proximate analysis, elemental composition, gas physisorption, XPS, SEM, TEM, FTIR, and XRD were used to characterize the biochar’s properties. Pyrolysis under NH₃ gas generated more pores in biochar than conventional pyrolysis. Doping biochar with N and Fe improved nitrate adsorption capacity from aqueous solutions. The maximum nitrate adsorption capacity of Fe-N-doped biochar produced at 800 °C was 20.67 mg g⁻¹ in sorption tests at pH 3.0. The formation of N-containing functional groups and Fe oxides on the biochar surface enhanced the nitrate removal efficiency of N-Fe biochar. The results indicate that biochar’s adsorption capacity for NO₃⁻ is largely affected by the solution’s pH and biochar’s surface chemistry. Electrostatic attraction is the primary mechanism for nitrate adsorption. Full article

The binary heterostructured semiconducting visible light photocatalyst of the iron-doped graphitic carbon nitride/bismuth molybdate (Fe-g-C₃N₄/Bi₂MoO₆) composite was prepared by coupling with Fe-doped g-C₃N₄ and Bi₂MoO₆ particles. In the present study, a comparison of structural characteristics, optical properties, and photocatalytic degradation efficiency and activity between Fe-doped g-C₃N₄ particles, Bi₂MoO₆ particles, and Fe-g-C₃N₄/Bi₂MoO₆ composite was investigated. The results of X-ray diffraction (XRD) examination indicate that the hydrothermal Bi₂MoO₆ particles have a single orthorhombic phase and Fourier transform infrared (FTIR) spectroscopy analysis confirms the formation of Fe-doped g-C₃N₄. The optical bandgaps of the Fe-doped g-C₃N₄ and Bi₂MoO₆ particles are 2.74 and 2.73 eV, respectively, as estimated from the Taut plots obtained from UV-Vis diffuse reflectance spectroscopy (DRS) spectra. This characteristic indicates that the two semiconductor materials are suitable for absorbing visible light. The transmission electron microscopy (TEM) micrograph reveals the formation of the heterojunction Fe-g-C₃N₄/Bi₂MoO₆ composite. The results of photocatalytic degradation revealed that the developed Fe-g-C₃N₄/Bi₂MoO₆ composite photocatalyst exhibited significantly better photodegradation performance than the other two single semiconductor photocatalysts. This property can be attributed to the heterostructured nanostructure, which could effectively prevent the recombination of photogenerated carriers (electron–hole pairs) and enhance photocatalytic activity. Furthermore, cycling test showed that the Fe-g-C₃N₄/Bi₂MoO₆ heterostructured photocatalyst exhibited good reproducibility and stability for organic dye photodegradation. Full article

This current study assessed the impacts of morphology adjustment of perovskite BiFeO₃ (BFO) on the construction and photocatalytic activity of P-infused g-C₃N₄/U-BiFeO₃ (U-BFO/PCN) heterostructured composite photocatalysts. Favorable formation of U-BFO/PCN composites was attained via urea-aided morphology-controlled hydrothermal synthesis of BFO followed by solvosonication-mediated fusion with already synthesized P-g-C₃N₄ to form U-BFO/PCN composites. The prepared bare and composite photocatalysts’ morphological, textural, structural, optical, and photocatalytic performance were meticulously examined through various analytical characterization techniques and photodegradation of aqueous rhodamine B (RhB). Ellipsoids and flakes morphological structures were obtained for U-BFO and BFO, and their effects on the successful fabrication of the heterojunctions were also established. The U-BFO/PCN composite exhibits 99.2% efficiency within 20 min of visible-light irradiation, surpassing BFO/PCN (88.5%), PCN (66.8%), and U-BFO (26.1%). The pseudo-first-order kinetics of U-BFO/PCN composites is 2.41 × 10⁻¹ min⁻¹, equivalent to 2.2 times, 57 times, and 4.3 times of BFO/PCN (1.08 × 10⁻¹ min⁻¹), U-BFO, (4.20 × 10⁻³ min⁻¹), and PCN, (5.60 × 10⁻² min⁻¹), respectively. The recyclability test demonstrates an outstanding photostability for U-BFO/PCN after four cyclic runs. This improved photocatalytic activity exhibited by the composites can be attributed to enhanced visible-light utilization and additional accessible active sites due to surface and electronic band modification of CN via P-doping and effective charge separation achieved via successful composites formation. Full article

Fe/N-doped carbon (Fe-NC) is an excellent base-metal catalyst for use in an electrocatalytic oxygen reduction reaction (ORR) with high activity. In this paper, graphite phase carbon nitride (g-C₃N₄) was first obtained from the pyrolyzing of melamine, and then different proportions of FeCl₃ were separately doped into g-C₃N₄ to further prepare the Fe-NC catalyst. The Fe-NC catalyst was applied in an ORR reaction, and the results show that the Fe-NC catalyst doped with 0.5 mmol FeCl₃ possesses exceptional electrocatalytic performance, with an onset potential of 0.96 V and a half-wave potential of 0.81 V, which approaches that of a Pt/C catalyst. Meanwhile, the Fe-NC catalyst displays high stability and methanol resistance. The results supply a new way to prepare efficient ORR electrocatalysts. Full article

Graphite carbon nitride (g-C₃N₄) has been employed as an emerging metal-free catalyst in heterogeneous catalysis. However, the catalyst has a poor activation property for peroxymonosulfate (PMS). In this study, Bi-Fe oxide co-doped g-C₃N₄ (Bi@Fe/CN) was synthesized for PMS activation to degrade sulfamethoxazole (SMX). In particular, Bi@Fe/CN-3 presented remarkable catalytic performance with 99.7% removal of SMX within 60 min in the PMS system. Additionally, Bi@Fe/CN-3 presented good stability and recyclability through the cycling experiments. Moreover, it was shown that free radicals (O₂^•−, ^•OH, and SO₄^•−) and non-free radicals (¹O₂) were the primary active species in the Bi@Fe/CN-3/PMS system. Bi, Fe, and surface lattice oxygen were confirmed to be the main contributors to the active species. This work elucidates the mechanism of activation of PMS by Bi@Fe/CN-3, which is beneficial to promote the application of bimetallic oxide-modified g-C₃N₄/PMS systems in wastewater treatment. Full article

5-hydroxymethylfurfural (HMF) oxidation in aqueous media using visible photocatalysis is a green and sustainable route for the valorization of lignocellulosic biomass derivatives. Several semiconductors have already been applied for this purpose; however, the use of Poly(heptazine imides), which has high crystallinity and a special cation exchange property that allows the replacement of the cation held between the layers of C₃N₄ structure by transition metal ions (TM), remains scarce. In this study, PHI(Na) was synthesized using a melamine/NaCl method and used as precursor to prepare metal (Fe, Co, Ni, or Cu)-doped PHI catalysts. The catalysts were tested for selective oxidation of HMF to 2,5-diformylfuran (DFF) in water and O₂ atmosphere under blue LED radiation. The catalytic results revealed that the 0.1 wt% PHI(Fe) catalyst is the most efficient photocatalyst while higher Fe loading (1 and 2 wt%) favors the formation of Fe³⁺ clusters, which are responsible for the drop in HMF oxidation. Moreover, the 0.1 wt% PHI(Fe) photocatalyst has strong oxidative power due to its efficiency in H₂O₂ production, thus boosting the generation of nonselective hydroxyl radicals (^●OH) via different pathways that can destroy HMF. We found that using 50 mM, the highest DFF production rate (393 μmol·h⁻¹·g⁻¹) was obtained in an aqueous medium under visible light radiation. Full article

The high specific capacity of transition metal sulfides (TMSs) opens up a promising new development direction for lithium-ion batteries with high energy storage. However, the poor conductivity and serious volume expansion during charge and discharge hinder their further development. In this work, trimetallic sulfide Zn–Co–Fe–S@nitrogen-doped carbon (Zn–Co–Fe–S@N–C) polyhedron composite with a core–shell structure is synthesized through a simple self-template method using ZnCoFe–ZIF as precursor, followed by a dopamine surface polymerization process and sulfidation during high-temperature calcination. The obvious space between the internal core and the external shell of the Zn–Co–Fe–S@N–C composites can effectively alleviate the volume expansion and shorten the diffusion path of Li ions during charge and discharge cycles. The nitrogen-doped carbon shell not only significantly improves the electrical conductivity of the material, but also strengthens the structural stability of the material. The synergistic effect between polymetallic sulfides improves the electrochemical reactivity. When used as an anode in lithium-ion batteries (LIBs), the prepared Zn–Co–Fe–S@N–C composite exhibits a high specific capacity retention (966.6 mA h g⁻¹ after 100 cycles at current rate of 100 mA g⁻¹) and good cyclic stability (499.17 mA h g⁻¹ after 120 cycles at current rate of 2000 mA g⁻¹). Full article

SrCo_0.2Zn_0.2Fe_11.6O_18.8 hexaferrite was obtained by a “one-pot” green sol-gel synthesis method utilizing aqueous mandarin orange (Citrus reticulata) peel extract as an eco-friendly reactant. The research objective was to analyze the influence of cobalt and zinc co-doping and the synthesis process on the structure, morphology, magnetic, dielectric and ferroelectric properties of strontium hexaferrite in view of future applications. Structural and morphological characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled to energy dispersive X-ray spectrometry (SEM-EDX) confirmed the formation of a Co and Zn ion incorporated M-type magnetoplumbite with c/a lattice parameter ratio of 3.919 as crystallite nanoplatelets of 32 and 53 nm in thickness and width, respectively. The magnetic hysteresis loop of the synthesized powder recorded by a vibrating sample magnetometer (VSM) at room temperature confirmed its ferromagnetic nature with a coercive field (H_c) of 2539 Oe and a saturation magnetization (M_s) and remanent magnetization (M_r) of 44.6 emu/g and 21.4 emu/g, respectively. Room temperature ferroelectric loops measured at 100 Hz showed a maximal (P_max) and a remanent (P_r) polarization of 195.4 and 31.0 nC/cm², respectively. Both increased when the magnitude of the applied electrical field increased in the 1–24 kV/cm range. The dielectric constant decreased with the frequency increase, in accordance with the Maxwell–Wagner model, while the conductivity changed according to the Jonscher power law. The complex impedance was modeled with an equivalent circuit, enabling identification of the dominant contribution of grain boundary resistance (272.3 MΩ) and capacitance (7.16 pF). Full article

This Special Issue includes 12 research papers on the development of various materials for adsorbing different contaminants in water, such as Sb, Cr(VI), Cu(II), Zn(II), fluorine, phenol, dyes (indigo carmine, Congo red, methylene blue, and crystal violet), and drugs (dlevofloxacin, captopril, and diclofenac, and paracetamol). The commercial, natural, and synthetic materials used as adsorbents comprise commercial activated carbon, natural clay and montmorillonite, biosorbent based on sugarcane bagasse or algal, graphene oxide, graphene oxide-based magnetic nanomaterial, mesoporous Zr-G-C₃N₄ nanomaterial, nitrogen-doped core–shell mesoporous carbonaceous nano-sphere, magnetic Fe-C-N composite, polyaniline-immobilized ZnO nanorod, and hydroxy-iron/acid–base-modified sepiolite composite. Various operational conditions are evaluated under batch adsorption experiments, such as pH, NaCl, solid/liquid ratio, stirring speed, contact time, solution temperature, initial adsorbate concentration. The re-usability of laden materials is evaluated through adsorption–desorption cycles. Adsorption kinetics, isotherm, thermodynamics, and mechanisms are studied and discussed. Machine learning processes and statistical physics models are also applied in the field of adsorption science and technology. Full article

Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe₃C/Fe₂O₃ nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe₃C/Fe₂O₃ during charge–discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g⁻¹ at 2 A g⁻¹, superior to that of NCNF-supported Fe₃C nanoparticles (NCFC, 261.7 F g⁻¹), and NCNFs/Fe₂O₃ (NCFO, 398.3 F g⁻¹). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg⁻¹ at 800 W kg⁻¹. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe₃C/Fe₂O₃. Full article

At present, it is still a challenge to prepare multifunctional composite nanomaterials with simple composition and favorable structure. Here, multifunctional Fe₃O₄@nitrogen-doped carbon (N-C) nanocomposites with hollow porous core-shell structure and significant electrochemical, adsorption and sensing performances were successfully synthesized through the hydrothermal method, polymer coating, then thermal annealing process in nitrogen (N₂) and lastly etching in hydrochloric acid (HCl). The morphologies and properties of the as-obtained Fe₃O₄@N-C nanocomposites were markedly affected by the etching time of HCl. When the Fe₃O₄@N-C nanocomposites after etching for 30 min (Fe₃O₄@N-C-3) were applied as the anodes for lithium-ion batteries (LIBs), the invertible capacity could reach 1772 mA h g⁻¹ after 100 cycles at the current density of 0.2 A g⁻¹, which is much better than that of Fe₃O₄@N-C nanocomposites etched, respectively, for 15 min and 45 min (948 mA h g⁻¹ and 1127 mA h g⁻¹). Additionally, the hollow porous Fe₃O₄@N-C-3 nanocomposites also exhibited superior rate capacity (950 mA h g⁻¹ at 0.6 A g⁻¹). The excellent electrochemical properties of Fe₃O₄@N-C nanocomposites are attributed to their distinctive hollow porous core-shell structure and appropriate N-doped carbon coating, which could provide high-efficiency transmission channels for ions/electrons, improve the structural stability and accommodate the volume variation in the repeated Li insertion/extraction procedure. In addition, the Fe₃O₄@N-C nanocomposites etched by HCl for different lengths of time, especially Fe₃O₄@N-C-3 nanocomposites, also show good performance as adsorbents for the removal of the organic dye (methyl orange, MO) and surface-enhanced Raman scattering (SERS) substrates for the determination of a pesticide (thiram). This work provides reference for the design and preparation of multifunctional materials with peculiar pore structure and uncomplicated composition. Full article

Synthetic organic pigments from the direct discharge of textile effluents are considered as colossal global concern and attract the attention of scholars. The efficient construction of heterojunction systems involving precious metal co-catalysis is an effective strategy for obtaining highly efficient photocatalytic materials. Herein, we report the construction of a Pt-doped BiFeO₃/O-g-C₃N₄ (Pt@BFO/O-CN) S-scheme heterojunction system for photocatalytic degradation of aqueous rhodamine B (RhB) under visible-light irradiation. The photocatalytic performances of Pt@BFO/O-CN and BFO/O-CN composites and pristine BiFeO₃ and O-g-C₃N₄ were compared, and the photocatalytic process of the Pt@BFO/O-CN system was optimized. The results exhibit that the S-scheme Pt@BFO/O-CN heterojunction has superior photocatalytic performance compared to its fellow catalysts, which is due to the asymmetric nature of the as-constructed heterojunction. The as-constructed Pt@BFO/O-CN heterojunction reveals high performance in photocatalytic degradation of RhB with a degradation efficiency of 100% achieved after 50 min of visible-light irradiation. The photodegradation fitted well with pseudo-first-order kinetics proceeding with a rate constant of 4.63 × 10⁻² min⁻¹. The radical trapping test reveals that h⁺ and ^•O₂⁻ take the leading role in the reaction, while the stability test reveals a 98% efficiency after the fourth cycle. As established from various interpretations, the considerably enhanced photocatalytic performance of the heterojunction system can be attributed to the promoted charge carrier separation and transfer of photoexcited carriers, as well as the strong photo-redox ability established. Hence, the S-scheme Pt@BFO/O-CN heterojunction is a good candidate in the treatment of industrial wastewater for the mineralization of organic micropollutants, which pose a grievous threat to the environment. Full article

The lithium-sulfur (Li-S) battery has been regarded as an important candidate for the next-generation energy storage system due to its high theoretical capacity (1675 mAh g⁻¹) and high energy density (2600 Wh kg⁻¹). However, the shuttle effect of polysulfide seriously affects the cycling stability of the Li-S battery. Here, a novel Fe₃C-decorated folic acid-derived graphene-like N-doped carbon sheet (Fe₃C@N-CS) was successfully prepared as the polysulfide catalyst to modify the separator of Li-S batteries. The porous layered structures can successfully capture polysulfide as a physical barrier and the encapsulated Fe₃C catalyst can effectively trap and catalyze the conversion of polysulfide, thus accelerating the redox reaction kinetics. Together with the highly conductive networks, a cell with the Fe₃C@N-CS-modified separator evinces superior cycling stability with 0.06% capacity decay per cycle at 1 C rate over 500 cycles and excellent specific capacity with an initial capacity of 1260 mAh g⁻¹ at 0.2 C. Furthermore, at a high sulfur loading of 4.0 mg cm⁻², the batteries also express superb cycle stability and rate performance. Full article