Magnetic Fe3O4/CeO2/g-C3N4 composites with a visible-light response as a high efficiency Fenton photocatalyst to synergistically degrade tetracycline

Distinct pathway of multiferroic silver-decorated zinc ferrite nanocatalyst performance for Acinate insecticide oxidation

The current study investigating the preparation and application of a Multiferroic nano-scale silver zinc ferrite substance (Ag0.5Zn0.5Fe2O4 nanocatalyst) has been established. Multiferroic silver zinc ferrite substance is prepared by co-precipitation technique as hybridized composite. This synethsized nanoparticles was characterized via X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) as well as Scanning Electron Miscospopy (SEM). Such nanoparticles are used as a sustainable recyclable photo-Fenton's reagent precursor for treating insecticide in wastewater. The results revealed a high Acinate oxidation rate reached to 97% removal within 40 min of irradiance time. To increase the performance, the operating variables are optimized. pH 3.0 and 40 and 400 mg/L for Ag0.5Zn0.5Fe2O4 and hydrogen peroxide, respectively are identified as the optimum values. Also, kinetics and thermodynamic are evaluated and the reaction is subsequent the first-order kinetics model and exothermic and non-spontaneous in nature with a low energy barrier of 35.02 kJ/mol. The advantage of Ag0.5Zn0.5Fe2O4 catalyst is its sustainability since it recovered for multiple reuse with a high activity reached to 80% removal rate after six cyclic use compared to 97% of fresh catalyst use.

CeFe nanofibrous carbon nanozyme integrated with smartphone for the point-of-care testing of norfloxacin in water

The overuse of antibiotics has led to the severe contamination of water bodies, posing a considerable hazard to human health. Therefore, the development of an accurate and rapid point-of-care testing (POCT) platform for the quantitative detection of antibiotics is necessary. In this study, Cerium oxide (CeO2) and Ferrosoferric oxide (Fe3O4) nanoparticles were simultaneously encapsulated into N-doped nanofibrous carbon microspheres to form of a novel nanozyme (CeFe-NCMzyme) with a porous structure, high surface area, and N-doped carbon material properties, leading to a considerable enhancement of the peroxidase (POD)-like activity compared with that of the CeO2 or Fe3O4 nanoparticles alone. The POD-like activity of CeFe-NCMzyme can be quenched using L-Cysteine (Cys) and subsequently restored by the addition of a quinolone antibiotic (norfloxacin, NOR). Therefore, CeFe-NCMzyme was used as a colorimetric sensor to detect NOR via an "On-Off" model of POD-like activity. The sensor possessed a wide linear range of 0.05-20.0 μM (R 2 = 0.9910) with a detection limit of 35.70 nM. Furthermore, a smartphone-assisted POCT platform with CeFe-NCMzyme was fabricated for quantitative detection of NOR based on RGB analysis. With the use of the POCT platform, a linear range of 0.1-20.0 μM and a detection limit of 54.10 nM were obtained. The spiked recoveries in the water samples were ranged from 97.73% to 102.01%, and the sensor exhibited good accuracy and acceptable reliability. This study provides a portable POCT platform for the on-site and quantitative monitoring of quinolone antibiotics in real samples, particularly in resource-constrained settings.

Decolorization of RhB on three-dimensional porous CeO2/LaFeO3/SrTiO3 catalyst via photo-fenton-like catalysis

The catalysts with three-dimensional porous (3DP) CeO2, LaFeO3 and SrTiO3 are synthesized by sol-gel method and chemical precipitation method. The resulting multi-component 3DP CeO2/LaFeO3/SrTiO3 composite material featured a high specific surface area (26.08 m2/g), which can provide more surface active sites to improve adsorption capacity and catalytic performance. The photocatalytic, Fenton-like, photo-Fenton-like performance of the catalyst are studied on decolorization of RhB under UV irradiation, respectively. 3DP CeO2/LaFeO3/SrTiO3 exhibits high catalytic performance. Compared with photocatalytic or Fenton-like performance, 3DP CeO2/LaFeO3/SrTiO3 catalyst exhibits higher photo-Fenton-like performance, facilitating efficient decolorization of the rhodamine B. Moreover, the initial reaction rate on decolorization of RhB with 3DP CeO2/LaFeO3/SrTiO3 is 10.55, 5.52, 3.67 and 1.51 times higher than that with SrTiO3, LaFeO3, 3DP CeO2 and 3DP CeO2/LaFeO3, respectively. Meanwhile, 3DP LaFeO3/CeO2/SrTiO3 has a wider pH usage range in the synergistic reaction. Finally, a catalytic mechanism for the decolorization of rhodamine B is proposed. The continuous cycling of Fe3+/Fe2+ and Ce4+/Ce3+ and the production of active substances are achieved under the photo-Fenton-like effect of the catalyst.

Effective degradation of tetracycline in aqueous solution by an electro-Fenton process using chemically modified carbon/α-FeOOH as catalyst

This study applied an electro-Fenton process using chemically modified activated carbon derived from rubber seed shells loaded with α-FeOOH (RSCF) as catalyst to remove tetracycline residues from aquatic environment. Catalyst characteristics were evaluated using SEM, EDS, XRD, and XPS, showing successful insertion of iron onto the activated carbon. The effects of the parameters were investigated, and the highest treatment efficiency was achieved at pH of 3, Fe: H2O2 ratio (w/w) of 500:1, catalyst dose of 1 g/L, initial TCH concentration of 100 mg/L, and electric current of 150 mA, with more than 90% of TCH being eliminated within 30 min. Furthermore, even after five cycles of use, the treatment efficiency remains above 90%. The rate constant is calculated to be 0.218 min-1, with high regression coefficients (R 2 = 0.93). The activation energy (Ea) was found to be 32.2 kJ/mol, indicating that the degradation of TCH was a simple reaction with a low activation energy. These findings showed that the RSCF is a highly efficient and cost-effective catalyst for TCH degradation. Moreover, the use of e-Fenton process has the advantage of high efficiency, low cost thanks to the recyclability of the catalyst, and environmental friendliness thanks to less use of H2O2.

Construction of site-specific magnetic Z-scheme CdS/Fe3O4@N-doped graphene aerogel microtube/N-doped TiO2 with porous structure: enhanced catalytic performance in photo-Fenton reaction

The development of composite photocatalysts with high charge transfer efficiency, great visible light absorption, and quick recovery has aroused the interest of many researchers. Herein, based on the hydrothermal assisted vacuum freeze drying method, CdS, Fe3O4, and N-TiO2 were, respectively, fixed in the inner, middle, and outer layers of nitrogen-doped graphene aerogel for preparation of the site-specific magnetic porous Z-scheme CdS/Fe3O4@N-doped graphene aerogel microtube/N-doped TiO2 (CdS/Fe3O4@NGAM/N-TiO2) photocatalyst. For the composite, Fe3O4@NGAM carrier with porous and tubular structure not only helps the recycle and reactants/productions mass transport in the photocatalytic process but also ensures the well-steered transfer of electrons and holes from CdS and N-TiO2 in the Z-type heterojunction system, greatly improving the separation of photogenerated carriers. Besides, Fe3O4 can also work as a Fenton catalyst to activate hydrogen peroxide which is generated in situ by CdS. Thus, the CdS/Fe3O4@NGAM/N-TiO2 composite presents excellent degradation efficiencies towards methyl orange ((MO) 98% removal rate within 50 min), bisphenol A ((BPA) 96% removal rate within 50 min), tetracycline hydrochloride ((TCH) 96% removal rate within 120 min) and strong stabilities after 6 cycles. The free radical removal experiments show that ·O2- and ·OH are the main active substances of catalysis, which further confirms the synergistic effect of photocatalysis and Fenton catalysis.

Nanotechnology-assisted treatment of pharmaceuticals contaminated water

The presence of pharmaceutical compounds in wastewater due to an increase in industrialization and urbanization is a serious health concern. The demand for diverse types of pharmaceutical compounds is expected to grow as there is continuous improvement in the global human health standards. Discharge of domestic pharmaceutical personal care products and hospital waste has aggravated the burden on wastewater management. Further, the pharmaceutical water is toxic not only to the aquatic organism but also to terrestrial animals coming in contact directly or indirectly. The pharmaceutical wastes can be removed by adsorption and/or degradation approach. Nanoparticles (NPs), such as 2D layers materials, metal-organic frameworks (MOFs), and carbonaceous nanomaterials are proven to be more efficient for adsorption and/or degradation of pharmaceutical waste. In addition, inclusion of NPs to form various composites leads to improvement in the waste treatment efficacy to a greater extent. Overall, carbonaceous nanocomposites have advantage in the form of being produced from renewable resources and the nanocomposite material is biodegradable either completely or to a great extent. A comprehensive literature survey on the recent advancement of pharmaceutical wastewater is the focus of the present article.

Nexus Advances Using Marine Biopolymeric Gel Material as a Photocatalyst for the Oxidation of Agricultural Wastewater Containing Insecticides

The attention of the research community is focused not only on waste elimination, but also on waste valorization. The natural marine biopolymer gel substance chitosan, which can be derived from the waste substances of marine life, is a polymer-matrix-based nanocomposite. Chitosan attracts special attention due to its potential applications, especially in wastewater treatment. In this regard, magnetite-incorporated chitosan powders of nanometer scale were synthesized by a simple co-precipitation method to attain the dual functions of chitosan gel and magnetite. The synthesized magnetite-incorporated chitosan nanopowders were verified using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, a vibrating-sample magnetometer (VSM), a scanning electron microscope (SEM), and transmission electron microscopy (TEM) images, which showed that the synthesized magnetite-incorporated chitosan was nanosized. The superior application of such a material to offset the deterioration of the environment caused by insecticides is attained through a photocatalytic reaction. The experimental results verified the function of magnetite-incorporated chitosan, since it increased the composite-specific surface area, resulting in high methomyl molecule oxidation. Methomyl oxidation reached almost complete insecticide removal (99%) within only one hour of irradiance time. The optimal operational conditions were investigated, and the maximal removal rate occurred when the aqueous solution was at an acidic pH of 3.0. The reaction was affected by differing hydrogen peroxide and catalyst doses, and the optimized reagent was recorded at the levels of 40 and 400 mg/L of catalyst and hydrogen peroxide, respectively. Also, catalyst reusability was attained, confirming its sustainability, since it could be used for successive cycles. From the current investigation, it is proposed that magnetite-chitosan nanoparticles could serve as a promising photocatalyst for the elimination of insecticides from wastewater in a green manner.

Photocatalytic Self-Fenton System of g-C3N4-Based for Degradation of Emerging Contaminants: A Review of Advances and Prospects

The discharge of emerging pollutants in the industrial process poses a severe threat to the ecological environment and human health. Photocatalytic self-Fenton technology combines the advantages of photocatalysis and Fenton oxidation technology through the in situ generation of hydrogen peroxide (H2O2) and interaction with iron (Fe) ions to generate a large number of strong reactive oxygen species (ROS) to effectively degrade pollutants in the environment. Graphite carbon nitride (g-C3N4) is considered as the most potential photocatalytic oxygen reduction reaction (ORR) photocatalyst for H2O2 production due to its excellent chemical/thermal stability, unique electronic structure, easy manufacturing, and moderate band gap (2.70 eV). Hence, in this review, we briefly introduce the advantages of the photocatalytic self-Fenton and its degradation mechanisms. In addition, the modification strategy of the g-C3N4-based photocatalytic self-Fenton system and related applications in environmental remediation are fully discussed and summarized in detail. Finally, the prospects and challenges of the g-C3N4-based photocatalytic self-Fenton system are discussed. We believe that this review can promote the construction of novel and efficient photocatalytic self-Fenton systems as well as further application in environmental remediation and other research fields.

Insights into the Degradation Mechanisms of TCH by Magnetic Fe3S4/Cu2O Composite

Unique Fe₃S₄/Cu₂O composites were constructed with high Fenton-like photocatalytic activity through the impregnation coprecipitation method. The structure, morphology, optical, magnetic, and photocatalytic properties of the as-prepared composites were explored in detail. The findings suggest that small Cu₂O particles were grown on the surface of Fe₃S₄. The removal efficiency of TCH by Fe₃S₄/Cu₂O was 65.7, 4.75, and 3.67 times higher than that of pure Fe₃S₄, Cu₂O, and the Fe₃S₄ + Cu₂O mixture, respectively, when the mass ratio of Fe₃S₄ and Cu₂O was 1:1 at pH 7.2. The synergistic effect between Cu₂O and Fe₃S₄ was the main factor for TCH degradation. The Cu⁺ species from Cu₂O increased the Fe³⁺/Fe²⁺ cycle during the Fenton reaction. ^•O₂^- and h⁺ were the main active radicals; however, ^•OH and e^- played the second role in the photocatalytic degradation reaction. Moreover, the Fe₃S₄/Cu₂O composite retained good recyclability and versatility, and could be conveniently separated by a magnet.

Tuning the intrinsic catalytic sites of magnetite to concurrently enhance the reduction of H2O2 and O2: Mechanism analysis and application potential evaluation

Heterogeneous Fenton-like process based on H₂O₂ activation has been widely tested for water purification, but its application still faces some challenges such as the use of high doses of chemicals (including catalysts and H₂O₂). Herein, a facile co-precipitation method was utilized for small-scale production (∼50 g) of oxygen vacancies (OVs)-containing Fe₃O₄ (V_o-Fe₃O₄) for H₂O₂ activation. Experimental and theoretical results collaboratively verified that H₂O₂ adsorbed on the Fe site of Fe₃O₄ tended to lose electrons and generate O₂^•-. While the localized electron from OVs of V_o-Fe₃O₄ could assist in donating electrons to H₂O₂ adsorbed on OVs sites, this allowed more H₂O₂ to be activated to ^•OH, which was 3.5 folds higher than Fe₃O₄/H₂O₂ system. Moreover, the OVs sites promoted dissolved oxygen activation and decreased the quenching of O₂^•- by Fe(III), thus promoting the generation of ¹O₂. Consequently, the fabricated V_o-Fe₃O₄ achieved much higher oxytetracycline (OTC) degradation rate (91.6%) than Fe₃O₄ (35.4%) at a low catalyst (50 mg/L) and H₂O₂ dosage (2 mmol/L). Importantly, further integration of V_o-Fe₃O₄ into fixed-bed Fenton-like reactor could effectively eliminate OTC (>80%) and chemical oxygen demand (COD) (21.3%∼50%) within the running period. This study provides promising strategies for enhancing the H₂O₂ utilization of Fe mineral.

Tuning Band Gap in Fe-Doped g-C3N4 by Zn for Enhanced Fenton-Like Catalytic Performance

Multiple oxidation states of first-row transition-metal cations were always doped in g-C₃N₄ to enhance the catalytic activity by the synergistic action between the cations in the Fenton-like reaction. It remains a challenge for the synergistic mechanism when the stable electronic centrifugation (3d¹⁰) of Zn²⁺ was used. In this work, Zn²⁺ was facilely introduced in Fe-doped g-C₃N₄ (named xFe/yZn-CN). Compared with Fe-CN, the rate constant of the tetracycline hydrochloride (TC) degradation increased from 0.0505 to 0.0662 min^-1 for 4Fe/1Zn-CN. The catalytic performance was more outstanding than those of similar catalysts reported. The catalytic mechanism was proposed. With the introduction of Zn²⁺ in 4Fe/1Zn-CN, the atomic percent of Fe (Fe²⁺ and Fe³⁺) and the molar ratio of Fe²⁺ to Fe³⁺ at the catalyst's surface increased, where Fe²⁺ and Fe³⁺ were the active sites for adsorption and degradation. In addition, the band gap of 4Fe/1Zn-CN decreased, leading to enhanced electron transfer and conversion from Fe³⁺ to Fe²⁺. These changes resulted in the excellent catalytic performance of 4Fe/1Zn-CN. Radicals •OH, •O₂^-, and ¹O₂ formed in the reaction and took different actions under various pH values. 4Fe/1Zn-CN exhibited excellent stability after five cycles under the same conditions. These results may give a strategy for synthesizing Fenton-like catalysts.

Removal of tetracycline from wastewater using g-C3N4 based photocatalysts: A review

Tetracycline is currently one of the most consumed antibiotics for human therapy, veterinary purpose, and agricultural activities. Tetracycline worldwide consumption is expected to rise by about more than 30% by 2030. The persistence of tetracycline has necessitated implementing and adopting strategies to protect aquatic systems and the environment from noxious pollutants. Here, graphitic carbon nitride-based photocatalytic technology is considered because of higher visible light photocatalytic activity, low cost, and non-toxicity. Thus, this review highlights the recent progress in the photocatalytic degradation of tetracycline using g-C₃N₄-based photocatalysts. Additionally, properties, worldwide consumption, occurrence, and environmental impacts of tetracycline are comprehensively addressed. Studies proved the occurrence of tetracycline in all water matrices across the world with a maximum concentration of 54 μg/L. Among different g-C₃N₄-based materials, heterojunctions exhibited the maximum photocatalytic degradation of 100% with the reusability of 5 cycles. The photocatalytic membranes are found to be feasible due to easiness in recovery and better reusability. Limitations of g-C₃N₄-based wastewater treatment technology and efficient solutions are also emphasized in detail.

Functionalized magnetic nanostructured composites and hybrids for photocatalytic elimination of pharmaceuticals and personal care products

Due to rapid urbanization and globalization, an enormous use of pharmaceuticals and personal care products (PPCPs) has resulted their excessive release in water bodies leading to several environmental issues. This release into the environment takes place via household sewage, hospital effluents, manufacturing units and landfill sites etc. The pharmaceuticals and personal care products (PPCPs) are recently listed as emerging contaminants having many adverse effects towards aquatic life, human beings, and the whole ecosystem. The alarming threats of PPCPs demand efficient methods to cope up their hazardous impacts. The conventional wastewater remediations are not specifically designed for the removal of PPCPs and hence, they require advanced technologies and materials for their elimination to ensure water safety. Among various methods employed so far, photocatalysis is considered to be one of the most cost effective and eco-friendly method but it requires a suitable candidate as a photocatalyst. Thanks to the magnetic nanocomposites which have improved the limitations (poor stability, agglomeration, and difficult separation, etc.) of classically used nanomaterials. Magnetic nanocomposites contain at least one component having magnetic properties making their separation easy from the aqueous media after the photodegradation phenomenon. These can be further functionalized with other materials to obtain maximum advantage as photocatalyst. Few examples of such functionalized nanocomposites are inorganic material based magnetic nanocomposites, carbon based magnetic nanocomposites, biomaterial based magnetic nanocomposites, metal-organic framework based magnetic nanocomposites and polymer based magnetic nanocomposites etc. This review covers the global environmental issue of water pollution especially with respect to the PPCPs, their occurrence in aqueous environment and toxic effects on living beings. A comprehensive discussion of the recently reported functionalized magnetic nanocomposites for the photocatalytic removal of PPCPs from water is the main aim of this review. The synthetic/morphological approaches of various functionalized magnetic composites and their mechanism of action are also elaborated. The possible research challenges in the field of magnetic nanocomposites and future research directions are discussed to apply magnetic nanocomposites for wastewater treatment in near future.

Facile synthesis of Mn, Ce co-doped g-C3N4 composite for peroxymonosulfate activation towards organic contaminant degradation

Peroxymonosulfate (PMS)-based advanced oxidation processes for wastewater treatment have received extensive attention in the past years. Here, a novel Mn, Ce co-modified g-C₃N₄ (MnCe-CN) composite was successfully synthesized by one-step pyrolysis for activating PMS. The physical and chemical characterization of MnCe-CN/PMS was conducted, indicating that Mn and Ce were evenly distributed on g-C₃N₄ and existed in the form of Mn-N structure and CeO₂, respectively. The MnCe-CN/PMS system could effectively degrade pollutants such as acetaminophen (ACT), methylparaben (MeP), p-nitrophenol (PNP), and 2,4-dichlorophenol (2,4-DCP). Among them, 2,4-DCP could be rapidly degraded, reaching 100% within 30 min. The masking experiments and electrochemical testing results revealed that 2,4-DCP was degraded via superoxide radicals (O₂˙-), singlet oxygen (¹O₂), and electron transfer path. The cyclic experiments and real water treatment experiments testified that the oxidative system had excellent stability and applicability. This study provides a facile synthetic method to fabricate bimetallic co-modified g-C₃N₄ for the enhancement of PMS activation.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.