Ce-Fe-reduced graphene oxide nanocomposite as an efficient catalyst for sulfamethazine degradation in aqueous solution

Application of MXene-based materials in Fenton-like systems for organic wastewater treatment: A review

Recently, Fenton-like systems have been widely explored and applied for the removal of organic matter from wastewater. Two-dimensional (2D) MXene-based materials exhibit excellent adsorption and catalysis capacity for organic pollutants removal, which has been reported widely. However, there is no summary on the application of MXene-based materials in Fenton-like systems for organic matter removal. In this review, four types of MXene-based materials were introduced, including 2D MXene, MXene/Metal complex, MXene/Metal oxide complex, and MXene/3D carbon material complex. In addition, the Fenton-like system usually consists of adsorption and degradation processes. The oxidation process might contain hydrogen peroxide (H₂O₂) or persulfate (PS) oxidants. This review summarizes the performance and mechanisms of organic pollutants adsorption and oxidants activation by MXene-based materials systematically. Finally, the existing problems and future research directions of MXene-based materials are proposed in Fenton-like wastewater treatment systems.

Degradation of sulfamethazine in water by sulfite activated with zero-valent Fe-Cu bimetallic nanoparticles

In this work, zero-valent Fe-Cu bimetallic nanoparticles were synthesized using a facile method, and applied to activate sulfite for the degradation of sulfamethazine (SMT) from the aqueous solution. The key factors influencing SMT degradation were investigated, namely the theoretical loading of Cu, Fe-Cu catalyst dosage, sulfite concentration and initial solution pH. The experimental results showed that the Fe-Cu/sulfite system exhibited a much better performance in SMT degradation than the bare Fe⁰/sulfite system. The mechanism and possible degradation pathway of SMT in Fe-Cu/sulfite system were revealed. The reactive radicals that played a dominant role in the SMT degradation process were •OH and SO₄^•-, while the loading of Cu induced the synergistic effect between Fe and Cu. The redox cycle between Cu(I)/Cu(II) remarkably contributed to the conversion of Fe(III) to Fe(II), greatly enhancing the catalytic performance of Fe-Cu bimetal. In real groundwater applications, the Fe-Cu/sulfite system also exhibited satisfactory SMT degradation. The 30-day aging tests of Fe-Cu particles demonstrated that the aging of catalyst was not obviously affecting the removal of SMT. Furthermore, the reusability of catalyst was evidenced by the recycling experiments. This study provides a promising application of bimetal activated sulfite for enhanced contaminant degradation in groundwater.

Cerium functionalized graphene nano-structures and their applications; A review

Graphene-based nanomaterials with remarkable properties, such as good biocompatibility, strong mechanical strength, and outstanding electrical conductivity, have dramatically shown excellent potential in various applications. Increasing surface area and porosity percentage, improvement of adsorption capacities, reduction of adsorption energy barrier, and also prevention of agglomeration of graphene layers are the main advantages of functionalized graphene nanocomposites. On the other hand, Cerium nanostructures with remarkable properties have received a great deal of attention in a wide range of fields; however, in some cases low conductivity limits their application in different applications. Therefore, the combination of cerium structures and graphene networks has been widely invesitaged to improve properties of the composite. In order to have a comprehensive information of these nanonetworks, this research reviews the recent developments in cerium functionalized graphene derivatives (graphene oxide (GO), reduced graphene oxide (RGO), and graphene quantum dot (GQD) and their industrial applications. The applications of functionalized graphene derivatives have also been successfully summarized. This systematic review study of graphene networks decorated with different structure of Cerium have potential to pave the way for scientific research not only in field of material science but also in fluorescent sensing, electrochemical sensing, supercapacitors, and catalyst as a new candidate.

Fe-based Fenton-like catalysts for water treatment: Preparation, characterization and modification

Fenton reaction based on hydroxyl radicals () is effective for environment remediation. Nevertheless, the conventional Fenton reaction has several disadvantages, such as working at acidic pH, producing iron-containing sludge, and the difficulty in catalysts reuse. Fenton-like reaction using solid catalysts rather than Fe²⁺ has received increasing attention. To date, Fe-based catalysts have received increasing attention due to their earth abundance, good biocompatibility, comparatively low toxicity and ready availability, it is necessary to review the current status of Fenton-like catalysts. In this review, the recent advances in Fe-based Fenton-like catalysts were systematically analyzed and summarized. Firstly, the various preparation methods were introduced, including template-free methods (precipitation, sol gel, impregnation, hydrothermal, thermal, and others) and template-based methods (hard-templating method and soft-templating method); then, the characterization techniques for Fe-based catalysts were summarized, such as X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET), SEM (scanning electron microscopy)/TEM (transmission electron microscopy)/HRTEM (high-resolution TEM), FTIR (Fourier transform infrared spectroscopy)/Raman, XPS (X-ray photoelectron spectroscopy), ⁵⁷Fe Mössbauer spectroscopy etc.; thirdly, some important conventional Fe-based catalysts were introduced, including iron oxides and oxyhydroxides, zero-valent iron (ZVI) and iron disulfide and oxychloride; fourthly, the modification strategies of Fe-based catalysts were discussed, such as microstructure controlling, introduction of support materials, construction of core-shell structure and incorporation of new metal-containing component; Finally, concluding remarks were given and the future perspectives for further study were discussed. This review will provide important information to further advance the development and application of Fe-based catalysts for water treatment.

Comparative overview of advanced oxidation processes and biological approaches for the removal pharmaceuticals

Nowadays, pharmaceuticals are the center of significant environmental research due to their complex and highly stable bioactivity, increasing concentration in the water streams and high persistence in aquatic environments. Conventional wastewater treatment techniques are generally inadequate to remove these pollutants. Aiming to tackle this issue effectively, various methods have been developed and investigated on the light of chemical, physical and biological procedures. Increasing attention has recently been paid to the advanced oxidation processes (AOPs) as efficient methods for the complete mineralization of pharmaceuticals. Their high operating costs compared to other processes, however, remain a challenge. Hence, this review summarizes the current and state of art related to AOPs, biological treatment and their effective exploitation for the degradation of various pharmaceuticals and other emerging molecules present in wastewater. The review covers the last decade with a particular focus on the previous five years. It is further envisioned that this review of advanced oxidation methods and biological treatments, discussed herein, will help readers to better understand the mechanisms and limitations of these methods for the removal of pharmaceuticals from the environment. In addition, we compared AOPs and biological treatments for the disposal of pharmaceuticals from the point of view of cost, effectiveness, and popularity of their use. The exploitation of coupling AOPs and biological procedures for the degradation of pharmaceuticals in wastewater was also presented. It is worthy of note that an integrated AOPs/biological system is essential to reach the complete degradation of pharmaceuticals; other advantages of this hybrid technique involve low energy cost, an efficient degradation process and generation of non-toxic by-products.

Degradation of metoprolol from wastewater in a bio-electro-Fenton system

Advanced oxidation processes (AOPs) have been intensely studied for the removal of refractory pollutants because of the strong oxidizing capacity of hydroxyl radical. One of the emerging AOP methods gaining increased attention is bio-electro-Fenton (BEF) which can generate hydroxyl radical in-situ in the cathode chamber using the energy harvested by exoelectrogenic bacteria in the anode. In this study, the feasibility of BEF technology for the removal of metoprolol, a typical micropollutant widely found in the water environment, was for the first time investigated. It was found that applied voltage and working pH had a significant effect on removal efficiency while Fe²⁺ dosage as catalyst showed a little effect. Besides removal by hydroxyl radical, metoprolol might be adsorbed on the surface of the reactor, electrode, and precipitated with iron sludge, especially at neutral pH. In a batch experiment with a supplied voltage of 0.2 V, pH 3, and a Fe²⁺ dose of 0.2 mM, the removal rate of metoprolol in the BEF for the synthetic wastewater and the real effluent from the secondary sediment tank was 66% and 55% within 12 h, respectively. A possible degradation pathway was proposed. Then the removal of metoprolol in a continuous flow BEF system was further studied at different hydraulic retention times (HRTs) of 2, 4, and 6 h, about 77%, 92%, and 95% removal was observed. A toxicity test (less than 20% inhibition on bioluminescence) during treatment and energy cost analysis (5.269 × 10^-3 kWh/order/m³) in treating 10 μg/L of metoprolol containing wastewater effluent at continuous flow mode implied that the proposed BEF has a potential for wastewater treatment.

Efficient activation of peroxymonosulfate by Co-doped mesoporous CeO2 nanorods as a heterogeneous catalyst for phenol oxidation

Sulfate radical-based advanced oxidation processes have received considerable attentions in the remediation of organic pollutants due to their high oxidation ability. In this study, a novel Co3O4/CeO2 catalyst was fabricated and employed as a peroxymonosulfate (PMS) activator to generate SO4•- for phenol degradation. The Co3O4/CeO2 catalyst exhibited a good catalytic performance at a wide pH range of 3.4 to 10.8, and 100% phenol (20 mg/L) was removed within 50-min reaction under optimal conditions with 0.2 g/L catalyst and 2.0 g/L PMS at room temperature. The transformation products and total organic carbon during the degradation process were also determined. The quenching experiments and electron paramagnetic resonance spectra revealed that sulfate radical (SO4•-) rather than other species such as singlet oxygen (1O2) and hydroxyl radical (•OH) was primarily responsible for phenol degradation in the Co3O4/CeO2/PMS system, and a rational mechanism was proposed. Moreover, the recycling experiments as well as low cobalt leaching concentration manifested satisfactory reusability and stability. The effects of various inorganic anions and natural organic matter in real water matrix on phenol oxidation were further evaluated. We believe that the Co3O4/CeO2 composites have promising applications of PMS activation for the degradation of organic pollutants in wastewater treatment.

Rhodamine B dye is efficiently degraded by polypropylene-based cerium wet catalytic materials

Polypropylene-based cerium wet catalytic materials (Ce/PPNW-g-PAA) were prepared through ultraviolet grafting and ion exchange technology. They were used as effective and reusable heterogeneous catalysts for rhodamine B (RhB) degradation. The physicochemical properties of Ce/PPNW-g-PAA were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), specific surface area measurements (BET), and X-ray photoelectron spectroscopy (XPS). The catalytic capacity of the Ce/PPNW-g-PAA-H2O2 system for the removal of RhB was tested in comparison with several other systems, which demonstrated that Ce/PPNW-g-PAA effectively promoted the oxidation and degradation of RhB by catalytic wet H2O2 oxidation. The results of the RhB degradation showed that Ce/PPNW-g-PAA exhibited excellent degradation performance by achieving a high removal rate for RhB (97.5%) at an initial RhB concentration of 100 mg L-1, H2O2 dosage of 5.0 mmol, Ce/PPNW-g-PAA dosage of 0.15 g L-1, and initial pH of 5.0 at 298 K. The degradation of RhB by Ce/PPNW-g-PAA conformed to the first-order kinetic reaction model. Consecutive experiments performed with the Ce/PPNW-g-PAA sample showed little activity decay, further confirming the high stability of the catalyst. In addition, the possible degradation mechanism of RhB was also investigated by XPS and electron paramagnetic resonance. The results suggested that Ce3+ and hydroxyl radical played important roles during the RhB degradation process.

Degradation of antibiotics by advanced oxidation processes: An overview

Antibiotics are becoming emerging contaminants due to their extensive production and consumption, which have caused hazards to the ecological environment and human health. Various techniques have been studied to remove antibiotics from water and wastewater, including biological, physical and chemical methods. Among them, advanced oxidation processes (AOPs) have received increasing attention due to their fast reaction rate and strong oxidation capability, which are effective for the degradation of antibiotics in aquatic environments. In this review paper, a variety of AOPs, such as Fenton or Fenton-like reaction, ozonation or catalytic ozonation, photocatalytic oxidation, electrochemical oxidation, and ionizing radiation were briefly introduced, including their principles, characteristics, main influencing factors and applications. The current applications of AOPs for the degradation of antibiotics in water and wastewater were analyzed and summarized, the concluding remarks were given and their future perspectives and challenges were discussed.

Kinetics of PMS activation by graphene oxide and biochar

Carbon-based materials have been studied as metal-free catalyst for persulfate activation. At present, the activation performance of carbon materials for persulfate is usually characterized by the removal efficiency of organic pollutants. However, the kinetics of persulfate activation by carbon materials has not been investigated. In this study, the kinetics of peroxymonosulfate (PMS) activation by reduced graphene oxide (RGO) and sludge-derived biochar (BC) were investigated. The experimental results showed that the kinetics of PMS activation followed the two-phase kinetic model (fast phase (a₁) and slow phase (a₂)). In the absence of organic pollutants, the a₁ and a₂ were calculated to be 0.320 and 0.0471 min^-1 for BC, respectively, and 0.322 and 0.0850 min^-1 for RGO, respectively. Based on the characterization of BC and RGO, it can be concluded that the fast phase was mainly due to the formation of surface-bound active species. Competitive adsorption between PMS and targeted pollutants decreased the kinetic constant for the first phase (a₁) and the kinetic constant for the second phase (a₂) for both BC and RGO. The value of a₁ and a₂ increased for BC after the addition of phenol, due to the enhanced PMS activation by surface adsorbed phenol. The increase of phenol concentration decreased slightly the value of a₁ and a₂. The increase of PMS concentration increased significantly the value of a₁ and a₂. The decrease of a₁ and a₂ in repeated use of carbon materials could be due to the decrease of oxygen-containing functional groups and defect intensity.

Enhanced capacity of fluoride scavenging from contaminated water by nano-architectural reorientation of cerium-incorporated hydrous iron oxide with graphene oxide

An in situ wet chemical deposition method has been applied for the successful surface modification of Ce (IV)-incorporated hydrous Fe(III) oxide (CIHFO) with a hydrophilic graphene precursor, graphene oxide (GO). The surface area of as-prepared composite (GO-CIHFO) has enhanced (189.57 m² g^-1) compared with that of pristine CIHFO (140.711 m² g^-1) and has irregular surface morphology consisting of microcrystals (~ 2-3 nm) and mesoporous (3.5486 nm) structure. The GO-CIHFO composite shows enhanced fluoride scavenging capacity (136.24 mg F g^-1) than GO (3 mg F g^-1) and pristine CIHFO (32.62 mg F g^-1) at pH 7.0. Also, in acidic pH range and at 323 K temperature, the Langmuir capacity of as-prepared composite is 190.61 mg F g^-1. It has been observed that fluoride removal by GO-CIHFO occurs from solutions obeying pseudo-second-order kinetics and multilayer adsorption process. The film/boundary layer diffusion process is also the rate-determining step. The nature of the adsorption reaction is reasonably spontaneous and endothermic in thermodynamic sense. It was observed that 1.2 g.L^-1 of GO-CIHFO dosage can effectively optimise the fluoride level of natural groundwater samples (9.05 mg L^-1) to the desirable permissible limit. Reactivation of used material up to a level of 73.77% with a solution of alkaline pH has proposed reusability of nanocomposites ensuring sustainability of the proposed material as fluoride scavenger in future.

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles as efficient micro-electrolysis-promoted Fenton-like catalysts for metronidazole removal

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles (3D-GN@Cu⁰) were synthesized using a self-assembly process of liquid-phase reduction and characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectrum analysis, and X-ray photoelectron spectroscopy. The catalytic activity of 3D-GN@Cu⁰ was evaluated in view of the effects of various systems, the pH value, catalyst dosage, initial metronidazole concentration and temperature, and it showed a high efficiency for removing metronidazole with saturated dissolved oxygen (without adding extra H₂O₂) in a wide range of pH value from 3.2 to 9.8. Combined with the results of dissolved oxygen activation, determination of reactive oxidizing species, and X-ray photoelectron spectroscopy (XPS) analysis, the surface-bounded ·OH_ads formed by the reaction of the in situ generation H₂O₂ with 3D-GN@Cu⁰ was mainly responsible for the removal of metronidazole. The charge distribution and electrostatic potential (ESP) of 3D-GN@Cu⁰ further illustrated the distribution and transfer of electrons on the catalyst surface, which predicted a micro-electrolysis-promoted Fenton-like reaction mechanism.

Fenton oxidation of municipal secondary effluent: comparison of Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts

The advanced treatment of municipal secondary effluent by heterogeneous and homogeneous Fenton processes using Fe/Ce-RGO (reduced graphene oxide) and Fe²⁺ as catalysts was studied and compared. Sulfamethazine (SMT) was spiked in the effluent to examine the effectiveness of the emerging contaminant removal. The Fe/Ce-RGO catalyst was characterized using a scanning electron microscope (SEM) and cycle voltammetry curves. The removal of dissolved organic carbon (DOC), soluble chemical oxygen demand (SCOD), SMT, and ultraviolet-visible spectroscopy in 254 nm (UV₂₅₄) of municipal secondary effluents was examined. The DOC removal efficiency of secondary effluent (without addition of SMT) was 36.30% and 11.74% using Fe/Ce-RGO and Fe²⁺ as catalysts, respectively. The removal efficiency of DOC, SCOD, and SMT in heterogeneous Fenton process was higher than that in homogeneous Fenton process. The changes of three-dimensional excitation-emission matrix (3DEEM) fluorescence, soluble microbial products (SMPs), humic acids, and UV₂₅₄ were determined, and the results indicated that UV_254, aromatic proteins, and humic acids decreased rapidly in both processes; however, polysaccharides and protein-like substances were difficult to degrade. Although some toxic substances produced after Fenton-like treatment, the biodegradability of the treated effluent was enhanced.

Iron doped fibrous-structured silica nanospheres as efficient catalyst for catalytic ozonation of sulfamethazine

Sulfonamide antibiotics are ubiquitous pollutants in aquatic environments due to their large production and extensive application. In this paper, the iron doped fibrous-structured silica (KCC-1) nanospheres (Fe-KCC-1) was prepared, characterized, and applied as a catalyst for catalytic ozonation of sulfamethazine (SMT). The effects of ozone dosage, catalyst dosage, and initial concentration of SMT were examined. The experimental results showed that Fe-KCC-1 had large surface area (464.56 m2 g^-1) and iron particles were well dispersed on the catalyst. The catalyst had high catalytic performance especially for the mineralization of SMT, with mineralization ratio of about 40% in a wide pH range. With addition of Fe-KCC-1, the ozone utilization increased nearly two times than single ozonation. The enhancement of SMT degradation was mainly due to the surface reaction, and the increased mineralization of SMT was due to radical mechanism. Fe-KCC-1 was an efficient catalyst for SMT degradation in catalytic ozonation system.

Graphene-based materials supported advanced oxidation processes for water and wastewater treatment: a review

Advanced oxidation processes (AOPs) received much attention in the field of water and wastewater treatment due to its ability to mineralize persistent organic pollutants from water medium. The addition of graphene-based materials increased the efficiency of all AOPs significantly. The present review analyzes the performance of graphene-based materials that supported AOPs in detail. Recent developments in this field are highlighted. A special focus has been awarded for the performance enhancement mechanism of AOPs in the presence of graphene-based materials.

Removal of pharmaceuticals and personal care products (PPCPs) from wastewater: A review

The pharmaceutical and personal care products (PPCPs) are emerging pollutants which might pose potential hazards to environment and health. These pollutants are becoming ubiquitous in the environments because they cannot be effectively removed by the conventional wastewater treatment plants due to their toxic and recalcitrant performance. The presence of PPCPs has received increasing attention in recent years, resulting in great concern on their occurrence, transformation, fate and risk in the environments. A variety of technologies, including physical, biological and chemical processes have been extensively investigated for the removal of PPCPs from wastewater. In this paper, the classes, functions and the representatives of the frequently detected PPCPs in aquatic environments were summarized. The analytic methods for PPCPs were briefly introduced. The removal efficiency of PPCPs by wastewater treatment plants was analyzed and discussed. The removal of PPCPs from wastewater by physical, chemical and biological processes was analyzed, compared and summarized. Finally, suggestions are made for future study of PPCPs. This review can provide an overview for the removal of PPCPs from wastewater.

Ce-Doped zero-valent iron nanoparticles as a Fenton-like catalyst for degradation of sulfamethazine

Ce-Doped zero-valent iron (Ce/Fe) nanoparticles were prepared, characterized and used as a catalyst for degradation of sulfamethazine (SMT) antibiotics in a Fenton-like process.