WS2 as highly active co-catalyst for the regeneration of Fe(II) in the advanced oxidation processes

MIL-101(Fe)/WS2 composites activated Na2S2O8 with visible light for removal of tetracycline

MIL-101(Fe)/WS2 catalyst was composited using a solvothermal method. To study the physical and chemical properties of the composite material, a series of characterizations such as scanning electron microscope (SEM), X-ray diffraction (XRD), and catalytic experiments were carried out. The photocatalysis of the prepared catalyst in the degradation of tetracycline was investigated using persulfate (PS, Na2S2O8) as a cocatalyst under visible light illumination. The above system can remove about 80% of tetracycline within 40 min. After three cyclic experiments, the material showed good recycling. According to material characterization and various experimental results, the enhanced performance of the material was attributed to the reduction of the recombination efficiency of photogenerated e- and h+, and activated persulfate to produce a large number of free radicals such as O2•-, SO4•- and 1O2 produced by the active sites provided by the catalyst's high specific surface area.

Trends and prospects of 2-D tungsten disulphide (WS2) hybrid nanosystems for environmental and biomedical applications

Recently, 2D layered transition metal dichalcogenides (TMDCs) with their ultrathin sheet nanostructure and diversified electronic structure have drawn attention for various advanced applications to achieve high-performance parameters. Unique 2D TMDCs mainly comprise transition metal and chalcogen element where chalcogen element layers sandwich the transition metal element layer. In such a case, various properties can be enhanced and controlled depending on the targeted application. Among manipulative 2D TMDCs, tungsten disulphide (WS2) is one of the emerging nano-system due to its fascinating properties in terms of direct band gap, higher mobility, strong photoluminescence, good thermal stability, and strong magnetic field interaction. The advancement in characterization techniques, especially scattering techniques, can help in study of opto-electronic properties of 2D TMDCs along with determination of layer variations and investigation of defect. In this review, the fabrication and applications are well summarized to optimize an appropriate WS2-TMDCs assembly according to focused field of research. Here, the scientific investigations on 2D WS2 are studied in terms of its structure, role of scattering techniques to study its properties, and synthesis routes followed by its potential applications for environmental remediation (e.g., photocatalytic degradation of pollutants, gas sensing, and wastewater treatment) and biomedical domain (e.g., drug delivery, photothermal therapy, biomedical imaging, and biosensing). Further, a special emphasis is given to the significance of 2D WS2 as a substrate for surface-enhanced Raman scattering (SERS). The discussion is further extended to commercial and industrial aspects, keeping in view major research gaps in existing research studies.

Tungsten disulfide (WS2) is a highly active co-catalyst in Fe(III)/H2O2 Fenton-like reactions for efficient acetaminophen degradation

The most important factor that restricts the decomposition of H₂O₂ in the Fe³⁺/H₂O₂ reaction is the slow cycling efficiency of reducing Fe³⁺ to Fe²⁺. In this study, the addition of tungsten disulfide (WS₂) as a co-catalyst achieved a rapid cycling of the reaction rate-limiting step and a significant enhancement of H₂O₂ decomposition, which resulted in the effective degradation of acetaminophen (APAP). Results show that 99.6% of APAP (5 mg L^-1) could be degraded by H₂O₂/Fe³⁺/WS₂ system within 2.5 min. The conversion of Fe³⁺ to Fe²⁺ occurred mainly on the surface of WS₂ due to the redox reaction of the exposed W⁴⁺ active sites with Fe³⁺ after the unsaturated S atoms were bound to protons. Electron paramagnetic resonance (EPR) and radical quenching experiments evaluated the contribution of hydroxyl radical (•OH) and superoxide radical (O₂^•-) in the degradation of pollutants. WS₂ showed good recoverability after four cycles of the reaction. This study provides a new perspective to improve the efficiency of Fe³⁺/H₂O₂ and provides a reference for the involvement of transition metal sulfides in advanced oxidation processes (AOPs).

Enhancement of peroxymonosulfate activation for 2,4-dichlorophenoxyacetic acid removal by MoSe2 induced Fe redox cycles

The limited regeneration of Fe2+ in the Fe-catalyzed advanced oxidation processes (AOPs) constrained its application for the removal of organic pollutants. Herein, MoSe2 was introduced to promote the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the Fe2+/PMS system. Compared with Fe2+/PMS processes, the 2,4-D degradation efficiency and PMS decomposition rate respectively increased by 73.8% and 84.2% in the MoSe2/Fe2+/PMS system. DFT simulation results suggested that Se atoms acted smoothly as the bridge supporting the charge transfer from Mo to adjacent Fe atoms, which led to the reduction of Fe3+. The rapid regeneration of Fe2+ boosted the activation of PMS and the degradation of pollutants. Additionally, the electron paramagnetic resonance (EPR) and quenching experiments results indicated that SO4∙-, ∙OH, and 1O2 accounted for 2,4-D degradation, and SO4∙- and 1O2 predominated the reaction. The Mo based co-catalysts showed better co-catalytic effect than the W counterparts, and the moderate adsorption for PMS and lower electron transfer electron transfer resistance accounted for the more excellent co-catalytic performance of MoSe2 than that of WSe2. In addition, the degradation efficiency of 2,4-D was up to 95.5% after five cycles of MoSe2 in the co-catalytic system. The coexistent humic acid (HA) and Cl- showed ignorant negative effect on the degradation, while HCO3- would depress the oxidation reaction. The acidic etching wastewater can be applied as the Fe ions source in this co-catalytic process to remove 2,4-D effectively.

WS2 significantly enhances the degradation of sulfachloropyridazine by Fe(III)/persulfate

The use of antibiotics has become an indispensable part of the production and life of human society. Among them, sulfonamide antibiotics widely used in humans and animals are considered to be one of the most crucial antibiotics. However, antibiotics are difficult to degrade naturally, leading to an accumulation in the environment and a potential hazard to human health. In this paper, WS₂ as a co-catalyst could reduce trace Fe(III) to Fe(II) which exhibited a great activating ability to PS through the exposed W(IV) active sites, and formed the Fe(III)/Fe(II) cycle to degrade sulfachloropyridazine (SCP) continuously. This paper systematically discussed the degradation of SCP under different conditions in the PS/WS₂/Fe(III) system, including the amount of WS₂, Fe(III) concentration, PS concentration, initial pH, natural organic matter (NOM) and common anions (NO₃^-, Cl^-, HCO₃^-, HPO₄^2- and H₂PO₄^-). The experimental results showed that PS/WS₂/Fe(III) system possessed a strong degradation ability for SCP in a wide pH range. NO₃^- and Cl^- could promote the degradation of SCP a little. HCO₃^-, HPO₄^2- and H₂PO₄^- could significantly inhibit the degradation of SCP. The main types of free radicals that degraded SCP were explored. In addition, the stability and reusability of WS₂ were examined, and two possible degradation pathways of SCP were proposed.

Enhanced activation of PMS by a novel Fenton-like composite Fe3O4/S-WO3 for rapid chloroxylenol degradation

Chloroxylenol (PCMX) is widely used as disinfectant since the epidemic outbreak due to its effective killing of Covid-19 virus. Its stable chemical properties make it frequently detected in surface water. Herein, we successfully modified Fe₃O₄ nanoparticles with S-WO₃ (X-Fe₃O₄/S-WO₃) to accelerate the Fe²⁺/Fe³⁺ cycle. The composite has outstanding PCMX degradation and peroxymonosulfate (PMS) decomposition efficiency over a wide pH range (3.0 ∼ 9.0). 80-Fe₃O₄/S-WO₃/PMS system not only increased PMS decomposition efficiency from 27.7% to 100.0%, but also realized an enhancement of PCMX degradation efficiency by 16 times in comparison with that of Fe₃O₄ alone. The catalyst utilization efficiency reached 0.3506 mmol∙g^-1∙min^-1 which stands out among most Fenton-like catalysts. The composite has excellent degradation ability to a variety of emerging pollutants, such as antibiotics, drugs, phenols and endocrine disrupters, and at least a 90% removal efficiency reached in 10 min. The degradation of PCMX was dominated by HO^•, SO₄ ^•- and ¹O₂. The degradation pathways of PCMX were analyzed in detail. The component WS₂ in S-WO₃ plays a co-catalytic role instead of WO₃. And the exposed active W⁴⁺ _surf. efficiently enhanced the Fe³⁺/Fe²⁺ cycle, thereby complete PMS decomposition and high catalytic efficiency were achieved. Our findings clarify that applying two-dimensional transition metal sulfide WS₂ to modify heterogeneous Fe₃O₄ is a feasible strategy to improve Fenton-like reaction and provide a promising catalyst for PCMX degradation.

Differential pulse voltammetry determination of salbutamol using disulfite tungsten/activated carbon modified glassy carbon electrode

In the present article, the disulfide tungsten/activated carbon derived from Eichhornia crassipes (WS₂/AC) was synthesized by the hydrothermal process. The received materials were examined by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray - mapping, and nitrogen adsorption/desorption isotherms. The morphology of WS₂/AC was tailored to have a micro/meso/macro structure that facilized large electric conductivity and quick ion diffusion. The WS₂/AC sample was used as an electrode modifier for developing an electrochemical sensor for salbutamol detection. WS₂/AC exhibited excellent oxidation toward salbutamol. Through some optimized conditions, the electrochemical signal of the proposed sensor varied linearly to the salbutamol concentration ranging from 1 to 210 μM with a low LOD (detection limit) of 0.52 μM. The developed sensor showed several merits: easy producing, convenient usage, fabulous selectivity, and good repeatability as well as reproducibility. Finally, the suggested technique can be applied to determine salbutamol in people's biological fluid with satisfactory recoveries of 98.5-104.4% and without statistics different from standard HPLC.

Efficient peroxymonosulfate activation by N-rich pyridyl-iron phthalocyanine derivative for the elimination of pharmaceutical contaminants under solar irradiation

It is of great significance for improving electron transmission performance by changing of the outer ring structure of iron phthalocyanine. Herein, 4 (pyridine-2, 3-yl) iron phthalocyanine (FepyPc), as N-rich pyridyl-iron phthalocyanine derivative, was introduced to degrade pharmaceutical contaminants. The catalytic degradation of organic pollutants with FepyPc was studied by activating peroxymonosulfate (PMS) at room temperature. The results clarified that the removal rate of carbamazepine (CBZ) was close to 100% within 60 min and the calculated apparent rate constant was about 2 times larger than FePc, which proved that FepyPc had superior performance. Four active species were identified for the degradation of CBZ, including superoxide radical (•O₂^-), singlet oxygen (¹O₂), sulfate radical (SO₄•^-) and hydroxyl radical (•OH). In addition, the possible reaction mechanism was inferred in FepyPc/PMS/sunlight system for CBZ removal. Finally, the CBZ degradation pathway was proposed by using ultra-performance liquid chromatography and high definition mass spectrometry (UPLC/HDMS). This research provided a meaningful and efficient method for the elimination of pharmaceutical contaminants.

Mechanism study of CoS2/Fe(III)/peroxymonosulfate catalysis system: The vital role of sulfur vacancies

Peroxymonosulfate (PMS) activation methods have attractive advantages in advanced oxidation process (AOPs) due to their powerful ability of directly or indirectly generating various reactive oxygen species (ROS). Herein, trace amount of Fe(III) ions were added into the commercial-CoS₂/PMS system to improve the CoS₂/PMS decomposition for organics removal. The organics removal efficiency could reach >90% towards methylene blue (MB), diclofenac sodium (DCF), sulfamethoxazole (SMX) and bisphenol A (BPA) in the CoS₂/Fe(III)/PMS system, with the kinetic apparent rate constant k_obs of 0.141, 0.206, 0.247 and 0.091 min^-1, respectively. The synergistic effect between Fe(III) ions and sulfur-vacancies on CoS₂ for PMS degradation were revealed for the first time in cobalt sulfides/PMS system. Quenching experiments and ESR analysis proved that ¹O₂ was the major ROS and was produced mainly by the hydrolysis of SO₅^•-. Besides, the high degradation efficiency was obtained by the contribution of SO₄^•- and ^•OH. Electron spin-resonance spectroscopy (ESR), cyclic voltammetry (CV) and Raman spectrum data revealed that the addition of Fe(III) ions could optimize the intensity of sulfur vacancies on the CoS₂ surface, which hindered the PMS reduction ability of Co(II), but accelerated the PMS oxidation to form ¹O₂. The degradation path of MB was analyzed by liquid chromatograph-mass spectrometer (LC-MS). The mechanism studies speculated that the sulfur vacancies of CoS₂ provided the binding sites for Fe(III) ions with Co(II), which facilitated the PMS activation by Co(III).

Investigation of EG-Bi2S3 nanorods photocatalytic activity under visible light for dye degradation from aquatic system

Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ were synthesized by employing solvothermal route. X-ray diffraction, UV-vis absorption, photoluminescence, Raman, scanning electron microscopic studies confirmed the structural, optical, morphological behaviors. The XRD pattern of Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ was correlated well with JCPDS # 65-2435. The crystallite size was found to be 57, 49, and 40 nm. The photoluminescence spectra showed semiconducting property of prepared Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃. The absorption spectra of Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ nanorods were well matched with the spectra of a previous report. The bandgap values of Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ were calculated to be 1.56, 1.45, and 1.3 eV in reducing order. The morphology of Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ samples showed the development of nanorods. The 10 ml EG-Bi₂S₃ sample showed better development of nanorods with the addition of ethylene glycol. The agglomeration was considerably reduced with the mixing of solvent. Bi₂S₃, 5 ml EG-Bi₂S₃, and 10 ml EG-Bi₂S₃ catalysts were added to the methylene blue dye solution and its photocatalytic properties were investigated by reducing toxic pollutants under light. The 10 ml EG-Bi₂S₃ sample with neutral pH and 0.1 g of catalyst was added and investigated which showed 86% of efficiency towards dye degradation. The narrow bandgap, defined morphology of 10 ml EG-Bi₂S₃, made a positive result towards efficient photocatalytic activity.

Cu2+/Cu+ cycle promoted PMS decomposition with the assistance of Mo for the degradation of organic pollutant

The limited production of Cu⁺ in the Cu²⁺/PMS processes constrained its large-scan application for the elimination of organic pollutants. In this study, molybdenum powder (Mo) was applied as the co-catalyst to improve the degradation of 2,4-dichlorophenol (2,4-DCP) in Cu²⁺/PMS system at pH 5.6. By the assistance of Mo, Cu²⁺ was rapidly reduced to Cu⁺ which exhibited super activity for the peroxymonosulfate (PMS) activation. Compared with Cu²⁺/PMS processes, the PMS decomposition rate and 2,4-DCP degradation efficiency respectively increased by 62.1% and 83.6% in the Mo co-catalytic Cu²⁺/PMS system after reaction for 20 min. The degradation of 2,4-DCP was completed via both the free radical and non-radical pathways and the free radicals rather than Cu³⁺ contributed most to the reaction. In contrast to fresh Mo, the ratio of Mo⁴⁺ increased and Mo⁶⁺ decreased in the used Mo powder, due to the oxidation of Mo⁰ by Cu²⁺ and/or ∙OH and the reduction of Mo⁶⁺ by O₂∙^-. Additionally, the coexistence of Cl^- and humic acid with low concentrations showed little effects on the Mo/Cu²⁺/PMS system while HCO₃^- presented an obvious depression for 2,4-DCP degradation. During five cycling runs, all the degradation rates were higher than 92.8%, indicating the good stability of Mo/Cu²⁺/PMS system.

Photocatalytic degradation of organic dyes and phenol by iron-silicate glass prepared by the sol–gel method

A highly efficient photo-Fenton catalyst iron silicate glass was successfully prepared by a simple sol–gel method.