Design of direct Z-scheme superb magnetic nanocomposite photocatalyst Fe3O4/Ag3PO4@Sep for hazardous dye degradation

Construction of a Wood Nanofiber-Bismuth Halide Photocatalyst and Catalytic Degradation Performance of Tetracycline from Aqueous Solutions

Nanostructured bismuth oxide bromide (BiOBr) has attracted considerable attention as a visible light catalyst. However, its photocatalytic degradation efficiency is limited by its low specific surface area. In this study, a solvothermal approach was employed to synthesize BiOBr, which was subsequently loaded onto cellulose nanofibers (CNFs) to obtain a bismuth halide composite catalyst. The performance of this catalyst in the removal of refractory organic pollutants such as tetracycline (TC) from solutions under visible light excitation was examined. Our results indicate that BiOBr/CNF effectively removes TC from the solution under light conditions. At a catalyst dosage of 100 mg/L, the removal efficiency for TC (with an initial concentration of 100 mg/L) was 94.2%. This study elucidates the relationship between the microstructure of BiOBr/CNF composite catalysts and their improved photocatalytic activity, offering a new method for effectively removing pollutants from water.

Antibiotic photocatalysis and antimicrobial activity of low-cost multifunctional Fe3O4@HAp nanocomposites

Water contamination by multiple pollutants is a serious environmental issue originating from the many diverse sources of pollution. It has worsened with the appearance of new contaminants, named emerging micropollutants, such as drug residues which are considered a potential threat to human health and/or ecosystems. These require prior treatment before release into the environment. Simultaneous adsorption and photocatalysis as well as solid-liquid separation are promising technologies for water treatment. In order to obtain low cost photoactive nanocomposites, porous and magnetic Fe3O4-hydroxyapatite (wFeHAp) nanocomposites were prepared by soft chemistry from the dissociation of natural phosphate into Ca2+ and H3PO4 precursors, further neutralized by ammonia in the presence of preformed Fe3O4 particles. The magnetic nanocomposites were characterized and examined as effective antibacterial agents. Fe3O4 association with apatite modifies the surface properties of the wFeHAp nanocomposite materials, yielding efficient antimicrobial activity for S. aureus, B. subtilis, E. coli and K. pneumoniae strains. The photocatalytic removal of ciprofloxacin (CPF) and oxytetracyclin (OXT) antibiotics in water was also evaluated. The wFeHAp nanocomposites adsorbed and degraded the selected antibiotics successfully. Toxicity evaluation of the treated water after photodegradation using the four strains demonstrates the absence of toxic by-products at the end of the reaction. Therefore, Fe3O4@HAp nanoparticles are valuable for antimicrobial and photocatalysis applications.

Efficient photodegradation of paraquat herbicide over TiO2-WO3 heterojunction embedded in diatomite matrix and process optimization

Photodegradation of paraquat herbicide was assessed over several TiO2-WO3 heterojunctions embedded in the diatomite matrix. The characterization results indicated that WO3 embedding in the TiO2 decorated-diatomite matrix could not only enhance the adsorption capacity, visible-light response, and distribution of semiconductor species but also lessen the recombination rate and band gap energy. These characteristics were more noticeable as 5 wt.% of WO3 was embedded. Despite better optical properties of immobilized TiO2-WO3 nanocomposites, overloading WO3 generally alleviates the synergetic effect of tungsten due to surface coverage of diatomite matrix and, subsequently, the significant attenuation of textural properties, more formation of agglomerations and defects as trapping centers in the oxidation sites of heterostructures, and also, less likely of forming TiO2-WO3 heterojunction. In accordance with characterization results, the highest UV-photodegradation of paraquat was attained over heterostructured nanocomposite containing 5 wt.% WO3 (T25-W5/Di). The effects of significant operating parameters were also investigated, modeled, and optimized using response surface methodology (RSM)-central composite design (CCD). Under optimized operation conditions, the experimental removal efficiency of paraquat reached 97.1 and 80% using UV and simulated solar light, respectively. Moreover, the reusability results confirm the sustained activity of the T25-W5/Di nanocomposite.

Improved catalytic performance of ZnO via coupling with CoFe2O4 and carbon nanotubes: A new, photocatalysis-mediated peroxymonosulfate activation system, applied towards Cefixime degradation

In this study, a ternary ZnO@spinel cobalt ferrite@carbon nanotube magnetic photocatalyst (ZSCF@CNT) was successfully synthesized and used to activate peroxymonosulfate (PMS) for Cefixime (CFX) antibiotic degradation under UVC irradiation. The morphology, optical, structural, and physicochemical properties of ZSCF@CNT were characterized and analyzed by XPS, XRD, FESEM-EDX, TEM, BET, VSM, UV-vis DRS and PL analysis. The results indicated that the ternary ZSCF@CNT photocatalyst exhibited superior catalytic activity on CFX elimination than that of individual components and binary composite catalysts, in which CFX with was rapidly removed under UVC irradiation and PMS. The effect of operational parameters including initial PMS, catalyst, and CFX concentrations and solution pH on the catalytic activity was investigated in detail; the optimal conditions were: pH: 7.0, catalyst: 0.3 g/L, PMS: 3.0 mM, leading to total CFX (10 mg/L) elimination in ∼20 min. Based on the radical scavenger tests, various radicals and non-radical species including sulfate, hydroxyl and superoxide radicals, singlet oxygen and electrons were involved in the ZSCF@CNT/PMS/UVC system. The high surface area, reduced agglomeration formation and excellent separation of photogenerated electron-hole pairs embodied in ZSCF@CNT photocatalyst conferred its superior catalytic activity and stability. The results from the tests in real water matrices revealed that ZSCF@CNT could be a promising photocatalyst to activate PMS for actual aqueous matrices' treatment.

Photo-Fenton assisted AgCl and P-doped g-C3N4 Z-scheme photocatalyst coupled with Fe3O4/H2O2 system for 2, 4-dimethylphenol degradation

In this study graphitic carbon nitride (g-C₃N₄ or GCN) and phosphorus doped graphitic carbon nitride (p-g-C₃N₄ or PCN) were prepared using facile thermal polycondensation method. Phosphorus doping was employed to preserve the non-metallic nature of GCN. The AgCl/PCN/Fe₃O₄ heterojunction was synthesized using a simple in-situ route. The photocatalytic performance of the GCN, PCN, Fe₃O₄ and AgCl/PCN/Fe₃O₄ was tested towards 2, 4-dimethylphenol (DMP) pollutant. The work explored improvement in physiochemical properties and reduction of band gap of GCN after P doping (through Tauc's plot method). Coupling with AgCl (silver halide) also enhanced photoinduced charge carriers' separation and migration ability due to apt band alignment among both AgCl and PCN photocatalysts which resulted in formation of direct Z-scheme charge transfer mechanism. Similarly, the incorporation of ferrimagnetic material i.e. Fe₃O₄ enhanced the generation of hydroxyl (^•OH) radicals via photo-Fenton process and facilitated photocatalysts easy separation from the aqueous medium. Through PL and EIS analysis the enhanced charge separation and migration ability in AgCl/PCN/Fe₃O₄ nanocomposite was validated. The attained DMP degradation efficiency of photo-Fenton assisted AgCl/PCN/Fe₃O₄/H₂O₂ Z-scheme nanocomposite was much higher i.e. 99% compared to other photocatalysts within 60 min of visible light irradiation following pseudo-first-order kinetics. Electron paramagnetic resonance (EPR) and scavenging tests confirmed the substantial role of ^•OH and ^•O₂^- radicals in the photo-Fenton reaction. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis detected the generated oxidative products and mineralization pathways associated with DMP degradation. The proposed direct Z-scheme charge transfer route presented efficient charge separation and migration ability in AgCl/PCN/Fe₃O₄ nanocomposite. Recycle ability of the fabricated AgCl/PCN/Fe₃O₄ photocatalyst was tested up to 5 cycles with 90% removal efficacy, confirming the excellent reusability and stability of AgCl/PCN/Fe₃O₄ photocatalyst.

Combined molecular dynamics simulations and experimental studies of the removal of cationic dyes on the eco-friendly adsorbent of activated carbon decorated montmorillonite Mt@AC

In recent years, the combination of experimental and theoretical study to explain adsorbate/adsorbent interactions has attracted the attention of researchers. In this context, this work aims to study the adsorption of two cationic dyes, namely methylene blue (MB) and crystal violet (CV), on a green adsorbent Montmorillonite@activated carbon (Mt@AC) composite and to explain the adsorption behavior of each dye by the molecular dynamics (MD) simulation method. The eco-friendly nanocomposite Mt@AC is synthesized and characterized by the analysis methods: XRD, FTIR, BET, TGA/DTA, SEM-EDS, EDS-mapping and zeta potential. The experimental results of adsorption equilibrium show that the adsorption of the two dyes is well suited to the Langmuir adsorption model. The maximum adsorption capacity of the two dyes reaches 801.7 mg g^-1 for methylene blue and 1110.8 mg g^-1 for crystal violet. The experimental kinetics data fit well with a pseudo-first order kinetic model for the two dyes with coefficient of determination R ² close to unity, non-linear chi-square χ ² close to zero and lower Root Mean Square Error RMSE (R ² → 1 and χ ² → 0, RMSE lower). Molecular dynamic simulations are run to gain insights on the adsorption process. According to the RDF analysis and interaction energy calculations, the obtained results reveal a better affinity of the CV molecule with both the AC sheet and montmorillonite framework as compared with MB. This finding suggests that CV is adsorbed to a larger extent onto the nanocomposite material which is in good agreement with the adsorption isothermal experiment observations.

Anchoring ZnO on spinel cobalt ferrite for highly synergic sono-photo-catalytic, surfactant-assisted PAH degradation from soil washing solutions

In this study, the photocatalytic activity of ZnO was effectively improved via its combination with spinel cobalt ferrite (SCF) nanoparticles. The catalytic performance of ZnO@SCF (ZSCF) was investigated in coupling with UV irradiation and ultrasound (US), as a heterogeneous sono-photocatalytic process, for the decontamination of phenanthrene (PHE) from contaminated soil. Soil washing tests were conducted in a batch environment, after extraction assisted by using Tween 80. Several characterization techniques such as XRD, FESEM-EDS, BET, TEM, UV-vis DRS, PL and VSM were utilized to determine the features of the as-prepared catalysts. ZSCF showed an excellent catalytic activity toward degradation of PHE in the presence of US and UV with a significant synergic effect. It was found that more than 93% of PHE (35 mg/L) and 87.5% of TOC could be eliminated by the integrated ZSCF/US/UV system under optimum operational conditions (pH: 8.0, ZSCF: 1.5 g/L, UV power: 6.0 W and US power: 70 W) within 90 min of reaction. After five times of use, ZSCF illustrated good reusability in the decontamination of PHE (87%) and TOC (79%). Quenching tests revealed the contribution of h⁺, HO^• and e^- species during PHE degradation over ZSCF/UV/US and an S-scheme photocatalytic mechanisms was proposed for the possible charge transfer routes under the ZSCF system. This study provides the important role of SCF in enhancing the ZnO photocatalytic activity due to its high performance, easy recovery and excellent durability, which it make an efficient and promising catalyst in environmental clean-up applications.

Near-Infrared (NIR) Silver Sulfide (Ag2S) Semiconductor Photocatalyst Film for Degradation of Methylene Blue Solution

A silver sulfide (Ag₂S) semiconductor photocatalyst film has been successfully synthesized using a solution casting method. To produce the photocatalyst films, two types of Ag₂S powder were used: a commercialized and synthesized powder. For the commercialized powder (CF/comAg₂S), the Ag₂S underwent a rarefaction process to reduce its crystallite size from 52 nm to 10 nm, followed by incorporation into microcrystalline cellulose using a solution casting method under the presence of an alkaline/urea solution. A similar process was applied to the synthesized Ag₂S powder (CF/syntAg₂S), resulting from the co-precipitation process of silver nitrate (AgNO₃) and thiourea. The prepared photocatalyst films and their photocatalytic efficiency were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV-visible spectroscopy (UV-Vis). The results showed that the incorporation of the Ag₂S powder into the cellulose films could reduce the peak intensity of the oxygen-containing functional group, which indicated the formation of a composite film. The study of the crystal structure confirmed that all of the as-prepared samples featured a monoclinic acanthite Ag₂S structure with space group P₂₁/C. It was found that the degradation rate of the methylene blue dye reached 100% within 2 h under sunlight exposure when using CF/comAg₂S and 98.6% for the CF/syntAg₂S photocatalyst film, and only 48.1% for the bare Ag₂S powder. For the non-exposure sunlight samples, the degradation rate of only 33-35% indicated the importance of the semiconductor near-infrared (NIR) Ag₂S photocatalyst used.

Construction of Ag nanocluster-modified Ag3PO4 containing silver vacancies via in-situ reduction: With enhancing the photocatalytic degradation activity of sulfamethoxazole

Photocatalytic removal of sulfonamide antibiotics is an effective strategy to solve environmental pollution. Ag3PO4 is a promising anode material for photocatalytic material with photocatalytic degradation ability under ultraviolet light or natural light. Unfortunately, due to its instability, Ag+ could be reduced to Ag0 which loaded onto the surface of Ag3PO4 during the photocatalytic process, causing self-photocorrosion and resulting in the reduction of photocatalytic activity and stability. Herein, Ag3PO4 nanoparticles loaded with Ag nanoclusters containing Ag vacancies (Ag/Ag3PO4-VAg) were constructed by an in-situ reduction strategy to achieve effectively photocatalytic degradation behavior. The Ag nanoclusters loaded on the surface of Ag3PO4 can not only effectively inhibit the self-photocorrosion but also affords a localized surface plasmon resonance (LSPR) effect in the photocatalytic process, thus leading to the efficient generation and rapid transfer of photogenerated carriers behavior. In addition, the Ag vacancies in Ag3PO4 are crucial to increasing the adsorption energy of H2O for further enhancing the capture and accumulation of electrons. In detail, according to Zeta potential analysis, the strong adsorption sites of sulfamethoxazole (SMX) molecules are generated at the interface of Ag and Ag3PO4, which promote the activation of SMX molecules. A 100 ml of 20 mg/L SMX could be completely degraded within 15 min with an apparent rate constant (Kapp) of 0.306 min-1, which far exceeds the activity of most of the photocatalysts. This work may provide an attractive strategy to address the activity, stability of Ag3PO4 and and realizing the green remediation of SMX wastewater.

ZnO Nanostructures Doped with Various Chloride Ion Concentrations for Efficient Photocatalytic Degradation of Methylene Blue in Alkaline and Acidic Media

In this study, chloride (Cl−) ions were successfully doped into ZnO nanostructures by the solvothermal method. The effect of various Cl− concentrations on the photocatalytic activity of ZnO towards the photodegradation of methylene blue (MB) under the illumination of ultraviolet light was studied. The as-prepared Cl−-doped ZnO nanostructures were analyzed in terms of morphology, structure, composition and optical properties. XRD data revealed an average crystallite size of 23 nm, and the XRD patterns were assigned to the wurtzite structure of ZnO even after doping with Cl−. Importantly, the optical band gap of various Cl ion-doped ZnO nanostructures was successively reduced from 3.42 to 3.16 eV. The photodegradation efficiency of various Cl− ion-doped ZnO nanostructures was studied for MB in aqueous solution, and the relative performance of each Cl ion-doped ZnO sample was as follows: 20% Cl−-doped ZnO > 15% Cl−-doped ZnO > 10% Cl−-doped ZnO > 5% Cl−-doped ZnO > pristine ZnO. Furthermore, the correlation of the pH of the MB solution and each Cl ion dopant concentration was also investigated. The combined results of varying dopant levels and the effect of the pH of the MB solution on the photodegradation process verified the crucial role of Cl− ions in activating the degradation kinetics of MB. Therefore, these newly developed photocatalysts could be considered as alternative materials for practical applications such as wastewater treatment.

Efficient Degradation of Congo Red in Water by UV-Vis Driven CoMoO4/PDS Photo-Fenton System

In order to improve the catalytic activity of cobalt molybdate (CoMoO₄), a PDS-activated and UV-vis assisted system was constructed. CoMoO₄ was prepared by coprecipitation and calcination, and characterized by XRD, FTIR, Raman, SEM, TEM, XPS, TGA Zeta potential, BET, and UV-Vis DRS. The results showed that the morphology of the CoMoO₄ nanolumps consisted of stacked nanosheets. XRD indicated the monoclinic structures with C2/m (C³_2h, #12) space group, which belong to α-CoMoO₄, and both Co²⁺ and Mo⁶⁺ ions occupy distorted octahedral sites. The pH of the isoelectric point (pHIEP) of CMO-8 at pH = 4.88 and the band gap of CoMoO₄ was 1.92 eV. The catalytic activity of CoMoO₄ was evaluated by photo-Fenton degradation of Congo red (CR). The catalytic performance was affected by calcination temperature, catalyst dosage, PDS dosage, and pH. Under the best conditions (0.8 g/L CMO-8, PDS 1 mL), the degradation efficiency of CR was 96.972%. The excellent catalytic activity of CoMoO₄ was attributed to the synergistic effect of photo catalysis and CoMoO₄-activated PDS degradation. The capture experiments and the ESR showed that superoxide radical (·O₂^-), singlet oxygen (¹O₂), hole (h⁺), sulfate (SO₄^-·), and hydroxyl (·OH^-) were the main free radicals leading to the degradation of CR. The results can provide valuable information and support for the design and application of high-efficiency transition metal oxide catalysts.

ZIF-8 metal organic framework materials as a superb platform for the removal and photocatalytic degradation of organic pollutants: a review

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis. In particular, zeolitic imidazolate framework 8 (ZIF-8), which is composed of zinc ions and imidazolate ligands, have been applied in different areas of catalysis due to its outstanding structural and textural properties. It possesses a highly porous structure and chemical and thermal stability under varying reaction conditions. When used alone in the reaction medium, the ZIF-8 particles tend to agglomerate, which inhibits their removal efficiency and selectivity. This results in their mediocre reusability and separation from aqueous conditions. Thus, to overcome these drawbacks, several well-designed ZIF-8 structures have emerged by forming composites and heterostructures and doping. This review focuses on the recent advances on the use of ZIF-8 structures (doping, composites, heterostructures, etc.) in the removal and photodegradation of persistent organic pollutants. We focus on the adsorption and photocatalysis of three main organic pollutants (methylene blue, rhodamine B, and malachite green). Finally, the key challenges, prospects and future directions are outlined to give insights into game-changing breakthroughs in this area.

Activation of peroxymonosulfate by α-MnO2 for Orange Ⅰ removal in water

Developing high-efficiency catalysts for peroxymonosulfate (PMS)-based advanced oxidation processes is important for eliminating pollutants in water. Herein, α-MnO₂ with major exposed {110} and {100} facets prepared via a hydrothermal method were used as catalysts to activate PMS for the degradation of Orange Ⅰ (OⅠ). α-MnO₂-100, with more abundant surface hydroxyl groups and greater reductive ability, performed remarkably better than α-MnO₂-110 for degrading OⅠ. OⅠ removal of 86.20% was obtained in the α-MnO₂-100/PMS system. The apparent rate constant of OⅠ removal over α-MnO₂-100 was 2.11 times higher than that of α-MnO₂-110. The effects of PMS concentration, catalyst dosage, OⅠ concentration, initial pH, anions and humic acid (HA) on OⅠ degradation in the α-MnO₂-100/PMS system were systematically investigated. Quenching experiments and electron paramagnetic resonance (EPR) demonstrated that SO₄^•-, •OH, O₂^•- and ¹O₂ were the reactive oxygen species (ROS) in the α-MnO₂-100/PMS system. Moreover, the possible degradation pathway of OⅠ in the α-MnO₂-100/PMS system was proposed. This work provides an ideal metal oxide catalyst for sewage remediation.

Green construction of eco-friendly phosphotungstic acid Sr-MOF catalysts for crystal violet removal and synthesis of coumarin and xanthene compounds

There is an urgent need to improve engineering and synthetic chemistry, either through the use of eco-friendly starting materials or the proper design of novel synthesis routes. This reduces the contamination of toxic chemicals and helps the disposal of organic dyes. In the current work, a metal–organic framework-based Sr(ii) was fabricated to achieve the desired goal for dye removal and catalysis. Sr-MOF-based phosphotungstic acid (PWA/Sr-MOF) was hydrothermally synthesized to study its adsorption and catalytic activities. Remarkably, about 99.9% of crystal violet (CV) dye was removed using PWA/Sr-MOF within 90 min at room temperature. Various factors have been studied to investigate the optimum conditions such as pH of solution, initial dye concentration, contact time, and temperature. The maximum adsorption capacity of CV dye was reached after 90 min and well fitted the pseudo-second kinetic order and Langmuir adsorption isotherm. Coumarin and xanthene reactions were chosen to test the catalytic activity of the prepared PWA/Sr-MOF at 373 K. Furthermore, structural and chemical characterization of the fabricated samples was obtained using FT-IR, XRD, TGA, DTA, TEM, EDX, and XPS. PWA/Sr-MOF can be considered as a promising and green framework in the material design used to study catalytic and adsorption performances.

There is an urgent need to improve engineering and synthetic chemistry, either through the use of eco-friendly starting materials or the proper design of novel synthesis routes.

Phase Transformation, Photocatalytic and Photoluminescent Properties of BiPO4 Catalysts Prepared by Solid-State Reaction: Degradation of Rhodamine B

Polycrystalline bismuth phosphate BiPO4 was synthesized by solid-state reaction at different temperatures varying from 500 to 900 °C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The low-temperature phase of BiPO4 has monoclinic structure with a space group P21/n, and was transformed into the monoclinic phase P21/m with a slight distortion of monoclinic lattice when it was heated above 500 °C. The effect of the transformation on the structure, morphology and photocatalytic properties was examined. The photocatalytic activity of each sample, in presence of Rhodamine B (RhB) in aqueous solution, was carried out and analyzed under UV light irradiation. Photoexperiments showed that the material prepared at 500 °C is the best catalyst with degradation efficiency of the order of 96% after 12 min of reaction time under UV light irradiation. This high photocatalytic efficiency could be due to their structural and morphological changes. The photocatalytic degradation mechanism of RhB in the presence of the best photocatalyst BiP-500 °C is proposed. The stability of the catalyst was also examined by carrying out four successive tests of the degradation in the presence of BiP-500 °C. Total organic carbon (TOC) was used to further estimate the rate of mineralization in the presence of BiP-500 °C (83% TOC removal). Photoluminescence experiments performed under UV-laser light irradiation revealed emissions in the green-orange range, with optimal intensities for the mix systems observed at 550 °C.