CuO and CeO2 assisted Fe2O3/attapulgite catalyst for heterogeneous Fenton-like oxidation of methylene blue

In this paper, CuO and CeO₂ were screened as co-catalyst components for Fe₂O₃/attapulgite (ATP) catalyst, and three new catalysts (CuO–Fe₂O₃/ATP, CeO₂–Fe₂O₃/ATP and CuO–CeO₂–Fe₂O₃/ATP) were prepared for degradation of methylene blue (MB). The three catalysts'' characteristics were determined by BET, XRD, FT-IR, SEM and XPS. MB degradation in different systems and at different pH values was also studied. Under the conditions of H₂O₂ concentration of 4.9 mmol L⁻¹, catalyst dosage of 5 g L⁻¹, pH of 5, reaction temperature of 60 °C and MB initial concentration of 100 mg L⁻¹, the as-synthesized catalysts showed much greater reaction rate and degradation efficiency of MB than Fe₂O₃/ATP catalyst. In addition, the reusability of the as-prepared composites was evaluated. The intermediate products of MB degradation were identified by LC-MS and the possible degradation process of MB was put forward.

A novel heterogeneous catalyst CuO–CeO₂–Fe₂O₃/ATP was synthesized for MB degradation and the catalytic mechanism was put forward.     

A Fenton-like method using ZnO doped MIL-88A for degradation of methylene blue dyes

MIL-88A with different sizes was prepared by hydrothermal method by changing the content of ZnO. The samples were characterized by SEM, TEM, XRD, XPS and FT-IR. The synthesized material was used for the removal of methylene blue dye in a Fenton-like reaction, and the optimal reaction conditions were studied through single factor experiments. The experimental results show that when the molar ratio of the amount of ZnO introduced to FeCl₃·6H₂O is 1 : 1, the obtained materials have better catalytic performance than others. Under the optimal conditions, MIL-88A(Fe₁Zn₁) has the best catalytic performance for 300 mg L⁻¹ methylene blue. The removal rate can reach 96.15% within 40 minutes.

MIL-88A with different sizes were prepared by changing the content of ZnO. The prepared nanocomposites were used as catalysts in Fenton-like reaction of removing MB. The effects of the main reaction parameters on the reaction activity were studied.     

A facile heterogeneous system for persulfate activation by CuFe2O4 under LED light irradiation

In this study, the removal performance for rhodamine B (RB) by persulfate (PS) activated by the CuFe₂O₄ catalyst in a heterogeneous catalytic system under LED light irradiation was investigated. The effect of vital experimental factors, including initial solution pH, CuFe₂O₄ dosage, PS concentration, co-existing anion and initial RB concentration on the removal of RB was systematically studied. The removal of RB was in accordance with the pseudo first-order reaction kinetics. Over 96% of 20 mg L⁻¹ RB was removed in 60 min using 0.5 g L⁻¹ CuFe₂O₄ catalyst and 0.2 mM PS at neutral pH. In addition, free radical quenching experiments and electron spin resonance (EPR) experiments were performed, which demonstrated the dominant role of sulfate radical, photogenerated holes and superoxide radical in the CuFe₂O₄/PS/LED system. The morphology and physicochemical properties of the catalyst were characterized by XRD, SEM-EDS, TEM, N₂ adsorption–desorption isotherm, UV-vis DRS, and XPS measurements. Moreover, 18.23% and 38.79% total organic carbon (TOC) removal efficiency was reached in 30 min and 60 min, respectively. The catalyst revealed good performance during the reusability experiments with limited iron and copper leaching. Eventually, the major intermediates in the reaction were detected by GC/MS, and the possible photocatalytic pathway for the degradation of RB in the CuFe₂O₄/PS/LED system was proposed. The results suggest that the CuFe₂O₄/PS/LED system has good application for further wastewater treatment.

In this study, the removal performance for rhodamine B (RB) by persulfate (PS) activated by the CuFe₂O₄ catalyst in a heterogeneous catalytic system under LED light irradiation was investigated.     

Preparation of new adsorbent-supported Fe/Ni particles for the removal of crystal violet and methylene blue by a heterogeneous Fenton-like reaction

Prepared material-supported Fe/Ni particles (PM-Fe/Ni) were produced and applied as an adsorbent, reductant and Fenton-like catalyst for removing methylene blue (MB) and crystal violet (CV) from aqueous solutions. Fe/Ni particles were prepared by reducing ferric chloride with sodium borohydride and supported on the produced porous material. Various techniques including X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy analysis (SEM) were employed to characterize the crystal phase, surface area, surface morphology and functional groups. Removal experiments were conducted to study the effects of different factors such as PM-Fe/Ni dosage, initial pH, H₂O₂ concentration, initial concentrations and temperature on MB and CV removal. The removal efficiency of CV and MB by PM-Fe/Ni/H₂O₂ were 91.86% and 61.41% under the conditions of dye concentration of 1000 mg L⁻¹, H₂O₂ concentration of 50 mM, PM-Fe/Ni dosage of 0.20 g and temperature of 293 K. The analysis of the degradation kinetics showed that the degradation of MB and CV followed well pseudo-first-order kinetics. A possible mechanism of removal of MB and CV was proposed, including the adsorption, reduction and dominating Fenton oxidation. The regeneration experiments of PM-Fe/Ni demonstrated that PM-Fe/Ni with H₂O₂ still showed a high removal efficiency after six reaction cycles.

Possible reaction mechanism for CV and MB removal by the PM-Fe/Ni with H₂O₂ system.     

Degradation of methylene blue with magnetic Co-doped Fe3O4@FeOOH nanocomposites as heterogeneous catalysts of peroxymonosulfate

Magnetic Co-doped Fe₃O₄@FeOOH nanocomposites were prepared in one step using the hydrothermal synthesis process for catalyzing peroxymonosulfate (PMS) to degrade refractory methylene blue (MB) at a wide pH range (3.0–10.0). The catalysts'' physiochemical properties were characterized by different equipment; Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ were confirmed to coexist in the nanocomposite by X-ray photoelectron spectroscopy. The nanocomposite effectively catalyzed PMS''s decoloration (99.2%) and mineralization (64.7%) of MB. The formation of Co/Fe–OH complexes at the surface of nanoparticles was proposed to facilitate heterogeneous PMS activation. Compared with the observation for Fe₃O₄@FeOOH, the pseudo-first-order reaction constant was enhanced by 36 times due to Co substitution (0.1620 min⁻¹vs. 0.0045 min⁻¹), which was assigned to the redox recycle of Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ in Co-doped Fe₃O₄@FeOOH. Besides, the catalyst could be easily reused by magnetic separation and exhibited relatively long-term stability.

Magnetic Co-doped Fe₃O₄@FeOOH nanocomposites were prepared in one step using the hydrothermal synthesis process for catalyzing peroxymonosulfate (PMS) to degrade refractory methylene blue (MB) at a wide pH range (3.0–10.0).     

A highly active Z-scheme SnS/Zn2SnO4 photocatalyst fabricated for methylene blue degradation

Herein, a highly active Z-scheme SnS/Zn₂SnO₄ photocatalyst is fabricated by a one-step hydrothermal route. The structure, composition, photoelectric and photocatalytic properties of the as-prepared photocatalysts are systematically researched. The results demonstrate that SZS-6 displays a good photocatalytic performance with an efficiency of 94.5% to degrade methylene blue (MB) under visible light irradiation (λ > 420 nm). And its degradation rate constant is up to 0.0331 min⁻¹, which is 3.9 and 4.4 times faster than SnS and Zn₂SnO₄, respectively. The formation of a Z-scheme heterojunction facilitates the separation and transfer of charges, which improves the degradation of MB. The Z-scheme charge transfer pathway of the SnS/Zn₂SnO₄ photocatalyst is verified by the shifted peaks of the X-ray photoelectron spectroscopy (XPS) spectrum, the relative position of the bandgap, work function as well as free radical trapping experiments. The photocatalytic mechanism for the degradation of MB by SnS/Zn₂SnO₄ is proposed.

Herein, a highly active Z-scheme SnS/Zn₂SnO₄ photocatalyst is fabricated by a one-step hydrothermal route.     

Performance and mechanism of methylene blue degradation by an electrochemical process

An exciting electrochemical oxidation (EO) process has been developed. Compared with electro-Fenton (EF) and electro-coagulation (EC) processes, this process had more advantages in the degradation of methylene blue. It is observed that methylene blue can be quickly degraded by EO, in which an iron rod is used as an anode, graphite is used as a cathode, and fly ash–red mud particles are used as particle electrodes. Compared to EC and EF processes that are affected by specific pH values, EO has excellent performance in the pH range of 3.0–11.0. In addition, the electric energy consumption (EEC) of EF, EC and EO is 81.51, 36.55 and 21.35 kW h m⁻³ respectively, suggesting EO is more economical. The free radical scavenging mechanism of i-PrOH is studied, and the contribution of EC, EF and fly ash–red mud particle electrodes in EO is inferred. Particle electrodes before and after use are characterized by SEM, EDS and BET to illustrate the role of particle electrodes in the EO system. Analysis of flocs and solutions by FTIR and GC-MS proves that EO can effectively degrade methylene blue, and the degradation route of methylene blue is speculated. The particle electrode dissolution experiment shows that the prepared fly ash–red mud particle electrode is considered to be suitable and safe for wastewater treatment. Finally, in actual surface water experiments, the EO process still has great potential.

An exciting electrochemical oxidation (EO) process has been developed.     

Photocatalytic degradation of methylene blue by a cocatalytic PDA/TiO2 electrode produced by photoelectric polymerization

This study reports a new method for photocatalysts to degrade organic dyes on organic semiconductors. A novel strategy is reported to form TiO₂ nanorod (NR)/polydopamine (PDA) electrodes with a photoelectric polymerization strategy for PDA (pep-PDA) to produce cocatalytic electrodes. Amperometric i–t curves and UV-vis diffuse reflectance spectra were recorded and showed that compared with traditional self-polymerization (sp-PDA) and electropolymerization (ep-PDA), TiO₂ NR/pep-PDA exhibited an enhanced photocatalytic activity under visible light. As expected, TiO₂ NR/pep-PDA showed a significant improvement for the degradation of methylene blue (MB) under visible light, which can be attributed to the strong absorption of PDA in the visible light region and the more complete and uniform coverage of the TiO₂ NRs by the pep-PDA film. This study not only proposes a novel and highly efficient way to load PDA on TiO₂ NRs but also provides useful insights for the loading of other photocatalysts on organic semiconductors to degrade organic dyes.

This study reports a new method for photocatalysts to degrade organic dyes on organic semiconductors.     

Synthesis of Zn3(VO4)2/BiVO4 heterojunction composite for the photocatalytic degradation of methylene blue organic dye and electrochemical detection of H2O2

In this study, a Zn₃(VO₄)₂/BiVO₄ heterojunction nanocomposite photocatalyst was prepared using a hydrothermal route with different molar concentration ratios. The as-synthesized nanophotocatalyst was characterized using XRD, SEM, EDS, XPS, FT-IR, Raman, BET, UV-vis DRS, EPR and PL. The effect of molar ratio on composition and morphology was studied. The as-prepared nanocomposite exhibited excellent photocatalytic response by completely degrading the model pollutant methylene blue (MB) dye in 60 min at molar concentration ratio of 2 : 1. In basic medium at pH 12, the Zn₃(VO₄)₂/BiVO₄ nanocomposite degrades MB completely within 45 min. The nanocomposite was also successfully used for the electrochemical detection of an important analyte hydrogen peroxide (H₂O₂). This study opens up a new horizon for the potential applications of Zn₃(VO₄)₂/BiVO₄ nanocomposite in environmental wastewater remediation as well as biosensing sciences.

In this study, a Zn₃(VO₄)₂/BiVO₄ heterojunction nanocomposite photocatalyst was prepared using a hydrothermal route with different molar concentration ratios.     

Correction: A highly active Z-scheme SnS/Zn2SnO4 photocatalyst fabricated for methylene blue degradation

Correction for ‘A highly active Z-scheme SnS/Zn₂SnO₄ photocatalyst fabricated for methylene blue degradation’ by Yingjing Wang et al., RSC Adv., 2022, 12, 31985–31995, https://doi.org/10.1039/D2RA05519H.

The authors regret that an incorrect version of Fig. 1 was included in the original article. The correct version of Fig. 1 is presented below.Open in a separate windowFig. 1(a) XRD spectra, (b) XPS survey, (c) Zn 2p, (d) Sn 3d, (e) S2p and (f) O 1s spectra of samples.The authors regret that there was an error in the text in lines 5–10 in the right column on page 31987 of the original article. The text originally read, “The binding energy at 530.1 eV and 531.3 eV belongs to the oxygen atom coordinated with a metal atom (Sn–O–Sn) and (Sn–O–Zn), respectively.³⁷ The peak at 531.3 eV is attributed to oxygen in absorbed water, and the binding energy at 532.2 eV is attributed to the oxygen atoms on defect atoms.³⁷” This text should read, “The binding energy at 530.1 eV and 531.3 eV corresponds to the oxygen atom coordinated with a metal atom (Sn–O–Sn) and (Sn–O–Zn),³⁷ and the binding energy at 532.2 eV is attributed to the hydrated species O–H.³⁶”The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Tubular g-C3N4/carbon framework for high-efficiency photocatalytic degradation of methylene blue

The preparation of high-efficiency, pollution-free photocatalysts for water treatment has always been one of the research hotspots. In this paper, a carbon framework formed from waste grapefruit peel is used as the carrier. A simple one-step chemical vapor deposition (CVD) method allows tubular g-C₃N₄ to grow on the carbon framework. Tubular g-C₃N₄ increases the specific surface area of bulk g-C₃N₄ and enhances the absorption of visible light. At the same time, the carbon framework can effectively promote the separation and transfer of charges. The dual effects of static adsorption and photodegradation enable the g-C₃N₄/carbon (CNC) framework to quickly remove about 98% of methylene blue within 180 min. The recyclability indicates that the tubular g-C₃N₄ can stably exist on the carbon framework during the photodegradation process. In the dynamic photocatalytic test driven by gravity, roughly 77.65% of the methylene blue was degraded by the CNC framework. Our work provides an attractive strategy for constructing a composite carbon framework photocatalyst based on the tubular g-C₃N₄ structure and improving the photocatalytic performance.

Tubular g-C₃N₄ grown on a carbon framework increased the surface area of bulk g-C₃N₄, enhanced the absorption of visible light and promoted the photocatalytic performance.     

Sulfate radical-induced transformation of trimethoprim with CuFe2O4/MWCNTs as a heterogeneous catalyst of peroxymonosulfate: mechanisms and reaction pathways

Trimethoprim (TMP), a typical antibiotic pharmaceutical, has received extensive attention due to its potential biotoxicity. In this study, CuFe₂O₄, which was used to decorate MWCNTs via a sol–gel combustion synthesis method, was introduced to generate powerful radicals from peroxymonosulfate (PMS) for TMP degradation in an aqueous solution. The results showed that almost 90% of TMP was degraded within 24 min with the addition of 0.6 mM PMS and 0.2 g L⁻¹ CuFe₂O₄/MWCNTs. The degradation rate was enhanced with the increase in initial PMS doses, catalyst loading and pH. A fairly low leaching of Cu and Fe was observed during the reaction, indicating the high potential recyclability and stability of CuFe₂O₄/MWCNTs. Electron paramagnetic resonance analysis confirmed that the CuFe₂O₄/MWCNT-PMS system had the capacity to generate ·OH and SO₄˙⁻, whereas quenching experiments further confirmed that the catalytic reaction was dominated by SO₄˙⁻. A total of 11 intermediate products of TMP was detected via mass spectrometry, and different transformation pathways were further proposed. Overall, this study showed a systematic evaluation regarding the degradation process of TMP by the CuFe₂O₄/MWCNT-PMS system.

The degradation of trimethoprim (TMP) in heterogeneously activated peroxymonosulfate (PMS) oxidation processes using CuFe₂O₄/MWCNTs as the catalyst.     

A carbon membrane-mediated CdSe and TiO2 nanofiber film for enhanced photoelectrochemical degradation of methylene blue

In this study, a carbon membrane-mediated CdSe and TiO₂ ternary film (CdSe/C/TiO₂) was prepared to degrade methylene blue (MB). Carbon membrane and CdSe were introduced to the surface of a TiO₂ nanofiber film via an in situ hydrothermal deposition process successively. The investigation shows that the carbon membrane not only provides a charge transfer channel to promote the transfer of electron from the conduction band of CdSe to that of TiO₂, but also improves the poor conduct between the TiO₂ film and electrolyte. The synergies between the carbon membrane and CdSe can make the ternary system harvest more visible light energy and facilitate the charge transfer property of TiO₂. The current density of CdSe/C/TiO₂ was about 9 folds higher compared with that of pure TiO₂ under UV and visible light irradiations. This ternary hybrid exhibits a superior activity during the photoelectrochemical (PEC) degradation of MB, and 92.43% can be removed after 120 min irradiation, which is improved by 21.14% than that of TiO₂.

A CdSe/C/TiO₂ nanofiber film was prepared for enhanced photoelectrochemical degradation ability, and carbon membrane as a carrier-transfer-channel could promote electron transfer.     

A facile route to synthesize n-SnO2/p-CuFe2O4 to rapidly degrade toxic methylene blue dye under natural sunlight

In the present study, the n-SnO₂/p-CuFe₂O₄ (p-CFO) complex was prepared by a two-step process. p-CFO synthesized by the molten salt method was coated with SnO₂ synthesized by a facile in situ chemical precipitation method. The formation of n-SnO₂/p-CFO was confirmed by powder X-ray diffraction (PXRD). Scanning electron microscopy (SEM) images showed that the sharp edges of uncoated pyramid-like p-CFO particles were covered by a thick layer of n-SnO₂ on coated p-CFO particles. The complete absence of Cu and only 3 wt% Fe on the surface of the n–p complex observed in the elemental analysis using energy-dispersive X-ray spectroscopy (EDX) on the n–p complex confirmed the presence of a thick layer of SnO₂ on the p-CFO surface. Diffuse reflectance spectroscopy (DRS) was employed to elucidate the bandgap engineering. The n-SnO₂/p-CFO complex and p-CFO showed 87% and 58.7% methylene blue (MB) degradation in 120 min under sunlight, respectively. The efficiency of the n–p complex recovered after 5 cycles (73.5%) and was found to be higher than that of the uncoated p-CFO (58.7%). The magnetically separable property of the n–p complex was evaluated by using vibration sample magnetometry (VSM) measurements and it was confirmed that the prepared photocatalyst can be easily recovered using an external magnet. The study reveals that the prepared complex could be a potential candidate for efficient photodegradation of organic dyes under sunlight due to its efficient recovery and reusability owing to its magnetic properties.

The synthesis of n-SnO₂/p-CuFe₂O₄ to degrade toxic methylene blue dye under natural sunlight and its mechanism.     

Synchronous oxidation and sequestration for As(iii) from aqueous solution by modified CuFe2O4 coupled with peroxymonosulfate: a fast and stable heterogeneous process

Bifunctional heterogeneous catalytic processes for highly efficient removal of arsenic (As(iii)) are receiving increased attention. However, the agglomerated nature and stability of nanoparticles are major concerns. Herein, we report a new process regarding the anchoring of CuFe₂O₄ nanoparticles on a substrate material, a kind of Fe–Ni foam, to form porous CuFe₂O₄ foam (CuFe₂O₄-foam) by in situ synthesis. The prepared material was then applied to activate peroxymonosulfate (PMS) for fast and efficient removal of As(iii) from water. The results of removal experiments show that the complete removal of arsenic (<10 μg L⁻¹) from 1 mg L⁻¹ As(iii) aqueous solution can be achieved within shorter time (<10 min) using this adsorbent coupled with PMS. The maximum adsorption capability of As(iii) and As(v) on the prepared adsorbent is observed to be about 105.78 mg g⁻¹ and 120.32 mg g⁻¹, respectively. CuFe₂O₄-foam/PMS couple could work effectively in a wide pH range (3.0–9.0) and temperature range (10–60 °C), which is more beneficial to its application in actual water treatment engineering. The exhausted adsorbents can be refreshed for cyclic runs (at least 7 cycles) with insignificant capacity loss using alkaline solution as a regeneration strategy, suggesting this process has good stability. Investigation of the mechanism reveals that the route to the removal of As(iii) is synchronous oxidation and sequestration in the arsenic removal process. The large As(iii) removal capability and stability of CuFe₂O₄-foam/PMS show its potential as a promising candidate in real As(iii)-contaminated groundwater treatment.

Bifunctional heterogeneous catalytic processes for highly efficient removal of arsenic (As(iii)) are receiving increased attention.     

Removal of methylene blue dye by solvothermally reduced graphene oxide: a metal-free adsorption and photodegradation method

In this work, reduced graphene oxide (rGO) was fabricated at different reduction temperatures via an environmentally friendly solvothermal approach. The rGO formed at 160 °C clearly showed the partial restoration of the sp² hybridization brought about by the elimination of oxygenated functionalities from the surface. Owing to the augmented surface area and the band gap reduction, rGO-160 exhibited the best adsorption (29.26%) and photocatalytic activity (32.68%) towards the removal of MB dye. The effects of catalyst loading, initial concentration of dye, light intensity, and initial pH of solution were evaluated. It was demonstrated that rGO-160 could achieve a higher adsorptive removal (87.39%) and photocatalytic degradation (98.57%) of MB dye when 60 mg of catalyst, 50 ppm of dye at pH 11, and 60 W m⁻² of UV-C light source were used. The MB photodegradation activity of rGO-160 displayed no obvious decrease after five successive cycles. This study provides a potential metal-free adsorbent-cum-photocatalyst for the decontamination of dyes from wastewater.

A metal-free MB dye removal process was carried out by solvothermally synthesized rGO. After optimization, near-complete dye removal was achieved via an adsorption and UV photodegradation route.     

Effective photocatalytic degradation and physical adsorption of methylene blue using cellulose/GO/TiO2 hydrogels

Environmentally friendly cellulose/GO/TiO₂ hydrogel photocatalyst has been successfully fabricated via a green, simple, and one-step method and evaluated as the photocatalyst and adsorbent for the removal of methylene blue (MB). The XRD and FTIR analysis suggested the strong interaction among cellulose, GO and TiO₂, resulting from the formation of hydrogen bonds. Due to the unique porous structure of cellulose hydrogel and introduction of GO, the cellulose/GO/TiO₂ hydrogel showed superior (degradation ratio ∼ 93%) and reproducible (no significant change during the ten consecutive cycles) performance in the removal of MB under UV light. Consequently, the prepared cellulose/GO/TiO₂ hydrogel can be applied as an eco-friendly, high-performance, reproducible, and stable photocatalyst and adsorbent for the removal of MB. This green hydrogel is a promising candidate for dye wastewater treatment. Moreover, this work is expected to extend the scope of bio-templated synthesis of other nanomaterials for various applications.

New functional cellulose/GO/TiO₂ hydrogels are prepared via a simple method, showing superior and reproducible performance in the removal of MB.     

Rapid photodegradation of methylene blue by laser-induced plasma

A new strategy was established for the degradation of wastewater-based organic pollutants. Laser-induced plasma (LIP) was used as an alternative UV light source to realise rapid photodegradation of methylene blue (MB), an organic pollutant. A conventional 1064 nm Nd:YAG laser was used for plasma excitation to degrade MB solutions. The results show that the LIP effectively degraded the organic matter, and the degradation efficiency was related to the UV component with wavelength less than 400 nm. The compositions of the plasma excited by different dielectric substrates are different owing to various mechanisms involving moderate heat dissipation and sonoluminescence. However, metallic substrates, especially Fe, can enhance the proportion of UV light and accelerate the degradation efficiency. In the process of methylene blue degradation, solution parameters, such as initial dye concentration, pH, irradiation time and hydrogen peroxide concentration, will affect the degradation efficiency. The conditions of effective degradation of methylene blue (10 mg L⁻¹ MB⁻¹ concentration, 50 mL L⁻¹ H₂O₂ concentration, pH = 3 and P = 60 mW) were obtained in this study, which can provide reference for practical application.

A new strategy was established for the degradation of wastewater-based organic pollutants.