Enhanced heterogeneous Fenton-like degradation of methylene blue by reduced CuFe2O4

To facilitate rapid dye removal in oxidation processes, copper ferrite (CuFe₂O₄) was isothermally reduced in a H₂ flow and used as a magnetically separable catalyst for activation of hydrogen peroxide (H₂O₂). The physicochemical properties of the reduced CuFe₂O₄ were characterized with several techniques, including transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and magnetometry. In the catalytic experiments, reduced CuFe₂O₄ showed superior catalytic activity compared to raw CuFe₂O₄ for the removal of methylene blue (MB) due to its relatively high surface area and loading Fe⁰/Cu⁰ bimetallic particles. A limited amount of metal ions leached from the reduced CuFe₂O₄ and these leached ions could act as homogeneous Fenton catalysts in MB degradation. The effects of experimental parameters such as pH, catalyst dosage and H₂O₂ concentration were investigated. Free radical inhibition experiments and electron spin resonance (ESR) spectroscopy revealed that the main reactive species was hydroxyl radical (˙OH). Moreover, reduced CuFe₂O₄ could be easily separated by using an external magnet after the reaction and remained good activity after being recycled five times, demonstrating its promising long-term application in the treatment of dye wastewater.

CuFe₂O₄ was reduced for activation of hydrogen peroxide and the reduced CuFe₂O₄ showed a relatively higher catalytic activity.     

The efficient degradation of organic pollutants in an aqueous environment under visible light irradiation by persulfate catalytically activated with kaolin-Fe2O3

In recent years, persulfate (PS) has been widely studied as a promising oxidant. In this work, a new K-Fe₂O₃ catalyst was synthesized via a facile impregnation method. K-Fe₂O₃ samples were utilized as heterogeneous photocatalysts for the degradation of aquatic organic pollutants (rhodamine, RhB, and ciprofloxacin, CIP). The catalysts showed excellent catalytic activity in the presence of PS under the irradiation of visible light, owing to the generation of SO₄˙⁻ and ·OH active radicals. The degradation ratio and COD removal ratio for RhB were 99.8% and 88.3%. More importantly, the system retained a high degradation activity for RhB within a wide operating pH range of 2.9–10. The results of cycling degradation experiments confirmed that the K-Fe₂O₃ catalyst was stable and recoverable. Large-scale experiments for treating dye wastewater under irradiation by natural sunlight were carried out, showing that this study can provide a new perspective for the treatment of wastewater.

Characterizations and properties of catalysts.     

Efficient activation of persulfate by Fe3O4@β-cyclodextrin nanocomposite for removal of bisphenol A

Experimental studies were conducted to investigate the degradation of bisphenol A (BPA) by using persulfate (PS) as the oxidant and Fe₃O₄@β-cyclodextrin (β-CD) nanocomposite as a heterogeneous activator. The catalytic activity was evaluated in consideration of the effect of various parameters, such as pH value, PS concentration and Fe₃O₄@β-CD load. The results showed that 100% removal of BPA was gained at pH 3.0 with 5 mM PS, 1.0 g L⁻¹ Fe₃O₄@β-CD, and 0.1 mM BPA in 120 min. Further, the catalytic activity of Fe₃O₄@β-CD nanocomposite was observed as much higher when compared with Fe₃O₄ nanoparticles alone. The sulfate and hydroxyl radicals referred to in the Fe₃O₄@β-CD/PS system were determined as the reactive species responsible for the degradation of BPA by radical quenching and electron spin resonance (ESR) tests. In addition, the catalyst also possessed with accepted reusability and stability. On the basis of the results of the effect of chloride ions (Cl⁻), β-CD was found to play a crucial role in reducing interference from Cl⁻ ions, and lead to achieve higher removal efficiency for BPA in Fe₃O₄@β-CD/PS system. A possible mechanistic process of BPA degradation was proposed according to the identified intermediates by gas chromatography-mass spectroscopy (GC-MS).

Persulfate (PS), the most commonly used activator for in situ chemical oxidation (ISCO), could couple with Fe₃O₄@β-CD for effectively degrading BPA.     

Photocatalytic activity of BiFeO3/ZnFe2O4 nanocomposites under visible light irradiation

Herein, BiFeO₃/ZnFe₂O₄ nanocomposites were synthesized via a glyoxylate precursor method using a two-pot approach. Phase evolution is investigated by X-ray diffraction and Raman spectroscopy, which confirm that no impurity phases are formed between BiFeO₃ and ZnFe₂O₄ following calcination at 600 °C. The specific surface area characterized by N₂ adsorption–desorption isotherms decreases from 30.56 to 13.13 m² g⁻¹ with the addition of zinc ferrite. In contrast, the magnetization increases from 0.28 to 1.8 emu g⁻¹ with an increase in the amount of ZnFe₂O₄. The composites show strong absorption in the visible region with the optical band gap calculated from the Tauc''s plot in the range from 2.17 to 2.22 eV, as measured by diffuse reflectance spectroscopy. Furthermore, the maximum efficiency for the photodegradation of methylene blue under visible light is displayed by the composite containing 25 wt% ZnFe₂O₄ due to the synergic effect between BiFeO₃ and ZnFe₂O₄, as confirmed by photoluminescence spectroscopy.

BiFeO₃-25 wt% ZnFe₂O₄ exhibits a low specific surface area, high magnetization, and maximum photocatalytic efficiency of 97%.     

Co2+ substituted for Bi3+ in BiVO4 and its enhanced photocatalytic activity under visible LED light irradiation

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄. The X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) results indicated that the substitution of Co²⁺ ions for Bi³⁺ sites in BiVO₄ was successful, although a change in the crystal phase of BiVO₄ did not occur. UV-vis DRS and PL results suggested that the Co-incorporation could slightly improve the visible light absorption of BiVO₄ and induce the separation of photoinduced electron–hole pairs; therefore, a significant enhancement of photocatalytic performance was achieved. The Bi_0.8Co_0.2VO_4+δ sample showed superior photocatalytic activity in comparison with other samples, achieving 96.78% methylene blue (MB) removal within 180 min. In addition, the proposed mechanism of improved photocatalytic activities and the stability of the catalyst were also investigated.

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄.     

A facile synthesis of nanostructured CoFe2O4 for the electrochemical sensing of bisphenol A

This work reports a novel, highly sensitive and cost-effective electrochemical sensor for the detection of bisphenol A in environmental water samples. Attractive non-noble transition metal oxide CoFe₂O₄ nanoparticles were successfully synthesized using a sol–gel combustion method and further characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Under optimal conditions, the CoFe₂O₄ nanoparticle modified glassy carbon electrode exhibits high electrochemical activity and good catalytic performance for the detection of bisphenol A. The linear calibration curves are obtained within a wide concentration range from 0.05 μmol L⁻¹ to 10 μmol L⁻¹, and the limit of detection is 3.6 nmol L⁻¹ for bisphenol A. Moreover, this sensor also demonstrates excellent reproducibility, stability, and good anti-interference ability. The sensor was successfully applied to determine bisphenol A in practical samples, and the satisfactory recovery rate was between 95.5% and 102.0%. Based on the great electrochemical properties and practical application results, this electrochemical sensor has broad application prospects in the sensing of bisphenol A.

A new electrochemical sensor for bisphenol A is reported. CoFe₂O₄ nanoparticles were synthesized by a sol–gel combustion method. A nanoparticle-modified glassy carbon electrode exhibited outstanding electrochemical performance for the detection of bisphenol A.     

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.     

Heterogeneous activation of persulfate by ZnCoxFe2−xO4 loaded on rice hull carbon for degrading bisphenol A

A new low-cost composite of ZnCo_xFe_2−xO₄ loaded on rice hull carbon (ZnCo_xFe_2−xO₄-RHC) was synthesized via waste ferrous sulfate (the industrial waste produced in the process of producing titanium dioxide) and rice hull as raw materials, which was applied for the degradation of bisphenol A (BPA) by heterogeneous activated peroxodisulfate (PS). A series of characterizations including XRD, SEM, FTIR, and BET analysis were carried out to analyze the structure and morphology of the materials. It is confirmed that the ZnCo_xFe_2−xO₄-RHC composites show better catalytic activity and performance than other control samples, which can be attributed to the synergistic effect of Fe and Co, ZnCo_xFe_2−xO₄ and RHC based on these analyses. The degradation rate of BPA by ZnCo_1.3Fe_0.7O₄-50%RHC reached 100% within 15 min, and it can still maintain good catalytic efficiency after 5 cycles. ESR test and XPS results showed that free radical and non-free radical processes were involved in BPA degradation. These findings offer a novel, low cost and simple strategy for rational design and modulation of catalysts for the industrial degradation of organic pollutants, and provide a new idea for the utilization of waste ferrous sulphate in titanium dioxide industry.

Mechanism of the activation on PS by ZnCo_1.3Fe_0.7O₄-RHC for the degradation of BPA.     

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.     

Enhanced photoreduction degradation of polybromodiphenyl ethers with Fe3O4-g-C3N4 under visible light irradiation

As typical persistent organic pollutants, polybrominated diphenyl ethers (PBDEs) have aroused high environmental concern due to their toxicity and recalcitrant degradation. Herein, we report the enhanced photoreduction degradation of polybromodiphenyl ethers with Fe₃O₄-g-C₃N₄ under visible light irradiation (>420 nm). A series of high activity photocatalysts Fe₃O₄-g-C₃N₄ (named FeOCN-x) have been synthesized by an in situ growth method. The characterization of the prepared FeOCN-x nanocomposites has been examined by SEM, TEM, ultraviolet-visible diffuse reflectance spectroscopy, a vibrating sample magnetometer, X-ray diffraction, X-ray photoelectron spectroscopy and Brunauer–Emmer–Teller surface area analysis. FeOCN-x hybrids all exhibit good magnetic separation properties with the saturation magnetization at 300 K varying from 0.4 to 6.3 emu g⁻¹. Under visible light irradiation, FeOCN-x hybrids show enhanced photocatalytic activity for the debromination of PBDEs compared with g-C₃N₄. Among all the hybrids, FeOCN-4 with a 4 wt% Fe₃O₄ content gives the highest reaction rate, which is 6.7 times as high as that in pure g-C₃N_4. The FeOCN-x nanocomposites not only exhibit good photostability, but could also be easily recovered by magnetism. The results of the kinetic isotope effects (KIE) and the trapping agent experiments show that the rate determining step in the degradation reaction of PBDEs with FeOCN-x is the rate of electron accumulation in the conductive band. A possible photoreductive mechanism has been proposed. This study shows that the easily magnetically separable recycled photocatalyst FeOCN-x, with high visible light activity, could be an excellent candidate for dealing with halogen pollutants.

The enhanced photoreduction degradation of polybrominated diphenyl ethers with magnetic separable Fe₃O₄-g-C₃N₄ under visible light irradiation is reported.     

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.     

Bi2O3 and g-C3N4 quantum dot modified anatase TiO2 heterojunction system for degradation of dyes under sunlight irradiation

A facile and feasible method was successfully utilized to incorporate Bi₂O₃ and g-C₃N₄ quantum dots on TiO₂ surface to synthesize a novel composite g-C₃N₄/TiO₂/Bi₂O₃. The photocatalytic activity of the composite g-C₃N₄/TiO₂/Bi₂O₃ for degradation of dyes under sunlight and UV light irradiation was evaluated. It possessed the higher photocatalytic performance than that of pristine TiO₂ or g-C₃N₄ under the same conditions. Under sunlight irradiation, the reaction rate constants of the g-C₃N₄/TiO₂/Bi₂O₃ was about 4.2 times and 3.3 times higher than that of TiO₂ and g-C₃N₄, respectively. The promising photocatalytic performance was attributed to the broader light absorption range and efficient separation of photoinduced carriers. Moreover, based on the TEM, XPS, XRD, UV-vis spectrum, radicals scavenging test and Mott–Schottky analysis systematic mechanism for photodegradation process was proposed. This work provides a promising strategy for the modification of TiO₂-based semiconductors by incorporating different quantum dots and promoting the efficiency of the photocatalysts in practical application.

A facile and feasible method was successfully utilized to incorporate Bi₂O₃ and g-C₃N₄ quantum dots on TiO₂ surface to synthesize a novel composite g-C₃N₄/TiO₂/Bi₂O₃.     

Synergetic effect of photocatalysis and peroxymonosulfate activated by MFe2O4 (M = Co,Mn, or Zn) for enhanced photocatalytic activity under visible light irradiation

Nanosized MFe₂O₄ (M = Co, Mn, or Zn) photocatalysts were synthesized via a simple sol–gel method. MFe₂O₄ photocatalysts exhibited lower photocatalytic activity for the degradation of levofloxacin hydrochloride under visible light irradiation. For enhancement of photocatalytic activity, MFe₂O₄ was used to activate peroxymonosulfate and degrade levofloxacin hydrochloride under visible light irradiation. The influences of peroxymonosulfate dosage, levofloxacin hydrochloride concentration, pH value, and temperature on peroxymonosulfate activation to degrade levofloxacin hydrochloride were investigated in detail. The mechanism of activation of peroxymonosulfate by MFe₂O₄ was proposed and proved by radical quenching experiments, electron spin resonance analysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and transient photocurrent responses. The combined activation effects of photogenerated e⁻/h⁺ and transition metals on peroxymonosulfate to produce sulfate radical clearly enhanced the degradation efficiency.

The combined activation effects of photogenerated e⁻/h⁺, Fe, Co, Mn, and Zn on peroxymonosulfate to produce SO₄˙⁻ clearly enhanced the degradation efficiency.     

TiO2/Fe2O3 heterostructures with enhanced photocatalytic reduction of Cr(vi) under visible light irradiation

We report a study on the synthesis of TiO₂/Fe₂O₃ (TF) nanocomposites and their photocatalytic performance under visible-light irradiation. The characterization of structure and morphology shows that hematite Fe₂O₃ was deposited on anatase TiO₂ nanoparticles with particle sizes in the range of 20–100 nm. In contrast to pure TiO₂ and pure Fe₂O₃, the nanocomposites exhibited remarkable photocatalytic activity. For example, the photoreduction efficiency of TF0.5 reaches 100% for a 100 ppm Cr(vi) solution within 160 minutes. The photochemical properties were studied by various methods. Finally, we conclude that the excellent performance of the photocatalysts is mainly attributed to two aspects: the enhanced absorption of visible light and the synergistic effect of an internal electric field at the heterojunction and citric acid for promoting the separation of electron–hole pairs.

A TiO₂/Fe₂O₃ heterojunction with an internal electric field was constructed for enhancing photocatalytic reduction efficiency of Cr(vi).     

Comparative study of atrazine degradation by magnetic clay activated persulfate and H2O2

To effectively remove the endocrine disrupting chemicals (EDCs) in water, Fe₃O₄ was loaded on the surface of modified sepiolite clay by the method of co-precipitation to catalyze potassium persulfate (K₂S₂O₈) and hydrogen peroxide (H₂O₂) respectively to generate SO₄˙⁻ and ·OH for atrazine (ATZ) removal. The magnetic clay catalyst was characterized by XRD, SEM, N₂ adsorption–desorption and isoelectric point. The degradation efficiency of ATZ in the two systems was systematically compared in terms of initial pH, oxidant dosage and oxidant utilization rate. The results revealed that, after 90 minutes, systems with K₂S₂O₈ and H₂O₂ can remove 65.7% and 57.8% of the ATZ under the given conditions (30 °C, catalyst load: 1 g L⁻¹, initial pH: 5, [ATZ]₀: 10 mg L⁻¹, [H₂O₂]₀: 46 mmol L⁻¹, [PDS]₀: 46 mmol L⁻¹). The magnetic clay catalyst still maintained good catalytic activity and stability during the four consecutive runs. Based on the quenching experiments, it was demonstrated that the dominant radical species in the two systems were SO₄˙⁻/·OH and ·OH, respectively. However, the degradation efficiency of the two systems presented different responses toward the condition variations; the system with K₂S₂O₈ was relatively more sensitive to solution pH, the oxidant efficiency was generally higher than that of the H₂O₂ system (except 184 mmol L⁻¹).

To effectively remove the EDCs in water, Fe₃O₄ was loaded on the surface of modified sepiolite clay by co-precipitation to catalyze K₂S₂O₈ and H₂O₂ respectively to generate SO₄˙⁻ and ·OH for ATZ removal.     

A facile one-step hydrothermal approach to synthesize hierarchical core–shell NiFe2O4@NiFe2O4 nanosheet arrays on Ni foam with large specific capacitance for supercapacitors

In this contribution, NiFe₂O₄@NiFe₂O₄ nanosheet arrays (NSAs) with three-dimensional (3D) hierarchical core–shell structures were synthesized by a facile one-step hydrothermal method and they were used as electrode materials for supercapacitors (SCs). The NiFe₂O₄@NiFe₂O₄ composite electrode showed a high specific capacitance of 1452.6 F g⁻¹ (5 mA cm⁻²). It also exhibited a superior cycling stability (93% retention after 3000 cycles). Moreover, an asymmetric supercapacitor (ASC) was constructed utilizing NiFe₂O₄@NiFe₂O₄ NSAs and activated carbon (AC) as the positive and negative electrode, respectively. The optimized ASC shows extraordinary performances with a high energy density of 33.6 W h kg⁻¹ at a power density of 367.3 W kg⁻¹ and an excellent cycling stability of 95.3% capacitance retention over 3000 cycles. Therefore, NiFe₂O₄@NiFe₂O₄ NSAs have excellent pseudocapacitance properties and are good electrode materials for high energy density.

Hierarchical NiFe₂O₄@NiFe₂O₄ core–shell nanosheet arrays synthesized via one-step hydrothermal method with a successive annealing exhibited outstanding electrochemical performance.     

Cobalt-loaded cherry core biochar composite as an effective heterogeneous persulfate catalyst for bisphenol A degradation

Persulfate (PS)-based advanced oxidation processes have drawn tremendous attention for the degradation of recalcitrant pollutants, and cobalt composites are effective for PS activation to generate reactive species. In this study, composites of cobalt species loaded on cherry core-derived biochar (Co/C) were prepared with a one-step pyrolysis method. The Co/C catalyst was applied as a catalyst for PS activation to degrade bisphenol A (BPA). Factors influencing the degradation efficiency were examined, including the ratio of raw materials, Co/C and PS dosages, temperature, and solution pH. The Co/C catalyst prepared when the ratio of raw material was 1 : 1 (Co/C-50) could efficiently activate both peroxymonosulfate (PMS) and peroxydisulfate (PDS). When the initial concentration of BPA was 20 mg L⁻¹, complete removal of BPA was achieved in the Co/C-50-PMS and Co/C-50-PDS systems within 8 min and 10 min, respectively. More than 70% of BPA could be mineralized in the Co/C-50-PS system. The free radical quenching experiments demonstrated that in the Co/C-50-PS system, the degradation of BPA was achieved through free radical, surface-bound free radical, and non-free radical pathways. The successful preparation of the Co/C-50-PS catalyst broadens the application of cobalt-based carbon materials in the activation of PS to remove organic pollutants.

Co/C composites were prepared with a one-step pyrolysis method for the activation of persulfate to degrade organic pollutants.     

A facile method for the preparation of black TiO2 by Al reduction of TiO2 and their visible light photocatalytic activity

Black TiO₂ has attracted widespread attention due to its visible light absorption and wide range of applications. However, the currently reported preparation methods for black TiO₂ are not suitable for large-scale production due to its being prepared under high vacuum and over a long time. We have successfully prepared black TiO₂ under normal pressure and short time conditions. The as-prepared black titanium dioxide was characterized by XRD, XPS, TEM, UV-visible absorption spectrum and other characterization methods. The result shows that the as prepared black titanium dioxide had a disordered structure and oxygen vacancy defects on the surface, and exhibits excellent visible and near infrared absorption performance. The black TiO₂ sample was prepared under 650 °C 60 min exhibits excellent visible light photocatalytic performance, and can degrade 56% MO after visible light irradiation for 120 min.

Black TiO₂ has attracted widespread attention due to its visible light absorption and wide range of applications.     

Synthesis of V-modified TiO2 nanorod-aggregates by a facile microwave-assisted hydrothermal process and photocatalytic degradation towards PCP-Na under solar light

Herein, novel V-modified titania nanorod-aggregates (VTNA), consisting of fine individual nanorods in radial direction, were fabricated via an efficient microwave-assisted hydrothermal (MWH) route. VTNA with high crystallinity and homogeneous mesopores were obtained by 30 min MWH processing at 190 °C; moreover, a mixed rutile–anatase phase appeared after vanadium doping. XPS analysis revealed that vanadium existed in the forms of V⁴⁺ and V⁵⁺ on the surface of MWV05 with V⁵⁺ being the dominant component, the content of which was approximately 3.5 times that of V⁴⁺. Vanadium implanting was achieved efficiently by doping 0.5 and 1 at% V using a rapid MWH process and contributed towards the dramatic improvement of the visible-light response, with E_g decreasing from 2.91 to 2.71 and 2.57 eV with the increasing V doping content. MWV05 exhibited optimal photocatalytic degradation activity of water-soluble PCP-Na under solar light irradiation. The enhanced photodecomposition was attributed to the red-shift in the TiO₂ band-gap caused by vanadium impregnation, efficient charge separation due to the V⁴⁺/V⁵⁺ synergistic effects and the free migration of charge carriers along the radial direction of the nanorods arranged in a self-assembled VTNA microstructure.

V-modified titania nanorod-aggregates were fabricated by microwave hydrothermal route. MWV05 exhibited optimal solar activity towards PCP-Na, due to red-shift by V-doping, carriers separation by V⁴⁺/V⁵⁺ synergistic effects and charge migration along the nanorods.