Peroxotungstic Acid Research Articles

Tungsten trioxide coatings prepared by inkjet printing of a water based formulation: structural characteristics and electrophotocatalytic properties

Thin compact layers of monoclinic tungsten trioxide (WO3) were prepared through printing of a water soluble dopamine peroxo-tungstic acid complex (DoPTA). The effect of different layer thicknesses, achieved through the sequential overlapping of layers (from one to five), on the resulting structure and photo(electrochemical) properties was investigated. After a powder XRD analysis, 450 °C was determined to be the most suitable temperature for calcination due to the formation of a crystalline phase of WO3 within a relatively short time (after 1 h) and, at the same time, this temperature does not cause any damage to the glass substrates used for the deposition of the WO3 layers. Linear scanning voltammetry as well as chronoamperometry were used, with periodic illumination, to measure the influence of the number of layers on the final electro-photocatalytic properties. The thickness of the samples prepared ranged from 0.25 µm to 1.25 µm and the three-layer sample was found to have the best performance. It had a thickness of 0.83 µm, and the incident photon to current efficiency (IPCE) was calculated to be 40.8%.

Selectively extracting H2WO4 of high purity from the H2SO4 decomposition product of scheelite through hydrogen peroxide coordination followed by purification using ion-exchange and solvent extraction and thermal decomposition

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is <1%. The conversion of tungsten from the product to peroxotungstic acid was investigated. After the purification using ion-exchange and solvent extraction, high-purity tungstic acid was obtained through thermal decomposition, with the content of each impurity element being lower than 15 mg/l. This study offers a new approach to producing high-purity tungstic acid from the sulfuric acid decomposition product of scheelite while eliminating the issues of ammonium-containing wastewater and saline wastewater.

Separation of molybdenum from peroxotungstic acid solution by solvent extraction with TBP and TRPO

An increasing problem facing the tungsten industry is developing an effective separation of molybdenum from peroxotungstic acid solutions due to the similarities of these two metals. This study herein separates molybdenum from peroxotungstic acid solution for the selective production of tungsten from scheelite acid decomposition residue using hydrogen peroxide. Solvent extraction was the main method employed, and the feed was peroxotungstic acid solution containing peroxomolybdic acid. The concentration of tungsten and molybdenum in the feed and the raffinate were measured by Inductively Coupled Plasma (ICP) to characterize the separation efficiency. The results showed that in the peroxide solution, an organic phase of tributyl phosphate (80 %), trialkyl phosphine oxide (2 %), and sulfonated kerosene (18 %) was used effectively to separate molybdenum from tungsten in acid leach solutions. A maximum single-stage separation coefficient of 400 was reached under the following extraction conditions: temperature, 25 °C; contact time 4–6 min; separation time 4 min; and organic to aqueous ratio, 1.2. Using ammonium bicarbonate as the stripping agent, the stripping ratio of molybdenum and tungsten were 83 % and 33 %, respectively, and the corresponding separation coefficient was 10.

Effects of Additives on Electrochromic Properties of Nanocrystalline Tungsten Oxide Films Prepared by Complexation-Assisted Sol-Gel Method.

To improve the electrochromic (EC) properties of sol-gel-derived WO3 films, a series of organic small molecules, such as dopamine (DA), catechol, tyramine, phenol and 2-phenylethylamine, were added into peroxotungstic acid precursor sols as structure-directing additives, and five modified WO3 films were prepared by a simple and low-cost complexation-assisted sol-gel method. The effects of the above additives on the EC properties of the modified WO3 films have been studied in detail. Compared with the pure WO3 polycrystalline film, all the modified films combine the advantages of nanocrystalline and amorphous phases and show higher EC properties attributed to the unique nanocrystal-embedded amorphous structure. The results indicate that different additives with different numbers and types of functional groups (hydroxyl and amino groups) can change the microstructure, morphology, and thus electrochemical and EC properties of the films in various degrees. The additives, in order of their strong interactions with the sols, are DA, catechol, tyramine, phenol and 2-phenylethylamine, primarily depending on the number of hydroxyl groups. Of all the additives, DA with both catechol hydroxyl and amino groups shows the most positive effect; that is, the WO3 film modified with DA exhibits the best EC properties in terms of contrast, switching speed, stability, and coloration efficiency.

МОДЕРНИЗАЦИЯ ТЕХНОЛОГИЧЕСКИХ ПРОЦЕССОВ ИЗГОТОВЛЕНИЯ АЛКОЗОЛЯ WO3

Alkosol WO3 is used for the production of functional nanocoatings that exhibit electrochromic effect. These nanocoatings have a wide range of applications, but the most promising and economically feasible is their use in the structure of architectural "smart" windows to regulate the passing light and heat flows. Practical application of electrochromic windows will allow to reduce electric energy losses for heating and cooling of buildings and vehicles up to 40%. This article is devoted to the description of the developed technological approaches for the production of WO3 alcosol by the peroxide method. Modernization of the technological process of manufacturing this material made it possible to minimize the formation of a side insoluble crystalline phase of H2WO5, to automate the process of polycondensation of peroxotungstic acid, to obtain a WO3•nH2O2•mH2O hydrogel of a uniform composition, and to accelerate the dissolution of the hydrogel in ethanol from 12 hours to 5 minutes. The total time of all stages of the technological process for the production of alcosol WO3 was reduced from 3 days to 8 hours.

Enhancing catalytic activity through the construction of praseodymium tungstate decorated on hierarchical three-dimensional porous biocarbon for determination of furazolidone in aquatic samples

Boosting catalytic performance as a vital role for an electrochemical sensor for monitoring various hazardous nitro drugs. Herein, an inexpensive, facile, and eco-friendly construction of praseodymium tungstate decorated on three dimensional porous biocarbon (PrW/3D-PBC) for electrochemical determination of carcinogenic residue furazolidone (FZ). The nanostructured PrW nanoparticles were prepared by solvent evaporation from peroxo-tungstic acid and 3D-PBC was prepared from biomass precursor under the carbonization method. Furthermore, the composite of PrW decorated on 3D-PBC was prepared by an ultrasonic-assisted wet chemical approach. Besides, the composite characterization of crystalline, functional group, degree of carbonization, chemical states, and morphology were utilized by theXRD, FTIR, RAMAN, XPS, and FESEM analysis. These 3D porous carbon decorated PrW nanoparticles facilitate the electrochemical anchoring sites, surface area, and ease of diffusion layers towards the detection of hazardous nitro pollutant FZ by using CV analysis. The low LOD and high sensitivity were achieved by FZ determination through using LSV and DPV techniques. The practical capability of the PrW/3D-PBC/GCE sensor was determined by using aquatic samples to achieve a good recovery result. These results instigate that the PrW/3D-PBC will be an efficient electrocatalytic material for FZ sensor in environmental aquatic samples.

Synergistically improved electrochemical performance by the assembly of nanosized praseodymium tungstate on reduced graphene oxide for the detection of dimetridazole in biological and aquatic samples

Over the years, widely increasing overdose and improper disposal of drugs are harmful to public health and the ecosystem. Herein, the nanostructured praseodymium tungstate decorated on reduced graphene oxide (PW NPs/R-GO) composite was used for the detection of antiprotozoal drug dimetridazole (DMZ). The nanostructured PW NPs were prepared by solvent evaporation from peroxo-tungstic acid and the composite of PW NPs/R-GO was assembled through a facile ultrasonication method. Under the suitable circumstance, the fabricated PW NPs/R-GO/GCE sensor displays outstanding electrocatalytic performance towards DMZ, and significantly, provided a higher reduction response than PW NPs/GCE, R-GO/GCE, and bare GCE. This fabricated sensor achieved a nanomolar detection limit (1.2 nM) and a wide linear range (0.001–965 µM) of DMZ by using highly sensitive DPV techniques. The constructed sensor endows excellent repeatability, reproducibility, selectivity, and storage stability performance. However, the practical capability of constructed PW NPs/R-GO/GCE sensor was successfully verified in biological, and environmental fluids to achieve a good recovery result. Therefore, this work endows a new perception for real-time sensing of DMZ in biological and aquatic samples.

A cleaning approach for the preparation of nano tungsten oxide from waste tungsten powder by hydrogen peroxide leaching and spray pyrolysis

In the production process of tungsten powder, waste tungsten powder with excessive impurities is generated due to the contact between tungsten oxide and iron boats. Currently, there is no cost-effective direct utilization method. This study proposes to use the green oxidant H2O2 to selectively leach waste tungsten powder to obtain a pure peroxotungstic acid solution and then to directly prepare nano-WO3 by spray pyrolysis. First, the leaching of tungsten was investigated in detail. Under the conditions of a reaction time of 60 min, temperature of 40 °C, raw material particle size of 5–13 μm, liquid-to-solid ratio of 15:1 ml/g, and H2O2 concentration of 16 mol/L, the leaching efficiency of tungsten reached 97.89%, where the impurity elements (Fe, Ni and Cr) were all below 1%. The analysis of the leachate confirmed that W was leached in the form of peroxotungstic acid (PTA). Second, the thermal decomposition mechanism of PTA was investigated. The decomposition process was divided into three stages. The first stage (50–135 °C) was [WO2(O2)H2O]·nH2O to remove crystal water; the second stage (137–230 °C) was when the WO2(O2)H2O crystals decomposed into amorphous tungsten oxide and released H2O and O2. The third stage (350–420 °C) was when amorphous tungsten oxide transformed into WO3 crystals. Finally, under the conditions of an initial PTA concentration of 20 g/L, temperature of 240 °C and air velocity of 90 L/min, spray pyrolysis of the PTA leachate was performed, and hollow nanosphere WO3 with an average particle size of less than 500 nm was obtained. This novel method realizes the clean and efficient preparation of nano-WO3 and the short-process reuse of waste tungsten powder.

Tungsten extraction from scheelite hydrochloric acid decomposition residue by hydrogen peroxide

• W was leached from crude tungstic acid or residue by an efficient and clean method. • H 2 O 2 dissolved W from crude tungstic acid or residue selectively. • The W leaching ratio exceeded 96% for crude tungstic acid and 99% for the residue. • Pure tungstic acid was obtained from peroxotungstic acid solution. • More than 99.6% of W was precipitated from peroxotungstic acid solution. To reduce the amount of ammonia wastewater produced during traditional tungsten metallurgy, a novel method has been developed. Hydrogen peroxide was first used to selectively dissolve tungsten from crude tungstic acid and scheelite hydrochloric acid decomposition residue. Then, the peroxotungstic acid solution obtained was heated to prepare pure tungstic acid through thermal decomposition . The results showed that when the temperature was 40–45 °C, the molar ratio of hydrogen peroxide to tungstic acid was 2:1, and the reaction time was 60 min, more than 96 % of the crude tungstic acid was dissolved. Tungsten was easily leached from the hydrochloric acid decomposition residue under the conditions of a hydrogen peroxide concentration of 1.95 mol/L, 60 min, and 30 °C. The tungsten leaching ratio was 99.4 %. Using a decomposition temperature higher than 95 °C, seed addition amount more than 2.5 g/L, an acid concentration of 1 mol/L, and a reaction time of 120 min, the final W concentration in the mother liquor was 0.5 g/L and the decomposition ratio of peroxotungstic acid was more than 99.6 % with the product being WO 3 ·H 2 O. This research showed that hydrogen peroxide could dissolve tungstic acid and scheelite hydrochloric acid decomposition residue, and that the peroxotungstic acid obtained was readily decomposed into tungstic acid, which made it possible to leach scheelite cleanly and efficiently.

Characterization of nanoparticulated WO3 electrochromic thin films prepared via precipitation reaction of peroxotungstic acid solution

Amorphous WO3 thin films with a nanoparticulated morphology were fabricated using a combination of electrodeposition and electrophoretic deposition via the precipitation reaction of a peroxotungstic acid (PTA) solution. Due to the presence of the precipitated WO3 nanoparticles in the aged PTA solution, the electrophoretic deposition and electrodeposition occur simultaneously, which results in a grainy surface morphology in which nano-sized WO3 particles are embedded on a smooth WO3 thin film. The WAT-5 sample prepared with a PTA solution aged for 5 days exhibited faster ion intercalation/de-intercalation kinetics (coloration time of 3 s and bleaching time of 1 s), a greater transmittance modulation (68.36%), and a higher coloration efficiency (41.29 cm2/C) with better cyclic stability (91% retention during 300 cycles) than a WO3 thin film fabricated using the PTA solution without the aging process. The nanoparticulated morphology enhanced the active reaction area by expanding the interface between the electrolyte and the electrochromic material. Such results indicate that the electrochromic characteristics of WO3 thin films can be improved simply by adjusting the aging period of the PTA solution.

Selective Synthesis of γ-WO3 and β-WO3⋅H2O by the Hydrothermal Treatment of Peroxotungstic Acid

Selective Synthesis of γ-WO3 and β-WO3⋅H2O by the Hydrothermal Treatment of Peroxotungstic Acid

Investigation of WO3 Electrodeposition Leading to Nanostructured Thin Films

Nanostructured WO3 represents a promising material for electrochromic and sensing devices. In this scenario, electrodeposition is a promising low-cost approach for careful production. The electrodeposition of tungsten oxide film from a peroxo-tungstic-acid (PTA) solution is investigated. WO3 is synthetized onto Indium doped Tin Oxide (ITO) substrates, in a variety of shapes, from a fragmentary, thin layer up to a thick continuous film. Samples were investigated by scanning electron (SEM) and atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), X-ray Diffraction analysis (XRD), energy gap measurement. Electrodeposition current curves are compared with characterization results to model the growth process. Early stages of electrodeposition are characterized by a transient cathodic current revealing an instantaneous nucleation followed by a diffusion limited process. A quantitative analysis of W deposition rate and current at working electrode validates a microscopic model for WO3 electrodeposition driving the process towards nanostructured versus continuous WO3 film.

Drop-cast tungsten trioxide semiconducting films in Photoelectrocatalysis

Polycrystalline, monoclinic, uniform WO 3 films of up to 2.5 μm thickness were prepared by drop casting onto F:SnO 2 /glass using as precursor peroxo-tungstic acid and polyethylene glycol in water, and firing in air at 520 °C. The n-type WO 3 layers produced photocurrents in junctions with aqueous electrolytes. Under depletion conditions, IPCEs (incident photon to current efficiencies) of up to 0.7 at 365 nm and 0.2 at 405 nm were obtained. The photosensitivity of WO 3 thin films extended into the visible range up to 470 nm. The photoelectrocatalytic activity of such layers was examined using the azo-dye “acid orange 7” (AO7) as a model pollutant. Degradation of AO7 was carried out under backside UVA broadband illumination of electrodes of 62 cm 2 active surface area, in a parallel plate flow-through reactor equipped with a stainless steel counter electrode under electrical bias of 1.1–1.3 V. Rapid recirculation of the electrolyte was maintained in order to derive true kinetic parameters. During illumination, the concentration of AO7 (initial value 1 mM) decreased exponentially. At the beginning of a degradation experiment the Faradaic efficiency, f 0 , was 0.48. • Polycrystalline WO 3 films of up to 2.5 μm thickness were prepared by drop casting onto F:SnO 2 /glass peroxo-tungstic acid and polyethylene glycol in water, and firing in air at 520 °C. • The n-type WO 3 layers produced photocurrents up to 470 nm in junctions with aqueous electrolytes. • Photoelectrocatalytic activity of such layers was examined using the azo-dye “acid orange 7” (AO7) under backside UVA illumination of electrodes of 62 cm 2 active surface area, in a parallel plate flow-through reactor under electrical bias of 1.1–1.3 V. • During UVA illumination, the concentration of AO7 (initial value 1 mM) decreased exponentially. The initial Faradaic efficiency, f 0 , was 0.48.

DIRECT ULTRASONIC SYNTHESIS OF WO3/TiO2 NANOCOMPOSITES AND APPLYING THEM IN THE PHOTODECOLORIZATION OF EOSIN YELLOW DYE

This research reported a direct, environmentally friendly, economical, and simple method of using an ultrasonic instrument as a green technique to combine WO3 with TiO2 in ratios 0.5:1, 0.25:1, and 0.16:1 as composites 1, 2 and 3 respectively. Powder X-Ray Diffraction data identified the mean crystalline sizes of the commercial WO3, commercial TiO2, and of the prepared WO3/TiO2 nanocomposites in the different ratios in ranged from 17.897 nm to 48.672 nm. AFM analysis noted the surface morphology for all studied samples is spherical. The mean crystal sizes and practical sizes for prepared composites are found to be in the nanometer range, and these values rise with the raising in the TiO2 quantity in prepared nano-composites. The incorporated of W with Ti in the matrix is successful happened; because the ionic radius of W6+ is fewer values than it for Ti4+. The band gaps values for all samples have been investigated. The band gaps of prepared nanocomposites 1, 2, 3, and TiO2 are occurred as an indirect type, while the band gap of WO3 is found as direct type. The studied samples were tested by using them as photocatalysts in the decolorization of an aqueous solution, the eosin yellow dye Edecol.%. The sequence of decoloration grows from the left to the right as: Edecol.% (composite 3) Edecol.% (WO3) Edecol.% (TiO2) Edecol.% (composite 2) Edecol.% (composite 1). The activity of WO3 is inhibited with addition of H2O2 to the aqueous solution of eosin yellow dye because of the formation of peroxotungstic acid (WO3H2O2.H2O or WO2(O2)H2O.nH2O), but the modified surface by incorporation of TiO2, improves the activity hence, nano-composite 1 in the ratio of 0.5:1 is given a maximum photodecolorization efficiency of this dye and changed from 25.11% to 73.88%.

Poly(vinyl alcohol) as a structuring agent for peroxotungstic acid

Poly(vinyl alcohol) (PVAL) is an interesting architecture-directing material and is useful for synthesizing transition metal oxides through the sol-gel method. In this work, the interaction between PVAL and peroxotungstic acid (PTA) in aqueous media was investigated by conductivity, zeta potential, small-angle X-ray scattering, isothermal titration calorimetry and fluorescence measurements. The strong exothermic effect and the change in organization in aqueous media, from extended chains to compact chains forming fractal structures, confirm the interaction between PTA and PVAL. Powders were obtained from these systems by removal of water and subsequent calcination. An increase in the crystal size and changes in morphology were observed with the increasing of PVAL concentration. The band gap values, obtained by diffuse reflectance spectroscopy, were between 2.50 and 2.60 eV and showed that the obtained oxides are able to absorb light in the visible part of the electromagnetic spectra.

Mesoporous TiO2 with WO3 functioning as dopant and light-sensitizer: A highly efficient photocatalyst for degradation of organic compound

The suitable doping or modification on TiO2 holds promise for improving charge separation and extending light absorption range. Here, WO3 modifying reduced band gap mesoporous TiO2 (WO3/RM-TiO2) due to WO3 doping was successfully fabricated by immersing mesoporous TiO2 nanoparticles in the peroxotungstic acid sol with controllable reaction time (0–1 h). The W6+ ions were first incorporated into the TiO2 lattice to form WOTi bonds, resulting in the formation of WO3 doping TiO2. Then, WO3 nanoparticles gradually formed and attached on the TiO2 surface, constructing a novel heterojunction catalyst with WO3 serving as both dopant and light-sensitizer for TiO2. Photocatalytic activity of the resulting WO3/RM-TiO2 depends on the immersing duration in the peroxotungstic acid. The BET analysis shows that 0.5 h-WO3/RM-TiO2 has the largest pore volume of 0.491 cm3 g−1 and the highest surface area of 82.3 m2 g−1, whereas these values decline with prolonged immersing duration. As expected, the optimal efficiency in removing p-nitrophenol (PNP) is achieved over 0.5 h-WO3/RM-TiO2 under visible light irradiation, which is 2.33 times that of the unmodified M-TiO2. This should be attributed to the suitable WO3 doping and WO3 modification.

The electrochromic property of MoO3/WO3 nanocomposite films

Electrochromic films of molybdenum / tungsten trioxide (MoO3/WO3) prepared from a solution of peroxotungstic acid (PTA) were formed on indium doped tin oxide (ITO) glass substrate using the sol-gel and dip coating methods at difference ratios of MoO3 of 15, 30 and 50 %mol. The effect of MoO3 on the structure, morphology, optical and electrochromic properties of films were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Atomic force microscope (AFM), Scanning electron microscope (SEM), UV-vis spectrophotometer and Cyclic voltammogram (CV), respectively. The 30 %mol MoO3 doped WO3 film demonstrated a good electrochemical properties in terms of diffusion coefficient better than other ratios and pure WO3 due to its large surface area of the high roughness composite film.

Highly enhancing photoelectrochemical performance of facilely-fabricated Bi-induced (002)-oriented WO3 film with intermittent short-time negative polarization

WO3 photoelectrode should have high photoactivity and stability for application in solar water splitting. By introducing Bi3+ ions, a highly ordered (002)-oriented WO3 film with a high photocurrent was easily prepared on FTO glass by spin coating a simple Bi-doped peroxotungstic acid (PTA) gel followed by calcination. In situ XRD, pole figures, and HR-TEM were performed to elucidate the formation process and epitaxial properties. The flat Bi-WO3 film achieved a remarkable photocurrent density of 2.06 mA cm−2 at 1.5 V vs. Ag/AgCl. By introducing intermittent short-time negative polarization (ISNP) into the process of PEC water splitting, the O2 gas product yield is enhanced by ca. 75% with high faradaic efficiency, as ISNP can efficiently eliminate peroxo species on the surface of the WO3 film. This demonstrates that ISNP can enhance the photostability and photoactivity of WO3 films.

Insights on Structuration of Peroxotungstic Acid in Aqueous Media

Recent studies on tungsten oxide preparation are mainly motivated by its applications in smart windows, energy harvesting and, recently, in cancer therapy. Peroxotungstic acid (PTA) is an important precursor to obtain tungsten oxide in an environmentally-friendly way, through the colloidal synthesis in aqueous media. Despite giving chemically pure products, PTA originates oxides with various morphologies depending on the experimental conditions, a subject open to discussion. PTA, in the presence of sodium dodecyl sulfate (SDS) as architecture-directing agent, was investigated in ethanol/water medium by small angle X-ray scattering (SAXS), fluorescence, surface tension and conductivity measurements; the morphology of tungsten oxide obtained from the precursor systems was also characterized by scanning electron microscopy (SEM). PTA/SDS/ethanol/water systems show a two-level organization in which small micelles are aggregated as fractal structures. There is an inverse correlation between gyration radius of the fractal structures of the PTA/SDS systems and particle size of the tungsten oxide films. The interaction of PTA with SDS is observed by reducing the Gibbs energy of micellization; also, it is evidenced that the supressive effect of PTA on pyrene emission is overrided in presence of SDS.

Role of reactive species in the photocatalytic degradation of amaranth by highly active N-doped $$\mathbf{WO}_{\mathbf{3}}$$ WO 3

A novel, highly visible light active N-doped $$\hbox {WO}_{3}$$ ( $$\hbox {N}$$ - $$\hbox {WO}_{3})$$ is successfully synthesized via thermal decomposition of peroxotungstic acid–urea complex. The photocatalytic activity of $$\hbox {N}$$ - $$\hbox {WO}_{3}$$ is evaluated for the degradation of amaranth (AM) dye under visible and UVA light along with the role of reactive species, which has not yet been studied for $$\hbox {N}$$ - $$\hbox {WO}_{3}$$ photocatalysts. Doping of N into substitutional and interstitial sites of $$\hbox {WO}_{3}$$ is confirmed by X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy. At a pH of 7, 1 g $$\hbox {l}^{-1}$$ of $$\hbox {N}$$ - $$\hbox {WO}_{3}$$ can completely degrade $$10\,\hbox {mg } \hbox {l}^{-1}$$ of AM within 1 h under visible and UVA light. For the degradation of AM by $$\hbox {N}$$ - $$\hbox {WO}_{3}$$ under visible and UVA light, $$\hbox {h}^{+}$$ is found to be the main reactive species, while $$\cdot \hbox {OH}$$ contributes to a lesser extent. On the contrary, $$^{1}\hbox {O}_{2}, \cdot \hbox {O}_{2}^{-}$$ and $$\hbox {e}^{-}$$ show negligible roles. The crucial role of $$\hbox {h}^{+}$$ indicates effective suppression of electron–hole recombination after N doping. Dye sensitization and oxidation by reactive species are found to be the major pathway for the degradation of AM under visible and UVA light, respectively.