Dechlorination Of Chlorophenols Research Articles

Far-UVC (UV222) based photolysis, photooxidation, and photoreduction of chlorophenols using a KrCl-excimer lamp: Degradation, dechlorination, and detoxification

The KrCl-excimer lamp, emitting far-UVC light at 222 nm (UV222), offers a promising alternative to conventional UVC light at 254 nm (UV254) for the photolysis of organic pollutants and the activation of radical sensitizers. This study was aimed to investigate the efficiencies of UV222 in the treatment of halogenated aromatics, focusing on its performance in degradation, dechlorination and detoxification. Chlorophenols, representative recalcitrant and toxic halogenated aromatics, were used as target pollutants. The pathways of direct photolysis, photooxidation and photoreduction under UV222 illumination were compared. UV222 outperformed UV254 in photolyzing chlorophenols (1.4−34.1 times faster), especially protonated chlorophenols, due to substantially higher UV absorption (17.1−108.0 times) and quantum yields (2.1−3.4 times). The quantum yields of chlorophenols were influenced by the inducive electron-withdrawing effect of Cl-substitutes. Moreover, UV222 improved the dechlorination of chlorophenols to 95 % compared to 60 % by UV254. The introduction of radical sensitizer (e.g., H2O2, nitrate, and sulfite) reduced 4-chlorophenol photolysis by competing for UV222 absorption, though the sensitizers partially increased radical oxidation via generating •OH or eaq−. UV222 photolysis of 4-chlorophenol increased the toxicity by 88.6 times through forming toxic intermediates (e.g., hydroquinone and resorcinol). Notably, •OH and eaq− (i.e., UV222/H2O2 and UV222/sulfite) increased the dechlorination and •OH (i.e., UV222/H2O2) detoxified the mixture solution. Moreover, UV222 photolysis remained effective for 4-chlorophenol removal in real paper-mill wastewater, indicating the potential application of KrCl* lamp UV222.

Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites.

Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

Modulating adsorption of active hydrogen atoms on palladium nanoparticles: Doping ruthenium into metal–organic frameworks for efficient electrocatalytic hydrodechlorination

To simultaneously optimize the dispersion and electrocatalytic activity of palladium (Pd) nanoparticles, we report a novel Pd-NiRu-MOF/NF composite electrode with low noble metal dosage for electrocatalytic hydrodechlorination. The as-prepared electrode exhibits outstanding activity, particularly the complete dechlorination of 2-chlorophenol within 75 min at −0.85 V, outperforming reported state-of-the-art electrode materials. Moreover, the catalytic activity could be well-maintained after continuous five catalytic cycles and even 30-day exposure to air as well as deliver excellent catalytic performance for other priority chlorophenols. CO-stripping experiments demonstrate that the dispersion of Pd nanoparticles increases the electrochemically active surface area of Pd. X-ray photoelectron spectroscopy and density functional theory analysis disclose that the electronic structure of Pd is modulated via introducing Ru atoms into Pd-Ni-MOF/NF, thereby enhancing the adsorption of H*ads on Pd-NiRu-MOF/NF and boosting the electroreductive remediation of chlorophenols. Notably, the electrochemical dechlorination of chlorophenols remains effective in natural water or soil, indicating that Pd-NiRu-MOF/NF composite electrode has a good application potential in removing organic halides in wastewater or soil.

Impact of different zero valent iron-based particles on anaerobic microbial dechlorination of 2,4-dichlorophenol: Comparison of dechlorination performance and the underlying mechanism

The integration of iron-based materials and anaerobic microbial consortia has been extensively studied owing to its potential to enhance pollutant degradation. However, few studies have compared how different iron materials enhance the dechlorination of chlorophenols in coupled microbial systems. This study systematically compared the combined performances of microbial community (MC) and iron materials (Fe0/FeS2 +MC, S-nZVI+MC, n-ZVI+MC, and nFe/Ni+MC) for the dechlorination of 2,4-dichlorophenol (DCP) as one representative of chlorophenols. DCP dechlorination rate was significantly higher in Fe0/FeS2 +MC and S-nZVI+MC (1.92 and 1.67 times, with no significant difference between two groups) than in nZVI+MC and nFe/Ni+MC (1.29 and 1.25 times, with no significant difference between two groups). Fe0/FeS2 had better performance for the reductive dechlorination process as compared with other three iron-based materials via the consumption of any trace amount of oxygen in anoxic condition and accelerated electron transfer. On the other hand, nFe/Ni could induce different dechlorinating bacteria as compared to other iron materials. The enhanced microbial dechlorination was mainly due to some putative dechlorinating bacteria (Pseudomonas, Azotobacter, Propionibacterium), and due to improved electron transfer of sulfidated iron particles. Therefore, Fe0/FeS2 as a biocompatible as well as low-cost sulfidated material can be a good alternative for possible engineering applications in groundwater remediation.

Electrically Conductive Ni-P Nanoporous Membrane Reactors for Electrochemical Reductive Dechlorination of Organic Pollutants

Transition-metal phosphides (TMPs) are emerging electrocatalysts for both hydrogen evolution and the conversion of reactants/contaminants by various electrochemical reactions. TMPs are promising catalysts because they are earth abundant, have high electrical conductivity, and have high chemical stability. In this seminal work, a low-priced nickel phosphorus (Ni-P) ultrafiltration membrane was fabricated and used for electrochemical reductive dechlorination of chlorophenols. Amorphous Ni-P nanoparticles were grown on an ultrafiltration poly(ether sulfone) (PES) membrane via electroless deposition. The prepared Ni-P membrane was used as a cathode for electrochemical reductive dechlorination of 2-chlorophenol (2-CP) in flow-through mode. It was observed that a dechlorination efficiency of 42.7%, a reaction rate constant of 1.621 min–1, and a Faradaic efficiency of 24.5% were achieved at an optimized cathodic potential of −2.50 V. The dechlorination was primarily attributed to the partial positively charged Niδ+ on the Ni-P membrane surface, which facilitated atomic H* evolution by forming reactive Ni–H* bonds for dechlorination. Additionally, doping P atoms in Ni retarded the deactivation of electrocatalytic Ni sites. This work demonstrates that the cost-effective Ni-P membrane electrocatalyst is a promising technology to degrade chlorinated compounds with applications to industrial wastewaters and landfill leachates.

Complete pentachlorophenol biodegradation in a dual-working electrode bioelectrochemical system: Performance and functional microorganism identification

Bioelectrochemical system (BES) can effectively promote the reductive dechlorination of chlorophenols (CPs). However, the complete degradation of CPs with sequential dechlorination and mineralization processes has rarely achieved from the BES. Here, a dual-working electrode BES was constructed and applied for the complete degradation of pentachlorophenol (PCP). Combined with DNA-stable isotope probing (DNA-SIP), the biofilms attached on the anodic and cathodic electrode in the BES were analyzed to explore the dechlorinating and mineralizing microorganisms. Results showed that PCP removal efficiency in the dual-working BES (84% for 21 days) was 4.1 and 4.7 times higher than those of conventional BESs with a single anodic or cathodic working electrode, respectively. Based on DNA-SIP and high-throughput sequencing analysis, the cathodic working electrode harbored the potential dechlorinators (Comamonas, Pseudomonas, Methylobacillus, and Dechlorosoma), and the anodic working enriched the potential intermediate mineralizing bacteria (Comamonas, Stenotrophomonas, and Geobacter), indicating that PCP could be completely degraded under the synergetic effect of these functional microorganisms. Besides, the potential autotrophic functional bacteria that might be involved in the PCP dechlorination were also identified by SIP labeled with 13C-NaHCO3. Our results proved that the dual-working BES could accelerate the complete degradation of PCP and enrich separately the functional microbial consortium for the PCP dechlorination and mineralization, which has broad potential for bioelectrochemical techniques in the treatment of wastewater contaminated with CPs or other halogenated organic compounds.

Studies on the inhibition of methanogenesis and dechlorination by (4-hydroxyphenyl) chloromethanesulfonate.

The purpose of this study was to demonstrate the inhibitory effect of chemicals on methane emissions in paddy soil. We found that (4-hydroxyphenyl) chloromethanesulfonate (C-1) has a methanogenic inhibition activity, and we studied its inhibition mechanism using laboratory tests. The study found that C-1 treatment of flooded soil did not significantly affect the bacterial community but rather the archaeal community; particularly, Methanosarcina spp. C-1 strongly inhibited the aceticlastic methanogenesis route. It was suggested that the inhibitory target of C-1 was different from the well-known methanogenic inhibitor 2-bromoethanesulfonate, which targets methyl-coenzyme M reductase of methanogen. In addition, C-1 had a secondary effect of inhibiting the dechlorination of chlorophenols. Although field trials are required as the next development step, C-1 can be used to reduce methane emissions from paddy fields, one of the largest sources in the agricultural sector.

Resource-Efficient Low-Temperature Synthesis of Microcrystalline Pb2 B5 O9 X (X = Cl, Br) for Surfaces Studies by Optical Second Harmonic Generation.

Optically nonlinear Pb2 B5 O9 X (X = Cl, Br) borate halides are an important group of materials for second harmonic generation (SHG). Additionally, they also possess excellent photocatalytic activity and stability in the process of dechlorination of chlorophenols, which are typical persistent organic pollutants. It would be of great interest to conduct in situ (photo-) catalysis investigations during the whole photocatalytic process by SHG when considering them as photocatalytic materials. In order to get superior photocatalytic efficiency and maximum surface information, small particles are highly desired. Here, a low-cost and fast synthesis route that allows growing microcrystalline optically nonlinear Pb2 B5 O9 X borate halides at large quantities is introduced. When applying the ionothermal growth process at temperatures between 130 and 170 °C, microcrystallites with an average size of about 1 µm precipitate with an orthorhombic hilgardite-like borate halide structure. Thorough examinations using powder X-ray diffraction and scanning electron microscopy, the Pb2 B5 O9 X microcrystals are indicated to be chemically pure and single-phased. Besides, the Pb2 B5 O9 X borate halides' SHG efficiencies are confirmed using confocal SHG microscopy. The low-temperature synthesis route thus makes these borate halides a highly desirable material for surface studies such as monitoring chemical reactions with picosecond time resolution and in situ (photo-) catalysis investigations.

Electrocatalytic dechlorination of chlorophenols on palladium/graphene-Nafion/titanium mesh electrode

The electrocatalytic dechlorination of 3,5-dichlorophenol (3,5-DCP) and 2,3,5-trichlorophenol (2,3,5-TCP) on palladium/graphene-Nafion/titanium mesh electrode (Pd/rGO-Nafion/Ti electrode) was studied. The preparation conditions of Pd/rGO-Nafion/Ti electrode were investigated by electrochemical workstation, and the results showed that the addition of the graphene-Nafion middle layer could improve the electrocatalytic ability. The Pd/rGO-Nafion/Ti electrode was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The influences of dechlorination current and initial pH value of reaction solution on the conversion efficiency and the current efficiency of dechlorination on Pd/rGO-Nafion/Ti electrode were investigated. Complete dechlorination of 3,5-DCP and 2,3,5-TCP could be achieved within 90 min under initial pH of 2.3 and current of 5 mA. The dechlorination intermediate products of 3,5-DCP and 2,3,5-TCP were detected and the dechlorination pathways were inferred. The kinetics results revealed that the dechlorination of 3,5-DCP and 2,3,5-TCP followed a two-stage mixed order kinetics.

Comparative studies on the oxidative dechlorination of chlorophenols by a superoxide complex

The chlorophenols (CPs), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), are potent environmental hazards. They can be dechlorinated to safer products by reacting them with the Co(III)-bound superoxo complex [(NH3)5Co(µ-O2)Co(NH3)5]5+ (1). In acidic media, the redox reactions between 1 and all three CPs follow a first-order process and the observed rate constant ko values increase with increasing concentrations of CPs and pH of the medium. Our observations suggest that the deprotonated forms of the CPs are ~ 105 times more reactive than the protonated forms, and the reactions proceed via a common free radical mechanism. Initially, the CP molecules undergo 2-e− oxidations by complex 1 to generate phenolic radicals, which then form unstable quinones. Through the aromatic ring opening, the latter intermediates finally degrade to different products. The reactivity order for these CPs is 4-CP ≈ 2,4,6-TCP > 2,4-DCP.

Promotion of Para-Chlorophenol Reduction and Extracellular Electron Transfer in an Anaerobic System at the Presence of Iron-Oxides.

Anaerobic dechlorination of chlorophenols often subjects to their toxicity and recalcitrance, presenting low loading rate and poor degradation efficiency. In this study, in order to accelerate p-chlorophenol (p-CP) reduction and extracellular electron transfer in an anaerobic system, three iron-oxide nanoparticles, namely hematite, magnetite and ferrihydrite, were coupled into an anaerobic system, with the performance and underlying role of iron-oxide nanoparticles elucidated. The reductive dechlorination of p-CP was notably improved in the anaerobic systems coupled by hematite and magnetite, although ferrihydrite did not plays a positive role. Enhanced dechlorination of p-CP in hematite or magnetite coupled anaerobic system was linked to the obvious accumulation of acetate, lower oxidation–reduction potential and pH, which were beneficial for reductive dechlorination. Electron transfer could be enhanced by Fe2+/Fe3+ redox couple on the iron oxides surface formed through dissimilatory iron-reduction. This study demonstrated that the coupling of iron-oxide nanoparticles such as hematite and magnetite could be a promising alternative to the conventional anaerobic reduction process for the removal of CPs from wastewater.

Exploring the Origin of High Dechlorination Activity in Polar Materials M2B5O9Cl (M = Ca, Sr, Ba, Pb) with Built-In Electric Field

Polar photocatalyst materials usually exhibit ferroelectric characteristics giving rise to spontaneous polarization behavior which works as a driving force for the separation of photogenerated electrons and holes and mitigates the effect of charge recombination. This study shows that the surface potential changes for a polar phtotocatalyst before and after photoirradiation can be used to predict the photocatalytic activities among different phtotocatalysts. We systematically investigated the correlation among the surface properties, crystal structure, electronic band structure, photocatalytic activity, and stability of four B–O and alkaline earth cations containing photocatalysts, M2B5O9Cl (M = Ca, Sr, Ba, Pb). Among the four studied photocatalysts, Ba2B5O9Cl exhibits the greatest changes in the surface potential after photoirradiation and also shows the highest photocatalytic activity for dechlorination of chlorophenols under UV light irradiation. Its photocatalytic activity is about 1.3, 2.8, 4.4, and 1...

A Bulk Boron-Based Photocatalyst for Efficient Dechlorination: K3B6O10Br

Nanoparticles of a borate nonlinear optical material, K3B6O10Br (KBB), have been fabricated and demonstrated excellent catalytic activity in UV-induced dechlorination of chlorophenols, which are typical persistent organic pollutants. The obtained dechlorination efficiency is 2 orders of magnitude higher than that of a commercial P25 TiO2 catalyst under UV (λ > 254 nm) light irradiation. The noncentrosymmetric structure of KBB gives rise to an intrinsic large polarization effect as evidenced by Kelvin probe force microscopy, and the polarization promotes separation of photogenerated electron–hole pairs, leading to efficient cleavage of chlorophenols into small molecular fragments and dissociative Cl– anions. This work suggests that nonlinear materials open a new window for designing efficient photocatalysts.

Highly dispersive PdCoB catalysts for dechlorination of chlorophenols

Highly dispersive PdCoB nano-particles were prepared by precipitation–reduction with NaBH4 at 273K. Characterization showed that the dispersion of amorphous alloy PdCoB nano-particles increased with decrease in both Pd/Co ratio and preparation temperature. The size of PdCoB-L(273) (Pd/Co ratio of 0.0005) nano-particles prepared at 273K was 5nm and BET specific surface area was estimated to be 177m2/g, much higher than those of bimetallic catalysts reported in literature. During the hydrodechlorination of 4-chlorophenol, PdCoB catalysts were effective within pH range from 2.5 to 11. The activity of PdCoB can be promoted by the increase in B/Co ratio on the surface. PdCoB-L(273) sample presented the highest efficiency, and the reaction constants described in different terms for 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were much higher than those obtained over PdFe in literature, probably ascribed to smaller particle sizes, less agglomerations and strong synergistic effect between Pd, Co and B species.

Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solid electrode

Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solidelectrode was studied. As solid electrodes, carbon cloth (CC), carbon felt (CF) and titanium mesh were used, and palladium was plated on solid electrodes by either electrolytic or electroless method. On each electrode with Pd, chlorophenols were qualitatively dechlorinated to phenol, while they were entirely intact on electrodes without Pd. Moreover, neither base electrode nor plating method significantly affected the activity of Pd as far as it was sufficiently loaded on the electrode. Based on the results in the experiments using one electrode repeatedly, Pd catalyst proved to possess a satisfactory duarability under the present condition. It was suggested that the reactive species responsinble for the dechlorination of chlorophenols could be formed during preliminary electrolysis. Thus, (Pd)x-H resulting from the adsorption of electrogenerated hydrogen on metallic Pd might be assumed most probable.

Chlorophenols breakdown by a sequential hydrodechlorination-oxidation treatment with a magnetic Pd–Fe/γ-Al2O3 catalyst

Degradation of chlorophenols by a sequential combination of hydrodechlorination (HDC) and catalytic wet peroxide oxidation (CWPO) using a new magnetic Pd–Fe/γ-Al2O3 catalyst has been studied. This catalyst is active in both hydrodechlorination of chlorophenols and decomposition of H2O2 for the oxidation of organic compounds. The sequential combination of HDC and CWPO allows overcoming some of the drawbacks of both treatments applied independently. The HDC step achieves the complete dechlorination of chlorophenols, so that the subsequent CWPO does not lead to the formation of highly toxic chlorinated by-products and reduces significantly the organic load of the effluent. The results showed that the presence of iron in the Pd catalyst improved significantly its hydrodechlorination rate, achieving the complete dechlorination of chlorophenols in a short reaction time (≈15 min), giving rise to phenol and cyclohexanone. The CWPO of synthetic mixtures of phenol and cyclohexanone showed that a high phenol concentration promotes the oxidation of all the organic species, but the presence of cyclohexanone seems to hinder the formation of aromatic radicals limiting the effectiveness of the CWPO step. Therefore, the effective combination of HDC and CWPO requires that the HDC step achieves the complete dechlorination of chlorophenols but no further hydrogenation is needed. The Pd–Fe/γ-Al2O3 catalyst showed a high activity in both HDC and subsequent CWPO of chlorophenols being easily separated and recovered from the reaction medium due to its ferromagnetic properties. In spite of a moderate loss of activity, the complete dechlorination of chlorophenol and a negligible ecotoxicity of the final effluents were maintained upon successive applications of HDC + CWPO in a four-cycles test.

Enhanced reduction of chlorophenols by nanoscale zerovalent iron supported on organobentonite

The reactivity of nanoscale zerovalent iron (NZVI) on removing chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) was remarkably enhanced by using a hydrophobic support of organobentonite (CTMA-Bent), namely the bentonite modified with organic cetyltrimethylammonium (CTMA) cations. The complete dechlorination of chlorophenols and total conversion into phenol using this novel NZVI/CTMA-Bent combination was observed in batch experiments. The kinetic studies suggested that the reduction of chlorophenols by NZVI was accelerated due to the enhanced adsorption onto CTMA-Bent, which facilitated the mass transfer of chlorophenols from aqueous to iron surface. The enhanced reduction rate by NZVI/CTMA-Bent was positively related to the hydrophobicity of chlorophenols, and an increasing linear relationship was obtained between the relative enhancement on reaction rate constants (k2/k1) and logKow values of chlorophenols. XPS results suggested there were fewer precipitates of ferric (hydro)xides formed on the surface of NZVI/CTMA-Bent, which may also lead to the improved reactivity and repetitive usability of NZVI/CTMA-Bent on removing chlorophenols.

Dechlorination of chlorophenols by zero valent iron impregnated silica

AbstractLaboratory studies were conducted to find out the efficacy of uniquely prepared zero valent iron impregnated silica in transforming xenobiotic chlorophenols namely 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol. Continuous mode column experiments were performed to investigate the transformation of chlorophenols by varying pH, column height, flow rate and initial chlorophenol concentration. Reusability study of the zero valent iron impregnated silica was studied as well as the morphological changes and the chemical composition of the catalyst medium were also investigated. Dechlorination kinetic studies were conducted and the order of dechlorination of chlorophenols was found to be 2,4,6-trichlorophenol > 2,4-dichlorophenol > 4-chlorophenol. The optimum pH, column height and flow rate were found to be 7, 20 cm and 0.75 L/hr respectively for all chlorophenols in the reaction duration of 4 hr. Intermediates formed during dechlorination study were identified by gas chromatography-mass spectroscopy analysis. This method was applied to real pulp and paper wastewater and was found satisfactory.

Rapid dechlorination of chlorophenols in aqueous solution by [Ni|Cu] microcell

The [Ni|Cu] microcell was prepared by mixing the Ni0 and Cu0 particles. The composition and crystal form were characterized by X-ray diffraction (XRD) and scanning electron microscope. The results evidenced the zero-valence metals Ni and Cu were exposed on the surface of particles mixture. The [Ni|Cu] microcell was employed to decompose chlorophenols in aqueous solution by reductive dechlorination. The dechlorination rates of chlorophenols by [Ni|Cu] were >10 times faster than those by [Fe|Cu], [Zn|Cu], [Sn|Cu], and [Fe|Ni] mixtures under the same conditions. [Ni|Cu] is different from other zero valent metals (ZVMs) in that it performed the best at neutral pH. The main products of chlorophenol dechlorination were cyclohexanol and cyclohexanone. The reduction kinetics was between pseudo zero-order and first-order, depending on the pH, concentration, and temperature. These results, combined with electrochemical analysis, suggested that Ni0 acted as a reductant and catalyst in dechlorination reaction. The H* corridor mechanism from Ni0 to Cu0 was also proposed based on hydrogen spillover. The inhibition on the release of Ni2+ by adding natural organic matters and adjusting pH was investigated.

Phosphorous-Modified TiO2 with Excellent Thermal Stability and Its Application to the Degradation of Pollutants in Water

The phosphorous-modified TiO 2 (P-TiO 2 ) was synthesized by a hydrothermal method. The as-prepared P-TiO 2 was evaluated for the degradation of methylene blue, the dechlorination of 4-chlorophenol, and the inactivation of Escherichia coli . In all these experiments, P-TiO 2 shows superior activity compared with pure TiO 2 and even better activity than the commercially available P25 in most cases. By carrying out methylene blue degradation in the presence of different scavengers, ·OH radicals were found to be the dominant reactive oxidizing species. The excellent performance of P-TiO 2 was correlated with its pronounced ability to generate ·OH radicals under illumination. We also found that P-TiO 2 is extraordinarily stable against annealing. Its transformation from anatase to rutile does not occur until calcination as high as 950 °C. This phase transformation is retarded since the phosphate species on the surface of the particles acts as a barrier to grain boundary nucleation. This peculiar feature of P-TiO 2 gives it reliable performance during water decontamination even after calcination at 900 °C since it retains a 100% anatase phase at this stage.