Phenol Degradation Pathway Research Articles

One-pot synthesis of N-doped graphene for metal-free advanced oxidation processes

Recently, graphene and its derivatives as novel metal-free materials have attracted considerable attention in environmental remediation technologies. One of the barriers to practical applications is the mass production of high quality graphene-based catalysts. In this study, high-quality nitrogen-doped graphene (NG) nanomaterials were synthesized by controlled pyrolysis of a mixture of glucose, ferric chloride and urea. Glucose serves as a carbon precursor, urea as a nitrogen precursor, and hexahydrate ferric chloride as both a template and a catalyst. It was found that a low oxygen level of 2–4 at% and a nitrogen doping level of 0.5–1.8 at% were achieved at a moderate temperature. The obtained nitrogen-doped graphene was employed as a metal-free catalyst for efficient phenol degradation by peroxymonosulfate (PMS) activation. Kinetic studies showed that the phenol degradation facilitated by NG catalysis followed first-order reaction kinetics. Electron paramagnetic resonance (EPR) was performed to detect radical generation in order to reveal the mechanism of PMS activation processes and phenol degradation pathways on nanocarbons. It was found that both •OH and SO4•− were produced in the catalytic oxidation processes and played significant roles in phenol oxidation.

Phenol degradation mechanism by electrooxidation using stainless steel electrodes

The pathway of phenol degradation by electrochemical oxidation was studied in an aqueous solution using AISI 304 stainless steel electrodes. The increase in pH due to the generation of NaOH in the aqueous solution was found to be critical for the proposed degradation mechanism since the deprotonation of phenol occurs at pH 10. The phenoxy anion produced as a result of deprotonation is resonance stabilized. The Fe+3 ions (Lewis catalyst) released from the stainless steel anode and the chlorine gas formed by the electrolysis of sodium chloride are found to be responsible for the chlorination of phenoxy anion ensuing the formation of 2-, 4-, 6-substituted chlorophenols. The mechanism was proposed for elucidating the possible degradation pathway of phenol under the above specified conditions.

Characterization of phenol and cresol biodegradation by compound-specific stable isotope analysis

Microbial degradation of phenol and cresols can occur under oxic and anoxic conditions by different degradation pathways. One recent technique to take insight into reaction mechanisms is compound-specific isotope analysis (CSIA). While enzymes and reaction mechanisms of several degradation pathways have been characterized in (bio)chemical studies, associated isotope fractionation patterns have been rarely reported, possibly due to constraints in current analytical methods. In this study, carbon enrichment factors and apparent kinetic isotope effects (AKIEc) of the initial steps of different aerobic and anaerobic phenol and cresols degradation pathways were analyzed by isotope ratio mass spectrometry connected with liquid chromatography (LC-IRMS). Significant isotope fractionation was detected for aerobic ring hydroxylation, anoxic side chain hydroxylation, and anoxic fumarate addition, while anoxic carboxylation reactions produced small and inconsistent fractionation. The results suggest that several microbial degradation pathways of phenol and cresols are detectable in the environment by CSIA.

Assessment of phenol-degrading ability of Acinetobacter sp. B9 for its application in bioremediation of phenol-contaminated industrial effluents

Successful bioremediation of a phenol-contaminated environment requires application of those microbial strains that have acquired phenol tolerance and phenol-degrading abilities. A newly isolated strain B9 of Acinetobacter sp. was adapted to a high phenol concentration by growing sequentially from low- to high-strength phenol. The acclimatised strain was able to grow and completely degrade up to 14 mM of phenol in 136 h. The degradation rates were found to increase with an increase in the phenol concentration from 2.0 to 7.5 mM. The strain preferred neutral to alkaline pH range for growth and phenol degradation, with the optimum being pH 8.0. The optimum temperature for phenol degradation was found to be in the range of 30–35°C. Transmission electron micrographs showed a disorganised and convoluted cell membrane in the case of phenol-stressed cells, showing a major effect of phenol on the membrane. Enzymatic and gas chromatography-mass spectrometry studies show the presence of an ortho-cleavage pathway for phenol degradation. Efficient phenol degradation was observed even in the presence of pyridine and heavy metals as co-toxicants showing the potential of strain in bioremediation of industrial wastes. Application of strain B9 to real tannery wastewater showed 100% removal of initial 0.5 mM phenol within 48 h of treatment.

Biodegradation of phenol by a novel diatom BD1IITG-kinetics and biochemical studies

A phenol-degrading novel diatom BD1IITG was isolated from petroleum refinery wastewater and characterized (GenBank Accession No. KJOO2533). HPLC analysis showed the diatom could degrade phenol in the concentration range of 50–250 mg/l in Fog’s media. The highest specific growth and degradation rate were achieved at 100 mg/l phenol. It could also mineralize phenol along with aliphatics in petroleum refinery wastewater. Growth kinetic modeling shows that Haldane model best represents the growth behavior of the diatom in nutrient media as well as refinery wastewater. Biokinetic parameters suggest that the diatom possesses higher maximum specific growth rate (µ max = 0.4 day−1), better tolerance to toxicity (K I = 90.24 mg/l) and high phenol affinity (K s = 20.99 mg/l) in refinery wastewater as compared to Fog’s media confirming practical applicability of the strain for wastewater treatment. FTIR fingerprinting of biomass indicates intercellular phenol uptake and breakdown into its intermediates via phenol degradation pathway. Pathway was elucidated using HPLC, LC–MS and UV–visible spectrophotometry confirming prominence of ortho- over meta pathway for phenol metabolism. The diatom produces biosurfactant with highest emulsifying activity at 100 mg/l phenol which may contribute to highest degradation rate at this concentration. Infrared analysis confirms increased biosynthesis of lipids and polysaccharides in phenol-degrading biomass, indicating its potential use as feedstock of clean ecofriendly energy sources as biodiesel or bioethanol. The phenol degradation capability coupled with potential applicability of the spent biomass as biofuel feedstock makes diatom BD1IITG a potential candidate for a clean environmentally sustainable process.

A Comprehensive Study on Chlorella pyrenoidosa for Phenol Degradation and its Potential Applicability as Biodiesel Feedstock and Animal Feed.

The present work evaluates the phenol degradative performance of microalgae Chlorella pyrenoidosa. High-performance liquid chromatography (HPLC) analysis showed that C. pyrenoidosa degrades phenol completely up to 200 mg/l. It could also metabolize phenol in refinery wastewater. Biokinetic parameters obtained are the following: growth kinetics, μ max (media) > μ max (refinery wastewater), K s(media) < K s(refinery wastewater), K I(media) > K I(refinery wastewater); degradation kinetics, q max (media) > q max (refinery wastewater), K s(media) < K s(refinery wastewater), K I(media) > K I(refinery wastewater). The microalgae could cometabolize the alkane components present in refinery wastewater. Fourier transform infrared (FTIR) fingerprinting of biomass indicates intercellular phenol uptake and breakdown into its intermediates. Phenol was metabolized as an organic carbon source leading to higher specific growth rate of biomass. Phenol degradation pathway was elucidated using HPLC, liquid chromatography-mass spectrometry (LC-MS) and ultraviolet-visible (UV-visible) spectrophotometry. It involved both ortho- and meta-pathway with prominence of ortho-pathway. SEM analysis shows that cell membrane gets wrinkled on phenol exposure. Phenol degradation was growth and photodependent. Infrared analysis shows increased intracellular accumulation of neutral lipids opening possibility for utilization of spent biomass as biodiesel feedstock. The biomass after lipid extraction could be used as protein supplement in animal feed owing to enhanced protein content. The phenol remediation ability coupled with potential applicability of the spent biomass as biofuel feedstock and animal feed makes it a potential candidate for an environmentally sustainable process.

Degradation kinetics and pathway of phenol by Pseudomonas and Bacillus species

This article elucidates that strain Pseudomonas aeruginosa (IES-Ps-1) is a versatile toxic organic compound degrader. With the degradation of malathion and cypermethrin (studied by other researchers previously), this strain was able to degrade phenol. Two other indigenous soil flora (i.e., Pseudomonas sp. (IES-S) and Bacillus subtilis (IES-B)) were also found to be potential phenol degraders.Phenol was degraded with Monod kinetics during growth in nutrient broth and mineral salts medium. Before entering into the growth inhibition phase, strains IES-Ps-1, IES-S and IES-B could tolerate up to 400, 700 and 500 mg/L phenol, respectively, when contained in nutrient broth. However, according to the Luong–Levenspiel model, the growth of strains IES-Ps-1, IES-S and IES-B would cease at 2000, 2174 and 2190 mg/L phenol, respectively. Strain IES-Ps-1 degraded 700, 900 and 1050 mg/L phenol contained in mineral salts medium with the specific rates of 0.034, 0.075 and 0.021 h−1, respectively. All these strains grew by making clusters when exposed to phenol in order to prevent damages due to high substrate concentration. These strains transformed phenol into catechol, which was then degraded via ortho-cleavage pathway.

Isolation and Genetic Characterization of Phenol-Utilizing Marine Bacteria and Their Phenol Degradation Pathway

Phenolic compounds are widely distributed toxic pollutants in seawater, and their effective degradation is very important for bioremediation programs. In this study, nine phenol-degrading bacteria were isolated from seawater samples, which were collected from the coastal areas of Japan. Besides the enrichment substrate phenol, all isolates could utilize at least one isomer of cresol as the sole source of carbon. A 16S rRNA gene sequence analysis indicated that all strains were affiliated with the class Gammaproteobacteria, four strains were closely related to Spongiibacter, four were closely related to Marinobacter, and one was closely related to Photobacterium. During growth on phenol, all isolates produced a yellow product, and a whole-cell study indicated that it was an extradiol meta-ring cleavage product of catechol, 2-hydroxymuconate semialdehyde. Phylogenetic analysis revealed that the partial gene encoding the largest subunit of the multicomponent phenol hydroxylase of the isolates was similar to that of terrestrial bacteria, thereby suggesting that phenol is converted into catechol by marine bacteria. We also suggest that horizontal transfer of the gene may occur not only among marine bacteria but also between the genera Marinobacter and Pseudomonas.

New insights into heterogeneous generation and evolution processes of sulfate radicals for phenol degradation over one-dimensional α-MnO2 nanostructures

Heterogeneous activation of peroxymonosulfate (PMS) has become an attractive approach for catalytic oxidation since it can not only provide sulfate radicals as an alternative to hydroxyl radicals, but also avoid the metal toxicity in homogeneous catalysis. In this study, three one-dimensional (1D) α-MnO2 nanostructures, nanorods, nanotubes and nanowires, were fabricated by a one-pot hydrothermal method without addition of any surfactants. Shape-dependent performance of 1D α-MnO2 was observed in catalytic degradation of phenol solutions. The phenol oxidation can be described by a first-order kinetic model and the activation energies of phenol oxidation on three α-MnO2 materials were estimated to be 20.3, 39.3 and 87.1kJ/mol on nanowires, nanorods, and nanotubes, respectively. Both electron paramagnetic resonance (EPR) spectra and competitive radical tests were applied to investigate the PMS activation processes and to differentiate the major reactive species dominating the catalytic oxidation. The processes of PMS activation, evolution of sulfate radicals, and phenol degradation pathways were clearly illustrated.

Phenol degradation studies using microbial consortium isolated from environmental sources

A microbial consortium consisting of five phenol-degrading strains was developed. The consortium could degrade 99% of 1000mgl−1 phenol after 72h incubation with a biomass increase of 2.6×107 to 4×1012CFUml−1. Characterization of the members revealed that consortium consisted of Candida tropicalis (1.2×105CFUml−1), Aspergillus fumigatus (1.1×105CFUml−1), Candida albicans (3.0×103CFUml−1), Candida haemulonis (2.6×103CFUml−1) and Streptomyces alboflavus (1.1×105CFUml−1). Performance of consortium was accessed by specific growth rate (μ) and yield coefficient (Yx/s). The consortium exhibited activity of phenol hydroxylase and catechol 1,2-dioxygenase suggesting that members in consortium followed ortho pathway for phenol degradation. Response surface methodology (RSM) has been adopted to evaluate the effect of different parameter such as initial phenol concentration, temperature, pH and time on phenol degradation. The maximum percentage of phenol degradation is observed at optimized value of process variables such as initial concentration 1000mgl−1, temperature 35°C, pH 7 and incubation time of 96h.

Efficacy of Acinetobacter sp. B9 for simultaneous removal of phenol and hexavalent chromium from co-contaminated system.

The present study shows the feasibility of a newly isolated strain Acinetobacter sp. B9 for concurrent removal of phenol and Cr (VI) from wastewater. The experiments were conducted in a batch reactor under aerobic conditions. Initially, when mineral salt solution was used as the culture medium, the strain was found to utilize phenol as sole carbon and energy source while no Cr (VI) removal was observed. However, the addition of glucose as co-carbon source resulted in the removal of both toxicants. This co-removal efficiency of the strain was further improved with nutrient-rich media (NB). Optimum co-removal was determined at 188 mg L(-1) of phenol and 3.5 mg L(-1) of Cr (VI) concentrations at pH 7.0. Strain B9 followed the orthometabolic pathway for phenol degradation. Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) studies showed sorption of chromium as one of the major mechanisms for Cr (VI) removal by B9 cells. Acinetobacter sp. B9 was later on checked for bioremediation of real tannery wastewater. After 96 h of batch treatment of tannery effluent containing an initial 47 mg L(-1) phenol and 16 mg L(-1) Cr (VI), complete removal of phenol and 87 % reduction of Cr (VI) were attained, showing high efficiency of the bacterial strain for potential application in industrial pollution control.

Induction and carbon catabolite repression of phenol degradation genes in Rhodococcus erythropolis and Rhodococcus jostii.

Rhodococcus erythropolis CCM2595 is able to efficiently utilize phenol and other aromatic compounds. We cloned and sequenced its complete gene cluster - catA, catB, catC, catR, pheR, pheA2, pheA1 - involved in the ortho-cleavage pathway of phenol. The activity of the key enzyme of the phenol degradation pathway, two-component phenol hydroxylase, was found to be induced by phenol. When both phenol and succinate were present in the medium, phenol hydroxylase activity decreased substantially. To analyze the regulation of phenol degradation at the transcriptional level, the transcriptional fusions of the divergently oriented promoters PpheA2 and PpheR with the gfpuv reporter gene were constructed. The promoters driving expression of the genes of the pheR-pheA2pheA1 cluster were localized by determining the respective transcriptional start points. Measurements of GFP fluorescence as well as quantitative RT-PCR revealed that expression of the phe genes is induced by phenol at the transcriptional level. The transcription of pheA2A1 and pheR was repressed by succinate, whereas no repression by glucose or glycerol was observed. Activation of the R. erythropolis CCM2595 pheA2 promoter by PheR, an AraC-type transcriptional regulator, was demonstrated by overexpression of the pheR gene. Analysis of the transcriptional regulation of two similar phe clusters from R. jostii RHA1 by various substrates showed that the type of carbon catabolite repression and the temporal transcriptional pattern during cultivation are different in each of the three phe clusters analyzed.

Biochemical, transcriptional and translational evidences of the phenol-meta-degradation pathway by the hyperthermophilic Sulfolobus solfataricus 98/2.

Phenol is a widespread pollutant and a model molecule to study the biodegradation of monoaromatic compounds. After a first oxidation step leading to catechol in mesophilic and thermophilic microorganisms, two main routes have been identified depending on the cleavage of the aromatic ring: ortho involving a catechol 1,2 dioxygenase (C12D) and meta involving a catechol 2,3 dioxygenase (C23D). Our work aimed at elucidating the phenol-degradation pathway in the hyperthermophilic archaea Sulfolobus solfataricus 98/2. For this purpose, the strain was cultivated in a fermentor under different substrate and oxygenation conditions. Indeed, reducing dissolved-oxygen concentration allowed slowing down phenol catabolism (specific growth and phenol-consumption rates dropped 55% and 39%, respectively) and thus, evidencing intermediate accumulations in the broth. HPLC/Diode Array Detector and LC-MS analyses on culture samples at low dissolved-oxygen concentration (DOC = 0.06 mg.L−1) suggested, apart for catechol, the presence of 2-hydroxymuconic acid, 4-oxalocrotonate and 4-hydroxy-2-oxovalerate, three intermediates of the meta route. RT-PCR analysis on oxygenase-coding genes of S. solfataricus 98/2 showed that the gene coding for the C23D was expressed only on phenol. In 2D-DIGE/MALDI-TOF analysis, the C23D was found and identified only on phenol. This set of results allowed us concluding that S. solfataricus 98/2 degrade phenol through the meta route.

Response of low-strength phenol-acclimated activated sludge to shock loading of high phenol concentrations

(ii) investigate the degradation pathways and (iii) model the growth and biodegradation kinetics, all under the condition of increasingly higher phenol concentrations (step-up shock loading). With the use of activated sludge acclimated to phenol concentration of 140 mg∙l−1 (low-strength phenol-acclimated activated sludge), complete degradation of phenol with a COD removal efficiency of more than 95% was achieved up to 1 050 mg∙l −1 of initial phenol concentration. At low initial phenol concentrations, the experimental results were indicative of the meta-cleavage pathway for phenol degradation. When the initial phenol concentration was above 630 mg∙l −1 , the degradation results were indicative of both meta- and ortho-cleavage pathways. The values of the Haldane kinetic parameters indicated a low degree of inhibition exerted by the presence of increasing phenol concentration. This was substantiated by the observation that the rate constant of phenol removal decreased by only 33% even though the initial phenol concentration was increased by 15 times from 70 to 1 050 mg∙l −1 . Thus, the activated sludge acclimated to only 140 mg∙l −1 of phenol could successfully treat up to 1 050 mg∙l −1 of phenol without experiencing complete inhibition during the degradation process. Keywords: Phenol removal, low-strength phenol-acclimated activated sludge, degradation pathway, Haldane kinetic parameter

Characterization and genomic analysis of kraft lignin biodegradation by the beta-proteobacterium Cupriavidus basilensis B-8

BackgroundLignin materials are abundant and among the most important potential sources for biofuel production. Development of an efficient lignin degradation process has considerable potential for the production of a variety of chemicals, including bioethanol. However, lignin degradation using current methods is inefficient. Given their immense environmental adaptability and biochemical versatility, bacterial could be used as a valuable tool for the rapid degradation of lignin. Kraft lignin (KL) is a polymer by-product of the pulp and paper industry resulting from alkaline sulfide treatment of lignocellulose, and it has been widely used for lignin-related studies.ResultsBeta-proteobacterium Cupriavidus basilensis B-8 isolated from erosive bamboo slips displayed substantial KL degradation capability. With initial concentrations of 0.5–6 g L-1, at least 31.3% KL could be degraded in 7 days. The maximum degradation rate was 44.4% at the initial concentration of 2 g L-1. The optimum pH and temperature for KL degradation were 7.0 and 30°C, respectively. Manganese peroxidase (MnP) and laccase (Lac) demonstrated their greatest level of activity, 1685.3 U L-1 and 815.6 U L-1, at the third and fourth days, respectively. Many small molecule intermediates were formed during the process of KL degradation, as determined using GC-MS analysis. In order to perform metabolic reconstruction of lignin degradation in this bacterium, a draft genome sequence for C. basilensis B-8 was generated. Genomic analysis focused on the catabolic potential of this bacterium against several lignin-derived compounds. These analyses together with sequence comparisons predicted the existence of three major metabolic pathways: β-ketoadipate, phenol degradation, and gentisate pathways.ConclusionThese results confirmed the capability of C. basilensis B-8 to promote KL degradation. Whole genomic sequencing and systematic analysis of the C. basilensis B-8 genome identified degradation steps and intermediates from this bacterial-mediated KL degradation method. Our findings provide a theoretical basis for research into the mechanisms of lignin degradation as well as a practical basis for biofuel production using lignin materials.

Proteome Analysis of Phenol-Degrading Achromobacter sp. Strain C-1, Isolated from an Industrial Area

This paper reports the successful isolation and characterization of a new phenol-degrading bacterium, Achromobacter sp. strain C-1, from an industrial area (Cubatão, Brazil). Achromobacter sp. is a non-motile, strictly aerobic, gram-negative, short-rod or coccobacillary bacterium, which can occur singly, in pairs or in clusters. 16S rRNA gene sequence analysis revealed that Achromobacter sp. strain C-1 belongs to the gamma group of Proteobacteria, with 99% similarity to 16S rRNA gene sequences of Achromobacter xylosoxidans. Strain C-1 can grow aerobically on a number of aromatic compounds, such as phenol, catechol, m-cresol and o-cresol. In particular, it can degrade up to 600 mg/L of phenol at 37°C. In order to understand the phenol degradation pathway used by strain C-1, phenol or glucose cultured C-1 proteomes were comparatively analyzed with two-dimensional SDS-polyacrylamide gel (2D SDS PAGE). Nine protein spots were exclusively induced from phenol-cultures of strain C-1. Of these 9 spots, three phenol-degrading enzymes (phenol degradation meta-pathway protein, hydroxymuconic semialdehyde dehydrogenase and 4-hydroxy-2-oxovalerate aldolase) were identified by peptide mass fingerprinting, and the results were confirmed by tandem mass spectrometry of selected peptides, which suggests that strain C-1 degrades phenol via the β-ketoadipate pathway. Analysis of the metabolite produced from phenol proved that this enzyme is a catechol 2,3 dioxygenase, which is able to utilize phenol as a substrate. These results suggest that comparative proteomic analysis of biodegrading bacteria cultures under different conditions may be a useful initial step toward the elucidation of an aromatic compound degradation pathway and the strain C-1 could be an excellent candidate for the biotreatment of phenol-containing industrial wastewaters.

RETRACTED: Mechanism of phenol photodegradation in the presence of pure and modified-TiO2: A review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its costly effectiveness, inert nature and photostability. A substantial amount of research has focused on the enhancement of TiO(2) photocatalysis by modification with metal, non-metal and ion doping. This paper aims to review and summarize the recent works on the titanium dioxide (TiO(2)) photocatalytic oxidation of phenol and discusses various mechanisms of phenol photodegradation (indicating the intermediates products) and formation of OH radicals. Phenol degradation pathway in both systems, TiO(2)/UV and doped-TiO(2)/Vis, are described.

CatA Gene in a Potential Corynebacterium Strain is Responsible for its Efficiency in Phenol Bioremoval

Out of 10 bacterial strains isolated out of wastewater of a pharmaceutical industry the most efficient bacterium, which could tolerate 5,000 mgl−1 of phenol in the minimal medium, was identified to be Corynebacterium sp.DST1 through 16S rDNA analysis. This strain could remove 99.4% of phenol from the minimal medium containing 4,000 mgl−1 of phenol. The ortho catalytic pathway using the enzyme catechol 1, 2- dioxygenase was found to be the major pathway for phenol degradation in the bacterium. The gene for catechol 1, 2-dioxygenase (catA) could also be amplified using degenerate primers. Corynebacterium sp.DST1 cells were attached to sawdust and removal of phenol from industrial effluents was evaluated. About 92.7% of phenol could be removed from the effluent of a heavy electrical industry. The results of this study not only suggest the potentiality of the strain to remove phenol efficiently from crude industrial effluents but also display a cheap method of bioremediation using sawdust.

Biodegradation of phenol using recombinant plasmid-carrying Rhodococcus erythropolis strains

The aim of the study was to utilize current knowledge of the phenol catabolic genes in Rhodococcus erythropolis CCM2595 to construct improved phenol degraders and test their bioremediation potential using real industrial wastewater. The genes pheA2A1-pheR-catR-catABC, coding for enzymes of the phenol degradation pathway and transcriptional regulators in R. erythropolis CCM2595, were cloned in various combinations in the multicopy R. erythropolis plasmid vector pSRK21 and the resulting constructs were introduced into R. erythropolis cells. All plasmid-carrying strains showed increased phenol hydroxylase activity. The strains harboring constructs pSRKAphe-cat and pSRKBphe-cat (both carrying all enzyme-coding genes of the phenol catabolic gene cluster) exhibited the highest phenol hydroxylase activities and proved to be the most efficient phenol degraders in minimal medium with 0.3 g L−1 phenol. The recombinant strains were up to 50% more efficient than the wild-type strain in the bioremediation of medium based on wastewater containing phenol (0.6 g L−1). The plasmids pSRKAphe-cat and pSRKBphe-cat with the unchanged size were isolated from R. erythropolis cells after a 288-h cultivation in wastewater medium under non-selective conditions. The results provide a basis for the construction of further manipulated phenol-degrading strains and for the development of consortia of various R. erythropolis derivatives.

Promotion of Phenol Photodecomposition over TiO2 Using Au, Pd, and Au–Pd Nanoparticles

Noble metal nanoparticles (Au, Pd, Au-Pd alloys) with a narrow size distribution supported on nanocrystalline TiO(2) (M/TiO(2)) have been synthesized via a sol-immobilization route. The effect of metal identity and size on the photocatalytic performance of M/TiO(2) has been systematically investigated using phenol as a probe molecule. A different phenol degradation pathway was observed when using M/TiO(2) catalysts as compared to pristine TiO(2). We propose a mechanism to illustrate how the noble metal nanoparticles enhance the efficiency of phenol decomposition based on photoreduction of p-benzoquinone under anaerobic conditions. Our results suggest that the metal nanoparticles not only play a role in capturing photogenerated electrons, but are strongly involved in the photocatalytic reaction mechanism. The analysis of the reaction intermediates allows us to conclude that on M/TiO(2) undesired redox reactions that consume photogenerated radicals are effectively suppressed. The analysis of the final products shows that the reusability performance of the catalyst is largely dependent on the pretreatment of the catalyst and the identity of the metal nanoparticle. Interestingly, the as-prepared Pd and Au-Pd decorated TiO(2) materials exhibit excellent long-term photoactivity, in which ~90% of the phenol can be fully decomposed to CO(2) in each cycle.