Mineralization Pathways Research Articles

Reactivity of novel Ceria–Perovskite composites CeO2- LaMO3 (MCu, Fe) in the catalytic wet peroxidative oxidation of the new emergent pollutant ‘Bisphenol F’: Characterization, kinetic and mechanism studies

In the present study, ceria, pristine perovskites LaMO3 (Cu, Fe) and novel ceria-perovskite composites CeO2-LaMO3 were successfully prepared and applied as heterogeneous Fenton like- catalysts for the degradation and mineralization of a new emergent compound- bisphenol F (BPF) in aqueous solution. The catalysts were characterized by X-ray diffraction spectrometer (XRD), BET surface area determination, scanning electron microscopy (SEM), Energy Dispersive X-ray (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. Catalytic bisphenol F behavior shows that the activity of pristine perovskites was improved due to the introduction of cerium. Catalytic activity in terms of TOC removal followed the order of CeO2-LaCuO3>CeO2-LaFeO3>LaCuO3>LaFeO3>CeO2 with about 83, 79, 68, 64 and 28% respectively. Only the novel composite oxide CeO2-LaCuO3 was found to be effective for Bisphenol F degradation at neutral conditions. EPR analyses and scavenging experiments revealed that BPF was mainly decomposed by the attack of OH, especially the surface-bounded OH. BPF decay followed pseudo-first-order reaction kinetics. The absolute rate constant for BPF oxidation by OH was found to 2.09109M−1s−1, as determined by the competition kinetic method. Six stable organics intermediates were observed and five of them were identified p-benzoquinone, hydroquinone, 4-hydroxybenzaldehyde and Bis (4-hyroxyphenyl) methanol. Subsequent attack of these intermediates by OH radicals led to the formation of short chain acids: malonic, succinic, acetic, formic and oxalic acids. On the basis of the analytical results for the intermediate products and the assumption that hydroxyls radicals are the major reactive species, a plausible pathway of BPF mineralization during the heterogeneous Fenton process was proposed. Furthermore, the CeO2-LaCuO3 composite exhibited excellent long-term stability in the heterogeneous Fenton-like process. These results suggested that the novel ceria perovskite material would be a promising candidate for practical wastewater treatment.

Characteristics and fate of natural organic matter during UV oxidation processes

Advanced oxidation processes (AOPs) are widely used in water treatments. During oxidation processes, natural organic matter (NOM) is modified and broken down into smaller compounds that affect the characteristics of the oxidized NOM by AOPs. In this study, NOM was characterized and monitored in the UV/hydrogen peroxide (H2O2) and UV/persulfate (PS) processes using a liquid chromatography–organic carbon detector (LC-OCD) technique, and a combination of excitation–emission matrices (EEM) and parallel factor analysis (PARAFAC). The percentages of mineralization of NOM in the UV/H2O2 and UV/PS processes were 20.5 and 83.3%, respectively, with a 10 mM oxidant dose and a contact time of 174 s (UV dose: approximately 30,000 mJ). Low-pressure, Hg UV lamp (254 nm) was applied in this experiment. The steady-state concentration of SO4− was 38-fold higher than that of OH at an oxidant dose of 10 mM. With para-chlorobenzoic acid (pCBA) as a radical probe compound, we experimentally determined the rate constants of Suwannee River NOM (SRNOM) with OH (kOH/NOM = 3.3 × 108 M−1s−1) and SO4− (kSO4-/NOM = 4.55 × 106 M−1s−1). The hydroxyl radical and sulfate radical showed different mineralization pathways of NOM, which have been verified by the use of LC-OCD and EEM/PARAFAC. Consequently, higher steady-state concentrations of SO4−, and different reaction preferences of OH and SO4− with the NOM constituent had an effect on the mineralization efficiency.

Thermodynamic Aspects of Molluscan Shell Ultrastructural Morphogenesis

Over the years, molluscan shells have become an exemplar model system to study the process of mineral formation by living organisms, the process of biomineralization. Typically, the shells consist of a number of mineralized ultrastructural motifs, each exhibiting a specific mineral‐organic composite architecture. These are made of calcium carbonate building blocks having a well‐defined three‐dimensional morphology that is significantly different from the shape of inorganically formed counterparts. Shell ultrastructures are known to form via a biologically controlled extracellular mineralization pathway in which the organism has no direct control over mineral formation. The cellular tissue, responsible for shell biomineralization, forms an organic framework and sets‐up the physical conditions necessary for the deposition of a specific morphology, whereas the growth of the mineral part of the shell proceeds spontaneously via the process of self‐assembly. In this feature article, the ability to employ thermodynamic models from classical materials science to describe the process of self‐assembly and structural evolution of a variety of shell architectures is reviewed. Having the potential to offer an analytical framework to express ultrastructure formation in time and in space, these models not only provide a deeper insight into shell biomineralization, but also suggest tools for novel composite materials design.

Runoff changes have a land cover specific effect on the seasonal fluxes of terminal electron acceptors in the boreal catchments

Climate change influences the volume and seasonal distribution of runoff in the northern regions. Here, we study how the seasonal variation in the runoff affects the concentrations and export of terminal electron acceptors (i.e. TEAs: NO3, Mn, Fe and SO4) in different boreal land-cover classes. Also, we make a prediction how the anticipated climate change induced increase in runoff will alter the export of TEAs in boreal catchments. Our results show that there is a strong positive relationship between runoff and the concentration of NO3-N, Mn and Fe in agricultural catchments. In peaty catchments, the relationship is poorer and the concentrations of TEAs tend to decrease with increasing runoff. In forested catchments, the correlation between runoff and TEA concentrations was weak. In most catchments, the concentrations of SO4 decrease with an increase in runoff regardless of the land cover or season. The wet years export much higher amounts of TEAs than the dry years. In southern agricultural catchments, the wet years increased the TEA export for both spring (January–May) and autumn (September–December) periods, while in the peaty and forested catchments in eastern and northern Finland the export only increased in the autumn. Our predictions for the year 2099 indicate that the export of TEAs will increase especially from agricultural but also from forested catchments. Additionally, the predictions show an increase in the export of Fe and SO4 for all the catchments for the autumn. Thus, the climate induced change in the runoff regime is likely to alter the exported amount of TEAs and the timing of the export downstream. The changes in the amounts and timing in the export of TEAs have a potential to modify the mineralization pathways in the receiving water bodies, with feedbacks in the cycling of C, nutrients and metals in aquatic ecosystems.

Electro-Fenton oxidation of para-aminosalicylic acid: degradation kinetics and mineralization pathway using Pt/carbon-felt and BDD/carbon-felt cells.

Degradation of a widely used antibiotic, the para-aminosalicylic acid (PAS), and mineralization of its aqueous solution was investigated by electro-Fenton process using Pt/carbon-felt and boron-doped diamond (BDD)/carbon-felt cells with applied currents in the range of 50-1000mA. This process produces the highly oxidizing species, the hydroxyl radical (•OH), which is mainly responsible for the oxidative degradation of PAS. An absolute rate constant of 4.17×109M-1s-1 for the oxidation of PAS by ●OH was determined from the competition kinetics method. Degradation rate of PAS increased with current reaching an optimal value of 500mA with complete disappearance of 0.1mM PAS at 7min using Pt/carbon-felt cell. The optimum degradation rate was reached at 300mA for BDD/carbon-felt. The latter cell was found more efficient in total organic carbon (TOC) removal where a complete mineralization was achieved within 240min. A multi-step mineralization process was observed with the formation of a number of aromatic intermediates, short-chain carboxylic acids, and inorganic ions. Eight aromatic intermediate products were identified using both LC-Q-ToF-MS and GC-MS techniques. These products were the result of hydroxylation of PAS followed by multiple additions of hydroxyl radicals to form polyhydroxylated derivatives. HPLC and GC/MS analyses demonstrated that extended oxidation of these intermediate products conducted to the formation of various short-chain carboxylic acids. Prolonged electrolysis resulted in a complete mineralization of PAS with the evolution of inorganic ions such as NO3- and NH4+. Based on the identified intermediates, carboxylic acids and inorganic ions, a plausible mineralization pathway is also deduced. The remarkably high degree of mineralization (100%) achieved by the present EF process highlights the potential application of this technique to the complete removal of salicylic acid-based pharmaceuticals from contaminated water.

Use of Sub-stoichiometric Titanium Oxide as a Ceramic Electrode in Anodic Oxidation and Electro-Fenton Degradation of the Beta-blocker Propranolol: Degradation Kinetics and Mineralization Pathway

Oxidative degradation of aqueous acidic solutions of the beta-blocker propranolol (PPN) has been studied by anodic oxidation (AO) and for the first time by electro-Fenton (EF) process using sub-stoichiometric titanium oxide (Ti4O7) anode elaborated by plasma deposition. The oxidative degradation of the PPN by Ti4O7(OH) formed at the surface of the Ti4O7 anode and OH generated via electrochemically assisted Fenton’s reaction was investigated. Decay of PPN concentration followed pseudo-first order reaction kinetics with degradation rates influenced by both applied current and initial PPN concentration. The absolute rate constant of the reaction between PPN and OH/Ti4O7(OH) was determined by competition kinetics and found to be (2.99±0.02) × 109Lmol−1s−1. Relatively high mineralization efficiency of PPN solution (82% TOC removal) was achieved by AO with Ti4O7 anode at 120mA after 480min of treatment, whereas almost complete mineralization (96% TOC removal) was reached at similar conditions in EF process. Analogous EF treatment with DSA anode showed lower mineralization (89% TOC removal) compared to Ti4O7 anode. The initial N content of PPN was mainly released as NH4+, with smaller proportion of NO3−. Aromatic intermediates such as 1-naphtol; hydroxylated 1-naphtol and phthalic acid were identified by both reversed-phase HPLC and GC-MS analyses. Oxalic, oxamic, maleic and glycoxylic acids were the main short-chain carboxylic acid detected. Based on the identified intermediates, carboxylic acids and inorganic end-products as well as TOC removal results, a plausible reaction sequence for mineralization of PPN by electrogenerated hydroxyl radicals is proposed.

Electrocatalytic properties of N-doped graphite felt in electro-Fenton process and degradation mechanism of levofloxacin

The degradation of antibiotic levofloxacin was investigated by dimensionally stable anode as well as modified cathode using low-cost chemical reagents of hydrazine hydrate and ethanol for electro-Fenton in an undivided cell at pH 3.0 under room temperature. Comparison of unmodified and modified cathode was performed. The apparent rate constant of levofloxacin decay was found to be 0.2883 min−1 for graphite felt-10 with the best performance at 200 mA, which is lower than graphite felt at 400 mA. The optimum modified cathode showed a significant improvement of complete mineralization of levofloxacin, reaching a 92% TOC removal at 200 mA for 480 min higher than unmodified one at twice the current. Surface physicochemical properties and morphology were investigated by scanning electron microscope, contact angle and X-ray photoelectron spectroscopy. The electrochemical characterization of hydrogen evolution reaction was adopted to clarify a possible pathway for the higher mineralization of levofloxacin, indicating a potential pilot-scale study to the pollution with the similar structure.

Dental Pulp Cells Isolated from Teeth with Superficial Caries Retain an Inflammatory Phenotype and Display an Enhanced Matrix Mineralization Potential.

We have isolated dental pulp cells (DPCs) from three healthy (hDPCs) and three carious (cDPCs) donors and shown that compared to hDPCs cells isolated from superficial carious lesions show higher clonogenic potential; show an equivalent proportion of cells with putative stem cell surface markers; show enhanced matrix mineralization capability; have enhanced angiogenic marker expression and retain the inflammatory phenotype in vitro characteristic of superficial caries lesions in vivo. Our findings suggest that cDPCs may be used for further investigation of the cross talk between inflammatory, angiogenic and mineralization pathways in repair of carious pulp. In addition cells derived from carious pulps (almost always discarded) may have potential for future applications in mineralized tissue repair and regeneration.

Kinetics of oxidative degradation/mineralization pathways of the antibiotic tetracycline by the novel heterogeneous electro-Fenton process with solid catalyst chalcopyrite

The degradation of solutions of the antibiotic tetracycline (TC) has been studied by a novel electrochemical advanced oxidation process, consisting in electro-Fenton (EF) process using chalcopyrite as heterogeneous catalyst. In fact, chalcopyrite powder was the source of Fe2+ and Cu2+ ions instead of a soluble catalyst salt used in conventional EF. Experiments were performed in an undivided cell equipped with a Pt or boron-doped diamond (BDD) anode and a carbon felt cathode, where TC and its oxidation intermediate products were destroyed by hydroxyl radicals (OH) formed both, in the bulk solution from electrochemically induced Fenton’s reaction (Fe2+ and H2O2) and Fenton’s-like reaction (Cu+ and H2O2), and at the anode surface from water oxidation. The effects of operating parameters such as applied current, chalcopyrite concentration and anode material were investigated. TC decay followed pseudo-first-order reaction kinetics. The absolute rate constant for TC oxidation by OH was found to be 3.2×109M−1s−1, as determined by the competition kinetic method. EF process using chalcopyrite as heterogeneous catalyst showed to be more efficient than conventional EF, achieving almost total mineralization of the TC solution (98% of total organic carbon removal) after 360min under optimum operating conditions. A plausible mineralization pathway for mineralization of TC aqueous solution by OH was proposed based on the identification of different oxidation by-products. Moreover, toxicity tests pointed out that this heterogeneous EF process was able to detoxify the TC solutions.

A biomineralization study of the Indo-Pacific giant clam Tridacna gigas

The giant clam, Tridacna gigas, is an important faunal component of reef ecosystems of the Indo-Pacific region. In addition to its ecological role, shells of this bivalve species are useful bioarchives for past climate and environmental reconstructions. However, the biomineralization processes involved in shell aragonite deposition are insufficiently understood. Here, we present a study of the shell microstructure of modern specimens from Palm Island, Great Barrier Reef (GBR), Australia, and Huon Peninsula, Papua New Guinea (PNG), using a combination of petrography, scanning electron microscopy, electron backscatter diffraction, Raman spectroscopy and stable carbon isotope ratios. Daily growth increments were recognizable in all specimens through ontogeny, and counting these growth lines provides a robust specimen age estimate. For the internal layers, paired increments of organized aragonitic needles and compact, oblong crystals were recognized in a specimen from PNG, whereas specimens from GBR were composed of shield-like crystals that were not definable at the microscale. The combination of nutrient availability, rainfall and solar irradiance are likely to be the most significant factors controlling shell growth and may explain the observed differences in microstructure. The external layer, identical in all specimens, was composed of dendritic microstructure that is significantly enriched in 13C compared to the internal layer, suggesting different metabolic controls on layer deposition. We propose that the mineralization of the internal and external layers is independent from each other and associated with the activity of specific mantles. Future studies using T. gigas shells as bioarchives should consider the microstructure as it reflects the environment in which the individual lived and the differences in mineralization pathways of internal and external layers.

Calcium carbonate with nanogranular microstructure yields enhanced toughness.

The presence of nanogranular microstructures is a widely reported feature of biominerals that form by classical and non-classical mineralization pathways. Inspired by nature, we have synthesized amorphous calcium carbonate nanoparticles with nanogranular microstructures, whose grain size is tuned by varying the polymer concentration. The response to indentation of single calcium carbonate nanoparticles proceeds via an intermittent stick-slip that reflects the characteristics of the nanogranular microstructure. A two-fold mechanism is thus proposed to enhance the toughness of the nanoparticles, namely nanogranular rearrangement and intergranular bridging by an organic phase and/or hydration. This work not only provides a synthesis route to design biologically inspired mineral nanoparticles with nanogranular structure, but also helps in understanding toughening mechanisms of biominerals arising from their nanoscale heterogeneity.

Comparative study of electrochemical oxidation of herbicide 2,4,5-T: Kinetics, parametric optimization and mineralization pathway

Abstract Oxidative degradation of herbicide 2,4,5-T was studied by electrochemical advanced oxidation processes anodic oxidation and electro-Fenton (EF) using Pt/carbon felt and BDD/carbon felt cells. The effect of main operating parameters on oxidation of 2,4,5-T and mineralization of its aqueous solution were investigated. The rate constant for oxidation of 2,4,5-T by OH was determined as (3.7 ± 0.2) × 10 9 M − 1 s − 1 using competition kinetics method. The EF process with BDD anode was shown to be very efficient reaching 94% mineralization in 3 h treatment. Based on identified aromatic intermediates, short-chain carboxylic acids, released inorganic ions and total organic carbon removal measurements, a plausible oxidation pathway for mineralization of 2,4,5-T by hydroxyl radical was proposed. In addition, the evolution of solution toxicity during treatment was monitored by Microtox method showing the formation of toxic aromatic/cyclic intermediates. The results showed also that EF process was able to remove efficiently toxic intermediates and consequently solution toxicity.

Visible-Light-Controlled Oxidation of Glucose using Titania-Supported Silver Photocatalysts.

The visible‐light‐mediated photo‐catalytic selective valorisation of glucose using TiO2‐supported Ag nanoparticles is shown for the first time. The optimisation of the catalyst composition, substrate‐to‐catalyst ratio and reaction medium proved that a near total suppression of the mineralisation pathway could be achieved with a selectivity to partial oxidation products and small‐chain monosaccharides as high as 98 %. The primary products were determined to be gluconic acid, arabinose, erythrose, glyceraldehyde and formic acid. Under UVA light, the selectivity to organics decreases because of the production of CO2 from mineralisation. A reaction mechanism is proposed based on an α‐scission process combined with the Ruff degradation reaction, which explains the presence of the oxidation products, the smaller carbohydrates and formic acid. X‐ray photoelectron spectroscopy, UV/Vis spectroscopy and microscopy studies showed the presence of plasmonic 4 nm particles of silver that were oxidised to silver oxide over the course of the reaction, and recycling studies revealed that this was not detrimental to activity.

Abatement of the fluorinated antidepressant fluoxetine (Prozac) and its reaction by-products by electrochemical advanced methods

The degradation of the fluorinated antidepressant fluoxetine, as hydrochloride, was comparatively studied in sulfate medium at pH 3.0 by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Experiments were performed with 100mL solutions in an undivided tank reactor equipped with a Pt, RuO2-based or boron-doped diamond (BDD) anode and an air-diffusion cathode for continuous H2O2 production. The BDD anode showed higher mineralization rate due to the great production of physisorbed BDD(OH), which has large reactivity to oxidize the drug and intermediates. The degradation rate was enhanced by EF with 0.50mM Fe2+ due to the additional production of OH in the bulk from Fenton’s reaction. The degradation was even faster using PEF owing to the additional photolytic action of UVA radiation. The most effective process was PEF with a BDD anode achieving 94% mineralization at 300min. The fluoxetine decay followed a pseudo-first-order kinetics, being quicker in the order:AO-H2O2<EF<PEF. The effect of the current density and drug concentration on the mineralization rate and fluoxetine decay was clarified. Oxidation of fluoxetine by hydroxyl radicals yielded four aromatic by-products, as found by GC–MS. Additionally, a chloroaromatic compound was identified as a result of the reaction of active chlorine, which was formed in situ from the oxidation of chloride ion at the BDD anode. Four short-chain linear carboxylic acids, being oxalic and formic acid more abundant, were identified. In PEF, fluorine atoms of fluoxetine were completely released as fluoride ion, whereas the initial nitrogen was converted into nitrate ion in all cases. A reaction pathway for fluoxetine mineralization by the electrochemical advanced methods is finally proposed.

Degradation pathways of aniline in aqueous solutions during electro-oxidation with BDD electrodes and UV/H2O2 treatment

In this work, it has been studied the mineralization of aniline, a toxic substance of low biodegradability typically found in many industrial wastewaters, through electro-oxidation using boron doped diamond (BDD) electrodes and photo-oxidation (UV photolysis and UV/H2O2 treatments). It was observed that in electro-oxidation and UV/H2O2, it was feasible to reach aniline mineralizations higher than 85%. Two different degradation routes have been observed during the aniline oxidation in these two treatments. The first route was the mineralization pathway, in which aniline was oxidized to CO2, water and nitrate. The second route was the polyaniline pathway in which polyanilines of high molecular weight are formed. The intermediate compounds involved in both degradation routes are different depending on the treatment used. In the electro-oxidation, denitrification processes were also observed. From an economical point of view, electro-oxidation of aniline using BDD electrodes is more interesting than UV/H2O2 due it has an 87% lower operational cost. So, electro-oxidation using BDD electrodes seems to be a more suitable technique for the mineralization of wastewater containing aniline than UV or H2O2 based technologies.

Sub-stoichiometric titanium oxide (Ti4O7) as a suitable ceramic anode for electrooxidation of organic pollutants: A case study of kinetics, mineralization and toxicity assessment of amoxicillin

Electrochemical degradation of aqueous solutions containing antibiotic amoxicillin (AMX) has been extensively studied in an undivided electrolytic cell using a sub-stoichiometric titanium oxide (Ti4O7) anode, elaborated by plasma deposition. Oxidative degradation of AMX by hydroxyl radicals was assessed as a function of applied current and was found to follow pseudo-first order kinetics. The use of carbon-felt cathode enhanced oxidation capacity of the process due to the generation of H2O2. Comparative studies at low current intensity using dimensional stable anode (DSA) and Pt anodes led to the lower mineralization efficiencies compared to Ti4O7 anode: 36 and 41% TOC removal for DSA and Pt respectively compared to 69% for Ti4O7 anode. Besides, the use of boron doped diamond (BDD) anode under similar operating conditions allowed reaching higher mineralization (94%) efficiency. Although Ti4O7 anode provides a lesser mineralization rate compared to BDD, it exhibits better performance compared to the classical anodes Pt and DSA and can constitutes an alternative to BDD anode for a cost effective electro-oxidation process. Moreover several aromatic and aliphatic oxidation reaction intermediates and inorganic end-products were identified and a plausible mineralization pathway of AMX involving these intermediates was proposed.

Dynamic behavior of hydroxyl radical in sono-photo-Fenton mineralization of synthetic municipal wastewater effluent containing antipyrine

The aim of this study was to examine the kinetics of the different mechanisms (radical pathway, photolysis, molecular reaction with H2O2 and reaction with ultrasonically generated oxidative species) involved in the homogeneous sono-photoFenton (US/UV/H2O2/Fe) mineralization of antipyrine present in a synthetic municipal wastewater effluent (ASMWE). The dynamic behavior of hydroxyl (HO) radical generation and consumption in mineralization reaction under different systems was investigated by measuring hydroxyl radical concentration during the reaction. The overall mineralization process was optimized using a Central-Composite Experimental Design (CCED) with four variables (initial concentrations of H2O2 and Fe(II), amplitude and pulse length). The response functions (pseudo-first order mineralization kinetic rate constants) were fitted using neural networks (NNs). Under the optimal conditions ([H2O2]o=500mgL−1, [Fe(II)]o=27mgL−1, Amplitude (%)=20andPulse length=1), the TOC removal was 79% in 50min. The radical reaction in the bulk solution was found be the primary mineralization pathway (94.8%), followed by photolysis (3.65%), direct reaction with H2O2 (0.86%), and reaction by ultrasonically generated oxidative species (0.64%). The role of the Fe catalyst on the radical reaction and the presence of refractory intermediates towards hydroxyl radical were also studied.

Photodecomposition of organic phosphorus in aquatic solution under solar irradiation with nitrate: Kinetics and influencing water parameters

The transformation of organic phosphorus plays an important role in the phosphorus cycle in the natural environment. In this study, a series of laboratory‐based experiments were conducted to address the influence of nitrate ( ) photochemical activity on the transformation of methyl parathion under solar irradiation. It is demonstrated that the photodecomposition of methyl parathion by obeys pseudo‐first‐order reaction kinetics, with the photodecomposition rate increasing with concentration. The photodecomposition rates of methyl parathion by were strongly influenced by pH, concentration of humic acid and Fe3+. Higher concentrations of Fe3+ and lower concentrations of humic acid accelerated the photodegradation induced by . Moreover, compared to alkaline media the acidic media can enhance the rate of methyl parathion degradation. Formation of the hydroxyl radical (•OH) was identified through the measurement of photoluminescence spectra (PL) using terephthalic acid as the trapping molecule. The primary transformation pathways of methyl parathion in the presence of under solar irradiation were proposed through the qualitative and quantitative analysis of byproducts. Intermediates, such as paraoxon, 4‐nitrophenol and orthophosphate, were identified, and a mineralization pathway from methyl parathion to orthophosphate was proposed. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 404–411, 2017

Visible light selective photocatalytic conversion of glucose by TiO2

The visible-light mediated selective photo-oxidation of glucose using unmodified TiO2 as a catalyst is reported for the first time. The effect of the catalyst to substrate ratio, lamp power and TiO2 crystalline phases on the conversion and product distribution under both visible and UVA light is explored. Higher conversions were obtained under UVA light but as a result of substantial mineralization through an unselective pathway. Optimization of the reaction conditions resulted in 42% glucose conversion under visible light with 7% selectivity to gluconic acid and 93% selectivity to other partial oxidation products with the total suppression of a mineralization pathway to CO2. It is also shown that selective glucose conversion can occur under natural sunlight light after 7h exposure. In this systematic study, we prove that it is indeed possible to use TiO2 as a photocatalyst to upgrade biomass derivatives selectively by tailoring the reaction conditions. Most importantly, we find the ligand-to-metal charge-transfer effect as a result of glucose adsorption to the surface of TiO2 determinant in the photo-activity observed under visible light irradiation. Knowledge of this effect along with the careful control of reaction conditions means that the selective photo-catalytic conversion of other biomass derived carbohydrates under visible light is a viable route to higher value chemicals.

Characterization and genome functional analysis of a novel metamitron-degrading strain Rhodococcus sp. MET via both triazinone and phenyl rings cleavage

A novel bacterium capable of utilizing metamitron as the sole source of carbon and energy was isolated from contaminated soil and identified as Rhodococcus sp. MET based on its morphological characteristics, BIOLOG GP2 microplate profile, and 16S rDNA phylogeny. Genome sequencing and functional annotation of the isolate MET showed a 6,340,880 bp genome with a 62.47% GC content and 5,987 protein-coding genes. In total, 5,907 genes were annotated with the COG, GO, KEGG, Pfam, Swiss-Prot, TrEMBL, and nr databases. The degradation rate of metamitron by the isolate MET obviously increased with increasing substrate concentrations from 1 to 10 mg/l and subsequently decreased at 100 mg/l. The optimal pH and temperature for metamitron biodegradation were 7.0 and 20–30 °C, respectively. Based on genome annotation of the metamitron degradation genes and the metabolites detected by HPLC-MS/MS, the following metamitron biodegradation pathways were proposed: 1) Metamitron was transformed into 2-(3-hydrazinyl-2-ethyl)-hydrazono-2-phenylacetic acid by triazinone ring cleavage and further mineralization; 2) Metamitron was converted into 3-methyl-4-amino-6(2-hydroxy-muconic acid)-1,2,4-triazine-5(4H)-one by phenyl ring cleavage and further mineralization. The coexistence of diverse mineralization pathways indicates that our isolate may effectively bioremediate triazinone herbicide-contaminated soils.