Presence Of Electron Acceptors Research Articles

DABCO‐Promoted Selective Photochemical C−N Coupling: Access to Unsymmetrical Azahelicenes

AbstractA multifaceted study on the effect of various factors on the efficiency of photocyclization of naphthofuran O‐acyl oximes was performed. It showed that without any additives or in the presence of electron acceptors, the reaction occurs by a radical pathway and with low chemoselectivity, while DABCO promotes intramolecular cyclization to give naphthofuroquinolines (NFQs) in 34–87% yields. The iminyl radical formed under UV irradiation in the presence of DABCO due to single electron transfer (SET) and N−O bond cleavage undergoes selective intramolecular homolytic aromatic substitution (HAS) with formation of a new C−N bond. This route to quinoline‐annulated scaffolds is based on the use of DABCO both as an electron transfer agent and a proton acceptor.

Renewable biohydrogen production from Clostridium sp. LQ25 using different forms of ferric as electron acceptor

Clostridium sp. LQ25 was cultured in different forms of ferric (ferric citrate and ferric hydroxide) as electron acceptors to investigate growth, ferric reduction, hydrogen production, fermentation products and fermentation process. The growth of the strain LQ25 detected by protein was 82.8 ± 2.1 mg/L and 73.5 ± 1.7 mg/L using ferric citrate and ferric hydroxide as electron acceptors, which was 33.3 % and 18.4 % higher than without ferric, respectively. The accumulation concentration of Fe(II) was 9.0 ± 0.6 mg/L and 5.0 ± 0.2 mg/L when using ferric citrate and ferric hydroxide as electron acceptors, and ferric citrate was 1.8-fold higher than ferric hydroxide, which indicated that the ability of ferric reduction was higher using ferric citrate as electron acceptor. The hydrogen production of strain LQ25 was 238.0 ± 1.0 mmol/mol glucose and 113.0 ± 1.3 mmol/mol glucose under condition of ferric citrate and ferric hydroxide as electron acceptors, which was 2.6 and 1.2-fold higher than without ferric, respectively. The growth and hydrogen production of strain LQ25 was promoted by using ferric as electron acceptor, while the fermentation type of strain did not change and was always butyrate type. The differential expression of the genes of strain LQ25 was significant when using ferric as electron acceptor, mainly in NADH and PFL pathway. This study provided preliminary evidence for hydrogen production by Clostridium sp. LQ25 in the presence of electron acceptor.

Exploring the genome of Lactobacillaceae spp. Sy-1 isolated from Heterotrigona itama honey.

BackgroundHoney produced by Heterotrigona itama is highly preferred among consumers due to its high-value as a functional food and beneficial lactic acid bacteria (LAB) reservoir. Fructophilic lactic acid bacteria (FLAB) are a group of LAB with unique growth characteristics and are regarded as promising producers of bioactive compounds. Hence, it is not surprising that LAB, especially FLAB, may be involved with the excellent bioactivity of H. itama honey. With the trending consumer preference for H. itama honey coupled with increasing awareness for healthy food, the genomic background of FLAB isolated from this honey must, therefore, be clearly understood. In this study, one FLAB strain designated as Sy-1 was isolated from freshly collected H. itama honey. Its FLAB behavior and genomic features were investigated to uncover functional genes that could add value to functional food.MethodsThe fructophilic characteristics of strain Sy-1 were determined, and the genome was sequenced using Illumina iSeq100 and Oxford Nanopore. The average nucleotide identity and phylogenetic analyses based on 16S rRNA, 92 core genes, and whole-genome sequence were performed to unravel the phylogenetic position of strain Sy-1. NCBI Prokaryotic Genome Annotation Pipeline annotated the genome, while the EggNOG-mapper, BLASTKoala, and GHOSTKoala were used to add functional genes and pathways information.ResultsStrain Sy-1 prefers D-fructose over D-glucose and actively metabolizes D-glucose in the presence of electron acceptors. Genomic annotation of strain Sy-1 revealed few genes involved in carbohydrate transport and metabolism, and partial deletion of adhE gene, in line with the characteristic of FLAB. The 16S rRNA gene sequence of strain Sy-1 showed the highest similarity to unknown LAB species isolated from the gut of honeybees. The phylogenetic analyses discovered that strain Sy-1 belonged to the Lactobacillaceae family and formed a separate branch closer to type strain from the genera of Acetilactobacillus and Apilactobacillus. The ANI analysis showed the similarity of the closest relative, Apilactobacillus micheneri Hlig3T. The assembled genome of Sy-1 contains 3 contigs with 2.03 Mbp and a 41% GC content. A total of 1,785 genes were identified, including 1,685 protein-coding genes, 68 tRNA, and 15 rRNA. Interestingly, strain Sy-1 encoded complete genes for the biosynthesis of folate and riboflavin. High-performance liquid chromatography analysis further confirmed the high production of folic acid (1.346 mg/L) by Sy-1.DiscussionBased on phylogenetic and biochemical characteristics, strain Sy-1 should be classified as a novel genus in the family of Lactobacillaceae and a new member of FLAB. The genome information coupled with experimental studies supported the ability of strain Sy-1 to produce high folic acid. Our collective findings support the suitable application of FLAB strain Sy-1 in the functional food and pharmaceutical industries.

Electron Transfer-Mediated Photodegradation of Phototoxic Antipsychotic Drug Quetiapine.

Quetiapine (QTP) (1), a psychotropic agent belonging to a chemical class, dibenzothiazepine derivatives, is photosensitive and photolabile. Its photochemistry was studied in the presence of an electron donor N,N-dimethylaniline (DMA) and an electron acceptor 1,4-dicyanobenzene (DCB) under anaerobic conditions. This resulted in photoinduced electron transfer-mediated transformation of drug QTP. Irradiation of Quetiapine (QTP, 1) in the presence of electron donor N,N-dimethylaniline (DMA) under anaerobic conditions in a photochemical reactor afforded one major photoproduct 2 when irradiation of QTP (1) was carried out in the presence of electron acceptor 1,4-dicyanobenzene (DCB) under similar conditions; it afforded 3 as a major photoproduct. These photoproducts were isolated and characterized on the basis of their spectral (IR, UV, 1H NMR, 13C NMR, and mass spectra) studies. The photophysical properties of Quetiapine were also determined in several solvents to investigate the relevance of the molecular structure in their photophysics and consequently in their photochemistry.

Nanoplasmonic zirconium nitride photocatalyst for direct overall water splitting

The ability of plasmonic nanostructures to efficiently harvest light energy and generate energetic hot carriers makes them promising materials for utilization in photocatalytic water spitting. Apart from the traditional Au and Ag based plasmonic photocatalysts, more recently the noble–metal–free alternative plasmonic materials have attracted ever–increasing interest. Here we report the first use of plasmonic zirconium nitride (ZrN) nanoparticles as a promising photocatalyst for water splitting. Highly crystalline ZrN nanoparticles with sizes dominating at 30–50 nm were synthesized that exhibit intense visible and near–infrared absorption due to localized surface plasmon resonance (LSPR). Without utilizing any noble metal cocatalysts such as Pt, the plasmonic ZrN nanoparticles alone showed stable photocatalytic activity for H2 evolution in aqueous solution with methanol as sacrificial electron donor. The addition of a cobalt oxide (CoOx) cocatalyst can facilitate the separation of photogenerated charge carriers and further improve the photocatalytic activity. The optimized CoOx modified ZrN photocatalyst was observed not only to activate the O2 evolution reaction with presence of electron acceptor, but also to drive overall water splitting for the simultaneous H2 and O2 evolution in the absence of any sacrificial agents.

Degradation of atenolol by CuFe2O4/visible light/oxidant: Effects of electron acceptors, synergistic effects, degradation pathways, and mechanism

In this work, CuFe2O4 nanoparticle was prepared through sol-gel method and used for removing atenolol (ATL) through photocatalytic process under visible light (VL) radiation in the presence of electron acceptors. The physicochemical properties of the photocatalyst such as XRD, FESEM, EDX, BET, TEM, VSM, FTIR, and UV–Vis DRS techniques as well as effective factors in ATL removal such as electron acceptors (peroxymonosulfate (PMS), peroxydisulfate (PDS), H2O2), solution pH, reaction time, CuFe2O4 loading, ATL concentration, and inorganic anions (i.e., HCO3−, NO3−, SO42−, and H2PO4−) were determined. The results showed the efficiency of ATL removal was as follows: CuFe2O4/VL/PMS > CuFe2O4/VL/PDS > CuFe2O4/VL/H2O2. At the concentration of 10 mg L−1 of ATL, the removal and mineralization rates of ATL were 90% and 68.35%, respectively. Moreover, the reusability test showed the catalyst efficiency decreased by less than 19% after 6 recycles, which indicated good catalyst stability. Among the reactive species (i.e., HO●, SO4●−, and O2•−), SO4●− radical had a dominant role based on the scavenging tests. In addition, the possible ATL degradation pathway was determined by evaluating transformation products. Overall, this study indicated the CuFe2O4/VL/PMS system can be used to remove the pharmaceutical organic matter.

Unique niche-specific adaptation of fructophilic lactic acid bacteria and proposal of three Apilactobacillus species as novel members of the group

BackgroundFructophilic lactic acid bacteria (FLAB) found in D-fructose rich niches prefer D-fructose over D-glucose as a growth substrate. They need electron acceptors for growth on D-glucose. The organisms share carbohydrate metabolic properties. Fructobacillus spp., Apilactobacillus kunkeei, and Apilactobacillus apinorum are members of this unique group. Here we studied the fructophilic characteristics of recently described species Apilactobacillus micheneri, Apilactobacillus quenuiae, and Apilactobacillus timberlakei.ResultsThe three species prefer D-fructose over D-glucose and only metabolize D-glucose in the presence of electron acceptors. The genomic characteristics of the three species, i.e. small genomes and thus a low number of coding DNA sequences, few genes involved in carbohydrate transport and metabolism, and partial deletion of adhE gene, are characteristic of FLAB. The three species thus are novel members of FLAB. Reduction of genes involved in carbohydrate transport and metabolism in accordance with reduction of genome size were the common characteristics of the family Lactobacillaceae, but FLAB markedly reduced the gene numbers more than other species in the family. Pan-genome analysis of genes involved in metabolism displayed a lack of specific carbohydrate metabolic pathways in FLAB, leading to a unique cluster separation.ConclusionsThe present study expanded FLAB group. Fructose-rich environments have induced similar evolution in phylogenetically distant FLAB species. These are examples of convergent evolution of LAB.

X-Ray Photoelectron Study of the Formation of the Chemical Bond and the Atomic Magnetic Moment in Nickel-Carbon Nanocomposites Modified by d-Metal Oxides

X-ray photoelectron spectroscopy is used to study the modification of Ni/C nickel-carbon nanocomposites with oxides (NiO, CuO, and Fe2O3) in the ratio of 0.5–1.0. Depending on the type of modifier used and its content, the magnetic moment of Ni atoms changes in the nanocomposite, i.e., during the redox process, the nanocomposite structure changes and the interaction between the carbon skeleton and the modifier metal is enhanced. In the presence of electron acceptors, the paired d electrons of the nanocomposite metal become unpaired and move to higher orbitals. This is indicative of self-organization processes in nanostructures, which leads to an increase in the atomic magnetic moment of the metal.

Contrasting response of organic carbon mineralisation to iron oxide addition under conditions of low and high microbial biomass in anoxic paddy soil

In contrast to what is observed in aerobic uplands, microbial biomass and the presence of electron acceptors, such as iron oxides, play a crucial role in regulating soil organic C (SOC) mineralisation in paddy soils. However, the related underlying mechanisms are still poorly explored. We conducted an anaerobic incubation study to investigate changes in CO2 emissions from SOC and acetate (13C-labeleld) in response to iron oxide (ferrihydrite and goethite) addition in chloroform-fumigated and unfumigated paddy soils. The iron oxides, as electron acceptors, increased CO2 emissions from SOC with stronger impact under ferrihydrite than goethite addition. However, the acetate addition, as a preferable C source for reducing microbes, decreased SOC mineralisation and caused a negative priming effect. CO2 emission from both acetate and SOC was affected by microbial biomass change. In the acetate-treated soil, goethite in the fumigated soil (i.e. high microbial biomass) increased CO2 emissions from acetate, providing electron acceptors, and decreased CO2 emissions from SOC. Ferrihydrite accepted electrons and adsorbed acetate, resulting in a slight decline in CO2 emission from acetate. However, in the fumigated soil (i.e. low microbial biomass), both iron oxide additions reduced CO2 emissions from acetate and SOC and likely the dominant role of both iron oxides shifted from being electron acceptors to being adsorbents, thus limiting acetate accessibility to microorganisms. The results suggest that microbial biomass is a key driver in shifting the effects of iron oxides on organic C mineralisation in anaerobic paddy soils.

Photocatalytic degradation of aniline blue, brilliant green and direct red 80 using NiO/CuO, CuO/ZnO and ZnO/NiO nanocomposites

Photocatalytic degradation of three dyes, aniline blue (AB), brilliant green (BG) and direct red 80 (DR 80) by transition metal oxide nanocomposites having p-p isotype heterojunction, NiO/CuO and p-n type heterojunction, CuO/ZnO and ZnO/NiO has been explored under sun light and UV light. The effect of reaction conditions such as initial dye concentration, catalyst dosage, pH, contact time and presence of electron acceptor on photocatalytic degradation of these dyes was investigated. A suitable mechanism has been proposed for the photocatalytic degradation of dyes by the nanocomposites with illustration. The results show that NiO/CuO has higher degradation ability on AB dye (91 %) than BG (82 %) and DR 80 dyes (67 %). Among the three nanocomposites, the enhanced degradation ability shown by NiO/CuO are due to its lowest particle size, reduced electron/hole pair recombination, high BET surface area and increased OH radical generation during the photocatalytic reaction. The percentage degradation of all the dyes was carried out under sun light and UV light. It has been found that the rate of dye degradation under sun light is slightly higher than in UV light due to the existence of all type of radiations in sun light.

Influence of Electron Acceptors and Donors on the Dye-Photosensitized Decomposition of 2-Mercaptobenzothiazole

It has been shown that the quantum yield of the dye-photosensitized decomposition of 2-mercaptobenzothiazole (MBT) in aqueous solutions increases in the case of irradiation of dyes in the presence of electron acceptors. In the presence of electron donors, the quantum yields of the photosensitized decomposition reaction of MBT either remains unchanged or decreases. The donor thiocyanate and iodide ions were the exception; in this case, this was due to the formation of radical anions in the subsequent reactions of iodine and thiocyanate radicals with their anions, respectively. A mechanism has been suggested for the photosensitization of 2-mercaptobenzothiazole decomposition by dyes in the presence of electron acceptors and donors.

Understanding the complexity of wastewater: The combined impacts of carbohydrates and sulphate on the performance of bioelectrochemical systems

Bioelectrochemical systems (BES) have long been viewed as a promising wastewater treatment technology. However, in reality, the performance of bioelectrochemical systems fed with real (and therefore complex) wastewaters is often disappointing. We have sought to investigate the combined impacts of complex substrates and presence of electron acceptors. In particular, this study illustrates and systematically evaluates the disparity in performance between a BES acclimatised with acetate and those acclimatised with more complex carbohydrates (glucose, sucrose or starch) and in the presence and absence of sulphate. Relative to acetate only, operating with complex carbohydrates reduced current by 73%–87% and coulombic efficiency by 4%–50%. Acclimation with complex carbohydrates seriously impeded the colonisation anode by Geobacteraceae, resulting in substantially reduced capacity to produce current (60.2% on average). Combined acclimation with sulphate further reduced current by 35% on average, and resulted in a total reduction of 83%–93% relative to the acetate control. However, the presence of an electrogenic sulphide-sulphur shuttle meant sulphate had little effect on the coulombic efficiency of the BES. The results indicate that a reduction in current and coulombic efficiency is, at present, an unavoidable consequence of operating a BES fed with complex wastewater. Researchers, designers and policy makers should incorporate such losses in both their plans and their prognostications.

Decomposition and detoxification of the insecticide thiacloprid by TiO2‐mediated photocatalysis: kinetics, intermediate products and transformation pathways

AbstractBackgroundPesticides are listed among the main environmental stressors directly correlated with severe impacts on ecosystems and human health. Here, the potential of TiO2‐mediated photocatalytic oxidation of the insecticide thiacloprid, in aqueous media, is investigated thoroughly.ResultsDegradation was investigated under various operational conditions, including the initial concentration of the pesticide, the type and amount of catalyst, pH and the presence of electron acceptors. The prevalence of TiO2 P25 in comparison to the other titania employed, is obvious both in the case of decomposition and carbon mineralization. Twenty‐seven transformation products generated during the photocatalytic decomposition of thiacloprid under UV‐A irradiation were elucidated by high‐resolution liquid chromatography mass spectrometry analysis, enabling the proposition of potential fragmentation pathways. The initial ecotoxicity of the insecticide determined by measurements of the bioluminescence of marine bacteria Vibrio fischeri was eliminated within 240 min of UV‐A irradiation in the presence of TiO2 P25. A phytotoxicity evaluation based on three eukaryotic plant species led to similar conclusions, resulting in the complete removal of phytotoxicity within 240 min of UV‐A illumination in the presence of TiO2 P25.ConclusionsThese findings suggest that TiO2‐mediated photocatalytic oxidation has the potential to efficiently detoxify water containing neonicotinoid pesticides. © 2019 Society of Chemical Industry

Visible-light-driven MIL-53(Fe)/BiOCl composite assisted by persulfate: Photocatalytic performance and mechanism

The novel semiconductor heterojunction of MIL-53(Fe)/BiOCl composite was first prepared through the solvothermal reaction. The prepared materials were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and ultraviolet-visible diffuse reflectance spectroscopy (DRS). MIL-53(Fe)/BiOCl heterojunction is a kind of photoexcited materials and it accelerates the photoreactivity of BiOCl under the visible light irradiation. It was used to remove Rhodamine B (RhB) with the existence of persulfate (PS). The UV–vis spectrophotometer and the TOC detector show that the degradation rate and TOC removal efficiency of RhB (20 mg/L) are 99.5% and 69.4%within 30 min visible-light irradiation, respectively. Due to the proper band gap of material and the presence of electron acceptor, PS, the survival time of active radicals are increased. The active species h+, ·SO4− and ·OH are found to play the important roles during the reaction system. The possible mechanism for the RhB degradation of MIL-53(Fe)/BiOCl/PS is also proposed. Furthermore, the results of the material reusability for the degradation of RhB indicate that the MIL-53(Fe)/BiOCl has a good stability and can be used in the environmental water sample treatment.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge: Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products (SMP) with the shift of the substrate condition from a feast to a famine phase in biological treatment systems. This study demonstrated that the formation of SMP could be suppressed by up to 75% during the famine phase with the addition of essential nutrients. In contrast, presence of electron acceptor did not play any significant role during the stress condition, showing the similar amounts of SMP (r = 0.98, p < 0.05) formation between the bioreactors supplied with air and N2. The SMP formed in the famine phase was more bio-refractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition (R2 > 0.95). The fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM-PARAFAC) revealed the presence of four different fluorescent components, including two protein-like (C1 and C4), fulvic-like (C2), and humic-like (C3) components, in the SMP and bEPS formed at different conditions. Both C1 and C4 showed increasing trends (R2 > 0.95) with the length of starvation in the bioreactors without essential nutrients. Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers. This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules (particularly proteins), which typically exert many environmental concerns to effluent organic matter quality.

Photocatalytic degradation performance and mechanism of dibutyl phthalate by graphene/TiO2 nanotube array photoelectrodes

Graphene loaded TiO2 nanotube array (GR/TNA) photoelectrodes were prepared by using anodization and electrodeposition approaches. The effects of different pH values, anions, bias potentials and electron acceptors on the photocatalytic activity of GR/TNA photoelectrodes in the degradation of dibutyl phthalate (DBP) were systematically investigated. Enhanced DBP removal ratio of 87.9% was achieved by GR/TNA photoelectrodes after 90 min of illumination. As a result, with the increase of initial pH values, the DBP removal ratio was also gradually increased. The addition of anions negatively affect the photocatalytic degradation of DBP by the order of NO3− > HCO3− > SO42− > Cl−. After applying a bias potential of +1.0 V, the highest DBP removal ratio of 98% was obtained. In addition, the presence of electron acceptors, KBrO3, K2S2O8 and H2O2, improved the photocatalytic activity of GR/TNA photoelectrodes. Furthermore, to better understand the underlying pathways in the photocatalytic degradation of DBP, the involved reactive species and produced intermediates were detected and analyzed. The major reactive species involved in this system were testified to be hydroxyl, superoxide radicals and holes by performing trapping experiments. The possible mechanism for the photocatalytic degradation of DBP was also proposed and discussed in detail.

Eco-friendly green synthesis of Ag@Fe bimetallic nanoparticles: Antioxidant, antimicrobial and photocatalytic degradation of bromothymol blue

Silver-iron bimetallic nanoparticles (BMNPs) were synthesized by using AgNO3 and Fe(NO3)3 as an Ag/Fe source in presence of Palm dates fruit. Upon addition of extract to a solution of Ag+ and Fe3+, a prefect transparent stable dark brown color appears with in a few minuets at room temperature. In order to conform the nature of resulting color, UV–visible spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) techniques were used. The absence of surface plasmon resonance (SPR) peaks in the entire UV–visible region suggests the formation of silvercore-ironshell BMNPs. The obtained nanoparticles were used as a catalyst for the degradation of bromothymol blue (BTB) in absence and presence of sunlight. The degradation kinetics was studied in presence of electron acceptors and scavengers, such as hydrogen peroxide, ammonium oxalate, ammonium per sulphate, benzoquinone, isopropyl alcohol, n-butanol, potassium bromate and potassium iodide. Radical trapping experiments demonstrates that active holes (h+) and generated hydroxy radical are primary species involved in H2O2 assisted catalytic degradation process. The free-radical scavenging, antioxidant and antimicrobial activities were determined for extract and BMNPs. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities were found to increase with increasing the amounts of extract. The silver-iron showed good invitro antibacterial activities against human pathogens.

Effects of different external carbon sources and electron acceptors on interactions between denitrification and phosphorus removal in biological nutrient removal processes.

The effects of two different external carbon sources (acetate and ethanol) and electron acceptors (dissolved oxygen, nitrate, and nitrite) were investigated under aerobic and anoxic conditions with non-acclimated process biomass from a full-scale biological nutrient removal-activated sludge system. When acetate was added as an external carbon source, phosphate release was observed even in the presence of electron acceptors. The release rates were 1.7, 7.8, and 3.5 mg P/(g MLVSS·h) (MLVSS: mixed liquor volatile suspended solids), respectively, for dissolved oxygen, nitrate, and nitrite. In the case of ethanol, no phosphate release was observed in the presence of electron acceptors. Results of the experiments with nitrite showed that approximately 25 mg NO2-N/L of nitrite inhibited anoxic phosphorus uptake regardless of the concentration of the tested external carbon sources. Furthermore, higher denitrification rates were obtained with acetate (1.4 and 0.8 mg N/(g MLVSS·h)) compared to ethanol (1.1 and 0.7 mg N/ (g MLVSS·h)) for both anoxic electron acceptors (nitrate and nitrite).

Electron acceptors effect on photocatalytic degradation of metformin under sunlight irradiation

The water purification is a serious issue especially with the unprecedented growth of pollutants from pharmaceutical industries. The metformin, an antidiabetic drug, is one of pharmaceutical pollutants that can be found in domestic and hospital wastewater which are suspected to affect the balance of ecosystems and the human health even at low concentrations. In this paper, we study the metformin elimination from wastewater using heterogeneous photocatalysis. We investigate the metformin degradation in aqueous medium under sunlight irradiation in the presence of titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) as catalyst and in a semi-pilot solar reactor. Contrary to existing works, we use electron acceptors such as hydrogen peroxide (H2O2), potassium persulphate K2S2O8 and sodium persulphate Na2S2O8 to improve the TiO2 photocatalytic activity. Different TiO2 photocatalysts were used (P25, EL10, DT51, PC105, PC500 and T42) for preliminary study before selecting P25. The solar reactor was (i) set facing south and (ii) a peristaltic pump is used to re-circulate the treated mixture between the reactor and the reservoir in a closed circuit. During sunlight irradiation, the solution of metformin was homogenized by magnetic stirrer. The degradation was monitored by measuring the metformin concentration using a UV-visible spectrophotometer at wavelength of 236 nm. The used photocatalysts were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average crystallite size was estimated using X-ray diffraction. The experimental results showed that metformin degradation rate in presence of electron acceptors was increased significantly during photocatalysis compared to photolysis and adsorption. The apparent rate constant of every reaction involved was evaluated and the kinetics of degradation was described by the Langmuir-Hinshelwood (L-H) model.

Crystal transformation of 2D tungstic acid H2WO4 to WO3 for enhanced photocatalytic water oxidation

New photocatalytic materials for stable reduction and/or oxidization of water by harvesting a wider range of visible light are indispensable to achieve high practical efficiency in artificial photosynthesis. In this work, we prepared 2D WO3·H2O and WO3 nanosheets by a one-pot hydrothermal method and sequent calcination, focusing on the effects of crystal transformation on band structure and photocatalytic performance for photocatalytic water oxidation in the presence of electron acceptors (Ag+) under simulated solar light irradiation. The as-prepared WO3 nanosheets exhibit enhanced rate of photocatalytic water oxidation, which is 6.3 and 3.6 times higher than that of WO3·H2O nanosheets and commercial WO3, respectively. It is demonstrated that the releasing of water molecules in the crystal phase of tungstic acid results in transformation of the crystal phase from orthorhombic WO3·H2O to monoclinic WO3, significantly improving the activity of photocatalytic water oxidation in the presence of Ag+ because the shift-up of conduction band of WO3 matches well with the electrode potential of Ag+/Ag(s), leading to efficient separation of photoinduced electrons and holes in pure WO3 nanosheets.