Electron Donor Source Research Articles

Sustainable Abiotic-Biotic Dechlorination of Perchloroethene with Sulfidated Nanoscale Zero-Valent Iron as Electron Donor Source.

Combining organohalide-respiring bacteria with nanoscale zero-valent iron (nZVI) represents a promising approach for remediating chloroethene-contaminated aquifers. However, limited information is available regarding their synergistic dechlorinating ability for chloroethenes when nZVI is sulfidated (S-nZVI) under the organic electron donor-limited conditions typically found in deep aquifers. Herein, we developed a combined system utilizing a mixed culture containing Dehalococcoides (Dhc) and S-nZVI particles, which achieved sustainable dechlorination with repeated rounds of spiking with 110 μM perchloroethene (PCE). The relative abundance of Dhc considerably increased from 5.2 to 91.5% after five rounds of spiking with PCE, as evidenced by 16S rRNA gene amplicon sequencing. S-nZVI corrosion generated hydrogen as an electron donor for Dhc and other volatile fatty acid (VFA)-producing bacteria. Electron balance analysis indicated that 68.1% of electrons from Fe0 consumed in S-nZVI were involved in dechlorination, and 6.2, 1.1, and 3.2% were stored in formate, acetate, and other VFAs, respectively. The produced acetate possibly served as a carbon source for Dhc. Metagenomic analysis revealed that Desulfovibrio, Syntrophomonas, Clostridium, and Mesotoga were likely involved in VFA production. These findings provide valuable insights into the synergistic mechanisms of biotic and abiotic dechlorination, with important implications for sustainable remediation of electron donor-limited aquifers contaminated by chloroethenes.

Unveiling the Significance of tert-Butoxides in Transition Metal-Free Cross-Coupling Reactions.

The astounding reactivity of tert-butoxides in transition metal-free coupling reactions is driving the scientific community towards a new era of environmental friendly, as well as cost-effective, transformation strategies. Transition metal-catalyzed coupling reactions generate hazardous wastes and require harsh reaction conditions, mostly at elevated temperature, which increases not only costs but also environmental concerns regarding the methodology. Tert-butoxide-catalyzed/mediated coupling reactions have several advantages and potential applications. They can form carbon-carbon, carbon-heteroatom, and heteroatom-heteroatom bonds under mild reaction conditions. Mechanistic insights into these reactions include both ionic and radical pathways, with the fate of the intermediates depending on the reaction conditions and/or additives used in the reactions. Among all of the known tert-butoxides, potassium tert-butoxide has pronounced applications in transition metal-free coupling reactions as compared to other tert-butoxides, such as sodium and lithium tert-butoxides, because of the higher electropositivity of potassium compared to sodium and lithium. Moreover, potassium tert-butoxide can act as a source of base, nucleophile and single electron donors in various important transformations. In this review, we provide an extensive overview and complete compilation of transition metal-free cross-coupling reactions catalyzed/promoted by tert-butoxides during the past 10years.

Characterisation of dissolved organic matter in two contrasting arsenic-prone sites in Kandal Province, Cambodia

Aquifers throughout Asia are impacted by the release of geogenic arsenic (As) into groundwater by microbial reduction of As-bearing Fe(III) (oxy)hydroxide minerals, severely impacting water quality. Groundwater dissolved organic matter (DOM) is likely key to As release, mainly as electron donor or electron shuttles. This study used optical analyses and ultra-high resolution mass spectrometry to examine the sources and composition of groundwater DOM in the As-prone aquifers of Kandal Province, Cambodia, at boreholes with differing host lithology (clay- and sand-dominated). Groundwater and surface water DOM composition were related to As concentrations, to infer the potential role of DOM in promoting As release. Optical and molecular-level analyses indicated an overall dominance of terrestrial-derived DOM in the groundwater samples, with higher freshness index and relative abundance (RA) of aliphatic compounds in clay compared to sand-dominated lithology. Compared to surface water, groundwater DOM had relatively lower O/C ratios and nominal oxidation state of carbon (−0.19 to −0.13 compared to 0.04 for ground and surface water, respectively), with a lower %RA of aliphatic compounds and higher %RA of carboxyl-rich alicyclic molecules, suggesting microbial processing of DOM since percolation into the aquifer. Concentrations of As across both sites were negatively correlated with DOM tryptophan:fulvic-like fluorescence and the %RA of aliphatics, potentially indicating microbial degradation of biolabile DOM in connection with As release, which is consistent with its role as an electron donor source. Together these data support DOM composition as an important control on microbial mediated As release.

Enhanced indigenous consortia for the remediation of uranium-contaminated groundwater by bioaugmentation: Reducing and phosphate-solubilizing consortia

To investigate the strengthening effects and mechanisms of bioaugmentation on the microbial remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization, two exogenous microbial consortia with reducing and phosphate-solubilizing functions were screened and added to uranium-contaminated groundwater as the experimental groups (group B, reducing consortium added; group C, phosphate-solubilizing consortium added). β-glycerophosphate (GP) was selected to stimulate the microbial community as the sole electron donor and phosphorus source. The results showed that bioaugmentation accelerated the consumption of GP and the proliferation of key functional microbes in groups B and C. In group B, Dysgonomonas, Clostridium_sensu_stricto_11 and Clostridium_sensu_stricto_13 were the main reducing bacteria, and Paenibacillus was the main phosphate-solubilizing bacteria. In group C, the microorganisms that solubilized phosphate were mainly unclassified_f_Enterobacteriaceae. Additionally, bioaugmentation promoted the formation of unattached precipitates and alleviated the inhibitory effect of cell surface precipitation on microbial metabolism. As a result, the formation rate of U-phosphate precipitates and the removal rates of aqueous U(VI) in both groups B and C were elevated significantly after bioaugmentation. The U(VI) removal rate was poor in the control group (group A, with only an indigenous consortium). Propionispora, Sporomusa and Clostridium_sensu_stricto_11 may have played an important role in the removal of uranium in group A. Furthermore, the addition of a reducing consortium promoted the reduction of U(VI) to U(IV), and immobilized uranium existed in the form of U(IV)-phosphate and U(VI)-phosphate precipitates in group B. In contrast, U was present mainly as U(VI)-phosphate precipitates in groups A and C. Overall, bioaugmentation with an exogenous consortium resulted in the rapid removal of uranium from groundwater and the formation of U-phosphate minerals and served as an effective strategy for improving the treatment of uranium-contaminated groundwater in situ.

Hantzsch Esters Enabled [2π+2σ] Cycloadditions of Bicyclo [1.1.0] butanes and Alkenes under Photo Conditions.

Hantzsch esters (HEs) are widely recognized as sources of hydride ions (H-) and sacrificial electron donors in their ground state. Here, we report the application of HE as a mediator in [2π+2σ] cycloaddition of bicyclo[1.1.0]butanes (BCBs) with alkenes under photo conditions. Through this strategy, various substituted bicyclo[2.1.1]hexanes can be efficiently prepared.

Thiovibrio frasassiensis gen. nov., sp. nov., an autotrophic, elemental sulphur disproportionating bacterium isolated from sulphidic karst sediment, and proposal of Thiovibrionaceae fam. nov.

A novel, autotrophic, mesophilic bacterium, strain RS19-109T, was isolated from sulphidic stream sediments in the Frasassi Caves, Italy. The cells of this strain grew chemolithoautotrophically under anaerobic conditions while disproportionating elemental sulphur (S0) and thiosulphate, but not sulphite with bicarbonate/CO2 as a carbon source. Autotrophic growth was also observed with molecular hydrogen as an electron donor, and S0, sulphate, thiosulphate, nitrate and ferric iron as electron acceptors. Oxygen was not used as an electron acceptor and sulphide was not used as an electron donor. Weak growth was observed with sulphate as an electron acceptor and organic carbon as an electron donor and carbon source. The strain also showed weak growth by fermentation of tryptone. It grew at pH 5.5–7.5 (optimum, pH 7.0), 4–35 °C (optimum, 30 °C) and between 0–1.7 % NaCl. Strain RS19-109T was found to be phylogenetically distinct based on 16S rRNA gene sequence similarity (89.2 %) to its closest relative, Desulfurivibrio alkaliphilus AHT2T. The draft genome sequence for strain RS19-109T had average nucleotide identity, average amino acid identity and in silico DNA–DNA hybridization values of 72.2, 63.0 and 18.3 %, respectively, compared with the genome sequence of D. alkaliphilus AHT2T. On the basis of its physiological and genomic properties, strain RS19-109T is proposed as the type strain of a novel species of a novel genus, Thiovibrio frasassiensis gen. nov., sp. nov. A novel family, Thiovibrionaceae fam. nov., is proposed to accommodate Thiovibrio within the order Desulfobulbales . Strain RS19-109T has been deposited at the DSMZ-German Collection of Microorganisms and Cell Cultures (=DSM 115074T) and the American Type Culture Collection (=ATCC TSD-325T).

Characterizing Atrazine Degradation by Molybdenum-reducing Pseudomonas sp.

The most feasible and economical technique for removal of toxic compounds in the polluted environment is bioremediation. This technique surpasses other physicochemical methods in recent time for being effective particularly at a lower concentration of the toxicant. In this study, seven (7) previously isolated molybdenum-reducing bacteria were screened for their potential to degrade atrazine herbicide as sole carbon source for growth. Bacterial colony count on mineral salt medium supplemented with atrazine was used for the screening, while the effects of incubation time, concentration, temperature, pH, inoculum size and heavy metals on atrazine biodegradation was used in characterizing the candidate isolate. Of the seven isolates, an isolate identified as Pseudomonas sp. that grew best with a count of 195 CFU/mL was chosen. The optimum conditions supporting atrazine degradation by Pseudomonas sp. were found to be temperature 35 °C, pH 7.0, incubation time 48 hours and 400 µL inoculum. The use of atrazine as carbon and electron donor source for molybdenum reduction, poorly support molybdenum blue (Mo-blue) production. At a concentration (2 ppm), heavy metals such as lead and copper did not significantly (p>0.05) affect atrazine biodegradation relative to control, iron and silver shows a relative stimulatory effect to the process, while mercury and zinc showed significant (p<0.05) inhibitory effect when compared to control. The ability of the isolate to degrade atrazine makes it an important instrument for bioremediation of this herbicide.

A Red Light-Inducible Copper-Photodeposited All-Solid-State Z-Scheme Photocatalyst for Carbon Dioxide Reduction to Methane Using Water as an Electron Donor

We selectively loaded various amounts of copper (Cu) as a cocatalyst for the reduction reaction onto zinc rhodium oxide (ZnRh2O4 (ZRO)) in a heterojunction photocatalyst and silver (Ag)-inserted ZRO and bismuth vanadium oxide (Bi4V2O11 (BVO)) solid-state photocatalyst (ZRO/Ag/BVO (ZAB)) to form Cu/ZAB. The amount of deposited Cu was controlled by the photodeposition time to generate Cu/ZAB with up to 0.14 wt % Cu cocatalyst vs ZAB. All the prepared Cu/ZAB samples accomplished overall water splitting under red light irradiation at a wavelength of 700 nm, enhancing the stoichiometric evolutions of hydrogen and oxygen from water compared with bare ZAB. Moreover, the apparent quantum efficiency increased up to 0.13 wt % Cu cocatalyst, which thereafter tended to decrease. The optimized Cu/ZAB photocatalyst was confirmed to reduce carbon dioxide (CO2) to methane using water as an electron donor and proton source under irradiation with visible light at a wavelength of 700 nm, which is, to our knowledge, the longest wavelength reported to date for CO2 reduction.

Biointeraction of cerium oxide and neodymium oxide nanoparticles with pure culture Methylobacterium extorquens AM1

Rare earth elements (REE) are valuable raw materials in our modern life. Extensive REE application from electronic devices to medical instruments and wind turbines, and non-uniform distribution of these resources around the world, make them strategically and economically important for countries. Current REE physical and chemical mining and recycling methods could have negative environmental consequences, and biologically-mediated techniques could be applied to overcome this issue. In this study, the bioextraction of cerium oxide and neodymium oxide nanoparticles (REE-NP) by a pure culture Methylobacterium extorquens AM1 (ATCC®14718™) was investigated in batch experiments. Results show that adding up to 1000 ppm CeO2 or Nd2O3 nanoparticles (REE-NP) did not seem to affect the bacterial growth over 14-days contact time. Effect of methylamine hydrochloride as an essential electron donor and carbon source for microbial oxidation and growth was also observed inasmuch as there was approximately no growth when it does not exist in the medium. Although very low concentrations of cerium and neodymium in the liquid phase were measured, concentrations of 45 μg/gcell Ce and 154 μg/gcell Nd could be extracted by M. extorquens AM1. Furthermore, SEM-EDS and STEM-EDS confirmed surface and intracellular accumulation of nanoparticles. These results confirmed the ability of M. extorquens to accumulate REE nanoparticles.

Understanding the impacts of intermittent electro field on the bioelectrochemical aniline degradation system: Performance, microbial community and functional enzyme

On account of the lack of a sustainable electron donor source and the inhibitory effect of aniline on denitrogenation make it tough to achieve simultaneous removal of aniline and nitrogen. Herein, the strategy of adjusting electric field mode was applied to the electro-enhanced sequential batch reactors (E-SBRs: R1 (continuous ON), R2 (2 h-ON/2 h-OFF), R3 (12 h-ON/12 h-OFF), R4 (in the aerobic phase ON), R5 (in the anoxic phase ON)) to treat aniline wastewater. Aniline removal rate reached approximately 99% in the five systems. Decreasing electrical stimulation interval from 12 to 2 h significantly improved the electron utilization efficiency for aniline degradation and nitrogen metabolism. The total nitrogen removal was achieved from 70.31% to 75.63%. Meanwhile, the hydrogenotrophic denitrifiers of Hydrogenophaga, Thauera, and Rhodospirillales, enriched in reactors of minor electrical stimulation interval. Accordingly, the expression of functional enzyme related to electron transport was incremental with the proper electrical stimulation frequency.

Fe(III) enhances Cr(VI) bioreduction in a MFC-granular sludge coupling system: Experimental evidence and metagenomics analysis

The influence of Fe(III) on the bioreduction efficiency of Cr(VI) in a microbial fuel cell (MFC)-granular sludge coupling system using dissolved methane as an electron donor and carbon source was explored, and the mechanism of Fe(III) mediating enhancement in the bioreduction process of Cr(VI) in the coupling system was also investigated. Results showed that the presence of Fe(III) enhanced the ability of the coupling system to reduce Cr(VI). The average removal efficiencies of Cr(VI) in the anaerobic zone in response to 0, 5, and 20 mg/L of Fe(III) were 16.53±2.12%, 24.17±2.10%, and 46.33±4.41%, respectively. Fe(III) improved the reducing ability and output power of the system. In addition, Fe(III) enhanced the electron transport systems activity of the sludge, the polysaccharide and protein content in the anaerobic sludge. Meanwhile, X-ray photoelectron spectrometer (XPS) spectra demonstrated that Cr(VI) was reduced to Cr(III), while Fe2p participated in reducing Cr(VI) in the form of Fe(III) and Fe(II). Proteobacteria, Chloroflexi, and Bacteroidetes were the dominant phylum in the Fe(III)-enhanced MFC-granular sludge coupling system, accounting for 49.7%-81.83% of the microbial community. The relative abundance of Syntrophobacter and Geobacter increased after adding Fe(III), indicating that Fe(III) contributed to the microbial mediated anaerobic oxidation of methane (AOM) and bioreduction of Cr(VI). The genes mcr, hdr, and mtr were highly expressed in the coupling system after the Fe(III) concentration increased. Meanwhile, the relative abundances of coo and aacs genes were up-regulated by 0.014% and 0.075%, respectively. Overall, these findings deepen understanding of the mechanism of the Cr(VI) bioreduction in the MFC-granular sludge coupling system driven by methane under the influence of Fe(III).

Glyphosate Biodegradation by Molybdenum-Reducing Pseudomonas sp.

Bioremediation of pollutants, such as herbicides, is an economic and environmentally friendly process. Glyphosate is an active ingredient in most herbicides utilized for weed control and desiccation on cereal and other grain crops globally. Glyphosate pollution poses a threat to the environment and the habitats in it. In this study, an isolated molybdenum-reducing bacterium was characterized for its potential to degrade glyphosate and utilized as the sole source of carbon and electron donor. The effects of incubation time, glyphosate concentration (carbon source), inoculum size, pH, temperature, aeration and heavy metals on the growth of this bacterium were spectrophotometrically assayed as OD600 nm. The bacterium degrades glyphosate faster under shaking conditions, optimally at pH 7.0, concentration 1.0 g/L, temperature 40 ºC, and inoculum size 400 µL. Growth of this bacterium was significantly inhibited by heavy metals in the order of Cu>Zn>Pb>Hg>Ag>Fe compared to the control. Glyphosate can serve as an electron donor source in hexavalent molybdenum reduction, but poorly supports molybdenum blue (Mo-blue) production compared to glucose. The dual role of this isolate as a metal reducer and glyphosate degrader makes it unique already and an important instrument for the bioremediation of mixed pollutants.

A Minimal Light‐Driven System to Study the Enzymatic CO2Reduction of Formate Dehydrogenase

AbstractA minimal light‐driven approach was established for studying enzymatic CO2conversion spectroscopically. The system consists of a photosensitizer Eosin Y, EDTA as a sacrificial electron donor and substrate source, and formate dehydrogenase fromRhodobacter capsulatus(RcFDH) as a biocatalyst. This simplified three‐component system provides a photo‐triggered control forin situcharacterization of the entire catalytic reaction. Direct reduction ofRcFDH by the photosensitizer without additional electron carriers was confirmedviaUV‐Vis spectroscopy, while GC‐MS and IR spectroscopy were used to follow photoinduced CO2generation from EDTA and its subsequent enzymatic reduction, yielding the product formate. Photo‐driven andin vitro, dye‐based CO2reduction was inhibited by azide under a mixed (competitive‐non‐competitive) inhibition mode. IR spectroscopy reveals displacement of the competitively‐bound azide by CO2, reflecting an interaction of both with the active site cofactor. This work comprises a proof‐of‐concept for a new approach to employ light for regulating the reaction of formate dehydrogenases and other CO2reductases.

Coremoval of Energetics and Oxyanions via the In Situ Coupling of Catalytic and Enzymatic Destructions: A Solution to Ammunition Wastewater Treatment.

Ammunition wastewater contains toxic nitrated explosives like RDX and oxyanions like nitrate and perchlorate. Its treatment is challenged by low efficiency due to contaminant recalcitrance and high cost due to multiple processes needed for separately removing different contaminant types. This paper reports a H2-based low-energy strategy featuring the treatment of explosives via catalytic denitration followed by microbial mineralization coupled with oxyanion reduction. After a nitrate- and perchlorate-reducing biofilm incapable of RDX biodegradation was coated with palladium nanoparticles (Pd0NPs), RDX was rapidly denitrated with a specific catalytic activity of 8.7 gcat-1 min-1, while biological reductions of nitrate and perchlorate remained efficient. In the subsequent 30-day continuous test, >99% of RDX, nitrate, and perchlorate were coremoved, and their effluent concentrations were below their respective regulation levels. Detected intermediates and shallow metagenome analysis suggest that the intermediates after Pd-catalytic denitration of RDX ultimately were enzymatically utilized by the nitrate- and perchlorate-reducing bacteria as additional electron donor sources.

Molecular Z-Scheme for Solar Fuel Production via Dual Photocatalytic Cycles.

Natural photosynthesis uses an array of molecular structures in a multiphoton Z-scheme for the conversion of light energy into chemical bonds (i.e., solar fuels). Here, we show that upon excitation of both a molecular photocatalyst (PC) and a substituted naphthol (ROH) in the presence of a sacrificial electron donor and proton source, we achieve photocatalytic synthesis of H2. Data support a multiphoton mechanism that is catalytic with respect to both PC and ROH. The use of a naphthol molecule as both a light absorber and H2 producing catalyst is a unique motif for Z-scheme systems. This molecular Z-scheme can drive a reaction that is uphill by 511 kJ mol-1 and circumvents the high-energy constraints associated with the reduction of weak acids in their ground state, thus offering a new paradigm for the production of solar fuels.

Impact of bakery waste as an organic substrate on microbial fuel cell performance

A microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system. The current research focuses on the use of bakery waste as an organic substrate that can be a good source of electron donors. However, MFC is experiencing organic substrate instability. In this study, the bakery waste offered 71 days of stability in the continuous operation of MFC with the presence of a toxic metal inoculation source. Within 60 days, the energy 1.001 mW/m2 (power density) and 103.94 mA/m2 (current density). Electrochemical experiments also revealed that electron generation and transportation were quite high on day 60. The specific capacitance values (14 × 10-4F/g) demonstrated that biofilm growth was relatively constant throughout the operation until day 60. On the other hand, the removal efficiency of Cd2+, Pb2+, and Cr3+ was 89.90 %, 96.00 %, and 92.20 %, respectively. Bakery waste gave significantly good removal efficiency when compared to prior literate. Finally, a brief mechanism of bakery waste oxidation by bacterial species, as well as future possibilities, are discussed.

Geobacter sulfurreducens metabolism at different donor/acceptor ratios.

Geobacter species have great application potential in remediation processes and electrobiotechnology. In all applications, understanding the metabolism will enable target‐oriented optimization of the processes. The typical electron donor and carbon source of the Geobacter species is acetate, while fumarate is the usual electron acceptor. Here, we could show that depending on the donor/acceptor ratio in batch cultivation of Geobacter sulfurreducens different product patterns occur. With a donor/acceptor ratio of 1:2.5 malate accumulated as an intermediate product but was metabolized to succinate subsequently. At the end of the cultivation, the ratio of fumarate consumed and succinate produced was approximately 1:1. When fumarate was added in excess, malate accumulated in the fermentation broth without further metabolization. After the addition of acetate to stationary cells, malate concentration decreased immediately and additional succinate was synthesized. Finally, it was shown that also resting cells of G. sulfurreducens could efficiently convert fumarate to malate without an additional electron donor. Overall, it was demonstrated that by altering the donor/acceptor ratio, targeted optimization of the metabolite conversion by G. sulfurreducens can be realized.

An investigation on the ion exchange membrane bioreactor with a spiral wound contactor for nitrate removal from contaminated groundwater

In the present study, we report the first operation of a pilot scale ion exchange membrane bioreactor (IEMB). It treated 1–2 m3/d of water contaminated with nitrate. IEMB was made up of anion exchange membrane spiral module integrated with a fixed bed bioreactor (FBBR), a novel configuration for an IEMB system. Nitrate elimination was accomplished through Donnan dialysis using chloride as counter ion followed by heterotrophic denitrification in an anoxic FBBR employing glycerol as electron donor and carbon source. The performance of IEMB revealed an excellent nitrate removal at the selected operating conditions, successfully eliminating a nitrate loading rate of 5.0 kg NO3−/m3/d and producing 30 ± 5 mg/L nitrate in the effluent at steady state. Anion exchange membrane being non-selective also transferred a significant concentration of sulphate from the feed-side to the bio-side leading to sulphate accumulation in FBBR. As a result, denitrification performance was affected due to the activation of sulphate reducing bacteria leading to the upset of FBBR. Batch experimental study aiming to screen the effect of nitrate to sulphate ratio on denitrification, demonstrated the possible occurrence of sulphate reduction at [nitrate]/[sulphate] < 0.2, exhibiting a highly negative oxidation reduction potential (ORP) value (−450 mV). This signifies that a minimum [nitrate]/[sulphate] > 0.2 is required as to suppress sulphate reduction phenomenon during denitrification. IEMB calibration for denitrification using glycerol as a carbon source revealed that 100 % stoichiometric donor/acceptor (C/N) ratio was suitable for producing sufficient nitrate biodegradation and acceptable ORP value (~−220 mV). Present work established promising application prospects of IEMB comprising nitrate selective membrane module for the treatment of high nitrate wastewater with a treatment capacity of 1.5 m3/d at optimized operating conditions.

Potato waste as an effective source of electron generation and bioremediation of pollutant through benthic microbial fuel cell

The goal of this research was to improve electron generation in BMFC by utilizing potatoes waste as an electron donor source for bacterial species. Pollutant remediation is a secondary applications of BMFC, hence the current research investigated heavy metal remediation from wastewater and energized the system using potato waste. Within 20 days of operation, the present study provided 112 mV, with a maximum current density of 36.84 mA/m2. The cell measured an internal resistance of 1557 Ω, which is bit higher than the external resistance. Several electrochemical studies were also carried out to validate the BMFC findings. On day 30, the specific capacitance was measured with a cyclic voltameter at 0.00057F/g to investigate the biofilm. It demonstrates that the biofilm remains stable throughout the BMFC process. Overall, the electrochemical studies demonstrated that potato waste was a good source of bacterial activity. The Enterobacter, Proteus, and Xenorhabdus species are detected on the surface of anode. Lastly, within 40 days, the maximum efficiency of metal remediation was found to be 94.20 % (Cd2+), 97.34 % (Pb2+), and 84.12 % (Cr3+).

Sustainable hydrogen peroxide production based on dopamine through Janus-like mechanism transition from chemical to photocatalytic reactions

With increasing interest in hydrogen peroxide (H2O2) as an environmentally friendly oxidant for environmental remediation and a promising liquid fuel, we present herein a novel method for green and sustainable H2O2 production using versatile dopamine-based materials, demonstrating the conversion of H2O2 generation mechanism from a chemical to a photocatalytic process along with the structural transformation of dopamine to polydopamine. During the auto-oxidation of dopamine in the presence of oxygen, which involved the transition of catechol to hydroquinone groups and the ring closure of the amine group, H2O2 was chemically generated at a rate of 1.61 mmol g-1h−1 without an extra electron donor and additional energy sources. In contrast, self-polymerized polydopamine exhibited an effective photocatalytic H2O2 generation at a rate of 0.53 mmol g-1h−1 owing to its visible light absorptivity and semiconducting property. We anticipate that these unique properties of dopamine will provide a new class of organic-based, highly efficient solar-to-H2O2 conversion and sustainable energy systems in the future.