Performance of Graphene/Polydimethylsiloxane Surfaces against S. aureus and P. aeruginosa Single- and Dual-Species Biofilms

The increasing incidence of implant-associated infections has prompted the development of effective strategies to prevent biofilm formation on these devices. In this work, pristine graphene nanoplatelet/polydimethylsiloxane (GNP/PDMS) surfaces containing different GNP loadings (1, 2, 3, 4, and 5 wt%) were produced and evaluated on their ability to mitigate biofilm development. After GNP loading optimization, the most promising surface was tested against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. The antibiofilm activity of GNP/PDMS surfaces was determined by the quantification of total, viable, culturable, and viable but nonculturable (VBNC) cells, as well as by confocal laser scanning microscopy (CLSM). Results showed that 5 wt% GNP loading reduced the number of total (57%), viable (69%), culturable (55%), and VBNC cells (85%) of S. aureus biofilms compared to PDMS. A decrease of 25% in total cells and about 52% in viable, culturable, and VBNC cells was observed for P. aeruginosa biofilms. Dual-species biofilms demonstrated higher resistance to the antimicrobial activity of GNP surfaces, with lower biofilm cell reductions (of up to 29% when compared to single-species biofilms). Still, the effectiveness of these surfaces in suppressing single- and dual-species biofilm formation was confirmed by CLSM analysis, where a decrease in biofilm biovolume (83% for S. aureus biofilms and 42% for P. aeruginosa and dual-species biofilms) and thickness (on average 72%) was obtained. Overall, these results showed that pristine GNPs dispersed into the PDMS matrix were able to inhibit biofilm growth, being a starting point for the fabrication of novel surface coatings based on functionalized GNP/PDMS composites

Effect of different carbon materials on the performance of microbial electrolysis cells (MECs) operated on urine and their microbial composition

ISMET 6 - General Meeting of the International Society for Microbial Electrochemistry and TechnologyUrine is rich in nitrogen and phosphorous and can considerably reduce domestic wastewater treatment requirements if collected separately. Source separated urine has been shown to be suitable for energy production and nutrients recovery in bioelectrochemical systems. However, there are still several challenges to overcome mainly related to organics conversion into electrical energy. In this study, anode performance of three microbial electrolysis cells (MECs) fed with urine using different carbon anodes, Keynol (phenolic-based), C-Tex (cellulose-based) and PAN (polyacrylonitrilebased) was compared. Two strategies were used to supply energy to the MECs; cell potential control (1' 1 assay) and anode potential control (2"d assay). In both assays, the C-Tex MEC outperformed MECs using Keynol and PAN. The C-Tex MEC with anode potential control at -0.300 V generated the highest current density of 904 mA m·2 , which was almost 3-fold higher than the MEC with Keynol, and 8-fold higher than the MEC with PAN. Analysis of anodes textural, chemical and electrochemical characteristics suggest that the higher external surface area of C-Tex enabled the higher current density generation compared to Keynol and PAN. The microbial composition on each anode and its correlation with the generated current was also investigated. No significant differences were observed in microbial diversity of the biofilm present in the studied anodes. Nonetheless, C-Tex had higher dominance of bacteria belonging to Luctobucillu/es and Enterobucteriules suggesting its relation with higher current generation.info:eu-repo/semantics/publishedVersio

Influence of carbon anode properties on performance and microbiome of Microbial Electrolysis Cells operated on urine

"Available online 15 February 2018"Anode performance of Microbial Electrolysis Cells (MECs) fed with urine using different anodes, Keynol (phenolic-based), C-Tex (cellulose-based) and PAN (polyacrylonitrile-based) was compared under cell potential control (1st assay) and anode potential control (2nd assay). In both assays, C-Tex MEC outperformed MECs using Keynol and PAN. C-Tex MEC under anode potential control (0.300V vs. Ag/AgCl) generated the highest current density (904mAm2), which was almost 3-fold higher than the Keynol MEC and 8-fold higher than the PAN MEC. Analysis of anodes textural, chemical and electrochemical characteristics suggest that the higher external surface area of C-Tex enabled higher current density generation compared to Keynol and PAN. Anodes properties did not influence significantly the microbial diversity of the developed biofilm. Nonetheless, C-Tex had higher relative abundance of bacteria belonging to Lactobacillales and Enterobacteriales suggesting its correlation with the higher current generation.This study was supported by the European Union's Seventh Programme for research, technological development and demonstration [Grant number 308535] and by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 [POCI-01- 0145-FEDER-006684], of Project RECI/BBB-EBI/0179/2012 [FCOMP01-0124-FEDER-027462], POCI-01-0145-FEDER-007679 [UID/CTM/ 50011/2013], and by BioTecNorte operation [NORTE-01-0145- FEDER-000004] funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. This work is a result of project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) and of Project POCI-01-0145- FEDER-006984 e Associate Laboratory LSRE-LCM funded by ERDF through COMPETE2020 - Programa Operacional Competitividade e Internacionalizaçao (POCI) e and by national funds through FCT. The authors also would like to acknowledge the support of Wetsus, European Centre of Excellence for Sustainable Water Technology.info:eu-repo/semantics/publishedVersio

Green synthesis of polypyrrole-supported metal catalysts: application to nitrate removal in water

Pt and Pt/Sn catalysts supported on polypyrrole (PPy) have been prepared using Ar plasma to reduce the metal precursors dispersed on the polymer. The PPy support was synthesized by chemical polymerization of pyrrole with FeCl3·6H2O, this leading to the conducting form of the polymer (conductimetric measurements). The Ar plasma treatment produced a partial reduction of platinum ions, anchored as platinum chloro-complexes to the PPy chain, into metallic platinum. A homogeneous distribution of Pt and Sn nanoparticles was observed by TEM. Activity of the PPy-supported catalysts was evaluated in the reduction of aqueous nitrate with H2 at room temperature. Nitrate concentration in water below the maximum acceptable level of 50 mg L−1 was achieved with all catalysts. However, considering not only efficiency in nitrate reduction, but also minimized concentrations of undesired nitrite and ammonium, the monometallic Pt catalyst seems to be the most promising one.Financial support from Generalitat Valenciana, Spain (PROMETEO/2009/002 – FEDER and PROMETEOII/2014/004) is gratefully acknowledged. Support by PEst-C/EQB/LA0020/2013, financed by FEDER through COMPETE – Programa Operacional Factores de Competitividade, and by FCT – Fundação para a Ciência e a Tecnologia; NORTE-07-0162-FEDER-000050, financed by QREN, ON2 and FEDER is acknowledged by LCM group. O. S. G. P. Soares acknowledges the grant received from FCT (SFRH/BPD/97689/2013)

Multi-walled carbon nanotubes enhance methanogenesis from diverse organic compounds in anaerobic sludge and river sediments

Conductive nanomaterials affect anaerobic digestion (AD) processes usually by improving methane production. Nevertheless, their effect on anaerobic communities, and particularly on specific trophic groups such as syntrophic bacteria or methanogens, is not extensively reported. In this work, we evaluate the effect of multi-walled carbon nanotubes (MWCNT) on the activity of two different anaerobic microbial communities: an anaerobic sludge and a river sediment. Methane production by anaerobic sludge was assessed in the presence of different MWCNT concentrations, with direct methanogenic substrates (acetate, hydrogen) and with typical syntrophic substrates (ethanol, butyrate). MWCNT accelerated the initial specific methane production rate (SMPR) from all compounds, with a more pronounced effect on the assays with acetate and butyrate, i.e., 2.1 and 2.6 times, respectively. In the incubations with hydrogen and ethanol, SMPR increased 1.1 and 1.2 times. Experiments with the river sediment were performed in the presence of MWCNT and MWCNT impregnated with 2% iron (MWCNT-Fe). Cumulative methane production was 10.2 and 4.5 times higher in the assays with MWCNT-Fe and MWCNT, respectively, than in the assays without MWCNT. This shows the high potential of MWCNT toward bioenergy production, in waste/wastewater treatment or ex situ bioremediation in anaerobic digesters.This research was funded by the Portuguese Foundation for Science and Technology(FCT) under the scope of project MORE (POCI-01-0145-FEDER-016575), of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020-Programa Operacional Regional do Norte, as well as FCT/MCTES trough national funds (PIDDAC) and Base Funding-UIDB/50020/20 of the Associate Laboratory LSRE-LCM-funded by national funds rough FCT/MCTES (PIDDAC). Research of O.S.G.P.S. was funded by FCT under the Scientific Employment Stimulus-Institutional Call EECINST/00049/2018.info:eu-repo/semantics/publishedVersio

Size and frequency of natural forest disturbances and Amazon carbon balance

Forest inventory studies in the Amazon indicate a large terrestrial carbon sink. However, field plots may fail to represent forest mortality processes at landscape-scales of tropical forests. Here we characterize the frequency distribution of disturbance events in natural forests from 0.01 ha to 2,651 ha size throughout Amazonia using a novel combination of forest inventory, airborne lidar and satellite remote sensing data. We find that small-scale mortality events are responsible for aboveground biomass losses of B1.28 Pg C y 1 over the entire Amazon region. We also find that intermediate-scale disturbances account for losses of B0.01 Pg C y 1 , and that the largest-scale disturbances as a result of blow-downs only account for losses of B0.003 Pg C y 1 . Simulation of growth and mortality indicates that even when all carbon losses from intermediate and large-scale disturbances are considered, these are outweighed by the net biomass accumulation by tree growth, supporting the inference of an Amazon carbon sink

Engineering single-atom Fe-N active sites on hollow carbon spheres for oxygen reduction reaction

Seeking alternatives to noble metals-based electrocatalysts for oxygen reduction reaction (ORR), hollow carbon spheres (CSs) were finely tuned with stable single-atom Fe-N species through a synthesis methodology requiring only earth-abundant metal precursors. CSs with different sizes were synthesized by sol-gel polycondensation of resorcinol with formaldehyde over silica nanoparticles, followed by thermal annealing and silica etching. A catalyst screening revealed the positive impact of both the hollow core and structural defects of the CSs for ORR. Single-atom Fe-N active sites were introduced on the best performing CSs through simultaneous incorporation of iron and nitrogen precursors, and glucose. A significant enhancement in ORR activity was observed despite the small iron load introduced (0.12 wt%). ORR performance indicators, advanced characterization, and molecular simulation studies revealed nitrogen's crucial role in anchoring individual iron atoms and modulating the charge density nearby the active sites (increase of 80 mV in the half-wave potential). Adding glucose as a chelating agent enhances the metal-heteroatom coordination and subsequent dispersion of iron, accounting for an increase of 20 mV in the half-wave potential, an average of electrons transferred as high as 3.9 (at 0.4 V vs. RHE), and higher stability (99%) than that of a platinum-based (20 wt%) electrocatalyst (92%).11 página

Covalent organic frameworks as catalyst support: A case study of thermal, hydrothermal, and mechanical pressure stability of β-ketoenamine-linked TpBD-Me2

Covalent organic frameworks (COFs) are crystalline, ordered networks, that, due to their high surface areas and the opportunity for periodic placement of catalytically active sites, are interesting materials for catalysis. Despite the great interest in the use of COFs for this application, there is currently a lack of fundamental understanding on how catalytically relevant conditions affect the integrity of the materials. To gain insight into the stability of COFs as catalyst supports, we herein subjected a β-ketoenamine-linked COF to thermal treatment at high temperatures, to autogenous pressure in water at different temperatures, and to mechanical pressure during pelletizing, after which the materials were thoroughly characterized to gain insight into the structural changes occurring during these catalytically relevant treatments. The COF was largely stable under all hydrothermal conditions studied, highlighting the applicability of β-ketoenamine-linked COFs under aqueous and vapor conditions. On the other hand, thermal and pressure treatments led to a rapid decline in the surface area already at the lowest temperatures and pressures studied. Theoretical calculations indicated this loss to stem from interlayer rearrangement or buckling of the COF layers induced by the applied conditions. This study demonstrates the suitability of β-ketoenamine-linked COFs for use under hydrothermal conditions, and sheds light on the degradation pathways under thermal and pressure treatments, opening the path to the design of COFs with increased stability under such conditions.Fundação para a Ciência e a Tecnologia | Ref. UTA-EXPL/NPN/0055/2019Fundação para a Ciência e a Tecnologia | Ref. PTDC/QUI-OUT/2095/2021Fundação para a Ciência e a Tecnologia | Ref. PTDC/EQU-EQU/1707/2020Agencia Estatal de Investigación | Ref. RYC2020-030414-IUniversidade de Vigo/CISU

Highly N2-Selective Activated Carbon-Supported Pt-In Catalysts for the Reduction of Nitrites in Water

The catalytic reduction of nitrites over Pt-In catalysts supported on activated carbon has been studied in a semi-batch reactor, at room temperature and atmospheric pressure, and using hydrogen as the reducing agent. The influence of the indium content on the activity and selectivity was evaluated. Monometallic Pt catalysts are very active for nitrite reduction, but the addition of up to 1 wt% of indium significantly increases the nitrogen selectivity from 0 to 96%. The decrease in the accessible noble metal surface area reduces the amount of hydrogen available at the catalyst surface, this favoring the combination of nitrogen-containing intermediate molecules to promote the formation of N2 instead of being deeply hydrogenated into NH4+. Several activated carbon-supported Pt-In catalysts, activated under different calcination and reduction temperatures, have been also evaluated in nitrite reduction. The catalyst calcined and reduced at 400°C showed the best performance considering both the activity and the selectivity to nitrogen. This enhanced selectivity is ascribed to the formation of Pt-In alloy. The electronic properties of Pt change upon alloy formation, as it is demonstrated by XPS.This work was financially supported by Base-UIDB/50020/2020 and Programmatic-UIDP/50020/2020 Funding of LSRE-LCM, funded by natiunal funds through FCT/MCTES (PIDDAC). Financial support from Ministerio de Ciencia e Innovación (Spain, Project PID 2019-108453GB-C21 and PID 2020-116998RB-I00) is gratefully acknowledged