Suitability of Co-Composted Biochar with Spent Coffee Grounds Substrate for Tomato (<i>Solanum lycopersicum</i>) Fruiting Stage

Peat is the predominant component of growing media in soilless horticultural systems. However, peat extraction from peatlands destroys these fragile ecosystems and emits greenhouse gas emissions (GHG). Peat replacement by other growing media is, thus, paramount to ensure a more sustainable horticultural sector. This study investigated the agronomical performances of two spent coffee ground-based composts with and without biochar, during three different stages of tomato (Solanum lycopersicum L.) development: seeds germination (0–6 days), seedling development (7–49 days), and plant-to-fruit maturity (36–100 days). The two composts were used as peat replacement and mixed with peat at four different volumetric proportions: 100% (pure compost), 50%, 30%, and 15%. The substrates had a stimulant effect on seed germination but induced stunted growth due to the elevated electrical conductivity. For the latest stages of plant development, compost with and without biochar mixed with peat at 50% promoted an increase in fruit production of 60.8% and 100.3%, compared to the control substrate. The present study provides evidence that combining biochar with spent coffee ground compost represents a potential alternative for peat-based growing media promoting a circular production model in the horticultural sector, but the results are dilution- and plant development stage-dependent

Fabrication of high surface area graphene electrodes with high performance towards enzymatic oxygen reduction

High surface area graphene electrodes were prepared by simultaneous electrodeposition and electroreduction of graphene oxide. The electrodeposition process was optimized in terms of pH and conductivity of the solution and the obtained graphene electrodes were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and electrochemical methods (cyclic voltammetry and impedance spectroscopy). Electrodeposited electrodes were further functionalized to carry out covalent immobilization of two oxygen-reducing multicopper oxidases: laccase and bilirubin oxidase. The enzymatic electrodes were tested as direct electron transfer based biocathodes and catalytic currents as high as 1 mA/cm2 were obtained. Finally, the mechanism of the enzymatic oxygen reduction reaction was studied for both enzymes calculating the Tafel slopes and transfer coefficients.This work has received funding from the European Union’s Seventh Framework Programme under grant agreement BIOENERGY, FP7-PEOPLE-2013-ITN-607793.Peer Reviewe

Response of water-biochar interactions to physical and biochemical aging

Biochar aging may affect the interactions of biochar with water and thus its performance as soil amendment; yet the specific mechanisms underlying these effects are poorly understood. By means of FTIR, N adsorption, Hg intrusion porosimetry, thermogravimetric analysis, C solid state nuclear magnetic resonance (NMR) and H NMR relaxometry, we investigated changes in the chemistry and structure of biochar as well as its interaction with water after biochar aging, both physical (simulated by ball-milling) and biochemical (simulated by co-composting). Three different porosities of biochar were examined: <5 nm, 1 μm and 10 μm diameter sizes. Physical aging caused the disappearance of the porosity at 10 μm. With biochemical aging, biochar underwent an enrichment of oxygenated functional groups either as a result of surface functionalisation processes or by the deposition of fresh organic matter layers on the surface and pores of biochar. H NMR relaxometry revealed that the proportion of water strongly interacting with biochar increased with both physical and biochemical aging. Although biochemical aging significantly altered the composition of biochar surface and modulates its interaction with water, H NMR relaxometry proved that physical aging had a relatively stronger influence on water mobility and dynamics in biochar, lowering both T and T relaxation times in the initial contact times of biochar and water.This study was financially supported by the Comunidad de Madrid (Spain) and the Spanish National Research Council (CSIC) research grant Atracci ́on de Talento [grant number 2019T1/AMB14503]. The authors acknowledge the funding received from the Spanish National Research Council and the French National Centre for Scientific Research through the cooperation projects PICS [grant number 018FR0044] and IEA (ex-PICS) [grant number 203026]. This work was also partially funded by the Spanish Ministerio de Ciencia e Innovaci ́on (PTA 2018- 015282-I and PID 2020-119047RB-I00) and Comunidad de Madrid (PEJ-2018-TL/IND-11075). The authors want to thank the analytical services for the 1H relaxometry NMR at ICTP-CSIC, for the solid state 13C NMR at IRNAS-CSIC and for FT-IR, TGA and porosimetry analyses at ICA-CSIC. Technical support provided by Mr. H ́ector Fritis, Ms. Cristina G ́omez Ruano, Mr. David Mabilais, Mr. Fernando Martín Salamanca and Dr. Rebeca Herrero is gratefully acknowledged

Fabrication of high surface area graphene electrodes with high performance towards enzymatic oxygen reduction

Trabajo presentado en el 6th workshop Early Stage Researchers in Nanoscience, celebrado en Madrid el 22 y 23 de junio de 2016.Graphene-based electrodes have been used for several applications, such as biosensing or as support for further immobilization of enzymes for the preparation of biocathodes and/ or bioanodes. In order to overcome the low reproducibility of the current fabrication methods of graphene-based electrodes, in the present work the electrodeposition of graphene oxide and its simultaneous electrochemical reduction on the electrode surface is proposed as a reproducible method for the fabrication of stable and high surface area electrodes. The electrodeposition process was optimized in terms of pH and conductivity of the solution and the obtained graphene electrodes were characterized by X-ray photoelectron spectroscopy, Fourirer transform infrared spectroscopy, scanning electron microscopy and electrochemical methods (cyclic voltammetry and impendanc e spectroscopy). The characterization results indicate that electrochemical reduction of GO yielded a highly porous conductive surface that has still oxygen based functional groups. These functional groups have been used to immobilize two distint biocatalysts: laccase and bilirubin oxidase. The enzymatic electrodes were tested as direct electron transfer based biocathodes and catalytic currents as high as 1 mA/cm2 were obtained.N

Effect of Cu-doped graphene on the flammability and thermal properties of epoxy composites

Cu-doped graphene (graphenit-Cu) was successfully prepared through chemical reduction method, and its surface morphology, crystalline structure and Cu content in graphenit-Cu were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductive couple plasma (ICP) and electrochemical cyclic voltammetry, respectively. Graphenit-ox/epoxy systems and graphenit-Cu/epoxy systems were prepared, and the contents of graphenit-ox and graphenit-Cu were kept as 1 and 3 wt%, respectively. The effect of graphenit-ox or graphenit-Cu on the flame retardancy, combustion properties, thermal degradation and thermomechanical properties of epoxy resin was investigated systematically by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Compared to graphenit-ox, the addition of graphenit-Cu reduced the heat release rate (HRR), total smoke production (TSP) and smoke production rate (SPR), and improved LOI values of epoxy composites. Moreover, the addition of graphenit-ox also had little flame retardant effect on epoxy composite. The possible synergistic effect between graphene and Cu was confirmed in the flame retardant epoxy composites. TGA and DMA results also indicated the considerable effect on the thermal degradation and thermomechanical properties of epoxy composites with the addition of graphenit-Cu. The results supplied an effective solution for developing excellent flame retardant epoxy composites.The authors acknowledged the financial support of China Scholarship Council (CSC: 201308420380), National Natural Science Foundation of China (Grant No. U1201243) and the European Union's Seventh Framework Program for Research, Technological Development and Demonstration (607793). This research is also partly supported by Spanish Ministry of Economy and Competitiveness (MINECO) under Ramón y Cajal grant (RYC-2012-10737).Peer reviewe