PVA Hydrogel Electrolyte and Porous Polyisoprene Carbon Nanostructure Composite Based Pressure Sensitive Supercapacitor

Special gratitude is in order to Raimonds Orlovs for temperature dependent resistance measurements. Financial support of project 1.1.1.1/16/A/013, “Hybrid energy harvesting systems” is greatly appreciated.Narrow operational voltage window can be considered as one of the greatest limitations for aqueous polymer electrolytes. Using freeze-thaw hydrogel preparation method we have synthesized wider potential window electrolytic polyvinyl alcohol (PVA)/Na2SO4 and PVA/K2SO4 electrolytes. Supercapacitors (SC) have been assembled using novel porous polyisoprene and carbon black composite electrodes. Our SC exhibit pressure sensitive properties therefore this effect is deeper explored here, giving explanation for capacitance increase during pressure application. It is found that up to 2 MPa the capacitance increases due to greater interface between electrode and electrolyte.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Identification of Active Sites for Oxygen Reduction Reaction on Nitrogen- and Sulfur-Codoped Carbon Catalysts

This research was financially supported by ERA.Net RUS Plus funding mechanism (Project HeDoCat) and by the European Regional Development Fund project TK134.Nitrogen- and sulfur-codoped carbon catalysts were prepared as electrocatalytic materials for the oxygen reduction reaction (ORR). Herein, we propose a novel and effective one-pot synthetic approach to prepare a NS-doped carbon catalyst by using the mixture of graphene oxide and multi-walled carbon nanotubes as a carbon support. Successful NS-doping of carbon and formation of the catalytically active sites were confirmed by X-ray photoelectron spectroscopy and with energy dispersion spectroscopy. The ORR activity of NS-codoped carbon was investigated by using a rotating disc electrode method. The NS-doped carbon shows superior ORR performance in alkaline media, and the electrocatalytic mechanism for the reduction of oxygen was well explained by density functional theory calculations of graphene sheets.ERA.Net RUS Plus Project HeDoCat; ERDF TK134; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Influence of PDA Coating on the Structural, Optical and Surface Properties of ZnO Nanostructures

Polydopamine (PDA) is a new biocompatible material, which has prospects in biomedical and sensor applications. Due to functional groups, it can host wide range of biomolecules. ZnO nanostructures are well known templates for optical sensors and biosensors. The combination of ZnO and PDA results in a change of optical properties of ZnO–PDA composites as a shift of photoluminescence (PL) peaks and PL quenching. However, to date, the effect of the PDA layer on fundamental properties of ZnO–PDA nanostructures has not been studied. The presented paper reports on optical and surface properties of novel ZnO–PDA nanocomposites. PDA layers were chemically synthesized on ZnO nanostructures from different solution concentrations of 0.3, 0.4, 0.5 and 0.7 mg/mL. Structure, electronic and optical properties were studied by SEM, Raman, FTIR, diffuse reflectance and photoluminescence methods. The Z-potential of the samples was evaluated in neutral pH (pH = 7.2). The response of the samples towards poly-l-lysine adsorption, as a model molecule, was studied by PL spectroscopy to evaluate the correlation between optical and surface properties. The role of the PDA concentration on fundamental properties was discussed

Technical Hemp Fibres Treatment by Steam Explosion

Natural fibres as a renewable resource attract attention of scientists and practitioners and their applications are spreading in different industry branches. Hemp is a prospective historical agro-industrial culture grown in Latvia for fibres. The nano-, micro- and supra-molecular structure of hemp fibres is highly complex and not clearly understood to make any final decisions. In the current study of steam explosion (SE) auto-hydrolysis the Bialobrzeckie variety grown in the Agricultural Science Centre of Latgale region in Latvia is used to treat the hemp fibres

Effect of Steam Explosion on Fibre Lignin Structure for Self-Binding Fiber Boards

The structural changes induced in fiber lignin by steam explosion was studied to better understand the effect of steam explosion conditions on bonding mechanisms of lignin containing fibers in self-binding fiber boards. In all the steam exploded lignin samples, the main lignin inter-unit linkage after 1 min treatment was the β–O–4´ alkyl aryl ether that accounts for up to nearly 80% of all inter-unit linkages. With increased steam explosion times a drastic decrease in the content of β-O-4 linkages was detected, which was accompanied with the formation of new phenolic units and decrease in molar mass. However, at the same time, some condensation of lignin occurred as well. After steam explosion, the lignin was more prone to thermally induced condensation reactions. The formation of the new phenolic groups during steam explosion, and the enhanced tendency to condensate during thermal processing, most likely contribute to the higher bonding ability of steam exploded fibers when manufacturing self-binding fiber boards