Graphene-Oxide-Based Fluoro- and Chromo-Genic Materials and Their Applications

Composite materials and their applications constitute a hot field of research nowadays due to the fact that they comprise a combination of the unique properties of each component of which they consist. Very often, they exhibit better performance and properties compared to their combined building blocks. Graphene oxide (GO), as the most widely used derivative of graphene, has attracted widespread attention because of its excellent properties. Abundant oxygen-containing functional groups on GO can provide various reactive sites for chemical modification or functionalization of GO, which in turn can be used to develop novel GO-based composites. This review outlines the most recent advances in the field of novel dyes and pigments encompassing GO as a key ingredient or as an important cofactor. The interactions of graphene with other materials/compounds are highlighted. The special structure and unique properties of GO have a great effect on the performance of fabricated hybrid dyes and pigments by enhancing the color performance of dyes, the anticorrosion properties of pigments, the viscosity and rheology of inks, etc., which further expands the applications of dyes and pigments in dyeing, optical elements, solar-thermal energy storage, sensing, coatings, and microelectronics devices. Finally, challenges in the current development as well as the future prospects of GO-based dyes and pigments are also discussed. This review provides a reference for the further exploration of novel dyes and pigments.

Non-enzymatic electrochemical dopamine sensing probe based on hexagonal shape zinc-doped cobalt oxide (Zn-Co2O4) nanostructure

A non-enzymatic dopamine electrochemical sensing probe was developed. A hexagonal shape zinc-doped cobalt oxide (Zn-Co₂O₄) nanostructure was prepared by a facile hydrothermal approach. The combination of Zn, which has an abundance of electrons, and Co₃O₄ exhibited a synergistically electron-rich nanocomposite. The crystallinity of the nanostructure was investigated using X-ray diffraction. A scanning electron microscope (SEM) was used to examine the surface morphology, revealing hexagonal nanoparticles with an average particle size of 400 nm. High-resolution transmission electron microscopy (HR-TEM) was used to confirm the nanostructure of the doped material. The nanostructure's bonding and functional groups were verified using Fourier transform infrared spectroscopy (FTIR). The electrochemical characterization was conducted by using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and amperometry. The resistivity of the electrode was confirmed through EIS and showed that the bare glassy carbon electrode (GCE) exhibited higher charge transfer resistance as compared to modified Zn-Co₂O₄/GCE. The sensing probe was developed by modifying the surface of GCE with Zn-Co₂O₄ nanostructure and tested as an electrochemical sensor for dopamine oxidation; it operated best at a working potential of 0.17 V (vs Ag/AgCl). The developed sensor exhibited a low limit of detection (0.002 µM), a high sensitivity (126 µA. µM^-1 cm^-2), and a wide linear range (0.2 to 185 µM). The sensor showed a short response time of < 1 s. The sensor's selectivity was investigated in the presence of coexisting species (uric acid, ascorbic acid, adrenaline, epinephrine, norepinephrine, histamine, serotonin, tyramine, phenethylamine, and glucose) with no effects on dopamine determination results. The developed sensor was also successfully used for determining dopamine concentrations in a real sample.

Perioperative intravenous contrast administration and the incidence of acute kidney injury after major gastrointestinal surgery: prospective, multicentre cohort study

BACKGROUND

This study aimed to determine the impact of preoperative exposure to intravenous contrast for CT and the risk of developing postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery.

METHODS

This prospective, multicentre cohort study included adults undergoing gastrointestinal resection, stoma reversal or liver resection. Both elective and emergency procedures were included. Preoperative exposure to intravenous contrast was defined as exposure to contrast administered for the purposes of CT up to 7 days before surgery. The primary endpoint was the rate of AKI within 7 days. Propensity score-matched models were adjusted for patient, disease and operative variables. In a sensitivity analysis, a propensity score-matched model explored the association between preoperative exposure to contrast and AKI in the first 48 h after surgery.

RESULTS

A total of 5378 patients were included across 173 centres. Overall, 1249 patients (23·2 per cent) received intravenous contrast. The overall rate of AKI within 7 days of surgery was 13·4 per cent (718 of 5378). In the propensity score-matched model, preoperative exposure to contrast was not associated with AKI within 7 days (odds ratio (OR) 0·95, 95 per cent c.i. 0·73 to 1·21; P = 0·669). The sensitivity analysis showed no association between preoperative contrast administration and AKI within 48 h after operation (OR 1·09, 0·84 to 1·41; P = 0·498).

CONCLUSION

There was no association between preoperative intravenous contrast administered for CT up to 7 days before surgery and postoperative AKI. Risk of contrast-induced nephropathy should not be used as a reason to avoid contrast-enhanced CT.

High-capacity conductive nanocellulose paper sheets for electrochemically controlled extraction of DNA oligomers

Highly porous polypyrrole (PPy)-nanocellulose paper sheets have been evaluated as inexpensive and disposable electrochemically controlled three-dimensional solid phase extraction materials. The composites, which had a total anion exchange capacity of about 1.1 mol kg⁻¹, were used for extraction and subsequent release of negatively charged fluorophore tagged DNA oligomers via galvanostatic oxidation and reduction of a 30–50 nm conformal PPy layer on the cellulose substrate. The ion exchange capacity, which was, at least, two orders of magnitude higher than those previously reached in electrochemically controlled extraction, originated from the high surface area (i.e. 80 m² g⁻¹) of the porous composites and the thin PPy layer which ensured excellent access to the ion exchange material. This enabled the extractions to be carried out faster and with better control of the PPy charge than with previously employed approaches. Experiments in equimolar mixtures of (dT)₆, (dT)₂₀, and (dT)₄₀ DNA oligomers showed that all oligomers could be extracted, and that the smallest oligomer was preferentially released with an efficiency of up to 40% during the reduction of the PPy layer. These results indicate that the present material is very promising for the development of inexpensive and efficient electrochemically controlled ion-exchange membranes for batch-wise extraction of biomolecules.

Spatial mapping of elemental distributions in polypyrrole-cellulose nanofibers using energy-filtered transmission electron microscopy

The energy-filtered transmission electron microscopy (EFTEM) technique has been used to study ion-exchange processes in conductive polymer composite nanofibers. The elemental distributions of carbon, nitrogen, oxygen, chlorine, boron, phosphorus, molybdenum, and sulfur within polypyrrole-cellulose nanofibers, used as potential controlled electrochemical solid phase extraction media, have been studied by EFTEM. The distribution of ions within the polypyrrole-cellulose nanofibers and the penetration depth of ions into the material as a function of the size and charge of the latter were investigated. Further, the spatial distribution of single stranded DNA hexamers inside polypyrrole-cellulose nanofibers was mapped subsequent to the electrochemically controlled extraction of DNA from a borate buffer solution. The results show that the EFTEM mapping technique provides unpreceded possibilities for studies of the distribution of ions inside conductive polymer composites.

A nanocellulose polypyrrole composite based on microfibrillated cellulose from wood

It is demonstrated that it is possible to coat the individual fibers of wood-based nanocellulose with polypyrrole using in situ chemical polymerization to obtain an electrically conducting continuous high-surface-area composite. The experimental results indicate that the high surface area of the water dispersed material, to a large extent, is maintained upon normal drying without the use of any solvent exchange. Thus, the employed chemical polymerization of polypyrrole on the microfibrillated cellulose (MFC) nanofibers in the hydrogel gives rise to a composite, the structure of which—unlike that of uncoated MFC paper—does not collapse upon drying. The dry composite has a surface area of ∼90 m²/g and a conductivity of ∼1.5 S/cm, is electrochemically active, and exhibits an ion-exchange capacity for chloride ions of 289 C/g corresponding to a specific capacity of 80 mAh/g. The straightforwardness of the fabrication of the present nanocellulose composites should significantly facilitate industrial manufacturing of highly porous, electroactive conductive paper materials for applications including ion-exchange and paper-based energy storage devices.

Ultrafast all-polymer paper-based batteries

Conducting polymers for battery applications have been subject to numerous investigations during the last two decades. However, the functional charging rates and the cycling stabilities have so far been found to be insufficient for practical applications. These shortcomings can, at least partially, be explained by the fact that thick layers of the conducting polymers have been used to obtain sufficient capacities of the batteries. In the present letter, we introduce a novel nanostructured high-surface area electrode material for energy storage applications composed of cellulose fibers of algal origin individually coated with a 50 nm thin layer of polypyrrole. Our results show the hitherto highest reported charge capacities and charging rates for an all polymer paper-based battery. The composite conductive paper material is shown to have a specific surface area of 80 m(2) g(-1) and batteries based on this material can be charged with currents as high as 600 mA cm(-2) with only 6% loss in capacity over 100 subsequent charge and discharge cycles. The aqueous-based batteries, which are entirely based on cellulose and polypyrrole and exhibit charge capacities between 25 and 33 mAh g(-1) or 38-50 mAh g(-1) per weight of the active material, open up new possibilities for the production of environmentally friendly, cost efficient, up-scalable and lightweight energy storage systems.

Influence of the type of oxidant on anion exchange properties of fibrous Cladophora cellulose/polypyrrole composites

The electrochemically controlled anion absorption properties of a novel large surface area composite paper material composed of polypyrrole (PPy) and cellulose derived from Cladophora sp. algae, synthesized with two oxidizing agents, iron(III) chloride and phosphomolybdic acid (PMo), were analyzed in four different electrolytes containing anions (i.e., chloride, aspartate, glutamate, and p-toluenesulfonate) of varying size.The composites were characterized with scanning and transmission electron microscopy, N2 gas adsorption,and conductivity measurements. The potential-controlled ion exchange properties of the materials were studied by cyclic voltammetry and chronoamperometry at varying potentials. The surface area and conductivity of the iron(III) chloride synthesized sample were 58.8 m2/g and 0.65 S/cm, respectively, while the corresponding values for the PMo synthesized sample were 31.3 m2/g and 0.12 S/cm. The number of absorbed ions per sample mass was found to be larger for the iron(III) chloride synthesized sample than for the PMo synthesized one in all four electrolytes. Although the largest extraction yields were obtained in the presence of the smallest anion (i.e., chloride) for both samples, the relative degree of extraction for the largest ions (i.e., glutamate and p-toluenesulfonate) was higher for the PMo sample. This clearly shows that it is possible to increase the extraction yield of large anions by carrying out the PPy polymerization in the presence of large anions. The results likewise show that high ion exchange capacities, as well as extraction and desorption rates, can be obtained for large anions with high surface area composites coated with relatively thin layers of PPy.