An ex situ electrocatalytic analysis of κ-, ι-, and λ-carrageenan on mercury electrode in seawater

Metal-Organic Frameworks-Derived FeS-Co9S8/NCA Porous Aerogel Electrocatalyst as a High-Performance Cathode for Zinc-Air Batteries

Herein, a novel strategy to establish a porous FeS-Co9S8/carbon aerogel (FeS-Co9S8/NCA) electrocatalyst for oxygen evolution reaction (OER) is fabricated via applying a green biomass carrageenan sulfuration method to CoFe-metal-organic frameworks (MOFs). The FeS-Co9S8/NCA exhibits optimized catalytic activity toward the OER with a lower overpotential of 322 mV, which is overmatched to the majority of transition metal sulfides (TMSs), as well as lifted long-term durability without evident variation in the LSV curves after 3000 cycles. Rechargeable liquid zinc-air battery (ZAB) assembled with FeS-Co9S8/NCA as the OER catalyst indicated a maximum power density of 176 mW cm-2 and superior cycling stability without raised polarization even after 48 h, outperforms commercial RuO2-based ZAB. Furthermore, the flexible solid-state ZAB built with FeS-Co9S8/NCA also demonstrated outdistance properties and bendability. The excellent performance stems from the hierarchical porous aerogel structure, which offers a multiscale mass/electron transport channel, together with the interfacial synergy effect between FeS and Co9S8, which serves as the active site of the OER reaction. Thus, this work instituted a novel strategy for obtaining both clean and efficient transition metal sulfide electrocatalysts for the OER reaction and an environmentally friendly biomass material-based sustainable electrocatalyst.

A new tool for the determination of humic substances in natural waters: Pulsed voltammetry approach

Humic substances (HS) in natural waters can be determined with a new, simple and sensitive method based on their influence on the background current in a differential pulse - adsorptive cathodic stripping voltammetry. The proposed method, termed PB-HS (pulsed background - humic substances) is discussed in detail, including its application in natural samples from the Krka River estuary. The method was additionally compared with absorbance measurements as well as with the typical electrochemical HS quantification in natural waters based on HS complexation with molybdenum (Mo). A good correlation between methods was observed, with PB-HS showing slightly better sensitivity to humic compounds than classical spectrophotometry. Higher HS concentrations measured with the Mo-method may be due to the enhanced hydrophobicity reached at pH 2 that is required by the method. Advantages of the proposed PB-HS method, compared to existing voltammetric methods for HS quantification, are that it does not require any reagent addition (except buffer) and that it can be used at the natural pH of water as well as in a wide salinity range, which is crucial for its application in estuarine waters.

Novel DNA Biosensor for Direct Determination of Carrageenan

A novel disposable electrochemical biosensor based on immobilized calf thymus double-stranded DNA (dsDNA) on the carbon-based screen-printed electrode (SPE) is developed for rapid biorecognition of carrageenan by using methylene blue (MB) redox indicator. The biosensor protocol for the detection of carrageenan is based on the concept of competitive binding of positively charged MB to the negatively charged dsDNA and carrageenan. The decrement in the MB cathodic peak current (i_pc) signal as a result of the released MB from the immobilized dsDNA, and attracted to the carrageenan can be monitored via differential pulse voltammetry (DPV). The biosensor showed high sensitivity and selectivity to carrageenan at low concentration without interference from other polyanions such as alginate, gum arabic and starch. Calibration of the biosensor with carrageenan exhibited an excellent linear dependence from 1–10 mg L⁻¹ (R² = 0.98) with a detection limit of 0.08 mg L⁻¹. The DNA-based carrageenan biosensor showed satisfactory reproducibility with 5.6–6.9% (n = 3) relative standard deviations (RSD), and possessing several advantages such as simplicity, fast and direct application to real sample analysis without any prior extensive sample treatments, particularly for seaweeds and food analyses.

Rapid determination of kappa-carrageenan using a biosensor from immobilized Pseudomonas carrageenovora cells

A potentiometric whole cell biosensor based on immobilized marine bacterium, Pseudomonas carrageenovora producing κ-carrageenase and glycosulfatase enzymes for specific and direct determination of κ-carrageenan, is described. The bacterial cells were immobilized on the self-plasticized hydrogen ion (H+)-selective acrylic membrane electrode surface to form a catalytic layer. Hydrogen ionophore I was incorporated in the poly(n-butyl acrylate) [poly(nBA)] as a pH ionophore. Catalytic decomposition of κ-carrageenan by the bienzymatic cascade reaction produced neoagarobiose, an inorganic sulfate ion and a proton. The latter was detectable by H+ ion transducer for indirect potentiometric quantification of κ-carrageenan concentration. The use of a disposable screen-printed Ag/AgCl electrode (SPE) provided no cleaning requirement and enabled κ-carrageenan detection to be carried out conveniently without cross contamination in a complex food sample. The SPE-based microbial biosensor response was found to be reproducible with high reproducibility and relative standard deviation (RSD) at 2.6% (n = 3). The whole cell biosensor demonstrated a broad dynamic linear response range to κ-carrageenan from 0.2-100 ppm in 20 mM phosphate buffer saline (PBS) at pH 7.5 with a detection limit at 0.05 ppm and a Nernstian sensitivity of 58.78±0.87 mV/decade (R2 = 0.995). The biosensor showed excellent selectivity towards κ-carrageenan compared to other types of carrageenans tested e.g. ι-carrageenan and λ-carrageenan. No pretreatment to the food sample was necessary when the developed whole cell biosensor was employed for direct assay of κ-carrageenan in dairy product.

κ-Carrageenan/locust bean gum as hard capsule gelling agents

A novel gelling agent, comprising blended κ-carrageenan (κ-C), a seaweed polysaccharide and locust bean gum (LBG), was used to prepare hard capsules. The distinct synergism between κ-C and LBG were verified by the textural profile analysis (TPA), FTIR and rheological measurement. Afterwards, films and hard capsules were prepared with the optimized LBG/κ-C blend gel. And the mechanical properties and morphology of films and hard capsules were analyzed by tensile testing and SEM, respectively. The results showed that the LBG/κ-C at 1:3 ratio could serve as an excellent gelling agent, which endowed hard capsule with the promoted mechanical properties, homogenous and smooth surface morphology. This work suggests that a novel blended LBG/κ-C gelling agent successfully prepared for hard capsules with improving physicochemical properties.