Search

In this study, novel chitosan/silica composites with different mass ratios were prepared by in-situ hydrolysis using chitosan (from shrimp shell) as a carrier, triblock copolymer (P123) as the structure-directing agent, and ethyl orthosilicate as a silicon source. These nanocomposites were characterized by different techniques, including the FT-IR, XRD, TGA, SEM, TEM and N2 adsorption–desorption. The results indicated that the morphology and properties of composites changed with the introduction of silica. When the CS/TEOS mass ratio was 0.0775, the CS−2/SiO2 composite displayed a coral-like three-dimensional porous structure with specific surface area of 640.37 m2/g and average pore size of 1.869 nm. The adsorption properties for methylene blue (MB) were investigated as well and the CS−2/SiO2 showed better adsorption performance. The removal rate for MB reached 94.01% with absorbents dosage of 6 g/L, initial concentration of 40 mg/L, initial pH value of 7, temperature of 35 °C, and adsorption time of 40 min. The adsorption process well fitted the Langmuir isothermal model and quasi-second-order adsorption kinetics model. The maximum adsorption capacity for MB was 13.966 mg/g based on Langmuir fitting. The surface functional groups of the composites can play an important role in the adsorption. The adsorption mechanism of CS−2/SiO2 on MB involved electrostatic interaction, hydrogen bonding and functional group complexation. In addition, the prepared chitosan/silica composites showed good reusability at six cycles, making them a promising material in the application of removing dyeing wastewater. [ABSTRACT FROM AUTHOR]

Accurate and rapid determination of inorganic carbon constituents in ocean environments is important for understanding the carbon cycle, especially in the context of ocean-acidification research. A microsensor capable of directly measuring carbonate ion (CO) concentrations would be desirable. In this study, a carbonate microsensor with a polymeric liquid membrane was fabricated, and two calibration methods were used to evaluate its performance. The first method was based on continuous titration. Small increments of HCl were added to seawater or NaCO solution to adjust the total alkalinity and pH values and thus obtain a series of carbonate concentrations. The second method used a series of discrete standards. Varying amounts of HCl or NaOH were added to separate seawater aliquots, and the CO concentration of each standard was calculated from the resulting total alkalinity and total dissolved inorganic carbon. Both methods were found to be adequate for achieving accurate calibration of the CO sensor, and both are suitable for field work. The discrete standards method, however, is more convenient and may provide a better linear range at low CO concentrations (detection range: 2-300 μmol/kg) than the continuous titration method in seawater (detection range: 10-250 μmol/kg). This CO microsensor can be used for 5-7 d and detects changes in carbonate concentration as low as 2 μmol/kg in the inorganic carbon constituents of the environments where marine calcareous organisms grow. The CO microelectrode was further assessed by applying it to the measurement of pore-water CO concentration profiles in a marine sediment core. [ABSTRACT FROM AUTHOR]

The development of all-solid-state precise pH electrodes holds significant importance in various fields, particularly in marine scientific research. To achieve this goal, we proposed a novel fabrication technique for an all-solid-state ruthenium oxide (Ti/RuO x ) pH electrode. We thin-coated the RuCl 3 precursor solution on a titanium wire substrate using a heat gun repeatedly and then calcined it in a mixture of Li 2 CO 3 and Na 2 O 2 at 400 °C to obtain a ruthenium oxide (RuO x ) film. This RuO x film was subjected to acid treatment with dilute nitric acid, and a polytetrafluoroethylene heat shrink tube was wrapped around the non-RuO x film area. Finally, the RuO x film was fully immersed in a pH 4.00 buffer solution, finalizing the electrode preparation. The RuO x film exhibits a dense and regular conical morphology. The Ti/RuO x electrode demonstrates a good near-Nernstian response slope (e.g., -59.04 mV/pH at 25 °C), high linearity (e.g., R 2 = 0.9999), rapid response (<1 s), low hysteresis (<3 mV), excellent reversibility, and good repeatability in the pH range of 2.00-10.00. After full hydration, the Ti/RuO x electrode shows a potential drift of 8.5 mV and a drift rate of approximately 0.27 mV/day over a period of 25 days, indicating good long-term stability. Furthermore, the Ti/RuO x electrode exhibits robust resistance against interference from various ions and low-concentration redox substances, ensuring a long storage life (at least 280 days), and high measurement accuracy (e.g., ± 0.02 pH units) for diverse water samples, including seawater, freshwater, and tap water. This study has evaluated the potential of the Ti/RuO x electrode as a reliable and accurate tool for pH measurements in marine scientific applications.