Effect of Electrolytic Medium on the Electrochemical Reduction of Graphene Oxide on Si(111) as Probed by XPS

Polymeric Wet-Strength Agents in the Paper Industry: An Overview of Mechanisms and Current Challenges

Polymeric wet-strength agents are important additives used in the paper industry to improve the mechanical properties of paper products, especially when they come into contact with water. These agents play a crucial role in enhancing the durability, strength, and dimensional stability of paper products. The aim of this review is to provide an overview of the different types of wet-strength agents available and their mechanisms of action. We will also discuss the challenges associated with the use of wet-strength agents and the recent advances in the development of more sustainable and environmentally friendly agents. As the demand for more sustainable and durable paper products continues to grow, the use of wet-strength agents is expected to increase in the coming years.

Influence of Immobilization Strategies on the Antibacterial Properties of Antimicrobial Peptide-Chitosan Coatings

It is key to fight bacterial adhesion to prevent biofilm establishment on biomaterials. Surface immobilization of antimicrobial peptides (AMP) is a promising strategy to avoid bacterial colonization. This work aimed to investigate whether the direct surface immobilization of Dhvar5, an AMP with head-to-tail amphipathicity, would improve the antimicrobial activity of chitosan ultrathin coatings. The peptide was grafted by copper-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry by either its C- or N- terminus to assess the influence of peptide orientation on surface properties and antimicrobial activity. These features were compared with those of coatings fabricated using previously described Dhvar5-chitosan conjugates (immobilized in bulk). The peptide was chemoselectively immobilized onto the coating by both termini. Moreover, the covalent immobilization of Dhvar5 by either terminus enhanced the antimicrobial effect of the chitosan coating by decreasing colonization by both Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. Relevantly, the antimicrobial performance of the surface on Gram-positive bacteria depended on how Dhvar5-chitosan coatings were produced. An antiadhesive effect was observed when the peptide was grafted onto prefabricated chitosan coatings (film), and a bactericidal effect was exhibited when coatings were prepared from Dhvar5-chitosan conjugates (bulk). This antiadhesive effect was not due to changes in surface wettability or protein adsorption but rather depended on variations in peptide concentration, exposure, and surface roughness. Results reported in this study show that the antibacterial potency and effect of immobilized AMP vary greatly with the immobilization procedure. Overall, independently of the fabrication protocol and mechanism of action, Dhvar5-chitosan coatings are a promising strategy for the development of antimicrobial medical devices, either as an antiadhesive or contact-killing surface.

Rational design of dense microporous carbon derived from coal tar pitch towards high mass loading supercapacitors

The compact carbon materials with huge specific surface area (SSA) and proper pore structure are highly desirable towards high-performance supercapacitors at the cell level. However, to well balance of porosity and density is still an on-going task. Herein, a universal and facile strategy of pre-oxidation-carbonization-activation is employed to prepare the dense microporous carbons from coal tar pitch. The optimized sample POCA800 not only possesses a well-developed porous structure with the SSA of 2142 m² g^-1 and total pore volume (V_t) of 1.540 cm³ g^-1, but also exhibits a high packing density of 0.58 g cm^-3 and proper graphitization. Owing to these advantages, POCA800 electrode at areal mass loading of 10 mg cm^-2 shows a high specific capacitance of 300.8 F g^-1 (174.5 F cm^-3) at 0.5 A g^-1 and good rate performance. The POCA800 based symmetrical supercapacitor with a total mass loading of 20 mg cm^-2 displays a large energy density of 8.07 Wh kg^-1 at 125 W kg^-1 and remarkable cycling durability. It is revealed that the prepared density microporous carbons are promising for practical applications.

One-pot carboxyl enrichment fosters water-dispersibility of reduced graphene oxide: a combined experimental and theoretical assessment

Graphene, one of the allotropic forms of carbon, has attracted enormous interest in the last few years due to its unique properties. Reduced graphene oxide (RGO) is known as the nanomaterial most similar to graphene in terms of electronic, chemical, mechanical, and optical properties. It is prepared from graphene oxide (GO) in the presence of different types of reducing agents. Nevertheless, the application of RGO is still limited, owing to its tendency to irreversibly aggregate in an aqueous medium. Herein, we disclosed the preparation of water-dispersible RGO from GO previously enriched with additional carboxyl functional groups through a one-pot reaction, followed by chemical reduction. This novel and unprecedentedly reported reactivity of GO toward the acylating agent succinic anhydride (SA) was experimentally investigated through XPS, Raman, FT-IR, and UV-Vis, and corroborated by DFT calculations, which have shown a peculiar involvement in the functionalization reaction of both epoxide and hydroxyl functional groups. This proposed synthetic protocol avoids use of sodium cyanide, previously reported for carboxylation of graphene, and focuses on the sustainable and scalable preparation of a water-dispersible RGO, paving the way for its application in many fields where the colloidal stability in aqueous medium is required.

High-performance asymmetric supercapacitor based on a CdCO3/CdO/Co3O4 composite supported on Ni foam – part II: a three-electrode electrochemical study†

A binder-free CdCO₃/CdO/Co₃O₄ compound with a micro-cube-like morphology on a nickel foam (NF) made via a facile two-step hydrothermal + annealing procedure has been developed. The morphological, structural and electrochemical behavior of both the single compounds constituting this final product and the final product itself has been studied. The synergistic contribution effect of the single compounds in the final compounded resulting specific capacitance values are presented and discussed. The CdCO₃/CdO/Co₃O₄@NF electrode exhibits excellent supercapacitive performance with a high specific capacitance (C_S) of 1.759 × 10³ F g⁻¹ at a current density of 1 mA cm⁻² and a C_S value of 792.3 F g⁻¹ at a current density of 50 mA cm⁻² with a very good rate capability. The CdCO₃/CdO/Co₃O₄@NF electrode also demonstrates a high coulombic efficiency of 96% at a current density as high as 50 mA cm⁻² and also exhibits a good cycle stability with capacitance retention of ca. 100% after 1000 cycles at a current density of 10 mA cm⁻² along with a potential window of 0.4 V. The obtained results suggest that the facilely synthesized CdCO₃/CdO/Co₃O₄ compound has great potential in high-performance electrochemical supercapacitor devices.

Schematic illustration of the two-step process involved in the preparation of the different chemical compounds supported on the nickel foam substrates.