Electrochemical Reaction Assisted 2D π-Stacking of Benzene on a MWCNT Surface and its Unique Redox and Electrocatalytic Properties

Electrical Wiring of Malarial Parasite Intermediate Hematin on a Tailored N-Doped Carbon Nanomaterial Surface and Its Bioelectrocatalytic Hydrogen Peroxide Reduction and Sensing

Hematin, an iron-containing porphyrin compound, plays a crucial role in various biological processes, including oxygen transport, storage, and functionality of the malarial parasite. Specifically, hematin-Fe interacts with the nitrogen atom of antimalarial drugs, forming an intermediate step crucial for their function. The electron transfer functionality of hematin in biological systems has been scarcely investigated. In this study, we developed a biomimicking electrical wiring of hematin-Fe with a model N-drug system, represented as {hematin-Fe---N-drug}. We achieved this by immobilizing hematin on a multiwalled carbon nanotube (MWCNT)/N-graphene quantum dot (N-GQD) modified electrode (MWCNT/N-GQD@Hemat). N-GQD serves as a model molecular drug system containing nitrogen atoms to mimic the {hematin-Fe---N-drug} interaction. The prepared bioelectrode exhibited a distinct redox peak at a measured potential (E1/2) of -0.410 V vs Ag/AgCl, accompanied by a surface excess value of 3.54 × 10-9 mol cm-2. This observation contrasts significantly with the weak or electroinactive electrochemical responses documented in literature-based hematin systems. We performed a comprehensive set of physicochemical and electrochemical characterizations on the MWCNT/N-GQD@Hemat system, employing techniques including FESEM, TEM, Raman spectroscopy, IR spectroscopy, and AFM. To evaluate the biomimetic electrode's electroactivity, we investigated the selective-mediated reduction of H2O2 as a model system. As an important aspect of our research, we demonstrated the use of scanning electrochemical microscopy to visualize the in situ electron transfer reaction of the biomimicking electrode. In an independent study, we showed enzyme-less electrocatalytic reduction and selective electrocatalytic sensing of H2O2 with a detection limit of 319 nM. We achieved this using a batch injection analysis-coupled disposable screen-printed electrode system in physiological solution.

Multi-Redox Active Carbons and Hydrocarbons: Control of their Redox Properties and Potential Applications

Precise control over redox properties is essential for high-performance organic electronic devices such as organic batteries, electrochromic devices, and information storage devices. In this context, multi-redox active carbons and hydrocarbons, represented as C_x H_y molecules (x≥1, y≥0), are highly sought after, because they can switch between multiple redox states. Herein, we outline the redox properties of C_x H_y molecules as solutes and adsorbed species. Furthermore, the limitations of evaluating their redox properties and the possible solutions are summarized. Additionally, the theoretical capacity (mAh/g) and gravimetric energy density (Wh/kg) of secondary batteries were estimated based on the redox properties of 185 C_x H_y molecules, which have primarily been reported in the last decade. Among them, seven C_x H_y molecules were found to have the potential to surpass the energy density of LiNi_0.6 Mn_0.2 Co_0.2 O₂ /graphite batteries. The use of C_x H_y molecules in multielectrochromic devices and multi-bit memory is also explained. We believe that this review will encourage further utilization of C_x H_y molecules thereby promoting its applications in organic electronic devices.

Highly Selective Adsorption and Desorption of Charged Molecules in Three-Dimensional Networks of Polydopamine-Modified Carbon Nanotube Sponges

We investigated the selective adsorption and desorption behaviors of charged molecules (calcein, brilliant green, and methylene blue) dissolved in water using polydopamine-modified carbon nanotube (CNT) sponges. Porous CNT sponges (CNTSs) as a scaffold for the selective adsorption and desorption of aqueous molecules were fabricated by using a chemical vapor deposition technique. To improve the hydrophilicity of porous CNTS and to control the adsorption and desorption of aqueous molecules, CNT sidewalls were decorated with a hydrophilic polydopamine layer through noncovalent interactions between CNT sidewalls and polydopamine. After this noncovalent chemical modification, the water contact angle of CNTS was close to 0, and the aqueous solution can rapidly infiltrate the three-dimensional (3D) networks of polydopamine-modified CNTS (Pdop-CNTS). The incorporation of pH-responsive polydopamine in CNTS showed an evident advantage of adsorbing positively charged molecules over a pH range of 10.5-4. In aqueous solutions with pH value of ≤3, Pdop-CNTS selectively adsorbed negatively charged molecules. Aqueous molecules carrying net charges were successfully separated from mixture solutions. Moreover, charged calcein and methylene blue molecules adsorbed on the 3D networks of Pdop-CNTS were selectively desorbed from Pdop-CNTS by tuning the pH value of the desorption solution.