Nanoarchitectonics of heteroatom-doped hierarchical porous carbon derived from carboxymethyl cellulose carbon aerogel and metal-organic framework for capacitive deionization

N, O-codoped carbon aerogel electrode improves capacitive deionization performance

Capacitive deionization (CDI) using porous carbon materials provides an environmentally friendly and sustainable solution to produce affordable fresh water. However, low salt adsorption rates significantly limit its practical application. In this study, N, O-codoped carbon aerogel (NOCA) was prepared by a simple sol-gel method using agar as the carbon framework, NaCl as the template, NH4HCO3 as the nitrogen source and self-blowing agent. The electrochemical and electrosorption properties of the NOCA electrode were significantly better than compared to commercial activated carbon (CAC) electrodes. The NOCA material had the following characteristics: (i) During the rapid freeze-drying process, NaCl crystals provide a three-dimensional network structure for effective dispersion of agar, reducing the agglomeration of particles. The volatile gas generated during the thermal decomposition of NH4HCO3 reduces the plugging of pores. (ii) The fluffy interconnecting network structure of the material enhances its electrical conductivity, providing sufficient channels and adsorption sites for the entry and exit of salt ions. (iii) The abundant hydroxyl and ether groups in the agar enhance the hydrophilicity of the material, whereas N doping further improves the electrical conductivity and reduces the ion transport resistance. The electrosorption capacity and adsorption rate of the NOCA material in 500 mg/L NaCl solution were 22.1 mg/g and 4.4 mg/(g·min), respectively. These values correspond to low energy consumption and high energy recovery efficiency in the electrosorption process. The adsorption capacity remained at 95.5 % after 50 adsorption/desorption cycles. These findings show that NOCA is a novel and potential electrode material for CDI applications.

Fabrication of Silver Nanoparticle Loaded into Nanocellulose Derived from Hemp and Poly(vinyl alcohol)-Based Composite as an Electrode for Electrochemical Sensors for Lactate Determination

Nanocellulose derived from hemp (HNC) with the addition of silver nanoparticles (AgNPs) is utilized for improving the electrochemical sensing performances for lactate detection. Initially, HNC is chemically extracted and purified by using alkali treatment and acid hydrolysis. Then, AgNPs are nucleated in situ by the self-reduction process prior to forming a composite with poly(vinyl alcohol) (PVA). This nanocomposite significantly improves the electrochemical properties of the electrode, including electrochemical conductivity and electrocatalysis. The morphologies and chemical alterations of the HNC/AgNPs-PVA nanocomposite are investigated by field emission scanning electron microscopy. It demonstrates a three-dimensional network with random orientation of the nanocellulose fiber. The AgNPs are well-dispersed in the nanocomposite. Moreover, the nanocomposite provides high thermal stability up to 450 °C. Then, it is remarkably noted that 10 wt % HNC/AgNPs-PVA modified on the electrode provides the highest current responses, with a standard redox couple [(Fe(CN)6]3-/4-]. For lactate detection, this modified screen-printed graphene electrode with nonimmobilized lactate oxidase exhibits an increase in the current signal with the increment of lactate concentration and offered a linear range of 0-25 mM, covering a cutoff value (12.5 mM) for muscle fatigue indication. Eventually, this sensor is successfully applied for lactate detection with high potential for a wearable lactate sensor.

Flexible ultrathin Nitrogen-Doped carbon mediates the surface charge redistribution of a hierarchical tin disulfide nanoflake electrode for efficient capacitive deionization

Constructing pseudocapacitive electrodes with high specific capacities is indispensable for increasing the large-scale application of capacitive deionization (CDI). However, the insufficient CDI rate and cycling performance of pseudocapacitive-based electrodes have led to a decline in their use due to the corresponding volumetric expansion and contraction that occurs during long-term CDI processes. Herein, hierarchical porous SnS2 nanoflakes are encapsulated inside an N-doped carbon (NC) matrix to achieve efficient CDI. Benefiting from the synergistic properties of the pseudocapacitive SnS2 nanoflakes and few-layered N-doped carbon, the heterogeneous interface simultaneously provides more available vigorous sites and demonstrates rapid charge-transfer kinetics, resulting in a superior desalination capability (49.86 mg g-1 at 1.2 V), rapid desalination rate (1.66 mg g-1 min-1) and better cyclic stability. Computational research reveals a work function-induced surface charge redistribution of the SnS2@NC heterojunction, which can lead to an auspicious surface electronic structure that reduces the adsorption energy to improve the diffusion kinetics toward sodium adsorption. This work contributes to providing a thoughtful understanding of the interface engineering between transition metal dichalcogenides and NC to construct high-performance CDI electrode materials for further industrialization.

Controllable Preparation of a N-Doped Hierarchical Porous Carbon Framework Derived from ZIF-8 for Highly Efficient Capacitive Deionization

Capacitive deionization (CDI) is a promising desalination technology, and metal-organic framework (MOF)-derived carbon as an electrode material has received more and more attention due to its designable structure. However, MOF-derived carbon materials with single-pore structures have been difficult to meet the technical needs of related fields. In this work, the ordered hierarchical porous carbon framework (OMCF) was prepared by the template method using zeolitic imidazolate frameworks-8 (ZIF-8) as a precursor. The pore structures, surface properties, electrochemical properties, and CDI performances of the OMCF were investigated and compared with the microporous carbon framework (MCF), also derived from ZIF-8. The results show that the hierarchical porous carbon OMCF possessed a higher specific surface area, better hydrophilic surface (with a contact angle of 13.45°), and higher specific capacitance and ion diffusion rate than those of the MCF, which made the OMCF exhibit excellent CDI performances. The adsorption capacity and salt adsorption rate of the OMCF in a 500 mg·L-1 NaCl solution at 1.2 V and a 20 mL·min-1 flow rate were 12.17 mg·g-1 and 3.34 mg·g-1·min-1, respectively, higher than those of the MCF. The deionization processes of the OMCF and MCF closely follow the pseudo-first-order kinetics, indicating the double-layer capacitance control. This work serves as a valuable reference for the CDI application of N-doped hierarchical porous carbon derived from MOFs.