Porous carbon (PC) derived from coal tar pitch (CTP) is a suitable electrode material for energy storage devices due to its high surface area, high conductivity, cost-effectiveness, and eco-friendliness. Phosphorous-doping (P-doping) may augment the physicochemical and electrochemical characteristics of PC. Herein, the phosphorus-doped porous carbon material was synthesized by a one-step carbonization-activation method using coal tar pitch as a carbon precursor and zinc phytate as a hard template and a phosphorus source. The phosphorus-doped mesoporous carbon (PMC-900) delivered a specific capacitance of 277 Fg− 1 at a current density of 0.1 A g− 1 and excellent cycle performance with no capacitance decay after 10,000 cycles at 5 A g− 1 in 6 M KOH aqueous electrolyte. Furthermore, it delivered a high energy density of 13.5 Whkg− 1 at a power density of 43.8 Wkg− 1. The proposed study indicates promising application prospects of the CTP-derived mesoporous carbon in supercapacitors application.

MXene experiences significant oxidation and gradual deterioration in aqueous media due to its inadequate chemical stability, which hinders its further advancement. This study presents a simple and effective approach to prevent the degradation of Ti3C2Tx MXene nanosheets in aqueous media by chemically encapsulating with butanedioic acid (succinic acid (SSA)). Specifically, the impact of pH and antioxidant content on the rate of oxidation of Ti3C2Tx is investigated together with their electrochemical behavior at different intervals. The research demonstrates that the oxidation rate of MXene must be prevented at a suitable concentration of antioxidants; higher doses of antioxidants cause aggregation, while lower concentrations accelerate the oxidation process. Furthermore, fluctuations in pH levels within the dispersion indicate that under acidic conditions, MXene experiences a greater level of oxidation as a result of elevated proton reactivity, which ultimately leads to material degradation. On the other hand, alkaline environments tend to reduce oxidative reactions, leading to increased stability of MXene. Consequently, MXene-SSA can demonstrate long-term stability in water for up to 35 weeks. The electrochemical properties of SSA-encapsulated MXene sheets are assessed as a supercapacitor electrode throughout a time gradient. In comparison to fresh MXene (299 F g(-1) at 1 A g(-1)), the specific capacitances of SSA-protected MXene (321 F g(-1) at 1 A g(-1)) remain unchanged after a long time. Based on DFT calculations, it has been observed that succinic acid creates beneficial hydrogen bonding interactions with Ti sites that possess a lower coordination number, hence improving the stability of Ti3C2Tx.

The shelf life of 2D MXenes in functional devices and colloidal dispersions is compromised due to oxidation in the aqueous system. Herein, a systematic investigation was carried out to explore the potential of various amino compounds as antioxidants for Ti3C2Tx MXenes. A range of basic, acidic, and neutral amino acids were examined for their effectiveness, where certain antioxidants failed to protect MXenes from oxidation, while others accelerated their decomposition. Serine, threonine, and asparagine demonstrated excellent antioxidant activity, likely due to their evenly distributed molecular charges. These neutral amino acids outperformed glutamic acid, which possesses an electron-withdrawing COOH group, and lysine, with an electron-donating NH2 group. Serine-functionalized MXene realized a stabilization time constant reaching 128 days, as determined by first-order reaction kinetics. Additionally, when employed as supercapacitor electrodes, aged MXene and serine-functionalized MXene exhibited specific capacitance values of 219.2 and 280.3 F g-1 at 5 A g-1 after 6 weeks, respectively. This work addresses the gap in the practical work on ionic stabilization of 2D MXenes and has significant implications for the long-term colloidal storage of MXenes using greener chemicals.

2D Ti3C2Tx‐MXenes have gained attention as highly promising materials owing to their distinctive characteristics. Even so, the limited ionic kinetics and active site exposure of these materials are hindered by the significant degradation caused by oxidation, as well as the challenges in ink formulation processability and nanosheet restacking. Here, this study presents a single‐step and economical method to embellish cysteine onto titanium carbide (MX‐C) nanosheets. Cysteine is found to facilitate the tuning of the interlayer spacing in MXene nanosheets. The idea is then applied in the development of micro‐supercapacitors (MSCs) and the removal of toxic metal ions, specifically lead. In addition, the investigation reveals that MX‐C exhibits antioxidant behavior and possesses excellent qualities as inks. The MX‐C‐printed MSC exhibits ultra‐high areal capacitance (68 mF cm−2 ( = 5)) and power density (170.6 µW cm−2) compared to the reported printed MSC system. Similarly, the MX‐C facilitates a high capacity for selectively adsorbing lead while also exhibiting excellent performance in terms of adsorption–desorption. The adsorption‐induced effectiveness of cysteine is additionally validated by density functional theory simulations. The versatile approach emphasizes the potential of MX‐C inks with antioxidation properties for the invention of MSCs and metal uptake for printable electronics and clean water applications, respectively.

Aqueous MXene dispersion suffers from a bottleneck issue of oxidation, leading to its gradual deterioration and ultimately compromised physicochemical characteristics. Herein, Tris-HCl buffer is employed to stabilize the diluted Ti3C2Tx-MXene dispersion (0.05 mg mL-1) through the synergy of its potent pH-regulation capability and capping effect toward oxidation-susceptible defects/edges. Tris-HCl functionalized Ti3C2Tx maintained its original morphology, structure, and favorable dispersity even after 150 days of aging under naturally aerated conditions. The pH-regulation nature of Tris-HCl is elucidated through solution monitoring of Ti3C2Tx dispersion, while the adsorption of Tris-HCl onto defects/edges is revealed by spectral analysis and multi-scale simulations. Tris-HCl at the neutral pH can bind to the negatively charged basal plane of Ti3C2Tx via +HTris moiety, while the other moiety (Tris) interacts with the exposed edge-based Ti atoms and/or intrinsic defects, forming a Ti─N bond that prevents MXene from attack by H2O and O2. Besides, Tris-HCl stabilized Ti3C2Tx exhibited nearly identical capacitive characteristics to its freshly-etched counterpart, indicating the minimal impact of Tris-HCl on electrochemical performance of Ti3C2Tx during long-term storage. This study provides practical guidance for stabilizing MXene in their native aqueous dispersion without compromising the inherent properties.

Improving metal oxides intrinsic electrochemical characteristics without altering their structural or compositional elements is a challenge, especially when designing a single component-based analytical sensor for monitoring emerging pollutants. Herein we propose the induction of oxygen vacancies in hierarchical NiO nanostructures using a simple wet-chemical reduction route to improve its inherent electrochemical redox characteristics. The synthesized NiO nanostructures possessed a thistle-like morphology with nanoprickles based structural features. The 3D prickle-like nanostructures with abundant surface-oxygen vacancies realized robust redox characteristics during the electrochemical oxidation of enrofloxacin (ENF) antibiotics. The existence of oxygen vacancies in NiO (ov-NiO NPKs) increased electrochemical conductivity and elevated redox activity, resulting in a 1.46-fold increase in the oxidation response of ENF compared to its non-vacancy counterpart. The ov-NiO NPKs based sensor showed an excellent linear working response for ENF in the concentration range of 0.001 to 0.15 µM, with a detection limit of 0.12 nM. Moreover, the sensor could effectively detect ENF from environmental samples with a high recovery rate confirming its suitability for practical applications. The suggested engineering of generating oxygen vacancies in metal oxides for improving intrinsic performance opens up new avenues for developing sophisticated single-platform-based sensors for rapid and efficient monitoring of emerging environmental contaminants.

Transition metal carbonate hydroxides (TMCHs) and their composites have appeared as highly capable materials for energy conversion and storage applications. This is primarily due to their many features, including stable porosity, controlled architectures, long-term stability, and enhanced reaction kinetics. This study briefly overviews the advancements in TMCH-based materials and their resulting composites for lithium-ion batteries (LIBs) and electrolyzers. The emphasis lies on the efficacy of morphological tuning to enhance the performance of the TMCH-based system. The article also examines the research obstacles and potential for creating electrode materials based on TMCHs for future studies on electrochemical energy storage and conversion devices. In the framework of multi-energy applications, this article aims to provide the centralized strategy of TMCHs-based material and highlight the accomplishments currently made in this area.

The development of advanced carbon materials is indispensable for high-performance supercapacitors. Herein, we report the direct pyrolysis of waste coal-tar pitch (CTP) with ZnO nanoparticles (Zn NPs) to produce hierarchical porous carbon materials (HPCs). The CTP served as a carbon source, and the embedded ZnO NPs as a simultaneous templating and activating agent for HPCs. At an optimum temperature of 800 °C, the produced HPCs (HPC-800) realized an optimal specific surface area (1267 m2 g-1) and pore volume of 1.71 cm3 g-1, enabling the devised capacitor to exhibit a specific capacitance of 172 F g-1 at a current density of 0.1 A g-1 in 6 M KOH electrolyte and a capacitance retention of 81

Transition metal carbonate hydroxides (TMCHs) and their composites have emerged as a highly promising material for supercapacitors. These materials possess a multitude of advantageous characteristics, including permanent porosity, tunable architectures, high theoretical capacity, long-term stability, and enhanced reaction kinetics. Herein, a comprehensive discussion is proposed on the developments of TMCH-based materials and their composite for supercapacitors with a focus on morphological tuning, bi- or tri-metallic approaches, composites, or heterostructures, and doping or substitution. The review also discusses research challenges and prospects for developing TMCHs-based electrode materials for upcoming research on electrochemical energy storage devices. This discussion can help to provide a platform to introduce the centralized approach of TMCHs-based material in multi-energy storage application and their advancement.

The rapid-charge carrier recombination and low conductivity are critical in devising an efficient photoelectrochemical (PEC) sensor. Herein, we propose partial oxidation of few-layered MXene (Ti3C2Tx) to construct a photo-active TiO2/Ti3C2Tx platform that could be configured for PEC sensing of folate receptors (FR), particularly, FR-expressing breast cancer cells (MDA-MB-231). MXene-Ti3C2Tx dispersion was oxidized in natural-open air conditions, where continuous exposure for six (06) days allowed for homogeneous in-situ growth of TiO2 over MXenes nanosheets (MX-06). This exposure enabled partial oxidation of MXene-sheets with a balanced TiO2 to MXene content that could exhibit improved photoresponsive characteristics owing to the synergism of redox-active TiO2 and highly conductive underlying Ti3C2Tx. The photoelectrode was then adapted for biorecognition by conjugating chitosan and folic acid (FA) networks, which permitted selective detection of FR-expressed cells with significant antifouling capabilities against common proteins such as bovine serum album (BSA), hemoglobin, and immunoglobulin G. (Ig G). The detection mechanism relies on FA's strong affinity for cancer cell folate receptors, which proportionally inhibited the photoelectrodes PEC oxidation response to ascorbic acid (AA)(mediator). The proposed inhibition strategy enabled sensitive detection of FR-expressed MDA-MB-231 cells in the concentration range of 1 × 102 to 2 × 107 cells/mL with a detection limit of 1.01 cells/mL (S/N = 3).

Layered double hydroxides (LDH) are regarded as attractive pseudocapacitive materials due to their impressive capacitive qualities that may be adjustable to their morphological features. However, the layered structure of LDH renders them susceptible to structural aggregation, which inhibits effective electrolyte transport and limits their practical applicability after limited exposure to active areas. Herein, we propose a simple template-free strategy to synthesize hierarchical hollow sphere NiMn-LDH material with high surface area and exposed active as anode material for supercapacitor application. The template-free approach enables the natural nucleation of Ni-Mn ions resulting in thin sheets that self-assemble into a hollow sphere, offering expended interlayer spaces and abundant redox-active active sites. The optimal NiMn-LDH-12 achieved a specific capacitance of 1010.4 F g−1 at a current density of 0.2 A g−1 with capacitance retention of 70% at 5 A g−1 after 5000 cycles with lower charge transfer impedance. When configured into an asymmetric supercapacitors (ASC) device as NiMn-LDH//AC, the material realized a specific capacitance of 192.4 F g−1 at a current density of 0.2 A g−1 with a good energy density of 47.9 Wh kg−1 and a power density of 196.8 W kg−1. The proposed morphological-tuning route is promising for designing template-free NiMn-LDHs spheres with practical pseudocapacitive characteristics.

The increasing need for high-performance energy storage systems necessitates the exploration of novel electrode materials. In this study, the utilization of polyaniline/multiwalled carbon nanotubes (PANI/MWCNTs) was demonstrated as a conductive scaffold for the formation of heterostructures comprising nickel manganese phosphate (NiMn(PO4)2) using probe sonication, leading to the development of an efficient hybrid super-capacitor. The PANI/MWCNTs composite exhibits favorable conductive properties, acting as a suitable frame-work for the nucleation/growth and integrating NiMn(PO4)2 structures. The synergistic combination of PANI/ MWCNTs and NiMn(PO4)2 resulted in the development of a highly efficient hybrid anode, exhibiting a remarkable specific capacitance of 917.3 F g-1 (912.2 C g  1) at 1 A g-1 in a 1 M KOH electrolyte. The optimized composite, PCNT-NMP-40, as a positive electrode in a two-electrode cell configuration with activated carbon (AC) as the negative electrode, operates within an extended output potential range of 0-1.6 V in a 2 M KOH electrolyte, delivering an outstanding energy density of 58 Wh kg  1 and a power density of 918 W kg  1, reflecting the substantial potential use of PCNT-NMP-40 as an excellent candidate for advanced energy storage applications.

Metal oxide-based electrochemical sensors, despite their robust redox activity, lack sufficient conductivity to overcome their sluggish kinetics. Herein, we propose a unique self-assembled hybrid configuration based on redox-active Co3O4 hexagons (Co3O4-HX) and the highly conductive, few-layer-thick Ti3C2Tx sheets. The self-assembly approach enabled the compact interfacial formation and moderate intercalation of Ti3C2Tx sheets, allowing the Co3O4/Ti3C2Tx composite (Co3O4-MX) to exhibit a synergetic improvement in the charge-transfer rate and oxidation current response toward isoprenaline (ISPT), a neurotransmitter drug. The hybrid composite when devised as an electrochemical sensor gives rise to a 7.9-fold higher oxidation current response to 0.65 mu M ISPT than its pristine Co3O4 counterpart. The improved charge kinetics and generation of a superior oxidation current emphasized the critical role of Ti3C2Tx as an interactive substrate in the Co3O4-MX hybrid. The analytical detection capability assessed via differential pulse voltammetry (DPV) confirmed the sensor's high selectivity and marked stability both in low and high concentration ranges of ISPT ((0.01 to 0.33 mu M) and 0.5 to 0.9 mu M) with a limit of detection (LOD) of 3 x 10(-3) mu M (for low concentrations). Importantly, the fabricated sensor could detect ISPT from harsh biological environments such as human urine samples with a recovery rate of 99%. Moreover, the sensor exhibited a stable working response during its prolonged storage of 30 days in an aqueous PBS system. The proposed route of using MXenes as a conductive substrate paves the way for developing a robust metal-oxide-based redox-active hybrid system for the sensitive detection of important therapeutic compounds.

A sensitive electroactive platform relies directly upon the efficient and conductive interface. This work offers a simple and effective method for synthesizing NiCo2O4 using CTAB surfactant, suited for trace-level antibiotic detection. The route realized the controlled growth of tiny NiCo2O4 nanoboulders with an exposed interface. A comparative evaluation of the bimetallic nanostructures with their pristine compositional counterparts, i.e., NiO and Co3O4, supports its superior electrochemical characteristics based on the synergism of strong redox activity and conductivity from the bimetallic components. The NiCo2O4 nanoboulders exhibited strong electrochemical activity when configured as electrode material for detecting ofloxacin (OFL), a common antibiotic. The sensor exhibited excellent working linearity in a low-concentration range of 0.01–5 ​μM with a detection limit of 1 ​× ​10−3 ​μM for OFL. The kinetics of the NiCo2O4 further supported the electrocatalytic oxidation of OFL to be diffusion controlled with an estimated diffusion coefficient of 2.03310−6 ​cm2 ​s−1. Moreover, the constructed sensor is applicable for detecting OFL from environmental samples, reflecting its workability in complex real-environment.

The inferior conductivity and structural durability are key issues in engineering suitable metal oxide-based hybrid electrodes for supercapacitor application. Herein, we propose using an in-situ route to couple Ni-Zn-Co trimetallic oxides (NZC) with CoWO4 (CWO) to construct an efficient hybrid composite electrode. The approach offers an intimate/compact interfacial arrangement with a better synergy of multi-atom conductivity, surface area, and numerous redox-active sites, resulting in superior electrochemical characteristics compared to its pristine counterparts. Hybrid composites with varying mass combination ratios were studied for enhanced electrochemical performance, where ZNC@CWO-10 realized a comparatively better capacitance of 370.9 F g(-1) at 0.5 A g(-1) with a capacitance retention value of 90% after 500 cycles. The corresponding ASC devise exhibited a high specific capacitance of 140 F g(-1) at 0.5 A g(-1) in the potential window of -1 to 0.8 V with maintained retention of 80% during 5000 cycles. The enhanced electrochemical characteristics were attributed to the improved composting strategy, allowing for synergism of ZNC and CoWO4 with superior interfacial arrangement paving the route towards excellent metal/metal oxide electrode material for supercapacitor applications.

Energy storage devices (ESD) are getting significant attention regarding their ability to reduce fossil fuel usage. Batteries and electrochemical supercapacitors are two well-known ESDs with supercapacitors preferred for their high energy discharge potential. The metal oxides (MOs) with robust redox characteristics are ideal candidates for supercapacitors, although their capacitance still lacks behind the theoretical values. Here, partial reduced or oxygen-deficient MOs have been identified have proven promising to reach the desired capacitance. The introduction of oxygen vacancies into MOs can effectively enhance their electrochemical properties without altering the inherent characteristics of MOs. This review discusses the recent progress on new oxygen-deficient MOs and their performance as a supercapacitor. The importance of oxygen vacancy is described, followed by the traditional synthesis route to producing MOs. The present pathways for generating oxygen vacancies and their analytical assessment are covered in-depth, followed by a section on the most advanced analytical techniques for detecting and interpreting the creation of such vacancies. The influence of oxygen vacancies on the supercapacitive performance of the most researched MOs is provided with the challenges and prospects of oxygen-deficient MOs in supercapacitor application.

MXenes-Ti3C2Tx, based on their versatile surface characteristics, has rapidly advanced as an interactive substrate to develop electrochemical sensors for clinical applications. Herein, Ni embedded Ti3C2Tx (MX−Ni) composites were prepared using a self-assembly approach where Ti3C2Tx sheets served as an interactive conductive substrate as well as a protective layer to nickel nanoparticles (Ni NPs), preventing their surface oxidation and aggregation. The composite displayed a cluster-like morphology with an intimate interfacial arrangement between Ni, Ti3C2Tx and Ti3C2Tx-derived TiO2. The configuration of MX−Ni into an electrochemical sensor realized a robust cathodic reduction current against methylmalonic acid (MMA), a biomarker to vitamin B12 deficiency. The synergism of Ni NPs strong redox characteristics with conductive Ti3C2Tx enabled sensitive signal output in wide detection ranges of 0.001 to 0.003 µM and 0.0035 to 0.017 µM and a detection sensitivity down to 0.12 pM of MMA. Importantly, the sensor demonstrated high signal reproducibility and excellent operational capabilities for MMA in a complex biological matrix such as human urine samples.

he green nanocomposite materials, especially nanocomposites derived from biomass resources, have attracted several environmental remediation applications. One of the major applications of these nanocomposite materials is the wastewater treatment. These nanocomposites come with engineered functional groups, high porosity, active sites, characteristics of catalytic degradation, and easy to separation. These materials are effective for photocatalytic degradation of dyes, color removal, adsorption of heavy metals, organic and organic wastes, and membranes for wastewater purification. The green nanocomposite materials can be synthesized from wastes of various biomasses such as guar gum, wheat, maize, amylomaize, potato, cotton wood, rice husk, empty fruit bunch, etc. This chapter centers on the characterization, development, and utilization of waste and biomass-based nanocomposites for wastewater treatment. This chapter further focuses on feedstocks of material, process conditions, specific contaminant removal, material efficiency, recyclability, and contaminant removal mechanisms.