Electrochemical sensor based on covalent organic frameworks/MWCNT for simultaneous detection of catechol and hydroquinone

Determination of hydroquinone in beverages using colorimetric and electrochemical sensors on paper-based device

Hydroquinone (HQ) is a phenolic compound used in industry processes. We aim to demonstrate a rapid and simple procedure for the determination of HQ. This work has developed two techniques, including colorimetric and electrochemical sensors on paper-based devices. Firstly, we have developed the colorimetric detection for the rapid screening test of HQ using 1.5% 4-(dimethylamino) benzaldehyde with alkaline condition (5 M NaOH). Under suitable conditions, the calibration curve between the intensity and HQ concentration was in the range of 50-500 mg L-1. Then, we developed a multi-walled carbon nanotube/graphene oxide/copper/palladium/platinum (MWCNT/GO/Cu/Pd/Pt) onto a screen-printed carbon electrode (SPCE). The optimal amount of MWCNT/GO/Cu/Pd/Pt nanomaterial is 2 mg for HQ detection. The linear concentration range was found in the range 1 to 20 mg L-1 and a detection limit was found to be 0.40 mg L-1 (3.6 µM) for HQ. Moreover, the proposed device can be applied to determine HQ in real samples and is inexpensive technique, portable, and low consumer time.

2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

Molecularly imprinted photoelectrochemical sensor for ultrasensitive and selective detection of hydroquinone using 0D CdS nanoparticle/3D flower-like ZnIn2S4 microsphere nanocomposite

A novel photoelectrochemical (PEC) sensor was developed for the ultra-sensitive and highly selective detection of hydroquinone (HQ), featuring a composite structure that combines 0D CdS nanoparticles with a 3D flower-like ZnIn2S4 microsphere. The sensor, termed rMIP/CdS/ZnIn2S4, employed molecularly imprinted polymers (MIPs) to achieve specific recognition of HQ. An p-phenylenediamine (pPD) polymer film was electrochemically polymerized onto the surface of the CdS/ZnIn2S4 composite-coated glassy carbon electrode (GCE). Through hydrogen bonding, HQ molecules were imprinted onto the polymer film. Subsequent elution removed these molecules, leaving behind specific recognition sites, enabling selective detection of HQ. The unique spatial structure and heterojunction properties of the 0D CdS nanoparticle/3D flower-like ZnIn2S4 composite, combined with molecular imprinting, significantly enhanced the photocurrent response and increased the selectivity and sensitivity for HQ detection. Under optimal conditions, the rMIP/CdS/ZnIn2S4 sensor demonstrated a low detection limit (0.7 nmol·L-1, S/N=3) over a wide linear range of 1-1200 nmol·L-1. The sensor was successfully applied to detect HQ in real water samples, showing promise for environmental pollution control applications.

Microbial synthesis of antimony sulfide to prepare catechol and hydroquinone electrochemical sensor by pyrolysis and carbonization

The application of antimony sulfide sensors, characterized by their exceptional stability and selectivity, is of emerging interest in detection research, and the integration of graphitized carbon materials is expected to further enhance their electrochemical performance. This study represents a pioneering effort in the synthesis of carbon-doped antimony sulfide materials through the pyrolysis of the mixture of microorganisms and their synthetic antimony sulfide. The prepared materials are subsequently applied to electrochemical sensors for monitoring the highly toxic compounds catechol (CC) and hydroquinone (HQ) in the environment. Via cyclic voltammetry (CV) and impedance testing, we concluded that the pyrolytic product at 700 °C (Sb-700) demonstrated the best electrochemical properties. Differential pulse voltammetry (DPV) revealed impressive separation when utilizing Sb-700/GCE for simultaneous detection of CC and HQ, exhibiting good linearity within the concentration range of 0.1-140 μM. The achieved sensitivities of 24.62 μA μM-1 cm-2 and 22.10 μA μM-1 cm-2 surpassed those of most CC and HQ electrochemical sensors. Meanwhile, the detection limits for CC and HQ were as low as 0.18 μM and 0.16 μM (S/N = 3), respectively. Additional tests confirmed the good selectivity, reproducibility, and long-term stability of Sb-700/GCE, which was effective in detecting CC and HQ in tap water and river water, with recovery rates of 100.7%-104.5% and 96.5%-101.4%, respectively. It provides a method that combines green microbial synthesis and simple pyrolysis for the preparation of electrode materials in CC and HQ electrochemical sensors, and also offers a new perspective for the application of microbial synthesized materials.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs), a rapidly developing category of crystalline conjugated organic polymers, possess highly ordered structures, large specific surface areas, stable chemical properties, and tunable pore microenvironments. Since the first report of boroxine/boronate ester-linked COFs in 2005, COFs have rapidly gained popularity, showing important application prospects in various fields, such as sensing, catalysis, separation, and energy storage. Among them, COFs-based electrochemical (EC) sensors with upgraded analytical performance are arousing extensive interest. In this review, therefore, we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry, with special emphasis on their usages in the fabrication of chemical sensors, ions sensors, immunosensors, and aptasensors. Notably, the emerged COFs in the electrochemiluminescence (ECL) realm are thoroughly covered along with their preliminary applications. Additionally, final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors, as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

Covalent organic frameworks as highly versatile materials for the removal and electrochemical sensing of organic pollutants

The presence of persistent organic compounds in water has become a worldwide issue due to its resistance to natural degradation, inducing its environmental resilience. Therefore, the accumulation in water bodies, soils, and humans produces toxic effects. Also, low levels of organic pollutants can lead to serious human health issues, such as cancer, chronic diseases, thyroid complications, immune system suppression, etc. Therefore, developing efficient and economically viable remediation strategies motivates researchers to delve into novel domains within material science. Moreover, finding approaches to detect pollutants in drinking water systems is vital for safeguarding water safety and security. Covalent organic frameworks (COFs) are valuable materials constructed through strong covalent interactions between blocked monomers. These materials have tremendous potential in removing and detecting persistent organic pollutants due to their high adsorption capacity, large surface area, tunable porosity, porous structure, and recyclability. This review discusses various synthesis routes for constructing non-functionalized and functionalized COFs and their application in the remediation and electrochemical sensing of persistent organic compounds from contaminated water sources. The development of COF-based materials has some major challenges that need to be addressed for their suitability in the industrial configuration. This review also aims to highlight the importance of COFs in the environmental remediation application with detailed scrutiny of their challenges and outcomes in the current research scenario.

Synthesis of Graphene Oxide-Coupled CoNi Bimetallic MOF Nanocomposites for the Simultaneous Analysis of Catechol and Hydroquinone

Herein, a three-dimensional flower-like cobalt-nickel bimetallic metal-organic framework (CoNi-MOF) coupled with two-dimensional graphene oxide (GO) nanocomposites was successfully synthesized for the selective and simultaneous electrochemical determination of catechol (CC) and hydroquinone (HQ). The three-dimensional flower-like structure of the CoNi-MOF/GO nanocomposite has a multilayer structure and a large surface area, which greatly improves its electrocatalytic activity towards CC and HQ. Differential pulse voltammetry (DPV) results showed that the peak-to-peak separation of CC (0.223 V) and HQ (0.120 V) was 103 mV at a CoNi-MOF/GO modified glassy carbon electrode (CoNi-MOF/GO/GCE), suggesting that the proposed modified electrode can selectively and simultaneously determine them. Under optimal conditions, the CoNi-MOF/GO/GCE showed an excellent analytical performance for the simultaneous determination of CC and HQ, including a wide linear range (0.1-100 μM), low detection limit (0.04 μM for HQ and 0.03 μM for CC) and high anti-interference ability. As expected, the developed modified electrode has been used to analyze CC and HQ in river water, with acceptable results.

Electrochemically reduced graphene oxide films from Zn-C battery waste for the electrochemical determination of paracetamol and hydroquinone

Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO) films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer's method. The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k⁰) were observed for all redox systems studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 μmol L^-1 and 0.65 μmol L^-1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determination of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources.

Recent Progress of Covalent Organic Frameworks Applied in Electrochemical Sensors

As an emerging porous crystalline organic material, the covalent organic frameworks (COFs) are given more and more attention in many fields, such as gas storage and separation, catalysis, energy storage and conversion, luminescent devices, drug delivery, pollutant adsorption and removal, analysis and detection due to their special advantages of high crystallinity, flexible designability, controllable porosities and topologies, intrinsic chemical and thermal stability. In recent years, the COFs are applied in analytical chemistry, for instance, chromatography, solid-phase microextraction, luminescent and colorimetric sensing, surface-enhanced Raman scattering and electroanalytical chemistry. The COFs decorated electrodes show high performance for detecting trace substances with remarkable selectivity and sensitivity, such as heavy metal ions, glucose, hydrogen peroxide, drugs, antibiotics, explosives, phenolic compounds, pesticides, disease metabolites and so on. This review mainly summarized the application of COF based electrochemical sensor according to different target analytes.

MOF-derived CeO2/Co3O4-Fe2O3@CC nanocomposites as highly sensitive electrochemical sensor for bisphenol a detection

A novel CeO₂/Co₃O₄-Fe₂O₃@CC electrode derived from CeCo-MOFs was developed for detecting the endocrine disruptor bisphenol A (BPA). Firstly, bimetallic CeCo-MOFs were prepared by hydrothermal method, and obtained material was calcined to form metal oxides after doping Fe element. The results suggested that hydrophilic carbon cloth (CC) modified with CeO₂/Co₃O₄-Fe₂O₃ had good conductivity and high electrocatalytic activity. By the analyses of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the introduction of Fe increased the current response and conductivity of the sensor, greatly increasing the effective active area of the electrode. Significantly, electrochemical test proves that the prepared CeO₂/Co₃O₄-Fe₂O₃@CC had excellent electrochemical response to BPA with a low detection limit of 8.7 nM, an excellent sensitivity of 20.489 μA/μM·cm², a linear range of 0.5-30 μM, and strong selectivity. In addition, the CeO₂/Co₃O₄-Fe₂O₃@CC sensor had a high recovery rate for the detection of BPA in real tap water, lake water, soil eluent, seawater, and PET bottle samples, which showed its potential in practical applications. To sum up, the CeO₂/Co₃O₄-Fe₂O₃@CC sensor prepared in this work had excellent sensing performance, good stability and selectivity for BPA, which can be well used for the detection of BPA.

A highly explicit electrochemical biosensor for catechol detection in real samples based on copper-polypyrrole

Catechol is a pollutant that can lead to serious health issues. Identification in aquatic environments is difficult. A highly specific, selective, and sensitive electrochemical biosensor based on a copper-polypyrrole composite and a glassy carbon electrode has been created for catechol detection. The novelty of this newly developed biosensor was tested using electrochemical techniques. The charge and mass transfer functions and partially reversible oxidation kinetics of catechol on the redesigned electrode surface were examined using electrochemical impedance spectroscopy and cyclic voltammetry scan rates. Using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry, the characteristics of sensitivity (8.5699 μA cm^-2), LOD (1.52 × 10^-7 μM), LOQ (3.52 × 10^-5 μM), linear range (0.02-2500 μM), specificity, interference, and real sample detection were investigated. The morphological, structural, and bonding characteristics were investigated using XRD, Raman, FTIR, and SEM. Using an oxidation-reduction technique, a suitable biosensor material was produced. In the presence of interfering compounds, it was shown that it was selective for catechol, like an enzyme.

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as electrochemical sensors for the efficient detection of pharmaceutical residues

Pharmaceutical residues are the undecomposed remains from drugs used in the medical and food industries. Due to their potential adverse effects on human health and natural ecosystems, they are of increasing worldwide concern. The acute detection of pharmaceutical residues can give a rapid examination of their quantity and then prevent them from further contamination. Herein, this study summarizes and discusses the most recent porous covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) for the electrochemical detection of various pharmaceutical residues. The review first introduces a brief overview of drug toxicity and its effects on living organisms. Subsequently, different porous materials and drug detection techniques are discussed with materials' properties and applications. Then the development of COFs and MOFs has been addressed with their structural properties and sensing applications. Further, the stability, reusability, and sustainability of MOFs/COFs are reviewed and discussed. Besides, COFs and MOFs' detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles are analyzed and discussed. Lastly, this review summarized and discussed the MOF@COF composite as sensors, the fabrication strategies to enhance detection potential, and the current challenges in this area.

A light-driven photoelectrochemical sensor for highly selective detection of hydroquinone based on type-II heterojunction formed by carbon nanotubes immobilized in 3D honeycomb CdS/SnS2

The ecological environment and public safety are seriously threatened by the typical phenolic contaminant hydroquinone (HQ). Here, using a straightforward physical mixing technique, we created an n-n heterojunction by uniformly immobilizing cadmium sulfide (CdS) nanoparticles on the surface of a three-dimensionally layered, flower-like structure made of tin sulfide (SnS₂). Then, as photosensitizers, carbon nanotubes (CNTs) were added to the CdS/SnS₂ complex to create a type-II heterostructure of CdS/SnS₂/CNTs with synergistic effects. Subsequently, the detector HQ was bound to the modified photoelectrodes, which was accompanied by the hole oxidation of the bound HQ, leading to a significant increase in the photocurrent signal, thus allowing specific and sensitive detection of HQ. Under optimized detection conditions, the proposed photoelectrochemical sensor shows a wide detection range of 0.2 to 100 μM for HQ with a detection limit as low as 0.1 μM. The high accuracy of the sensor was demonstrated by comparison with the detection results of UV-vis spectrophotometry. In addition, the photoelectrochemical sensor exhibits good reproducibility, stability, selectivity, and specificity, providing a light-driven method to detect HQ.