Porous materials as effective chemiresistive gas sensors.

Chemiresistive gas sensors (CGSs) have revolutionized the field of gas sensing by providing a low-power, low-cost, and highly sensitive means of detecting harmful gases. This technology works by measuring changes in the conductivity of materials when they interact with a testing gas. While semiconducting metal oxides and two-dimensional (2D) materials have been used for CGSs, they suffer from poor selectivity to specific analytes in the presence of interfering gases and require high operating temperatures, resulting in high signal-to-noise ratios. However, nanoporous materials have emerged as a promising alternative for CGSs due to their high specific surface area, unsaturated metal actives, and density of three-dimensional inter-connected conductive and pendant functional groups. Porous materials have demonstrated excellent response and recovery times, remarkable selectivity, and the ability to detect gases at extremely low concentrations. Herein, our central emphasis is on all aspects of CGSs, with a primary focus on the use of porous materials. Further, we discuss the basic sensing mechanisms and parameters, different types of popular sensing materials, and the critical explanations of various mechanisms involved throughout the sensing process. We have provided examples of remarkable performance demonstrated by sensors using these materials. In addition to this, we compare the performance of porous materials with traditional metal-oxide semiconductors (MOSs) and 2D materials. Finally, we discussed future aspects, shortcomings, and scope for improvement in sensing performance, including the use of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous organic polymers (POPs), as well as their hybrid counterparts. Overall, CGSs using porous materials have the potential to address a wide range of applications, including monitoring water quality, detecting harmful chemicals, improving surveillance, preventing natural disasters, and improving healthcare.

Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies.

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough".

Raman spectroscopy, an ideal tool for studying the physical properties and applications of metal-organic frameworks (MOFs).

Metal-organic frameworks (MOFs) are a unique family of materials constructed by coordinating metal ions or clusters to bridging organic ligands. Many of these materials are well known for their intricate structures, and exceptional gas adsorption properties, and have potential applications in the separation of alkanes, catalysis, energy storage, surface-enhanced Raman spectroscopy (SERS) based detections, and diagnostics. In situ or in operando Raman spectroscopic studies provide real-time information about the different processes and associated structural changes in MOFs. In the last few decades, there has been phenomenal growth in the publications on MOFs containing insights from Raman spectroscopy. Such studies have helped the research community in identifying the adsorption sites, defect sites, structural or spin transitions, reaction centers, intermediates, etc. In this review, we present the current research status of Raman spectroscopy in probing the structure, guest adsorption, catalytic activity, and reaction mechanisms of MOFs, and their application in energy storage and SERS detection. We highlight the advancements in the Raman spectroscopy technique that have facilitated in situ studies in atmosphere as well as various chemical environments. We briefly discuss the relevance of computational studies in understanding phonon modes and predicting the stability of MOFs. Although this review is particularly focussed on works related to Raman spectroscopy of MOFs, we do discuss infrared studies on MOFs, where such results or analyses are missing from the Raman studies. These discussions have been provided with the intent to develop similar analysis techniques or methods in Raman spectroscopy research.

Cyclodextrin metal-organic frameworks and derivatives: recent developments and applications.

While there is a tremendous amount of scientific research on metal organic frameworks (MOFs) for gas storage/separation, catalysis and energy storage, the development and application of biocompatible MOFs still poses major challenges. In general, they can be synthesised from various biocompatible linkers and metal ions but particularly cyclodextrins (CDs) as cyclic oligosaccharides are an astute choice for the former. Although the field of CD-MOF materials is still in the early stages and their design and fabrication comes with many hurdles, the benefits coming from CDs built in a porous framework are exciting. Versatile host-guest complexation abilities, high encapsulation capacity and hydrophilicity are among the valuable properties inherent to CDs and offer extended and novel applications to MOFs. In this review, we provide an overview of the state-of-the-art synthesis, design, properties and applications of these materials. Initially, a rationale for the preparation of CD-based MOFs is provided, based on the chemical and structural properties of CDs and including their advantages and disadvantages. Further on, the review exhaustively surveys CD-MOF based materials by categorising them into three sub-classes, namely (i) CD-MOFs, (ii) CD-MOF hybrids, obtained via combination with external materials, and (iii) CD-MOF-derived materials prepared under pyrolytic conditions. Subsequently, CD-based MOFs in practical applications, such as drug delivery and cancer therapy, sensors, gas storage, (enantiomer) separations, electrical devices, food industry, and agriculture, are discussed. We conclude by summarizing the state of the art in the field and highlighting some promising future developments of CD-MOFs.

Hierarchical porous metal-organic gels and derived materials: from fundamentals to potential applications.

Metal-organic gels (MOGs) emerged as a novel class of functional soft materials in which the scaffolding framework is fabricated by metal-ligand coordination in combination with other supramolecular interactions (for example, hydrogen bonding or π-π stacking). Through the combination of organic and inorganic (metal/metal-oxo clusters) building blocks, significant steps forward have been made in the development of new electrochemical sensors, superhydrophobic materials and ion storage devices, among others. These leaps forward are to some extend induced by the intrinsic hierarchical microporous/mesoporous pore structure of these metal-organic materials. Within this review we give an overview of recent developments of this growing field. First, we shed light onto the parallels to the well-established field of conventional gels and outline similarities and differences. Afterwards, we classify different types of MOGs according to their architectural/structural nature: (1) pristine MOGs, (2) hybrid MOGs, (3) crosslinking-based MOGs and (4) MOG-derived materials. Furthermore, we look at the different properties of MOGs and the requirements for the preparation of spatially patterned macro-structured MOGs by emerging additive manufacturing technologies. Moreover, different potential fields of application for MOGs and MOG derived materials are critically evaluated and potential improvements and pitfalls in comparison to traditional gel-based materials are given. Finally, a comprehensive outlook into future directions for the development of MOGs is provided.

Carbon Nanotube Based Metal-Organic Framework Hybrids From Fundamentals Toward Applications.

Metal-organic frameworks (MOFs) materials constructed by the coordination chemistry of metal ions and organic ligands are important members of the crystalline materials family. Owing to their exceptional properties, for example, high porosity, tunable pore size, and large surface area, MOFs have been applied in several fields such as gas or liquid adsorbents, sensors, batteries, and supercapacitors. However, poor conductivity and low stability hamper their potential applications in several attractive fields such as energy and gas storage. The integration of MOFs with carbon nanotubes (CNTs), a well-established carbon allotrope that exhibits high conductivity and stability, has been proposed as an efficient strategy to overcome such limitations. By combining the advantages of MOFs and CNTs, a wide variety of composites can be prepared with properties superior to their parent materials. This review provides a comprehensive summary of the preparation of CNT@MOF composites and focuses on their recent applications in several important fields, such as water purification, gas storage and separation, sensing, electrocatalysis, and energy storage (supercapacitors and batteries). Future challenges and prospects for CNT@MOF composites are also discussed.

Metal Halide Perovskite@Metal-Organic Framework Hybrids: Synthesis, Design, Properties, and Applications.

Metal halide perovskites (MHPs) have excellent optoelectronic and photovoltaic applications because of their cost-effectiveness, tunable emission, high photoluminescence quantum yields, and excellent charge carrier properties. However, the potential applications of the entire MHP family are facing a major challenge arising from its weak resistance to moisture, polar solvents, temperature, and light exposure. A viable strategy to enhance the stability of MHPs could lie in their incorporation into a porous template. Metal-organic frameworks (MOFs) have outstanding properties, with a unique network of ordered/functional pores, which render them promising for functioning as such a template, accommodating a wide range of MHPs to the nanosized region, alongside minimizing particle aggregation and enhancing the stability of the entrapped species. This review highlights recent advances in design strategies, synthesis, characterization, and properties of various hybrids of MOFs with MHPs. Particular attention is paid to a critical review of the emergence of MHP@MOF for comprehensive studies of next-generation materials for various technological applications including sensors, photocatalysis, encryption/decryption, light-emitting diodes, and solar cells. Finally, by summarizing the state-of-the-art, some promising future applications of reported hybrids are proposed. Considering the inherent correlation and synergic functionalities of MHPs and MOFs, further advancement; new functional materials; and applications can be achieved through designing MHP@MOF hybrids.

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors.

The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

Biomimetic Superhydrophobic/Superoleophilic Highly Fluorinated Graphene Oxide and ZIF-8 Composites for Oil-Water Separation.

Superhydrophobic/superoleophilic composites HFGO@ZIF-8 have been prepared from highly fluorinated graphene oxide (HFGO) and the nanocrystalline zeolite imidazole framework ZIF-8. The structure-directing and coordination-modulating properties of HFGO allow for the selective nucleation of ZIF-8 nanoparticles at the graphene surface oxygen functionalities. This results in localized nucleation and size-controlled ZIF-8 nanocrystals intercalated in between HFGO layers. The composite microstructure features fluoride groups bonded at the graphene. Self-assembly of a unique micro-mesoporous architecture is achieved, where the micropores originate from ZIF-8 nanocrystals, while the functionalized mesopores arise from randomly organized HFGO layers separated by ZIF-8 nanopillars. The hybrid material displays an exceptional high water contact angle of 162° and low oil contact angle of 0° and thus reveals very high sorption selectivity, fast kinetics, and good absorbencies for nonpolar/polar organic solvents and oils from water. Accordingly, Sponge@HFGO@ZIF-8 composites are successfully utilized for oil-water separation.

Redox-Active Metal-Organic Frameworks: Highly Stable Charge-Separated States through Strut/Guest-to-Strut Electron Transfer.

Molecular organization of donor and acceptor chromophores in self-assembled materials is of paramount interest in the field of photovoltaics or mimicry of natural light-harvesting systems. With this in mind, a redox-active porous interpenetrated metal-organic framework (MOF), {[Cd(bpdc)(bpNDI)]⋅4.5 H2 O⋅DMF}n (1) has been constructed from a mixed chromophoric system. The µ-oxo-bridged secondary building unit, {Cd2 (µ-OCO)2 }, guides the parallel alignment of bpNDI (N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) acceptor linkers, which are tethered with bpdc (bpdcH2 =4,4'-biphenyldicarboxylic acid) linkers of another entangled net in the framework, resulting in photochromic behaviour through inter-net electron transfer. Encapsulation of electron-donating aromatic molecules in the electron-deficient channels of 1 leads to a perfect donor-acceptor co-facial organization, resulting in long-lived charge-separated states of bpNDI. Furthermore, 1 and guest encapsulated species are characterised through electrochemical studies for understanding of their redox properties.

Synergistic metal halide perovskite@metal-organic framework hybrids for photocatalytic CO2 reduction.

The photocatalytic reduction of carbon dioxide (CO2) into multi-electron carbon products remains challenging due to the inherent stability of CO2 and slow multi-electron transfer kinetics. Here in, we synthesized a hybrid material, cesium copper halide (Cs3Cu2I5) intercalated onto two-dimensional (2D) cobalt-based zeolite framework (ZIF-9-III) nanosheets (denoted as Cs3Cu2I5@ZIF-1) through a simple mechanochemical grinding. The synergy in the hybrid effectively reduces CO2 to carbon monoxide (CO) at 110 µmol/g/h and methane at 5 µmol/g/h with high selectivity, suppressing hydrogen evolution. Further, we have investigated additional Cs3Cu2I5@ZIF hybrids with varying ZIF-9-III amounts, confirming their selective CO2 reduction to methane over hydrogen. Density functional theory (DFT) calculations reveal a non-covalent interaction between Cs3Cu2I5 and ZIF-9-III, with electron transfer suggesting potential for improved photocatalysis.

Temperature induced structural transformations and gas adsorption in the zeolitic imidazolate framework ZIF-8: a Raman study.

Here we have used Raman spectroscopy to investigate molecular level changes in the zeolitic imidazolate framework ZIF-8 (a prototypical zeolite-like porous metal organic framework) as a function of temperature. Temperature dependent Raman spectra suggest that at low temperature the softening of the C-H stretching frequencies is due to the decrease in steric hindrance between the methyl groups of methyl imidazole. The larger separation between the methyl groups opens the window for increased nitrogen and methane uptake at temperatures below 153 K. The appearance of Raman bands at 2323 cm(-1) and 2904 cm(-1) at or below 153 K in ZIF-8 are characteristic signatures of the adsorbed nitrogen and methane gases respectively. Nanoscale ZIF-8 uptakes more molecules than bulk ZIF-8, and as a result we could provide evidence for encaged CO2 at 203 K yielding its Raman mode at 1379 cm(-1).

Lewis Acid Catalyzed Amide Bond Formation in Covalent Graphene-MOF Hybrids.

Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.

Acidic graphene organocatalyst for the superior transformation of wastes into high-added-value chemicals.

Our dependence on finite fossil fuels and the insecure energy supply chains have stimulated intensive research for sustainable technologies. Upcycling glycerol, produced from biomass fermentation and as a biodiesel formation byproduct, can substantially contribute in circular carbon economy. Here, we report glycerol's solvent-free and room-temperature conversion to high-added-value chemicals via a reusable graphene catalyst (G-ASA), functionalized with a natural amino acid (taurine). Theoretical studies unveil that the superior performance of the catalyst (surpassing even homogeneous, industrial catalysts) is associated with the dual role of the covalently linked taurine, boosting the catalyst's acidity and affinity for the reactants. Unlike previous catalysts, G-ASA exhibits excellent activity (7508 mmol g-1 h-1) and selectivity (99.9%) for glycerol conversion to solketal, an additive for improving fuels' quality and a precursor of commodity and fine chemicals. Notably, the catalyst is also particularly active in converting oils to biodiesel, demonstrating its general applicability.

Luminescent microporous metal-organic framework with functional lewis basic sites on the pore surface: specific sensing and removal of metal ions.

A three-dimensional luminescent metal-organic framework, {Mg(DHT)(DMF)(2)}(n) (1), based on an excited-state intramolecular proton-transfer (ESIPT) responsive linker, 2,5-dihydroxyterephthalic acid (H(2)DHT), has been synthesized, and its desolvated microporous framework with pendent -OH groups on the pore surface was exploited for the binding and specific sensing of metal ions via Lewis acid-base interactions. The luminescence intensity significantly quenches with Cu(II) among various s- and d-block metal ions, and highly selective sensing of Cu(II) ions has been realized in both solid and solution states (up to nanomolar concentration). The immobilized Cu(II) metal ions can be selectively removed by chelating agents like ethylenediaminetetraacetic acid without any structural disintegration of the framework, as revealed by the luminescence and gas-adsorption studies.

Three-dimensional metal-organic framework with highly polar pore surface: H2 and CO2 storage characteristics.

A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) (1), (bipy =4,4'-bipyridine and Himdc = 4,5-imidazoledicarboxylate) has been synthesized and structurally characterized. The highly rigid and stable framework contains a 3D channel structure with highly polar pore surfaces decorated with pendant oxygen atoms of the Himdc linkers. The desolvated framework [Cd(bipy)(0.5)(Himdc)](n) (1') is found to exhibit permanent porosity with high H(2) and CO(2) storage capacities. Two H(2) molecules occluded per unit formula of 1' and the corresponding heat of H(2) adsorption (ΔH(H2)) is about ∼9.0 kJ/mol. The high value of ΔH(H2) stems from the preferential electrostatic interaction of H(2) with the pendent oxygen atoms of Himdc and aromatic bipy linkers as determined from first-principles density functional theory (DFT) based calculations. Similarly, DFT studies indicate CO(2) to preferentially interact electrostatically (C(δ+)···O(δ-)) with the uncoordinated pendent oxygen of Himdc. It also interacts with bipy through C-H···O bonding, thus rationalizing the high heat (ΔH(CO2) ∼ 35.4 kJ/mol) of CO(2) uptake. Our work unveiled that better H(2) or CO(2) storage materials can be developed through the immobilization of reactive hetero atoms (O, N) at the pore surfaces in a metal-organic framework.

Emerging MXene@Metal-Organic Framework Hybrids: Design Strategies toward Versatile Applications.

Rapid progress on developing smart materials and design of hybrids is motivated by pressing challenges associated with energy crisis and environmental remediation. While emergence of versatile classes of nanomaterials has been fascinating, the real excitement lies in the design of hybrid materials with tunable properties. Metal-organic frameworks (MOFs) are the key materials for gas sorption and electrochemical applications, but their sustainability is challenged by limited chemical stability, poor electrical conductivity, and intricate, inaccessible pores. Despite tremendous efforts towards improving the stability of MOF materials, little progress has made researchers inclined toward developing hybrid materials. MXenes, a family of two-dimensional transition-metal carbides, nitrides and carbonitrides, are known for their compositional versatility and formation of a range of structures with rich surface chemistry. Hybridization of MOFs with functional layered MXene materials may be beneficial if the host structure provides appropriate interactions for stabilizing and improving the desired properties. Recent efforts have focused on integrating Ti3C2Tx and V2CTx MXenes with MOFs to result in hybrid materials with augmented electrochemical and physicochemical properties, widening the scope for emerging applications. This review discusses the potential design strategies of MXene@MOF hybrids, attributes of tunable properties in the resulting hybrids, and their applications in water treatment, sensing, electrochemical energy storage, smart textiles, and electrocatalysis. Comprehensive discussions on the recent efforts on rapidly evolving MXene@MOF materials for various applications and potential future directions are highlighted.

Rational Design of Graphene Derivatives for Electrochemical Reduction of Nitrogen to Ammonia.

The conversion of nitrogen to ammonia offers a sustainable and environmentally friendly approach for producing precursors for fertilizers and efficient energy carriers. Owing to the large energy density and significant gravimetric hydrogen content, NH3 is considered an apt next-generation energy carrier and liquid fuel. However, the low conversion efficiency and slow production of ammonia through the nitrogen reduction reaction (NRR) are currently bottlenecks, making it an unviable alternative to the traditional Haber-Bosch process for ammonia production. The rational design and engineering of catalysts (both photo- and electro-) represent a crucial challenge for improving the efficiency and exploiting the full capability of the NRR. In the present review, we highlight recent progress in the development of graphene-based systems and graphene derivatives as catalysts for the NRR. Initially, the history, fundamental mechanism, and importance of the NRR to produce ammonia are briefly discussed. We also outline how surface functionalization, defects, and hybrid structures (single-atom/multiatom as well as composites) affect the N2 conversion efficiency. The potential of graphene and graphene derivatives as NRR catalysts is highlighted using pertinent examples from theoretical simulations as well as machine learning based performance predictive methods. The review is concluded by identifying the crucial advantages, drawbacks, and challenges associated with principal scientific and technological breakthroughs in ambient catalytic NRR.

Covalent Graphene-MOF Hybrids for High-Performance Asymmetric Supercapacitors.

In this work, the covalent attachment of an amine functionalized metal-organic framework (UiO-66-NH2  = Zr6 O4 (OH)4 (bdc-NH2 )6 ; bdc-NH2  = 2-amino-1,4-benzenedicarboxylate) (UiO-Universitetet i Oslo) to the basal-plane of carboxylate functionalized graphene (graphene acid = GA) via amide bonds is reported. The resultant GA@UiO-66-NH2 hybrid displayed a large specific surface area, hierarchical pores and an interconnected conductive network. The electrochemical characterizations demonstrated that the hybrid GA@UiO-66-NH2 acts as an effective charge storing material with a capacitance of up to 651 F g-1 , significantly higher than traditional graphene-based materials. The results suggest that the amide linkage plays a key role in the formation of a π-conjugated structure, which facilitates charge transfer and consequently offers good capacitance and cycling stability. Furthermore, to realize the practical feasibility, an asymmetric supercapacitor using a GA@UiO-66-NH2 positive electrode with Ti3 C2 TX MXene as the opposing electrode has been constructed. The cell is able to deliver a power density of up to 16 kW kg-1 and an energy density of up to 73 Wh kg-1 , which are comparable to several commercial devices such as Pb-acid and Ni/MH batteries. Under an intermediate level of loading, the device retained 88% of its initial capacitance after 10 000 cycles.

Hierarchical Porous Graphene-Iron Carbide Hybrid Derived From Functionalized Graphene-Based Metal-Organic Gel as Efficient Electrochemical Dopamine Sensor.

A metal-organic gel (MOG) similar in constitution to MIL-100 (Fe) but containing a lower connectivity ligand (5-aminoisophthalate) was integrated with an isophthalate functionalized graphene (IG). The IG acted as a structure-directing templating agent, which also induced conductivity of the material. The MOG@IG was pyrolyzed at 600°C to obtain MGH-600, a hybrid of Fe/Fe3C/FeOx enveloped by graphene. MGH-600 shows a hierarchical pore structure, with micropores of 1.1 nm and a mesopore distribution between 2 and 6 nm, and Brunauer-Emmett-Teller surface area amounts to 216 m2/g. Furthermore, the MGH-600 composite displays magnetic properties, with bulk saturation magnetization value of 130 emu/g at room temperature. The material coated on glassy carbon electrode can distinguish between molecules with the same oxidation potential, such as dopamine in presence of ascorbic acid and revealed a satisfactory limit of detection and limit of quantification (4.39 × 10-7 and 1.33 × 10-6 M, respectively) for the neurotransmitter dopamine.