Hydrothermal synthesis is typically adopted to produce sustainable metal-ligand bonds across the framework, which yields the most comprehensive dynamical products [32]. Long-term heating of the reaction mixture at high pressure and temperature enables the hydrothermal synthesis of MOF [33]. Based on the material’s dissolution rate in hot water under intense vapor tension upheld at a temperature variation allying, the reactor’s opposite nodes yield single crystals. Moreover, the ‘solvothermal’ process utilizes suitable solvents besides water in the material synthesis. The method results from the growth of high-quality crystals, but generally, Hydrothermal/Solvothermal processes gradually and necessitate elevated performing temperatures [34]. Fig. 1 illustrates a schematic of the steps in the synthetic approach using hydrothermal and solvothermal processes.

The hydrothermal method synthesizes the Cu (4, 4′-bpy)NO₃ (H₂0) crystals with rectangular parallelepiped-shaped, utilizing the 4, 4′-bipyridine as a nitrogen donor aromatic ligand [35]. Similarly, the hydrothermal method synthesizes the [Cu₃(TMA)₂(H₂O)₃]_n complex known as HKUST-1 using the carboxylic as a functional group [19]. The hydrothermal route by simple metal ions self-assembling at the adaptive bis-(imidazole) binding sites using the transition metals (cobalt, nickel, and zinc) synthesizes the MOFs having various applications [36]. The hydrothermal reaction yielded a polycrystalline Fe-MIL-100 powder with a significantly large attainable and enduring porosity, demonstrating an intriguing Friedel-Crafts reaction with catalytic activity employing the redox properties of Fe(III) [37]. Ni (II) is a typical transition metal ion with varied interest because of its inexpensive cost, high abundance, superior catalytic activity, and electrochemical characteristics [38,39]. Ni-MOFs are synthesized by the hydrothermal process using Ni(II) and the 1,3,5-benzene tricarboxylate as a ligand [40]. Nickel-based compounds with the proper design showed considerable potential for usage in the electrochemical industry as electrode surface modifications and electrocatalysts [41–43]. The solvothermal method synthesizes the Mg-MOF-nNH₂ with double ligands. The metal center is magnesium, and the ligands are 2,5-dihydroxyterephthalic acid and 2-amino terephthalic acid. The micropore volume of Mg-MOF-1/8NH₂ measures 0.46 cm³g⁻¹ for these MOF samples. Additionally, the synthesized materials have a high specific surface area of 924.19 m²g⁻¹ [44]. Similarly, a single-step solvothermal method obtains the Mn/Fe-MOF@Pd1.0. The Mn²⁺ and Fe³⁺ are the metal sources of MOF, and Pd is doped within the MOF. The catalytic activity of Fe-MOF resembles that of an enzyme. Bimetallic active sites enhance the catalytic activity, and the presence of Pd further synergizes the acid tolerance and stability of Mn/Fe-MOF solid [45].

Ultrasonic-assisted synthesis offers a relatively environment-friendly technique for MOF synthesis in an enclosing reaction condition (i.e., enclosing temperature and atmospheric pressure) with a shorter reaction time. Furthermore, the ultrasonication synthesis approaches avoid safety concerns, providing an opportunity to expand on the twelve principles of green chemistry [46]. Amongst some of the diverse MOF synthetic techniques, the ultrasonication method is affordable and environmentally benign. It could produce a high yield while operating under ambient temperature and pressure in a solvent-free reaction [47].

Compared to other methods, ultrasonic-aided MOF synthesis is practically viable and containable and quickly produces the product with a significant yield [48]. Ultrasonic cavitation for producing MOFs is relatively new and has recently attracted greater attention [49]. In 2009, Khan et al. [50] conducted the first study on the impact of ultrasonic irradiation on the [Cu₃ (TMA)₂(H₂O)₃]_n, also known as Cu-BTC MOF. The ultrasonically assisted synthesis of MOFs significantly reduces the reaction time compared to the electronically controlled and microwave irradiation methods. Additionally, a limited sonication enabled the shrinking of the size of the MOF particles; however, an increased sonication time from 6 to 45 min caused aggregation of the MOFs [51].

Sonochemical irradiation technique synthesizing the urea-containing metal-organic frameworks, i.e., TMU-31 and TMU-32. Further, various parameters, such as the initial reagent concentrations and irradiation periods, determine the morphology of MOF. The results reveal that these MOFs can achieve homogeneous plate shape at 0.005 M concentration with a maximum power supply of 360 W. Furthermore, phenol sensing was assessed and compared using these MOFs. The results indicate that hydrogen-bonding and packing interactions have a substantial role in detecting the phenol. Incorporating urea into the MOF structure is crucial for the framework’s ability to detect phenol [52]. The synthesis of MOFs containing embedded porphyrin units still needs to be done. Under well-regulated reaction conditions, it takes a long time to synthesize, and a combined phase with diverse crystal shapes is nevertheless often observed. The sonochemical synthesis produces the high-purity uniform-sized Zr-based porphyrinic MOF-525 and MOF-545 using the tetrakis (4-carboxyphenyl) porphyrin and zirconyl chloride octahydrate.

Moreover, benzoic acid modulated MOF-525, while trifluoroacetic acid modulated the formation of MOF-545 [53]. Solvothermal and sonochemical techniques synthesize the zinc-based MOF using adipic acid as an aliphatic ditopic linker. Ultrasonic irradiation enables MOF formation efficiency; also, the particle sizes shrunk due to ultrasonic irradiation. The samples’ catalytic effectiveness was assessed using the electrochemical reduction of CO₂, with the only byproducts being carbon monoxide and hydrogen [54].

On the other hand, the possible role of solvent in the yield of MOF production using the ultrasound method was reported [55]. The study investigates the effects of solvents, both binary and ternary combinations, on the textural features of Cu-BTC. Additionally, various ultrasonic parameters, such as sonication duration and power supply, determine the formation of MOF (Cf Fig. 2). The sonication process was carried out for 2 h at 750 watts using a mixture of three solvents, namely water (H₂O), ethanol (C₂H₅OH), and dimethylformamide (DMF). This process enhances the yield of copper metal-organic framework (Cu-MOF) [55].

Microwave-aided synthesis is the most efficient approach for carrying out many reactions. Compared to conventional solvothermal synthesis, microwave irradiation reduces the reaction time and enhances the crystal growth of porous materials that take several days or weeks in conventional methods [56]. The microwave irradiation energy, time of exposure, solvent concentration, and solvent systems are the key parameters regulating the yield and crystal growth of the MOFs, and microwave irradiation showed a positive impact on material characteristics and properties [57]. Microwave-assisted synthesis acknowledges rapid heating, fast kinetics, phase purity, increased yield, improved dependability, and repeatability over hydrothermal synthesis [58–61]. Additionally, it offers an effective method to regulate the distribution of macroscopic morphology, particle size, and phase selectivity during the synthesis of inorganic solids and nanocomposite materials. Although the synthesis is much faster, the properties of the crystals produced by the microwave-assisted technique are comparable to those produced by the conventional solvothermal process [62–64]. Microwave-assisted approaches, on the other hand, have sparked more interest in studying the effects of irradiation period, power, temperature, solvent concentration, and metal ion/organic linker ratio, for example, on the synthesis of MOF-5 by employing the microwave-assisted technique [65]. The nanocrystal crystallization process optimizes for several parameters: time, temperature, and power as 1 h at 130°C and 600–1000 W, respectively. This study showed that the crystal formation occurred under microwave irradiation of 15 min and produced a high-quality crystal between 30 min and 24 h. Similarly, microwave-assisted synthesis produces the Zr-based MOF (Zr-fum-fcu-MOF), which has an octahedral shape at the reaction temperature of 100°C. Fig. 3 depicts an overview of the synthesis procedure [66].

The electrochemical process of MOF synthesis possesses several advantages over conventional MOF synthesis, including relatively short reaction time, relatively simple equipment setup, real-time MOF structure modification, quick synthesis, no necessity of precursor metal salts, and direct accumulation of MOFs on the preferred substrates, etc. [67,68]. In addition to its simple process, the electrochemical synthesis of MOFs has provided numerous favorable circumstances, such as random and quick synthesis with lesser use of linker and solvent, excellent yield, and low energy consumption [69]. The mild reaction conditions, which perform at ambient temperature and pressure, are the most attractive feature of electrochemical synthesis. Despite these advantages, it is a less utilized approach, particularly in synthesizing functionalized framework materials [70]. This approach also constantly altered the real-time response, enabling the direct output of crack-free nanostructures without a pre-treated surface at high temperatures.

On the other hand, relatively high reaction temperatures, longer reaction times, and thermal-induced cracking on the films are shown in the solvothermal or hydrothermal techniques [71]. Electrochemically synthesized the Zn-based MOF, and the physicochemical parameters, viz., reaction time, electrolyte quantity, current, and voltage, are optimized for greater solid yield. The results indicated that both reaction time and current density significantly impacted the purity and yield, and at an applied current of 60 mA and a reaction time of 2 h, yielded 87% of the product [72]. Fig. 4 shows the instrumentation of a simple electrochemical synthesis of Zn₃(BTC)₂ MOF [73].

Mechanochemical synthesis is one of the most exciting chemical modifications employed to obtain high purity with enhanced yield of several MOFs [74]. Most coordination polymerization processes involving multisite ligands with metal ions proceed readily in a suitable solution environment. The solvent-free or solid-state formation of MOFs without any toxic or hazardous solvents has progressively received attention in recent years due to significant advances in mechanochemical synthesis [50]. Coordination polymerization, broadly, involves the reaction in the presence of solution, multisite ligands, and metal ions. However, the mechanochemical synthesis of MOFs utilizes minimal solvents, is solvent-free, or is a solid-state organic process without unfavorable and toxic solvents [75].

Furthermore, compared to the diffusion and solvothermal methods, this technique is advantageous for large-scale MOF manufacturing in a shorter reaction time and at room temperature [76,77]. The solid-solid reaction has the potential to synthesize a large-scale production of materials and provides simplicity in handling since it directly produces the products in powdered forms. Although mechanochemical synthesis is solvent-free or solvent-less, a solvent-based purification step is required. Despite this, the mechanochemical synthesis is reasonably environmentally friendly and commercially exciting for MOF production [78]. The liquid-assisted mechanochemical synthesis produced the MOF-5, showing that the solid possessed a relatively low BET surface area and contained many amide precursor by-products [79]. A copper-based MOF with a product yield of 97% was synthesized in the mechanochemical process using the Cu(OAc)_2.H₂O and H₃BTC and at 30 Hz and 20 min of reaction time produced a dark blue color solid [55]. The framework structures produced by the mechanochemical method are easily separable from the host molecules, providing repeatable free pore access for additional uses [80]. The mechanochemical synthesis of HKUST-1 and MOF-14 showed the method’s applicability in efficient MOF production [74]. Fig. 5 demonstrates the mechanochemical method of synthesizing MOF.

The different types of MOF have different routes of synthesis. The organic linker should be chosen wisely depending on the central metal atom. Table 1 displays the different types of MOF synthesized using different routes under varying conditions.

In the slow evaporation approach, reagent solutions are blended and allowed to undergo gradual evaporation. A critical concentration produces the crystals, facilitating deposition and subsequent crystal development. Since slow evaporation requires no external energy, it is a straightforward process for preparing MOF compounds. Nonetheless, this approach occasionally designs the MOF, but the primary disadvantage is that the crystal takes a long time to form. Slow evaporation may involve using a solvent combination to increase the starting material’s solubility or a low-boiling solvent to hurry up slow evaporation [81,82].

A two-dimensional coordination polymer, denoted as [Cu(SCN) (hmp)]_n CP (1), was synthesized using the slow evaporation technique. The reaction of CuSO₄·5H₂O, 2-pyridine-methanol (hmpH), sodium thiocyanate, and sodium hydroxide in water are involved, aiming for specific practical uses. The CP (1) explores the fluorescence sensing capabilities of various nitroaromatic compounds and toxic metal complexes. Notably, CP (1) exhibited exceptional sensitivity and selectivity to nitrobenzene, also in competing nitroaromatics. Additionally, CP (1) displayed exceptional sensitivity and selectivity towards Fe³⁺ compared to many metal ions. CP (1) demonstrated impressive recyclability for both analytes, nearly restoring its initial intensity after multiple washings. Furthermore, CP (1) is an excellent material for the adsorption of organic dyes with different sizes and charges, such as methylene blue (MB), methyl orange (MO), and Rhodamine-B. The CP (1) is designed by bridging the coordination chemistry, having various intriguing functional applications [83].

In the diffusion technique, reagent solutions are either stacked atop one another with a solvent layer in between or undergo a gradual diffusion process facilitated by physical barriers. Occasionally, gels serve as both the medium for crystallization and diffusion. At the interface of these layers, crystals emerge following the gradual dissipation of the precipitating solvent into the subsequent layer [84]. In particular, the diffusion approach is practical when the products have limited solubility. A technique combining ultrasonic and vapor phase diffusion was used for rapidly synthesizing [Tb(1,3,5-BTC)]_n, a terbium-based metal-organic framework (MOF).

Compared with existing solvothermal and ultrasound-assisted approaches, this combined ultrasound-vapour phase diffusion strategy produces nanoscale MOF crystals at a significantly higher rate. Notably, the resultant [Tb(1,3,5-BTC)]_n nanocrystals showed exceptional selectivity in detecting picric acid (PA), with no interference from other nitroaromatic chemicals such as nitrobenzene, 2-nitrotoluene, 4-nitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene. As a result, they are considered attractive candidates for developing novel luminescence sensors designed for the exact detection of PA [85].

An alternative approach for synthesizing unique MOFs involves incorporating template molecules into the reaction mixture, a practice seldom seen in conventional synthetic methods, and this template synthesis technique is an effective tool for studying hierarchical porous materials [86]. Organic solvents are one of the template molecules that have been used frequently [87,88], small organic ligands, organic amines [89,90], carboxylic acids or carboxylate groups [91–93], and heterocyclic aromatic compounds [94–96]. Each template molecule exerts distinct influences on MOFs’ crystallization and synthesis processes. The solubility and polarity of the solvent are the primary factors influencing the crystallization of MOF [87]. Organic amines influence the reaction’s pH and make it easier for organic ligands to deprotonate. [97]. Using carboxylate groups as ligands allows the filling of MOF pores, while heterocyclic compounds can act as counterions and weak organic bases when protonated. Surfactants produce micelles within solvents, controlling the shape and size of the final MOFs, while ionic liquids serve as solvents and counterions [98].

This technique is widely employed in the production of nanoparticles and has recently found application in synthesizing MOFs [99]. Water microemulsions having nanometer-sized water droplets sustained within the organic phase by a surfactant. The micelles in these microemulsions act as nanoreactors, regulating nucleation and crystal growth rates. The water-surfactant ratio and the surfactant type regulate the microemulsion’s size and number of micelles. This approach provides exact control over the size of nanoscale materials. However, it comes with notable drawbacks, including high costs and the use of surfactants that are often environmental pollutants [100–102]. The microemulsion method synthesizes the zeolitic imidazolate framework-8 (ZIF-8), employing mild reaction conditions at standard temperature and pressure and a short reaction time. ZIF-8’s amine groups reacted with the epoxy group, producing exceptional adhesion between ZIF-8 and the epoxy matrix. This prevented the overall ZIF-8 clustering and resulted in increased cross-linking densities. Leveraging these upper hands, incorporating ZIF-8 substantially enhanced the composite coating’s mechanical properties and anti-corrosion efficacy compared to an epoxy cover alone. This study delves into the influence of ZIF-8 content on the coating’s protective performance and identifies the optimal ZIF-8 bulk in the epoxy coating. This finding is a pivotal reference for future applications of metal-organic framework materials in anti-corrosive coatings [103]. The advantages and limitations of various methods employed to synthesize MOFs are summarized and given in Table 2.

Among several electrode modifiers used in electrochemical processes, MOFs have shown potential due to their large surface area, copious adsorption sites, and versatile functionality that helps the detection efficiently for several analytes, including heavy metal ions [145,146]. In general, the carbon allotropes deployed in the fabrication of electrodes are graphite or derived materials intended to modify the carbon paste electrode (CPE) and glassy carbon (GC) for solid carbon electrodes. The conductivity of carbon-based materials allotropes is enhanced primarily due to sp² hybridized bonds and six-membered aromatic rings [147]. It is essential to pre-modify carbon-based electrodes to follow a specific protocol for introducing MOF modifiers at the electrode surface. In the case of glassy carbon electrodes, the modification involves a direct coating of the polished surface by MOF. In contrast, the modifier fabricates the carbon paste electrode by mixing graphite powder with MOF using a specific organic binder [148].

Biomolecules are the essentials of living organisms that control various biochemical functions of the body. Understanding the essential physiological roles that biomolecules play in guiding the healthy growth and development of the human body is made possible by studying these molecules [164]. Therefore, the quantitative determination of biomolecules is necessary for chemical pathology or even food chemistry. The electrochemical technique has been prominent in quantifying various biomolecules in different matrices [165]. Various methods were employed to detect biomolecules; however, the electrochemical methods are promising and show potential in the trace detection of several biomolecules [166]. Although there is a substantial amount of literature on MOFs, there needs to be more research focused on comprehending the impact of MOF particle characteristics on their biocompatibility [167].

Electroanalytical sensing methods are essential for quantitatively or qualitatively detecting or identifying target analytes in an electrochemical cell by evaluating electrochemical signals such as current or potential [168]. The electrochemical detection of biomolecules utilizing fabricated electrodes operates in two ways: i) Enzyme-modified electrodes and ii) Non-enzymatic or electrodes modified with novel materials (MOF, nanomaterials, metal oxides, etc.). Electrochemical techniques are widely recognized, uncomplicated, economical, and convenient for detecting different biomolecules. It also holds the potential for downsizing healthcare devices [169]. MOFs have the potential to be efficient electrochemical sensors for detecting biomolecules due to their large surface area, regulated varied pore structure, increased functionality, and unique catalytic activity [170]. In order to obtain an enhanced selectivity for an analyte, the methods primarily utilize a variety of enzymes to modify the carbon-based electrodes.

Nevertheless, enzyme-modified electrodes showed several limitations in the sensing process since some enzymes are often less mobile on the electrode surface and are stable only at specific temperatures and pH levels [171,172]. These limiting factors encourage the use of non-enzymatic modified sensors. The enzyme replaces this electrode type with novel materials, especially MOF, which has an exceptional physicochemical property with high sensitivity and selectivity towards various analytes [155].

The MOFs synthesized using transition metals like Fe²⁺, Cu²⁺, Co³⁺, and Ni²⁺ are promising in low-level electrochemical detection of several biomolecules, viz., glucose, ascorbic acid, urea, and H₂O₂ [173]. The MOF-based biosensors have garnered significant interest among researchers in developing tools to sense different diseases and health disorders [174]. The detection of glucose is a widely accepted electrochemical method; Cu-MOF@Pt was effectively used to measure the glucose level in human serum samples with excellent recovery and repeatability [175]. The glassy carbon electrode was modified with the nickel-based MOF and employed in cyclic voltammetry (CV) to detect glucose. NiO and Ni/NiO/CNTs display well-defined NiO redox peaks in the absence of glucose and increased peak currents in the addition of glucose.

Furthermore, in the presence and absence of glucose, Ni/NiO/CNTs exhibit significantly greater peak current than NiO, indicating enhanced electrochemical performance. As glucose concentrations rise, the oxidation peak currents rise, with a minor positive shift in peak potential and a drop in the reduction peak currents. The results indicate that Ni/NiO/CNTs have outstanding electrocatalytic activity on glucose oxidation. The Eq. (1 & 2) demonstrate the mechanism of glucose oxidation [176]:

On the other hand, the copper and nickel MOF-based electrodes were fabricated and utilized in the electrochemical detection of glucose. A redox couple of Cu²⁺/Cu³⁺ and Ni²⁺/Ni³⁺ occurs in an alkaline medium, which in turn leads to the oxidation of transition metals used (i.e., copper or nickel) as shown in Eq. (1) and Eq. (2), which further catalyzes the oxidation of glucose. Fig. S1 shows the reaction mechanism [177].

The mechanism of glucose oxidation on the electrode surface proceeded as [178,179]:

The first step oxidizes the M²⁺ to M³⁺, and these species take part at the electrode surface in glucose oxidation. The most crucial species for glucose oxidation is M³⁺, which also serves as the primary electron transfer mediator. M²⁺ in the MOF undergoes oxidation to produce M³⁺ throughout the potential scan between 0.3 and 0.5 V. M³⁺ preferentially oxidizes the glucose to produce gluconolactone, which produces gluconic acid by hydrolysis [179]. Fig. S2(A) shows the differential pulse voltammogram produced when 50.0 μM of glucose in 0.10 M NaOH. Adding 50.0 μM glucose to 0.10 M NaOH gives an oxidation peak current at +0.380 V. Fig. S2(B) demonstrates the amperometric i-t curves for glucose produced by GC/CuO electrode in 0.10 M NaOH agitated solution at an applied voltage of 0.500 V. The initial current response of the GC/CuO electrode was due to 5.0 μM glucose, and the continued supply of 5.0 μM glucose in every step with a sample interval of 50.0 sec enhances the response of the current [177].

A chromium-based metal-organic framework (MIL-101) modified with platinum nanoparticles (PtNPs) simultaneously detects the Xanthine, uric acid, and dopamine in spiked serum samples using the differential pulse voltammetry (DPV) [180]. The sensor has an extensive linear range (0.50 – 162.0 μM), a low detection limit (0.420 μM), and excellent selectivity, according to differential pulse voltammetry. The simultaneous presence of dopamine, uric acid, and hypoxanthine in the detection of Xanthine at working potentials of 0.130, 0.280, 0.680, and 1.050 V (vs. 3 M KCl saturated Ag/AgCl), estimating the concentration of Xanthine in spiked blood specimens. Fig. S3 shows the DPV curves of the simultaneous detection of dopamine (DA), uric acid (UA), Xanthine (XA), and hypoxanthine (HXA) [173]. Further, Table S1 comprises several MOF-based materials utilized in the electrochemical detection of various biomolecules in real and complex samples. Moreover, Table S1 includes the LOD and the linear range of detection of these biologically important molecules.

Hydrogen peroxide (H₂O₂) has physical and chemical significance in different research fields, viz., pharmaceutical industry, food and chemical industry, environment, and biological samples [153,181,182]. Additionally, it plays a significant role as an intermediate in biological and environmental interactions [183,184]. In the food industry, bleaching or disinfection utilizes hydrogen peroxide during food processing. However, higher concentrations of hydrogen peroxide residues in food products negatively affect human health. Excessive levels of retained hydrogen peroxide in food showed several harmful effects, which include cancer, rapid aging, coronary artery disease, severe gastrointestinal issues, and neurological illnesses [185]. Hydrogen peroxide (H₂O₂) is an active oxygen compound with antimicrobial characteristics and a significant molecular signaling molecule in many biological tissues [186]. The necessity of detecting hydrogen peroxide is manifold, and the miniaturized device for on-site detection is a prerequisite for various biological or environmental samples. The utilization of natural enzymes in electrochemical sensors is highly effective. The voltammetric response of these sensors demonstrates excellent charge transport through the MOF composite and quick electron exchange between the MOF and electrode. These MOF nanosheets have enzyme-like properties that catalyze them to oxidize hydrogen peroxide. This characteristic allows for developing an electrochemical sensor with fast and accurate quantitative detection. The sensor also demonstrates exceptional sensitivity, selectivity, stability, and durability at the desired pH level. Consequently, these sensors offer an alternative approach for detecting H₂O₂ [187]. The electrochemical methods are promising because of their robustness in operation, selectivity, dependability, and sensitivity towards the analyte, and the on-site detection with a miniaturized device added to the method’s suitability [188].

A novel electrochemical sensing platform detects hydrogen peroxide (H₂O₂) using the Pt/MoSe₂ nanomesh, which offers an increased active site and a larger specific surface area. The Pt/MoSe₂ nanomesh sensors show exceptional sensitivity and specificity towards H₂O₂. The correlation coefficient (R²) and the limit of detection (LOD) are 0.9983 and 2.56 μM, respectively, at a signal-to-noise (S/N) ratio of 3. In addition, the Pt/MoSe₂ nanomesh exhibits excellent resistance to interference, even when exposed to potentially interfering tiny molecules found within cells, such as ascorbic acid (AA), glucose (Glc), and others [189]. A poly(amidoamine)-dendrimer/poly (PAMAM/PNR) modified electrode is utilized to concurrently detect the electrochemical oxidation of L-dopa and the reduction of H₂O₂. The sensor electrode modified with PAMAM/PNR shows a linear response between the L-dopa concentration (0.08 to 2400 μM) and the current with a lower limit of detection (LOD) of 0.026 μM [190]. Cobalt-based MOF (Co(pbda) (4,4-bpy)·2H₂O]_n) was incorporated on GCE and used for the detection of hydrogen peroxide (H₂O₂) at 0.1 M NaOH solution employing cyclic voltammetry (CV) [182]. Three reduction peaks occur on the cyclic voltammogram of the Co-MOF modified GC electrode: (a) in the absence of H₂O₂, (b) with the addition of 0.1 M NaOH solution containing 1 mM H₂O₂ and (c) with the addition of 0.1 M NaOH solution containing 2 mM H₂O₂ at approximately −0.40 V. The amperometric response indicates that the Co-MOF modified GC electrode shows enhanced electrocatalytic response towards the H₂O₂ reduction current, and the calibration line obtains for a wide concentration range of H₂O₂ between 5.0 μM and 9.0 mM. The method provides a low detection limit of 3.76 μM and a good sensitivity of 83.100 A μmM⁻¹ cm² at an applied potential of −0.40 V. Additionally, the detection method demonstrates stable performance over time with excellent selectivity. Furthermore, the mechanism indicated that the Co-MOF is highly efficient in intrinsic peroxidase-like activity, which allows it to catalyze H₂O₂ decomposition to form hydroxyl radical, which then oxidizes the peroxidase substrate (terephthalic acid) to produce color. Fig. S4 shows the reduction of H₂O₂ at an applied potential of −0.4V without the presence of H₂O₂, along with the addition of 0.1M NaOH solution containing 1 and 2 mM H₂O₂. It also depicts the Co-MOF-modified GCE’s amperometric response at a potential range of −0.4 to −0.6V [118].

Similarly, a solvothermal method synthesizes the Sn-based metal-organic framework (Sn-MOF@CNT) by incorporating carbon nanotubes (CNT) with Sn-MOF. A specifically designed approach efficiently detects hydrogen peroxide. The MOF possesses a large surface area and pore volume and maintains crystallinity even after the addition of CNT onto its surface [191]. The cyclic voltammogram of the bare electrode does not exhibit any oxidation or reduction peaks within the voltage range of −0.2 V to −0.8 V. Moreover, the gold electrode modified with the Sn-MOF@CNT shows no significant reduction in peak current in the absence of H₂O₂. The different concentrations of H₂O₂ (0.01, 0.03, and 0.05 mM) are present, resulting in a significant reduction in peak current (−0.6 V). The absence of H₂O₂ results in no electrochemical signals on the Sn-MOF@CNT/Au electrode. However, 0.2 μM H₂O₂ caused the electrode to display both cathodic and anodic peak currents. The observations prove that hydrogen peroxide undergoes a disproportionate reaction, i.e., the hydrogen peroxide decomposes into two products through oxidation and reduction half-reactions. The reaction results in the formation of water and oxygen at the electrode surface, as shown in equations given below:

As a result, the amperometric response of the Sn-MOF@CNT modified Au electrode shows a low detection limit of about 4.7 ×10⁻³ μM of hydrogen peroxide. Table S2 comprises the use of different MOFs in the electrochemical detection of hydrogen peroxide in various samples. Table S2 includes the limit of detection and experimental parameters for various systems.

Wastewater containing different industrial effluents impacts ecological stability because micro-pollutants can harm living organisms even at low concentrations [192]. Aromatic organic compounds such as phenol, nitrobenzene, hydrazine, chlorinated phenols, polyaromatic hydrocarbons, pesticides, nitrites, and pharmaceuticals have shown more significant environmental concerns, contaminated water bodies, and severely affecting human health. The detection and elimination of these pollutants in the aquatic environment have been a source of desperation for environmentalists for the past few years [193]. Drug and pharmaceutical residue toxicity refer to the harm inflicted on an organism by these chemical compounds. Drug toxicity can have a detrimental impact on organs such as the liver, kidney, heart, and other parts of the body. Drug toxicity is directly proportional to the dose and manifests a range of undesirable consequences when it surpasses the therapeutic level. Excessive consumption and over-administration of drugs result in acute toxicity within an individual’s body.

Similarly, the overutilization of drugs can lead to the occurrence of drug toxicity in both food and the environment since these substances migrate from the circulatory system to various organs [194,195]. Metol (N-methyl-p-aminophenol sulphate) is a prevalent phenol compound used as a chemical raw material in the production of photographic development and is a potential environmental pollutant. A cerium-based metal-organic framework shows an excellent sensing material for detecting metol by voltammetry. The detection method achieves a linear range from 0.1 to 200 μM, with a detection limit of 30 nM [196–198]. Chlorophenols, an organic pollutant, are widely present in several industries and extensively utilized as pesticides, fungicides, herbicides, dyes, and solvents. Chlorophenols are extremely hazardous organic contaminants that pose serious environmental concerns. Chlorophenols are toxic to people and can accumulate in the food chain, impacting human health. The modified GCEs are excellent in detecting chlorophenol with a low limit of detection (LOD = 0.328 μM) at a wide linear detection range from 10 to 160 μM. The electrode shows strong stability and selectivity towards these pollutants. Furthermore, the results of the recovery studies show the electrochemical sensor’s suitability for detecting actual samples. The findings indicate that the HP-UiO66@Ni-BDC MOF shows potential in the low-level detection of chlorophenol [199–201].

Yadav et al. demonstrate the synthesis of zinc (II) based MOF (MOF-5) decorated with the Au(NPs), and the material modifies the glassy carbon electrode and detects the nitrobenzene and nitrite in an aqueous medium [202]. Fig. S5(a) shows cyclic voltammograms of nitrite (1.0 mM) using the GC/Au-MOF-5, GC/MOF-5, and GC electrodes in 0.1 M phosphate buffer (PBS) (pH 7.0) at 20 mV/s. Without nitrite, no peaks occur at GC and GC/MOF-5 (Fig. S5(a): a & b), but well-defined peaks occur at GC/Au-MOF-5 due to the formation of surface Au oxide and their reduction (Fig. S5 (a): c′). The surface of Au oxidized at 0.85 V and reduced at 0.46 V during the reverse scan. On the other hand, the nitrite shows oxidation at 0.93 V and 1.01 V using the GC and GC/MOF-5 electrodes, respectively (Fig. S5(a): a′& b′). Similar oxidation occurs at 0.76 V at the GC/Au-MOF-5 (Fig. S5(a): c′) with enhanced anodic peak current. The higher nitrite oxidation potential at GC/MOF-5 is due to the interaction of free carboxylate groups of MOF-5 and nitrite. The results imply a significant increase in peak currents at low applied potentials using the GC/Au-MOF-5 electrode. Therefore, Au(NPs) in Au-MOF-5 showed an efficient electrocatalytic activity for nitrite oxidation. Fig. S5(b) shows the cyclic voltammograms of nitrobenzene (NB) using the GC, GC/MOF-5, and GC/Au-MOF-5 electrodes in an N₂ saturated atmosphere employing 0.1 M pH 7.0 phosphate buffer. In the absence of NB, no peak current appeared in the voltammograms, and a distinct reduction of nitrobenzene is observed at an applied potential of −0.77, 0.79, and 0.77 V for the GC, GC/MOF-5 and GC/Au-MOF-5 electrodes, respectively [202].

Many countries have limited the use of patulin residues due to their severe toxicity and ubiquitous occurrence in foods. The Food and Drug Administration of the United States and China mandates a maximum amount of patulin at 50 μM in fruit juice and processing products, and the European Union mandates a limit of 10 μM in newborn and child meals [203]. Because of the widespread occurrence and high toxicity of patulin in food, a rapid and sensitive detection method averts the possible harmful effects of patulin on human health [132]. Copper-based MOF decorated with the Au(NPs) was used to modify the GCE, which electrochemically detects patulin in apple juice. The square wave voltammograms of patulin show that the cathodic signal increases with the patulin concentration rising from 0.001 nM to 1.0 nM and 1.0 nM to 250.0 nM. The LOQ was 0.001 nM, and the LOD was 3.33 × 10⁻⁴ nM. RSDs of 1.65% and 0.83% were found for six repeat observations of 1.0 nM and 250.0 nM patulin, respectively [204].

Similarly, the HKUST-1 MOF incorporated with Au(NPs)-GCE electrochemically detects the paracetamol. The MOF/AuNP modified GCE detects the paracetamol efficiently, and a wide linear range of paracetamol concentration (0.01 μM to 100 μM) provides the detection limit of 0.0011 μM [205]. Cu-BTC nanocrystals/CNTs modified GC electrode showed an improved oxidation current for the metformin detection. Peak current demonstrated good linearity with concentrations ranging from 0.5 μM to 25 μM with a detection limit of 0.12 μM under optimal conditions. Further, the detection method detects metformin in pharmaceutical samples [206]. The EPC-modified GCE showed good sensitivity and low detection limit (i.e., 2.9 μM) in detecting chloramphenicol residual in honey. Using the electrochemical detection method, an aluminum-based metal-organic framework (DUT-4) detects chloramphenicol (CAP), a commonly used broad-spectrum antibiotic. The presence of reduced graphene oxide (rGO) with the DUT-4 significantly enhances the electrocatalytic activity of the electrode in detecting the CAP. The synthesized sensor demonstrates exceptional sensitivity, covering a wide linear range of 1–1000 μM of CAP, and achieves a remarkably low detection limit of 76.97 nM [207]. Table S3 lists different types of MOFs used to detect organic contaminants.

Heavy metals that pose a significant hazard to human health and the marine environment include lead, mercury, cadmium, chromium, and arsenic. [208]. These heavy metals contaminate the environment due to many geological and human-caused phenomena, including agricultural, industrial, and domestic wastes [209]. Heavy metal ions (HMIs), a primary form of food pollutants, pose a significant risk to human health even at lower levels due to their persistence, elevated toxicity, and prolonged build-up in the body [210]. Heavy metals are metallic elements that have a density of more than 5, primarily including zinc (Zn), chromium (Cr), mercury (Hg), copper (Cu), lead (Pb), and arsenic (As). Despite not being a metal element, As exhibits a toxicity level comparable to that of heavy metals, and its relative density satisfies the criteria for heavy metals [211]. Hazardous metallic ions (HMIs) within the human body damage the skin, bones, liver, kidneys, and perhaps the brain system [212]. As an illustration, Pb is one of the most detrimental HMIs and has the potential to adversely affect the brain, kidney, neurological system, and reproductive system [213]. Excessive amounts of Zn lead to gastrointestinal discomfort and aberrant pancreatic enzyme levels. Elevated concentrations of copper cause the development of cancer and genetic abnormalities [214]. Recently, emphasis has been drawn to detecting heavy metals utilizing various MOF-based sensors in various environmental matrices [144]. Electrochemical analysis is one of the prominent and robust techniques due to its accuracy and reliability. The exceptional features of MOF, i.e., high porosity, homogeneous structures, large surface area, and ease of functionalization, received greater attention in the efficient and selective use in sensor developments for detecting several heavy metals [215]. The bulk organic linkers coordinate with the core metal atom, restricting MOFs’ electrical conductivity [216]. Therefore, MOFs are typically coupled with high-conductivity elements such as metal oxides, metal nanoparticles, and carbon compounds to overcome the limitations. Furthermore, MOFs with high conductivity are alternative materials for the trace detection of several heavy metal toxic ions. However, the repeatability of the signal due to the micro-sized MOFs is one of the challenges in the detection system [24, 217, 218].

A hydrothermal technique obtains the zinc-based metal-organic framework (Zn-MOF), and the material shows exceptional stability in water at various pH. The molecule exhibits high selectivity, sensitivity, and a low detection limit, 4.10 μM for Cr₂O₇²⁻ and 6.63 μM for CrO₄²⁻ in aqueous solution [219]. Similarly, a hydrothermal method synthesizes the Eu-MOF, {[Eu₂(L)(phen)₂(ox)₂(H₂O)₂]·10H₂O·phen}_n, which exhibits stability in water at varied pH values. The Eu-MOF has good sensitivity and selectivity in detecting gas/liquid benzaldehyde, Hg²⁺, and Cr₂O₇²⁻/CrO₄²⁻ by luminescence quenching effects, making it a potential luminous sensor. Eu-MOF exhibits exceptional adsorption capabilities for Hg²⁺ and can effectively be employed for the quantitative detection of Hg²⁺ in tap water, green tea, and river water. The sensor demonstrates a recovery rate ranging from 99.88% to 102.66% for detecting Hg²⁺ [220]. A novel electrochemical aptasensor utilizing aptamer detects the Cd²⁺ and Pb²⁺ concurrently in fruits and vegetables. The double-stranded DNA, including aptamers, obtains the electrode by forming an Au-S link. The electrochemical labeling of Cd²⁺ and Pb²⁺ aptamers with Methylene Blue and Ferrocene groups resulted in competition between the metal ions and the complementary sequences (CP), leading to variations in the electrochemical signal. Consequently, both Cd²⁺ and Pb²⁺ can be simultaneously detected. The electrochemical aptasensor demonstrates a linear response for Cd²⁺ and Pb²⁺ detection within the concentration range of 0.1 to 1000 nmol/L under ideal conditions. The detection limits for Cd²⁺ and Pb²⁺ were 89.31 and 16.44 nmol/L, respectively [216]. Cd²⁺ and Pb²⁺ were simultaneously and selectively detected in water samples using the Yb-MOF-modified electrode [221]. Under ideal circumstances, the Yb-MOF/GCE electrode detects the Cd²⁺ and Pb²⁺ independently at values ranging from 0 to 40 ppb. I (μA) = 0.2045 * C (ppb) − 0.0838 (Cd²⁺) and I (μA) = 0.1971 * C (ppb) + 0.0686 (Pb²⁺) are the recorded current responses on DPASV curves that grow linearly with increasing ion concentration. For Cd²⁺ and Pb²⁺, the detection limits (LOD) were 7.40 ppb and 2.02 ppb, respectively. The Yb-MOF/GCE detects the Cd²⁺ and Pb²⁺ simultaneously in the 0 to 50 ppb concentration range. The peak current increased linearly with the ion concentrations, as shown in Fig. S6. The sensitivities were 469 μA ppm⁻¹ cm⁻² and 397 μA ppm⁻¹ cm⁻² for Cd²⁺ and Pb²⁺, respectively. The detection limits for Cd²⁺ and Pb²⁺ were 3.0 ppb and 1.6 ppb, respectively. Pb²⁺ was more favorably absorbed and reduced on the porous structure of the Yb-MOF framework than Cd²⁺ [222]. A susceptible electrochemical sensor detects the Pb²⁺ ions using the Bi-MOFs. The solvothermal method synthesizes the MOF (Bi/Bi₂O₃) followed by the co-doping of porous carbon composite (Bi/Bi₂O₃@C) through one-step carbonization. The material demonstrates the ability to retain Bi-MOFs’ structure, which is essential for its functionality. Additionally, it exhibits a relatively large specific surface area, indicating its potential for increased adsorption and reactivity. Furthermore, the material shows high electron-transfer capabilities, suggesting its suitability for various electrochemical applications. The square wave anodic stripping voltammetry (SWASV) using the MOF-modified electrode efficiently detects the Pb²⁺. It had a wide linear range, ranging from 37.5 nM to 2.0 μM, indicating its ability to measure a wide range of concentrations accurately. Additionally, the sensor had a low detection limit of 6.3 nM. The sensor exhibits favorable stability, reproducibility, and satisfactory selectivity [223]. Table S4 shows the latest developments in the pH and potential optimization for the electrochemical detection of heavy metals utilizing MOFs.

In aqueous solutions, the Fe@YAU-101/GCE quantifies various metal ions, viz., Cd²⁺, Pb²⁺, and Hg²⁺. The oxidation peak current signals of the Fe@YAU-101/GCE exhibit an upward trend as the concentration of Cd²⁺, Pb²⁺, and Hg²⁺ increases, allowing for the identification of these ions. The Cd²⁺, Pb²⁺, and Hg²⁺ in solution are carried within the concentration range of 0.003 to 42 μM, 0.004 to 80 μM, and 0.045 to 66 μM, respectively. The presence of Cd²⁺, Pb²⁺, and Hg²⁺ in a solution does not affect the DPV response signal using the Fe@YAU-101/GCE, hence enabling the detection of these ions simultaneously. The sensor exhibits a notably greater current signal for Hg²⁺ and Pb²⁺ than Cd²⁺, suggesting better sensitivity for Hg²⁺ and Pb²⁺ than Cd²⁺. The regression equations for Cd²⁺, Pb²⁺ and Hg²⁺ are: I =0.0141C +0.0349 (R² = 0.9954), y = 0.2861C-0.0554 (R² = 0.9975), and y = 0.2701C + 0.3320 (R² = 0.9955), respectively. The limit of detection (LOD) values for Cd²⁺, Pb²⁺, and Hg²⁺ were 1 ×10⁻⁹ M, 1.5 × 10⁻⁸ M, and 1.33 ×10⁻⁹ M, respectively [224].