Acidic hydrolysis uses concentrated sulfuric, nitric, or phosphoric acid as catalysts to swiftly convert PET into high-purity TPA and EG. For instance, Dermanaki Farahani et al. attained over 99% TPA purity by degrading PET at room temperature with concentrated sulfuric acid, followed by two pH adjustments^[85]. While efficient, this approach produces substantial inorganic salt waste and presents equipment corrosion issues. Efforts to recycle acid catalysts address environmental concerns but typically necessitate prolonged reaction times and high temperatures, restricting large-scale application^[95].

Alkaline hydrolysis in 4%-20% sodium hydroxide (NaOH) or potassium hydroxide (KOH) solutions effectively recovers high-purity TPA from PET. Complete degradation into terephthalate salts (Na₂TPA or K₂TPA) typically requires high temperature and pressure. However, direct use of these salts in MOF synthesis can lead to undesired hydroxide incorporation, reducing the specific surface area of the final material^[96]. Therefore, a post-treatment step involving acidification (e.g., H₂SO₄ or HCl) and recrystallization is commonly employed to obtain high-purity BDC suitable for MOF synthesis^[97,98].

Recent advancements have markedly enhanced the efficiency and sustainability of alkaline hydrolysis. Rotary autoclave-assisted hydrolysis improves TPA recovery, while techniques like microwave, plasma, and ultrasound accelerate degradation kinetics^[99]. Allaf et al. reduced hydrolysis time from 3 h to 5 min using microwave irradiation, with gamma rays and ultraviolet (UV) pre-irradiation further increasing yield^[100]. Jung et al. achieved nearly complete PET conversion (> 99.9%) through ultrasound-assisted hydrolysis^[87]. Štrukil et al. developed an integrated approach combining ball milling and alkaline hydrolysis, which enabled near-quantitative TPA yields under mild conditions while minimizing alkali consumption, thereby reducing the environmental impact^[101]. Building upon this work, Wang et al. further optimized the process by introducing an alcohol or ether co-solvent system, facilitating highly efficient PET degradation (TPA purity: 99.73%) under mild conditions (80 °C, 60 min)^[102]. These innovations address the limitations of traditional high-temperature, long-duration hydrolysis methods and enhance the overall sustainability of PET conversion.

Alcoholysis, generally conducted in EG with a catalyst, primarily produces DMT or BHET, with oligomer formation also common. Traditional methods necessitate 210 °C for 8 h^[93,103], though optimization can mitigate these harsh conditions^[104,105]. Despite these advancements, industrial application faces hurdles, notably low TPA yields (~55%) and complicated purification processes. Researchers have investigated deep eutectic solvents (DESs) as catalysts to overcome existing limitations, offering a unique reaction environment that boosts BHET yield and significantly shortens glycolysis time^[106]. A solvent-free “grind-bake” method has also been developed for converting PET-derived BHET into MOFs. This approach facilitates the efficient mechanochemical synthesis of UiO-66(Zr) and alkaline-earth-metal BDC-based MOFs (e.g., Ca-BDC, Ba-BDC)^[107]. By eliminating the need for organic solvents, this method simplifies reaction steps, adheres to green chemistry principles, and expands the potential use of alcoholysis-derived PET intermediates in MOF synthesis.

Using colored PET in MOF synthesis presents additional complexities compared to clear PET. The presence of dyes and additives can interfere with the crystallization and porosity of the resulting MOFs. For instance, Dyosiba et al. reported that alcoholysis-derived BDC from colored PET produced MOFs with reduced specific surface areas (933-1,085 m²·g^-1) compared to those derived from commercial BDC (1,368 m²·g^-1)^[34]. Similarly, Andini et al. observed reduced yields of BHET from dye-containing PET waste compared to undyed counterparts^[10].

To address these limitations, researchers have devised dye-removal strategies. Chang et al. effectively hydrolyzed colored PET waste using HNO₃, employing acid-mediated dye degradation to obtain high-purity TPA, which facilitated the synthesis of catalytically active UiO-66^[108]. Another method uses EG vapor-assisted decolorization, where dye molecules are selectively dissolved and removed before alcoholysis, achieving decolorization rates over 90.2%^[109]. These advancements improve the feasibility of upcycling colored PET for MOF synthesis and create new opportunities for sustainable PET recycling.

In this phase, degradation products from the initial step, such as TPA or its salts, react with metal salts and organic ligands to synthesize MOF materials [Figure 4]. For instance, TPA from the alkaline hydrolysis of waste PET bottles can react with Cu(NO₃)₂·3H₂O to form Cu-based MOFs with high porosity^[86]. As MOF varieties and synthesis techniques rapidly expand, common methods include hydrothermal/solvothermal synthesis, assisted synthesis methods, and mechanical ball milling. Hydrothermal/solvothermal synthesis remains the most established, while ball milling is gaining attention for its eco-friendly and efficient nature.

The solvothermal synthesis method is commonly employed to produce MOFs. This approach involves placing reactants in a reactor containing water or an organic solvent, and applying autogenous pressure at elevated temperatures to facilitate the slow nucleation and growth of MOF crystals. This technique has been successfully utilized to synthesize a range of well-established MOFs, including MOF-5(Zn)^[98,115-117], MIL-101(Cr)^[118-122], MIL-53(Al)^[123-126], and UiO-66(Zr)^{[34,100,107,116,127-130]}. Fe-MOFs^{[87,96,100,116,131]}, Cu-MOFs^{[32,86,95,97,132,133]}, and Ca-MOFs^{[85,107,134,135]} are commonly synthesized using this method. However, hydrothermal/solvothermal synthesis typically necessitates significant amounts of toxic solvents like N,N-dimethylformamide (DMF) and hydrofluoric acid (HF) and involves high-temperature and high-pressure conditions^[85,136], resulting in elevated costs and energy consumption.

To address these challenges, researchers have developed several optimization strategies. These include the use of water-soluble organic ligands^[96], the adoption of solvent-free synthesis techniques^[107,129], and the promotion of reactions through stirring instead of high-temperature treatments^[137]. Furthermore, studies have demonstrated that MIL-101(Cr) synthesized under HF-free conditions can exhibit comparable specific surface area and gas adsorption performance, thus eliminating the need for HF^[138-140]. Citric acid, dimethyl sulfoxide (DMSO), and trifluoroacetic acid (TFA) have been investigated as environmentally benign alternatives to H₂SO₄ and HNO₃ for the synthesis of MOFs^[141]. These modified approaches not only reduce the costs and energy demands of the synthesis process but also enable the scalable production of MOFs from waste-derived feedstocks. This advancement supports efforts to mitigate global plastic pollution and facilitate the commercial deployment of MOF-based technologies.

Emerging auxiliary technologies, such as microwave-assisted^[142] and electrically assisted^[143] synthesis, have been explored to optimize MOF fabrication. For instance, TPA derived from PET waste can be used to synthesize MOFs via microwave-assisted methods. Compared to traditional solvothermal approaches, microwave-assisted synthesis of MOF-5 and Cu-MOF yields materials with identical crystalline structures, while significantly accelerating crystal growth, reducing reaction times to approximately five min, and improving overall yield^[32]. Moreover, microwave irradiation enables precise control over MOF morphology and particle size, enhancing material performance for targeted applications.

Mechanical ball milling, an eco-friendly and solvent-free synthesis method, is applicable for both alkaline hydrolysis of PET and direct MOF synthesis^[144]. During this process, PET degrades into terephthalate ions when milled with NaOH. These ions then react with metal precursors under mechanochemical forces, forming short-range ordered structures that yield metal-based MOFs (e.g., Cu, Ca, La)^[99,145,146].

The two-step ball milling method has been further optimized, enabling direct mechanochemical synthesis of MOFs through assisted alkaline hydrolysis. This approach has facilitated the synthesis of a variety of MOFs, including those based on La, Zr, Ni, Co, Mn, and Ca, with large-scale production of Ni-MOF already demonstrated^[147]. The ongoing advancements in ball milling techniques underscore its potential as a scalable and sustainable pathway for MOF synthesis, particularly from waste-derived precursors.

Complete PET degradation is crucial for successful MOF formation in a one-pot process. Elevated temperatures and extended durations are typically required to ensure full hydrolysis of PET into terephthalate ions (BDC^2-), preventing the precipitation of unstable oxides or hydroxides due to incomplete ligand formation^[148]. Furthermore, the degree of deprotonation of BDC significantly influences the stabilization of the MOF framework^[151-153].

DMF is often employed as a solvent in the one-pot synthesis method due to its ability to both dissolve reactants and promote H₂BDC deprotonation, aiding the formation of stable MOFs like MIL-53(Al), UiO-66, and MOF-5^[154-157]. Nonetheless, concerns over DMF’s toxicity and environmental impact have driven the exploration of greener alternatives. Acetone, for example, has been effectively utilized as a solvent, with formic acid serving as a crystallization regulator, to synthesize UiO-66 in one step^[158]. A promising method uses Na₂BDC, derived from PET through alkaline hydrolysis, as a precursor, streamlining reaction steps and minimizing environmental impact. The acidic conditions in the one-pot process both dissolve metal ions and subtly adjust carboxyl group deprotonation, allowing for controlled crystal growth. For instance, MOFs like MIL-53(Cr), MIL-101(Cr), and MIL-47(V) have been hydrothermally synthesized in DMF using HF as a growth modifier^[149]. However, due to rising environmental and safety concerns, HF has been largely replaced by less toxic alternatives such as hydrochloric and acetic acids, which preserve crystal quality while minimizing risks^[159-162].

Alkaline conditions, such as those provided by NaOH or KOH, facilitate the direct formation of BDC^2- from PET hydrolysis, bypassing the need for a deprotonation step. These conditions also prevent the formation of metal hydroxides or oxides, enhancing the purity of MOF products. To enhance metal ion stability, localized pH adjustments using weak acids like acetic acid facilitate low-temperature, rapid synthesis, exemplified by Cu-MOF production^[153]. Bai et al. and Fan et al. further streamlined the process by synthesizing Co-MOF and Mn-MOF without acids or bases, but this method necessitates high temperatures, leading to increased energy consumption and equipment demands^[163,164].

Amid increasing focus on sustainable chemistry, researchers are investigating innovative reaction systems like ionic liquids and microwave-assisted techniques to improve PET depolymerization and MOF synthesis^[165,166]. Functionalized ionic liquids act as acid/base catalysts, enhancing both the efficiency and selectivity of depolymerization^[167,168]. For example, Ni-MOF nanorods were synthesized using an N-methyl-2-pyrrolidone-nickel(II) chloride (NMP-NiCl₂) ionic liquid system, where NMP aided in PET dissolution and provided a biodegradable, sustainable option for one-pot MOF synthesis^[169,170].

The one-pot method offers a compelling approach for large-scale MOF production, leveraging its efficiency, simplicity, and cost-effectiveness. However, its strong dependence on precise reaction conditions warrants a balanced consideration of the two-step method when targeting high-purity or structurally complex MOFs. Ongoing advancements in catalyst design, solvent selection, and process optimization hold promise to further enhance the potential of the one-pot method for large-scale MOF synthesis and PET upcycling applications.

MOFs synthesized from waste PET show significant promise for CO₂ adsorption and separation. Given that CO₂ is a major industrial greenhouse gas contributing to climate change, advancing efficient CO₂ capture technologies is crucial. Owing to their high specific surface area and customizable organic functionalities, MOFs have emerged as a focal point in gas adsorption and separation research^[199,200]. Recent progress in industrial MOF-based carbon capture, such as the scale-up of CALF-20 for post-combustion CO₂ capture, further highlights the practical relevance of stable and cost-effective MOF adsorbents, although such systems are not derived from PET waste^[201]. For example, MIL-53(Al) synthesized using BDC ligands extracted from waste PET exhibits a CO₂ adsorption capacity of 3.67 mmol·g^-1, comparable to that of commercial MIL-53(Al) (3.89 mmol·g^-1), while its production cost is only one-third of the latter. The synthesis employs recycled aluminum from food packaging, such as foil and cans, as the aluminum source, thereby enhancing the sustainability of the process^[124]. This green methodology not only reduces production costs but also minimizes the overall carbon footprint. More recently, Choi et al. reported synthesizing MIL-53(Al)-R using TPA recovered by acidic hydrolysis of post-consumer PET waste. The resulting MIL-53(Al)-R showed comparable crystal structure, morphology, porosity, and gas adsorption behavior to MIL-53(Al)-C synthesized from commercial TPA, confirming the feasibility of using rPET-derived TPA as a reliable linker source for gas separation and storage applications [Figure 7]^[202]. PET-derived MOFs demonstrate significant potential for clean-energy gas storage. Specifically, Cr-MOF and UiO-66 offer exceptional thermal and humidity stability, rendering them effective for hydrogen storage with adsorption capacities of 2.1 and 1.2 wt%, respectively^[90,203]. The Cr-MOF derived from PET exhibits superior textural characteristics and hydrogen storage efficiency compared to commercially available BDC-based MOFs. This is attributed to its exceptionally high pore volume, extensive surface area, and numerous unsaturated chromium active sites. However, while these materials demonstrate promising performance, they remain at the laboratory research stage and have not yet been industrialized.

Another representative example is MOF-5, which possesses a CO₂ adsorption capacity ranging from 1.12 to 1.50 mmol·g^-1[204,205], but its poor moisture stability constrains practical applications^[206,207]. To address this limitation, Rocha et al. optimized the extraction of BDC ligands from waste PET, synthesizing MOF-5 with enhanced crystallinity and structural stability^[115]. The resulting material demonstrated an improved CO₂ adsorption capacity of 2.5 mmol·g^-1 and retained 80% of its adsorption performance after 24 h of moisture exposure. UiO-66 is notable among industrial-grade CO₂ adsorbents for its exceptional thermal, mechanical, and chemical stability^[208,209]. Synthesized with BDC ligands from waste PET, UiO-66 develops significant structural defects, enhancing its surface area and porosity. Consequently, it achieves a CO₂ adsorption capacity of 2.06 mmol·g^-1, positioning it as a promising option for efficient carbon capture^[156]. Overall, these studies show that PET-derived MOFs can achieve gas adsorption performance comparable to commercial linker-derived analogs while reducing dependence on virgin petrochemical linkers and supporting circular material design^[202].

Separating complex gas mixtures is another promising application of MOFs. For instance, Zhou et al. synthesized a Zr₁₂-cluster MOF (hcp UiO-66) derived from waste PET, which exhibited exceptional selectivity in the separation of cyclohexane and benzene^[158]. The material’s exceptional performance is attributed to its pore size (~6.0 Å), which closely matches the kinetic diameters of cyclohexane and benzene, enabling a molecular sieving effect^[158,210]. This selective adsorption capacity is environmentally relevant, as it extends beyond greenhouse gases to the capture and removal of volatile organic compounds (VOCs). Compounds such as toluene, which pose serious risks to air quality and human health, particularly in confined spaces, can be effectively mitigated through this adsorption process^[211-213]. MOFs demonstrate enhanced VOC adsorption compared to traditional materials such as activated carbon and zeolites, largely due to robust π-π and cation-π interactions. Notably, MIL-101(Cr) synthesized from waste PET achieves a toluene adsorption capacity of 40.3 mmol·g^-1, closely matching the 42.2 mmol·g^-1 of its commercial BDC-derived counterpart, suggesting that the green synthesis method maintains adsorption efficacy^{[161,214,215]}. Fe-based MOFs demonstrate exceptional adsorption efficiency for aromatic VOCs through the synergistic effects of π-π interactions and hydrogen bonding between the benzene rings in their framework and the target VOCs^[216]. In a recent study, Chen et al.^[182] synthesized MIL-101(Fe) using waste PET as the organic linker, achieving maximum adsorption capacities of 68.72, 91.63, and 78.47 mg·g^-1 for benzene, toluene, and m-xylene, respectively. These results underscore the promising potential of PET-derived MOFs for effective VOC removal applications.

The escalation of global water pollution, characterized by industrial wastewater laden with organic dyes, heavy metals, pesticides, and pharmaceutical residues, poses serious risks to ecosystems and human health^[87,135]. MOFs, with their high specific surface area, adjustable porous structures, and superior adsorption capabilities, offer notable benefits for water purification. Recent research highlights their potential to adsorb and remove plastic nanoparticles like polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC), broadening their applicability in managing emerging pollutants^[98]. Recent studies further indicate that PET-derived MOFs are being extended from conventional dye adsorption toward heavy-metal capture and pesticide-contaminated water treatment, demonstrating the growing application scope of waste-derived MOFs in aqueous remediation^{[119,217-219]}. More importantly, recent studies have moved beyond single-waste PET valorization by combining PET-derived terephthalate linkers with metal sources recovered from inorganic or industrial wastes, thereby enabling dual-waste-derived MOFs for phosphate removal and water-sorption-related applications [Figure 8]^[184,187].

MOFs effectively remove organic dyes through electrostatic interactions, hydrogen bonding, and π-π stacking^[220-225]. Structural modifications are often necessary to improve selectivity for specific dyes. Amino-functionalized MIL-101(Cr) significantly enhances methylene blue (MB) adsorption through hydrogen bonding and electrostatic interactions^[118]. To reduce environmental and safety concerns associated with HF, HF-free synthesis methods have been introduced for MIL-101(Cr)^[138]. MIL-101(Cr) synthesized without HF maintains excellent adsorption capacities, achieving 662.87 mg·g^-1 for RR2 and 863.67 mg·g^-1 for RB19^[119], while another MIL-101(Cr) system showed a maximum adsorption capacity of 2,176 mg·g^-1 for AB-92^[121]. These results indicate that HF is not indispensable for achieving high dye-adsorption performance in MIL-101(Cr)-based systems^[119,121]. More recently, Ngo et al. converted PET plastic into MOF materials for organic dye adsorption, further confirming that PET-derived linkers can be used to construct efficient dye adsorbents for water purification^[217]. Cheng et al. also reported waste PET-derived MIL-101(Cr) for the efficient adsorption and removal of anionic dyes, providing a 2025 example that directly strengthens the anionic dye-removal subsection^[119]. Beyond dye adsorption, MOF-based adsorbents have also been reported for toxic metal-ion removal from acid rock drainage, further supporting their relevance to water-remediation applications^[226]. Additionally, Cr-based MOFs demonstrate reduced toxicity, underscoring their environmental benefits in practical applications^[227,228]. Similarly, Ca-MOF is a low-toxicity option that can function effectively under non-acidic conditions and has been synthesized for the removal of Alizarin Red S dye, achieving an adsorption capacity of 979.0 mg·g^-1[85].

MOFs have also demonstrated strong adsorption capacities for pharmaceutical and pesticide residues, particularly in antibiotic degradation^[229-232]. MOF-5 synthesized from waste PET exhibits a maximum tetracycline (TC) adsorption capacity of 2,325.55 mg·g^-1, attributed to hydrogen bonding and ionic interactions between MOF frameworks and TC’s unsaturated bonds^[92,229,233]. Moreover, UiO-66, with its high porosity and thermal stability, efficiently adsorbs the nonsteroidal anti-inflammatory drug ketorolac tromethamine (KTC) under acidic conditions, with an adsorption capacity of 729.92 mg·g^-1[130]. By introducing defects, UiO-66 achieves enhanced pore structures and more exposed metal active sites, significantly improving its adsorption efficiency for lomefloxacin^[129].

Neonicotinoid pesticides, such as imidacloprid, pose significant ecological threats^[234-236]. To address this issue, several MOFs, including MIL-101(Cr)-NH₂^[237], MIL-101(Fe)^[238], and UiO-66^[239], have been developed to remove imidacloprid. Notably, UiO-66 derived from PET exhibits remarkable efficiency in capturing imidacloprid, with enhanced permeability further improving its adsorption performance^[179]. Compared to commercially available MOFs, the superior permeability of PET-derived UiO-66 enables more effective adsorption and removal of imidacloprid. A recent study further extended this direction by using a PET-derived MIL-53(Al)/PMMA nanofiber-incorporated poly(vinylidene fluoride) (PVDF) membrane for removing hazardous pesticides, including atrazine and chlorpyrifos, demonstrating the potential of PET-derived MOF-based membranes for agricultural runoff treatment^[219]. MOFs have emerged as promising adsorbents for removing oxygen-containing anionic pollutants, such as phosphates and arsenates, which significantly impact water quality and soil health^[240]. Notably, Fe- and Zr-based MOFs have demonstrated adsorption capacities of 72.16 mg·g^-1 and 66.63 mg·g^-1 for phosphate at pH 6.5, respectively^[96]. By optimizing surface charge properties, Sn(II)-MOF further enhances adsorption, achieving capacities of 90.90 mg·g^-1 and 126.58 mg·g^-1 for arsenate and phosphate, respectively, under acidic conditions^[93]. A more recent example is the ultrarapid synthesis of a trimetallic CrNiFe-MOF from stainless-steel waste and disodium terephthalate derived from PET waste [Figure 8A]^[187]. This strategy is particularly significant because both the organic linker and metal nodes originate from waste streams, while the MOF can be produced in water at room temperature within only 5-10 min. As shown in Figure 8B, CrNiFe-MOF displayed faster phosphate uptake than MIL-101(Fe), reaching 61.40 mg·g^-1 within the first 10 min and a maximum phosphate adsorption capacity of 179.97 mg·g^-1. The enhanced performance was attributed to the stronger phosphate affinity of Cr-containing oxo-trimer sites and possible defect/mesoporosity contributions, demonstrating that multimetallic waste-derived MOFs can provide both sustainable synthesis and efficient oxyanion removal.

MOFs synthesized using BDC ligands derived from rPET bottles have shown promising adsorption capabilities for removing arsenate and perfluorooctanoic acid (PFOA) from aqueous environments. Specifically, La-MOF exhibits an arsenate adsorption capacity of 114.28 mg·g^-1 at pH 7, while La-MOF and Zr-MOF achieve PFOA adsorption capacities of 310 mg·g^-1 and 290 mg·g^-1, respectively^[241,242]. The superior adsorptive capacity of La-MOF has been attributed to its slower permeation rate and extended adsorption activity^[241]. Similarly, Ba-MOF^[137] and MIL-101(Al)^[123] have been effectively employed to remove sulfate and orthophosphate. In addition to liquid-phase pollutant adsorption, waste-derived Cr-BDC MOFs have also been explored for water-sorption-related applications. Delhali et al. synthesized MIL-101(Cr) and MIL-53(Cr) by combining Cr(III) recovered from tannery effluent with TPA obtained from waste PET bottles^[184]. The H₂O adsorption isotherms show that waste-derived MIL-101(Cr) exhibits a sigmoidal water adsorption profile comparable to that of its commercial precursor-based counterpart, confirming that waste-derived precursors can preserve the intrinsic water-sorption behavior of MIL-101(Cr) [Figure 8C and D]. Moreover, the cyclic water adsorption isotherms and water uptake at 90% relative humidity demonstrate stable adsorption-desorption performance over repeated cycles [Figure 8E and F], highlighting the potential of dual-waste-derived Cr-MOFs for humidity control, water harvesting, and adsorption-based water-management applications.

MOFs have demonstrated remarkable potential for the removal of heavy metal pollutants. For instance, a Ca-based MOF has been reported to achieve removal efficiencies of 98.99% and 99.18% for U(VI) and Th(IV) ions, respectively, at pH 5^[243,244]. This high performance can be attributed to the biocompatibility of the Ca ions, which helps minimize the risk of secondary environmental pollution. Kumar et al. reported an efficient and economical approach to synthesize Ca-MOF using waste eggshells as a Ca²⁺ source and waste plastics as an organic ligand^[134]. The resulting material effectively removed Pb²⁺, Cd²⁺, and Cu²⁺ from wastewater, with maximum adsorption capacities of 644.07 ± 47, 391.4 ± 26, and 260.5 ± 14 mg·g^-1, respectively. More recently, Kim et al. developed a waste PET-derived MOF-grafted polyaniline (PANI) composite for heavy-metal adsorption from aqueous solution, providing a 2025 example of composite engineering to improve the practical performance of PET-derived MOF adsorbents^[218].

Researchers have investigated MOF growth on flexible substrates to boost practical applicability. UiO-66-NH₂ synthesized on PET-based polymer substrates yielded a flexible MOF-coated material with a Pb(II) adsorption capacity of 711.99 mg·g^-1[177]. This enhancement is due to the improved thermal stability and increased surface area of aminated UiO-66, underscoring the potential of MOF-functionalized polymer substrates for large-scale water purification^[245].

Collectively, PET-derived MOFs show significant promise in environmental remediation, especially for removing persistent organic pollutants [Table 2]. Their high surface area, adjustable porosity, and varied active sites enhance their catalytic efficiency, while their structural stability across different environmental conditions supports long-term performance. These characteristics make PET-derived MOFs strong contenders for sustainable and scalable water remediation technologies.

The utilization of PET-derived MOFs as electrode materials in lithium-ion batteries (LIBs) has garnered significant attention owing to their tailorable porosity, high specific surface area, and environmentally benign synthetic protocols. The seminal work by Tarascon and colleagues in 2009 showcased the viability of MIL-53(Fe) as an anode material for LIBs through a conversion reaction mechanism^[251]. Since then, PET-derived MOFs have been regarded as promising anode candidates for LIBs. Notably, Ca-MOF and Ba-MOF, synthesized from the abundant elements calcium and barium, demonstrate exceptional electrochemical performance. After 100 charge/discharge cycles, Ca-MOF and Ba-MOF achieve specific capacities of 403 and 167 mAh·g^-1, respectively^[107]. The choice of metal centers in MOFs is a critical factor influencing their lithium storage capabilities^[252]. Co-based MOFs, for instance, enable efficient electron transport owing to their accessible redox states (+1 to +4), rendering them highly promising for advanced energy storage technologies. Metal-ion doping significantly enhances electrochemical performance by boosting conductivity. PET-derived Co/Ni-MOF and Co/Zn-MOF, created through bimetallic doping, demonstrate exceptional lithium storage capabilities. Co/Ni-MOF shows initial discharge/charge capacities of 2,496 and 1,729 mAh·g^-1, respectively, maintaining a Coulombic efficiency above 99% after 200 cycles. Similarly, Co/Zn-MOF achieves a first-cycle discharge/charge capacity of 2,774/1,971 mAh·g^-1, with a Coulombic efficiency of 71%, markedly surpassing single-metal Co-MOF [Figure 9]^[102,103].

Porous MOFs derived from PET have been extensively investigated as electrode materials for supercapacitors. Their high specific surface areas and hierarchical micro-/mesoporous structures provide ideal conditions for charge storage and rapid charge-discharge kinetics^[253-255]. For instance, Cu-, Zr-, and Ti-based MOFs synthesized by Dubey^[133] exhibit Brunauer-Emmett-Teller (BET) surface areas of 1,321, 720, and 574 m²·g^-1, respectively. Among these, the Cu-MOF exhibits superior electrochemical performance, achieving a specific capacitance of 104.8 F·g^-1 at a current density of 0.5 A·g^-1 in a three-electrode system, attributed to its high surface area and efficient ion transport properties. Carbonized MOFs can be converted into conductive materials like porous and graphitized carbon, boosting conductivity and electrochemical stability^{[117,256,257]}. For instance, PET-derived Ni-MOF, once carbonized, offers a surface area of 1,523 m²·g^-1 with enhanced mesopores (11-13 nm), achieving a specific capacitance of 581.30 F·g^-1 at a scan rate of 5 mV·s^-1[104]. Additionally, doping with heteroatoms such as boron, nitrogen, sulfur, and phosphorus further improves electron and ion transport, optimizing supercapacitor performance^[258,259].

The potential of PET-derived MOFs in thermal energy storage is increasingly recognized, particularly for water adsorption-based heat storage applications. MOFs with high adsorption capacity and thermal stability are especially promising. A comparative study of five MOFs - MIL-101(Cr), UiO-66, MIL-101(Fe), MIL-88B(Fe), and Al fumarate - revealed that MIL-101(Cr) demonstrated superior hydrothermal stability and rapid adsorption kinetics. At a relative pressure (p/p₀) of 0.99 and 55 °C, MIL-101(Cr) achieved a water uptake capacity of 1.53 g H₂O g^-1, underscoring the importance of high surface area and mesoporosity in enhancing thermal storage performance^[120]. In addition to adsorption-based heat storage, recent work has extended waste PET-derived MOFs toward passive thermal management. Wu et al. developed a betaine-assisted one-reactor strategy to convert waste PET and other polyesters directly into functional MOFs. When PET-derived Zn-BDC was incorporated into PVDF films, the resulting composite showed high solar reflectance of 94.4%, mid-infrared emissivity of 95.5%, and an average cooling effect of 9.3 °C below ambient temperature^[260].

Energy conversion represents an important energy-related application of PET-derived MOFs. PET-derived Cr-MOF and UiO-66 have been investigated for hydrogen storage, with reported H₂ uptake values of 2.1 and 1.2 wt%, respectively^[90,203]. The superior hydrogen-storage behavior of PET-derived Cr-MOF has been attributed to its large surface area, high pore volume, and abundant unsaturated chromium sites. Nevertheless, these systems remain at the laboratory stage, and future studies should evaluate cycling stability, regeneration behavior, moisture tolerance, and scalability under realistic storage conditions. Beyond physical gas storage, PET-derived MOFs also show potential for photocatalytic CO₂ conversion. A PET-based Ni-MOF has been studied as a photocatalyst for CO₂ reduction, achieving a CO production rate of 9.68 × 10³ μmol·h^-1·g^-1 with 96.7% selectivity for CO over H₂^[89]. This high selectivity favors the formation of value-added carbon-based products while suppressing competitive hydrogen evolution, highlighting the potential of PET-derived MOFs for carbon-neutral energy conversion. In addition, PET-derived MOFs can serve as sacrificial precursors for energy-conversion-related electrochemical materials. For example, waste PET bottles were directly converted into MIL-53(Al), and the resulting MOF was further carbonized into accordion-like hierarchical porous carbon for Zn-ion capacitors, delivering a high capacitance of 335 F·g^-1 at 0.1 A·g^-1, an energy density of 150.3 Wh·kg^-1, and 92.2% capacitance retention after 10,000 cycles^[155]. This result suggests that PET-derived MOFs are not limited to direct gas-storage or photocatalytic functions, but can also act as intermediate platforms for constructing carbon-based energy devices.

Porous MOFs derived from PET demonstrate remarkable potential for energy storage and conversion applications, including supercapacitors, LIBs, thermal energy storage, and photocatalysis [Table 3]. Their hierarchical porosity, tailorable electronic characteristics, and structural robustness contribute to enhanced energy density, power density, and long-term cycling performance. Ongoing developments in MOF design, metal doping, and structural engineering are poised to further unlock the potential of PET-derived MOFs for next-generation sustainable energy technologies.

Advanced oxidation and catalytic treatment technologies, including photo-Fenton reactions, photocatalysis, electro-Fenton processes, and peroxymonosulfate (PMS)/peroxydisulfate (PDS) activation, have emerged as efficient strategies for degrading persistent organic pollutants in water^[262-264]. MOFs have emerged as a focus of substantial interest because their high specific surface area and tunable porosity enable enhanced catalytic performance. Fe-MOFs have shown significant promise as Fenton catalysts due to their inherent water stability, environmental friendliness, and numerous exposed iron active sites^[265]. Additionally, their excellent light absorption enables them to act as photocatalytic semiconductors under irradiation, making them ideal for incorporation into photo-Fenton systems^[266,267]. MOFs offer potential in reducing the negative impacts of algaecides, which are commonly used to manage harmful algal blooms (HABs) in freshwater systems but are often detrimental to water quality^[268,269]. Integrating copper with MOFs represents a novel approach to water remediation. The Cu-based MOFs act as indirect sources of reactive oxygen species (ROS), effectively inhibiting cyanobacterial growth, inducing colony aggregation, and disrupting photosynthetic systems, while exhibiting negligible toxicity toward aquatic organisms such as Daphnia magna^[95].

PET-derived Fe-MOFs have been extensively explored for environmental catalysis. For example, a PET-derived Fe-MOF@Fe₂O₃ composite exhibited exceptional catalytic performance, achieving 99.3% degradation of 15 mg·L^-1 malachite green (MG) within 30 min under visible light irradiation, with a remarkably short residence time of only 20 min^[165]. Similarly, PET-derived MIL-53(Fe), synthesized by Sun et al.^[181], demonstrated remarkable photocatalytic efficiency in a photo-Fenton system, achieving 99% degradation of the disinfection byproduct 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) in 30 min. It also effectively degraded phenol (98%) and bisphenol A (BPA) (> 95%) within 60 min. More recently, Zhang et al. reported a room-temperature waste-to-MOF strategy using PET-derived TPA and Fe(III) recovered from spent acid pickling baths to synthesize MIL-88B(Fe). The resulting framework activated PMS and removed 87% of TC hydrochloride within 15 min, while maintaining 96% activity after five cycles^[247].

MOFs have been extensively utilized in the catalytic degradation of dyes and organic contaminants in aqueous environments, beyond their application in photo-Fenton reactions. For instance, MIL-101(Ag) has demonstrated exceptional catalytic capabilities in the reduction of MB, 4-nitrophenol (4-NP), and 4-nitroaniline (4-NA) in the presence of NaBH₄, achieving degradation efficiencies exceeding 93% within 5-10 min^[270] [Figure 10]. In addition, Waribam et al. developed a solvent-free rapid synthesis of magnetic MOFs from waste-derived precursors. The resulting Mag-MOF completely degraded an azo dye through a Fenton-like pathway within 30 min and retained 84% activity after five cycles, highlighting the value of solvent-free synthesis and magnetic recoverability for practical environmental cleanup^[248]. Bimetallic MOFs frequently demonstrate enhanced catalytic activity compared to their monometallic counterparts, owing to synergistic effects between the distinct metal centers^[271]. For example, a Ni/Cu-MOF derived from PET displayed 99% MB degradation under sunlight within 4 h^[272]. Similarly, a Cr-MOF achieved a 92.4% photocatalytic degradation efficiency for TC^[273]. Additionally, MOFs have proven effective in electro-Fenton systems, illustrated by MIL-53(Fe)@Fe₃O₄@C, which reached a degradation efficiency of 91.68% ± 3.61% for salicylic acid (SA)^[131], thereby expanding the potential of MOFs in advanced water treatment strategies. A further example is the construction of a MOF-based photocatalyst from PET waste bottles and spent zinc-carbon batteries for the photodegradation of organophosphorus pesticides, demonstrating that dual-waste-derived MOF catalysts can simultaneously address plastic waste valorization, battery-waste reuse, and pesticide detoxification^[274].

The exceptional physicochemical properties of MOFs derived from post-consumer PET have stimulated increasing interest in their use as heterogeneous catalysts or catalyst precursors for value-added chemical conversion. In addition to environmental remediation, PET-derived MOFs have been explored for CO₂ fixation, nitroaromatic reduction, ODS, and hydrogen generation from liquid hydrogen carriers. Their high specific surface area, hierarchical porosity, accessible metal nodes, and tunable linker environments provide abundant active sites and confined microenvironments for heterogeneous catalytic reactions.

In 2016, Lo et al. conducted a seminal study on PET-derived MOF catalysis, demonstrating the catalytic capability of PET-based MIL-47 and MIL-101(Cr) in CO₂ fixation^[149]. The system efficiently converted CO₂ and epoxides into cyclic carbonates under mild conditions, emphasizing its potential for carbon capture and utilization (CCU). This research highlights the viability of PET-derived MOFs as heterogeneous catalysts and supports sustainable CO₂ valorization strategies, providing an energy-efficient method for producing high-value chemicals. Beyond CO₂ fixation, PET-derived MOFs show strong catalytic performance in reduction reactions. Notably, Cu-MOF serves as an eco-friendly catalyst for converting 4-NP to 4-aminophenol (4-AP), a crucial intermediate in pharmaceuticals and dyes, and the amine-functionalized Cu-MOF exhibited an impressive catalytic normalized kinetic rate of 11.28 mol·min^-1·mg^-1, achieving full reduction within 5 min under ambient conditions^[99]. This enhanced performance results from the synergistic interaction between the MOF structure and surface amination, which improves electron transfer and access to active sites.

PET-derived MOFs have exhibited promising potential in ODS and denitrification processes, which are crucial for the deep purification of fossil fuels and the mitigation of environmental pollutants. For instance, an Al-MOF was effectively employed to remove thiophene-based sulfur compounds from both simulated and actual crude oil samples. By optimizing key catalytic parameters, such as temperature, reaction time, and catalyst loading, the desulfurization efficiency reached 90% in real oil samples^[125]. This finding highlights the potential of PET-derived MOFs as next-generation catalysts for industrial-scale fuel purification, offering an eco-friendly alternative to conventional desulfurization methods.

PET-derived MOFs are gaining attention as catalysts for sustainable hydrogen production. A prominent example is the UiO-66-derived Co@Cr(OH)₃/ZrO₂ hybrid catalyst, created through PET carbonization, which demonstrated outstanding catalytic efficiency in formic acid dehydrogenation. At room temperature, it achieved a turnover frequency (TOF) of 7,685 h^-1, releasing 120 mL of hydrogen in just 1.5 min^[127]. The efficiency and stability of this catalyst highlight the promise of PET-derived MOFs in hydrogen storage and production, which are crucial for the clean energy transition.

Recent studies further suggest that MOF catalysis is expanding from PET-derived MOFs toward broader plastic and polyester catalytic upgrading. Qin et al. reported a MOF-based photocatalytic strategy for polyester plastic valorization by regulating active sites, demonstrating that MOFs can also serve as catalytic platforms for polyester waste conversion^[275]. In another related study, Das et al. reported the selective electrocatalytic production of formic acid from plastic waste using a nickel MOF constructed from a biomass-derived ligand^[276]. Although these two examples are not PET-derived MOFs in the strict sense, they reveal an emerging complementary direction: MOFs can either be synthesized from PET-derived linkers as value-added products or be used as catalysts for plastic-waste upgrading. A significant advantage of PET-derived MOFs in industrial catalysis is their inherent thermal and chemical stability, ensuring sustained catalytic performance. Unlike traditional catalysts prone to deactivation from sintering or leaching, MOF-based catalysts retain structural integrity through multiple catalytic cycles. Future research should aim to refine MOF architectures via ligand functionalization, metal doping, and hybridization with conductive supports to further boost their catalytic efficiency and selectivity.

PET-derived MOFs show significant promise in industrial catalysis, providing sustainable and scalable solutions for CO₂ fixation, hydrogenation, desulfurization, and hydrogen production. Their modular tunability and exceptional catalytic properties position them as next-generation green catalysts that tackle urgent energy and environmental sustainability challenges. Advancements in structural engineering, composite fabrication, and mechanistic insights will be crucial for transitioning these materials from laboratory research to large-scale industrial use. MOFs demonstrate outstanding cyclic and thermal stability during catalysis, ensuring their long-term viability in industrial applications. Future advancements in material design and synthesis are anticipated to expand their use in chemistry and industrial catalysis [Table 4], offering innovative solutions for green chemistry and sustainable development.