Comparative evaluation of Fe-, Zr-, and La-based metal-organic frameworks derived from recycled PET plastic bottles for arsenate removal

Sustainable Strategies for Converting Organic, Electronic, and Plastic Waste From Municipal Solid Waste Into Functional Materials

The valorization of municipal solid waste permits to obtain sustainable functional materials. As the urban population burgeons, so does the volume of discarded waste, presenting both a challenge and an opportunity. Harnessing the materials and the latent energy within this solid waste not only addresses the issue of disposal but also contributes to the innovation of functional materials with applications in the energy, electronics, and environment sectors. In this perspective, technologies for converting, after sorting, municipal solid waste into valuable metals, chemicals, and fuels are critically analyzed. Innovative approaches to convert organic waste into functional carbon materials and to create, from plastic and electronic wastes, metal-organic frameworks for energy conversion, storage, and CO2 adsorption and conversion are proposed. Green hydrometallurgy routes that permit the recovery of precious metals avoiding noble metals' oxidative leaching, thus avoiding their downcycling, are also highlighted. The reclaimed precious metals hold promise for use in optoelectronic devices.

Fe-based metal-organic frameworks: performance and advantages on removal organophosphate pesticides in water for human consumption

The study of real-world applications of adsorbent materials for water treatment enhances the feasibility of wastewater reuse and upgrades purifying processes for water supplies, thereby decreasing risks to public health. This study examined the removal of organophosphate pesticides from agricultural runoff samples using MIL-101(Fe). Rapid microwave-assisted synthesis, stability up to 350 °C, environmental safety, and potential reusability were promising features related to synthesized MIL-101(Fe). The MIL-101(Fe) performance in the simultaneous adsorptive removal of glyphosate (GLY), glufosinate (GLU), and aminomethylphosphonic acid (AMPA) was evaluated. It achieved a 99.2% removal efficiency (%RE) for GLY within 15 min of contact and 85.4 and 64.2% for AMPA and GLU after 120 min, respectively. Good experimental adsorption capacities (≥ 97 mg/g) for the three pollutants were obtained. Characterization analysis after adsorption indicates the possible synergistic effects of hydrogen bonding, active sites of material, pore filling, and inner-sphere surface complex as likely to predominate the mechanism of adsorption. MIL-101(Fe) exhibited satisfactory recycling results for GLY and AMPA, with %RE that decreased from 99 to 83% and 87 to 59%, respectively, after 5 recycles. The high stability of the adsorbent was confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Finally, the MIL-101(Fe) potential for practical applications was demonstrated with the successful removal in real water samples above 92, 80 and 60% for GLY, AMPA, and GLU, respectively. The obtained findings provide further progress in the MIL-101(Fe) remarkable use for large-scale future applications for pesticide removal in complex aqueous environments.

Catalyst- and Solvent-Free Upcycling of Poly(Ethylene Terephthalate) Waste to Biodegradable Plastics

Poly(ethylene terephthalate) (PET) is an important polymer with annual output second only to polyethylene. Due to its low biodegradability, a large amount of PET is recycled for sustainable development. However, current strategies for PET recycling are limited by low added value or small product scale. It is urgent to make a breakthrough on the principle of PET macromolecular reaction and efficiently prepare products with high added value and wide applications. Here, the catalyst- and solvent-free synthesis of biodegradable plastics are reported through novel carboxyl-ester transesterification between PET waste and bio-based hydrogenated dimer acid (HDA), which can directly substitute some terephthalic acid (TPA) units in PET chain by HDA unit. This macromolecular reaction can be facilely carried out on current equipment in the polyester industry without any additional catalyst and solvent, thus enabling low-cost and large-scale production. Furthermore, the product semi-bio-based copolyester shows excellent mechanical properties, regulable flexibility and good biodegradability, which is expected to substitute poly(butylene adipate-co-terephthalate) (PBAT) plastic as high value-added biodegradable materials. This work provides an environmental-friendly and economic strategy for the large-scale upcycling of PET waste.

When microplastics/plastics meet metal-organic frameworks: turning threats into opportunities

Significant efforts have been devoted to removal and recycling of microplastics (MPs; <5 mm) to address the environmental crises caused by their ubiquitous presence and improper treatment. Metal-organic frameworks (MOFs) demonstrate compatibility with MPs/plastics through adsorption, degradation, or assembly with the MPs/plastic polymers. Above 90% of MPs/plastic particles can be adsorbed on MOF materials via the hydrophobic interaction, electrical attraction, π-π stacking, and van der Waals forces. Meanwhile, certain MOFs have successfully converted various types of plastics into high-valued small molecules through thermocatalysis and photocatalysis. In thermocatalysis, the primary process should be C-O bond cleavage, whereas in photocatalysis it ought to be the generation of reactive oxygen species (ROS). Moreover, the construction of novel MOFs using waste MPs/plastics as the ligands was mostly accomplished through three dominant ways, including glycolysis, hydrolysis and methanolysis. Once successfully composited, the MOF@plastic materials illustrated tremendous promise for interdisciplinary research in multifunctional applications, including sewage treatment, gas adsorption/separation, and the preparation of microbial fuel cells, plastic scintillators and other sensors. The review explicated the relationships between MPs/plastics and MOF materials, as well as the challenges and perspectives for their development. It can provide a deeper understanding of how MOFs remove/degrade MP/plastic particles, how MPs/plastics are recycled to prepare MOFs, and how to build multifunctional MOF@plastic composites. Overall, this analysis is anticipated to outline future prospects for turning the threats (MPs/plastics contamination) into opportunities (e.g., as ligands to prepare MOF or MOF@plastic materials for further applications).

A waste-to-wealth conversion of plastic bottles into effective carbon-based adsorbents for removal of tetracycline antibiotic from water

Currently, plastic waste and antibiotic wastewater are two of the most critical environmental problems, calling for urgent measures to take. A waste-to-wealth strategy for the conversion of polyethylene terephthalate (PET) plastic bottles into value-added materials such as carbon composite is highly recommended to clean wastewater contaminated by antibiotics. Inspired by this idea, we develop a novel PET-AC-ZFO composite by incorporating PET plastic-derived KOH-activated carbon (AC) with ZnFe2O4 (ZFO) particles for adsorptive removal of tetracycline (TTC). PET-derived carbon (PET-C), KOH-activated PET-derived carbon (PET-AC), and PET-AC-ZFO were characterized using physicochemical analyses. Central composite design (CCD) was used to obtain a quadratic model by TTC concentration (K), adsorbent dosage (L), and pH (M). PET-AC-ZFO possessed micropores (d ≈ 2 nm) and exceptionally high surface area of 1110 m2 g-1. Nearly 90% TTC could be removed by PET-AC-ZFO composite. Bangham kinetic and Langmuir isotherm were two most fitted models. Theoretical maximum TTC adsorption capacity was 45.1 mg g-1. This study suggested the role of hydrogen bonds, pore-filling interactions, and π-π interactions as the main interactions of the adsorption process. Thus, a strategy for conversion of PET bottles into PET-AC-ZFO can contribute to both plastic recycling and antibiotic wastewater mitigation.

Design and application of metal organic frameworks for heavy metals adsorption in water: a review

The growing apprehension surrounding heavy metal pollution in both environmental and industrial contexts has spurred extensive research into adsorption materials aimed at efficient remediation. Among these materials, Metal-Organic Frameworks (MOFs) have risen as versatile and promising contenders due to their adjustable properties, expansive surface areas, and sustainable characteristics, compared to traditional options like activated carbon and zeolites. This exhaustive review delves into the synthesis techniques, structural diversity, and adsorption capabilities of MOFs for the effective removal of heavy metals. The article explores the evolution of MOF design and fabrication methods, highlighting pivotal parameters influencing their adsorption performance, such as pore size, surface area, and the presence of functional groups. In this perspective review, a thorough analysis of various MOFs is presented, emphasizing the crucial role of ligands and metal nodes in adapting MOF properties for heavy metal removal. Moreover, the review delves into recent advancements in MOF-based composites and hybrid materials, shedding light on their heightened adsorption capacities, recyclability, and potential for regeneration. Challenges for optimization, regeneration efficiency and minimizing costs for large-scale applications are discussed.

Applications of waste polyethylene terephthalate (PET) based nanostructured materials: A review

While polyethylene terephthalate (PET) has enjoyed widespread use, a large volume of plastic waste has also been produced as a result, which is detrimental to the environment. Traditional treatment of plastic waste, such as landfilling and incinerating waste, causes environmental pollution and poses risks to public health. Recycling PET waste into useful chemicals or upcycling the waste into high value-added materials can be remedies. This review first provides a brief introduction of the synthesis, structure, properties, and applications of virgin PET. Then the conversion process of waste PET into high value-added materials for different applications are introduced. The conversion mechanisms (including degradation, recycling and upcycling) are detailed. The advanced applications of these upgraded materials in energy storage devices (supercapacitors, lithium-ion batteries, and microbial fuel cells), and for water treatment (to remove dyes, heavy metals, and antibiotics), environmental remediation (for air filtration, CO2 adsorption, and oil removal) and catalysis (to produce H2, photoreduce CO2, and remove toxic chemicals) are discussed at length. In general, this review details the exploration of advanced technologies for the transformation of waste PET into nanostructured materials for various applications, and provides insights into the role of high value-added waste products in sustainability and economic development.

A label-free ratiometric fluorescent aptasensor based on a peroxidase-mimetic multifunctional ZrFe-MOF for the determination of tetrodotoxin

A Fe/Zr bimetal-organic framework (ZrFe-MOF) is utilized to establish a ratiometric fluorescent aptasensor for the determination of tetrodotoxin (TTX). The multifunctional ZrFe-MOF possesses inherent fluorescence at 445 nm wavelength, peroxidase-mimetic activity, and specific recognition and adsorption capabilities for aptamers, owing to its organic ligand, and Fe and Zr nodes. The peroxidation of o-phenylenediamine (OPD) substrate generates fluorescent 2,3-diaminophenazine (OPDox) at 555 nm wavelength, thus quenching the inherent fluorescence of ZrFe-MOF because of the fluorescence resonance energy transfer (FRET) effect. TTX aptamers, which are absorbed on the material surface without immobilization or fluorescent labeling, inhibit the peroxidase-mimetic activity of ZrFe-MOF. It causes the decreased OPDox fluorescence at 555 nm wavelength and the inverse restoration of ZrFe-MOF fluorescence at 445 nm wavelength. With TTX, the aptamers specifically bind to TTX, triggering rigid complex release from ZrFe-MOF surface and reactivating its peroxidase-mimetic activity. Consequently, the two fluorescence signals exhibit opposite changes. Employing this ratiometric strategy, the determination of TTX is achieved with a detection limit of 0.027 ng/mL and a linear range of 0.05-500 ng/mL. This aptasensor also successfully determines TTX concentrations in puffer fish and clam samples, demonstrating its promising application for monitoring trace TTX in food safety.

Co-based metal-organic frameworks synthesized from poly(ethylene terephthalate) waste plastics for rapid detection of p-phenylenediamine

The environmental issues and health problems of waste plastics have attracted remarkable attention. It is quite important to convert waste plastics into high value-added electrochemical materials. Herein, four kinds of Co-based metal-organic frameworks (CoMOFs) were synthesized from poly(ethylene terephthalate) plastic, and their electrochemical applications were examined. A mixture of N,N-dimethylformamide (DMF) and H2O was used as the solvent, and hydrothermal reaction was employed. It is found that the surface area and porous structure of CoMOFs are closely related to the volume ratio of DMF/H2O. As a result, the prepared CoMOFs exhibit different catalytic enhancement activities toward the oxidation of p-phenylenediamine (PPD). Based on the solvent-controlled sensing performance of CoMOFs, a highly sensitive and rapid detection method has been developed for PPD, with a linear range from 0.05 to 8.0 μM. The detection limit was 45 nM, and the practical application in hair dye samples was successfully demonstrated.

The interactions between mixed waste from discarded surgical masks and face shields during the degradation in supercritical water

The widespread use of surgical masks made of polyolefin and face shields made of polyester during pandemics contributes significantly to plastic pollution. An eco-friendly approach to process plastic waste is using supercritical water, but the reaction of mixed polyolefin and polyester in this solvent is not well understood, which hinders practical applications. This study aimed to investigate the reaction of waste surgical masks (SM) and face shields (FS) mixed in supercritical water. Results showed that the optimal treatment conditions were 400 °C and 60 min, achieving a liquid oil yield of 823.03 mg·g-1 with 25 wt% FS. The interaction between polypropylene (PP), polyethylene terephthalate (PET), and iron (Fe) in SM and FS mainly determined the production of liquid oil products such as olefins and benzoic acid. The methyl-branched structure of PP enhanced PET hydrolysis, resulting in higher production of terephthalic acid (TPA). The degradation of PP was facilitated by the acidic environment created by TPA and benzoic acid in the reaction. Moreover, the hydrolysis of PET produced carboxylic acid, which coordinated with Fe3+ to form Fe-H that catalyzed the polymerization of small olefins, contributing to higher selectivity for C9 olefins. Therefore, this study provides valuable insights into the degradation mechanism of mixed PPE waste in supercritical water and guidance for industrial treatment.

Layered bimetallic hydroxide nanocage assembled on MnO2 nanotubes: A hierarchical porous sugar gourd-like electrocatalyst for the sensitive detection of hydrogen peroxide in food

Hydrogen peroxide is used widely as a disinfection or bleaching additive during processing in the food industry. However, excessive residues of hydrogen peroxide in food have serious human health implications. In the present study, a novel electrochemical sensing electrode (MnO₂/ZIF-67@LDH) with hierarchical porous sugar gourd-like structure was fabricated through a multi-step hydrothermal method using ZIF as the precursor. The unique porous nanocage structure of the sensing electrode provided multidimensional charge transfer channels and accelerated the electron transfer rate. As a hydrogen peroxide sensor, the electrode had two detection linear ranges of 1×10^-3-4 mmol L^-1 and 4-8 mmol L^-1, and the detection limit was 0.26 µmol L^-1. The MnO₂/ZIF-67@LDH sensor was also applied to determine the content of hydrogen peroxide in actual food samples of juice and milk, and satisfactory recovery were achieved. The present study provides a novel and effective design strategy for the construction of electrochemical sensing electrodes.

Review on arsenic environment behaviors in aqueous solution and soil

Arsenic pollution in environment has always been an important environmental problem that has attracted wide attention in recent years. Adsorption is one of the main methods of treatment for arsenic in the aqueous solution and soil because of the advantages of high efficiency, low cost and wide application. Firstly, this report summarizes the commonly and widely used adsorbent materials such as metal-organic frameworks, layered bimetallic hydroxides, chitosan, biochar and their derivatives. The adsorption effects and mechanisms of these materials are further discussed, and the application prospects of these adsorbents are considered. Meanwhile, the gaps and deficiencies in the study of adsorption mechanism was pointed out. Then, this study comprehensively evaluated the effects of various factors on arsenic transport, including (i) the effects of pH and redox potential on the existing form of As; (ii) complexation mechanism of dissolved organic matter and As; (iii) factors affecting the plant enrichment of As. Finally, the latest scientific researches on microbial remediation of arsenic and the mechanisms were summarized. The review finally enlightens the subsequent development of more efficient and practical adsorption material.

Cyanobacteria control using Cu-based metal organic frameworks derived from waste PET bottles

Copper sulfate (CuSO₄) is actively used to control the proliferation of harmful algal blooms because of its fast and effective killing mechanism. However, its use unintentionally harms innocuous aquatic organisms. Therefore, there is a need to find non-toxic solutions for controlling algal blooms. In this study, Cu-based metal-organic framework (Cu-BDC MOF) chips (ca. 2 × 2 cm) were synthesized using waste polyethylene terephthalate (PET) bottles. The as-synthesized Cu-BDC MOF chips efficiently inhibited the cyanobacteria species Microcystis aeruginosa, which was comparable to the conventional dose of CuSO₄ algaecide (1.00 mg L^-1). Moreover, unlike the CuSO₄ algaecide, Cu-BDC MOF chips did not cause any acute toxicity (48 h) to the water flea Daphnia magna. Both Cu-BDC MOF and Cu₂O seemed to be responsible for the generation of reactive oxygen species, which resulted in the aggregation, photosynthesis disruption, and eventually growth inhibition of M. aeruginosa. This study suggests that the environmentally safe Cu-BDC MOF chip is a promising agent to sustainably control harmful algal blooms.

Metal-organic frameworks and plastic: an emerging synergic partnership

Mismanagement of plastic waste results in its ubiquitous presence in the environment. Despite being durable and persistent materials, plastics are reduced by weathering phenomena into debris with a particle size down to nanometers. The fate and ecotoxicological effects of these solid micropollutants are not fully understood yet, but they are raising increasing concerns for the environment and people's health. Even if different current technologies have the potential to remove plastic particles, the efficiency of these processes is modest, especially for nanoparticles. Metal-organic frameworks (MOFs) are crystalline nano-porous materials with unique properties, have unique properties, such as strong coordination bonds, large and robustus porous structures, high accessible surface areas and adsorption capacity, which make them suitable adsorbent materials for micropollutants. This review examines the preliminary results reported in literature indicating that MOFs are promising adsorbents for the removal of plastic particles from water, especially when MOFs are integrated in porous composite materials or membranes, where they are able to assure high removal efficiency, superior water flux and antifouling properties, even in the presence of other dissolved co-pollutants. Moreover, a recent trend for the alternative preparation of MOFs starting from plastic waste, especially polyethylene terephthalate, as a sustainable source of organic linkers is also reviewed, as it represents a promising route for mitigating the impact of the costs deriving from the widescale MOFs production and application. This connubial between MOFs and plastic has the potential to contribute at implementing a more effective waste management and the circular economy principles in the polymer life cycle.

Mechanochemistry Milling of Waste Poly(Ethylene Terephthalate) into Metal-Organic Frameworks

Converting poly(ethylene terephthalate) (PET) into metal-organic frameworks (MOFs) has emerged as a promising innovation for upcycling of waste plastics. However, previous solvothermal methods suffer from toxic solvent consumption, long reaction time, high pressure, and high temperature. Herein, a mechanochemical milling strategy was reported to transform waste PET into a series of MOFs with high yields. This strategy had the merits of solvent-free conditions, ambient reaction temperature, short running time, and easy scale-up for large-scale production of MOFs. The as-prepared MOFs exhibited definite crystal structure and porous morphology composed of agglomerated nanoparticles. It was proven that, under mechanochemical milling, PET was firstly decomposed into 1,4-benzenedicarboxylate, which acted as linkers to coordinate with metal ions for forming fragments, followed by the gradual arrangement of fragments into MOFs. This work not only promotes high value-added conversion of waste polyesters but also offers a new opportunity to produce MOFs in a green and scalable manner.

Novel magnetic Fe@NSC nanohybrid material for arsenic removal from aqueous media

Polymer-derived carbon nanohybrids present a remarkable potential for the elimination of water pollutants. Herein, an Fe-modified C, N, and S (Fe@NSC) nanohybrid network, synthesized via polymerization of aniline followed by calcination, is used for As removal from aquatic media. The Langmuir isotherm and pseudo-second-order kinetic models fit well the experimental data for the adsorptive removal of As(III) and As(V) by the as-synthesized Fe@NSC nanohybrid, indicating that adsorption is a monolayer chemisorption process. The maximum adsorption capacities of the fabricated Fe@NSC nanohybrid for As(III) and As(V) were 129.54 and 178.65 mg/g, respectively, which are considerably higher than those reported previously for other adsorbents. In particular, the Fe₃O₄/FeS nanoparticles (18.4-38.7 nm) of the prepared Fe@NSC nanohybrid play a critical role in As adsorption and oxidation. Spectroscopy data indicate that the adsorption of As on Fe@NSC nanohybrid involved oxidation, ligand exchange, surface complexation, and electrostatic attraction. Furthermore, the magnetic Fe@NSC nanohybrid was easily separated after As adsorption using an external magnet and did not induce acute toxicity (48 h) in Daphnia magna. Moreover, the Fe@NSC nanohybrid selectively removed As species in the presence of competing anions and was effectively regenerated for up to three cycles using a 0.1 M HNO₃ solution. These findings suggest that Fe@NSC nanohybrid is a promising adsorbent for As remediation in aquatic media.