Plastic Waste Recycling, Applications, and Future Prospects for a Sustainable Environment

: Plastic waste accumulation has been recognized as one of the most critical challenges of modern societies worldwide. Traditional waste management practices include open burning, landﬁll-ing, and incineration, resulting in greenhouse gas emissions and economic loss. In contrast, emerging techniques for plastic waste management include microwave-assisted conversion, plasma-assisted conversion, supercritical water conversion, and photo reforming to obtain high-value products. Problems with poorly managed plastic waste are particularly serious in developing countries. This review article examines the emerging strategies and production of various high-value-added products from plastic waste. Additionally, the uses of plastic waste in different sectors, such as construction, fuel production, wastewater treatment, electrode materials, carbonaceous nanomaterials, and other high-value-added products are reviewed. It has been observed that there is a pressing need to utilize plastic waste for a circular economy and recycling for different value-added products. More speciﬁ-cally, there is limited knowledge on emerging plastic waste conversion mechanisms and efﬁciency. Therefore, this review will help to highlight the negative environmental impacts of plastic waste accumulation and the importance of modern techniques for waste management.


Introduction
Considering stability and flexibility, the plastics are impeccably adequate for use with numerous accomplishments [1][2][3]. Plastics are now the world's third-largest production 1.1. Production, Types, and Characteristics of Plastic Waste Figure 1a shows the global contribution of plastic waste in MSW. However, the organic matter, plastic, glass, paper, metal, and others in MSW are 46%, 10%, 4%, 17%, 5%, and 18%, respectively [36]. Figure 1b shows the trend of waste generated, discarded, recycled, and incinerated from 1950 to the data projections for 2050. Figure 1c shows the distribution of global plastic waste generated (in million tons). Updated data show that since 1950, the global plastics industry has increased at an average annual rate of 2.7 times. In 2018, the global market for plastic products was estimated at 359 million tons [38]. The economic developments of many countries worldwide show that the greater the economic growth, the higher the use of plastic. According to statistics, the average annual plastic consumption in the United States is 170 kg, in Belgium 200 kg, in China 46 kg, and in India just 9.7 kg per capita [39]. The classification of plastic is given in Figure 1d. Thermoplastics, e.g., polyethylene, poly(vinyl chloride), polypropylene, polystyrene, polycarbonate, and poly(tetrafluoroethylene) are hardened when cooled [40]. Thermosetting plastics do not undergo plastic deformations when heated [41]. The available plastic materials are abundant, the output is large, the application is wide, the cost is low, and the molding process is easy [42]. Different types of plastics and their characteristics are given in Table 1. Updated data show that since 1950, the global plastics industry has increased at an average annual rate of 2.7 times. In 2018, the global market for plastic products was estimated at 359 million tons [38]. The economic developments of many countries worldwide show that the greater the economic growth, the higher the use of plastic. According to statistics, the average annual plastic consumption in the United States is 170 kg, in Belgium 200 kg, in China 46 kg, and in India just 9.7 kg per capita [39]. The classification of plastic is given in Figure 1d. Thermoplastics, e.g., polyethylene, poly(vinyl chloride), polypropylene, polystyrene, polycarbonate, and poly(tetrafluoroethylene) are hardened when cooled [40]. Thermosetting plastics do not undergo plastic deformations when heated [41]. The available plastic materials are abundant, the output is large, the application is wide, the cost is low, and the molding process is easy [42]. Different types of plastics and their characteristics are given in Table 1. Updated data show that since 1950, the global plastics industry has increased at an average annual rate of 2.7 times. In 2018, the global market for plastic products was estimated at 359 million tons [38]. The economic developments of many countries worldwide show that the greater the economic growth, the higher the use of plastic. According to statistics, the average annual plastic consumption in the United States is 170 kg, in Belgium 200 kg, in China 46 kg, and in India just 9.7 kg per capita [39]. The classification of plastic is given in Figure 1d. Thermoplastics, e.g., polyethylene, poly(vinyl chloride), polypropylene, polystyrene, polycarbonate, and poly(tetrafluoroethylene) are hardened when cooled [40]. Thermosetting plastics do not undergo plastic deformations when heated [41]. The available plastic materials are abundant, the output is large, the application is wide, the cost is low, and the molding process is easy [42]. Different types of plastics and their characteristics are given in Table 1.

Plastic Waste Degradation and Socioeconomic Impacts
Although the use of plastics brings many benefits, unmanaged manufacturing, utilization, and discarding methods lead to the exhaustion of non-renewable assets, environmental problems, climate change, and a negative impact on the subsistence of flora and fauna [81]. Petroleum-based plastics in 2015, during their life cycle, emitted an equivalent of 1781 Mt CO 2 . If the same trend is sustained, the emissions of petroleum-based plastics are expected to rise to an equivalent of 6500 Mt CO 2 . in 2050 [82]. More specifically, between 1950 and 2015, 79% of plastic waste was reported as poorly managed. This means there are 5 billion tons of plastic waste in landfills or the natural environment. By 2050, the cumulative amount of plastic produced will reach 34 billion tons. According to the current consumption level, plastic waste in landfills or the environment will reach 12 billion tons [14]. Sub-Saharan Africa is one of the regions lacking waste-control resources. Waste produced by 2050 will surge by 300%, which coincides with the expected boom in plastic manufacturing in the region, demonstrating the determination of area [83]. Plastic waste, because of its stability, may be categorized as 'persistent pollutants'. Figure 2 displays the time required for numerous plastic objects to degrade, for instance, the degradation of plastic bottles takes 450 years [84], but microplastics are formed that are ingested by the marine species [85,86] and appear in the form of seafood, salt, and water to us [85]. In oceans, nearly 51 trillion microplastics are floating. These floating microplastics are 500 times more than the stars in our galaxy. Synthetic fabrics, tires, road markings, ship coatings, and plastic particles add microplastics to oceans. Large numbers of animals are entangled in plastics. As per UNESCO statistics [87], more than 1 million birds and more than 0.1 million marine species die each year after ingestion or entanglement of plastic waste. Mato et al. [88] reported that the uptake of hazardous chemicals, i.e., pesticides by plastics, pollute the marine food chain, whereas Tanaka et al. [89] reported high levels of polybrominated diphenyl ethers in 3 of the 12 seabirds analyzed.  Furthermore, humans are worried about the potential impact of consuming marine species containing toxins that are harmful to humans [90], but their impact is still not fully understood [91]. This is worrying, so it is critical to carry out such potential impact assessments. Land animals, including goats, buffaloes, sheep, etc., face similar risks from ingesting plastic, blocking the gastrointestinal tract, and causing death. Chemical substances can escape from such plastics affecting beef and milk. In addition, clogged rainwater drainage systems, parasitic diseases as a breeding ground, indiscriminate fires, and possible respiratory disorders are associated with plastic waste pollution. According to reports, the total annual loss caused by plastic waste is approximately USD 13 billion, including tourism because of lessened aesthetics, recreational actions, and fishing [92]. Figure 3a shows the socioeconomic and environmental impacts of mismanaged plastic waste, and Figure 3b shows sustainable development goals. Furthermore, humans are worried about the potential impact of consuming marine species containing toxins that are harmful to humans [90], but their impact is still not fully understood [91]. This is worrying, so it is critical to carry out such potential impact assessments. Land animals, including goats, buffaloes, sheep, etc., face similar risks from ingesting plastic, blocking the gastrointestinal tract, and causing death. Chemical substances can escape from such plastics affecting beef and milk. In addition, clogged rainwater drainage systems, parasitic diseases as a breeding ground, indiscriminate fires, and possible respiratory disorders are associated with plastic waste pollution. According to reports, the total annual loss caused by plastic waste is approximately USD 13 billion, including tourism because of lessened aesthetics, recreational actions, and fishing [92]. Figure 3a shows the socioeconomic and environmental impacts of mismanaged plastic waste, and Figure 3b shows sustainable development goals.

Plastic Waste Management Strategies
Due to the non-degradable nature and poor waste management practices, a huge quantity of plastic waste has been accumulated in the environment [93,94]. Post-consumer plastic waste is generally managed through landfills, incineration, and recycling [95]. However, these methods have no substantial effects on decreasing the quantity of discarded plastic waste. Therefore, such techniques have nothing to do with practice because landfills and incineration cause serious environmental issues. Innumerable stakeholders have attempted to substitute the current discarded plastic waste control practices. In addition, reusing and recycling plastic waste is more effective than incineration and landfilling [96]. However, because of the increase in the amount of plastic waste generated every day, the current recycling strategies cannot reduce the negative effects of plastic pollution [97]. Therefore, it is necessary to find sustainable applications for plastic waste management to overcome these problems [98]. Figure 4 shows conventional and emerging strategies to overcome plastic waste problems.

Plastic Waste Management Strategies
Due to the non-degradable nature and poor waste management practices, a huge quantity of plastic waste has been accumulated in the environment [93,94]. Post-consumer plastic waste is generally managed through landfills, incineration, and recycling [95]. However, these methods have no substantial effects on decreasing the quantity of discarded plastic waste. Therefore, such techniques have nothing to do with practice because landfills and incineration cause serious environmental issues. Innumerable stakeholders have attempted to substitute the current discarded plastic waste control practices. In addition, reusing and recycling plastic waste is more effective than incineration and landfilling [96]. However, because of the increase in the amount of plastic waste generated every day, the current recycling strategies cannot reduce the negative effects of plastic pollution [97]. Therefore, it is necessary to find sustainable applications for plastic waste management to overcome these problems [98]. Figure 4 shows conventional and emerging strategies to overcome plastic waste problems.

Plastic Waste Landfill
Landfilling is an ancient technique to handle solid waste issues, including plastic waste [100]. As per the OECD statistics, it is assessed that 79% of plastic waste is managed using landfills or leaked into the environment [8]. Plastic landfills are considered the last resort for managing plastic waste, as they require a lot of space and can cause long-term pollution problems [101]. Compared to other waste management practices; the operating costs of plastic waste-based landfill processes can be quite low, but the environmental issues of this technique are regularly questioned. Over time, toxic additives and other possible pollutants decomposing from discarded plastic will eventually contaminate the soil and water bodies [102]. Moreover, it is hard for discarded plastic (which has good physiochemical strength and long service life) to decompose naturally. At the same time, plastic waste is light and can float in the wind or on water [103]. Nevertheless, landfilling has severe disadvantages; discarded plastic, due to its low density, large volume, and large landfill space, has aggravated the scarcity of land resources [104]. The engineered landfill can produce synthesis gas that can be collected and used for energy production.

Incineration
Incineration is extensively applied as one of the treatment approaches used to decrease the volume of solid waste [105]. Incineration can reduce approximately 80% to 90% of different kinds of debris, which is an important advantage [106]. The incineration of plastic waste would emit hazardous emissions and detrimental constituents, including particulate matter, dioxins, CO, furans; metals, and volatile organic chlorides [107]. The incineration process helps to dispose of plastic waste on an industrial scale. Moreover, it produces heat energy used for electricity generation and other accomplishments [108].

Plastic Waste Landfill
Landfilling is an ancient technique to handle solid waste issues, including plastic waste [100]. As per the OECD statistics, it is assessed that 79% of plastic waste is managed using landfills or leaked into the environment [8]. Plastic landfills are considered the last resort for managing plastic waste, as they require a lot of space and can cause long-term pollution problems [101]. Compared to other waste management practices; the operating costs of plastic waste-based landfill processes can be quite low, but the environmental issues of this technique are regularly questioned. Over time, toxic additives and other possible pollutants decomposing from discarded plastic will eventually contaminate the soil and water bodies [102]. Moreover, it is hard for discarded plastic (which has good physiochemical strength and long service life) to decompose naturally. At the same time, plastic waste is light and can float in the wind or on water [103]. Nevertheless, landfilling has severe disadvantages; discarded plastic, due to its low density, large volume, and large landfill space, has aggravated the scarcity of land resources [104]. The engineered landfill can produce synthesis gas that can be collected and used for energy production.

Incineration
Incineration is extensively applied as one of the treatment approaches used to decrease the volume of solid waste [105]. Incineration can reduce approximately 80% to 90% of different kinds of debris, which is an important advantage [106]. The incineration of plastic waste would emit hazardous emissions and detrimental constituents, including particulate matter, dioxins, CO, furans; metals, and volatile organic chlorides [107]. The incineration process helps to dispose of plastic waste on an industrial scale. Moreover, it produces heat energy used for electricity generation and other accomplishments [108]. Incineration of waste with a high moisture content of 60% to 65% is not feasible because it will affect the rate of energy production during incineration [109].

Pyrolysis
In pyrolysis, plastic waste is broken down into carbon monoxide, hydrogen, methane, and high-quality hydrocarbons, which can be used as fuel. Ruj et al. [110] established a process of directly converting mixed discarded plastic, except PVC, into synthesis gas, which is utilized to generate electricity. Huang et al. [111] and colleagues showed that, through accelerated decomposition, plasma pyrolysis reacted completely to the low molecular weight compound methane. The advantage of pyrolysis is that it has the ability to 'carry out' dirty and unsorted plastic waste. Pyrolysis is also non-toxic and has non-environmentally harmful emissions, unlike incineration. The disadvantages of pyrolysis are the lack of product control and low energy efficiency.

Gasification
Plastic waste is degraded by using gasification technology, such as air, steam, and oxygen to generate synthesis gas mainly comprising CO, H 2 , and CH 4 [112]. The most frequently used technologies for plastic waste gasification are fixed beds, fluidized beds, and entrained flow gasifiers [113]. The combustion of discarded plastic produces hazardous gases, i.e., carbon dioxide, nitrogen oxide, sulfur oxide, and hydrocarbons [114]. Therefore, syngas produced through gasification is environmentally friendly compared to combustion [115]. The disadvantage of gasification involves air being used as a gasifying agent resulting in a decrease in the calorific value of produced syngas.

Mechanical Reprocessing
The primary recycling method for plastic waste is mechanical reprocessing, which comprises heating, shredding, and remolding [116]. This method of mechanical treatment of plastic waste mainly produces plastics with inferior properties [19]. The number of mechanical reprocessing cycles is limited. Thermal conversion processes, such as gasification and pyrolysis, are commonly used to produce low-value-added products, including syngas and other carbonaceous derivatives [117]. Moreover, in thermochemical conversion processes, high temperatures of 400 • C to 900 • C are maintained to overcome the unfavorable kinetics and thermodynamics of these reactions [117]. The advantages of mechanical reprocessing are that it is less energy intensive and does not use toxic chemicals. The disadvantage is that mechanical reprocessing often decreases the tensile strength of plastics.

Biochemical Conversion
Synthetic polymers having high molecular weights are biodegraded using microorganisms. However, the application of such microorganisms for biodegrading high molecular weight synthetic polymers is limited commercially [118,119]. The microorganisms interact with abiotic elements, particularly light and heat, to alter polymer structures and provide a favorable environment for enzymatic degradation [120]. The bacteria mainly involve the biodegradation of plastic waste, algae fungi found in compost, landfill leachate, and sewage sludge. The bacteria are capable of biodegrading synthetic and natural polymers. Microbial biomass is a waste product of biodegradation [121]. Biochemical conversion of plastic has the advantage of low processing temperatures and high selectivity of products produced. However, they usually require preprocessing phases and long treating times.
The pyrolysis and gasification of plastic waste are most suited for plastic waste conversion into valuable products. Furthermore, these methods are environment-friendly and do not require large spaces for plant installation.

Microwave-Assisted Conversion
Compared to conventional strategies of plastic waste management, microwave-assisted conversion provides an efficient route for recycling plastic waste [122]. Microwave-assisted recycling of plastic waste accelerates the chemical reactions by reducing the reaction temperature and time, thus acquiring higher chemo-selectivity and production [123]. Furthermore, water as a reaction medium absorbs microwave energy efficiently and can be superheated. Microwave irradiation depolymerized biopolymers, including starch and cellulose, are rapid, efficient, and environmentally friendly [122]. Microwave-assisted conversion provides a circular economy because it produces chemicals used as property enhancers in polymers [124]. Microwave-assisted conversion has some advantages, such as non-contact volumetric heating and higher energy efficiency. The disadvantages are the electrical power and required microwave adsorbents.

Plasma Assisted Conversion
Polystyrene (under atmospheric pressure and ambient temperature) is efficiently hydrogenated using nonthermal plasma-assisted conversion [125]. Plasma-assisted nonthermal H 2 offers a unique source for obtaining a relative hydrogen species, particularly in radicals and ions that effectively break the C-C bond in the polymer structure. Furthermore, the plasma-assisted non-isothermal hydrogenolysis procedure directly valorizes products, excluding pretreatment importance, allowing minimum influence by impurities and contaminants [126]. Plasma-assisted conversion has some advantages, such as a higher yield of syngas and lower tar content. The limitation involves higher energy utilization during the plasma-assisted conversion process.

Supercritical Water Conversion
Traditional plastic waste management strategies cannot produce clean energy [127]. Therefore, supercritical water conversion technology produces efficient and clean energy from plastic waste. Different studies have been conducted to investigate the effect of supercritical water on plastic waste recycling [128]. Bai et al. [129] investigated the pyrolysis behavior of low-density polyethylene and heavy oil using supercritical water at a temperature of 420 • C and observed that HDPE as an H-donor tremendously inhibited the aromatic component condensation and coke formation. High H 2 , low CO yields, a high reaction rate, and low tar and char formation are the advantages of this method. This method shows drawbacks for large-scale feasibility and might cause the plugging of reactors during long runs.

Photo Reforming
Researchers have extensively investigated photocatalytic reforming of plastic waste because of its high efficiency and environmentally friendly behavior [130]. Photo-reforming of plastic waste is a promising technology among various plastic waste management techniques, having the potential to harvest solar energy [131]. After harvesting solar energy, it is efficiently converted into high-energy-density hydrogen fuel. The promising solution to the energy crisis involves the photo-reforming of plastic waste because hydrogen is an ideal gas possessing a high energy value and zero environmental emissions [132]. A pretreatment method of plastic waste is commonly applied to enhance the reactivity of plastic photo-reforming to hydrolyze plastic into monomeric ethylene glycol. Moreover, numerous photocatalysts are synthesized for plastic photo-improving to produce hydrogen, including CN/Ni 2 P and TiO 2 /Pt [132,133].

Compatibilization
Additives allow two polymer resins to bond to improve the final product in compatibilization. Adding additives in plastic recycling facilitates the adherence of plastic blends that are difficult to mix with or adhere to. The plastic materials that are not easily recycled include composite plastics, flexible packaging, and other plastic materials best suited for chemical recycling through compatibilizers. There are high costs associated with the reactions that involve long residence times. Furthermore, such resins may be used as secondary raw material in another product, mitigating dependence on crude oil.

Polymer Design and Modification
In recent years, chemically recyclable polymers have been designed and developed to manage plastic waste at the end of its useable life. The mechanical reprocess degrades polymer quality and results in residual impurities after multiple reuse cycles [134]. Nevertheless, via depolymerization, chemical recycling can recover the precursor building blocks. The polymers that can easily be converted into monomers require low temperature (e.g., −40 • C) polymerization and are not suited for practical use. Moreover, chemically recyclable polymers suffer poor performance and are not extensively used as many virgin polymers. The recyclable liquid crystalline polymer composite was developed by Kort et al. [135] that can be recycled several times without a decrease in the mechanical properties by maintaining the molecular weight of the polymer. Although, the polymer design and modification are not used extensively because of the poor performance as compared to virgin plastic.

Application of Plastic Waste in Construction
Currently, the application of discarded plastic in construction is considered one of the emerging concepts for managing large amounts of plastic waste and reducing environmental risks. The use of plastic waste is becoming one of the most stimulating processes in construction and has been extensively investigated in the last few years [136,137]. The application of discarded plastic in civil construction reduces the intake of natural aggregates. Many scientists have worked on the possibility of using various types of plastic waste for construction activities [138]. Much research has been conducted on multiple applications, such as masonry [139,140], pavement [141], and aggregate replacement in concrete [142,143]. Several investigations have previously been performed to evaluate the characteristics of discarded plastic as a fine and coarse aggregate.
Most plastic waste from previous research was refined into small particles to obtain a suitable size [144]. Then small plastic particles were added to various building activities including bricks, mortar, pavement, concrete, and others. Coppola et al. [145] showed that 10% and 25% of mortar comprising plastic aggregate could achieve tensile strengths of 35.12 and 22.86 MPa, respectively, which passed the American Concrete Institute's buildings standards (17.25 MPa). It is eminent that several patents have been approved for the use of discarded plastic as a composite material. Despite the proliferation of research, the making and use of discarded plastic as a manufacturing material is limited. The discarded plastic treatment industry has not yet developed, and most plastic waste products are used on a small-scale [146]. Figure 5 shows the schematic of plastic waste applications in construction activities.
Since construction materials are made from plastic waste, various environmental problems significantly impact the successful implementation. According to Zhang et al. [147], plastic trash can release small pollutants, negatively affecting the public and industry. Research studies on plastic waste applications in different construction activities are given in Table 2. Since construction materials are made from plastic waste, various environmental problems significantly impact the successful implementation. According to Zhang et al. [147], plastic trash can release small pollutants, negatively affecting the public and industry. Research studies on plastic waste applications in different construction activities are given in Table 2.

Types of Composites Types of Replacement Types of Plastic Percentage of Replacement (%) Reference
Concrete Fine

Application of Plastic Waste as an Electrode Material
Microbial fuel cell (MFC) is an emerging technique used for sustainably obtaining bioelectricity from the treatment of organic waste [207,208]. This method uses microorganisms and organic debris as raw materials and biocatalysts to generate bioelectricity. In recent years, numerous researchers have worked on improving MFC performance. In this regard, advanced conductive electrode materials have been introduced as anodes and cathodes to reduce MFC construction and operation costs [209]. Table 3 compares the bio-electrochemical system's different electrode materials derived from plastic waste. The electrodes based on Fe-t-MOF and PANI composite materials in MFC applications require more investigation. The high-efficiency MOF-based electrode catalytic performance provides new insight into the field of MFC electrodes. The PANI-based composite material improves the prepared electrode material conductivity and is cheaper than the platinumbased electrode. The diagram of converting plastic waste into electrode materials is shown in Figure 6.

Application of Plastic Waste in the Formation of Carbonaceous Nanomaterials
The beneficial impacts on the ecological system have made the recycling of plastic waste a captivating issue in the scientific world. Chaudhary et al. [219] highlighted the sustainable approach of transforming plastic waste comprising bottles, used cups, and polyethylene bags via simple heating to fluorescent carbon dots (C-dots). The obtained Cdots displayed absorption peaks at around 260 nm with sizes of 5-30 nm. Recycling has produced structural changes in plastic waste and affected the optical properties of C-dots. The toxicity profiling of C-dots has been successfully tested by employing multi-assay biocompatible activities, i.e., antibacterial and antifungal activities. The potential prospective of C-dots derived from plastic waste has been explored in analytical applications involving selective copper metal ion sensing in aqueous media. Chaudhary et al. [219] highlighted the potential accomplishment in preserving the environmental fate and responding to the budding social hitch of plastic waste. The conversion of plastic debris in forming different types of carbonaceous nanomaterials is depicted in Figure 7.

Application of Plastic Waste in the Formation of Carbonaceous Nanomaterials
The beneficial impacts on the ecological system have made the recycling of plastic waste a captivating issue in the scientific world. Chaudhary et al. [219] highlighted the sustainable approach of transforming plastic waste comprising bottles, used cups, and polyethylene bags via simple heating to fluorescent carbon dots (C-dots). The obtained C-dots displayed absorption peaks at around 260 nm with sizes of 5-30 nm. Recycling has produced structural changes in plastic waste and affected the optical properties of C-dots. The toxicity profiling of C-dots has been successfully tested by employing multi-assay biocompatible activities, i.e., antibacterial and antifungal activities. The potential prospective of C-dots derived from plastic waste has been explored in analytical applications involving selective copper metal ion sensing in aqueous media. Chaudhary et al. [219] highlighted the potential accomplishment in preserving the environmental fate and responding to the budding social hitch of plastic waste. The conversion of plastic debris in forming different types of carbonaceous nanomaterials is depicted in Figure 7.
waste a captivating issue in the scientific world. Chaudhary et al. [219] highlighted the sustainable approach of transforming plastic waste comprising bottles, used cups, and polyethylene bags via simple heating to fluorescent carbon dots (C-dots). The obtained Cdots displayed absorption peaks at around 260 nm with sizes of 5-30 nm. Recycling has produced structural changes in plastic waste and affected the optical properties of C-dots. The toxicity profiling of C-dots has been successfully tested by employing multi-assay biocompatible activities, i.e., antibacterial and antifungal activities. The potential prospective of C-dots derived from plastic waste has been explored in analytical applications involving selective copper metal ion sensing in aqueous media. Chaudhary et al. [219] highlighted the potential accomplishment in preserving the environmental fate and responding to the budding social hitch of plastic waste. The conversion of plastic debris in forming different types of carbonaceous nanomaterials is depicted in Figure 7.

Application of Plastic Waste in Fuel Production
Single-use plastic bags, disposable food containers, food wrap films, and their main components of polyethylene, polypropylene, and poly(vinyl chloride) can be photocatalytically transformed into valuable fuels without using sacrificial agents. Jiao et al. [221] described that plastic wastes could be converted into C 2 fuels over a photocatalyst under simulated natural environment conditions. Plastic waste was degraded into CO 2 by a photooxidative C-C bond cleavage; then the produced CO 2 was reduced into valuable C 2 fuels by a photoinduced C-C bond coupling. Szarka et al. [222,223] noted that PVC could be converted into oily products by a simple (and relatively low temperature) thermo-oxidative process. Figure 8 shows the schematic diagram of converting plastic waste into C2 fuel production via the photocatalytic process. Liu et al. [224] reported a direct method to selectively convert polyolefins to branched, liquid fuels, including diesel, jet, and gasoline-range hydrocarbons over nanomaterials in hydrogen. The process proceeds via tandem catalysis with the initial activation of the polymer, then subsequent cracking. Transforming plastic waste into fuel may help address the white pollution crisis and harvest highly valuable multi-carbon fuels.

Application of Plastic Waste in Wastewater Treatment
Plastic waste materials can be used to synthesize membranes and carbon-based adsorbent materials for wastewater treatment and reclamation. Adamczak et al. [225] synthesized an ultrafiltration membrane from polystyrene waste material. The synthesized membrane was used to treat river surface water. The polystyrene waste ultrafiltration membrane was tested with different concentrations of waste polymer to determine the membrane with the most favorable properties. Kumari et al. [226] converted solid waste plastic into activated carbon nanofibers through chemical activation and carbonization processes. The synthesized activated carbon nanofibers treated the thymol blue dye in wastewater via adsorption. These applications offered a great avenue for recycling plastic waste regardless of modifications or technical works to fulfill the important objective of water and wastew-ater treatment [227,228]. Fabrication of activated carbon materials from plastic waste for wastewater treatment is shown in Figure 9.
tooxidative C-C bond cleavage; then the produced CO2 was reduced into valuable C2 fuels by a photoinduced C-C bond coupling. Szarka et al. [222,223] noted that PVC could be converted into oily products by a simple (and relatively low temperature) thermo-oxidative process. Figure 8 shows the schematic diagram of converting plastic waste into C2 fuel production via the photocatalytic process. Liu et al. [224] reported a direct method to selectively convert polyolefins to branched, liquid fuels, including diesel, jet, and gasoline-range hydrocarbons over nanomaterials in hydrogen. The process proceeds via tandem catalysis with the initial activation of the polymer, then subsequent cracking. Transforming plastic waste into fuel may help address the white pollution crisis and harvest highly valuable multi-carbon fuels. Figure 8. The schematic diagram for converting plastic wastes into valuable fuel production. Reprinted with permission from Reference [99]. Copyright 2022 Elsevier.

Application of Plastic Waste in Wastewater Treatment
Plastic waste materials can be used to synthesize membranes and carbon-based adsorbent materials for wastewater treatment and reclamation. Adamczak et al. [225] synthesized an ultrafiltration membrane from polystyrene waste material. The synthesized membrane was used to treat river surface water. The polystyrene waste ultrafiltration membrane was tested with different concentrations of waste polymer to determine the membrane with the most favorable properties. Kumari et al. [226] converted solid waste plastic into activated carbon nanofibers through chemical activation and carbonization processes. The synthesized activated carbon nanofibers treated the thymol blue dye in wastewater via adsorption. These applications offered a great avenue for recycling plastic waste regardless of modifications or technical works to fulfill the important objective of water and wastewater treatment [227,228]. Fabrication of activated carbon materials from plastic waste for wastewater treatment is shown in Figure 9.  Figure 10 shows plastic waste conversion into valuable textile products [229]. Recently, the Anta group had a breakthrough; overcoming many technical barriers, they developed a proficient method for producing polyester fiber from plastic bottles. The waste plastic bottles of 1 L and 550 mL were recycled using single energy technology clothing and resulted in a 30-50% reduction in overall processing costs compared to international brands. In China, carpet making by using waste plastic is well developed. A Shandongbased carpet manufacturing company has recycled around 2.6 billion waste plastic bottles  Figure 10 shows plastic waste conversion into valuable textile products [229]. Recently, the Anta group had a breakthrough; overcoming many technical barriers, they developed a proficient method for producing polyester fiber from plastic bottles. The waste plastic bottles of 1 L and 550 mL were recycled using single energy technology clothing and resulted in a 30-50% reduction in overall processing costs compared to international brands. In China, carpet making by using waste plastic is well developed. A Shandong-based carpet manufacturing company has recycled around 2.6 billion waste plastic bottles to make 6 million blankets. Recycling plastic bottles not only reduces pollution but also comes with economic benefits. Another example is the red carpet used in China's military parade in 2019; it was spectacular, environmentally friendly, and prepared with 400,000 waste plastic bottles. The better functional properties observed in textiles and carpets produced by this technology are abrasion resistance, better elasticity, mildew, and insect resistance compared to animal and plant fibers [230].

Application of Plastic Waste in Other High-Value-Added Products
Biological valorization can be used to recycle plastic waste and develop effective plastic waste recycling strategies. Kim et al. [232] evaluated the feasibility of the valorization of plastic waste for its recycling. For biological plastic waste valorization, plastic debris was depolymerized by chemical hydrolysis, and terephthalic acid and ethylene glycol monomers were converted to a variety of higher-value chemicals using various metabolically engineered whole-cell microbial catalysts. By introducing a terephthalic acid degradation pathway into microbes, terephthalic acid was converted into high-value-added aromatic or aromatic derived chemicals, namely, protocatechuic acid, gallic acid, pyrogallol, catechol, muconic acid, and vanillic acid, to be used for manufacturing pharmaceuticals, cosmetics, sanitizers, animal feeds, and bioplastic monomers, as shown in Figure 11. Watson et al., 2020, reported that 50-75% of synthetic textiles collected in Europe had been recycled or reused in other value-added textile products. Most non-reusable synthetic materials have been landfilled or incinerated [231]. PET is the most common fiber for sportswear, but acrylic, elastane, nylon, and propylene are also used. Fiber blends and functional coatings are commonly used in textiles for specific applications, such as footwear, which is comfortable, resistant to extreme weather, and fashionable. In sportswear textiles, moisture regulation and temperature are important characteristics to assure adequate thermal insulation while releasing body heat and sweat during exercise. A textile in sportswear also requires stretch ability for free movement and coatings for reduced wear and tear or injuries.

Application of Plastic Waste in Other High-Value-Added Products
Biological valorization can be used to recycle plastic waste and develop effective plastic waste recycling strategies. Kim et al. [232] evaluated the feasibility of the valorization of plastic waste for its recycling. For biological plastic waste valorization, plastic debris was depolymerized by chemical hydrolysis, and terephthalic acid and ethylene glycol monomers were converted to a variety of higher-value chemicals using various metabolically engineered whole-cell microbial catalysts. By introducing a terephthalic acid degradation pathway into microbes, terephthalic acid was converted into high-value-added aromatic or aromatic derived chemicals, namely, protocatechuic acid, gallic acid, pyrogallol, catechol, muconic acid, and vanillic acid, to be used for manufacturing pharmaceuticals, cosmetics, sanitizers, animal feeds, and bioplastic monomers, as shown in Figure 11.
Biological valorization can be used to recycle plastic waste and develop effective plastic waste recycling strategies. Kim et al. [232] evaluated the feasibility of the valorization of plastic waste for its recycling. For biological plastic waste valorization, plastic debris was depolymerized by chemical hydrolysis, and terephthalic acid and ethylene glycol monomers were converted to a variety of higher-value chemicals using various metabolically engineered whole-cell microbial catalysts. By introducing a terephthalic acid degradation pathway into microbes, terephthalic acid was converted into high-value-added aromatic or aromatic derived chemicals, namely, protocatechuic acid, gallic acid, pyrogallol, catechol, muconic acid, and vanillic acid, to be used for manufacturing pharmaceuticals, cosmetics, sanitizers, animal feeds, and bioplastic monomers, as shown in Figure 11. Figure 11. Schematic diagram of plastic waste recycling into high-value-added products. Reprinted with permission from Reference [99]. Copyright 2022 Elsevier.

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Human activities pose ecological consequences and the increasing demand for resources and energy has resulted in a significant perspective on plastic waste management. The government and other related stakeholders should attain proper sustainable waste management strategies to maintain environmental sustainability.

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From the perspective of plastic waste recycling, most current studies focus on PET.
Research should be expanded to other types of plastic waste (such as PP, PS, PVC, etc.) to minimize the burden on the environment.

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The government and responsible agencies should set regulations that will promote the further use of recycled plastic waste for construction purposes. • Current plastic waste technologies for the conversion of plastic waste into textile products are not mature. Further research may be carried out to overcome the technical issues associated with this technology. • Awareness sessions may be conducted in educational institutions and public places for the importance of plastic waste management and environmental sustainability. • Innovation is an integrated approach used to achieve meaningful improvement and highlight the issues and challenges of fossil-based plastics.

Conclusions
Over the years, humans have massively deteriorated Earth's natural ecosystems, i.e., due to the high rate of synthetic plastic production/consumption, which is being discarded in the open environment without proper handling. A landfill is currently one of the main methods used for plastic waste management; however, its real-world application is extremely inefficient and inadequate. Recycling is another important method for handling plastic waste. The most effective plastic treatment method is to convert plastic waste into high-value-added components, such as tiles, paver blocks, concrete, sanitizers, perfumes, graphene, electrode materials, carbon nanotubes, etc. It has been determined that plastic is an unavoidable part of our lives, and its demand is increasing. Due to poor waste management practices, the current usage of plastic is unsustainable. Society faces a serious threat of plastic waste pollution that is being underestimated. We must decrease the amount of plastic waste dispersed on roads and rivers; construction materials established from recycled plastic waste are more durable and cost-effective. Appropriate handling of plastic waste provides a platform for creating wealth. Contact with toxic chemicals utilized during plastic production and improper waste control can pose serious problems to humans and the environment. Therefore, governments, regulatory bodies, and health administrations worldwide must take action, and consider the sustainable manufacturing, applications, and disposal of plastic waste.

Conflicts of Interest:
The authors declare no conflict of interest.