Solar-driven plastic waste conversion: A mini-review on photoreforming for Co-producing hydrogen and chemical feedstocks

Abstract

The increasing accumulation of discarded plastics has already caused serious environmental pollution. Simple landfills and incineration will inevitably lead to the loss of the abundant carbon resources contained in plastic waste. In contrast, photoconversion technology provides a green and sustainable solution to the global plastic waste crisis by converting plastics into hydrogen fuel and valuable chemicals. This review briefly introduces the advantages of photoconversion technology and highlights recent research progress, with a focus on photocatalyst design as well as the thermodynamics and kinetics of the reaction process. It discusses in detail the degradation of typical common plastic types into hydrogen and fine chemicals via photoconversion. Additionally, it outlines future research directions, including the application of artificial intelligence in catalyst design. Although photocatalytic technology remains at the laboratory stage, with challenges in catalyst performance and industrial scalability, the potential for renewable energy generation and plastic valorization is promising.

Graphical abstract

Keywords

photoreforming / waste plastics / hydrogen production / chemical feedstock / photocatalysts

1 Introduction

Plastics like polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polylactic acid (PLA), polyethylene terephthalate (PET), and polyurethane (PUR) are among the most widespread and commonly encountered synthetic materials in daily life [1–5]. Their applications range from everyday shopping bags to circuit boards in electronic products. Since the 1950s, plastics have been produced on an industrial scale in vast quantities [6]. Global plastic production is projected to an astonishing 20 billion tons by 2040 [7]. However, the extensive use of plastics presents significant challenges in terms of recovery and disposal [8]. Figure 1 lists common plastic types and their typical products [9]. Alarmingly, only a small fraction of plastic waste is recycled, while approximately 80% ends up in landfills or is released into the natural environment, where decomposition can take centuries [10–14]. Therefore, developing green and efficient technologies for valorization of plastic waste is essential to mitigate environmental pollution.

Traditional plastic waste management approaches, such as incineration, landfill disposal, and mechanical recycling, remain prevalent owing to their operational simplicity and cost-effectiveness in current industrial practices [15–19]. However, these approaches suffer from various limitations [7,20]. Compared to virgin polymers, recycled plastics often have reduced value, adverse environmental impacts, and inferior properties. Specifically, these approaches may reduce material value, cause environmental pollution, and result in lower-quality products [21]. In contrast, catalytic upcycling has recently attracted considerable research interest [22–24], offering pathways to convert plastic waste into valuable chemicals, fuels, and other useful functional materials [25].

Photoreforming is a technology that utilizes light energy to drive catalytic reactions for converting organic waste into hydrogen and other high-value-added chemicals. Compared to pyrolysis, plastic photoreforming is considered a potentially sustainable process for treating plastic waste [26–33]. This environmentally friendly process not only transforms plastic waste into valuable chemical products but also facilitates off-grid solar energy storage in the form of renewable fuels [34–36]. Utilizing water as a solvent and solar light as the energy source, this method produces hydrogen through water splitting at ambient temperature and pressure [37–40]. Simultaneously, it breaks down plastic waste into useful chemical intermediates with potential industrial applications [41–43].

In the context of plastic photoreforming, conversion processes can be categorized into two main types: degradation and upcycling, which differ significantly in purpose, mechanism, and outcome. Degradation refers to the breakdown of plastics into smaller molecules or compounds, primarily to mitigate environmental impact, though it usually does not yield high-value-added products. Upcycling, by contrast, involves converting plastic waste into higher-value-added products, thereby reducing environmental harm while efficiently utilizing resources. This approach enables the transformation of plastics into useful chemicals or fuels, providing a novel solution for the sustainable management of plastic waste. The photoreforming technologies discussed in this review are mainly focused on upcycling.

This review aims to provide an overview of recent advances and challenges in the field of plastic photoreforming. First, current plastic treatment technologies are introduced. Next, the fundamental principles underlying the coupling plastic photoreforming with hydrogen evolution are emphasized. Common plastic pretreatment methods employed prior to photoreforming are also examined.

Recent advances in the design and characterization of photocatalysts specifically tailored for photoreforming is then summarized. Finally, existing challenges are outlines and an outlook on future development pathways for photoreforming plastic waste is presented.

2 Current plastic treatment technologies

Various technologies for the plastic waste treatment have been developed, including landfill, incineration, mechanical recycling, pyrolysis, and photoreforming (Fig. 1). Among these, landfill and incineration remain the most widely used conventional methods, primarily due to their operational simplicity, cost-effectiveness, and capacity to handle diverse types of plastic waste at a large scale [15,21,44]. However, these methods offer limited environmental benefits and have adverse environmental impacts. Landfilled plastics can leach harmful substances into groundwater and soil, while incineration emits toxic compounds and greenhouse gases, contributing to air pollution.

Mechanical recycling, a commonly used downcycling method, involves physical procedures such as milling, extrusion, blending, and granulation, while preserving the original chemical composition of the plastic [45]. Nevertheless, repeated recycling leads to a deterioration in the structural and mechanical properties of the material, often resulting in products of reduced value [46]. As a result, mechanical recycling is primarily suitable for non-contaminating, single-component plastics.

As an upcycling method, pyrolysis involves the thermal decomposition of long-chain organic materials (plastics) in an inert atmosphere and can be performed with or without catalysts, the latter known as catalytic pyrolysis [57–59]. This process is notable for its efficiency and stability in rapidly breaking carbon–carbon bonds, resulting in the production of valuable chemicals. However, pyrolysis is associated with certain drawbacks, particularly the requirement for high temperatures and significant energy input.

Photocatalytic conversion, often referred to as photoreforming, is a promising and sustainable alternative for handling plastic waste [60–62]. This method selectively breaks down and transforms plastics into valuable chemical products by harnessing solar energy, offering a significant advancement over traditional photodegradation methods [63]. Table 1 compares the energy inputs of pyrolysis and photoconversion to give a clearer picture of the differences between the two methods.

3 From photocatalytic water splitting to plastic photoreforming

Since the 1970s, photocatalytic water splitting for hydrogen production has been a major focus of intensive research [64]. However, the inherent thermodynamic stability of water poses a significant challenge, making it difficult to decompose water into hydrogen and oxygen via photocatalytic processes. The proton reduction and water oxidation steps in photocatalytic water splitting require energy inputs that exceed the Gibbs free energy change of + 237 kJ/mol, as well as the thermodynamic barrier (ΔE⁰) of 1.23 eV for the oxygen evolution reaction (Fig. 2(a)) [35,65]. To address this issue, sacrificial electron donors, often costly and environmentally harmful, are frequently employed.

In comparison, plastic photoreforming for hydrogen production requires substantially less energy. The oxidation of plastics proceeds more directly and rapidly than that of water. Moreover, the oxidation reactions of plastics not only exhibit thermodynamic advantage (ΔG⁰ < + 237 kJ/mol), but also generally encounter fewer kinetic limitations (ΔE⁰ < 0 eV, Fig. 2(b)). For instance, the photoreforming of ethylene glycol (ΔG⁰ = + 9.2 kJ/mol), a constituent monomer of PET plastics, demonstrates greater thermodynamic feasibility than conventional water splitting systems [66]. Furthermore, the rapid hole scavenging associated with plastic oxidation effectively minimizes charge recombination in the photocatalyst, thereby promoting the hydrogen evolution reaction.

Overall, plastic photoreforming offers the opportunity to simultaneously produce hydrogen fuel and address the urgent issue of plastic waste.

3.1 Photoreforming reaction mechanism

Photoreforming is a process that integrates photocatalytic water splitting (Fig. 2(c)) with organic photoredox catalysis. The underlying mechanism of photoreforming plastic waste resembles that of traditional photocatalytic hydrogen production, which typically utilizes organic sacrificial agents [9]. In general, when a photocatalyst is illuminated with light of energy equal to or greater than its band gap energy (E_g), electrons (e⁻) are excited from the valence band (VB) to the conduction band (CB), leaving behind corresponding holes (h⁺). These photogenerated charge carriers then migrate to the surface of the photocatalyst, where redox reactions take place. The electrons (e⁻) at the reduction sites facilitate the reduction of protons (H⁺) to hydrogen (H₂), while the holes (h⁺) at the oxidation sites oxidize water (H₂O) to oxygen (O₂). Co-catalyst are often employed to suppress charge recombination and improve charge separation efficiency.

However, in plastic photoreforming, the process typically occurs under anaerobic conditions, where plastics serve as sacrificial electron donors. he photogenerated oxidize these polymers to yield valuable chemical products, while the photoexcited electrons reduce protons (H⁺) to generate hydrogen (Fig. 2(d)). Thermodynamically, the CB of the photocatalyst must be more negative than the reduction potential for proton-to-hydrogen conversion, and its VB must be more positive than the oxidation potential of polymeric substrates. Under illumination, the electrons in the CB reduce adsorbed protons to H₂, while the photogenerated holes in the VB oxidize the plastic either via direct charge transfer or through the generation of reactive oxygen species, such as hydroxyl radicals (•OH).

Plastic photoreforming offers both thermodynamic and kinetic advantages over conventional photocatalytic water splitting. Thermodynamically, water decomposition involves breaking strong O–H bonds to produce hydrogen and oxygen. This demanding process makes water decomposition thermodynamically unfavorable and requires a large amount of energy input to overcome free-energy barriers. In contrast, photoreforming targets the C−C and C−H bonds in plastics, which are more easily cleaved by reactive oxygen species (ROS) produced during the photocatalytic process. The resulting small organic molecules are more easily formed than molecular oxygen, thus lowering the overall thermodynamic threshold of the reaction.

Kinetically, the main bottleneck of water splitting lies in the water oxidation self-reaction, which has a high activation energy and proceeds slowly. Photoreforming overcomes this bottleneck through the use of ROS that efficiently break down C−C and C−H bonds, thus accelerating the overall reaction. Moreover, optimization of the energy band structure and active sites of the photocatalyst can further reduce activation energy and enhance reaction rates [9,38].

3.2 Pretreatment of plastics

The inherent insolubility and chemical inertness of plastics pose major challenges to efficient plastic photoreforming reactions [26]. As a result, pretreatment is often essential to enhance the interaction between photocatalysts and the plastic substrates to increase photoforming efficiency [67]. Common pretreatment methods are mainly classified into three main categories: physical, chemical, and biological methods (Fig. 3) [42].

Physical methods, such as mechanical chipping, grinding, or milling, are employed to reduce the polymerization degree or crystallinity of plastics. These processes increase the specific surface area and improve the solubility of plastic material, thereby facilitating the generation of monomeric subunits. This improved physical accessibility aids in achieving higher selectivity and reactivity in photoreforming.

Given the monomers or oligomers derived from plastic depolymerization are more amenable to photoreforming, chemical methods such as hydrolysis, alcoholysis, and ammonolysis are commonly applied to depolymerize to depolymerize plastic waste [68–70]. Among these, hydrolysis, particularly acid or alkaline hydrolysis, is the most commonly method. This approach involves breaking the chemical bonds between monomer units to enable subsequent photocatalytic conversion. Solutions of sodium hydroxide, potassium hydroxide, or nitric acid (typically 5 to 10 M) are often utilized to disintegrate plastic into smaller molecular compounds. For instance, alkaline hydrolysis using KOH was employed to pretreat PET and PUR in photoreforming studies by Riesner’s group. Higher alkaline concentrations accelerate polymers decomposition, thus enhancing photoreforming efficiency. However, excessive alkalinity can negatively impact catalyst stability and reduce overall conversion efficiency due to catalyst corrosion. Additionally, extreme alkaline conditions may trigger side reactions, such as aldol condensation, leading to uncertainty in the outcome of the final product.

Biological pretreatment methods, such as microbial or enzymatic hydrolysis, offer a more environmentally friendly alternative. For instance, Taniguchi et al. [71] demonstrated the depolymerization of PET into monomers using PET hydrolase from Ideonella sakaiensis under ambient conditions. These enzymatic approaches target plastics with C−C and C−O bonds [38]. Moreover, the high selectivity of enzymatic reactions enables plastics to be precisely converted into specific components, which can serve as platform molecules for the subsequent photoreforming reactions and further be upgraded to produce high-value fuels or chemicals. For instance, Bhattacharjee et al. [72] presented a chemoenzymatic photoreforming strategy, integrating DuraPETase (Dura) pretreatment with the photoreforming of polyester plastics, achieving clean hydrogen production and high-value chemicals at mild temperatures.

Biological pretreatment is usually conducted under mild conditions, which preserve enzyme activity and enable the efficient breakdown of plastics into monomers or oligomers. Enzymes are highly influenced by the environment and the efficiency of the treatment varies depending on the type of plastic and the choice of enzyme. Biological pretreatment methods are environmentally friendly and the enzymes are reusable, making them ideal for large-scale applications, but the high cost of enzymes and the specific conditions required for the reaction greatly limit the economics of large-scale applications. In contrast, chemical pretreatment has a shorter reaction time and is well-suited for industrial-scale processing, though it may require corrosive reagents and harsh conditions, resulting in high energy consumption, side-product formation, and environmental burdens.

Physical pretreatment is advantageous for bulk treatment but often require additional subsequent processing to achieve complete plastic degradation. Although straightforward and scalable, these methods generally demand energy-intensive equipment.

Each pretreatment method presents distinct advantages and limitations. The selection of an appropriate strategy depends on factors such as plastic type, desired treatment outcome, and application context. Future research may benefit from hybrid pretreatment schemes, for example, combining biological and chemical methods, to enhance overall efficiency and sustainability [69,72,73].

The selectivity of the pretreatment method significantly influences the downstream photocatalytic conversion. Highly selective methods, such as enzymatic pretreatment, yield defined intermediates and reduce by-product formation, thus improving photoreforming efficiency and product quality. In contrast, non-selective chemical methods (e.g., acid or alkaline hydrolysis) often lead to extensive cleavage of C−C bonds and generate a wide range of low-molecular-weight by-products such as formic acid, acetic acid, and lactic acid, which complicate product separation and reduce selectivity.

Therefore, the development of more selective pretreatment methods is crucial for improving the efficiency of photocatalytic conversion and product quality. Innovative pretreatment strategies, such as photothermal catalysis, solar heating, and multi-technology coupling, are gaining attention due to their environmentally friendliness and sustainability. Multi-technology coupling, integrating photoreforming with external electric, magnetic, or ultrasonic fields, can significantly reduce chemical reagents, lower wastewater discharges, and improve overall pretreatment efficiency. Moreover, continuous-flow pretreatment systems may be designed to process higher concentrations of plastic waste while reducing energy consumption and operational costs.

In future, studies priority should be given to the development of low-energy, low-pollution pretreatment technologies to promote the industrial-scale implementation of photocatalytic plastic wastes conversion [38,72,74].

Table 2 summarizes the advantages and disadvantages of different pretreatment methods for plastic waste photoreforming. Overall, pretreatment plays a pivotal role in plastic photoreforming, significantly influencing the efficiency and outcome of the subsequent photocatalytic conversion. The choice of pretreatment method and its specific conditions determine how effectively the polymer backbone is broken down into intermediate products, each exhibiting distinct reactivity in the subsequent photoreforming process. To achieve high selectivity of the final products, the initial pretreatment step should be carefully designed to generate intermediates with a narrow molecular weight distribution and limited structural diversity. This targeted approach minimizes side reactions and enhances the efficiency and specificity of downstream photocatalytic transformations.

4 Progress in photocatalysts for plastic photoreforming

Photocatalysts are essential for converting plastic waste into hydrogen through sunlight-driven photoreforming. A pivotal development in this field occurred in the 1980s when Kawai and Sakata first demonstrated the photoreforming of PVC into hydrogen using Pt/TiO₂ [75]. Although their work was limited to ultraviolet (UV) spectrum, this pioneering work showcased the potential of photoreforming as a means of eliminating synthetic organic compounds and generating fuels. Inspired by this groundbreaking work, research in this domain has progressed steadily, despite ongoing challenges posed complex molecular structures and poor water solubility of plastics.

A major breakthrough occurred in 2018 when Reisner and colleagues reported the photoreforming of three widely used polymers, PLA, PET, and PU, into hydrogen using CdS/CdO_x photocatalysts. This groundbreaking achievement has sparked renewed global interest in plastic photoreforming, establishing it as an emerging and promising research frontier. More recently, research has explored the integration of photocatalytic conversion of plastics with thermal catalysis to degrade plastics while simultaneously producing hydrogen. This hybrid approach significantly reduces the reaction temperature compared to conventional thermocatalysis, improving both energy efficiency and overall performance.

For example, Lin et al. [76] developed a hierarchical porous carbon nitride-supported single-atom iron catalyst (FeSA-hCN) to catalyze microplastic degradation and hydrogenation production. This system enabled nearly complete conversion of ultra-high-molecular-weight PE (UHMWPE) into C₃−C₂₀ organics, achieving a remarkable carboxylic acid selectivity as high as 64% at neutral pH while surpassing the efficiency, selectivity, eco-friendliness, and stability over 6 cycles. The FeSA-hCN catalyst efficiently activates H₂O₂ in solution via a Fenton-like reaction, generating hydroxyl radicals that oxidize the C−H bonds and cleave C−C bonds in UHMWPE, introduce C=O functional groups in the induction phase, and form hydroxyl groups on carbonyl-containing carbonyl chains, which ultimately leads to the decomposition of UHMWPE, as well as to the formation of oxygen-containing intermediates in which the carboxylic acid (R-COOH) can reach 64% selectivity. The solution of FeSA-hCN/H₂O₂/UHMWPE after the reaction was subjected to simulated sunlight, and the dissociative oxygen-containing functional group of carboxylic acid (-COOH) reacted with photogenerated cavities to promote the separation of photogenerated carriers, which could finally realize the hydrogen production.

To date, a wide variety of photocatalysts for plastic photoreforming have been developed (Fig. 4) [77]. The properties of these photocatalysts, such as surface area, chemical stability, and bandgap, energy, significantly influence the conversion efficiency of plastic conversion. A high surface area enhances the availability of active sites and promotes charge carrier separation which is particularly beneficial for recalcitrant plastics like PP and PE. Catalyst stability is crucial long-term reactions especially for polymers requiring extended degradation periods. The bandgap of the photocatalyst determines its light absorption range. For example, TiO₂, with a bandgap of 3.2 eV, is limited to ultraviolet light, while C₃N₄, with a bandgap of 2.7 eV, can utilize visible light, which is more suitable for solar-driven processes.

Meanwhile, the VB and CB positions of the catalyst determine oxidative and reductive abilities of a photocatalyst. A higher VB enhances the oxidation potential, critical for cleaving strong C–C bonds, while a higher CB facilitates proton reduction to hydrogen. The chemical bonding of different plastics requires different redox potentials. For example, the strong C−C bonds in PE and PP require highly oxidative environments, while the benzene aromatic structure of PS requires milder conditions. Thus, careful tailoring of band structure is vital for optimizing photocatalytic performance across various plastics [7,74,77].

In general, photocatalysts for plastic photoreforming are categorized into three main types: metal oxide-based, metal sulfide-based, and non-metal-based photocatalysts [78–80]. The following sections will focus on recent advancements within each of these categories.

4.1 Metal oxides

Since Kawai and Sakata [75] first reported the successful photoreforming of plastics using a Pt/TiO₂ photocatalyst in 1981, metal oxides have remained a central focus in plastic photoreforming research. Due to their VB derived from deep O 2p orbitals, metal oxides typically demonstrate strong oxidation abilities. Upon light irradiation, they generate highly oxidative photoinduced holes that effectively cleave the C−C and C−H bonds in the of plastic polymer backbone [81].

For instance, the Reisner group employed a 6 wt% nitric acid solution combined with a hydrothermal process to transform PE into diverse liquid-phase products, primarily succinic acid and glutaric acid (Fig. 5(b)). Then, experiments on photoreforming of PE decomposition solutions (succinic acid) were conducted in a sealed glass photoreactor using a P25|Pt TiO₂ photocatalyst (Fig. 5(c)). After 24 h of reaction, the P25|Pt TiO₂ exhibited photocatalytic hydrogen evolution activity of 242 μmol/(g·h)), alongside the production of ethane (56.3 μmol/(g·h)), ethylene (1.3 μmol/(g·h)), CO₂ (832 μmol/(g·h)), propanoic acid (964.7 μmol/(g·h)), and adipic acid (23.5 μmol/(g·h)).

They discovered that ethane and propane were the main alkane products generated from the photoreforming of succinic, while CO₂ and H₂ arose primarily from decarboxylation reactions. Moreover, they established a flow photocatalytic reactor system (Fig. 5(h)) where a steady output of ethane (55.8 μmol/m²) and propane (38.5 μmol/m²) was achieved using P25|Pt (Figs. 5(e) and 5(f)). This flow setup employed a flow cell equipped with a photocatalyst panel, onto which the photocatalyst was deposited on a frosted glass sheet by drop-casting of a suspension (Fig. 5(h)). Notably, photocatalysis primarily yielded alkanes (ethane and propane), whereas electrocatalysis primarily produced alkenes (ethylene and propylene) (Fig. 5(g)).

Besides TiO₂, recently Nb₂O₅ and Ga₂O₃ have also been applied as photocatalysts for plastic photoreforming. Xu et al. [56] and Jiao et al. [82] has extensively studied the photoreforming of PE and PET, applying Nb₂O₅ and Ga₂O₃ photocatalysts to directly photoreform PE and PET under ambient air conditions without any pretreatment, respectively.

In one study, they developed a single-cell Nb₂O₅ layer catalyst capable of achieving complete photodegradation of PE into CO₂, with the generated CO₂ subsequently selectively photoreduced to acetic acid (CH₃COOH) (Figs. 6(a) and 6(b)). Furthermore, they demonstrated that the oxidative cleavage of the C−C bonds in PE was facilitated by O₂ and •OH radicals, leading primarily to CO₂ production. The CH₃COOH observed originated from the photoreduction of CO₂ via photoinduced C−C coupling of •COOH intermediates, rather than from direct photodegradation of PE itself. This research marked the first demonstration of rapid plastic photodegradation coupled with a two-step photoconversion mechanism (Fig. 6(c)).

Moreover, Xu et al. [56] also proposed using Co-Ga₂O₃ nanosheet photocatalysis to convert plastic waste, including PE, PP and PVC, into syngas under ambient conditions (Fig. 6(d)). In this process, hydrogen is produced via photoreduction of H₂O, whereas CO₂ originates from photodegradation of plastics such as PE bags, PP containers, and PET bottles, which is subsequently selectively photoreduced to CO (Figs. 6(e) and 6(g)).

In situ FTIR spectra (Fig. 6(h)) confirmed that CO₂ produced from plastic mineralization undergoes further reduction to CO via *COOH intermediates. Gibbs free energy calculations indicated that the rate-determining step for CO₂ photoreduction to CO was the formation of the *COOH intermediates, while for H₂O reduction to H₂, it is the formation of H* intermediates. Compared to Ga₂O₃ nanosheets, Co-Ga₂O₃ nanosheets exhibited lower energy barriers for both *COOH intermediate formation and a reduced energy requirement for H* intermediate generation, resulting in enhanced catalytic efficiency (Figs. 6(i) and 6(j)).

4.2 Metal sulfide

Most metal sulfide photocatalysts reported for plastic photoreforming are cadmium-based (Cd-based) catalysts [53,83,84], such as cadmium sulfide quantum dots (CdS QDs) [53] and Cd_xZn_1–xS solid solutions [84]. Especially, CdS has been extensively studied owing to its favorable band structure that is conducive to photoreforming reactions. Nevertheless, the CdS suffers from poor stability caused by photocorrosion, which necessitates further modifications to improve its photocatalytic durability.

Reisner and colleagues developed a CdS/CdO_x photocatalytic system for hydrogen production from polymers like PET, PLA, and PUR in alkaline media (Fig. 7(a)) [53,85]. In this system, photogenerated holes in the CdS/CdO_x photocatalyst oxidize polyesters to produce organic compounds such as formate, acetate, and pyruvate, while photogenerated electrons reduce protons (H⁺) to yield hydrogen (Fig. 7(b)). Compared to earlier studies utilizing platinized TiO₂, this system enhanced hydrogen evolution rates by at least an order of magnitude, achieving 64.3 ± 14.7, 3.42 ± 0.87, and 0.85 ± 0.28 mmol/(g·h) for PLA, PET, and PUR, respectively (Fig. 7(c)).

A brief pretreatment of plastics in aqueous NaOH solution further enhanced the photoreforming activity of PUR and PET by approximately fourfold, with hydrogen evolution rates increasing to 3.22 and 12.4 mmol/(g·h), respectively. This alkaline pretreatment facilitated cleavage of PUR and PET into short-chain monomers, significantly improving their photoreformability. However, this pretreatment had minimal impact on PLA, which readily dissolves in the alkaline reaction medium. They also studied the photoreforming of a commercial PET bottle using the CdS/CdO_x QDs photocatalysis system, observing that consistent hydrogen generation over 6 consecutive days, with a notable activity of 4.13 mmol/(g·h) (Fig. 7(d)). Moreover, despite the high initial activity, the overall conversion rate for all polymers remained below 40%, suggesting partial mineralization that suppresses greenhouse gas emissions while concurrently enriching the solution with value-added chemicals.

In a related study, Du et al. [83] developed a MoS₂-decorated CdS nanorod heterostructure (MoS₂/CdS) for photoreforming of pretreated PE, PLA, and PET, achieving simultaneous hydrogen production and value-added organic compound synthesis (Fig. 7(e)). MoS₂ exhibited selective epitaxial growth at the terminus of CdS nanorods, forming a MoS₂/CdS heterostructure that facilitated photoinduced charge carrier separation and directional transfer from CdS to MoS₂. The TEM image distinctly reveals the epitaxial growth of MoS₂ nanosheets localized at the terminal regions of CdS nanorods (Fig. 7(f)).

In addition, selective deposition studies revealed that MnO_x nanosheets preferentially attach to the sidewalls of CdS, while Pt nanoparticles selectively deposit on the tip of MoS₂. CdS nanorods act as photoabsorbents, generating electron-hole pairs under light conditions, and with energy level matching and interfacial coupling between MoS₂ and CdS, the photogenerated electrons tend to be transferred from the CdS nanorods to the tips of MoS₂, while the holes are mainly retained in the sidewalls of the CdS nanorods, and the electrons enriched in the tips of MoS₂ act as the reduction active sites, reducing water molecules to generate hydrogen in aqueous solution. CdS nanorod sidewall cavities act as oxidizing active sites to directly oxidize the pretreated plastic. These findings demonstrate that photogenerated electrons are preferentially localized at the terminus of MoS₂ nanosheets, whereas holes accumulate on the sidewalls of CdS. The photocatalytic efficiency of the MoS₂/CdS heterostructure for the photoreforming of pretreated PE, PLA, and PET was systematically investigated.

Photocatalyst tests showed that the MoS₂/CdS heterostructure achieved maximum hydrogen evolution rate of 6.68 ± 0.10 mmol/(g·h) during the photoreforming of pretreated PLA in a 10 mol/L KOH aqueous solution (Fig. 7(g)). Besides enhancing hydrogen production, this heterostructure enabled valorization of PET waste into value-added organics such as formate, acetate (Fig. 7(h)).

Zhang’s group [87] developed a direct photoreforming process for commercial PLA plastics, employing the Pd-CdS photocatalyst under visible light, notably without any alkali treatment (Fig. 8(a)), which efficiently produced hydrogen at a rate of 49.8 μmol/(g·h), sustaining activity for over 100 h, while demonstrating outstanding selectivity toward pyruvic acid with a yield of 95.9% (Figs. 8(c) and 8(d)). To enhance photoreforming, different metals were individually deposited onto CdS as cocatalysts_, resulting in significantly improved hydrogen evolution rates in the following decreasing order: Pd (715.8 ± 45.4 μmol) > Rh (532.3 ± 26.1 μmol) > Ni (232.7 ± 17.9 μmol) > Pt (198.6 ± 1.9 μmol) > Ru (193.4 ± 64.3 μmol) > Ag (116.6 ± 4.5 μmol) > bare CdS (110.2 ± 15.8 μmol) (Fig. 8(b)). The high selectivity is attributed to the dual function of Pd sites, which not only serve as cocatalysts to promote hydrogen production but also inhibit competing side reactions such as lactate coupling and decarboxylation. This research offers a direct and sustainable pathway for photocatalytic conversion, simultaneously reducing plastic waste and transforming it into valuable chemicals.

In another study, Qiao’s group developed a defect-rich NiPS₃-coupled CdS photocatalyst (d-NiPS₃/CdS) that exhibited an exceptional hydrogen evolution rate of 39.76 mmol/(g·h) during the initial hour of PLA photoreforming (Figs. 8(f) and 8(h)). The rate is almost 43 times and 1.5 times higher than bare CdS (0.92 mmol/(g·h)) and NiPS₃/CdS (26.68 mmol/(g·h)), with similar improvements in PET photoreforming. Moreover, hydrogen production from PLA and PET increased linearly with illumination time and was stable over three consecutive runs (Fig. 8(i)). When d-NiPS₃/CdS was used instead of NiPS₃/CdS, an increase in the product yield was noted for both PLA and PET. After 9 h of PLA photoreforming, the d-NiPS₃/CdS catalyst produced acetates (13.6 μmol) and pyruvate-based products (64.5 μmol), which included pyruvate and its derivatives under alkaline conditions (Fig. 8(j)). In addition, the photoreforming of PET substrates yielded the following products: formate (23.6 μmol), acetate (13.8 μmol), and glycolate (25.0 μmol) (Fig. 8 (j)).

More recently, Zhang’s group [80] designed a photothermal catalyst, NCS-ZCS, consisting of metallic NiCo₂S₄ (NCS) and semiconducting Zn_xCd_1-xS (ZCS), replacing precious expensive noble metals like Au and Pt with cost-effective NiCo₂S₄. During the reaction, photogenerated electrons transfer from the conduction band of ZCS to NCS and are excited into hot electrons by the localized surface plasmon resonance (LSPR) effect of NCS, which significantly improves hydrogen production efficiency. Meanwhile, holes remain in the valence band of ZCS, which oxidizes plastics to generate carboxylic acids and other high value-added chemicals. This approach eliminates the need for harsh acid or base pretreatment, enabling direct photoreforming of plastics into hydrogen fuel and valuable chemicals such as acetic acid and pyruvic acid, aligning with green and sustainable development goals.

The NCS-ZCS catalyst combines broad-spectrum light absorption by ZCS with the plasmonic resonance of NCS to achieve a full-spectrum UV to IR response, thereby broadening light energy utilization, and achieving hydrogen production rates of 57.0 and 106.0 mmol/(g·h) for PET and PLA, respectively, under visible-infrared light (420–2500 nm). Corresponding carboxylic acid yields were 39.18 and 206.05 μmol/mL, representing a 2.6-fold enhancement over pure ZCS. Moreover, the catalyst maintained over 90% activity after 5 cycles, with no significant change in morphology and structure [80]. Table 3 summarizes studies of several metal sulfide photocatalysts for plastic photoreforming. It gives a clear picture of the research progress in plastic metal sulfide photoreforming.

4.3 Non-metal based photocatalyst-carbon nitride

Carbon nitride has emerged as the most frequently reported non-metal based photocatalyst owing to its low toxicity, natural abundance, cost-effectiveness, excellent light absorption, favorable redox properties, and high chemical stability [88]. For example, Reisner’s group [88] developed a cyanamide-functionalized carbon nitride (CN_x) coupled with a nickel phosphide (Ni₂P) cocatalyst for plastic waste photoreforming (Fig. 9(a)). This CN_x|Ni₂P system efficiently produces hydrogen using PET and PLA as feedstocks. TEM images reveal that Ni₂P nanoparticles are uniformly dispersed within the CN_x matrix, with lattice fringes of 0.22 nm corresponding to the (111) plane of hexagonal Ni₂P (Fig. 9(b)). After 50 h of irradiation, the photoreforming of PET and PLA yielded hydrogen evolution rates of 82.5 ± 7.3 and 178 ± 12 μmol/g, respectively (Fig. 9(c)). The system was also upscaled from 2 to 120 mL reaction volumes (Fig. 9(d)), and over 5 days, photoreforming of microfibers produced 53.5 μmol/g of hydrogen.

In another study, Guo et al. [89] developed a carbon nitride porous microtube (CN_xPM) photocatalyst for PET plastic photoreforming (Fig. 9(e)). The photocatalytic performance of CN_xPM with PET substrates was systematically evaluated under visible light irradiation without cocatalysts. The hydrogen evolution rate exhibited a volcano-shaped dependence on the L-arginine content during synthesis, peaking at 9.39 μmol/(g·h) before declining at higher precursor concentrations (Fig. 9(f)). After 4 h of visible light irradiation, the CN_0.14PM catalyst achieved a hydrogen evolution rate approximately 23.5 times greater than the PET-free system (0.4 μmol/(g·h)). In contrast, bulk carbon nitride (BCN) exhibited negligible activity regardless of PET presence (Fig. 9(g)). To evaluate the alkaline stability of CN_0.14PM, the reacted catalyst suspension was hermetically sealed and stored in the dark for long-term durability testing. After 12 d, subsequent testing for 11 h revealed only a slight decrease in hydrogen production compared to the first 4-h test (Fig. 9(h)). These findings highlight the significant potential of carbon nitride-based photocatalysts for plastic photoreforming. Table 4 summarizes the experimental results and reaction conditions discussed in this section.

4.4 AI-driven catalyst design

AI-driven catalyst design currently focuses on four key areas:

(1) Data-driven rational screening

This involves constructing extensive material databases from density functional theory (DFT) calculations and experimental data, then using high-throughput computations to predict catalytic properties such as adsorption energies and overpotentials. Machine learning (ML) models, including graphical neural networks (GNNs) combined with transfer learning, leverage structural and electronic features (e.g., atomic configurations) to reduce the reliance on experimental data. For example, Amil Merchant and Ekin Dogus Cubuk from Google DeepMind developed a deep learning framework called GNOME, based on large-scale GNNs, which significantly accelerates the discovery of inorganic crystalline materials. They coupled active learning with DFT calculations in a closed-loop system: candidate materials predicted by the GNN are validated by DFT, and results iteratively improve the model. This method expands the known stable crystal structures by discovering 381000 new materials out of 2.2 million predicted stable crystal structures. Experimental validation shows that 736 of these structures have been synthesized independently, further demonstrating their effectiveness. In addition, the large-scale data set generated supports the development of high-precision, zero-sample generalized interatomic potential models for dynamic property predictions such as ionic conductivity. This work not only dramatically expands the variety of stable materials known to mankind but also provides generalized computational tools for materials science, advancing the potential of deep learning for applications in cross-distribution scientific discovery [93].

(2) Generative design and inverse optimization

Generative design is the generation of novel catalyst structures (e.g., high-entropy alloys, single-atom sites) by generative adversarial networks (GANs) and variational autoencoders (VAEs) that break through the limitations of traditional trial-and-error methods. Reverse optimization refers to the dynamic optimization of material composition and microstructure (e.g., pore size distribution, active site density) through reinforcement learning (RL) with catalytic efficiency and stability as the objective function. Lifar et al. [94] optimizes the dynamic control of CO catalytic oxidation reaction through reinforcement learning and finds that dynamic adjustment of gas pressure (CO and O₂) significantly improves the CO₂ generation rate, especially at low reaction rates. The reinforcement learning algorithm also successfully adapted to changes in external conditions (e.g., CO pressure fluctuations), demonstrating its potential for application in complex environments.

(3) Multi-scale simulation and mechanism analysis

This area integrates molecular dynamics (MD), microdynamics modeling, and AI f to reveal detailed reaction pathways and active site evolution cross scales, enabling deeper understanding of catalytic mechanisms.

(4) Automated experiment closed loops

Robotic experiment platform integrates AI-guided synthesis, characterization, and testing to accelerate the “design‒validation‒optimization” cycle. Active learning strategies, such as Bayesian optimization, minimize experimental iterations and improve research and development efficiency.

4.5 Industrial scalability analysis in photocatalysts for plastic photoreforming

Despite significant progress in photocatalytic plastic conversion, the technology is still in its infancy, with ample opportunities to improve efficiency, selectivity, stability, and economic viability. Chu et al. [7] highlight future directions, starting with the design of low-cost, highly efficient photocatalysts for photocatalytic plastics conversion. Equally critical is advancing the collection, sorting, and pretreatment of real plastic waste streams to enable large-scale application of photocatalytic plastic conversion technologies.

As the technology evolves, photocatalytic plastic conversion could become economically competitive with existing technologies, provided catalyst efficiency and longevity can be significantly improved. Unlike recycling technologies, photoreforming offer a relatively simple setup and multifunctionality, enabling simultaneous recovery of the energy and chemical value from waste. This makes it particularly promising for small-scale, decentralized applications, where waste feedstock and hydrogen production can be tailored to specific customer demands.

Looking forward, researchers and engineers will need to develop photoreforming as an integrated system, incorporating waste collection, pretreatment, photocatalysis, liquid treatment or recovery, and product distribution, rather than just focusing on photocatalyst design [95].

4.6 Sustainability analysis of photoreforming technology

Photoreforming, as an emerging technology for the treating plastic waste, has significant sustainability benefits. Its core mechanism involves several key steps: light absorption and charge carrier separation, redox reactions, product separation, and utilization. Compared to traditional waste treatment methods such as incineration, landfilling, and mechanical recycling, photoreforming has advantages of low carbon emissions, effective resource recovery, and greater environmental friendliness.

Life cycle analysis reveal that incineration has a high carbon footprint, releasing 2–3 tons of per ton of plastic incinerated, along with harmful emissions like microplastics and toxic gases. Landfilling also carries a substantial carbon footprint and causes long-term ecological harm. While mechanical recycling has a lower carbon footprint, its resource efficiency is limited, especially when processing mixed plastic waste. In contrast, photoreforming has a significantly lower carbon footprint, about 20% less than steam methane reforming (SMR) and 40% less than landfilling. Through the photocatalytic reaction, the C and H in waste plastics are efficiently converted into clean energy and chemicals, avoiding wasted resources [38,95]. With ongoing technological advancement and enhanced policy support, photoreforming is expected to become a key technological tool for realizing circular economy goals and carbon neutrality.

5 Summary and perspectives

In summary, plastic waste photoreforming offers a transformative approach to converting a large quantity of environmental pollutant into valuable organic compounds and green hydrogen. However, this technology is still in its infancy and faces significant challenges, especially in the preparation of plastic waste for photoreforming. This review systematically examines recent advances in plastic waste photoreforming, covering the underlying mechanisms, waste pretreatment methods, and progress in photocatalysts. It not only offers critical guidance for optimizing photocatalysts but also facilitates the practical implementation of plastic waste photoreforming technologies that simultaneously produce hydrogen and fine chemicals.

Despite these advancements, several challenges remain. Current plastic pretreatment methods often involve strong alkalis or acids, which are costly and environmentally harmful, limiting their feasibility for large-scale applications. Thus, it is essential to develop pretreatment techniques that require lower chemical and energy inputs for practical deployment. Additionally, the efficiency, selectivity, and stability of photocatalysts still constrain the performance of the technology. Continuous efforts are required to develop efficient, durable photocatalysts and to discover new photocatalysts with superior properties. Understanding the underlying mechanisms and exploring novel reaction pathways are crucial to rationally engineer next-generation photocatalysts with enhanced plastic photoreforming capabilities.

While current investigations into photocatalytic plastic photoreforming predominantly have focused on laboratory-scale systems, scaling up to industrial deployment necessitates overcoming significant hurdles in reactor engineering, catalyst recyclability, and cost-effectiveness metrics. Furthermore, advances in AI are poised to revolutionize plastic waste the photoreforming by enabling data-driven optimization of photocatalytic systems, reaction pathways, and real-time process control. AI-driven analysis can precisely map localized chemical microenvironments, overcoming limitations of traditional characterization techniques. Machine learning models trained on extensive datasets of catalyst structures and reaction mechanisms can predict optimal material configurations, significantly accelerating catalyst design cycles. Furthermore, AI-enabled automation of data synthesis and simulations can streamline the research pipeline, shortening the timeline from laboratory innovation to industrial applications.

References

[1] Son S , Haider Z , Lee D Y . . Ambivalent photocatalytic strategies for plastic waste conversion: Alkalinized carbon nitride for H₂O₂ production and complete mineralization. Applied Catalysis B: Environmental, 2025, 365: 124847

[2] Talebian-Kiakalaieh A , Li H , Guo M . . Photocatalytic reforming raw plastic in seawater by atomically-engineered GeS/ZnIn₂S₄. Advanced Energy Materials, 2025, 15(19): 2404963

[3] Qin J , Wu F , Dou Y . . Advanced catalysts for the chemical recycling of plastic waste. Advanced Materials, 2025,

[4] Miao P , Zhao J , Wang P . . Enhanced photocatalytic hydrogen production from poly (vinyl alcohol) plastic-dissolved wastewater. ACS Materials Letters, 2024, 6(2): 590–597

[5] Kang H , Washington A , Capobianco M D . . Concentration-dependent photocatalytic upcycling of poly (ethylene terephthalate) plastic waste. ACS Materials Letters, 2023, 5(11): 3032–3041

[6] Geyer R , Jambeck J R , Law K L . Production, use, and fate of all plastics ever made. Science Advances, 2017, 3(7): e1700782

[7] Chu S , Zhang B , Zhao X . . Photocatalytic conversion of plastic waste: From photodegradation to photosynthesis. Advanced Energy Materials, 2022, 12(22): 2200435

[8] Iqbal B , Zhao T , Yin W . . Impacts of soil microplastics on crops: A review. Applied Soil Ecology, 2023, 181: 104680

[9] Cao R , Xiao D , Wang M . . Solar-driven photocatalysis for recycling and upcycling plastics. Applied Catalysis B: Environmental, 2024, 341: 123357

[10] Jehanno C , Alty J W , Roosen M . . Critical advances and future opportunities in upcycling commodity polymers. Nature, 2022, 603(7903): 803–814

[11] Tang X , Han X , Sulaiman N H M . . Recent advances in the photoreforming of plastic waste: Principles, challenges, and perspectives. Industrial & Engineering Chemistry Research, 2023, 62(23): 9032–9045

[12] Kang S , Yuan W , Chen W . . Recent advances on solar-driven valorization of polyethylene terephthalate plastics into value-added chemicals. Nanotechnology, 2023, 34(46): 462001

[13] Payanthoth N S , Mut N N N , Samanta P . . A review of biodegradation and formation of biodegradable microplastics in soil and freshwater environments. Applied Biological Chemistry, 2024, 67(1): 110

[14] Zhang Y F , Huang Z Y , Li Y F . . The degradability of microplastics may not necessarily equate to environmental friendliness: A case study of cucumber seedlings with disturbed photosynthesis. Agriculture, 2023, 14(1): 53

[15] Yang Z , Lü F , Zhang H . . Is incineration the terminator of plastics and microplastics. Journal of Hazardous Materials, 2021, 401: 123429

[16] Redko V , Wolska L , Potrykus M . . Environmental impacts of 5-year plastic waste deposition on municipal waste landfills: A follow-up study. Science of the Total Environment, 2024, 906: 167710

[17] Schade A , Melzer M , Zimmermann S . . Plastic waste recycling—A chemical recycling perspective. ACS Sustainable Chemistry & Engineering, 2024, 12(33): 12270–12288

[18] Zhao X , Boruah B , Chin K F . . Upcycling to sustainably reuse plastics. Advanced Materials, 2022, 34(25): 2100843

[19] Qureshi M S , Oasmaa A , Pihkola H . . Pyrolysis of plastic waste: Opportunities and challenges. Journal of Analytical and Applied Pyrolysis, 2020, 152: 104804

[20] Ellis L D , Rorrer N A , Sullivan K P . . Chemical and biological catalysis for plastics recycling and upcycling. Nature Catalysis, 2021, 4(7): 539–556

[21] Cudjoe D , Wang H . Plasma gasification versus incineration of plastic waste: Energy, economic and environmental analysis. Fuel Processing Technology, 2022, 237: 107470

[22] Tan T , Wang W , Zhang K . . Upcycling plastic wastes into value-added products by heterogeneous catalysis. ChemSusChem, 2022, 15(14): e202200522

[23] Weng Y , Hong C B , Zhang Y . . Catalytic depolymerization of polyester plastics toward closed-loop recycling and upcycling. Green Chemistry, 2024, 26(2): 571–592

[24] Wang C , Han H , Wu Y . . Nanocatalyzed upcycling of the plastic wastes for a circular economy. Coordination Chemistry Reviews, 2022, 458: 214422

[25] Chen X , Wang Y , Zhang L . Recent progress in the chemical upcycling of plastic wastes. ChemSusChem, 2021, 14(19): 4137–4151

[26] Uekert T , Bajada M A , Schubert T . . Scalable photocatalyst panels for photoreforming of plastic, biomass and mixed waste in flow. ChemSusChem, 2021, 14(19): 4190–4197

[27] Feng S , Nguyen P T T , Ma X . . Photorefinery of biomass and plastics to renewable chemicals using heterogeneous catalysts. Angewandte Chemie International Edition, 2024, 63(37): e202408504

[28] He D , Huang G , Zhou Z . . Recent progress for designing of catalysts for photothermal conversion of plastic wastes. Advanced Functional Materials, 2024,

[29] Hu Q , Zhang Z , He D . . Progress and perspective for “green” strategies of catalytic plastics conversion into fuels by regulating half-reactions. Journal of the American Chemical Society, 2024, 146(25): 16950–16962

[30] Zhang X , Jun M , Zu W . . Photoreforming of microplastics: Challenges and opportunities for sustainable environmental remediation. Small, 2024, 20(46): 2403347

[31] Wang J , Zhang C , Wang Y . Current advances in the photoconversion of plastics: the catalysts and reaction pathways. ChemSusChem, 2025, 18(7): e202401700

[32] Li Z , Yang Y , Zhang C . . Atomically engineering the metal-support interaction of single-atom Cu/TiO₂ for efficient polyethylene terephthalate plastic photoreforming. Chem Catalysis, 2024, 4(3): 100902

[33] Paiman S H , Md Noor S F , Ngadi N . . Insight into photocatalysis technology as a promising approach to tackle microplastics pollution through degradation and upcycling. Chemical Engineering Journal, 2023, 467: 143534

[34] Mountanea O G , Skolia E , Kokotos C G . Photochemical upcycling and recycling of plastics: Achievements and future opportunities. Green Chemistry, 2024, 26(15): 8528–8549

[35] Anh Nguyen T K , Trần-Phú T , Daiyan R . . From plastic waste to green hydrogen and valuable chemicals using sunlight and water. Angewandte Chemie International Edition, 2024, 63(32): e202401746

[36] Bhattacharjee S , Andrei V , Pornrungroj C . . Reforming of soluble biomass and plastic derived waste using a bias-free Cu₃₀Pd₇₀| perovskite| Pt photoelectrochemical device. Advanced Functional Materials, 2022, 32(7): 2109313

[37] Zhang B , Zhang H , Pan Y . . Photoelectrochemical conversion of plastic waste into high-value chemicals coupling hydrogen production. Chemical Engineering Journal, 2023, 462: 142247

[38] Yue S , Zhao Z , Zhang T . . Photoreforming of plastic waste to sustainable fuels and chemicals: Waste to energy. Environmental Science & Technology, 2024, 58(52): 22865–22879

[39] Miao H , Zeng G , Wu J . . In situ construction of metal phosphide-anchored Zn_0.5Cd_0.5S Schottky junction photocatalysts for efficient hydrogen evolution via photocatalytic reforming of plastics. International Journal of Hydrogen Energy, 2025, 102: 963–971

[40] Shelake S P , Sutar D N , Abraham B M . . Emerging photoreforming process to hydrogen production: A future energy. Advanced Functional Materials, 2024, 34(40): 2403795

[41] Zheng K , Wu Y , Hu Z . . Progress and perspective for conversion of plastic wastes into valuable chemicals. Chemical Society Reviews, 2023, 52(1): 8–29

[42] Kang S , Sun T , Ma Y . . Artificial photosynthesis bringing new vigor into plastic wastes. SmartMat, 2023, 4(4): e1202

[43] Han M , Zhu S , Xia C . . Photocatalytic upcycling of poly(ethylene terephthalate) plastic to high-value chemicals. Applied Catalysis B: Environmental, 2022, 316: 121662

[44] Shen M , Hu T , Huang W . . Can incineration completely eliminate plastic wastes? An investigation of microplastics and heavy metals in the bottom ash and fly ash from an incineration plant. Science of the Total Environment, 2021, 779: 146528

[45] Vollmer I , Jenks M J , Roelands M C . . Beyond mechanical recycling: giving new life to plastic waste. Angewandte Chemie International Edition, 2020, 59(36): 15402–15423

[46] Suzuki G , Uchida N , Tuyen L H . . Mechanical recycling of plastic waste as a point source of microplastic pollution. Environmental Pollution, 2022, 303: 119114

[47] Jung S H , Cho M H , Kang B S . . Pyrolysis of a fraction of waste polypropylene and polyethylene for the recovery of BTX aromatics using a fluidized bed reactor. Fuel Processing Technology, 2010, 91(3): 277–284

[48] Anuar Sharuddin S D , Abnisa F , Wan Daud W M A . . A review on pyrolysis of plastic wastes. Energy Conversion and Management, 2016, 115: 308–326

[49] Lopez G , Artetxe M , Amutio M . . Thermochemical routes for the valorization of waste polyolefinic plastics to produce fuels and chemicals. A review. Renewable & Sustainable Energy Reviews, 2017, 73: 346–368

[50] Mastral F J , Esperanza E , García P . . Pyrolysis of high-density polyethylene in a fluidised bed reactor. Influence of the temperature and residence time. Journal of Analytical and Applied Pyrolysis, 2002, 63(1): 1–15

[51] Maqsood T , Dai J , Zhang Y . . Pyrolysis of plastic species: A review of resources and products. Journal of Analytical and Applied Pyrolysis, 2021, 159: 105295

[52] Sil D , Chakrabarti S . Photocatalytic degradation of PVC–ZnO composite film under tropical sunlight and artificial UV radiation: A comparative study. Solar Energy, 2010, 84(3): 476–485

[53] Uekert T , Kuehnel M F , Wakerley D W . . Plastic waste as a feedstock for solar-driven H₂ generation. Energy & Environmental Science, 2018, 11(10): 2853–2857

[54] Jiang R , Lu G , Yan Z . . Microplastic degradation by hydroxy-rich bismuth oxychloride. Journal of Hazardous Materials, 2021, 405: 124247

[55] Gong X , Tong F , Ma F . . Photoreforming of plastic waste poly (ethylene terephthalate) via in-situ derived CN-CNTs-NiMo hybrids. Applied Catalysis B. Environment and Energy, 2022, 307: 121143

[56] Xu J , Jiao X , Zheng K . . Plastics-to-syngas photocatalysed by Co–Ga₂O₃ nanosheets. National Science Review, 2022, 9(9): nwac011

[57] Jahirul M , Rasul M , Schaller D . . Transport fuel from waste plastics pyrolysis—A review on technologies, challenges and opportunities. Energy Conversion and Management, 2022, 258: 115451

[58] Dai L , Zhou N , Lv Y . . Pyrolysis technology for plastic waste recycling: A state-of-the-art review. Progress in Energy and Combustion Science, 2022, 93: 101021

[59] Gebre S H , Sendeku M G , Bahri M . Recent trends in the pyrolysis of non-degradable waste plastics. ChemistryOpen, 2021, 10(12): 1202–1226

[60] Deng Y , Chen J , Zhang Q . . Photocatalytic upcycling of different types of plastic wastes: A mini review. ChemPlusChem, 2024, 89(11): e202400336

[61] Eisenreich F . Photocatalysis as an effective tool for upcycling polymers into value-added molecules. Angewandte Chemie International Edition, 2023, 62(29): e202301303

[62] Li C , Kong X Y , Lyu M . . Upcycling of non-biodegradable plastics by base metal photocatalysis. Chem, 2023, 9(9): 2683–2700

[63] Jiang Y , Zhang H , Hong L . . An integrated plasma–photocatalytic system for upcycling of polyolefin plastics. ChemSusChem, 2023, 16(14): e202300106

[64] Fujishima A , Honda K . Electrochemical photolysis of water at a semiconductor electrode. Nature, 1972, 238(5358): 37–38

[65] Ashraf M , Ullah N , Khan I . . Photoreforming of waste polymers for sustainable hydrogen fuel and chemicals feedstock: waste to energy. Chemical Reviews, 2023, 123(8): 4443–4509

[66] Agosti A , Nakibli Y , Amirav L . . Photosynthetic H₂ generation and organic transformations with CdSe@CdS-Pt nanorods for highly efficient solar-to-chemical energy conversion. Nano Energy, 2020, 70: 104510

[67] Lin L , Yi J , Wang J . . Enhancing microplastic degradation through synergistic photocatalytic and pretreatment approaches. Langmuir, 2024, 40(43): 22582–22590

[68] Guo Z , He Q , Wang H . . Chemical recycling of various PET plastic waste under alkaline hydrolysis via the LSR method. Inorganic Chemistry Communications, 2024, 159: 111744

[69] Fang P , Lu X , Zhou Q . . Controlled alcoholysis of PET to obtain oligomers for the preparation of PET-PLA copolymer. Chemical Engineering Journal, 2023, 451: 138988

[70] Barnard E , Rubio Arias J J , Thielemans W . Chemolytic depolymerisation of PET: A review. Green Chemistry, 2021, 23(11): 3765–3789

[71] Taniguchi I , Yoshida S , Hiraga K . . Biodegradation of PET: Current status and application aspects. ACS Catalysis, 2019, 9(5): 4089–4105

[72] Bhattacharjee S , Guo C , Lam E . . Chemoenzymatic photoreforming: A sustainable approach for solar fuel generation from plastic feedstocks. Journal of the American Chemical Society, 2023, 145(37): 20355–20364

[73] Kang S , Sun T , Ma Y . . Artificial photosynthesis bringing new vigor into plastic wastes. SmartMat, 2023, 4(4): e1202

[74] Chen A , Yang M Q , Wang S . . Recent advancements in photocatalytic valorization of plastic waste to chemicals and fuels. Frontiers in Nanotechnology, 2021, 3: 723120

[75] Kawai T , Sakata T . Photocatalytic hydrogen production from water by the decomposition of poly-vinylchloride, protein, algae, dead insects, and excrement. Chemistry Letters, 1981, 10(1): 81–84

[76] Lin J , Hu K , Wang Y . . Tandem microplastic degradation and hydrogen production by hierarchical carbon nitride-supported single-atom iron catalysts. Nature Communications, 2024, 15(1): 8769

[77] Feng S , Nguyen P T T , Ma X . . Photorefinery of biomass and plastics to renewable chemicals using heterogeneous catalysts. Angewandte Chemie International Edition, 2024, 63(37): e202408504

[78] Qin J , Dou Y , Zhou J . . Photocatalytic valorization of plastic waste over zinc oxide encapsulated in a metal-organic framework. Advanced Functional Materials, 2023, 33(28): 2214839

[79] Yin Z , Chen H , Wang Q . . Construction of an interface interaction in a g-C₃N₄/CdS/NiS for photoreforming of plastic and clean hydrogen regeneration. Journal of Colloid and Interface Science, 2024, 675: 218–225

[80] Su W , Zhang Y , Kuklin A . . Enhanced charge transfer dynamics in a NiCo₂S₄–Zn_xCd_1–xS photothermal catalyst for efficient photoreforming of waste plastic. ACS Catalysis, 2024, 14(18): 13927–13939

[81] Li T , Vijeta A , Casadevall C . . Bridging plastic recycling and organic catalysis: Photocatalytic deconstruction of polystyrene via a C–H oxidation pathway. ACS Catalysis, 2022, 12(14): 8155–8163

[82] Jiao X , Zheng K , Chen Q . . Photocatalytic conversion of waste plastics into C₂ fuels under simulated natural environment conditions. Angewandte Chemie International Edition, 2020, 59(36): 15497–15501

[83] Du M , Zhang Y , Kang S . . Trash to treasure: Photoreforming of plastic waste into commodity chemicals and hydrogen over MoS₂-tipped CdS nanorods. ACS Catalysis, 2022, 12(20): 12823–12832

[84] Li Y , Wan S , Lin C . . Engineering of 2D/2D MoS₂/Cd_xZn_1−xS photocatalyst for solar H₂ evolution coupled with degradation of plastic in alkaline solution. Solar RRL, 2021, 5(6): 2000427

[85] Wakerley D W , Kuehnel M F , Orchard K L . . Solar-driven reforming of lignocellulose to H₂ with a CdS/CdO_x photocatalyst. Nature Energy, 2017, 2(4): 17021

[86] Zhang S , Li H , Wang L . . Boosted photoreforming of plastic waste via defect-rich NiPS₃ nanosheets. Journal of the American Chemical Society, 2023, 145(11): 6410–6419

[87] Miao Y , Zhao Y , Gao J . . Direct photoreforming of real-world polylactic acid plastics into highly selective value-added pyruvic acid under visible light. Journal of the American Chemical Society, 2024, 146(7): 4842–4850

[88] Uekert T , Kasap H , Reisner E . Photoreforming of nonrecyclable plastic waste over a carbon nitride/nickel phosphide catalyst. Journal of the American Chemical Society, 2019, 141(38): 15201–15210

[89] Guo S , Huang Y , Li D . . Visible-light-driven photoreforming of poly(ethylene terephthalate) plastics via carbon nitride porous microtubes. Chemical Communications, 2023, 59(50): 7791–7794

[90] Han M , Zhu S , Xia C . . Photocatalytic upcycling of poly (ethylene terephthalate) plastic to high-value chemicals. Applied Catalysis B: Environmental, 2022, 316: 121662

[91] Cao R , Zhang M Q , Hu C . . Catalytic oxidation of polystyrene to aromatic oxygenates over a graphitic carbon nitride catalyst. Nature Communications, 2022, 13(1): 4809

[92] Liu X , Yang Y , Wan S . . Tuning the surface hydrophilicity of a C₃N₄ nanosheet for efficient photocatalytic H₂ evolution coupled with microplastic degradation. International Journal of Hydrogen Energy, 2023, 48(71): 27599–27610

[93] Merchant A , Batzner S , Schoenholz S S . . Scaling deep learning for materials discovery. Nature, 2023, 624(7990): 80–85

[94] Lifar M S , Tereshchenko A A , Bulgakov A N . . Optimal dynamic regimes for CO oxidation discovered by reinforcement learning. ACS Omega, 2024, 9(26): 27987–27997

[95] Uekert T , Pichler C M , Schubert T . . Solar-driven reforming of solid waste for a sustainable future. Nature Sustainability, 2020, 4(5): 383–391

RIGHTS & PERMISSIONS

Higher Education Press 2025