Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production
Abstract
:1. Introduction
2. Fundamentals of Plastic Photoreforming
2.1. Overview of Photoreforming
- The catalyst absorbs photons, exciting electrons from the highest occupied molecular orbital to the lowest unoccupied molecular orbital, resulting in an activated catalyst.
- The excited catalyst interacts with reactants, generating active intermediates through H2 atom transfer or electron transfer, thereby selectively facilitating plastic conversion.
2.2. Reaction Pathways and Mechanisms
2.3. Thermodynamic and Kinetic Considerations
3. Types of Plastics and Their Suitability for Photoreforming
3.1. Common Plastics
3.2. Characteristics Affecting Photoreforming
4. Photocatalysts and Catalyst Engineering
4.1. Semiconductor Photocatalysts
4.2. Metal–Organic Frameworks (MOFs)
4.3. Carbon-Based and Heterojunction Composites
4.4. Noble Metal and Transition Metal Co-Catalysts
4.5. Design and Fabrication Strategies
4.6. Catalyst Characterization Techniques
5. Reactor Configurations and Photoreforming Conditions
5.1. Bench-Scale Reactors and Scale-Up Challenges
5.2. Light Sources and Illumination Strategies
5.3. Operational Parameters
6. Performance Metrics and Process Evaluation
6.1. Hydrogen Yield and Production Rates
Catalyst | Experimental Conditions | Hydrogen Yield (µmol g−1 h−1) | Reference |
---|---|---|---|
Pt/TiO2 | 500 W Xe lamp, 5 M NaOH, PET | 1130 | [134] |
CNx|Ni2P | AM 1.5 sunlight, ambient temperature, PET | 82 | [58] |
CNx|Ni2P | AM 1.5 sunlight, ambient temperature, PLA | 178 | |
Zn|n2S4 (mesoporous) | Simulated sunlight, PET | 23.6 | [139] |
Zn|n2S4 (conventional) | Simulated sunlight, PET | 8.9 | |
CdS/CdOx | Simulated sunlight, PET | 6.6 | [140] |
NiCr2O4/TiO2-Zn0.5Cd0.5S | Visible light, mixed plastics | 81.4 × 103 | [141] |
NiPS3/CdS | Solar-driven, PET | 31.4 × 103 | [142] |
NiPS3/CdS | Solar-driven, PLA | 39.8 × 103 | |
g-C3N4/Pt | With NaOH pre-treatment, PET | 533 | [136] |
Au0.28Pd0.72/TiO2 HS | 5 M NaOH, 300 W Xe, PET | 0.85 × 103 | [134] |
MoS2/CdS | 300 W Xe lamp AM 1.5, 10 M KOH | PLA: 6.68 × 103 PET: 3.90 × 103 PE: 1.13 × 103 | |
Co–Ga2O3 | 300 W Xe lamp, AM 1.5, 10 M KOH, PE | 692 | [143] |
d-NiPS3/CdS | 43× and 1.5 × 300 W xenon lamp (PLS-SXE 300), λ > 400 nm, 2 M KOH, PLA | 39.76 × 103 | [137] |
6.2. Selectivity and Byproduct Formation
6.2.1. Liquid-Phase Organics
6.2.2. Gas-Phase Organics
6.2.3. Solid Residues
6.2.4. Treatment and Opportunities with Byproducts
6.3. Life Cycle Assessment (LCA) and Techno-Economic Analyses (TEA)
6.4. Comparative Benchmarking
7. Environmental and Sustainability Perspectives
7.1. Waste Management and the Circular Economy Context
7.2. Policy and Regulatory Landscape
- Increased R&D Funding: Governments could allocate research grants to accelerate the development of high efficiency photocatalysts and scalable reactor designs.
- Market-Based Incentives: Carbon credits or renewable energy credits could be extended to photoreforming projects.
- Mandated Recycled Content: Setting minimum thresholds for recycled plastic usage in industrial applications could further drive investment in advanced recycling technologies.
8. Challenges and Future Directions
8.1. Technical Hurdles
8.2. Materials Innovation
9. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Heterojunction Type | Catalyst System | Function | Ref. |
---|---|---|---|
Type-II | ZnO/UiO-66-NH2 | Enhanced charge separation via staggered bands | [82] |
Type-II | g-C3N4/rGO | Improved e− transport, recombination suppression | [84] |
Z-scheme | CdS/MOF hybrid | High redox potential with suppressed recombination | [83] |
Z-scheme | C3N5/g-C3N4/graphene | Dual heterojunction with enhanced light absorption | [86] |
Multi-junction | NiCoP/rGO/g-C3N4 | Synergistic multi-phase charge mediation | [87] |
Category | Noble Metal Co-Catalysts (Pt, Pd, Au) | Non-Noble Metal Co-Catalysts (Ni, Co, Fe, Cu, Mo, etc.) |
---|---|---|
H2 Evolution Efficiency | High activity, excellent electron trapping, and fast proton reduction | Moderate to high activity dependent on material engineering (doping, alloying, or structuring) |
Charge Separation | Forms Schottky junctions, effectively suppressing electron–hole recombination | Requires heterojunctions or defect engineering to achieve similar charge separation efficiency |
Stability and Durability | Chemically stable under reaction conditions, low corrosion rate | Some non-noble metals (e.g., Fe) can corrode or deactivate over time unless properly stabilized. |
Cost and Scalability | Very expensive and scarce, limiting large-scale applications | Earth-abundant and low-cost, catalysts are highly scalable for industrial use |
Environmental Impact | Mining and refining noble metals have significant environmental impacts | More sustainable, widely available, and eco-friendly |
Versatility | Effective across a range of photocatalytic systems (e.g., plastic reforming, water splitting) | Catalysts can be engineered into various alloys and oxides to enhance versatility and selectivity |
Activation Energy and Reaction Kinetics | Low activation energy, enabling rapid reaction kinetics | Requires co-doping (e.g., Ni2P, CoP, MoS2) to reduce activation energy for HER |
Long-Term Performance | Maintains high catalytic performance over extended use | Some non-noble metals may degrade or lose efficiency over prolonged cycles |
Engineering Potential | Limited modification potential due to intrinsic properties of noble metals | High tunability is achieved through the capabilities of doping, alloying, or nanostructuring for enhanced photocatalytic properties |
Characterization Technique | Key Findings | Advantages | Limitation |
---|---|---|---|
X-ray Diffraction (XRD) | Determines the crystalline structure and phase composition of catalysts | Identifies crystalline phases | Limited to crystalline materials |
X-ray Absorption Spectroscopy (XAS) | Probes local electronic and structural environment of specific elements | Elucidates oxidation states, coordination numbers, and bond distances | Requires synchrotron radiation sources |
Electron Microscopy (SEM and TEM) | Provides high-resolution images of catalyst morphology and nanostructure | Observes particle size, shape, and dispersion | Sample preparation can be intricate |
Surface Area and Porosity Analysis (BET Method) | Assesses surface area and porosity of catalysts | Determines the availability of active sites | Assumes idealized models that may not fit all materials |
UV-Vis Diffuse Reflectance Spectroscopy (DRS) | Investigates optical properties and bandgap energies | Assesses light absorption capabilities | Interpretation can be challenging for complex materials |
Photoluminescence (PL) Spectroscopy | Measures recombination rate of photogenerated electron–hole pairs | Indicates efficiency of charge separation | PL signals can be weak and require sensitive detection |
Fourier Transform Infrared (FTIR) Spectroscopy | Identifies functional groups and chemical bonds on catalyst surfaces | Provides insights into surface modifications and interactions with reactants | Surface sensitivity can be limited |
Raman Spectroscopy | Offers information about molecular vibrations and crystal structures | Identifies structural defects and phase compositions | Fluorescence interference can obscure Raman signals |
X-ray Photoelectron Spectroscopy (XPS) | Provides information on elemental composition and chemical states of surface elements | Surface-sensitive technique | Limited to surface analysis (typically 1–10 nm depth) |
Mass Spectrometry (MS) | Analyze reaction intermediates and products | Offers insights into catalytic processes and efficiency | Requires coupling with other techniques for comprehensive analysis |
Cost Factor | Key Points |
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Catalyst Synthesis |
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Photoreactor Setup |
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Operational Costs |
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Feedstock Pre-treatment |
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Edirisooriya, E.M.N.T.; Senanayake, P.S.; Ahasan, T.; Xu, P.; Wang, H. Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production. Catalysts 2025, 15, 453. https://doi.org/10.3390/catal15050453
Edirisooriya EMNT, Senanayake PS, Ahasan T, Xu P, Wang H. Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production. Catalysts. 2025; 15(5):453. https://doi.org/10.3390/catal15050453
Chicago/Turabian StyleEdirisooriya, E. M. N. Thiloka, Punhasa S. Senanayake, Tarek Ahasan, Pei Xu, and Huiyao Wang. 2025. "Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production" Catalysts 15, no. 5: 453. https://doi.org/10.3390/catal15050453
APA StyleEdirisooriya, E. M. N. T., Senanayake, P. S., Ahasan, T., Xu, P., & Wang, H. (2025). Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production. Catalysts, 15(5), 453. https://doi.org/10.3390/catal15050453