Hydrogen Generation from PS and PE Microplastics via UV Photocatalysis

Hydrogen Generation from PS and PE Microplastics via UV Photocatalysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hydrogen Generation from PS and PE Microplastics via UV Photocatalysis Miroslava Filip Edelmannová, Petr Praus, Lenka Řeháčková, Rudolf Ricka, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8616863/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract UV-driven photolysis and TiO 2 -based photocatalysis are explored as potential pathways for hydrogen generation from polystyrene and polyethylene microplastics. The study compares the behavior of PS, LDPE, and HDPE under UVC irradiation, focusing on how polymer structure, surface properties, and reaction conditions influence hydrogen evolution. Thermodynamic considerations, polymer–photocatalyst interactions, and system-level effects such as particle dispersion and light accessibility are examined to clarify the factors governing reactivity. By addressing both photochemical and hydrodynamic aspects of microplastic conversion, this work provides insight into the opportunities and challenges of using UV-based processes for hydrogen recovery from plastic waste. Catalysis hydrogen production microplastics PS LDPE HDPE photocatalysis TiO2 1. Introduction Microplastics are persistent pollutants formed either through the breakdown of bulk plastics or by direct release as fine particles, and they are now ubiquitous across natural environments. Their small dimensions, high chemical resistance, and affinity for contaminants make polymers such as polystyrene and polyethylene (LDPE and HDPE) environmentally significant despite their limited degradability. [1–11]. Established plastic waste treatments, including recycling and thermal disposal, are poorly suited to microplastics because of their small size, wide dispersion, and frequent chemical complexity. As a result, effective removal or conversion strategies remain largely undeployed at the scale of wastewater treatment and are still predominantly confined to laboratory studies. [2, 3, 12]. Photocatalytic processes offer a route to couple microplastic degradation with hydrogen generation, linking waste mitigation with energy recovery. Under UV irradiation, semiconductors such as TiO 2 initiate redox reactions that enable polymer fragments to serve as electron donors, a concept increasingly explored in studies on microplastic photoreforming. [1, 7, 13–20]. Previous studies have demonstrated that TiO 2 -assisted UV irradiation can induce extensive degradation of both polystyrene and polyethylene microplastics, ultimately leading to advanced mineralization [21]. The degradation kinetics of microplastics are strongly influenced by particle morphology, with reduced dimensions accelerating breakdown. [22, 23]. Studies using modified TiO 2 have shown that particle size plays a key role in the photocatalytic degradation of polyethylene microplastics, with smaller fractions exhibiting enhanced reactivity [24]. This work examines UV-driven transformation of polystyrene and polyethylene microplastics under direct irradiation and in the presence of commercial TiO 2 . Emphasis is placed on gaseous product formation and on identifying conditions under which photocatalysis offers advantages over photolysis alone. 2. Experimental 2.1 Preparation of microplasics The polymer granulates of PS, HDPE and LDPE were ground in a cryogenic mill CryoMill (Retsch GmbH, Haan, Germany) and granulometry was adjusted to < 0.16 mm using an analytical sieve shaker AS200 by Restch (Haan, Germany) and a sieve by Preciselekt (Dolní Loučky, Czech Republic). 2.2 Characterization of microplastics Infrared spectra of powdered samples were obtained by FT-IR using the KBr pellet technique, while bulk materials were analyzed by ATR-FT-IR with a diamond crystal. All measurements were performed on a Nicolet iS50 spectrometer under standard conditions, with baseline correction applied during spectral processing. Sample densities were measured by helium pycnometry using a Pycnomatic ATC instrument. The calorific value of the samples was determined by bomb calorimetry using an AC600 instrument calibrated with certified standards. Elemental composition (C, H, N) was determined by CHNS analysis using a LECO 628 analyzer. Approximately 100 mg of sample was analyzed following calibration with certified reference materials under standard CHNS operating conditions. Surface morphology of the plastic samples was examined by scanning electron microscopy after gold coating under standard operating conditions. 2.3 Photocatalytic experiments Photocatalytic experiments were conducted in a sealed batch photoreactor containing an aqueous suspension of microplastics, with or without commercial TiO 2 , under an inert atmosphere. The system was irradiated with a 254 nm UVC source, and gaseous products were periodically sampled and analyzed by gas chromatography with a dielectric barrier ionization detector. All experiments were repeated to ensure reproducibility, and catalyst stability was assessed through consecutive reuse tests. 3. Results and discussion 3.1. Thermodynamic analysis Thermodynamic feasibility of microplastic photoreforming was assessed by deriving overall oxidation reactions for representative polymers and calculating the corresponding standard reaction enthalpies, entropies, and Gibbs energies. The calculations were based on experimentally determined combustion enthalpies and tabulated thermodynamic data using Hess’s law. 3.2. IR spectroscopy No detectable changes were observed in the IR spectra of powdered samples after UV exposure. In contrast, bulk samples showed a weak band in the carbonyl region, suggesting limited surface oxidation induced by UV irradiation. 3.3. Elemental composition and physicochemical properties Elemental, calorimetric, and density analyses reflect the distinct molecular structures of polystyrene and polyethylene microplastics. Differences in carbon and hydrogen content, combustion heat, and density are consistent with aromatic versus aliphatic polymer backbones and provide a coherent physicochemical context for subsequent experiments. 3.4. SEM Surface morphology of the polymers was examined by SEM before and after UVC exposure. While untreated samples displayed smooth and compact surfaces, irradiation induced pronounced roughening and fragmentation, with the extent of degradation depending on polymer structure. 3.5. Photocatalytic measurements UV irradiation at 254 nm was applied to induce photoreforming of PS and polyethylene microplastics, leading to the formation of gaseous products dominated by hydrogen, followed by methane and carbon monoxide. 3.5.1 Mixing effect The influence of stirring on photocatalytic conversion was evaluated using LDPE II under stirred and unstirred conditions. Stirring significantly enhanced hydrogen formation, while methane was largely unaffected and carbon monoxide formation was reduced. The influence of stirring on photocatalytic conversion was evaluated using LDPE II under stirred and unstirred conditions. Mixing enhanced hydrogen formation by improving particle dispersion, suppressing agglomeration, and ensuring more uniform light distribution, while also favoring higher selectivity toward hydrogen. On this basis, all subsequent photolytic and photocatalytic experiments were conducted under continuous stirring. 3.5.2 Photolysis Photolytic experiments were performed without a photocatalyst to probe the intrinsic UV reactivity of the investigated microplastics. In all cases, hydrogen was the dominant gaseous product, while methane and carbon monoxide were formed only in minor amounts. The overall gas yields followed a clear polymer-dependent trend, with polyethylene samples showing higher activity than polystyrene. Among the polyethylenes, the modified LDPE II exhibited the highest hydrogen formation, whereas PS displayed the lowest reactivity. Low CO levels suggest limited oxidative degradation, while methane formation indicates partial cleavage of C–C bonds and recombination of carbon-centered radicals during photolysis. 3.5.2 Photocatalysis Photocatalytic experiments revealed pronounced polymer-dependent differences in gas formation under UV irradiation. Hydrogen remained the dominant product for all materials, while methane and carbon monoxide were produced in smaller amounts. Compared to photolysis, the presence of TiO 2 altered the relative reactivity of the polymers, with polystyrene showing a marked increase in activity despite its thermodynamic stability. In contrast, highly crystalline polyethylene exhibited lower gas yields, indicating limited interaction with the photocatalyst. LDPE-based samples showed the highest overall photocatalytic performance, consistent with their more disordered structure and enhanced accessibility of reactive sites. Comparison of photolysis and photocatalysis shows that the effect of a photocatalyst depends not only on polymer chemistry but also on physical properties governing particle behaviour in the reaction medium. The presence of TiO 2 enhanced gas formation only for polystyrene, whereas polyethylene-based materials exhibited reduced yields under photocatalytic conditions. This contrasting behaviour reflects differences in particle density, suspension stability, and accessibility of the polymer–photocatalyst interface. Denser polymers remain better dispersed and maintain effective contact with the catalyst, enabling interfacial charge transfer and radical formation. In contrast, floating polyethylene particles experience limited interaction with TiO 2 , which suppresses photocatalytic pathways. Under these conditions, direct photolysis remains the more effective conversion route for polyethylene microplastics. 4. Conclusion This work explores UV-driven pathways for the transformation of common microplastics, emphasizing how polymer-specific chemical and physical characteristics shape photochemical behaviour. The observations point to distinct response patterns under photolytic and photocatalytic conditions, reflecting differences in interfacial interactions, surface evolution, and reaction environments. Rather than a universal solution, the results suggest that microplastic conversion processes must be evaluated on a case-by-case basis, providing a conceptual framework for future studies on light-assisted valorisation of plastic waste. Declarations Acknowledgement This work was financially supported of the European Union under the REFRESH – Research Excellence For REgion Sustainability and High-tech Industries (Project No. CZ.10.03.01/ 00/22_003/0000048) via the Operational Programme Just Transition, the OP JAK project "INOVO!!!", No. CZ.02.01.01/00/23_021/0008588 supported by the Ministry of Education, Youth and Sports and co-financed by the European Union and the authors also thank the Large Research Infrastructure ENREGAT (Project No. LM2023056). During the preparation of this work the author(s) used ChatGPT solely for language editing purposes. After using this tool, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication. References D. Bertagna Silva, A. Marques, TiO₂-based photocatalytic degradation of microplastics in water: Current status, challenges and future perspectives, Journal of Water Process Engineering, 72 (2025) 107465. J. Ge, Z. Zhang, Z. Ouyang, M. Shang, P. Liu, H. Li, X. Guo, Photocatalytic degradation of (micro)plastics using TiO 2 -based and other catalysts: Properties, influencing factor, and mechanism, Environ. Res., 209 (2022) 112729. W. Hamd, E.A. Daher, T.S. Tofa, J. Dutta, Recent Advances in Photocatalytic Removal of Microplastics: Mechanisms, Kinetic Degradation, and Reactor Design, Volume 9 - 2022 (2022). R. Xu, L. Cui, S. Kang, Countering microplastics pollution with photocatalysis: Challenge and prospects, Progress in Natural Science: Materials International, 33 (2023) 251-266. S. Yousafzai, M. Farid, M. Zubair, N. Naeem, W. Zafar, Z.u. Zaman Asam, S. Farid, S. Ali, Detection and degradation of microplastics in the environment: a review, Environmental Science Advances, 4 (2025) 1142-1165. R. Cao, D. Xiao, M. Wang, Y. Gao, D. Ma, Solar-driven photocatalysis for recycling and upcycling plastics, Applied Catalysis B: Environmental, 341 (2024) 123357. C. Ran, Z. Li, Y.-F. Zhang, X. Luo, Z. Liang, Y. Mao, Recent advances in photocatalytic plastic degradation and upcycling: Catalysts, experiments, and mechanisms, Journal of Environmental Chemical Engineering, 14 (2026) 120526. H. Li, Y. Huang, Y. Zhang, H. Li, C. Shen, D. Xia, Y. Zheng, Plastic photoreforming: catalytic production of hydrogen and valuable chemicals, Green Chemistry, 27 (2025) 12050-12069. A.F. Gouveia, G.C. de Assis, L.K. Ribeiro, L.H. Mascaro, M. Calatayud, A.C.S.C. Teixeira, Heterogeneous photocatalysis as an efficient process for degrading MPs/NPs in aqueous media: A systematic review, Journal of Environmental Chemical Engineering, 13 (2025) 117878. H. Cui, X. Chen, F. Lan, B. An, X. Zhang, Photocatalysis as a tool for upcycling of polymers, Trends in Chemistry, 6 (2024) 392-405. K.J. Ramírez-Escárcega, K.J. Amaya-Galván, J.C. García-Prieto, F.d.J. Silerio-Vázquez, J.B. Proal-Nájera, Advancing photocatalytic strategies for microplastic degradation in aquatic systems: Insights into key challenges and future pathways, Journal of Environmental Chemical Engineering, 13 (2025) 115594. G.A.O. Tiago, S. Martins-Dias, L.P. Marcelino, A.C. Marques, Promoting LDPE microplastic biodegradability: The combined effects of solar and gamma irradiation on photodegradation, J. Hazard. Mater., 492 (2025) 138227. P. Praus, Photoreforming for microplastics recycling: A critical review, Journal of Environmental Chemical Engineering, 12 (2024) 112525. E.M.N.T. Edirisooriya, P.S. Senanayake, T. Ahasan, P. Xu, H. Wang, Comprehensive Insights into Photoreforming of Waste Plastics for Hydrogen Production, Catalysts, 2025. C. Rex M, A. Mukherjee, Prospects of TiO 2 -based photocatalytic degradation of microplastic leachates related disposable facemask, a major COVID-19 waste, Volume 4 - 2022 (2022). Y. Yeszhan, K. Bexeitova, S. Yermekbayev, Z. Toktarbay, J. Lee, R. Berndtsson, S. Azat, Photocatalytic Degradation of Microplastics in Aquatic Environments: Materials, Mechanisms, Practical Challenges, and Future Perspectives, Water, 2025. Y. Miyah, N. El Messaoudi, M. Benjelloun, M. El-Habacha, J. Georgin, G.H. Angeles, S. Knani, Comprehensive review on advanced coordination chemistry and nanocomposite strategies for wastewater microplastic remediation via adsorption and photocatalysis, Surfaces and Interfaces, 72 (2025) 106955. Y. Ma, K. Jin, X. Yin, X. Zhao, Z. Liu, Y. Dou, T. Ao, Y. Li, X. Duan, Advanced oxidation in the treatment of microplastics in water: A Review, Desalination and Water Treatment, 322 (2025) 101135. D. Castilla-Caballero, O. Sadak, J. Martínez-Díaz, V. Martínez-Castro, J. Colina-Márquez, F. Machuca-Martínez, A. Hernandez-Ramirez, S. Vazquez-Rodriguez, S. Gunasekaran, Solid-state photocatalysis for plastics abatement: A review, Materials Science in Semiconductor Processing, 149 (2022) 106890. P. Praus, L. Řeháčková, M. Filip Edelmanová, A. Gavlová, M. Koštejn, R. Škuta, J. Bednárek, P. Bednář, K. Kočí, Photoreforming of PET and PLA microplastics for sustainable hydrogen production using TiO 2 and g-C 3 N 4 photocatalysts, Journal of Environmental Chemical Engineering, 13 (2025) 116998. I. Nabi, A.U. Bacha, K. Li, H. Cheng, T. Wang, Y. Liu, S. Ajmal, Y. Yang, Y. Feng, L. Zhang, Complete Photocatalytic Mineralization of Microplastic on TiO 2 Nanoparticle Film, iScience, 23 (2020) 101326. Y. Yeszhan, K. Bexeitova, S. Yermekbayev, Z. Toktarbay, J. Lee, R. Berndtsson, S. Azat, Photocatalytic Degradation of Microplastics in Aquatic Environments: Materials, Mechanisms, Practical Challenges, and Future Perspectives, 17 (2025) 2139. Y. He, A.U. Rehman, M. Xu, C.A. Not, A.M.C. Ng, A.B. Djurišić, Photocatalytic degradation of different types of microplastics by TiO x /ZnO tetrapod photocatalysts, Heliyon, 9 (2023) e22562. E. Mbuci Kinyua, G.W. Atwoki Nyakairu, E. Tebandeke, O.N. Odume, Photocatalytic Degradation of Microplastics: Parameters Affecting Degradation, Advances in Environmental and Engineering Research, 04 (2023) 039. Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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Introduction","content":"\u003cp\u003eMicroplastics are persistent pollutants formed either through the breakdown of bulk plastics or by direct release as fine particles, and they are now ubiquitous across natural environments. Their small dimensions, high chemical resistance, and affinity for contaminants make polymers such as polystyrene and polyethylene (LDPE and HDPE) environmentally significant despite their limited degradability. [1\u0026ndash;11].\u003c/p\u003e \u003cp\u003eEstablished plastic waste treatments, including recycling and thermal disposal, are poorly suited to microplastics because of their small size, wide dispersion, and frequent chemical complexity. As a result, effective removal or conversion strategies remain largely undeployed at the scale of wastewater treatment and are still predominantly confined to laboratory studies. [2, 3, 12].\u003c/p\u003e \u003cp\u003ePhotocatalytic processes offer a route to couple microplastic degradation with hydrogen generation, linking waste mitigation with energy recovery. Under UV irradiation, semiconductors such as TiO\u003csub\u003e2\u003c/sub\u003e initiate redox reactions that enable polymer fragments to serve as electron donors, a concept increasingly explored in studies on microplastic photoreforming. [1, 7, 13\u0026ndash;20].\u003c/p\u003e \u003cp\u003ePrevious studies have demonstrated that TiO\u003csub\u003e2\u003c/sub\u003e-assisted UV irradiation can induce extensive degradation of both polystyrene and polyethylene microplastics, ultimately leading to advanced mineralization [21]. The degradation kinetics of microplastics are strongly influenced by particle morphology, with reduced dimensions accelerating breakdown. [22, 23]. Studies using modified TiO\u003csub\u003e2\u003c/sub\u003e have shown that particle size plays a key role in the photocatalytic degradation of polyethylene microplastics, with smaller fractions exhibiting enhanced reactivity [24].\u003c/p\u003e \u003cp\u003eThis work examines UV-driven transformation of polystyrene and polyethylene microplastics under direct irradiation and in the presence of commercial TiO\u003csub\u003e2\u003c/sub\u003e. Emphasis is placed on gaseous product formation and on identifying conditions under which photocatalysis offers advantages over photolysis alone.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of microplasics\u003c/h2\u003e \u003cp\u003eThe polymer granulates of PS, HDPE and LDPE were ground in a cryogenic mill CryoMill (Retsch GmbH, Haan, Germany) and granulometry was adjusted to \u0026lt;\u0026thinsp;0.16 mm using an analytical sieve shaker AS200 by Restch (Haan, Germany) and a sieve by Preciselekt (Doln\u0026iacute; Loučky, Czech Republic).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Characterization of microplastics\u003c/h2\u003e \u003cp\u003eInfrared spectra of powdered samples were obtained by FT-IR using the KBr pellet technique, while bulk materials were analyzed by ATR-FT-IR with a diamond crystal. All measurements were performed on a Nicolet iS50 spectrometer under standard conditions, with baseline correction applied during spectral processing. Sample densities were measured by helium pycnometry using a Pycnomatic ATC instrument. The calorific value of the samples was determined by bomb calorimetry using an AC600 instrument calibrated with certified standards. Elemental composition (C, H, N) was determined by CHNS analysis using a LECO 628 analyzer. Approximately 100 mg of sample was analyzed following calibration with certified reference materials under standard CHNS operating conditions. Surface morphology of the plastic samples was examined by scanning electron microscopy after gold coating under standard operating conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Photocatalytic experiments\u003c/h2\u003e \u003cp\u003ePhotocatalytic experiments were conducted in a sealed batch photoreactor containing an aqueous suspension of microplastics, with or without commercial TiO\u003csub\u003e2\u003c/sub\u003e, under an inert atmosphere. The system was irradiated with a 254 nm UVC source, and gaseous products were periodically sampled and analyzed by gas chromatography with a dielectric barrier ionization detector. All experiments were repeated to ensure reproducibility, and catalyst stability was assessed through consecutive reuse tests.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Thermodynamic analysis\u003c/h2\u003e \u003cp\u003eThermodynamic feasibility of microplastic photoreforming was assessed by deriving overall oxidation reactions for representative polymers and calculating the corresponding standard reaction enthalpies, entropies, and Gibbs energies. The calculations were based on experimentally determined combustion enthalpies and tabulated thermodynamic data using Hess\u0026rsquo;s law.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2. IR spectroscopy\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eNo detectable changes were observed in the IR spectra of powdered samples after UV exposure. In contrast, bulk samples showed a weak band in the carbonyl region, suggesting limited surface oxidation induced by UV irradiation.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Elemental composition and physicochemical properties\u003c/h2\u003e \u003cp\u003eElemental, calorimetric, and density analyses reflect the distinct molecular structures of polystyrene and polyethylene microplastics. Differences in carbon and hydrogen content, combustion heat, and density are consistent with aromatic versus aliphatic polymer backbones and provide a coherent physicochemical context for subsequent experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4. SEM\u003c/h2\u003e \u003cp\u003eSurface morphology of the polymers was examined by SEM before and after UVC exposure. While untreated samples displayed smooth and compact surfaces, irradiation induced pronounced roughening and fragmentation, with the extent of degradation depending on polymer structure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Photocatalytic measurements\u003c/h2\u003e \u003cp\u003eUV irradiation at 254 nm was applied to induce photoreforming of PS and polyethylene microplastics, leading to the formation of gaseous products dominated by hydrogen, followed by methane and carbon monoxide.\u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1 Mixing effect\u003c/h2\u003e \u003cp\u003eThe influence of stirring on photocatalytic conversion was evaluated using LDPE II under stirred and unstirred conditions. Stirring significantly enhanced hydrogen formation, while methane was largely unaffected and carbon monoxide formation was reduced. The influence of stirring on photocatalytic conversion was evaluated using LDPE II under stirred and unstirred conditions. Mixing enhanced hydrogen formation by improving particle dispersion, suppressing agglomeration, and ensuring more uniform light distribution, while also favoring higher selectivity toward hydrogen. On this basis, all subsequent photolytic and photocatalytic experiments were conducted under continuous stirring.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2 Photolysis\u003c/h2\u003e \u003cp\u003ePhotolytic experiments were performed without a photocatalyst to probe the intrinsic UV reactivity of the investigated microplastics. In all cases, hydrogen was the dominant gaseous product, while methane and carbon monoxide were formed only in minor amounts. The overall gas yields followed a clear polymer-dependent trend, with polyethylene samples showing higher activity than polystyrene. Among the polyethylenes, the modified LDPE II exhibited the highest hydrogen formation, whereas PS displayed the lowest reactivity. Low CO levels suggest limited oxidative degradation, while methane formation indicates partial cleavage of C\u0026ndash;C bonds and recombination of carbon-centered radicals during photolysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2 Photocatalysis\u003c/h2\u003e \u003cp\u003ePhotocatalytic experiments revealed pronounced polymer-dependent differences in gas formation under UV irradiation. Hydrogen remained the dominant product for all materials, while methane and carbon monoxide were produced in smaller amounts. Compared to photolysis, the presence of TiO\u003csub\u003e2\u003c/sub\u003e altered the relative reactivity of the polymers, with polystyrene showing a marked increase in activity despite its thermodynamic stability. In contrast, highly crystalline polyethylene exhibited lower gas yields, indicating limited interaction with the photocatalyst. LDPE-based samples showed the highest overall photocatalytic performance, consistent with their more disordered structure and enhanced accessibility of reactive sites.\u003c/p\u003e \u003cp\u003eComparison of photolysis and photocatalysis shows that the effect of a photocatalyst depends not only on polymer chemistry but also on physical properties governing particle behaviour in the reaction medium. The presence of TiO\u003csub\u003e2\u003c/sub\u003e enhanced gas formation only for polystyrene, whereas polyethylene-based materials exhibited reduced yields under photocatalytic conditions. This contrasting behaviour reflects differences in particle density, suspension stability, and accessibility of the polymer\u0026ndash;photocatalyst interface. Denser polymers remain better dispersed and maintain effective contact with the catalyst, enabling interfacial charge transfer and radical formation. In contrast, floating polyethylene particles experience limited interaction with TiO\u003csub\u003e2\u003c/sub\u003e, which suppresses photocatalytic pathways. Under these conditions, direct photolysis remains the more effective conversion route for polyethylene microplastics.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis work explores UV-driven pathways for the transformation of common microplastics, emphasizing how polymer-specific chemical and physical characteristics shape photochemical behaviour. The observations point to distinct response patterns under photolytic and photocatalytic conditions, reflecting differences in interfacial interactions, surface evolution, and reaction environments. Rather than a universal solution, the results suggest that microplastic conversion processes must be evaluated on a case-by-case basis, providing a conceptual framework for future studies on light-assisted valorisation of plastic waste.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgement\u003c/h2\u003e \u003cp\u003eThis work was financially supported of the European Union under the REFRESH \u0026ndash; Research Excellence For REgion Sustainability and High-tech Industries (Project No. CZ.10.03.01/ 00/22_003/0000048) via the Operational Programme Just Transition, the OP JAK project \"INOVO!!!\", No. CZ.02.01.01/00/23_021/0008588 supported by the Ministry of Education, Youth and Sports and co-financed by the European Union and the authors also thank the Large Research Infrastructure ENREGAT (Project No. LM2023056).\u003c/p\u003e \u003cp\u003eDuring the preparation of this work the author(s) used ChatGPT solely for language editing purposes. After using this tool, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eD. Bertagna Silva, A. Marques, TiO₂-based photocatalytic degradation of microplastics in water: Current status, challenges and future perspectives, Journal of Water Process Engineering, 72 (2025) 107465.\u003c/li\u003e\n\u003cli\u003eJ. Ge, Z. Zhang, Z. Ouyang, M. Shang, P. Liu, H. Li, X. Guo, Photocatalytic degradation of (micro)plastics using TiO\u003csub\u003e2\u003c/sub\u003e-based and other catalysts: Properties, influencing factor, and mechanism, Environ. Res., 209 (2022) 112729.\u003c/li\u003e\n\u003cli\u003eW. Hamd, E.A. Daher, T.S. Tofa, J. Dutta, Recent Advances in Photocatalytic Removal of Microplastics: Mechanisms, Kinetic Degradation, and Reactor Design, Volume 9 - 2022 (2022).\u003c/li\u003e\n\u003cli\u003eR. Xu, L. Cui, S. 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Djuri\u0026scaron;ić, Photocatalytic degradation of different types of microplastics by TiO\u003csub\u003ex\u003c/sub\u003e/ZnO tetrapod photocatalysts, Heliyon, 9 (2023) e22562.\u003c/li\u003e\n\u003cli\u003eE. Mbuci Kinyua, G.W. Atwoki Nyakairu, E. Tebandeke, O.N. Odume, Photocatalytic Degradation of Microplastics: Parameters Affecting Degradation, Advances in Environmental and Engineering Research, 04 (2023) 039.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"ee1757d5-90f5-41bf-93da-0353094640ba","identifier":"10.13039/501100001823","name":"Ministerstvo Školství, Mládeže a Tělovýchovy","awardNumber":"CZ.02.01.01/00/23_021/0008588","order_by":0},{"identity":"f803a790-f7a3-4ad0-be3d-70bc206910db","identifier":"10.13039/501100001823","name":"Ministerstvo Školství, Mládeže a Tělovýchovy","awardNumber":"LM2023056","order_by":1},{"identity":"645eace2-a0d6-4dd4-98e3-e029791663a2","identifier":"10.13039/501100013855","name":"Ministerstvo Životního Prostředí","awardNumber":"CZ.10.03.01/ 00/22_003/0000048","order_by":2}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Institute of Environmental Technology, CEET, VSB-Technical University of Ostrava","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"hydrogen production, microplastics, PS, LDPE, HDPE, photocatalysis, TiO2","lastPublishedDoi":"10.21203/rs.3.rs-8616863/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8616863/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eUV-driven photolysis and TiO\u003csub\u003e2\u003c/sub\u003e-based photocatalysis are explored as potential pathways for hydrogen generation from polystyrene and polyethylene microplastics. The study compares the behavior of PS, LDPE, and HDPE under UVC irradiation, focusing on how polymer structure, surface properties, and reaction conditions influence hydrogen evolution. Thermodynamic considerations, polymer\u0026ndash;photocatalyst interactions, and system-level effects such as particle dispersion and light accessibility are examined to clarify the factors governing reactivity. By addressing both photochemical and hydrodynamic aspects of microplastic conversion, this work provides insight into the opportunities and challenges of using UV-based processes for hydrogen recovery from plastic waste.\u003c/p\u003e","manuscriptTitle":"Hydrogen Generation from PS and PE Microplastics via UV Photocatalysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-19 08:29:47","doi":"10.21203/rs.3.rs-8616863/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"931a5d05-c497-4163-a919-f8adf7697845","owner":[],"postedDate":"January 19th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":61245859,"name":"Catalysis"}],"tags":[],"updatedAt":"2026-01-19T08:29:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-19 08:29:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8616863","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8616863","identity":"rs-8616863","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}