Photoreforming of Non-Recyclable Plastic Waste over a Carbon Nitride/Nickel Phosphide Catalyst

With over 8 billion tons of plastic produced since 1950, polymers represent one of the most widely used – and most widely discarded – materials. Ambient-temperature photoreforming offers a simple and low-energy means for transforming plastic waste into fuel and bulk chemicals, but has previously only been reported using precious-metal- or Cd-based photocatalysts. Here, an inexpensive and non-toxic carbon nitride/nickel phosphide (CNx|Ni2P) photocatalyst is utilized to successfully reform polyethylene terephthalate (PET) and polylactic acid (PLA) to clean H2 fuel and a variety of organic chemicals under alkaline aqueous conditions. Ni2P synthesized on cyanamide-functionalized carbon nitride is shown to promote efficient charge separation and catalysis, with a photostability of at least five days. The real-world applicability of photoreforming is further verified by generating H2 and organics from a selection of non-recyclable waste – including microplastics (polyester microfibers) and food-contaminated plastic – and up-scaling the system from 2 mL to 120 mL while maintaining its efficiency for plastic conversion.This work was supported by the Christian Doppler Research Association, Austrian Federal Ministry for Digital and Economic Affairs, National Foundation for Research, Technology and Development, OMV Group, and EPSRC (NanoDTC, EP/L015978/1). XPS data collection was performed at the EPSRC National Facility for XPS (HarwellXPS), operated by Cardiff University and UCL, under contract No. PR 16195

Photoreforming of biomass in metal salt hydrate solutions.

Metal salt hydrate (MSH) solutions allow for the complete solubilisation of biomass and we demonstrate its use as a reaction medium for the photocatalytic reforming of lignocellulose. Different types of photocatalysts such as TiO2 and carbon nitride can be employed in MSH to produce H2 and organic products under more benign conditions than the commonly required extreme pH aqueous solutions

Conversion of Polyethylene Waste into Gaseous Hydrocarbons via Integrated Tandem Chemical-Photo/Electrocatalytic Processes.

The chemical inertness of polyethylene makes chemical recycling challenging and motivates the development of new catalytic innovations to mitigate polymer waste. Current chemical recycling methods yield a complex mixture of liquid products, which is challenging to utilize in subsequent processes. Here, we present an oxidative depolymerization step utilizing diluted nitric acid to convert polyethylene into organic acids (40% organic acid yield), which can be coupled to a photo- or electrocatalytic decarboxylation reaction to produce hydrocarbons (individual hydrocarbon yields of 3 and 20%, respectively) with H2 and CO2 as gaseous byproducts. The integrated tandem process allows for the direct conversion of polyethylene into gaseous hydrocarbon products with an overall hydrocarbon yield of 1.0% for the oxidative/photocatalytic route and 7.6% for the oxidative/electrolytic route. The product selectivity is tunable with photocatalysis using TiO2 or carbon nitride, yielding alkanes (ethane and propane), whereas electrocatalysis on carbon electrodes produces alkenes (ethylene and propylene). This two-step recycling process of plastics can use sunlight or renewable electricity to convert polyethylene into valuable, easily separable, gaseous platform chemicals

Scalable Photocatalyst Panels for Photoreforming of Plastic, Biomass and Mixed Waste in Flow.

Solar-driven reforming uses sunlight and a photocatalyst to generate H2 fuel from waste at ambient temperature and pressure. However, it faces practical scaling challenges such as photocatalyst dispersion and recyclability, competing light absorption by the waste solution, slow reaction rates and low conversion yields. Here, the immobilisation of a noble-metal-free carbon nitride/nickel phosphide (CNx |Ni2 P) photocatalyst on textured glass is shown to overcome several of these limitations. The 1 cm2 CNx |Ni2 P panels photoreform plastic, biomass, food and mixed waste into H2 and organic molecules with rates comparable to those of photocatalyst slurries. Furthermore, the panels enable facile photocatalyst recycling and novel photoreactor configurations that prevent parasitic light absorption, thereby promoting H2 production from turbid waste solutions. Scalability is further verified by preparing 25 cm2 CNx |Ni2 P panels for use in a custom-designed flow reactor to generate up to 21 μmolH 2  m-2  h-1 under "real-world" (seawater, low sunlight) conditions. The application of inexpensive and readily scalable CNx |Ni2 P panels to photoreforming of a variety of real waste streams provides a crucial step towards the practical deployment of this technology

Solar-driven reforming of solid waste for a sustainable future

Approximately 70% of global municipal solid waste is lost to landfills or the environment each year, an emblem of our increasingly unsustainable economic system in which materials and energy are produced, used and promptly discarded. Photoreforming is a sunlight-driven technology that can help disrupt this linear model by simultaneously reclaiming the value in waste and contributing to renewable hydrogen production. This Review examines the advantages and challenges of photoreforming of real waste streams. By reviewing literature on photoreforming and conducting basic techno-economic and life cycle assessments, we identify key pathways for enhancing the impact of photoreforming for a carbon-neutral future

Rational Design of Carbon Nitride Photoelectrodes with High Activity Toward Organic Oxidations

Carbon nitride (CNx) is a light-absorber with excellent performance in photocatalytic suspension systems, but the activity of CNx photoelectrodes has remained low. Here, cyanamide-functionalized CNx (NCNCNx) was co-deposited with ITO nanoparticles on a 1.8 Å thick alumina-coated FTO electrode. Transient absorption spectroscopy and impedance measurements support that ITO acts as a conductive binder and improves electron extraction from the NCNCNx, whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al2O3|ITO : NCNCNx film displays a benchmark performance for CNx-based photoanodes with an onset of −0.4 V vs a reversible hydrogen electrode (RHE), and 1.4±0.2 mA cm−2 at 1.23 V vs RHE during AM1.5G irradiation for the selective oxidation of 4-methylbenzyl alcohol. This assembly strategy will improve the exploration of CNx in fundamental and applied photoelectrochemical (PEC) studies.The authors thank Dr. Carla Casadevall, Dr. Motiar Rahaman, and Dr. Mark Bajada (University of Cambridge) for helpful discussions. This work was funded by the European Union's Horizon 2020 project SOLAR2CHEM (Marie Skłodowska-Curie Actions with Grant Agreement No. 861151, C.P., E.R.) and Methasol (Grant Agreement No. 101022649, S.A.J.H., J.D.), the EPSRC (NanoDTC, EP/L015978/1, and EP/S022953, T.U., E.R.), Generalitat Valenciana (APOSTD/2021/251 fellowship, C.A.M.), and the project PID2020-116093RB-C41 by MCIN/AEI/10.13039/501100011033/ (S.G.). The authors acknowledge the use of the Cambridge XPS System, which is part of Sir Henry Royce Institute - Cambridge Equipment, EPSRC grant EP/P024947/1, and the EPSRC Underpinning Multi-User Equipment Call (EP/P030467/1) for the Talos F200X G2 TEM

Net-zero solutions and research priorities in the 2020s

Key messages • Technological, societal and nature-based solutions should work together to enable systemic change towards a regenerative society, and to deliver net-zero greenhouse gas (GHG) emissions. • Prioritise research into efficient, low-carbon and carbon-negative solutions for sectors that are difficult to decarbonise; i.e. energy storage, road transport, shipping, aviation and grid infrastructure. • Each solution should be assessed with respect to GHG emissions reductions, energy efficiency and societal implications to provide a basis for developing long-term policies, maximising positive impact of investment and research effort, and guiding industry investors in safe and responsible planning

Plastic and mixed waste as feedstocks for solar-driven H₂ production

As the world strives toward a carbon-neutral future powered by a circular economy, photoreforming enables the simultaneous generation of renewable fuel and mitigation of waste. In this simple process, a photocatalyst utilises the energy in sunlight to reduce water to H₂ and oxidise waste into other organics under ambient temperature and pressure. To date, the majority of photoreforming research has relied on ultraviolet-driven photocatalysts coupled with precious metal co-catalysts to convert ‘model’ molecules rather than complex waste. In this thesis, photoreforming of plastic, food and mixed wastes over visible-light-driven and noble-metal-free photocatalysts is reported. Cadmium sulphide quantum dots are first shown to generate H₂ and a range of organic oxidation products from polar polymers and food components following a low-temperature pre-treatment step under alkaline conditions. In order to develop a less toxic and corrosive system, carbon nitride coupled with a nickel phosphide co-catalyst (CNₓ|Ni₂P) is next explored for plastic and food photoreforming at both neutral and alkaline pH. The oxidation mechanisms of polyethylene terephthalate and polylactic acid over CNₓ are examined in further detail by a combination of nuclear magnetic resonance spectroscopy, photoelectrochemistry and adsorption experiments. Surface interactions, rather than reaction thermodynamics, are suggested to determine which oxidation intermediates are observed during photoreforming. The scaling potential of photoreforming is subsequently investigated. CNₓ|Ni₂P panels are prepared by immobilisation on frosted glass and used to generate H₂ and organics from plastic, biomass and mixed waste over multiple panel reuse cycles. The photocatalyst panels are then up-scaled to 25 cm² and applied in a custom-designed flow reactor, where irradiation configuration is shown to be crucial for enabling the reforming of highly turbid waste streams. Finally, techno-economic and life cycle analyses of the photoreforming process are conducted in order to identify key areas for further improvement, including photocatalyst efficiency and stability, substrate solubilisation, and light intensity and duration. Through its focus on alternative photocatalysts, expanded substrate scope, and preliminary scaling, this thesis aims to serve as a platform for further research on – and application of – waste photoreforming

Raw data for Photoreforming of biomass in metal salt hydrate solutions

The raw data include studies from dissolving cellulose, quantification of hydrogen and organic products by HPLC, infrared data of photocatalysts, estimations of OH radical amounts and powder xray data

Raw data supporting article: Photoreforming of non-recyclable plastic waste over a carbon nitride/nickel phosphide catalyst

This is raw data for the publication “Photoreforming of non-recyclable plastic waste over a carbon nitride/nickel phosphide catalyst.” It includes Origin files of photocatalytic experiments, characterization (UV-Vis, FTIR, Fluorimetry, XRD and XPS), and NMR data, as well as microscopy images (SEM and TEM) and ChemDraw figures. See the Readme.txt files for more information.Christian Doppler Research Association, Austrian Federal Ministry for Digital and Economic Affairs, National Foundation for Research, Technology and Development, OMV Group, and EPSRC (NanoDTC, EP/L015978/1)