Sonnengetriebene Wasserstofferzeugung aus Lignocellulose

Visible-Light-Driven Photocatalytic Cellulose-to-H2 Conversion by MoS2/ZnIn2S4 Photocatalyst with the Assistance of Cellulase

Visible-light-driven photocatalytic cellulose-to-H 2 conversion system was successfully constructed by using MoS 2 /ZnIn 2 S 4 as the photocatalyst and cellulase as the enzyme catalyst. In this smartly-designed system, the cellulose was firstly converted to glucose by the action of cellulase, and the generated glucose acted as an efficient holes trapper and electron donor which was further converted into H 2 through photocatalytic reaction over MoS 2 /ZnIn 2 S 4 photocatalyst under visible light irradiation. The optimum H 2 generation rate achieves 12.2 μmol·h -1 ·g -1 with respect to photocatalyst under visible light irradiation (λ>420 nm) in photocatalytic system in the presence of 100 mg 3% MoS 2 /ZnIn 2 S 4 , 100 mg cellulase and 2 g poplar wood chip. These results open up a new possibility for the development of efficient visible-light-responding photocatalytic cellulose -to-H 2 conversion system that combine photocatalysis and enzyme technology.

A TiO2 -Co(terpyridine)2 Photocatalyst for the Selective Oxidation of Cellulose to Formate Coupled to the Reduction of CO2 to Syngas

Immobilization of a phosphonated cobalt bis(terpyridine) catalyst on TiO₂ nanoparticles generates a photocatalyst that allows coupling aqueous CO₂ -to-syngas (CO and H₂ ) reduction to selective oxidation of biomass-derived oxygenates or cellulose to formate. An enzymatic saccharification pre-treatment process is employed that enables the use of insoluble cellulose as an electron-donating substrate under benign aqueous conditions suitable for photocatalytic CO₂ conversion. The hybrid photocatalyst consists of solely earth-abundant components, and its heterogeneous nature allows for reuse and operation in aqueous solution for several days at 25 °C, reaching a cellulose-to-formate conversion yield of 17 %. Thus, the proof-of-concept for valorizing two waste streams (CO₂ and biomass) simultaneously into value-added chemicals through solar-driven catalysis is demonstrated.

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 (CN_x |Ni₂ P) photocatalyst on textured glass is shown to overcome several of these limitations. The 1 cm² CN_x |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 CN_x |Ni₂ P panels for use in a custom-designed flow reactor to generate up to 21 μmol_H 2  m^-2  h^-1 under "real-world" (seawater, low sunlight) conditions. The application of inexpensive and readily scalable CN_x |Ni₂ P panels to photoreforming of a variety of real waste streams provides a crucial step towards the practical deployment of this technology.

Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol (FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3 C2 Tx /CdS under Visible Light

Acceptorless photocatalytic dehydrogenation is not only a promising alternative to photocatalytic water splitting for hydrogen generation but also provides a green and sustainable strategy for the synthesis of value-added organic compounds. In this work, Ti₃ C₂ T_x /CdS nanocomposites were obtained by self-assembly of hexagonal CdS in the presence of preformed Ti₃ C₂ T_x nanosheets, which serves as a photocatalyst for acceptorless dehydrogenation of biomass-derived furfuryl alcohol (FOL) to furfural (FAL) and furoic acid (FA) in neutral and alkaline medium respectively, with simultaneous generation of stoichiometric hydrogen under visible light. Ti₃ C₂ T_x MXene acts as an efficient cocatalyst for the photocatalytic dehydrogenation of FOL over CdS, with an optimum performance achieved over 0.50 wt%Ti₃ C₂ T_x /CdS nanocomposite. This study provides an economic and sustainable strategy for the simultaneous valorization of biomass-derived FOL to produce FAL and FA as well as the production of clean energy hydrogen under mild condition based on noble metal-free semiconductor-based photocatalysts.

Solar-Driven Lignocellulose-to-H2 Conversion in Water using 2D-2D MoS2 /TiO2 Photocatalysts

As an alternative strategy for H₂ production under ambient conditions, solar-driven lignocellulose-to-H₂ conversion provides a very attractive approach to store and utilize solar energy sustainably. Exploiting efficient photocatalyst for photocatalytic lignocellulose-to-H₂ conversion is of huge significance and remains the key challenge for development of solar H₂ generation from lignocellulose. Herein, 2D-2D MoS₂ /TiO₂ photocatalysts with large 2D nanojunction were constructed for photocatalytic lignocellulose-to-H₂ conversion. In this smart structure, the 2D nanojunctions acted as efficient channel for charge transfer from TiO₂ to MoS₂ to improve charge separation efficiency and thus enhance photocatalytic lignocellulose-to-H₂ conversion activity. The 2 % MoS₂ /TiO₂ photocatalyst showed the highest photocatalytic lignocellulose-to-H₂ conversion performance with the maximal H₂ generation rate of 201 and 21.4 μmol h^-1  g^-1 in α-cellulose and poplar wood chip aqueous solution, respectively. The apparent quantum yield at 380 nm reached 1.45 % for 2 % 2D-2D TiO₂ /MoS₂ photocatalyst in α-cellulose aqueous solution. This work highlights the importance of optimizing the interface structures of photocatalyst for solar-driven lignocellulose-to-H₂ conversion.

Unconventional Photocatalysis in Conductive Polymers: Reversible Modulation of PEDOT:PSS Conductivity by Long-Lived Poly(Heptazine Imide) Radicals

In photocatalysis, small organic molecules are converted into desired products using light responsive materials, electromagnetic radiation, and electron mediators. Substitution of low molecular weight reagents with redox active functional materials may increase the utility of photocatalysis beyond organic synthesis and environmental applications. Guided by the general principles of photocatalysis, we design hybrid nanocomposites composed of n-type semiconducting potassium poly(heptazine imide) (K-PHI), and p-type conducting poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the redox active substrate. Electrical conductivity of the hybrid nanocomposite, possessing optimal K-PHI content, is reversibly modulated combining a series of external stimuli ranging from visible light under inert conditions and to dark conditions under an O2 atmosphere. Using a conductive polymer as the redox active substrate allows study of the photocatalytic processes mediated by semiconducting photocatalysts through electrical conductivity measurements.

Solar Reforming of Biomass with Homogeneous Carbon Dots

A sunlight-powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2-8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long-lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD-based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization.

Facile Modification of Titania with Nickel Sulfide and Sulfate Species for the Photoreformation of Cellulose into Hydrogen

Photocatalytic cellulose reformation is regarded as a potential and affordable route for sustainable H₂ evolution. However, direct photoreformation still suffers from challenges such as the limited solubility of cellulose and the dependence on the catalytic activity of noble metals. Herein, we report a new photoreformation of cellulose into H₂ over TiO₂ that is modified with nickel sulfide (Ni_x S_y ) and chemisorbed sulfate species (SO₄^2- ) by a one-pot approach. A significant elevation in the photocatalytic hydrogen evolution rate is achieved with a maximal value of 3.02 mmol g^-1  h^-1 during the first 3 h, which is almost 76-fold higher than that of P25 and comparable to that of Pt-P25. Aided by systematic investigation, it is proposed that nickel sulfide and sulfate modification contribute synergistically to the remarkably increased efficiency of biomass transformation. Specifically, Ni_x S_y acts as a cocatalyst for photocatalytic H₂ production, and we infer that SO₄^2- ions promote cellulose hydrolysis and the consequent accessibility of the biomass to catalysts. Further, the accumulated formate intermediates have a poisoning effect on the catalysts, the desorption of which can be controlled by tuning the aqueous alkalinity. Overall, our strategy for the modification of TiO₂ with SO₄^2- and Ni_x S_y provides a new perspective for the concurrent acceleration of cellulose hydrolysis and increase of the number of hydrogen evolution sites for the efficient photocatalytic reformation of cellulose into H₂ .

Aerobic Conditions Enhance the Photocatalytic Stability of CdS/CdOx Quantum Dots

Photocatalytic H₂ production through water splitting represents an attractive route to generate a renewable fuel. These systems are typically limited to anaerobic conditions due to the inhibiting effects of O₂ . Here, we report that sacrificial H₂ evolution with CdS quantum dots does not necessarily suffer from O₂ inhibition and can even be stabilised under aerobic conditions. The introduction of O₂ prevents a key inactivation pathway of CdS (over-accumulation of metallic Cd and particle agglomeration) and thereby affords particles with higher stability. These findings represent a possibility to exploit the O₂ reduction reaction to inhibit deactivation, rather than catalysis, offering a strategy to stabilise photocatalysts that suffer from similar degradation reactions.