Photoreforming of lignocellulose into H2 using nano-engineered carbon nitride under benign conditions

Photoreforming of lignocellulose is a promising approach toward sustainable H2 generation, but this kinetically challenging reaction currently requires UV-absorbing or toxic light absorbers under harsh conditions. Here, we report a cyanamide-functionalized carbon nitride, NCNCNx, which shows enhanced performance upon ultra-sonication. This activated NCNCNx allows for the visible-light driven conversion of purified and raw lignocellulose samples into H2 in the presence of various proton reduction co-catalysts. The reported room-temperature photoreforming process operates under benign aqueous conditions (pH ~2-15) without the need for toxic components.Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development, OM

Redox-based electrochemical adsorption technologies for energy-efficient water purification and wastewater treatment

Water scarcity, both economic and physical, affects close to a third of the world population. Efficient, affordable and robust purification technologies are needed for a range of separation contexts, from point-of-source treatment or remote in-situ purification devices to large-scale, centralized wastewater treatment facilities. Micropollutants (e.g., organic endocrine disruptors, pesticides, household chemicals, dyes and heavy metal cations) pose a particularly vexing problem in wastewater treatment, since current technologies suffer from high energetic penalties and performance limitations when confronted with pollutants at these very low concentrations (nM to μM), often in the presence of excess competing species. Redox-based electrochemical technologies offer a next-generation purification technology. Through specifically designed chemical selectivity at the electrode interface, redox-based systems can achieve high separation factors towards toxic pollutants, at low overpotentials and much higher current efficiencies than needed for capacitive-based methods. We present a novel redox-mediated electrochemical system, utilizing organometallic polymeric electrodes, to target pollutants ranging from pesticides to toxic heavy metals. Capture and release are controlled solely by electrochemical potential, thus there is no need for chemical regenerants or post-treatment, with little chemical waste produced and low water usage ratios (\u3c0.05). In addition, an asymmetric configuration can be implemented to achieve higher electrochemical performance and energy storage; at the same time, we control the water chemistry (i.e., no current diversion to water reduction and pH changes) and thus enhance separation factors \u3e300 towards target pesticides and organic pollutants in the μM range. Finally, through materials optimization, we show the strong stability of these electrodes for \u3e500 cycles with over 95% current efficiency. Please click Additional Files below to see the full abstract

Uncovering the Charge Transfer between Carbon Dots and Water by In Situ Soft X-ray Absorption Spectroscopy.

Carbon dots (CDs) exhibit outstanding physicochemical properties that render them excellent materials for various applications, often occurring in an aqueous environment, such as light harvesting and fluorescence bioimaging. Here we characterize the electronic structures of CDs and water molecules in aqueous dispersions using in situ X-ray absorption spectroscopy. Three types of CDs with different core structures (amorphous vs graphitic) and compositions (undoped vs nitrogen-doped) were investigated. Depending on the CD core structure, different ionic currents generated upon X-ray irradiation of the CD dispersions at the carbon K-edge were detected, which are interpreted in terms of different charge transfer to the surrounding solvent molecules. The hydrogen bonding networks of water molecules upon interaction with the different CDs were also probed at the oxygen K-edge. Both core graphitization and nitrogen doping were found to endow the CDs with enhanced electron transfer and hydrogen bonding capabilities with the surrounding water molecules.Volkswagen foundation (Freigeist Fellowship No. 89592), Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs National Foundation for Research, Technology and Development) OMV

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

Σύνθεση συμπολυμερών αποκρινόμενων σε πολλαπλά ερεθίσματα για την ανάπτυξη "έξυπνων" οργανικών/ανόργανων υβριδίων

Στα πλαίσια της εργασία αυτής συντέθηκαν πολυμερικές αλυσίδες, υβριδικά υλικά και νανοκάψουλες (ΝΚ) που βασίζονται σε μόρια σπιροπυρανίου (ΣΠ). Τα υλικά συντέθηκαν με τη μέθοδο ριζικού πολυμερισμού μεταφοράς ατόμου στην παρουσία ή απουσία διαλύτη από μόρια εκκινητή στο διάλυμα ή αγκυροβολημένα σε επιφάνειες. Η απόκριση των υλικών αυτών σε μεταβολές της πολικότητας του διαλύτη, του pH, και στην επίδραση ηλεκτρομαγνητικής ακτινοβολίας καθώς επίσης και η ιδιότητα τους να φθορίζουν μελετήθηκαν εκτενώς. Συμπολυμερή που βασίζονται σε μόρια ΣΠ και είναι αποκρίσιμα σε πολλά ερεθίσματα συντέθηκαν με τυχαίο συμπολυμερισμό του 2-(dimethylamino)ethyl methacrylate (DMAEMA) και του 1',3',3'-trimethyl-6-methacryloyloxy-spiro(2H-1-benzopyran-2,2'-indoline). Τα πολυμερή εμφανίζουν «ανάστροφο φωτοχρωμισμό» και «αρνητικό διαλυτοχρωμισμό» όταν η πολικότητα του μέσου αυξάνεται. Αποκρίνονται επίσης αντιστρεπτά σε αλλαγές του pH, ενώ η ευαισθησία τους σε μεταβολές της θερμοκρασίας εξαρτάται από την περιεκτικότητα τους σε μεροκυανίνη (ΜΕ) και τον φωτοεπαγώμενο επανασχηματισμό του ΣΠ. Ένα τυχαίο συμπολυμερές που εμφανίζει «κανονικό φωτοχρωμισμό» και βασίζεται στο μονομερές 1΄-(2-methacryloxyethyl)-3΄,3΄-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2΄-indoline) (SPMA), επίσης συντέθηκε. Μετά από ακτινοβόληση με υπεριώδες φώς, το ΣΠ ισομερίστηκε σε ένα μόριο Χ και δύο ισομερή ΜΕ. Αυτό είχε σαν αποτέλεσμα τη συντονιζόμενη μεταφορά ενέργειας Förster (ΣΜΕF) μεταξύ των μορίων Χ και ΜΕ, τα οποία αποτελούν ζεύγη δότη και δέκτη, αντίστοιχα, και τα οποία βρίσκονται στην ίδια ή σε διαφορετικές πολυμερικές αλυσίδες. Το φαινόμενο προάγεται από την συσσωμάτωση των πολυμερικών αλυσίδων στο νερό και την εγγύτητα των χρωμοφόρων. Στην εργασία αυτή, συντέθηκαν επίσης πολυμερικές ψήκτρες στην επιφάνεια νανοσωματιδίων σίλικας με τυχαία κατανομή μορίων DMAEMA και SPMA. Όταν τα υβρίδια ακτινοβολήθηκαν με υπεριώδες φώς, το ΣΠ ισομερίστηκε σε μόρια Χ και ΜΕ. Κατά συνέπεια, τα υβρίδια εμφανίζουν ΣΜΕF μεταξύ χρωμοφόρων που βρίσκονται στο ίδιο σωματίδιο. Το φαινόμενο ευνοείται από την εγγύτητα των μορίων στις πολυμερικές ψήκτρες και μπορεί να εφαρμοστεί για την ανίχνευση πρωτεϊνών και αμινοξέων. Τέλος, χρησιμοποιήθηκε μια πρωτοποριακή μέθοδος για τον αντιστρεπτό σχηματισμό ΝΚ που προάγεται από φώς και βασίζεται στην ανάπτυξη π-π αλληλεπιδράσεων μεταξύ ΣΠ που βρίσκονται σε πολυμερικές ψήκτρες. Η ιδιότητα των ΝΚ αυτών να φθορίζουν, να αποκρίνονται σε αλλαγές του pH στο νερό, και να καταστρέφονται μετά από ακτινοβόληση με ορατό φώς, δημιουργεί νέες προοπτικές για την ανάπτυξη ΝΚ με βιοϊατρικές εφαρμογές.The aim of this work is the synthesis and the investigation of the responsive behavior of a range of spiropyran (SP)-based materials including random copolymers, spherical polymer brushes and hollow nanoparticles. The ability of these materials to respond to a variety of applied external stimuli such as light, pH, temperature and solvent polarity renders them excellent candidates for various applications. Multiresponsive SP-based random copolymers which vary in the content of the SP moieties, were synthesized by the random copolymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) or methyl methacrylate (MMA) with the in-house synthesized SP monomer 1',3',3'-trimethyl-6-methacryloyloxy-spiro(2H-1-benzopyran-2,2'-indoline) by ATRP in solution. The PDMAEMA-co-PSP copolymers exhibited “reverse photochromism” and “negative solvatochromism” upon increasing the polarity of the solvent, in contrast to the PMMA-co-PSP analogue. Moreover, the PDMAEMA-co-PSP copolymers exhibited a reversible pH-responsive character in aqueous media with an acid-induced the SP-to-merocyanine (MC) isomerization and the formation of [MC-OH]+ and [SP-NH]+ species. The lower critical solution temperature (LCST) of the copolymers increased with their content in hydrophilic MC moieties, while the recovery of the hydrophobic SP species decreased the LCST. Finally, the copolymers exhibited a first-order photoinduced bleaching of the chromophore units in water and acetonitrile, with a slower decoloration rate in the aqueous medium due to the effective stabilization of the bipolar MC form. A PDMAEMA-co-(1΄-(2-methacryloxyethyl)-3΄,3΄-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2΄-indoline)) (PSPMA) random copolymer which exhibited “normal photochromism”, that is the SP-to-MC isomerization upon stimulation with UV light was also synthesized using the in-house synthesized monomer SPMA. The stimulation of the PDMAEMA-co-PSPMA copolymer with UV light in water resulted in the generation of three switterionic moieties from the same parent SP molecule; namely the non-planar X isomer and two different planar MC species, MC1 and MC2 which differ in polarity. The photo-isomers followed a biexponential thermal bleaching mechanism originated from localized barriers inherent in the polymer matrix which establish a non-homogeneous microenvironment around the chromophores. Moreover, the copolymer exhibited an intra- and inter-chain fluorescence resonance energy transfer (FRET) upon the photo-induced generation of both X and MC species which are FRET donor-acceptor pairs, respectively, from the SP isomers. The photo-regulated energy transfer was favored by the close proximity of the bipolar isomers promoted by the association of the random copolymers in water and the spectral overlap of the emission and absorption bands of X and MC isomers, respectively. The FRET process is interrupted by the thermal MC-to-SP isomerization which is retarded by the polar microenvironment and enabled before relaxation of the acceptors the read-out process. In the second part of this work, SiO2-g-(PDMAEMA-co-PSPMA) spherical brushes were synthesized from the surface of silica particles via copper-mediated ATRP in bulk. Stimulation of the hybrids with UV light resulted in the isomerization of the SP units to two different bipolar species; the cisoid non-planar X and the planar MC isomers which followed a biexponential thermal relaxation process to reform the SP isomers due to variations in the microenvironment polarity and the free volume in the polymer brush layer. The generation of two different bipolar species, X and MC, in aqueous media from the same parent SP molecule upon UV irradiation of the hybrids provided the unique property to the system of exhibiting FRET between X and MC residues. In this case, the proximity of the donor-acceptor pairs was promoted by the steric crowding within the polymer brush layer. The energy transfer was switched “off” upon the thermal fading of the MC species which exhibited adequate kinetic rates and enabled the monitoring of the process. This property of the nanohybrids can be successfully applied for the detection of biological substances such as proteins and aminoacids. In particular, the presence of bovine serum albumin (BSA) in the aqueous dispersion of the hybrids was proved to enhance significantly the FRET efficiency of the system, due to the accelerated MC formation catalyzed by the protein, while L-histidine did not affect the FRET efficiency of the hybrids however it retarded the MC bleaching by interaction with the MC dipoles. Finally, the light-driven supramolecular engineering of fluorescent nanocapsules (NCPs) utilizing the appropriate phototrigger to stimulate the SiO2-g-(PDMAEMA-co-PSPMA) spherical brushes, was also studied. The fabrication of the nanospheres was based on the formation of π-π H-type interactions between the MC photoisomers being in close proximity within the sterically crowded environment of the polymer brushes by applying UV irradiation which enabled the SP-to-MC isomerization of the photosensitive species. HF etching of the inorganic core resulted in the formation of dual-responsive polymeric vesicles whose wall’s robustness is provided by the MC-MC cross-link points. The disruption of the NCPs could be achieved remotely and progressively by applying a harmless trigger such as visible light irradiation. The hydrophilic nature of the DMAEMA comonomer not only provided dispersability of the vesicles in the environmentally benign aqueous media but also enabled the controlled alteration of the NCPs size stimulated by variations in the solution pH. The inherent ability of the NCPs to fluoresce in water opens new possibilities for the development of addressable nanoscale capsules for biomedical applications

End-Grafted Polymer Chains onto Inorganic Nano-Objects

Organic/inorganic nanohybrid materials have attracted particular scientific and technological interest because they combine the properties of the organic and the inorganic component. Inorganic nanoparticles exhibit interesting electrical, optical, magnetic and/or catalytic properties, which are related with their nano-scale dimensions. However, their high surface-to-volume ratio often induces agglomeration and leads to the loss of their attractive properties. Surface modification of the inorganic nano-objects with physically or chemically end-tethered polymer chains has been employed to overcome this problem. Covalent tethered polymer chains are realized by three different approaches: the “grafting to”, the “grafting from” and the “grafting through” method. This article reviews the synthesis of end-grafted polymer chains onto inorganic nanoparticles using “controlled/living” polymerization techniques, which allow control over the polymer characteristics and the grafting density of the end-tethered polymer chains

Selective Molecularly Mediated Pseudocapacitive Separation of Ionic Species in Solution

We report the development of a dual-electrode pseudocapacitive separation technology (PSST) to capture quantitatively, remotely, and in a reversible manner value-added carboxylate salts of environmental and industrial significance. The nanostructured pseudocapacitive cell exhibits elegant molecular selectivity toward ionic species: upon electrochemical oxidation, a poly­(vinylferrocene) (PVF)-based anodic electrode shows high selectivity toward carboxylates based on their basicity and hydrophobicity. Simultaneously, on the other side of the electrochemical cell, a poly­(anthraquinone) (PAQ)-based cathodic electrode undergoes electrochemical reduction and captures the counterions of these carboxylates. The separation and regeneration capability of the electrochemical cell was evaluated through the variations in concentration of the carboxylates in polar organic solvents (often used in electrocatalytic processes) upon electrochemical charging and neutralization of the polymeric cargo of the electrodes, respectively. The strong separation efficiency of the system was indicated by its ability to capture an individual carboxylate (acetate, formate, or benzoate) selectively over other competing ions present in solution in significant excess, with an electrosorption capacity in the range of 122–157 mg anions/g_cell (polymer and CNT components on the anodic and cathodic side of the cell). The ion sorption capacity of the cell was high even after five adsorption/desorption cycles (18 000 s of continuous operation). In addition, the cell exhibited molecular selectivity even between two carboxylates (e.g., between benzoate and acetate or formate) which differ only in terms of basicity and hydrophobicity. We anticipate that this strategy can be employed as a versatile platform for selective ion separations. In particular, the functionalization of electrochemical cells with the proper polymers would enable the remote and economically viable electro-mediated separation of the desired ionic species in a quantitative and reversible manner

Light-Regulated Supramolecular Engineering of Polymeric Nanocapsules

This article describes the light-driven supramolecular engineering of water-dispersible nanocapsules (NCPs). The novelty of the method lies in the utilization of an appropriate phototrigger to stimulate spherical polymer brushes, consisting of dual-responsive 2-(dimethylamino)­ethyl methacrylate (DMAEMA) and light-sensitive spiropyran (SP) moieties, for the development or disruption of the NCPs in a controlled manner. The fabrication of the nanocarriers is based on the formation of H-type π–π interactions between merocyanine (MC) isomers within the sterically crowded environment of the polymer brushes upon UV irradiation, which enables the SP-to-MC isomerization of the photosensitive species. After HF etching of the inorganic core, dual-responsive polymeric vesicles whose walls’ robustness is provided by the MC–MC cross-link points are formed. Disruption of the vesicles can be achieved remotely by applying a harmless trigger such as visible-light irradiation. The hydrophilic nature of the DMAEMA comonomer facilitates the engineering of the vesicles in environmentally benign aqueous media and enables the controlled alteration of the NCPs size upon variation of the solution pH. The inherent ability of the NCPs to fluoresce in water opens new possibilities for the development of addressable nanoscale capsules for biomedical applications

FexNi9-xS8 (x = 3-6) as potential photocatalysts for solar-driven hydrogen production?

The efficient reduction of protons by non-noble metals under mild conditions is a challenge for our modern society. Nature utilises hydrogenases, enzymatic machineries that comprise iron- and nickel- containing active sites, to perform the conversion of protons to hydrogen. We herein report a straightforward synthetic pathway towards well-defined particles of the bio-inspired material FexNi9-xS8, a structural and functional analogue of hydrogenase metal sulfur clusters. Moreover, the potential of pentlandites to serve as photocatalysts for solar-driven H2-production is assessed for the first time. The FexNi9-xS8 materials are visible light responsive (band gaps between 2.02 and 2.49 eV, depending on the pentlandite's Fe : Ni content) and display a conduction band energy close to the thermodynamic potential for proton reduction. Despite the limited driving force, a modest activity for photocatalytic H2 has been observed. Our observations show the potential for the future development of pentlandites as photocatalysts. This work provides a basis to explore powerful synergies between biomimetic chemistry and material design to unlock novel applications in solar energy conversion.The authors acknowledge financial support of the Fonds of the Chemical Industry (Liebig grant to U.-P. A.), the Deutsche Forschungsgemeinschaft (Emmy Noether grant to U.-P. A., Cluster of Excellence RESOLV (EXC2033), AP242/2-1; AP242/6-1; MA 5392/7-1), the Fraunhofer Internal Programs under Grant No. Attract 097-602175 as well as the Christian Doppler Association (Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development) and OMV