Design and study of pillared graphenes and nanoporous carbon materials for energy, environmental and catalytic applications

Η χρήση νανοπορωδών υλικών απαντάται από την αρχαιότητα σε μία πληθώρα εφαρμογών χάρη στη δυνατότητα ελέγχου του μεγέθους των πόρων, της ποικιλόμορφης γεωμετρίας, των επιφανειακών ιδιοτήτων και της ικανότητάς τους να αλληλοεπιδρούν με μόρια και άτομα, ή να τα απορροφούν/απελευθερώνουν. Δεδομένου ότι ο άνθρακας συγκαταλέγεται μεταξύ των πλέον άφθονων στοιχείων στη γη και ότι μπορεί να βρεθεί σε πληθώρα μορφών, τα υλικά άνθρακα αποτελούν εξαιρετικές επιλογές για εφαρμογές που μπορούν να συνεισφέρουν για ένα πιο πράσινο μέλλον, χωρίς απόβλητα, και χαμηλότερο ενεργειακό και υλικό αποτύπωμα, και οι νέες μορφές πορώδους άνθρακα έχουν να παίξουν ένα σημαντικό ρόλο σε αυτό το πλαίσιο. Το πορώδες στα υλικά μπορεί να σχηματιστεί με πολλούς τρόπους: η παρούσα διδακτορική διατριβή εστιάζει στους πορώδεις άνθρακες που προκύπτουν από την ανθρακοποίηση, τη «χημική χάραξη», τη σύνθεση με χρήση προτύπου και την ενεργοποίηση, αλλά και υποστυλωμένες δομές που προσομοιάζουν αυτή του Παρθενώνα. Τα τελευταία κατασκευάστηκαν μέσω της παρεμβολής στιβαρών οργανικών ή/και ανόργανων πυλώνων μεταξύ φύλλων γραφενίου ώστε να διαχωρίζονται τα στρώματα και να δημιουργούνται διασυνδεδεμένοι κενοί χώροι με καλοσχηματισμένους πόρους και χημική συγγένεια. Προς την επίτευξη αυτού του στόχου, δύο νέα σύνθετα υλικά, ένα στο οποίο ένα πυριτικό δίκτυο δημιουργήθηκε στον ενδοστρωματικό χώρο ενός οργανικά τροποποιημένου οξειδίου του γραφενίου, και ένα άλλο στο οποίο το οξείδιο του γραφενίου υποστυλώθηκε με σιλοξάνια, εξετάστηκαν ως υλικά αποθήκευσης διοξειδίου του άνθρακα. Επιπλέον, διερευνήθηκε η ικανότητα εμπλουτισμένου με χαλκό πορώδους κυβοειδούς άνθρακα να δεσμεύει υδρόθειο, και παρουσιάστηκε το πώς ιεραρχημένοι πορώδεις άνθρακες με υψηλή ειδική επιφάνεια και όγκους πόρων μπορούν να παραχθούν κάνοντας χρήση αποβλήτων ζάχαρης και καφέ.

Monolithic in-plane integration of gate-modulated switchable supercapacitors (ipG‐Cap)

Monolithic integration of iontronic devices is a key challenge for future miniaturization and system integration, in particular the interconnection of multiple functional elements as required for ion computing. The G-Cap, a novel iontronic element, is a switchable supercapacitor with gating characteristics comparable to transistors in electronic circuits, but switching relies on ionic currents and ion electroadsorption. We report here the first monolithic in-plane G-Cap integration through 3D-inkjet printing of non-toxic nanoporous carbon precursors. The printed G-Cap has a three-electrode architecture integrating a symmetric "working" micro-supercapacitor (W-Cap) and a third "gate" electrode (G-electrode) that reversibly depletes/injects electrolyte ions into the system, effectively controlling the "working" capacitance. The printed precursor structures were directly converted into nanoporous carbon materials with a specific surface area of 544 m2 g−1. The symmetric W‐Cap operates with a proton conducting hydrogel electrolyte based on PVA/H2SO4 and shows a high capacitance (1.3 mF cm−2) that can be switched “on” and “off” by applying a DC bias potential (- 1.0 V) at the G-electrode. This effectively suppresses AC electroadsorption in the nanoporous carbon electrodes of the W-Cap, resulting in a high capacitance drop from an "on" to an "off" state. Printing offers far-reaching freedom of design for varying the device structure achieving superior device performance. The new monolithic structures achieve high rate performance, reversible on-off switching with an off-value as low as 0.5 % surpassing values reported so far. Establishing technologies and device architectures for functional ionic electroadsorption devices is crucial for diverse fields ranging from microelectronics and iontronics to biointerfacing and neuromodulation.

Application of Carbons Produced from Rice Husk in the Process of Capacitive Deionization

Nanoporous carbon materials are well recognized as the main components of electrodes in capacitive deionization. Herein, the activated carbons were produced based on rice husk which is an abundant waste material in southern regions of Kazakhstan. The resulting carbons were characterized electrochemically by comparing their performance with well-known brands of commercial porous carbons (i.e. Norit DLC Super 30, Kuraray YP 50F). The features of carbon/ carbon electrochemical cells were analyzed using the means of galvanostatic cycling with potential limitation and cyclic voltammetry. Whilst the surface morphology and elemental composition of carbons were observed using scanning electron microscopy combined with energy dispersive X-ray spectroscopy. Using the method of low-temperature nitrogen adsorption it has been established that the specific surface of home-made carbon produced based on rice husk is equal to 2290 m2g-1. The salt adsorption analysis has been performed using different concentrations of inlet solutions of sodium chloride. Our study has shown that the manufacturing and application of activated carbons based on rice husk can be highly efficient because the resulting electrode materials exhibit a high electrosorption capacity of 20.02 mg g-1, which exceeds similar values obtained in the case of application of commercial porous carbons.

An Electrochemical Aptasensor for Pb2+ Detection Based on Metal–Organic-Framework-Derived Hybrid Carbon

A new double-shelled carbon nanocages material was synthesized and developed an aptasensor for determining Pb2+ in aqueous solution. Herein, nanoporous carbon materials derived from core–shell zeolitic imidazolate frameworks (ZIFs) demonstrated excellent electrochemical activity, stability, and high specificity surface area, consequently resulting in the strong binding with aptamers. The aptamer strands would be induced to form G-quadruplex structure when Pb2+ was introduced. Under optimal conditions, the aptasensor exhibited a good linear relationship of Pb2+ concentration ranging from 0.1 to 10 μg L−1 with the detection limits of 0.096 μg L−1. The feasibility was proved by detecting Pb2+ in spiked water samples and polluted soil digestion solution. The proposed aptasensor showed excellent selectivity and reproducibility, indicating promising applications in environmental monitoring.

Nanoarchitectonics of Lotus Seed Derived Nanoporous Carbon Materials for Supercapacitor Applications

Of the available environmentally friendly energy storage devices, supercapacitors are the most promising because of their high energy density, ultra-fast charging-discharging rate, outstanding cycle life, cost-effectiveness, and safety. In this work, nanoporous carbon materials were prepared by applying zinc chloride activation of lotus seed powder from 600 °C to 1000 °C and the electrochemical energy storage (supercapacitance) of the resulting materials in aqueous electrolyte (1M H2SO4) are reported. Lotus seed-derived activated carbon materials display hierarchically porous structures comprised of micropore and mesopore architectures, and exhibited excellent supercapacitance performances. The specific surface areas and pore volumes were found in the ranges 1103.0–1316.7 m2 g−1 and 0.741–0.887 cm3 g−1, respectively. The specific capacitance of the optimum sample was ca. 317.5 F g−1 at 5 mV s−1 and 272.9 F g−1 at 1 A g−1 accompanied by high capacitance retention of 70.49% at a high potential sweep rate of 500 mV s−1. The electrode also showed good rate capability of 52.1% upon increasing current density from 1 to 50 A g−1 with exceptional cyclic stability of 99.2% after 10,000 cycles demonstrating the excellent prospects for agricultural waste stuffs, such as lotus seed, in the production of the high performance porous carbon materials required for supercapacitor applications.