Scientific publications

We present a versatile strategy to tailor the nanostructure of monolithic carbon aerogels. By use of an aqueous colloidal solution of polystyrene in the sol-gel processing of resorcinol-formaldehyde gels, we can prepare, after supercritical drying and successive carbonization, freestanding monolithic carbon aerogels, solely composed of interconnected and uniformly sized hollow spheres, which we name carbon spherogels. Each sphere is enclosed by a microporous carbon wall whose thickness can be adjusted by the polystyrene concentration, which affects the pore texture as well as the mechanical properties of the aerogel monolith. In this study, we used monodisperse polystyrene spheres of approximately 250 nm diameter, which result in an inner diameter of the final hollow carbon spheres of approximately 200 ± 5 nm due to shrinkage during the carbonization process. The excellent homogeneity of the samples, as well as uniform sphere geometries, are confirmed by small- and angle X-ray scattering. The presence of macropores between the hollow spheres creates a monolithic network with the benefit of being reversibly compressible up to 10% linear strain without destruction. Electrochemical tests demonstrate the applicability of ground and CO2 activated carbon spherogels as electrode materials.

High demand for safer and more stable lithium-ion batteries brings up the challenge for finding better electrode materials. In this work, we study the functionalities of titanium niobium oxide (TNO)/carbon hybrid materials using carbon onions (OLC) and carbon nanohorns (NS), which are synthesized by well-controlled sol-gel chemistry, for anodes in lithium-ion batteries. We used two different molar ratios of titanium to niobium oxide (1:2 and 1:5), and we compared the TNO-OLC and TNO-NS hybrid materials to conventional electrodes using physically admixed carbon black. TNO-OLC-1:2 and TNO-OLC-1:5 nanohybrid materials displayed good electrochemical performance, with initial capacity values of 284 mAh/g and 290 mAh/g, respectively, normalized to the metal oxide mass. Moreover, they maintained 68% (TNO-OLC-1:2) and 69% (TNO-OLC-1:5) of the initial capacity at 1 A/g, outperforming the carbon nanohorns hybridized and composited electrode which maintained less than 50%. The long-term cycling stability of 800 cycles presents good capacity retention of 73% (TNO-OLC-1:2) and 76% (TNO-OLC-1:5), while the TNO-NS-1:2 hybrid material yields better capacity retention of 90% despite its low capacity. Our study demonstrates that the combination of TNO with appropriate carbon substrates enables good electrochemical performance but requires careful evaluation of the interplay of crystal structure, phase content, and particle morphology.

Technologies for the effective and energy efficient removal of salt from saline media for advanced water remediation are in high demand. Capacitive deionization using carbon electrodes is limited to highly diluted salt water. Our work demonstrates the high desalination performance of the silver/silver chloride conversion reaction by a chloride ion rocking-chair desalination mechanism. Silver nanoparticles are used as positive electrodes while their chlorination into AgCl particles produces the negative electrode in such a combination that enables a very low cell voltage of only Δ200 mV. We used a chloride-ion desalination cell with two flow channels separated by a polymeric cation exchange membrane. The optimized electrode paring between Ag and AgCl achieves a low energy consumption of 2.5 kT per ion when performing treatment with highly saline feed (600 mM NaCl). The cell affords a stable desalination capacity of 115 mg g−1 at a charge efficiency of 98%. This performance aligns with a charge capacity of 110 mA h g−1.

In nanoconfinement, the reversible electrochemisorption of hydrogen extends the voltage window of aqueous electrolytes. This process has been well studied for different aqueous electrolytes but not compared to the performance of heavy water. Herein, we study hydrogen and deuterium electrosorption on a porous carbon electrode under negative polarization using sodium chloride as the salt. As electrodes, we use microporous carbons with an average pore size in the sub-nanometer range and, for comparison, mesoporous carbon nanotube bucky paper. We show that the hydrogen electrochemisorption and gas evolution processes are more pronounced than for deuterium while the same potential is applied. Our data confirm lower ion mobility of D2O compared to H2O, and a shift of the reversible charging and discharging process toward more negative potentials.

Abstract Engineered cell–nanostructured interfaces generated by vertically aligned silicon nanowire (SiNW) arrays have become a promising platform for orchestrating cell behavior, function, and fate. However, the underlying mechanism in SiNW-mediated intracellular access and delivery is still poorly understood. This study demonstrates the development of a gene delivery platform based on conical SiNW arrays for mechanical cell transfection, assisted by centrifugal force, for both adherent and nonadherent cells in vitro. Cells form focal adhesions on SiNWs within 6 h, and maintain high viability and motility. Such a functional and dynamic cell–SiNW interface features conformational changes in the plasma membrane and in some cases the nucleus, promoting both direct penetration and endocytosis; this synergistically facilitates SiNW-mediated delivery of nucleic acids into immortalized cell lines, and into difficult-to-transfect primary immune T cells without pre-activation. Moreover, transfected cells retrieved from SiNWs retain the capacity to proliferate—crucial to future biomedical applications. The results indicate that SiNW-mediated intracellular delivery holds great promise for developing increasingly sophisticated investigative and therapeutic tools.

Ultraviolet absorbing materials have important applications in which graphene is a strong candidate, yet, few efforts are being exerted to improve its absorption in the UV-region. We show that UV absorption in single-layer graphene can be enhanced by manoeuvring its electronic properties through converting it to a nanomembrane-like structure, or nanomesh. Regular and irregular pores were created by Electron Beam Lithography and a lithography-free process respectively. Theoretical calculations, using density functional theory, confirmed the experimental results, and indicated that the absorption peaks are a result of changes in the band structures of the nanomembrane graphene (NMGs) arising from the pore superlattice.

A comprehensive study on the engineering of titanium dioxide-functionalized nanoporous anodic alumina distributed Bragg reflectors (TiO2–NAA-DBRs) for photocatalysis enhanced by the “slow photon” effect is presented. The photocatalytic performance of these composite photonic crystals (PCs) is assessed by monitoring photodegradation of a variety of organic molecules with absorbance bands across the spectral regions. This study demonstrates that photocatalytic performance of TiO2–NAA-DBRs is enhanced by the “slow photon” effect when the edges of the PC’s photonic stopband (PSB) fall within the absorbance band of the organic molecules. The photocatalytic performance is significantly enhanced when the PSB’s red edge is in close proximity to the absorbance band of the organic molecules. Overall photocatalytic degradation is also dependent on the total pore length of the PC structure, charge of the organic molecules, percentage of vis–near-IR irradiation, and matrix complexity (i.e., interfering ions and molecules) when the PC’s PSB is partially or entirely misaligned with respect to the absorbance band of the organic molecules. Finally, the real-life application of TiO2–NAA-DBRs to degrade pollutants such as pesticides in environmental matrices is demonstrated. This study provides new insights into the development of rationally engineered, high-performing, safe, and reusable photocatalyst systems.

In the last few years, the development of versatile coating chemistries has become a hot topic in surface science after the discovery that catecholamines can lead to conformal coatings upon oxidation from aqueous solutions. Recently, it was found that aminomalononitrile (AMN), a molecule implicated in the appearance of life on earth, is an excellent prototype of novel material-independent surface functionalizing agents leading to conformal and biocompatible coatings in a simple and direct chemical process from aqueous solutions. So far, very little insight has been gained regarding the mechanisms underlying coating deposition. In this paper, we show that the chemical evolution of AMN film deposition under slightly basic conditions is different in solution and on silica. Thereon, the coating proceeds via a nucleation process followed by further deposition of islands which evolve to produce nitrogen-rich superhydrophilic fibrillar structures. Additionally, we show that AMN-based material can form films at the air–solution interface from unshaken solutions. These results open new vistas into the chemistry of HCN-derived species of potential relevance in materials science.

The head articulation of the beetle Pachnoda marginata is a micro-tribological system which consists of the ventral convex structure called gula and the corresponding concave surface of the prothorax. The surfaces of both parts are in contact and are expected to be optimised for friction reduction. The relationship between structure, mechanical properties of the cuticle material and friction properties of this micro-tribological system are investigated. The surface and material structure of the gula and its prothoracic counterpart were studied in fractured pieces of the cuticle using scanning electron microscopy (SEM). Friction force measurements and contact area estimations between the gula and a glass plate were carried out for different normal loads (0.1–10.0 mN) using two different microtribometers. The tribological behavior of the gula cuticle was studied on the (1) fresh, (2) dry, and (3) dry chemically (chloroform-methanol) treated samples. The dry samples exhibited a considerably rougher surface compared to the fresh ones. Furthermore, the chemical treatment led to some decrease in surface roughness. The fresh gula cuticle had the largest contact area and the highest friction coefficient. The drying out of the cuticle led to a decrease in both the contact area and friction coefficient. The friction coefficient was the lowest in the chemically treated gula, although the contact area was larger than in the dry condition. The tribological results were partly explained by direct measurements of the contact area fitted by the Hertz and JKR contact models.

Dry adhesives using surface microstructures inspired by climbing animals have been recognized for their potentially novel capabilities, with relevance to a range of applications including pick-and-place handling. Past work has suggested that performance may be strongly dependent on variability in the critical defect size among fibrillar sub-contacts. However, it has not been directly verified that the resulting adhesive strength distribution is well described by the statistical theory of fracture used. Using in situ contact visualization, we characterize adhesive strength on a fibril-by-fibril basis for a synthetic fibrillar adhesive. Two distinct detachment mechanisms are observed. The fundamental, design-dependent mechanism involves defect propagation from within the contact. The secondary mechanism involves defect propagation from fabrication imperfections at the perimeter. The existence of two defect populations complicates characterization of the statistical properties. This is addressed by using the mean order ranking method to isolate the fundamental mechanism. The statistical properties obtained are subsequently used within a bimodal framework, allowing description of the secondary mechanism. Implications for performance are discussed, including the improvement of strength associated with elimination of fabrication imperfections. This statistical analysis of defect-dependent detachment represents a more complete approach to the characterization of fibrillar adhesives, offering new insight for design and fabrication.