Additive effects of rice husk-based carbon-silica composites on adsorption of diclofenac sodium and carbamazepine from aqueous solutions.

The present study investigated the adsorption of diclofenac sodium (DCF) and carbamazepine (CBZ) on carbon-silica composites (CSC), activated carbon (RH-AC) and biogenic silica (RH-BS) based on rice husks from aqueous solutions. The materials were characterised using scanning electron microscopy, infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, nitrogen sorption and elemental analysis. These methods provided essential information on the morphology, chemical composition, textural properties and surface characteristics of porous materials. The results of the adsorption studies demonstrate that the investigated materials exhibit varying adsorption capacities for DCF and CBZ. The maximum adsorption capacity was achieved by CSCs, with 1111 mg g-1 for DCF and 455 mg g-1 for CBZ and indicates additive effects on the adsorption capacity of CSCs compared to RH-AC and RH-BS. In addition to the hydrogen bonds and the π-π electron donor-acceptor interactions of the carbon component, further hydrogen bonds are formed by the silanol groups of the silica component. The CSCs derived from rice husks represent an innovative approach to the more efficient removal of pharmaceutical residues from wastewater. This is accomplished by utilizing a single starting material for both components, thereby yielding a unique structural combination.

Mesoporous Silica-Based Membranes in Transdermal Drug Delivery: The Role of Drug Loss in the Skin.

Compared to other forms of drug administration, the use of Transdermal Drug Delivery Systems (TDDSs) offers significant advantages, including uniform drug release profiles that contribute to lower side effects and higher tolerability, avoidance of direct exposure to the gastrointestinal tract, better patient compliance due to their non-invasive means of application and others. Mesoporous silica membranes are of particular interest in this regard, due to their chemical stability and their tunable porous system, with adjustable pore sizes, pore volumes and surface chemistries. While this allows for fine-tuning and, thus, the development of optimized TDDSs with high loading capacities and the desired release profile of a given drug, its systemic availability also relies on skin penetration. In this paper, using a TDDS based on mesoporous silica membranes in Franz cell experiments on porcine skin, we demonstrate surprisingly substantial drug loss during skin penetration. Drug passage through porcine skin was found to be dependent on the age and pre-treatment of the skin. pH and temperature were major determinants of drug recovery rates as well, indicating drug loss in the skin by enzymatic metabolization. Regarding the TDDS, higher loading obtained by SO3H surface modification of the mesoporous silica membranes reduced drug loss. Still, high loss rates in the skin were determined for different drugs, including anastrozole, xylazine and imiquimod. We conclude that, beyond the fine-tuned drug release profiles from the mesoporous silica membrane TDDS, remarkably high drug loss in the skin is a major issue for achieving desired skin penetration and, thus, the systemic availability of drugs. This also poses critical requirements for defining an optimal TDDS based on mesoporous silica membranes.

Increased Readiness for Water Splitting: NiO-Induced Weakening of Bonds in Water Molecules as Possible Cause of Ultra-Low Oxygen Evolution Potential.

The development of non-precious metal-based electrodes that actively and stably support the oxygen evolution reaction (OER) in water electrolysis systems remains a challenge, especially at low pH levels. The recently published study has conclusively shown that the addition of haematite to H2SO4 is a highly effective method of significantly reducing oxygen evolution overpotential and extending anode life. The far superior result is achieved by concentrating oxygen evolution centres on the oxide particles rather than on the electrode. However, unsatisfactory Faradaic efficiencies of the OER and hydrogen evolution reaction (HER) parts as well as the required high haematite load impede applicability and upscaling of this process. Here it is shown that the same performance is achieved with three times less metal oxide powder if NiO/H2SO4 suspensions are used along with stainless steel anodes. The reason for the enormous improvement in OER performance by adding NiO to the electrolyte is the weakening of the intramolecular O─H bond in the water molecules, which is under the direct influence of the nickel oxide suspended in the electrolyte. The manipulation of bonds in water molecules to increase the tendency of the water to split is a ground-breaking development, as shown in this first example.

Reproducibility of inverse gas chromatography under infinite dilution: Results and interpretations of an interlaboratory study.

Over the last years, inverse gas chromatography (IGC) proved to be a versatile and sensitive analytical technique for physicochemical properties. However, the comparability of results obtained by different users and devices remains a topic for debate. This is the first time, an interlaboratory study using different types of IGC instruments is reported. Eight organizations with different IGC devices defined a common lab measurement protocol to analyse two standard materials, silica and lactose. All data was collected in a standard result form and has been treated identically with the objective to identify experimentally observed differences and not potentially different data treatments. The calculated values of the dispersive surface energy vary quite significantly (silica: 22 mJ/m2 - 34 mJ/m2, lactose 37 mJ/m2 - 51 mJ/m2) and so do the ISP values and retention volumes for both materials. This points towards significant and seemingly undiscovered differences in the operation of the instruments and the obtained underlying primary data, even under the premise of standard conditions. Variations are independent of the instrument type and uncertainties in flow rates or the injected quantities of probe molecules may be potential factors for the differences. This interlaboratory study demonstrates that the IGC is a very sensitive analytical tool, which detects minor changes, but it also shows that for a proper comparison, the measurement conditions have to be checked with great care. A publicly available standard protocol and material, for which this study can be seen as a starting point, is still needed to judge on the measurements and the resulting parameters more objectively.

Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy-entropy compensation effect.

Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in the infinite dilution mode on macro-porous micro glass spheres before and after surface modification with (3-mercaptopropyl)trimethoxysilane. To provide information about the polar interactions between probe molecules and the silica surface, in particular, eleven polar molecules have been injected. In summary, the free surface energy for pristine silica ( γ S t o t a l = 229 mJ/m2) and for (3-mercaptopropyl)trimethoxysilane-modified silica ( γ S t o t a l = 135 mJ/m2) indicates a reduced wettability after surface modification. This is due to the reduction of the polar component of the free surface energy ( γ S S P ) from 191 mJ/m2 to 105 mJ/m2. Simultaneously, with the reduction of surface silanol groups caused by surface modification of silica and, therefore, the decrease in polar interactions, a substantial loss of Lewis acidity was observed by various IGC approaches. Experiments with all silica materials have been conducted at temperatures in the range from 90°C to 120°C to determine the thermodynamic parameters, such as adsorption enthalpy ( Δ H a d s ) and adsorption entropy ( Δ S a d s ), using the Arrhenius regression procedure evaluating the IGC data. With the help of the enthalpy-entropy compensation, two types of adsorption complexes are assumed between polar probe molecules and the silica surface because of different isokinetic temperatures. Identical adsorption complexes with an isokinetic temperature of 370°C have been assigned to alkanes and weakly interacting polar probes such as benzene, toluene, dichloromethane, and chloroform. Polar probe molecules with typical functional groups such as OH, CO, and CN, having the ability to form hydrogen bonds to the silica surface, exhibit a lower isokinetic temperature of 60°C. Quantum chemical calculations of the probe molecules on a non-hydroxylated and hydroxylated silica cluster supported the formation of hydrogen bonds in the case of a strong polar adsorption complex with a bonding distance of 1.7 nm-1.9 nm to the silica surface.

Towards High Surface Area α-Al2O3-Mn-Assisted Low Temperature Transformation.

When impregnated with manganiferous precursors, γ-Al2O3 may be converted into α-Al2O3 under relatively mild and energy-saving conditions. In this work, a manganese assisted conversion to corundum at temperatures as low as 800 °C is investigated. To observe the alumina phase transition, XRD and solid-state 27Al-MAS-NMR are applied. By post-synthetical treatment in concentrated HCl, residual manganese is removed up to 3 wt.-%. Thereby, α-Al2O3 with a high specific surface area of 56 m2 g-1 is obtained after complete conversion. Just as for transition alumina, thermal stability is an important issue for corundum. Long-term stability tests were performed at 750 °C for 7 days. Although highly porous corundum was synthesized, the porosity decreased with time at common process temperatures.

Drying of Hierarchically Organized Porous Silica Monoliths-Comparison of Evaporative and Supercritical Drying.

In this study, we present a detailed comparison between a conventional supercritical drying process and an evaporative drying technique for hierarchically organized porous silica gel monoliths. These gels are based on a model system synthesized by the aqueous sol-gel processing of an ethylene-glycol-modified silane, resulting in a cellular, macroporous, strut-based network comprising anisotropic, periodically arranged mesopores formed by microporous amorphous silica. The effect of the two drying procedures on the pore properties (specific surface area, pore volume, and pore widths) and on the shrinkage of the monolith is evaluated through a comprehensive characterization by using nitrogen physisorption, electron microscopy, and small-angle X-ray scattering. It can clearly be demonstrated that for the hierarchically organized porous solids, the evaporative drying procedure can compete without the need for surface modification with the commonly applied supercritical drying in terms of the material and textural properties, such as specific surface area and pore volume. The thus obtained materials deliver a high specific surface area and exhibit overall comparable or even improved pore characteristics to monoliths prepared by supercritical drying. Additionally, the pore properties can be tailored to some extent by adjusting the drying conditions, such as temperature.

Dispersible SnO2 :Sb and TiO2 Nanocrystals After Calcination at High Temperature.

High-temperature treatment of functional nanomaterials, through postsynthesis calcination, often represents an important step to unlock their full potential. However, such calcination steps usually severely limit the preparation of colloidal solutions of the nanoparticles due to the formation of sintered agglomerates. Herein, a simple route is reported to obtain colloidal solutions of calcined n-conductive antimony doped tin oxide (ATO) as well as titanium dioxide (TiO2 ) nanoparticles without the need for additional sacrificial materials. This is achieved by making use of the reduced contact between individual nanoparticles when they are assembled into aerogels. Following the calcination of the aerogels at 500 °C, redispersion of the nanoparticles into stable colloidal solutions with various solvents can be achieved. Although a slight degree of sintering is inevitable, the size of the resulting aggregates in solution is still remarkably small with values below 30 nm.

Reactive Additive Capillary Stamping with Double Network Hydrogel-Derived Aerogel Stamps under Solvothermal Conditions.

Integration of solvothermal reaction products into complex thin-layer architectures is frequently achieved by combinations of layer transfer and subtractive lithography, whereas direct additive substrate patterning with solvothermal reaction products has remained challenging. We report reactive additive capillary stamping under solvothermal conditions as a parallel contact-lithographic access to patterns of solvothermal reaction products in thin-layer configurations. To this end, corresponding precursor inks are infiltrated into mechanically robust mesoporous aerogel stamps derived from double-network hydrogels. The stamp is then brought into contact with a substrate to be patterned under solvothermal reaction conditions inside an autoclave. The precursor ink forms liquid bridges between the topographic surface pattern of the stamp and the substrate. Evaporation-driven enrichment of the precursors in these liquid bridges, along with their liquid-bridge-guided conversion into the solvothermal reaction products, yields large-area submicron patterns of the solvothermal reaction products replicating the stamp topography. For example, we prepared thin hybrid films, which contained ordered monolayers of superparamagnetic submicron nickel ferrite dots prepared by solvothermal capillary stamping surrounded by nickel electrodeposited in a second orthogonal substrate functionalization step. The submicron nickel ferrite dots acted as a magnetic hardener, halving the remanence of the ferromagnetic nickel layer. In this way, thin-layer electromechanical systems, transformers, and positioning systems may be customized.

Synthesis of Turbostratic Boron Nitride: Effect of Urea Decomposition.

Since the recent discovery of the template-free synthesis of porous boron nitride, research on the synthesis and application of the material has steadily increased. Nevertheless, the formation mechanism of boron nitride is not yet fully understood. Especially for the complex precursor decomposition of urea-based turbostratic boron nitride (t-BN), a profound understanding is still lacking. Therefore, in this publication, we investigate the influence of different common pre-heating temperatures of 100, 200, 300, and 400 °C on the subsequent properties of t-BN. We show that the structure and porosity of t-BN can be changed by preheating, where a predominantly mesoporous material can be obtained. Within these investigations, the sample BN-300/2 depicts the highest mesopore surface area of 242 m2 g-1 with a low amount of micropores compared to other BNs. By thermal gravimetric analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy, valid details about the formation of intermediates, types of chemical bonds, and the generation of t-BN are delivered. Hence, we conclude that the formation of a mesoporous material arises due to a more complete decomposition of the urea precursor by pre-heating.