Chloromethylation of Lignin as a Route to Functional Material with Catalytic Properties in Cross-Coupling and Click Reactions.

Invited for this issue's cover are researchers from Tallinn University of Technology (TalTech). The image depicts the lignin chemical evolution route from raw biomass through a greener chloromethylation procedure developed by the research team. It showcases the transformation into lignin-supported metal nanoparticles, serving as a catalyst for various chemical reactions in both batch and continuous flow conditions. The Research Article itself is available at 10.1002/cssc.202301588.

Chloromethylation of Lignin as a Route to Functional Material with Catalytic Properties in Cross-Coupling and Click Reactions.

We present a novel, greener chloromethylation procedure for organosolv aspen lignin under mild reaction conditions without Lewis acid as a catalyst and in acetic acid as a solvent. This synthetic protocol provides a reliable approach to chloromethylated lignin (CML) and means to obtain valuable lignin derivatives. The resulted CML was subsequently transformed into 1-methylimidazolium lignin (ImL), which effectively serves as a stabilizing agent for Pd/CuO nanoparticles (Pd/CuO-NPs). To evaluate the versatility of developed lignin-based catalyst, we investigate its performance in a series of carbon-carbon bond formation reactions, including Suzuki-Miyaura, Sonogashira, Heck reactions, and azide-alkyne cycloaddition (click) reaction. Remarkably, this catalyst exhibited a high degree of catalytic efficiency, resulting in reactions with yields ranging from average to excellent. The heterogeneous catalyst demonstrated outstanding recyclability, enabling its reuse for at least 10 consecutive reaction cycles, with yields consistently falling within the range of 42 % to 84 %. A continuous flow reactor cartridge prototype employing Lignin@Pd/CuO-NPs was developed, yielding results comparable to those achieved in batch reactions. The utilization of Lignin@Pd/CuO-NPs as a catalyst showcases its potential to facilitate diverse carbon-carbon bond formation reactions and underscores its promising recyclability, aligning with the green chemistry metrics and principles of sustainability in chemical processes.

Sunlight-Driven Photocatalytic Degradation of Methylene Blue with Facile One-Step Synthesized Cu-Cu2O-Cu3N Nanoparticle Mixtures.

Sunlight-driven photocatalytic degradation is an effective and eco-friendly technology for the removal of organic pollutants from contaminated water. Herein, we describe the one-step synthesis of Cu-Cu2O-Cu3N nanoparticle mixtures using a novel non-aqueous, sol-gel route and their application in the solar-driven photocatalytic degradation of methylene blue. The crystalline structure and morphology were investigated with XRD, SEM and TEM. The optical properties of the as-prepared photocatalysts were investigated with Raman, FTIR, UV-Vis and photoluminescence spectroscopies. The influence of the phase proportions of Cu, Cu2O and Cu3N in the nanoparticle mixtures on the photocatalytic activity was also investigated. Overall, the sample containing the highest quantity of Cu3N exhibits the highest photocatalytic degradation efficiency (95%). This enhancement is attributed to factors such as absorption range broadening, increased specific surface of the photocatalysts and the downward band bending in the p-type semiconductors, i.e., Cu3N and Cu2O. Two different catalytic dosages were studied, i.e., 5 mg and 10 mg. The higher catalytic dosage exhibited lower photocatalytic degradation efficiency owing to the increase in the turbidity of the solution.

Solution-Mediated Inversion of SnSe to Sb2Se3 Thin-Films.

New facile and controllable approaches to fabricating metal chalcogenide thin films with adjustable properties can significantly expand the scope of these materials in numerous optoelectronic and photovoltaic devices. Most traditional and especially wet-chemical synthetic pathways suffer from a sluggish ability to regulate the composition and have difficulty achieving the high-quality structural properties of the sought-after metal chalcogenides, especially at large 2D length scales. In this effort, and for the first time, we illustrated the fast and complete inversion of continuous SnSe thin-films to Sb2Se3 using a scalable top-down ion-exchange approach. Processing in dense solution systems yielded the formation of Sb2Se3 films with favorable structural characteristics, while oxide phases, which are typically present in most Sb2Se3 films regardless of the synthetic protocols used, were eliminated. Density functional theory (DFT) calculations performed on intermediate phases show strong relaxations of the atomic lattice due to the presence of substitutional and vacancy defects, which likely enhances the mobility of cationic species during cation exchange. Our concept can be applied to customize the properties of other metal chalcogenides or manufacture layered structures.

A Novel Thermochemical Metal Halide Treatment for High-Performance Sb2Se3 Photocathodes.

The fabrication of cost-effective photostable materials with optoelectronic properties suitable for commercial photoelectrochemical (PEC) water splitting represents a complex task. Herein, we present a simple route to produce Sb2Se3 that meets most of the requirements for high-performance photocathodes. Annealing of Sb2Se3 layers in a selenium-containing atmosphere persists as a necessary step for improving device parameters; however, it could complicate industrial processability. To develop a safe and scalable alternative to the selenium physical post-processing, we propose a novel SbCl3/glycerol-based thermochemical treatment for controlling anisotropy, a severe problem for Sb2Se3. Our procedure makes it possible to selectively etch antimony-rich oxyselenide presented in Sb2Se3, to obtain high-quality compact thin films with a favorable morphology, stoichiometric composition, and crystallographic orientation. The treated Sb2Se3 photoelectrode demonstrates a record photocurrent density of about 31 mA cm-2 at -248 mV against the calomel electrode and can thus offer a breakthrough option for industrial solar fuel fabrication.

Pulsed laser deposition of Zn(O,Se) layers in nitrogen background Pressure.

Zinc oxy-selenide Zn(O,Se) is a novel material, that can replace the toxic CdS buffer layer in thin film solar cells and other optoelectronic devices. In this paper a systematic study of the structural, optical and electrical properties of Zn(O,Se) layers, grown by pulsed laser deposition under 50 mTorr of nitrogen background pressure, over a wide range of the substrate temperature, from RT to 600 °C, is reported. XRD, Raman, HR-SEM, XPS, UV-Vis techniques and Hall effect measurements have been used to investigate the structural, and optoelectronic properties of Zn(O,Se) layers. XRD analysis revealed that the polycrystalline ternary Zn(O,Se) phase formed at 500 °C. Raman analysis confirmed the formation of the polycrystalline Zn(O,Se) phase at 500 °C and an amorphous phase at substrate temperatures below 500 °C. Similarly, XPS analysis accompanied with the modified Auger parameters confirmed formation of ternary Zn(O,Se) layer at 500 °C as well. HR-SEM investigation showed the growth of homogenous, dense and adherent films onto a glass substrate. Furthermore, optical studies revealed that all prepared films are practically transparent in the visible region of the spectrum, with a band gap around 3 eV. Hall effect measurements revealed that conductivity, and electron concentration, increased by four orders of magnitude at 600 °C. It was found, that nitrogen background pressure maintained stable ratios of elemental contents in the whole range of the substrate temperature for Zn(O,Se) layers.

Aerosol-Assisted Fine-Tuning of Optoelectrical Properties of SWCNT Films.

We propose a novel, scalable, and simple method for aerosol doping of single-walled carbon nanotube (SWCNT) films. This method is based on aerosolization of a dopant solution (HAuCl4 in ethanol) and time-controlled deposition of uniform aerosol particles on the nanotube film surface. The approach developed allows fine-tuning of the SWCNT work function in the range of 4.45 (for pristine nanotubes) to 5.46 eV, controllably varying the sheet resistance of the films from 79 to 3.2 Ω/□ for the SWCNT films with 50% transmittance (at 550 nm). This opens a new avenue for traditional and flexible optoelectronics, both to replace existing indium-tin oxide electrodes and to develop novel applications of the highly conductive transparent films.

Postdeposition Processing of SnS Thin Films and Solar Cells: Prospective Strategy To Obtain Large, Sintered, and Doped SnS Grains by Recrystallization in the Presence of a Metal Halide Flux.

Postdeposition treatments (PDTs) are common technological approaches to achieve high-efficiency chalcogenide solar cells. For SnS, a promising solar cell material, most PDT strategies to control the SnS properties are overwhelmingly based on an annealing in sulfur-containing ambient atmosphere that is described by condensed-state reactions and vapor-phase transport. In this work, a systematic study of the impact of PDTs in a N2 atmosphere, ampules at temperatures between 400 and 600 °C, and a SnCl2 treatment at 250-500 °C on the properties of SnS films and SnS/CdS solar cells prepared by close-spaced sublimation is reported. The ampule and N2 annealing conditions do not affect the grain size of the SnS layers but significantly impact the concentration of intrinsic point defects, carrier density, and mobility. Annealing at 500-600 °C strongly enhances the hole concentration and decreases the carrier mobility, having detrimental impacts on the device performance. SnCl2 treatment promotes grain growth, sintering, and doping by mass transport through the melted phase; it adjusts the hole density and improves the carrier mobility in the SnS layers. SnS/CdS solar cells with an efficiency of 2.8% are achieved in the SnCl2 treatment step, opening new possibilities to further improve the performance of SnS-based devices.

Thermal stability of red algal galactans: Effect of molecular structure and counterions.

Thermal degradation of κ-, ι-, λ-carrageenans, furcellaran, funoran and agarose samples in dry and sol states was investigated. The polysaccharides subjected to heat treatment were characterized by 1H NMR, 13C NMR and FTIR spectroscopy, size exclusion chromatography and static rheometry methods. The microstructure of galactan gels was studied using a cryofixation method in combination with freeze-drying and SEM techniques. Thermal stability at high temperatures decreases in the order of agarose>furcellaran>funoran>κ-carrageenan>λ-carrageenan>ι-carrageenan for dry preparations. The respective sequence for sol state is ι-carrageenan>λ-carrageenan>κ-carrageenan>furcellaran>funoran>agarose. The presence of methoxy groups stabilizes algal polysaccharides whereas divalent cations as counterions increase the susceptibility towards thermal degradation. In dry state the thermal treatment leads to significant desulfation of the galactan before the complete depolymerization occurs. Depending on the sulfation degree and the presence of 3,6-anhydrogalactose residues in the galactan, a notable amount of 5-hydroxymethylfurfural (yield 0.7-21.8%) is formed during the decomposition in sol state.

Polydopamine as an adhesive coating for open tubular capillary electrochromatography.

Polydopamine (PolyD) coating was used as an adhesive layer in the preparation of biological stationary phases for open tubular capillary electrochromatography (OT-CEC). The influence of coating solution freshness, coating time, temperature and dopamine hydrochloride concentration on the PolyD layer formation was studied. The performance of the polyD coating was monitored by measuring the electro-osmotic flow in coated capillaries. Following polyD coating of the capillary, secondary layer material (e.g. cell membrane solutions, phospholipid mixtures or mitochondria) was inserted into the capillary for at least 1 h. The performance of these double-coated capillaries (a polyD layer+a biological material layer) was compared with capillaries containing the respective biological material directly attached to the capillary wall. The study reveals that the presence of polyD layer in fused silica capillaries improves the performance of lipid and membrane fragment coatings in capillaries. At the same time, the thickness of the polyD layer does not have marked impact on the secondary coatings. Analysis with test analytes demonstrated that double-coated capillaries can be applied to study membrane-drug interactions.

ZnO Nanorods via Spray Deposition of Solutions Containing Zinc Chloride and Thiocarbamide.

In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ∼2.5 to 12 spraying ZnCl2and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However, tiny 'spot'-like formations of ZnS were detected on the side planes of hexagonal rods prepared from the thiocarbamide containing solutions. Being adsorbed on the side facets of the crystals ZnS inhibits width growth and promotes longitudinalc-axis growth.