CEJOR special issue of Croatian Operational Research Society

Central European Journal of Operations Research -     

Readily accessible mesoporous silica nanoparticles supported chiral urea-amine bifunctional catalysts for enantioselective reactions

The main objective of this study is to develop readily accessible and recyclable solid catalysts for enantioselective reactions. To achieve this, magnetic MCM-41 and non-magnetic SBA-15 mesoporous supports were prepared, then mesoporous silica supported chiral urea-amine bifunctional catalysts were synthesized by grafting of chiral urea-amine ligand onto SBA-15 and magnetic MCM-41. The magnetic and non-magnetic supports and so-prepared solid catalysts were characterized by using different methods such as N₂ sorption measurements, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope-energy dispersive X-ray analysis (FESEM-EDX), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results showed that (1R, 2R) or (1S, 2S)-1,2-diphenylethane-1,2-diamine was successively immobilized onto magnetic MCM-41 and SBA-15 pores. The heterogeneous chiral solid catalysts and their homogenous counterparts exhibited high activities both enantioselective transfer hydrogenation reaction (up to 99% conversion and 65% ee) and enantioselective Michael reaction (up to 98% conversion and 26% ee). Moreover, the SBA-15 supported solid catalysts were separated from the reaction mixture by simple filtration, whereas the magnetic MCM-41 supported solid catalysts were separated by simple magnetic decantation and reused in three consecutive catalytic experiments.     

Accelerated Photo-Induced Degradation of Benzidine-p-Aminothiophenolate Immobilized at Light-Enhancing TiO2 Nanotube Electrodes

Herein, the enhanced visible-light-induced degradation of the azo-dye benzidine-p-aminothiophenolate immobilized on TiO₂ nanotube electrodes is reported. Exploiting the reported photonic properties of the TiO₂ support and the strong electronic absorption of the dye allowed for employing surface-enhanced resonance Raman spectroscopy at 413 nm to simultaneously trigger the photoreaction and follow the time-dependent decay process. Degradation rate constants of up to 25 s⁻¹ were observed, which stand among the highest reported values for laser-induced degradation of immobilized dyes on photonically active supports. Contrast experiments with two differently light-enhancing TiO₂ nanotube electrodes establish the direct correlation of the material's optical response, that is, electromagnetic field enhancement, on the interfacial photocatalytic reaction.     

Tuning the Electrochemical Properties of Novel Asymmetric Integral Sulfonated Polysulfone Cation Exchange Membranes

In this study, novel asymmetric integral cation exchange membranes were prepared by the wet phase inversion of sulfonated polysulfone (SPSf) solutions. SPSf with different degrees of sulfonation (DS) was synthesized by variation in the amount of chlorosulfonic acid utilized as a sulfonating agent. The characterization of SPSf samples was performed using FTIR and ¹H-NMR techniques. SPSf with a DS of 0.31 (0.67 meq/g corresponding ion exchange capacity) was chosen to prepare the membranes, as polymers with a higher DS resulted in poor mechanical properties and excessive swelling in water. By a systematic study, the opportunity to tune the properties of SPSf membranes by acting on the composition of the polymeric solution was demonstrated. The effect of two different phase inversion parameters, solvent type and co-solvent ratio, were investigated by morphological and electrochemical characterization. The best properties (permselectivity of 0.86 and electrical resistance of 6.3 Ω∙cm²) were obtained for the membrane prepared with 2-propanol (IPA):1-Methyl-2-pyrrolidinone (NMP) in a 20:80 ratio. This membrane was further characterized in different solution concentrations to estimate its performance in a Reverse Electrodialysis (RED) operation. Although the estimated generated power was less than that of the commercial CMX (Neosepta) membrane, used as a benchmark, the tailor-made membrane can be considered as a cost-effective alternative, as one of the main limitations to the commercialization of RED is the high membrane price.     

Synthesis,characterization and catalytic performance in enantioselective reactions by mesoporous silica materials functionalized with chiral thiourea-amine ligand

Chiral heterogeneous catalysts have been synthesized by grafting of silyl derivatives of (1R, 2R)- or (1S, 2S)-1,2-diphenylethane-1,2-diamine on SBA-15 mesoporous support. The mesoporous material SBA-15 and so-prepared chiral heterogeneous catalysts were characterized by a combination of different techniques such as X-ray diffractometry (XRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) surface area. Results showed that (1R, 2R)- and (1S, 2S)-1,2-diphenylethane-1,2-diamine were successively immobilized on SBA-15 mesoporous support. Chiral heterogeneous catalysts and their homogenous counterparts were tested in enantioselective transfer hydrogenation of aromatic ketones and enantioselective Michael addition of acetylacetone to β-nitroolefin derivatives. The catalysts demonstrated notably high catalytic conversions (up to 99%) with moderate enantiomeric excess (up to 30% ee) for the heterogeneous enantioselective transfer hydrogenation. The catalytic performances for enantioselective Michael reaction showed excellent activities (up to 99%) with poor enantioselectivities. Particularly, the chiral heterogeneous catalysts could be readily recycled for Michael reaction and reused in three consecutive catalytic experiments with no loss of catalytic efficacies.

     

Dispersive Solid-Phase Extraction of Rhodium from Water,Street Dust,and Catalytic Converters Using a Cellulose–Graphite Oxide Composite

A cellulose–graphite oxide composite was synthesized and characterized as an adsorbent for dispersive solid-phase extraction of rhodium from various samples before atomic absorption detection. The pH, adsorbent volume, centrifugation time and rate, eluent concentration, volume and type, adsorption and elution contact time, sample volume, and matrix interferences were optimized. The developed method is simple, rapid, and inexpensive. The tolerance limits for rhodium were 10,000?mg?L^?1 sodium, 25,000?mg?L^?1 potassium, 10,000?mg?L^?1 magnesium, and 20,000?mg?L^?1 calcium. The recovery for rhodium exceeded 95%. Elution was performed with 10?mL of 2.5?mol?L^?1 H₂SO₄. The adsorption and elution contact times were 30 and 60?s, respectively. The detection limit of the method for rhodium was 5.4?µg?L^?1 and the precision as the relative standard deviation was 1.6%. A certified reference material 2556 (used auto catalyst pellets) and fortified samples were analyzed to evaluate the accuracy of the method. The optimized method was used for the preconcentration of rhodium from tap water, well water, wastewater, seawater, catalytic converters, and street dust.