Microwave-Assisted Synthesis of trans-Cinnamic Acid for Highly Efficient Removal of Copper from Aqueous Solution.

trans-Cinnamic acid was synthesized under microwave irradiation, and it was used for the removal of copper, a toxic metal found in industrial wastewater, from synthetic polluted aqueous solutions. Copper removal is more favorable at pH 5 and was enhanced by increasing the copper initial concentration, reaching a maximum uptake capacity of 389.5 mg/g, which is higher than those reported in the literature. Temperature exhibited a negligible effect on the removal of copper by trans-cinnamic acid. The isotherm equilibrium uptake data were found to be described by the Langmuir model. In addition, the study of the removal kinetics shows that the uptake of copper by trans-cinnamic acid follows pseudo-first order kinetics, and equilibrium is attained at approximately 30 min. Based on the X-ray photoelectron spectroscopy, X-ray diffraction, scanning transmission electron microscopy, and Fourier-transform infrared spectroscopy studies, a copper-cinnamic acid complex [Cu(CA)2] is formed during the removal process. The reusability of this coordination compound was investigated using HCl, HNO3, and NaOH 0.1 M as desorption eluents; HCl was capable of completely desorbing copper from [Cu(CA)2], and trans-cinnamic acid was recovered as the trans-isomer. Alternatively, the [Cu(CA)2] was used to remove octamethylcyclotetrasiloxane from gaseous streams for biogas purification, obtaining an adsorption capacity of 3.37 mg/g. These promising results demonstrate the feasibility of copper removal by trans-cinnamic acid because of its high uptake capacity and potential reusability.

Dehydration of fructose over thiol- and sulfonic- modified alumina in a continuous reactor for 5-HMF production: Study of catalyst stability by NMR.

In the present study, the synthesis of an organic group-modified alumina by the sol-gel method is proposed. This material has shown to have an enhanced catalytic performance with grafted organic groups and showed an improved stability. The prepared material has shown to have several O - H groups and an enhanced surface acidity. The alumina acidity was improved by incorporating thiol groups by grafting method, which promotes the tautomerization of fructose to its furanose form. Furthermore, the grafting of sulfonic groups catalyzes its dehydration. The modified alumina was thermally treated up to 200 °C to improve the functional groups stability. After, this modified material was packed into a continuous reactor system, designed and built by this group, to obtain 5-hydroxymethylfurfural (5-HMF) from fructose dissolved in a single-phase solution of tetrahydrofuran (THF) and H2O (4:1 w/w). The catalytic activity of this material was evaluated by the reaction of fructose dehydration at different reaction temperatures (60, 70, 80 and 90 °C). Fructose conversion and selectivity toward 5-HMF were determined by high performance liquid chromatography (HPLC), obtaining 95% and 73% respectively for the highest temperature. The catalyst showed an efficient stability after 24 hours in continuous flow at 70 °C. The loss of sulfur content was 15%, but the fructose conversion yield and the selectivity to 5-HMF after 24 hours of continuous reaction did not undergo significant changes (less than 5%). The nuclear magnetic resonance (NMR) tests confirmed the presence of the thiol and sulfonic groups before and after 24 hours of reaction, as well as the conservation of the same structure, demonstrating the efficient catalytic performance of the material. The catalysts were characterized by nitrogen adsorption/desorption, X-ray diffraction and infrared (IR) spectroscopy. Also, before and after use by utilizing elemental analysis and   1 H - 13 C cross-polarization magic-angle spinning (CPMAS) and dynamic-nuclear polarization (DNP)-enhanced   1 H - 13 C and   1 H - 29 Si CPMAS as well as directly excited   29 Si magic-angle spinning (MAS) NMR methods in solid-state.

Supercapacitance from cellulose and carbon nanotube nanocomposite fibers.

Multiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from ∼230 to ∼180 kJ mol(-1). They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g(-1) at a current density of 10 A g(-1), which increases to 145 F g(-1) upon the addition of 6% of MWNTs.