Experimental and Theoretical Estimations of Atrazine's Adsorption in Mangosteen-Peel-Derived Nanoporous Carbons.

Nanoporous carbons were prepared via chemical and physical activation from mangosteen-peel-derived chars. The removal of atrazine was studied due to the bifunctionality of the N groups. Pseudo-first-order, pseudo-second-order, and intraparticle pore diffusion kinetic models were analyzed. Adsorption isotherms were also analyzed according to the Langmuir and Freundlich models. The obtained results were compared against two commercially activated carbons with comparable surface chemistry and porosimetry. The highest uptake was found for carbons with higher content of basic surface groups. The role of the oxygen-containing groups in the removal of atrazine was estimated experimentally using the surface density. The results were compared with the adsorption energy of atrazine theoretically estimated on pristine and functionalized graphene with different oxygen groups using periodic DFT methods. The energy of adsorption followed the same trend observed experimentally, namely the more basic the pH, the more favored the adsorption of atrazine. Micropores played an important role in the uptake of atrazine at low concentrations, but the presence of mesoporous was also required to inhibit the pore mass diffusion limitations. The present work contributes to the understanding of the interactions between triazine-based pollutants and the surface functional groups on nanoporous carbons in the liquid-solid interface.

Performance of a C-containing Cu-based photocatalyst for the degradation of tartrazine: Comparison of performance in a slurry and CPC photoreactor under artificial and natural solar light.

A carbon-containing Cu-based material (Cu@C) was used as photocatalyst for the degradation of a commonly food-industry azo-dye (tartrazine, also called Y5), under solar light at laboratory and pilot scale photoreactors. Important performance parameters such as dark adsorption capacity, catalyst́s loading and initial concentration of the dye were first optimized in a slurry photoreactor at laboratory scale under artificial solar light following the kinetics of degradation of the dye. Afterwards, the photocatalytic activity was investigated at pilot scale in a compound parabolic collector (CPC) photoreactor operating for 10 h of irradiation. The degradation of tartrazine is among the highest values reported for alternative metal oxide semiconductors, in both photoreactor configurations. Catalytic data revealed a 3 times faster degradation kinetics of tartrazine in the CPC photoreactor under natural solar light than in the slurry reactor under artificial solar light. This behavior indicates that a moderate photon flux in the CPC is more adequate to operate with the prepared photocatalyst, as it minimizes the recombination of charge carriers in the catalyst. This is important, since most of the photocatalytic tests designed to evaluate the activity of novel materials are frequently carried out under simulated solar light and disregard the impact of photon flux in outdoor conditions.

Upgrading of pine tannin biochars as electrochemical capacitor electrodes.

Biochar derived from the pyrolysis of pine tannin is a green and available by-product of oil manufacturing that presents interesting features after having been activated by KOH at 650 °C. Different weight ratios of KOH to biochar were used and the resulting activated carbons (ACs) presented highly developed specific surface areas of up to 2190 m2 g-1, well-connected porosity and high oxygen content, leading to enhanced electrochemical performance when used as electrochemical capacitor electrodes in a 1 M H2SO4 aqueous electrolyte. Galvanostatic charge/discharge experiments evidenced that the best material achieved a maximum electrode capacitance of up to 232 F g-1 (at 0.5 A g-1) with a capacitance retention of 70% at 10 A g-1 using commercial mass loadings (i.e., approx. 10 mg cm-2). In addition, long cycling stability with a residual capacitance of 92 to 94% after 10,000 cycles at 5 A g-1 was achieved. These results prove that ACs derived from pine tannin biochars have great potential for their commercial use as electrochemical energy storage devices.

The Cramer's rule for the parametrization of phenol and its hydroxylated byproducts: UV spectroscopy vs. high performance liquid chromatography.

A linear algebra theorem like Cramer's rule was used for the analysis of a system of equations obtained from UV spectroscopy, and results were compared against those obtained from HPLC analysis. This parametrization allowed to quantify the concentration of the main intermediate products detected along the photodegradation of phenol under UV-Vis irradiation of TiO2. UV spectroscopy data for phenol, hydroquinone, and benzoquinone were analyzed using the Cramer's rule. The overlapping interference of the intermediate products in the UV spectra was corrected. It can be concluded that the Cramer's rule can be used for the parametrization of the UV absorbance data of phenol and its main intermediate products. This methodology permitted to obtain the concentration of phenol and their intermediate products by UV-visible with a high precision in comparison of HPLC. The parametrization showed a correlation coefficient of ca. 0.9775 between the phenol concentration obtained by UV spectroscopy and values obtained from HPLC analysis. In this sense, results can be considered with good precision, and accordingly, it can be concluded that the methodology is reliable, and UV-visible spectroscopy can be selected instead of HPLC in much of the experiments concerning with aqueous-phase reactions.

Sustainable production of nanoporous carbons: Kinetics and equilibrium studies in the removal of atrazine.

Nanoporous carbons have been prepared from mangosteen peels-derived chars by physical activation under CO2 flow as a function of temperature. As an example of circular bioeconomy, these sustainable adsorbents were used to remove atrazine, a common pesticide from the agroindustry. Several adsorption models such as Langmuir (two parameter), Sips and Redlich-Peterson (three parameters) were applied to verify the influence of carbon's properties on the uptake of atrazine. Additional kinetic models (pseudo-first order, pseudo-second order and Avrami's) allowed to establish that a mixture of physisorption and chemisorption describes the interaction between the nanoporous carbons and atrazine. As a general fact, an important diffusion of atrazine from the bulk of solution to the surface of carbons was observed. All samples were able to remove atrazine, but the highest uptake was found in the carbon with the highest contribution of micropores to the total pore of volume and with the lowest content of basic surface groups. Several correlations between the kinetic and equilibrium parameters for the atrazine adsorption were found as a function of the textural properties and surface chemistry. Based on the kinetics and equilibrium parameters, the present work proposes a mechanism for the atrazine adsorption on nanoporous carbons contributing to the understanding of the interactions between pollutant molecules and the surface functional groups on nanoporous carbons in the liquid-solid interface.

TiO2/S-Doped Carbons Hybrids: Analysis of Their Interfacial and Surface Features.

Hybrids containing approximately equal amounts of P25 TiO2 and S-doped porous carbons were prepared using a water-based slurry mixing method. The materials were extensively characterized by adsorption of nitrogen, potentiometric titration, thermal analysis in air and in helium, XRD, XPS and SEM. The collected results showed the significant blockage of carbon micropores by TiO2 particles deposited on their outer surface. The formation of a new interface, especially for the S-rich samples, might also contribute to the porosity alteration. Analysis of surface chemistry suggested the presence of Ti-S bonds with an involvement of sulfur from thiophenic species in the carbon phase. The latter, especially when polymer-derived, was mainly deposited on the TiO2 nanoparticles. Formation of Ti-S stabilized sulfur and increased the ignition temperature of the hybrids, especially those with a high content of sulfur, in comparison with the ignition temperature of carbons. The surfaces of hybrid with S-containing carbons was also thermally very stable and of basic chemical nature. The formation of interfacial structures Ti-C was detected by XPS analysis suggesting a partial reduction of the Ti.

C-doped anatase TiO2: Adsorption kinetics and photocatalytic degradation of methylene blue and phenol, and correlations with DFT estimations.

This work shows an easy and eco-friendly methodology to obtain almost pristine anatase phase of TiO2 by using furfural, a biomass-derived molecule, as a bio-template. The photocatalytic activity was studied following the degradation of methylene blue and phenol under artificial solar irradiation. Results were compared against those obtained on a commercial pristine anatase TiO2. The pseudo first-order, the second-order and the intraparticle diffusion kinetic models were verified. The textural and surface chemistry properties of the materials were correlated with the surface density of molecules adsorbed in equilibrium. The reaction-rate showed an almost perfect quadratic regression as a function of the surface density. Theoretical estimations of the density of states by DFT + U were performed showing that the total electron charge in the oxygen bonded to anatase TiO2 increased due to carbon doping in agreement with the prediction of appearance of atomic orbitals 2p from carbon atom in the hybrid material. C-doping is responsible of the red-shift from 3.14 to 2.94 eV observed for a Ti15O32C super-cell than pristine anatase Ti16O32. The increase in the activity of the C-doped TiO2 photocatalyst was due to the decrease in the energy band-gap promoting a higher absorption of photons from the visible light.

Hybrid Material Based on an Amorphous-Carbon Matrix and ZnO/Zn for the Solar Photocatalytic Degradation of Basic Blue 41.

Innovative composites based on an amorphous-carbon matrix containing a second phase ZnO oxide and/or highly dispersed Zn metallic were synthesized via a modified Pechini route, in which a partial pyrolysis method was reached. Studies of adsorption in the dark and the photocatalytic activity for the cationic azo-dye, basic blue 41, and degradation were carried out. X-ray diffraction patterns for the carbon matrix and its composite with Zn show characteristics of the amorphous carbon. The infrared in the mid region of the composite prepared with ZnO and Zn exhibit vibrational bands related to bonds zinc oxide. The surface pH of the material is the main factor responsible for the adsorption of the azo-dye, but the contribution of mesopores favored the diffusion of molecules from the bulk of solution to the pore framework. Esters-like functional groups on the surface of carbons hinder the adsorption of the azo-dye. When Zn is embedded within amorphous carbon the photocatalytic activity of the composites showed up to 2.4 higher than neat ZnO. The enhancement in the photocatalytic activity and stability of C/ZnO/Zn and C/Zn composites is discussed in terms of a protector effect by the carbon layers inserted in composites. Carbon layers are responsible to inhibit the lixiviation of ZnO particles along irradiation.

Design of Ag/ and Pt/TiO2-SiO2 nanomaterials for the photocatalytic degradation of phenol under solar irradiation.

The design of hybrid mesoporous TiO2-SiO2 (TS1) materials decorated with Ag and Pt nanoparticles was performed. The photocatalytic degradation of phenol under artificial solar irradiation was studied and the activity and selectivity of the intermediate products were verified. TiO2-SiO2 was prepared by sol-gel method while Ag- and Pt-based photocatalysts (TS1-Ag and TS1-Pt) were prepared by photodeposition of the noble metals on TS1. Two series of photocatalysts were prepared varying Ag and Pt contents (0.5 and 1.0 wt%). An increase in the photocatalytic activity up to two and five times higher than TS1 was found on TS1-Ag-1.0 and TS1-Pt-1.0, respectively. Changes in the intermediate products were detected on Ag- and Pt-based photocatalysts with an increase in the catechol formation up to 3.3 and 6.6 times higher than that observed on TS1, respectively. A two-parallel reaction mechanism for the hydroquinone and catechol formation is proposed. A linear correlation between the photocatalytic activity and the surface concentration of noble metals was found indicating that the electron affinity of noble metals is the driven force for both the increase in the photoactivity and for the remarkable changes in the selectivity of products.

Synthesis of 8-methyl-1-tetralone, a potential intermediate for (±)-platyphyllide.

An alternative method for the synthesis of the 8-methyl-1-tetralone from the commercially available 5-methoxy-1-tetralone has been developed. The transformation involves eight steps and affords an overall yield 25%.