Improvement of the photocatalytic activity of ZnO thin films doped with manganese.

In the herein report, we synthesized ZnO thin films doped with manganese (Mn). We studied the impact of Mn doping loads (1 %, 3 %, 5 % wt.) on physicochemical properties of the compounds. Furthermore, we presented the photocatalytic efficiency in removal of methylene blue dye. The structural assay indicated ZnO conserve the wurtzite crystalline structure after dopant insertion. Furthermore, the crystalline size of catalysts was reduced after dopant incorporation. The SEM analysis showed a change in surface morphology after modification of ZnO thin films. Furthermore, Raman spectroscopy verified the Mn insertion inside the ZnO lattice. After the doping process, band gap was reduced by 16 %, in comparison to bare ZnO. After the photocatalytic test, the doped catalysts showed better performance than bare ZnO in removing MB. The best test showed a kinetics constant value of 2.9 × 10-3 min-1 after 120 min of visible irradiation. Finally, the Mn(5 %):ZnO thin film was suitable after five degradation cycles, and the degradation process efficiency was reduced by 32%.

Adsorption and Photocatalytic Degradation of Methylene Blue on TiO2 Thin Films Impregnated with Anderson-Evans Al-Polyoxometalates: Experimental and DFT Study.

In this work, we fabricated a TiO2 thin film, and the same film was modified with an Anderson aluminum polyoxometalate (TiO2-AlPOM). Physical-chemical characterization of the catalysts showed a significant change in morphological and optical properties of the TiO2 thin films after surface modification. We applied the kinetic and isothermal models to the methylene blue (MB) adsorption process on both catalysts. The pseudo-second order model was the best fitting model for the kinetic results; qe (mg/g) was 11.9 for TiO2 thin films and 14.6 for TiO2-AlPOM thin films, and k2 (g mg-1 min-1) was 16.3 × 10-2 for TiO2 thin films and 28.2 × 10-2 for TiO2-AlPOM thin films. Furthermore, the Freundlich model was suitable to describe the isothermal behavior of TiO2, KF (5.42 mg/g), and 1/n (0.312). The kinetics of photocatalytic degradation was fitted using the Langmuir-Hinshelwood model; kap was 7 × 10-4 min-1 for TiO2 and 13 × 10-4 min-1 for TiO2-AlPOM. The comparative study showed that TiO2 thin films reach a 19.6% MB degradation under UV irradiation and 9.1% MB adsorption, while the TiO2-AlPOM thin films reach a 32.6% MB degradation and 12.2% MB adsorption on their surface. The surface modification improves the morphological, optical, and photocatalytic properties of the thin films. Finally, the DFT study supports all the previously shown results.

Kinetic and Thermodynamic Study of Methylene Blue Adsorption on TiO2 and ZnO Thin Films.

In this work, we fabricated and characterized ZnO and TiO2 thin films, determining their structural, optical, and morphological properties. Furthermore, we studied the thermodynamics and kinetics of methylene blue (MB) adsorption onto both semiconductors. Characterization techniques were used to verify thin film deposition. The semiconductor oxides reached different removal values, 6.5 mg/g (ZnO) and 10.5 mg/g (TiO2), after 50 min of contact. The pseudo-second-order model was suitable for fitting the adsorption data. ZnO had a greater rate constant (45.4 × 10-3) than that of TiO2 (16.8 × 10-3). The removal of MB by adsorption onto both semiconductors was an endothermic and spontaneous process. Finally, the stability of the thin films showed that both semiconductors maintained their adsorption capacity after five consecutive removal tests.

Photophysical characterization of tetrahydroxyphenyl porphyrin Zn(II) and V(IV) complexes: experimental and DFT study.

Photodynamic therapy (PDT) is a promising technique for the treatment of various diseases. In this sense, the singlet oxygen quantum yield (Φ∆) is a physical-chemical property that allows to stablish the applicability of a potential photosensitizers (PS) as a drug for PDT. In the herein report, the Φ∆ of three photosensitizers was determined: metal-free tetrahydroxyphenyl porphyrin (THPP), THPP-Zn and the THPP-V metal complexes. Their biological application was also evaluated. Therefore, the in vitro study was carried out to assess their biological activity against Escherichia coli. The metal-porphyrin complexes exhibited highest activities against the bacterial strain Escherichia coli. at the highest concentration (175 µg/mL) and show better activity than the free base ligand (salts and blank solution). Results indicated a relation between Φ∆ and the inhibitory activity against Escherichia coli, thus, whereas higher is the Φ∆, higher is the inhibitory activity. The values of the Φ∆ and the inhibitory activity follows the tendency THPP-Zn > THPP > THPP-V. Furthermore, quantum chemical calculations allowed to gain deep insight into the electronic and optical properties of THPP-Zn macrocycle, which let to verify the most probable energy transfer pathway involved in the singlet oxygen generation.

New Polyaniline Derivative with Two Central Ester Groups: Synthesis, Characterization, and Theoretical Study.

A new polyaniline derivative was prepared to study the formation of quinoid-diimine units in its polymer. The monomer and polymer were experimentally and theoretically characterized. Both polymers have one or two electron-withdrawing groups as side substituents. The polymers' quinoid-diimine unit composition is affected by the electron-withdrawing side groups of aniline. The presence of the quinoid-diimine group diminished for the two electron-withdrawing groups of aniline. The polymer conductivity is different than with respect to polyemeraldine, associated with the quinoid-diimine units' composition. The quinoid-diimine composition is strongly increased in the polymer containing one electron-withdrawing group. Moreover, the polymer presented good solubility in organic solvents and moderate thermal stability.

Prosopis juliflora Seed Waste as Biochar for the Removal of Blue Methylene: A Thermodynamic and Kinetic Study.

In this work, we studied the methylene blue (MB) dye adsorption capacity on biochar derived from residues of Prosopis juliflora seed waste, a species found in the region of the tropical dry forest of Piojó in the Department of Atlántico, Colombia. The materials were obtained by pyrolysis at temperatures of 300, 500, and 700 °C. Biochar was characterized using Fourier transform infrared (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX), TGA, and Brunauer-Emmett-Teller (BET) techniques. The three biochar samples presented a macroporous, rough structure with pore size between 6 and 28 µm. The largest pore surface area observed was 1.28 m2/g for pyrolyzed biochar produced at 500 °C, larger than that of biochar produced at 700 °C, which was 0.83 m2/g. The adsorption results show that the maximum percentage of MB removal was 69%. According to SEM results, the material's pore sizes varied on average from 6 to 28 µm. We modeled MB adsorption on biomass through three different isotherm models. The Freundlich model was the best-fitting model for the removal of MB (K F = 1.447; 1/n = 0.352). The kinetic results showed that the pseudo-second-order model was the best-fitting model for the sorption process (q e = 2.94 mg/g; k 2 = 0.087 g/(mg/min-1)). Furthermore, the recycling test showed that the biochar did not change its adsorption capacity significantly. Finally, under the experimental conditions, the thermodynamic parameters indicated that the removal of MB using biochar was an endothermic and spontaneous process; all ΔG° values ranged from -2.14 to -0.95 kJ/mol; ΔH° was 23.54 kJ/mol and ΔS° was 79.5 J/mol.

Google Colab and Virtual Simulations: Practical e-Learning Tools to Support the Teaching of Thermodynamics and to Introduce Coding to Students.

Various studies have reported the versatility and great scope of programming tools in all areas of knowledge. Coding is generally of paramount importance to chemistry students regardless of whether they intend to work with theoretical chemistry. Google Colab notebooks can introduce students to programming concepts and could be a convenient tool to assist in the chemistry teaching process. In this article, we implemented Google Colab notebooks to aid in the teaching of thermodynamics in a physical chemistry class. We presented six notebooks, covering introductory concepts of both coding and thermodynamics as a set of learning objects that can be useful in a virtual learning environment. In addition, in some of the notebooks, we included a step-by-step guide on how to run virtual lab simulations. The Colab notebooks were created for students without previous experience in programming. All of the Colab notebooks contain exercises of the activities and the solutions of the proposed exercises. Furthermore, all of the Colab notebooks can be modified and downloaded from the Github repository. Finally, we used the Python programming language and Colab because they are free and widely used by the academic community.

Photophysical characterization and in vitro anti-leishmanial effect of 5,10,15,20-tetrakis(4-fluorophenyl) porphyrin and the metal (Zn(II), Sn(IV), Mn(III) and V(IV)) derivatives.

In this report 5 compounds were synthesized and structural and their photophysical characterization was performed (ΦΔ and Φf). Furthermore, in this in vitro study, their biological activity against Leishmania panamensis was evaluated. The photophysical behavior of these compounds was measured and high ΦΔ and low Φf was observed. Besides, DFT quantum calculations on the electronic structures were performed. Finally, the biological activity was determined by means of the compounds capacity to inhibit the viability of parasites using the MTT assay. The inclusion of the metal ions substantially modified the photophysical and biological properties in comparison with the free metal porphyrin (1). In fact, Zn2+ porphyrin derivative (2) showed a marked decrease of Φf and increase of ΦΔ. In this sense, using TDDFT approaches, a luminescent process for Sn4+ derivative (3) was described, where emissive states involve the ML-LCT transition. So, this led to a decrease in the singlet oxygen production (0.82-0.67). Biological results showed that all compounds inhibit the viability of L. panamensis with high efficiency; the decrease in the viability was greater as the concentration of exposure increased. Finally, under light irradiation the IC50 of L. panamensis against the Zn(II)-porphyrin (2) and V(IV)-porphyrin (5) was lower than the IC50 of the Glucantime control (IC50 = 2.2 and 6.95 µM Vs IC50 = 12.7 µM, respectively). We showed that the use of porphyrin and metalloporphyrin-type photosensitizers with exceptional photophysical properties can be successful in photodynamic therapy (PDT) against L. panamensis, being the diamagnetic ion Zn2+ a candidate for the preparation of metalloporphyrins with high singlet oxygen production.

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).

Background: Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV). Methods: Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and 13C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φ f) was measured using fluorescein as a standard, the singlet oxygen quantum yield (Φ D) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF). Results: UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φ f from 0.15 to 0.05 and the Φ D increased from 0.55 to 0.59. Finally, the effect of the compounds on the viability of L. panamensis was evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC 50 of 16.5 µM and the Sn(IV)-porphyrin complex had IC 50 of 19.2 µM. Conclusion: The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability of L. panamensis.

Zn(II)-tetracarboxy-phthalocyanine-Sensitized TiO2 Thin Films as Antimicrobial Agents under Visible Irradiation: a Combined DFT and Experimental Study.

In this article, we studied the antimicrobial activity of TiO2 sensitized by the Zn(II)-tetracarboxy-phthalocyanine (TcPcZn) complex using TiO2-Degussa P25 as a semiconductor source. The TiO2 thin films were deposited by the doctor blade method and were sensitized by the chemisorption process. The obtained compounds were characterized using Fourier transform infrared spectroscopy, UV-vis spectrophotometry, Raman spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy. Furthermore, we studied the stability of the adsorbed sensitizer on the semiconductor surface by using the density functional theory (DFT). Additionally, we determined the antimicrobial activity of TcPcZn-TiO2 against methicillin-resistant Staphylococcus aureus (MRSA). The Raman and optical results confirmed the sensitizing process. The TcPcZn-TiO2 thin films showed radiation absorption in the visible range of the electromagnetic spectrum (600-750 nm), and the dye anchored on the TiO2 surface had a band gap of 1.58 eV. The DFT study showed that TcPcZn supported on any phase of Degussa P25 is stable, making them suitable to act as catalysts in the proposed reactions. Finally, the TcPcZn-TiO2 thin films reached 76.5% of inhibition activity against MRSA.

In Vitro Anti-Leishmanial Effect of Metallic Meso-Substituted Porphyrin Derivatives against Leishmania braziliensis and Leishmania panamensis Promastigotes Properties.

In this study, a family of porphyrins based on 5,10,15,20-Tetrakis(4-ethylphenyl)porphyrin (1, Ph) and six metallo-derivatives (Zn2+(2, Ph-Zn), Sn4+(3, Ph-Sn), Mn2+ (4, Ph-Mn), Ni2+ (5, Ph-Ni), Al3+ (6, Ph-Al), and V3+ (7, Ph-V)) were tested as photosensitizers for photodynamic therapy against Leishmania braziliensis and panamensis. The singlet oxygen quantum yield value (ΦΔ) for (1-7) was measured using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen trapping agent and 5,10,15,20-(tetraphenyl)-porphyrin (H2TPP) as a reference standard; besides, parasite viability was estimated by the MTT assay. After metal insertion into the porphyrin core, the ΦΔ increased from 0.76-0.90 and cell viability changed considerably. The ΦΔ and metal type changed the cytotoxic activity. Finally, (2) showed both the highest ΦΔ (0.90) and the best photodynamic activity against the parasites studied (IC50 of 1.2 µM).

Do-it-yourself methodology for calorimeter construction based in Arduino data acquisition device for introductory chemical laboratories.

Many experimental thermochemical laboratories require monitoring temperatures during a reaction or physical procedure. Nowadays, there are many alternatives to fulfill this requirement; however, they are expensive for basic scholars and first-year undergraduates. In this paper, we describe an inexpensive and useful data acquisition device developed with the open-source Arduino software. In this work, we presented a methodology for easy calorimeter construction based in Arduino data acquisition device for introductory chemical laboratories, we used an LM35 transistor as a temperature sensor connected to an Arduino UNO microcontroller for temperature sensing and an aquarium air pump for agitation of reaction system. Besides, the hardware required for implementation is explained in detail. The device was built using the (DIY) do-it -yourself method, and the complete system had a total cost under $40. We showed details of all components for data acquisition construction. Finally, we tested the device in order to determine the exothermic dissolution heat (ΔH) for NaOH in water.

Physical-Chemical Study of Anthracene Selective Oxidation by a Fe(III)-Phenylporhyrin Derivative.

In this work, we studied the anthracene oxidation by hydroxyl radicals. Hydroxyl radical was generated by reaction of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Fe (III) (TPPFe) with hydrogen peroxide under visible radiation at a nitrogen atmosphere. The TPPFe was synthesized by Adler Method followed by metal complexation with Fe (III) chloride hexahydrate. Hydroxyl radical was detected by fluorescence emission spectroscopy and we studied kinetic of anthracene selective oxidation by hydroxyl radicals through the differential method. The TPPFe was characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) measurements. The results indicated that TPPFE was compound by micro-particles with a size distribution of around 2500 nm. Kinetic results showed that the apparent rate constant for the oxidation of anthracene increased exponentially on as temperature increases, furthermore, the activation energy for the Anthracene oxidation by hydroxyl radicals under visible irradiation was 51.3 kJ/mol. Finally, anthraquinone was the main byproduct generated after oxidation of anthracene by TPP-Fe under visible irradiation.

Photocatalytic activity of graphene oxide-TiO2 thin films sensitized by natural dyes extracted from Bactris guineensis.

This study synthesized and characterized composites of graphene oxide and TiO2 (GO-TiO2). GO-TiO2 thin films were deposited using the doctor blade technique. Subsequently, the thin films were sensitized with a natural dye extracted from a Colombian source (Bactris guineensis). Thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements were used for physico-chemical characterization. All the samples were polycrystalline in nature, and the diffraction signals corresponded to the TiO2 anatase crystalline phase. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) verified the synthesis of composite thin films, and the SEM analysis confirmed the TiO2 films morphological modification after the process of GO incorporation and sensitization. XPS results suggested a possibility of appearance of titanium (III) through the formation of oxygen vacancies (Ov). Furthermore, the optical results indicated that the presence of the natural sensitizer and GO improved the optical properties of TiO2 in the visible range. Finally, the photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution, and pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. These results indicated that the presence of GO has an important synergistic effect in conjunction with the natural sensitizer, reaching a photocatalytic yield of 33%.

Kinetic study of the quenching of singlet oxygen by naringin isolated from peels of the fruit of bitter orange (Citrus aurantium I)

Introduction: antioxidant activity is the capacity of a substance to inhibit oxidative degradation, mainly through its ability to react with both radical and non-radical species (e.g. singlet oxygen). Interest by scientific communities in the study of the antioxidant capacity of natural compounds has increased in recent years, due to their possible applications in the pharmaceutical, cosmetic and food industries. Objective: estimate the antioxidant capacity of naringin against singlet oxygen using the rubrene method. Methods: naringin was isolated from peels of the fruit of bitter orange (Citrus aurantium) and characterized using several spectroscopic techniques (UV-Vis and FTIR). The global rate constant for the reaction of 1O2 with naringin was determined with the Stern-Volmer plot derived from a stationary kinetic state based on the competition reaction with rubrene. Results: results showed that naringin acted as singlet oxygen quenching agent with a global rate constant of 2.1 x 107 M-1s-1 (derived from the linear relationship of Stern-Volmer). Conclusion: the kinetic study conducted suggests that naringin could be used as a singlet oxygen quenching agent in biological systems to protect them from oxidative damage(AU)

Introducción: la actividad antioxidante es la capacidad de una sustancia para inhibir la degradación oxidativa y actúa principalmente a través de su capacidad para reaccionar con las especies de radicales y no radicales (por ejemplo, oxígeno singulete). En los últimos años, se han incrementado el interés de las comunidades científicas en el estudio de la capacidad antioxidante de los compuestos naturales debido a sus posibles aplicaciones en la industria farmacéutica, cosmética y alimentaria. Objetivo: estimar la capacidad antioxidante de la naringina contra el oxígeno singulete usando el método de rubreno. Métodos: la naringina se aisló de cáscaras del fruto de la naranja agria (Citrus aurantium) y se caracterizó por algunas técnicas espectroscópicas (UV-Vis y FT-IR). La constante de velocidad global para la reacción de 1O2 con la naringina se determinó por medio del gráfico de Stern-Volmer derivado de una cinética en estado estacionario basada en la reacción de competición con el rubreno. Resultados: los resultados mostraron que la naringina actuó como un quenching del oxígeno singulete con una constante de velocidad global de 2.1 x 10 7 M-1s-1 (derivado de la relación lineal de Stern-Volmer). Conclusión: el estudio cinético sugiere que la naringina se podría utilizar como un quenching del oxígeno singulete en sistemas biológicos y protegerlos del daño oxidativo(AU)