Use of Nanostructured Photocatalysts for Dye Degradation: A Review

Among the technologies proposed for wastewater treatment, the Advanced Oxidation Processes are viable and technological strategies for dyes degradation. Different photocatalytic systems classified in metal oxides alone or combined through hybrid composites or immobilized onto supports have been designed in various nanostructured shapes for their application in the photodegradation of polluting dyes. This review aims to describe the dyes as an environmental threat, photocatalysis as an effective process to remove dyes from water and provide an overview of the recent studies using photocatalytic systems grouped according to their development. Furthermore, this review describes the main parameters of a photocatalytic system with an important role in dye photodegradation. Finally, we discuss the limitations of photocatalysis for real industrial applications and the challenges for this environmental nanotechnology

Effect of Mixed Oxide-Based TiO2 on the Physicochemical Properties of Chitosan Films

The physicochemical, mechanical, and structural properties of chitosan-based films (CS) alone or CS-films with mixed oxide nanoparticles (TiO2-ZnO-MgO, TZM; CSTZM) at different concentrations (125, 250, and 500 μg mL−1) were investigated. The addition of nano-TZM promoted a color change (from colorless to white) in the film-forming solution, which increased its turbidity and it decreased viscosity. CSTZM were semitransparent (transmittance, T% decreased up to 49%) compared to CS-based films (T% = 95.5). CSTZM (particularly at a concentration of 500 μg mL−1) exhibited an improvement in the moisture content (decreased from 12.6 to 9.67%), water solubility (decreased from 14.94 to 10.22%), degree of swelling (increased from 19.79 to 36.28%), water vapor barrier (decreased from 6.62 x 10−16 to 4.33 x 10−16 g m−1 h−1 Pa−1), thermal stability (the endotherm peak increased from 99.5 to 157.7 °C), and mechanical properties (tensile strength and elongation at break increased from 4.15 to 4.98 kPa and 6.96 to 56.18%, respectively, while the modulus of elasticity decreased from 144 kPa to 4.11 kPa), without toxicity effects on Artemia salina (93.33% survival). X-ray diffraction and Fourier transform infrared studies demonstrated an interaction between CS-based films and nano-TZM. Overall, this film exhibited great potential for diverse industrial applications

Effect of TiO2-ZnO-MgO Mixed Oxide on Microbial Growth and Toxicity against Artemia salina

Mixed oxide nanoparticles (MONs, TiO2–ZnO–MgO) obtained by the sol-gel method were characterized by transmission electron microscopy, (TEM, HRTEM, and SAED) and thermogravimetric analysis (TGA/DTGA–DTA). Furthermore, the effect of MONs on microbial growth (growth profiling curve, lethal and sublethal effect) of Escherichia coli, Salmonella paratyphi, Staphylococcus aureus and Listeria monocytogenes, as well as the toxicity against Artemia salina by the lethal concentration test (LC50) were evaluated. MONs exhibited a near-spherical in shape, polycrystalline structure and mean sizes from 17 to 23 nm. The thermal analysis revealed that the anatase phase of MONs is completed around 480–500 °C. The normal growth of all bacteria tested is affected by the MONs presence compared with the control group. MONs also exhibited a reduction on the plate count from 0.58 to 2.10 log CFU/mL with a sublethal cell injury from 17 to 98%. No significant toxicity within 24 h was observed on A. salina. A bacteriostatic effect of MONs on bacteria was evidenced, which was strongly influenced by the type of bacteria, as well as no toxic effects (LC50 >1000 mg/L; TiO2–ZnO (5%)–MgO (5%)) on A. salina were detected. This study demonstrates the potential of MONs for industrial applications

Nutrimental composition and physicochemical parameters of thermosonicated soursop nectar

Se evaluó el efecto de la termosonicación (TS) a dos diferentes condiciones experimentales [TS1 = 24 kHz, 1,3 W/mL de densidad de energía acústica (AED), 51 °C durante 8 min y TS2 = 24 kHz, 1,4 W/mL AED, 54 °C durante 10 min] sobre la composición nutrimental  y parámetros fisicoquímicos de néctar de guanábana almacenado a 4ºC. Como testigos se emplearon un néctar sin tratar y otro pasteurizado tradicionalmente (65 °C, 30 min). La TS no causó cambios en la mayoría de nutrientes y parámetros fisicoquímicos evaluados. Sin embargo, fue medido un mayor contenido de fibra dietética soluble (33%), turbidez (30%) y viscosidad (5%), en particular cuando el TS2 fue aplicado. La fibra dietética soluble es uno de los compuestos funcionales con efectos potenciales demostrados en la salud; por lo tanto, la TS podría incrementar la calidad funcional del néctar de guanábana. Así mismo, los cambios en algunos parámetros fisicoquímicos mejoraron su apariencia física. La TS puede ser considerada una excelente alternativa para procesar bebidas a base de guanábana.Effect of thermosonication (TS) at two different experimental conditions [TS1 = 24 kHz, 1.3 W/mL of acoustic energy density (AED), 51 °C for 8 min and TS2 = 24 kHz, 1.4 W/mL AED, 54 °C for 10 min] on the nutrimental composition and physicochemical parameters of soursop nectar stored at 4 ºC were evaluated. Fresh (untreated) and traditionally pasteurized (65 °C, 30 min) soursop nectars were used as controls. TS did not cause changes in the most nutrients and physicochemical parameters evaluated. However, it was measured a highest dietary fiber content (33 %), turbidity (30%) and viscosity (5%), when TS2 was applied. The soluble dietary fiber is one of the functional compounds with demonstrated potential effects on the health; therefore TS could increase the functional quality of soursop nectar. Also, the changes in some physicochemical characteristics improved its physical appearance. TS can be considered an excellent alternative to process soursop beverages.

Nutrimental Composition and physicochemical parameters of thermosonicated soursop Nectar

Se evaluó el efecto de la termosonicación (TS) a dos diferentes condiciones experimentales [TS1 = 24 kHz, 1,3 W/mL de densidad de energía acústica (AED), 51 °C durante 8 min y TS2 = 24 kHz, 1,4 W/mL AED, 54 °C durante 10min] sobre la composición nutrimental y parámetros fisicoquímicos de néctar de guanábana almacenado a 4ºC.Como testigos se emplearon un néctar sin tratar y otro pasteurizado tradicionalmente (65 °C, 30 min). La TS nocausó cambios en la mayoría de nutrientes y parámetros fisicoquímicos evaluados. Sin embargo, fue medido unmayor contenido de fibra dietética soluble (33%), turbidez (30%) y viscosidad (5%), en particular cuando el TS2 fueaplicado. La fibra dietética soluble es uno de los compuestos funcionales con efectos potenciales demostradosen la salud; por lo tanto, la TS podría incrementar la calidad funcional del néctar de guanábana. Así mismo, loscambios en algunos parámetros fisicoquímicos mejoraron su apariencia física. La TS puede ser considerada unaexcelente alternativa para procesar bebidas a base de guanábana

Funcionalización de los recubrimientos a base de quitosano para la conservación postcosecha de frutas y hortalizas

In recent years, the development and application of safe and biodegradable edible coatings, with superior technological and functional properties have been studied to extend the shelf life of fresh fruit and vegetables. Chitosan is one of the most promising biomaterials for the development of edible coatings. However, the main disadvantage of this polysaccharide is related to the high water vapor permeability that it presents, therefore, an alternative to improve its performance, is its functionalization through the incorporation of organic (essential oils, natural extracts, ascorbic acid, protein hydrolysates, and polysaccharides) and inorganic compounds (SiO2, TiO2, ZnO, Ag, and montmorillonite), but also, the addition of microorganisms (yeast) in the chitosan matrix. The application of edible functionalized-chitosan coatings on fruits and vegetables has given better results (significant prolongation of the shelf life and minimal changes in quality parameters) than those obtained when pure chitosan-coating was applied. This review describes the advantages and limitations of functionalization of edible chitosan films in the preservation of post-harvest of fruit and vegetables.En años recientes, se ha buscado el desarrollo y aplicación de recubrimientos comestibles que sean seguros, biodegradables y con adecuadas propiedades tecnológicas y funcionales que ayuden a extender la vida de anaquel de frutas y hortalizas. El quitosano es uno de los biomateriales con mayor potencial para la elaboración de recubrimientos comestibles. Sin embargo, su principal desventaja es la alta permeabilidad al vapor de agua que exhibe, por lo que, una alternativa para mitigar esta limitante, es su funcionalización mediante la incorporación de compuestos orgánicos (aceites esenciales, extractos naturales, ácido ascórbico, hidrolizados de proteína, polisacáridos) e inorgánicos (SiO2, TiO2, ZnO, Ag y montmorillonita), además, de la adición de microorganismos (levaduras) a la matriz polimérica. El quitosano funcionalizado, aplicado a productos hortofrutícolas, ha mostrado mejores resultados (mayor vida de anaquel y cambios mínimos en parámetros de calidad) que los obtenidos al emplear quitosano sin funcionalizar. El objetivo de esta revisión es describir y discutir los beneficios y limitaciones de la funcionalización del quitosano y su aplicación en productos hortofrutícolas

Synthesis and Characterization of TiO₂-ZnO-MgO Mixed Oxide and Their Antibacterial Activity

TiO2-ZnO-MgO mixed oxide nanomaterials (MONs) were synthetized via the sol-gel method and characterized by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), nitrogen physisorption analysis, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Fourier transform infrared spectroscopy (FTIR), and color (Luminosity (L), a, b, Chrome, hue) parameters. Furthermore, the antimicrobial activity of the MONs was tested against Escherichia coli (EC), Salmonella paratyphi (SP), Staphylococcus aureus (SA), and Listeria monocytogenes (LM). The MONs presented a semi globular-ovoid shape of ≤100 nm. Samples were classified as mesoporous materials and preserved in the TiO2 anatase phase, with slight changes in the color parameters of the MONs in comparison with pure TiO2. The MONs exhibited antimicrobial activity, and their effect on the tested bacteria was in the following order: EC > SP > SA > LM. Therefore, MONs could be used as antimicrobial agents for industrial applications

Co, Cu, Fe, and Ni Deposited over TiO₂ and Their Photocatalytic Activity in the Degradation of 2,4-Dichlorophenol and 2,4-Dichlorophenoxyacetic Acid

Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method was studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model

Co, Cu, Fe, and Ni Deposited over TiO2 and Their Photocatalytic Activity in the Degradation of 2,4-Dichlorophenol and 2,4-Dichlorophenoxyacetic Acid

Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method was studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model

Effect of the Precursor on the Synthesis of ZnO and Its Photocatalytic Activity

Zinc nitrate (ZnON) and zinc acetate (ZnOA) were used as precursors for the synthesis of zinc oxide (ZnO) nanoparticles by the sol–gel method. The ZnO powder was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy, X-ray diffraction (UV–Vis DRS), Fourier transform infrared spectroscopy (FTIR), physisorption of nitrogen, and X-ray photoelectron spectroscopy (XPS). On the other hand, the photocatalytic activity of the samples was tested in the degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4-Dichlorophenol (2,4-DCP) under UV-light irradiation. The ZnON and ZnOA showed polycrystalline irregular structures and rod-like morphology with mean sizes of 40 and 99 nm, respectively. The precursor type influenced the bandgap, crystallite size, surface area, total pore volume, and pore diameter. The XPS results showed high contents of C and N in the ZnO samples, and as a consequence, the solids present remarkable differences in the C/N, O/C, and O/Zn atomic ratios, which significantly influenced the physicochemical characteristics. The ZnON and ZnOA exhibit photocatalytic properties against 2,4-D (74.7 and 90.9%, respectively) and 2,4-DCP (78.4 and 86.7%, respectively) and better performance of ZnOA. These results are promising and indicate the potential to use this material as a photocatalyst to degrade organic pesticides