Dr. Valdes-Morales, Hector

Tomatoes (Solanum lycopersicum L.) are widely cultivated and consumed, but ripening should be carried out in controlled storage conditions to extend their shelf life and avoid economic losses. The aim of this study was to investigate the effects of visible artificial light on the ripening and quality of fresh market tomatoes stored at a low temperature and high humidity. The postharvest performance with respect to the ripening of organically grown tomatoes in the Toscano cultivar, with a long storage life, was studied in the presence and the absence of visible LED light. The maturation kinetics of the tomatoes was modeled using the Power Law equation. Results showed that tomatoes stored in the presence of light exhibited an increased respiration rate and a faster preclimacteric phase. Lycopene content, total soluble solids, and maturity index increased in the presence of light. Hence, light increased the postharvest ripening of tomatoes, affecting their shelf life.

In this work, we prepared bismuth oxide (Bi2O3) nanoparticles with and without fuels (citric acid and urea) using a one-pot solid-state combustion method at 400 °C for visible light photocatalytic degradation of acid blue 25 (AB). The nanoparticle prepared with fuel greatly influences the Bi2O3 properties such as morphology, chemical, structural, and optical properties. Bi2O3 prepared with citric acid as fuel act as an effective photocatalyst for the breakdown of acid blue 25 within 60 min under visible light irradiation. The enhanced photocatalytic property of Bi2O3 is due to the narrow band gap, high crystallinity, flower-like morphology with high active sites, and light stability of the material. Furthermore, an effective photogenerated charge separation, high charge transfer, and lower band gap, improved the absorbing capacity in the visible region of Bi2O3 (1) and enhanced its photocatalytic ability. In the photocatalytic process, the superoxide radicals (O2·) anion played a significant role during the degradation of acid blue 25. The Bi2O3 (1) maintained its effectiveness after three reaction cycles without suffering any appreciable change in structural and functional stability. These findings demonstrated an easy method for treating the hazardous effluents into non-toxic small molecules, which can be potentially applied to purify the various textile effluent.

Glutathione (GSH) is the most abundant antioxidant in the majority of cells and tissues; and its use as a biomarker has been known for decades. In this study, a facile electrochemical method was developed for glutathione sensing using voltammetry and amperometry analyses. In this study, a novel glassy carbon electrode composed of graphene quantum dots (GQDs) embedded on amine-functionalized silica nanoparticles (SiNPs) was synthesized. GQDs embedded on amine-functionalized SiNPs were physical-chemically characterized by different techniques that included high resolution-transmission electron microscopy (HR-TEM), X-ray diffraction spectroscopy (XRD), UV–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The newly developed electrode exhibits a good response to glutathione with a wide linear range (0.5–7 µM) and a low detection limit (0.5 µM) with high sensitivity(2.64 µA µM−1). The fabricated GQDs-SiNPs/GC electrode shows highly attractive electrocatalytic activity towards glutathione detection in the neutral media at low potential due to a synergistic surface effect caused by the incorporation of GQDs over SiNPs. It leads to higher surface area and conductivity, improving electron transfer and promoting redox reactions. Besides, it provides outstanding selectivity, reproducibility, long-term stability, and can be used in the presence of interferences typically found in real sample analysis.

Fluoroquinolones are extensively used in medicine due to their antimicrobial activity. Their presence in water inhibits microorganism activity in conventional wastewater treatment plants. This study aims to evaluate the technical feasibility of applying heterogeneous catalytic ozonation to eliminate ciprofloxacin (CIP) as a representative of fluoroquinolone antibiotics normally present in municipal wastewater discharges. Experiments were conducted in a semi-batch stirred slurry reactor, using 0.7 L of 100 mg L−1 CIP aqueous solution, at pH 3 and 30 °C. Experimental results show that single ozonation can easily oxidise CIP molecules (68%) within the first 5 min, leading to the generation of refractory oxidation by-products. However, when heterogeneous catalytic ozonation is applied using iron oxide supported on MFI synthetic zeolite, total degradation of CIP is observed at 5 min and a higher mineralisation rate is obtained. A novel sequential process is developed for CIP mineralisation. In a first step, a flash single ozonation is applied and CIP molecules are broken down. Then, a catalytic ozonation step is conducted by adding the Fe/MFI catalyst into the reactor. As a result of catalyst addition, 44% of Total Organic Carbon (TOC) is eliminated within the first 15 min, compared to single ozonation where only 13% of TOC removal is reached in the same time. The application of this sequential process to a real wastewater effluent spiked with CIP leads to 52% of TOC removal.

A great number of pollution problems come as a result of the emission of Volatile Organic Compounds (VOCs) into the environment and their control becomes a serious challenge for the global chemical industry. Adsorption is a widely used technique for the removal of VOCs due to its high efficiency, low cost, and convenient operation. In this study, the feasibility to use a locally available clay, as adsorbent material to control VOCs emissions is evaluated. Natural clay is characterised by different physical-chemical methods and adsorptive interaction features between VOCs and natural clay are identified. Toluene (T), methanol (M) and benzaldehyde (B) are used here as representatives of three different kinds of VOCs. Adsorption isotherms onto natural clay and faujasite-Y type zeolite (Fau Y) are obtained at room temperature. According to Langmuir model data, maximum adsorption capacities (qm) of Fez natural clay and zeolite toward methanol (M), toluene (T) and benzaldehyde (B) at 300 K are 8, 0.89 and 3.1 mmol g–1, and 15, 1.91 and 13.9 mmol g–1 respectively. In addition, the effect of temperature on the adsorption of toluene onto natural clay is evaluated in the range from 300 to 323K. An increase on temperature reduces the adsorption capacity of natural clay toward toluene, indicating that an exothermic physical adsorption process takes place. The enthalpy of adsorption of toluene onto Fez natural clay was found to be –54 kJ mol–1. A preliminary cost analysis shows that natural clay could be used as an alternative low cost adsorbent in the control of VOCs from contaminated gas streams with a cost of US$ 0.02 kg–1 compared to Fau Y zeolite with US$ 10 kg–1.

Light-induced photocatalytic degradation of ceftiofur sodium (CFS) has been assessed in the presence of plasmonic zinc oxide nanostructures (ZnONSTs), like, ZnO nanoparticles, ZnO nanorods (ZnONRs) and ZnO nanoflowers (ZnONFs). Silver nanoparticles (Ag NPs) loaded ZnO nanostructures (Ag-ZnONSTs) are obtained through seed-assisted chemical reaction followed by chemical reduction of silver. The surface modification of ZnO nanostructures by Ag NPs effectually altered their optical properties. Further, the surface plasmonic effect of Ag NPs facilitates visible light absorption by ZnONSTs and improved the photogenerated electron and hole separation, which makes the ZnONSTs a more active photocatalyst than TiO2 (P25) nanoparticles. Especially, Ag-ZnONRs showed higher CFS oxidation rate constant (k' = 4.6 × 10−4 s−1) when compared to Ag-ZnONFs (k' = 2.8 × 10−4 s−1) and Ag-ZnONPs (k' = 2.5 × 10−4 s−1), owing to their high aspect ratio (60:1). The unidirectional transport of photogenerated charge carriers on the Ag-ZnONRs may be accountable for the observed high photocatalytic oxidation of CFS. The photocatalytic oxidation of CFS mainly proceeds through •OH radicals generated on the Ag-ZnONRs surface under light illumination. In addition, heterogeneous activation of peroxymonosulfate by Ag-ZnONRs accelerates the rate of photocatalytic mineralization of CFS. The quantification of oxidative radicals supports the proposed CFS oxidation mechanism. Stability studies of plasmonic Ag-ZnONSTs strongly suggests that it could be useful to clean large volume of pharmaceutical wastewater under direct solar light irradiation.

Anatase nanoparticles containing surface oxygen vacancies (VO) and Ti3+ are of great importance for applications in photocatalysis, batteries, catalysis, sensors among other uses. The properties of VO and their dependence on the size of nanoparticles are of great research interest and could allow obtaining advanced functional materials. In this work, a complete set of oxygen vacancies in an anatase nanoparticle of size 1.1 nm was investigated and compared to those of a twice larger nanoparticle, having the same shape and surface hydroxylation pattern. It turned out that the decrease in the size of the anatase nanoparticle strongly facilitated creation of surface oxygen vacancies and Ti3+. After their creation, oxygen vacancies undergo three transformation paths — (1) small repulsion of surrounding Ti cations with retention of the vacancy, (2) transfer of oxygen anion, leading to the movement of oxygen vacancy to a more stable position, and (3) collapse of oxygen vacancy accompanied by structure deformation towards Magneli-like phase.

Ethylene stimulates ripening and senescence by promoting chlorophyll loss, red pigment synthesis, and softening of tomatoes and diminishes their shelf-life. The aim of this work was to study the performance of a novel copper- and zinc-based ethylene scavenger supported by ion-exchange on a naturally occurring zeolite by analyzing its ethylene adsorption capacity and the influence of ethylene scavenging on quality attributes during the postharvest life of tomatoes. The influence of copper- and zinc-modified zeolites on ethylene and carbon dioxide concentrations and postharvest quality of tomatoes was compared with unmodified zeolite. Interactions among ethylene molecules and zeolite surface were studied by diffuse reflectance infrared Fourier transform spectroscopy in operando mode. The percentage of ethylene removal after eight days of storage was 57% and 37% for the modified zeolite and pristine zeolite, respectively. The major ethylene increase appeared at 9.5 days for the modified zeolite treatment. Additionally, modified zeolite delayed carbon dioxide formation by six days. Zeolite modified with copper and zinc cations favors ethylene removal and delays tomato fruit ripening. However, the single use of unmodified zeolite should be reconsidered due to its ripening promoting effects in tomatoes at high moisture storage conditions, as water molecules block active sites for ethylene adsorption.

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 ◦C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.

This article presents the adsorption of Methylene Blue (MB) onto diatomite, in order to develop a low-cost treatment technology as a process alternative for dye removal. Diatomite used in this work was taken from the Nador area in the northeast of Morocco. Diatomite is characterised by different physical–chemical methods (X-ray diffraction, nitrogen adsorption-desorption isotherm, scanning electron microscopy and Fourier transform infrared). Results showed that the adsorption of MB onto diatomite mineral is affected by various operating parameters like contact time, initial dye concentration, adsorbent dosage, pH and temperature. Adsorption equilibrium is reached after 1.5 h of contact time. Maximum MB removal is obtained at pH = 12. MB removal rate decreases as pH decreases. Adsorption equilibrium data are fitted to Langmuir, Freundlich, Redlich–Peterson and Toth models. Adsorption data are well described by Langmuir isotherm model indicating that a homogeneous adsorption occurs. A maximum adsorption capacity (or monolayer coverage) of 11 mg g–1 is obtained at 45°C. A value of the enthalpy of adsorption of 12.78 kJ mol–1 is found confirming the endothermic nature of adsorption process, while a Gibb’s free energy change (∆G°) falling in the range −30.8 to −35.34 kJ mol–1 confirms the spontaneity of the process. Adsorption kinetics are fitted to a pseudo-second-order kinetic model. Experimental results indicate that the Moroccan diatomite could be used as a potential adsorbent for the removal of cationic dye molecules, at lower cost.