Dr. Valdes-Morales, Hector

In this article, the role of surface sites of modified zeolites with semiconductor nanoparticles as alternative photocatalyts for protecting post-harvest foodstuff from the detrimental effects of ethylene is addressed. Two single and one double catalyst based on zinc and copper oxides supported over modified zeolite samples were prepared. Physical, chemical, and surface properties of prepared materials were studied by several characterization methods. UV-Vis absorption spectra show that the applied modification procedures increase the optical absorption of light in the UV and visible regions, suggesting that an increase in the photocatalytic activity could take place mainly in the obtained co-impregnated catalyst. An ethylene conversion around 50% was achieved when the parent natural zeolite support was modified with both transition metal oxides, obtaining higher removal efficiency in comparison to single oxide catalysts. Adsorption and photocatalytic oxidation experiments were also performed using single and double catalysts supported over fumed silica, attaining lower ethylene conversion and thus highlighting the role of zeolite surfaces as adsorption sites for ethylene during photocatalytic reactions. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that a synergistic mechanism occurs, involving ethylene adsorption at acidic sites of zeolite and its photocatalytic oxidation due to the generation of radicals by the light activation of nanoparticles of zinc and copper oxides.

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.

This article presents a combination of coagulation–flocculation and powder activated carbon (PAC) adsorption as a treatment process for landfill leachate. Leachates were collected from a municipal solid waste landfill in Mediouna site, Casablanca city. Ferric chloride (FeCl3) is used here as a coagulant to study the optimum conditions for the removal of chemical oxygen demand (COD), colour, total suspended solids (TSS) and turbidity in jar tests. This coagulant showed the highest removal efficiency in terms of COD (62.5%), turbidity (92.5%), colour (80%) and least sludge volume generation (30% v/v) for an optimum coagulant dose of 12 g Fe3+ L–1. Combining coagulation with adsorption process onto PAC enhances the removal of COD, turbidity and colour reduction by a 77%, a 99% and a 99.7%, respectively. These results show that coagulation-adsorption could be used as a promising hybrid process for the treatment of landfill leachates.

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.