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A novel 3 wt.% Fe-containing clinoptilolite catalyst was prepared starting from a natural zeolite followed by a ion-exchange synthesis. A Fe-containing ZSM-5 catalyst (commercial zeolite as support) was also prepared for comparison purpose. Both Fe-based catalysts, along with the unexchanged samples, were characterized by complementary techniques (e.g. X-ray powder diffraction (XRD), N2 physisorption at -196°C, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometry (EDS) microanalysis). Then, their possible application in wastewater remediation was tested with a solution of azo-dyes acid orange 7 (AO7), as target molecule for azo dyes. As a whole, remarkable results in the AO7 degradation were obtained with the Fe-clinoptilolite in the presence of both ascorbic acid (AA) and H2O2. Specifically, AO7 conversion of about 60% was observed over the Fe-clinoptilolite (reaction time = 60 min). Lower performances were achieved in the presence of Fe-ZSM-5 coupled with ascorbic acid and H2O2 (AO7 conversion ~ 40%, t = 60 min.), despite the significantly higher SSA of the commercial ZSM-5. Noteworthy, the beneficial role of the ascorbic acid coupled with H2O2 was observed for both Fe-containing catalysts, thus confirming the key role of both oxidant and reductant agents in Fenton-like processes. [ABSTRACT FROM AUTHOR]

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In recent decades, several abatement techniques have been proposed for organic dyes and metal cations. In this scenario, adsorption is the most known and studied. Clinoptilolite was considered, since it is a zeolite with a relatively low cost (200-600 $ tons -1 ) compared to the most well-known adsorbent used in wastewater treatment. In this work, Clinoptilolite was used for the adsorption of Methylene Blue (MB) at three different concentrations, namely, 100, 200, and 250 ppm. Furthermore, the adsorption capacity of the natural zeolite was compared with that of Activated Charcoal (250 ppm of MB). The two adsorbents were characterized by complementary techniques, such as N 2 physisorption at -196 °C, X-ray diffraction, and field emission scanning electron microscopy. During the adsorption tests, Clinoptilolite exhibited the best adsorption capacities at 100 ppm: the abatement reached 98% (t = 15 min). Both Clinoptilolite and Activated Charcoal, at 250 ppm, exhibited the same adsorption capacities, namely, 96%. Finally, at 250 ppm MB, the adsorption capacity of Clinoptilolite was analyzed with the copresence of Zn 2+ and Cd 2+ (10 ppm), and the adsorption capacities were compared with those of Activated Charcoal. The results showed that both adsorbents achieved 100% MB abatement (t = 40 min). However, cation adsorption reached a plateau after 120 min (Zn 2+ = 86% and 57%; Cd 2+ = 53% and 50%, for Activated Charcoal and Clinoptilolite, respectively) due to the preferential adsorption of MB molecules. Furthermore, kinetic studies were performed to fully investigate the adsorption mechanism. It was evidenced that the pseudo-second-order kinetic model is effective in describing the adsorption mechanism of both adsorbents, highlighting the chemical interaction between the adsorbent and adsorbate.

In this work, the co-immobilization of formate dehydrogenase (FDH) and glycerol dehydrogenase (GlyDH) enzymes is proposed to reduce CO 2 into formic acid, an important chemical intermediate. The reduction of carbon dioxide is carried out by FDH to obtain formic acid, simultaneously, the GlyDH regenerated the nicotinamide cofactor in the reduced form (NADH) by the oxidation of glycerol into dihydroxyacetone. Natural zeolite was selected as immobilization support given its good properties and low cost. The natural zeolite was modified with subsequent acid-alkaline attacks to obtain a mesostructurization of the clinoptilolite. The two enzymes were co-immobilized on clinoptilolite, previously hetero-functionalized with amino and glyoxyl groups. The distribution of the enzymes was confirmed by fluorescence microscopy analysis. Furthermore, a great increase in the retained activity for the formate dehydrogenase enzyme was noted, passing from 18% to 89%, when the mesostructured clinoptilolite was used as support. The immobilization yield of formate dehydrogenase and glycerol dehydrogenase is around 100% with all the supports studied. The promising results suggest a possible development of this procedure in enzyme immobilization and biocatalysis. The biocatalysts were characterized to find the optimal pH and temperature. Furthermore, a thermal stability test at 50 °C was carried out on both enzymes, in free and immobilized forms. Finally, it was shown that the biocatalyst is effective in reducing CO 2 , both by using the cofactor in the reduced form (NADH) or the oxidized form (NAD + ), obtaining NADH through the regeneration with glycerol in this latter case., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Many industries discharge wastewater from processing into surface and underground waterways, and then, these waste waters must therefore be treated in order to remove heavy metals. The most common treatment used is the activated carbon adsorption, a particularly competitive and effective process; however, the use of activated carbon is not suitable due to the high costs. Then, in order to minimize processing cost, recent investigations have been focused on the use of low-cost adsorbents as zeolites. In particular, clinoptilolite is known to have high selectivity for certain heavy metals. In this paper, the capability of clinoptilolite as a low-cost adsorbent for the removal of zinc and cadmium ions from wastewater was analyzed in a batch system. Preliminary characterization was performed on adsorbent material in order to evaluate the chemical-physical structure. Tests in batch for analyzing adsorbing capacity of clinoptilolite were carried out varying zinc and cadmium concentrations between 10 and 200 mg/L with different amounts of sorbent in the solution (10-60 g/L). For both zinc and cadmium ions, complete adsorption was reached when the concentration was equal to 10 mg/L and adsorption capacity decreased increasing metals amount. In particular, clinoptilolite permitted high Cd 2+ abatement, probably due to its greater affinity with adsorbent in the single system. Binary system was then analyzed, and, contrary to previous tests, the adsorbent in the simultaneous presence of the two metals demonstrated a greater affinity toward zinc, showing a higher percentage of absorption, due to a different absorption mechanism in the presence of two ions.

This work studied the influence of the pore size and morphology of the mesoporous silica as support for formate dehydrogenase (FDH), the first enzyme of a multi-enzymatic cascade system to produce methanol, which catalyzes the reduction of carbon dioxide to formic acid. Specifically, a set of mesoporous silicas was modified with glyoxyl groups to immobilize covalently the FDH obtained from Candida boidinii. Three types of mesoporous silicas with different textural properties were synthesized and used as supports: i) SBA-15 (D P  = 4 nm); ii) MCF with 0.5 wt% mesitylene/pluronic ratio (D P  = 20 nm) and iii) MCF with 0.75 wt% mesitylene/pluronic ratio (D P  = 25 nm). As a whole, the immobilized FDH on MCF 0.75 exhibited higher thermal stability than the free enzyme, with 75% of residual activity after 24 h at 50 °C. FDH/MCF 0.5 exhibited the best immobilization yields: 69.4% of the enzyme supplied was covalently bound to the support. Interestingly, the specific activity increased as a function of the pore size of support and then the FDH/MCF 0.75 exhibited the highest specific activity (namely, 1.05 IU/g MCF0.75 ) with an immobilization yield of 52.1%. Furthermore, it was noted that the immobilization yield and the specific activity of the FDH/MCF 0.75 varied as a function of the supported enzyme: as the enzyme loading increased the immobilization yield decreased while the specific activity increased. Finally, the reuse test has been carried out, and a residual activity greater than 70% was found after 5 cycles of reaction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)

The aim of this work is to study the activity of novel TiO 2 -based photocatalysts doped with either phosphorus or zirconium under a UV-Vis source. A set of mesoporous catalysts was prepared by the direct synthesis: TiO 2 _A and TiO 2 _B (titanium oxide synthesized by two different procedures), P-TiO 2 and Zr-TiO 2 (binary oxides with either nonmetal or metal into the TiO 2 framework). Complementary characterizations (N 2 physisorption at 77 K, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, X-ray Photoelectron Spectroscopy (XPS), and (DR)UV-Vis spectroscopy) were used to investigate the physicochemical properties of the prepared catalysts. Then, the photocatalysts were tested for the oxidation of propylene and ethylene under UV-Vis light. As a result, the most promising catalyst for both the propylene and ethylene oxidation reactions was the P-TiO 2 (propylene conversion = 27.8% and ethylene conversion = 13%, TOS = 3 h), thus confirming the beneficial effect of P-doping into the TiO 2 framework on the photocatalytic activity.