Public health, production and preservation of food, development of environmentally friendly (cosmeto-)textiles and plastics, synthesis processes using green technology, and improvement of water quality, among other domains, can be controlled with the help of chitosan. It has been demonstrated that this biopolymer exhibits advantageous properties, such as biocompatibility, biodegradability, antimicrobial effect, mucoadhesive properties, film-forming capacity, elicitor of plant defenses, coagulant-flocculant ability, synergistic effect and adjuvant along with other substances and materials. In part, its versatility is attributed to the presence of ionizable and reactive primary amino groups that provide strong chemical interactions with small inorganic and organic substances, macromolecules, ions, and cell membranes/walls. Hence, chitosan has been used either to create new materials or to modify the properties of conventional materials applied on an industrial scale. Considering the relevance of strategic topics around the world, this review integrates recent studies and key background information constructed by different researchers designing chitosan-based materials with potential applications in the aforementioned concerns.
The aim of this contribution is to provide a comprehensive comparison between chitosan and Moringa oleifera seed flour (MOSF) as coagulant-flocculants. MOSF was obtained as a byproduct in a biodiesel process. Turbidity and heavy metal ion removal, using both ecofriendly materials, was assessed. Jar tests were performed on samples taken from river water, agricultural wastewater, and mixed wastewater (contaminated with agricultural and urban residues). Bioflocculant dosages within the range of 0.005-20 mg L À1 were tested. Irrespective of the initial turbidity, the optimal dosage of chitosan and MOSF for decreasing turbidity in river water was 1 and 5 mg L À1 , respectively. Furthermore, from river water, Pb removal up to 95% was achieved irrespective of the bioflocculant; for Mn removal, MOSF performed better than chitosan, with the adsorbent trapping close to 90% of this metal. MOSF decreased turbidity levels and heavy metal content (Mn and Pb) to under the permissible limits (Mexican environmental regulation for potable water, NOM-127-SSA1-1994). Additionally, kinetic data were fitted to kinetic models of adsorption for the pollutants. For agricultural wastewater, a chitosan dosage of 10 mg L À1 reduced turbidity to 5-10 nephelometric turbidity units (NTU), and a MOSF dosage of 10 mg L À1 decreased the turbidity to values lower than 5 NTU. For the mixed wastewater, chitosan achieved a high turbidity removal, while MOSF was not suitable.
Iron oxide-supported gold samples were characterized by X-ray absorption near edge structure (XANES) spectroscopy during treatments in flowing H 2 at increasing temperature. Spectra were recorded at the Au L III and Fe K edges to monitor the reduction of both metals and to determine the influence of gold on the reducibility of the support. The results show that reduction of Fe 3+ to Fe 2+ on the support occurs at lower temperatures in samples containing gold than on samples of the bare support, with the reduction temperature being dependent on the gold content. X-ray diffraction patterns characterizing samples after H 2 treatments at various temperatures complement the XANES data and indicate that the presence of gold favors the crystallization of the support to give Fe 3 O 4 . Our data emphasize the power of XANES spectroscopy in following changes in the oxidation states of both gold and iron and suggest that the role that gold might have in promoting the reduction and crystallization of iron oxide support is to provide sites for hydrogen dissociation. Hydrogen moieties might spillover from the gold nanoparticles to the support, promoting its reduction and ensuing structural changes. ' INTRODUCTIONSupported gold catalysts have recently attracted attention because they are active for many industrially relevant chemical reactions and because their catalytic properties were unexpected, as gold is the most inert metal in its bulk form. Among the many reactions catalyzed by supported gold, the waterÀgas shift 1À3 and the oxidations of carbon monoxide 4À6 and alcohols 7À9 have been widely investigated. For these reactions, it has been observed that the catalysts are typically more active when the gold particles are dispersed on reducible metal oxides (e.g., Fe 2 O 3 , 4,10,11 TiO 2 , 5,12,13 CeO 2 , 1,2,14 La 2 O 3 , 5,15 etc. 16 ) than when they are on nonreducible metal oxides (e.g., γ-Al 2 O 3 , 6 MgO, 17 SiO 2 , 18 etc. 16 ). This observation has led some authors 19À21 to conclude that the interaction between the gold and the support is important in determining the activity of the catalysts, with the existence of a synergistic effect between the gold and reducible metal oxides at the gold-support interface. It has been hypothesized that such effect might involve redox processes, in which the gold particles favor the reduction of the metal oxide, thus allowing lattice oxygen atoms from the support to become activated species available for the oxidation reactions. 19À21
During several reactions, similar to dehydrogenation of propane to propylene, coke is one of the main reasons for the catalyst deactivation. The coke formation and further deactivation of the catalyst are strongly dependent to the active site in the catalyst and/or the properties of the support. KIT-6 with interconnected porous and high surface area can handle with the coke formation, and can disperse easily the deposited Pt nanoparticles. In this sense, a series of Pt-Sn/KIT-6 catalysts were synthesized with distinct Sn loadings and used in the dehydrogenation of propane. The performance of these catalysts during reaction varied with the Sn loading. The specific activities for propylene formation obtained with the catalysts were comparable to the best result reported in the literature. The nanoparticles present in the catalyst through pretreatment and reaction condition was the Pt-Sn alloy (1:1 atomic ratio), and that alloy is suggested to be the active phase. This Pt-Sn alloy was stable during the entire reaction time, that even in two catalysts containing a considerable amount of coke, deactivation was not observed. Also, the support (KIT-6) with high connectivity helped to avoid deactivation by coke.
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