Cryogels with Noble Metal Nanoparticles as Catalyst for “Green” Decomposition of Chlorophenols

Abstract

Pollution of the aquatic environment by halogen derivatives widely used as antiseptic compounds, as well as chemicals for various industrial purposes, is significant. Existing systems of bioremediation poorly solve the problem of eliminating pollution. This paper discusses the preparation of novel macroporous chitosan-based cryogels with in situ-immobilized Pd or Pt nanoparticles as a catalyst for dichlorination reactions. The formation mechanism of metal coordinated chitosan gels using Medusa software modelling and rheology (G’ and G’’) is discussed. Metal coordinated chitosan gels were subsequently converted into covalently cross-linked macroporous cryogels with in situ-immobilized Pd or Pt nanoparticles using the redox potentials difference of the reaction mixture. Noble metal nanoparticles of average size, 2.4 nm, were evenly distributed in the cryogel structure. The effectiveness of these gels as a catalyst for the decomposition of chloro-compounds o-chlorophenol, p-chlorophenol and 2,4-dichlorophenol was tested. The catalytic hydrogenation reaction was carried out using the “green reducing agent” formic acid. Increasing the excess of formic acid with heating increases the degree of conversion up to 80–90%. The CHI-GA-PdNPs cryogel at pH 6 showed better efficiency in the hydrogenation process compared to the CHI-GA-PtNPs cryogel; however, no significant difference in the degree of conversion at pH 3 was observed. The termination of a catalytic reaction in a batch mode have been studied. Several control tests were carried out to elucidate the mechanism of catalyst poisoning. The presented catalytic system may be of interest for studying reactions in a flow through mode, including the reactions for obtaining valuable chemicals.

Nanoparticle‐Based Cryogels from Colloidal Aqueous Dispersion: Synthesis, Properties and Applications

“…Nanocrystal-based cryogels are highly promising novel materials showcasing high surface areas and a porous structure which bridge the gap between the macroscopic scale and the nanoscopic properties of the building blocks. The huge library of options for these building blocks, either regarding on their composition (semiconducting, magnetic, plasmonic or mixtures of them [86] ), their size and shape (nanowires [26,112,118] , nanoplatelets [103,119] , spheres, cubes …) or their surface functionalization, open the possibility to tackle a broad range of societal problems, such as environmental remediation [25,55,120] or energy saving and conversion. [15,121] Their superior performance in several applications such as electro-or photocatalysis in comparison to the colloidal counterpart has been extensively proven, [21,85,87,110] being possible to obtain better catalysts with lower loads of noble metals, which decrease considerably the price and overcome the problem of the scarcity of these elements.…”

“…[30][31][32][33] Several years later, fabrication of polymer based cryogels was extended to involve the addition of inorganic nanocrystals. Several works on cryogels obtained from mixing polymeric matrices with various types of nanoparticles have been reported including Ag, [23,24,[34][35][36][37][38][39][40][41][42][43][44][45][46][47] Au, [48][49][50][51][52][53][54] Pd, [55,56] Pt, [55,56] Co, [57][58][59][60][61][62][63] Ni, [59][60][61][62][63][64] Cu, [60][61][62]64,65] Fe 3 O 4, [66]…”

“…Several years later, fabrication of polymer based cryogels was extended to involve the addition of inorganic nanocrystals. Several works on cryogels obtained from mixing polymeric matrices with various types of nanoparticles have been reported including Ag, [23,24,34–47] Au, [48–54] Pd, [55,56] Pt, [55,56] Co, [57–63] Ni, [59–64] Cu, [60–62,64,65] Fe 3 O 4, [66–71] ZnO, [72,73] SiO 2, [74] AlO 3, [75] SnO 2, [76] On one hand, the presence of the polymer matrix gives the cryogel material some features including: elastic texture, high water retention capacity and biocompatibility [16,77] . On the other hand, incorporation of inorganic nanoparticles adds other physical and chemical properties to the cryogel structure and allows the preparation of thermo‐responsive, fluorescent, conductive and magnetic cryogels, for example [78–81] …”

Chitosan Glutaraldegyde Cryogels for Wastewater Treatment and Extraction of Silver Nanoparticles

“…The CHI-GA-2 cryogels obtained in a conventional freezer at −22 °C and without freezing control were studied. It is known that the moment of freezing is quite crucial for the microstructure of a material [31,38,56] due to the condensation re-…”

“…The CHI-GA-2 cryogels obtained in a conventional freezer at −22 • C and without freezing control were studied. It is known that the moment of freezing is quite crucial for the microstructure of a material [31,38,56] due to the condensation reaction taking place; at some point, a frozen hydrogel may be formed, resulting in the formation of closed pores, which in turn results in decreases in adsorption capacity and filtration efficiency. The cryogel obtained in freezer was characterized by a significantly higher water permeability rate (10 mL/min) compared to CHI-GA-1.…”