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Herein, we are reporting a facile route to synthesize magnetically separable copper loaded L-DOPA functionalized magnetite nanoparticles (Fe.sub.3O.sub.4-DOPA-CuNPs), which are well characterized by FT-IR, PXRD, SEM, EDAX, HRTEM, XPS, TGA and VSM techniques. This single catalyst exhibits excellent catalytic activity towards (i) synthesis of DHPMs via Biginelli reaction (ii) synthesis of imidazoles (iii) synthesis of 2-amino-4H-chromenes (iv) 1,2,3-triazole derivatives by 'Click reaction' under microwave irradiation (MWI). Interestingly it can be easily recovered and reused for subsequent cycles for above mentioned four important multicomponent reactions without any significant decrease in its catalytic activity.

We describe a magnetic metal-organic framework for preconcentration of Hg(II). The material is obtained from magnetite (Fe.sub.3O.sub.4) nanoparticles that were modified with 4-(5)-imidazoledithiocarboxylic acid and then reacted with trimesic acid and Cu(II) acetate to form the metal-organic framework capable of extracting Hg(II). The sorption time, amount of the magnetic nanocomposite, and pH value of the sample were selected as the main affecting factors in sorption, and central composite design and response surface methodology were applied to optimize these parameters. Following sorption of Hg(II), the sorbent is removed by a magnet, Hg(II) is eluted with a solution of thiourea and then quantified by cold vapor AAS. The type, volume and concentration of the eluent, and the elution time were selected for the optimization of the elution. The results showed the sorption process to obey the Langmuir model. The maximum monolayer capacity is as high as 254 mg g.sup.-1, and the Langmuir constant is 0.330 L mg.sup.-1. The findings can be well described by pseudo second-order kinetics. High sorption capacity means that one needs less sorbent. Under the optimal conditions, the limit of detection and limit of quantification for Hg(II) were 10 ng L.sup.-1 and 40 ng L.sup.-1, respectively and the relative standard deviations are <8.3 %. The nanocomposite was successfully applied to the rapid extraction of trace amounts of mercury ions from fish and canned tuna samples.

This work carries out a study of the heterogeneous photocatalysis process using TiO.sub.2 and the composite TiO.sub.2/iron oxides as catalysts, in order to perform the degradation of propylparaben. The composite produced aims to maintain the catalytic capacity of the precursor material, while improving the recovery of the material after its application. Magnetic removal is a quick and efficient way of reapplying the catalyst. The photocatalysts produced were characterized by XRD, FTIR, SEM, TEM/EDS, PL and UV-vis. The composite obtained showed the predominant crystalline phases anatase and magnetite, as well as photocatalytic activity which was increased by the decrease of the material bandgap, promoted by the materials combination. The materials efficiency was determined under ultraviolet irradiation through the degradation of propylparaben, in which the highest efficiency was obtained with the composite was the removal of 16.2 ppm, around 80.83% from 20 ppm, and for pure TiO.sub.2 it was the degradation of 4.7 ppm, around 94.52% from 5 ppm of propylparaben. These findings present a valuable alternative to a highly effective photocatalyst that can be magnetically removed from the treated solution and be reused in another treatment run.

[This corrects the article DOI: 10.1371/journal.pone.0292737.].