Ferric-oxalate system

The destruction of formaldehyde does not exceed 40% under UV treatment for 20 min in presence of ferric-oxalate system, which appears after oxalic acid addition. Increasing the time of UV irradiation up to 40 min leads to a signiflcant... 

The ferric-oxalate system that is formed in the presence of oxalic acid and under UV radiation using samples based on nitrides of silicon (528) and boron (B90) is also quite promising for the destruction of phenol. However, the efficiency of the catalyst is determined not only by the fullness of the pollutant oxidation but also by the depth of its destruction. In this regard, the depth of phenol degradation (under conditions of maximal activity of composites) was assessed and products of phenol degradation determined by gas chromatography-mass spectrometry... 

GC-MS) technique. Deeper pollutant degradation is observed under the ozonation [26] (Table 7.9). Three new substances appear in a mixture in trace amounts (<10 %). The ferric-oxalate system produced four new products of phenol oxidation below maximum permissible concentration (MPC) level. 

At this juncture, van Niel s concept of a redox reaction taking place in the reaction center became very useful for understanding the Hill reaction. Although CO2 was not assimilated under illumination, it appeared that the other reactions responsible for the splitting of water were still active. The ferric oxalate used by Hill apparently served as a substitute for the natural oxidant CO2 to intercept electrons produced at the reaction center and thus allow oxygen to be evolved. The Hill reaction shows that CO2 assimilation and oxygen evolution are not obligatorily linked and two physically distinct enzymatic systems may exist. 

Capability of B-N-Fe composition samples to remove oxalic acid (OA) from water was investigated [24] and it was established (Table 7.5) that sorption of OA depends on surface and porosity properties of the material used and does not exceed 40%. H2C2O4 decomposition degree under UV in presence of each sample is rather high (80-90%). Addition of HgOg (photo-Fenton system) does not affect the catalytic activity of composites. Adsorption and catalytic activity of materials were investigated used by XRD and IR methods. Formation of photoactive ferric-oxalate complexes explains efficiency of catalytic systems (Equations 7.11-7.15). 

Catalytic activity of composites B-N-Fe and Si-N-Fe when applying UV radiation in presence of hydrogen peroxide, oxalic acid, and EDTA is determined by formation of photo-Fenton, ferric-oxalate, and Fe-EDTA systems in the solution which leads to generation of the super-oxidant-hydroxyl radicals. At the same time, solutions practically are not polluted by iron. High catalytic activity of the composites is determined by combination of heterogeneous and homogeneous catalyses. 

The percentage distribution of various complexes in such systems can be calculated using the equations above and the results are presented in Fig. 6.25. It may be seen that in the presence of oxalic acid, the dominant ferric complex is FeLj , even at lower dosage. The dominant complexes of Fe " are FeL and FeLj ,... 

The effect of some additives on aqueous polymerization of aCTylamide initiated by the permanganate/oxalic acid redox system was studied by Husain and Gupta [252]. The rate of polymerization was increased in the presence of alkali metal chlorides. However, the rate was decreased in the presence of cupric chloride and ferric chloride. Anionic and cationic detergents showed a marked influence on the rate of polymerization. 

Binary systems synthesized consisted of Cu/Fe, Ni/Fe, Cu/Al and Ni/Al and Cu/Cr for 4-10 wt percent Cu or Ni in the calcined mixed oxide. Anionic complexing agents acetic, citric and oxalic acids and EDTA were used in molar ratios of 1 1 with the initial copper or nickel. Two stage precipitations were used starting with an initial formation of aluminum, chromium or ferric hydroxide by addition of NaOH to an aqueous solution of A1 nitrate, Cr nitrate or Fe chloride. In the second stage aqueous solutions of Cu sulfate or Ni nitrate were mixed with the initial precipitate with or without the presence of a 1 1 mole ratio of selected anionic complexing agents to complete the precipitation. A second mode of coprecipitation used was to preadsorb oxalic acid on the initially precipitated AI, Cr or Fe hydroxide. 

It has been demonstrated that sequential precipitation in a moderately acid pH range for the binary metal systems Cu/Al, Cu/Cr, Cu/Fe and Nl/Fe in the presence of oxalic acid with aluminum or ferric hydroxide as the first stage and adsorption/precipitation of copper or nickel as the second stage provides metal oxides (after 250-350° C air calcine) with considerable enhancement in dispersion and in catalytic activity, notable for Cu/Al, for the room temperature decomposition of hydrogen peroxide and benzaldehyde oxidation by hydrogen peroxide. 

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