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Humic acids (HAs) content of raw water is an important analytical parameter in water treatment facilities because HAs in the presence of chlorine may lead to the formation of dangerous by-products (e.g., trihalomethanes). The concentration of HAs in water is not directly accessible by common analytical methods due to their heterogeneous chemical structure. The aim of this study was to compare two methods to assess humic acids (HAs) in surface water namely absorbance of ultraviolet light at 254 nm (UV(254)) and total organic carbon (TOC), as well as to evaluate the effects of calcium and magnesium concentrations, pH and sample filtration on the methods' results. An aqueous solution of a commercial HA with 10 mg L(-1) was used in the present work. Quantification of the HA was carried out by both UV(254) and TOC (combustion-infrared method) measurements. UV(254) results were converted to TOC using a calibration curve. The effects of calcium (0-136.3 mg L(-1)) and magnesium (0-34.5 mg L(-1)) concentrations, pH (4.0, 7.0 and 9.0) and sample filtration on UV(254) and TOC measurements of the HA suspension were evaluated. More accurate TOC values of HA suspensions were obtained by the combustion-infrared method than by the UV(254) absorbance method. The higher differences of TOC values between unfiltered and filtered samples were detected in the presence of calcium at pH 9.0 using the spectrophotometric method.

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The present work reports the solvent-free, one-pot functionalization of multiwall carbon nanotubes (CNTs) based on the 1,3-dipolar cycloaddition of azomethine ylides using N-benzyloxycarbonyl glycine and formaldehyde. The surface morphology of the functionalized CNTs was investigated by scanning tunneling microscopy. The effect of temperature on the reaction was studied by thermogravimetry and X-ray photoelectron spectroscopy (XPS). XPS was a key technique for the detailed chemical analysis of the CNT surface. The formation of two major reaction products was observed, namely a cyclic benzyl carbamate and a pyrrolidine. The concentration of the two products varied with reaction temperature and time. At 180 °C, the main product was the cyclic benzyl carbamate, while at 250 °C the major product was the pyrrolidine. This simple, solvent-free chemical procedure yields CNTs with fine-tuned surface functionality.

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