Non-selective oxidation of humic acid in heterogeneous aqueous systems: a comparative investigation on the effect of clay minerals

Abstract

Application of photocatalysis for degradation of natural organic matter (NOM) has received wide interest during the last decades. Besides NOM, model compounds more specifically humic acids (HAs) were also studied. As a continuation of the previous research, TiO2 photocatalytic degradation of HA was investigated in the presence of clay minerals, i.e., montmorillonite (Mt) and kaolinite (Kt). Degradation of HA was expressed by the pseudo-first-order kinetic modelling of dissolved organic carbon (DOC) and UV-VIS parameters (Colour436 and UV254). A slight rate enhancement was attained for Colour436 and UV254 in the presence of either Mt or Kt. The presence of clay particles did not significantly change the DOC degradation rate of HA. The effect of ionic strength (Ca2+ loading from 5 x 10(-4) M to 5 x 1(-3) M) was also assessed for the photocatalytic degradation of sole HA and HA in the presence of either Mt or Kt. Following photocatalytic treatment, molecular size distribution profiles of HA were presented. Besides the effective removal of higher molecular size fractions (100 and 30 kDa fractions), transformation to lower molecular size fractions (<3 kDa) was more pronounced for sole HA rather than HA in the presence of clay minerals. Scanning electron microscopic images with the energy dispersive X-ray analysis confirmed the diversities in surface morphologies of the binary and ternary systems composed of HA, TiO2 and Mt or Kt both prior to and following photocatalysis. This study demonstrated that photocatalysis could be applicable for DOC degradation in the presence of clay minerals in natural waters.

An improved gray-scale transformation method for pseudo-color image enhancement

“…According to the principle of colorimetry, divide the gray-scale range of the original image f (x, y) into multiple regions and turns it into three primary colors IR (x, y), IG (x, y) and IB (x, y) after three different transformations of red, green and blue: TR, TG and TB. Then, use them to control the red, green and blue in the color display and combine into a color image in the screen of color display device [9]. Fig.1 is a group of transfer function of grayscale-color transformation.…”

“…Finally, add the value of every pixel obtained through three channels and perform pseudo-color processing on every pixel. At the end, get the pseudo-color image [9], [10].…”

Mechanistic Study on Size Exclusion of NOM onto Porous TiO2 for Target Contaminants Decomposition

“…In particular, the process is effective to decompose many toxic and recalcitrant chemicals such as pharmaceutical compounds and biological toxins in water (Chong et al, 2010;Hapeshi et al, 2010;Pelaez et al, 2011). TiO 2 photocatalysis is characterized with nonselective attack and powerful oxidation (Kavurmaci and Bekbolet, 2014;Lazar and Daoud, 2013;Rasoulifard et al, 2014). The nonselectivity of the process implies that it works versatilely even for a mixture of various organic chemicals.…”