คำศัพท์เฉพาะทางเคมีIntroduction
Chemical oxygen demand (COD) is one of the most widely used
parameter for water quality assessment as it can be used to collectively
represent the organic pollution level [1]. The standard
method for COD determination is defined as the number of oxygen
equivalently consumed in the oxidation of organic compounds
by dichromate which is a strong oxidant. However, this method
has several drawbacks. Firstly, to achieve complete oxidation of
organic pollutants, it requires a long time consuming process of
refluxing samples in highly acidic medium under high temperature
and high pressure. Moreover, it also consumes expensive (Ag2SO4),
highly corrosive (H2SO4), and toxic (K2Cr2O7 and HgSO4) reagents
[2,3]. Thus, it unavoidably increases both the cost and the risk of
secondary pollution.
Currently, a COD determination method based on photocatalytic
(PC) oxidation approach has attracted increasing attention
[4–6]. The photocatalysis technology has some advantages such as
high oxidation ability, non-toxicity and low cost [7]. The method
utilizes TiO2 nanoparticles as photocatalystto oxidize organic compounds
under UV irradiation. The TiO2 particle has a fully filled
valence band separated from a vacant conduction band by a gap
whose energy is Eg. When excited by photons with energy higher
than the gap energy (Eg), a great number of electrons are promoted
from valence band (VB) to the conduction band (CB) of TiO2,