*3.2.5. Analyses of phenols*

photocatalyst provides much higher phenol degradation efficiency than immobilized photocatalysts [15]. Our research group used few different types of photoreactors for the degradation of phenol and phenolic compounds. Chen and Ray [14] used two-phase monolithic-type photoreactor for the photodegradation of 4-nitrophenol under UV light. Sengupta et al. [48] used a Taylor vortex reactor (TVR) for the degradation of phenol under UV light. Chowdhury et al. [7] used slurry photoreactor with dye-sensitized photocatalyst, and Malekshoar et al. [5] used slurry photoreactor with graphene-based photocatalyst for phenol degradation under solar light. Studies by other researchers reported degradation of phenols with (i) TiO2-coatedfiber-optic cable reactor [16], (ii) tubular photoreactor [49], (iii) continuous flow photoreactor

Photocatalysis process efficiency largely depends on photocatalyst surface area and incident photons. Ray [17] combined these two factors and came up with a parameter called illuminated

inside the photoreactor to undergo the photocatalysis process. Therefore, distribution of light inside the photoreactor is a crucial factor. In majority cases of phenol degradation, photoreactors use an external light source (UV or solar) with a slurry reactor. Chen and Ray [14] used 125 W high-pressure Hg vapor lamp (Philips) in a swirl-flow reactor. However, such externaltype photoreactors are limited by the low value of κ, and thus scale up is not possible. Sengupta et al. [48] used a TVR with immersion-type lamp and immobilized photocatalyst for phenol

with larger reactor volume [52]. Chowdhury et al. [7] used a solar simulator (1000 W Xe arc lamp with AM 1.5 G filter) in an external-type slurry photoreactor for dye-sensitized phenol degradation under solar-visible light. Gimenez et al. [51] studied the photocatalytic degradation of phenol and 2, 4-dichlorophenol under natural sunlight using compound parabolic collectors (CPCs) and the flat reactor (cylindrical tank). CPCs showed higher phenol degra-

Degussa P25 TiO2 (DP25) is the most common photocatalyst used for phenol degradation under UV light. Some other commercial TiO2 photocatalysts such as Hombikat UV100, TTP, and PC500 are also used for the same. Among them, DP25 provides the highest photocatalytic activity due to slow electron-hole recombination during photocatalysis [53]. Several visiblelight-active photocatalysts such as eosin Y-sensitized TiO2/Pt [7], dye-sensitized TiO2[11], MWNT-TiO2 composite [13], S-doped TiO2 [12], and BiO4 [43] are also used for degradation of

Aqueous solutions of target compounds (phenol and/or phenolic compounds) are prepared at a desired initial concentration. Solution pH is adjusted with HCl or HNO3 or NaOH solutions. In some cases, buffer solutions are used to maintain the solution pH. In the case of

dation efficiency, but it is technologically more complicated than the flat reactor.

m−3) which mainly represents the illuminated photocatalyst

m−3. In such case, photoreactor, scale up is possible

[50], and (iv) solar photoreactor (CPC modules and flat reactor) [51].

404 Phenolic Compounds - Natural Sources, Importance and Applications

*3.2.2. Light sources*

*3.2.3. Photocatalysts*

phenol and phenolic compounds.

*3.2.4. Experimental procedure*

photocatalyst surface area (κ, m2

degradation and achieved a κ value of 80 m2

Chowdhury et al. [7] used high-pressure liquid chromatography (HPLC) to quantify the concentration of phenol and phenolic compounds in aqueous medium The instrument is equipped with a column oven and a diode array detector. AC18 column (5 μm × 150 mm × 4.6 mm) and a mobile phase of methanol and water (67/33% v/v) at a flow rate of 0.5 ml min−1 are used. The temperature of the column oven is kept at 25°C throughout the analysis. The wavelengths of analyses for phenol and reaction intermediates catechol, hydroquinone, and 1,4-benzoquinone are done at 270, 290, 275, and 255 nm, respectively.
