Degradation of trinitrophenol by sequential catalytic wet air oxidation and solar TiO2 photocatalysis

Abstract

a b s t r a c tCatalytic wet air oxidation (CWAO) and solar TiO 2 photocatalysis were investigated as advanced oxidation processes to degrade trinitrophenol (TNP) in model aqueous solutions. An activated carbon (AC) treated with sulphuric acid of different concentrations (5, 10 and 18 M) at two different temperatures (353 and 423 K) was investigated as a metal-free CWAO catalyst, while a commercially available P25 TiO 2 powder was used as a photocatalyst. CWAO experiments were conducted at 448 K, 0.7 MPa oxygen pressure (4.7 MPa of total pressure), 1.3 g L −1 AC loading and 270 mg L −1 TNP concentration, while photocatalytic experiments were conducted at ambient temperature, 1 g L −1 photocatalyst loading, 500-1000 W m irradiance provided by a solar simulator and 32-270 mg L −1 TNP concentration. Treatment efficiency was assessed by measuring the concentrations of TNP and nitrates, total organic carbon (TOC) and biochemical oxygen demand (BOD 5 ). Up to 90% TNP degradation was attained during CWAO over 120 min, from an initial concentration of 270 mg L −1 . For the same TNP concentration, TiO 2 photocatalysis gives only 13% conversion over the same 120 min. However, for TNP concentrations below 144 mg L −1 , photocatalysis can be effectively used: 100 and 80% TNP degradation obtained in 120 min of irradiation for initial TNP concentrations of 64 and 144 mg L −1 , respectively. In this respect, CWAO and photocatalysis were employed sequentially to treat TNP; complete TNP conversion being achieved after 120 min of CWAO followed by 60 min of photocatalysis at 1000 W m −2 irradiance, and this was accompanied by 82% TOC reduction, as well as an increase of BOD 5 /TOC ratio from 0 to 2.28.

The role of O- and S-containing surface groups on carbon nanotubes for the elimination of organic pollutants by catalytic wet air oxidation

“…For instance, carbon xerogels [2,3], activated carbons [3][4][5][6][7][8][9][10][11], carbon fibres and foams [12] and carbon nanotubes [13][14][15] were already studied as catalysts for the CWAO process. It is known that the catalytic performance of these carbon materials depends on their surface chemistry and textural properties, which can be tuned by adequate methods of synthesis and/or by post-treatments [1,16,17].…”

Effect of lanthanum and lead doping on the microstructure and visible light photocatalysis of bismuth titanate prepared by the oxidant peroxide method (OPM)

“…Many studies have demonstrated the degradation of organic pollutants such as phenol, chlorinated hydrocarbons, chlorophenols, insecticides, dyes and others, using the photocatalysis process in the presence of TiO 2 under solar radiation [4][5][6]. However, due to the high energy required for activation of TiO 2 for generating the hydroxyl radicals (band gap equal to 3.2 eV), the yield of the process is limited by the absorption of radiation up to 385 nm, which corresponds to only about 5% of the solar spectrum [7,8].…”

UV and solar-based photocatalytic degradation of organic pollutants by nano-sized TiO2 grown on carbon nanotubes

“…producing mineral salts, CO2 and H2O. However, AOPs are known to lead to degradation products in the common practice of water treatment, namely when employing reaction time in the range of 5-30 min [21][22][23][24][25].…”