Synergistic effect of sonication on photocatalytic oxidation of pharmaceutical drug carbamazepine

Abstract

Photocatalytic, sono-photocatalytic oxidation of pharmaceutical drug of carbamazepine was successfully carried out using Ag/AgCl supported BiVO₄ catalyst. For this purpose, firstly, photocatalytic oxidation was optimized by central composite design methodology and then synergistic effect of sonication was investigated. Low frequency (20 kHz) probe type and high frequency (850 kHz) plate type sonication at pulse and continuous mode were studied to degrade the carbamazepine (CBZ) containing wastewater. Pulse duties of 1:5 and 5:1 (on : off) were tested using the high frequency sonication system in the sono-photocatalytic oxidation of CBZ. The effects of frequency, power density measured from calorimetry by changing amplitudes were discussed in the sono-photocatalytic oxidation of CBZ. Complete carbamazepine removal was achieved at the optimum conditions of 5 ppm CBZ initial concentration with 1.5 g/L of catalysts loading and at an alkaline pH of 10 at the end of 4 h of photocatalytic reaction under visible LED light irradiation. Both low frequency and high frequency sonication systems caused an increase in photocatalytic efficiency in a shorter treatment time of 60 min. CBZ removal increased from 44% to 65.42% in low frequency sonication of 20 kHz at the amplitude of 20% (0.15 W/mL power density). In the case of high frequency ultrasonic system (850 kHz), CBZ removal increased significantly from 44% to 89.5 % at 75% amplitude (0.12 W/mL power density) within 60 min of reaction. Continuous mode sonication was observed to be more effective than that of pulse mode sonication not only for degradation efficiency and also for electrical energy consumption needed to degrade CBZ. Sono-catalytic oxidation was also conducted with simulated wastewater that contains SO₄^2-, CO₃^2-, NO^3-, Cl^- anions and natural organic component of fulvic acid. The CBZ degradation was inhibited slightly in the presence of NO₃^- and Cl^-, and fulvic acid, however, the existence of SO₄^2- and CO₃^2- increased the degradation degree of CBZ. Toxicity tests were performed to determine the toxicity of untreated CBZ, and treated CBZ by photocatalytic, and sono-photocatalytic oxidations.

Keywords: Carbamazepine; Continuous mode sonication; Pharmaceutical drug; Pulse mode sonication; Sono-photocatalytic; Synergistic effect.

Fig. 1

Schematic diagram of catalyst preparation.

Fig. 2

Experimental Set-up, a) photocatalytic oxidation, b) sono-photocatalytic oxidation with ultrasonic probe system, and c) sono-photocatalytic oxidation with high frequency ultrasonic reactor.

Fig. 3

Interaction plot for degradation % of CBZ.

Fig. 4

Surface plots of: a) degradation (%) vs pH, catalyst loading, b) degradation (%) vs pH, initial CBZ concentration, and c) degradation (%) vs catalyst loading, initial CBZ concentration.

Fig. 5

Actual (experimental) vs. predicted degradation values for photocatalytic oxidation of CBZ.

Fig. 6

HPLC chromatography analysis.

Fig. 7

Effect of temperature on a) photocatalytic oxidation of CBZ over Ag/AgCl/BiVO₄ photocatalyst b) TOC reductions and CBZ degradation after 240 min of reaction ([CBZ]₀: 10 ppm, Catalyst loading = 1 g/L, T = 298 K, 303 K, 308 K, 313 K, without pH regulation, and LED light power = 93.4 W, continuous stirring of 200 rpm).

Fig. 8

First order kinetic model of photocatalytic oxidation of CBZ.

Fig. 9

lnk versus 1/T relationship.

Fig. 10

Effect of sonolysis on photocatalytic oxidation of CBZ a) using low frequency (20 kHz) US at 0.15 W/mL b) using high frequency (850 kHz) ultrasonic bath at 0.12 W/mL ([CBZ]₀ = 10 ppm, Catalyst loading = 1 g/L, T = 298 K, without pH regulation, and LED light power = 93.4 W, continuous stirring of 200 rpm).

Fig. 11

Degradation of CBZ without photocatalyst with visible light under different conditions ([CBZ]₀ = 10 ppm, T = 298 K, without pH regulation, LED light power = 93.4 W, frequency = 20 kHz or 850 kHz, power density = 0.15 W/mL or 0.12 W/mL, continuous stirring of 1500 rpm).

Fig. 12

Effect of stirring speed and sonication on degradation of CBZ ([CBZ]₀ = 10 ppm, T = 298 K, without pH regulation, LED light power = 93.4 W, frequency = 20 kHz or 850 kHz, power density = 0.15 W/mL or 0.12 W/mL, continuous stirring of 200, 500 and 1500 rpm).

Fig. 13

Effect of power density of sonication in sono-photocatalytic oxidation of CBZ a) using low frequency (20 kHz) b) using high frequency (850 kHz) ultrasonic bath ([CBZ]₀ = 10 ppm, Catalyst loading = 1 g/L, T = 298 K, without pH regulation, and LED light power = 93.4 W, continuous stirring of 200 rpm).

Fig. 14

Effect of sonication mode in sono-photocatalytic oxidation of CBZ using high frequency (850 kHz) ultrasonic reactor ([CBZ]₀ = 10 ppm, Catalyst loading = 1 g/L, T = 298 K, without pH regulation, and LED light power = 93.4 W, continuous stirring of 200 rpm).

Fig. 15

Effects of different anions and fulvic acid on the sono-catalytic oxidation of CBZ using high frequency (850 kHz) ultrasonic reactor ([CBZ]₀ = 10 ppm, Catalyst loading = 1 g/L, T = 298 K, without pH regulation, power density = 0.12 W/mL, continuous stirring of 200 rpm).

Fig. 16

Root length of cress seeds for untreated (a) and treated CBZ by photocatalytic (b) and sono-photocatalytic oxidation using ultrasonic probe (c) and ultrasonic reactor (d) systems.