Sonochemical enhancement of hydrogen peroxide production by inert glass beads and TiO2-coated glass beads in water

In this study, a series of experiments were carried out to determine the effects of ultrasound frequency at 28, 580, and 1000 kHz on H2O2 production in the presence of both inert and TiO2-coated glass beads. Several different sizes (no addition, 0.05, 0.1, 1, 2, 3, and 5 mm) and amounts (no addition, 10, 25, 50, 100, and 200 g L−1) of inert glass beads were tested at a power density of 0.2 W mL−1. The production of H2O2 with a contact time of 60 min at different frequencies follows the order: 580 kHz (339 μM/no addition–105 μM/2 mm) > 1000 kHz (208 μM/no addition–4.0 μM/1 mm) > 28 kHz (71.2 μM/0.1 mm–18.5 μM/no addition). For a constant glass-bead size of 0.1 mm and at a frequency of 28 kHz, the zero-order rate constant is highest in the presence of glass beads of the amount 10 g L−1 (3.3 μM−1 min−1), and it decreases significantly with increasing inert glass-bead amounts (2.7 μM−1 min−1/25 g L−1 to 0.45 μM−1 min−1/200 g L−1). The zero-order rate constant is the lowest (0.31 μM−1 min−1) with no addition of glass beads. Sonocatalysis at a low frequency of 28 kHz with the addition of TiO2-coated glass beads (5 mm) of amount 100 g L−1 was significantly more effective (1540 μM) than sonocatalysis carried out with no addition and inert glass beads (12–18 μM) and those carried out at the high frequencies of 580 kHz (33.4 μM) and 1000 kHz (8.77 μM), with the other conditions remaining the same.