Nannan Geng,Wei Chen,Hang Xu,Tao Lin,Mingmei Ding,Yi Wang,Hui Tao,Kai Hu
In order to remove the humic acid (HA) from the drinking water efficiently, novel quaternary Fe 3 O 4 /TiO 2 –N-GO (FTNG) sonocatalysts with different amounts of Fe 3 O 4 were simply synthesized, and a sono-photocatalytic system was used by combining photocatalysis and ultrasound processes. A series of characterizations were performed to confirm the successful synthesis of FTNG and some of its properties, and the results showed that FTNG with an appropriate amount of Fe 3 O 4 can extend the range of light absorption to over 400nm (UV-vis spectra) and improve the separation efficiency of electrons and holes (Photocurrent responses). Raman spectra indicated the reduction of GO. Sono-photocatalytic performance was investigated under visible light irradiation and the effect of ultrasound was studied. Among all the catalysts, FTNG-0.2 with 0.2 g Fe 3 O 4 , exhibited the best HA removal abilities, about 80% for sono-adsorption and 93% for sono-photocatalysis. The removal efficiency in sono-photocatalytic system was about 42% higher than only adsorption and 26% higher than only photocatalysis. Finally, we proposed the possible reaction mechanisms. First, ultrasound pretreatment had a positive effect on HA removal, and a Fenton-like system was then established with H 2 O 2 produced by cavitation effect. Second, the doping of Fe 3 O 4 , N and GO improved the quantum efficiency. The improvement of visible light catalytic performance is mainly attributed to the doping of N. This work is significant for the field of ultrasonic and catalytic degradation, especially for the removal of humic acid in drinking water.
As a precursor of disinfection byproducts, humic acid (HA) has adverse effects on aquatic environments and human health. Currently, many advanced oxidation processes (AOPs) have been proposed to remove HA from drinking water, one of which is photocatalysis. However, the long reaction time required for degradation and drawbacks of the photocatalysts limit the large-scale application of photocatalysis. Therefore, two principal objectives were achieved in this work. First regarding the technology, we combined photocatalysis with ultrasonic waves to remove HA. Second regarding the photocatalyst, quaternary Fe 3 O 4 /TiO 2 -N-GO (FTNG) sono-photocatalysts with different amounts of Fe 3 O 4 were first synthesized using a simple hydrothermal method. Characterizations were performed to confirm the successful synthesis of the sono-photocatalyst and to determine some of its properties. The influence of different experimental factors such as Fe 3 O 4 content, ultrasonic power, catalyst dosage and initial HA concentration were studied. The first-order kinetic and second-order kinetic equations were used to simulate the experimental data. The results showed that FTNG-0.2 with 0.2 g of Fe 3 O 4 , which was added upon preparation, showed the highest sono-photocatalytic ability. In our experimental setup, greater than 99% removal efficiency (UV 254 ) and 94% mineralization rate (TOC) were achieved within 90 min at the optimum conditions (60 W ultrasound power and 1.0 g/L catalyst dosage for 30 mg/L HA). Compared with the pseudo-first-order kinetic model, pseudo-second-order model fitted better with the experimental data and it had higher R 2 values of 0.92, 0.98 and 0.98 for 30, 40 and 50 mg/L of HA, respectively. According to the scavenging tests and the ESR analysis, both of the OH and O 2 − were produced in the reaction, however, O 2 − radicals were assumed to be the dominating reactive species for the HA degradation. Moreover, after five repetitive experiments, the removal efficiency of HA can still reach 88.5%, indicating high stability of FTNG-0.2 sono-photocatalyst. The mechanism of degradation of HA by FTNG-0.2 in sono-photocatalytic system was mentioned based on several factors including the ultrasonic cavitation effect, Fenton-like reactions, photocatalytic reactions, etc. In fact, this was the first study to treat HA through sono-photocatalytic process, which showed great potential in drinking water treatment.
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