Study on Fenton-like degradation of bisphenol A by α-MnO2 and α-MnO2/AC (1:1, w/w)

Bisphenol A is used in various industrial productions and large amounts of industrial wastewater containing bisphenol A is produced. Heterogeneous Fenton-like process in advanced oxidation technology can oxidize and degrade most organic compounds non-selectively, and it has become an effective method to treat bisphenol A. The aim is to overcome the shortcomings of the traditional Fenton method and synthesize catalysts by a simple method, which can help to degrade bisphenol A effectively under neutral conditions, with less catalyst and less H 2 O 2 consumption. In this experiment, α-MnO 2 and α-MnO 2 /AC (1:1, w/w) were synthesized by a simple method, and the degradation rate of bisphenol A by α-MnO 2 and α-MnO 2 /AC (1:1, w/w) under different conditions were studied. The optimal conditions for the degradation of bisphenol A by the two materials were determined by single factor and orthogonal experiments. When the dosage of α-MnO 2 catalyst is 6.5g/L and the concentration of H 2 O 2 is 200 mg/L with pH = 4.5 at 328K, the degradation rate of 50mg/L bisphenol A can reach 91.02% within 70 minutes. When α-MnO 2 /AC (1:1, w/w) has a catalyst dosage of 1.5g/L, at 298K with no pH adjustment, the degradation rate of 50 mg/L of bisphenol A within 70 minutes can be reached 94.17%.

complete treatment, no pollution, and wide application range.
The Fenton method is one of the classic AOPs processes, and the •OH generated by the Fenton system has a higher redox potential 8 , which can perform non-selective oxidative degradation of organic pollutants. Once hydroxyl radicals are formed, they will induce a series of free radical chain reactions, attack various organic pollutants in water, and nally mineralize them into H 2 O, CO 2 and inorganic salts 9 .
Fenton process has the advantages of high pollutant removal e ciency, mild reaction conditions, simple operation and low cost 10 , and has been widely used in sewage treatment in recent years. However, there are some problems in the traditional Fenton process, including the di culty in separating and recovering the catalyst, and prone to secondary pollution and so on. In addition, the traditional Fenton reaction can be applied to a very narrow pH range, generally from 3 to 5. When treating organic wastewater, the wastewater needs to be pre-acidi ed. Therefore, reducing the cost of polluting wastewater treatment and simplifying the treatment process while ensuring that the water quality treatment requirements meet the standards have become an important direction for the development of industrial wastewater treatment technology.
In recent years, there have been many studies on the degradation of bisphenol A, Matz Dietrich 11 et al.
used a low frequency (24 kHz) ultrasonic horn and two boron-doped diamond electrodes to study the degradation of bisphenol A by a electrochemical hybrid system. It is found that under the synergistic effect of ultrasound and electrochemical oxidation, the degradation rate of bisphenol A with an initial concentration of 1 mg/L can reach 90% within 30 minutes. Anakovai et al. 12 had studied the degradation of bisphenol A from lab-scale to pilot-scale, in which the degradation rate of bisphenol A can reach 90% under certain conditions. Cai et al. 13 proposed an effective method to remove bisphenol A from water using HP-β-CD polymer, which can quickly remove bisphenol A. Yiguang Qian 14 et al. used the activated sludge biodegradation method to treat bisphenol A and achieved good results.
In the past, many researches on the removal of bisphenol A also have some shortcomings, such as the high cost of material synthesis, some need to add more acid to adjust the pH, the treatment process is complicated, and the treatment time is long and so on.
In this experiment, the con gured bisphenol A solution was used to simulate organic wastewater. This paper aims to overcome the shortcomings of the traditional Fenton method. A simple method is used to synthesize a green and pollution-free catalyst, and under neutral conditions, can achieve a good treatment effect on bisphenol A with less amount of catalyst and H 2 O 2 . In this way, the treatment time and treatment cost is reduced, and the organic wastewater treatment process is simpli ed.
MnO 2 is one of the most effective transition metal oxides to degrade organic pollutants, and it is also favored because of its low cost and environmental friendliness 15 . MnO 2 has a good adsorption and degradation effect on phenolic organic matter in water. Among the many crystal phases of MnO 2 , α-MnO 2 has better catalytic activity than other crystal phases. The catalytic activity in the many crystal phases of MnO 2 has the following order: α-MnO 2 > γ-MnO 2 > λ-MnO 2 > β- MnO 2 16 . Saputra  This experiment used bisphenol A as the target pollutant, the α-MnO 2 and α-MnO 2 /AC were synthesized by a simple method, the degradation e ciency of α-MnO 2 and α-MnO 2 /AC on bisphenol A was studied.
The mechanism of degradation of bisphenol A by α-MnO 2 is seen in Fig. 1   In Fig. 4, 492 cm -1 is the stretching vibration peak of Mn-O-Mn, and 609 cm -1 is the stretching vibration peak of Mn-O 22 . It shows that the production of manganese oxide was not affected during the material preparation process.

XRD analysis
The instrument model used is Broker D8 Discove, the test condition is Cu target, Wavelength 1.5418 Å, Scan range 10-80°, the scanning speed is 6°/min. It can be seen from the SEM image of α-MnO 2 (Fig. 6) that the synthesized material has a rich pore structure. From the TEM image of α-MnO 2 , it can be seen that the material has a sheet structure of tens to Page 6/21 300 nm.
From the SEM image of α-MnO 2 /AC (1:1, w/w) (Fig. 7), it can be seen that the structure of α-MnO 2 /AC (1:1, w/w) composite material is looser and more porous than the single α-MnO 2 , and then it has a larger speci c surface area than α-MnO 2 . From the TEM image of α-MnO 2 /AC (1:1, w/w), it can be seen that the prepared material is 30nm small spherical particles while the single α-MnO 2 has a sheet structure of tens to 300 nm.

UV-Vis analysis
It can be seen from Fig. 8 and Fig. 9 that the two materials have better absorption in the ultraviolet wavelength range. In the catalysis process of this experiment, a 365nm UV lamp was selected as the illumination source. At the same time, UV radiation can also directly promote the production of •OH from H 2 O 2 .

Results And Discussion Of Degradation Of Bisphenol A By α-mno2
The experiments were carried out in a magnetically stirred batch reactor with a certain amount of 50 mg/L bisphenol A aqueous solution. The temperature was controlled by immersed in a thermostatic bath. After a certain amount of α-MnO 2 was added, the solution would be stirred for 30min in the dark to reach the equilibrium of adsorption and desorption. The solution pH was adjusted with 0.1mol/L and 0.01mol/L HCl, then we turned on the 365nm UV lamp, magnetically stirred, took a sample every 10 minutes, and lter it with a 0.22μm PTFE needle lter. The absorbance of the ltered ltrate was measured with the ultraviolet-visible spectrophotometer, and the degradation rate was calculated as follows: A 0 is the initial concentration of bisphenol A before degradation, A is the concentration of bisphenol A after degradation. . It can be seen from the gure that as the amount of catalyst increases, the degradation rate of bisphenol A gradually increases. When the amount of catalyst is increased to 6g/L, increasing the amount of catalyst does not signi cantly improve the degradation rate of bisphenol A, the reason may be that when the concentration of the catalyst is low, the number of active sites is small and the degradation rate is not high. When the concentration of the catalyst is high, the absorption of light is affected, and the utilization rate of light is reduced, resulting in low degradation e ciency 23 . The optimal amount of catalyst is 6g/L 3.1.2 The effect of temperature on degradation rate Fig. 11 shows the degradation rate of α-MnO 2 to bisphenol A within 70 min at different temperatures (other conditions being the same). It can be seen from the gure that the degradation effect is best when the temperature is 323K. Too high or low temperature will affect the degradation e ciency, the reason may be that when the temperature is low, it is unable to provide su cient energy for α-

Orthogonal experiment
According to the above single factor experiment results, we determined the level of several factors in the orthogonal experiment. The amount of catalyst selected is 5g/L, 5.5g/L, 6g/L, 6.5g/L. The temperature selection is 298K, 308K, 318K, 328K.Choose pH 4.5, 5, 5.5, no HCl. The amount of H 2 O 2 is selected as 0mg/L, 100mg/L, 200mg/L, 300mg/L. Then we used Orthogonal Design Assistant to design orthogonal experiments, the following Table 1 is the result of orthogonal experiment design.

Results And Discussion Of Degradation Of Bisphenol A By
The experiments were carried out in the same conditions as part 3, but with AC supported catalyst of α-MnO 2 /AC (1:1, w/w). , it can be seen from the gure that the degradation effect is best when the amount of catalyst is 2 g/L, the degradation rate reaches 93.71% within 70 minutes, the reason may be that when the concentration of the catalyst is low, the number of active sites is small and the degradation rate is not high. When the concentration of the catalyst is high, the absorption of light is affected, and the utilization rate of light is reduced, resulting in low degradation e ciency. We choose 2 g/L as the best condition.

Orthogonal experiment
According to the above single-factor experiment results, the levels of several factors in the orthogonal experiment are determined as the amount of catalyst is 1g/L, 1.5g/L, 2g/L, 2.5g/L, and the temperature is 293K, 298K, 303K and 308K, the amount of H 2 O 2 is selected as 0mg/L, 100mg/L, 200mg/L, 300mg/L. we used the Orthogonal Design Assistant to design the orthogonal experiment, the following Table 2 shows the results of the orthogonal experiment design.  adding a small amount of catalyst, and it don't need too high temperature, the degradation rate of 50 mg/L bisphenol A can reach 94.17%. Compared with the traditional Fenton method, which requires preacidi cation of the solution and the need to add a large amount of H 2 O 2 , it has been greatly improved.
The synthesis method of the materials in this experiment is very simple, and the synthesis reagents are cheap and easy to obtain. The modi ed α-MnO 2 /AC (1:1, w/w) can achieve a higher degradation rate under neutral conditions resulting to low equipment requirements. It can be a good process for treating bisphenol A wastewater and has certain application prospects.