Piezoelectric hydroxyapatite synthesized from municipal solid waste incineration fly ash and its underlying mechanism for high efficiency in degradation of xanthate

Municipal solid waste incineration fly ash (MSWI-FA) is a typical hazardous waste and contains various harmful heavy metals. MSWI-FA can be transformed into mineral-containing materials (MCMs) by hydrothermal treatment, which stabilize the heavy metals in MSWI-FA synchronously. However, whether MCMs are capable of catalyzing the degradation of organic pollutants remains elusive. In this study, the hydroxyapatite (HAP; sample numbers were HAP-1, HAP-2, and HAP-3) with piezoelectric property was successfully synthesized from MSWIFA using hydrothermal approach, and simultaneous stabilization of heavy metals in MSWI-FA was achieved. The piezoelectric coefficient (d33) and piezocatalytic performance of HAP could be improved by regulating Ca/P molar ratio of the synthesized HAP to the theoretical value of 1.67. The d33 of HAP-2 (Ca/P molar ratio = 1.49) was 4.39 pm V-1 which was 3.4 times that of HAP-1 (Ca/P molar ratio = 2.48), while HAP-3 (Ca/P molar ratio = 0.74) had no significant piezoelectric signal. Meanwhile, HAP-2 showed that the best piezocatalytic degradation efficiency of 92.0 % of potassium butyl xanthate (PBX, 10 mg/L) within 60 min, and it was almost 1.37 and 1.92 times that of HAP-1 and HAP-3, respectively. Free radical scavenging and reactive species quantitative experiments showed that center dot O-2(-) and center dot OH were the dominant reactive oxygen species in the piezocatalytic degradation of PBX by HAP. The generation rates of center dot O-2(-) and center dot OH in piezocatalysis of HAP-2 were 3.28 and 12.60 mu mol g(-1)h(-1), respectively, implying that the degradation of PBX was mainly determined by center dot O-2(-) and center dot OH. This work provides a useful reference for converting MSWI-FA into the promising mineral materials with highly efficient catalytic performance for the treatment of organic pollutants from domestic and industrial wastewater.