A piezoelectric catalyst with a built-in lattice strain gradient structure was prepared hap@fap exhibited high catalytic activity for the degradation of PHE in soil. **Jianmei Lu and Najun Li, Soochow University, China.
The removal of polycyclic aromatic hydrocarbons (PAHs) from the soil environment is of great significance for the restoration of long-term damaged ecosystems. However, most conventional methods have poor mass transfer processes and low catalytic activity, resulting in limited removal efficiency.
A group of scientists constructed a gradient F-doped hydroxyapatite core-shell structure (hap@fap) with flexible electric and piezoelectric coupling, which can degrade PAHs in soil and provide an innovative approach for soil remediation. Their findings were published in the journal Industrial Chemistry and Materials.
Poor mass transfer process in traditional soil remediation methods is still an important factor hindering its further application. In recent years, piezoelectric catalysis has been developed as a new energy conversion technology. Mechanical vibration (ultrasonic or agitation, etc.) can induce lattice distortion of piezoelectric catalysts, accelerate mass transfer in soil systems, and lead to enhanced compressive catalytic degradation of PAHs in soil, showing great potential in soil remediation.
Hydroxyapatite (CA10 (PO 4) 6 (Ohio) 2, HAP) as a natural mineral piezoelectric catalyst has shown unique environmentally friendly advantages in the field of piezoelectric catalytic soil remediation. However, the biggest challenge is the weak piezoelectric coefficient (1-16 pm v-1), which results in low catalytic activity.
How to construct a HAP-based mineral piezoelectric catalyst with high-pressure catalytic activity for soil remediation is the direction of our team's efforts," explains Jianmei Lu, a professor at Soochow University.
The researchers successfully prepared the core-shell structure hap@fap gradient F-doped by a simple ion exchange method, and enhanced the piezoelectric catalytic activity by inducing the coupling effect of piezoelectric and flexible electricity through a built-in strain gradient.
The oxidative degradation of phenanthrene (PHE) in soil (200 mg kg-1) evaluated the piezoelectric catalytic activity of the catalyst. hap@fap exhibited optimized piezoelectric catalytic activity, and 79% of PHE120 min could be degraded under ultrasonic vibration. This is significantly better than primitive HAP and F-HAP with solid solution structures. In addition, the effects of catalyst dosage, water-soil ratio and ultrasonic power on degradation performance were also studied.
The research team also proposed a possible mechanism by which piezoelectric polarization leads to PHE degradation. The lattice strain gradient generated in the direction of the gradient F-doped core-shell induces flexible electricity and enhances the piezoelectric catalytic activity.
Under continuous ultrasonic vibration, the polarized electric field in the hap@fap drives the charge carriers to the surface, generating reactive oxygen species, and finally oxidizing and degrading PHE to CO2 and H2O, achieving the goal of harmless treatment of soil pollutants.
Looking ahead, the research team hopes that their work will provide insights into the modification of piezoelectric catalysts to remediate organic-contaminated soils in industrial land. "We plan to scale up next to achieve the ultimate goal of industrial applications. The catalysts we have developed may be used in a variety of industrial sites contaminated with POPs, such as PCBs and naphthalene.
More information: Jun Han et al., Flexible electricity in hydroxyapatite for enhanced piezocatalytic degradation of phenanthrene in soil, Industrial Chemistry & Materials (2023). doi： 10.1039/d3im00093a