Photo-thermal synergy for boosting photo-Fenton activity with rGO-ZnFe2O4: Novel photo-activation process and mechanism toward environment remediation

Full light photo-Fenton and photo-thermal effect are of great importance but deserve attentions far insufficient in advanced oxidation progresses for extensive environmental remediation. Herein, ultraviolet-visible-near infrared (UV–vis-NIR) light absorbance and photo-thermal conversion were induced into H2O2 activation towards refractory antibiotics elimination from wastewater through green recyclable rGO-ZnFe2O4 developed via ultrasonic method. Interestingly, photo-thermal synergy presents much superior performance than that of solely photo-Fenton or thermal-Fenton process. Multiple light reflection inner ZnFe2O4 microsphere strengthens UV–vis capture and thermal conversion in degradation reaction. Orbital hybridization and electron rearrangement endow rGO-ZnFe2O4 wide NIR absorbency, fast thermal transfer and photo-generated electrons-holes separation for photo-thermal Fenton progress. Degradation rate of ciprofloxacin on rGO-ZnFe2O4 is found 3 times of ZnFe2O4 under full light exposure which can heat solution from room temperature to 70 °C, while 4 times under NIR irradiation where solution is heated to 46 °C. The great differences are mainly originated from photo-induced thermal energy, which in-situ heating active sites to lower H2O2 activation barrier, accelerate Fe2+/Fe3+ cycle and facilitate spread of radicals. Radicals contribute in OH > h+ > O2− under full light irradiation, while perform in h+ > O2− > OH when taking away photo-generated heat. Results based on systematic experiments and theory calculation imply the strong potential of photo-thermal Fenton in pollutants control, which proposes novel strategy in Fenton reaction for environmental remediation with effective utilization of solar energy.