Upcycling Of Cadmium Hyperaccumulators Biomass Into CdS@C Photocatalysts And Its Application For Dye Degradation

Removal of cadmium from soil by cadmium hyperaccumulators has become a new technology in the field of environmental remediation.It is considered as one of the economical,effective and feasible in-situ remediation strategies for cadmium-contaminated soil.However,the safe disposalandresourceutilizationtechnologiesofcadmium hyperaccumulators are still lacking,which could lead to a risk of secondary pollution,which seriously restricts the application of phytoremediation technology.Therefore,it is of great significance to develop a universality technology for cadmium hyperaccumulators biomass reduction,harmlessness and resource utilization for its application in remediation of cadmium-contaminated soils.In this paper,high performance carbon-supported cadmium sulfide photocatalytic materials were prepared from cadmium hyperaccumulators Perilla frutescens and Sedum alfredii.The application and mechanism of catalysts in photocatalytic degradation of dyes were further discussed.The main conclusions of this work are listed as follows:（1）Preparation of CdS@C photocatalyst:the biomass of Cd accumulated Perilla frutescens and Sedum alfredii was recycled in the form of CdS@C-Perilla/Sedum photocatalyst through the processes of carbonization,Cd concentration and hydrothermal vulcanization step by step.The CdS nanoparticles in the two catalysts prepared were mixed crystal phases（cubic phase and hexagonal phase crystal form）.Among them,the band gap of CdS@C-Perilla catalyst was 2.21 eV.While the other CdS@C-Sedum catalyst has a band gap of 2.01 eV.Two materials was considerably lower than that of nano-CdS.Band-gap narrowing that was observed for nanocomposites indicated excellent light harvesting ability and exhibits better catalytic performance.（2）Application of CdS@C-Perilla/Sedum in photocatalytic degradation dyes:In the reaction system of 20 mg catalyst and 50 ml rhodamine B（RhB）dye solution（40 mg/kg）,CdS@C-Perilla/Sedum could photocatalytic degraded many types of dyes.The degradation rate of RhB was more than 98%in 90 min.Among them,the photocatalytic efficiency of CdS@C-Perilla is more than 27 times that of nano-CdS,while the CdS@C-Sedum catalyst with the reaction rate constant more than 40 times that of nano-CdS with better photocatalytic dye degradation performance.Both catalysts retained more than 75%of the photocatalytic activity after four cycles of experiments,and the morphology of CdS did not change significantly.The reaction mechanism of the composite photocatalyst was explored by Mott-Schottky,transient photocurrent and electron paramagnetic resonance.In this system,the main active molecules for O₂·^-,·OH and photogenerated holes.Among them,O₂·-plays a major role in the entire photocatalytic reaction.（3）Based on the above research,CdS@C-Sedum was further used for photocatalytic degradation of dyes in actual printing and dyeing wastewater.The results indicated that the chemical requirement（COD）of dyeing wastewater was reduced from 252 mg/L to 72 mg/L in the present of CdS@C-Sedum under visible light.After four cycles of experiments,it still maintains a good crystal form and crystal phase of CdS,and has more than 70%photocatalytic activity,showing superior stability and photocatalytic activity.In summary,the biomass of Cd-accumulated hyperaccumulators could be transformed into CdS@C with high performance of photocatalytic efficiency in degradation of various organic dyes under visible light.This study provides a new strategy for Upcycling of cadmium hyperaccumulators biomass,and will further promote the application of phytoremediation technology for cadmium contaminated soil.