۱- Introduction

۲- Experimental

۳- Results and discussion

۴- Conclusions

References

Abstract

Organic dyes generating from many industries are considered as a potential source of water-pollution and have negative effects on human health. The present study was aimed to construct a green synthesis method for fabrication of ZnS-based dual nano-semiconductors and to compare the photocatalytic properties for removing cationic and anionic dyes. ZnS nanoparticles were synthesized using a template synthesis in bovine serum albumin (BSA) solution and then ZnS/PbS, ZnS/CdS and ZnS/Ag2S dual nano-semiconductors were prepared using ion-exchange method. Prepared nano-semiconductors were characterized by using HR-TEM, XRD, FTIR, TG/DTA and AAS. Moreover, photocatalytic activity of prepared nano-semiconductors was tested against Rhodamine B (cationic dye) and Methyl Orange (anionic dye). Results revealed that a controllable ZnS/PbS, ZnS/CdS and ZnS/Ag2S ratio in nano-semiconductors can be achieved by adjusting the ion-exchange time. Prepared ZnS based composites exhibited higher photocatalytic efficiency than that of ZnS alone. In addition, photocatalytic activity of ZnS-based dual nano-semiconductors was found to be dependent upon composition and ratio of sulphides in nano-semiconductors with environmental pH. It was concluded that the combination of template synthesis and ion-exchange method is a feasible approach to fabricate new photocatalysts with higher photocatalytic activity.

Introduction

With every year passing, problem of water pollution is increasing because of industrialization. Industrial wastes contain different organic solvents, dyes, residues of products such as waste from pharmaceutical industry may contain drug or residues[1,2]. Out of them, dyes are rendering serious problems as they are not naturally degradable and difficult to degrade by using routine physical or chemical methods of water purification, however, these methods can reduce the concentration of these dyes[3]. Retention of these dyes in water can cause serious health problems such as methyl orange (MO), a widely used azo-dye, can induce DNA damage[4,5]. In addition to that, metabolite of methyl orange is more toxic and is one of the causes for intestinal tumor induction[6,7]. Therefore, it is necessary to remove such toxic organic dyes from water in order to reduce their health hazards. In this regard, photocatalysis process was emerged as a promising approach for degradation of such dyes[3]. In photocatalysis, free electron-hole pair generation due to light absorption lead to production of free radicals which have superior oxidizing property leading to decomposition of organic contaminants [8]. To achieve higher photocatalytic activity, photocatalysts are commonly employed during photocatalysis process, therefore; development of suitable photocatalysts is promising research area and different kinds of photocatalysts have been reported[9]. Metal sulfide nano-semiconductors have gathered a significant attention due to their exceptional chemical and physical characteristics[9].