Dopant Effects on the Photocatalytic Activity of Colloidal Zinc Sulfide Semiconductor Nanocrystals for the Oxidation of 2-Chlorophenol

Abstract

In this work, colloidal zinc sulfide nanocrystals, prepared with selected concentrations of manganese(II) ions in the range of 0-2% and stabilized with a polymeric capping agent, were used in the photocatalytic degradation of 2-chlorophenol in aqueous solutions. Particle sizes for the synthesized nanocrystals were determined using UV-vis absorbance spectroscopy and X-ray diffraction (XRD). UV-vis spectra for all of the synthesized nanocrystals display an excitonic peak at around 290 nm, which corresponds to a particle size of approximately 3 nm, in agreement with the XRD analysis. Photoluminescence emission spectra recorded for undoped ZnS nanocrystals exhibit an emission peak at 460 nm in the spectrum, whereas peaks corresponding to the dopant ion are red-shifted to 590 nm. With increasing addition of the dopant ion, the area of the peak at 460 nm first increases and then decreases for higher dopant concentrations, whereas the area of the peak at 590 nm increases. This finding clearly indicates that the presence of the dopant ion alters the electronic states of the nanocrystals, which, in turn, affects the photocatalytic properties of the colloidal nanocrystals. Apparent rate constants for the photodegradation of 2-chlorophenol in aqueous solution utilizing undoped and doped colloidal ZnS nanocrystals were calculated using pseudo-first-order kinetic analysis. As the dopant concentration used during synthesis was increased, the apparent rate constants increased initially and then decreased. Results from kinetic experiments performed after nitrogen purging showed a decrease in the apparent rate constant, suggesting that the reaction mechanism involves a reactive oxygen species such as superoxide. Taken together, these results provide further insight into the effects of dopants on the activity of colloidal semiconductor nanocrystals employed as photocatalysts in environmental remediation applications.

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“…35,36 Aqueous solutions of 1.0 M Zn(C 2 H 3 O 2 ) 2 , 0.85 M Na 2 S, and 0.010 M Mn(C 2 H 3 O 2 ) 2 were prepared. Next, 0.56 g of (PVP) was dissolved in 5 mL of the zinc acetate solution obtaining a concentration of 1.0 M. Five milliliters of the manganese acetate solution was then added to this mixture.…”

“…Un-doped ZnS NPs were synthesized with a similar procedure except for the addition of manganese acetate. 35 [Zinc acetate dihydrate, sodium sulfide nonahydrate, manganese (II) acetate tetrahydrate, and PVP were purchased from Sigma-Aldrich. ]…”

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“…Synthesis of colloidal ZnS semiconductor nanocrystals capped with PVP and prepared using 1% concentration of Mn +2 ion as a dopant: The NPs were synthesized via wetchemical techniques [86]. Undoped ZnS NPs were synthesized with a similar procedure except for the addition of manganese acetate [87].…”

B-Chronic Lymphocytic Leukemia Autophagyc Cell Death by the Use of Manganese Doped Zinc Oxide Nanoparticles and Photo-Dynamic Therapy.

“…The NPs were synthesized via wet-chemical techniques 42,43 . Aqueous solution of 1.0 M Zn acetate dihydrate, 0.85 M sodium sulfide nonahydrate , and 0.010 M manganese (II) acetate tetrahydrate were prepared.…”

“…The nano-crystals were re-dispersed in water to make a 0.01 M solution. Un-doped ZnS NPs were synthesized with a similar procedure except for the addition of manganese acetate 42,43 . (Zinc acetate dihydrate, sodium sulfide nonahydrate, manganese (II) acetate tetrahydrate, poly(vinylpyrrolidone) were all purchased from Sigma-Aldrich).…”