Abstract
We present the preparation of octadecylamine-capped ZnS quantum dots from bis(morpholinyldithiocarbamato)Zn(II) complex. The complex was thermolyzed at 130 °C in octadecylamine at different times, to study the effect of reaction time on the morphological and photocatalytic properties of the ZnS quantum dots. Powder X-ray diffraction patterns confirmed a hexagonal wurtzite crystalline phase of ZnS, while HRTEM images showed particle sizes of about 1–3 nm, and energy band gaps of 3.68 eV (ZnS–1), 3.87 eV (ZnS–2), and 4.16 eV (ZnS–3) were obtained from the Tauc plot for the ZnS nanoparticles. The as-prepared ZnS were used as photocatalysts for the degradation of brilliant green, rhodamine B, and binary dye consisting of a mixture of brilliant green-rhodamine B. The highest photocatalytic degradation efficiency of 94% was obtained from ZnS–3 with low photoluminescence intensity. The effect of catalytic dosage and pH of the dyes solution on the photocatalytic process shows that pH 8 is optimal for the degradation of brilliant green, while pH 6.5 is the best for photocatalytic degradation of rhodamine B. The degradation of the binary dyes followed the same trends. The effect of catalytic dosage shows that 1 mg mL−1 of the ZnS nano-photocatalyst is the optimum dosage for the degradation of organic dyes. Reusability studies show that the ZnS quantum dots can be reused five times without a significant reduction in degradation efficiency.
Highlights
Rapid industrialization over decades has resulted in the release of organic contaminants into water bodies [1,2]
HRTEM micrographs of the as-prepared ZnS quantum dots show that ZnS–1 (Figure 1a) prepared at 30 min is spherical in shape with a particle size of 1.3 nm, while ZnS–2 (Figure 1d), prepared at 1 h have particle sizes in the range of 1.08–3.42 nm, and the particle sizes of ZnS–3 (Figure 1g), prepared at 2 h are in the range of 0.80–2.88 nm
The SAED patterns of the ZnS–1 quantum dot (Figure 1c) confirmed that the as-prepared ZnS are highly crystalline in nature [34]
Summary
Rapid industrialization over decades has resulted in the release of organic contaminants into water bodies [1,2]. An advanced oxidation process is one of the methods being used for wastewater treatment, especially the removal of organic contaminants [7,8,9]. An advanced oxidation process such as photocatalysis is based on the photogeneration of electron-hole pairs through a redox reaction at the semiconductor interface, to generate reactive species that interact with organic pollutants [10,11]. Interest in the use of semiconductor nanoparticles as photocatalysts for the degradation of organic dyes and subsequent removal from the environment is ascribed to the process being economical, without generating secondary pollutants [12,13,14]. Zinc-based nanomaterials are environmentally friendly at low concentration, and it is one of the most abundant trace metals in the human body [21]. Zinc sulfide is among the semiconductor nanoparticles that can be used as a photocatalyst due to its high surface-area-to-volume ratio [22], which could enhance photon absorption at the nanointerface
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