The wastes from textile industries and the dyeing industries are the major source of causing water pollution [1]. The dyes from coloring industries are chemically stable and show low biodegradability (~10% to 15%) in water, which causes environmental imbalance [2]. Xanthene dyes, especially Rhodamine B (RhB) dye is used as genotoxic, mutagenic, cytotoxic and cytostatic [3] and [4]. RhB-dye is a highly soluble organic dye and vastly used in coloring wool, papers, silk and cottons. The discharges of RhB-dye severely damage aquatic ecosystem [5]. Last few decades, the physical, chemical and biological techniques have been exploited for the waste water treatment but it requires expensive setup [6] and [7]. In the search of effective techniques, recently, the photocatalytic degradation has been considered as an economical and convenient process for the decomposition of non-biodegradable organic chemicals to less harmful minerals [8]. At present, the inorganic semiconducting nanomaterials are receiving a great of interest as the promising photocatalysts for the degradation of organic dyes into less harmful products [9] and [10].
The metal oxides semiconducting nanomaterials, especially, zinc oxide (ZnO) nanomaterials with a wide band gap of ~3.4 eV have shown good photocatalytic behavior owing to their non-toxic nature, inexpensive, excellent chemical and mechanical stability [11] and [12]. Additionally, ZnO based nanomaterials express numerous applications in photocatalysis, chemical sensors, memory resistors and photovoltaics because of their excellent dielectric, ferroelectric, piezoelectric, pyroelectric properties [11]. Peculiarly, ZnO is also a promising material for spintronics since it can (dependent on manufacturing conditions) possess the ferromagnetic properties [13]. Ameen synthesized ZnO-flowers by a simple chemical route and demonstrated enormously high degradation rate of Crystal-violet dye of ~96% within ~80 min under UV-light illumination [14]. Recently, the high degradation of Crystal-violet dye by ~95% within ~80 min was observed over the surface of ZnO–GO nanohybrid [15]. Previously, Ameen reported the synthesis and the photocatalytic application of rose-like ZnO nanomaterials toward the degradation of Rhodamine 6G-dye under light irradiation and observed very rapid and high degradation rate of ~96% within ~60 min [16]. In this work, the highly dense ZnO-NDs are synthesized by low temperature chemical route and applied as effective photocatalyst for the degradation of RhB-dye under UV-light illumination. It has been observed that the RhB-dye is considerably degraded by ~90% within ~90 min over the surface of synthesized ZnO-NDs.