Water scarcity in parallel to the improve of the water demand appears as one of the greatest worldwide challenges of the century. At the same time, the release of perilous compounds into the water from the urban and the industrial sectors remains an issue because of the presence of a large variety of chemical species at various concentrations.Water plays an impotant role in plants rather than all human beings .water is tasteless, odourless and incompressible .water has high dielectric constant.
water is a reagent in many chemical reaction.water has maximum solvent power as compared to other liquids. Water consumption for human activities is increasing in both mounting and industrialized countries. High throughput, lowcost, and robust methods to disinfect and decontaminate waters are needed from source to point-of-use, without further stressing the environment or endangering human health by the treatment method itself.
Quantum dot are the superior candidate for water purification. Carbon dots (denoted as C quantum dots) are a new part of fluorescent carbon material with the diameter below 10 nm.
Their discovery should be traced back to a 2004 report on the components of _fluorescent nanoparticles derived from single wall carbon nano tubes (SWNTs . Till 2006, these fluorescent carbon nanoparticles received their name “carbon quantum dots” from Sun et al.4 who proposed a synthesis route to produce CQDs with much enhanced_fluorescence emission viaCQDs separate the unique optical properties of quantum dots with the prominent electronic properties of carbon materials,making them typical from long-established semiconductor quantum or another carbon nanomaterial.
Cdots are becoming a promising substitute to metal-based quantum dots because of their composition and biocompatibility.
CQ dots were explored as biosensors, gene transmission, drug carriers, and bioimaging probes due to their excellent fluorescence properties, good biocompatibility and low toxicity. The favorable fluorescence properties of C-dots exhibited a great potential for the applications in analytical chemistry, especially in environmental and biological sensing and imaging surface passivation. the term ‘quantum dot’ in the literature is mostly associated with nanoscale entities exhibiting size-dependent multicolor fluorescence emissions, despite the fact that the quantum confinement has many consequences, especially with respect to photo induced redox processe.CQDs are commonly described in terms of a carbogenic core with surface functional groups. Most CQDs consist of an amorphous to a nano crystalline core with mainly sp2 carbon, the lattice spacings of which are consistent with graphitic or turbostratic carbon.
Quantum dots are presice crystals. Typical methods include molecular beam epitaxial, ion implantation, and X-ray lithography. These researches divided carbon materials into Cdots by using physical or chemical methods, and therefore denoted as “top-down” method. With the development of microwave and hydrothermal technologies, various “bottom-up” methods were explored to prepare Cdots from small molecules, biomolecules, and biomass. For example, organic molecules on the surface of SiO2 were carbonized to prepare Cdots. Microwave method was convenient for prepare Cdots within 10 min. Cdots in hydrothermal method and studied their formation mechanism, sensing, and multi-color imaging. As is known, the photocatalytic process involves the generation of charge carriers, i.e., electrons and holes induced by light. Different sized quantum dots change the color emitted or absorbed by the crystal, due to the energy levels within the crystal.
CQDs can not only act as an electron mediator,but also as a photosensitizer, a spectral converter or a sole photocatalyst in photocatalytic processes.Jonas et al.has fabricated high a novel high throughput photocatalyst eﬃciency assessment method based on 96-well microplates and UV−vis spectroscopy for Methyl orange degradation. Keiji Nagai,*,† et al has designed a full-spectrum visible-light-responsive organophotocatalyst film array is designed and employed for a one-pass-ﬂow water puriﬁcation system. Whereas previous photocatalyst systems required strong light source, the present design manages with natural sunlight intensity, owing to multilayerization of a newly optimized low-absorbance organophotocatalyst. Pooja Devia,b, report an environmental friendly, superficial and completely green synthetic method for producing carbon quantum dots (CQDs) from whey, a major dairy waste.
The as-prepared monodispersed diameter CQDs exhibit blue luminescence with noteworthy quantum yield (~11.4%) and excitation dependent emission behaviour. Nuclear magnetic resonance (NMR) analysis reveals the presence of aromatized carbon peaks, leading to polymerized CQDs diameter architecture during whey pyrolysis. The X-ray and selected area electron diﬀraction patterns conﬁrm their amorphous nature. Gianluca Li Puma*,† presented a novel, thin-film, slurry “fountain” photocatalytic reactor for water treatment and purification is presented. The novelty of the reactor centers on the design of a special nozzle through which water is pumped to generate a thin film. The film emerges from the nozzle in the shape of a smooth and radially expanding water fountain. A radiation source (solar or UV lamps) is situated above the fountain.